Pull the torbutton design back from the archives.
Mike Perry

Mike Perry commited on 2010-10-14 22:13:19
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+- Investigation of Privacy Mode:
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+  - Good:
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+    - Cookies Cleared+memory only
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+    - Cache cleared and memory-only
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+    - History not available via javascript or CSS
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+    - Safe because currently unsupported:
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+      - Geolocation not supported in browser
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+      - DOM Storage not supported
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+      - HTML5 Storage not supported
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+    - Http auth is cleared
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+    - Do they have a session store?
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+      - Yes. It is disabled.
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+    - Form history disabled
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+      - But non-private entries still available
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+    - Malware and phishing protection
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+      - Per-url check?
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+        - Doesn't seem like it..
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+  - Bad:
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+    - RLZ Identifier sent with all queries even in Incognito mode
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+      - http://www.google.com/support/chrome/bin/answer.py?hl=en&answer=107684
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+    - Flash cookies not cleared
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+    - Google gears are still available
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+      - Do they have their own storage?
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+        - Yes. Completely ignores private mode.
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+    - Safebrowsing API key not cleared?
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+      - but updates may not happen "under" the incognito window
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+    - Desktop resolution available
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+    - Browser resolution is available
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+    - SSL session keys
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+      - Not cleared!
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+      - They clear trusted certs tho
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+    - Timezone not spoofed
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+
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+- Misc Features we definitely need:
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+  - Incognito-specific proxy settings
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+    - Browser proxy settings currently do not apply immediately
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+  - Plugin enable/disable controls
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+  - Spoof user agent
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+  - Referer alteration API
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+  - Autolaunching of remote apps needs to be disabled
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+  - API to opt-out of all the opt-in tracking for incognito mode
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+  - Cookie API would be nice
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+  - Need network.security.ports.banned
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+    - http://www.remote.org/jochen/sec/hfpa/hfpa.pdf
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+  - Resize windows (content-window side possibly ok)
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+
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+- Future investigation
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+  - Non-private form history still available
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+    - Forms seem to not be auto-filled, but this may be different
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+      for some fields?
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+  - How evil is google update? will it happen over incognito?
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+    - http://en.wikipedia.org/wiki/Google_Updater#Google_Updater
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+    - http://en.wikipedia.org/wiki/SRWare_Iron#Differences_from_Chrome
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+    - http://foliovision.com/2008/12/09/adwords-ppc-organic-rlz/
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+  - Test in more detail with sysinternals for disk writes
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+  - What about safebrowsing requests? Can they bypass proxy?
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+  - Video tag supports H264 and ogg via ffmpeg
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+    - Hrmm.. proxy bypass ability?
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+
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+- Test results. Used Incognito Mode with the test suites from:
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+  https://www.torproject.org/torbutton/design/#SingleStateTesting
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+  - Decloak.net:
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+    - Recovers IP and DNS via Java
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+    - Recovers IP via flash
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+  - Deanonymizer.com
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+    - Failed NNTP and FTP quicktime
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+  - JohnDo's hated some headers
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+  - Mr. T got a lot of shit wrong...
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+  - http://labs.isecpartners.com/breadcrumbs/breadcrumbs.html
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+
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+- Comparison with Torora
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+  - http://github.com/mwenge/torora/tree/master/doc/DESIGN.torora
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+  - Good ideas for both chrome and torbutton:
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+    - Cache/Cookie expiry every 24hrs
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+    - Random preturbation on Date() object..
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+      - No longer possible without js hooks :/
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+      - Possible if Chrome allows non-delatable shadowing of window.Date()
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+        from user scripts. ECMA says it should
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+
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+==========================================
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+
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+- Incognito Issues:
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+  - SSL session keys
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+    - Not cleared!
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+  - Flash cookies not cleared
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+    - Better Privacy? Permissions?
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+  - Google gears are still available
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+    - Do they have their own storage?
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+      - Yes. Completely ignores private mode.
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+  - RLZ override/disable for incognito
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+  - Opt out of opt-in tracking?
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+  - Source code:
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+    http://src.chromium.org/viewvc/chrome/trunk/src/chrome/browser/profile.cc
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+
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+- Privacy Enhancing API Wishlist (remove existing items):
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+  - http://code.google.com/chrome/extensions/devguide.html
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+  - Prefs (copy-on-write for incognito mode)
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+    - Incognito-specific proxy settings
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+      - Should not be used for safebrowsing or app/addon update
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+    - pref to disable autolaunch of apps/warn user
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+    - network.security.ports.banned
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+    - User agent (that also govern navigator.*)
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+      - could be done (better) via http headers and good hook support
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+  - Core APIs:
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+    - Per-Plugin enable/disable controls
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+    - Cookie API
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+    - Cache control
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+    - HTTP header alteration ("on-modify-request")
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+      - Referrer, accept, user agent
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+  - Javascript hooks:
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+    - http://code.google.com/chrome/extensions/content_scripts.html
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+      - Bleh, these suck... Too limited.
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+    - ECMA compliance
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+    - desktop+screen resolution
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+    - Date hooking
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+    - navigator.* hooking
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+
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+- Posted at:
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+  - http://groups.google.com/group/chromium-extensions/t/ceba26ca9e2f6a78
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+
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+First pass: Quick Review of Firefox Features
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+- Video Tag
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+  - Docs:
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+    - https://developer.mozilla.org/En/HTML/Element/Audio
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+    - https://developer.mozilla.org/En/HTML/Element/Video
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+    - https://developer.mozilla.org/En/HTML/Element/Source
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+    - https://developer.mozilla.org/En/Manipulating_video_using_canvas
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+    - https://developer.mozilla.org/En/nsIDOMHTMLMediaElement
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+    - https://developer.mozilla.org/En/Media_formats_supported_by_the_audio_and_video_elements
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+    - http://en.flossmanuals.net/TheoraCookbook
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+  - nsIContentPolicy is checked on load
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+  - Uses NSIChannels for initial load
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+  - Wrapped in nsHTMLMediaElement::mDecoder
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+    - is nsOggDecoder() or nsWaveDecoder()
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+    - liboggplay
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+  - Governed by media.* prefs
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+  - Preliminary audit shows they do not use the liboggplay tcp functions
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+- Geolocation
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+  - Wifi:
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+    - https://developer.mozilla.org/En/Monitoring_WiFi_access_points
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+    - Requires security policy to allow. Then still prompted
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+  - navigator.geolocation
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+    - Governed by geo.enabled
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+    - "2 week access token" is set
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+      - geo.wifi.access_token.. Clearing is prob a good idea
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+    - http://mxr.mozilla.org/mozilla1.9.1/source/dom/src/geolocation/NetworkGeolocationProvider.js
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+    - https://developer.mozilla.org/En/Using_geolocation
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+- DNS prefetching after toggle
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+  - prefetch pref? Always disable for now?
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+    - network.dns.disablePrefetch
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+    - Also disabled in netwerk/dns/src/nsDNSService2.cpp when manual proxies
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+      are set..
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+    - This should prevent prefetching of non-tor urls in tor mode..
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+    - But the reverse is unclear.
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+    - DocShell attribute!!1 YAY
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+      - http://www.oxymoronical.com/experiments/apidocs/interface/nsIDocShell
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+      - "Takes effect for the NEXT document loaded...."
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+        - Do we win this race? hrmm.. If we do, the tor->nontor direction
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+          should also be safe.
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+  - Content policy called?
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+    - No. See content/html/content/src/nsHTMLDNSPrefetch.cpp
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+- Storage
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+  - https://developer.mozilla.org/en/Storage
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+  - "It is available to trusted callers, meaning extensions and Firefox
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+    components only."
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+- New content policy
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+  - Content Security Policy. Addon-only
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+- "Offline resources"
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+  - https://developer.mozilla.org/en/Offline_resources_in_Firefox
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+  - https://developer.mozilla.org/en/nsIApplicationCache
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+  - browser.cache.offline.enable toggles
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+  - browser.cache.disk.enable does not apply. Seperate "device".
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+  - Does our normal cache clearing mechanism apply?
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+    - We call nsICacheService.evictEntries()
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+    - May need: nsOfflineCacheDevice::EvictEntries(NULL)
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+  - Code is smart enough to behave cleanly if we simply set
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+    browser.cache.offline.enable or enable private browsing.
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+- Mouse gesture and other new DOM events
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+- Fonts
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+  - Remote fonts obey content policy. Good.
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+  - XXX: Are they cached independent of regular cache? Prob not.
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+  - Hrmm can probe for installed fonts:
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+    http://remysharp.com/2008/07/08/how-to-detect-if-a-font-is-installed-only-using-javascript/
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+    http://www.lalit.org/lab/javascript-css-font-detect
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+    http://www.ajaxupdates.com/cssjavascript-font-detector/
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+    http://code.google.com/p/jquery-fontavailable/
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+- Drag and drop
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+  - https://developer.mozilla.org/En/DragDrop/Drag_and_Drop
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+  - https://developer.mozilla.org/En/DragDrop/Drag_Operations
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+  - https://developer.mozilla.org/En/DragDrop/Dragging_and_Dropping_Multiple_Items
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+  - https://developer.mozilla.org/En/DragDrop/Recommended_Drag_Types
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+  - https://developer.mozilla.org/En/DragDrop/DataTransfer
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+  - Should be no different than normal url handling..
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+- Local Storage
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+  - https://developer.mozilla.org/en/DOM/Storage#localStorage
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+  - Disabled by dom storage pref..
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+  - Private browsing mode has its own DB
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+    - Memory only?
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+  - Disk Avoidance of gStorage and local storage:
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+    - mSessionOnly set via nsDOMStorage::CanUseStorage()
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+      - Seems to be set to true if cookies are session-only or private
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+        browsing mode
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+        - Our cookies are NOT session-only with dual cookie jars
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+          - but this is ok if we clear the session storage..
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+            - XXX: Technically clearing session storage may break
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+              sites if cookies remain though
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+      - nsDOMStoragePersistentDB not used if mSessionOnly
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+  - Can clear with nsDOMStorage::ClearAll() or nsIDOMStorage2::clear()?
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+    - These only work for a particular storage. There's both global now
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+      and per-origin storage instances
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+    - Each docshell has tons of storages for each origin contained in it
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+    - Toggling dom.storage.enabled does not clear existing storage
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+    - Oh HOT! cookie-changed to clear cookies clears all storages!
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+      - happens for both ff3.0 and 3.5 in dom/src/storage/nsDOMStorage.cpp
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+  - Conclusion:
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+    - can safely enable dom storage
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+      - May have minor buggy usability issues unless we preserve it
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+        when user is preserving cookies..
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+
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+Second Pass: Verification of all Torbutton Assumptions
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+- "Better privacy controls"
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+  - Basically UI stuff for prefs we set already
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+  - address bar search disable option is interesting, but not
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+    torbutton's job to toggle. Users will hate us.
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+- Private browsing
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+  - https://developer.mozilla.org/En/Supporting_private_browsing_mode
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+    - We should consider an option (off by default) to enable PBM during
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+      toggle
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+      - It is a good idea because it will let our users use DOM storage
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+        safely and also may cause their plugins and other addons to be
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+        safe
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+      - Doing it always will cause the user to lose fine-grained control
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+        of many settings
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+        - Also we'll need to prevent them from leaving without toggling tor
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+        - Stuff the emit does (grep for NS_PRIVATE_BROWSING_SWITCH_TOPIC and
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+          "private-browsing")
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+          - XXX:  clear mozilla.org/security/sdr;1. We should too! Wtf is it??
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+            - Neg. Best to let them handle this. Users will be annoyed
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+              at having to re-enter their passwords..
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+          - They also clear the console service..
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+          - Recommend watching private-browsing-cancel-vote and blocking if
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+            we are performing a db operation
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+            - Maybe we want to block transitions during our toggle for safety
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+          - XXX: They also clear general.open_location.last_url
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+          - XXX: mozilla.org/permissionmanager
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+          - XXX: mozilla.org/content-pref/service
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+          - XXX: Sets browser.zoom.siteSpecific to false
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+          - Interesting.. They clear their titles.. I wonder if some
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+            window managers log titles.. But that level of surveillance is
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+            unbeatable..
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+            - XXX: Unless there is some way for flash or script to read titles?
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+          - They empty the clipboard..
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+            - Can js access the clipboard?? ...
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+            - Yes, but needs special pref+confirmation box
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+              - http://www.dynamic-tools.net/toolbox/copyToClipboard/
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+          - They clear cache..
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+          - Cookies:
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+            - Use in-memory table that is different than their default
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+              - This could fuck up our cookie storage options
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+              - We could maybe prevent them from getting this
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+                event by wrapping nsCookieService::Observe(). Lullz..
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+          - NavHistory:
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+            - XXX: nsNavHistory::AutoCompleteFeedback() doesn't track
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+              awesomebar choices for feedback.. Is this done on disk?
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+            - Don't add history entries
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+            - We should block this observe event too if we can..
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+          - The session store stops storing tabs
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+            - We could block this observe
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+          - XXX: They expunge private temporary files on exit from PMB
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+            - This is not done normally until browser exit or
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+              "on-profile-change"
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+            - emits browser:purge-domain-data.. Mostly just for session
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+              editing it appears
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+            - Direct component query for pbs.privateBrowsingEnabled
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+              - This is where we have no ability to provide certain option
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+                control
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+              - browser.js seems to prevent user from allowing blocked
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+                popups?
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+              - Some items in some places context menu get blocked:
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+                - Can't delete items from history? placesContext_deleteHost
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+              - nsCookiePermission::InPrivateBrowsing() calls direct
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+                - but is irellevant
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+              - Form history cannot be saved while in PBM.. :(
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+              - User won't be prompted for adding login passwords..
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+              - Can't remember prefs on content types
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+              - Many components read this value upon init:
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+                - This fucks up our observer game if tor starts enabled
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+                - NavHistory and cookie and dl manager
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+                - We could just wrap the bool on startup and lie
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+                  and emit later... :/
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+                  - Or! emit an exit and an enter always at startup if tor is
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+                    enabled.
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+  - Read iSec report
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+  - Compare to Chrome
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+    - API use cases
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+- SessionStore
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+  - Has been reworked with observers and write methods. Should use those.
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+- security.enable_ssl2 to clear session id
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+  - Still cleared
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+- browser.sessionstore.max_tabs_undo
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+  - Yep.
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+- SafeBrowsing Update Key removed on cookie clear still?
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+  - Yep.
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+- Livemark updates have kill events now
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+- Test if nsICertStore is still buggy...
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+
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+Third Pass: Exploit Auditing
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+- Remote fonts
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+- SVG with HTML
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+- Javascript threads+locking
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+- Ogg theora and vorbis codecs
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+- SQLite
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+
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+
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+- https://developer.mozilla.org/en/Firefox_3_for_developers
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+xsltproc  --output index.html.en  --stringparam section.autolabel.max.depth 2 --stringparam  section.autolabel 1 /usr/share/sgml/docbook/xsl-stylesheets-1.75.2/xhtml/docbook.xsl design.xml 
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+<?xml version="1.0" encoding="ISO-8859-1"?>
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+<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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+     "file:///usr/share/sgml/docbook/xml-dtd-4.4-1.0-30.1/docbookx.dtd">
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+
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+<article id="design">
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+ <articleinfo>
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+  <title>Torbutton Design Documentation</title>
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+   <author>
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+    <firstname>Mike</firstname><surname>Perry</surname>
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+    <affiliation>
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+     <address><email>mikeperry.fscked/org</email></address>
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+    </affiliation>
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+   </author>
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+   <pubdate>Jun 28 2010</pubdate>
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+ </articleinfo>
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+
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+<sect1>
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+  <title>Introduction</title>
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+  <para>
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+
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+This document describes the goals, operation, and testing procedures of the
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+Torbutton Firefox extension. It is current as of Torbutton 1.2.5.
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+
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+  </para>
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+  <sect2 id="adversary">
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+   <title>Adversary Model</title>
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+   <para>
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+
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+A Tor web browser adversary has a number of goals, capabilities, and attack
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+types that can be used to guide us towards a set of requirements for the
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+Torbutton extension. Let's start with the goals.
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+
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+   </para>
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+   <sect3 id="adversarygoals">
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+    <title>Adversary Goals</title>
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+    <orderedlist>
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+<!-- These aren't really commands.. But it's the closest I could find in an
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+acceptable style.. Don't really want to make my own stylesheet -->
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+     <listitem><command>Bypassing proxy settings</command>
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+     <para>The adversary's primary goal is direct compromise and bypass of 
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+Tor, causing the user to directly connect to an IP of the adversary's
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+choosing.</para>
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+     </listitem>
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+     <listitem><command>Correlation of Tor vs Non-Tor Activity</command>
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+     <para>If direct proxy bypass is not possible, the adversary will likely
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+happily settle for the ability to correlate something a user did via Tor with
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+their non-Tor activity. This can be done with cookies, cache identifiers,
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+javascript events, and even CSS. Sometimes the fact that a user uses Tor may
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+be enough for some authorities.</para>
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+     </listitem>
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+     <listitem><command>History disclosure</command>
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+     <para>
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+The adversary may also be interested in history disclosure: the ability to
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+query a user's history to see if they have issued certain censored search
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+queries, or visited censored sites.
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+     </para>
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+     </listitem>
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+     <listitem><command>Location information</command>
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+     <para>
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+
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+Location information such as timezone and locality can be useful for the
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+adversary to determine if a user is in fact originating from one of the
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+regions they are attempting to control, or to zero-in on the geographical
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+location of a particular dissident or whistleblower.
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+
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+     </para>
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+     </listitem>
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+     <listitem><command>Miscellaneous anonymity set reduction</command>
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+     <para>
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+
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+Anonymity set reduction is also useful in attempting to zero in on a
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+particular individual. If the dissident or whistleblower is using a rare build
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+of Firefox for an obscure operating system, this can be very useful
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+information for tracking them down, or at least <link
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+linkend="fingerprinting">tracking their activities</link>.
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+
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+     </para>
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+     </listitem>
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+     <listitem><command>History records and other on-disk
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+information</command>
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+     <para>
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+In some cases, the adversary may opt for a heavy-handed approach, such as
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+seizing the computers of all Tor users in an area (especially after narrowing
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+the field by the above two pieces of information). History records and cache
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+data are the primary goals here.
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+     </para>
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+     </listitem>
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+    </orderedlist>
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+   </sect3>
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+
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+   <sect3 id="adversarypositioning">
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+    <title>Adversary Capabilities - Positioning</title>
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+    <para>
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+The adversary can position themselves at a number of different locations in
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+order to execute their attacks.
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+    </para>
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+    <orderedlist>
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+     <listitem><command>Exit Node or Upstream Router</command>
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+     <para>
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+The adversary can run exit nodes, or alternatively, they may control routers
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+upstream of exit nodes. Both of these scenarios have been observed in the
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+wild.
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+     </para>
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+     </listitem>
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+     <listitem><command>Adservers and/or Malicious Websites</command>
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+     <para>
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+The adversary can also run websites, or more likely, they can contract out
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+ad space from a number of different adservers and inject content that way. For
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+some users, the adversary may be the adservers themselves. It is not
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+inconceivable that adservers may try to subvert or reduce a user's anonymity 
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+through Tor for marketing purposes.
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+     </para>
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+     </listitem>
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+     <listitem><command>Local Network/ISP/Upstream Router</command>
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+     <para>
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+The adversary can also inject malicious content at the user's upstream router
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+when they have Tor disabled, in an attempt to correlate their Tor and Non-Tor
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+activity.
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+     </para>
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+     </listitem>
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+     <listitem><command>Physical Access</command>
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+     <para>
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+Some users face adversaries with intermittent or constant physical access.
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+Users in Internet cafes, for example, face such a threat. In addition, in
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+countries where simply using tools like Tor is illegal, users may face
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+confiscation of their computer equipment for excessive Tor usage or just
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+general suspicion.
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+     </para>
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+     </listitem>
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+    </orderedlist>
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+   </sect3>
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+
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+   <sect3 id="attacks">
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+    <title>Adversary Capabilities - Attacks</title>
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+    <para>
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+
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+The adversary can perform the following attacks from a number of different 
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+positions to accomplish various aspects of their goals. It should be noted
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+that many of these attacks (especially those involving IP address leakage) are
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+often performed by accident by websites that simply have Javascript, dynamic 
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+CSS elements, and plugins. Others are performed by adservers seeking to
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+correlate users' activity across different IP addresses, and still others are
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+performed by malicious agents on the Tor network and at national firewalls.
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+
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+    </para>
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+    <orderedlist>
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+     <listitem><command>Inserting Javascript</command>
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+     <para>
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+If not properly disabled, Javascript event handlers and timers
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+can cause the browser to perform network activity after Tor has been disabled,
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+thus allowing the adversary to correlate Tor and Non-Tor activity and reveal
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+a user's non-Tor IP address. Javascript
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+also allows the adversary to execute <ulink
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+url="http://whattheinternetknowsaboutyou.com/">history disclosure attacks</ulink>:
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+to query the history via the different attributes of 'visited' links to search
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+for particular google queries, sites, or even to <ulink
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+url="http://www.mikeonads.com/2008/07/13/using-your-browser-url-history-estimate-gender/">profile
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+users based on gender and other classifications</ulink>. Finally,
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+Javascript can be used to query the user's timezone via the
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+<function>Date()</function> object, and to reduce the anonymity set by querying
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+the <function>navigator</function> object for operating system, CPU, locale, 
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+and user agent information.
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+     </para>
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+     </listitem>
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+
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+     <listitem><command>Inserting Plugins</command>
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+     <para>
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+
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+Plugins are abysmal at obeying the proxy settings of the browser. Every plugin
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+capable of performing network activity that the author has
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+investigated is also capable of performing network activity independent of
172
+browser proxy settings - and often independent of its own proxy settings.
173
+Sites that have plugin content don't even have to be malicious to obtain a
174
+user's
175
+Non-Tor IP (it usually leaks by itself), though <ulink
176
+url="http://decloak.net">plenty of active
177
+exploits</ulink> are possible as well. In addition, plugins can be used to store unique identifiers that are more
178
+difficult to clear than standard cookies. 
179
+<ulink url="http://epic.org/privacy/cookies/flash.html">Flash-based
180
+cookies</ulink> fall into this category, but there are likely numerous other
181
+examples.
182
+
183
+     </para>
184
+     </listitem>
185
+     <listitem><command>Inserting CSS</command>
186
+     <para>
187
+
188
+CSS can also be used to correlate Tor and Non-Tor activity and reveal a user's
189
+Non-Tor IP address, via the usage of
190
+<ulink url="http://www.tjkdesign.com/articles/css%20pop%20ups/">CSS
191
+popups</ulink> - essentially CSS-based event handlers that fetch content via
192
+CSS's onmouseover attribute. If these popups are allowed to perform network
193
+activity in a different Tor state than they were loaded in, they can easily
194
+correlate Tor and Non-Tor activity and reveal a user's IP address. In
195
+addition, CSS can also be used without Javascript to perform <ulink
196
+url="http://ha.ckers.org/weird/CSS-history.cgi">CSS-only history disclosure
197
+attacks</ulink>.
198
+     </para>
199
+     </listitem>
200
+     <listitem><command>Read and insert cookies</command>
201
+     <para>
202
+
203
+An adversary in a position to perform MITM content alteration can inject
204
+document content elements to both read and inject cookies for
205
+arbitrary domains. In fact, many "SSL secured" websites are vulnerable to this
206
+sort of <ulink url="http://seclists.org/bugtraq/2007/Aug/0070.html">active
207
+sidejacking</ulink>.
208
+
209
+     </para>
210
+     </listitem>
211
+     <listitem><command>Create arbitrary cached content</command>
212
+     <para>
213
+
214
+Likewise, the browser cache can also be used to <ulink
215
+url="http://crypto.stanford.edu/sameorigin/safecachetest.html">store unique
216
+identifiers</ulink>. Since by default the cache has no same-origin policy,
217
+these identifiers can be read by any domain, making them an ideal target for
218
+adserver-class adversaries.
219
+
220
+     </para>
221
+     </listitem>
222
+     <listitem id="fingerprinting"><command>Fingerprint users based on browser
223
+attributes</command>
224
+<para>
225
+
226
+There is an absurd amount of information available to websites via attributes
227
+of the browser. This information can be used to reduce anonymity set, or even
228
+<ulink url="http://mandark.fr/0x000000/articles/Total_Recall_On_Firefox..html">uniquely
229
+fingerprint individual users</ulink>. </para>
230
+<para>
231
+For illustration, let's perform a
232
+back-of-the-envelope calculation on the number of anonymity sets for just the
233
+resolution information available in the <ulink
234
+url="http://developer.mozilla.org/en/docs/DOM:window">window</ulink> and
235
+<ulink
236
+url="http://developer.mozilla.org/en/docs/DOM:window.screen">window.screen</ulink>
237
+objects. Browser window resolution information provides something like
238
+(1280-640)*(1024-480)=348160 different anonymity sets. Desktop resolution
239
+information contributes about another factor of 5 (for about 5 resolutions in
240
+typical use). In addition, the dimensions and position of the desktop taskbar
241
+are available, which can reveal hints on OS information. This boosts the count
242
+by a factor of 5 (for each of the major desktop taskbars - Windows, OSX, KDE
243
+and Gnome, and None). Subtracting the browser content window
244
+size from the browser outer window size provide yet more information.
245
+Firefox toolbar presence gives about a factor of 8 (3 toolbars on/off give
246
+2<superscript>3</superscript>=8). Interface effects such as titlebar fontsize
247
+and window manager settings gives a factor of about 9 (say 3 common font sizes
248
+for the titlebar and 3 common sizes for browser GUI element fonts).
249
+Multiply this all out, and you have (1280-640)*(1024-480)*5*5*8*9 ~=
250
+2<superscript>29</superscript>, or a 29 bit identifier based on resolution
251
+information alone. </para>
252
+
253
+<para>
254
+
255
+Of course, this space is non-uniform and prone to incremental changes.
256
+However, if a bit vector space consisting of the above extracted attributes
257
+were used instead of the hash approach from <ulink
258
+url="http://mandark.fr/0x000000/articles/Total_Recall_On_Firefox..html">The Hacker
259
+Webzine article above</ulink>, minor changes in browser window resolution will
260
+no longer generate totally new identifiers. 
261
+
262
+</para>
263
+<para>
264
+
265
+To add insult to injury, <ulink
266
+url="http://pseudo-flaw.net/content/tor/torbutton/">chrome URL disclosure
267
+attacks</ulink> mean that each and every extension on <ulink
268
+url="https://addons.mozilla.org">addons.mozilla.org</ulink> adds another bit
269
+to that 2<superscript>29</superscript>. With hundreds of popular extensions
270
+and thousands of extensions total, it is easy to see that this sort of
271
+information is an impressively powerful identifier if used properly by a
272
+competent and determined adversary such as an ad network.  Again, a
273
+nearest-neighbor bit vector space approach here would also gracefully handle
274
+incremental changes to installed extensions.
275
+
276
+</para>
277
+
278
+     </listitem>
279
+     <listitem><command>Remotely or locally exploit browser and/or
280
+OS</command>
281
+     <para>
282
+Last, but definitely not least, the adversary can exploit either general 
283
+browser vulnerabilities, plugin vulnerabilities, or OS vulnerabilities to
284
+install malware and surveillance software. An adversary with physical access
285
+can perform similar actions. Regrettably, this last attack capability is
286
+outside of Torbutton's ability to defend against, but it is worth mentioning
287
+for completeness.
288
+     </para>
289
+     </listitem>
290
+    </orderedlist>
291
+   </sect3>
292
+
293
+  </sect2>
294
+
295
+  <sect2 id="requirements">
296
+   <title>Torbutton Requirements</title>
297
+<note>
298
+
299
+Since many settings satisfy multiple requirements, this design document is
300
+organized primarily by Torbutton components and settings. However, if you are
301
+the type that would rather read the document from the requirements
302
+perspective, it is in fact possible to search for each of the following
303
+requirement phrases in the text to find the relevant features that help meet
304
+that requirement.
305
+
306
+</note>
307
+   <para>
308
+
309
+From the above Adversary Model, a number of requirements become clear. 
310
+
311
+   </para>
312
+
313
+<orderedlist> 
314
+<!-- These aren't really commands.. But it's the closest I could find in an
315
+acceptable style.. Don't really want to make my own stylesheet -->
316
+ <listitem id="proxy"><command>Proxy Obedience</command> 
317
+ <para>The browser
318
+MUST NOT bypass Tor proxy settings for any content.</para></listitem>
319
+ <listitem id="isolation"><command>Network Isolation</command>
320
+ <para>Pages MUST NOT perform any network activity in a Tor state different
321
+ from the state they were originally loaded in.</para></listitem>
322
+ <listitem id="state"><command>State Separation</command>
323
+ <para>Browser state (cookies, cache, history, 'DOM storage'), accumulated in
324
+ one Tor state MUST NOT be accessible via the network in
325
+ another Tor state.</para></listitem>
326
+ <listitem id="undiscoverability"><command>Tor Undiscoverability</command><para>With
327
+the advent of bridge support in Tor 0.2.0.x, there are now a class of Tor
328
+users whose network fingerprint does not obviously betray the fact that they
329
+are using Tor. This should extend to the browser as well - Torbutton MUST NOT 
330
+reveal its presence while Tor is disabled.</para></listitem>
331
+ <listitem id="disk"><command>Disk Avoidance</command><para>The browser SHOULD NOT write any Tor-related state to disk, or store it
332
+ in memory beyond the duration of one Tor toggle.</para></listitem>
333
+ <listitem id="location"><command>Location Neutrality</command><para>The browser SHOULD NOT leak location-specific information, such as
334
+ timezone or locale via Tor.</para></listitem>
335
+ <listitem id="setpreservation"><command>Anonymity Set
336
+Preservation</command><para>The browser SHOULD NOT leak any other anonymity set reducing information 
337
+ (such as user agent, extension presence, and resolution information)
338
+automatically via Tor. The assessment of the attacks above should make it clear
339
+that anonymity set reduction is a very powerful method of tracking and
340
+eventually identifying anonymous users.
341
+</para></listitem>
342
+ <listitem id="updates"><command>Update Safety</command><para>The browser
343
+SHOULD NOT perform unauthenticated updates or upgrades via Tor.</para></listitem>
344
+ <listitem id="interoperate"><command>Interoperability</command><para>Torbutton SHOULD interoperate with third-party proxy switchers that
345
+ enable the user to switch between a number of different proxies. It MUST
346
+ provide full Tor protection in the event a third-party proxy switcher has
347
+ enabled the Tor proxy settings.</para></listitem>
348
+</orderedlist>
349
+  </sect2>
350
+  <sect2 id="layout">
351
+   <title>Extension Layout</title>
352
+
353
+<para>Firefox extensions consist of two main categories of code: 'Components' and
354
+'Chrome'. Components are a fancy name for classes that implement a given
355
+interface or interfaces. In Firefox, components <ulink
356
+url="https://developer.mozilla.org/en/XPCOM">can be
357
+written</ulink> in C++,
358
+Javascript, or a mixture of both. Components have two identifiers: their
359
+'<ulink
360
+url="http://www.mozilla.org/projects/xpcom/book/cxc/html/quicktour2.html#1005005">Contract
361
+ID</ulink>' (a human readable path-like string), and their '<ulink
362
+url="http://www.mozilla.org/projects/xpcom/book/cxc/html/quicktour2.html#1005329">Class
363
+ID</ulink>' (a GUID hex-string). In addition, the interfaces they implement each have a hex
364
+'Interface ID'. It is possible to 'hook' system components - to reimplement
365
+their interface members with your own wrappers - but only if the rest of the
366
+browser refers to the component by its Contract ID. If the browser refers to
367
+the component by Class ID, it bypasses your hooks in that use case.
368
+Technically, it may be possible to hook Class IDs by unregistering the
369
+original component, and then re-registering your own, but this relies on
370
+obsolete and deprecated interfaces and has proved to be less than
371
+stable.</para>
372
+
373
+<para>'Chrome' is a combination of XML and Javascript used to describe a window.
374
+Extensions are allowed to create 'overlays' that are 'bound' to existing XML
375
+window definitions, or they can create their own windows. The DTD for this XML
376
+is called <ulink
377
+url="http://developer.mozilla.org/en/docs/XUL_Reference">XUL</ulink>.</para>
378
+  </sect2>
379
+</sect1>
380
+<sect1>
381
+  <title>Components</title>
382
+  <para>
383
+
384
+Torbutton installs components for two purposes: hooking existing components to
385
+reimplement their interfaces; and creating new components that provide
386
+services to other pieces of the extension.
