Inital move of torbutton we...
Jacob Appelbaum authored 15 years ago
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2) <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 V1.73.2" /></head><body><div class="article" lang="en" xml:lang="en"><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"><<a class="email" href="mailto:mikeperry.fscked/org">mikeperry.fscked/org</a>></code></p></div></div></div></div><div><p class="pubdate">July 4 2008</p></div></div><hr /></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#id2970568">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="#id2980698">2. Components</a></span></dt><dd><dl><dt><span class="sect2"><a href="#id3000781">2.1. Hooked Components</a></span></dt><dt><span class="sect2"><a href="#id2988472">2.2. New Components</a></span></dt></dl></dd><dt><span class="sect1"><a href="#id2981568">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="#id2984229">3.2. Preferences Window - preferences.xul</a></span></dt><dt><span class="sect2"><a href="#id2988730">3.3. Other Windows</a></span></dt></dl></dd><dt><span class="sect1"><a href="#id2986171">4. Toggle Code Path</a></span></dt><dd><dl><dt><span class="sect2"><a href="#id2990959">4.1. Button Click</a></span></dt><dt><span class="sect2"><a href="#id2984082">4.2. Proxy Update</a></span></dt><dt><span class="sect2"><a href="#id3001325">4.3. Settings Update</a></span></dt></dl></dd><dt><span class="sect1"><a href="#id2984248">5. Description of Options</a></span></dt><dd><dl><dt><span class="sect2"><a href="#id2980079">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="#id2978605">5.3. Isolate Dynamic Content to Tor State (crucial)</a></span></dt><dt><span class="sect2"><a href="#jshooks">5.4. Hook Dangerous Javascript (crucial)</a></span></dt><dt><span class="sect2"><a href="#id2992126">5.5. Resize windows to multiples of 50px during Tor usage (recommended)</a></span></dt><dt><span class="sect2"><a href="#id3004184">5.6. Disable Updates During Tor (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2997514">5.7. Disable Search Suggestions during Tor (recommended)</a></span></dt><dt><span class="sect2"><a href="#id3000110">5.8. Block Tor/Non-Tor access to network from file:// urls (recommended)</a></span></dt><dt><span class="sect2"><a href="#id2998307">5.9. Close all Tor/Non-Tor tabs and windows on toggle (optional)</a></span></dt><dt><span class="sect2"><a href="#id2996566">5.10. Isolate Access to History navigation to Tor state (crucial)</a></span></dt><dt><span class="sect2"><a href="#id2998342">5.11. History Access Settings</a></span></dt><dt><span class="sect2"><a href="#id2957709">5.12. Clear History During Tor Toggle (optional)</a></span></dt><dt><span class="sect2"><a href="#id2962370">5.13. Block Password+Form saving during Tor/Non-Tor</a></span></dt><dt><span class="sect2"><a href="#id2962437">5.14. Block Tor disk cache and clear all cache on Tor Toggle</a></span></dt><dt><span class="sect2"><a href="#id2962492">5.15. Block disk and memory cache during Tor</a></span></dt><dt><span class="sect2"><a href="#id2962549">5.16. Clear Cookies on Tor Toggle</a></span></dt><dt><span class="sect2"><a href="#id2962603">5.17. Store Non-Tor cookies in a protected jar</a></span></dt><dt><span class="sect2"><a href="#id2962662">5.18. Store both Non-Tor and Tor cookies in a protected jar (dangerous)</a></span></dt><dt><span class="sect2"><a href="#id2962702">5.19. Manage My Own Cookies (dangerous)</a></span></dt><dt><span class="sect2"><a href="#id2962718">5.20. Disable DOM Storage during Tor usage (crucial)</a></span></dt><dt><span class="sect2"><a href="#id2962826">5.21. Clear HTTP Auth on Tor Toggle (recommended)</a></span></dt><dt><span class="sect2"><a href="#id3005721">5.22. Clear cookies on Tor/Non-Tor shutdown</a></span></dt><dt><span class="sect2"><a href="#id3005775">5.23. Reload cookie jar/clear cookies on Firefox crash</a></span></dt><dt><span class="sect2"><a href="#id3005850">5.24. On crash recovery or session restored startup, restore via: Tor, Non-Tor</a></span></dt><dt><span class="sect2"><a href="#id3005910">5.25. On normal startup, set state to: Tor, Non-Tor, Shutdown State</a></span></dt><dt><span class="sect2"><a href="#id3005958">5.26. Prevent session store from saving Non-Tor/Tor-loaded tabs</a></span></dt><dt><span class="sect2"><a href="#id3006023">5.27. Set user agent during Tor usage (crucial)</a></span></dt><dt><span class="sect2"><a href="#id3006210">5.28. Spoof US English Browser</a></span></dt><dt><span class="sect2"><a href="#id3006297">5.29. Don't send referrer during Tor Usage</a></span></dt><dt><span class="sect2"><a href="#id3006338">5.30. 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="#Categories">7.1. Single state testing</a></span></dt><dt><span class="sect2"><a href="#id3007257">7.2. Multi-state testing</a></span></dt><dt><span class="sect2"><a href="#id3007328">7.3. Active testing (aka How to Hack Torbutton)</a></span></dt></dl></dd></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2970568"></a>1. Introduction</h2></div></div></div><p>
3)
4) This document describes the goals, operation, and testing procedures of the
5) Torbutton Firefox extension. It is current as of Torbutton 1.2.0rc5.
6)
7) </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="adversary"></a>1.1. Adversary Model</h3></div></div></div><p>
8)
9) A Tor web browser adversary has a number of goals, capabilities, and attack
10) types that can be used to guide us towards a set of requirements for the
11) Torbutton extension. Let's start with the goals.
12)
13) </p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2997298"></a>Adversary Goals</h4></div></div></div><div class="orderedlist"><ol type="1"><li><span class="command"><strong>Bypassing proxy settings</strong></span><p>The adversary's primary goal is direct compromise and bypass of
14) Tor, causing the user to directly connect to an IP of the adversary's
15) choosing.</p></li><li><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
16) happily settle for the ability to correlate something a user did via Tor with
17) their non-Tor activity. This can be done with cookies, cache identifiers,
18) javascript events, and even CSS. Sometimes the fact that a user uses Tor may
19) be enough for some authorities.</p></li><li><span class="command"><strong>History disclosure</strong></span><p>
20) The adversary may also be interested in history disclosure: the ability to
21) query a user's history to see if they have issued certain censored search
22) queries, or visited censored sites.
23) </p></li><li><span class="command"><strong>Location information</strong></span><p>
24)
25) Location information such as timezone and locality can be useful for the
26) adversary to determine if a user is in fact originating from one of the
27) regions they are attempting to control, or to zero-in on the geographical
28) location of a particular dissident or whistleblower.
29)
30) </p></li><li><span class="command"><strong>Miscellaneous anonymity set reduction</strong></span><p>
31)
32) Anonymity set reduction is also useful in attempting to zero in on a
33) particular individual. If the dissident or whistleblower is using a rare build
34) of Firefox for an obscure operating system, this can be very useful
35) information for tracking them down, or at least <a class="link" href="#fingerprinting">tracking their activities</a>.
36)
37) </p></li><li><span class="command"><strong>History records and other on-disk
38) information</strong></span><p>
39) In some cases, the adversary may opt for a heavy-handed approach, such as
40) seizing the computers of all Tor users in an area (especially after narrowing
41) the field by the above two pieces of information). History records and cache
42) data are the primary goals here.
43) </p></li></ol></div></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2970954"></a>Adversary Capabilities - Positioning</h4></div></div></div><p>
44) The adversary can position themselves at a number of different locations in
45) order to execute their attacks.
46) </p><div class="orderedlist"><ol type="1"><li><span class="command"><strong>Exit Node or Upstream Router</strong></span><p>
47) The adversary can run exit nodes, or alternatively, they may control routers
48) upstream of exit nodes. Both of these scenarios have been observed in the
49) wild.
50) </p></li><li><span class="command"><strong>Adservers and/or Malicious Websites</strong></span><p>
51) The adversary can also run websites, or more likely, they can contract out
52) ad space from a number of different adservers and inject content that way. For
53) some users, the adversary may be the adservers themselves. It is not
54) inconceivable that adservers may try to subvert or reduce a user's anonymity
55) through Tor for marketing purposes.
56) </p></li><li><span class="command"><strong>Local Network/ISP/Upstream Router</strong></span><p>
57) The adversary can also inject malicious content at the user's upstream router
58) when they have Tor disabled, in an attempt to correlate their Tor and Non-Tor
59) activity.
60) </p></li><li><span class="command"><strong>Physical Access</strong></span><p>
61) Some users face adversaries with intermittent or constant physical access.
62) Users in Internet cafes, for example, face such a threat. In addition, in
63) countries where simply using tools like Tor is illegal, users may face
64) confiscation of their computer equipment for excessive Tor usage or just
65) general suspicion.
66) </p></li></ol></div></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2972854"></a>Adversary Capabilities - Attacks</h4></div></div></div><p>
67) The adversary can perform the following attacks from a number of different
68) positions to accomplish various aspects of their goals.
69) </p><div class="orderedlist"><ol type="1"><li><span class="command"><strong>Inserting Javascript</strong></span><p>
70) Javascript allows the adversary the opportunity to accomplish a number of
71) their goals. If not properly disabled, Javascript event handlers and timers
72) can cause the browser to perform network activity after Tor has been disabled,
73) thus allowing the adversary to correlate Tor and Non-Tor activity. Javascript
74) also allows the adversary to execute <a class="ulink" href="http://gemal.dk/browserspy/css.html" target="_top">history disclosure attacks</a>:
75) to query the history via the different attributes of 'visited' links. Finally,
76) Javascript can be used to query the user's timezone via the
77) <code class="function">Date()</code> object, and to reduce the anonymity set by querying
78) the <code class="function">navigator</code> object for operating system, CPU, and user
79) agent information.
