projects/torbrowser/design/index.html.en (8cf46843a) - tor-webwml.git

8cf46843a14d29175e2b2e0cf599447c1396d8ba

Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1) <?xml version="1.0" encoding="UTF-8"?>`
More fingerprinting clarifi... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 2) <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>The Design and Implementation of the Tor Browser [DRAFT]</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1" /></head><body><div class="article"><div class="titlepage"><div><div><h2 class="title"><a id="design"></a>The Design and Implementation of the Tor Browser [DRAFT]</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#torproject org">mikeperry#torproject org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Erinn</span> <span class="surname">Clark</span></h3><div class="affiliation"><div class="address"><p><code class="email"><<a class="email" href="mailto:erinn#torproject org">erinn#torproject org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Steven</span> <span class="surname">Murdoch</span></h3><div class="affiliation"><div class="address"><p><code class="email"><<a class="email" href="mailto:sjmurdoch#torproject org">sjmurdoch#torproject org</a>></code></p></div></div></div></div><div><p class="pubdate">November 6th, 2014</p></div></div><hr /></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="#idp59720528">1. Introduction</a></span></dt><dd><dl><dt><span class="sect2"><a href="#components">1.1. Browser Component Overview</a></span></dt></dl></dd><dt><span class="sect1"><a href="#DesignRequirements">2. Design Requirements and Philosophy</a></span></dt><dd><dl><dt><span class="sect2"><a href="#security">2.1. Security Requirements</a></span></dt><dt><span class="sect2"><a href="#privacy">2.2. Privacy Requirements</a></span></dt><dt><span class="sect2"><a href="#philosophy">2.3. Philosophy</a></span></dt></dl></dd><dt><span class="sect1"><a href="#adversary">3. Adversary Model</a></span></dt><dd><dl><dt><span class="sect2"><a href="#adversary-goals">3.1. Adversary Goals</a></span></dt><dt><span class="sect2"><a href="#adversary-positioning">3.2. Adversary Capabilities - Positioning</a></span></dt><dt><span class="sect2"><a href="#attacks">3.3. Adversary Capabilities - Attacks</a></span></dt></dl></dd><dt><span class="sect1"><a href="#Implementation">4. Implementation</a></span></dt><dd><dl><dt><span class="sect2"><a href="#proxy-obedience">4.1. Proxy Obedience</a></span></dt><dt><span class="sect2"><a href="#state-separation">4.2. State Separation</a></span></dt><dt><span class="sect2"><a href="#disk-avoidance">4.3. Disk Avoidance</a></span></dt><dt><span class="sect2"><a href="#app-data-isolation">4.4. Application Data Isolation</a></span></dt><dt><span class="sect2"><a href="#identifier-linkability">4.5. Cross-Origin Identifier Unlinkability</a></span></dt><dt><span class="sect2"><a href="#fingerprinting-linkability">4.6. Cross-Origin Fingerprinting Unlinkability</a></span></dt><dt><span class="sect2"><a href="#new-identity">4.7. Long-Term Unlinkability via "New Identity" button</a></span></dt><dt><span class="sect2"><a href="#other-security">4.8. Other Security Measures</a></span></dt></dl></dd><dt><span class="sect1"><a href="#BuildSecurity">5. Build Security and Package Integrity</a></span></dt><dd><dl><dt><span class="sect2"><a href="#idp60597904">5.1. Achieving Binary Reproducibility</a></span></dt><dt><span class="sect2"><a href="#idp60632800">5.2. Package Signatures and Verification</a></span></dt><dt><span class="sect2"><a href="#idp60636736">5.3. Anonymous Verification</a></span></dt></dl></dd><dt><span class="appendix"><a href="#Transparency">A. Towards Transparency in Navigation Tracking</a></span></dt><dd><dl><dt><span class="sect1"><a href="#deprecate">A.1. Deprecation Wishlist</a></span></dt><dt><span class="sect1"><a href="#idp60669376">A.2. Promising Standards</a></span></dt></dl></dd></dl></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="idp59720528"></a>1. Introduction</h2></div></div></div><p>
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 3)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 4) This document describes the <a class="link" href="#adversary" title="3. Adversary Model">adversary model</a>,`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 5) <a class="link" href="#DesignRequirements" title="2. Design Requirements and Philosophy">design requirements</a>, and <a class="link" href="#Implementation" title="4. Implementation">implementation</a> of the Tor Browser. It is current as of Tor Browser`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 6) 4.5-alpha-1.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 7) projects/en/torbrowser/design/index.html.en 8) </p><p> projects/en/torbrowser/design/index.html.en 9) projects/en/torbrowser/design/index.html.en 10) This document is also meant to serve as a set of design requirements and to projects/en/torbrowser/design/index.html.en 11) describe a reference implementation of a Private Browsing Mode that defends`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 12) against active network adversaries, in addition to the passive forensic local projects/torbrowser/design/index.html.en 13) adversary currently addressed by the major browsers.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 14)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 15) </p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="components"></a>1.1. Browser Component Overview</h3></div></div></div><p>`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 16)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 17) The Tor Browser is based on <a class="ulink" href="https://www.mozilla.org/en-US/firefox/organizations/" target="_top">Mozilla's Extended`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 18) Support Release (ESR) Firefox branch</a>. We have a <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git" target="_top">series of patches</a> projects/torbrowser/design/index.html.en 19) against this browser to enhance privacy and security. Browser behavior is projects/torbrowser/design/index.html.en 20) additionally augmented through the <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/tree/master" target="_top">Torbutton projects/torbrowser/design/index.html.en 21) extension</a>, though we are in the process of moving this functionality projects/torbrowser/design/index.html.en 22) into direct Firefox patches. We also <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/blob/refs/heads/tor-browser-31.2.0esr-4.x-1:/browser/app/profile/000-tor-browser.js" target="_top">change
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 23) a number of Firefox preferences</a> from their defaults.`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 24)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 25) </p><p>`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 26) Tor process management and configuration is accomplished through the <a class="ulink" href="https://gitweb.torproject.org/tor-launcher.git" target="_top">Tor Launcher</a> projects/torbrowser/design/index.html.en 27) addon, which provides the initial Tor configuration splash screen and projects/torbrowser/design/index.html.en 28) bootstrap progress bar. Tor Launcher is also compatible with Thunderbird,`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 29) Instantbird, and XULRunner.`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 30) projects/torbrowser/design/index.html.en 31) </p><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 32)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 33) To help protect against potential Tor Exit Node eavesdroppers, we include`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 34) <a class="ulink" href="https://www.eff.org/https-everywhere" target="_top">HTTPS-Everywhere</a>. To`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 35) provide users with optional defense-in-depth against Javascript and other`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 36) potential exploit vectors, we also include <a class="ulink" href="http://noscript.net/" target="_top">NoScript</a>. We also modify <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/blob/refs/heads/master:/Bundle-Data/linux/Data/Browser/profile.default/preferences/extension-overrides.js" target="_top">several`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 37) extension preferences</a> from their defaults.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 38)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 39) </p><p> projects/torbrowser/design/index.html.en 40) projects/torbrowser/design/index.html.en 41) To provide censorship circumvention in areas where the public Tor network is projects/torbrowser/design/index.html.en 42) blocked either by IP, or by protocol fingerprint, we include several <a class="ulink" href="https://trac.torproject.org/projects/tor/wiki/doc/AChildsGardenOfPluggableTransports" target="_top">Pluggable projects/torbrowser/design/index.html.en 43) Transports</a> in the distribution. As of this writing, we include <a class="ulink" href="https://gitweb.torproject.org/pluggable-transports/obfsproxy.git/blob/HEAD:/doc/obfs3/obfs3-protocol-spec.txt" target="_top">Obfsproxy</a>, projects/torbrowser/design/index.html.en 44) <a class="ulink" href="https://trac.torproject.org/projects/tor/wiki/doc/meek" target="_top">meek</a>, projects/torbrowser/design/index.html.en 45) <a class="ulink" href="https://fteproxy.org/" target="_top">FTE</a>, and <a class="ulink" href="https://crypto.stanford.edu/flashproxy/" target="_top">FlashProxy</a>. projects/torbrowser/design/index.html.en 46) projects/torbrowser/design/index.html.en 47) </p></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="DesignRequirements"></a>2. Design Requirements and Philosophy</h2></div></div></div><p>
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 48) projects/en/torbrowser/design/index.html.en 49) The Tor Browser Design Requirements are meant to describe the properties of a`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 50) Private Browsing Mode that defends against both network and local forensic projects/torbrowser/design/index.html.en 51) adversaries.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 52) projects/en/torbrowser/design/index.html.en 53) </p><p> projects/en/torbrowser/design/index.html.en 54) projects/en/torbrowser/design/index.html.en 55) There are two main categories of requirements: <a class="link" href="#security" title="2.1. Security Requirements">Security Requirements</a>, and <a class="link" href="#privacy" title="2.2. Privacy Requirements">Privacy Requirements</a>. Security Requirements are the`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 56) minimum properties in order for a browser to be able to support Tor and projects/torbrowser/design/index.html.en 57) similar privacy proxies safely. Privacy requirements are the set of properties`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 58) that cause us to prefer one browser over another.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 59) projects/en/torbrowser/design/index.html.en 60) </p><p> projects/en/torbrowser/design/index.html.en 61)`
Update TBB design doc with... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 62) While we will endorse the use of browsers that meet the security requirements, projects/torbrowser/design/index.html.en 63) it is primarily the privacy requirements that cause us to maintain our own projects/torbrowser/design/index.html.en 64) browser distribution. projects/torbrowser/design/index.html.en 65) projects/torbrowser/design/index.html.en 66) </p><p> projects/torbrowser/design/index.html.en 67) projects/torbrowser/design/index.html.en 68) The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL projects/torbrowser/design/index.html.en 69) NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and projects/torbrowser/design/index.html.en 70) "OPTIONAL" in this document are to be interpreted as described in
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 71) <a class="ulink" href="https://www.ietf.org/rfc/rfc2119.txt" target="_top">RFC 2119</a>.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 72)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 73) </p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="security"></a>2.1. Security Requirements</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 74) projects/en/torbrowser/design/index.html.en 75) The security requirements are primarily concerned with ensuring the safe use projects/en/torbrowser/design/index.html.en 76) of Tor. Violations in these properties typically result in serious risk for`
Add a couple extra sentence... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 77) the user in terms of immediate deanonymization and/or observability. With`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 78) respect to browser support, security requirements are the minimum properties projects/torbrowser/design/index.html.en 79) in order for Tor to support the use of a particular browser.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 80)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 81) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="link" href="#proxy-obedience" title="4.1. Proxy Obedience"><span class="command"><strong>Proxy`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 82) Obedience</strong></span></a><p>The browser`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 83) MUST NOT bypass Tor proxy settings for any content.</p></li><li class="listitem"><a class="link" href="#state-separation" title="4.2. State Separation"><span class="command"><strong>State`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 84) Separation</strong></span></a><p> projects/torbrowser/design/index.html.en 85) projects/torbrowser/design/index.html.en 86) The browser MUST NOT provide the content window with any state from any other projects/torbrowser/design/index.html.en 87) browsers or any non-Tor browsing modes. This includes shared state from`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 88) independent plugins, and shared state from operating system implementations of`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 89) TLS and other support libraries. projects/torbrowser/design/index.html.en 90)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 91) </p></li><li class="listitem"><a class="link" href="#disk-avoidance" title="4.3. Disk Avoidance"><span class="command"><strong>Disk`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 92) Avoidance</strong></span></a><p>`
Update TBB design doc with... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 93) projects/torbrowser/design/index.html.en 94) The browser MUST NOT write any information that is derived from or that projects/torbrowser/design/index.html.en 95) reveals browsing activity to the disk, or store it in memory beyond the projects/torbrowser/design/index.html.en 96) duration of one browsing session, unless the user has explicitly opted to projects/torbrowser/design/index.html.en 97) store their browsing history information to disk. projects/torbrowser/design/index.html.en 98)
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 99) </p></li><li class="listitem"><a class="link" href="#app-data-isolation" title="4.4. Application Data Isolation"><span class="command"><strong>Application Data`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 100) Isolation</strong></span></a><p>`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 101)`
Additional comments from Ge... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 102) The components involved in providing private browsing MUST be self-contained,`
Update TBB design doc with... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 103) or MUST provide a mechanism for rapid, complete removal of all evidence of the projects/torbrowser/design/index.html.en 104) use of the mode. In other words, the browser MUST NOT write or cause the projects/torbrowser/design/index.html.en 105) operating system to write <span class="emphasis"><em>any information</em></span> about the use projects/torbrowser/design/index.html.en 106) of private browsing to disk outside of the application's control. The user
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 107) must be able to ensure that secure deletion of the software is sufficient to`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 108) remove evidence of the use of the software. All exceptions and shortcomings`
Additional comments from Ge... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 109) due to operating system behavior MUST be wiped by an uninstaller. However, due`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 110) to permissions issues with access to swap, implementations MAY choose to leave`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 111) it out of scope, and/or leave it to the operating system/platform to implement`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 112) ephemeral-keyed encrypted swap.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 113)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 114) </p></li></ol></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="privacy"></a>2.2. Privacy Requirements</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 115) projects/en/torbrowser/design/index.html.en 116) The privacy requirements are primarily concerned with reducing linkability:`
Add a couple extra sentence... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 117) the ability for a user's activity on one site to be linked with their activity projects/torbrowser/design/index.html.en 118) on another site without their knowledge or explicit consent. With respect to`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 119) browser support, privacy requirements are the set of properties that cause us projects/torbrowser/design/index.html.en 120) to prefer one browser over another.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 121)`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 122) </p><p> projects/torbrowser/design/index.html.en 123) projects/torbrowser/design/index.html.en 124) For the purposes of the unlinkability requirements of this section as well as`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 125) the descriptions in the <a class="link" href="#Implementation" title="4. Implementation">implementation`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 126) section</a>, a <span class="command"><strong>url bar origin</strong></span> means at least the projects/torbrowser/design/index.html.en 127) second-level DNS name. For example, for mail.google.com, the origin would be projects/torbrowser/design/index.html.en 128) google.com. Implementations MAY, at their option, restrict the url bar origin`
Additional comments from Ge... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 129) to be the entire fully qualified domain name.`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 130)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 131) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="link" href="#identifier-linkability" title="4.5. Cross-Origin Identifier Unlinkability"><span class="command"><strong>Cross-Origin`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 132) Identifier Unlinkability</strong></span></a><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 133)`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 134) User activity on one url bar origin MUST NOT be linkable to their activity in`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 135) any other url bar origin by any third party automatically or without user projects/torbrowser/design/index.html.en 136) interaction or approval. This requirement specifically applies to linkability projects/torbrowser/design/index.html.en 137) from stored browser identifiers, authentication tokens, and shared state. The projects/torbrowser/design/index.html.en 138) requirement does not apply to linkable information the user manually submits`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 139) to sites, or due to information submitted during manual link traversal. This`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 140) functionality SHOULD NOT interfere with interactive, click-driven federated projects/torbrowser/design/index.html.en 141) login in a substantial way.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 142)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 143) </p></li><li class="listitem"><a class="link" href="#fingerprinting-linkability" title="4.6. Cross-Origin Fingerprinting Unlinkability"><span class="command"><strong>Cross-Origin`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 144) Fingerprinting Unlinkability</strong></span></a><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 145)`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 146) User activity on one url bar origin MUST NOT be linkable to their activity in projects/torbrowser/design/index.html.en 147) any other url bar origin by any third party. This property specifically applies to`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 148) linkability from fingerprinting browser behavior. projects/en/torbrowser/design/index.html.en 149)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 150) </p></li><li class="listitem"><a class="link" href="#new-identity" title="4.7. Long-Term Unlinkability via "New Identity" button"><span class="command"><strong>Long-Term`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 151) Unlinkability</strong></span></a><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 152)`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 153) The browser MUST provide an obvious, easy way for the user to remove all of projects/torbrowser/design/index.html.en 154) its authentication tokens and browser state and obtain a fresh identity.`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 155) Additionally, the browser SHOULD clear linkable state by default automatically projects/torbrowser/design/index.html.en 156) upon browser restart, except at user option.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 157)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 158) </p></li></ol></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="philosophy"></a>2.3. Philosophy</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 159) projects/en/torbrowser/design/index.html.en 160) In addition to the above design requirements, the technology decisions about projects/en/torbrowser/design/index.html.en 161) Tor Browser are also guided by some philosophical positions about technology. projects/en/torbrowser/design/index.html.en 162)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 163) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Preserve existing user model</strong></span><p>`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 164) projects/en/torbrowser/design/index.html.en 165) The existing way that the user expects to use a browser must be preserved. If projects/en/torbrowser/design/index.html.en 166) the user has to maintain a different mental model of how the sites they are projects/en/torbrowser/design/index.html.en 167) using behave depending on tab, browser state, or anything else that would not projects/en/torbrowser/design/index.html.en 168) normally be what they experience in their default browser, the user will projects/en/torbrowser/design/index.html.en 169) inevitably be confused. They will make mistakes and reduce their privacy as a projects/en/torbrowser/design/index.html.en 170) result. Worse, they may just stop using the browser, assuming it is broken. projects/en/torbrowser/design/index.html.en 171) projects/en/torbrowser/design/index.html.en 172) </p><p> projects/en/torbrowser/design/index.html.en 173)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 174) User model breakage was one of the <a class="ulink" href="https://blog.torproject.org/blog/toggle-or-not-toggle-end-torbutton" target="_top">failures`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 175) of Torbutton</a>: Even if users managed to install everything properly, projects/en/torbrowser/design/index.html.en 176) the toggle model was too hard for the average user to understand, especially projects/en/torbrowser/design/index.html.en 177) in the face of accumulating tabs from multiple states crossed with the current`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 178) Tor-state of the browser.`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 179) projects/en/torbrowser/design/index.html.en 180) </p></li><li class="listitem"><span class="command"><strong>Favor the implementation mechanism least likely to projects/en/torbrowser/design/index.html.en 181) break sites</strong></span><p> projects/en/torbrowser/design/index.html.en 182) projects/en/torbrowser/design/index.html.en 183) In general, we try to find solutions to privacy issues that will not induce projects/en/torbrowser/design/index.html.en 184) site breakage, though this is not always possible. projects/en/torbrowser/design/index.html.en 185) projects/en/torbrowser/design/index.html.en 186) </p></li><li class="listitem"><span class="command"><strong>Plugins must be restricted</strong></span><p> projects/en/torbrowser/design/index.html.en 187) projects/en/torbrowser/design/index.html.en 188) Even if plugins always properly used the browser proxy settings (which none of projects/en/torbrowser/design/index.html.en 189) them do) and could not be induced to bypass them (which all of them can), the projects/en/torbrowser/design/index.html.en 190) activities of closed-source plugins are very difficult to audit and control. projects/en/torbrowser/design/index.html.en 191) They can obtain and transmit all manner of system information to websites, projects/en/torbrowser/design/index.html.en 192) often have their own identifier storage for tracking users, and also projects/en/torbrowser/design/index.html.en 193) contribute to fingerprinting. projects/en/torbrowser/design/index.html.en 194) projects/en/torbrowser/design/index.html.en 195) </p><p> projects/en/torbrowser/design/index.html.en 196) projects/en/torbrowser/design/index.html.en 197) Therefore, if plugins are to be enabled in private browsing modes, they must projects/en/torbrowser/design/index.html.en 198) be restricted from running automatically on every page (via click-to-play projects/en/torbrowser/design/index.html.en 199) placeholders), and/or be sandboxed to restrict the types of system calls they
