projects/torbrowser/design/index.html.en (2b143bac2) - tor-webwml.git

2b143bac2753100c1312719048341416a7271183

Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1) <?xml version="1.0" encoding="UTF-8"?>`
Update Tor Browser design doc. 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">May 6th, 2015</p></div></div><hr /></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="#idp54432272">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="#idp56215504">5.1. Achieving Binary Reproducibility</a></span></dt><dt><span class="sect2"><a href="#idp56237264">5.2. Package Signatures and Verification</a></span></dt><dt><span class="sect2"><a href="#idp56241792">5.3. Anonymous Verification</a></span></dt><dt><span class="sect2"><a href="#update-safety">5.4. Update Safety</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="#idp56278768">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="idp54432272"></a>1. Introduction</h2></div></div></div><p>
Add design doc draft. Mike Perry authored 13 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 Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 6) 4.5.`
Add design doc draft. Mike Perry authored 13 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 13 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 13 years ago	`projects/en/torbrowser/design/index.html.en 14)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 15) </p><p> projects/torbrowser/design/index.html.en 16) projects/torbrowser/design/index.html.en 17) For more practical information regarding Tor Browser development, please projects/torbrowser/design/index.html.en 18) consult the <a class="ulink" href="https://trac.torproject.org/projects/tor/wiki/doc/TorBrowser/Hacking" target="_top">Tor projects/torbrowser/design/index.html.en 19) Browser Hacking Guide</a>. projects/torbrowser/design/index.html.en 20)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 21) </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 13 years ago	`projects/torbrowser/design/index.html.en 22)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 23) 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 10 years ago	`projects/torbrowser/design/index.html.en 24) 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 25) against this browser to enhance privacy and security. Browser behavior is`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 26) additionally augmented through the <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/tree/" target="_top">Torbutton`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 27) extension</a>, though we are in the process of moving this functionality`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 28) into direct Firefox patches. We also <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/tree/browser/app/profile/000-tor-browser.js?h=tor-browser-31.6.0esr-4.5-1" target="_top">change`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 29) a number of Firefox preferences</a> from their defaults.`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 30)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 31) </p><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 32) 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 33) addon, which provides the initial Tor configuration splash screen and projects/torbrowser/design/index.html.en 34) bootstrap progress bar. Tor Launcher is also compatible with Thunderbird,`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 35) Instantbird, and XULRunner.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 36) projects/torbrowser/design/index.html.en 37) </p><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 38)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 39) 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 40) <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 41) provide users with optional defense-in-depth against Javascript and other`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 42) 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/tree/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 43) extension preferences</a> from their defaults.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 44)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 45) </p><p> projects/torbrowser/design/index.html.en 46) projects/torbrowser/design/index.html.en 47) To provide censorship circumvention in areas where the public Tor network is projects/torbrowser/design/index.html.en 48) 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`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 49) Transports</a> in the distribution. As of this writing, we include <a class="ulink" href="https://gitweb.torproject.org/pluggable-transports/obfs4.git" target="_top">Obfs4proxy</a>,`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 50) <a class="ulink" href="https://trac.torproject.org/projects/tor/wiki/doc/meek" target="_top">meek</a>, projects/torbrowser/design/index.html.en 51) <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 52) projects/torbrowser/design/index.html.en 53) </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 13 years ago	`projects/en/torbrowser/design/index.html.en 54) projects/en/torbrowser/design/index.html.en 55) The Tor Browser Design Requirements are meant to describe the properties of a`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 56) Private Browsing Mode that defends against both network and local forensic projects/torbrowser/design/index.html.en 57) adversaries.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 58) projects/en/torbrowser/design/index.html.en 59) </p><p> projects/en/torbrowser/design/index.html.en 60) projects/en/torbrowser/design/index.html.en 61) 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 13 years ago	`projects/torbrowser/design/index.html.en 62) minimum properties in order for a browser to be able to support Tor and projects/torbrowser/design/index.html.en 63) 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 64) that cause us to prefer one browser over another.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 65) projects/en/torbrowser/design/index.html.en 66) </p><p> projects/en/torbrowser/design/index.html.en 67)`
Update TBB design doc with... Mike Perry authored 13 years ago	projects/torbrowser/design/index.html.en 68) While we will endorse the use of browsers that meet the security requirements, projects/torbrowser/design/index.html.en 69) it is primarily the privacy requirements that cause us to maintain our own projects/torbrowser/design/index.html.en 70) browser distribution. projects/torbrowser/design/index.html.en 71) projects/torbrowser/design/index.html.en 72) </p><p> projects/torbrowser/design/index.html.en 73) projects/torbrowser/design/index.html.en 74) The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL projects/torbrowser/design/index.html.en 75) NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and projects/torbrowser/design/index.html.en 76) "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 77) <a class="ulink" href="https://www.ietf.org/rfc/rfc2119.txt" target="_top">RFC 2119</a>.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 78)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 79) </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 13 years ago	`projects/en/torbrowser/design/index.html.en 80) projects/en/torbrowser/design/index.html.en 81) The security requirements are primarily concerned with ensuring the safe use projects/en/torbrowser/design/index.html.en 82) of Tor. Violations in these properties typically result in serious risk for`
Add a couple extra sentence... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 83) 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 84) respect to browser support, security requirements are the minimum properties projects/torbrowser/design/index.html.en 85) in order for Tor to support the use of a particular browser.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 86)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 87) </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 13 years ago	`projects/torbrowser/design/index.html.en 88) Obedience</strong></span></a><p>The browser`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 89) 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 90) Separation</strong></span></a><p> projects/torbrowser/design/index.html.en 91) projects/torbrowser/design/index.html.en 92) The browser MUST NOT provide the content window with any state from any other projects/torbrowser/design/index.html.en 93) browsers or any non-Tor browsing modes. This includes shared state from`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 94) 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 95) TLS and other support libraries. projects/torbrowser/design/index.html.en 96)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 97) </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 13 years ago	`projects/torbrowser/design/index.html.en 98) Avoidance</strong></span></a><p>`
Update TBB design doc with... Mike Perry authored 13 years ago	projects/torbrowser/design/index.html.en 99) projects/torbrowser/design/index.html.en 100) The browser MUST NOT write any information that is derived from or that projects/torbrowser/design/index.html.en 101) reveals browsing activity to the disk, or store it in memory beyond the projects/torbrowser/design/index.html.en 102) duration of one browsing session, unless the user has explicitly opted to projects/torbrowser/design/index.html.en 103) store their browsing history information to disk. projects/torbrowser/design/index.html.en 104)
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 105) </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 13 years ago	`projects/torbrowser/design/index.html.en 106) Isolation</strong></span></a><p>`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 107)`
Additional comments from Ge... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 108) The components involved in providing private browsing MUST be self-contained,`
Update TBB design doc with... Mike Perry authored 13 years ago	projects/torbrowser/design/index.html.en 109) or MUST provide a mechanism for rapid, complete removal of all evidence of the projects/torbrowser/design/index.html.en 110) use of the mode. In other words, the browser MUST NOT write or cause the projects/torbrowser/design/index.html.en 111) operating system to write <span class="emphasis"><em>any information</em></span> about the use projects/torbrowser/design/index.html.en 112) 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 113) must be able to ensure that secure deletion of the software is sufficient to`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 114) remove evidence of the use of the software. All exceptions and shortcomings`
Additional comments from Ge... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 115) due to operating system behavior MUST be wiped by an uninstaller. However, due`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 116) to permissions issues with access to swap, implementations MAY choose to leave`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 117) 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 118) ephemeral-keyed encrypted swap.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 119)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 120) </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 13 years ago	`projects/en/torbrowser/design/index.html.en 121) projects/en/torbrowser/design/index.html.en 122) The privacy requirements are primarily concerned with reducing linkability:`
Add a couple extra sentence... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 123) the ability for a user's activity on one site to be linked with their activity projects/torbrowser/design/index.html.en 124) 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 125) browser support, privacy requirements are the set of properties that cause us projects/torbrowser/design/index.html.en 126) to prefer one browser over another.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 127)`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 128) </p><p> projects/torbrowser/design/index.html.en 129) projects/torbrowser/design/index.html.en 130) 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 131) the descriptions in the <a class="link" href="#Implementation" title="4. Implementation">implementation`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 132) section</a>, a <span class="command"><strong>URL bar origin</strong></span> means at least the`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 133) second-level DNS name. For example, for mail.google.com, the origin would be`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 134) google.com. Implementations MAY, at their option, restrict the URL bar origin`
Additional comments from Ge... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 135) to be the entire fully qualified domain name.`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 136)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 137) </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 13 years ago	`projects/torbrowser/design/index.html.en 138) Identifier Unlinkability</strong></span></a><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 139)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 140) User activity on one URL bar origin MUST NOT be linkable to their activity in projects/torbrowser/design/index.html.en 141) any other URL bar origin by any third party automatically or without user`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 142) interaction or approval. This requirement specifically applies to linkability projects/torbrowser/design/index.html.en 143) from stored browser identifiers, authentication tokens, and shared state. The projects/torbrowser/design/index.html.en 144) 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 145) 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 146) functionality SHOULD NOT interfere with interactive, click-driven federated projects/torbrowser/design/index.html.en 147) login in a substantial way.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 148)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 149) </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 13 years ago	`projects/torbrowser/design/index.html.en 150) Fingerprinting Unlinkability</strong></span></a><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 151)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 152) User activity on one URL bar origin MUST NOT be linkable to their activity in projects/torbrowser/design/index.html.en 153) any other URL bar origin by any third party. This property specifically applies to`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 154) linkability from fingerprinting browser behavior. projects/en/torbrowser/design/index.html.en 155)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 156) </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 13 years ago	`projects/torbrowser/design/index.html.en 157) Unlinkability</strong></span></a><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 158)`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 159) The browser MUST provide an obvious, easy way for the user to remove all of projects/torbrowser/design/index.html.en 160) its authentication tokens and browser state and obtain a fresh identity.`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 161) Additionally, the browser SHOULD clear linkable state by default automatically projects/torbrowser/design/index.html.en 162) upon browser restart, except at user option.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 163)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 164) </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 13 years ago	`projects/en/torbrowser/design/index.html.en 165) projects/en/torbrowser/design/index.html.en 166) In addition to the above design requirements, the technology decisions about projects/en/torbrowser/design/index.html.en 167) Tor Browser are also guided by some philosophical positions about technology. projects/en/torbrowser/design/index.html.en 168)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 169) </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 13 years ago	projects/en/torbrowser/design/index.html.en 170) projects/en/torbrowser/design/index.html.en 171) The existing way that the user expects to use a browser must be preserved. If projects/en/torbrowser/design/index.html.en 172) the user has to maintain a different mental model of how the sites they are projects/en/torbrowser/design/index.html.en 173) using behave depending on tab, browser state, or anything else that would not projects/en/torbrowser/design/index.html.en 174) normally be what they experience in their default browser, the user will projects/en/torbrowser/design/index.html.en 175) inevitably be confused. They will make mistakes and reduce their privacy as a projects/en/torbrowser/design/index.html.en 176) result. Worse, they may just stop using the browser, assuming it is broken. projects/en/torbrowser/design/index.html.en 177) projects/en/torbrowser/design/index.html.en 178) </p><p> projects/en/torbrowser/design/index.html.en 179)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 180) 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 13 years ago	`projects/en/torbrowser/design/index.html.en 181) of Torbutton</a>: Even if users managed to install everything properly, projects/en/torbrowser/design/index.html.en 182) the toggle model was too hard for the average user to understand, especially projects/en/torbrowser/design/index.html.en 183) 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 184) Tor-state of the browser.`