387
+
388
+  </para>
389
+
390
+  <sect2>
391
+   <title>Hooked Components</title>
392
+
393
+<para>Torbutton makes extensive use of Contract ID hooking, and implements some
394
+of its own standalone components as well.  Let's discuss the hooked components
395
+first.</para>
396
+
397
+<sect3 id="sessionstore">
398
+ <title><ulink
399
+url="http://developer.mozilla.org/en/docs/nsISessionStore">@mozilla.org/browser/sessionstore;1</ulink> -
400
+<ulink
401
+url="https://git.torproject.org/checkout/torbutton/master/src/components/nsSessionStore36.js">components/nsSessionStore36.js</ulink></title>
402
+
403
+<para>These components address the <link linkend="disk">Disk Avoidance</link>
404
+requirements of Torbutton. As stated in the requirements, Torbutton needs to
405
+prevent Tor tabs from being written to disk by the Firefox session store for a
406
+number of reasons, primary among them is the fact that Firefox can crash at
407
+any time, and a restart can cause you to fetch tabs in the incorrect Tor
408
+state.</para>
409
+
410
+<para>These components illustrate a complication with Firefox hooking: you can
411
+only hook member functions of a class if they are published in an
412
+interface that the class implements. Unfortunately, the sessionstore has no
413
+published interface that is amenable to disabling the writing out of Tor tabs
414
+in specific. As such, Torbutton had to include the <emphasis>entire</emphasis>
415
+nsSessionStore from both Firefox 2.0, 3.0, 3.5 and 3.6
416
+with a couple of modifications to prevent tabs that were loaded with Tor
417
+enabled from being written to disk, and some version detection code to
418
+determine which component to load. The <ulink
419
+url="https://git.torproject.org/checkout/torbutton/master/src/components/nsSessionStore36.diff">diff against the original session
420
+store</ulink> is included in the git repository.</para>
421
+</sect3>
422
+<sect3 id="appblocker">
423
+ <title><ulink
424
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/uriloader/external-protocol-service%3B1">@mozilla.org/uriloader/external-protocol-service;1
425
+</ulink>, <ulink
426
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/uriloader/external-helper-app-service%3B1">@mozilla.org/uriloader/external-helper-app-service;1</ulink>,
427
+and <ulink url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/mime%3B1">@mozilla.org/mime;1</ulink>
428
+- <ulink
429
+  url="https://git.torproject.org/checkout/torbutton/master/src/components/external-app-blocker.js">components/external-app-blocker.js</ulink></title>
430
+ <para>
431
+Due to <link linkend="FirefoxBugs">Firefox Bug</link> <ulink
432
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=440892">440892</ulink> allowing Firefox 3.x to automatically launch some
433
+applications without user intervention, Torbutton had to wrap the three
434
+components involved in launching external applications to provide user
435
+confirmation before doing so while Tor is enabled. Since external applications
436
+do not obey proxy settings, they can be manipulated to automatically connect
437
+back to arbitrary servers outside of Tor with no user intervention. Fixing
438
+this issue helps to satisfy Torbutton's <link linkend="proxy">Proxy
439
+Obedience</link> Requirement.
440
+ </para>
441
+</sect3>
442
+<sect3>
443
+<title><ulink
444
+url="http://lxr.mozilla.org/seamonkey/source/browser/components/sessionstore/src/nsSessionStartup.js">@mozilla.org/browser/sessionstartup;1</ulink> -
445
+    <ulink
446
+url="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js">components/crash-observer.js</ulink></title>
447
+
448
+<para>This component wraps the Firefox Session Startup component that is in
449
+charge of <ulink
450
+url="http://developer.mozilla.org/en/docs/Session_store_API">restoring saved
451
+sessions</ulink>. The wrapper's only job is to intercept the
452
+<function>doRestore()</function> function, which is called by Firefox if it is determined that the
453
+browser crashed and the session needs to be restored. The wrapper notifies the
454
+Torbutton chrome that the browser crashed by setting the pref
455
+<command>extensions.torbutton.crashed</command>, or that it is a normal
456
+startup via the pref <command>extensions.torbutton.noncrashed</command>. The Torbutton Chrome <ulink
457
+url="https://developer.mozilla.org/en/NsIPrefBranch2#addObserver.28.29">listens for a
458
+preference change</ulink> for this value and then does the appropriate cleanup. This
459
+includes setting the Tor state to the one the user selected for crash recovery
460
+in the preferences window (<command>extensions.torbutton.restore_tor</command>), and
461
+restoring cookies for the corresponding cookie jar, if it exists.</para>
462
+
463
+<para>By performing this notification, this component assists in the 
464
+<link linkend="proxy">Proxy Obedience</link>, and <link
465
+linkend="isolation">Network Isolation</link> requirements.
466
+</para>
467
+
468
+
469
+</sect3>
470
+<sect3>
471
+<title><ulink url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/global-history;2">@mozilla.org/browser/global-history;2</ulink>
472
+- <ulink
473
+  url="https://git.torproject.org/checkout/torbutton/master/src/components/ignore-history.js">components/ignore-history.js</ulink></title>
474
+
475
+<para>This component was contributed by <ulink
476
+url="http://www.collinjackson.com/">Collin Jackson</ulink> as a method for defeating
477
+CSS and Javascript-based methods of history disclosure. The global-history
478
+component is what is used by Firefox to determine if a link was visited or not
479
+(to apply the appropriate style to the link). By hooking the <ulink
480
+url="https://developer.mozilla.org/en/nsIGlobalHistory2#isVisited.28.29">isVisited</ulink>
481
+and <ulink 
482
+url="https://developer.mozilla.org/en/nsIGlobalHistory2#addURI.28.29">addURI</ulink>
483
+methods, Torbutton is able to selectively prevent history items from being
484
+added or being displayed as visited, depending on the Tor state and the user's
485
+preferences.
486
+</para>
487
+<para>
488
+This component helps satisfy the <link linkend="state">State Separation</link>
489
+and <link linkend="disk">Disk Avoidance</link> requirements of Torbutton.
490
+</para>
491
+</sect3>
492
+<sect3 id="livemarks">
493
+<title><ulink
494
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/livemark-service;2">@mozilla.org/browser/livemark-service;2</ulink>
495
+- <ulink
496
+  url="https://git.torproject.org/checkout/torbutton/master/src/components/block-livemarks.js">components/block-livemarks.js</ulink></title>
497
+<para>
498
+
499
+The <ulink
500
+url="http://www.mozilla.com/en-US/firefox/livebookmarks.html">livemark</ulink> service
501
+is started by a timer that runs 5 seconds after Firefox
502
+startup. As a result, we cannot simply call the stopUpdateLivemarks() method to
503
+disable it. We must wrap the component to prevent this start() call from
504
+firing in the event the browser starts in Tor mode.
505
+
506
+</para>
507
+<para>
508
+This component helps satisfy the <link linkend="isolation">Network
509
+Isolation</link> and <link linkend="setpreservation">Anonymity Set
510
+Preservation</link> requirements.
511
+</para>
512
+</sect3>
513
+</sect2>
514
+<sect2>
515
+<title>New Components</title>
516
+
517
+<para>Torbutton creates four new components that are used throughout the
518
+extension. These components do not hook any interfaces, nor are they used
519
+anywhere besides Torbutton itself.</para>
520
+
521
+<sect3>
522
+<title><ulink
523
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js">@torproject.org/cookie-jar-selector;2
524
+- components/cookie-jar-selector.js</ulink></title>
525
+
526
+<para>The cookie jar selector (also based on code from <ulink
527
+url="http://www.collinjackson.com/">Collin
528
+Jackson</ulink>) is used by the Torbutton chrome to switch between
529
+Tor and Non-Tor cookies. Its operations are simple: sync cookies to disk, then
530
+move the current cookies.txt file to the appropriate backup location
531
+(cookies-tor.txt or cookies-nontor.txt), and then moving the other cookie jar
532
+into place.</para>
533
+
534
+<para>
535
+This component helps to address the <link linkend="state">State
536
+Isolation</link> requirement of Torbutton.
537
+</para>
538
+
539
+</sect3>
540
+<sect3>
541
+<title><ulink
542
+url="https://git.torproject.org/checkout/torbutton/master/src/components/torbutton-logger.js">@torproject.org/torbutton-logger;1
543
+- components/torbutton-logger.js</ulink></title>
544
+
545
+<para>The torbutton logger component allows on-the-fly redirection of torbutton
546
+logging messages to either Firefox stderr
547
+(<command>extensions.torbutton.logmethod=0</command>), the Javascript error console
548
+(<command>extensions.torbutton.logmethod=1</command>), or the DebugLogger extension (if
549
+available - <command>extensions.torbutton.logmethod=2</command>). It also allows you to
550
+change the loglevel on the fly by changing
551
+<command>extensions.torbutton.loglevel</command> (1-5, 1 is most verbose).
552
+</para>
553
+</sect3>
554
+<sect3 id="windowmapper">
555
+
556
+<title><ulink
557
+url="https://git.torproject.org/checkout/torbutton/master/src/components/window-mapper.js">@torproject.org/content-window-mapper;1
558
+- components/window-mapper.js</ulink></title>
559
+
560
+<para>Torbutton tags Firefox <ulink
561
+url="https://developer.mozilla.org/en/XUL_Tutorial/Tabboxes">tabs</ulink> with a special variable that indicates the Tor
562
+state the tab was most recently used under to fetch a page. The problem is
563
+that for many Firefox events, it is not possible to determine the tab that is
564
+actually receiving the event. The Torbutton window mapper allows the Torbutton
565
+chrome and other components to look up a <ulink
566
+url="https://developer.mozilla.org/en/XUL/tabbrowser">browser
567
+tab</ulink> for a given <ulink
568
+url="https://developer.mozilla.org/en/nsIDOMWindow">HTML content
569
+window</ulink>. It does this by traversing all windows and all browsers, until it
570
+finds the browser with the requested <ulink
571
+url="https://developer.mozilla.org/en/XUL/tabbrowser#p-contentWindow">contentWindow</ulink> element. Since the content policy
572
+and page loading in general can generate hundreds of these lookups, this
573
+result is cached inside the component.
574
+</para>
575
+</sect3>
576
+<sect3 id="contentpolicy">
577
+<title><ulink
578
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cssblocker.js">@torproject.org/cssblocker;1
579
+- components/cssblocker.js</ulink></title>
580
+
581
+<para>This is a key component to Torbutton's security measures. When Tor is
582
+toggled, Javascript is disabled, and pages are instructed to stop loading.
583
+However, CSS is still able to perform network operations by loading styles for
584
+onmouseover events and other operations. In addition, favicons can still be
585
+loaded by the browser. The cssblocker component prevents this by implementing
586
+and registering an <ulink
587
+url="https://developer.mozilla.org/en/nsIContentPolicy">nsIContentPolicy</ulink>.
588
+When an nsIContentPolicy is registered, Firefox checks every attempted network
589
+request against its <ulink
590
+url="https://developer.mozilla.org/en/nsIContentPolicy#shouldLoad()">shouldLoad</ulink>
591
+member function to determine if the load should proceed. In Torbutton's case,
592
+the content policy looks up the appropriate browser tab using the <link
593
+linkend="windowmapper">window mapper</link>,
594
+and checks that tab's load tag against the current Tor state. If the tab was
595
+loaded in a different state than the current state, the fetch is denied.
596
+Otherwise, it is allowed.</para> This helps to achieve the <link
597
+linkend="isolation">Network
598
+Isolation</link> requirements of Torbutton.
599
+
600
+<para>In addition, the content policy also blocks website javascript from
601
+<ulink url="http://pseudo-flaw.net/content/tor/torbutton/">querying for
602
+versions and existence of extension chrome</ulink> while Tor is enabled, and
603
+also masks the presence of Torbutton to website javascript while Tor is
604
+disabled. </para>
605
+
606
+<para>
607
+
608
+Finally, some of the work that logically belongs to the content policy is
609
+instead handled by the <command>torbutton_http_observer</command> and
610
+<command>torbutton_weblistener</command> in <ulink
611
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js">torbutton.js</ulink>. These two objects handle blocking of
612
+Firefox 3 favicon loads, popups, and full page plugins, which for whatever
613
+reason are not passed to the Firefox content policy itself (see Firefox Bugs 
614
+<ulink
615
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=437014">437014</ulink> and 
616
+<ulink
617
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=401296">401296</ulink>).
618
+
619
+</para>
620
+
621
+<!-- 
622
+FIXME: Hrmm, the content policy doesn't really lend itself well to display 
623
+this way.. People looking for this much detail should consult the source.
624
+
625
+<para>
626
+    <table rowheader="firstcol" frame='all'><title>Access Permissions Table</title>
627
+    <tgroup cols='5' align='left' colsep='1' rowsep='1'>
628
+       <tbody>
629
+       <row>
630
+         <entry></entry>
631
+         <entry>chrome/resource</entry>
632
+         <entry>a3</entry>
633
+         <entry>a4</entry>
634
+         <entry>a5</entry>
635
+       </row>
636
+       <row>
637
+         <entry>file</entry>
638
+         <entry>b2</entry>
639
+         <entry>b3</entry>
640
+         <entry>b4</entry>
641
+         <entry>b5</entry>
642
+       </row>
643
+       <row>
644
+         <entry>c1</entry>
645
+         <entry>c2</entry>
646
+         <entry>c3</entry>
647
+         <entry>c4</entry>
648
+         <entry>c5</entry>
649
+       </row>
650
+       <row>
651
+         <entry>d1</entry>
652
+         <entry>d2</entry>
653
+         <entry>d3</entry>
654
+         <entry>d4</entry>
655
+         <entry>d5</entry>
656
+       </row>
657
+       </tbody>
658
+       </tgroup>
659
+       </table>
660
+</para>
661
+-->
662
+
663
+<para>
664
+
665
+This helps to fulfill both the <link
666
+linkend="setpreservation">Anonymity Set Preservation</link> and the <link
667
+linkend="undiscoverability">Tor Undiscoverability</link> requirements of
668
+Torbutton.</para>
669
+
670
+</sect3>
671
+</sect2>
672
+</sect1>
673
+<sect1>
674
+ <title>Chrome</title>
675
+
676
+<para>The chrome is where all the torbutton graphical elements and windows are
677
+located. Each window is described as an <ulink
678
+url="http://developer.mozilla.org/en/docs/XUL_Reference">XML file</ulink>, with zero or more Javascript
679
+files attached. The scope of these Javascript files is their containing
680
+window.</para>
681
+
682
+<sect2 id="browseroverlay">
683
+<title>Browser Overlay - <ulink
684
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.xul">torbutton.xul</ulink></title>
685
+
686
+<para>The browser overlay, torbutton.xul, defines the toolbar button, the status
687
+bar, and events for toggling the button. The overlay code is in <ulink
688
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js">chrome/content/torbutton.js</ulink>.
689
+It contains event handlers for preference update, shutdown, upgrade, and
690
+location change events.</para>
691
+
692
+<para>The <ulink
693
+url="https://developer.mozilla.org/en/nsIWebProgressListener#onLocationChange">location
694
+change</ulink> <ulink
695
+url="https://developer.mozilla.org/en/nsIWebProgress">webprogress
696
+listener</ulink>, <command>torbutton_weblistener</command> is one of the most
697
+important parts of the chrome from a security standpoint. It is a <ulink
698
+url="https://developer.mozilla.org/en/nsIWebProgressListener">webprogress
699
+listener</ulink> that handles receiving an event every time a page load or
700
+iframe load occurs. This class eventually calls down to
701
+<function>torbutton_update_tags()</function> and
702
+<function>torbutton_hookdoc()</function>, which apply the browser Tor load
703
+state tags, plugin permissions, and install the Javascript hooks to hook the
704
+<ulink
705
+url="https://developer.mozilla.org/en/DOM/window.screen">window.screen</ulink>
706
+object to obfuscate browser and desktop resolution information.
707
+
708
+</para>
709
+
710
+<para>
711
+The browser overlay helps to satisfy a number of Torbutton requirements. These
712
+are better enumerated in each of the Torbutton preferences below. However,
713
+there are also a number of Firefox preferences set in
714
+<function>torbutton_update_status()</function> that aren't governed by any
715
+Torbutton setting. These are:
716
+</para>
717
+<orderedlist>
718
+
719
+<!--
720
+Not set any more.
721
+ <listitem><ulink
722
+url="http://kb.mozillazine.org/Browser.bookmarks.livemark_refresh_seconds">browser.bookmarks.livemark_refresh_seconds</ulink>
723
+<para>
724
+This pref is set in an attempt to disable the fetching of LiveBookmarks via
725
+Tor. Since users can potentially collect a large amount of live bookmarks to
726
+very personal sites (blogs of friends, wikipedia articles they maintain,
727
+comment feeds of their own blog), it is not possible to cleanly isolate these
728
+fetches and they are simply disabled during Tor usage.
729
+This helps to address the <link
730
+linkend="state">State Separation</link> requirement.
731
+Unfortunately <ulink
732
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=436250">Firefox Bug
733
+436250</ulink> prevents this from
734
+functioning completely correctly.
735
+</para>
736
+  </listitem>
737
+-->
738
+
739
+ <listitem><ulink
740
+url="http://kb.mozillazine.org/Network.security.ports.banned">network.security.ports.banned</ulink>
741
+ <para>
742
+Torbutton sets this setting to add ports 8123, 8118, 9050 and 9051 (which it
743
+reads from <command>extensions.torbutton.banned_ports</command>) to the list
744
+of ports Firefox is forbidden to access. These ports are Polipo, Privoxy, Tor,
745
+and the Tor control port, respectively. This is set for both Tor and Non-Tor
746
+usage, and prevents websites from attempting to do http fetches from these
747
+ports to see if they are open, which addresses the <link
748
+linkend="undiscoverability">Tor Undiscoverability</link> requirement.
749
+ </para>
750
+ </listitem>
751
+ <listitem><ulink url="http://kb.mozillazine.org/Browser.send_pings">browser.send_pings</ulink>
752
+ <para>
753
+This setting is currently always disabled. If anyone ever complains saying
754
+that they *want* their browser to be able to send ping notifications to a
755
+page or arbitrary link, I'll make this a pref or Tor-only. But I'm not holding
756
+my breath. I haven't checked if the content policy is called for pings, but if
757
+not, this setting helps with meeting the <link linkend="isolation">Network
758
+Isolation</link> requirement.
759
+ </para>
760
+ </listitem>
761
+ <listitem><ulink
762
+url="http://kb.mozillazine.org/Browser.safebrowsing.remoteLookups">browser.safebrowsing.remoteLookups</ulink>
763
+ <para>
764
+Likewise for this setting. I find it hard to imagine anyone who wants to ask
765
+Google in real time if each URL they visit is safe, especially when the list
766
+of unsafe URLs is downloaded anyway. This helps fulfill the <link
767
+linkend="disk">Disk Avoidance</link> requirement, by preventing your entire
768
+browsing history from ending up on Google's disks.
769
+ </para>
770
+ </listitem>
771
+ <listitem><ulink
772
+url="http://kb.mozillazine.org/Browser.safebrowsing.enabled">browser.safebrowsing.enabled</ulink>
773
+ <para>
774
+Safebrowsing does <ulink
775
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=360387">unauthenticated
776
+updates under Firefox 2</ulink>, so it is disabled during Tor usage. 
777
+This helps fulfill the <link linkend="updates">Update
778
+Safety</link> requirement. Firefox 3 has the fix for that bug, and so
779
+safebrowsing updates are enabled during Tor usage.
780
+ </para>
781
+ </listitem>
782
+ <listitem><ulink
783
+url="http://kb.mozillazine.org/Network.protocol-handler.warn-external.%28protocol%29">network.protocol-handler.warn-external.(protocol)</ulink>
784
+ <para>
785
+If Tor is enabled, we need to prevent random external applications from
786
+launching without at least warning the user. This group of settings only
787
+partially accomplishes this, however. Applications can still be launched via
788
+plugins. The mechanisms for handling this are described under the "Disable
789
+Plugins During Tor Usage" preference. This helps fulfill the <link
790
+linkend="proxy">Proxy Obedience</link> requirement, by preventing external
791
+applications from accessing network resources at the command of Tor-fetched
792
+pages. Unfortunately, due to <link linkend="FirefoxBugs">Firefox Bug</link>
793
+<ulink
794
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=440892">440892</ulink>,
795
+these prefs are no longer obeyed. They are set still anyway out of respect for
796
+the dead.
797
+ </para>
798
+</listitem>
799
+  <listitem><ulink
800
+url="http://kb.mozillazine.org/Browser.sessionstore.max_tabs_undo">browser.sessionstore.max_tabs_undo</ulink>
801
+   <para>
802
+
803
+To help satisfy the Torbutton <link linkend="state">State Separation</link>
804
+and <link linkend="isolation">Network Isolation</link> requirements,
805
+Torbutton needs to purge the Undo Tab history on toggle to prevent repeat
806
+"Undo Close" operations from accidentally restoring tabs from a different Tor
807
+State. This purge is accomplished by setting this preference to 0 and then
808
+restoring it to the previous user value upon toggle.
809
+
810
+   </para>
811
+  </listitem>
812
+
813
+  <listitem><command>security.enable_ssl2</command>
814
+   <para>
815
+TLS Session IDs can persist for an indefinite duration, providing an
816
+identifier that is sent to TLS sites that can be used to link activity. This
817
+is particularly troublesome now that we have certificate verification in place
818
+in Firefox 3: The OCSP server can use this Session ID to build a history of
819
+TLS sites someone visits, and also correlate their activity as users move from
820
+network to network (such as home to work to coffee shop, etc), inside and
821
+outside of Tor. To handle this and to help satisfy our <link
822
+linkend="state">State Separation Requirement</link>, we currently 
823
+toggle
824
+<command>security.enable_ssl2</command>, which clears the SSL Session ID
825
+cache via the pref observer at <ulink
826
+url="http://mxr.mozilla.org/security/source/security/manager/ssl/src/nsNSSComponent.cpp#2134">nsNSSComponent.cpp
827
+line 2134</ulink>. This is an arcane and potentially fragile fix. It would be
828
+better if there were a more standard interface for accomplishing the same
829
+thing. <link linkend="FirefoxBugs">Firefox Bug</link> <ulink
830
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=448747">448747</ulink> has
831
+been filed for this.
832
+
833
+   </para>
834
+  </listitem>
835
+
836
+  <listitem><command><ulink url="http://www.mozilla.com/en-US/firefox/geolocation/">geo.enabled</ulink></command>
837
+   <para>
838
+
839
+Torbutton disables Geolocation support in Firefox 3.5 and above whenever tor
840
+is enabled. This helps Torbutton maintain its
841
+<link linkend="location">Location Neutrality</link> requirement.
842
+While Firefox does prompt before divulging geolocational information,
843
+the assumption is that Tor users will never want to give their
844
+location away during Tor usage, and even allowing websites to prompt
845
+them to do so will only cause confusion and accidents to happen. Moreover,
846
+just because users may approve a site to know their location in non-Tor mode
847
+does not mean they want it divulged during Tor mode.
848
+
849
+   </para>
850
+  </listitem>
851
+
852
+  <listitem><command><ulink
853
+url="http://kb.mozillazine.org/Browser.zoom.siteSpecific">browser.zoom.siteSpecific</ulink></command>
854
+   <para>
855
+
856
+Firefox actually remembers your zoom settings for certain sites. CSS
857
+and Javascript rule can use this to recognize previous visitors to a site.
858
+This helps Torbutton fulfill its <link linkend="state">State Separation</link>
859
+requirement.
860
+
861
+   </para>
862
+  </listitem>
863
+
864
+  <listitem><command><ulink
865
+url="https://developer.mozilla.org/en/controlling_dns_prefetching">network.dns.disablePrefetch</ulink></command>
866
+   <para>
867
+
868
+Firefox 3.5 and above implement prefetching of DNS resolution for hostnames in
869
+links on a page to decrease page load latency. While Firefox does typically
870
+disable this behavior when proxies are enabled, we set this pref for added
871
+safety during Tor usage. Additionally, to prevent Tor-loaded tabs from having
872
+their links prefetched after a toggle to Non-Tor mode occurs,
873
+we also set the docShell attribute
874
+<ulink
875
+url="http://www.oxymoronical.com/experiments/apidocs/interface/nsIDocShell">
876
+allowDNSPrefetch</ulink> to false on Tor loaded tabs. This happens in the same
877
+positions in the code as those for disabling plugins via the allowPlugins
878
+docShell attribute. This helps Torbutton fulfill its <link
879
+linkend="isolation">Network Isolation</link> requirement.
880
+
881
+   </para>
882
+  </listitem>
883
+
884
+  <listitem><command><ulink
885
+url="http://kb.mozillazine.org/Browser.cache.offline.enable">browser.cache.offline.enable</ulink></command>
886
+   <para>
887
+
888
+Firefox has the ability to store web applications in a special cache to allow
889
+them to continue to operate while the user is offline. Since this subsystem
890
+is actually different than the normal disk cache, it must be dealt with
891
+separately. Thus, Torbutton sets this preference to false whenever Tor is
892
+enabled. This helps Torbutton fulfill its <link linkend="disk">Disk
893
+Avoidance</link> and <link linkend="state">State Separation</link>
894
+requirements.
895
+
896
+   </para>
897
+  </listitem>
898
+
899
+<!-- FIXME: We should make it possible to search for ALL modified FF prefs -->
900
+
901
+</orderedlist>
902
+</sect2>
903
+<sect2>
904
+ <title>Preferences Window - <ulink
905
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.xul">preferences.xul</ulink></title>
906
+
907
+<para>The preferences window of course lays out the Torbutton preferences, with
908
+handlers located in <ulink
909
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.js">chrome/content/preferences.js</ulink>.</para>
910
+</sect2>
911
+<sect2>
912
+ <title>Other Windows</title>
913
+
914
+<para>There are additional windows that describe popups for right clicking on
915
+the status bar, the toolbutton, and the about page.</para>
916
+
917
+</sect2>
918
+</sect1>
919
+
920
+<sect1>
921
+ <title>Toggle Code Path</title>
922
+ <para>
923
+
924
+The act of toggling is connected to <function>torbutton_toggle()</function>
925
+via the <ulink
926
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.xul">torbutton.xul</ulink>
927
+and <ulink
928
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/popup.xul">popup.xul</ulink>
929
+overlay files. Most of the work in the toggling process is present in <ulink
930
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js">torbutton.js</ulink> 
931
+
932
+</para>
933
+<para>
934
+
935
+Toggling is a 3 stage process: Button Click, Proxy Update, and
936
+Settings Update. These stages are reflected in the prefs
937
+<command>extensions.torbutton.tor_enabled</command>,
938
+<command>extensions.torbutton.proxies_applied</command>, and
939
+<command>extensions.torbutton.settings_applied</command>. The reason for the
940
+three stage preference update is to ensure immediate enforcement of <link
941
+linkend="isolation">Network Isolation</link> via the <link
942
+linkend="contentpolicy">content policy</link>. Since the content window
943
+javascript runs on a different thread than the chrome javascript, it is
944
+important to properly convey the stages to the content policy to avoid race
945
+conditions and leakage, especially with <ulink
946
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=409737">Firefox Bug 
947
+409737</ulink> unfixed. The content policy does not allow any network activity
948
+whatsoever during this three stage transition.
949
+
950
+ </para>
951
+ <sect2>
952
+  <title>Button Click</title>
953
+  <para>
954
+
955
+This is the first step in the toggling process. When the user clicks the
956
+toggle button or the toolbar, <function>torbutton_toggle()</function> is
957
+called. This function checks the current Tor status by comparing the current
958
+proxy settings to the selected Tor settings, and then sets the proxy settings
959
+to the opposite state, and sets the pref
960
+<command>extensions.torbutton.tor_enabled</command> to reflect the new state.
961
+It is this proxy pref update that gives notification via the <ulink
962
+url="https://developer.mozilla.org/en/NsIPrefBranch2#addObserver.28.29">pref
963
+observer</ulink>
964
+<command>torbutton_unique_pref_observer</command> to perform the rest of the
965
+toggle.
966
+
967
+  </para>
968
+ </sect2>
969
+ <sect2>
970
+  <title>Proxy Update</title>
971
+  <para>
972
+
973
+When Torbutton receives any proxy change notifications via its
974
+<command>torbutton_unique_pref_observer</command>, it calls
975
+<function>torbutton_set_status()</function> which checks against the Tor
976
+settings to see if the Tor proxy settings match the current settings. If so,
977
+it calls <function>torbutton_update_status()</function>, which determines if
978
+the Tor state has actually changed, and sets
979
+<command>extensions.torbutton.proxies_applied</command> to the appropriate Tor
980
+state value, and ensures that
981
+<command>extensions.torbutton.tor_enabled</command> is also set to the correct
982
+value. This is decoupled from the button click functionalty via the pref
983
+observer so that other addons (such as SwitchProxy) can switch the proxy
984
+settings between multiple proxies.
985
+
986
+  </para>
987
+ </sect2>
988
+ <sect2>
989
+  <title>Settings Update</title>
990
+  <para>
991
+
992
+The next stage is also handled by
993
+<function>torbutton_update_status()</function>. This function sets scores of
994
+Firefox preferences, saving the original values to prefs under
995
+<command>extensions.torbutton.saved.*</command>, and performs the history
996
+clearing, cookie jaring, and ssl certificate jaring work of Torbutton. At the
997
+end of its work, it sets
998
+<command>extensions.torbutton.settings_applied</command>, which signifies the
999
+completion of the toggle operation to the <link
1000
+linkend="contentpolicy">content policy</link>.
1001
+
1002
+  </para>
1003
+ </sect2>
1004
+</sect1>
1005
+
1006
+<sect1>
1007
+ <title>Description of Options</title>
1008
+<!-- FIXME: Review+update these during FF3.5 audit -->
1009
+<para>This section provides a detailed description of Torbutton's options. Each
1010
+option is presented as the string from the preferences window, a summary, the
1011
+preferences it touches, and the effect this has on the components, chrome, and
1012
+browser properties.</para>
1013
+ <sect2>
1014
+  <title>Test Settings</title>
1015
+  <para>
1016
+This button under the Proxy Settings tab provides a way to verify that the 
1017
+proxy settings are correct, and actually do route through the Tor network. It
1018
+performs this check by issuing an <ulink
1019
+url="http://developer.mozilla.org/en/docs/XMLHttpRequest">XMLHTTPRequest</ulink>
1020
+for <ulink
1021
+url="https://check.torproject.org/?TorButton=True">https://check.torproject.org/?Torbutton=True</ulink>.
1022
+This is a special page that returns very simple, yet well-formed XHTML that
1023
+Torbutton can easily inspect for a hidden link with an id of
1024
+<command>TorCheckResult</command> and a target of <command>success</command>
1025
+or <command>failure</command> to indicate if the
1026
+user hit the page from a Tor IP, a non-Tor IP. This check is handled in
1027
+<function>torbutton_test_settings()</function> in <ulink
1028
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js">torbutton.js</ulink>.
1029
+Presenting the results to the user is handled by the <ulink
1030
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.xul">preferences
1031
+window</ulink>
1032
+callback <function>torbutton_prefs_test_settings()</function> in <ulink
1033
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.js">preferences.js</ulink>.  
1034
+
1035
+  </para>
1036
+ </sect2>
1037
+ <sect2 id="plugins">
1038
+  <title>Disable plugins on Tor Usage (crucial)</title>
1039
+ <para>Option: <command>extensions.torbutton.no_tor_plugins</command></para>
1040
+
1041
+ <para>Java and plugins <ulink
1042
+url="http://java.sun.com/j2se/1.5.0/docs/api/java/net/class-use/NetworkInterface.html">can query</ulink> the <ulink
1043
+url="http://www.rgagnon.com/javadetails/java-0095.html">local IP
1044
+address</ulink> and report it back to the
1045
+remote site. They can also <ulink
1046
+url="http://decloak.net">bypass proxy settings</ulink> and directly connect to a
1047
+remote site without Tor. Every browser plugin we have tested with Firefox has
1048
+some form of network capability, and every one ignores proxy settings or worse - only
1049
+partially obeys them. This includes but is not limited to:
1050
+QuickTime, Windows Media Player, RealPlayer, mplayerplug-in, AcroRead, and
1051
+Flash. 
1052
+
1053
+ </para>
1054
+ <para>
1055
+Enabling this preference causes the above mentioned Torbutton chrome web progress
1056
+ listener <command>torbutton_weblistener</command> to disable Java via <command>security.enable_java</command> and to disable
1057
+ plugins via the browser <ulink
1058
+ url="https://developer.mozilla.org/en/XUL%3aProperty%3adocShell">docShell</ulink>
1059
+ attribute <command>allowPlugins</command>. These flags are set every time a new window is
1060
+ created (<function>torbutton_tag_new_browser()</function>), every time a web
1061
+load
1062
+event occurs
1063
+ (<function>torbutton_update_tags()</function>), and every time the tor state is changed
1064
+ (<function>torbutton_update_status()</function>). As a backup measure, plugins are also
1065
+ prevented from loading by the content policy in <ulink
1066
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cssblocker.js">@torproject.org/cssblocker;1</ulink> if Tor is
1067
+ enabled and this option is set.
1068
+ </para>
1069
+
1070
+ <para>All of this turns out to be insufficient if the user directly clicks
1071
+on a plugin-handled mime-type. <ulink
1072
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=401296">In this case</ulink>,
1073
+the browser decides that maybe it should ignore all these other settings and
1074
+load the plugin anyways, because maybe the user really did want to load it
1075
+(never mind this same load-style could happen automatically  with meta-refresh
1076
+or any number of other ways..). To handle these cases, Torbutton stores a list
1077
+of plugin-handled mime-types, and sets the pref
1078
+<command>plugin.disable_full_page_plugin_for_types</command> to this list.
1079
+Additionally, (since nothing can be assumed when relying on Firefox
1080
+preferences and internals) if it detects a load of one of them from the web
1081
+progress listener, it cancels the request, tells the associated DOMWindow to
1082
+stop loading, clears the document, AND throws an exception. Anything short of
1083
+all this and the plugin managed to find some way to load.
1084
+ </para>
1085
+
1086
+<!--
1087
+
1088
+FIXME: Hrmm, technically this behavior is not covered by this pref.