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 200) can execute. If the user agent allows the user to craft an exemption to allow projects/torbrowser/design/index.html.en 201) a plugin to be used automatically, it must only apply to the top level url bar projects/torbrowser/design/index.html.en 202) domain, and not to all sites, to reduce cross-origin fingerprinting projects/torbrowser/design/index.html.en 203) linkability.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 204) projects/en/torbrowser/design/index.html.en 205) </p></li><li class="listitem"><span class="command"><strong>Minimize Global Privacy Options</strong></span><p> projects/en/torbrowser/design/index.html.en 206)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 207) <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3100" target="_top">Another`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 208) failure of Torbutton</a> was the options panel. Each option`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 209) that detectably alters browser behavior can be used as a fingerprinting tool.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 210) Similarly, all extensions <a class="ulink" href="http://blog.chromium.org/2010/06/extensions-in-incognito.html" target="_top">should be projects/torbrowser/design/index.html.en 211) disabled in the mode</a> except as an opt-in basis. We should not load`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 212) system-wide and/or operating system provided addons or plugins.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 213) projects/en/torbrowser/design/index.html.en 214) </p><p>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 215) Instead of global browser privacy options, privacy decisions should be made`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 216) <a class="ulink" href="https://wiki.mozilla.org/Privacy/Features/Site-based_data_management_UI" target="_top">per`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 217) url bar origin</a> to eliminate the possibility of linkability`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 218) between domains. For example, when a plugin object (or a Javascript access of projects/en/torbrowser/design/index.html.en 219) window.plugins) is present in a page, the user should be given the choice of`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 220) allowing that plugin object for that url bar origin only. The same`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 221) goes for exemptions to third party cookie policy, geolocation, and any other`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 222) privacy permissions. projects/en/torbrowser/design/index.html.en 223) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 224) If the user has indicated they wish to record local history storage, these`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 225) permissions can be written to disk. Otherwise, they should remain memory-only.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 226) </p></li><li class="listitem"><span class="command"><strong>No filters</strong></span><p> projects/en/torbrowser/design/index.html.en 227)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 228) Site-specific or filter-based addons such as <a class="ulink" href="https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/" target="_top">AdBlock projects/torbrowser/design/index.html.en 229) Plus</a>, <a class="ulink" href="http://requestpolicy.com/" target="_top">Request Policy</a>, projects/torbrowser/design/index.html.en 230) <a class="ulink" href="http://www.ghostery.com/about" target="_top">Ghostery</a>, <a class="ulink" href="http://priv3.icsi.berkeley.edu/" target="_top">Priv3</a>, and <a class="ulink" href="http://sharemenot.cs.washington.edu/" target="_top">Sharemenot</a> are to be
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 231) avoided. We believe that these addons do not add any real privacy to a proper`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 232) <a class="link" href="#Implementation" title="4. Implementation">implementation</a> of the above <a class="link" href="#privacy" title="2.2. Privacy Requirements">privacy requirements</a>, and that development efforts projects/torbrowser/design/index.html.en 233) should be focused on general solutions that prevent tracking by all projects/torbrowser/design/index.html.en 234) third parties, rather than a list of specific URLs or hosts. projects/torbrowser/design/index.html.en 235) </p><p>
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 236) Filter-based addons can also introduce strange breakage and cause usability projects/en/torbrowser/design/index.html.en 237) nightmares, and will also fail to do their job if an adversary simply projects/en/torbrowser/design/index.html.en 238) registers a new domain or creates a new url path. Worse still, the unique`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 239) filter sets that each user creates or installs will provide a wealth of projects/torbrowser/design/index.html.en 240) fingerprinting targets.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 241) </p><p> projects/en/torbrowser/design/index.html.en 242) projects/en/torbrowser/design/index.html.en 243) As a general matter, we are also generally opposed to shipping an always-on Ad projects/en/torbrowser/design/index.html.en 244) blocker with Tor Browser. We feel that this would damage our credibility in projects/en/torbrowser/design/index.html.en 245) terms of demonstrating that we are providing privacy through a sound design`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 246) alone, as well as damage the acceptance of Tor users by sites that support`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 247) themselves through advertising revenue. projects/en/torbrowser/design/index.html.en 248) projects/en/torbrowser/design/index.html.en 249) </p><p> projects/en/torbrowser/design/index.html.en 250) Users are free to install these addons if they wish, but doing projects/en/torbrowser/design/index.html.en 251) so is not recommended, as it will alter the browser request fingerprint. projects/en/torbrowser/design/index.html.en 252) </p></li><li class="listitem"><span class="command"><strong>Stay Current</strong></span><p> projects/en/torbrowser/design/index.html.en 253) We believe that if we do not stay current with the support of new web projects/en/torbrowser/design/index.html.en 254) technologies, we cannot hope to substantially influence or be involved in projects/en/torbrowser/design/index.html.en 255) their proper deployment or privacy realization. However, we will likely disable
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 256) high-risk features pending analysis, audit, and mitigation.`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 257) </p></li></ol></div></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="adversary"></a>3. Adversary Model</h2></div></div></div><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 258) projects/torbrowser/design/index.html.en 259) A Tor web browser adversary has a number of goals, capabilities, and attack projects/torbrowser/design/index.html.en 260) types that can be used to illustrate the design requirements for the projects/torbrowser/design/index.html.en 261) Tor Browser. Let's start with the goals. projects/torbrowser/design/index.html.en 262)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 263) </p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="adversary-goals"></a>3.1. Adversary Goals</h3></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Bypassing proxy settings</strong></span><p>The adversary's primary goal is direct compromise and bypass of`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 264) Tor, causing the user to directly connect to an IP of the adversary's projects/torbrowser/design/index.html.en 265) choosing.</p></li><li class="listitem"><span class="command"><strong>Correlation of Tor vs Non-Tor Activity</strong></span><p>If direct proxy bypass is not possible, the adversary will likely projects/torbrowser/design/index.html.en 266) happily settle for the ability to correlate something a user did via Tor with projects/torbrowser/design/index.html.en 267) their non-Tor activity. This can be done with cookies, cache identifiers,
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 268) Javascript events, and even CSS. Sometimes the fact that a user uses Tor may`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 269) be enough for some authorities.</p></li><li class="listitem"><span class="command"><strong>History disclosure</strong></span><p> projects/torbrowser/design/index.html.en 270) The adversary may also be interested in history disclosure: the ability to projects/torbrowser/design/index.html.en 271) query a user's history to see if they have issued certain censored search projects/torbrowser/design/index.html.en 272) queries, or visited censored sites. projects/torbrowser/design/index.html.en 273) </p></li><li class="listitem"><span class="command"><strong>Correlate activity across multiple sites</strong></span><p> projects/torbrowser/design/index.html.en 274) projects/torbrowser/design/index.html.en 275) The primary goal of the advertising networks is to know that the user who projects/torbrowser/design/index.html.en 276) visited siteX.com is the same user that visited siteY.com to serve them projects/torbrowser/design/index.html.en 277) targeted ads. The advertising networks become our adversary insofar as they projects/torbrowser/design/index.html.en 278) attempt to perform this correlation without the user's explicit consent. projects/torbrowser/design/index.html.en 279) projects/torbrowser/design/index.html.en 280) </p></li><li class="listitem"><span class="command"><strong>Fingerprinting/anonymity set reduction</strong></span><p> projects/torbrowser/design/index.html.en 281) projects/torbrowser/design/index.html.en 282) Fingerprinting (more generally: "anonymity set reduction") is used to attempt
TBB design doc: More review... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 283) to gather identifying information on a particular individual without the use projects/torbrowser/design/index.html.en 284) of tracking identifiers. If the dissident or whistleblower's timezone is projects/torbrowser/design/index.html.en 285) available, and they are using a rare build of Firefox for an obscure operating projects/torbrowser/design/index.html.en 286) system, and they have a specific display resolution only used on one type of projects/torbrowser/design/index.html.en 287) laptop, this can be very useful information for tracking them down, or at projects/torbrowser/design/index.html.en 288) least <a class="link" href="#fingerprinting">tracking their activities</a>.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 289) projects/torbrowser/design/index.html.en 290) </p></li><li class="listitem"><span class="command"><strong>History records and other on-disk projects/torbrowser/design/index.html.en 291) information</strong></span><p>`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 292)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 293) In some cases, the adversary may opt for a heavy-handed approach, such as projects/torbrowser/design/index.html.en 294) seizing the computers of all Tor users in an area (especially after narrowing projects/torbrowser/design/index.html.en 295) the field by the above two pieces of information). History records and cache`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 296) data are the primary goals here. Secondary goals may include confirming projects/torbrowser/design/index.html.en 297) on-disk identifiers (such as hostname and disk-logged spoofed MAC adddress projects/torbrowser/design/index.html.en 298) history) obtained by other means. projects/torbrowser/design/index.html.en 299)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 300) </p></li></ol></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="adversary-positioning"></a>3.2. Adversary Capabilities - Positioning</h3></div></div></div><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 301) The adversary can position themselves at a number of different locations in projects/torbrowser/design/index.html.en 302) order to execute their attacks.`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 303) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Exit Node or Upstream Router</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 304) The adversary can run exit nodes, or alternatively, they may control routers projects/torbrowser/design/index.html.en 305) upstream of exit nodes. Both of these scenarios have been observed in the projects/torbrowser/design/index.html.en 306) wild. projects/torbrowser/design/index.html.en 307) </p></li><li class="listitem"><span class="command"><strong>Ad servers and/or Malicious Websites</strong></span><p> projects/torbrowser/design/index.html.en 308) The adversary can also run websites, or more likely, they can contract out projects/torbrowser/design/index.html.en 309) ad space from a number of different ad servers and inject content that way. For projects/torbrowser/design/index.html.en 310) some users, the adversary may be the ad servers themselves. It is not projects/torbrowser/design/index.html.en 311) inconceivable that ad servers may try to subvert or reduce a user's anonymity projects/torbrowser/design/index.html.en 312) through Tor for marketing purposes. projects/torbrowser/design/index.html.en 313) </p></li><li class="listitem"><span class="command"><strong>Local Network/ISP/Upstream Router</strong></span><p> projects/torbrowser/design/index.html.en 314) The adversary can also inject malicious content at the user's upstream router projects/torbrowser/design/index.html.en 315) when they have Tor disabled, in an attempt to correlate their Tor and Non-Tor projects/torbrowser/design/index.html.en 316) activity.
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 317) </p><p> projects/torbrowser/design/index.html.en 318) projects/torbrowser/design/index.html.en 319) Additionally, at this position the adversary can block Tor, or attempt to projects/torbrowser/design/index.html.en 320) recognize the traffic patterns of specific web pages at the entrance to the Tor projects/torbrowser/design/index.html.en 321) network. projects/torbrowser/design/index.html.en 322)`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 323) </p></li><li class="listitem"><span class="command"><strong>Physical Access</strong></span><p> projects/torbrowser/design/index.html.en 324) Some users face adversaries with intermittent or constant physical access. projects/torbrowser/design/index.html.en 325) Users in Internet cafes, for example, face such a threat. In addition, in projects/torbrowser/design/index.html.en 326) countries where simply using tools like Tor is illegal, users may face projects/torbrowser/design/index.html.en 327) confiscation of their computer equipment for excessive Tor usage or just projects/torbrowser/design/index.html.en 328) general suspicion.
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 329) </p></li></ol></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="attacks"></a>3.3. Adversary Capabilities - Attacks</h3></div></div></div><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 330) projects/torbrowser/design/index.html.en 331) The adversary can perform the following attacks from a number of different projects/torbrowser/design/index.html.en 332) positions to accomplish various aspects of their goals. It should be noted projects/torbrowser/design/index.html.en 333) that many of these attacks (especially those involving IP address leakage) are projects/torbrowser/design/index.html.en 334) often performed by accident by websites that simply have Javascript, dynamic projects/torbrowser/design/index.html.en 335) CSS elements, and plugins. Others are performed by ad servers seeking to projects/torbrowser/design/index.html.en 336) correlate users' activity across different IP addresses, and still others are projects/torbrowser/design/index.html.en 337) performed by malicious agents on the Tor network and at national firewalls. projects/torbrowser/design/index.html.en 338)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 339) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Read and insert identifiers</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 340) projects/torbrowser/design/index.html.en 341) The browser contains multiple facilities for storing identifiers that the projects/torbrowser/design/index.html.en 342) adversary creates for the purposes of tracking users. These identifiers are projects/torbrowser/design/index.html.en 343) most obviously cookies, but also include HTTP auth, DOM storage, cached projects/torbrowser/design/index.html.en 344) scripts and other elements with embedded identifiers, client certificates, and projects/torbrowser/design/index.html.en 345) even TLS Session IDs. projects/torbrowser/design/index.html.en 346) projects/torbrowser/design/index.html.en 347) </p><p> projects/torbrowser/design/index.html.en 348) projects/torbrowser/design/index.html.en 349) An adversary in a position to perform MITM content alteration can inject projects/torbrowser/design/index.html.en 350) document content elements to both read and inject cookies for arbitrary projects/torbrowser/design/index.html.en 351) domains. In fact, even many "SSL secured" websites are vulnerable to this sort of
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 352) <a class="ulink" href="http://seclists.org/bugtraq/2007/Aug/0070.html" target="_top">active`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 353) sidejacking</a>. In addition, the ad networks of course perform tracking projects/torbrowser/design/index.html.en 354) with cookies as well. projects/torbrowser/design/index.html.en 355) projects/torbrowser/design/index.html.en 356) </p><p> projects/torbrowser/design/index.html.en 357)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 358) These types of attacks are attempts at subverting our <a class="link" href="#identifier-linkability" title="4.5. Cross-Origin Identifier Unlinkability">Cross-Origin Identifier Unlinkability</a> and <a class="link" href="#new-identity" title="4.7. Long-Term Unlinkability via "New Identity" button">Long-Term Unlinkability</a> design requirements.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 359)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 360) </p></li><li class="listitem"><a id="fingerprinting"></a><span class="command"><strong>Fingerprint users based on browser`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 361) attributes</strong></span><p> projects/torbrowser/design/index.html.en 362) projects/torbrowser/design/index.html.en 363) There is an absurd amount of information available to websites via attributes projects/torbrowser/design/index.html.en 364) of the browser. This information can be used to reduce anonymity set, or even projects/torbrowser/design/index.html.en 365) uniquely fingerprint individual users. Attacks of this nature are typically projects/torbrowser/design/index.html.en 366) aimed at tracking users across sites without their consent, in an attempt to projects/torbrowser/design/index.html.en 367) subvert our <a class="link" href="#fingerprinting-linkability" title="4.6. Cross-Origin Fingerprinting Unlinkability">Cross-Origin
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 368) Fingerprinting Unlinkability</a> and <a class="link" href="#new-identity" title="4.7. Long-Term Unlinkability via "New Identity" button">Long-Term Unlinkability</a> design requirements.`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 369) projects/torbrowser/design/index.html.en 370) </p><p> projects/torbrowser/design/index.html.en 371) projects/torbrowser/design/index.html.en 372) Fingerprinting is an intimidating projects/torbrowser/design/index.html.en 373) problem to attempt to tackle, especially without a metric to determine or at projects/torbrowser/design/index.html.en 374) least intuitively understand and estimate which features will most contribute projects/torbrowser/design/index.html.en 375) to linkability between visits. projects/torbrowser/design/index.html.en 376) projects/torbrowser/design/index.html.en 377) </p><p> projects/torbrowser/design/index.html.en 378)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 379) The <a class="ulink" href="https://panopticlick.eff.org/about.php" target="_top">Panopticlick study projects/torbrowser/design/index.html.en 380) done</a> by the EFF uses the <a class="ulink" href="https://en.wikipedia.org/wiki/Entropy_%28information_theory%29" target="_top">Shannon`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 381) entropy</a> - the number of identifying bits of information encoded in`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 382) browser properties - as this metric. Their <a class="ulink" href="https://wiki.mozilla.org/Fingerprinting#Data" target="_top">result data</a> is`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 383) definitely useful, and the metric is probably the appropriate one for projects/torbrowser/design/index.html.en 384) determining how identifying a particular browser property is. However, some projects/torbrowser/design/index.html.en 385) quirks of their study means that they do not extract as much information as projects/torbrowser/design/index.html.en 386) they could from display information: they only use desktop resolution and do projects/torbrowser/design/index.html.en 387) not attempt to infer the size of toolbars. In the other direction, they may be projects/torbrowser/design/index.html.en 388) over-counting in some areas, as they did not compute joint entropy over projects/torbrowser/design/index.html.en 389) multiple attributes that may exhibit a high degree of correlation. Also, new projects/torbrowser/design/index.html.en 390) browser features are added regularly, so the data should not be taken as projects/torbrowser/design/index.html.en 391) final. projects/torbrowser/design/index.html.en 392) projects/torbrowser/design/index.html.en 393) </p><p> projects/torbrowser/design/index.html.en 394) projects/torbrowser/design/index.html.en 395) Despite the uncertainty, all fingerprinting attacks leverage the following projects/torbrowser/design/index.html.en 396) attack vectors: projects/torbrowser/design/index.html.en 397)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 398) </p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><span class="command"><strong>Observing Request Behavior</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 399) projects/torbrowser/design/index.html.en 400) Properties of the user's request behavior comprise the bulk of low-hanging projects/torbrowser/design/index.html.en 401) fingerprinting targets. These include: User agent, Accept-* headers, pipeline projects/torbrowser/design/index.html.en 402) usage, and request ordering. Additionally, the use of custom filters such as projects/torbrowser/design/index.html.en 403) AdBlock and other privacy filters can be used to fingerprint request patterns projects/torbrowser/design/index.html.en 404) (as an extreme example). projects/torbrowser/design/index.html.en 405) projects/torbrowser/design/index.html.en 406) </p></li><li class="listitem"><span class="command"><strong>Inserting Javascript</strong></span><p> projects/torbrowser/design/index.html.en 407) projects/torbrowser/design/index.html.en 408) Javascript can reveal a lot of fingerprinting information. It provides DOM projects/torbrowser/design/index.html.en 409) objects such as window.screen and window.navigator to extract information projects/torbrowser/design/index.html.en 410) about the useragent. projects/torbrowser/design/index.html.en 411) projects/torbrowser/design/index.html.en 412) Also, Javascript can be used to query the user's timezone via the
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 413) <code class="function">Date()</code> object, <a class="ulink" href="https://www.khronos.org/registry/webgl/specs/1.0/#5.13" target="_top">WebGL</a> can`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 414) reveal information about the video card in use, and high precision timing`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 415) information can be used to <a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf" target="_top">fingerprint the CPU and`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 416) interpreter speed</a>. In the future, new JavaScript features such as`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 417) <a class="ulink" href="http://w3c-test.org/webperf/specs/ResourceTiming/" target="_top">Resource`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 418) Timing</a> may leak an unknown amount of network timing related projects/torbrowser/design/index.html.en 419) information. projects/torbrowser/design/index.html.en 420) projects/torbrowser/design/index.html.en 421) projects/torbrowser/design/index.html.en 422) projects/torbrowser/design/index.html.en 423) </p></li><li class="listitem"><span class="command"><strong>Inserting Plugins</strong></span><p> projects/torbrowser/design/index.html.en 424) projects/torbrowser/design/index.html.en 425) The Panopticlick project found that the mere list of installed plugins (in projects/torbrowser/design/index.html.en 426) navigator.plugins) was sufficient to provide a large degree of projects/torbrowser/design/index.html.en 427) fingerprintability. Additionally, plugins are capable of extracting font lists, projects/torbrowser/design/index.html.en 428) interface addresses, and other machine information that is beyond what the projects/torbrowser/design/index.html.en 429) browser would normally provide to content. In addition, plugins can be used to projects/torbrowser/design/index.html.en 430) store unique identifiers that are more difficult to clear than standard
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 431) cookies. <a class="ulink" href="http://epic.org/privacy/cookies/flash.html" target="_top">Flash-based`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 432) cookies</a> fall into this category, but there are likely numerous other projects/torbrowser/design/index.html.en 433) examples. Beyond fingerprinting, plugins are also abysmal at obeying the proxy projects/torbrowser/design/index.html.en 434) settings of the browser. projects/torbrowser/design/index.html.en 435) projects/torbrowser/design/index.html.en 436) projects/torbrowser/design/index.html.en 437) </p></li><li class="listitem"><span class="command"><strong>Inserting CSS</strong></span><p> projects/torbrowser/design/index.html.en 438)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 439) <a class="ulink" href="https://developer.mozilla.org/En/CSS/Media_queries" target="_top">CSS media`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 440) queries</a> can be inserted to gather information about the desktop size, projects/torbrowser/design/index.html.en 441) widget size, display type, DPI, user agent type, and other information that projects/torbrowser/design/index.html.en 442) was formerly available only to Javascript. projects/torbrowser/design/index.html.en 443)`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 444) </p></li></ol></div></li><li class="listitem"><a id="website-traffic-fingerprinting"></a><span class="command"><strong>Website traffic fingerprinting</strong></span><p> projects/torbrowser/design/index.html.en 445) projects/torbrowser/design/index.html.en 446) Website traffic fingerprinting is an attempt by the adversary to recognize the`
TBB design doc: More review... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 447) encrypted traffic patterns of specific websites. In the case of Tor, this projects/torbrowser/design/index.html.en 448) attack would take place between the user and the Guard node, or at the Guard projects/torbrowser/design/index.html.en 449) node itself. projects/torbrowser/design/index.html.en 450) </p><p> The most comprehensive study of the statistical properties of this projects/torbrowser/design/index.html.en 451) attack against Tor was done by <a class="ulink" href="http://lorre.uni.lu/~andriy/papers/acmccs-wpes11-fingerprinting.pdf" target="_top">Panchenko