Add design doc draft. Mike Perry authored 13 years ago	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>Favor the implementation mechanism least likely to projects/en/torbrowser/design/index.html.en 187) break sites</strong></span><p> projects/en/torbrowser/design/index.html.en 188) projects/en/torbrowser/design/index.html.en 189) In general, we try to find solutions to privacy issues that will not induce projects/en/torbrowser/design/index.html.en 190) site breakage, though this is not always possible. projects/en/torbrowser/design/index.html.en 191) projects/en/torbrowser/design/index.html.en 192) </p></li><li class="listitem"><span class="command"><strong>Plugins must be restricted</strong></span><p> projects/en/torbrowser/design/index.html.en 193) projects/en/torbrowser/design/index.html.en 194) Even if plugins always properly used the browser proxy settings (which none of projects/en/torbrowser/design/index.html.en 195) them do) and could not be induced to bypass them (which all of them can), the projects/en/torbrowser/design/index.html.en 196) activities of closed-source plugins are very difficult to audit and control. projects/en/torbrowser/design/index.html.en 197) They can obtain and transmit all manner of system information to websites, projects/en/torbrowser/design/index.html.en 198) often have their own identifier storage for tracking users, and also projects/en/torbrowser/design/index.html.en 199) contribute to fingerprinting. projects/en/torbrowser/design/index.html.en 200) projects/en/torbrowser/design/index.html.en 201) </p><p> projects/en/torbrowser/design/index.html.en 202) projects/en/torbrowser/design/index.html.en 203) Therefore, if plugins are to be enabled in private browsing modes, they must projects/en/torbrowser/design/index.html.en 204) be restricted from running automatically on every page (via click-to-play projects/en/torbrowser/design/index.html.en 205) 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 206) can execute. If the user agent allows the user to craft an exemption to allow`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 207) a plugin to be used automatically, it must only apply to the top level URL bar`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 208) domain, and not to all sites, to reduce cross-origin fingerprinting projects/torbrowser/design/index.html.en 209) linkability.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 210) projects/en/torbrowser/design/index.html.en 211) </p></li><li class="listitem"><span class="command"><strong>Minimize Global Privacy Options</strong></span><p> projects/en/torbrowser/design/index.html.en 212)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 213) <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 214) failure of Torbutton</a> was the options panel. Each option`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 215) 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 216) 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 217) disabled in the mode</a> except as an opt-in basis. We should not load`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 218) system-wide and/or operating system provided addons or plugins.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 219) projects/en/torbrowser/design/index.html.en 220) </p><p>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 221) 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 222) <a class="ulink" href="https://wiki.mozilla.org/Privacy/Features/Site-based_data_management_UI" target="_top">per`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 223) URL bar origin</a> to eliminate the possibility of linkability`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 224) between domains. For example, when a plugin object (or a Javascript access of projects/en/torbrowser/design/index.html.en 225) window.plugins) is present in a page, the user should be given the choice of`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 226) allowing that plugin object for that URL bar origin only. The same`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 227) goes for exemptions to third party cookie policy, geolocation, and any other`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 228) privacy permissions. projects/en/torbrowser/design/index.html.en 229) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 230) 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 231) permissions can be written to disk. Otherwise, they should remain memory-only.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 232) </p></li><li class="listitem"><span class="command"><strong>No filters</strong></span><p> projects/en/torbrowser/design/index.html.en 233)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 234) 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 235) Plus</a>, <a class="ulink" href="http://requestpolicy.com/" target="_top">Request Policy</a>, projects/torbrowser/design/index.html.en 236) <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 13 years ago	`projects/en/torbrowser/design/index.html.en 237) 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 238) <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 239) should be focused on general solutions that prevent tracking by all projects/torbrowser/design/index.html.en 240) third parties, rather than a list of specific URLs or hosts. projects/torbrowser/design/index.html.en 241) </p><p>
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 242) Filter-based addons can also introduce strange breakage and cause usability projects/en/torbrowser/design/index.html.en 243) nightmares, and will also fail to do their job if an adversary simply`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 244) 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 245) filter sets that each user creates or installs will provide a wealth of projects/torbrowser/design/index.html.en 246) fingerprinting targets.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 247) </p><p> projects/en/torbrowser/design/index.html.en 248) projects/en/torbrowser/design/index.html.en 249) As a general matter, we are also generally opposed to shipping an always-on Ad projects/en/torbrowser/design/index.html.en 250) blocker with Tor Browser. We feel that this would damage our credibility in projects/en/torbrowser/design/index.html.en 251) 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 252) alone, as well as damage the acceptance of Tor users by sites that support`
Add design doc draft. Mike Perry authored 13 years ago	projects/en/torbrowser/design/index.html.en 253) themselves through advertising revenue. projects/en/torbrowser/design/index.html.en 254) projects/en/torbrowser/design/index.html.en 255) </p><p> projects/en/torbrowser/design/index.html.en 256) Users are free to install these addons if they wish, but doing projects/en/torbrowser/design/index.html.en 257) so is not recommended, as it will alter the browser request fingerprint. projects/en/torbrowser/design/index.html.en 258) </p></li><li class="listitem"><span class="command"><strong>Stay Current</strong></span><p> projects/en/torbrowser/design/index.html.en 259) We believe that if we do not stay current with the support of new web projects/en/torbrowser/design/index.html.en 260) technologies, we cannot hope to substantially influence or be involved in projects/en/torbrowser/design/index.html.en 261) 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 262) high-risk features pending analysis, audit, and mitigation.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 263) </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 264) projects/torbrowser/design/index.html.en 265) A Tor web browser adversary has a number of goals, capabilities, and attack projects/torbrowser/design/index.html.en 266) types that can be used to illustrate the design requirements for the projects/torbrowser/design/index.html.en 267) Tor Browser. Let's start with the goals. projects/torbrowser/design/index.html.en 268)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 269) </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 270) Tor, causing the user to directly connect to an IP of the adversary's projects/torbrowser/design/index.html.en 271) 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 272) happily settle for the ability to correlate something a user did via Tor with projects/torbrowser/design/index.html.en 273) their non-Tor activity. This can be done with cookies, cache identifiers,
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 274) 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 275) 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 276) The adversary may also be interested in history disclosure: the ability to projects/torbrowser/design/index.html.en 277) query a user's history to see if they have issued certain censored search projects/torbrowser/design/index.html.en 278) queries, or visited censored sites. projects/torbrowser/design/index.html.en 279) </p></li><li class="listitem"><span class="command"><strong>Correlate activity across multiple sites</strong></span><p> projects/torbrowser/design/index.html.en 280) projects/torbrowser/design/index.html.en 281) The primary goal of the advertising networks is to know that the user who projects/torbrowser/design/index.html.en 282) visited siteX.com is the same user that visited siteY.com to serve them projects/torbrowser/design/index.html.en 283) targeted ads. The advertising networks become our adversary insofar as they projects/torbrowser/design/index.html.en 284) attempt to perform this correlation without the user's explicit consent. projects/torbrowser/design/index.html.en 285) projects/torbrowser/design/index.html.en 286) </p></li><li class="listitem"><span class="command"><strong>Fingerprinting/anonymity set reduction</strong></span><p> projects/torbrowser/design/index.html.en 287) projects/torbrowser/design/index.html.en 288) 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 289) to gather identifying information on a particular individual without the use projects/torbrowser/design/index.html.en 290) of tracking identifiers. If the dissident or whistleblower's timezone is projects/torbrowser/design/index.html.en 291) available, and they are using a rare build of Firefox for an obscure operating projects/torbrowser/design/index.html.en 292) system, and they have a specific display resolution only used on one type of projects/torbrowser/design/index.html.en 293) laptop, this can be very useful information for tracking them down, or at projects/torbrowser/design/index.html.en 294) 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 295) projects/torbrowser/design/index.html.en 296) </p></li><li class="listitem"><span class="command"><strong>History records and other on-disk projects/torbrowser/design/index.html.en 297) information</strong></span><p>`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 298)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 299) In some cases, the adversary may opt for a heavy-handed approach, such as projects/torbrowser/design/index.html.en 300) seizing the computers of all Tor users in an area (especially after narrowing projects/torbrowser/design/index.html.en 301) the field by the above two pieces of information). History records and cache`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 302) data are the primary goals here. Secondary goals may include confirming`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 303) on-disk identifiers (such as hostname and disk-logged spoofed MAC address`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 304) history) obtained by other means. projects/torbrowser/design/index.html.en 305)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 306) </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 307) The adversary can position themselves at a number of different locations in projects/torbrowser/design/index.html.en 308) order to execute their attacks.`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 309) </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 310) The adversary can run exit nodes, or alternatively, they may control routers projects/torbrowser/design/index.html.en 311) upstream of exit nodes. Both of these scenarios have been observed in the projects/torbrowser/design/index.html.en 312) wild. projects/torbrowser/design/index.html.en 313) </p></li><li class="listitem"><span class="command"><strong>Ad servers and/or Malicious Websites</strong></span><p> projects/torbrowser/design/index.html.en 314) The adversary can also run websites, or more likely, they can contract out projects/torbrowser/design/index.html.en 315) ad space from a number of different ad servers and inject content that way. For projects/torbrowser/design/index.html.en 316) some users, the adversary may be the ad servers themselves. It is not projects/torbrowser/design/index.html.en 317) inconceivable that ad servers may try to subvert or reduce a user's anonymity projects/torbrowser/design/index.html.en 318) through Tor for marketing purposes. projects/torbrowser/design/index.html.en 319) </p></li><li class="listitem"><span class="command"><strong>Local Network/ISP/Upstream Router</strong></span><p> projects/torbrowser/design/index.html.en 320) The adversary can also inject malicious content at the user's upstream router projects/torbrowser/design/index.html.en 321) when they have Tor disabled, in an attempt to correlate their Tor and Non-Tor projects/torbrowser/design/index.html.en 322) activity.
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 323) </p><p> projects/torbrowser/design/index.html.en 324) projects/torbrowser/design/index.html.en 325) Additionally, at this position the adversary can block Tor, or attempt to projects/torbrowser/design/index.html.en 326) recognize the traffic patterns of specific web pages at the entrance to the Tor projects/torbrowser/design/index.html.en 327) network. projects/torbrowser/design/index.html.en 328)`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 329) </p></li><li class="listitem"><span class="command"><strong>Physical Access</strong></span><p> projects/torbrowser/design/index.html.en 330) Some users face adversaries with intermittent or constant physical access. projects/torbrowser/design/index.html.en 331) Users in Internet cafes, for example, face such a threat. In addition, in projects/torbrowser/design/index.html.en 332) countries where simply using tools like Tor is illegal, users may face projects/torbrowser/design/index.html.en 333) confiscation of their computer equipment for excessive Tor usage or just projects/torbrowser/design/index.html.en 334) general suspicion.