80) </p></li><li><span class="command"><strong>Inserting Plugins</strong></span><p>
81)
82) Plugins are abysmal at obeying the proxy settings of the browser. Every plugin
83) capable of performing network activity that the author has
84) investigated is also capable of performing network activity independent of
85) browser proxy settings - and often independent of its own proxy settings.
86) In addition, plugins can be used to store unique identifiers that are more
87) difficult to clear than standard cookies.
88) <a class="ulink" href="http://epic.org/privacy/cookies/flash.html" target="_top">Flash-based
89) cookies</a> fall into this category, but there are likely numerous other
90) examples.
91)
92) </p></li><li><span class="command"><strong>Inserting CSS</strong></span><p>
93)
94) CSS can also be used to correlate Tor and Non-Tor activity, via the usage of
95) <a class="ulink" href="http://www.tjkdesign.com/articles/css%20pop%20ups/" target="_top">CSS
96) popups</a> - essentially CSS-based event handlers that fetch content via
97) CSS's onmouseover attribute. If these popups are allowed to perform network
98) activity in a different Tor state than they were loaded in, they can easily
99) correlate Tor and Non-Tor activity and reveal a user's IP address. In
100) 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
101) attacks</a>.
102) </p></li><li><span class="command"><strong>Read and insert cookies</strong></span><p>
103)
104) An adversary in a position to perform MITM content alteration can inject
105) document content elements to both read and inject cookies for
106) arbitrary domains. In fact, many "SSL secured" websites are vulnerable to this
107) sort of <a class="ulink" href="http://seclists.org/bugtraq/2007/Aug/0070.html" target="_top">active
108) sidejacking</a>.
109)
110) </p></li><li><span class="command"><strong>Create arbitrary cached content</strong></span><p>
111)
112) Likewise, the browser cache can also be used to <a class="ulink" href="http://crypto.stanford.edu/sameorigin/safecachetest.html" target="_top">store unique
113) identifiers</a>. Since by default the cache has no same-origin policy,
114) these identifiers can be read by any domain, making them an ideal target for
115) adserver-class adversaries.
116)
117) </p></li><li><a id="fingerprinting"></a><span class="command"><strong>Fingerprint users based on browser
118) attributes</strong></span><p>
119)
120) There is an absurd amount of information available to websites via attributes
121) of the browser. This information can be used to reduce anonymity set, or even
122) <a class="ulink" href="http://0x000000.com/index.php?i=520&bin=1000001000" target="_top">uniquely
123) fingerprint individual users</a>. </p><p>
124) For illustration, let's perform a
125) back-of-the-envelope calculation on the number of anonymity sets for just the
126) resolution information available in the <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window" target="_top">window</a> and
127) <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.screen" target="_top">window.screen</a>
128) objects. Browser window resolution information provides something like
129) (1280-640)*(1024-480)=348160 different anonymity sets. Desktop resolution
130) information contributes about another factor of 5 (for about 5 resolutions in
131) typical use). In addition, the dimensions and position of the desktop taskbar
132) are available, which can reveal hints on OS information. This boosts the count
133) by a factor of 5 (for each of the major desktop taskbars - Windows, OSX, KDE
134) and Gnome, and None). Subtracting the browser content window
135) size from the browser outer window size provide yet more information.
136) Firefox toolbar presence gives about a factor of 8 (3 toolbars on/off give
137) 2<sup>3</sup>=8). Interface effects such as titlebar fontsize
138) and window manager settings gives a factor of about 9 (say 3 common font sizes
139) for the titlebar and 3 common sizes for browser GUI element fonts).
140) Multiply this all out, and you have (1280-640)*(1024-480)*5*5*8*9 ~=
141) 2<sup>29</sup>, or a 29 bit identifier based on resolution
142) information alone. </p><p>
143)
144) Of course, this space is non-uniform and prone to incremental changes.
145) However, if a bit vector space consisting of the above extracted attributes
146) were used instead of the hash approach from <a class="ulink" href="http://0x000000.com/index.php?i=520&bin=1000001000" target="_top">The Hacker
147) Webzine article above</a>, minor changes in browser window resolution will
148) no longer generate totally new identifiers.
149)
150) </p><p>
151)
152) To add insult to injury, <a class="ulink" href="http://pseudo-flaw.net/content/tor/torbutton/" target="_top">chrome URL disclosure
153) 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
154) to that 2<sup>29</sup>. With hundreds of popular extensions
155) and thousands of extensions total, it is easy to see that this sort of
156) information is an impressively powerful identifier if used properly by a
157) competent and determined adversary such as an ad network. Again, a
158) nearest-neighbor bit vector space approach here would also gracefully handle
159) incremental changes to installed extensions.
160)
161) </p></li><li><span class="command"><strong>Remotely or locally exploit browser and/or
162) OS</strong></span><p>
163) Last, but definitely not least, the adversary can exploit either general
164) browser vulnerabilities, plugin vulnerabilities, or OS vulnerabilities to
165) install malware and surveillance software. An adversary with physical access
166) can perform similar actions. Regrettably, this last attack capability is
167) outside of Torbutton's ability to defend against, but it is worth mentioning
168) for completeness.
169) </p></li></ol></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="requirements"></a>1.2. Torbutton Requirements</h3></div></div></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
170)
171) Since many settings satisfy multiple requirements, this design document is
172) organized primarily by Torbutton components and settings. However, if you are
173) the type that would rather read the document from the requirements
174) perspective, it is in fact possible to search for each of the following
175) requirement phrases in the text to find the relevant features that help meet
176) that requirement.
177)
178) </div><p>
179)
180) From the above Adversary Model, a number of requirements become clear.
181)
182) </p><div class="orderedlist"><ol type="1"><li><a id="proxy"></a><span class="command"><strong>Proxy Obedience</strong></span><p>The browser
183) MUST NOT bypass Tor proxy settings for any content.</p></li><li><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
184) from the state they were originally loaded in.</p></li><li><a id="state"></a><span class="command"><strong>State Separation</strong></span><p>Browser state (cookies, cache, history, 'DOM storage'), accumulated in
185) one Tor state MUST NOT be accessible via the network in
186) another Tor state.</p></li><li><a id="undiscoverability"></a><span class="command"><strong>Tor Undiscoverability</strong></span><p>With
187) the advent of bridge support in Tor 0.2.0.x, there are now a class of Tor
188) users whose network fingerprint does not obviously betray the fact that they
189) are using Tor. This should extend to the browser as well - Torbutton MUST NOT
190) reveal its presence while Tor is disabled.</p></li><li><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
191) in memory beyond the duration of one Tor toggle.</p></li><li><a id="location"></a><span class="command"><strong>Location Neutrality</strong></span><p>The browser SHOULD NOT leak location-specific information, such as
192) timezone or locale via Tor.</p></li><li><a id="setpreservation"></a><span class="command"><strong>Anonymity Set
193) Preservation</strong></span><p>The browser SHOULD NOT leak any other anonymity set reducing information
194) (such as user agent, extension presence, and resolution information)
195) automatically via Tor. The assessment of the attacks above should make it clear
196) that anonymity set reduction is a very powerful method of tracking and
197) eventually identifying anonymous users.
198) </p></li><li><a id="updates"></a><span class="command"><strong>Update Safety</strong></span><p>The browser
199) SHOULD NOT perform unauthenticated updates or upgrades via Tor.</p></li><li><a id="interoperate"></a><span class="command"><strong>Interoperability</strong></span><p>Torbutton SHOULD interoperate with third-party proxy switchers that
200) enable the user to switch between a number of different proxies. It MUST
201) provide full Tor protection in the event a third-party proxy switcher has
202) enabled the Tor proxy settings.</p></li></ol></div></div><div class="sect2" lang="en" xml:lang="en"><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
203) 'Chrome'. Components are a fancy name for classes that implement a given
204) interface or interfaces. In Firefox, components <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/creatingcomps.html" target="_top">can be
205) written</a> in C++,
206) Javascript, or a mixture of both. Components have two identifiers: their
207) '<a class="ulink" href="http://www.mozilla.org/projects/xpcom/book/cxc/html/quicktour2.html#1005005" target="_top">Contract
208) 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
209) ID</a>' (a GUID hex-string). In addition, the interfaces they implement each have a hex
210) 'Interface ID'. It is possible to 'hook' system components - to reimplement
211) their interface members with your own wrappers - but only if the rest of the
212) browser refers to the component by its Contract ID. If the browser refers to
213) the component by Class ID, it bypasses your hooks in that use case.
214) Technically, it may be possible to hook Class IDs by unregistering the
215) original component, and then re-registering your own, but this relies on
216) obsolete and deprecated interfaces and has proved to be less than
217) stable.</p><p>'Chrome' is a combination of XML and Javascript used to describe a window.
218) Extensions are allowed to create 'overlays' that are 'bound' to existing XML
219) window definitions, or they can create their own windows. The DTD for this XML
220) is called <a class="ulink" href="http://developer.mozilla.org/en/docs/XUL_Reference" target="_top">XUL</a>.</p></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2980698"></a>2. Components</h2></div></div></div><p>
221)
222) Torbutton installs components for two purposes: hooking existing components to
223) reimplement their interfaces; and creating new components that provide
224) services to other pieces of the extension.