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 452) et al</a>. Unfortunately, the publication bias in academia has encouraged projects/torbrowser/design/index.html.en 453) the production of a number of follow-on attack papers claiming "improved"`
TBB design doc: More review... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 454) success rates, in some cases even claiming to completely invalidate any projects/torbrowser/design/index.html.en 455) attempt at defense. These "improvements" are actually enabled primarily by projects/torbrowser/design/index.html.en 456) taking a number of shortcuts (such as classifying only very small numbers of projects/torbrowser/design/index.html.en 457) web pages, neglecting to publish ROC curves or at least false positive rates, projects/torbrowser/design/index.html.en 458) and/or omitting the effects of dataset size on their results). Despite these projects/torbrowser/design/index.html.en 459) subsequent "improvements", we are skeptical of the efficacy of this attack in projects/torbrowser/design/index.html.en 460) a real world scenario, <span class="emphasis"><em>especially</em></span> in the face of any
TBB design doc: Clarify web... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 461) defenses.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 462) projects/torbrowser/design/index.html.en 463) </p><p> projects/torbrowser/design/index.html.en 464)`
TBB design doc: Clarify web... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 465) In general, with machine learning, as you increase the <a class="ulink" href="https://en.wikipedia.org/wiki/VC_dimension" target="_top">number and/or complexity of projects/torbrowser/design/index.html.en 466) categories to classify</a> while maintaining a limit on reliable feature projects/torbrowser/design/index.html.en 467) information you can extract, you eventually run out of descriptive feature projects/torbrowser/design/index.html.en 468) information, and either true positive accuracy goes down or the false positive projects/torbrowser/design/index.html.en 469) rate goes up. This error is called the <a class="ulink" href="http://www.cs.washington.edu/education/courses/csep573/98sp/lectures/lecture8/sld050.htm" target="_top">bias projects/torbrowser/design/index.html.en 470) in your hypothesis space</a>. In fact, even for unbiased hypothesis projects/torbrowser/design/index.html.en 471) spaces, the number of training examples required to achieve a reasonable error projects/torbrowser/design/index.html.en 472) bound is <a class="ulink" href="https://en.wikipedia.org/wiki/Probably_approximately_correct_learning#Equivalence" target="_top">a
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 473) function of the complexity of the categories</a> you need to classify.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 474) projects/torbrowser/design/index.html.en 475) </p><p> projects/torbrowser/design/index.html.en 476) projects/torbrowser/design/index.html.en 477) projects/torbrowser/design/index.html.en 478) In the case of this attack, the key factors that increase the classification`
TBB design doc: Clarify web... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 479) complexity (and thus hinder a real world adversary who attempts this attack)`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 480) are large numbers of dynamically generated pages, partially cached content,`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 481) and also the non-web activity of entire Tor network. This yields an effective projects/torbrowser/design/index.html.en 482) number of "web pages" many orders of magnitude larger than even <a class="ulink" href="http://lorre.uni.lu/~andriy/papers/acmccs-wpes11-fingerprinting.pdf" target="_top">Panchenko's`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 483) "Open World" scenario</a>, which suffered continuous near-constant decline`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 484) in the true positive rate as the "Open World" size grew (see figure 4). This projects/torbrowser/design/index.html.en 485) large level of classification complexity is further confounded by a noisy and`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 486) low resolution featureset - one which is also relatively easy for the defender`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 487) to manipulate at low cost.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 488) projects/torbrowser/design/index.html.en 489) </p><p> projects/torbrowser/design/index.html.en 490)`
TBB Design Doc: Mention use... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 491) To make matters worse for a real-world adversary, the ocean of Tor Internet projects/torbrowser/design/index.html.en 492) activity (at least, when compared to a lab setting) makes it a certainty that projects/torbrowser/design/index.html.en 493) an adversary attempting examine large amounts of Tor traffic will ultimately projects/torbrowser/design/index.html.en 494) be overwhelmed by false positives (even after making heavy tradeoffs on the projects/torbrowser/design/index.html.en 495) ROC curve to minimize false positives to below 0.01%). This problem is known projects/torbrowser/design/index.html.en 496) in the IDS literature as the <a class="ulink" href="http://www.raid-symposium.org/raid99/PAPERS/Axelsson.pdf" target="_top">Base Rate
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 497) Fallacy</a>, and it is the primary reason that anomaly and activity projects/torbrowser/design/index.html.en 498) classification-based IDS and antivirus systems have failed to materialize in`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 499) the marketplace (despite early success in academic literature).`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 500) projects/torbrowser/design/index.html.en 501) </p><p> projects/torbrowser/design/index.html.en 502) projects/torbrowser/design/index.html.en 503) Still, we do not believe that these issues are enough to dismiss the attack projects/torbrowser/design/index.html.en 504) outright. But we do believe these factors make it both worthwhile and projects/torbrowser/design/index.html.en 505) effective to <a class="link" href="#traffic-fingerprinting-defenses">deploy projects/torbrowser/design/index.html.en 506) light-weight defenses</a> that reduce the accuracy of this attack by projects/torbrowser/design/index.html.en 507) further contributing noise to hinder successful feature extraction. projects/torbrowser/design/index.html.en 508) projects/torbrowser/design/index.html.en 509) </p></li><li class="listitem"><span class="command"><strong>Remotely or locally exploit browser and/or
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 510) OS</strong></span><p> projects/torbrowser/design/index.html.en 511) projects/torbrowser/design/index.html.en 512) Last, but definitely not least, the adversary can exploit either general projects/torbrowser/design/index.html.en 513) browser vulnerabilities, plugin vulnerabilities, or OS vulnerabilities to projects/torbrowser/design/index.html.en 514) install malware and surveillance software. An adversary with physical access`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 515) can perform similar actions. projects/torbrowser/design/index.html.en 516) projects/torbrowser/design/index.html.en 517) </p><p> projects/torbrowser/design/index.html.en 518) projects/torbrowser/design/index.html.en 519) For the purposes of the browser itself, we limit the scope of this adversary projects/torbrowser/design/index.html.en 520) to one that has passive forensic access to the disk after browsing activity projects/torbrowser/design/index.html.en 521) has taken place. This adversary motivates our
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 522) <a class="link" href="#disk-avoidance" title="4.3. Disk Avoidance">Disk Avoidance</a> defenses.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 523)`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 524) </p><p> projects/torbrowser/design/index.html.en 525) projects/torbrowser/design/index.html.en 526) An adversary with arbitrary code execution typically has more power, though. projects/torbrowser/design/index.html.en 527) It can be quite hard to really significantly limit the capabilities of such an`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 528) adversary. <a class="ulink" href="http://tails.boum.org/contribute/design/" target="_top">The Tails system</a> can`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 529) provide some defense against this adversary through the use of readonly media projects/torbrowser/design/index.html.en 530) and frequent reboots, but even this can be circumvented on machines without projects/torbrowser/design/index.html.en 531) Secure Boot through the use of BIOS rootkits. projects/torbrowser/design/index.html.en 532)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 533) </p></li></ol></div></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="Implementation"></a>4. Implementation</h2></div></div></div><p>`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 534) projects/torbrowser/design/index.html.en 535) The Implementation section is divided into subsections, each of which projects/torbrowser/design/index.html.en 536) corresponds to a <a class="link" href="#DesignRequirements" title="2. Design Requirements and Philosophy">Design Requirement</a>. projects/torbrowser/design/index.html.en 537) Each subsection is divided into specific web technologies or properties. The projects/torbrowser/design/index.html.en 538) implementation is then described for that property. projects/torbrowser/design/index.html.en 539) projects/torbrowser/design/index.html.en 540) </p><p> projects/torbrowser/design/index.html.en 541) projects/torbrowser/design/index.html.en 542) In some cases, the implementation meets the design requirements in a non-ideal projects/torbrowser/design/index.html.en 543) way (for example, by disabling features). In rare cases, there may be no projects/torbrowser/design/index.html.en 544) implementation at all. Both of these cases are denoted by differentiating projects/torbrowser/design/index.html.en 545) between the <span class="command"><strong>Design Goal</strong></span> and the <span class="command"><strong>Implementation
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 546) Status</strong></span> for each property. Corresponding bugs in the <a class="ulink" href="https://trac.torproject.org/projects/tor/report" target="_top">Tor bug tracker</a>`
Update TBB design doc w/ an... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 547) are typically linked for these cases. projects/torbrowser/design/index.html.en 548)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 549) </p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="proxy-obedience"></a>4.1. Proxy Obedience</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 550) projects/en/torbrowser/design/index.html.en 551) Proxy obedience is assured through the following:`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 552) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Firefox proxy settings, patches, and build flags`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 553) <p>`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 554) projects/torbrowser/design/index.html.en 555) Our <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/blob/refs/heads/tor-browser-31.2.0esr-4.x-1:/browser/app/profile/000-tor-browser.js" target="_top">Firefox projects/torbrowser/design/index.html.en 556) preferences file</a> sets the Firefox proxy settings to use Tor directly projects/torbrowser/design/index.html.en 557) as a SOCKS proxy. It sets <span class="command"><strong>network.proxy.socks_remote_dns</strong></span>,
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 558) <span class="command"><strong>network.proxy.socks_version</strong></span>, projects/torbrowser/design/index.html.en 559) <span class="command"><strong>network.proxy.socks_port</strong></span>, and projects/torbrowser/design/index.html.en 560) <span class="command"><strong>network.dns.disablePrefetch</strong></span>.`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 561)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 562) </p><p> projects/torbrowser/design/index.html.en 563)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 564) To prevent proxy bypass by WebRTC calls, we disable WebRTC at compile time projects/torbrowser/design/index.html.en 565) with the <span class="command"><strong>--disable-webrtc</strong></span> configure switch, as well projects/torbrowser/design/index.html.en 566) as set the pref <span class="command"><strong>media.peerconnection.enabled</strong></span> to false.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 567) projects/torbrowser/design/index.html.en 568) </p><p> projects/torbrowser/design/index.html.en 569)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 570) We also patch Firefox in order to provide several defense-in-depth mechanisms projects/torbrowser/design/index.html.en 571) for proxy safety. Notably, we <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/8527bec0ad59fb3d885c5639735fb188eefa336f" target="_top">patch projects/torbrowser/design/index.html.en 572) the DNS service</a> to prevent any browser or addon DNS resolution, and we projects/torbrowser/design/index.html.en 573) also <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/04c046e11f6622f44ca010bcb8ecf68cf470a4c0" target="_top">patch projects/torbrowser/design/index.html.en 574) OCSP and PKIX code</a> to prevent any use of the non-proxied command-line projects/torbrowser/design/index.html.en 575) tool utility functions from being functional while linked in to the browser. projects/torbrowser/design/index.html.en 576) In both cases, we could find no direct paths to these routines in the browser, projects/torbrowser/design/index.html.en 577) but it seemed better safe than sorry.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 578)`
Comments from Georg + proxy... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 579) </p><p> projects/torbrowser/design/index.html.en 580)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 581) During every Extended Support Release transition, we perform <a class="ulink" href="https://gitweb.torproject.org/tor-browser-spec.git/tree/HEAD:/audits" target="_top">in-depth projects/torbrowser/design/index.html.en 582) code audits</a> to verify that there were no system calls or XPCOM projects/torbrowser/design/index.html.en 583) activity in the source tree that did not use the browser proxy settings. projects/torbrowser/design/index.html.en 584) </p><p> projects/torbrowser/design/index.html.en 585)
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 586) We have verified that these settings and patches properly proxy HTTPS, OCSP,`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 587) HTTP, FTP, gopher (now defunct), DNS, SafeBrowsing Queries, all JavaScript`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 588) activity, including HTML5 audio and video objects, addon updates, wifi projects/torbrowser/design/index.html.en 589) geolocation queries, searchbox queries, XPCOM addon HTTPS/HTTP activity, projects/torbrowser/design/index.html.en 590) WebSockets, and live bookmark updates. We have also verified that IPv6 projects/torbrowser/design/index.html.en 591) connections are not attempted, through the proxy or otherwise (Tor does not projects/torbrowser/design/index.html.en 592) yet support IPv6). We have also verified that external protocol helpers, such projects/torbrowser/design/index.html.en 593) as smb urls and other custom protocol handlers are all blocked.
Comments from Georg + proxy... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 594)`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 595) </p></li><li class="listitem">Disabling plugins`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 596)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 597) <p>Plugins have the ability to make arbitrary OS system calls and <a class="ulink" href="http://decloak.net/" target="_top">bypass proxy settings</a>. This includes`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 598) the ability to make UDP sockets and send arbitrary data independent of the projects/en/torbrowser/design/index.html.en 599) browser proxy settings. projects/en/torbrowser/design/index.html.en 600) </p><p> projects/en/torbrowser/design/index.html.en 601) Torbutton disables plugins by using the projects/en/torbrowser/design/index.html.en 602) <span class="command"><strong>@mozilla.org/plugin/host;1</strong></span> service to mark the plugin tags`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 603) as disabled. This block can be undone through both the Torbutton Security UI, projects/torbrowser/design/index.html.en 604) and the Firefox Plugin Preferences.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 605) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 606) If the user does enable plugins in this way, plugin-handled objects are still projects/torbrowser/design/index.html.en 607) restricted from automatic load through Firefox's click-to-play preference projects/torbrowser/design/index.html.en 608) <span class="command"><strong>plugins.click_to_play</strong></span>.`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 609) </p><p>`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 610)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 611) In addition, to reduce any unproxied activity by arbitrary plugins at load projects/torbrowser/design/index.html.en 612) time, and to reduce the fingerprintability of the installed plugin list, we`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 613) also patch the Firefox source code to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/2ecf6c33618ecee554155f735a3e92860f519f9c" target="_top"> projects/torbrowser/design/index.html.en 614) prevent the load of any plugins except for Flash and Gnash</a>.`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 615)`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 616) </p></li><li class="listitem">External App Blocking and Drag Event Filtering`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 617) <p>`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 618) projects/torbrowser/design/index.html.en 619) External apps can be induced to load files that perform network activity. projects/torbrowser/design/index.html.en 620) Unfortunately, there are cases where such apps can be launched automatically projects/torbrowser/design/index.html.en 621) with little to no user input. In order to prevent this, Torbutton installs a projects/torbrowser/design/index.html.en 622) component to <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob_plain/HEAD:/src/components/external-app-blocker.js" target="_top"> projects/torbrowser/design/index.html.en 623) provide the user with a popup</a> whenever the browser attempts to launch projects/torbrowser/design/index.html.en 624) a helper app. projects/torbrowser/design/index.html.en 625) projects/torbrowser/design/index.html.en 626) </p><p> projects/torbrowser/design/index.html.en 627) projects/torbrowser/design/index.html.en 628) Additionally, modern desktops now pre-emptively fetch any URLs in Drag and projects/torbrowser/design/index.html.en 629) Drop events as soon as the drag is initiated. This download happens projects/torbrowser/design/index.html.en 630) independent of the browser's Tor settings, and can be triggered by something projects/torbrowser/design/index.html.en 631) as simple as holding the mouse button down for slightly too long while
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 632) clicking on an image link. We filter drag and drop events events <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob_plain/HEAD:/src/components/external-app-blocker.js" target="_top">from projects/torbrowser/design/index.html.en 633) Torbutton</a> before the OS downloads the URLs the events contained.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 634)`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 635) </p></li><li class="listitem">Disabling system extensions and clearing the addon whitelist projects/torbrowser/design/index.html.en 636) <p> projects/torbrowser/design/index.html.en 637) projects/torbrowser/design/index.html.en 638) Firefox addons can perform arbitrary activity on your computer, including projects/torbrowser/design/index.html.en 639) bypassing Tor. It is for this reason we disable the addon whitelist projects/torbrowser/design/index.html.en 640) (<span class="command"><strong>xpinstall.whitelist.add</strong></span>), so that users are prompted projects/torbrowser/design/index.html.en 641) before installing addons regardless of the source. We also exclude projects/torbrowser/design/index.html.en 642) system-level addons from the browser through the use of projects/torbrowser/design/index.html.en 643) <span class="command"><strong>extensions.enabledScopes</strong></span> and projects/torbrowser/design/index.html.en 644) <span class="command"><strong>extensions.autoDisableScopes</strong></span>. projects/torbrowser/design/index.html.en 645)
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 646) </p></li></ol></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="state-separation"></a>4.2. State Separation</h3></div></div></div><p>`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 647)`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 648) Tor Browser State is separated from existing browser state through use of a`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 649) custom Firefox profile, and by setting the $HOME environment variable to the projects/torbrowser/design/index.html.en 650) root of the bundle's directory. The browser also does not load any projects/torbrowser/design/index.html.en 651) system-wide extensions (through the use of projects/torbrowser/design/index.html.en 652) <span class="command"><strong>extensions.enabledScopes</strong></span> and`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 653) <span class="command"><strong>extensions.autoDisableScopes</strong></span>). Furthermore, plugins are`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 654) disabled, which prevents Flash cookies from leaking from a pre-existing Flash projects/torbrowser/design/index.html.en 655) directory. projects/torbrowser/design/index.html.en 656)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 657) </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="disk-avoidance"></a>4.3. Disk Avoidance</h3></div></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp60374176"></a>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote">`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 658) projects/torbrowser/design/index.html.en 659) The User Agent MUST (at user option) prevent all disk records of browser activity.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 660) The user should be able to optionally enable URL history and other history`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 661) features if they so desire.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 662)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 663) </blockquote></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp60375536"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote">`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 664)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 665) We achieve this goal through several mechanisms. First, we set the Firefox projects/torbrowser/design/index.html.en 666) Private Browsing preference projects/torbrowser/design/index.html.en 667) <span class="command"><strong>browser.privatebrowsing.autostart</strong></span>. In addition, four Firefox patches are needed to prevent disk writes, even if projects/torbrowser/design/index.html.en 668) Private Browsing Mode is enabled. We need to`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 669)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 670) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/4ebc3cda4b704c0149fb9e0fdcbb6e5ee3a8e75c" target="_top">prevent projects/torbrowser/design/index.html.en 671) the permissions manager from recording HTTPS STS state</a>, <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/8904bfc10cd537bd35be5ddd23c58fdaa72baa21" target="_top">prevent projects/torbrowser/design/index.html.en 672) intermediate SSL certificates from being recorded</a>, <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/86f6bc9dc28b6f8d7eae7974c7e9b537c3a08e41" target="_top">prevent projects/torbrowser/design/index.html.en 673) the clipboard cache from being written to disk for large pastes</a>, and projects/torbrowser/design/index.html.en 674) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/d5da6f8b7de089335e49e2f7dbd2b8d74e4cb613" target="_top">prevent projects/torbrowser/design/index.html.en 675) the content preferences service from recording site zoom</a>. We also had projects/torbrowser/design/index.html.en 676) to disable the media cache with the pref <span class="command"><strong>media.cache_size</strong></span>, projects/torbrowser/design/index.html.en 677) to prevent HTML5 videos from being written to the OS temporary directory, projects/torbrowser/design/index.html.en 678) which happened regardless of the private browsing mode setting.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 679) projects/torbrowser/design/index.html.en 680) </blockquote></div><div class="blockquote"><blockquote class="blockquote"> projects/torbrowser/design/index.html.en 681) projects/torbrowser/design/index.html.en 682) As an additional defense-in-depth measure, we set the following preferences:`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 683) <span class="command"><strong></strong></span>,`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 684) <span class="command"><strong>browser.cache.disk.enable</strong></span>, projects/en/torbrowser/design/index.html.en 685) <span class="command"><strong>browser.cache.offline.enable</strong></span>,`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 686) <span class="command"><strong>dom.indexedDB.enabled</strong></span>, projects/torbrowser/design/index.html.en 687) <span class="command"><strong>network.cookie.lifetimePolicy</strong></span>,`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 688) <span class="command"><strong>signon.rememberSignons</strong></span>,`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 689) <span class="command"><strong>browser.formfill.enable</strong></span>,`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 690) <span class="command"><strong>browser.download.manager.retention</strong></span>,`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 691) <span class="command"><strong>browser.sessionstore.privacy_level</strong></span>, projects/torbrowser/design/index.html.en 692) and <span class="command"><strong>network.cookie.lifetimePolicy</strong></span>. Many of these projects/torbrowser/design/index.html.en 693) preferences are likely redundant with projects/torbrowser/design/index.html.en 694) <span class="command"><strong>browser.privatebrowsing.autostart</strong></span>, but we have not done the projects/torbrowser/design/index.html.en 695) auditing work to ensure that yet.