1089
+
1090
+ <para>
1091
+Furthermore, with version 3.0 and above, Firefox
1092
+<ulink
1093
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=440892">began ignoring</ulink>
1094
+
1095
+<ulink
1096
+url="http://kb.mozillazine.org/Network.protocol-handler.warn-external.%28protocol%29">network.protocol-handler.warn-external.(protocol)</ulink>
1097
+prefs, which caused us to have to <link linkend="appblocker">wrap the external
1098
+app launcher components</link> to prevent external apps from being loaded to
1099
+bypass proxy settings.
1100
+ </para>
1101
+-->
1102
+
1103
+ <para>
1104
+ All this could be avoided, of course, if Firefox would either <ulink
1105
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=401296">obey
1106
+ allowPlugins</ulink> for directly visited URLs, or notify its content policy for such
1107
+ loads either <ulink
1108
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=309524">via</ulink> <ulink
1109
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=380556">shouldProcess</ulink> or shouldLoad. The fact that it does not is
1110
+ not very encouraging.
1111
+ </para>
1112
+
1113
+
1114
+ <para>
1115
+
1116
+Since most plugins completely ignore browser proxy settings, the actions
1117
+performed by this setting are crucial to satisfying the <link
1118
+linkend="proxy">Proxy Obedience</link> requirement.
1119
+
1120
+ </para>
1121
+</sect2>
1122
+<sect2>
1123
+ <title>Isolate Dynamic Content to Tor State (crucial)</title>
1124
+
1125
+ <para>Option: <command>extensions.torbutton.isolate_content</command></para>
1126
+
1127
+<para>Enabling this preference is what enables the <ulink
1128
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cssblocker.js">@torproject.org/cssblocker;1</ulink> content policy
1129
+mentioned above, and causes it to block content load attempts in pages an
1130
+opposite Tor state from the current state. Freshly loaded <ulink
1131
+url="https://developer.mozilla.org/en/XUL/tabbrowser">browser
1132
+tabs</ulink> are tagged
1133
+with a <command>__tb_load_state</command> member in
1134
+<function>torbutton_update_tags()</function> and this
1135
+value is compared against the current tor state in the content policy.</para>
1136
+
1137
+<para>It also kills all Javascript in each page loaded under that state by
1138
+toggling the <command>allowJavascript</command> <ulink
1139
+url="https://developer.mozilla.org/en/XUL%3aProperty%3adocShell">docShell</ulink> property, and issues a
1140
+<ulink
1141
+url="https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsIWebNavigation#stop()">webNavigation.stop(webNavigation.STOP_ALL)</ulink> to each browser tab (the
1142
+equivalent of hitting the STOP button).</para>
1143
+
1144
+<para>
1145
+
1146
+Unfortunately, <ulink
1147
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=409737">Firefox bug
1148
+409737</ulink> prevents <command>docShell.allowJavascript</command> from killing
1149
+all event handlers, and event handlers registered with <ulink
1150
+url="http://developer.mozilla.org/en/docs/DOM:element.addEventListener">addEventListener()</ulink>
1151
+are still able to execute. The <link linkend="contentpolicy">Torbutton Content
1152
+Policy</link> should prevent such code from performing network activity within
1153
+the current tab, but activity that happens via a popup window or via a
1154
+Javascript redirect can still slip by. For this reason, Torbutton blocks
1155
+popups by checking for a valid <ulink
1156
+url="http://developer.mozilla.org/en/docs/DOM:window.opener">window.opener</ulink>
1157
+attribute in <function>torbutton_check_progress()</function>. If the window
1158
+has an opener from a different Tor state, its load is blocked. The content
1159
+policy also takes similar action to prevent Javascript redirects. This also
1160
+has the side effect/feature of preventing the user from following any links
1161
+from a page loaded in an opposite Tor state.
1162
+
1163
+</para>
1164
+
1165
+<para>
1166
+This setting is responsible for satisfying the <link
1167
+linkend="isolation">Network Isolation</link> requirement.
1168
+</para>
1169
+
1170
+</sect2>
1171
+<sect2 id="jshooks">
1172
+
1173
+<title>Hook Dangerous Javascript</title>
1174
+
1175
+ <para>Option: <command>extensions.torbutton.kill_bad_js</command></para>
1176
+
1177
+<para>This setting enables injection of the <ulink
1178
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/jshooks.js">Javascript
1179
+hooking code</ulink>. This is done in the chrome in
1180
+<function>torbutton_hookdoc()</function>, which is called ultimately by both the 
1181
+<ulink
1182
+url="https://developer.mozilla.org/en/nsIWebProgressListener">webprogress
1183
+listener</ulink> <command>torbutton_weblistener</command> and the <link
1184
+linkend="contentpolicy">content policy</link> (the latter being a hack to handle
1185
+javascript: urls).
1186
+
1187
+In the Firefox 2 days, this option did a lot more than
1188
+it does now. It used to be responsible for timezone and improved useragent
1189
+spoofing, and history object cloaking. However, now it only provides
1190
+obfuscation of the <ulink
1191
+url="https://developer.mozilla.org/en/DOM/window.screen">window.screen</ulink>
1192
+object to mask your browser and desktop resolution.
1193
+The resolution hooks
1194
+effectively make the Firefox browser window appear to websites as if the renderable area
1195
+takes up the entire desktop, has no toolbar or other GUI element space, and
1196
+the desktop itself has no toolbars.
1197
+These hooks drastically reduce the amount of information available to do <link
1198
+linkend="fingerprinting">anonymity set reduction attacks</link> and help to
1199
+meet the <link linkend="setpreservation">Anonymity Set Preservation</link>
1200
+requirements. Unfortunately, Gregory Fleischer discovered it is still possible
1201
+to retrieve the original screen values by using <ulink
1202
+url="http://pseudo-flaw.net/tor/torbutton/unmask-sandbox-xpcnativewrapper.html">XPCNativeWrapper</ulink>
1203
+or <ulink
1204
+url="http://pseudo-flaw.net/tor/torbutton/unmask-components-lookupmethod.html">Components.lookupMethod</ulink>.
1205
+We are still looking for a workaround as of Torbutton 1.2.5.
1206
+
1207
+<!-- FIXME: Don't forget to update this -->
1208
+
1209
+</para>
1210
+</sect2>
1211
+<sect2>
1212
+<title>Resize windows to multiples of 50px during Tor usage (recommended)</title>
1213
+
1214
+ <para>Option: <command>extensions.torbutton.resize_windows</command></para>
1215
+
1216
+<para>
1217
+
1218
+This option drastically cuts down on the number of distinct anonymity sets
1219
+that divide the Tor web userbase. Without this setting, the dimensions for a
1220
+typical browser window range from 600-1200 horizontal pixels and 400-1000
1221
+vertical pixels, or about 600x600 = 360000 different sets. Resizing the
1222
+browser window to multiples of 50 on each side reduces the number of sets by
1223
+50^2, bringing the total number of sets to 144. Of course, the distribution
1224
+among these sets are not uniform, but scaling by 50 will improve the situation
1225
+due to this non-uniformity for users in the less common resolutions.
1226
+Obviously the ideal situation would be to lie entirely about the browser
1227
+window size, but this will likely cause all sorts of rendering issues, and is
1228
+also not implementable in a foolproof way from extension land.
1229
+
1230
+</para>
1231
+<para>
1232
+
1233
+The implementation of this setting is spread across a couple of different
1234
+locations in the Torbutton javascript <link linkend="browseroverlay">browser
1235
+overlay</link>. Since resizing minimized windows causes them to be restored,
1236
+and since maximized windows remember their previous size to the pixel, windows
1237
+must be resized before every document load (at the time of browser tagging)
1238
+via <function>torbutton_check_round()</function>, called by
1239
+<function>torbutton_update_tags()</function>. To prevent drift, the extension
1240
+tracks the original values of the windows and uses this to perform the
1241
+rounding on document load. In addition, to prevent the user from resizing a
1242
+window to a non-50px multiple, a resize listener
1243
+(<function>torbutton_do_resize()</function>) is installed on every new browser
1244
+window to record the new size and round it to a 50px multiple while Tor is
1245
+enabled. In all cases, the browser's contentWindow.innerWidth and innerHeight
1246
+are set. This ensures that there is no discrepancy between the 50 pixel cutoff
1247
+and the actual renderable area of the browser (so that it is not possible to
1248
+infer toolbar size/presence by the distance to the nearest 50 pixel roundoff).
1249
+
1250
+</para>
1251
+<para>
1252
+This setting helps to meet the <link
1253
+linkend="setpreservation">Anonymity Set Preservation</link> requirements.
1254
+</para>
1255
+</sect2>
1256
+<sect2>
1257
+<title>Disable Updates During Tor</title>
1258
+
1259
+  <para>Option: <command>extensions.torbutton.no_updates</command></para>
1260
+
1261
+  <para>This setting causes Torbutton to disable the four <ulink
1262
+url="http://wiki.mozilla.org/Update:Users/Checking_For_Updates#Preference_Controls_and_State">Firefox
1263
+update settings</ulink> during Tor
1264
+  usage: <command>extensions.update.enabled</command>,
1265
+<command>app.update.enabled</command>,
1266
+  <command>app.update.auto</command>, and
1267
+<command>browser.search.update</command>.  These prevent the
1268
+  browser from updating extensions, checking for Firefox upgrades, and
1269
+  checking for search plugin updates while Tor is enabled.
1270
+  </para>
1271
+<para>
1272
+This setting satisfies the <link
1273
+linkend="updates">Update Safety</link> requirement.
1274
+</para>
1275
+</sect2>
1276
+<sect2>
1277
+<title>Redirect Torbutton Updates Via Tor (recommended)</title>
1278
+
1279
+  <para>Option: <command>extensions.torbutton.update_torbutton_via_tor</command></para>
1280
+
1281
+  <para>This setting causes Torbutton to install an
1282
+
1283
+<ulink
1284
+url="https://developer.mozilla.org/en/nsIProtocolProxyFilter">nsIProtocolProxyFilter</ulink>
1285
+in order to redirect all version update checks and Torbutton update downloads
1286
+via Tor, regardless of if Tor is enabled or not. This was done both to address
1287
+concerns about data retention done by <ulink
1288
+url="https://www.addons.mozilla.org">addons.mozilla.org</ulink>, as well as to
1289
+help censored users meet the <link linkend="undiscoverability">Tor
1290
+Undiscoverability</link> requirement.
1291
+
1292
+  </para>
1293
+</sect2>
1294
+
1295
+<sect2>
1296
+
1297
+<title>Disable Search Suggestions during Tor (recommended)</title>
1298
+
1299
+  <para>Option: <command>extensions.torbutton.no_search</command></para>
1300
+
1301
+<para>
1302
+This setting causes Torbutton to disable <ulink
1303
+url="http://kb.mozillazine.org/Browser.search.suggest.enabled"><command>browser.search.suggest.enabled</command></ulink>
1304
+during Tor usage.
1305
+This governs if you get Google search suggestions during Tor
1306
+usage. Your Google cookie is transmitted with google search suggestions, hence
1307
+this is recommended to be disabled.
1308
+
1309
+</para>
1310
+<para>
1311
+While this setting doesn't satisfy any Torbutton requirements, the fact that
1312
+cookies are transmitted for partially typed queries does not seem desirable
1313
+for Tor usage.
1314
+</para>
1315
+</sect2>
1316
+<sect2>
1317
+<title>Disable livemarks updates during Tor usage (recommended)</title>
1318
+  <para>Option:
1319
+   <simplelist>
1320
+   <member><command>extensions.torbutton.disable_livemarks</command></member>
1321
+   </simplelist>
1322
+  </para>
1323
+
1324
+<para>
1325
+This option causes Torbutton to prevent Firefox from loading <ulink
1326
+url="http://www.mozilla.com/firefox/livebookmarks.html">Livemarks</ulink> during
1327
+Tor usage. Because people often have very personalized Livemarks (such as RSS
1328
+feeds of Wikipedia articles they maintain, etc). This is accomplished both by
1329
+<link linkend="livemarks">wrapping the livemark-service component</link> and
1330
+by calling stopUpdateLivemarks() on the <ulink
1331
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/livemark-service;2">Livemark
1332
+service</ulink> when Tor is enabled.
1333
+
1334
+</para>
1335
+
1336
+<para>
1337
+This helps satisfy the <link linkend="isolation">Network
1338
+Isolation</link> and <link linkend="setpreservation">Anonymity Set
1339
+Preservation</link> requirements.
1340
+</para>
1341
+
1342
+</sect2>
1343
+<sect2>
1344
+<title>Block Tor/Non-Tor access to network from file:// urls (recommended)</title>
1345
+  <para>Options:
1346
+   <simplelist>
1347
+   <member><command>extensions.torbutton.block_tor_file_net</command></member>
1348
+   <member><command>extensions.torbutton.block_nontor_file_net</command></member>
1349
+   </simplelist>
1350
+  </para>
1351
+
1352
+<para>
1353
+
1354
+These settings prevent file urls from performing network operations during the
1355
+respective Tor states. Firefox 2's implementation of same origin policy allows
1356
+file urls to read and <ulink
1357
+url="http://www.gnucitizen.org/blog/content-disposition-hacking/">submit
1358
+arbitrary files from the local filesystem</ulink> to arbitrary websites. To
1359
+make matters worse, the 'Content-Disposition' header can be injected
1360
+arbitrarily by exit nodes to trick users into running arbitrary html files in
1361
+the local context. These preferences cause the <link
1362
+linkend="contentpolicy">content policy</link> to block access to any network
1363
+resources from File urls during the appropriate Tor state.
1364
+
1365
+</para>
1366
+<para>
1367
+
1368
+This preference helps to ensure Tor's <link linkend="isolation">Network
1369
+Isolation</link> requirement, by preventing file urls from executing network
1370
+operations in opposite Tor states. Also, allowing pages to submit arbitrary
1371
+files to arbitrary sites just generally seems like a bad idea.
1372
+
1373
+</para>
1374
+</sect2>
1375
+<sect2>
1376
+
1377
+<title>Close all Tor/Non-Tor tabs and windows on toggle (optional)</title>
1378
+
1379
+  <para>Options:
1380
+   <simplelist>
1381
+   <member><command>extensions.torbutton.close_nontor</command></member>
1382
+   <member><command>extensions.torbutton.close_tor</command></member>
1383
+   </simplelist>
1384
+  </para>
1385
+
1386
+<para>
1387
+
1388
+These settings cause Torbutton to enumerate through all windows and close all
1389
+tabs in each window for the appropriate Tor state. This code can be found in
1390
+<function>torbutton_update_status()</function>.  The main reason these settings
1391
+exist is as a backup mechanism in the event of any Javascript or content policy
1392
+leaks due to <ulink
1393
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=409737">Firefox Bug
1394
+409737</ulink>.  Torbutton currently tries to block all Javascript network
1395
+activity via the content policy, but until that bug is fixed, there is some
1396
+risk that there are alternate ways to bypass the policy. This option is
1397
+available as an extra assurance of <link linkend="isolation">Network
1398
+Isolation</link> for those who would like to be sure that when Tor is toggled
1399
+all page activity has ceased. It also serves as a potential future workaround
1400
+in the event a content policy failure is discovered, and provides an additional
1401
+level of protection for the <link linkend="disk">Disk Avoidance</link>
1402
+protection so that browser state is not sitting around waiting to be swapped
1403
+out longer than necessary.
1404
+
1405
+</para>
1406
+<para>
1407
+While this setting doesn't satisfy any Torbutton requirements, the fact that
1408
+cookies are transmitted for partially typed queries does not seem desirable
1409
+for Tor usage.
1410
+</para>
1411
+</sect2>
1412
+
1413
+<sect2>
1414
+<title>Isolate Access to History navigation to Tor state (crucial)</title>
1415
+  <para>Option: <command>extensions.torbutton.block_js_history</command></para>
1416
+  <para>
1417
+This setting determines if Torbutton installs an <ulink
1418
+url="http://www.oxymoronical.com/experiments/apidocs/interface/nsISHistoryListener">nsISHistoryListener</ulink>
1419
+attached to the <ulink
1420
+url="http://www.oxymoronical.com/experiments/apidocs/interface/nsISHistory">sessionHistory</ulink> of 
1421
+of each browser's <ulink
1422
+url="https://developer.mozilla.org/en/XUL%3aProperty%3awebNavigation">webNavigatator</ulink>.
1423
+The nsIShistoryListener is instantiated with a reference to the containing
1424
+browser window and blocks the back, forward, and reload buttons on the browser
1425
+navigation bar when Tor is in an opposite state than the one to load the
1426
+current tab. In addition, Tor clears the session history during a new document
1427
+load if this setting is enabled. 
1428
+
1429
+  </para>
1430
+  <para>
1431
+
1432
+This is marked as a crucial setting in part
1433
+because Javascript access to the history object is indistinguishable from 
1434
+user clicks, and because
1435
+<ulink
1436
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=409737">Firefox Bug
1437
+409737</ulink> allows javascript to execute in opposite Tor states, javascript
1438
+can issue reloads after Tor toggle to reveal your original IP. Even without
1439
+this bug, however, Javascript is still able to access previous pages in your
1440
+session history that may have been loaded under a different Tor state, to
1441
+attempt to correlate your activity.
1442
+
1443
+   </para>
1444
+   <para>
1445
+
1446
+This setting helps to fulfill Torbutton's <link linkend="state">State
1447
+Separation</link> and (until Bug 409737 is fixed) <link linkend="isolation">Network Isolation</link>
1448
+requirements.
1449
+
1450
+   </para>
1451
+</sect2>
1452
+
1453
+
1454
+<sect2>
1455
+<title>History Access Settings</title>
1456
+
1457
+  <para>Options:
1458
+  <simplelist>
1459
+   <member><command>extensions.torbutton.block_thread</command></member>
1460
+   <member><command>extensions.torbutton.block_nthread</command></member>
1461
+   <member><command>extensions.torbutton.block_thwrite</command></member>
1462
+   <member><command>extensions.torbutton.block_nthwrite</command></member>
1463
+  </simplelist>
1464
+  </para>
1465
+
1466
+<para>These four settings govern the behavior of the <ulink
1467
+url="https://git.torproject.org/checkout/torbutton/master/src/components/ignore-history.js">components/ignore-history.js</ulink>
1468
+history blocker component mentioned above. By hooking the browser's view of
1469
+the history itself via the <ulink
1470
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/global-history;2">@mozilla.org/browser/global-history;2</ulink>
1471
+and <ulink
1472
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/nav-history-service;1">@mozilla.org/browser/nav-history-service;1</ulink>
1473
+components, this mechanism defeats all document-based <ulink
1474
+url="http://whattheinternetknowsaboutyou.com/">history disclosure
1475
+attacks</ulink>, including <ulink
1476
+url="http://ha.ckers.org/weird/CSS-history.cgi">CSS-only attacks</ulink>.
1477
+
1478
+The component also hooks functions involved in writing history to disk via
1479
+both the <ulink
1480
+url="http://developer.mozilla.org/en/docs/Places_migration_guide#History">Places
1481
+Database</ulink> and the older Firefox 2 mechanisms.
1482
+
1483
+</para>
1484
+
1485
+<para>
1486
+This setting helps to satisfy the <link
1487
+linkend="state">State Separation</link> and <link
1488
+linkend="disk">Disk Avoidance</link> requirements.
1489
+</para>
1490
+
1491
+</sect2>
1492
+<sect2>
1493
+
1494
+<title>Clear History During Tor Toggle (optional)</title>
1495
+
1496
+<para>Option: <command>extensions.torbutton.clear_history</command></para>
1497
+
1498
+<para>This setting governs if Torbutton calls
1499
+<ulink
1500
+url="https://developer.mozilla.org/en/nsIBrowserHistory#removeAllPages.28.29">nsIBrowserHistory.removeAllPages</ulink>
1501
+and <ulink
1502
+url="http://www.oxymoronical.com/experiments/apidocs/interface/nsISHistory">nsISHistory.PurgeHistory</ulink>
1503
+for each tab on Tor toggle.</para>
1504
+<para>
1505
+This setting is an optional way to help satisfy the <link
1506
+linkend="state">State Separation</link> requirement.
1507
+</para>
1508
+
1509
+</sect2>
1510
+<sect2>
1511
+
1512
+<title>Block Password+Form saving during Tor/Non-Tor</title>
1513
+
1514
+<para>Options:
1515
+  <simplelist>
1516
+  <member><command>extensions.torbutton.block_tforms</command></member>
1517
+  <member><command>extensions.torbutton.block_ntforms</command></member>
1518
+  </simplelist>
1519
+  </para>
1520
+
1521
+<para>These settings govern if Torbutton disables
1522
+<command>browser.formfill.enable</command>
1523
+and <command>signon.rememberSignons</command> during Tor and Non-Tor usage.
1524
+Since form fields can be read at any time by Javascript, this setting is a lot
1525
+more important than it seems.
1526
+</para>
1527
+
1528
+<para>
1529
+This setting helps to satisfy the <link
1530
+linkend="state">State Separation</link> and <link
1531
+linkend="disk">Disk Avoidance</link> requirements.
1532
+</para>
1533
+
1534
+</sect2>
1535
+<sect2>
1536
+  <title>Block Tor disk cache and clear all cache on Tor Toggle</title>
1537
+
1538
+  <para>Option: <command>extensions.torbutton.clear_cache</command>
1539
+  </para>
1540
+
1541
+<para>This option causes Torbutton to call <ulink
1542
+url="https://developer.mozilla.org/en/nsICacheService#evictEntries.28.29">nsICacheService.evictEntries(0)</ulink>
1543
+on Tor toggle to remove all entries from the cache. In addition, this setting
1544
+causes Torbutton to set <ulink
1545
+url="http://kb.mozillazine.org/Browser.cache.disk.enable">browser.cache.disk.enable</ulink> to false.
1546
+</para>
1547
+<para>
1548
+This setting helps to satisfy the <link
1549
+linkend="state">State Separation</link> and <link
1550
+linkend="disk">Disk Avoidance</link> requirements.
1551
+</para>
1552
+
1553
+</sect2>
1554
+<sect2>
1555
+  <title>Block disk and memory cache during Tor</title>
1556
+
1557
+<para>Option: <command>extensions.torbutton.block_cache</command></para>
1558
+
1559
+<para>This setting
1560
+causes Torbutton to set <ulink
1561
+url="http://kb.mozillazine.org/Browser.cache.memory.enable">browser.cache.memory.enable</ulink>,
1562
+<ulink
1563
+url="http://kb.mozillazine.org/Browser.cache.disk.enable">browser.cache.disk.enable</ulink> and
1564
+<ulink
1565
+url="http://kb.mozillazine.org/Network.http.use-cache">network.http.use-cache</ulink> to false during tor usage.
1566
+</para>
1567
+<para>
1568
+This setting helps to satisfy the <link
1569
+linkend="state">State Separation</link> and <link
1570
+linkend="disk">Disk Avoidance</link> requirements.
1571
+</para>
1572
+
1573
+</sect2>
1574
+<sect2>
1575
+  <title>Clear Cookies on Tor Toggle</title>
1576
+
1577
+<para>Option: <command>extensions.torbutton.clear_cookies</command>
1578
+  </para>
1579
+
1580
+<para>
1581
+
1582
+This setting causes Torbutton to call <ulink
1583
+url="https://developer.mozilla.org/en/nsICookieManager#removeAll.28.29">nsICookieManager.removeAll()</ulink> on
1584
+every Tor toggle. In addition, this sets <ulink
1585
+url="http://kb.mozillazine.org/Network.cookie.lifetimePolicy">network.cookie.lifetimePolicy</ulink>
1586
+to 2 for Tor usage, which causes all cookies to be demoted to session cookies,
1587
+which prevents them from being written to disk. 
1588
+
1589
+</para>
1590
+<para>
1591
+This setting helps to satisfy the <link
1592
+linkend="state">State Separation</link> and <link
1593
+linkend="disk">Disk Avoidance</link> requirements.
1594
+</para>
1595
+
1596
+</sect2>
1597
+<sect2>
1598
+  
1599
+  <title>Store Non-Tor cookies in a protected jar</title>
1600
+
1601
+<para>Option: <command>extensions.torbutton.cookie_jars</command>
1602
+  </para>
1603
+
1604
+<para>
1605
+
1606
+This setting causes Torbutton to use <ulink
1607
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js">@torproject.org/cookie-jar-selector;2</ulink> to store
1608
+non-tor cookies in a cookie jar during Tor usage, and clear the Tor cookies
1609
+before restoring the jar.
1610
+</para>
1611
+<para>
1612
+This setting also sets <ulink
1613
+url="http://kb.mozillazine.org/Network.cookie.lifetimePolicy">network.cookie.lifetimePolicy</ulink>
1614
+to 2 for Tor usage, which causes all cookies to be demoted to session cookies,
1615
+which prevents them from being written to disk. 
1616
+
1617
+</para>
1618
+
1619
+<para>
1620
+This setting helps to satisfy the <link
1621
+linkend="state">State Separation</link> and <link
1622
+linkend="disk">Disk Avoidance</link> requirements.
1623
+</para>
1624
+
1625
+
1626
+</sect2>
1627
+<sect2>
1628
+
1629
+  <title>Store both Non-Tor and Tor cookies in a protected jar (dangerous)</title>
1630
+
1631
+<para>Option: <command>extensions.torbutton.dual_cookie_jars</command>
1632
+  </para>
1633
+
1634
+<para>
1635
+
1636
+This setting causes Torbutton to use <ulink
1637
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js">@torproject.org/cookie-jar-selector;2</ulink> to store
1638
+both Tor and Non-Tor cookies into protected jars.
1639
+</para>
1640
+
1641
+<para>
1642
+This setting helps to satisfy the <link
1643
+linkend="state">State Separation</link> requirement.
1644
+</para>
1645
+
1646
+
1647
+</sect2>
1648
+
1649
+
1650
+<sect2>
1651
+
1652
+  <title>Manage My Own Cookies (dangerous)</title>
1653
+
1654
+<para>Options: None</para>
1655
+<para>This setting disables all Torbutton cookie handling by setting the above
1656
+cookie prefs all to false.</para>
1657
+</sect2>
1658
+<sect2>
1659
+
1660
+<sect2>
1661
+  <title>Do not write Tor/Non-Tor cookies to disk</title>
1662
+  <para>Options:
1663
+  <simplelist>
1664
+  <member><command>extensions.torbutton.tor_memory_jar</command></member>
1665
+  <member><command>extensions.torbutton.nontor_memory_jar</command></member>
1666
+  </simplelist>
1667
+  </para>
1668
+
1669
+<para>
1670
+These settings (contributed by arno) cause Torbutton to set <ulink
1671
+url="http://kb.mozillazine.org/Network.cookie.lifetimePolicy">network.cookie.lifetimePolicy</ulink>
1672
+to 2 during the appropriate Tor state, and to store cookies acquired in that
1673
+state into a Javascript
1674
+<ulink
1675
+url="http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Guide:Processing_XML_with_E4X">E4X</ulink>
1676
+object as opposed to writing them to disk.
1677
+</para>
1678
+
1679
+<para>
1680
+This allows Torbutton to provide an option to preserve a user's 
1681
+cookies while still satisfying the <link linkend="disk">Disk Avoidance</link>
1682
+requirement.
1683
+</para>
1684
+</sect2>
1685
+
1686
+
1687
+  <title>Disable DOM Storage during Tor usage (crucial)</title>
1688
+
1689
+<para>Option: <command>extensions.torbutton.disable_domstorage</command>
1690
+  </para>
1691
+
1692
+<para>
1693
+
1694
+This setting causes Torbutton to toggle <command>dom.storage.enabled</command> during Tor
1695
+usage to prevent 
1696
+<ulink
1697
+  url="http://developer.mozilla.org/en/docs/DOM:Storage">DOM Storage</ulink> from
1698
+  being used to store persistent information across Tor states.</para>
1699
+<para>
1700
+This setting helps to satisfy the <link
1701
+linkend="state">State Separation</link> requirement.
1702
+</para>
1703
+
1704
+</sect2>
1705
+
1706
+<sect2>
1707
+  <title>Clear HTTP Auth on Tor Toggle (recommended)</title>
1708
+<para>Option: <command>extensions.torbutton.clear_http_auth</command>
1709
+  </para>
1710
+
1711
+<para>
1712
+This setting causes Torbutton to call <ulink
1713
+url="http://www.oxymoronical.com/experiments/apidocs/interface/nsIHttpAuthManager">nsIHttpAuthManager.clearAll()</ulink>
1714
+every time Tor is toggled.
1715
+</para>
1716
+
1717
+<para>
1718
+This setting helps to satisfy the <link
1719
+linkend="state">State Separation</link> requirement.
1720
+</para>
1721
+</sect2>
1722
+
1723
+<sect2>
1724
+
1725
+  <title>Clear cookies on Tor/Non-Tor shutdown</title>
1726
+
1727
+<para>Option: <command>extensions.torbutton.shutdown_method</command>
1728
+  </para>
1729
+
1730
+<para> This option variable can actually take 3 values: 0, 1, and 2. 0 means no
1731
+cookie clearing, 1 means clear only during Tor-enabled shutdown, and 2 means
1732
+clear for both Tor and Non-Tor shutdown. When set to 1 or 2, Torbutton listens
1733
+for the <ulink
1734
+url="http://developer.mozilla.org/en/docs/Observer_Notifications#Application_shutdown">quit-application-granted</ulink> event in
1735
+<function>https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js</function> and use <ulink
1736
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js">@torproject.org/cookie-jar-selector;2</ulink>
1737
+to clear out all cookies and all cookie jars upon shutdown.  </para>
1738
+<para>
1739
+This setting helps to satisfy the <link
1740
+linkend="state">State Separation</link> requirement.
1741
+</para>
1742
+
1743
+
1744
+</sect2>
1745
+<sect2>
1746
+
1747
+  <title>Reload cookie jar/clear cookies on Firefox crash</title>
1748
+  <para>Options:
1749
+  <simplelist>
1750
+    <member><command>extensions.torbutton.reload_crashed_jar</command></member>
1751
+    <member><command>extensions.torbutton.crashed</command></member>
1752
+  </simplelist>
1753
+  </para>
1754
+
1755
+  <para>This is no longer a user visible option, and is enabled by default. In
1756
+the event of a crash, the Torbutton <ulink
1757
+url="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js">components/crash-observer.js</ulink> 
1758
+  component will notify the Chrome (via the
1759
+  <command>extensions.torbutton.crashed</command> pref and a <ulink
1760
+url="https://developer.mozilla.org/en/NsIPrefBranch2#addObserver.28.29">pref
1761
+observer</ulink> in
1762
+the chrome that listens for this update), and Torbutton will load the
1763
+  correct jar for the current Tor state via the <ulink
1764
+url="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js">@torproject.org/cookie-jar-selector;2</ulink>
1765
+  component.</para>
1766
+
1767
+<para>
1768
+This setting helps to satisfy the <link
1769
+linkend="state">State Separation</link> requirement in the event of Firefox
1770
+crashes.
1771
+</para>
1772
+
1773
+</sect2>
1774
+
1775
+
1776
+<sect2>
1777
+  <title>On crash recovery or session restored startup, restore via: Tor, Non-Tor</title>
1778
+  <para>Options:
1779
+  <simplelist>
1780
+   <member><command>extensions.torbutton.restore_tor</command></member>
1781
+   <member><command>extensions.torbutton.crashed</command></member>
1782
+   <member><command>extensions.torbutton.normal_exit</command></member>
1783
+  </simplelist>
1784
+  </para>
1785
+
1786
+  <para>This option works with the Torbutton <ulink
1787
+url="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js">crash-observer.js</ulink> 
1788
+  to set the Tor state after a crash is detected (via the 
1789
+  <command>extensions.torbutton.crashed</command> pref). To confirm for
1790
+false positives (such as session restore failures, upgrade, normal
1791
+session restore, etc), Torbutton also sets the pref
1792
+extensions.torbutton.normal_exit during
1793
+Firefox exit and checks this value as well during startup.  
1794
+</para>
1795
+<para>
1796
+
1797
+Since the Tor state after a Firefox crash is unknown/indeterminate, this
1798
+setting helps to satisfy the <link linkend="state">State Separation</link>
1799
+requirement in the event of Firefox crashes by ensuring all cookies,
1800
+settings and saved sessions are reloaded from a fixed Tor state.
1801
+ 
1802
+</para>
1803
+</sect2>
1804
+
1805
+<sect2>
1806
+  <title>On normal startup, set state to: Tor, Non-Tor, Shutdown State</title>
1807
+
1808
+  <para>Options:
1809
+  <simplelist>
1810
+   <member><command>extensions.torbutton.startup_state</command></member>
1811
+  <member><command>extensions.torbutton.noncrashed</command></member>
1812
+   <member><command>extensions.torbutton.normal_exit</command></member>
1813
+  </simplelist>
1814
+  </para>
1815
+
1816
+  <para>This option also works with the Torbutton <ulink
1817
+url="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js">crash-observer.js</ulink> 
1818
+  to set the Tor state after a normal startup is detected (via the 
1819
+  <command>extensions.torbutton.noncrashed</command> pref). To confirm for
1820
+false positives
1821
+(such as session restore failures, etc), Torbutton also sets the pref
1822
+extensions.torbutton.normal_exit in torbutton_uninstall_observer() during
1823
+Firefox exit and checks this value as well during startup.