225)
226) </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3000781"></a>2.1. Hooked Components</h3></div></div></div><p>Torbutton makes extensive use of Contract ID hooking, and implements some
227) of its own standalone components as well. Let's discuss the hooked components
228) first.</p><div class="sect3" lang="en" xml:lang="en"><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> -
229) <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/nsSessionStore2.js" target="_top">components/nsSessionStore2.js</a>
230) and <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/nsSessionStore3.js" target="_top">components/nsSessionStore3.js</a></h4></div></div></div><p>These components address the <a class="link" href="#disk">Disk Avoidance</a>
231) requirements of Torbutton. As stated in the requirements, Torbutton needs to
232) prevent Tor tabs from being written to disk by the Firefox session store for a
233) number of reasons, primary among them is the fact that Firefox can crash at
234) any time, and a restart can cause you to fetch tabs in the incorrect Tor
235) state.</p><p>These components illustrate a complication with Firefox hooking: you can
236) only hook member functions of a class if they are published in an
237) interface that the class implements. Unfortunately, the sessionstore has no
238) published interface that is amenable to disabling the writing out of Tor tabs
239) in specific. As such, Torbutton had to include the <span class="emphasis"><em>entire</em></span>
240) nsSessionStore from both Firefox 2 and Firefox 3,
241) with a couple of modifications to prevent tabs that were loaded with Tor
242) enabled from being written to disk, and some version detection code to
243) determine which component to load. The <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/nsSessionStore3.diff" target="_top">diff against the original session
244) store</a> is included in the SVN repository.</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2985696"></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> -
245) <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/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
246) charge of <a class="ulink" href="http://developer.mozilla.org/en/docs/Session_store_API" target="_top">restoring saved
247) sessions</a>. The wrapper's only job is to intercept the
248) <code class="function">doRestore()</code> function, which is called by Firefox if it is determined that the
249) browser crashed and the session needs to be restored. The wrapper notifies the
250) Torbutton chrome that the browser crashed by setting the pref
251) <span class="command"><strong>extensions.torbutton.crashed</strong></span>, or that it is a normal
252) startup via the pref <span class="command"><strong>extensions.torbutton.noncrashed</strong></span>. The Torbutton Chrome <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIPrefBranch2.html#method_addObserver" target="_top">listens for a
253) preference change</a> for this value and then does the appropriate cleanup. This
254) includes setting the Tor state to the one the user selected for crash recovery
255) in the preferences window (<span class="command"><strong>extensions.torbutton.restore_tor</strong></span>), and
256) restoring cookies for the corresponding cookie jar, if it exists.</p><p>By performing this notification, this component assists in the
257) <a class="link" href="#proxy">Proxy Obedience</a>, and <a class="link" href="#isolation">Network Isolation</a> requirements.
258) </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2979678"></a><a class="ulink" href="http://www.xulplanet.com/references/xpcomref/comps/c_browserglobalhistory2.html" target="_top">@mozilla.org/browser/global-history;2</a>
259) - <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/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
260) CSS and Javascript-based methods of history disclosure. The global-history
261) component is what is used by Firefox to determine if a link was visited or not
262) (to apply the appropriate style to the link). By hooking the <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIGlobalHistory2.html#method_isVisited" target="_top">isVisited</a>
263) and <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIGlobalHistory2.html#method_addURI" target="_top">addURI</a>
264) methods, Torbutton is able to selectively prevent history items from being
265) added or being displayed as visited, depending on the Tor state and the user's
266) preferences.
267) </p><p>
268) This component helps satisfy the <a class="link" href="#state">State Separation</a>
269) and <a class="link" href="#disk">Disk Avoidance</a> requirements of Torbutton.
270) </p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2988472"></a>2.2. New Components</h3></div></div></div><p>Torbutton creates four new components that are used throughout the
271) extension. These components do not hook any interfaces, nor are they used
272) anywhere besides Torbutton itself.</p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2981164"></a><a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cookie-jar-selector.js" target="_top">@stanford.edu/cookie-jar-selector;2
273) - 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
274) Jackson</a>) is used by the Torbutton chrome to switch between
275) Tor and Non-Tor cookies. Its operations are simple: sync cookies to disk, then
276) move the current cookies.txt file to the appropriate backup location
277) (cookies-tor.txt or cookies-nontor.txt), and then moving the other cookie jar
278) into place.</p><p>
279) This component helps to address the <a class="link" href="#state">State
280) Isolation</a> requirement of Torbutton.
281) </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2995031"></a><a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/torbutton-logger.js" target="_top">@torproject.org/torbutton-logger;1
282) - components/torbutton-logger.js</a></h4></div></div></div><p>The torbutton logger component allows on-the-fly redirection of torbutton
283) logging messages to either Firefox stderr
284) (<span class="command"><strong>extensions.torbutton.logmethod=0</strong></span>), the Javascript error console
285) (<span class="command"><strong>extensions.torbutton.logmethod=1</strong></span>), or the DebugLogger extension (if
286) available - <span class="command"><strong>extensions.torbutton.logmethod=2</strong></span>). It also allows you to
287) change the loglevel on the fly by changing
288) <span class="command"><strong>extensions.torbutton.loglevel</strong></span> (1-5, 1 is most verbose).
289) </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="windowmapper"></a><a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/window-mapper.js" target="_top">@torproject.org/content-window-mapper;1
290) - components/window-mapper.js</a></h4></div></div></div><p>Torbutton tags Firefox <a class="ulink" href="http://www.xulplanet.com/references/elemref/ref_tabbrowser.html" target="_top">tabs</a> with a special variable that indicates the Tor
291) state the tab was most recently used under to fetch a page. The problem is
292) that for many Firefox events, it is not possible to determine the tab that is
293) actually receiving the event. The Torbutton window mapper allows the Torbutton
294) chrome and other components to look up a <a class="ulink" href="http://www.xulplanet.com/references/elemref/ref_tabbrowser.html" target="_top">browser
295) tab</a> for a given <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIDOMWindow.html" target="_top">HTML content
296) window</a>. It does this by traversing all windows and all browsers, until it
297) finds the browser with the requested <a class="ulink" href="http://www.xulplanet.com/references/elemref/ref_browser.html#prop_contentWindow" target="_top">contentWindow</a> element. Since the content policy
298) and page loading in general can generate hundreds of these lookups, this
299) result is cached inside the component.
300) </p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="contentpolicy"></a><a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cssblocker.js" target="_top">@torproject.org/cssblocker;1
301) - components/cssblocker.js</a></h4></div></div></div><p>This is a key component to Torbutton's security measures. When Tor is
302) toggled, Javascript is disabled, and pages are instructed to stop loading.
303) However, CSS is still able to perform network operations by loading styles for
304) onmouseover events and other operations. In addition, favicons can still be
305) loaded by the browser. The cssblocker component prevents this by implementing
306) and registering an <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIContentPolicy.html" target="_top">nsIContentPolicy</a>.
307) When an nsIContentPolicy is registered, Firefox checks every attempted network
308) request against its <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIContentPolicy.html#method_shouldLoad" target="_top">shouldLoad</a>
309) member function to determine if the load should proceed. In Torbutton's case,
310) 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>,
311) and checks that tab's load tag against the current Tor state. If the tab was
312) loaded in a different state than the current state, the fetch is denied.
313) Otherwise, it is allowed.</p> This helps to achieve the <a class="link" href="#isolation">Network
314) Isolation</a> requirements of Torbutton.
315)
316) <p>In addition, the content policy also blocks website javascript from
317) <a class="ulink" href="http://pseudo-flaw.net/content/tor/torbutton/" target="_top">querying for
318) versions and existence of extension chrome</a> while Tor is enabled, and
319) also masks the presence of Torbutton to website javascript while Tor is
320) disabled. </p><p>
321)
322) Finally, some of the work that logically belongs to the content policy is
323) instead handled by the <span class="command"><strong>torbutton_http_observer</strong></span> and
324) <span class="command"><strong>torbutton_weblistener</strong></span> in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/torbutton.js" target="_top">torbutton.js</a>. These two objects handle blocking of
325) Firefox 3 favicon loads, popups, and full page plugins, which for whatever
326) reason are not passed to the Firefox content policy itself (see Firefox Bugs
327) <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437014" target="_top">437014</a> and
328) <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=401296" target="_top">401296</a>).
329)
330) </p><p>
331)
332) 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
333) Torbutton.</p></div></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2981568"></a>3. Chrome</h2></div></div></div><p>The chrome is where all the torbutton graphical elements and windows are
334) 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
335) files attached. The scope of these Javascript files is their containing
336) window.</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="browseroverlay"></a>3.1. Browser Overlay - <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/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
337) bar, and events for toggling the button. The overlay code is in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/torbutton.js" target="_top">chrome/content/torbutton.js</a>.
338) It contains event handlers for preference update, shutdown, upgrade, and
339) location change events.</p><p>The <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/comps/c_docloaderservice1.html" target="_top">location
340) change</a> <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIWebProgressListener.html" target="_top">webprogress
341) listener</a>, <span class="command"><strong>torbutton_weblistener</strong></span> is perhaps the
342) most important part of the chrome from a security standpoint. It is a <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIWebProgressListener.html" target="_top">web
343) progress listener</a> that handles
344) receiving an event every time a page load or iframe load occurs. This class
345) eventually calls down to <code class="function">torbutton_update_tags()</code> and
346) <code class="function">torbutton_hookdoc()</code>, which apply the browser Tor load state tags, plugin
347) permissions, and install the Javascript hooks to hook the <a class="ulink" href="http://phrogz.net/objJob/object.asp?id=224" target="_top">Date</a> object and
348) the <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.navigator" target="_top">navigator</a> object (for timezone and platform information,
349) respectively).</p><p>
350) The browser overlay helps to satisfy a number of Torbutton requirements. These
351) are better enumerated in each of the Torbutton preferences below. However,
352) there are also a number of Firefox preferences set in
353) <code class="function">torbutton_update_status()</code> that aren't governed by any
354) Torbutton setting. These are:
355) </p><div class="orderedlist"><ol type="1"><li><a class="ulink" href="http://kb.mozillazine.org/Browser.bookmarks.livemark_refresh_seconds" target="_top">browser.bookmarks.livemark_refresh_seconds</a><p>
356) This pref is set in an attempt to disable the fetching of LiveBookmarks via
357) Tor. Since users can potentially collect a large amount of live bookmarks to
358) very personal sites (blogs of friends, wikipedia articles they maintain,
359) comment feeds of their own blog), it is not possible to cleanly isolate these
360) fetches and they are simply disabled during Tor usage.
361) This helps to address the <a class="link" href="#state">State Separation</a> requirement.
362) Unfortunately <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=436250" target="_top">Firefox Bug
363) 436250</a> prevents this from
364) functioning completely correctly.