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 696)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 697) </blockquote></div><div class="blockquote"><blockquote class="blockquote">`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 698)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 699) For more details on disk leak bugs and enhancements, see the <a class="ulink" href="https://trac.torproject.org/projects/tor/query?keywords=~tbb-disk-leak&status=!closed" target="_top">tbb-disk-leak tag in our bugtracker</a></blockquote></div></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="app-data-isolation"></a>4.4. Application Data Isolation</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 700) projects/en/torbrowser/design/index.html.en 701) Tor Browser Bundle MUST NOT cause any information to be written outside of the projects/en/torbrowser/design/index.html.en 702) bundle directory. This is to ensure that the user is able to completely and projects/en/torbrowser/design/index.html.en 703) safely remove the bundle without leaving other traces of Tor usage on their projects/en/torbrowser/design/index.html.en 704) computer. projects/en/torbrowser/design/index.html.en 705)
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 706) </p><p> projects/torbrowser/design/index.html.en 707) projects/torbrowser/design/index.html.en 708) To ensure TBB directory isolation, we set projects/torbrowser/design/index.html.en 709) <span class="command"><strong>browser.download.useDownloadDir</strong></span>, projects/torbrowser/design/index.html.en 710) <span class="command"><strong>browser.shell.checkDefaultBrowser</strong></span>, and projects/torbrowser/design/index.html.en 711) <span class="command"><strong>browser.download.manager.addToRecentDocs</strong></span>. We also set the projects/torbrowser/design/index.html.en 712) $HOME environment variable to be the TBB extraction directory.
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 713) </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="identifier-linkability"></a>4.5. Cross-Origin Identifier Unlinkability</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 714) projects/en/torbrowser/design/index.html.en 715) The Tor Browser MUST prevent a user's activity on one site from being linked projects/en/torbrowser/design/index.html.en 716) to their activity on another site. When this goal cannot yet be met with an projects/en/torbrowser/design/index.html.en 717) existing web technology, that technology or functionality is disabled. Our projects/en/torbrowser/design/index.html.en 718) <a class="link" href="#privacy" title="2.2. Privacy Requirements">design goal</a> is to ultimately eliminate the need to disable arbitrary projects/en/torbrowser/design/index.html.en 719) technologies, and instead simply alter them in ways that allows them to projects/en/torbrowser/design/index.html.en 720) function in a backwards-compatible way while avoiding linkability. Users projects/en/torbrowser/design/index.html.en 721) should be able to use federated login of various kinds to explicitly inform projects/en/torbrowser/design/index.html.en 722) sites who they are, but that information should not transparently allow a projects/en/torbrowser/design/index.html.en 723) third party to record their activity from site to site without their prior projects/en/torbrowser/design/index.html.en 724) consent. projects/en/torbrowser/design/index.html.en 725) projects/en/torbrowser/design/index.html.en 726) </p><p> projects/en/torbrowser/design/index.html.en 727) projects/en/torbrowser/design/index.html.en 728) The benefit of this approach comes not only in the form of reduced projects/en/torbrowser/design/index.html.en 729) linkability, but also in terms of simplified privacy UI. If all stored browser
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 730) state and permissions become associated with the url bar origin, the six or projects/torbrowser/design/index.html.en 731) seven different pieces of privacy UI governing these identifiers and`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 732) permissions can become just one piece of UI. For instance, a window that lists`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 733) the url bar origin for which browser state exists, possibly with a projects/torbrowser/design/index.html.en 734) context-menu option to drill down into specific types of state or permissions. projects/torbrowser/design/index.html.en 735) An example of this simplification can be seen in Figure 1.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 736)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 737) </p><div class="figure"><a id="idp60398240"></a><p class="title"><strong>Figure 1. Improving the Privacy UI</strong></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="NewCookieManager.png" align="middle" alt="Improving the Privacy UI" /></div><div class="caption"><p></p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 738)`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 739) This example UI is a mock-up of how isolating identifiers to the URL bar projects/torbrowser/design/index.html.en 740) origin can simplify the privacy UI for all data - not just cookies. Once projects/torbrowser/design/index.html.en 741) browser identifiers and site permissions operate on a url bar basis, the same projects/torbrowser/design/index.html.en 742) privacy window can represent browsing history, DOM Storage, HTTP Auth, search projects/torbrowser/design/index.html.en 743) form history, login values, and so on within a context menu for each site.
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 744)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 745) </div></div></div><br class="figure-break" /><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Cookies`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 746) <p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 747)`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 748) All cookies MUST be double-keyed to the url bar origin and third-party`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 749) origin. There exists a <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=565965" target="_top">Mozilla bug</a>`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 750) that contains a prototype patch, but it lacks UI, and does not apply to modern projects/torbrowser/design/index.html.en 751) Firefoxes.`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 752) projects/en/torbrowser/design/index.html.en 753) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 754) projects/en/torbrowser/design/index.html.en 755) As a stopgap to satisfy our design requirement of unlinkability, we currently projects/en/torbrowser/design/index.html.en 756) entirely disable 3rd party cookies by setting projects/en/torbrowser/design/index.html.en 757) <span class="command"><strong>network.cookie.cookieBehavior</strong></span> to 1. We would prefer that
Comments from Georg + proxy... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 758) third party content continue to function, but we believe the requirement for`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 759) unlinkability trumps that desire. projects/en/torbrowser/design/index.html.en 760) projects/en/torbrowser/design/index.html.en 761) </p></li><li class="listitem">Cache projects/en/torbrowser/design/index.html.en 762) <p>`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 763) projects/torbrowser/design/index.html.en 764) Cache is isolated to the url bar origin by using a technique pioneered by`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 765) Colin Jackson et al, via their work on <a class="ulink" href="http://www.safecache.com/" target="_top">SafeCache</a>. The technique re-uses the projects/torbrowser/design/index.html.en 766) <a class="ulink" href="https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsICachingChannel" target="_top">nsICachingChannel.cacheKey</a>`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 767) attribute that Firefox uses internally to prevent improper caching and reuse projects/torbrowser/design/index.html.en 768) of HTTP POST data. projects/torbrowser/design/index.html.en 769)`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 770) </p><p>`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 771)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 772) However, to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3666" target="_top">increase the projects/torbrowser/design/index.html.en 773) security of the isolation</a> and to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3754" target="_top">solve conflicts`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 774) with OCSP relying the cacheKey property for reuse of POST requests</a>, we`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 775) had to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/18dfd3064aff23a402fec248aab797036a9ba615" target="_top">patch`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 776) Firefox to provide a cacheDomain cache attribute</a>. We use the fully`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 777) qualified url bar domain as input to this field, to avoid the complexities projects/torbrowser/design/index.html.en 778) of heuristically determining the second-level DNS name.`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 779)`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 780) </p><p> projects/en/torbrowser/design/index.html.en 781)`
Update TBB design doc with... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 782) Furthermore, we chose a different projects/torbrowser/design/index.html.en 783) isolation scheme than the Stanford implementation. First, we decoupled the projects/torbrowser/design/index.html.en 784) cache isolation from the third party cookie attribute. Second, we use several projects/torbrowser/design/index.html.en 785) mechanisms to attempt to determine the actual location attribute of the projects/torbrowser/design/index.html.en 786) top-level window (to obtain the url bar FQDN) used to load the page, as
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 787) opposed to relying solely on the Referer property.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 788) projects/en/torbrowser/design/index.html.en 789) </p><p>`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 790)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 791) Therefore, <a class="ulink" href="http://crypto.stanford.edu/sameorigin/safecachetest.html" target="_top">the original`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 792) Stanford test cases</a> are expected to fail. Functionality can still be`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 793) verified by navigating to <a class="ulink" href="about:cache" target="_top">about:cache</a> and`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 794) viewing the key used for each cache entry. Each third party element should projects/torbrowser/design/index.html.en 795) have an additional "domain=string" property prepended, which will list the projects/torbrowser/design/index.html.en 796) FQDN that was used to source the third party element. projects/torbrowser/design/index.html.en 797)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 798) </p><p> projects/torbrowser/design/index.html.en 799) projects/torbrowser/design/index.html.en 800) Additionally, because the image cache is a separate entity from the content`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 801) cache, we had to patch Firefox to also <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/114cd22282f8b3cd6e6a5c29de8a8c396a79acc0" target="_top">isolate`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 802) this cache per url bar domain</a>. projects/torbrowser/design/index.html.en 803)`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 804) </p></li><li class="listitem">HTTP Auth projects/en/torbrowser/design/index.html.en 805) <p> projects/en/torbrowser/design/index.html.en 806) projects/en/torbrowser/design/index.html.en 807) HTTP authentication tokens are removed for third party elements using the`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 808) <a class="ulink" href="https://developer.mozilla.org/en/Setting_HTTP_request_headers#Observers" target="_top">http-on-modify-request projects/torbrowser/design/index.html.en 809) observer</a> to remove the Authorization headers to prevent <a class="ulink" href="http://jeremiahgrossman.blogspot.com/2007/04/tracking-users-without-cookies.html" target="_top">silent`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 810) linkability between domains</a>.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 811) </p></li><li class="listitem">DOM Storage`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 812) <p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 813)`
Additional comments from Ge... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 814) DOM storage for third party domains MUST be isolated to the url bar origin,`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 815) to prevent linkability between sites. This functionality is provided through a`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 816) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/973468a07fb9e7d9995d01b250223a8df16d6cfd" target="_top">patch`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 817) to Firefox</a>.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 818)`
Describe our efforts agains... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 819) </p></li><li class="listitem">Flash cookies projects/torbrowser/design/index.html.en 820) <p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 821) projects/torbrowser/design/index.html.en 822) Users should be able to click-to-play flash objects from trusted sites. To projects/torbrowser/design/index.html.en 823) make this behavior unlinkable, we wish to include a settings file for all platforms that disables flash
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 824) cookies using the <a class="ulink" href="http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager03.html" target="_top">Flash`
Describe our efforts agains... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 825) settings manager</a>.`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 826)`
Describe our efforts agains... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 827) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/torbrowser/design/index.html.en 828)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 829) We are currently <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3974" target="_top">having`
Describe our efforts agains... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 830) difficulties</a> causing Flash player to use this settings`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 831) file on Windows, so Flash remains difficult to enable.`
Describe our efforts agains... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 832)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 833) </p></li><li class="listitem">SSL+TLS session resumption, HTTP Keep-Alive and SPDY`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 834) <p><span class="command"><strong>Design Goal:</strong></span>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 835)`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 836) TLS session resumption tickets and SSL Session IDs MUST be limited to the url projects/torbrowser/design/index.html.en 837) bar origin. HTTP Keep-Alive connections from a third party in one url bar projects/torbrowser/design/index.html.en 838) origin MUST NOT be reused for that same third party in another url bar origin.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 839) projects/en/torbrowser/design/index.html.en 840) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 841)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 842) We currently clear SSL Session IDs upon <a class="link" href="#new-identity" title="4.7. Long-Term Unlinkability via "New Identity" button">New`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 843) Identity</a>, we disable TLS Session Tickets via the Firefox Pref projects/torbrowser/design/index.html.en 844) <span class="command"><strong>security.enable_tls_session_tickets</strong></span>. We disable SSL Session`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 845) IDs via a <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/5524ae43780e4738310852cc2a0b7c5d25aa69ed" target="_top">patch`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 846) to Firefox</a>. To compensate for the increased round trip latency from disabling projects/torbrowser/design/index.html.en 847) these performance optimizations, we also enable`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 848) <a class="ulink" href="https://tools.ietf.org/html/draft-bmoeller-tls-falsestart-00" target="_top">TLS`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 849) False Start</a> via the Firefox Pref projects/torbrowser/design/index.html.en 850) <span class="command"><strong>security.ssl.enable_false_start</strong></span>. projects/torbrowser/design/index.html.en 851) </p><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 852)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 853) Because of the extreme performance benefits of HTTP Keep-Alive for interactive`
Update design doc. Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 854) web apps, and because of the difficulties of conveying urlbar origin projects/torbrowser/design/index.html.en 855) information down into the Firefox HTTP layer, as a compromise we currently projects/torbrowser/design/index.html.en 856) merely reduce the HTTP Keep-Alive timeout to 20 seconds (which is measured projects/torbrowser/design/index.html.en 857) from the last packet read on the connection) using the Firefox preference projects/torbrowser/design/index.html.en 858) <span class="command"><strong>network.http.keep-alive.timeout</strong></span>. projects/torbrowser/design/index.html.en 859)
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 860) </p><p> projects/torbrowser/design/index.html.en 861) However, because SPDY can store identifiers and has extremely long keepalive projects/torbrowser/design/index.html.en 862) duration, it is disabled through the Firefox preference projects/torbrowser/design/index.html.en 863) <span class="command"><strong>network.http.spdy.enabled</strong></span>.`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 864) </p></li><li class="listitem">Automated cross-origin redirects MUST NOT store identifiers`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 865) <p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 866) projects/torbrowser/design/index.html.en 867) To prevent attacks aimed at subverting the Cross-Origin Identifier projects/torbrowser/design/index.html.en 868) Unlinkability <a class="link" href="#privacy" title="2.2. Privacy Requirements">privacy requirement</a>, the browser`
Update design doc. Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 869) MUST NOT store any identifiers (cookies, cache, DOM storage, HTTP auth, etc) projects/torbrowser/design/index.html.en 870) for cross-origin redirect intermediaries that do not prompt for user input. projects/torbrowser/design/index.html.en 871) For example, if a user clicks on a bit.ly url that redirects to a projects/torbrowser/design/index.html.en 872) doubleclick.net url that finally redirects to a cnn.com url, only cookies from projects/torbrowser/design/index.html.en 873) cnn.com should be retained after the redirect chain completes.