1824
+  
1825
+</para>
1826
+
1827
+</sect2>
1828
+
1829
+<sect2>
1830
+  <title>Prevent session store from saving Non-Tor/Tor-loaded tabs</title>
1831
+
1832
+  <para>Options: 
1833
+  <simplelist>
1834
+    <member><command>extensions.torbutton.nonontor_sessionstore</command></member>
1835
+    <member><command>extensions.torbutton.notor_sessionstore</command></member>
1836
+  </simplelist>
1837
+  </para>
1838
+
1839
+  <para>If these options are enabled, the <ulink
1840
+url="https://git.torproject.org/checkout/torbutton/master/src/components/nsSessionStore3.js">replacement nsSessionStore.js</ulink>
1841
+  component checks the <command>__tb_tor_fetched</command> tag of tabs before writing them
1842
+  out. If the tag is from a blocked Tor state, the tab is not written to disk.
1843
+  </para>
1844
+<para>
1845
+This setting helps to satisfy the <link linkend="disk">Disk Avoidance</link>
1846
+requirement, and also helps to satisfy the <link
1847
+linkend="state">State Separation</link> requirement in the event of Firefox
1848
+crashes.
1849
+
1850
+</para>
1851
+
1852
+</sect2>
1853
+
1854
+<sect2>
1855
+
1856
+  <title>Set user agent during Tor usage (crucial)</title>
1857
+  <para>Options:
1858
+   <simplelist>
1859
+    <member><command>extensions.torbutton.set_uagent</command></member>
1860
+    <member><command>extensions.torbutton.platform_override</command></member>
1861
+    <member><command>extensions.torbutton.oscpu_override</command></member>
1862
+    <member><command>extensions.torbutton.buildID_override</command></member>
1863
+    <member><command>extensions.torbutton.productsub_override</command></member>
1864
+    <member><command>extensions.torbutton.appname_override</command></member>
1865
+    <member><command>extensions.torbutton.appversion_override</command></member>
1866
+    <member><command>extensions.torbutton.useragent_override</command></member>
1867
+    <member><command>extensions.torbutton.useragent_vendor</command></member>
1868
+    <member><command>extensions.torbutton.useragent_vendorSub</command></member>
1869
+  </simplelist>
1870
+   </para>
1871
+
1872
+<para>On face, user agent switching appears to be straight-forward in Firefox.
1873
+It provides several options for controlling the browser user agent string:
1874
+<command>general.appname.override</command>,
1875
+<command>general.appversion.override</command>,
1876
+<command>general.platform.override</command>,
1877
+<command>general.oscpu.override</command>,
1878
+<command>general.productSub.override</command>,
1879
+<command>general.buildID.override</command>,
1880
+<command>general.useragent.override</command>,
1881
+<command>general.useragent.vendor</command>, and
1882
+<command>general.useragent.vendorSub</command>. If
1883
+the Torbutton preference <command>extensions.torbutton.set_uagent</command> is
1884
+true, Torbutton copies all of the other above prefs into their corresponding
1885
+browser preferences during Tor usage.</para>
1886
+
1887
+
1888
+<para>
1889
+
1890
+It also turns out that it is possible to detect the original Firefox version
1891
+by <ulink url="http://ha.ckers.org/blog/20070516/read-firefox-settings-poc/">inspecting
1892
+certain resource:// files</ulink>. These cases are handled by Torbutton's
1893
+<link linkend="contentpolicy">content policy</link>.
1894
+
1895
+</para>
1896
+
1897
+<para>
1898
+This setting helps to satisfy the <link
1899
+linkend="setpreservation">Anonymity Set Preservation</link> requirement.
1900
+</para>
1901
+
1902
+
1903
+</sect2>
1904
+<sect2>
1905
+
1906
+  <title>Spoof US English Browser</title>
1907
+<para>Options:
1908
+<simplelist>
1909
+ <member><command>extensions.torbutton.spoof_english</command></member>
1910
+ <member><command>extensions.torbutton.spoof_charset</command></member>
1911
+ <member><command>extensions.torbutton.spoof_language</command></member>
1912
+</simplelist>
1913
+</para>
1914
+
1915
+<para> This option causes Torbutton to set
1916
+<command>general.useragent.locale</command>
1917
+<command>intl.accept_languages</command> to the value specified in
1918
+<command>extensions.torbutton.spoof_locale</command>,
1919
+<command>extensions.torbutton.spoof_charset</command> and
1920
+<command>extensions.torbutton.spoof_language</command> during Tor usage, as
1921
+well as hooking <command>navigator.language</command> via its <link
1922
+linkend="jshooks">javascript hooks</link>.
1923
+ </para>
1924
+<para>
1925
+This setting helps to satisfy the <link
1926
+linkend="setpreservation">Anonymity Set Preservation</link> and <link
1927
+linkend="location">Location Neutrality</link> requirements.
1928
+</para>
1929
+
1930
+</sect2>
1931
+<sect2>
1932
+
1933
+  <title>Don't send referrer during Tor Usage</title>
1934
+
1935
+<para>Option: <command>extensions.torbutton.disable_referer</command>
1936
+</para>
1937
+
1938
+<para> 
1939
+This option causes Torbutton to set <ulink
1940
+url="http://kb.mozillazine.org/Network.http.sendSecureXSiteReferrer">network.http.sendSecureXSiteReferrer</ulink> and
1941
+<ulink
1942
+url="http://kb.mozillazine.org/Network.http.sendRefererHeader">network.http.sendRefererHeader</ulink> during Tor usage.</para>
1943
+
1944
+<para>
1945
+This setting also does not directly satisfy any Torbutton requirement, but
1946
+some may desire to mask their referrer for general privacy concerns.
1947
+</para>
1948
+</sect2>
1949
+<sect2>
1950
+  <title>Strip platform and language off of Google Search Box queries</title>
1951
+
1952
+<para>Option: <command>extensions.torbutton.fix_google_srch</command>
1953
+</para>
1954
+
1955
+<para> 
1956
+
1957
+This option causes Torbutton to use the <ulink
1958
+url="https://wiki.mozilla.org/Search_Service:API">@mozilla.org/browser/search-service;1</ulink>
1959
+component to wrap the Google search plugin. On many platforms, notably Debian
1960
+and Ubuntu, the Google search plugin is set to reveal a lot of language and
1961
+platform information. This setting strips off that info while Tor is enabled.
1962
+
1963
+</para>
1964
+<para>
1965
+This setting helps Torbutton to fulfill its <link
1966
+linkend="setpreservation">Anonymity Set Preservation</link> requirement.
1967
+</para>
1968
+</sect2>
1969
+
1970
+<sect2>
1971
+  <title>Automatically use an alternate search engine when presented with a
1972
+Google Captcha</title>
1973
+
1974
+<para>Options:
1975
+<simplelist>
1976
+ <member><command>extensions.torbutton.asked_google_captcha</command></member>
1977
+ <member><command>extensions.torbutton.dodge_google_captcha</command></member>
1978
+ <member><command>extensions.torbutton.google_redir_url</command></member>
1979
+</simplelist>
1980
+</para>
1981
+
1982
+<para>
1983
+
1984
+Google's search engine has rate limiting features that cause it to
1985
+<ulink
1986
+url="http://googleonlinesecurity.blogspot.com/2007/07/reason-behind-were-sorry-message.html">present
1987
+captchas</ulink> and sometimes even outright ban IPs that issue large numbers
1988
+of search queries, especially if a lot of these queries appear to be searching
1989
+for software vulnerabilities or unprotected comment areas.
1990
+
1991
+</para>
1992
+<para>
1993
+
1994
+Despite multiple discussions with Google, we were unable to come to a solution
1995
+or any form of compromise that would reduce the number of captchas and
1996
+outright bans seen by Tor users issuing regular queries.
1997
+
1998
+</para>
1999
+<para>
2000
+As a result, we've implemented this option as an <ulink
2001
+url="https://developer.mozilla.org/en/XUL_School/Intercepting_Page_Loads#HTTP_Observers">'http-on-modify-request'</ulink>
2002
+http observer to optionally redirect banned or captcha-triggering Google
2003
+queries to search engines that do not rate limit Tor users. The current
2004
+options are ixquick.com, bing.com, yahoo.com and scroogle.org. These are
2005
+encoded in the preferences
2006
+<command>extensions.torbutton.redir_url.[1-4]</command>.
2007
+
2008
+</para>
2009
+</sect2>
2010
+
2011
+<sect2>
2012
+
2013
+  <title>Store SSL/CA Certs in separate jars for Tor/Non-Tor (recommended)</title>
2014
+
2015
+<para>Options:
2016
+<simplelist>
2017
+ <member><command>extensions.torbutton.jar_certs</command></member>
2018
+ <member><command>extensions.torbutton.jar_ca_certs</command></member>
2019
+</simplelist>
2020
+</para>
2021
+<para>
2022
+
2023
+These settings govern if Torbutton attempts to isolate the user's SSL
2024
+certificates into separate jars for each Tor state. This isolation is
2025
+implemented in <function>torbutton_jar_certs()</function> in <ulink
2026
+url="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js">chrome/content/torbutton.js</ulink>,
2027
+which calls <function>torbutton_jar_cert_type()</function> and
2028
+<function>torbutton_unjar_cert_type()</function> for each certificate type in
2029
+the <ulink
2030
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/security/nsscertcache;1">@mozilla.org/security/nsscertcache;1</ulink>.
2031
+Certificates are deleted from and imported to the <ulink
2032
+url="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/security/x509certdb;1">@mozilla.org/security/x509certdb;1</ulink>.
2033
+</para>
2034
+
2035
+<para>
2036
+The first time this pref is used, a backup of the user's certificates is
2037
+created in their profile directory under the name
2038
+<filename>cert8.db.bak</filename>. This file can be copied back to
2039
+<filename>cert8.db</filename> to fully restore the original state of the
2040
+user's certificates in the event of any error.
2041
+</para>
2042
+
2043
+<para>
2044
+Since exit nodes and malicious sites can insert content elements sourced to
2045
+specific SSL sites to query if a user has a certain certificate,
2046
+this setting helps to satisfy the <link linkend="state">State
2047
+Separation</link> requirement of Torbutton. Unfortunately, <ulink
2048
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=435159">Firefox Bug
2049
+435159</ulink> prevents it from functioning correctly in the event of rapid Tor toggle, so it
2050
+is currently not exposed via the preferences UI.
2051
+
2052
+</para>
2053
+
2054
+</sect2>
2055
+</sect1>
2056
+
2057
+<sect1 id="FirefoxBugs">
2058
+  <title>Relevant Firefox Bugs</title>
2059
+  <para>
2060
+
2061
+  </para>
2062
+  <sect2 id="FirefoxSecurity">
2063
+   <title>Bugs impacting security</title>
2064
+   <para>
2065
+
2066
+Torbutton has to work around a number of Firefox bugs that impact its
2067
+security. Most of these are mentioned elsewhere in this document, but they
2068
+have also been gathered here for reference. In order of decreasing severity,
2069
+they are:
2070
+
2071
+   </para>
2072
+   <orderedlist>
2073
+
2074
+<!--
2075
+
2076
+XXX: We should just consider this one fixed. FF3.0 is pretty much at EOL.
2077
+
2078
+   <listitem><ulink
2079
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=392274">Bug 392274 - Timezone
2080
+config/chrome API</ulink>
2081
+   <para>
2082
+
2083
+The lack of a config or API to configure the timezone requires Torbutton to
2084
+<link linkend="jshooks">insert client content window javascript</link> to hook
2085
+the Date object. Additionally, a way to <ulink
2086
+url="http://pseudo-flaw.net/tor/torbutton/unmask-date.html">remove the Date
2087
+hooks</ulink> was discovered by Greg Fleischer. Worse, on Firefox 3,
2088
+javascript sandboxing prevents most of the javascript hooks from being
2089
+installed, including the Date hooks. On Windows and Linux, you can set the TZ
2090
+environment variable to "UTC" as a workaround. Firefox will obey this
2091
+environment variable for your Timezone on those platforms, but on Windows this
2092
+does not take effect until browser restart. A fix for this has landed in
2093
+Firefox 3.5, but still has not been backported to Firefox 3.0. The lack of an
2094
+easy way to reliably spoof the timezone interferes with Torbutton's ability to
2095
+fulfill its <link linkend="location">Location Neutrality</link> requirement.
2096
+
2097
+
2098
+   </para>
2099
+   </listitem>
2100
+-->
2101
+    <listitem><ulink
2102
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=429070">Bug 429070 - exposing
2103
+Components.interfaces to untrusted content leaks information about installed
2104
+extensions</ulink>
2105
+     <para>
2106
+<ulink url="http://pseudo-flaw.net/">Gregory Fleischer</ulink> demonstrated at Defcon 17 that these interfaces can
2107
+also be used to <ulink
2108
+url="http://pseudo-flaw.net/tor/torbutton/fingerprint-firefox.html">fingerprint
2109
+Firefox down the to the minor version</ulink>. Note that his test has not been
2110
+updated since 3.5.3, hence it reports 3.5.3 for more recent Firefoxes. This
2111
+bug interferes with Torbutton's ability to satisfy its <link
2112
+linkend="setpreservation">Anonymity Set Preservation</link> requirement.
2113
+     </para>
2114
+    </listitem>
2115
+
2116
+   <listitem><ulink
2117
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=280661">Bug 280661 - SOCKS proxy server
2118
+connection timeout hard-coded</ulink>
2119
+    <para>
2120
+
2121
+This bug prevents us from using the Firefox SOCKS layer directly, and
2122
+currently requires us to ship an auxiliary HTTP proxy called <ulink
2123
+url="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo</ulink>. If this
2124
+patch were landed, we would no longer need to ship Polipo, which has a number
2125
+of privacy and security issues of its own (in addition to being unmaintained).
2126
+
2127
+    </para>
2128
+   </listitem>
2129
+   <listitem><ulink
2130
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=418986">Bug 418986 - window.screen
2131
+provides a large amount of identifiable information</ulink>
2132
+   <para>
2133
+
2134
+As <link linkend="fingerprinting">mentioned above</link>, a large amount of
2135
+information is available from <ulink
2136
+url="http://developer.mozilla.org/en/docs/DOM:window.screen">window.screen</ulink>.
2137
+Currently, there is no way to obscure this information without Javascript
2138
+hooking. This bug is a feature request to provide some other method to change
2139
+these values. This bug interferes with Torbutton's ability to fulfill its
2140
+<link linkend="setpreservation">Anonymity Set Preservation</link>
2141
+requirement.
2142
+
2143
+   </para>
2144
+   </listitem>
2145
+   <listitem><ulink
2146
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=435159">Bug 435159 -
2147
+nsNSSCertificateDB::DeleteCertificate has race conditions</ulink>
2148
+      <para>
2149
+
2150
+In Torbutton 1.2.0rc1, code was added to attempt to isolate SSL certificates
2151
+the user has installed. Unfortunately, the method call to delete a certificate
2152
+from the current certificate database acts lazily: it only sets a variable
2153
+that marks a cert for deletion later, and it is not cleared if that
2154
+certificate is re-added. This means that if the Tor state is toggled quickly,
2155
+that certificate could remain present until it is re-inserted (causing an
2156
+error dialog), and worse, it would still be deleted after that.  The lack of
2157
+this functionality is considered a Torbutton security bug because cert
2158
+isolation is considered a <link linkend="state">State Separation</link>
2159
+feature.
2160
+
2161
+      </para>
2162
+     </listitem>
2163
+
2164
+     <listitem><ulink
2165
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=575230">Bug 575230 - Provide option to
2166
+reduce precision of Date()</ulink>
2167
+      <para>
2168
+
2169
+Currently it is possible to <ulink
2170
+url="http://arstechnica.com/tech-policy/news/2010/02/firm-uses-typing-cadence-to-finger-unauthorized-users.ars">fingerprint
2171
+users based on their typing cadence</ulink> using the high precision timer
2172
+available to javascript. Using this same precision, it is possible to compute
2173
+an identifier based upon the clock drift of the client from some nominal
2174
+source. The latter is not much of a concern for Tor users, as the variable
2175
+delay to load and run a page is measured on the order of seconds, but the high
2176
+precision timer can still be used to fingerprint aspects of a browser's
2177
+javascript engine and processor, and apparently also a user's typing cadence.
2178
+This bug hinders Torbutton's ability to satisfy its <link
2179
+linkend="setpreservation">Anonymity Set Preservation</link> requirement.
2180
+
2181
+      </para>
2182
+     </listitem>
2183
+
2184
+     <listitem><ulink
2185
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=409737">Bug 409737 -
2186
+javascript.enabled and docShell.allowJavascript do not disable all event
2187
+handlers</ulink>
2188
+     <para>
2189
+
2190
+This bug allows pages to execute javascript via addEventListener and perhaps
2191
+other callbacks. In order to prevent this bug from enabling an attacker to
2192
+break the <link linkend="isolation">Network Isolation</link> requirement,
2193
+Torbutton 1.1.13 began blocking popups and history manipulation from different
2194
+Tor states.  So long as there are no ways to open popups or redirect the user
2195
+to a new page, the <link linkend="contentpolicy">Torbutton content
2196
+policy</link> should block Javascript network access. However, if there are
2197
+ways to open popups or perform redirects such that Torbutton cannot block
2198
+them, pages may still have free reign to break that requirement and reveal a
2199
+user's original IP address.
2200
+
2201
+     </para>
2202
+     </listitem>
2203
+     <listitem><ulink
2204
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=448743">Bug 448743 -
2205
+Decouple general.useragent.locale from spoofing of navigator.language</ulink>
2206
+     <para>
2207
+
2208
+Currently, Torbutton spoofs the <command>navigator.language</command>
2209
+attribute via <link linkend="jshooks">Javascript hooks</link>. Unfortunately,
2210
+these do not work on Firefox 3. It would be ideal to have
2211
+a pref to set this value (something like a
2212
+<command>general.useragent.override.locale</command>),
2213
+to avoid fragmenting the anonymity set of users of foreign locales. This issue
2214
+impedes Torbutton from fully meeting its <link
2215
+linkend="setpreservation">Anonymity Set Preservation</link>
2216
+requirement on Firefox 3.
2217
+
2218
+     </para>
2219
+     </listitem>
2220
+    </orderedlist>
2221
+  </sect2>
2222
+  <sect2 id="FirefoxWishlist">
2223
+   <title>Bugs blocking functionality</title>
2224
+   <para>
2225
+The following bugs impact Torbutton and similar extensions' functionality.
2226
+   </para>
2227
+
2228
+    <orderedlist>
2229
+
2230
+
2231
+   <listitem><ulink
2232
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=445696">Bug 445696 -
2233
+Extensions cannot determine if firefox is fullScreen</ulink>
2234
+   <para>
2235
+
2236
+The windowState property of <ulink
2237
+url="https://developer.mozilla.org/en/XUL/window">ChromeWindows</ulink> does not accurately reflect the true
2238
+state of the window in some cases on Linux. This causes Torbutton to attempt
2239
+to resize maximized and minimized windows when it should not.
2240
+
2241
+   </para>
2242
+   </listitem>
2243
+   <listitem><ulink
2244
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=290456">Bug 290456 -
2245
+Block/clear Flash MX "cookies" as well</ulink>
2246
+   <para>
2247
+
2248
+Today, it is possible to allow plugins if you have a transparent proxy such as
2249
+<ulink url="http://anonymityanywhere.com/incognito/">Incognito</ulink> to prevent proxy bypass. However, flash cookies can still be used to
2250
+link your Tor and Non-Tor activity, and this reveal your IP to an adversary
2251
+that does so. This can be solved by manually removing your flash cookies (like
2252
+<ulink
2253
+url="https://addons.mozilla.org/en-US/firefox/addon/6623">BetterPrivacy</ulink> does), but
2254
+it would be nice if there was a standard way to do this from a Firefox API.
2255
+
2256
+   </para>
2257
+   </listitem>
2258
+   <listitem><ulink
2259
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=417869">Bug 417869 -
2260
+Browser context is difficult to obtain from many XPCOM callbacks</ulink>
2261
+   <para>
2262
+
2263
+It is difficult to determine which tabbrowser many XPCOM callbacks originate
2264
+from, and in some cases absolutely no context information is provided at all.
2265
+While this doesn't have much of an effect on Torbutton, it does make writing
2266
+extensions that would like to do per-tab settings and content filters (such as
2267
+FoxyProxy) difficult to impossible to implement securely.
2268
+
2269
+   </para>
2270
+   </listitem>
2271
+   <listitem><ulink
2272
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=418321">Bug 418321 -
2273
+Components do not expose disk interfaces</ulink>
2274
+   <para>
2275
+
2276
+Several components currently provide no way of reimplementing their disk
2277
+access to easily satisfy Torbutton's <link linkend="disk">Disk
2278
+Avoidance</link> requirements. Workarounds exist, but they are <link
2279
+linkend="sessionstore">clunky</link>, and
2280
+some of them involve disabling functionality during Tor usage.
2281
+
2282
+   </para>
2283
+   </listitem>
2284
+
2285
+<!--
2286
+FIXME: Need to use new observer methods if possible
2287
+   <listitem><ulink
2288
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=448741">Bug 448741 -
2289
+nsISessionStore uses private methods and is not extensible</ulink>
2290
+   <para>
2291
+
2292
+Similar to the above bug, in the specific case of the sessionstore component,
2293
+the API is not amenable to Contract ID hooking, and this requires that
2294
+Torbutton include modified copies of this component for Firefox 2 and 3, which
2295
+has <ulink
2296
+url="https://bugs.torproject.org/flyspray/index.php?do=details&amp;id=722">raised
2297
+objections</ulink> from some developers.
2298
+
2299
+   </para>
2300
+   </listitem>
2301
+   <listitem><ulink
2302
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=439384">Bug 439384 -
2303
+"profile-do-change" event does not cause cookie table reload</ulink>
2304
+   <para>
2305
+
2306
+In Firefox 3, the change to the new SQLlite database for cookie storage has a
2307
+bug that prevents Torbutton's cookie jaring from working properly. The
2308
+"profile-do-change" observer event no longer properly causes either a sync or
2309
+reload of the cookie database from disk after it is copied into place.
2310
+Torbutton currently works around this by issuing the SQLLite queries manually
2311
+to store and rebuild the cookie database.
2312
+
2313
+   </para>
2314
+   </listitem>
2315
+
2316
+   <listitem><ulink
2317
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=248970">Bug 248970 (PrivateBrowsing) - Private Browsing mode (global toggle for
2318
+saving/caching everything)</ulink>
2319
+   <para>
2320
+
2321
+This bug catalogs the discussion of a 'Private Mode' in Firefox that would
2322
+perform many, but not all, of the activities of Torbutton. It would be useful
2323
+to leverage the resulting setting to simplify Torbutton. This bug is listed so
2324
+we can track this progress and ensure that it doesn't end up defining
2325
+behaviors contrary to and incompatible with Torbutton's requirements (though a
2326
+subset of the <link linkend="requirements">requirements</link> is of course fine).
2327
+
2328
+   </para>
2329
+   </listitem>
2330
+-->
2331
+
2332
+
2333
+
2334
+  </orderedlist>
2335
+  </sect2>
2336
+  <sect2 id="FirefoxMiscBugs">
2337
+   <title>Low Priority Bugs</title>
2338
+   <para>
2339
+The following bugs have an effect upon Torbutton, but are superseded by more
2340
+practical and more easily fixable variant bugs above; or have stable, simple
2341
+workarounds.
2342
+  </para>
2343
+
2344
+    <orderedlist>
2345
+    <listitem><ulink
2346
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=435151">Bug 435151 - XPCSafeJSObjectWrapper breaks evalInSandbox</ulink>
2347
+     <para>
2348
+
2349
+Under Firefox 3, the XPCSafeJSObjectWrapper breaks when you try to use
2350
+constructors of classes defined from within the scope of the sandbox, among
2351
+other things. This prevents Torbutton from applying the Timezone hooks under
2352
+Firefox 3, but a better solution for Torbutton's specific date hooking needs 
2353
+would be a fix for the above mentioned Bug 392274. Of course, many more
2354
+extensions may be interested in the sandbox hooking functionality working
2355
+properly though.
2356
+
2357
+     </para>
2358
+     </listitem>
2359
+     <listitem><ulink
2360
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=440892">Bug 440892 -
2361
+network.protocol-handler.warn-external are ignored</ulink>
2362
+     <para>
2363
+
2364
+Sometime in the Firefox 3 development cycle, the preferences that governed
2365
+warning a user when external apps were launched got disconnected from the code
2366
+that does the launching. Torbutton depended on these prefs to prevent websites
2367
+from launching specially crafted documents and application arguments that
2368
+caused Proxy Bypass. We currently work around this issue by <link
2369
+linkend="appblocker">wrapping the app launching components</link> to present a
2370
+popup before launching external apps while Tor is enabled. While this works,
2371
+it would be nice if these prefs were either fixed or removed.
2372
+
2373
+     </para>
2374
+     </listitem>
2375
+    <listitem><ulink
2376
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=437014">Bug 437014 -
2377
+nsIContentPolicy::shouldLoad no longer called for favicons</ulink>
2378
+    <para>
2379
+
2380
+Firefox 3.0 stopped calling the shouldLoad call of content policy for favicon
2381
+loads. Torbutton had relied on this call to block favicon loads for opposite
2382
+Tor states. The workaround it employs for Firefox 3 is to cancel the request
2383
+when it arrives in the <command>torbutton_http_observer</command> used for
2384
+blocking full page plugin loads. This seems to work just fine, but is a bit
2385
+dirty.
2386
+
2387
+    </para>
2388
+    </listitem>
2389
+<!--
2390
+    <listitem><ulink
2391
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=437016">Bug 437016 -
2392
+nsIContentPolicy::shouldLoad not called for livemarks</ulink>
2393
+    <para>
2394
+
2395
+An alternative fix for the livemarks bug above would be to block livemarks
2396
+fetches from the content policy. Unfortunately shouldLoad is not called for
2397
+livemarks fetches.
2398
+
2399
+    </para>
2400
+    </listitem>
2401
+-->
2402
+ 
2403
+     <listitem><ulink
2404
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=309524">Bug 309524</ulink>
2405
+and <ulink url="https://bugzilla.mozilla.org/show_bug.cgi?id=380556">Bug
2406
+380556</ulink> - nsIContentPolicy::shouldProcess is not called.
2407
+     <para>
2408
+
2409
+This is a call that would be useful to develop a better workaround for the
2410
+allowPlugins issue above. If the content policy were called before a URL was
2411
+handed over to a plugin or helper app, it would make the workaround for the
2412
+above allowPlugins bug a lot cleaner. Obviously this bug is not as severe as
2413
+the others though, but it might be nice to have this API as a backup.
2414
+
2415
+     </para>
2416
+     </listitem>
2417
+
2418
+     <listitem><ulink
2419
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=401296">Bug 401296 - docShell.allowPlugins
2420
+not honored for direct links</ulink> (Perhaps subset of <ulink
2421
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=282106">Bug 282106</ulink>?)
2422
+     <para>
2423
+
2424
+Similar to the javascript plugin disabling attribute, the plugin disabling
2425
+attribute is also not perfect &mdash; it is ignored for direct links to plugin
2426
+handled content, as well as meta-refreshes to plugin handled content.  This
2427
+requires Torbutton to listen to a number of different http events to intercept
2428
+plugin-related mime type URLs and cancel their requests. Again, since plugins
2429
+are quite horrible about obeying proxy settings, loading a plugin pretty much
2430
+ensures a way to break the <link linkend="isolation">Network Isolation</link>
2431
+requirement and reveal a user's original IP address. Torbutton's code to
2432
+perform this workaround has been subverted at least once already by Kyle
2433
+Williams.
2434
+
2435
+     </para>
2436
+     </listitem>
2437
+<!--
2438
+
2439
+XXX: This is likely fixed with nsICrypto.logout()
2440
+
2441
+     <listitem><ulink
2442
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=448747">Bug 448747 -
2443
+Provide Mechanism to clear TLS Session IDs</ulink>
2444
+     <para>
2445
+
2446
+As <link linkend="browseroverlay">mentioned above</link>, Torbutton currently
2447
+toggles <command>security.enable_ssl2</command> to clear the SSL
2448
+Session ID cache via the pref observer at <ulink
2449
+url="http://mxr.mozilla.org/security/source/security/manager/ssl/src/nsNSSComponent.cpp#2134">nsNSSComponent.cpp
2450
+line 2134</ulink>. This is an arcane and potentially fragile fix. It would be
2451
+better if there were a more standard interface for accomplishing the same
2452
+thing.
2453
+
2454
+     </para>
2455
+     </listitem>
2456
+-->
2457
+
2458
+   <listitem><ulink
2459
+url="https://bugzilla.mozilla.org/show_bug.cgi?id=419598">Bug 419598 - 'var
2460
+Date' is deletable</ulink>
2461
+     <para>
2462
+
2463
+Based on Page 62 of the <ulink
2464
+url="http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf">ECMA-262
2465
+Javascript spec</ulink>, it seems like it should be possible to do something
2466
+like the following to prevent the Date object from being unmasked:
2467
+<screen>
2468
+with(window) {
2469
+    var Date = fakeDate;
2470
+    var otherVariable = 42;
2471
+}
2472
+
2473
+delete window.Date; // Should fail. Instead succeeds, revealing original Date.
2474
+delete window.otherVariable; // Fails, leaving window.otherVariable set to 42.
2475
+</screen>
2476
+
2477
+From the ECMA-262 spec:
2478
+
2479
+<blockquote>
2480
+If the variable statement occurs inside a FunctionDeclaration, the variables
2481
+are defined with function-local scope in that function, as described in
2482
+s10.1.3. Otherwise, they are defined with global scope (that is, they are
2483
+created as members of the global object, as described in 10.1.3) using
2484
+property attributes { DontDelete }. Variables are created when the execution
2485
+scope is entered. A Block does not define a new execution scope. Only Program
2486
+and FunctionDeclaration produce a new scope. Variables are initialized to
2487
+undefined when created. A variable with an Initialiser is assigned the value
2488
+of its AssignmentExpression when the VariableStatement is executed, not when
2489
+the variable is created.
2490
+</blockquote>
2491
+
2492
+In fact, this is exactly how the with statement with a variable declaration
2493
+behaves <emphasis>for all other variables other than ones that shadow system
2494
+variables</emphasis>. Some variables (such as
2495
+<command>window.screen</command>, and <command>window.history</command>) can't
2496
+even be shadowed in this way, and give an error about lacking a setter. If
2497
+such shadowing were possible, it would greatly simplify the Javascript hooking
2498
+code, which currently relies on undocumented semantics of
2499
+<command>__proto__</command> to copy the original values in the event of a
2500
+delete. This <command>__proto__</command> hack unfortunately does not work for
2501
+the Date object though.
2502
+
2503
+     </para>
2504
+    </listitem>
2505
+
2506
+  </orderedlist>
2507
+  </sect2>
2508
+</sect1>
2509
+
2510
+<sect1 id="TestPlan">
2511
+  <title>Testing</title>
2512
+  <para>
2513
+
2514
+The purpose of this section is to cover all the known ways that Tor browser
2515
+security can be subverted from a penetration testing perspective. The hope
2516
+is that it will be useful both for creating a &quot;Tor Safety Check&quot;
2517
+page, and for developing novel tests and actively attacking Torbutton with the
2518
+goal of finding vulnerabilities in either it or the Mozilla components,
2519
+interfaces and settings upon which it relies.
2520
+
2521
+  </para>
2522
+  <sect2 id="SingleStateTesting">
2523
+   <title>Single state testing</title>
2524
+   <para>
2525
+
2526
+Torbutton is a complicated piece of software. During development, changes to
2527
+one component can affect a whole slough of unrelated features.  A number of
2528
+aggregated test suites exist that can be used to test for regressions in
2529
+Torbutton and to help aid in the development of Torbutton-like addons and
2530
+other privacy modifications of other browsers. Some of these test suites exist
2531
+as a single automated page, while others are a series of pages you must visit
2532
+individually. They are provided here for reference and future regression
2533
+testing, and also in the hope that some brave soul will one day decide to
2534
+combine them into a comprehensive automated test suite.
2535
+
2536
+     <orderedlist>
2537
+      <listitem><ulink url="http://decloak.net/">Decloak.net</ulink>
2538
+       <para>
2539
+
2540
+Decloak.net is the canonical source of plugin and external-application based
2541
+proxy-bypass exploits. It is a fully automated test suite maintained by <ulink
2542
+url="http://digitaloffense.net/">HD Moore</ulink> as a service for people to
2543
+use to test their anonymity systems.
2544
+
2545
+       </para>
2546
+      </listitem>
2547
+      <listitem><ulink url="http://deanonymizer.com/">Deanonymizer.com</ulink>
2548
+       <para>
2549
+
2550
+Deanonymizer.com is another automated test suite that tests for proxy bypass
2551
+and other information disclosure vulnerabilities. It is maintained by Kyle
2552
+Williams, the author of <ulink url="http://www.janusvm.com/">JanusVM</ulink>
2553
+and <ulink url="http://www.januspa.com/">JanusPA</ulink>.
2554
+
2555
+       </para>
2556
+      </listitem>
2557
+      <listitem><ulink url="https://www.jondos.de/en/anontest">JonDos
2558
+AnonTest</ulink>
2559
+       <para>
2560
+
2561
+The <ulink url="https://www.jondos.de">JonDos people</ulink> also provide an
2562
+anonymity tester. It is more focused on HTTP headers than plugin bypass, and
2563
+points out a couple of headers Torbutton could do a better job with
2564
+obfuscating.