365) </p></li><li><a class="ulink" href="http://kb.mozillazine.org/Network.security.ports.banned" target="_top">network.security.ports.banned</a><p>
366) Torbutton sets this setting to add ports 8123, 8118, 9050 and 9051 (which it
367) reads from <span class="command"><strong>extensions.torbutton.banned_ports</strong></span>) to the list
368) of ports Firefox is forbidden to access. These ports are Polipo, Privoxy, Tor,
369) and the Tor control port, respectively. This is set for both Tor and Non-Tor
370) usage, and prevents websites from attempting to do http fetches from these
371) ports to see if they are open, which addresses the <a class="link" href="#undiscoverability">Tor Undiscoverability</a> requirement.
372) </p></li><li><a class="ulink" href="http://kb.mozillazine.org/Browser.send_pings" target="_top">browser.send_pings</a><p>
373) This setting is currently always disabled. If anyone ever complains saying
374) that they *want* their browser to be able to send ping notifications to a
375) page or arbitrary link, I'll make this a pref or Tor-only. But I'm not holding
376) my breath. I haven't checked if the content policy is called for pings, but if
377) not, this setting helps with meeting the <a class="link" href="#isolation">Network
378) Isolation</a> requirement.
379) </p></li><li><a class="ulink" href="http://kb.mozillazine.org/Browser.safebrowsing.remoteLookups" target="_top">browser.safebrowsing.remoteLookups</a><p>
380) Likewise for this setting. I find it hard to imagine anyone who wants to ask
381) Google in real time if each URL they visit is safe, especially when the list
382) of unsafe URLs is downloaded anyway. This helps fulfill the <a class="link" href="#disk">Disk Avoidance</a> requirement, by preventing your entire
383) browsing history from ending up on Google's disks.
384) </p></li><li><a class="ulink" href="http://kb.mozillazine.org/Browser.safebrowsing.enabled" target="_top">browser.safebrowsing.enabled</a><p>
385) Safebrowsing does <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=360387" target="_top">unauthenticated
386) updates under Firefox 2</a>, so it is disabled during Tor usage.
387) This helps fulfill the <a class="link" href="#updates">Update
388) Safety</a> requirement. Firefox 3 has the fix for that bug, and so
389) safebrowsing updates are enabled during Tor usage.
390) </p></li><li><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>
391) If Tor is enabled, we need to prevent random external applications from
392) launching without at least warning the user. This group of settings only
393) partially accomplishes this, however. Applications can still be launched via
394) plugins. The mechanisms for handling this are described under the "Disable
395) Plugins During Tor Usage" preference. This helps fulfill the <a class="link" href="#proxy">Proxy Obedience</a> requirement, by preventing external
396) applications from accessing network resources at the command of Tor-fetched
397) pages.
398) </p></li></ol></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2984229"></a>3.2. Preferences Window - <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/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
399) handlers located in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/preferences.js" target="_top">chrome/content/preferences.js</a>.</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2988730"></a>3.3. Other Windows</h3></div></div></div><p>There are additional windows that describe popups for right clicking on
400) the status bar, the toolbutton, and the about page.</p></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2986171"></a>4. Toggle Code Path</h2></div></div></div><p>
401)
402) The act of toggling is connected to <code class="function">torbutton_toggle()</code>
403) via the <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/torbutton.xul" target="_top">torbutton.xul</a>
404) and <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/popup.xul" target="_top">popup.xul</a>
405) overlay files. Most of the work in the toggling process is present in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/torbutton.js" target="_top">torbutton.js</a>
406)
407) </p><p>
408)
409) Toggling is a 3 stage process: Button Click, Proxy Update, and
410) Settings Update. These stages are reflected in the prefs
411) <span class="command"><strong>extensions.torbutton.tor_enabled</strong></span>,
412) <span class="command"><strong>extensions.torbutton.proxies_applied</strong></span>, and
413) <span class="command"><strong>extensions.torbutton.settings_applied</strong></span>. The reason for the
414) 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
415) javascript runs on a different thread than the chrome javascript, it is
416) important to properly convey the stages to the content policy to avoid race
417) conditions and leakage, especially with <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox Bug
418) 409737</a> unfixed. The content policy does not allow any network activity
419) whatsoever during this three stage transition.
420)
421) </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2990959"></a>4.1. Button Click</h3></div></div></div><p>
422)
423) This is the first step in the toggling process. When the user clicks the
424) toggle button or the toolbar, <code class="function">torbutton_toggle()</code> is
425) called. This function checks the current Tor status by comparing the current
426) proxy settings to the selected Tor settings, and then sets the proxy settings
427) to the opposite state, and sets the pref
428) <span class="command"><strong>extensions.torbutton.tor_enabled</strong></span> to reflect the new state.
429) It is this proxy pref update that gives notification via the <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIPrefBranch2.html#method_addObserver" target="_top">pref
430) observer</a>
431) <span class="command"><strong>torbutton_unique_pref_observer</strong></span> to perform the rest of the
432) toggle.
433)
434) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2984082"></a>4.2. Proxy Update</h3></div></div></div><p>
435)
436) When Torbutton receives any proxy change notifications via its
437) <span class="command"><strong>torbutton_unique_pref_observer</strong></span>, it calls
438) <code class="function">torbutton_set_status()</code> which checks against the Tor
439) settings to see if the Tor proxy settings match the current settings. If so,
440) it calls <code class="function">torbutton_update_status()</code>, which determines if
441) the Tor state has actually changed, and sets
442) <span class="command"><strong>extensions.torbutton.proxies_applied</strong></span> to the appropriate Tor
443) state value, and ensures that
444) <span class="command"><strong>extensions.torbutton.tor_enabled</strong></span> is also set to the correct
445) value. This is decoupled from the button click functionalty via the pref
446) observer so that other addons (such as SwitchProxy) can switch the proxy
447) settings between multiple proxies.
448)
449) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3001325"></a>4.3. Settings Update</h3></div></div></div><p>
450)
451) The next stage is also handled by
452) <code class="function">torbutton_update_status()</code>. This function sets scores of
453) Firefox preferences, saving the original values to prefs under
454) <span class="command"><strong>extensions.torbutton.saved.*</strong></span>, and performs the history
455) clearing, cookie jaring, and ssl certificate jaring work of Torbutton. At the
456) end of its work, it sets
457) <span class="command"><strong>extensions.torbutton.settings_applied</strong></span>, which signifies the
458) completion of the toggle operation to the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a>.
459)
460) </p></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2984248"></a>5. Description of Options</h2></div></div></div><p>This section provides a detailed description of Torbutton's options. Each
461) option is presented as the string from the preferences window, a summary, the
462) preferences it touches, and the effect this has on the components, chrome, and
463) browser properties.</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2980079"></a>5.1. Test Settings</h3></div></div></div><p>
464) This button under the Proxy Settings tab provides a way to verify that the
465) proxy settings are correct, and actually do route through the Tor network. It
466) performs this check by issuing an <a class="ulink" href="http://developer.mozilla.org/en/docs/XMLHttpRequest" target="_top">XMLHTTPRequest</a>
467) for <a class="ulink" href="https://check.torproject.org/?TorButton=True" target="_top">https://check.torproject.org/?Torbutton=True</a>.
468) This is a special page that returns very simple, yet well-formed XHTML that
469) Torbutton can easily inspect for a hidden link with an id of
470) <span class="command"><strong>TorCheckResult</strong></span> and a target of <span class="command"><strong>success</strong></span>
471) or <span class="command"><strong>failure</strong></span> to indicate if the
472) user hit the page from a Tor IP, a non-Tor IP. This check is handled in
473) <code class="function">torbutton_test_settings()</code> in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/torbutton.js" target="_top">torbutton.js</a>.
474) Presenting the results to the user is handled by the <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/preferences.xul" target="_top">preferences
475) window</a>
476) callback <code class="function">torbutton_prefs_test_settings()</code> in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/preferences.js" target="_top">preferences.js</a>.
477)
478) </p></div><div class="sect2" lang="en" xml:lang="en"><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>Enabling this preference causes the above mentioned Torbutton chrome web progress
479) 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
480) plugins via the browser <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIDocShell.html" target="_top">docShell</a>
481) attribute <span class="command"><strong>allowPlugins</strong></span>. These flags are set every time a new window is
482) created (<code class="function">torbutton_tag_new_browser()</code>), every time a web
483) load
484) event occurs
485) (<code class="function">torbutton_update_tags()</code>), and every time the tor state is changed
486) (<code class="function">torbutton_update_status()</code>). As a backup measure, plugins are also
487) prevented from loading by the content policy in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cssblocker.js" target="_top">@torproject.org/cssblocker;1</a> if Tor is
488) enabled and this option is set.
489) </p><p>Even all this turns out to be insufficient if the user directly
490) clicks on a plugin-handled mime-type. <a class="ulink" href="http://www.janusvm.com/goldy/pdf/" target="_top">In this case</a> (and also <a class="ulink" href="http://www.janusvm.com/goldy/side-channels/frames/" target="_top">this
491) one</a>), the browser decides that
492) maybe it should ignore all these other settings and load the plugin anyways,
493) because maybe the user really did want to load it (never mind this same
494) load-style could happen automatically with meta-refresh or any number of
495) other ways..). To handle these cases, Torbutton stores a list of plugin-handled
496) mime-types, and sets the pref
497) <span class="command"><strong>plugin.disable_full_page_plugin_for_types</strong></span> to this list.
498) Additionally, (since nothing can be assumed when relying on Firefox
499) preferences and internals) if it detects a load of one of them from the web progress
500) listener, it cancels the request, tells the associated DOMWindow
501) to stop loading, clears the document, AND throws an exception. Anything short
502) of all this and
503) the plugin managed to find some way to load.
504) </p><p>
505) 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
506) allowPlugins</a> for directly visited URLs, or notify its content policy for such
507) 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
508) not very encouraging.
509) </p><p>
510)
511) Since most plugins completely ignore browser proxy settings, the actions
512) performed by this setting are crucial to satisfying the <a class="link" href="#proxy">Proxy Obedience</a> requirement.