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 874) projects/torbrowser/design/index.html.en 875) </p><p> projects/torbrowser/design/index.html.en 876)`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 877) Non-automated redirect chains that require user input at some step (such as projects/torbrowser/design/index.html.en 878) federated login systems) SHOULD still allow identifiers to persist.`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 879)`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 880) </p><p><span class="command"><strong>Implementation status:</strong></span> projects/torbrowser/design/index.html.en 881) projects/torbrowser/design/index.html.en 882) There are numerous ways for the user to be redirected, and the Firefox API`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 883) support to detect each of them is poor. We have a <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3600" target="_top">trac bug`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 884) open</a> to implement what we can. projects/torbrowser/design/index.html.en 885)`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 886) </p></li><li class="listitem">window.name`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 887) <p> projects/en/torbrowser/design/index.html.en 888)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 889) <a class="ulink" href="https://developer.mozilla.org/En/DOM/Window.name" target="_top">window.name</a> is`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 890) a magical DOM property that for some reason is allowed to retain a persistent value projects/en/torbrowser/design/index.html.en 891) for the lifespan of a browser tab. It is possible to utilize this property for`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 892) <a class="ulink" href="http://www.thomasfrank.se/sessionvars.html" target="_top">identifier`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 893) storage</a>. projects/en/torbrowser/design/index.html.en 894) projects/en/torbrowser/design/index.html.en 895) </p><p> projects/en/torbrowser/design/index.html.en 896)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 897) In order to eliminate non-consensual linkability but still allow for sites projects/torbrowser/design/index.html.en 898) that utilize this property to function, we reset the window.name property of`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 899) tabs in Torbutton every time we encounter a blank Referer. This behavior`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 900) allows window.name to persist for the duration of a click-driven navigation projects/torbrowser/design/index.html.en 901) session, but as soon as the user enters a new URL or navigates between projects/torbrowser/design/index.html.en 902) https/http schemes, the property is cleared.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 903)`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 904) </p></li><li class="listitem">Auto form-fill projects/torbrowser/design/index.html.en 905) <p> projects/torbrowser/design/index.html.en 906) projects/torbrowser/design/index.html.en 907) We disable the password saving functionality in the browser as part of our`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 908) <a class="link" href="#disk-avoidance" title="4.3. Disk Avoidance">Disk Avoidance</a> requirement. However,`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 909) since users may decide to re-enable disk history records and password saving,`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 910) we also set the <a class="ulink" href="http://kb.mozillazine.org/Signon.autofillForms" target="_top">signon.autofillForms</a>`
Update TBB design doc based... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 911) preference to false to prevent saved values from immediately populating projects/torbrowser/design/index.html.en 912) fields upon page load. Since Javascript can read these values as soon as they projects/torbrowser/design/index.html.en 913) appear, setting this preference prevents automatic linkability from stored passwords. projects/torbrowser/design/index.html.en 914) projects/torbrowser/design/index.html.en 915) </p></li><li class="listitem">HSTS supercookies projects/torbrowser/design/index.html.en 916) <p>
Additional comments from Ge... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 917)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 918) An extreme (but not impossible) attack to mount is the creation of <a class="ulink" href="http://www.leviathansecurity.com/blog/archives/12-The-Double-Edged-Sword-of-HSTS-Persistence-and-Privacy.html" target="_top">HSTS`
Additional comments from Ge... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 919) supercookies</a>. Since HSTS effectively stores one bit of information per domain`
Update TBB design doc based... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 920) name, an adversary in possession of numerous domains can use them to construct projects/torbrowser/design/index.html.en 921) cookies based on stored HSTS state. projects/torbrowser/design/index.html.en 922) projects/torbrowser/design/index.html.en 923) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 924) projects/torbrowser/design/index.html.en 925) There appears to be three options for us: 1. Disable HSTS entirely, and rely
Additional comments from Ge... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 926) instead on HTTPS-Everywhere to crawl and ship rules for HSTS sites. 2. projects/torbrowser/design/index.html.en 927) Restrict the number of HSTS-enabled third parties allowed per url bar origin. projects/torbrowser/design/index.html.en 928) 3. Prevent third parties from storing HSTS rules. We have not yet decided upon projects/torbrowser/design/index.html.en 929) the best approach.`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 930) projects/torbrowser/design/index.html.en 931) </p><p><span class="command"><strong>Implementation Status:</strong></span> Currently, HSTS state is`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 932) cleared by <a class="link" href="#new-identity" title="4.7. Long-Term Unlinkability via "New Identity" button">New Identity</a>, but we don't`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 933) defend against the creation of these cookies between <span class="command"><strong>New projects/torbrowser/design/index.html.en 934) Identity</strong></span> invocations. projects/torbrowser/design/index.html.en 935) </p></li><li class="listitem">Exit node usage`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 936) <p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 937)`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 938) All content elements associated with a given URL bar domain (including the projects/torbrowser/design/index.html.en 939) main page) are given a SOCKS username and password for this domain, which projects/torbrowser/design/index.html.en 940) causes Tor to isolate all of these requests on their own set of Tor circuits.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 941)`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 942) </p></li></ol></div><p>`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 943) For more details on identifier linkability bugs and enhancements, see the <a class="ulink" href="https://trac.torproject.org/projects/tor/query?keywords=~tbb-linkability&status=!closed" target="_top">tbb-linkability tag in our bugtracker</a>`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 944) </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="fingerprinting-linkability"></a>4.6. Cross-Origin Fingerprinting Unlinkability</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 945) projects/en/torbrowser/design/index.html.en 946) In order to properly address the fingerprinting adversary on a technical projects/en/torbrowser/design/index.html.en 947) level, we need a metric to measure linkability of the various browser`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 948) properties beyond any stored origin-related state. <a class="ulink" href="https://panopticlick.eff.org/about.php" target="_top">The Panopticlick Project</a>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 949) by the EFF provides us with a prototype of such a metric. The researchers projects/torbrowser/design/index.html.en 950) conducted a survey of volunteers who were asked to visit an experiment page projects/torbrowser/design/index.html.en 951) that harvested many of the above components. They then computed the Shannon projects/torbrowser/design/index.html.en 952) Entropy of the resulting distribution of each of several key attributes to projects/torbrowser/design/index.html.en 953) determine how many bits of identifying information each attribute provided.
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 954) projects/en/torbrowser/design/index.html.en 955) </p><p> projects/en/torbrowser/design/index.html.en 956)`
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 957) Unfortunately, there are limitations to the way the Panopticlick study was projects/torbrowser/design/index.html.en 958) conducted. Because the Panopticlick dataset is based on browser data spanning projects/torbrowser/design/index.html.en 959) a number of widely deployed browsers over a number of years, any projects/torbrowser/design/index.html.en 960) fingerprinting defenses attempted by browsers today are very likely to cause projects/torbrowser/design/index.html.en 961) Panopticlick to report an <span class="emphasis"><em>increase</em></span> in fingerprintability projects/torbrowser/design/index.html.en 962) and entropy, because those defenses will stand out in sharp contrast to projects/torbrowser/design/index.html.en 963) historical data. Moreover, because fingerprinting is a problem that projects/torbrowser/design/index.html.en 964) potentially touches every aspect of the browser, we do not believe it is projects/torbrowser/design/index.html.en 965) possible to solve cross-browser fingerprinting issues. We reduce the efforts projects/torbrowser/design/index.html.en 966) for fingerprinting resistance by only concerning ourselves with reducing the projects/torbrowser/design/index.html.en 967) fingerprintable differences <span class="emphasis"><em>among</em></span> Tor Browser users.
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 968) projects/en/torbrowser/design/index.html.en 969) </p><p> projects/en/torbrowser/design/index.html.en 970)`
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 971) The unsolvable nature of the cross-browser fingerprinting problem also means projects/torbrowser/design/index.html.en 972) that the Panopticlick test website itself is not useful for evaluating the projects/torbrowser/design/index.html.en 973) actual effectiveness of our defenses, or the fingerprinting defenses of any projects/torbrowser/design/index.html.en 974) other web browser. We are interested in deploying an improved version of projects/torbrowser/design/index.html.en 975) Panopticlick that measures entropy and variance only among a specific user projects/torbrowser/design/index.html.en 976) agent population, but until then, intuition serves as a decent guide. projects/torbrowser/design/index.html.en 977) Essentially, anything that reveals custom user configuration, third party projects/torbrowser/design/index.html.en 978) software, highly variable hardware details, and external devices attached to projects/torbrowser/design/index.html.en 979) the users computer is likely to more fingerprintable than things like projects/torbrowser/design/index.html.en 980) operating system type and even processor speed.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 981)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 982) </p><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="fingerprinting-defenses"></a>Fingerprinting defenses in the Tor Browser</h4></div></div></div><p> projects/torbrowser/design/index.html.en 983) projects/torbrowser/design/index.html.en 984) The following defenses are listed roughly in order of most severe`
Another fix to the design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 985) fingerprinting threat first. This ordering is based on the above intuition that`
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 986) user configurable aspects of the computer are the most severe source of projects/torbrowser/design/index.html.en 987) fingerprintability, though we are in need of updated measurements to determine projects/torbrowser/design/index.html.en 988) this with certainty. projects/torbrowser/design/index.html.en 989) projects/torbrowser/design/index.html.en 990) </p><p> projects/torbrowser/design/index.html.en 991) Where our actual implementation differs from projects/torbrowser/design/index.html.en 992) an ideal solution, we separately describe our <span class="command"><strong>Design Goal</strong></span> projects/torbrowser/design/index.html.en 993) and our <span class="command"><strong>Implementation Status</strong></span>.
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 994) projects/torbrowser/design/index.html.en 995) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Plugins`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 996) <p> projects/en/torbrowser/design/index.html.en 997)`
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 998) Plugins add to fingerprinting risk via two main vectors: their mere presence projects/torbrowser/design/index.html.en 999) in window.navigator.plugins (because they are optional, end-user installed projects/torbrowser/design/index.html.en 1000) third party software), as well as their internal functionality.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1001) projects/en/torbrowser/design/index.html.en 1002) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1003)`
Update TBB design doc with... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1004) All plugins that have not been specifically audited or sandboxed MUST be`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1005) disabled. To reduce linkability potential, even sandboxed plugins should not projects/en/torbrowser/design/index.html.en 1006) be allowed to load objects until the user has clicked through a click-to-play projects/en/torbrowser/design/index.html.en 1007) barrier. Additionally, version information should be reduced or obfuscated`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1008) until the plugin object is loaded. For flash, we wish to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3974" target="_top">provide a`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1009) settings.sol file</a> to disable Flash cookies, and to restrict P2P`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1010) features that are likely to bypass proxy settings. We'd also like to restrict projects/torbrowser/design/index.html.en 1011) access to fonts and other system information (such as IP address and MAC projects/torbrowser/design/index.html.en 1012) address) in such a sandbox.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1013) projects/en/torbrowser/design/index.html.en 1014) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1015) projects/en/torbrowser/design/index.html.en 1016) Currently, we entirely disable all plugins in Tor Browser. However, as a`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1017) compromise due to the popularity of Flash, we allow users to re-enable Flash, projects/torbrowser/design/index.html.en 1018) and flash objects are blocked behind a click-to-play barrier that is available projects/torbrowser/design/index.html.en 1019) only after the user has specifically enabled plugins. Flash is the only plugin`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1020) available, the rest are <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/1ef32dcf0cc64876f5b92a583b788dc921f22c5d" target="_top">entirely`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1021) blocked from loading by a Firefox patch</a>. We also set the Firefox projects/torbrowser/design/index.html.en 1022) preference <span class="command"><strong>plugin.expose_full_path</strong></span> to false, to avoid projects/torbrowser/design/index.html.en 1023) leaking plugin installation information. projects/torbrowser/design/index.html.en 1024) projects/torbrowser/design/index.html.en 1025) </p></li><li class="listitem">HTML5 Canvas Image Extraction projects/torbrowser/design/index.html.en 1026) <p> projects/torbrowser/design/index.html.en 1027)
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1028) After plugins and plugin-provided information, we believe that the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/HTML/Canvas" target="_top">HTML5 projects/torbrowser/design/index.html.en 1029) Canvas</a> is the single largest fingerprinting threat browsers face projects/torbrowser/design/index.html.en 1030) today. <a class="ulink" href="http://www.w2spconf.com/2012/papers/w2sp12-final4.pdf" target="_top">Initial`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1031) studies</a> show that the Canvas can provide an easy-access fingerprinting projects/torbrowser/design/index.html.en 1032) target: The adversary simply renders WebGL, font, and named color data to a projects/torbrowser/design/index.html.en 1033) Canvas element, extracts the image buffer, and computes a hash of that image projects/torbrowser/design/index.html.en 1034) data. Subtle differences in the video card, font packs, and even font and projects/torbrowser/design/index.html.en 1035) graphics library versions allow the adversary to produce a stable, simple, projects/torbrowser/design/index.html.en 1036) high-entropy fingerprint of a computer. In fact, the hash of the rendered projects/torbrowser/design/index.html.en 1037) image can be used almost identically to a tracking cookie by the web server. projects/torbrowser/design/index.html.en 1038) projects/torbrowser/design/index.html.en 1039) </p><p> projects/torbrowser/design/index.html.en 1040)
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1041) In some sense, the canvas can be seen as the union of many other`
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1042) fingerprinting vectors. If WebGL is normalized through software rendering, projects/torbrowser/design/index.html.en 1043) system colors were standardized, and the browser shipped a fixed collection of projects/torbrowser/design/index.html.en 1044) fonts (see later points in this list), it might not be necessary`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1045) to create a canvas permission. However, until then, to reduce the threat from projects/torbrowser/design/index.html.en 1046) this vector, we have patched Firefox to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/3b53f525cfb68880e676e64f13cbc0b928ae3ecf" target="_top">prompt projects/torbrowser/design/index.html.en 1047) before returning valid image data</a> to the Canvas APIs, and for <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/fb9f463fe3a69499d6896c217786bafdf0cda62f" target="_top">access projects/torbrowser/design/index.html.en 1048) to isPointInPath and related functions</a>. If the user hasn't previously projects/torbrowser/design/index.html.en 1049) allowed the site in the URL bar to access Canvas image data, pure white image projects/torbrowser/design/index.html.en 1050) data is returned to the Javascript APIs. projects/torbrowser/design/index.html.en 1051) projects/torbrowser/design/index.html.en 1052) </p><p> projects/torbrowser/design/index.html.en 1053) </p></li><li class="listitem">Open TCP Port Fingerprinting projects/torbrowser/design/index.html.en 1054) <p> projects/torbrowser/design/index.html.en 1055) projects/torbrowser/design/index.html.en 1056) In Firefox, by using either WebSockets or XHR, it is possible for remote projects/torbrowser/design/index.html.en 1057) content to <a class="ulink" href="http://www.andlabs.org/tools/jsrecon.html" target="_top">enumerate projects/torbrowser/design/index.html.en 1058) the list of TCP ports open on 127.0.0.1</a>. In other browsers, this can projects/torbrowser/design/index.html.en 1059) be accomplished by DOM events on image or script tags. This open vs filtered
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1060) vs closed port list can provide a very unique fingerprint of a machine, projects/torbrowser/design/index.html.en 1061) because it essentially enables the detection of many different popular third projects/torbrowser/design/index.html.en 1062) party applications and optional system services (Skype, Bitcoin, Bittorrent projects/torbrowser/design/index.html.en 1063) and other P2P software, SSH ports, SMB and related LAN services, CUPS and projects/torbrowser/design/index.html.en 1064) printer daemon config ports, mail servers, and so on). It is also possible to projects/torbrowser/design/index.html.en 1065) determine when ports are closed versus filtered/blocked (and thus probe projects/torbrowser/design/index.html.en 1066) custom firewall configuration).
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1067) projects/torbrowser/design/index.html.en 1068) </p><p>In Tor Browser, we prevent access to projects/torbrowser/design/index.html.en 1069) 127.0.0.1/localhost by ensuring that even these requests are still sent by projects/torbrowser/design/index.html.en 1070) Firefox to our SOCKS proxy (ie we set projects/torbrowser/design/index.html.en 1071) <span class="command"><strong>network.proxy.no_proxies_on</strong></span> to the empty string). The local projects/torbrowser/design/index.html.en 1072) Tor client then rejects them, since it is configured to proxy for internal IP projects/torbrowser/design/index.html.en 1073) addresses by default.
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1074) </p></li><li class="listitem">Invasive Authentication Mechanisms (NTLM and SPNEGO) projects/torbrowser/design/index.html.en 1075) <p> projects/torbrowser/design/index.html.en 1076) projects/torbrowser/design/index.html.en 1077) Both NTLM and SPNEGO authentication mechanisms can leak the hostname, and in projects/torbrowser/design/index.html.en 1078) some cases the current username. The only reason why these aren't a more projects/torbrowser/design/index.html.en 1079) serious problem is that they typically involve user interaction, and likely projects/torbrowser/design/index.html.en 1080) aren't an attractive vector for this reason. However, because it is not clear projects/torbrowser/design/index.html.en 1081) if certain carefully-crafted error conditions in these protocols could cause projects/torbrowser/design/index.html.en 1082) them to reveal machine information and still fail silently prior to the projects/torbrowser/design/index.html.en 1083) password prompt, these authentication mechanisms should either be disabled, or projects/torbrowser/design/index.html.en 1084) placed behind a site permission before their use. We simply disable them. projects/torbrowser/design/index.html.en 1085) projects/torbrowser/design/index.html.en 1086) </p></li><li class="listitem">USB Device ID Enumeration
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1087) <p> projects/torbrowser/design/index.html.en 1088) projects/torbrowser/design/index.html.en 1089) The <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Web/Guide/API/Gamepad" target="_top">GamePad projects/torbrowser/design/index.html.en 1090) API</a> provides web pages with the <a class="ulink" href="https://dvcs.w3.org/hg/gamepad/raw-file/default/gamepad.html#widl-Gamepad-id" target="_top">USB projects/torbrowser/design/index.html.en 1091) device id, product id, and driver name</a> of all connected game projects/torbrowser/design/index.html.en 1092) controllers, as well as detailed information about their capabilities. This API projects/torbrowser/design/index.html.en 1093) should be behind a site permission in Private Browsing Modes, or should present a generic projects/torbrowser/design/index.html.en 1094) controller type (perhaps a two button controller that can be mapped to the keyboard) in all cases. projects/torbrowser/design/index.html.en 1095) We simply disable it via the pref <span class="command"><strong>dom.gamepad.enabled</strong></span>.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1096)`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 1097) </p></li><li class="listitem">Fonts projects/en/torbrowser/design/index.html.en 1098) <p> projects/en/torbrowser/design/index.html.en 1099) projects/en/torbrowser/design/index.html.en 1100) According to the Panopticlick study, fonts provide the most linkability when projects/en/torbrowser/design/index.html.en 1101) they are provided as an enumerable list in filesystem order, via either the projects/en/torbrowser/design/index.html.en 1102) Flash or Java plugins. However, it is still possible to use CSS and/or projects/en/torbrowser/design/index.html.en 1103) Javascript to query for the existence of specific fonts. With a large enough projects/en/torbrowser/design/index.html.en 1104) pre-built list to query, a large amount of fingerprintable information may
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1105) still be available, especially given that additional fonts often end up projects/torbrowser/design/index.html.en 1106) installed by third party software and for multilingual support.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1107)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1108) </p><p><span class="command"><strong>Design Goal:</strong></span> The sure-fire way to address font projects/torbrowser/design/index.html.en 1109) linkability is to ship the browser with a font for every language, typeface, projects/torbrowser/design/index.html.en 1110) and style, and to only use those fonts at the exclusion of system fonts. We are projects/torbrowser/design/index.html.en 1111) <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/13313" target="_top">currently projects/torbrowser/design/index.html.en 1112) investigating</a> this approach, and our current favorite font sets for projects/torbrowser/design/index.html.en 1113) this purpose are the <a class="ulink" href="http://www.droidfonts.com/droidfonts/" target="_top">Droid projects/torbrowser/design/index.html.en 1114) fonts</a>, the <a class="ulink" href="http://hangeul.naver.com/" target="_top">Nanum fonts</a>, projects/torbrowser/design/index.html.en 1115) and <a class="ulink" href="https://fedorahosted.org/lohit/" target="_top">Lohit fonts</a>. The Droid projects/torbrowser/design/index.html.en 1116) font set is fairly complete by itself, but Nanum and Lohit have smaller projects/torbrowser/design/index.html.en 1117) versions of many South Asian languages. When combined in a way that chooses the projects/torbrowser/design/index.html.en 1118) smallest font implementations for each locale, these three font sets provide
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1119) poverage for the all languages used on Wikipedia with more than`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1120) 10,000 articles, and several others as well, in approximately 3MB of compressed projects/torbrowser/design/index.html.en 1121) overhead. The <a class="ulink" href="https://www.google.com/get/noto/" target="_top">Noto font projects/torbrowser/design/index.html.en 1122) set</a> is another font set that aims for complete coverage, but is projects/torbrowser/design/index.html.en 1123) considerably larger than the combination of the Droid, Nanum, and Lohit fonts.