2565
+
2566
+       </para>
2567
+      </listitem>
2568
+      <listitem><ulink url="http://browserspy.dk">Browserspy.dk</ulink>
2569
+       <para>
2570
+
2571
+Browserspy.dk provides a tremendous collection of browser fingerprinting and
2572
+general privacy tests. Unfortunately they are only available one page at a
2573
+time, and there is not really solid feedback on good vs bad behavior in
2574
+the test results.
2575
+
2576
+       </para>
2577
+      </listitem>
2578
+      <listitem><ulink url="http://analyze.privacy.net/">Privacy
2579
+Analyzer</ulink>
2580
+       <para>
2581
+
2582
+The Privacy Analyzer provides a dump of all sorts of browser attributes and
2583
+settings that it detects, including some information on your origin IP
2584
+address. Its page layout and lack of good vs bad test result feedback makes it
2585
+not as useful as a user-facing testing tool, but it does provide some
2586
+interesting checks in a single page.
2587
+
2588
+       </para>
2589
+      </listitem>
2590
+      <listitem><ulink url="http://ha.ckers.org/mr-t/">Mr. T</ulink>
2591
+       <para>
2592
+
2593
+Mr. T is a collection of browser fingerprinting and deanonymization exploits
2594
+discovered by the <ulink url="http://ha.ckers.org">ha.ckers.org</ulink> crew
2595
+and others. It is also not as user friendly as some of the above tests, but it
2596
+is a useful collection.
2597
+
2598
+       </para>
2599
+      </listitem>
2600
+      <listitem>Gregory Fleischer's <ulink
2601
+url="http://pseudo-flaw.net/content/tor/torbutton/">Torbutton</ulink> and
2602
+<ulink
2603
+url="http://pseudo-flaw.net/content/defcon/dc-17-demos/d.html">Defcon
2604
+17</ulink> Test Cases
2605
+       <para>
2606
+
2607
+Gregory Fleischer has been hacking and testing Firefox and Torbutton privacy
2608
+issues for the past 2 years. He has an excellent collection of all his test
2609
+cases that can be used for regression testing. In his Defcon work, he
2610
+demonstrates ways to infer Firefox version based on arcane browser properties.
2611
+We are still trying to determine the best way to address some of those test
2612
+cases.
2613
+
2614
+       </para>
2615
+      </listitem>
2616
+      <listitem><ulink url="https://torcheck.xenobite.eu/index.php">Xenobite's
2617
+TorCheck Page</ulink>
2618
+       <para>
2619
+
2620
+This page checks to ensure you are using a valid Tor exit node and checks for
2621
+some basic browser properties related to privacy. It is not very fine-grained
2622
+or complete, but it is automated and could be turned into something useful
2623
+with a bit of work.
2624
+
2625
+       </para>
2626
+      </listitem>
2627
+     </orderedlist>
2628
+    </para>
2629
+  </sect2>
2630
+  <sect2>
2631
+   <title>Multi-state testing</title>
2632
+   <para>
2633
+
2634
+The tests in this section are geared towards a page that would instruct the
2635
+user to toggle their Tor state after the fetch and perform some operations:
2636
+mouseovers, stray clicks, and potentially reloads.
2637
+
2638
+   </para>
2639
+   <sect3>
2640
+    <title>Cookies and Cache Correlation</title>
2641
+    <para>
2642
+The most obvious test is to set a cookie, ask the user to toggle tor, and then
2643
+have them reload the page. The cookie should no longer be set if they are
2644
+using the default Torbutton settings. In addition, it is possible to leverage
2645
+the cache to <ulink
2646
+url="http://crypto.stanford.edu/sameorigin/safecachetest.html">store unique
2647
+identifiers</ulink>. The default settings of Torbutton should also protect
2648
+against these from persisting across Tor Toggle.
2649
+
2650
+    </para>
2651
+   </sect3>
2652
+   <sect3>
2653
+    <title>Javascript timers and event handlers</title>
2654
+    <para>
2655
+
2656
+Javascript can set timers and register event handlers in the hopes of fetching
2657
+URLs after the user has toggled Torbutton. 
2658
+    </para>
2659
+   </sect3>
2660
+   <sect3>
2661
+    <title>CSS Popups and non-script Dynamic Content</title>
2662
+    <para>
2663
+
2664
+Even if Javascript is disabled, CSS is still able to 
2665
+<ulink url="http://www.tjkdesign.com/articles/css%20pop%20ups/">create popup-like
2666
+windows</ulink>
2667
+via the 'onmouseover' CSS attribute, which can cause arbitrary browser
2668
+activity as soon as the mouse enters into the content window. It is also
2669
+possible for meta-refresh tags to set timers long enough to make it likely
2670
+that the user has toggled Tor before fetching content.
2671
+
2672
+    </para>
2673
+   </sect3>
2674
+  </sect2>
2675
+  <sect2 id="HackTorbutton">
2676
+   <title>Active testing (aka How to Hack Torbutton)</title>
2677
+   <para>
2678
+
2679
+The idea behind active testing is to discover vulnerabilities in Torbutton to
2680
+bypass proxy settings, run script in an opposite Tor state, store unique
2681
+identifiers, leak location information, or otherwise violate <link
2682
+linkend="requirements">its requirements</link>. Torbutton has ventured out
2683
+into a strange and new security landscape. It depends on Firefox mechanisms
2684
+that haven't necessarily been audited for security, certainly not for the
2685
+threat model that Torbutton seeks to address. As such, it and the interfaces
2686
+it depends upon still need a 'trial by fire' typical of new technologies. This
2687
+section of the document was written with the intention of making that period
2688
+as fast as possible. Please help us get through this period by considering
2689
+these attacks, playing with them, and reporting what you find (and potentially
2690
+submitting the test cases back to be run in the standard batch of Torbutton
2691
+tests.
2692
+
2693
+   </para>
2694
+   <sect3>
2695
+    <title>Some suggested vectors to investigate</title>
2696
+    <para>
2697
+    <itemizedlist>
2698
+     <listitem>Strange ways to register Javascript <ulink
2699
+url="http://en.wikipedia.org/wiki/DOM_Events">events</ulink> and <ulink
2700
+url="http://www.devshed.com/c/a/JavaScript/Using-Timers-in-JavaScript/">timeouts</ulink> should
2701
+be verified to actually be ineffective after Tor has been toggled.</listitem>
2702
+     <listitem>Other ways to cause Javascript to be executed after
2703
+<command>javascript.enabled</command> has been toggled off.</listitem>
2704
+     <listitem>Odd ways to attempt to load plugins. Kyle Williams has had
2705
+some success with direct loads/meta-refreshes of plugin-handled URLs.</listitem>
2706
+     <listitem>The Date and Timezone hooks should be verified to work with
2707
+crazy combinations of iframes, nested iframes, iframes in frames, frames in
2708
+iframes, and popups being loaded and
2709
+reloaded in rapid succession, and/or from one another. Think race conditions and deep, 
2710
+parallel nesting, involving iframes from both <ulink
2711
+url="http://en.wikipedia.org/wiki/Same_origin_policy">same-origin and
2712
+non-same-origin</ulink> domains.</listitem>
2713
+     <listitem>In addition, there may be alternate ways and other
2714
+methods to query the timezone, or otherwise use some of the Date object's
2715
+methods in combination to deduce the timezone offset. Of course, the author
2716
+tried his best to cover all the methods he could foresee, but it's always good
2717
+to have another set of eyes try it out.</listitem>
2718
+     <listitem>Similarly, is there any way to confuse the <link
2719
+linkend="contentpolicy">content policy</link>
2720
+mentioned above to cause it to allow certain types of page fetches? For
2721
+example, it was recently discovered that favicons are not fetched by the
2722
+content, but the chrome itself, hence the content policy did not look up the
2723
+correct window to determine the current Tor tag for the favicon fetch. Are
2724
+there other things that can do this? Popups? Bookmarklets? Active bookmarks? </listitem>
2725
+     <listitem>Alternate ways to store and fetch unique identifiers. For example, <ulink
2726
+url="http://developer.mozilla.org/en/docs/DOM:Storage">DOM Storage</ulink>
2727
+caught us off guard. 
2728
+It was
2729
+also discovered by <ulink url="http://pseudo-flaw.net">Gregory
2730
+Fleischer</ulink> that <ulink
2731
+url="http://pseudo-flaw.net/content/tor/torbutton/">content window access to
2732
+chrome</ulink> can be used to build <link linkend="fingerprinting">unique
2733
+identifiers</link>. 
2734
+Are there any other
2735
+arcane or experimental ways that Firefox provides to create and store unique
2736
+identifiers? Or perhaps unique identifiers can be queried or derived from
2737
+properties of the machine/browser that Javascript has access to? How unique
2738
+can these identifiers be?
2739
+     </listitem>
2740
+     <listitem>Is it possible to get the browser to write some history to disk
2741
+(aside from swap) that can be retrieved later? By default, Torbutton should
2742
+write no history, cookie, or other browsing activity information to the
2743
+harddisk.</listitem>
2744
+     <listitem>Do popup windows make it easier to break any of the above
2745
+behavior? Are javascript events still canceled in popups? What about recursive
2746
+popups from Javascript, data, and other funky URL types? What about CSS
2747
+popups? Are they still blocked after Tor is toggled?</listitem>
2748
+     <listitem>Chrome-escalation attacks. The interaction between the
2749
+Torbutton chrome Javascript and the client content window javascript is pretty
2750
+well-defined and carefully constructed, but perhaps there is a way to smuggle
2751
+javascript back in a return value, or otherwise inject network-loaded
2752
+javascript into the chrome (and thus gain complete control of the browser).
2753
+</listitem>
2754
+</itemizedlist>
2755
+
2756
+    </para>
2757
+   </sect3>
2758
+  </sect2>
2759
+</sect1>
2760
+</article>
... ...
@@ -0,0 +1,1482 @@
1
+<?xml version="1.0" encoding="UTF-8"?>
2
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
3
+<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Torbutton Design Documentation</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /></head><body><div class="article" title="Torbutton Design Documentation"><div class="titlepage"><div><div><h2 class="title"><a id="design"></a>Torbutton Design Documentation</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Mike</span> <span class="surname">Perry</span></h3><div class="affiliation"><div class="address"><p><code class="email">&lt;<a class="email" href="mailto:mikeperry.fscked/org">mikeperry.fscked/org</a>&gt;</code></p></div></div></div></div><div><p class="pubdate">Jun 28 2010</p></div></div><hr /></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#id2910402">1. Introduction</a></span></dt><dd><dl><dt><span class="sect2"><a href="#adversary">1.1. Adversary Model</a></span></dt><dt><span class="sect2"><a href="#requirements">1.2. Torbutton Requirements</a></span></dt><dt><span class="sect2"><a href="#layout">1.3. Extension Layout</a></span></dt></dl></dd><dt><span class="sect1"><a href="#id2907285">2. Components</a></span></dt><dd><dl><dt><span class="sect2"><a href="#id2927418">2.1. Hooked Components</a></span></dt><dt><span class="sect2"><a href="#id2922900">2.2. New Components</a></span></dt></dl></dd><dt><span class="sect1"><a href="#id2907191">3. Chrome</a></span></dt><dd><dl><dt><span class="sect2"><a href="#browseroverlay">3.1. Browser Overlay - torbutton.xul</a></span></dt><dt><span class="sect2"><a href="#id2922887">3.2. Preferences Window - preferences.xul</a></span></dt><dt><span class="sect2"><a href="#id2922834">3.3. Other Windows</a></span></dt></dl></dd><dt><span class="sect1"><a href="#id2917336">4. Toggle Code Path</a></span></dt><dd><dl><dt><span class="sect2"><a href="#id2934128">4.1. Button Click</a></span></dt><dt><span class="sect2"><a href="#id2915503">4.2. Proxy Update</a></span></dt><dt><span class="sect2"><a href="#id2931338">4.3. Settings Update</a></span></dt></dl></dd><dt><span class="sect1"><a href="#id2898010">5. Description of Options</a></span></dt><dd><dl><dt><span class="sect2"><a href="#id2910532">5.1. Test Settings</a></span></dt><dt><span class="sect2"><a href="#plugins">5.2. Disable plugins on Tor Usage (crucial)</a></span></dt><dt><span class="sect2"><a href="#id2917719">5.3. Isolate Dynamic Content to Tor State (crucial)</a></span></dt><dt><span class="sect2"><a href="#jshooks">5.4. Hook Dangerous Javascript</a></span></dt><dt><span class="sect2"><a href="#id2897638">5.5. Resize windows to multiples of 50px during Tor usage (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2924640">5.6. Disable Updates During Tor</a></span></dt><dt><span class="sect2"><a href="#id2892217">5.7. Redirect Torbutton Updates Via Tor (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2892261">5.8. Disable Search Suggestions during Tor (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2892300">5.9. Disable livemarks updates during Tor usage (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2892371">5.10. Block Tor/Non-Tor access to network from file:// urls (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2892443">5.11. Close all Tor/Non-Tor tabs and windows on toggle (optional)</a></span></dt><dt><span class="sect2"><a href="#id2892524">5.12. Isolate Access to History navigation to Tor state (crucial)</a></span></dt><dt><span class="sect2"><a href="#id2892609">5.13. History Access Settings</a></span></dt><dt><span class="sect2"><a href="#id2892721">5.14. Clear History During Tor Toggle (optional)</a></span></dt><dt><span class="sect2"><a href="#id2934267">5.15. Block Password+Form saving during Tor/Non-Tor</a></span></dt><dt><span class="sect2"><a href="#id2934328">5.16. Block Tor disk cache and clear all cache on Tor Toggle</a></span></dt><dt><span class="sect2"><a href="#id2934378">5.17. Block disk and memory cache during Tor</a></span></dt><dt><span class="sect2"><a href="#id2934430">5.18. Clear Cookies on Tor Toggle</a></span></dt><dt><span class="sect2"><a href="#id2934481">5.19. Store Non-Tor cookies in a protected jar</a></span></dt><dt><span class="sect2"><a href="#id2934538">5.20. Store both Non-Tor and Tor cookies in a protected jar (dangerous)</a></span></dt><dt><span class="sect2"><a href="#id2934577">5.21. Manage My Own Cookies (dangerous)</a></span></dt><dt><span class="sect2"><a href="#id2934592">5.22. Disable DOM Storage during Tor usage (crucial)</a></span></dt><dt><span class="sect2"><a href="#id2934696">5.23. Clear HTTP Auth on Tor Toggle (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2934733">5.24. Clear cookies on Tor/Non-Tor shutdown</a></span></dt><dt><span class="sect2"><a href="#id2934788">5.25. Reload cookie jar/clear cookies on Firefox crash</a></span></dt><dt><span class="sect2"><a href="#id2934863">5.26. On crash recovery or session restored startup, restore via: Tor, Non-Tor</a></span></dt><dt><span class="sect2"><a href="#id2934935">5.27. On normal startup, set state to: Tor, Non-Tor, Shutdown State</a></span></dt><dt><span class="sect2"><a href="#id2934994">5.28. Prevent session store from saving Non-Tor/Tor-loaded tabs</a></span></dt><dt><span class="sect2"><a href="#id2935059">5.29. Set user agent during Tor usage (crucial)</a></span></dt><dt><span class="sect2"><a href="#id2935233">5.30. Spoof US English Browser</a></span></dt><dt><span class="sect2"><a href="#id2935326">5.31. Don't send referrer during Tor Usage</a></span></dt><dt><span class="sect2"><a href="#id2935366">5.32. Strip platform and language off of Google Search Box queries</a></span></dt><dt><span class="sect2"><a href="#id2935407">5.33. Automatically use an alternate search engine when presented with a
4
+Google Captcha</a></span></dt><dt><span class="sect2"><a href="#id2935487">5.34. Store SSL/CA Certs in separate jars for Tor/Non-Tor (recommended)</a></span></dt></dl></dd><dt><span class="sect1"><a href="#FirefoxBugs">6. Relevant Firefox Bugs</a></span></dt><dd><dl><dt><span class="sect2"><a href="#FirefoxSecurity">6.1. Bugs impacting security</a></span></dt><dt><span class="sect2"><a href="#FirefoxWishlist">6.2. Bugs blocking functionality</a></span></dt><dt><span class="sect2"><a href="#FirefoxMiscBugs">6.3. Low Priority Bugs</a></span></dt></dl></dd><dt><span class="sect1"><a href="#TestPlan">7. Testing</a></span></dt><dd><dl><dt><span class="sect2"><a href="#SingleStateTesting">7.1. Single state testing</a></span></dt><dt><span class="sect2"><a href="#id2936532">7.2. Multi-state testing</a></span></dt><dt><span class="sect2"><a href="#HackTorbutton">7.3. Active testing (aka How to Hack Torbutton)</a></span></dt></dl></dd></dl></div><div class="sect1" title="1. Introduction"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2910402"></a>1. Introduction</h2></div></div></div><p>
5
+
6
+This document describes the goals, operation, and testing procedures of the
7
+Torbutton Firefox extension. It is current as of Torbutton 1.2.5.
8
+
9
+  </p><div class="sect2" title="1.1. Adversary Model"><div class="titlepage"><div><div><h3 class="title"><a id="adversary"></a>1.1. Adversary Model</h3></div></div></div><p>
10
+
11
+A Tor web browser adversary has a number of goals, capabilities, and attack
12
+types that can be used to guide us towards a set of requirements for the
13
+Torbutton extension. Let's start with the goals.
14
+
15
+   </p><div class="sect3" title="Adversary Goals"><div class="titlepage"><div><div><h4 class="title"><a id="adversarygoals"></a>Adversary Goals</h4></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Bypassing proxy settings</strong></span><p>The adversary's primary goal is direct compromise and bypass of 
16
+Tor, causing the user to directly connect to an IP of the adversary's
17
+choosing.</p></li><li class="listitem"><span class="command"><strong>Correlation of Tor vs Non-Tor Activity</strong></span><p>If direct proxy bypass is not possible, the adversary will likely
18
+happily settle for the ability to correlate something a user did via Tor with
19
+their non-Tor activity. This can be done with cookies, cache identifiers,
20
+javascript events, and even CSS. Sometimes the fact that a user uses Tor may
21
+be enough for some authorities.</p></li><li class="listitem"><span class="command"><strong>History disclosure</strong></span><p>
22
+The adversary may also be interested in history disclosure: the ability to
23
+query a user's history to see if they have issued certain censored search
24
+queries, or visited censored sites.
25
+     </p></li><li class="listitem"><span class="command"><strong>Location information</strong></span><p>
26
+
27
+Location information such as timezone and locality can be useful for the
28
+adversary to determine if a user is in fact originating from one of the
29
+regions they are attempting to control, or to zero-in on the geographical
30
+location of a particular dissident or whistleblower.
31
+
32
+     </p></li><li class="listitem"><span class="command"><strong>Miscellaneous anonymity set reduction</strong></span><p>
33
+
34
+Anonymity set reduction is also useful in attempting to zero in on a
35
+particular individual. If the dissident or whistleblower is using a rare build
36
+of Firefox for an obscure operating system, this can be very useful
37
+information for tracking them down, or at least <a class="link" href="#fingerprinting">tracking their activities</a>.
38
+
39
+     </p></li><li class="listitem"><span class="command"><strong>History records and other on-disk
40
+information</strong></span><p>
41
+In some cases, the adversary may opt for a heavy-handed approach, such as
42
+seizing the computers of all Tor users in an area (especially after narrowing
43
+the field by the above two pieces of information). History records and cache
44
+data are the primary goals here.
45
+     </p></li></ol></div></div><div class="sect3" title="Adversary Capabilities - Positioning"><div class="titlepage"><div><div><h4 class="title"><a id="adversarypositioning"></a>Adversary Capabilities - Positioning</h4></div></div></div><p>
46
+The adversary can position themselves at a number of different locations in
47
+order to execute their attacks.
48
+    </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Exit Node or Upstream Router</strong></span><p>
49
+The adversary can run exit nodes, or alternatively, they may control routers
50
+upstream of exit nodes. Both of these scenarios have been observed in the
51
+wild.
52
+     </p></li><li class="listitem"><span class="command"><strong>Adservers and/or Malicious Websites</strong></span><p>
53
+The adversary can also run websites, or more likely, they can contract out
54
+ad space from a number of different adservers and inject content that way. For
55
+some users, the adversary may be the adservers themselves. It is not
56
+inconceivable that adservers may try to subvert or reduce a user's anonymity 
57
+through Tor for marketing purposes.
58
+     </p></li><li class="listitem"><span class="command"><strong>Local Network/ISP/Upstream Router</strong></span><p>
59
+The adversary can also inject malicious content at the user's upstream router
60
+when they have Tor disabled, in an attempt to correlate their Tor and Non-Tor
61
+activity.
62
+     </p></li><li class="listitem"><span class="command"><strong>Physical Access</strong></span><p>
63
+Some users face adversaries with intermittent or constant physical access.
64
+Users in Internet cafes, for example, face such a threat. In addition, in
65
+countries where simply using tools like Tor is illegal, users may face
66
+confiscation of their computer equipment for excessive Tor usage or just
67
+general suspicion.
68
+     </p></li></ol></div></div><div class="sect3" title="Adversary Capabilities - Attacks"><div class="titlepage"><div><div><h4 class="title"><a id="attacks"></a>Adversary Capabilities - Attacks</h4></div></div></div><p>
69
+
70
+The adversary can perform the following attacks from a number of different 
71
+positions to accomplish various aspects of their goals. It should be noted
72
+that many of these attacks (especially those involving IP address leakage) are
73
+often performed by accident by websites that simply have Javascript, dynamic 
74
+CSS elements, and plugins. Others are performed by adservers seeking to
75
+correlate users' activity across different IP addresses, and still others are
76
+performed by malicious agents on the Tor network and at national firewalls.
77
+
78
+    </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Inserting Javascript</strong></span><p>
79
+If not properly disabled, Javascript event handlers and timers
80
+can cause the browser to perform network activity after Tor has been disabled,
81
+thus allowing the adversary to correlate Tor and Non-Tor activity and reveal
82
+a user's non-Tor IP address. Javascript
83
+also allows the adversary to execute <a class="ulink" href="http://whattheinternetknowsaboutyou.com/" target="_top">history disclosure attacks</a>:
84
+to query the history via the different attributes of 'visited' links to search
85
+for particular google queries, sites, or even to <a class="ulink" href="http://www.mikeonads.com/2008/07/13/using-your-browser-url-history-estimate-gender/" target="_top">profile
86
+users based on gender and other classifications</a>. Finally,
87
+Javascript can be used to query the user's timezone via the
88
+<code class="function">Date()</code> object, and to reduce the anonymity set by querying
89
+the <code class="function">navigator</code> object for operating system, CPU, locale, 
90
+and user agent information.
91
+     </p></li><li class="listitem"><span class="command"><strong>Inserting Plugins</strong></span><p>
92
+
93
+Plugins are abysmal at obeying the proxy settings of the browser. Every plugin
94
+capable of performing network activity that the author has
95
+investigated is also capable of performing network activity independent of
96
+browser proxy settings - and often independent of its own proxy settings.
97
+Sites that have plugin content don't even have to be malicious to obtain a
98
+user's
99
+Non-Tor IP (it usually leaks by itself), though <a class="ulink" href="http://decloak.net" target="_top">plenty of active
100
+exploits</a> are possible as well. In addition, plugins can be used to store unique identifiers that are more
101
+difficult to clear than standard cookies. 
102
+<a class="ulink" href="http://epic.org/privacy/cookies/flash.html" target="_top">Flash-based
103
+cookies</a> fall into this category, but there are likely numerous other
104
+examples.
105
+
106
+     </p></li><li class="listitem"><span class="command"><strong>Inserting CSS</strong></span><p>
107
+
108
+CSS can also be used to correlate Tor and Non-Tor activity and reveal a user's
109
+Non-Tor IP address, via the usage of
110
+<a class="ulink" href="http://www.tjkdesign.com/articles/css%20pop%20ups/" target="_top">CSS
111
+popups</a> - essentially CSS-based event handlers that fetch content via
112
+CSS's onmouseover attribute. If these popups are allowed to perform network
113
+activity in a different Tor state than they were loaded in, they can easily
114
+correlate Tor and Non-Tor activity and reveal a user's IP address. In
115
+addition, CSS can also be used without Javascript to perform <a class="ulink" href="http://ha.ckers.org/weird/CSS-history.cgi" target="_top">CSS-only history disclosure
116
+attacks</a>.
117
+     </p></li><li class="listitem"><span class="command"><strong>Read and insert cookies</strong></span><p>
118
+
119
+An adversary in a position to perform MITM content alteration can inject
120
+document content elements to both read and inject cookies for
121
+arbitrary domains. In fact, many "SSL secured" websites are vulnerable to this
122
+sort of <a class="ulink" href="http://seclists.org/bugtraq/2007/Aug/0070.html" target="_top">active
123
+sidejacking</a>.
124
+
125
+     </p></li><li class="listitem"><span class="command"><strong>Create arbitrary cached content</strong></span><p>
126
+
127
+Likewise, the browser cache can also be used to <a class="ulink" href="http://crypto.stanford.edu/sameorigin/safecachetest.html" target="_top">store unique
128
+identifiers</a>. Since by default the cache has no same-origin policy,
129
+these identifiers can be read by any domain, making them an ideal target for
130
+adserver-class adversaries.
131
+
132
+     </p></li><li class="listitem"><a id="fingerprinting"></a><span class="command"><strong>Fingerprint users based on browser
133
+attributes</strong></span><p>
134
+
135
+There is an absurd amount of information available to websites via attributes
136
+of the browser. This information can be used to reduce anonymity set, or even
137
+<a class="ulink" href="http://mandark.fr/0x000000/articles/Total_Recall_On_Firefox..html" target="_top">uniquely
138
+fingerprint individual users</a>. </p><p>
139
+For illustration, let's perform a
140
+back-of-the-envelope calculation on the number of anonymity sets for just the
141
+resolution information available in the <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window" target="_top">window</a> and
142
+<a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.screen" target="_top">window.screen</a>
143
+objects. Browser window resolution information provides something like
144
+(1280-640)*(1024-480)=348160 different anonymity sets. Desktop resolution
145
+information contributes about another factor of 5 (for about 5 resolutions in
146
+typical use). In addition, the dimensions and position of the desktop taskbar
147
+are available, which can reveal hints on OS information. This boosts the count
148
+by a factor of 5 (for each of the major desktop taskbars - Windows, OSX, KDE
149
+and Gnome, and None). Subtracting the browser content window
150
+size from the browser outer window size provide yet more information.
151
+Firefox toolbar presence gives about a factor of 8 (3 toolbars on/off give
152
+2<sup>3</sup>=8). Interface effects such as titlebar fontsize
153
+and window manager settings gives a factor of about 9 (say 3 common font sizes
154
+for the titlebar and 3 common sizes for browser GUI element fonts).
155
+Multiply this all out, and you have (1280-640)*(1024-480)*5*5*8*9 ~=
156
+2<sup>29</sup>, or a 29 bit identifier based on resolution
157
+information alone. </p><p>
158
+
159
+Of course, this space is non-uniform and prone to incremental changes.
160
+However, if a bit vector space consisting of the above extracted attributes
161
+were used instead of the hash approach from <a class="ulink" href="http://mandark.fr/0x000000/articles/Total_Recall_On_Firefox..html" target="_top">The Hacker
162
+Webzine article above</a>, minor changes in browser window resolution will
163
+no longer generate totally new identifiers. 
164
+
165
+</p><p>
166
+
167
+To add insult to injury, <a class="ulink" href="http://pseudo-flaw.net/content/tor/torbutton/" target="_top">chrome URL disclosure
168
+attacks</a> mean that each and every extension on <a class="ulink" href="https://addons.mozilla.org" target="_top">addons.mozilla.org</a> adds another bit
169
+to that 2<sup>29</sup>. With hundreds of popular extensions
170
+and thousands of extensions total, it is easy to see that this sort of
171
+information is an impressively powerful identifier if used properly by a
172
+competent and determined adversary such as an ad network.  Again, a
173
+nearest-neighbor bit vector space approach here would also gracefully handle
174
+incremental changes to installed extensions.
175
+
176
+</p></li><li class="listitem"><span class="command"><strong>Remotely or locally exploit browser and/or
177
+OS</strong></span><p>
178
+Last, but definitely not least, the adversary can exploit either general 
179
+browser vulnerabilities, plugin vulnerabilities, or OS vulnerabilities to
180
+install malware and surveillance software. An adversary with physical access
181
+can perform similar actions. Regrettably, this last attack capability is
182
+outside of Torbutton's ability to defend against, but it is worth mentioning
183
+for completeness.
184
+     </p></li></ol></div></div></div><div class="sect2" title="1.2. Torbutton Requirements"><div class="titlepage"><div><div><h3 class="title"><a id="requirements"></a>1.2. Torbutton Requirements</h3></div></div></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
185
+
186
+Since many settings satisfy multiple requirements, this design document is
187
+organized primarily by Torbutton components and settings. However, if you are
188
+the type that would rather read the document from the requirements
189
+perspective, it is in fact possible to search for each of the following
190
+requirement phrases in the text to find the relevant features that help meet
191
+that requirement.
192
+
193
+</div><p>
194
+
195
+From the above Adversary Model, a number of requirements become clear. 
196
+
197
+   </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a id="proxy"></a><span class="command"><strong>Proxy Obedience</strong></span><p>The browser
198
+MUST NOT bypass Tor proxy settings for any content.</p></li><li class="listitem"><a id="isolation"></a><span class="command"><strong>Network Isolation</strong></span><p>Pages MUST NOT perform any network activity in a Tor state different
199
+ from the state they were originally loaded in.</p></li><li class="listitem"><a id="state"></a><span class="command"><strong>State Separation</strong></span><p>Browser state (cookies, cache, history, 'DOM storage'), accumulated in
200
+ one Tor state MUST NOT be accessible via the network in
201
+ another Tor state.</p></li><li class="listitem"><a id="undiscoverability"></a><span class="command"><strong>Tor Undiscoverability</strong></span><p>With
202
+the advent of bridge support in Tor 0.2.0.x, there are now a class of Tor
203
+users whose network fingerprint does not obviously betray the fact that they
204
+are using Tor. This should extend to the browser as well - Torbutton MUST NOT 
205
+reveal its presence while Tor is disabled.</p></li><li class="listitem"><a id="disk"></a><span class="command"><strong>Disk Avoidance</strong></span><p>The browser SHOULD NOT write any Tor-related state to disk, or store it
206
+ in memory beyond the duration of one Tor toggle.</p></li><li class="listitem"><a id="location"></a><span class="command"><strong>Location Neutrality</strong></span><p>The browser SHOULD NOT leak location-specific information, such as
207
+ timezone or locale via Tor.</p></li><li class="listitem"><a id="setpreservation"></a><span class="command"><strong>Anonymity Set
208
+Preservation</strong></span><p>The browser SHOULD NOT leak any other anonymity set reducing information 
209
+ (such as user agent, extension presence, and resolution information)
210
+automatically via Tor. The assessment of the attacks above should make it clear
211
+that anonymity set reduction is a very powerful method of tracking and
212
+eventually identifying anonymous users.
213
+</p></li><li class="listitem"><a id="updates"></a><span class="command"><strong>Update Safety</strong></span><p>The browser
214
+SHOULD NOT perform unauthenticated updates or upgrades via Tor.</p></li><li class="listitem"><a id="interoperate"></a><span class="command"><strong>Interoperability</strong></span><p>Torbutton SHOULD interoperate with third-party proxy switchers that
215
+ enable the user to switch between a number of different proxies. It MUST
216
+ provide full Tor protection in the event a third-party proxy switcher has
217
+ enabled the Tor proxy settings.</p></li></ol></div></div><div class="sect2" title="1.3. Extension Layout"><div class="titlepage"><div><div><h3 class="title"><a id="layout"></a>1.3. Extension Layout</h3></div></div></div><p>Firefox extensions consist of two main categories of code: 'Components' and
218
+'Chrome'. Components are a fancy name for classes that implement a given
219
+interface or interfaces. In Firefox, components <a class="ulink" href="https://developer.mozilla.org/en/XPCOM" target="_top">can be
220
+written</a> in C++,
221
+Javascript, or a mixture of both. Components have two identifiers: their
222
+'<a class="ulink" href="http://www.mozilla.org/projects/xpcom/book/cxc/html/quicktour2.html#1005005" target="_top">Contract
223
+ID</a>' (a human readable path-like string), and their '<a class="ulink" href="http://www.mozilla.org/projects/xpcom/book/cxc/html/quicktour2.html#1005329" target="_top">Class
224
+ID</a>' (a GUID hex-string). In addition, the interfaces they implement each have a hex
225
+'Interface ID'. It is possible to 'hook' system components - to reimplement
226
+their interface members with your own wrappers - but only if the rest of the
227
+browser refers to the component by its Contract ID. If the browser refers to
228
+the component by Class ID, it bypasses your hooks in that use case.
229
+Technically, it may be possible to hook Class IDs by unregistering the
230
+original component, and then re-registering your own, but this relies on
231
+obsolete and deprecated interfaces and has proved to be less than
232
+stable.</p><p>'Chrome' is a combination of XML and Javascript used to describe a window.