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 335) </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 336) projects/torbrowser/design/index.html.en 337) The adversary can perform the following attacks from a number of different projects/torbrowser/design/index.html.en 338) positions to accomplish various aspects of their goals. It should be noted projects/torbrowser/design/index.html.en 339) that many of these attacks (especially those involving IP address leakage) are projects/torbrowser/design/index.html.en 340) often performed by accident by websites that simply have Javascript, dynamic projects/torbrowser/design/index.html.en 341) CSS elements, and plugins. Others are performed by ad servers seeking to projects/torbrowser/design/index.html.en 342) correlate users' activity across different IP addresses, and still others are projects/torbrowser/design/index.html.en 343) performed by malicious agents on the Tor network and at national firewalls. projects/torbrowser/design/index.html.en 344)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 345) </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 346) projects/torbrowser/design/index.html.en 347) The browser contains multiple facilities for storing identifiers that the projects/torbrowser/design/index.html.en 348) adversary creates for the purposes of tracking users. These identifiers are projects/torbrowser/design/index.html.en 349) most obviously cookies, but also include HTTP auth, DOM storage, cached projects/torbrowser/design/index.html.en 350) scripts and other elements with embedded identifiers, client certificates, and projects/torbrowser/design/index.html.en 351) even TLS Session IDs. projects/torbrowser/design/index.html.en 352) projects/torbrowser/design/index.html.en 353) </p><p> projects/torbrowser/design/index.html.en 354) projects/torbrowser/design/index.html.en 355) An adversary in a position to perform MITM content alteration can inject projects/torbrowser/design/index.html.en 356) document content elements to both read and inject cookies for arbitrary projects/torbrowser/design/index.html.en 357) 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 358) <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 359) sidejacking</a>. In addition, the ad networks of course perform tracking projects/torbrowser/design/index.html.en 360) with cookies as well. projects/torbrowser/design/index.html.en 361) projects/torbrowser/design/index.html.en 362) </p><p> projects/torbrowser/design/index.html.en 363)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 364) 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 365)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 366) </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 367) attributes</strong></span><p> projects/torbrowser/design/index.html.en 368) projects/torbrowser/design/index.html.en 369) There is an absurd amount of information available to websites via attributes projects/torbrowser/design/index.html.en 370) of the browser. This information can be used to reduce anonymity set, or even projects/torbrowser/design/index.html.en 371) uniquely fingerprint individual users. Attacks of this nature are typically projects/torbrowser/design/index.html.en 372) aimed at tracking users across sites without their consent, in an attempt to projects/torbrowser/design/index.html.en 373) 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 10 years ago	`projects/torbrowser/design/index.html.en 374) 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 375) projects/torbrowser/design/index.html.en 376) </p><p> projects/torbrowser/design/index.html.en 377) projects/torbrowser/design/index.html.en 378) Fingerprinting is an intimidating projects/torbrowser/design/index.html.en 379) problem to attempt to tackle, especially without a metric to determine or at projects/torbrowser/design/index.html.en 380) least intuitively understand and estimate which features will most contribute projects/torbrowser/design/index.html.en 381) to linkability between visits. projects/torbrowser/design/index.html.en 382) projects/torbrowser/design/index.html.en 383) </p><p> projects/torbrowser/design/index.html.en 384)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 385) The <a class="ulink" href="https://panopticlick.eff.org/about.php" target="_top">Panopticlick study projects/torbrowser/design/index.html.en 386) 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 387) 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 388) 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 389) definitely useful, and the metric is probably the appropriate one for projects/torbrowser/design/index.html.en 390) determining how identifying a particular browser property is. However, some projects/torbrowser/design/index.html.en 391) quirks of their study means that they do not extract as much information as projects/torbrowser/design/index.html.en 392) they could from display information: they only use desktop resolution and do projects/torbrowser/design/index.html.en 393) not attempt to infer the size of toolbars. In the other direction, they may be projects/torbrowser/design/index.html.en 394) over-counting in some areas, as they did not compute joint entropy over projects/torbrowser/design/index.html.en 395) multiple attributes that may exhibit a high degree of correlation. Also, new projects/torbrowser/design/index.html.en 396) browser features are added regularly, so the data should not be taken as projects/torbrowser/design/index.html.en 397) final. projects/torbrowser/design/index.html.en 398) projects/torbrowser/design/index.html.en 399) </p><p> projects/torbrowser/design/index.html.en 400) projects/torbrowser/design/index.html.en 401) Despite the uncertainty, all fingerprinting attacks leverage the following projects/torbrowser/design/index.html.en 402) attack vectors: projects/torbrowser/design/index.html.en 403)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 404) </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 405) projects/torbrowser/design/index.html.en 406) Properties of the user's request behavior comprise the bulk of low-hanging projects/torbrowser/design/index.html.en 407) fingerprinting targets. These include: User agent, Accept-* headers, pipeline projects/torbrowser/design/index.html.en 408) usage, and request ordering. Additionally, the use of custom filters such as projects/torbrowser/design/index.html.en 409) AdBlock and other privacy filters can be used to fingerprint request patterns projects/torbrowser/design/index.html.en 410) (as an extreme example). projects/torbrowser/design/index.html.en 411) projects/torbrowser/design/index.html.en 412) </p></li><li class="listitem"><span class="command"><strong>Inserting Javascript</strong></span><p> projects/torbrowser/design/index.html.en 413) projects/torbrowser/design/index.html.en 414) Javascript can reveal a lot of fingerprinting information. It provides DOM projects/torbrowser/design/index.html.en 415) objects such as window.screen and window.navigator to extract information
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 416) about the user agent.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 417) projects/torbrowser/design/index.html.en 418) 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 419) <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 420) 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 421) 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 422) 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 423) <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 424) Timing</a> may leak an unknown amount of network timing related projects/torbrowser/design/index.html.en 425) information. projects/torbrowser/design/index.html.en 426) projects/torbrowser/design/index.html.en 427) </p></li><li class="listitem"><span class="command"><strong>Inserting Plugins</strong></span><p> projects/torbrowser/design/index.html.en 428) projects/torbrowser/design/index.html.en 429) The Panopticlick project found that the mere list of installed plugins (in projects/torbrowser/design/index.html.en 430) navigator.plugins) was sufficient to provide a large degree of projects/torbrowser/design/index.html.en 431) fingerprintability. Additionally, plugins are capable of extracting font lists, projects/torbrowser/design/index.html.en 432) interface addresses, and other machine information that is beyond what the projects/torbrowser/design/index.html.en 433) browser would normally provide to content. In addition, plugins can be used to projects/torbrowser/design/index.html.en 434) 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 435) 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 436) cookies</a> fall into this category, but there are likely numerous other projects/torbrowser/design/index.html.en 437) examples. Beyond fingerprinting, plugins are also abysmal at obeying the proxy projects/torbrowser/design/index.html.en 438) settings of the browser. projects/torbrowser/design/index.html.en 439) projects/torbrowser/design/index.html.en 440) projects/torbrowser/design/index.html.en 441) </p></li><li class="listitem"><span class="command"><strong>Inserting CSS</strong></span><p> projects/torbrowser/design/index.html.en 442)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 443) <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 444) queries</a> can be inserted to gather information about the desktop size, projects/torbrowser/design/index.html.en 445) widget size, display type, DPI, user agent type, and other information that projects/torbrowser/design/index.html.en 446) was formerly available only to Javascript. projects/torbrowser/design/index.html.en 447)`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 448) </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 449) projects/torbrowser/design/index.html.en 450) 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 451) encrypted traffic patterns of specific websites. In the case of Tor, this projects/torbrowser/design/index.html.en 452) attack would take place between the user and the Guard node, or at the Guard projects/torbrowser/design/index.html.en 453) node itself. projects/torbrowser/design/index.html.en 454) </p><p> The most comprehensive study of the statistical properties of this projects/torbrowser/design/index.html.en 455) 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 456) et al</a>. Unfortunately, the publication bias in academia has encouraged projects/torbrowser/design/index.html.en 457) 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 458) success rates, in some cases even claiming to completely invalidate any projects/torbrowser/design/index.html.en 459) attempt at defense. These "improvements" are actually enabled primarily by projects/torbrowser/design/index.html.en 460) taking a number of shortcuts (such as classifying only very small numbers of projects/torbrowser/design/index.html.en 461) web pages, neglecting to publish ROC curves or at least false positive rates, projects/torbrowser/design/index.html.en 462) and/or omitting the effects of dataset size on their results). Despite these projects/torbrowser/design/index.html.en 463) subsequent "improvements", we are skeptical of the efficacy of this attack in projects/torbrowser/design/index.html.en 464) 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 465) defenses.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 466) projects/torbrowser/design/index.html.en 467) </p><p> projects/torbrowser/design/index.html.en 468)`
TBB design doc: Clarify web... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 469) 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 470) categories to classify</a> while maintaining a limit on reliable feature projects/torbrowser/design/index.html.en 471) information you can extract, you eventually run out of descriptive feature projects/torbrowser/design/index.html.en 472) information, and either true positive accuracy goes down or the false positive projects/torbrowser/design/index.html.en 473) 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 474) in your hypothesis space</a>. In fact, even for unbiased hypothesis projects/torbrowser/design/index.html.en 475) spaces, the number of training examples required to achieve a reasonable error projects/torbrowser/design/index.html.en 476) 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 477) 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 478) projects/torbrowser/design/index.html.en 479) </p><p> projects/torbrowser/design/index.html.en 480) projects/torbrowser/design/index.html.en 481) projects/torbrowser/design/index.html.en 482) 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 483) 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 484) 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 485) and also the non-web activity of entire Tor network. This yields an effective projects/torbrowser/design/index.html.en 486) 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 10 years ago	`projects/torbrowser/design/index.html.en 487) "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 488) in the true positive rate as the "Open World" size grew (see figure 4). This projects/torbrowser/design/index.html.en 489) 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 490) 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 491) to manipulate at low cost.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 492) projects/torbrowser/design/index.html.en 493) </p><p> projects/torbrowser/design/index.html.en 494)`
TBB Design Doc: Mention use... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 495) To make matters worse for a real-world adversary, the ocean of Tor Internet projects/torbrowser/design/index.html.en 496) activity (at least, when compared to a lab setting) makes it a certainty that projects/torbrowser/design/index.html.en 497) an adversary attempting examine large amounts of Tor traffic will ultimately projects/torbrowser/design/index.html.en 498) be overwhelmed by false positives (even after making heavy tradeoffs on the projects/torbrowser/design/index.html.en 499) ROC curve to minimize false positives to below 0.01%). This problem is known projects/torbrowser/design/index.html.en 500) 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 501) Fallacy</a>, and it is the primary reason that anomaly and activity projects/torbrowser/design/index.html.en 502) 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 503) 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 504) projects/torbrowser/design/index.html.en 505) </p><p> projects/torbrowser/design/index.html.en 506) projects/torbrowser/design/index.html.en 507) Still, we do not believe that these issues are enough to dismiss the attack projects/torbrowser/design/index.html.en 508) outright. But we do believe these factors make it both worthwhile and projects/torbrowser/design/index.html.en 509) effective to <a class="link" href="#traffic-fingerprinting-defenses">deploy projects/torbrowser/design/index.html.en 510) light-weight defenses</a> that reduce the accuracy of this attack by projects/torbrowser/design/index.html.en 511) further contributing noise to hinder successful feature extraction. projects/torbrowser/design/index.html.en 512) projects/torbrowser/design/index.html.en 513) </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 514) OS</strong></span><p> projects/torbrowser/design/index.html.en 515) projects/torbrowser/design/index.html.en 516) Last, but definitely not least, the adversary can exploit either general projects/torbrowser/design/index.html.en 517) browser vulnerabilities, plugin vulnerabilities, or OS vulnerabilities to projects/torbrowser/design/index.html.en 518) 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 519) can perform similar actions. projects/torbrowser/design/index.html.en 520) projects/torbrowser/design/index.html.en 521) </p><p> projects/torbrowser/design/index.html.en 522) projects/torbrowser/design/index.html.en 523) For the purposes of the browser itself, we limit the scope of this adversary projects/torbrowser/design/index.html.en 524) to one that has passive forensic access to the disk after browsing activity projects/torbrowser/design/index.html.en 525) has taken place. This adversary motivates our