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1124)`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1125) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1126)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1127) In the meantime while we investigate shipping our own fonts, we disable`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1128) plugins, which prevents font name enumeration. Additionally, we limit both the`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1129) number of font queries from CSS, as well as the total number of fonts that can`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1130) be used in a document <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/d515c79ffd115b132caade7f881e5b467448964d" target="_top">with`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1131) a Firefox patch</a>. We create two prefs,`
Update design doc to descri... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1132) <span class="command"><strong>browser.display.max_font_attempts</strong></span> and projects/torbrowser/design/index.html.en 1133) <span class="command"><strong>browser.display.max_font_count</strong></span> for this purpose. Once these projects/torbrowser/design/index.html.en 1134) limits are reached, the browser behaves as if`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1135) <span class="command"><strong>browser.display.use_document_fonts</strong></span> was set.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1136)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1137) </p><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1138)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1139) To improve rendering, we exempt remote <a class="ulink" href="https://developer.mozilla.org/en-US/docs/CSS/@font-face" target="_top">@font-face`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1140) fonts</a> from these counts, and if a font-family CSS rule lists a remote projects/torbrowser/design/index.html.en 1141) font (in any order), we use that font instead of any of the named local fonts.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1142)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1143) </p></li><li class="listitem">Monitor, Widget, and OS Desktop Resolution`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1144) <p> projects/en/torbrowser/design/index.html.en 1145)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1146) Both CSS and Javascript have access to a lot of information about the screen projects/torbrowser/design/index.html.en 1147) resolution, usable desktop size, OS widget size, toolbar size, title bar size,`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1148) and OS desktop widget sizing information that are not at all relevant to`
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1149) rendering and serve only to provide information for fingerprinting. Since many projects/torbrowser/design/index.html.en 1150) aspects of desktop widget positioning and size are user configurable, these projects/torbrowser/design/index.html.en 1151) properties yield customized information about the computer, even beyond the projects/torbrowser/design/index.html.en 1152) monitor size.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1153) projects/en/torbrowser/design/index.html.en 1154) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1155) projects/en/torbrowser/design/index.html.en 1156) Our design goal here is to reduce the resolution information down to the bare`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1157) minimum required for properly rendering inside a content window. We intend to`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1158) report all rendering information correctly with respect to the size and projects/en/torbrowser/design/index.html.en 1159) properties of the content window, but report an effective size of 0 for all`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1160) border material, and also report that the desktop is only as big as the inner projects/torbrowser/design/index.html.en 1161) content window. Additionally, new browser windows are sized such that their projects/torbrowser/design/index.html.en 1162) content windows are one of a few fixed sizes based on the user's desktop projects/torbrowser/design/index.html.en 1163) resolution. In addition, to further reduce resolution-based fingerprinting, we projects/torbrowser/design/index.html.en 1164) are <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/7256" target="_top">investigating projects/torbrowser/design/index.html.en 1165) zoom/viewport-based mechanisms</a> that might allow us to always report the projects/torbrowser/design/index.html.en 1166) same desktop resolution regardless of the actual size of the content window, projects/torbrowser/design/index.html.en 1167) and simply scale to make up the difference. Until then, the user should also projects/torbrowser/design/index.html.en 1168) be informed that maximizing their windows can lead to fingerprintability under projects/torbrowser/design/index.html.en 1169) this scheme.
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1170) projects/en/torbrowser/design/index.html.en 1171) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1172)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1173) projects/torbrowser/design/index.html.en 1174) We have implemented the above strategy using a window observer to <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob/HEAD:/src/chrome/content/torbutton.js#l2960" target="_top">resize`
Update design doc to descri... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1175) new windows based on desktop resolution</a>. Additionally, we patch`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1176) Firefox to use the client content window size <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/8fc2421becd0ab0cfb5ebbc19af67469552202b2" target="_top">for projects/torbrowser/design/index.html.en 1177) window.screen</a>. Similarly, we <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/81e7fc3a10d27b1d8f0832faf1685899d21f6fef" target="_top">patch projects/torbrowser/design/index.html.en 1178) DOM events to return content window relative points</a>. We also force projects/torbrowser/design/index.html.en 1179) popups to open in new tabs (via projects/torbrowser/design/index.html.en 1180) <span class="command"><strong>browser.link.open_newwindow.restriction</strong></span>), to avoid projects/torbrowser/design/index.html.en 1181) full-screen popups inferring information about the browser resolution. In projects/torbrowser/design/index.html.en 1182) addition, we prevent auto-maximizing on browser start, and are investigating a projects/torbrowser/design/index.html.en 1183) user-friendly way of informing users that maximized windows are detrimental projects/torbrowser/design/index.html.en 1184) to privacy in this mode. projects/torbrowser/design/index.html.en 1185)
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1186) </p></li><li class="listitem">Display Media information`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1187) <p>`
Update design doc to descri... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1188)`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1189) Beyond simple resolution information, a large amount of so-called "Media" projects/torbrowser/design/index.html.en 1190) information is also exported to content. Even without Javascript, CSS has projects/torbrowser/design/index.html.en 1191) access to a lot of information about the device orientation, system theme`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1192) colors, and other desktop and display features that are not at all relevant to projects/torbrowser/design/index.html.en 1193) rendering and also user configurable. Most of this`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1194) information comes from <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Media_queries" target="_top">CSS projects/torbrowser/design/index.html.en 1195) Media Queries</a>, but Mozilla has exposed <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Web/CSS/color_value#System_Colors" target="_top">several projects/torbrowser/design/index.html.en 1196) user and OS theme defined color values</a> to CSS as well.`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1197) projects/torbrowser/design/index.html.en 1198) </p><p><span class="command"><strong>Design Goal:</strong></span>`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1199) projects/torbrowser/design/index.html.en 1200) CSS should not be able infer anything that the user has configured about their projects/torbrowser/design/index.html.en 1201) computer. Additionally, it should not be able to infer machine-specific projects/torbrowser/design/index.html.en 1202) details such as screen orientation or type.`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1203) projects/torbrowser/design/index.html.en 1204) </p><p><span class="command"><strong>Implementation Status:</strong></span>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1205)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1206) We patch projects/torbrowser/design/index.html.en 1207) Firefox to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/30dc2c4290698af81ceafae9d628a34c53faabe1" target="_top">report projects/torbrowser/design/index.html.en 1208) a fixed set of system colors to content window CSS</a>, and <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/8f6e979d30598569dea14ac6f4eef4e96543b3d7" target="_top">prevent projects/torbrowser/design/index.html.en 1209) detection of font smoothing on OSX</a>. We also always projects/torbrowser/design/index.html.en 1210) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/09561f0e5452305b9efcb4e6169c613c8db33246" target="_top">report projects/torbrowser/design/index.html.en 1211) landscape-primary</a> for the screen orientation.
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1212)`
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1213) </p></li><li class="listitem">WebGL projects/torbrowser/design/index.html.en 1214) <p> projects/torbrowser/design/index.html.en 1215) projects/torbrowser/design/index.html.en 1216) WebGL is fingerprintable both through information that is exposed about the projects/torbrowser/design/index.html.en 1217) underlying driver and optimizations, as well as through performance projects/torbrowser/design/index.html.en 1218) fingerprinting. projects/torbrowser/design/index.html.en 1219) projects/torbrowser/design/index.html.en 1220) </p><p> projects/torbrowser/design/index.html.en 1221) projects/torbrowser/design/index.html.en 1222) Because of the large amount of potential fingerprinting vectors and the <a class="ulink" href="http://www.contextis.com/resources/blog/webgl/" target="_top">previously unexposed projects/torbrowser/design/index.html.en 1223) vulnerability surface</a>, we deploy a similar strategy against WebGL as projects/torbrowser/design/index.html.en 1224) for plugins. First, WebGL Canvases have click-to-play placeholders (provided projects/torbrowser/design/index.html.en 1225) by NoScript), and do not run until authorized by the user. Second, we projects/torbrowser/design/index.html.en 1226) obfuscate driver information by setting the Firefox preferences projects/torbrowser/design/index.html.en 1227) <span class="command"><strong>webgl.disable-extensions</strong></span> and projects/torbrowser/design/index.html.en 1228) <span class="command"><strong>webgl.min_capability_mode</strong></span>, which reduce the information projects/torbrowser/design/index.html.en 1229) provided by the following WebGL API calls: <span class="command"><strong>getParameter()</strong></span>, projects/torbrowser/design/index.html.en 1230) <span class="command"><strong>getSupportedExtensions()</strong></span>, and projects/torbrowser/design/index.html.en 1231) <span class="command"><strong>getExtension()</strong></span>. projects/torbrowser/design/index.html.en 1232) projects/torbrowser/design/index.html.en 1233) </p><p> projects/torbrowser/design/index.html.en 1234) projects/torbrowser/design/index.html.en 1235) Another option for WebGL might be to use software-only rendering, using a projects/torbrowser/design/index.html.en 1236) library such as <a class="ulink" href="http://www.mesa3d.org/" target="_top">Mesa</a>. The use of projects/torbrowser/design/index.html.en 1237) such a library would avoid hardware-specific rendering differences. projects/torbrowser/design/index.html.en 1238)
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1239) </p></li><li class="listitem">User Agent and HTTP Headers projects/torbrowser/design/index.html.en 1240) <p><span class="command"><strong>Design Goal:</strong></span>`
Update design doc to descri... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1241)`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1242) All Tor Browser users MUST provide websites with an identical user agent and projects/torbrowser/design/index.html.en 1243) HTTP header set for a given request type. We omit the Firefox minor revision, projects/torbrowser/design/index.html.en 1244) and report a popular Windows platform. If the software is kept up to date, projects/torbrowser/design/index.html.en 1245) these headers should remain identical across the population even when updated. projects/torbrowser/design/index.html.en 1246) projects/torbrowser/design/index.html.en 1247) </p><p><span class="command"><strong>Implementation Status:</strong></span>
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1248)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1249) Firefox provides several options for controlling the browser user agent string projects/torbrowser/design/index.html.en 1250) which we leverage. We also set similar prefs for controlling the projects/torbrowser/design/index.html.en 1251) Accept-Language and Accept-Charset headers, which we spoof to English by default. Additionally, we`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1252) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/95cd0e8071aa1fe3f4914331d4036f218007e31d" target="_top">remove`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1253) content script access</a> to Components.interfaces, which <a class="ulink" href="http://pseudo-flaw.net/tor/torbutton/fingerprint-firefox.html" target="_top">can be`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1254) used</a> to fingerprint OS, platform, and Firefox minor version. </p></li><li class="listitem">Locale Fingerprinting projects/torbrowser/design/index.html.en 1255) <p> projects/torbrowser/design/index.html.en 1256) projects/torbrowser/design/index.html.en 1257) In Tor Browser, we provide non-English users the option of concealing their OS projects/torbrowser/design/index.html.en 1258) and browser locale from websites. It is debatable if this should be as high of projects/torbrowser/design/index.html.en 1259) a priority as information specific to the user's computer, but for projects/torbrowser/design/index.html.en 1260) completeness, we attempt to maintain this property. projects/torbrowser/design/index.html.en 1261) projects/torbrowser/design/index.html.en 1262) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/torbrowser/design/index.html.en 1263) projects/torbrowser/design/index.html.en 1264) We set the fallback character set to set to windows-1252 for all locales, via projects/torbrowser/design/index.html.en 1265) <span class="command"><strong>intl.charset.default</strong></span>. We also patch Firefox to allow us to projects/torbrowser/design/index.html.en 1266) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/fe42a78575df7f460fa0ac48eabb57bc8812c23e" target="_top">instruct projects/torbrowser/design/index.html.en 1267) the JS engine</a> to use en-US as its internal C locale for all Date, Math, projects/torbrowser/design/index.html.en 1268) and exception handling. projects/torbrowser/design/index.html.en 1269)
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1270) </p></li><li class="listitem">Timezone and Clock Offset`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1271) <p> projects/torbrowser/design/index.html.en 1272) projects/torbrowser/design/index.html.en 1273) While the latency in Tor connections varies anywhere from milliseconds to`
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1274) a few seconds, it is still possible for the remote site to detect large projects/torbrowser/design/index.html.en 1275) differences between the user's clock and an official reference time source. projects/torbrowser/design/index.html.en 1276)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1277) </p><p><span class="command"><strong>Design Goal:</strong></span>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1278)`
Update TBB design doc with... Mike Perry authored 12 years ago	projects/torbrowser/design/index.html.en 1279) All Tor Browser users MUST report the same timezone to websites. Currently, we projects/torbrowser/design/index.html.en 1280) choose UTC for this purpose, although an equally valid argument could be made projects/torbrowser/design/index.html.en 1281) for EDT/EST due to the large English-speaking population density (coupled with projects/torbrowser/design/index.html.en 1282) the fact that we spoof a US English user agent). Additionally, the Tor projects/torbrowser/design/index.html.en 1283) software should detect if the users clock is significantly divergent from the projects/torbrowser/design/index.html.en 1284) clocks of the relays that it connects to, and use this to reset the clock
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1285) values used in Tor Browser to something reasonably accurate. Alternatively, projects/torbrowser/design/index.html.en 1286) the browser can obtain this clock skew via a mechanism similar to that used in`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1287) <a class="ulink" href="https://github.com/ioerror/tlsdate" target="_top">tlsdate</a>.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1288) projects/en/torbrowser/design/index.html.en 1289) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1290) projects/en/torbrowser/design/index.html.en 1291) We set the timezone using the TZ environment variable, which is supported on`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1292) all platforms.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1293)`
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1294) </p></li><li class="listitem">Javascript Performance Fingerprinting`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1295) <p> projects/en/torbrowser/design/index.html.en 1296)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1297) <a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf" target="_top">Javascript performance`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 1298) fingerprinting</a> is the act of profiling the performance projects/en/torbrowser/design/index.html.en 1299) of various Javascript functions for the purpose of fingerprinting the projects/en/torbrowser/design/index.html.en 1300) Javascript engine and the CPU. projects/en/torbrowser/design/index.html.en 1301) projects/en/torbrowser/design/index.html.en 1302) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1303)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1304) We have <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3059" target="_top">several potential`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1305) mitigation approaches</a> to reduce the accuracy of performance projects/en/torbrowser/design/index.html.en 1306) fingerprinting without risking too much damage to functionality. Our current projects/en/torbrowser/design/index.html.en 1307) favorite is to reduce the resolution of the Event.timeStamp and the Javascript`
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1308) Date() object, while also introducing jitter. We believe that Javascript time projects/torbrowser/design/index.html.en 1309) resolution may be reduced all the way up to the second before it seriously projects/torbrowser/design/index.html.en 1310) impacts site operation. Our goal with this quantization is to increase the projects/torbrowser/design/index.html.en 1311) amount of time it takes to mount a successful attack. <a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf" target="_top">Mowery et al</a> found projects/torbrowser/design/index.html.en 1312) that even with the default precision in most browsers, they required up to 120
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1313) seconds of amortization and repeated trials to get stable results from their projects/en/torbrowser/design/index.html.en 1314) feature set. We intend to work with the research community to establish the`
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1315) optimum trade-off between quantization+jitter and amortization time, as well projects/torbrowser/design/index.html.en 1316) as identify highly variable Javascript operations. As long as these attacks projects/torbrowser/design/index.html.en 1317) take several seconds or more to execute, they are unlikely to be appealing to projects/torbrowser/design/index.html.en 1318) advertisers, and are also very likely to be noticed if deployed against a projects/torbrowser/design/index.html.en 1319) large number of people.
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1320) projects/en/torbrowser/design/index.html.en 1321) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1322)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1323) Currently, the only mitigation against performance fingerprinting is to`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1324) disable <a class="ulink" href="http://www.w3.org/TR/navigation-timing/" target="_top">Navigation`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1325) Timing</a> through the Firefox preference projects/torbrowser/design/index.html.en 1326) <span class="command"><strong>dom.enable_performance</strong></span>. projects/torbrowser/design/index.html.en 1327)`
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1328) </p></li><li class="listitem">Keystroke Fingerprinting`
Add design doc draft. Mike Perry authored 12 years ago	projects/en/torbrowser/design/index.html.en 1329) <p> projects/en/torbrowser/design/index.html.en 1330) projects/en/torbrowser/design/index.html.en 1331) Keystroke fingerprinting is the act of measuring key strike time and key projects/en/torbrowser/design/index.html.en 1332) flight time. It is seeing increasing use as a biometric. projects/en/torbrowser/design/index.html.en 1333) projects/en/torbrowser/design/index.html.en 1334) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1335) projects/en/torbrowser/design/index.html.en 1336) We intend to rely on the same mechanisms for defeating Javascript performance projects/en/torbrowser/design/index.html.en 1337) fingerprinting: timestamp quantization and jitter. projects/en/torbrowser/design/index.html.en 1338) projects/en/torbrowser/design/index.html.en 1339) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1340) We have no implementation as of yet.
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1341) </p></li><li class="listitem">Operating System Type Fingerprinting`
Describe OS type fingerprin... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1342) <p> projects/torbrowser/design/index.html.en 1343) projects/torbrowser/design/index.html.en 1344) As we mentioned in the introduction of this section, OS type fingerprinting is projects/torbrowser/design/index.html.en 1345) currently considered a lower priority, due simply to the numerous ways that`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1346) characteristics of the operating system type may leak into content, and the`
Describe OS type fingerprin... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1347) comparatively low contribution of OS to overall entropy. In particular, there projects/torbrowser/design/index.html.en 1348) are likely to be many ways to measure the differences in widget size, projects/torbrowser/design/index.html.en 1349) scrollbar size, and other rendered details on a page. Also, directly exported projects/torbrowser/design/index.html.en 1350) OS routines, such as the Math library, expose differences in their projects/torbrowser/design/index.html.en 1351) implementations due to these results. projects/torbrowser/design/index.html.en 1352) projects/torbrowser/design/index.html.en 1353) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 1354) projects/torbrowser/design/index.html.en 1355) We intend to reduce or eliminate OS type fingerprinting to the best extent projects/torbrowser/design/index.html.en 1356) possible, but recognize that the effort for reward on this item is not as high projects/torbrowser/design/index.html.en 1357) as other areas. The entropy on the current OS distribution is somewhere around projects/torbrowser/design/index.html.en 1358) 2 bits, which is much lower than other vectors which can also be used to
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1359) fingerprint configuration and user-specific information. You can see the projects/torbrowser/design/index.html.en 1360) major areas of OS fingerprinting we're aware of using the <a class="ulink" href="https://trac.torproject.org/projects/tor/query?keywords=~tbb-fingerprinting-os" target="_top">tbb-fingerprinting-os projects/torbrowser/design/index.html.en 1361) tag on our bug tracker</a>.`
Describe OS type fingerprin... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1362) projects/torbrowser/design/index.html.en 1363) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/torbrowser/design/index.html.en 1364)`
Updates to fingerprinting s... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1365) At least two HTML5 features have different implementation status across the projects/torbrowser/design/index.html.en 1366) major OS vendors: the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/DOM/window.navigator.battery" target="_top">Battery projects/torbrowser/design/index.html.en 1367) API</a> and the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/DOM/window.navigator.connection" target="_top">Network projects/torbrowser/design/index.html.en 1368) Connection API</a>. We disable these APIs through the Firefox preferences projects/torbrowser/design/index.html.en 1369) <span class="command"><strong>dom.battery.enabled</strong></span> and projects/torbrowser/design/index.html.en 1370) <span class="command"><strong>dom.network.enabled</strong></span>.