513)
514) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2978605"></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://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cssblocker.js" target="_top">@torproject.org/cssblocker;1</a> content policy
515) mentioned above, and causes it to block content load attempts in pages an
516) opposite Tor state from the current state. Freshly loaded <a class="ulink" href="http://www.xulplanet.com/references/elemref/ref_tabbrowser.html" target="_top">browser
517) tabs</a> are tagged
518) with a <span class="command"><strong>__tb_load_state</strong></span> member in
519) <code class="function">torbutton_update_tags()</code> and this
520) 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
521) toggling the <span class="command"><strong>allowJavascript</strong></span> <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIDocShell.html" target="_top">docShell</a> property, and issues a
522) <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIWebNavigation.html#method_stop" target="_top">webNavigation.stop(webNavigation.STOP_ALL)</a> to each browser tab (the
523) equivalent of hitting the STOP button).</p><p>
524)
525) Unfortunately, <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox bug
526) 409737</a> prevents <span class="command"><strong>docShell.allowJavascript</strong></span> from killing
527) 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>
528) are still able to execute. The <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">Torbutton Content
529) Policy</a> should prevent such code from performing network activity within
530) the current tab, but activity that happens via a popup window or via a
531) Javascript redirect can still slip by. For this reason, Torbutton blocks
532) popups by checking for a valid <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.opener" target="_top">window.opener</a>
533) attribute in <code class="function">torbutton_check_progress()</code>. If the window
534) has an opener from a different Tor state, its load is blocked. The content
535) policy also takes similar action to prevent Javascript redirects. This also
536) has the side effect/feature of preventing the user from following any links
537) from a page loaded in an opposite Tor state.
538)
539) </p><p>
540) This setting is responsible for satisfying the <a class="link" href="#isolation">Network Isolation</a> requirement.
541) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="jshooks"></a>5.4. Hook Dangerous Javascript (crucial)</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://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/jshooks.js" target="_top">Javascript
542) hooking code</a>. Javascript is injected into
543) pages to hook the <a class="ulink" href="http://phrogz.net/objJob/object.asp?id=224" target="_top">Date
544) class</a> to mask your timezone. This is done in the chrome in
545) <code class="function">torbutton_hookdoc()</code>, which is called ultimately by both the
546) <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIWebProgressListener.html" target="_top">webprogress
547) 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
548) javascript: urls). This behavior helps to satisfy the <a class="link" href="#location">Location Neutrality</a> requirement.
549)
550) </p><p>
551)
552) In addition, this setting also hooks various resolution properties of the
553) <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window" target="_top">window</a>,
554) <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.screen" target="_top">window.screen</a>,
555) and <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.navigator" target="_top">window.navigator</a>
556) to mask window size information and user agent properties not handled by the
557) standard Firefox user agent override settings. The resolution hooks
558) effectively make the Firefox browser window appear to websites as if the renderable area
559) takes up the entire desktop, has no toolbar or other GUI element space, and
560) the desktop itself has no toolbars.
561) These hooks drastically reduce the amount of information available to do <a class="link" href="#fingerprinting">anonymity set reduction attacks</a> and help to
562) meet the <a class="link" href="#setpreservation">Anonymity Set Preservation</a>
563) requirements.
564)
565) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2992126"></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>
566)
567) This option drastically cuts down on the number of distinct anonymity sets
568) that divide the Tor web userbase. Without this setting, the dimensions for a
569) typical browser window range from 600-1200 horizontal pixels and 400-1000
570) vertical pixels, or about 600x600 = 360000 different sets. Resizing the
571) browser window to multiples of 50 on each side reduces the number of sets by
572) 50^2, bringing the total number of sets to 144. Of course, the distribution
573) among these sets are not uniform, but scaling by 50 will improve the situation
574) due to this non-uniformity for users in the less common resolutions.
575) Obviously the ideal situation would be to lie entirely about the browser
576) window size, but this will likely cause all sorts of rendering issues, and is
577) also not implementable in a foolproof way from extension land.
578)
579) </p><p>
580)
581) The implementation of this setting is spread across a couple of different
582) locations in the Torbutton javascript <a class="link" href="#browseroverlay" title="3.1. Browser Overlay - torbutton.xul">browser
583) overlay</a>. Since resizing minimized windows causes them to be restored,
584) and since maximized windows remember their previous size to the pixel, windows
585) must be resized before every document load (at the time of browser tagging)
586) via <code class="function">torbutton_check_round()</code>, called by
587) <code class="function">torbutton_update_tags()</code>. To prevent drift, the extension
588) tracks the original values of the windows and uses this to perform the
589) rounding on document load. In addition, to prevent the user from resizing a
590) window to a non-50px multiple, a resize listener
591) (<code class="function">torbutton_do_resize()</code>) is installed on every new browser
592) window to record the new size and round it to a 50px multiple while Tor is
593) enabled. In all cases, the browser's contentWindow.innerWidth and innerHeight
594) are set. This ensures that there is no discrepancy between the 50 pixel cutoff
595) and the actual renderable area of the browser (so that it is not possible to
596) infer toolbar size/presence by the distance to the nearest 50 pixel roundoff).
597)
598) </p><p>
599) This setting helps to meet the <a class="link" href="#setpreservation">Anonymity Set Preservation</a> requirements.
600) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3004184"></a>5.6. Disable Updates During Tor (recommended)</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
601) update settings</a> during Tor
602) usage: <span class="command"><strong>extensions.update.enabled</strong></span>,
603) <span class="command"><strong>app.update.enabled</strong></span>,
604) <span class="command"><strong>app.update.auto</strong></span>, and
605) <span class="command"><strong>browser.search.update</strong></span>. These prevent the
606) browser from updating extensions, checking for Firefox upgrades, and
607) checking for search plugin updates while Tor is enabled.
608) </p><p>
609) This setting satisfies the <a class="link" href="#updates">Update Safety</a> requirement.
610) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2997514"></a>5.7. Disable Search Suggestions during Tor (recommended)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.no_search</strong></span></p><p>
611) 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>
612) during Tor usage.
613) This governs if you get Google search suggestions during Tor
614) usage. Your Google cookie is transmitted with google search suggestions, hence
615) this is recommended to be disabled.
616)
617) </p><p>
618) While this setting doesn't satisfy any Torbutton requirements, the fact that
619) cookies are transmitted for partially typed queries does not seem desirable
620) for Tor usage.
621) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3000110"></a>5.8. Block Tor/Non-Tor access to network from file:// urls (recommended)</h3></div></div></div><p>Option:
622) </p><table class="simplelist" border="0" summary="Simple list"><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>
623) </p><p>
624)
625) These settings prevent file urls from performing network operations during the
626) respective Tor states. Firefox 2's implementation of same origin policy allows
627) file urls to read and <a class="ulink" href="http://www.gnucitizen.org/blog/content-disposition-hacking/" target="_top">submit
628) arbitrary files from the local filesystem</a> to arbitrary websites. To
629) make matters worse, the 'Content-Disposition' header can be injected
630) arbitrarily by exit nodes to trick users into running arbitrary html files in
631) 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
632) resources from File urls during the appropriate Tor state.
633)
634) </p><p>
635)
636) This preference helps to ensure Tor's <a class="link" href="#isolation">Network
637) Isolation</a> requirement, by preventing file urls from executing network
638) operations in opposite Tor states. Also, allowing pages to submit arbitrary
639) files to arbitrary sites just generally seems like a bad idea.
640)
641) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2998307"></a>5.9. Close all Tor/Non-Tor tabs and windows on toggle (optional)</h3></div></div></div><p>Options:
642) </p><table class="simplelist" border="0" summary="Simple list"><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>
643) </p><p>
644)
645) These settings cause Torbutton to enumerate through all windows and close all
646) tabs in each window for the appropriate Tor state. This code can be found in
647) <code class="function">torbutton_update_status()</code>. The main reason these settings
648) exist is as a backup mechanism in the event of any Javascript or content policy
649) leaks due to <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox Bug
650) 409737</a>. Torbutton currently tries to block all Javascript network
651) activity via the content policy, but until that bug is fixed, there is some
652) risk that there are alternate ways to bypass the policy. This option is
653) available as an extra assurance of <a class="link" href="#isolation">Network
654) Isolation</a> for those who would like to be sure that when Tor is toggled
655) all page activity has ceased. It also serves as a potential future workaround
656) in the event a content policy failure is discovered, and provides an additional
657) level of protection for the <a class="link" href="#disk">Disk Avoidance</a>
658) protection so that browser state is not sitting around waiting to be swapped
659) out longer than necessary.
660)
661) </p><p>
662) While this setting doesn't satisfy any Torbutton requirements, the fact that
663) cookies are transmitted for partially typed queries does not seem desirable
664) for Tor usage.
665) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2996566"></a>5.10. 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>
666) This setting determines if Torbutton installs an <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsISHistoryListener.html" target="_top">nsISHistoryListener</a>
667) attached to the <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsISHistory.html" target="_top">sessionHistory</a> of
668) of each browser's <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/comps/c_webshell1.html" target="_top">webNavigatator</a>.
669) The nsIShistoryListener is instantiated with a reference to the containing
670) browser window and blocks the back, forward, and reload buttons on the browser
671) navigation bar when Tor is in an opposite state than the one to load the
672) current tab. In addition, Tor clears the session history during a new document
673) load if this setting is enabled.
674)
675) </p><p>
676)
677) This is marked as a crucial setting in part
678) because Javascript access to the history object is indistinguishable from
679) user clicks, and because
680) <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Firefox Bug
681) 409737</a> allows javascript to execute in opposite Tor states, javascript
682) can issue reloads after Tor toggle to reveal your original IP. Even without
683) this bug, however, Javascript is still able to access previous pages in your
684) session history that may have been loaded under a different Tor state, to
685) attempt to correlate your activity.
686)
687) </p><p>
688)
689) This setting helps to fulfill Torbutton's <a class="link" href="#state">State
690) Separation</a> and (until Bug 409737 is fixed) <a class="link" href="#isolation">Network Isolation</a>
691) requirements.