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 526) <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 527)`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 528) </p><p> projects/torbrowser/design/index.html.en 529) projects/torbrowser/design/index.html.en 530) An adversary with arbitrary code execution typically has more power, though. projects/torbrowser/design/index.html.en 531) It can be quite hard to really significantly limit the capabilities of such an`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 532) 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 533) provide some defense against this adversary through the use of readonly media projects/torbrowser/design/index.html.en 534) and frequent reboots, but even this can be circumvented on machines without projects/torbrowser/design/index.html.en 535) Secure Boot through the use of BIOS rootkits. projects/torbrowser/design/index.html.en 536)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 537) </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 13 years ago	projects/torbrowser/design/index.html.en 538) projects/torbrowser/design/index.html.en 539) The Implementation section is divided into subsections, each of which projects/torbrowser/design/index.html.en 540) corresponds to a <a class="link" href="#DesignRequirements" title="2. Design Requirements and Philosophy">Design Requirement</a>. projects/torbrowser/design/index.html.en 541) Each subsection is divided into specific web technologies or properties. The projects/torbrowser/design/index.html.en 542) implementation is then described for that property. projects/torbrowser/design/index.html.en 543) projects/torbrowser/design/index.html.en 544) </p><p> projects/torbrowser/design/index.html.en 545) projects/torbrowser/design/index.html.en 546) In some cases, the implementation meets the design requirements in a non-ideal projects/torbrowser/design/index.html.en 547) way (for example, by disabling features). In rare cases, there may be no projects/torbrowser/design/index.html.en 548) implementation at all. Both of these cases are denoted by differentiating projects/torbrowser/design/index.html.en 549) 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 550) 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 13 years ago	`projects/torbrowser/design/index.html.en 551) are typically linked for these cases. projects/torbrowser/design/index.html.en 552)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 553) </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 13 years ago	`projects/en/torbrowser/design/index.html.en 554) projects/en/torbrowser/design/index.html.en 555) Proxy obedience is assured through the following:`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 556) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Firefox proxy settings, patches, and build flags</strong></span><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 557)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 558) Our <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/tree/browser/app/profile/000-tor-browser.js?h=tor-browser-31.6.0esr-4.5-1" target="_top">Firefox`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 559) preferences file</a> sets the Firefox proxy settings to use Tor directly projects/torbrowser/design/index.html.en 560) 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 561) <span class="command"><strong>network.proxy.socks_version</strong></span>, projects/torbrowser/design/index.html.en 562) <span class="command"><strong>network.proxy.socks_port</strong></span>, and projects/torbrowser/design/index.html.en 563) <span class="command"><strong>network.dns.disablePrefetch</strong></span>.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 564)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 565) </p><p> projects/torbrowser/design/index.html.en 566)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 567) To prevent proxy bypass by WebRTC calls, we disable WebRTC at compile time projects/torbrowser/design/index.html.en 568) with the <span class="command"><strong>--disable-webrtc</strong></span> configure switch, as well projects/torbrowser/design/index.html.en 569) 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 570) projects/torbrowser/design/index.html.en 571) </p><p> projects/torbrowser/design/index.html.en 572)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 573) We also patch Firefox in order to provide several defense-in-depth mechanisms`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 574) for proxy safety. Notably, we <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=8c6604d2b776f0d8e33ed9130c5f5b8cf744bac8" target="_top">patch`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 575) the DNS service</a> to prevent any browser or addon DNS resolution, and we`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 576) also <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=c96c854c0eca21fed1362d1ddd164b657d351795" target="_top">patch`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 577) OCSP and PKIX code</a> to prevent any use of the non-proxied command-line projects/torbrowser/design/index.html.en 578) tool utility functions from being functional while linked in to the browser. projects/torbrowser/design/index.html.en 579) In both cases, we could find no direct paths to these routines in the browser, projects/torbrowser/design/index.html.en 580) but it seemed better safe than sorry.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 581)`
Comments from Georg + proxy... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 582) </p><p> projects/torbrowser/design/index.html.en 583)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 584) During every Extended Support Release transition, we perform <a class="ulink" href="https://gitweb.torproject.org/tor-browser-spec.git/tree/audits" target="_top">in-depth`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 585) code audits</a> to verify that there were no system calls or XPCOM projects/torbrowser/design/index.html.en 586) activity in the source tree that did not use the browser proxy settings. projects/torbrowser/design/index.html.en 587) </p><p> projects/torbrowser/design/index.html.en 588)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 589) We have verified that these settings and patches properly proxy HTTPS, OCSP,`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 590) HTTP, FTP, gopher (now defunct), DNS, SafeBrowsing Queries, all JavaScript`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 591) activity, including HTML5 audio and video objects, addon updates, WiFi`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 592) geolocation queries, searchbox queries, XPCOM addon HTTPS/HTTP activity, projects/torbrowser/design/index.html.en 593) WebSockets, and live bookmark updates. We have also verified that IPv6 projects/torbrowser/design/index.html.en 594) connections are not attempted, through the proxy or otherwise (Tor does not projects/torbrowser/design/index.html.en 595) yet support IPv6). We have also verified that external protocol helpers, such`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 596) as SMB URLs and other custom protocol handlers are all blocked.`
Comments from Georg + proxy... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 597)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 598) </p></li><li class="listitem"><span class="command"><strong>Disabling plugins</strong></span><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 13 years ago	`projects/en/torbrowser/design/index.html.en 599) the ability to make UDP sockets and send arbitrary data independent of the projects/en/torbrowser/design/index.html.en 600) browser proxy settings. projects/en/torbrowser/design/index.html.en 601) </p><p> projects/en/torbrowser/design/index.html.en 602) Torbutton disables plugins by using the projects/en/torbrowser/design/index.html.en 603) <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 604) as disabled. This block can be undone through both the Torbutton Security UI, projects/torbrowser/design/index.html.en 605) and the Firefox Plugin Preferences.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 606) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 607) If the user does enable plugins in this way, plugin-handled objects are still projects/torbrowser/design/index.html.en 608) restricted from automatic load through Firefox's click-to-play preference projects/torbrowser/design/index.html.en 609) <span class="command"><strong>plugins.click_to_play</strong></span>.`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 610) </p><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 611)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 612) In addition, to reduce any unproxied activity by arbitrary plugins at load projects/torbrowser/design/index.html.en 613) time, and to reduce the fingerprintability of the installed plugin list, we`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 614) also patch the Firefox source code to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=465cb8295db58a6450dc14a593d29372cbebc71d" target="_top"> projects/torbrowser/design/index.html.en 615) prevent the load of any plugins except for Flash and Gnash</a>. Even for projects/torbrowser/design/index.html.en 616) Flash and Gnash, we also patch Firefox to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=e5531b1baa3c96dee7d8d4274791ff393bafd241" target="_top">prevent loading them into the projects/torbrowser/design/index.html.en 617) address space</a> until they are explicitly enabled.
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 618)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 619) </p></li><li class="listitem"><span class="command"><strong>External App Blocking and Drag Event Filtering</strong></span><p>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 620) projects/torbrowser/design/index.html.en 621) External apps can be induced to load files that perform network activity. projects/torbrowser/design/index.html.en 622) Unfortunately, there are cases where such apps can be launched automatically projects/torbrowser/design/index.html.en 623) with little to no user input. In order to prevent this, Torbutton installs a`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 624) component to <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/tree/src/components/external-app-blocker.js" target="_top">`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 625) provide the user with a popup</a> whenever the browser attempts to launch projects/torbrowser/design/index.html.en 626) a helper app. projects/torbrowser/design/index.html.en 627) projects/torbrowser/design/index.html.en 628) </p><p> projects/torbrowser/design/index.html.en 629) projects/torbrowser/design/index.html.en 630) Additionally, modern desktops now pre-emptively fetch any URLs in Drag and projects/torbrowser/design/index.html.en 631) Drop events as soon as the drag is initiated. This download happens projects/torbrowser/design/index.html.en 632) independent of the browser's Tor settings, and can be triggered by something projects/torbrowser/design/index.html.en 633) as simple as holding the mouse button down for slightly too long while
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 634) clicking on an image link. We filter drag and drop events events <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/tree/src/components/external-app-blocker.js" target="_top">from`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 635) 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 636)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 637) </p></li><li class="listitem"><span class="command"><strong>Disabling system extensions and clearing the addon whitelist</strong></span><p>`
TBB design doc: Fix typos,... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 638) projects/torbrowser/design/index.html.en 639) Firefox addons can perform arbitrary activity on your computer, including projects/torbrowser/design/index.html.en 640) bypassing Tor. It is for this reason we disable the addon whitelist projects/torbrowser/design/index.html.en 641) (<span class="command"><strong>xpinstall.whitelist.add</strong></span>), so that users are prompted projects/torbrowser/design/index.html.en 642) before installing addons regardless of the source. We also exclude projects/torbrowser/design/index.html.en 643) system-level addons from the browser through the use of projects/torbrowser/design/index.html.en 644) <span class="command"><strong>extensions.enabledScopes</strong></span> and projects/torbrowser/design/index.html.en 645) <span class="command"><strong>extensions.autoDisableScopes</strong></span>. projects/torbrowser/design/index.html.en 646)
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 647) </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 648)`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 649) 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 650) custom Firefox profile, and by setting the $HOME environment variable to the projects/torbrowser/design/index.html.en 651) root of the bundle's directory. The browser also does not load any projects/torbrowser/design/index.html.en 652) system-wide extensions (through the use of projects/torbrowser/design/index.html.en 653) <span class="command"><strong>extensions.enabledScopes</strong></span> and`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 654) <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 655) disabled, which prevents Flash cookies from leaking from a pre-existing Flash projects/torbrowser/design/index.html.en 656) directory. projects/torbrowser/design/index.html.en 657)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 658) </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="idp55920416"></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 659) projects/torbrowser/design/index.html.en 660) The User Agent MUST (at user option) prevent all disk records of browser activity.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 661) 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 662) features if they so desire.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 663)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 664) </blockquote></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp55921776"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote">`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 665)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 666) We achieve this goal through several mechanisms. First, we set the Firefox projects/torbrowser/design/index.html.en 667) Private Browsing preference projects/torbrowser/design/index.html.en 668) <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 669) Private Browsing Mode is enabled. We need to`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 670)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 671) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=44b8ae43a83191bbf5161cbdbf399e10c1b943d0" target="_top">prevent projects/torbrowser/design/index.html.en 672) the permissions manager from recording HTTPS STS state</a>, <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=e5abcb28f131aa96e8762212573488d303b3614d" target="_top">prevent projects/torbrowser/design/index.html.en 673) intermediate SSL certificates from being recorded</a>, <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=ee34e122ac2929a7668314483e36e58a88c98c08" target="_top">prevent
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 674) the clipboard cache from being written to disk for large pastes</a>, and`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 675) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=c8e357740dd7bafa2a129007f27d2b243e36f4a2" target="_top">prevent`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 676) the content preferences service from recording site zoom</a>. We also had projects/torbrowser/design/index.html.en 677) to disable the media cache with the pref <span class="command"><strong>media.cache_size</strong></span>, projects/torbrowser/design/index.html.en 678) to prevent HTML5 videos from being written to the OS temporary directory, projects/torbrowser/design/index.html.en 679) 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 680) projects/torbrowser/design/index.html.en 681) </blockquote></div><div class="blockquote"><blockquote class="blockquote"> projects/torbrowser/design/index.html.en 682) projects/torbrowser/design/index.html.en 683) 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 684) <span class="command"><strong></strong></span>,`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 685) <span class="command"><strong>browser.cache.disk.enable</strong></span>, projects/en/torbrowser/design/index.html.en 686) <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 687) <span class="command"><strong>dom.indexedDB.enabled</strong></span>, projects/torbrowser/design/index.html.en 688) <span class="command"><strong>network.cookie.lifetimePolicy</strong></span>,`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 689) <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 690) <span class="command"><strong>browser.formfill.enable</strong></span>,`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 691) <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 692) <span class="command"><strong>browser.sessionstore.privacy_level</strong></span>, projects/torbrowser/design/index.html.en 693) and <span class="command"><strong>network.cookie.lifetimePolicy</strong></span>. Many of these projects/torbrowser/design/index.html.en 694) preferences are likely redundant with projects/torbrowser/design/index.html.en 695) <span class="command"><strong>browser.privatebrowsing.autostart</strong></span>, but we have not done the projects/torbrowser/design/index.html.en 696) auditing work to ensure that yet.
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 697)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 698) </blockquote></div><div class="blockquote"><blockquote class="blockquote">`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 699)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 700) 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 13 years ago	projects/en/torbrowser/design/index.html.en 701) projects/en/torbrowser/design/index.html.en 702) Tor Browser Bundle MUST NOT cause any information to be written outside of the projects/en/torbrowser/design/index.html.en 703) bundle directory. This is to ensure that the user is able to completely and projects/en/torbrowser/design/index.html.en 704) safely remove the bundle without leaving other traces of Tor usage on their projects/en/torbrowser/design/index.html.en 705) computer. projects/en/torbrowser/design/index.html.en 706)
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 707) </p><p> projects/torbrowser/design/index.html.en 708) projects/torbrowser/design/index.html.en 709) To ensure TBB directory isolation, we set projects/torbrowser/design/index.html.en 710) <span class="command"><strong>browser.download.useDownloadDir</strong></span>, projects/torbrowser/design/index.html.en 711) <span class="command"><strong>browser.shell.checkDefaultBrowser</strong></span>, and projects/torbrowser/design/index.html.en 712) <span class="command"><strong>browser.download.manager.addToRecentDocs</strong></span>. We also set the projects/torbrowser/design/index.html.en 713) $HOME environment variable to be the TBB extraction directory.