Describe OS type fingerprin... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1371)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1372) </p></li></ol></div></div><p>`
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1373) For more details on fingerprinting bugs and enhancements, see the <a class="ulink" href="https://trac.torproject.org/projects/tor/query?keywords=~tbb-fingerprinting&status=!closed" target="_top">tbb-fingerprinting tag in our bug tracker</a>`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1374) </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="new-identity"></a>4.7. Long-Term Unlinkability via "New Identity" button</h3></div></div></div><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1375)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1376) In order to avoid long-term linkability, we provide a "New Identity" context projects/torbrowser/design/index.html.en 1377) menu option in Torbutton. This context menu option is active if Torbutton can projects/torbrowser/design/index.html.en 1378) read the environment variables $TOR_CONTROL_PASSWD and $TOR_CONTROL_PORT.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1379)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1380) </p><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp60545136"></a>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote">`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1381)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1382) All linkable identifiers and browser state MUST be cleared by this feature.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1383)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1384) </blockquote></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp60546384"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1385)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1386) First, Torbutton disables Javascript in all open tabs and windows by using`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1387) both the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIDocShell#Attributes" target="_top">browser.docShell.allowJavascript</a> projects/torbrowser/design/index.html.en 1388) attribute as well as <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIDOMWindowUtils#suppressEventHandling%28%29" target="_top">nsIDOMWindowUtil.suppressEventHandling()</a>. projects/torbrowser/design/index.html.en 1389) We then stop all page activity for each tab using <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIWebNavigation#stop%28%29" target="_top">browser.webNavigation.stop(nsIWebNavigation.STOP_ALL)</a>.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1390) We then clear the site-specific Zoom by temporarily disabling the preference`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1391) <span class="command"><strong>browser.zoom.siteSpecific</strong></span>, and clear the GeoIP wifi token URL projects/torbrowser/design/index.html.en 1392) <span class="command"><strong>geo.wifi.access_token</strong></span> and the last opened URL prefs (if projects/torbrowser/design/index.html.en 1393) they exist). Each tab is then closed.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1394)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1395) </p><p>`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1396)`
TBB design doc: More review... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1397) After closing all tabs, we then emit "<a class="ulink" href="https://developer.mozilla.org/en-US/docs/Supporting_private_browsing_mode#Private_browsing_notifications" target="_top">browser:purge-session-history</a>" projects/torbrowser/design/index.html.en 1398) (which instructs addons and various Firefox components to clear their session projects/torbrowser/design/index.html.en 1399) state), and then manually clear the following state: searchbox and findbox projects/torbrowser/design/index.html.en 1400) text, HTTP auth, SSL state, OCSP state, site-specific content preferences
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1401) (including HSTS state), content and image cache, offline cache, offline projects/torbrowser/design/index.html.en 1402) storage, Cookies, crypto tokens, DOM storage, the safe browsing key, and the`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1403) Google wifi geolocation token (if it exists). We also clear NoScript's site`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1404) and temporary permissions, and all other browser site permissions.`
Add design doc draft. Mike Perry authored 12 years ago	`projects/en/torbrowser/design/index.html.en 1405)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1406) </p><p>`
Update TBB design doc based... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1407)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1408) After the state is cleared, we then close all remaining HTTP keep-alive projects/torbrowser/design/index.html.en 1409) connections and then send the NEWNYM signal to the Tor control port to cause a projects/torbrowser/design/index.html.en 1410) new circuit to be created. projects/torbrowser/design/index.html.en 1411) </p><p> projects/torbrowser/design/index.html.en 1412) Finally, a fresh browser window is opened, and the current browser window is`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1413) closed (this does not spawn a new Firefox process, only a new window).`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1414) </p></blockquote></div><div class="blockquote"><blockquote class="blockquote"> projects/torbrowser/design/index.html.en 1415) If the user chose to "protect" any cookies by using the Torbutton Cookie projects/torbrowser/design/index.html.en 1416) Protections UI, those cookies are not cleared as part of the above.`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1417) </blockquote></div></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="other-security"></a>4.8. Other Security Measures</h3></div></div></div><p>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1418) projects/torbrowser/design/index.html.en 1419) In addition to the above mechanisms that are devoted to preserving privacy projects/torbrowser/design/index.html.en 1420) while browsing, we also have a number of technical mechanisms to address other projects/torbrowser/design/index.html.en 1421) privacy and security issues. projects/torbrowser/design/index.html.en 1422)`
Update design document base... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1423) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a id="security-slider"></a><span class="command"><strong>Security Slider</strong></span><p> projects/torbrowser/design/index.html.en 1424) projects/torbrowser/design/index.html.en 1425) In order to provide vulnerability surface reduction for users that need high projects/torbrowser/design/index.html.en 1426) security, we have implemented a "Security Slider" that essentially represents a projects/torbrowser/design/index.html.en 1427) tradeoff between usability and security. Using metrics collected from
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1428) Mozilla's bug tracker, we analyzed the vulnerability counts of core components,`
Update design document base... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1429) and used <a class="ulink" href="https://github.com/iSECPartners/publications/tree/master/reports/Tor%20Browser%20Bundle" target="_top">information projects/torbrowser/design/index.html.en 1430) gathered from a study performed by iSec Partners</a> to inform which projects/torbrowser/design/index.html.en 1431) features should be disabled at which security levels. projects/torbrowser/design/index.html.en 1432) projects/torbrowser/design/index.html.en 1433) </p><p> projects/torbrowser/design/index.html.en 1434) projects/torbrowser/design/index.html.en 1435) The Security Slider consists of four positions. At the lowest security level projects/torbrowser/design/index.html.en 1436) (the default), we disable projects/torbrowser/design/index.html.en 1437) <span class="command"><strong>gfx.font_rendering.graphite.enabled</strong></span> for Latin locales, as projects/torbrowser/design/index.html.en 1438) well as <span class="command"><strong>gfx.font_rendering.graphite.enabled</strong></span>. At the projects/torbrowser/design/index.html.en 1439) medium-low level, we disable most Javascript JIT and related optimizations projects/torbrowser/design/index.html.en 1440) (<span class="command"><strong>javascript.options.ion.content</strong></span>, projects/torbrowser/design/index.html.en 1441) <span class="command"><strong>javascript.options.typeinference</strong></span>, projects/torbrowser/design/index.html.en 1442) <span class="command"><strong>javascript.options.asmjs</strong></span>). We also make HTML5 media projects/torbrowser/design/index.html.en 1443) click-to-play (<span class="command"><strong>noscript.forbidMedia</strong></span>), and disable WebAudio projects/torbrowser/design/index.html.en 1444) (<span class="command"><strong>media.webaudio.enabled</strong></span>). At the medium-high level, we projects/torbrowser/design/index.html.en 1445) disable the baseline JIT projects/torbrowser/design/index.html.en 1446) (<span class="command"><strong>javascript.options.baselinejit.content</strong></span>), disable projects/torbrowser/design/index.html.en 1447) Javascript entirely all elements that are loaded when the URL bar is not projects/torbrowser/design/index.html.en 1448) HTTPS (<span class="command"><strong>noscript.globalHttpsWhitelist</strong></span>), and fully disable projects/torbrowser/design/index.html.en 1449) graphite font rendering for all locales projects/torbrowser/design/index.html.en 1450) (<span class="command"><strong>gfx.font_rendering.graphite.enable</strong></span>). At the highest level, projects/torbrowser/design/index.html.en 1451) Javascript is fully disabled (<span class="command"><strong>noscript.global</strong></span>), as well as projects/torbrowser/design/index.html.en 1452) all non-WebM HTML5 codecs (<span class="command"><strong>media.ogg.enabled</strong></span>, projects/torbrowser/design/index.html.en 1453) <span class="command"><strong>media.opus.enabled</strong></span>, <span class="command"><strong>media.opus.enabled</strong></span>, projects/torbrowser/design/index.html.en 1454) <span class="command"><strong>media.DirectShow.enabled</strong></span>, projects/torbrowser/design/index.html.en 1455) <span class="command"><strong>media.wave.enabled</strong></span>, and projects/torbrowser/design/index.html.en 1456) <span class="command"><strong>media.apple.mp3.enabled</strong></span>). projects/torbrowser/design/index.html.en 1457) projects/torbrowser/design/index.html.en 1458) </p></li><li class="listitem"><a id="traffic-fingerprinting-defenses"></a><span class="command"><strong>Website Traffic Fingerprinting Defenses</strong></span><p>
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1459) projects/torbrowser/design/index.html.en 1460) <a class="link" href="#website-traffic-fingerprinting">Website Traffic projects/torbrowser/design/index.html.en 1461) Fingerprinting</a> is a statistical attack to attempt to recognize specific projects/torbrowser/design/index.html.en 1462) encrypted website activity. projects/torbrowser/design/index.html.en 1463)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1464) </p><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp60574784"></a>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"><p>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1465)`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1466) We want to deploy a mechanism that reduces the accuracy of <a class="ulink" href="https://en.wikipedia.org/wiki/Feature_selection" target="_top">useful features</a> available`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1467) for classification. This mechanism would either impact the true and false projects/torbrowser/design/index.html.en 1468) positive accuracy rates, <span class="emphasis"><em>or</em></span> reduce the number of webpages projects/torbrowser/design/index.html.en 1469) that could be classified at a given accuracy rate. projects/torbrowser/design/index.html.en 1470) projects/torbrowser/design/index.html.en 1471) </p><p> projects/torbrowser/design/index.html.en 1472) projects/torbrowser/design/index.html.en 1473) Ideally, this mechanism would be as light-weight as possible, and would be projects/torbrowser/design/index.html.en 1474) tunable in terms of overhead. We suspect that it may even be possible to projects/torbrowser/design/index.html.en 1475) deploy a mechanism that reduces feature extraction resolution without any projects/torbrowser/design/index.html.en 1476) network overhead. In the no-overhead category, we have <a class="ulink" href="http://freehaven.net/anonbib/cache/LZCLCP_NDSS11.pdf" target="_top">HTTPOS</a> and projects/torbrowser/design/index.html.en 1477) <a class="ulink" href="https://blog.torproject.org/blog/experimental-defense-website-traffic-fingerprinting" target="_top">better
TBB Design Doc: Mention use... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1478) use of HTTP pipelining and/or SPDY</a>. projects/torbrowser/design/index.html.en 1479) In the tunable/low-overhead`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1480) category, we have <a class="ulink" href="http://freehaven.net/anonbib/cache/ShWa-Timing06.pdf" target="_top">Adaptive projects/torbrowser/design/index.html.en 1481) Padding</a> and <a class="ulink" href="http://www.cs.sunysb.edu/~xcai/fp.pdf" target="_top"> projects/torbrowser/design/index.html.en 1482) Congestion-Sensitive BUFLO</a>. It may be also possible to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/7028" target="_top">tune such projects/torbrowser/design/index.html.en 1483) defenses</a> such that they only use existing spare Guard bandwidth capacity in the Tor
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1484) network, making them also effectively no-overhead.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1485)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1486) </p></blockquote></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp60581680"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"><p>`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1487) Currently, we patch Firefox to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/27ef32d509ed1c9eeb28f7affee0f9ba11773f72" target="_top">randomize`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1488) pipeline order and depth</a>. Unfortunately, pipelining is very fragile. projects/torbrowser/design/index.html.en 1489) Many sites do not support it, and even sites that advertise support for projects/torbrowser/design/index.html.en 1490) pipelining may simply return error codes for successive requests, effectively projects/torbrowser/design/index.html.en 1491) forcing the browser into non-pipelined behavior. Firefox also has code to back projects/torbrowser/design/index.html.en 1492) off and reduce or eliminate the pipeline if this happens. These projects/torbrowser/design/index.html.en 1493) shortcomings and fallback behaviors are the primary reason that Google
TBB Design Doc: Mention use... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1494) developed SPDY as opposed simply extending HTTP to improve pipelining. It projects/torbrowser/design/index.html.en 1495) turns out that we could actually deploy exit-side proxies that allow us to projects/torbrowser/design/index.html.en 1496) <a class="ulink" href="https://gitweb.torproject.org/torspec.git/blob/HEAD:/proposals/ideas/xxx-using-spdy.txt" target="_top">use projects/torbrowser/design/index.html.en 1497) SPDY from the client to the exit node</a>. This would make our defense not projects/torbrowser/design/index.html.en 1498) only free, but one that actually <span class="emphasis"><em>improves</em></span> performance.
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1499) projects/torbrowser/design/index.html.en 1500) </p><p> projects/torbrowser/design/index.html.en 1501)`
TBB design doc: Clarify web... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1502) Knowing this, we created this defense as an <a class="ulink" href="https://blog.torproject.org/blog/experimental-defense-website-traffic-fingerprinting" target="_top">experimental`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1503) research prototype</a> to help evaluate what could be done in the best`
TBB design doc: Clarify web... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1504) case with full server support. Unfortunately, the bias in favor of compelling projects/torbrowser/design/index.html.en 1505) attack papers has caused academia to ignore this request thus far, instead projects/torbrowser/design/index.html.en 1506) publishing only cursory (yet "devastating") evaluations that fail to provide projects/torbrowser/design/index.html.en 1507) even simple statistics such as the rates of actual pipeline utilization during projects/torbrowser/design/index.html.en 1508) their evaluations, in addition to the other shortcomings and shortcuts <a class="link" href="#website-traffic-fingerprinting">mentioned earlier</a>. We can projects/torbrowser/design/index.html.en 1509) accept that our defense might fail to work as well as others (in fact we projects/torbrowser/design/index.html.en 1510) expect it), but unfortunately the very same shortcuts that provide excellent projects/torbrowser/design/index.html.en 1511) attack results also allow the conclusion that all defenses are broken forever. projects/torbrowser/design/index.html.en 1512) So sadly, we are still left in the dark on this point.
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1513) projects/torbrowser/design/index.html.en 1514) </p></blockquote></div></div></li><li class="listitem"><span class="command"><strong>Privacy-preserving update notification</strong></span><p> projects/torbrowser/design/index.html.en 1515) projects/torbrowser/design/index.html.en 1516) In order to inform the user when their Tor Browser is out of date, we perform a`
TBB design doc: Clarify web... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1517) privacy-preserving update check asynchronously in the background. The`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1518) check uses Tor to download the file <a class="ulink" href="https://check.torproject.org/RecommendedTBBVersions" target="_top">https://check.torproject.org/RecommendedTBBVersions</a> projects/torbrowser/design/index.html.en 1519) and searches that version list for the current value for the local preference projects/torbrowser/design/index.html.en 1520) <span class="command"><strong>torbrowser.version</strong></span>. If the value from our preference is projects/torbrowser/design/index.html.en 1521) present in the recommended version list, the check is considered to have projects/torbrowser/design/index.html.en 1522) succeeded and the user is up to date. If not, it is considered to have failed projects/torbrowser/design/index.html.en 1523) and an update is needed. The check is triggered upon browser launch, new projects/torbrowser/design/index.html.en 1524) window, and new tab, but is rate limited so as to happen no more frequently projects/torbrowser/design/index.html.en 1525) than once every 1.5 hours. projects/torbrowser/design/index.html.en 1526) projects/torbrowser/design/index.html.en 1527) </p><p> projects/torbrowser/design/index.html.en 1528) projects/torbrowser/design/index.html.en 1529) If the check fails, we cache this fact, and update the Torbutton graphic to projects/torbrowser/design/index.html.en 1530) display a flashing warning icon and insert a menu option that provides a link projects/torbrowser/design/index.html.en 1531) to our download page. Additionally, we reset the value for the browser projects/torbrowser/design/index.html.en 1532) homepage to point to a <a class="ulink" href="https://check.torproject.org/?lang=en-US&small=1&uptodate=0" target="_top">page that projects/torbrowser/design/index.html.en 1533) informs the user</a> that their browser is out of projects/torbrowser/design/index.html.en 1534) date. projects/torbrowser/design/index.html.en 1535)
Update design document base... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1536) </p><p> projects/torbrowser/design/index.html.en 1537) projects/torbrowser/design/index.html.en 1538) We also make use of the in-browser Mozilla updater, and have <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commitdiff/777695d09e3cff4c79c48839e1c9d5102b772d6f" target="_top">patched projects/torbrowser/design/index.html.en 1539) the updater</a> to avoid sending OS and Kernel version information as part projects/torbrowser/design/index.html.en 1540) of its update pings. projects/torbrowser/design/index.html.en 1541)
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1542) </p></li></ol></div></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="BuildSecurity"></a>5. Build Security and Package Integrity</h2></div></div></div><p>`
Update TBB design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1543)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1544) In the age of state-sponsored malware, <a class="ulink" href="https://blog.torproject.org/blog/deterministic-builds-part-one-cyberwar-and-global-compromise" target="_top">we projects/torbrowser/design/index.html.en 1545) believe</a> it is impossible to expect to keep a single build machine or projects/torbrowser/design/index.html.en 1546) software signing key secure, given the class of adversaries that Tor has to projects/torbrowser/design/index.html.en 1547) contend with. For this reason, we have deployed a build system projects/torbrowser/design/index.html.en 1548) that allows anyone to use our source code to reproduce byte-for-byte identical projects/torbrowser/design/index.html.en 1549) binary packages to the ones that we distribute.
Update TBB design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1550)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1551) </p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="idp60597904"></a>5.1. Achieving Binary Reproducibility</h3></div></div></div><p>`
Update TBB design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1552)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1553) The GNU toolchain has been working on providing reproducible builds for some projects/torbrowser/design/index.html.en 1554) time, however a large software project such as Firefox typically ends up projects/torbrowser/design/index.html.en 1555) embedding a large number of details about the machine it was built on, both projects/torbrowser/design/index.html.en 1556) intentionally and inadvertently. Additionally, manual changes to the build projects/torbrowser/design/index.html.en 1557) machine configuration can accumulate over time and are difficult for others to projects/torbrowser/design/index.html.en 1558) replicate externally, which leads to difficulties with binary reproducibility.