233
+Extensions are allowed to create 'overlays' that are 'bound' to existing XML
234
+window definitions, or they can create their own windows. The DTD for this XML
235
+is called <a class="ulink" href="http://developer.mozilla.org/en/docs/XUL_Reference" target="_top">XUL</a>.</p></div></div><div class="sect1" title="2. Components"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2907285"></a>2. Components</h2></div></div></div><p>
236
+
237
+Torbutton installs components for two purposes: hooking existing components to
238
+reimplement their interfaces; and creating new components that provide
239
+services to other pieces of the extension.
240
+
241
+  </p><div class="sect2" title="2.1. Hooked Components"><div class="titlepage"><div><div><h3 class="title"><a id="id2927418"></a>2.1. Hooked Components</h3></div></div></div><p>Torbutton makes extensive use of Contract ID hooking, and implements some
242
+of its own standalone components as well.  Let's discuss the hooked components
243
+first.</p><div class="sect3" title="@mozilla.org/browser/sessionstore;1 - components/nsSessionStore36.js"><div class="titlepage"><div><div><h4 class="title"><a id="sessionstore"></a><a class="ulink" href="http://developer.mozilla.org/en/docs/nsISessionStore" target="_top">@mozilla.org/browser/sessionstore;1</a> -
244
+<a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/nsSessionStore36.js" target="_top">components/nsSessionStore36.js</a></h4></div></div></div><p>These components address the <a class="link" href="#disk">Disk Avoidance</a>
245
+requirements of Torbutton. As stated in the requirements, Torbutton needs to
246
+prevent Tor tabs from being written to disk by the Firefox session store for a
247
+number of reasons, primary among them is the fact that Firefox can crash at
248
+any time, and a restart can cause you to fetch tabs in the incorrect Tor
249
+state.</p><p>These components illustrate a complication with Firefox hooking: you can
250
+only hook member functions of a class if they are published in an
251
+interface that the class implements. Unfortunately, the sessionstore has no
252
+published interface that is amenable to disabling the writing out of Tor tabs
253
+in specific. As such, Torbutton had to include the <span class="emphasis"><em>entire</em></span>
254
+nsSessionStore from both Firefox 2.0, 3.0, 3.5 and 3.6
255
+with a couple of modifications to prevent tabs that were loaded with Tor
256
+enabled from being written to disk, and some version detection code to
257
+determine which component to load. The <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/nsSessionStore36.diff" target="_top">diff against the original session
258
+store</a> is included in the git repository.</p></div><div class="sect3" title="@mozilla.org/uriloader/external-protocol-service;1 , @mozilla.org/uriloader/external-helper-app-service;1, and @mozilla.org/mime;1 - components/external-app-blocker.js"><div class="titlepage"><div><div><h4 class="title"><a id="appblocker"></a><a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/uriloader/external-protocol-service%3B1" target="_top">@mozilla.org/uriloader/external-protocol-service;1
259
+</a>, <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/uriloader/external-helper-app-service%3B1" target="_top">@mozilla.org/uriloader/external-helper-app-service;1</a>,
260
+and <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/mime%3B1" target="_top">@mozilla.org/mime;1</a>
261
+- <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/external-app-blocker.js" target="_top">components/external-app-blocker.js</a></h4></div></div></div><p>
262
+Due to <a class="link" href="#FirefoxBugs" title="6. Relevant Firefox Bugs">Firefox Bug</a> <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=440892" target="_top">440892</a> allowing Firefox 3.x to automatically launch some
263
+applications without user intervention, Torbutton had to wrap the three
264
+components involved in launching external applications to provide user
265
+confirmation before doing so while Tor is enabled. Since external applications
266
+do not obey proxy settings, they can be manipulated to automatically connect
267
+back to arbitrary servers outside of Tor with no user intervention. Fixing
268
+this issue helps to satisfy Torbutton's <a class="link" href="#proxy">Proxy
269
+Obedience</a> Requirement.
270
+ </p></div><div class="sect3" title="@mozilla.org/browser/sessionstartup;1 - components/crash-observer.js"><div class="titlepage"><div><div><h4 class="title"><a id="id2924906"></a><a class="ulink" href="http://lxr.mozilla.org/seamonkey/source/browser/components/sessionstore/src/nsSessionStartup.js" target="_top">@mozilla.org/browser/sessionstartup;1</a> -
271
+    <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js" target="_top">components/crash-observer.js</a></h4></div></div></div><p>This component wraps the Firefox Session Startup component that is in
272
+charge of <a class="ulink" href="http://developer.mozilla.org/en/docs/Session_store_API" target="_top">restoring saved
273
+sessions</a>. The wrapper's only job is to intercept the
274
+<code class="function">doRestore()</code> function, which is called by Firefox if it is determined that the
275
+browser crashed and the session needs to be restored. The wrapper notifies the
276
+Torbutton chrome that the browser crashed by setting the pref
277
+<span class="command"><strong>extensions.torbutton.crashed</strong></span>, or that it is a normal
278
+startup via the pref <span class="command"><strong>extensions.torbutton.noncrashed</strong></span>. The Torbutton Chrome <a class="ulink" href="https://developer.mozilla.org/en/NsIPrefBranch2#addObserver.28.29" target="_top">listens for a
279
+preference change</a> for this value and then does the appropriate cleanup. This
280
+includes setting the Tor state to the one the user selected for crash recovery
281
+in the preferences window (<span class="command"><strong>extensions.torbutton.restore_tor</strong></span>), and
282
+restoring cookies for the corresponding cookie jar, if it exists.</p><p>By performing this notification, this component assists in the 
283
+<a class="link" href="#proxy">Proxy Obedience</a>, and <a class="link" href="#isolation">Network Isolation</a> requirements.
284
+</p></div><div class="sect3" title="@mozilla.org/browser/global-history;2 - components/ignore-history.js"><div class="titlepage"><div><div><h4 class="title"><a id="id2921641"></a><a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/global-history;2" target="_top">@mozilla.org/browser/global-history;2</a>
285
+- <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/ignore-history.js" target="_top">components/ignore-history.js</a></h4></div></div></div><p>This component was contributed by <a class="ulink" href="http://www.collinjackson.com/" target="_top">Collin Jackson</a> as a method for defeating
286
+CSS and Javascript-based methods of history disclosure. The global-history
287
+component is what is used by Firefox to determine if a link was visited or not
288
+(to apply the appropriate style to the link). By hooking the <a class="ulink" href="https://developer.mozilla.org/en/nsIGlobalHistory2#isVisited.28.29" target="_top">isVisited</a>
289
+and <a class="ulink" href="https://developer.mozilla.org/en/nsIGlobalHistory2#addURI.28.29" target="_top">addURI</a>
290
+methods, Torbutton is able to selectively prevent history items from being
291
+added or being displayed as visited, depending on the Tor state and the user's
292
+preferences.
293
+</p><p>
294
+This component helps satisfy the <a class="link" href="#state">State Separation</a>
295
+and <a class="link" href="#disk">Disk Avoidance</a> requirements of Torbutton.
296
+</p></div><div class="sect3" title="@mozilla.org/browser/livemark-service;2 - components/block-livemarks.js"><div class="titlepage"><div><div><h4 class="title"><a id="livemarks"></a><a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/livemark-service;2" target="_top">@mozilla.org/browser/livemark-service;2</a>
297
+- <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/block-livemarks.js" target="_top">components/block-livemarks.js</a></h4></div></div></div><p>
298
+
299
+The <a class="ulink" href="http://www.mozilla.com/en-US/firefox/livebookmarks.html" target="_top">livemark</a> service
300
+is started by a timer that runs 5 seconds after Firefox
301
+startup. As a result, we cannot simply call the stopUpdateLivemarks() method to
302
+disable it. We must wrap the component to prevent this start() call from
303
+firing in the event the browser starts in Tor mode.
304
+
305
+</p><p>
306
+This component helps satisfy the <a class="link" href="#isolation">Network
307
+Isolation</a> and <a class="link" href="#setpreservation">Anonymity Set
308
+Preservation</a> requirements.
309
+</p></div></div><div class="sect2" title="2.2. New Components"><div class="titlepage"><div><div><h3 class="title"><a id="id2922900"></a>2.2. New Components</h3></div></div></div><p>Torbutton creates four new components that are used throughout the
310
+extension. These components do not hook any interfaces, nor are they used
311
+anywhere besides Torbutton itself.</p><div class="sect3" title="@torproject.org/cookie-jar-selector;2 - components/cookie-jar-selector.js"><div class="titlepage"><div><div><h4 class="title"><a id="id2909775"></a><a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js" target="_top">@torproject.org/cookie-jar-selector;2
312
+- components/cookie-jar-selector.js</a></h4></div></div></div><p>The cookie jar selector (also based on code from <a class="ulink" href="http://www.collinjackson.com/" target="_top">Collin
313
+Jackson</a>) is used by the Torbutton chrome to switch between
314
+Tor and Non-Tor cookies. Its operations are simple: sync cookies to disk, then
315
+move the current cookies.txt file to the appropriate backup location
316
+(cookies-tor.txt or cookies-nontor.txt), and then moving the other cookie jar
317
+into place.</p><p>
318
+This component helps to address the <a class="link" href="#state">State
319
+Isolation</a> requirement of Torbutton.
320
+</p></div><div class="sect3" title="@torproject.org/torbutton-logger;1 - components/torbutton-logger.js"><div class="titlepage"><div><div><h4 class="title"><a id="id2906606"></a><a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/torbutton-logger.js" target="_top">@torproject.org/torbutton-logger;1
321
+- components/torbutton-logger.js</a></h4></div></div></div><p>The torbutton logger component allows on-the-fly redirection of torbutton
322
+logging messages to either Firefox stderr
323
+(<span class="command"><strong>extensions.torbutton.logmethod=0</strong></span>), the Javascript error console
324
+(<span class="command"><strong>extensions.torbutton.logmethod=1</strong></span>), or the DebugLogger extension (if
325
+available - <span class="command"><strong>extensions.torbutton.logmethod=2</strong></span>). It also allows you to
326
+change the loglevel on the fly by changing
327
+<span class="command"><strong>extensions.torbutton.loglevel</strong></span> (1-5, 1 is most verbose).
328
+</p></div><div class="sect3" title="@torproject.org/content-window-mapper;1 - components/window-mapper.js"><div class="titlepage"><div><div><h4 class="title"><a id="windowmapper"></a><a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/window-mapper.js" target="_top">@torproject.org/content-window-mapper;1
329
+- components/window-mapper.js</a></h4></div></div></div><p>Torbutton tags Firefox <a class="ulink" href="https://developer.mozilla.org/en/XUL_Tutorial/Tabboxes" target="_top">tabs</a> with a special variable that indicates the Tor
330
+state the tab was most recently used under to fetch a page. The problem is
331
+that for many Firefox events, it is not possible to determine the tab that is
332
+actually receiving the event. The Torbutton window mapper allows the Torbutton
333
+chrome and other components to look up a <a class="ulink" href="https://developer.mozilla.org/en/XUL/tabbrowser" target="_top">browser
334
+tab</a> for a given <a class="ulink" href="https://developer.mozilla.org/en/nsIDOMWindow" target="_top">HTML content
335
+window</a>. It does this by traversing all windows and all browsers, until it
336
+finds the browser with the requested <a class="ulink" href="https://developer.mozilla.org/en/XUL/tabbrowser#p-contentWindow" target="_top">contentWindow</a> element. Since the content policy
337
+and page loading in general can generate hundreds of these lookups, this
338
+result is cached inside the component.
339
+</p></div><div class="sect3" title="@torproject.org/cssblocker;1 - components/cssblocker.js"><div class="titlepage"><div><div><h4 class="title"><a id="contentpolicy"></a><a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cssblocker.js" target="_top">@torproject.org/cssblocker;1
340
+- components/cssblocker.js</a></h4></div></div></div><p>This is a key component to Torbutton's security measures. When Tor is
341
+toggled, Javascript is disabled, and pages are instructed to stop loading.
342
+However, CSS is still able to perform network operations by loading styles for
343
+onmouseover events and other operations. In addition, favicons can still be
344
+loaded by the browser. The cssblocker component prevents this by implementing
345
+and registering an <a class="ulink" href="https://developer.mozilla.org/en/nsIContentPolicy" target="_top">nsIContentPolicy</a>.
346
+When an nsIContentPolicy is registered, Firefox checks every attempted network
347
+request against its <a class="ulink" href="https://developer.mozilla.org/en/nsIContentPolicy#shouldLoad()" target="_top">shouldLoad</a>
348
+member function to determine if the load should proceed. In Torbutton's case,
349
+the content policy looks up the appropriate browser tab using the <a class="link" href="#windowmapper" title="@torproject.org/content-window-mapper;1 - components/window-mapper.js">window mapper</a>,
350
+and checks that tab's load tag against the current Tor state. If the tab was
351
+loaded in a different state than the current state, the fetch is denied.
352
+Otherwise, it is allowed.</p> This helps to achieve the <a class="link" href="#isolation">Network
353
+Isolation</a> requirements of Torbutton.
354
+
355
+<p>In addition, the content policy also blocks website javascript from
356
+<a class="ulink" href="http://pseudo-flaw.net/content/tor/torbutton/" target="_top">querying for
357
+versions and existence of extension chrome</a> while Tor is enabled, and
358
+also masks the presence of Torbutton to website javascript while Tor is
359
+disabled. </p><p>
360
+
361
+Finally, some of the work that logically belongs to the content policy is
362
+instead handled by the <span class="command"><strong>torbutton_http_observer</strong></span> and
363
+<span class="command"><strong>torbutton_weblistener</strong></span> in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js" target="_top">torbutton.js</a>. These two objects handle blocking of
364
+Firefox 3 favicon loads, popups, and full page plugins, which for whatever
365
+reason are not passed to the Firefox content policy itself (see Firefox Bugs 
366
+<a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437014" target="_top">437014</a> and 
367
+<a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=401296" target="_top">401296</a>).
368
+
369
+</p><p>
370
+
371
+This helps to fulfill both the <a class="link" href="#setpreservation">Anonymity Set Preservation</a> and the <a class="link" href="#undiscoverability">Tor Undiscoverability</a> requirements of
372
+Torbutton.</p></div></div></div><div class="sect1" title="3. Chrome"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2907191"></a>3. Chrome</h2></div></div></div><p>The chrome is where all the torbutton graphical elements and windows are
373
+located. Each window is described as an <a class="ulink" href="http://developer.mozilla.org/en/docs/XUL_Reference" target="_top">XML file</a>, with zero or more Javascript
374
+files attached. The scope of these Javascript files is their containing
375
+window.</p><div class="sect2" title="3.1. Browser Overlay - torbutton.xul"><div class="titlepage"><div><div><h3 class="title"><a id="browseroverlay"></a>3.1. Browser Overlay - <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.xul" target="_top">torbutton.xul</a></h3></div></div></div><p>The browser overlay, torbutton.xul, defines the toolbar button, the status
376
+bar, and events for toggling the button. The overlay code is in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js" target="_top">chrome/content/torbutton.js</a>.
377
+It contains event handlers for preference update, shutdown, upgrade, and
378
+location change events.</p><p>The <a class="ulink" href="https://developer.mozilla.org/en/nsIWebProgressListener#onLocationChange" target="_top">location
379
+change</a> <a class="ulink" href="https://developer.mozilla.org/en/nsIWebProgress" target="_top">webprogress
380
+listener</a>, <span class="command"><strong>torbutton_weblistener</strong></span> is one of the most
381
+important parts of the chrome from a security standpoint. It is a <a class="ulink" href="https://developer.mozilla.org/en/nsIWebProgressListener" target="_top">webprogress
382
+listener</a> that handles receiving an event every time a page load or
383
+iframe load occurs. This class eventually calls down to
384
+<code class="function">torbutton_update_tags()</code> and
385
+<code class="function">torbutton_hookdoc()</code>, which apply the browser Tor load
386
+state tags, plugin permissions, and install the Javascript hooks to hook the
387
+<a class="ulink" href="https://developer.mozilla.org/en/DOM/window.screen" target="_top">window.screen</a>
388
+object to obfuscate browser and desktop resolution information.
389
+
390
+</p><p>
391
+The browser overlay helps to satisfy a number of Torbutton requirements. These
392
+are better enumerated in each of the Torbutton preferences below. However,
393
+there are also a number of Firefox preferences set in
394
+<code class="function">torbutton_update_status()</code> that aren't governed by any
395
+Torbutton setting. These are:
396
+</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="ulink" href="http://kb.mozillazine.org/Network.security.ports.banned" target="_top">network.security.ports.banned</a><p>
397
+Torbutton sets this setting to add ports 8123, 8118, 9050 and 9051 (which it
398
+reads from <span class="command"><strong>extensions.torbutton.banned_ports</strong></span>) to the list
399
+of ports Firefox is forbidden to access. These ports are Polipo, Privoxy, Tor,
400
+and the Tor control port, respectively. This is set for both Tor and Non-Tor
401
+usage, and prevents websites from attempting to do http fetches from these
402
+ports to see if they are open, which addresses the <a class="link" href="#undiscoverability">Tor Undiscoverability</a> requirement.
403
+ </p></li><li class="listitem"><a class="ulink" href="http://kb.mozillazine.org/Browser.send_pings" target="_top">browser.send_pings</a><p>
404
+This setting is currently always disabled. If anyone ever complains saying
405
+that they *want* their browser to be able to send ping notifications to a
406
+page or arbitrary link, I'll make this a pref or Tor-only. But I'm not holding
407
+my breath. I haven't checked if the content policy is called for pings, but if
408
+not, this setting helps with meeting the <a class="link" href="#isolation">Network
409
+Isolation</a> requirement.
410
+ </p></li><li class="listitem"><a class="ulink" href="http://kb.mozillazine.org/Browser.safebrowsing.remoteLookups" target="_top">browser.safebrowsing.remoteLookups</a><p>
411
+Likewise for this setting. I find it hard to imagine anyone who wants to ask
412
+Google in real time if each URL they visit is safe, especially when the list
413
+of unsafe URLs is downloaded anyway. This helps fulfill the <a class="link" href="#disk">Disk Avoidance</a> requirement, by preventing your entire
414
+browsing history from ending up on Google's disks.
415
+ </p></li><li class="listitem"><a class="ulink" href="http://kb.mozillazine.org/Browser.safebrowsing.enabled" target="_top">browser.safebrowsing.enabled</a><p>
416
+Safebrowsing does <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=360387" target="_top">unauthenticated
417
+updates under Firefox 2</a>, so it is disabled during Tor usage. 
418
+This helps fulfill the <a class="link" href="#updates">Update
419
+Safety</a> requirement. Firefox 3 has the fix for that bug, and so
420
+safebrowsing updates are enabled during Tor usage.
421
+ </p></li><li class="listitem"><a class="ulink" href="http://kb.mozillazine.org/Network.protocol-handler.warn-external.%28protocol%29" target="_top">network.protocol-handler.warn-external.(protocol)</a><p>
422
+If Tor is enabled, we need to prevent random external applications from
423
+launching without at least warning the user. This group of settings only
424
+partially accomplishes this, however. Applications can still be launched via
425
+plugins. The mechanisms for handling this are described under the "Disable
426
+Plugins During Tor Usage" preference. This helps fulfill the <a class="link" href="#proxy">Proxy Obedience</a> requirement, by preventing external
427
+applications from accessing network resources at the command of Tor-fetched
428
+pages. Unfortunately, due to <a class="link" href="#FirefoxBugs" title="6. Relevant Firefox Bugs">Firefox Bug</a>
429
+<a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=440892" target="_top">440892</a>,
430
+these prefs are no longer obeyed. They are set still anyway out of respect for
431
+the dead.
432
+ </p></li><li class="listitem"><a class="ulink" href="http://kb.mozillazine.org/Browser.sessionstore.max_tabs_undo" target="_top">browser.sessionstore.max_tabs_undo</a><p>
433
+
434
+To help satisfy the Torbutton <a class="link" href="#state">State Separation</a>
435
+and <a class="link" href="#isolation">Network Isolation</a> requirements,
436
+Torbutton needs to purge the Undo Tab history on toggle to prevent repeat
437
+"Undo Close" operations from accidentally restoring tabs from a different Tor
438
+State. This purge is accomplished by setting this preference to 0 and then
439
+restoring it to the previous user value upon toggle.
440
+
441
+   </p></li><li class="listitem"><span class="command"><strong>security.enable_ssl2</strong></span><p>
442
+TLS Session IDs can persist for an indefinite duration, providing an
443
+identifier that is sent to TLS sites that can be used to link activity. This
444
+is particularly troublesome now that we have certificate verification in place
445
+in Firefox 3: The OCSP server can use this Session ID to build a history of
446
+TLS sites someone visits, and also correlate their activity as users move from
447
+network to network (such as home to work to coffee shop, etc), inside and
448
+outside of Tor. To handle this and to help satisfy our <a class="link" href="#state">State Separation Requirement</a>, we currently 
449
+toggle
450
+<span class="command"><strong>security.enable_ssl2</strong></span>, which clears the SSL Session ID
451
+cache via the pref observer at <a class="ulink" href="http://mxr.mozilla.org/security/source/security/manager/ssl/src/nsNSSComponent.cpp#2134" target="_top">nsNSSComponent.cpp
452
+line 2134</a>. This is an arcane and potentially fragile fix. It would be
453
+better if there were a more standard interface for accomplishing the same
454
+thing. <a class="link" href="#FirefoxBugs" title="6. Relevant Firefox Bugs">Firefox Bug</a> <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=448747" target="_top">448747</a> has
455
+been filed for this.
456
+
457
+   </p></li><li class="listitem"><span class="command"><strong><a class="ulink" href="http://www.mozilla.com/en-US/firefox/geolocation/" target="_top">geo.enabled</a></strong></span><p>
458
+
459
+Torbutton disables Geolocation support in Firefox 3.5 and above whenever tor
460
+is enabled. This helps Torbutton maintain its
461
+<a class="link" href="#location">Location Neutrality</a> requirement.
462
+While Firefox does prompt before divulging geolocational information,
463
+the assumption is that Tor users will never want to give their
464
+location away during Tor usage, and even allowing websites to prompt
465
+them to do so will only cause confusion and accidents to happen. Moreover,
466
+just because users may approve a site to know their location in non-Tor mode
467
+does not mean they want it divulged during Tor mode.
468
+
469
+   </p></li><li class="listitem"><span class="command"><strong><a class="ulink" href="http://kb.mozillazine.org/Browser.zoom.siteSpecific" target="_top">browser.zoom.siteSpecific</a></strong></span><p>
470
+
471
+Firefox actually remembers your zoom settings for certain sites. CSS
472
+and Javascript rule can use this to recognize previous visitors to a site.
473
+This helps Torbutton fulfill its <a class="link" href="#state">State Separation</a>
474
+requirement.
475
+
476
+   </p></li><li class="listitem"><span class="command"><strong><a class="ulink" href="https://developer.mozilla.org/en/controlling_dns_prefetching" target="_top">network.dns.disablePrefetch</a></strong></span><p>
477
+
478
+Firefox 3.5 and above implement prefetching of DNS resolution for hostnames in
479
+links on a page to decrease page load latency. While Firefox does typically
480
+disable this behavior when proxies are enabled, we set this pref for added
481
+safety during Tor usage. Additionally, to prevent Tor-loaded tabs from having
482
+their links prefetched after a toggle to Non-Tor mode occurs,
483
+we also set the docShell attribute
484
+<a class="ulink" href="http://www.oxymoronical.com/experiments/apidocs/interface/nsIDocShell" target="_top">
485
+allowDNSPrefetch</a> to false on Tor loaded tabs. This happens in the same
486
+positions in the code as those for disabling plugins via the allowPlugins
487
+docShell attribute. This helps Torbutton fulfill its <a class="link" href="#isolation">Network Isolation</a> requirement.
488
+
489
+   </p></li><li class="listitem"><span class="command"><strong><a class="ulink" href="http://kb.mozillazine.org/Browser.cache.offline.enable" target="_top">browser.cache.offline.enable</a></strong></span><p>
490
+
491
+Firefox has the ability to store web applications in a special cache to allow
492
+them to continue to operate while the user is offline. Since this subsystem
493
+is actually different than the normal disk cache, it must be dealt with
494
+separately. Thus, Torbutton sets this preference to false whenever Tor is
495
+enabled. This helps Torbutton fulfill its <a class="link" href="#disk">Disk
496
+Avoidance</a> and <a class="link" href="#state">State Separation</a>
497
+requirements.
498
+
499
+   </p></li></ol></div></div><div class="sect2" title="3.2. Preferences Window - preferences.xul"><div class="titlepage"><div><div><h3 class="title"><a id="id2922887"></a>3.2. Preferences Window - <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.xul" target="_top">preferences.xul</a></h3></div></div></div><p>The preferences window of course lays out the Torbutton preferences, with
500
+handlers located in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.js" target="_top">chrome/content/preferences.js</a>.</p></div><div class="sect2" title="3.3. Other Windows"><div class="titlepage"><div><div><h3 class="title"><a id="id2922834"></a>3.3. Other Windows</h3></div></div></div><p>There are additional windows that describe popups for right clicking on
501
+the status bar, the toolbutton, and the about page.</p></div></div><div class="sect1" title="4. Toggle Code Path"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2917336"></a>4. Toggle Code Path</h2></div></div></div><p>
502
+
503
+The act of toggling is connected to <code class="function">torbutton_toggle()</code>
504
+via the <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.xul" target="_top">torbutton.xul</a>
505
+and <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/popup.xul" target="_top">popup.xul</a>
506
+overlay files. Most of the work in the toggling process is present in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js" target="_top">torbutton.js</a> 
507
+
508
+</p><p>
509
+
510
+Toggling is a 3 stage process: Button Click, Proxy Update, and
511
+Settings Update. These stages are reflected in the prefs
512
+<span class="command"><strong>extensions.torbutton.tor_enabled</strong></span>,
513
+<span class="command"><strong>extensions.torbutton.proxies_applied</strong></span>, and
514
+<span class="command"><strong>extensions.torbutton.settings_applied</strong></span>. The reason for the
515
+three stage preference update is to ensure immediate enforcement of <a class="link" href="#isolation">Network Isolation</a> via the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a>. Since the content window
516
+javascript runs on a different thread than the chrome javascript, it is
517
+important to properly convey the stages to the content policy to avoid race
518
+conditions and leakage, especially with <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox Bug 
519
+409737</a> unfixed. The content policy does not allow any network activity
520
+whatsoever during this three stage transition.
521
+
522
+ </p><div class="sect2" title="4.1. Button Click"><div class="titlepage"><div><div><h3 class="title"><a id="id2934128"></a>4.1. Button Click</h3></div></div></div><p>
523
+
524
+This is the first step in the toggling process. When the user clicks the
525
+toggle button or the toolbar, <code class="function">torbutton_toggle()</code> is
526
+called. This function checks the current Tor status by comparing the current
527
+proxy settings to the selected Tor settings, and then sets the proxy settings
528
+to the opposite state, and sets the pref
529
+<span class="command"><strong>extensions.torbutton.tor_enabled</strong></span> to reflect the new state.
530
+It is this proxy pref update that gives notification via the <a class="ulink" href="https://developer.mozilla.org/en/NsIPrefBranch2#addObserver.28.29" target="_top">pref
531
+observer</a>
532
+<span class="command"><strong>torbutton_unique_pref_observer</strong></span> to perform the rest of the
533
+toggle.
534
+
535
+  </p></div><div class="sect2" title="4.2. Proxy Update"><div class="titlepage"><div><div><h3 class="title"><a id="id2915503"></a>4.2. Proxy Update</h3></div></div></div><p>
536
+
537
+When Torbutton receives any proxy change notifications via its
538
+<span class="command"><strong>torbutton_unique_pref_observer</strong></span>, it calls
539
+<code class="function">torbutton_set_status()</code> which checks against the Tor
540
+settings to see if the Tor proxy settings match the current settings. If so,
541
+it calls <code class="function">torbutton_update_status()</code>, which determines if
542
+the Tor state has actually changed, and sets
543
+<span class="command"><strong>extensions.torbutton.proxies_applied</strong></span> to the appropriate Tor
544
+state value, and ensures that
545
+<span class="command"><strong>extensions.torbutton.tor_enabled</strong></span> is also set to the correct
546
+value. This is decoupled from the button click functionalty via the pref
547
+observer so that other addons (such as SwitchProxy) can switch the proxy
548
+settings between multiple proxies.
549
+
550
+  </p></div><div class="sect2" title="4.3. Settings Update"><div class="titlepage"><div><div><h3 class="title"><a id="id2931338"></a>4.3. Settings Update</h3></div></div></div><p>
551
+
552
+The next stage is also handled by
553
+<code class="function">torbutton_update_status()</code>. This function sets scores of
554
+Firefox preferences, saving the original values to prefs under
555
+<span class="command"><strong>extensions.torbutton.saved.*</strong></span>, and performs the history
556
+clearing, cookie jaring, and ssl certificate jaring work of Torbutton. At the
557
+end of its work, it sets
558
+<span class="command"><strong>extensions.torbutton.settings_applied</strong></span>, which signifies the
559
+completion of the toggle operation to the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a>.
560
+
561
+  </p></div></div><div class="sect1" title="5. Description of Options"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2898010"></a>5. Description of Options</h2></div></div></div><p>This section provides a detailed description of Torbutton's options. Each
562
+option is presented as the string from the preferences window, a summary, the
563
+preferences it touches, and the effect this has on the components, chrome, and
564
+browser properties.</p><div class="sect2" title="5.1. Test Settings"><div class="titlepage"><div><div><h3 class="title"><a id="id2910532"></a>5.1. Test Settings</h3></div></div></div><p>
565
+This button under the Proxy Settings tab provides a way to verify that the 
566
+proxy settings are correct, and actually do route through the Tor network. It
567
+performs this check by issuing an <a class="ulink" href="http://developer.mozilla.org/en/docs/XMLHttpRequest" target="_top">XMLHTTPRequest</a>
568
+for <a class="ulink" href="https://check.torproject.org/?TorButton=True" target="_top">https://check.torproject.org/?Torbutton=True</a>.
569
+This is a special page that returns very simple, yet well-formed XHTML that
570
+Torbutton can easily inspect for a hidden link with an id of
571
+<span class="command"><strong>TorCheckResult</strong></span> and a target of <span class="command"><strong>success</strong></span>
572
+or <span class="command"><strong>failure</strong></span> to indicate if the
573
+user hit the page from a Tor IP, a non-Tor IP. This check is handled in
574
+<code class="function">torbutton_test_settings()</code> in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js" target="_top">torbutton.js</a>.
575
+Presenting the results to the user is handled by the <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.xul" target="_top">preferences
576
+window</a>
577
+callback <code class="function">torbutton_prefs_test_settings()</code> in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/preferences.js" target="_top">preferences.js</a>.  
578
+
579
+  </p></div><div class="sect2" title="5.2. Disable plugins on Tor Usage (crucial)"><div class="titlepage"><div><div><h3 class="title"><a id="plugins"></a>5.2. Disable plugins on Tor Usage (crucial)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.no_tor_plugins</strong></span></p><p>Java and plugins <a class="ulink" href="http://java.sun.com/j2se/1.5.0/docs/api/java/net/class-use/NetworkInterface.html" target="_top">can query</a> the <a class="ulink" href="http://www.rgagnon.com/javadetails/java-0095.html" target="_top">local IP
580
+address</a> and report it back to the
581
+remote site. They can also <a class="ulink" href="http://decloak.net" target="_top">bypass proxy settings</a> and directly connect to a
582
+remote site without Tor. Every browser plugin we have tested with Firefox has
583
+some form of network capability, and every one ignores proxy settings or worse - only
584
+partially obeys them. This includes but is not limited to:
585
+QuickTime, Windows Media Player, RealPlayer, mplayerplug-in, AcroRead, and
586
+Flash. 
587
+
588
+ </p><p>
589
+Enabling this preference causes the above mentioned Torbutton chrome web progress
590
+ listener <span class="command"><strong>torbutton_weblistener</strong></span> to disable Java via <span class="command"><strong>security.enable_java</strong></span> and to disable
591
+ plugins via the browser <a class="ulink" href="https://developer.mozilla.org/en/XUL%3aProperty%3adocShell" target="_top">docShell</a>
592
+ attribute <span class="command"><strong>allowPlugins</strong></span>. These flags are set every time a new window is
593
+ created (<code class="function">torbutton_tag_new_browser()</code>), every time a web
594
+load
595
+event occurs
596
+ (<code class="function">torbutton_update_tags()</code>), and every time the tor state is changed
597
+ (<code class="function">torbutton_update_status()</code>). As a backup measure, plugins are also
598
+ prevented from loading by the content policy in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cssblocker.js" target="_top">@torproject.org/cssblocker;1</a> if Tor is
599
+ enabled and this option is set.
600
+ </p><p>All of this turns out to be insufficient if the user directly clicks
601
+on a plugin-handled mime-type. <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=401296" target="_top">In this case</a>,
602
+the browser decides that maybe it should ignore all these other settings and
603
+load the plugin anyways, because maybe the user really did want to load it
604
+(never mind this same load-style could happen automatically  with meta-refresh
605
+or any number of other ways..). To handle these cases, Torbutton stores a list
606
+of plugin-handled mime-types, and sets the pref
607
+<span class="command"><strong>plugin.disable_full_page_plugin_for_types</strong></span> to this list.