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 714) </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 13 years ago	`projects/en/torbrowser/design/index.html.en 715)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 716) The Cross-Origin Identifier Unlinkability design requirement is satisfied projects/torbrowser/design/index.html.en 717) through first party isolation of all browser identifier sources. First party projects/torbrowser/design/index.html.en 718) isolation means that all identifier sources and browser state are scoped projects/torbrowser/design/index.html.en 719) (isolated) using the URL bar domain. This scoping is performed in projects/torbrowser/design/index.html.en 720) combination with any additional third party scope. When first party isolation projects/torbrowser/design/index.html.en 721) is used with explicit identifier storage that already has a constrained third
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 722) party scope (such as cookies and DOM storage), this approach is`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 723) referred to as "double-keying".`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 724) projects/en/torbrowser/design/index.html.en 725) </p><p> projects/en/torbrowser/design/index.html.en 726) projects/en/torbrowser/design/index.html.en 727) The benefit of this approach comes not only in the form of reduced projects/en/torbrowser/design/index.html.en 728) linkability, but also in terms of simplified privacy UI. If all stored browser`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 729) state and permissions become associated with the URL bar origin, the six or`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 730) seven different pieces of privacy UI governing these identifiers and`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 731) permissions can become just one piece of UI. For instance, a window that lists`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 732) the URL bar origin for which browser state exists, possibly with a`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 733) context-menu option to drill down into specific types of state or permissions. projects/torbrowser/design/index.html.en 734) An example of this simplification can be seen in Figure 1.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 735)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 736) </p><div class="figure"><a id="idp55943472"></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 13 years ago	`projects/en/torbrowser/design/index.html.en 737)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 738) This example UI is a mock-up of how isolating identifiers to the URL bar projects/torbrowser/design/index.html.en 739) origin can simplify the privacy UI for all data - not just cookies. Once`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 740) browser identifiers and site permissions operate on a URL bar basis, the same`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 741) privacy window can represent browsing history, DOM Storage, HTTP Auth, search projects/torbrowser/design/index.html.en 742) form history, login values, and so on within a context menu for each site.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 743)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 744) </div></div></div><br class="figure-break" /><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp55946896"></a>Identifier Unlinkability Defenses in the Tor Browser</h4></div></div></div><p>`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 745) projects/torbrowser/design/index.html.en 746) Unfortunately, many aspects of browser state can serve as identifier storage, projects/torbrowser/design/index.html.en 747) and no other browser vendor or standards body has invested the effort to projects/torbrowser/design/index.html.en 748) enumerate or otherwise deal with these vectors for third party tracking. As projects/torbrowser/design/index.html.en 749) such, we have had to enumerate and isolate these identifier sources on a projects/torbrowser/design/index.html.en 750) piecemeal basis. Here is the list that we have discovered and dealt with to projects/torbrowser/design/index.html.en 751) date:
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 752)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 753) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Cookies</strong></span><p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 754) projects/torbrowser/design/index.html.en 755) 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 756) 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 13 years ago	`projects/torbrowser/design/index.html.en 757) that contains a prototype patch, but it lacks UI, and does not apply to modern`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 758) Firefox versions.`
Add design doc draft. Mike Perry authored 13 years ago	projects/en/torbrowser/design/index.html.en 759) projects/en/torbrowser/design/index.html.en 760) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 761) projects/en/torbrowser/design/index.html.en 762) As a stopgap to satisfy our design requirement of unlinkability, we currently projects/en/torbrowser/design/index.html.en 763) entirely disable 3rd party cookies by setting projects/en/torbrowser/design/index.html.en 764) <span class="command"><strong>network.cookie.cookieBehavior</strong></span> to 1. We would prefer that
Comments from Georg + proxy... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 765) third party content continue to function, but we believe the requirement for`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 766) unlinkability trumps that desire. projects/en/torbrowser/design/index.html.en 767)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 768) </p></li><li class="listitem"><span class="command"><strong>Cache</strong></span><p>`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 769)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 770) In Firefox, there are actually two distinct caching mechanisms: One for projects/torbrowser/design/index.html.en 771) general content (HTML, Javascript, CSS), and one specifically for images. The projects/torbrowser/design/index.html.en 772) content cache is isolated to the URL bar domain by <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=7c58be929777d386a03e1faaee648909151fd951" target="_top">altering projects/torbrowser/design/index.html.en 773) each cache key</a> to include an additional ID that includes the URL bar projects/torbrowser/design/index.html.en 774) domain. This functionality can be observed by navigating to <a class="ulink" href="about:cache" target="_top">about:cache</a> and viewing the key used for each cache projects/torbrowser/design/index.html.en 775) entry. Each third party element should have an additional "id=string"
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 776) property prepended, which will list the FQDN that was used to source it.`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 777)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 778) </p><p> projects/torbrowser/design/index.html.en 779) projects/torbrowser/design/index.html.en 780) Additionally, because the image cache is a separate entity from the content`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 781) cache, we had to patch Firefox to also <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=d8b98a75fb200268c40886d876adc19e00b933bf" target="_top">isolate`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 782) this cache per URL bar domain</a>.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 783)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 784) </p></li><li class="listitem"><span class="command"><strong>HTTP Authentication</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 785)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 786) HTTP Authorization headers can be used to encode <a class="ulink" href="http://jeremiahgrossman.blogspot.com/2007/04/tracking-users-without-cookies.html" target="_top">silent`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 787) third party tracking identifiers</a>. To prevent this, we remove HTTP projects/torbrowser/design/index.html.en 788) authentication tokens for third party elements through a <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=b8ce4a0760759431f146c71184c89fbd5e1a27e4" target="_top">patch`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 789) to nsHTTPChannel</a>.`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 790)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 791) </p></li><li class="listitem"><span class="command"><strong>DOM Storage</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 792)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 793) 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 794) to prevent linkability between sites. This functionality is provided through a`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 795) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=97490c4a90ca1c43374486d9ec0c5593d5fe5720" target="_top">patch`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 796) to Firefox</a>.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 797)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 798) </p></li><li class="listitem"><span class="command"><strong>Flash cookies</strong></span><p><span class="command"><strong>Design Goal:</strong></span>`
Describe our efforts agains... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 799) projects/torbrowser/design/index.html.en 800) Users should be able to click-to-play flash objects from trusted sites. To projects/torbrowser/design/index.html.en 801) 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 802) 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 13 years ago	`projects/torbrowser/design/index.html.en 803) settings manager</a>.`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 804)`
Describe our efforts agains... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 805) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/torbrowser/design/index.html.en 806)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 807) 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 13 years ago	`projects/torbrowser/design/index.html.en 808) difficulties</a> causing Flash player to use this settings`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 809) file on Windows, so Flash remains difficult to enable.`
Describe our efforts agains... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 810)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 811) </p></li><li class="listitem"><span class="command"><strong>SSL+TLS session resumption</strong></span><p><span class="command"><strong>Design Goal:</strong></span>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 812)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 813) TLS session resumption tickets and SSL Session IDs MUST be limited to the URL`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 814) bar origin.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 815) projects/en/torbrowser/design/index.html.en 816) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 817)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 818) 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 819) Identity</a>, we disable TLS Session Tickets via the Firefox Pref projects/torbrowser/design/index.html.en 820) <span class="command"><strong>security.enable_tls_session_tickets</strong></span>. We disable SSL Session`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 821) IDs via a <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=a01fb747d4b8b24687de538cb6a1304fe27d9d88" target="_top">patch`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 822) to Firefox</a>. To compensate for the increased round trip latency from disabling projects/torbrowser/design/index.html.en 823) these performance optimizations, we also enable`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 824) <a class="ulink" href="https://tools.ietf.org/html/draft-bmoeller-tls-falsestart-00" target="_top">TLS`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 825) False Start</a> via the Firefox Pref`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 826) <span class="command"><strong>security.ssl.enable_false_start</strong></span>.`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 827) </p></li><li class="listitem"><span class="command"><strong>Tor circuit and HTTP connection linkability</strong></span><p> projects/torbrowser/design/index.html.en 828) projects/torbrowser/design/index.html.en 829) Tor circuits and HTTP connections from a third party in one URL bar origin projects/torbrowser/design/index.html.en 830) MUST NOT be reused for that same third party in another URL bar origin.`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 831) projects/torbrowser/design/index.html.en 832) </p><p> projects/torbrowser/design/index.html.en 833) projects/torbrowser/design/index.html.en 834) This isolation functionality is provided by the combination of a <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=b3ea705cc35b79a9ba27323cb3e32d5d004ea113" target="_top">Firefox`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 835) patch to allow SOCKS usernames and passwords</a>, as well as a Torbutton`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 836) component that <a class="ulink" href="" target="_top">sets projects/torbrowser/design/index.html.en 837) the SOCKS username and password for each request</a>. The Tor client has projects/torbrowser/design/index.html.en 838) logic to prevent connections with different SOCKS usernames and passwords from`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 839) using the same Tor circuit. Firefox has existing logic to ensure that connections with projects/torbrowser/design/index.html.en 840) SOCKS proxies do not re-use existing HTTP Keep-Alive connections unless the projects/torbrowser/design/index.html.en 841) proxy settings match. We extended this logic to cover SOCKS username and projects/torbrowser/design/index.html.en 842) password authentication, providing us with HTTP Keep-Alive unlinkability.`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 843)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 844) </p></li><li class="listitem"><span class="command"><strong>SharedWorkers</strong></span><p>`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 845) projects/torbrowser/design/index.html.en 846) <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Web/API/SharedWorker" target="_top">SharedWorkers</a> projects/torbrowser/design/index.html.en 847) are a special form of Javascript Worker Threads that have a shared scope projects/torbrowser/design/index.html.en 848) between all threads from the same Javascript origin. projects/torbrowser/design/index.html.en 849) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 850) projects/torbrowser/design/index.html.en 851) SharedWorker scope MUST be isolated to the URL bar domain. A SharedWorker projects/torbrowser/design/index.html.en 852) launched from a third party from one URL bar domain MUST NOT have access to projects/torbrowser/design/index.html.en 853) the objects created by that same third party loaded under another URL bar domain.
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 854)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 855) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/torbrowser/design/index.html.en 856) projects/torbrowser/design/index.html.en 857) For now, we disable SharedWorkers via the pref projects/torbrowser/design/index.html.en 858) <span class="command"><strong>dom.workers.sharedWorkers.enabled</strong></span>. projects/torbrowser/design/index.html.en 859)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 860) </p></li><li class="listitem"><span class="command"><strong>blob: URIs (URL.createObjectURL)</strong></span><p>`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 861) projects/torbrowser/design/index.html.en 862) The <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Web/API/URL/createObjectURL" target="_top">URL.createObjectURL</a> projects/torbrowser/design/index.html.en 863) API allows a site to load arbitrary content into a random UUID that is stored projects/torbrowser/design/index.html.en 864) in the user's browser, and this content can be accessed via a URL of the form projects/torbrowser/design/index.html.en 865) <span class="command"><strong>blob:UUID</strong></span> from any other content element anywhere on the projects/torbrowser/design/index.html.en 866) web. While this UUID value is neither under control of the site nor projects/torbrowser/design/index.html.en 867) predictable, it can still be used to tag a set of users that are of high projects/torbrowser/design/index.html.en 868) interest to an adversary.