692)
693) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2998342"></a>5.11. History Access Settings</h3></div></div></div><p>Options:
694) </p><table class="simplelist" border="0" summary="Simple list"><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>
695) </p><p>These four settings govern the behavior of the <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/ignore-history.js" target="_top">components/ignore-history.js</a>
696) history blocker component mentioned above. By hooking the browser's view of
697) the history itself via the <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/comps/c_browserglobalhistory2.html" target="_top">mozilla.org/browser/global-history;2</a>
698) component, this mechanism defeats all document-based <a class="ulink" href="http://gemal.dk/browserspy/css.html" target="_top">history disclosure
699) attacks</a>, including <a class="ulink" href="http://ha.ckers.org/weird/CSS-history.cgi" target="_top">CSS-only attacks</a>.
700) </p><p>
701)
702) On Firefox 3, the history write settings also govern if Torbutton sets
703) <span class="command"><strong>browser.history_expire_days</strong></span> to 0 on the appropriate Tor
704) state, which <a class="ulink" href="http://developer.mozilla.org/en/docs/index.php?title=nsINavHistoryService#Attributes" target="_top">should
705) disable</a> all <a class="ulink" href="http://developer.mozilla.org/en/docs/Places" target="_top">Places</a> database
706) writes.
707)
708) </p><p>
709) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
710) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2957709"></a>5.12. 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
711) <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIBrowserHistory.html#method_removeAllPages" target="_top">nsIBrowserHistory.removeAllPages</a>
712) and <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsISHistory.html#method_PurgeHistory" target="_top">nsISHistory.PurgeHistory</a>
713) for each tab on Tor toggle.</p><p>
714) This setting is an optional way to help satisfy the <a class="link" href="#state">State Separation</a> requirement.
715) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962370"></a>5.13. Block Password+Form saving during Tor/Non-Tor</h3></div></div></div><p>Options:
716) </p><table class="simplelist" border="0" summary="Simple list"><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>
717) </p><p>These settings govern if Torbutton disables
718) <span class="command"><strong>browser.formfill.enable</strong></span>
719) and <span class="command"><strong>signon.rememberSignons</strong></span> during Tor and Non-Tor usage.
720) Since form fields can be read at any time by Javascript, this setting is a lot
721) more important than it seems.
722) </p><p>
723) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
724) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962437"></a>5.14. 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>
725) </p><p>This option causes Torbutton to call <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsICacheService.html#method_evictEntries" target="_top">nsICacheService.evictEntries(0)</a>
726) on Tor toggle to remove all entries from the cache. In addition, this setting
727) 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.
728) </p><p>
729) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
730) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962492"></a>5.15. 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
731) causes Torbutton to set <a class="ulink" href="http://kb.mozillazine.org/Browser.cache.memory.enable" target="_top">browser.cache.memory.enable</a>,
732) <a class="ulink" href="http://kb.mozillazine.org/Browser.cache.disk.enable" target="_top">browser.cache.disk.enable</a> and
733) <a class="ulink" href="http://kb.mozillazine.org/Network.http.use-cache" target="_top">network.http.use-cache</a> to false during tor usage.
734) </p><p>
735) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
736) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962549"></a>5.16. Clear Cookies on Tor Toggle</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.clear_cookies</strong></span>
737) </p><p>
738)
739) This setting causes Torbutton to call <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsICookieManager.html#method_removeAll" target="_top">nsICookieManager.removeAll()</a> on
740) every Tor toggle. In addition, this sets <a class="ulink" href="http://kb.mozillazine.org/Network.cookie.lifetimePolicy" target="_top">network.cookie.lifetimePolicy</a>
741) to 2 for Tor usage, which causes all cookies to be demoted to session cookies,
742) which prevents them from being written to disk.
743)
744) </p><p>
745) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
746) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962603"></a>5.17. Store Non-Tor cookies in a protected jar</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.cookie_jars</strong></span>
747) </p><p>
748)
749) This setting causes Torbutton to use <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cookie-jar-selector.js" target="_top">@stanford.edu/cookie-jar-selector;2</a> to store
750) non-tor cookies in a cookie jar during Tor usage, and clear the Tor cookies
751) before restoring the jar.
752) </p><p>
753) This setting also sets <a class="ulink" href="http://kb.mozillazine.org/Network.cookie.lifetimePolicy" target="_top">network.cookie.lifetimePolicy</a>
754) to 2 for Tor usage, which causes all cookies to be demoted to session cookies,
755) which prevents them from being written to disk.
756)
757) </p><p>
758) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> and <a class="link" href="#disk">Disk Avoidance</a> requirements.
759) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962662"></a>5.18. 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>
760) </p><p>
761)
762) This setting causes Torbutton to use <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cookie-jar-selector.js" target="_top">@stanford.edu/cookie-jar-selector;2</a> to store
763) both Tor and Non-Tor cookies into protected jars.
764) </p><p>
765) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
766) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962702"></a>5.19. 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
767) cookie prefs all to false.</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962718"></a>5.20. Disable DOM Storage during Tor usage (crucial)</h3></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962720"></a>5.20.1. Do not write Tor/Non-Tor cookies to disk</h3></div></div></div><p>Options:
768) </p><table class="simplelist" border="0" summary="Simple list"><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>
769) </p><p>
770) 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>
771) to 2 during the appropriate Tor state, and to store cookies acquired in that
772) state into a Javascript
773) <a class="ulink" href="http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Guide:Processing_XML_with_E4X" target="_top">E4X</a>
774) object as opposed to writing them to disk.
775) </p><p>
776) This allows Torbutton to provide an option to preserve a user's
777) cookies while still satisfying the <a class="link" href="#disk">Disk Avoidance</a>
778) requirement.
779) </p></div><p>Option: <span class="command"><strong>extensions.torbutton.disable_domstorage</strong></span>
780) </p><p>
781)
782) This setting causes Torbutton to toggle <span class="command"><strong>dom.storage.enabled</strong></span> during Tor
783) usage to prevent
784) <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:Storage" target="_top">DOM Storage</a> from
785) being used to store persistent information across Tor states.</p><p>
786) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
787) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2962826"></a>5.21. Clear HTTP Auth on Tor Toggle (recommended)</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.clear_http_auth</strong></span>
788) </p><p>
789) This setting causes Torbutton to call <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIHttpAuthManager.html#method_clearAll" target="_top">nsIHttpAuthManager.clearAll()</a>
790) every time Tor is toggled.
791) </p><p>
792) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
793) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3005721"></a>5.22. Clear cookies on Tor/Non-Tor shutdown</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.shutdown_method</strong></span>
794) </p><p> This option variable can actually take 3 values: 0, 1, and 2. 0 means no
795) cookie clearing, 1 means clear only during Tor-enabled shutdown, and 2 means
796) clear for both Tor and Non-Tor shutdown. When set to 1 or 2, Torbutton listens
797) for the <a class="ulink" href="http://developer.mozilla.org/en/docs/Observer_Notifications#Application_shutdown" target="_top">quit-application-granted</a> event in
798) <code class="function">torbutton_uninstall_observer()</code> and use <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cookie-jar-selector.js" target="_top">@stanford.edu/cookie-jar-selector;2</a>
799) to clear out all cookies and all cookie jars upon shutdown. </p><p>
800) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement.
801) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3005775"></a>5.23. Reload cookie jar/clear cookies on Firefox crash</h3></div></div></div><p>Options:
802) </p><table class="simplelist" border="0" summary="Simple list"><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>
803) </p><p>This is no longer a user visible option, and is enabled by default. In
804) the event of a crash, the Torbutton <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/crash-observer.js" target="_top">components/crash-observer.js</a>
805) component will notify the Chrome (via the
806) <span class="command"><strong>extensions.torbutton.crashed</strong></span> pref and a <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/ifaces/nsIPrefBranch2.html#method_addObserver" target="_top">pref
807) observer</a> in
808) the chrome that listens for this update), and Torbutton will load the
809) correct jar for the current Tor state via the <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/cookie-jar-selector.js" target="_top">@stanford.edu/cookie-jar-selector;2</a>
810) component.</p><p>
811) This setting helps to satisfy the <a class="link" href="#state">State Separation</a> requirement in the event of Firefox
812) crashes.
813) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3005850"></a>5.24. On crash recovery or session restored startup, restore via: Tor, Non-Tor</h3></div></div></div><p>Options:
814) </p><table class="simplelist" border="0" summary="Simple list"><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></table><p>
815) </p><p>This option works with the Torbutton <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/crash-observer.js" target="_top">crash-observer.js</a>
816) to set the Tor state after a crash is detected (via the
817) <span class="command"><strong>extensions.torbutton.crashed</strong></span> pref)</p><p>
818)
819) Since the Tor state after a Firefox crash is unknown/indeterminate, this
820) setting helps to satisfy the <a class="link" href="#state">State Separation</a>
821) requirement in the event of Firefox crashes by ensuring all cookies,
822) settings and saved sessions are reloaded from a fixed Tor state.
823)
824) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3005910"></a>5.25. On normal startup, set state to: Tor, Non-Tor, Shutdown State</h3></div></div></div><p>Options:
825) </p><table class="simplelist" border="0" summary="Simple list"><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></table><p>
826) </p><p>This option also works with the Torbutton <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/crash-observer.js" target="_top">crash-observer.js</a>
827) to set the Tor state after a normal startup is detected (via the
828) <span class="command"><strong>extensions.torbutton.noncrashed</strong></span> pref)</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3005958"></a>5.26. Prevent session store from saving Non-Tor/Tor-loaded tabs</h3></div></div></div><p>Options:
829) </p><table class="simplelist" border="0" summary="Simple list"><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>
830) </p><p>If these options are enabled, the <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/components/nsSessionStore3.js" target="_top">replacement nsSessionStore.js</a>
831) component checks the <span class="command"><strong>__tb_tor_fetched</strong></span> tag of tabs before writing them
832) out. If the tag is from a blocked Tor state, the tab is not written to disk.