608
+Additionally, (since nothing can be assumed when relying on Firefox
609
+preferences and internals) if it detects a load of one of them from the web
610
+progress listener, it cancels the request, tells the associated DOMWindow to
611
+stop loading, clears the document, AND throws an exception. Anything short of
612
+all this and the plugin managed to find some way to load.
613
+ </p><p>
614
+ All this could be avoided, of course, if Firefox would either <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=401296" target="_top">obey
615
+ allowPlugins</a> for directly visited URLs, or notify its content policy for such
616
+ loads either <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=309524" target="_top">via</a> <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=380556" target="_top">shouldProcess</a> or shouldLoad. The fact that it does not is
617
+ not very encouraging.
618
+ </p><p>
619
+
620
+Since most plugins completely ignore browser proxy settings, the actions
621
+performed by this setting are crucial to satisfying the <a class="link" href="#proxy">Proxy Obedience</a> requirement.
622
+
623
+ </p></div><div class="sect2" title="5.3. Isolate Dynamic Content to Tor State (crucial)"><div class="titlepage"><div><div><h3 class="title"><a id="id2917719"></a>5.3. Isolate Dynamic Content to Tor State (crucial)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.isolate_content</strong></span></p><p>Enabling this preference is what enables the <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cssblocker.js" target="_top">@torproject.org/cssblocker;1</a> content policy
624
+mentioned above, and causes it to block content load attempts in pages an
625
+opposite Tor state from the current state. Freshly loaded <a class="ulink" href="https://developer.mozilla.org/en/XUL/tabbrowser" target="_top">browser
626
+tabs</a> are tagged
627
+with a <span class="command"><strong>__tb_load_state</strong></span> member in
628
+<code class="function">torbutton_update_tags()</code> and this
629
+value is compared against the current tor state in the content policy.</p><p>It also kills all Javascript in each page loaded under that state by
630
+toggling the <span class="command"><strong>allowJavascript</strong></span> <a class="ulink" href="https://developer.mozilla.org/en/XUL%3aProperty%3adocShell" target="_top">docShell</a> property, and issues a
631
+<a class="ulink" href="https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsIWebNavigation#stop()" target="_top">webNavigation.stop(webNavigation.STOP_ALL)</a> to each browser tab (the
632
+equivalent of hitting the STOP button).</p><p>
633
+
634
+Unfortunately, <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox bug
635
+409737</a> prevents <span class="command"><strong>docShell.allowJavascript</strong></span> from killing
636
+all event handlers, and event handlers registered with <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:element.addEventListener" target="_top">addEventListener()</a>
637
+are still able to execute. The <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">Torbutton Content
638
+Policy</a> should prevent such code from performing network activity within
639
+the current tab, but activity that happens via a popup window or via a
640
+Javascript redirect can still slip by. For this reason, Torbutton blocks
641
+popups by checking for a valid <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.opener" target="_top">window.opener</a>
642
+attribute in <code class="function">torbutton_check_progress()</code>. If the window
643
+has an opener from a different Tor state, its load is blocked. The content
644
+policy also takes similar action to prevent Javascript redirects. This also
645
+has the side effect/feature of preventing the user from following any links
646
+from a page loaded in an opposite Tor state.
647
+
648
+</p><p>
649
+This setting is responsible for satisfying the <a class="link" href="#isolation">Network Isolation</a> requirement.
650
+</p></div><div class="sect2" title="5.4. Hook Dangerous Javascript"><div class="titlepage"><div><div><h3 class="title"><a id="jshooks"></a>5.4. Hook Dangerous Javascript</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.kill_bad_js</strong></span></p><p>This setting enables injection of the <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/jshooks.js" target="_top">Javascript
651
+hooking code</a>. This is done in the chrome in
652
+<code class="function">torbutton_hookdoc()</code>, which is called ultimately by both the 
653
+<a class="ulink" href="https://developer.mozilla.org/en/nsIWebProgressListener" target="_top">webprogress
654
+listener</a> <span class="command"><strong>torbutton_weblistener</strong></span> and the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a> (the latter being a hack to handle
655
+javascript: urls).
656
+
657
+In the Firefox 2 days, this option did a lot more than
658
+it does now. It used to be responsible for timezone and improved useragent
659
+spoofing, and history object cloaking. However, now it only provides
660
+obfuscation of the <a class="ulink" href="https://developer.mozilla.org/en/DOM/window.screen" target="_top">window.screen</a>
661
+object to mask your browser and desktop resolution.
662
+The resolution hooks
663
+effectively make the Firefox browser window appear to websites as if the renderable area
664
+takes up the entire desktop, has no toolbar or other GUI element space, and
665
+the desktop itself has no toolbars.
666
+These hooks drastically reduce the amount of information available to do <a class="link" href="#fingerprinting">anonymity set reduction attacks</a> and help to
667
+meet the <a class="link" href="#setpreservation">Anonymity Set Preservation</a>
668
+requirements. Unfortunately, Gregory Fleischer discovered it is still possible
669
+to retrieve the original screen values by using <a class="ulink" href="http://pseudo-flaw.net/tor/torbutton/unmask-sandbox-xpcnativewrapper.html" target="_top">XPCNativeWrapper</a>
670
+or <a class="ulink" href="http://pseudo-flaw.net/tor/torbutton/unmask-components-lookupmethod.html" target="_top">Components.lookupMethod</a>.
671
+We are still looking for a workaround as of Torbutton 1.2.5.
672
+
673
+
674
+
675
+</p></div><div class="sect2" title="5.5. Resize windows to multiples of 50px during Tor usage (recommended)"><div class="titlepage"><div><div><h3 class="title"><a id="id2897638"></a>5.5. Resize windows to multiples of 50px during Tor usage (recommended)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.resize_windows</strong></span></p><p>
676
+
677
+This option drastically cuts down on the number of distinct anonymity sets
678
+that divide the Tor web userbase. Without this setting, the dimensions for a
679
+typical browser window range from 600-1200 horizontal pixels and 400-1000
680
+vertical pixels, or about 600x600 = 360000 different sets. Resizing the
681
+browser window to multiples of 50 on each side reduces the number of sets by
682
+50^2, bringing the total number of sets to 144. Of course, the distribution
683
+among these sets are not uniform, but scaling by 50 will improve the situation
684
+due to this non-uniformity for users in the less common resolutions.
685
+Obviously the ideal situation would be to lie entirely about the browser
686
+window size, but this will likely cause all sorts of rendering issues, and is
687
+also not implementable in a foolproof way from extension land.
688
+
689
+</p><p>
690
+
691
+The implementation of this setting is spread across a couple of different
692
+locations in the Torbutton javascript <a class="link" href="#browseroverlay" title="3.1. Browser Overlay - torbutton.xul">browser
693
+overlay</a>. Since resizing minimized windows causes them to be restored,
694
+and since maximized windows remember their previous size to the pixel, windows
695
+must be resized before every document load (at the time of browser tagging)
696
+via <code class="function">torbutton_check_round()</code>, called by
697
+<code class="function">torbutton_update_tags()</code>. To prevent drift, the extension
698
+tracks the original values of the windows and uses this to perform the
699
+rounding on document load. In addition, to prevent the user from resizing a
700
+window to a non-50px multiple, a resize listener
701
+(<code class="function">torbutton_do_resize()</code>) is installed on every new browser
702
+window to record the new size and round it to a 50px multiple while Tor is
703
+enabled. In all cases, the browser's contentWindow.innerWidth and innerHeight
704
+are set. This ensures that there is no discrepancy between the 50 pixel cutoff
705
+and the actual renderable area of the browser (so that it is not possible to
706
+infer toolbar size/presence by the distance to the nearest 50 pixel roundoff).
707
+
708
+</p><p>
709
+This setting helps to meet the <a class="link" href="#setpreservation">Anonymity Set Preservation</a> requirements.
710
+</p></div><div class="sect2" title="5.6. Disable Updates During Tor"><div class="titlepage"><div><div><h3 class="title"><a id="id2924640"></a>5.6. Disable Updates During Tor</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.no_updates</strong></span></p><p>This setting causes Torbutton to disable the four <a class="ulink" href="http://wiki.mozilla.org/Update:Users/Checking_For_Updates#Preference_Controls_and_State" target="_top">Firefox
711
+update settings</a> during Tor
712
+  usage: <span class="command"><strong>extensions.update.enabled</strong></span>,
713
+<span class="command"><strong>app.update.enabled</strong></span>,
714
+  <span class="command"><strong>app.update.auto</strong></span>, and
715
+<span class="command"><strong>browser.search.update</strong></span>.  These prevent the
716
+  browser from updating extensions, checking for Firefox upgrades, and
717
+  checking for search plugin updates while Tor is enabled.
718
+  </p><p>
719
+This setting satisfies the <a class="link" href="#updates">Update Safety</a> requirement.
720
+</p></div><div class="sect2" title="5.7. Redirect Torbutton Updates Via Tor (recommended)"><div class="titlepage"><div><div><h3 class="title"><a id="id2892217"></a>5.7. Redirect Torbutton Updates Via Tor (recommended)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.update_torbutton_via_tor</strong></span></p><p>This setting causes Torbutton to install an
721
+
722
+<a class="ulink" href="https://developer.mozilla.org/en/nsIProtocolProxyFilter" target="_top">nsIProtocolProxyFilter</a>
723
+in order to redirect all version update checks and Torbutton update downloads
724
+via Tor, regardless of if Tor is enabled or not. This was done both to address
725
+concerns about data retention done by <a class="ulink" href="https://www.addons.mozilla.org" target="_top">addons.mozilla.org</a>, as well as to
726
+help censored users meet the <a class="link" href="#undiscoverability">Tor
727
+Undiscoverability</a> requirement.
728
+
729
+  </p></div><div class="sect2" title="5.8. Disable Search Suggestions during Tor (recommended)"><div class="titlepage"><div><div><h3 class="title"><a id="id2892261"></a>5.8. Disable Search Suggestions during Tor (recommended)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.no_search</strong></span></p><p>
730
+This setting causes Torbutton to disable <a class="ulink" href="http://kb.mozillazine.org/Browser.search.suggest.enabled" target="_top"><span class="command"><strong>browser.search.suggest.enabled</strong></span></a>
731
+during Tor usage.
732
+This governs if you get Google search suggestions during Tor
733
+usage. Your Google cookie is transmitted with google search suggestions, hence
734
+this is recommended to be disabled.
735
+
736
+</p><p>
737
+While this setting doesn't satisfy any Torbutton requirements, the fact that
738
+cookies are transmitted for partially typed queries does not seem desirable
739
+for Tor usage.
740
+</p></div><div class="sect2" title="5.9. Disable livemarks updates during Tor usage (recommended)"><div class="titlepage"><div><div><h3 class="title"><a id="id2892300"></a>5.9. Disable livemarks updates during Tor usage (recommended)</h3></div></div></div><p>Option:
741
+   </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.disable_livemarks</strong></span></td></tr></table><p>
742
+  </p><p>
743
+This option causes Torbutton to prevent Firefox from loading <a class="ulink" href="http://www.mozilla.com/firefox/livebookmarks.html" target="_top">Livemarks</a> during
744
+Tor usage. Because people often have very personalized Livemarks (such as RSS
745
+feeds of Wikipedia articles they maintain, etc). This is accomplished both by
746
+<a class="link" href="#livemarks" title="@mozilla.org/browser/livemark-service;2 - components/block-livemarks.js">wrapping the livemark-service component</a> and
747
+by calling stopUpdateLivemarks() on the <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/livemark-service;2" target="_top">Livemark
748
+service</a> when Tor is enabled.
749
+
750
+</p><p>
751
+This helps satisfy the <a class="link" href="#isolation">Network
752
+Isolation</a> and <a class="link" href="#setpreservation">Anonymity Set
753
+Preservation</a> requirements.
754
+</p></div><div class="sect2" title="5.10. Block Tor/Non-Tor access to network from file:// urls (recommended)"><div class="titlepage"><div><div><h3 class="title"><a id="id2892371"></a>5.10. Block Tor/Non-Tor access to network from file:// urls (recommended)</h3></div></div></div><p>Options:
755
+   </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.block_tor_file_net</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.block_nontor_file_net</strong></span></td></tr></table><p>
756
+  </p><p>
757
+
758
+These settings prevent file urls from performing network operations during the
759
+respective Tor states. Firefox 2's implementation of same origin policy allows
760
+file urls to read and <a class="ulink" href="http://www.gnucitizen.org/blog/content-disposition-hacking/" target="_top">submit
761
+arbitrary files from the local filesystem</a> to arbitrary websites. To
762
+make matters worse, the 'Content-Disposition' header can be injected
763
+arbitrarily by exit nodes to trick users into running arbitrary html files in
764
+the local context. These preferences cause the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a> to block access to any network
765
+resources from File urls during the appropriate Tor state.
766
+
767
+</p><p>
768
+
769
+This preference helps to ensure Tor's <a class="link" href="#isolation">Network
770
+Isolation</a> requirement, by preventing file urls from executing network
771
+operations in opposite Tor states. Also, allowing pages to submit arbitrary
772
+files to arbitrary sites just generally seems like a bad idea.
773
+
774
+</p></div><div class="sect2" title="5.11. Close all Tor/Non-Tor tabs and windows on toggle (optional)"><div class="titlepage"><div><div><h3 class="title"><a id="id2892443"></a>5.11. Close all Tor/Non-Tor tabs and windows on toggle (optional)</h3></div></div></div><p>Options:
775
+   </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.close_nontor</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.close_tor</strong></span></td></tr></table><p>
776
+  </p><p>
777
+
778
+These settings cause Torbutton to enumerate through all windows and close all
779
+tabs in each window for the appropriate Tor state. This code can be found in
780
+<code class="function">torbutton_update_status()</code>.  The main reason these settings
781
+exist is as a backup mechanism in the event of any Javascript or content policy
782
+leaks due to <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox Bug
783
+409737</a>.  Torbutton currently tries to block all Javascript network
784
+activity via the content policy, but until that bug is fixed, there is some
785
+risk that there are alternate ways to bypass the policy. This option is
786
+available as an extra assurance of <a class="link" href="#isolation">Network
787
+Isolation</a> for those who would like to be sure that when Tor is toggled
788
+all page activity has ceased. It also serves as a potential future workaround
789
+in the event a content policy failure is discovered, and provides an additional
790
+level of protection for the <a class="link" href="#disk">Disk Avoidance</a>
791
+protection so that browser state is not sitting around waiting to be swapped
792
+out longer than necessary.
793
+
794
+</p><p>
795
+While this setting doesn't satisfy any Torbutton requirements, the fact that
796
+cookies are transmitted for partially typed queries does not seem desirable
797
+for Tor usage.
798
+</p></div><div class="sect2" title="5.12. Isolate Access to History navigation to Tor state (crucial)"><div class="titlepage"><div><div><h3 class="title"><a id="id2892524"></a>5.12. Isolate Access to History navigation to Tor state (crucial)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.block_js_history</strong></span></p><p>
799
+This setting determines if Torbutton installs an <a class="ulink" href="http://www.oxymoronical.com/experiments/apidocs/interface/nsISHistoryListener" target="_top">nsISHistoryListener</a>
800
+attached to the <a class="ulink" href="http://www.oxymoronical.com/experiments/apidocs/interface/nsISHistory" target="_top">sessionHistory</a> of 
801
+of each browser's <a class="ulink" href="https://developer.mozilla.org/en/XUL%3aProperty%3awebNavigation" target="_top">webNavigatator</a>.
802
+The nsIShistoryListener is instantiated with a reference to the containing
803
+browser window and blocks the back, forward, and reload buttons on the browser
804
+navigation bar when Tor is in an opposite state than the one to load the
805
+current tab. In addition, Tor clears the session history during a new document
806
+load if this setting is enabled. 
807
+
808
+  </p><p>
809
+
810
+This is marked as a crucial setting in part
811
+because Javascript access to the history object is indistinguishable from 
812
+user clicks, and because
813
+<a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox Bug
814
+409737</a> allows javascript to execute in opposite Tor states, javascript
815
+can issue reloads after Tor toggle to reveal your original IP. Even without
816
+this bug, however, Javascript is still able to access previous pages in your
817
+session history that may have been loaded under a different Tor state, to
818
+attempt to correlate your activity.
819
+
820
+   </p><p>
821
+
822
+This setting helps to fulfill Torbutton's <a class="link" href="#state">State
823
+Separation</a> and (until Bug 409737 is fixed) <a class="link" href="#isolation">Network Isolation</a>
824
+requirements.
825
+
826
+   </p></div><div class="sect2" title="5.13. History Access Settings"><div class="titlepage"><div><div><h3 class="title"><a id="id2892609"></a>5.13. History Access Settings</h3></div></div></div><p>Options:
827
+  </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.block_thread</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.block_nthread</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.block_thwrite</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.block_nthwrite</strong></span></td></tr></table><p>
828
+  </p><p>These four settings govern the behavior of the <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/ignore-history.js" target="_top">components/ignore-history.js</a>
829
+history blocker component mentioned above. By hooking the browser's view of
830
+the history itself via the <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/global-history;2" target="_top">@mozilla.org/browser/global-history;2</a>
831
+and <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/browser/nav-history-service;1" target="_top">@mozilla.org/browser/nav-history-service;1</a>
832
+components, this mechanism defeats all document-based <a class="ulink" href="http://whattheinternetknowsaboutyou.com/" target="_top">history disclosure
833
+attacks</a>, including <a class="ulink" href="http://ha.ckers.org/weird/CSS-history.cgi" target="_top">CSS-only attacks</a>.
834
+
835
+The component also hooks functions involved in writing history to disk via
836
+both the <a class="ulink" href="http://developer.mozilla.org/en/docs/Places_migration_guide#History" target="_top">Places
837
+Database</a> and the older Firefox 2 mechanisms.
838
+
839
+</p><p>
840
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
841
+</p></div><div class="sect2" title="5.14. Clear History During Tor Toggle (optional)"><div class="titlepage"><div><div><h3 class="title"><a id="id2892721"></a>5.14. Clear History During Tor Toggle (optional)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.clear_history</strong></span></p><p>This setting governs if Torbutton calls
842
+<a class="ulink" href="https://developer.mozilla.org/en/nsIBrowserHistory#removeAllPages.28.29" target="_top">nsIBrowserHistory.removeAllPages</a>
843
+and <a class="ulink" href="http://www.oxymoronical.com/experiments/apidocs/interface/nsISHistory" target="_top">nsISHistory.PurgeHistory</a>
844
+for each tab on Tor toggle.</p><p>
845
+This setting is an optional way to help satisfy the <a class="link" href="#state">State Separation</a> requirement.
846
+</p></div><div class="sect2" title="5.15. Block Password+Form saving during Tor/Non-Tor"><div class="titlepage"><div><div><h3 class="title"><a id="id2934267"></a>5.15. Block Password+Form saving during Tor/Non-Tor</h3></div></div></div><p>Options:
847
+  </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.block_tforms</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.block_ntforms</strong></span></td></tr></table><p>
848
+  </p><p>These settings govern if Torbutton disables
849
+<span class="command"><strong>browser.formfill.enable</strong></span>
850
+and <span class="command"><strong>signon.rememberSignons</strong></span> during Tor and Non-Tor usage.
851
+Since form fields can be read at any time by Javascript, this setting is a lot
852
+more important than it seems.
853
+</p><p>
854
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
855
+</p></div><div class="sect2" title="5.16. Block Tor disk cache and clear all cache on Tor Toggle"><div class="titlepage"><div><div><h3 class="title"><a id="id2934328"></a>5.16. Block Tor disk cache and clear all cache on Tor Toggle</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.clear_cache</strong></span>
856
+  </p><p>This option causes Torbutton to call <a class="ulink" href="https://developer.mozilla.org/en/nsICacheService#evictEntries.28.29" target="_top">nsICacheService.evictEntries(0)</a>
857
+on Tor toggle to remove all entries from the cache. In addition, this setting
858
+causes Torbutton to set <a class="ulink" href="http://kb.mozillazine.org/Browser.cache.disk.enable" target="_top">browser.cache.disk.enable</a> to false.
859
+</p><p>
860
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
861
+</p></div><div class="sect2" title="5.17. Block disk and memory cache during Tor"><div class="titlepage"><div><div><h3 class="title"><a id="id2934378"></a>5.17. Block disk and memory cache during Tor</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.block_cache</strong></span></p><p>This setting
862
+causes Torbutton to set <a class="ulink" href="http://kb.mozillazine.org/Browser.cache.memory.enable" target="_top">browser.cache.memory.enable</a>,
863
+<a class="ulink" href="http://kb.mozillazine.org/Browser.cache.disk.enable" target="_top">browser.cache.disk.enable</a> and
864
+<a class="ulink" href="http://kb.mozillazine.org/Network.http.use-cache" target="_top">network.http.use-cache</a> to false during tor usage.
865
+</p><p>
866
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
867
+</p></div><div class="sect2" title="5.18. Clear Cookies on Tor Toggle"><div class="titlepage"><div><div><h3 class="title"><a id="id2934430"></a>5.18. Clear Cookies on Tor Toggle</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.clear_cookies</strong></span>
868
+  </p><p>
869
+
870
+This setting causes Torbutton to call <a class="ulink" href="https://developer.mozilla.org/en/nsICookieManager#removeAll.28.29" target="_top">nsICookieManager.removeAll()</a> on
871
+every Tor toggle. In addition, this sets <a class="ulink" href="http://kb.mozillazine.org/Network.cookie.lifetimePolicy" target="_top">network.cookie.lifetimePolicy</a>
872
+to 2 for Tor usage, which causes all cookies to be demoted to session cookies,
873
+which prevents them from being written to disk. 
874
+
875
+</p><p>
876
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
877
+</p></div><div class="sect2" title="5.19. Store Non-Tor cookies in a protected jar"><div class="titlepage"><div><div><h3 class="title"><a id="id2934481"></a>5.19. Store Non-Tor cookies in a protected jar</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.cookie_jars</strong></span>
878
+  </p><p>
879
+
880
+This setting causes Torbutton to use <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js" target="_top">@torproject.org/cookie-jar-selector;2</a> to store
881
+non-tor cookies in a cookie jar during Tor usage, and clear the Tor cookies
882
+before restoring the jar.
883
+</p><p>
884
+This setting also sets <a class="ulink" href="http://kb.mozillazine.org/Network.cookie.lifetimePolicy" target="_top">network.cookie.lifetimePolicy</a>
885
+to 2 for Tor usage, which causes all cookies to be demoted to session cookies,
886
+which prevents them from being written to disk. 
887
+
888
+</p><p>
889
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
890
+</p></div><div class="sect2" title="5.20. Store both Non-Tor and Tor cookies in a protected jar (dangerous)"><div class="titlepage"><div><div><h3 class="title"><a id="id2934538"></a>5.20. Store both Non-Tor and Tor cookies in a protected jar (dangerous)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.dual_cookie_jars</strong></span>
891
+  </p><p>
892
+
893
+This setting causes Torbutton to use <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js" target="_top">@torproject.org/cookie-jar-selector;2</a> to store
894
+both Tor and Non-Tor cookies into protected jars.
895
+</p><p>
896
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
897
+</p></div><div class="sect2" title="5.21. Manage My Own Cookies (dangerous)"><div class="titlepage"><div><div><h3 class="title"><a id="id2934577"></a>5.21. Manage My Own Cookies (dangerous)</h3></div></div></div><p>Options: None</p><p>This setting disables all Torbutton cookie handling by setting the above
898
+cookie prefs all to false.</p></div><div class="sect2" title="5.22. Disable DOM Storage during Tor usage (crucial)"><div class="titlepage"><div><div><h3 class="title"><a id="id2934592"></a>5.22. Disable DOM Storage during Tor usage (crucial)</h3></div></div></div><div class="sect2" title="5.22.1. Do not write Tor/Non-Tor cookies to disk"><div class="titlepage"><div><div><h3 class="title"><a id="id2934594"></a>5.22.1. Do not write Tor/Non-Tor cookies to disk</h3></div></div></div><p>Options:
899
+  </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.tor_memory_jar</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.nontor_memory_jar</strong></span></td></tr></table><p>
900
+  </p><p>
901
+These settings (contributed by arno) cause Torbutton to set <a class="ulink" href="http://kb.mozillazine.org/Network.cookie.lifetimePolicy" target="_top">network.cookie.lifetimePolicy</a>
902
+to 2 during the appropriate Tor state, and to store cookies acquired in that
903
+state into a Javascript
904
+<a class="ulink" href="http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Guide:Processing_XML_with_E4X" target="_top">E4X</a>
905
+object as opposed to writing them to disk.
906
+</p><p>
907
+This allows Torbutton to provide an option to preserve a user's 
908
+cookies while still satisfying the <a class="link" href="#disk">Disk Avoidance</a>
909
+requirement.
910
+</p></div><p>Option: <span class="command"><strong>extensions.torbutton.disable_domstorage</strong></span>
911
+  </p><p>
912
+
913
+This setting causes Torbutton to toggle <span class="command"><strong>dom.storage.enabled</strong></span> during Tor
914
+usage to prevent 
915
+<a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:Storage" target="_top">DOM Storage</a> from
916
+  being used to store persistent information across Tor states.</p><p>
917
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
918
+</p></div><div class="sect2" title="5.23. Clear HTTP Auth on Tor Toggle (recommended)"><div class="titlepage"><div><div><h3 class="title"><a id="id2934696"></a>5.23. Clear HTTP Auth on Tor Toggle (recommended)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.clear_http_auth</strong></span>
919
+  </p><p>
920
+This setting causes Torbutton to call <a class="ulink" href="http://www.oxymoronical.com/experiments/apidocs/interface/nsIHttpAuthManager" target="_top">nsIHttpAuthManager.clearAll()</a>
921
+every time Tor is toggled.
922
+</p><p>
923
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
924
+</p></div><div class="sect2" title="5.24. Clear cookies on Tor/Non-Tor shutdown"><div class="titlepage"><div><div><h3 class="title"><a id="id2934733"></a>5.24. Clear cookies on Tor/Non-Tor shutdown</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.shutdown_method</strong></span>
925
+  </p><p> This option variable can actually take 3 values: 0, 1, and 2. 0 means no
926
+cookie clearing, 1 means clear only during Tor-enabled shutdown, and 2 means
927
+clear for both Tor and Non-Tor shutdown. When set to 1 or 2, Torbutton listens
928
+for the <a class="ulink" href="http://developer.mozilla.org/en/docs/Observer_Notifications#Application_shutdown" target="_top">quit-application-granted</a> event in
929
+<code class="function">https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js</code> and use <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js" target="_top">@torproject.org/cookie-jar-selector;2</a>
930
+to clear out all cookies and all cookie jars upon shutdown.  </p><p>
931
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
932
+</p></div><div class="sect2" title="5.25. Reload cookie jar/clear cookies on Firefox crash"><div class="titlepage"><div><div><h3 class="title"><a id="id2934788"></a>5.25. Reload cookie jar/clear cookies on Firefox crash</h3></div></div></div><p>Options:
933
+  </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.reload_crashed_jar</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.crashed</strong></span></td></tr></table><p>
934
+  </p><p>This is no longer a user visible option, and is enabled by default. In
935
+the event of a crash, the Torbutton <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js" target="_top">components/crash-observer.js</a> 
936
+  component will notify the Chrome (via the
937
+  <span class="command"><strong>extensions.torbutton.crashed</strong></span> pref and a <a class="ulink" href="https://developer.mozilla.org/en/NsIPrefBranch2#addObserver.28.29" target="_top">pref
938
+observer</a> in
939
+the chrome that listens for this update), and Torbutton will load the
940
+  correct jar for the current Tor state via the <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/cookie-jar-selector.js" target="_top">@torproject.org/cookie-jar-selector;2</a>
941
+  component.</p><p>
942
+This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement in the event of Firefox
943
+crashes.
944
+</p></div><div class="sect2" title="5.26. On crash recovery or session restored startup, restore via: Tor, Non-Tor"><div class="titlepage"><div><div><h3 class="title"><a id="id2934863"></a>5.26. On crash recovery or session restored startup, restore via: Tor, Non-Tor</h3></div></div></div><p>Options:
945
+  </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.restore_tor</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.crashed</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.normal_exit</strong></span></td></tr></table><p>
946
+  </p><p>This option works with the Torbutton <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js" target="_top">crash-observer.js</a> 
947
+  to set the Tor state after a crash is detected (via the 
948
+  <span class="command"><strong>extensions.torbutton.crashed</strong></span> pref). To confirm for
949
+false positives (such as session restore failures, upgrade, normal
950
+session restore, etc), Torbutton also sets the pref
951
+extensions.torbutton.normal_exit during
952
+Firefox exit and checks this value as well during startup.  
953
+</p><p>
954
+
955
+Since the Tor state after a Firefox crash is unknown/indeterminate, this
956
+setting helps to satisfy the <a class="link" href="#state">State Separation</a>
957
+requirement in the event of Firefox crashes by ensuring all cookies,
958
+settings and saved sessions are reloaded from a fixed Tor state.
959
+ 
960
+</p></div><div class="sect2" title="5.27. On normal startup, set state to: Tor, Non-Tor, Shutdown State"><div class="titlepage"><div><div><h3 class="title"><a id="id2934935"></a>5.27. On normal startup, set state to: Tor, Non-Tor, Shutdown State</h3></div></div></div><p>Options:
961
+  </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.startup_state</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.noncrashed</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.normal_exit</strong></span></td></tr></table><p>
962
+  </p><p>This option also works with the Torbutton <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/crash-observer.js" target="_top">crash-observer.js</a> 
963
+  to set the Tor state after a normal startup is detected (via the 
964
+  <span class="command"><strong>extensions.torbutton.noncrashed</strong></span> pref). To confirm for
965
+false positives
966
+(such as session restore failures, etc), Torbutton also sets the pref
967
+extensions.torbutton.normal_exit in torbutton_uninstall_observer() during
968
+Firefox exit and checks this value as well during startup.
969
+  
970
+</p></div><div class="sect2" title="5.28. Prevent session store from saving Non-Tor/Tor-loaded tabs"><div class="titlepage"><div><div><h3 class="title"><a id="id2934994"></a>5.28. Prevent session store from saving Non-Tor/Tor-loaded tabs</h3></div></div></div><p>Options: 
971
+  </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.nonontor_sessionstore</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.notor_sessionstore</strong></span></td></tr></table><p>
972
+  </p><p>If these options are enabled, the <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/components/nsSessionStore3.js" target="_top">replacement nsSessionStore.js</a>
973
+  component checks the <span class="command"><strong>__tb_tor_fetched</strong></span> tag of tabs before writing them
974
+  out. If the tag is from a blocked Tor state, the tab is not written to disk.
975
+  </p><p>
976
+This setting helps to satisfy the <a class="link" href="#disk">Disk Avoidance</a>
977
+requirement, and also helps to satisfy the <a class="link" href="#state">State Separation</a> requirement in the event of Firefox
978
+crashes.
979
+
980
+</p></div><div class="sect2" title="5.29. Set user agent during Tor usage (crucial)"><div class="titlepage"><div><div><h3 class="title"><a id="id2935059"></a>5.29. Set user agent during Tor usage (crucial)</h3></div></div></div><p>Options:
981
+   </p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.set_uagent</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.platform_override</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.oscpu_override</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.buildID_override</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.productsub_override</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.appname_override</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.appversion_override</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.useragent_override</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.useragent_vendor</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.useragent_vendorSub</strong></span></td></tr></table><p>
982
+   </p><p>On face, user agent switching appears to be straight-forward in Firefox.
983
+It provides several options for controlling the browser user agent string:
984
+<span class="command"><strong>general.appname.override</strong></span>,
985
+<span class="command"><strong>general.appversion.override</strong></span>,
986
+<span class="command"><strong>general.platform.override</strong></span>,
987
+<span class="command"><strong>general.oscpu.override</strong></span>,
988
+<span class="command"><strong>general.productSub.override</strong></span>,
989
+<span class="command"><strong>general.buildID.override</strong></span>,
990
+<span class="command"><strong>general.useragent.override</strong></span>,
991
+<span class="command"><strong>general.useragent.vendor</strong></span>, and
992
+<span class="command"><strong>general.useragent.vendorSub</strong></span>. If
993
+the Torbutton preference <span class="command"><strong>extensions.torbutton.set_uagent</strong></span> is
994
+true, Torbutton copies all of the other above prefs into their corresponding
995
+browser preferences during Tor usage.</p><p>
996
+
997
+It also turns out that it is possible to detect the original Firefox version
998
+by <a class="ulink" href="http://ha.ckers.org/blog/20070516/read-firefox-settings-poc/" target="_top">inspecting
999
+certain resource:// files</a>. These cases are handled by Torbutton's
1000
+<a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a>.
1001
+
1002
+</p><p>
1003
+This setting helps to satisfy the <a class="link" href="#setpreservation">Anonymity Set Preservation</a> requirement.
1004
+</p></div><div class="sect2" title="5.30. Spoof US English Browser"><div class="titlepage"><div><div><h3 class="title"><a id="id2935233"></a>5.30. Spoof US English Browser</h3></div></div></div><p>Options:
1005
+</p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.spoof_english</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.spoof_charset</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.spoof_language</strong></span></td></tr></table><p>
1006
+</p><p> This option causes Torbutton to set
1007
+<span class="command"><strong>general.useragent.locale</strong></span>
1008
+<span class="command"><strong>intl.accept_languages</strong></span> to the value specified in
1009
+<span class="command"><strong>extensions.torbutton.spoof_locale</strong></span>,
1010
+<span class="command"><strong>extensions.torbutton.spoof_charset</strong></span> and
1011
+<span class="command"><strong>extensions.torbutton.spoof_language</strong></span> during Tor usage, as
1012
+well as hooking <span class="command"><strong>navigator.language</strong></span> via its <a class="link" href="#jshooks" title="5.4. Hook Dangerous Javascript">javascript hooks</a>.