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 869)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 870) </p><p>`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 871) projects/torbrowser/design/index.html.en 872) URIs created with URL.createObjectURL MUST be limited in scope to the first projects/torbrowser/design/index.html.en 873) party URL bar domain that created them. We provide this isolation in Tor projects/torbrowser/design/index.html.en 874) Browser via a <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=0d67ab406bdd3cf095802cb25c081641aa1f0bcc" target="_top">direct
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 875) patch to Firefox</a> and disable URL.createObjectURL in the WebWorker projects/torbrowser/design/index.html.en 876) context as a stopgap, due to an edge case with enforcing this isolation in projects/torbrowser/design/index.html.en 877) WebWorkers.`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 878)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 879) </p></li><li class="listitem"><span class="command"><strong>SPDY</strong></span><p>`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 880) projects/torbrowser/design/index.html.en 881) Because SPDY can store identifiers, it is disabled through the projects/torbrowser/design/index.html.en 882) Firefox preference <span class="command"><strong>network.http.spdy.enabled</strong></span>. projects/torbrowser/design/index.html.en 883)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 884) </p></li><li class="listitem"><span class="command"><strong>Automated cross-origin redirects</strong></span><p><span class="command"><strong>Design Goal:</strong></span>`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 885) projects/torbrowser/design/index.html.en 886) To prevent attacks aimed at subverting the Cross-Origin Identifier projects/torbrowser/design/index.html.en 887) 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 888) MUST NOT store any identifiers (cookies, cache, DOM storage, HTTP auth, etc) projects/torbrowser/design/index.html.en 889) for cross-origin redirect intermediaries that do not prompt for user input.`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 890) For example, if a user clicks on a bit.ly URL that redirects to a projects/torbrowser/design/index.html.en 891) doubleclick.net URL that finally redirects to a cnn.com URL, only cookies from`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 892) cnn.com should be retained after the redirect chain completes.`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 893) projects/torbrowser/design/index.html.en 894) </p><p> projects/torbrowser/design/index.html.en 895)`
Update design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 896) Non-automated redirect chains that require user input at some step (such as projects/torbrowser/design/index.html.en 897) federated login systems) SHOULD still allow identifiers to persist.`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 898)`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 899) </p><p><span class="command"><strong>Implementation status:</strong></span> projects/torbrowser/design/index.html.en 900) projects/torbrowser/design/index.html.en 901) 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 902) 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 13 years ago	`projects/torbrowser/design/index.html.en 903) open</a> to implement what we can. projects/torbrowser/design/index.html.en 904)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 905) </p></li><li class="listitem"><span class="command"><strong>window.name</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 906)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 907) <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 13 years ago	`projects/en/torbrowser/design/index.html.en 908) a magical DOM property that for some reason is allowed to retain a persistent value projects/en/torbrowser/design/index.html.en 909) 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 910) <a class="ulink" href="http://www.thomasfrank.se/sessionvars.html" target="_top">identifier`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 911) storage</a>. projects/en/torbrowser/design/index.html.en 912) projects/en/torbrowser/design/index.html.en 913) </p><p> projects/en/torbrowser/design/index.html.en 914)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 915) In order to eliminate non-consensual linkability but still allow for sites projects/torbrowser/design/index.html.en 916) 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 917) 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 918) allows window.name to persist for the duration of a click-driven navigation projects/torbrowser/design/index.html.en 919) session, but as soon as the user enters a new URL or navigates between`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 920) HTTPS/HTTP schemes, the property is cleared.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 921)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 922) </p></li><li class="listitem"><span class="command"><strong>Auto form-fill</strong></span><p>`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 923) projects/torbrowser/design/index.html.en 924) 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 925) <a class="link" href="#disk-avoidance" title="4.3. Disk Avoidance">Disk Avoidance</a> requirement. However,`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 926) 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 927) 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 13 years ago	`projects/torbrowser/design/index.html.en 928) preference to false to prevent saved values from immediately populating projects/torbrowser/design/index.html.en 929) fields upon page load. Since Javascript can read these values as soon as they projects/torbrowser/design/index.html.en 930) appear, setting this preference prevents automatic linkability from stored passwords. projects/torbrowser/design/index.html.en 931)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 932) </p></li><li class="listitem"><span class="command"><strong>HSTS supercookies</strong></span><p>`
Additional comments from Ge... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 933)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 934) 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 13 years ago	`projects/torbrowser/design/index.html.en 935) supercookies</a>. Since HSTS effectively stores one bit of information per domain`
Update TBB design doc based... Mike Perry authored 13 years ago	projects/torbrowser/design/index.html.en 936) name, an adversary in possession of numerous domains can use them to construct projects/torbrowser/design/index.html.en 937) cookies based on stored HSTS state. projects/torbrowser/design/index.html.en 938) projects/torbrowser/design/index.html.en 939) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 940) projects/torbrowser/design/index.html.en 941) There appears to be three options for us: 1. Disable HSTS entirely, and rely
Additional comments from Ge... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 942) instead on HTTPS-Everywhere to crawl and ship rules for HSTS sites. 2.`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 943) Restrict the number of HSTS-enabled third parties allowed per URL bar origin.`
Additional comments from Ge... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 944) 3. Prevent third parties from storing HSTS rules. We have not yet decided upon projects/torbrowser/design/index.html.en 945) the best approach.`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 946) projects/torbrowser/design/index.html.en 947) </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 948) 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 13 years ago	`projects/torbrowser/design/index.html.en 949) defend against the creation of these cookies between <span class="command"><strong>New projects/torbrowser/design/index.html.en 950) Identity</strong></span> invocations.`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 951) </p></li></ol></div><p>`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 952) 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 Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 953) </p></div></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 13 years ago	`projects/en/torbrowser/design/index.html.en 954)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 955) Browser fingerprinting is the act of inspecting browser behaviors and features in projects/torbrowser/design/index.html.en 956) an attempt to differentiate and track individual users. Fingerprinting attacks projects/torbrowser/design/index.html.en 957) are typically broken up into passive and active vectors. Passive projects/torbrowser/design/index.html.en 958) fingerprinting makes use of any information the browser provides automatically projects/torbrowser/design/index.html.en 959) to a website without any specific action on the part of the website. Active projects/torbrowser/design/index.html.en 960) fingerprinting makes use of any information that can be extracted from the projects/torbrowser/design/index.html.en 961) browser by some specific website action, usually involving Javascript. projects/torbrowser/design/index.html.en 962) Some definitions of browser fingerprinting also include supercookies and projects/torbrowser/design/index.html.en 963) cookie-like identifier storage, but we deal with those issues separately in projects/torbrowser/design/index.html.en 964) the <a class="link" href="#identifier-linkability" title="4.5. Cross-Origin Identifier Unlinkability">preceding section on identifier projects/torbrowser/design/index.html.en 965) linkability</a>.
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 966) projects/en/torbrowser/design/index.html.en 967) </p><p> projects/en/torbrowser/design/index.html.en 968)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 969) For the most part, however, we do not differentiate between passive or active projects/torbrowser/design/index.html.en 970) fingerprinting sources, since many active fingerprinting mechanisms are very projects/torbrowser/design/index.html.en 971) rapid, and can be obfuscated or disguised as legitimate functionality. projects/torbrowser/design/index.html.en 972) Instead, we believe fingerprinting can only be rationally addressed if we projects/torbrowser/design/index.html.en 973) understand where the problem comes from, what sources of issues are the most projects/torbrowser/design/index.html.en 974) severe, and how to study the efficacy of defenses properly. projects/torbrowser/design/index.html.en 975) projects/torbrowser/design/index.html.en 976) </p><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="fingerprinting-scope"></a>Sources of Fingerprinting Issues</h4></div></div></div><p> projects/torbrowser/design/index.html.en 977)
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 978) All browser fingerprinting issues arise from one of four primary sources: projects/torbrowser/design/index.html.en 979) end-user configuration details, device and hardware characteristics, operating projects/torbrowser/design/index.html.en 980) system vendor and version differences, and browser vendor and version projects/torbrowser/design/index.html.en 981) differences. Additionally, user behavior itself provides one more source of projects/torbrowser/design/index.html.en 982) potential fingerprinting. projects/torbrowser/design/index.html.en 983) projects/torbrowser/design/index.html.en 984) </p><p> projects/torbrowser/design/index.html.en 985) projects/torbrowser/design/index.html.en 986) In order to help prioritize and inform defenses, we now list these sources in projects/torbrowser/design/index.html.en 987) order from most severe to least severe in terms of the amount of information projects/torbrowser/design/index.html.en 988) they reveal, and describe them in more detail.
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 989) projects/torbrowser/design/index.html.en 990) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>End-user Configuration Details</strong></span><p> projects/torbrowser/design/index.html.en 991) projects/torbrowser/design/index.html.en 992) End-user configuration details are by far the most severe threat to projects/torbrowser/design/index.html.en 993) fingerprinting, as they will quickly provide enough information to uniquely projects/torbrowser/design/index.html.en 994) identify a user. We believe it is essential to avoid exposing platform projects/torbrowser/design/index.html.en 995) configuration details to website content at all costs. We also discourage projects/torbrowser/design/index.html.en 996) excessive fine-grained customization of Tor Browser by minimizing and projects/torbrowser/design/index.html.en 997) aggregating user-facing privacy and security options, as well as by projects/torbrowser/design/index.html.en 998) discouraging the use of additional addons. When it is necessary to expose projects/torbrowser/design/index.html.en 999) configuration details in the course of providing functionality, we strive to projects/torbrowser/design/index.html.en 1000) do so only on a per-site basis via site permissions, to avoid linkability. projects/torbrowser/design/index.html.en 1001) projects/torbrowser/design/index.html.en 1002) </p></li><li class="listitem"><span class="command"><strong>Device and Hardware Characteristics</strong></span><p> projects/torbrowser/design/index.html.en 1003)
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1004) Device and hardware characteristics can be determined in three ways: they can projects/torbrowser/design/index.html.en 1005) be reported explicitly by the browser, they can be inferred through browser projects/torbrowser/design/index.html.en 1006) functionality, or they can be extracted through statistical measurements of projects/torbrowser/design/index.html.en 1007) system performance. We are most concerned with the cases where this projects/torbrowser/design/index.html.en 1008) information is either directly reported or can be determined via a single use projects/torbrowser/design/index.html.en 1009) of an API or feature, and prefer to place such APIs either behind site projects/torbrowser/design/index.html.en 1010) permissions, alter their functionality to prevent exposing the most variable projects/torbrowser/design/index.html.en 1011) aspects of these characteristics, or disable them entirely. projects/torbrowser/design/index.html.en 1012)
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1013) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1014)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1015) On the other hand, because statistical inference of system performance projects/torbrowser/design/index.html.en 1016) requires many iterations to achieve accuracy in the face of noise and projects/torbrowser/design/index.html.en 1017) concurrent activity, we are less concerned with this mechanism of extracting projects/torbrowser/design/index.html.en 1018) this information. We also expect that reducing the resolution of Javascript's projects/torbrowser/design/index.html.en 1019) time sources will significantly increase the duration of execution required to projects/torbrowser/design/index.html.en 1020) extract accurate results, and thus make statistical approaches both projects/torbrowser/design/index.html.en 1021) unattractive and highly noticeable due to excessive resource consumption. projects/torbrowser/design/index.html.en 1022) projects/torbrowser/design/index.html.en 1023) </p></li><li class="listitem"><span class="command"><strong>Operating System Vendor and Version Differences</strong></span><p> projects/torbrowser/design/index.html.en 1024) projects/torbrowser/design/index.html.en 1025) Operating system vendor and version differences permeate many different projects/torbrowser/design/index.html.en 1026) aspects of the browser. While it is possible to address these issues with some projects/torbrowser/design/index.html.en 1027) effort, the relative lack of diversity in operating systems causes us to projects/torbrowser/design/index.html.en 1028) primarily focus our efforts on passive operating system fingerprinting projects/torbrowser/design/index.html.en 1029) mechanisms at this point in time. For the purposes of protecting user projects/torbrowser/design/index.html.en 1030) anonymity, it is not strictly essential that the operating system be projects/torbrowser/design/index.html.en 1031) completely concealed, though we recognize that it is useful to reduce this projects/torbrowser/design/index.html.en 1032) differentiation ability where possible, especially for cases where the projects/torbrowser/design/index.html.en 1033) specific version of a system can be inferred. projects/torbrowser/design/index.html.en 1034)
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1035) </p></li><li class="listitem"><span class="command"><strong>User Behavior</strong></span><p> projects/torbrowser/design/index.html.en 1036) projects/torbrowser/design/index.html.en 1037) While somewhat outside the scope of browser fingerprinting, for completeness projects/torbrowser/design/index.html.en 1038) it is important to mention that users themselves theoretically might be projects/torbrowser/design/index.html.en 1039) fingerprinted through their behavior while interacting with a website. This projects/torbrowser/design/index.html.en 1040) behavior includes e.g. keystrokes, mouse movements, click speed, and writing projects/torbrowser/design/index.html.en 1041) style. Basic vectors such as keystroke and mouse usage fingerprinting can be projects/torbrowser/design/index.html.en 1042) mitigated by altering Javascript's notion of time. More advanced issues like projects/torbrowser/design/index.html.en 1043) writing style fingerprinting are the domain of <a class="ulink" href="https://github.com/psal/anonymouth" target="_top">other tools</a>. projects/torbrowser/design/index.html.en 1044)