833) </p><p>
834) This setting helps to satisfy the <a class="link" href="#disk">Disk Avoidance</a>
835) requirement, and also helps to satisfy the <a class="link" href="#state">State Separation</a> requirement in the event of Firefox
836) crashes.
837)
838) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3006023"></a>5.27. Set user agent during Tor usage (crucial)</h3></div></div></div><p>Options:
839) </p><table class="simplelist" border="0" summary="Simple list"><tr><td><span class="command"><strong>extensions.torbutton.set_uagent</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.platform_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>
840) </p><p>On face, user agent switching appears to be straight-forward in Firefox.
841) It provides several options for controlling the browser user agent string:
842) <span class="command"><strong>general.appname.override</strong></span>,
843) <span class="command"><strong>general.appversion.override</strong></span>,
844) <span class="command"><strong>general.platform.override</strong></span>,
845) <span class="command"><strong>general.useragent.override</strong></span>,
846) <span class="command"><strong>general.useragent.vendor</strong></span>, and
847) <span class="command"><strong>general.useragent.vendorSub</strong></span>. If
848) the Torbutton preference <span class="command"><strong>extensions.torbutton.set_uagent</strong></span> is
849) true, Torbutton copies all of the other above prefs into their corresponding
850) browser preferences during Tor usage.</p><p>However, this is not the whole story. Additionally, even with the above
851) prefs set, the <span class="command"><strong>oscpu</strong></span>, <span class="command"><strong>buildID</strong></span>, and <span class="command"><strong>productSub</strong></span> fields of the
852) <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.navigator" target="_top">navigator</a> object are not changed appropriately by the above prefs.
853) Javascript hooks implemented in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/jshooks.js" target="_top">chrome/content/jshooks.js</a> are installed as part of the
854) same mechanism that hooks the date object.
855) </p><p>
856)
857) It also turns out that it is possible to detect the original Firefox version
858) by <a class="ulink" href="http://0x000000.com/index.php?i=523&bin=1000001011" target="_top">inspecting
859) certain resource:// files</a>. These cases are handled by Torbutton's
860) <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">content policy</a>.
861)
862) </p><p>
863) This setting helps to satisfy the <a class="link" href="#setpreservation">Anonymity Set Preservation</a> requirement.
864) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3006210"></a>5.28. Spoof US English Browser</h3></div></div></div><p>Options:
865) </p><table class="simplelist" border="0" summary="Simple list"><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>
866) </p><p> This option causes Torbutton to set
867) <span class="command"><strong>general.useragent.locale</strong></span>,
868) <span class="command"><strong>intl.accept_charsets</strong></span> and
869) <span class="command"><strong>intl.accept_languages</strong></span> to the value specified in
870) <span class="command"><strong>extensions.torbutton.spoof_locale</strong></span>,
871) <span class="command"><strong>extensions.torbutton.spoof_charset</strong></span> and
872) <span class="command"><strong>extensions.torbutton.spoof_language</strong></span> during Tor usage. </p><p>
873) 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.
874) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3006297"></a>5.29. Don't send referrer during Tor Usage</h3></div></div></div><p>Option: <span class="command"><strong>extensions.torbutton.disable_referer</strong></span>
875) </p><p>
876) This option causes Torbutton to set <a class="ulink" href="http://kb.mozillazine.org/Network.http.sendSecureXSiteReferrer" target="_top">network.http.sendSecureXSiteReferrer</a> and
877) <a class="ulink" href="http://kb.mozillazine.org/Network.http.sendRefererHeader" target="_top">network.http.sendRefererHeader</a> during Tor usage.</p><p>
878) This setting also does not directly satisfy any Torbutton requirement, but
879) some may desire to mask their referrer for general privacy concerns.
880) </p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id3006338"></a>5.30. Store SSL/CA Certs in separate jars for Tor/Non-Tor (recommended)</h3></div></div></div><p>Options:
881) </p><table class="simplelist" border="0" summary="Simple list"><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>
882) </p><p>
883)
884) These settings govern if Torbutton attempts to isolate the user's SSL
885) certificates into separate jars for each Tor state. This isolation is
886) implemented in <code class="function">torbutton_jar_certs()</code> in <a class="ulink" href="https://tor-svn.freehaven.net/svn/torbutton/trunk/src/chrome/content/torbutton.js" target="_top">chrome/content/torbutton.js</a>,
887) which calls <code class="function">torbutton_jar_cert_type()</code> and
888) <code class="function">torbutton_unjar_cert_type()</code> for each certificate type in
889) the <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/comps/c_securitynsscertcache1.html" target="_top">@mozilla.org/security/nsscertcache;1</a>.
890) Certificates are deleted from and imported to the <a class="ulink" href="http://www.xulplanet.com/references/xpcomref/comps/c_securityx509certdb1.html" target="_top">@mozilla.org/security/x509certdb;1</a>.
891) </p><p>
892) The first time this pref is used, a backup of the user's certificates is
893) created in their profile directory under the name
894) <code class="filename">cert8.db.bak</code>. This file can be copied back to
895) <code class="filename">cert8.db</code> to fully restore the original state of the
896) user's certificates in the event of any error.
897) </p><p>
898) Since exit nodes and malicious sites can insert content elements sourced to
899) specific SSL sites to query if a user has a certain certificate,
900) this setting helps to satisfy the <a class="link" href="#state">State
901) Separation</a> requirement of Torbutton. Unfortunately, <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=435159" target="_top">Firefox Bug
902) 435159</a> prevents it from functioning correctly in the event of rapid Tor toggle, so it
903) is currently not exposed via the preferences UI.
904)
905) </p></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="FirefoxBugs"></a>6. Relevant Firefox Bugs</h2></div></div></div><p>
906)
907) </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="FirefoxSecurity"></a>6.1. Bugs impacting security</h3></div></div></div><p>
908)
909) Torbutton has to work around a number of Firefox bugs that impact its
910) security. Most of these are mentioned elsewhere in this document, but they
911) have also been gathered here for reference. Several of these have fixes in
912) Firefox3.0/trunk, but are listed because they still have not been backported
913) to FF2.0. In order of decreasing severity, they are:
914)
915) </p><div class="orderedlist"><ol type="1"><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=392274" target="_top">Bug 392274 - Timezone
916) config/chrome API</a><p>
917) The lack of a config or API to configure the timezone requires Torbutton to
918) <a class="link" href="#jshooks" title="5.4. Hook Dangerous Javascript (crucial)">insert client content window javascript</a> to hook
919) the Date object. Additionally, a way to <a class="ulink" href="http://pseudo-flaw.net/tor/torbutton/unmask-date.html" target="_top">remove the Date
920) hooks</a> was discovered by Greg Fleischer. Worse, on Firefox 3,
921) javascript sandboxing prevents most of the javascript hooks from being
922) installed, including the Date hooks. On Windows and Linux, you can set the TZ
923) environment variable to "UTC" as a workaround. Firefox will obey this
924) environment variable for your Timezone on those platforms, but on Windows this
925) does not take effect until browser restart.
926) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=436250" target="_top">Bug 436250 - Livemarks can't be
927) disabled at runtime</a><p>
928)
929) The RSS Feed based "Livemarks"/"Live Bookmarks" update frequency is controlled
930) by the pref <span class="command"><strong>browser.bookmarks.livemark_refresh_seconds</strong></span>.
931) However, changing this preference does not cancel any pending timers, which
932) means that at least one livemarks pref fetch will happen over Tor, and once
933) this pref is set to disable livemarks for Tor, changing it back will never
934) cause the service to start back up again.
935)
936) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=435159" target="_top">Bug 435159 -
937) nsNSSCertificateDB::DeleteCertificate has race conditions</a><p>
938)
939) In Torbutton 1.2.0rc1, code was added to attempt to isolate SSL certificates
940) the user has installed. Unfortunately, the method call to delete a certificate
941) from the current certificate database acts lazily: it only sets a variable
942) that marks a cert for deletion later, and it is not cleared if that
943) certificate is re-added. This means that if the Tor state is toggled quickly,
944) that certificate could remain present until it is re-inserted (causing an
945) error dialog), and worse, it would still be deleted after that. The lack of
946) this functionality is considered a Torbutton security bug because cert
947) isolation is considered a <a class="link" href="#state">State Separation</a>
948) feature.
949)
950) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=409737" target="_top">Bug 409737 -
951) javascript.enabled and docShell.allowJavascript do not disable all event
952) handlers</a><p>
953)
954) This bug allows pages to execute javascript via addEventListener and perhaps
955) other callbacks. In order to prevent this bug from enabling an attacker to
956) break the <a class="link" href="#isolation">Network Isolation</a> requirement,
957) Torbutton 1.1.13 began blocking popups and history manipulation from different
958) Tor states. So long as there are no ways to open popups or redirect the user
959) to a new page, the <a class="link" href="#contentpolicy" title="@torproject.org/cssblocker;1 - components/cssblocker.js">Torbutton content
960) policy</a> should block Javascript network access. However, if there are
961) ways to open popups or perform redirects such that Torbutton cannot block
962) them, pages may still have free reign to break that requirement and reveal a
963) user's original IP address.
964)
965) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=405652" target="_top">Bug 405652 - In the
966) TLS ClientHello message the gmt_unix_time is incorrect</a><p>
967)
968) It turns out that Firefox's SSL implementation sends the machine uptime as the
969) current time. This essentially is a unique identifier that can be used for
970) the duration of your machine uptime. The issue has been fixed in Firefox 3.0,
971) but it has as of yet not been backported to 2.0.
972)
973) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=143220" target="_top">Bug 143220 - Script can get the value of a file control, including the path</a><p>
974)
975) Javascript can query the .value field of file input dialogs to retrieve
976) username and sometimes hostname/workgroup information. This is obviously very
977) dangerous for people who are attempting to submit files anonymously via
978) webforms (ie whistleblowers and anonymous publishers). It is also fixed in
979) Firefox 3.0, but has not yet been backported to 2.0.