1013
+ </p><p>
1014
+This setting helps to satisfy the <a class="link" href="#setpreservation">Anonymity Set Preservation</a> and <a class="link" href="#location">Location Neutrality</a> requirements.
1015
+</p></div><div class="sect2" title="5.31. Don't send referrer during Tor Usage"><div class="titlepage"><div><div><h3 class="title"><a id="id2935326"></a>5.31. Don't send referrer during Tor Usage</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.disable_referer</strong></span>
1016
+</p><p> 
1017
+This option causes Torbutton to set <a class="ulink" href="http://kb.mozillazine.org/Network.http.sendSecureXSiteReferrer" target="_top">network.http.sendSecureXSiteReferrer</a> and
1018
+<a class="ulink" href="http://kb.mozillazine.org/Network.http.sendRefererHeader" target="_top">network.http.sendRefererHeader</a> during Tor usage.</p><p>
1019
+This setting also does not directly satisfy any Torbutton requirement, but
1020
+some may desire to mask their referrer for general privacy concerns.
1021
+</p></div><div class="sect2" title="5.32. Strip platform and language off of Google Search Box queries"><div class="titlepage"><div><div><h3 class="title"><a id="id2935366"></a>5.32. Strip platform and language off of Google Search Box queries</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.fix_google_srch</strong></span>
1022
+</p><p> 
1023
+
1024
+This option causes Torbutton to use the <a class="ulink" href="https://wiki.mozilla.org/Search_Service:API" target="_top">@mozilla.org/browser/search-service;1</a>
1025
+component to wrap the Google search plugin. On many platforms, notably Debian
1026
+and Ubuntu, the Google search plugin is set to reveal a lot of language and
1027
+platform information. This setting strips off that info while Tor is enabled.
1028
+
1029
+</p><p>
1030
+This setting helps Torbutton to fulfill its <a class="link" href="#setpreservation">Anonymity Set Preservation</a> requirement.
1031
+</p></div><div class="sect2" title="5.33. Automatically use an alternate search engine when presented with a Google Captcha"><div class="titlepage"><div><div><h3 class="title"><a id="id2935407"></a>5.33. Automatically use an alternate search engine when presented with a
1032
+Google Captcha</h3></div></div></div><p>Options:
1033
+</p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.asked_google_captcha</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.dodge_google_captcha</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.google_redir_url</strong></span></td></tr></table><p>
1034
+</p><p>
1035
+
1036
+Google's search engine has rate limiting features that cause it to
1037
+<a class="ulink" href="http://googleonlinesecurity.blogspot.com/2007/07/reason-behind-were-sorry-message.html" target="_top">present
1038
+captchas</a> and sometimes even outright ban IPs that issue large numbers
1039
+of search queries, especially if a lot of these queries appear to be searching
1040
+for software vulnerabilities or unprotected comment areas.
1041
+
1042
+</p><p>
1043
+
1044
+Despite multiple discussions with Google, we were unable to come to a solution
1045
+or any form of compromise that would reduce the number of captchas and
1046
+outright bans seen by Tor users issuing regular queries.
1047
+
1048
+</p><p>
1049
+As a result, we've implemented this option as an <a class="ulink" href="https://developer.mozilla.org/en/XUL_School/Intercepting_Page_Loads#HTTP_Observers" target="_top">'http-on-modify-request'</a>
1050
+http observer to optionally redirect banned or captcha-triggering Google
1051
+queries to search engines that do not rate limit Tor users. The current
1052
+options are ixquick.com, bing.com, yahoo.com and scroogle.org. These are
1053
+encoded in the preferences
1054
+<span class="command"><strong>extensions.torbutton.redir_url.[1-4]</strong></span>.
1055
+
1056
+</p></div><div class="sect2" title="5.34. Store SSL/CA Certs in separate jars for Tor/Non-Tor (recommended)"><div class="titlepage"><div><div><h3 class="title"><a id="id2935487"></a>5.34. Store SSL/CA Certs in separate jars for Tor/Non-Tor (recommended)</h3></div></div></div><p>Options:
1057
+</p><table border="0" summary="Simple list" class="simplelist"><tr><td><span class="command"><strong>extensions.torbutton.jar_certs</strong></span></td></tr><tr><td><span class="command"><strong>extensions.torbutton.jar_ca_certs</strong></span></td></tr></table><p>
1058
+</p><p>
1059
+
1060
+These settings govern if Torbutton attempts to isolate the user's SSL
1061
+certificates into separate jars for each Tor state. This isolation is
1062
+implemented in <code class="function">torbutton_jar_certs()</code> in <a class="ulink" href="https://git.torproject.org/checkout/torbutton/master/src/chrome/content/torbutton.js" target="_top">chrome/content/torbutton.js</a>,
1063
+which calls <code class="function">torbutton_jar_cert_type()</code> and
1064
+<code class="function">torbutton_unjar_cert_type()</code> for each certificate type in
1065
+the <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/security/nsscertcache;1" target="_top">@mozilla.org/security/nsscertcache;1</a>.
1066
+Certificates are deleted from and imported to the <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/%40mozilla.org/security/x509certdb;1" target="_top">@mozilla.org/security/x509certdb;1</a>.
1067
+</p><p>
1068
+The first time this pref is used, a backup of the user's certificates is
1069
+created in their profile directory under the name
1070
+<code class="filename">cert8.db.bak</code>. This file can be copied back to
1071
+<code class="filename">cert8.db</code> to fully restore the original state of the
1072
+user's certificates in the event of any error.
1073
+</p><p>
1074
+Since exit nodes and malicious sites can insert content elements sourced to
1075
+specific SSL sites to query if a user has a certain certificate,
1076
+this setting helps to satisfy the <a class="link" href="#state">State
1077
+Separation</a> requirement of Torbutton. Unfortunately, <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=435159" target="_top">Firefox Bug
1078
+435159</a> prevents it from functioning correctly in the event of rapid Tor toggle, so it
1079
+is currently not exposed via the preferences UI.
1080
+
1081
+</p></div></div><div class="sect1" title="6. Relevant Firefox Bugs"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="FirefoxBugs"></a>6. Relevant Firefox Bugs</h2></div></div></div><p>
1082
+
1083
+  </p><div class="sect2" title="6.1. Bugs impacting security"><div class="titlepage"><div><div><h3 class="title"><a id="FirefoxSecurity"></a>6.1. Bugs impacting security</h3></div></div></div><p>
1084
+
1085
+Torbutton has to work around a number of Firefox bugs that impact its
1086
+security. Most of these are mentioned elsewhere in this document, but they
1087
+have also been gathered here for reference. In order of decreasing severity,
1088
+they are:
1089
+
1090
+   </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=429070" target="_top">Bug 429070 - exposing
1091
+Components.interfaces to untrusted content leaks information about installed
1092
+extensions</a><p>
1093
+<a class="ulink" href="http://pseudo-flaw.net/" target="_top">Gregory Fleischer</a> demonstrated at Defcon 17 that these interfaces can
1094
+also be used to <a class="ulink" href="http://pseudo-flaw.net/tor/torbutton/fingerprint-firefox.html" target="_top">fingerprint
1095
+Firefox down the to the minor version</a>. Note that his test has not been
1096
+updated since 3.5.3, hence it reports 3.5.3 for more recent Firefoxes. This
1097
+bug interferes with Torbutton's ability to satisfy its <a class="link" href="#setpreservation">Anonymity Set Preservation</a> requirement.
1098
+     </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=280661" target="_top">Bug 280661 - SOCKS proxy server
1099
+connection timeout hard-coded</a><p>
1100
+
1101
+This bug prevents us from using the Firefox SOCKS layer directly, and
1102
+currently requires us to ship an auxiliary HTTP proxy called <a class="ulink" href="http://www.pps.jussieu.fr/~jch/software/polipo/" target="_top">Polipo</a>. If this
1103
+patch were landed, we would no longer need to ship Polipo, which has a number
1104
+of privacy and security issues of its own (in addition to being unmaintained).
1105
+
1106
+    </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=418986" target="_top">Bug 418986 - window.screen
1107
+provides a large amount of identifiable information</a><p>
1108
+
1109
+As <a class="link" href="#fingerprinting">mentioned above</a>, a large amount of
1110
+information is available from <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.screen" target="_top">window.screen</a>.
1111
+Currently, there is no way to obscure this information without Javascript
1112
+hooking. This bug is a feature request to provide some other method to change
1113
+these values. This bug interferes with Torbutton's ability to fulfill its
1114
+<a class="link" href="#setpreservation">Anonymity Set Preservation</a>
1115
+requirement.
1116
+
1117
+   </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=435159" target="_top">Bug 435159 -
1118
+nsNSSCertificateDB::DeleteCertificate has race conditions</a><p>
1119
+
1120
+In Torbutton 1.2.0rc1, code was added to attempt to isolate SSL certificates
1121
+the user has installed. Unfortunately, the method call to delete a certificate
1122
+from the current certificate database acts lazily: it only sets a variable
1123
+that marks a cert for deletion later, and it is not cleared if that
1124
+certificate is re-added. This means that if the Tor state is toggled quickly,
1125
+that certificate could remain present until it is re-inserted (causing an
1126
+error dialog), and worse, it would still be deleted after that.  The lack of
1127
+this functionality is considered a Torbutton security bug because cert
1128
+isolation is considered a <a class="link" href="#state">State Separation</a>
1129
+feature.
1130
+
1131
+      </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=575230" target="_top">Bug 575230 - Provide option to
1132
+reduce precision of Date()</a><p>
1133
+
1134
+Currently it is possible to <a class="ulink" href="http://arstechnica.com/tech-policy/news/2010/02/firm-uses-typing-cadence-to-finger-unauthorized-users.ars" target="_top">fingerprint
1135
+users based on their typing cadence</a> using the high precision timer
1136
+available to javascript. Using this same precision, it is possible to compute
1137
+an identifier based upon the clock drift of the client from some nominal
1138
+source. The latter is not much of a concern for Tor users, as the variable
1139
+delay to load and run a page is measured on the order of seconds, but the high
1140
+precision timer can still be used to fingerprint aspects of a browser's
1141
+javascript engine and processor, and apparently also a user's typing cadence.
1142
+This bug hinders Torbutton's ability to satisfy its <a class="link" href="#setpreservation">Anonymity Set Preservation</a> requirement.
1143
+
1144
+      </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Bug 409737 -
1145
+javascript.enabled and docShell.allowJavascript do not disable all event
1146
+handlers</a><p>
1147
+
1148
+This bug allows pages to execute javascript via addEventListener and perhaps
1149
+other callbacks. In order to prevent this bug from enabling an attacker to
1150
+break the <a class="link" href="#isolation">Network Isolation</a> requirement,
1151
+Torbutton 1.1.13 began blocking popups and history manipulation from different
1152
+Tor states.  So long as there are no ways to open popups or redirect the user
1153
+to a new page, the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">Torbutton content
1154
+policy</a> should block Javascript network access. However, if there are
1155
+ways to open popups or perform redirects such that Torbutton cannot block
1156
+them, pages may still have free reign to break that requirement and reveal a
1157
+user's original IP address.
1158
+
1159
+     </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=448743" target="_top">Bug 448743 -
1160
+Decouple general.useragent.locale from spoofing of navigator.language</a><p>
1161
+
1162
+Currently, Torbutton spoofs the <span class="command"><strong>navigator.language</strong></span>
1163
+attribute via <a class="link" href="#jshooks" title="5.4. Hook Dangerous Javascript">Javascript hooks</a>. Unfortunately,
1164
+these do not work on Firefox 3. It would be ideal to have
1165
+a pref to set this value (something like a
1166
+<span class="command"><strong>general.useragent.override.locale</strong></span>),
1167
+to avoid fragmenting the anonymity set of users of foreign locales. This issue
1168
+impedes Torbutton from fully meeting its <a class="link" href="#setpreservation">Anonymity Set Preservation</a>
1169
+requirement on Firefox 3.
1170
+
1171
+     </p></li></ol></div></div><div class="sect2" title="6.2. Bugs blocking functionality"><div class="titlepage"><div><div><h3 class="title"><a id="FirefoxWishlist"></a>6.2. Bugs blocking functionality</h3></div></div></div><p>
1172
+The following bugs impact Torbutton and similar extensions' functionality.
1173
+   </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=445696" target="_top">Bug 445696 -
1174
+Extensions cannot determine if firefox is fullScreen</a><p>
1175
+
1176
+The windowState property of <a class="ulink" href="https://developer.mozilla.org/en/XUL/window" target="_top">ChromeWindows</a> does not accurately reflect the true
1177
+state of the window in some cases on Linux. This causes Torbutton to attempt
1178
+to resize maximized and minimized windows when it should not.
1179
+
1180
+   </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=290456" target="_top">Bug 290456 -
1181
+Block/clear Flash MX "cookies" as well</a><p>
1182
+
1183
+Today, it is possible to allow plugins if you have a transparent proxy such as
1184
+<a class="ulink" href="http://anonymityanywhere.com/incognito/" target="_top">Incognito</a> to prevent proxy bypass. However, flash cookies can still be used to
1185
+link your Tor and Non-Tor activity, and this reveal your IP to an adversary
1186
+that does so. This can be solved by manually removing your flash cookies (like
1187
+<a class="ulink" href="https://addons.mozilla.org/en-US/firefox/addon/6623" target="_top">BetterPrivacy</a> does), but
1188
+it would be nice if there was a standard way to do this from a Firefox API.
1189
+
1190
+   </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=417869" target="_top">Bug 417869 -
1191
+Browser context is difficult to obtain from many XPCOM callbacks</a><p>
1192
+
1193
+It is difficult to determine which tabbrowser many XPCOM callbacks originate
1194
+from, and in some cases absolutely no context information is provided at all.
1195
+While this doesn't have much of an effect on Torbutton, it does make writing
1196
+extensions that would like to do per-tab settings and content filters (such as
1197
+FoxyProxy) difficult to impossible to implement securely.
1198
+
1199
+   </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=418321" target="_top">Bug 418321 -
1200
+Components do not expose disk interfaces</a><p>
1201
+
1202
+Several components currently provide no way of reimplementing their disk
1203
+access to easily satisfy Torbutton's <a class="link" href="#disk">Disk
1204
+Avoidance</a> requirements. Workarounds exist, but they are <a class="link" href="#sessionstore" title="@mozilla.org/browser/sessionstore;1 - components/nsSessionStore36.js">clunky</a>, and
1205
+some of them involve disabling functionality during Tor usage.
1206
+
1207
+   </p></li></ol></div></div><div class="sect2" title="6.3. Low Priority Bugs"><div class="titlepage"><div><div><h3 class="title"><a id="FirefoxMiscBugs"></a>6.3. Low Priority Bugs</h3></div></div></div><p>
1208
+The following bugs have an effect upon Torbutton, but are superseded by more
1209
+practical and more easily fixable variant bugs above; or have stable, simple
1210
+workarounds.
1211
+  </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=435151" target="_top">Bug 435151 - XPCSafeJSObjectWrapper breaks evalInSandbox</a><p>
1212
+
1213
+Under Firefox 3, the XPCSafeJSObjectWrapper breaks when you try to use
1214
+constructors of classes defined from within the scope of the sandbox, among
1215
+other things. This prevents Torbutton from applying the Timezone hooks under
1216
+Firefox 3, but a better solution for Torbutton's specific date hooking needs 
1217
+would be a fix for the above mentioned Bug 392274. Of course, many more
1218
+extensions may be interested in the sandbox hooking functionality working
1219
+properly though.
1220
+
1221
+     </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=440892" target="_top">Bug 440892 -
1222
+network.protocol-handler.warn-external are ignored</a><p>
1223
+
1224
+Sometime in the Firefox 3 development cycle, the preferences that governed
1225
+warning a user when external apps were launched got disconnected from the code
1226
+that does the launching. Torbutton depended on these prefs to prevent websites
1227
+from launching specially crafted documents and application arguments that
1228
+caused Proxy Bypass. We currently work around this issue by <a class="link" href="#appblocker" title="@mozilla.org/uriloader/external-protocol-service;1 , @mozilla.org/uriloader/external-helper-app-service;1, and @mozilla.org/mime;1 - components/external-app-blocker.js">wrapping the app launching components</a> to present a
1229
+popup before launching external apps while Tor is enabled. While this works,
1230
+it would be nice if these prefs were either fixed or removed.
1231
+
1232
+     </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437014" target="_top">Bug 437014 -
1233
+nsIContentPolicy::shouldLoad no longer called for favicons</a><p>
1234
+
1235
+Firefox 3.0 stopped calling the shouldLoad call of content policy for favicon
1236
+loads. Torbutton had relied on this call to block favicon loads for opposite
1237
+Tor states. The workaround it employs for Firefox 3 is to cancel the request
1238
+when it arrives in the <span class="command"><strong>torbutton_http_observer</strong></span> used for
1239
+blocking full page plugin loads. This seems to work just fine, but is a bit
1240
+dirty.
1241
+
1242
+    </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=309524" target="_top">Bug 309524</a>
1243
+and <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=380556" target="_top">Bug
1244
+380556</a> - nsIContentPolicy::shouldProcess is not called.
1245
+     <p>
1246
+
1247
+This is a call that would be useful to develop a better workaround for the
1248
+allowPlugins issue above. If the content policy were called before a URL was
1249
+handed over to a plugin or helper app, it would make the workaround for the
1250
+above allowPlugins bug a lot cleaner. Obviously this bug is not as severe as
1251
+the others though, but it might be nice to have this API as a backup.
1252
+
1253
+     </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=401296" target="_top">Bug 401296 - docShell.allowPlugins
1254
+not honored for direct links</a> (Perhaps subset of <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=282106" target="_top">Bug 282106</a>?)
1255
+     <p>
1256
+
1257
+Similar to the javascript plugin disabling attribute, the plugin disabling
1258
+attribute is also not perfect — it is ignored for direct links to plugin
1259
+handled content, as well as meta-refreshes to plugin handled content.  This
1260
+requires Torbutton to listen to a number of different http events to intercept
1261
+plugin-related mime type URLs and cancel their requests. Again, since plugins
1262
+are quite horrible about obeying proxy settings, loading a plugin pretty much
1263
+ensures a way to break the <a class="link" href="#isolation">Network Isolation</a>
1264
+requirement and reveal a user's original IP address. Torbutton's code to
1265
+perform this workaround has been subverted at least once already by Kyle
1266
+Williams.
1267
+
1268
+     </p></li><li class="listitem"><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=419598" target="_top">Bug 419598 - 'var
1269
+Date' is deletable</a><p>
1270
+
1271
+Based on Page 62 of the <a class="ulink" href="http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf" target="_top">ECMA-262
1272
+Javascript spec</a>, it seems like it should be possible to do something
1273
+like the following to prevent the Date object from being unmasked:
1274
+</p><pre class="screen">
1275
+with(window) {
1276
+    var Date = fakeDate;
1277
+    var otherVariable = 42;
1278
+}
1279
+
1280
+delete window.Date; // Should fail. Instead succeeds, revealing original Date.
1281
+delete window.otherVariable; // Fails, leaving window.otherVariable set to 42.
1282
+</pre><p>
1283
+
1284
+From the ECMA-262 spec:
1285
+
1286
+</p><div class="blockquote"><blockquote class="blockquote">
1287
+If the variable statement occurs inside a FunctionDeclaration, the variables
1288
+are defined with function-local scope in that function, as described in
1289
+s10.1.3. Otherwise, they are defined with global scope (that is, they are
1290
+created as members of the global object, as described in 10.1.3) using
1291
+property attributes { DontDelete }. Variables are created when the execution
1292
+scope is entered. A Block does not define a new execution scope. Only Program
1293
+and FunctionDeclaration produce a new scope. Variables are initialized to
1294
+undefined when created. A variable with an Initialiser is assigned the value
1295
+of its AssignmentExpression when the VariableStatement is executed, not when
1296
+the variable is created.
1297
+</blockquote></div><p>
1298
+
1299
+In fact, this is exactly how the with statement with a variable declaration
1300
+behaves <span class="emphasis"><em>for all other variables other than ones that shadow system
1301
+variables</em></span>. Some variables (such as
1302
+<span class="command"><strong>window.screen</strong></span>, and <span class="command"><strong>window.history</strong></span>) can't
1303
+even be shadowed in this way, and give an error about lacking a setter. If
1304
+such shadowing were possible, it would greatly simplify the Javascript hooking
1305
+code, which currently relies on undocumented semantics of
1306
+<span class="command"><strong>__proto__</strong></span> to copy the original values in the event of a
1307
+delete. This <span class="command"><strong>__proto__</strong></span> hack unfortunately does not work for
1308
+the Date object though.
1309
+
1310
+     </p></li></ol></div></div></div><div class="sect1" title="7. Testing"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="TestPlan"></a>7. Testing</h2></div></div></div><p>
1311
+
1312
+The purpose of this section is to cover all the known ways that Tor browser
1313
+security can be subverted from a penetration testing perspective. The hope
1314
+is that it will be useful both for creating a "Tor Safety Check"
1315
+page, and for developing novel tests and actively attacking Torbutton with the
1316
+goal of finding vulnerabilities in either it or the Mozilla components,
1317
+interfaces and settings upon which it relies.
1318
+
1319
+  </p><div class="sect2" title="7.1. Single state testing"><div class="titlepage"><div><div><h3 class="title"><a id="SingleStateTesting"></a>7.1. Single state testing</h3></div></div></div><p>
1320
+
1321
+Torbutton is a complicated piece of software. During development, changes to
1322
+one component can affect a whole slough of unrelated features.  A number of
1323
+aggregated test suites exist that can be used to test for regressions in
1324
+Torbutton and to help aid in the development of Torbutton-like addons and
1325
+other privacy modifications of other browsers. Some of these test suites exist
1326
+as a single automated page, while others are a series of pages you must visit
1327
+individually. They are provided here for reference and future regression
1328
+testing, and also in the hope that some brave soul will one day decide to
1329
+combine them into a comprehensive automated test suite.
1330
+
1331
+     </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="ulink" href="http://decloak.net/" target="_top">Decloak.net</a><p>
1332
+
1333
+Decloak.net is the canonical source of plugin and external-application based
1334
+proxy-bypass exploits. It is a fully automated test suite maintained by <a class="ulink" href="http://digitaloffense.net/" target="_top">HD Moore</a> as a service for people to
1335
+use to test their anonymity systems.
1336
+
1337
+       </p></li><li class="listitem"><a class="ulink" href="http://deanonymizer.com/" target="_top">Deanonymizer.com</a><p>
1338
+
1339
+Deanonymizer.com is another automated test suite that tests for proxy bypass
1340
+and other information disclosure vulnerabilities. It is maintained by Kyle
1341
+Williams, the author of <a class="ulink" href="http://www.janusvm.com/" target="_top">JanusVM</a>
1342
+and <a class="ulink" href="http://www.januspa.com/" target="_top">JanusPA</a>.
1343
+
1344
+       </p></li><li class="listitem"><a class="ulink" href="https://www.jondos.de/en/anontest" target="_top">JonDos
1345
+AnonTest</a><p>
1346
+
1347
+The <a class="ulink" href="https://www.jondos.de" target="_top">JonDos people</a> also provide an
1348
+anonymity tester. It is more focused on HTTP headers than plugin bypass, and
1349
+points out a couple of headers Torbutton could do a better job with
1350
+obfuscating.
1351
+
1352
+       </p></li><li class="listitem"><a class="ulink" href="http://browserspy.dk" target="_top">Browserspy.dk</a><p>
1353
+
1354
+Browserspy.dk provides a tremendous collection of browser fingerprinting and
1355
+general privacy tests. Unfortunately they are only available one page at a
1356
+time, and there is not really solid feedback on good vs bad behavior in
1357
+the test results.
1358
+
1359
+       </p></li><li class="listitem"><a class="ulink" href="http://analyze.privacy.net/" target="_top">Privacy
1360
+Analyzer</a><p>
1361
+
1362
+The Privacy Analyzer provides a dump of all sorts of browser attributes and
1363
+settings that it detects, including some information on your origin IP
1364
+address. Its page layout and lack of good vs bad test result feedback makes it
1365
+not as useful as a user-facing testing tool, but it does provide some
1366
+interesting checks in a single page.
1367
+
1368
+       </p></li><li class="listitem"><a class="ulink" href="http://ha.ckers.org/mr-t/" target="_top">Mr. T</a><p>
1369
+
1370
+Mr. T is a collection of browser fingerprinting and deanonymization exploits
1371
+discovered by the <a class="ulink" href="http://ha.ckers.org" target="_top">ha.ckers.org</a> crew
1372
+and others. It is also not as user friendly as some of the above tests, but it
1373
+is a useful collection.
1374
+
1375
+       </p></li><li class="listitem">Gregory Fleischer's <a class="ulink" href="http://pseudo-flaw.net/content/tor/torbutton/" target="_top">Torbutton</a> and
1376
+<a class="ulink" href="http://pseudo-flaw.net/content/defcon/dc-17-demos/d.html" target="_top">Defcon
1377
+17</a> Test Cases
1378
+       <p>
1379
+
1380
+Gregory Fleischer has been hacking and testing Firefox and Torbutton privacy
1381
+issues for the past 2 years. He has an excellent collection of all his test
1382
+cases that can be used for regression testing. In his Defcon work, he
1383
+demonstrates ways to infer Firefox version based on arcane browser properties.
1384
+We are still trying to determine the best way to address some of those test
1385
+cases.
1386
+
1387
+       </p></li><li class="listitem"><a class="ulink" href="https://torcheck.xenobite.eu/index.php" target="_top">Xenobite's
1388
+TorCheck Page</a><p>
1389
+
1390
+This page checks to ensure you are using a valid Tor exit node and checks for
1391
+some basic browser properties related to privacy. It is not very fine-grained
1392
+or complete, but it is automated and could be turned into something useful
1393
+with a bit of work.
1394
+
1395
+       </p></li></ol></div><p>
1396
+    </p></div><div class="sect2" title="7.2. Multi-state testing"><div class="titlepage"><div><div><h3 class="title"><a id="id2936532"></a>7.2. Multi-state testing</h3></div></div></div><p>
1397
+
1398
+The tests in this section are geared towards a page that would instruct the
1399
+user to toggle their Tor state after the fetch and perform some operations:
1400
+mouseovers, stray clicks, and potentially reloads.
1401
+
1402
+   </p><div class="sect3" title="Cookies and Cache Correlation"><div class="titlepage"><div><div><h4 class="title"><a id="id2936545"></a>Cookies and Cache Correlation</h4></div></div></div><p>
1403
+The most obvious test is to set a cookie, ask the user to toggle tor, and then
1404
+have them reload the page. The cookie should no longer be set if they are
1405
+using the default Torbutton settings. In addition, it is possible to leverage
1406
+the cache to <a class="ulink" href="http://crypto.stanford.edu/sameorigin/safecachetest.html" target="_top">store unique
1407
+identifiers</a>. The default settings of Torbutton should also protect
1408
+against these from persisting across Tor Toggle.
1409
+
1410
+    </p></div><div class="sect3" title="Javascript timers and event handlers"><div class="titlepage"><div><div><h4 class="title"><a id="id2936567"></a>Javascript timers and event handlers</h4></div></div></div><p>
1411
+
1412
+Javascript can set timers and register event handlers in the hopes of fetching
1413
+URLs after the user has toggled Torbutton. 
1414
+    </p></div><div class="sect3" title="CSS Popups and non-script Dynamic Content"><div class="titlepage"><div><div><h4 class="title"><a id="id2936580"></a>CSS Popups and non-script Dynamic Content</h4></div></div></div><p>
1415
+
1416
+Even if Javascript is disabled, CSS is still able to 
1417
+<a class="ulink" href="http://www.tjkdesign.com/articles/css%20pop%20ups/" target="_top">create popup-like
1418
+windows</a>
1419
+via the 'onmouseover' CSS attribute, which can cause arbitrary browser
1420
+activity as soon as the mouse enters into the content window. It is also
1421
+possible for meta-refresh tags to set timers long enough to make it likely
1422
+that the user has toggled Tor before fetching content.
1423
+
1424
+    </p></div></div><div class="sect2" title="7.3. Active testing (aka How to Hack Torbutton)"><div class="titlepage"><div><div><h3 class="title"><a id="HackTorbutton"></a>7.3. Active testing (aka How to Hack Torbutton)</h3></div></div></div><p>
1425
+
1426
+The idea behind active testing is to discover vulnerabilities in Torbutton to
1427
+bypass proxy settings, run script in an opposite Tor state, store unique
1428
+identifiers, leak location information, or otherwise violate <a class="link" href="#requirements" title="1.2. Torbutton Requirements">its requirements</a>. Torbutton has ventured out
1429
+into a strange and new security landscape. It depends on Firefox mechanisms
1430
+that haven't necessarily been audited for security, certainly not for the
1431
+threat model that Torbutton seeks to address. As such, it and the interfaces
1432
+it depends upon still need a 'trial by fire' typical of new technologies. This
1433
+section of the document was written with the intention of making that period
1434
+as fast as possible. Please help us get through this period by considering
1435
+these attacks, playing with them, and reporting what you find (and potentially
1436
+submitting the test cases back to be run in the standard batch of Torbutton
1437
+tests.
1438
+
1439
+   </p><div class="sect3" title="Some suggested vectors to investigate"><div class="titlepage"><div><div><h4 class="title"><a id="id2936635"></a>Some suggested vectors to investigate</h4></div></div></div><p>
1440
+    </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem">Strange ways to register Javascript <a class="ulink" href="http://en.wikipedia.org/wiki/DOM_Events" target="_top">events</a> and <a class="ulink" href="http://www.devshed.com/c/a/JavaScript/Using-Timers-in-JavaScript/" target="_top">timeouts</a> should
1441
+be verified to actually be ineffective after Tor has been toggled.</li><li class="listitem">Other ways to cause Javascript to be executed after
1442
+<span class="command"><strong>javascript.enabled</strong></span> has been toggled off.</li><li class="listitem">Odd ways to attempt to load plugins. Kyle Williams has had
1443
+some success with direct loads/meta-refreshes of plugin-handled URLs.</li><li class="listitem">The Date and Timezone hooks should be verified to work with
1444
+crazy combinations of iframes, nested iframes, iframes in frames, frames in
1445
+iframes, and popups being loaded and
1446
+reloaded in rapid succession, and/or from one another. Think race conditions and deep, 
1447
+parallel nesting, involving iframes from both <a class="ulink" href="http://en.wikipedia.org/wiki/Same_origin_policy" target="_top">same-origin and
1448
+non-same-origin</a> domains.</li><li class="listitem">In addition, there may be alternate ways and other
1449
+methods to query the timezone, or otherwise use some of the Date object's
1450
+methods in combination to deduce the timezone offset. Of course, the author
1451
+tried his best to cover all the methods he could foresee, but it's always good
1452
+to have another set of eyes try it out.</li><li class="listitem">Similarly, is there any way to confuse the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a>
1453
+mentioned above to cause it to allow certain types of page fetches? For
1454
+example, it was recently discovered that favicons are not fetched by the
1455
+content, but the chrome itself, hence the content policy did not look up the
1456
+correct window to determine the current Tor tag for the favicon fetch. Are
1457
+there other things that can do this? Popups? Bookmarklets? Active bookmarks? </li><li class="listitem">Alternate ways to store and fetch unique identifiers. For example, <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:Storage" target="_top">DOM Storage</a>
1458
+caught us off guard. 
1459
+It was
1460
+also discovered by <a class="ulink" href="http://pseudo-flaw.net" target="_top">Gregory
1461
+Fleischer</a> that <a class="ulink" href="http://pseudo-flaw.net/content/tor/torbutton/" target="_top">content window access to
1462
+chrome</a> can be used to build <a class="link" href="#fingerprinting">unique
1463
+identifiers</a>. 
1464
+Are there any other
1465
+arcane or experimental ways that Firefox provides to create and store unique
1466
+identifiers? Or perhaps unique identifiers can be queried or derived from
1467
+properties of the machine/browser that Javascript has access to? How unique
1468
+can these identifiers be?
1469
+     </li><li class="listitem">Is it possible to get the browser to write some history to disk
1470
+(aside from swap) that can be retrieved later? By default, Torbutton should
1471
+write no history, cookie, or other browsing activity information to the
1472
+harddisk.</li><li class="listitem">Do popup windows make it easier to break any of the above
1473
+behavior? Are javascript events still canceled in popups? What about recursive
1474
+popups from Javascript, data, and other funky URL types? What about CSS
1475
+popups? Are they still blocked after Tor is toggled?</li><li class="listitem">Chrome-escalation attacks. The interaction between the
1476
+Torbutton chrome Javascript and the client content window javascript is pretty
1477
+well-defined and carefully constructed, but perhaps there is a way to smuggle
1478
+javascript back in a return value, or otherwise inject network-loaded
1479
+javascript into the chrome (and thus gain complete control of the browser).
1480
+</li></ul></div><p>
1481
+
1482
+    </p></div></div></div></div></body></html>
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