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1045) </p></li><li class="listitem"><span class="command"><strong>Browser Vendor and Version Differences</strong></span><p> projects/torbrowser/design/index.html.en 1046) projects/torbrowser/design/index.html.en 1047) Due to vast differences in feature set and implementation behavior even projects/torbrowser/design/index.html.en 1048) between different versions of the same browser, browser vendor and version projects/torbrowser/design/index.html.en 1049) differences are simply not possible to conceal in any realistic way. It projects/torbrowser/design/index.html.en 1050) is only possible to minimize the differences among different installations of projects/torbrowser/design/index.html.en 1051) the same browser vendor and version. We make no effort to mimic any other projects/torbrowser/design/index.html.en 1052) major browser vendor, and in fact most of our fingerprinting defenses serve to projects/torbrowser/design/index.html.en 1053) differentiate Tor Browser users from normal Firefox users. Because of this,
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1054) any study that lumps browser vendor and version differences into its analysis`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1055) of the fingerprintability of a population is largely useless for evaluating projects/torbrowser/design/index.html.en 1056) either attacks or defenses. Unfortunately, this includes popular large-scale projects/torbrowser/design/index.html.en 1057) studies such as <a class="ulink" href="https://panopticlick.eff.org/" target="_top">Panopticlick</a> and <a class="ulink" href="https://amiunique.org/" target="_top">Am I Unique</a>. projects/torbrowser/design/index.html.en 1058)
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1059) </p></li></ol></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="fingerprinting-defenses-general"></a>General Fingerprinting Defenses</h4></div></div></div><p> projects/torbrowser/design/index.html.en 1060) projects/torbrowser/design/index.html.en 1061) To date, the Tor Browser team has concerned itself only with developing`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1062) defenses for APIs that have already been standardized and deployed. Once an`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1063) API or feature has been standardized and widely deployed, defenses to the projects/torbrowser/design/index.html.en 1064) associated fingerprinting issues tend to have only a few options available to`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1065) compensate for the lack of up-front privacy design. In our experience, so far projects/torbrowser/design/index.html.en 1066) these options have been limited to value spoofing, subsystem reimplementation,`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1067) virtualization, site permissions, and feature removal. We will now describe projects/torbrowser/design/index.html.en 1068) these options and the fingerprinting sources they tend to work best with. projects/torbrowser/design/index.html.en 1069) projects/torbrowser/design/index.html.en 1070) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Value Spoofing</strong></span><p> projects/torbrowser/design/index.html.en 1071) projects/torbrowser/design/index.html.en 1072) Value spoofing can be used for simple cases where the browser directly projects/torbrowser/design/index.html.en 1073) provides some aspect of the user's configuration details, devices, hardware, projects/torbrowser/design/index.html.en 1074) or operating system directly to a website. It becomes less useful when the projects/torbrowser/design/index.html.en 1075) fingerprinting method relies on behavior to infer aspects of the hardware or projects/torbrowser/design/index.html.en 1076) operating system, rather than obtain them directly. projects/torbrowser/design/index.html.en 1077) projects/torbrowser/design/index.html.en 1078) </p></li><li class="listitem"><span class="command"><strong>Subsystem Reimplementation</strong></span><p> projects/torbrowser/design/index.html.en 1079) projects/torbrowser/design/index.html.en 1080) In cases where simple spoofing is not enough to properly conceal underlying projects/torbrowser/design/index.html.en 1081) device characteristics or operating system details, the underlying projects/torbrowser/design/index.html.en 1082) subsystem that provides the functionality for a feature or API may need projects/torbrowser/design/index.html.en 1083) to be completely reimplemented. This is most common in cases where projects/torbrowser/design/index.html.en 1084) customizable or version-specific aspects of the user's operating system are projects/torbrowser/design/index.html.en 1085) visible through the browser's featureset or APIs, usually because the browser projects/torbrowser/design/index.html.en 1086) directly exposes OS-provided implementations of underlying features. In these projects/torbrowser/design/index.html.en 1087) cases, such OS-provided implementations must be replaced by a generic projects/torbrowser/design/index.html.en 1088) implementation, or at least an implementation wrapper that makes effort to projects/torbrowser/design/index.html.en 1089) conceal any user-customized aspects of the system. projects/torbrowser/design/index.html.en 1090) projects/torbrowser/design/index.html.en 1091) </p></li><li class="listitem"><span class="command"><strong>Virtualization</strong></span><p> projects/torbrowser/design/index.html.en 1092) projects/torbrowser/design/index.html.en 1093) Virtualization is needed when simply reimplementing a feature in a different projects/torbrowser/design/index.html.en 1094) way is insufficient to fully conceal the underlying behavior. This is most projects/torbrowser/design/index.html.en 1095) common in instances of device and hardware fingerprinting, but since the projects/torbrowser/design/index.html.en 1096) notion of time can also be virtualized, virtualization also can apply to any projects/torbrowser/design/index.html.en 1097) instance where an accurate measurement of wall clock time is required for a projects/torbrowser/design/index.html.en 1098) fingerprinting vector to attain high accuracy. projects/torbrowser/design/index.html.en 1099) projects/torbrowser/design/index.html.en 1100) </p></li><li class="listitem"><span class="command"><strong>Site Permissions</strong></span><p> projects/torbrowser/design/index.html.en 1101) projects/torbrowser/design/index.html.en 1102) In the event that reimplementation or virtualization is too expensive in terms projects/torbrowser/design/index.html.en 1103) of performance or engineering effort, and the relative expected usage of a projects/torbrowser/design/index.html.en 1104) feature is rare, site permissions can be used to prevent the usage of a
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1105) feature for cross-site tracking. Unfortunately, site permissions become less projects/torbrowser/design/index.html.en 1106) effective once a feature is already widely overused and abused by many projects/torbrowser/design/index.html.en 1107) websites, since warning fatigue typically sets in for most users after just a projects/torbrowser/design/index.html.en 1108) few permission requests.`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1109)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1110) </p></li><li class="listitem"><span class="command"><strong>Feature or Functionality Removal</strong></span><p>`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1111) projects/torbrowser/design/index.html.en 1112) Due to the current bias in favor of invasive APIs that expose the maximum projects/torbrowser/design/index.html.en 1113) amount of platform information, some features and APIs are simply not projects/torbrowser/design/index.html.en 1114) salvageable in their current form. When such invasive features serve only a projects/torbrowser/design/index.html.en 1115) narrow domain or use case, or when there are alternate ways of accomplishing projects/torbrowser/design/index.html.en 1116) the same task, these features and/or certain aspects of their functionality projects/torbrowser/design/index.html.en 1117) may be simply removed. projects/torbrowser/design/index.html.en 1118)
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1119) </p></li></ol></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp56040528"></a>Randomization or Uniformity?</h4></div></div></div><p>`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1120)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1121) When applying a form of defense to a specific fingerprinting vector or source,`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1122) there are two general strategies available. Either the implementation for all`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1123) users of a single browser version can be made to behave as uniformly as`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1124) possible, or the user agent can attempt to randomize its behavior, so that projects/torbrowser/design/index.html.en 1125) each interaction between a user and a site provides a different fingerprint. projects/torbrowser/design/index.html.en 1126) projects/torbrowser/design/index.html.en 1127) </p><p> projects/torbrowser/design/index.html.en 1128) projects/torbrowser/design/index.html.en 1129) Although <a class="ulink" href="http://research.microsoft.com/pubs/209989/tr1.pdf" target="_top">some projects/torbrowser/design/index.html.en 1130) research suggests</a> that randomization can be effective, so far striving projects/torbrowser/design/index.html.en 1131) for uniformity has generally proved to be a better strategy for Tor Browser projects/torbrowser/design/index.html.en 1132) for the following reasons: projects/torbrowser/design/index.html.en 1133) projects/torbrowser/design/index.html.en 1134) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Randomization is not a shortcut</strong></span><p> projects/torbrowser/design/index.html.en 1135) projects/torbrowser/design/index.html.en 1136) While many end-user configuration details that the browser currently exposes projects/torbrowser/design/index.html.en 1137) may be safely replaced by false information, randomization of these details projects/torbrowser/design/index.html.en 1138) must be just as exhaustive as an approach that seeks to make these behaviors
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1139) uniform. When confronting either strategy, the adversary can still make use of projects/torbrowser/design/index.html.en 1140) any details which have not been altered to be either sufficiently uniform or projects/torbrowser/design/index.html.en 1141) sufficiently random.`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1142) projects/torbrowser/design/index.html.en 1143) </p><p> projects/torbrowser/design/index.html.en 1144) projects/torbrowser/design/index.html.en 1145) Furthermore, the randomization approach seems to break down when it is applied projects/torbrowser/design/index.html.en 1146) to deeper issues where underlying system functionality is directly exposed. In projects/torbrowser/design/index.html.en 1147) particular, it is not clear how to randomize the capabilities of hardware projects/torbrowser/design/index.html.en 1148) attached to a computer in such a way that it either convincingly behaves like
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1149) other hardware, or such that the exact properties of the hardware that vary projects/torbrowser/design/index.html.en 1150) from user to user are sufficiently randomized. Similarly, truly concealing projects/torbrowser/design/index.html.en 1151) operating system version differences through randomization may require projects/torbrowser/design/index.html.en 1152) multiple reimplementations of the underlying operating system functionality to projects/torbrowser/design/index.html.en 1153) ensure that every operating system version is covered by the range of possible projects/torbrowser/design/index.html.en 1154) behaviors.
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1155) projects/torbrowser/design/index.html.en 1156) </p></li><li class="listitem"><span class="command"><strong>Evaluation and measurement difficulties</strong></span><p> projects/torbrowser/design/index.html.en 1157) projects/torbrowser/design/index.html.en 1158) The fact that randomization causes behaviors to differ slightly with every projects/torbrowser/design/index.html.en 1159) site visit makes it appealing at first glance, but this same property makes it projects/torbrowser/design/index.html.en 1160) very difficult to objectively measure its effectiveness. By contrast, an projects/torbrowser/design/index.html.en 1161) implementation that strives for uniformity is very simple to measure. Despite projects/torbrowser/design/index.html.en 1162) their current flaws, a properly designed version of <a class="ulink" href="https://panopticlick.eff.org/" target="_top">Panopticlick</a> or <a class="ulink" href="https://amiunique.org/" target="_top">Am I Unique</a> could report the entropy and projects/torbrowser/design/index.html.en 1163) uniqueness rates for all users of a single user agent version, without the projects/torbrowser/design/index.html.en 1164) need for complicated statistics about the variance of the measured behaviors. projects/torbrowser/design/index.html.en 1165) projects/torbrowser/design/index.html.en 1166) </p><p> projects/torbrowser/design/index.html.en 1167) projects/torbrowser/design/index.html.en 1168) Randomization (especially incomplete randomization) may also provide a false projects/torbrowser/design/index.html.en 1169) sense of security. When a fingerprinting attempt makes naive use of randomized projects/torbrowser/design/index.html.en 1170) information, a fingerprint will appear unstable, but may not actually be projects/torbrowser/design/index.html.en 1171) sufficiently randomized to prevent a dedicated adversary. Sophisticated projects/torbrowser/design/index.html.en 1172) fingerprinting mechanisms may either ignore randomized information, or projects/torbrowser/design/index.html.en 1173) incorporate knowledge of the distribution and range of randomized values into projects/torbrowser/design/index.html.en 1174) the creation of a more stable fingerprint (by either removing the randomness,
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1175) modeling it, or averaging it out).`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1176) projects/torbrowser/design/index.html.en 1177) </p></li><li class="listitem"><span class="command"><strong>Usability issues</strong></span><p> projects/torbrowser/design/index.html.en 1178) projects/torbrowser/design/index.html.en 1179) When randomization is introduced to features that affect site behavior, it can projects/torbrowser/design/index.html.en 1180) be very distracting for this behavior to change between visits of a given`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1181) site. For the simplest cases, this will lead to minor visual nuisances. projects/torbrowser/design/index.html.en 1182) However, when this information affects reported functionality or hardware projects/torbrowser/design/index.html.en 1183) characteristics, sometimes a site will function one way on one visit, and projects/torbrowser/design/index.html.en 1184) another way on a subsequent visit.`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1185) projects/torbrowser/design/index.html.en 1186) </p></li><li class="listitem"><span class="command"><strong>Performance costs</strong></span><p> projects/torbrowser/design/index.html.en 1187) projects/torbrowser/design/index.html.en 1188) Randomizing involves performance costs. This is especially true if the projects/torbrowser/design/index.html.en 1189) fingerprinting surface is large (like in a modern browser) and one needs more projects/torbrowser/design/index.html.en 1190) elaborate randomizing strategies (including randomized virtualization) to projects/torbrowser/design/index.html.en 1191) ensure that the randomization fully conceals the true behavior. Many calls to projects/torbrowser/design/index.html.en 1192) a cryptographically secure random number generator during the course of a page projects/torbrowser/design/index.html.en 1193) load will both serve to exhaust available entropy pools, as well as lead to projects/torbrowser/design/index.html.en 1194) increased computation while loading a page. projects/torbrowser/design/index.html.en 1195) projects/torbrowser/design/index.html.en 1196) </p></li><li class="listitem"><span class="command"><strong>Increased vulnerability surface</strong></span><p> projects/torbrowser/design/index.html.en 1197) projects/torbrowser/design/index.html.en 1198) Improper randomization might introduce a new fingerprinting vector, as the projects/torbrowser/design/index.html.en 1199) process of generating the values for the fingerprintable attributes could be projects/torbrowser/design/index.html.en 1200) itself susceptible to side-channel attacks, analysis, or exploitation. projects/torbrowser/design/index.html.en 1201) projects/torbrowser/design/index.html.en 1202) </p></li></ol></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="fingerprinting-defenses"></a>Specific Fingerprinting Defenses in the Tor Browser</h4></div></div></div><p>