Update TBB design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1559)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1560) </p><p> projects/torbrowser/design/index.html.en 1561) For this reason, we decided to leverage the work done by the <a class="ulink" href="http://gitian.org/" target="_top">Gitian Project</a> from the Bitcoin community. projects/torbrowser/design/index.html.en 1562) Gitian is a wrapper around Ubuntu's virtualization tools that allows you to projects/torbrowser/design/index.html.en 1563) specify an Ubuntu version, architecture, a set of additional packages, a set projects/torbrowser/design/index.html.en 1564) of input files, and a bash build scriptlet in an YAML document called a projects/torbrowser/design/index.html.en 1565) "Gitian Descriptor". This document is used to install a qemu-kvm image, and projects/torbrowser/design/index.html.en 1566) execute your build scriptlet inside it. projects/torbrowser/design/index.html.en 1567) </p><p>
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1568)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1569) We have created a <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/refs/heads/master" target="_top">set projects/torbrowser/design/index.html.en 1570) of wrapper scripts</a> around Gitian to automate dependency download and projects/torbrowser/design/index.html.en 1571) authentication, as well as transfer intermediate build outputs between the projects/torbrowser/design/index.html.en 1572) stages of the build process. Because Gitian creates an Ubuntu build projects/torbrowser/design/index.html.en 1573) environment, we must use cross-compilation to create packages for Windows and projects/torbrowser/design/index.html.en 1574) Mac OS. For Windows, we use mingw-w64 as our cross compiler. For Mac OS, we
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1575) use crosstools-ng in combination with a binary redistribution of the Mac OS 10.6`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1576) SDK.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1577)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1578) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1579)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1580) The use of the Gitian system eliminates build non-determinism by normalizing projects/torbrowser/design/index.html.en 1581) the build environment's hostname, username, build path, uname output, projects/torbrowser/design/index.html.en 1582) toolchain versions, and time. On top of what Gitian provides, we also had to projects/torbrowser/design/index.html.en 1583) address the following additional sources of non-determinism:`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1584)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1585) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Filesystem and archive reordering projects/torbrowser/design/index.html.en 1586) <p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1587)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1588) The most prevalent source of non-determinism in the components of Tor Browser projects/torbrowser/design/index.html.en 1589) by far was various ways that archives (such as zip, tar, jar/ja, DMG, and projects/torbrowser/design/index.html.en 1590) Firefox manifest lists) could be reordered. Many file archivers walk the projects/torbrowser/design/index.html.en 1591) filesystem in inode structure order by default, which will result in ordering projects/torbrowser/design/index.html.en 1592) differences between two different archive invocations, especially on machines projects/torbrowser/design/index.html.en 1593) of different disk and hardware configurations.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1594)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1595) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1596)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1597) The fix for this is to perform an additional sorting step on the input list projects/torbrowser/design/index.html.en 1598) for archives, but care must be taken to instruct libc and other sorting routines projects/torbrowser/design/index.html.en 1599) to use a fixed locale to determine lexicographic ordering, or machines with projects/torbrowser/design/index.html.en 1600) different locale settings will produce different sort results. We chose the projects/torbrowser/design/index.html.en 1601) 'C' locale for this purpose. We created wrapper scripts for <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/blob/HEAD:/gitian/build-helpers/dtar.sh" target="_top">tar</a>, projects/torbrowser/design/index.html.en 1602) <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/blob/HEAD:/gitian/build-helpers/dzip.sh" target="_top">zip</a>, projects/torbrowser/design/index.html.en 1603) and <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/blob/HEAD:/gitian/build-helpers/ddmg.sh" target="_top">DMG</a> projects/torbrowser/design/index.html.en 1604) to aid in reproducible archive creation. projects/torbrowser/design/index.html.en 1605) projects/torbrowser/design/index.html.en 1606) </p></li><li class="listitem">Uninitialized memory in toolchain/archivers projects/torbrowser/design/index.html.en 1607) <p> projects/torbrowser/design/index.html.en 1608) projects/torbrowser/design/index.html.en 1609) We ran into difficulties with both binutils and the DMG archive script using projects/torbrowser/design/index.html.en 1610) uninitialized memory in certain data structures that ended up written to disk. projects/torbrowser/design/index.html.en 1611) Our binutils fixes were merged upstream, but the DMG archive fix remains an projects/torbrowser/design/index.html.en 1612) <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/blob/HEAD:/gitian/patches/libdmg.patch" target="_top">independent projects/torbrowser/design/index.html.en 1613) patch</a>. projects/torbrowser/design/index.html.en 1614) projects/torbrowser/design/index.html.en 1615) </p></li><li class="listitem">Fine-grained timestamps and timezone leaks projects/torbrowser/design/index.html.en 1616) <p> projects/torbrowser/design/index.html.en 1617) projects/torbrowser/design/index.html.en 1618) The standard way of controlling timestamps in Gitian is to use libfaketime, projects/torbrowser/design/index.html.en 1619) which hooks time-related library calls to provide a fixed timestamp. However,
Update design document base... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1620) due to our use of wine to run py2exe for python-based pluggable transports, projects/torbrowser/design/index.html.en 1621) pyc timestamps had to be address with an additional <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/blob/HEAD:/gitian/build-helpers/pyc-timestamp.sh" target="_top">helper projects/torbrowser/design/index.html.en 1622) script</a>. The timezone leaks were addressed by setting the projects/torbrowser/design/index.html.en 1623) <span class="command"><strong>TZ</strong></span> environment variable to UTC in our descriptors.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1624)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1625) </p></li><li class="listitem">Deliberately generated entropy projects/torbrowser/design/index.html.en 1626) <p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1627)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1628) In two circumstances, deliberately generated entropy was introduced in various projects/torbrowser/design/index.html.en 1629) components of the build process. First, the BuildID Debuginfo identifier projects/torbrowser/design/index.html.en 1630) (which associates detached debug files with their corresponding stripped projects/torbrowser/design/index.html.en 1631) executables) was introducing entropy from some unknown source. We removed this projects/torbrowser/design/index.html.en 1632) header using objcopy invocations in our build scriptlets, and opted to use GNU projects/torbrowser/design/index.html.en 1633) DebugLink instead of BuildID for this association.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1634)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1635) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1636)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1637) Second, on Linux, Firefox builds detached signatures of its cryptographic projects/torbrowser/design/index.html.en 1638) libraries using a temporary key for FIPS-140 certification. A rather insane projects/torbrowser/design/index.html.en 1639) subsection of the FIPS-140 certification standard requires that you distribute projects/torbrowser/design/index.html.en 1640) signatures for all of your cryptographic libraries. The Firefox build process projects/torbrowser/design/index.html.en 1641) meets this requirement by generating a temporary key, using it to sign the projects/torbrowser/design/index.html.en 1642) libraries, and discarding the private portion of that key. Because there are projects/torbrowser/design/index.html.en 1643) many other ways to intercept the crypto outside of modifying the actual DLL projects/torbrowser/design/index.html.en 1644) images, we opted to simply remove these signature files from distribution. projects/torbrowser/design/index.html.en 1645) There simply is no way to verify code integrity on a running system without projects/torbrowser/design/index.html.en 1646) both OS and co-processor assistance. Download package signatures make sense of projects/torbrowser/design/index.html.en 1647) course, but we handle those another way (as mentioned above).
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1648) projects/torbrowser/design/index.html.en 1649)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1650) </p></li><li class="listitem">LXC-specific leaks projects/torbrowser/design/index.html.en 1651) <p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1652)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1653) Gitian provides an option to use LXC containers instead of full qemu-kvm projects/torbrowser/design/index.html.en 1654) virtualization. Unfortunately, these containers can allow additional details projects/torbrowser/design/index.html.en 1655) about the host OS to leak. In particular, umask settings as well as the projects/torbrowser/design/index.html.en 1656) hostname and Linux kernel version can leak from the host OS into the LXC projects/torbrowser/design/index.html.en 1657) container. We addressed umask by setting it explicitly in our Gitian projects/torbrowser/design/index.html.en 1658) descriptor scriptlet, and addressed the hostname and kernel version leaks by projects/torbrowser/design/index.html.en 1659) directly patching the aspects of the Firefox build process that included this
Update design document base... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1660) information into the build. It also turns out that some libraries (in projects/torbrowser/design/index.html.en 1661) particular: libgmp) attempt to detect the current CPU to determine which projects/torbrowser/design/index.html.en 1662) optimizations to compile in. This CPU type is uniform on our KVM instances, projects/torbrowser/design/index.html.en 1663) but differs under LXC. We are also investigating currently <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/12239" target="_top">unknown sources of projects/torbrowser/design/index.html.en 1664) unitialized memory</a> that only appear in LXC mode, as well as projects/torbrowser/design/index.html.en 1665) <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/12240" target="_top">oddities related to projects/torbrowser/design/index.html.en 1666) time-based dependency tracking</a> that only appear in LXC containers. projects/torbrowser/design/index.html.en 1667)
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1668) </p></li></ol></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="idp60632800"></a>5.2. Package Signatures and Verification</h3></div></div></div><p>`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1669) projects/torbrowser/design/index.html.en 1670) The build process produces a single sha256sums.txt file that contains a sorted`
Update design document base... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1671) list of the SHA-256 hashes of every package produced for that build version. Each`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1672) official builder uploads this file and a GPG signature of it to a directory projects/torbrowser/design/index.html.en 1673) on a Tor Project's web server. The build scripts have an optional matching projects/torbrowser/design/index.html.en 1674) step that downloads these signatures, verifies them, and ensures that the projects/torbrowser/design/index.html.en 1675) local builds match this file.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1676)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1677) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1678)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1679) When builds are published officially, the single sha256sums.txt file is projects/torbrowser/design/index.html.en 1680) accompanied by a detached GPG signature from each official builder that projects/torbrowser/design/index.html.en 1681) produced a matching build. The packages are additionally signed with detached projects/torbrowser/design/index.html.en 1682) GPG signatures from an official signing key.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1683)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1684) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1685)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1686) The fact that the entire set of packages for a given version can be projects/torbrowser/design/index.html.en 1687) authenticated by a single hash of the sha256sums.txt file will also allow us projects/torbrowser/design/index.html.en 1688) to create a number of auxiliary authentication mechanisms for our packages, projects/torbrowser/design/index.html.en 1689) beyond just trusting a single offline build machine and a single cryptographic projects/torbrowser/design/index.html.en 1690) key's integrity. Interesting examples include providing multiple independent projects/torbrowser/design/index.html.en 1691) cryptographic signatures for packages, listing the package hashes in the Tor projects/torbrowser/design/index.html.en 1692) consensus, and encoding the package hashes in the Bitcoin blockchain.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1693)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1694) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1695)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1696) At the time of this writing, we do not yet support native code signing for Mac projects/torbrowser/design/index.html.en 1697) OS or Windows. Because these signatures are embedded in the actual packages, projects/torbrowser/design/index.html.en 1698) and by their nature are based on non-public key material, providing native projects/torbrowser/design/index.html.en 1699) code-signed packages while still preserving ease of reproducibility projects/torbrowser/design/index.html.en 1700) verification has not yet been achieved.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1701)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1702) </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="idp60636736"></a>5.3. Anonymous Verification</h3></div></div></div><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1703)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1704) Due to the fact that bit-identical packages can be produced by anyone, the projects/torbrowser/design/index.html.en 1705) security of this build system extends beyond the security of the official projects/torbrowser/design/index.html.en 1706) build machines. In fact, it is still possible for build integrity to be projects/torbrowser/design/index.html.en 1707) achieved even if all official build machines are compromised.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1708)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1709) </p><p>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1710)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1711) By default, all tor-specific dependencies and inputs to the build process are projects/torbrowser/design/index.html.en 1712) downloaded over Tor, which allows build verifiers to remain anonymous and projects/torbrowser/design/index.html.en 1713) hidden. Because of this, any individual can use our anonymity network to projects/torbrowser/design/index.html.en 1714) privately download our source code, verify it against public signed, audited, projects/torbrowser/design/index.html.en 1715) and mirrored git repositories, and reproduce our builds exactly, without being projects/torbrowser/design/index.html.en 1716) subject to targeted attacks. If they notice any differences, they can alert projects/torbrowser/design/index.html.en 1717) the public builders/signers, hopefully using a pseudonym or our anonymous
Updates to fingerprinting s... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1718) bug tracker account, to avoid revealing the fact that they are a build`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1719) verifier.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1720)`
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1721) </p></div></div><div class="appendix"><h2 class="title" style="clear: both"><a id="Transparency"></a>A. Towards Transparency in Navigation Tracking</h2><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1722) projects/torbrowser/design/index.html.en 1723) The <a class="link" href="#privacy" title="2.2. Privacy Requirements">privacy properties</a> of Tor Browser are based projects/torbrowser/design/index.html.en 1724) upon the assumption that link-click navigation indicates user consent to projects/torbrowser/design/index.html.en 1725) tracking between the linking site and the destination site. While this projects/torbrowser/design/index.html.en 1726) definition is sufficient to allow us to eliminate cross-site third party projects/torbrowser/design/index.html.en 1727) tracking with only minimal site breakage, it is our long-term goal to further projects/torbrowser/design/index.html.en 1728) reduce cross-origin click navigation tracking to mechanisms that are projects/torbrowser/design/index.html.en 1729) detectable by attentive users, so they can alert the general public if projects/torbrowser/design/index.html.en 1730) cross-origin click navigation tracking is happening where it should not be. projects/torbrowser/design/index.html.en 1731) projects/torbrowser/design/index.html.en 1732) </p><p> projects/torbrowser/design/index.html.en 1733) projects/torbrowser/design/index.html.en 1734) In an ideal world, the mechanisms of tracking that can be employed during a projects/torbrowser/design/index.html.en 1735) link click would be limited to the contents of URL parameters and other projects/torbrowser/design/index.html.en 1736) properties that are fully visible to the user before they click. However, the projects/torbrowser/design/index.html.en 1737) entrenched nature of certain archaic web features make it impossible for us to projects/torbrowser/design/index.html.en 1738) achieve this transparency goal by ourselves without substantial site breakage. projects/torbrowser/design/index.html.en 1739) So, instead we maintain a <a class="link" href="#deprecate" title="A.1. Deprecation Wishlist">Deprecation projects/torbrowser/design/index.html.en 1740) Wishlist</a> of archaic web technologies that are currently being (ab)used projects/torbrowser/design/index.html.en 1741) to facilitate federated login and other legitimate click-driven cross-domain projects/torbrowser/design/index.html.en 1742) activity but that can one day be replaced with more privacy friendly, projects/torbrowser/design/index.html.en 1743) auditable alternatives. projects/torbrowser/design/index.html.en 1744) projects/torbrowser/design/index.html.en 1745) </p><p> projects/torbrowser/design/index.html.en 1746) projects/torbrowser/design/index.html.en 1747) Because the total elimination of side channels during cross-origin navigation projects/torbrowser/design/index.html.en 1748) will undoubtedly break federated login as well as destroy ad revenue, we projects/torbrowser/design/index.html.en 1749) also describe auditable alternatives and promising web draft standards that would projects/torbrowser/design/index.html.en 1750) preserve this functionality while still providing transparency when tracking is projects/torbrowser/design/index.html.en 1751) occurring. projects/torbrowser/design/index.html.en 1752)
Update design doc for TBB 4.0. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1753) </p><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="deprecate"></a>A.1. Deprecation Wishlist</h2></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">The Referer Header`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1754) <p> projects/torbrowser/design/index.html.en 1755)`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1756) We haven't disabled or restricted the Referer ourselves because of the projects/torbrowser/design/index.html.en 1757) non-trivial number of sites that rely on the Referer header to "authenticate"`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1758) image requests and deep-link navigation on their sites. Furthermore, there projects/torbrowser/design/index.html.en 1759) seems to be no real privacy benefit to taking this action by itself in a`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1760) vacuum, because many sites have begun encoding Referer URL information into`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1761) GET parameters when they need it to cross http to https scheme transitions. projects/torbrowser/design/index.html.en 1762) Google's +1 buttons are the best example of this activity. projects/torbrowser/design/index.html.en 1763) projects/torbrowser/design/index.html.en 1764) </p><p> projects/torbrowser/design/index.html.en 1765) projects/torbrowser/design/index.html.en 1766) Because of the availability of these other explicit vectors, we believe the`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1767) main risk of the Referer header is through inadvertent and/or covert data`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1768) leakage. In fact, <a class="ulink" href="http://www2.research.att.com/~bala/papers/wosn09.pdf" target="_top">a great deal of`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1769) personal data</a> is inadvertently leaked to third parties through the projects/torbrowser/design/index.html.en 1770) source URL parameters. projects/torbrowser/design/index.html.en 1771) projects/torbrowser/design/index.html.en 1772) </p><p> projects/torbrowser/design/index.html.en 1773)`
Update design document base... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1774) We believe the Referer header should be made explicit, and believe that CSP projects/torbrowser/design/index.html.en 1775) 2.0 provides a <a class="ulink" href="http://www.w3.org/TR/CSP11/#directive-referrer" target="_top">decent step in this projects/torbrowser/design/index.html.en 1776) direction</a>. If a site wishes to transmit its URL to third party content projects/torbrowser/design/index.html.en 1777) elements during load or during link-click, it should have to specify this as a projects/torbrowser/design/index.html.en 1778) property of the associated HTML tag or CSP policy. With an explicit property projects/torbrowser/design/index.html.en 1779) or policy, it would then be possible for the user agent to inform the user if projects/torbrowser/design/index.html.en 1780) they are about to click on a link that will transmit Referer information projects/torbrowser/design/index.html.en 1781) (perhaps through something as subtle as a different color in the lower toolbar projects/torbrowser/design/index.html.en 1782) for the destination URL). This same UI notification can also be used for links projects/torbrowser/design/index.html.en 1783) with the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/HTML/Element/a#Attributes" target="_top">"ping"</a>
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1784) attribute. projects/torbrowser/design/index.html.en 1785) projects/torbrowser/design/index.html.en 1786) </p></li><li class="listitem">window.name projects/torbrowser/design/index.html.en 1787) <p>`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1788) <a class="ulink" href="https://developer.mozilla.org/En/DOM/Window.name" target="_top">window.name</a> is`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1789) a DOM property that for some reason is allowed to retain a persistent value projects/torbrowser/design/index.html.en 1790) for the lifespan of a browser tab. It is possible to utilize this property for`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1791) <a class="ulink" href="http://www.thomasfrank.se/sessionvars.html" target="_top">identifier`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1792) storage</a> during click navigation. This is sometimes used for additional projects/torbrowser/design/index.html.en 1793) XSRF protection and federated login. projects/torbrowser/design/index.html.en 1794) </p><p> projects/torbrowser/design/index.html.en 1795) projects/torbrowser/design/index.html.en 1796) It's our opinion that the contents of window.name should not be preserved for projects/torbrowser/design/index.html.en 1797) cross-origin navigation, but doing so may break federated login for some sites. projects/torbrowser/design/index.html.en 1798) projects/torbrowser/design/index.html.en 1799) </p></li><li class="listitem">Javascript link rewriting projects/torbrowser/design/index.html.en 1800) <p> projects/torbrowser/design/index.html.en 1801) projects/torbrowser/design/index.html.en 1802) In general, it should not be possible for onclick handlers to alter the projects/torbrowser/design/index.html.en 1803) navigation destination of 'a' tags, silently transform them into POST projects/torbrowser/design/index.html.en 1804) requests, or otherwise create situations where a user believes they are projects/torbrowser/design/index.html.en 1805) clicking on a link leading to one URL that ends up on another. This projects/torbrowser/design/index.html.en 1806) functionality is deceptive and is frequently a vector for malware and phishing projects/torbrowser/design/index.html.en 1807) attacks. Unfortunately, many legitimate sites also employ such transparent projects/torbrowser/design/index.html.en 1808) link rewriting, and blanket disabling this functionality ourselves will simply projects/torbrowser/design/index.html.en 1809) cause Tor Browser to fail to navigate properly on these sites. projects/torbrowser/design/index.html.en 1810) projects/torbrowser/design/index.html.en 1811) </p><p> projects/torbrowser/design/index.html.en 1812) projects/torbrowser/design/index.html.en 1813) Automated cross-origin redirects are one form of this behavior that is
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1814) possible for us to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3600" target="_top">address`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1815) ourselves</a>, as they are comparatively rare and can be handled with site projects/torbrowser/design/index.html.en 1816) permissions. projects/torbrowser/design/index.html.en 1817)`
More fingerprinting clarifi... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1818) </p></li></ol></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="idp60669376"></a>A.2. Promising Standards</h2></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="ulink" href="http://web-send.org" target="_top">Web-Send Introducer</a><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1819) projects/torbrowser/design/index.html.en 1820) Web-Send is a browser-based link sharing and federated login widget that is projects/torbrowser/design/index.html.en 1821) designed to operate without relying on third-party tracking or abusing other`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1822) cross-origin link-click side channels. It has a compelling list of <a class="ulink" href="http://web-send.org/features.html" target="_top">privacy and security features</a>,`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1823) especially if used as a "Like button" replacement. projects/torbrowser/design/index.html.en 1824)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1825) </p></li><li class="listitem"><a class="ulink" href="https://developer.mozilla.org/en-US/docs/Persona" target="_top">Mozilla Persona</a><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1826) projects/torbrowser/design/index.html.en 1827) Mozilla's Persona is designed to provide decentralized, cryptographically projects/torbrowser/design/index.html.en 1828) authenticated federated login in a way that does not expose the user to third projects/torbrowser/design/index.html.en 1829) party tracking or require browser redirects or side channels. While it does projects/torbrowser/design/index.html.en 1830) not directly provide the link sharing capabilities that Web-Send does, it is a projects/torbrowser/design/index.html.en 1831) better solution to the privacy issues associated with federated login than projects/torbrowser/design/index.html.en 1832) Web-Send is. projects/torbrowser/design/index.html.en 1833)