980)
981) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=418119" target="_top">Bug 418119 - nsIContentPolicy not called for external DTDs of XML documents</a><p>
982)
983) XML documents can source chrome and resource URLs in their DTDs without a call
984) to nsIContentPolicy::shouldLoad. Enumerating chrome URLs gives websites and
985) exit nodes a lot of information. They can use it to probe for vulnerable
986) versions of extensions, and can also use it to build an <a class="link" href="#fingerprinting">identifier for tracking purposes</a>. This bug
987) makes it impossible for extensions such as Adblock and Torbutton to prevent
988) chrome inspection and enumeration. There is no workaround for this bug as of
989) yet.
990)
991) </p></li></ol></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="FirefoxWishlist"></a>6.2. Bugs blocking functionality</h3></div></div></div><p>
992) The following bugs impact Torbutton and similar extensions' functionality.
993) </p><div class="orderedlist"><ol type="1"><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=439384" target="_top">Bug 439384 -
994) "profile-do-change" event does not cause cookie table reload</a><p>
995)
996) In Firefox 3, the change to the new sqlite database for cookie storage has a
997) bug that prevents Torbutton's cookie jaring from working properly. The
998) "profile-do-change" observer event no longer properly causes either a sync or
999) reload of the cookie database from disk after it is copied into place.
1000) Torbutton currently works around this by issuing the SQLLite queries manually
1001) to store and rebuild the cookie database.
1002)
1003) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=417869" target="_top">Bug 417869 -
1004) Browser context is difficult to obtain from many XPCOM callbacks</a><p>
1005)
1006) It is difficult to determine which tabbrowser many XPCOM callbacks originate
1007) from, and in some cases absolutely no context information is provided at all.
1008) While this doesn't have much of an effect on Torbutton, it does make writing
1009) extensions that would like to do per-tab settings and content filters (such as
1010) FoxyProxy) difficult to impossible to implement securely.
1011)
1012) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=418321" target="_top">Bug 418321 -
1013) Components do not expose disk interfaces</a><p>
1014)
1015) Several components currently provide no way of reimplementing their disk
1016) access to easily satisfy Torbutton's <a class="link" href="#disk">Disk
1017) Avoidance</a> requirements. Workarounds exist, but they are <a class="link" href="#sessionstore" title="@mozilla.org/browser/sessionstore;1 - components/nsSessionStore2.js and components/nsSessionStore3.js">clunky</a>, and
1018) some of them involve disabling functionality during Tor usage.
1019)
1020) </p></li></ol></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="FirefoxMiscBugs"></a>6.3. Low Priority Bugs</h3></div></div></div><p>
1021) The following bugs have an effect upon Torbutton, but are superseded by more
1022) practical and more easily fixable variant bugs above; or have stable, simple
1023) workarounds.
1024) </p><div class="orderedlist"><ol type="1"><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=435151" target="_top">Bug 435151 - XPCSafeJSObjectWrapper breaks evalInSandbox</a><p>
1025)
1026) Under Firefox 3, the XPCSafeJSObjectWrapper breaks when you try to use
1027) constructors of classes defined from within the scope of the sandbox, among
1028) other things. This prevents Torbutton from applying the Timezone hooks under
1029) Firefox 3, but a better solution for Torbutton's specific date hooking needs
1030) would be a fix for the above mentioned Bug 392274. Of course, many more
1031) extensions may be interested in the sandbox hooking functionality working
1032) properly though.
1033)
1034) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437014" target="_top">Bug 437014 -
1035) nsIContentPolicy::shouldLoad no longer called for favicons</a><p>
1036)
1037) Firefox 3.0 stopped calling the shouldLoad call of content policy for favicon
1038) loads. Torbutton had relied on this call to block favicon loads for opposite
1039) Tor states. The workaround it employs for Firefox 3 is to cancel the request
1040) when it arrives in the <span class="command"><strong>torbutton_http_observer</strong></span> used for
1041) blocking full page plugin loads. This seems to work just fine, but is a bit
1042) dirty.
1043)
1044) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437016" target="_top">Bug 437016 -
1045) nsIContentPolicy::shouldLoad not called for livemarks</a><p>
1046)
1047) An alternative fix for the livemarks bug above would be to block livemarks
1048) fetches from the content policy. Unfortunately shouldLoad is not called for
1049) livemarks fetches.
1050)
1051) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=418986" target="_top">Bug 418986 - window.screen
1052) provides a large amount of identifiable information</a><p>
1053)
1054) As <a class="link" href="#fingerprinting">mentioned above</a>, a large amount of
1055) information is available from <a class="ulink" href="http://developer.mozilla.org/en/docs/DOM:window.screen" target="_top">window.screen</a>.
1056) Currently, there is no way to obscure this information without Javascript
1057) hooking. This bug is a feature request to provide some other method to change
1058) these values.
1059)
1060) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=309524" target="_top">Bug 309524</a>
1061) and <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=380556" target="_top">Bug
1062) 380556</a> - nsIContentPolicy::shouldProcess is not called.
1063) <p>
1064)
1065) This is a call that would be useful to develop a better workaround for the
1066) allowPlugins issue above. If the content policy were called before a URL was
1067) handed over to a plugin or helper app, it would make the workaround for the
1068) above allowPlugins bug a lot cleaner. Obviously this bug is not as severe as
1069) the others though, but it might be nice to have this API as a backup.
1070)
1071) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=401296" target="_top">Bug 401296 - docShell.allowPlugins
1072) 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>?)
1073) <p>
1074)
1075) Similar to the javascript plugin disabling attribute, the plugin disabling
1076) attribute is also not perfect — it is ignored for direct links to plugin
1077) handled content, as well as meta-refreshes to plugin handled content. This
1078) requires Torbutton to listen to a number of different http events to intercept
1079) plugin-related mime type URLs and cancel their requests. Again, since plugins
1080) are quite horrible about obeying proxy settings, loading a plugin pretty much
1081) ensures a way to break the <a class="link" href="#isolation">Network Isolation</a>
1082) requirement and reveal a user's original IP address. Torbutton's code to
1083) perform this workaround has been subverted at least once already by Kyle
1084) Williams.
1085)
1086) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=418983" target="_top">Bug 41893 - Scoping
1087) issues with window.__defineGetter__()</a><p>
1088)
1089) For some reason, defining getters off of window seems to mess with the
1090) implicit window scoping in some documents. There is a workaround for this bug,
1091) so it is barely relevant. It would be far more useful to eliminate the need
1092) for Javascript hooking in the first place by addressing the above bugs. This
1093) bug is just listed for completeness.
1094)
1095) </p></li><li><a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=419598" target="_top">Bug 419598 - 'var
1096) Date' is deletable</a><p>
1097)
1098) 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
1099) Javascript spec</a>, it seems like it should be possible to do something
1100) like the following to prevent the Date object from being unmasked:
1101) </p><pre class="screen">
1102) with(window) {
1103) var Date = fakeDate;
1104) var otherVariable = 42;
1105) }
1106)
1107) delete window.Date; // Should fail. Instead succeeds, revealing original Date.
1108) delete window.otherVariable; // Fails, leaving window.otherVariable set to 42.
1109) </pre><p>
1110)
1111) From the ECMA-262 spec:
1112)
1113) </p><div class="blockquote"><blockquote class="blockquote">
1114) If the variable statement occurs inside a FunctionDeclaration, the variables
1115) are defined with function-local scope in that function, as described in
1116) s10.1.3. Otherwise, they are defined with global scope (that is, they are
1117) created as members of the global object, as described in 10.1.3) using
1118) property attributes { DontDelete }. Variables are created when the execution
1119) scope is entered. A Block does not define a new execution scope. Only Program
1120) and FunctionDeclaration produce a new scope. Variables are initialized to
1121) undefined when created. A variable with an Initialiser is assigned the value
1122) of its AssignmentExpression when the VariableStatement is executed, not when
1123) the variable is created.
1124) </blockquote></div><p>
1125)
1126) In fact, this is exactly how the with statement with a variable declaration
1127) behaves <span class="emphasis"><em>for all other variables other than ones that shadow system
1128) variables</em></span>. Some variables (such as
1129) <span class="command"><strong>window.screen</strong></span>, and <span class="command"><strong>window.history</strong></span>) can't
1130) even be shadowed in this way, and give an error about lacking a setter. If
1131) such shadowing were possible, it would greatly simplify the Javascript hooking
1132) code, which currently relies on undocumented semantics of
1133) <span class="command"><strong>__proto__</strong></span> to copy the original values in the event of a
1134) delete. This <span class="command"><strong>__proto__</strong></span> hack unfortunately does not work for
1135) the Date object though.
1136)
1137) </p></li></ol></div></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="TestPlan"></a>7. Testing</h2></div></div></div><p>
1138)
1139) The purpose of this section is to cover all the known ways that Tor browser
1140) security can be subverted from a testing and penetration perspective. The hope
1141) is that it will be useful both for creating a "Tor Safety Check"
1142) page, and for developing novel tests and actively attacking Torbutton with the
1143) goal of finding vulnerabilities in either it or the Mozilla components,
1144) interfaces and settings upon which it relies.
1145)
1146) </p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="Categories"></a>7.1. Single state testing</h3></div></div></div><p>
1147) The following tests can be run from a single web page in one visit without
1148) toggling Tor state or requiring user interaction. Currently they exist as their
1149) own individual tests, but conceivably a single "Tor Safety Check"
1150) page can be devised that contains all of these attacks.
1151) All of these tests are currently known to pass, but that does not mean that
1152) consolidating them into an easy to run test page is pointless. Torbutton is a
1153) complicated piece of software. During development, changes to one component
1154) can affect a whole slough of unrelated features. Having easy-to-verify
1155) comprehensive test pages would make it much easier to fix other issues as they
1156) present themselves without introducing regressions.
1157)
1158) </p><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id3007076"></a>Java and Plugin Decloaking</h4></div></div></div><p>
1159) As <a class="link" href="#plugins" title="5.2. Disable plugins on Tor Usage (crucial)">mentioned above</a>, 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
1160) address</a> and report it back to the
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Inital move of torbutton we...
Fix some wrong links