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1203) projects/torbrowser/design/index.html.en 1204) The following defenses are listed roughly in order of most severe`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1205) fingerprinting threat first. This ordering is based on the above intuition projects/torbrowser/design/index.html.en 1206) that user configurable aspects of the computer are the most severe source of projects/torbrowser/design/index.html.en 1207) fingerprintability, followed by device characteristics and hardware, and then projects/torbrowser/design/index.html.en 1208) finally operating system vendor and version information.`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1209) projects/torbrowser/design/index.html.en 1210) </p><p>`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1211) projects/torbrowser/design/index.html.en 1212) Where our actual implementation differs from an ideal solution, we separately projects/torbrowser/design/index.html.en 1213) describe our <span class="command"><strong>Design Goal</strong></span> and our <span class="command"><strong>Implementation projects/torbrowser/design/index.html.en 1214) Status</strong></span>.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1215)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1216) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Plugins</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1217)`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1218) Plugins add to fingerprinting risk via two main vectors: their mere presence projects/torbrowser/design/index.html.en 1219) in window.navigator.plugins (because they are optional, end-user installed projects/torbrowser/design/index.html.en 1220) third party software), as well as their internal functionality.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1221) projects/en/torbrowser/design/index.html.en 1222) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1223)`
Update TBB design doc with... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 1224) All plugins that have not been specifically audited or sandboxed MUST be`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1225) disabled. To reduce linkability potential, even sandboxed plugins should not projects/en/torbrowser/design/index.html.en 1226) be allowed to load objects until the user has clicked through a click-to-play projects/en/torbrowser/design/index.html.en 1227) 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 1228) 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 1229) settings.sol file</a> to disable Flash cookies, and to restrict P2P`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1230) features that are likely to bypass proxy settings. We'd also like to restrict projects/torbrowser/design/index.html.en 1231) access to fonts and other system information (such as IP address and MAC projects/torbrowser/design/index.html.en 1232) address) in such a sandbox.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1233) projects/en/torbrowser/design/index.html.en 1234) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1235) projects/en/torbrowser/design/index.html.en 1236) 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 1237) compromise due to the popularity of Flash, we allow users to re-enable Flash, projects/torbrowser/design/index.html.en 1238) and flash objects are blocked behind a click-to-play barrier that is available projects/torbrowser/design/index.html.en 1239) only after the user has specifically enabled plugins. Flash is the only plugin`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1240) available, the rest are entirely projects/torbrowser/design/index.html.en 1241) blocked from loading by the Firefox patches mentioned in the <a class="link" href="#proxy-obedience" title="4.1. Proxy Obedience">Proxy Obedience projects/torbrowser/design/index.html.en 1242) section</a>. We also set the Firefox`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1243) preference <span class="command"><strong>plugin.expose_full_path</strong></span> to false, to avoid projects/torbrowser/design/index.html.en 1244) leaking plugin installation information. projects/torbrowser/design/index.html.en 1245)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1246) </p></li><li class="listitem"><span class="command"><strong>HTML5 Canvas Image Extraction</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1247)`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1248) 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 1249) Canvas</a> is the single largest fingerprinting threat browsers face projects/torbrowser/design/index.html.en 1250) 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 1251) studies</a> show that the Canvas can provide an easy-access fingerprinting projects/torbrowser/design/index.html.en 1252) target: The adversary simply renders WebGL, font, and named color data to a projects/torbrowser/design/index.html.en 1253) Canvas element, extracts the image buffer, and computes a hash of that image projects/torbrowser/design/index.html.en 1254) data. Subtle differences in the video card, font packs, and even font and projects/torbrowser/design/index.html.en 1255) graphics library versions allow the adversary to produce a stable, simple, projects/torbrowser/design/index.html.en 1256) high-entropy fingerprint of a computer. In fact, the hash of the rendered projects/torbrowser/design/index.html.en 1257) image can be used almost identically to a tracking cookie by the web server. projects/torbrowser/design/index.html.en 1258) projects/torbrowser/design/index.html.en 1259) </p><p> projects/torbrowser/design/index.html.en 1260)
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1261) In some sense, the canvas can be seen as the union of many other`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1262) fingerprinting vectors. If WebGL is normalized through software rendering, projects/torbrowser/design/index.html.en 1263) system colors were standardized, and the browser shipped a fixed collection of`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1264) fonts (see later points in this list), it might not be necessary to create a projects/torbrowser/design/index.html.en 1265) canvas permission. However, until then, to reduce the threat from this vector,`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1266) we have patched Firefox to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=6a169ef0166b268b1a27546a17b3d7470330917d" target="_top">prompt before returning valid image data</a> to the Canvas APIs, projects/torbrowser/design/index.html.en 1267) and for <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=7d51acca6383732480b49ccdb5506ad6fb92e651" target="_top">access to isPointInPath and related functions</a>. projects/torbrowser/design/index.html.en 1268) If the user hasn't previously allowed the site in the URL bar to access Canvas projects/torbrowser/design/index.html.en 1269) image data, pure white image data is returned to the Javascript APIs.
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1270) projects/torbrowser/design/index.html.en 1271) </p><p>`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1272) </p></li><li class="listitem"><span class="command"><strong>Open TCP Port and Local Network Fingerprinting</strong></span><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1273) projects/torbrowser/design/index.html.en 1274) In Firefox, by using either WebSockets or XHR, it is possible for remote projects/torbrowser/design/index.html.en 1275) content to <a class="ulink" href="http://www.andlabs.org/tools/jsrecon.html" target="_top">enumerate`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1276) the list of TCP ports open on 127.0.0.1</a>, as well as on any other projects/torbrowser/design/index.html.en 1277) machines on the local network. In other browsers, this can be accomplished by projects/torbrowser/design/index.html.en 1278) DOM events on image or script tags. This open vs filtered vs closed port list projects/torbrowser/design/index.html.en 1279) can provide a very unique fingerprint of a machine, because it essentially projects/torbrowser/design/index.html.en 1280) enables the detection of many different popular third party applications and projects/torbrowser/design/index.html.en 1281) optional system services (Skype, Bitcoin, Bittorrent and other P2P software, projects/torbrowser/design/index.html.en 1282) SSH ports, SMB and related LAN services, CUPS and printer daemon config ports, projects/torbrowser/design/index.html.en 1283) mail servers, and so on). It is also possible to determine when ports are projects/torbrowser/design/index.html.en 1284) closed versus filtered/blocked (and thus probe custom firewall configuration). projects/torbrowser/design/index.html.en 1285) projects/torbrowser/design/index.html.en 1286) </p><p> projects/torbrowser/design/index.html.en 1287) projects/torbrowser/design/index.html.en 1288) In Tor Browser, we prevent access to 127.0.0.1/localhost by ensuring that even projects/torbrowser/design/index.html.en 1289) these requests are still sent by Firefox to our SOCKS proxy (ie we set
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1290) <span class="command"><strong>network.proxy.no_proxies_on</strong></span> to the empty string). The local projects/torbrowser/design/index.html.en 1291) Tor client then rejects them, since it is configured to proxy for internal IP`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1292) addresses by default. Access to the local network is forbidden via the same projects/torbrowser/design/index.html.en 1293) mechanism. projects/torbrowser/design/index.html.en 1294)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1295) </p></li><li class="listitem"><span class="command"><strong>Invasive Authentication Mechanisms (NTLM and SPNEGO)</strong></span><p>`
Updates to fingerprinting s... Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1296) projects/torbrowser/design/index.html.en 1297) Both NTLM and SPNEGO authentication mechanisms can leak the hostname, and in projects/torbrowser/design/index.html.en 1298) some cases the current username. The only reason why these aren't a more projects/torbrowser/design/index.html.en 1299) serious problem is that they typically involve user interaction, and likely projects/torbrowser/design/index.html.en 1300) aren't an attractive vector for this reason. However, because it is not clear projects/torbrowser/design/index.html.en 1301) if certain carefully-crafted error conditions in these protocols could cause projects/torbrowser/design/index.html.en 1302) them to reveal machine information and still fail silently prior to the projects/torbrowser/design/index.html.en 1303) password prompt, these authentication mechanisms should either be disabled, or projects/torbrowser/design/index.html.en 1304) placed behind a site permission before their use. We simply disable them. projects/torbrowser/design/index.html.en 1305)
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1306) </p></li><li class="listitem"><span class="command"><strong>USB Device ID Enumeration</strong></span><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1307) projects/torbrowser/design/index.html.en 1308) 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 1309) 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 1310) device id, product id, and driver name</a> of all connected game projects/torbrowser/design/index.html.en 1311) controllers, as well as detailed information about their capabilities. This API projects/torbrowser/design/index.html.en 1312) should be behind a site permission in Private Browsing Modes, or should present a generic projects/torbrowser/design/index.html.en 1313) controller type (perhaps a two button controller that can be mapped to the keyboard) in all cases. projects/torbrowser/design/index.html.en 1314) 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 1315)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1316) </p></li><li class="listitem"><span class="command"><strong>Fonts</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1317) projects/en/torbrowser/design/index.html.en 1318) According to the Panopticlick study, fonts provide the most linkability when`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1319) they are provided as an enumerable list in file system order, via either the`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1320) Flash or Java plugins. However, it is still possible to use CSS and/or projects/en/torbrowser/design/index.html.en 1321) Javascript to query for the existence of specific fonts. With a large enough projects/en/torbrowser/design/index.html.en 1322) pre-built list to query, a large amount of fingerprintable information may`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1323) still be available, especially given that additional fonts often end up projects/torbrowser/design/index.html.en 1324) installed by third party software and for multilingual support.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1325)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1326) </p><p><span class="command"><strong>Design Goal:</strong></span> The sure-fire way to address font projects/torbrowser/design/index.html.en 1327) linkability is to ship the browser with a font for every language, typeface, projects/torbrowser/design/index.html.en 1328) and style, and to only use those fonts at the exclusion of system fonts. We are projects/torbrowser/design/index.html.en 1329) <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/13313" target="_top">currently projects/torbrowser/design/index.html.en 1330) investigating</a> this approach, and our current favorite font sets for projects/torbrowser/design/index.html.en 1331) this purpose are the <a class="ulink" href="http://www.droidfonts.com/droidfonts/" target="_top">Droid projects/torbrowser/design/index.html.en 1332) fonts</a>, the <a class="ulink" href="http://hangeul.naver.com/" target="_top">Nanum fonts</a>, projects/torbrowser/design/index.html.en 1333) and <a class="ulink" href="https://fedorahosted.org/lohit/" target="_top">Lohit fonts</a>. The Droid projects/torbrowser/design/index.html.en 1334) font set is fairly complete by itself, but Nanum and Lohit have smaller projects/torbrowser/design/index.html.en 1335) versions of many South Asian languages. When combined in a way that chooses the projects/torbrowser/design/index.html.en 1336) smallest font implementations for each locale, these three font sets provide
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1337) coverage for the all languages used on Wikipedia with more than`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1338) 10,000 articles, and several others as well, in approximately 3MB of compressed projects/torbrowser/design/index.html.en 1339) overhead. The <a class="ulink" href="https://www.google.com/get/noto/" target="_top">Noto font projects/torbrowser/design/index.html.en 1340) set</a> is another font set that aims for complete coverage, but is projects/torbrowser/design/index.html.en 1341) considerably larger than the combination of the Droid, Nanum, and Lohit fonts.
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1342)`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1343) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1344)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1345) In the meantime while we investigate shipping our own fonts, we disable`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1346) plugins, which prevents font name enumeration. Additionally, we limit both the`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1347) number of font queries from CSS, as well as the total number of fonts that can`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1348) be used in a document <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=e78bc05159a79c1358fa9c64e565af9d98c141ee" target="_top">with`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1349) 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 1350) <span class="command"><strong>browser.display.max_font_attempts</strong></span> and projects/torbrowser/design/index.html.en 1351) <span class="command"><strong>browser.display.max_font_count</strong></span> for this purpose. Once these projects/torbrowser/design/index.html.en 1352) limits are reached, the browser behaves as if`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1353) <span class="command"><strong>browser.display.use_document_fonts</strong></span> was set.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1354)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1355) </p><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1356)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1357) 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 1358) fonts</a> from these counts, and if a font-family CSS rule lists a remote projects/torbrowser/design/index.html.en 1359) font (in any order), we use that font instead of any of the named local fonts.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1360)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1361) </p></li><li class="listitem"><span class="command"><strong>Monitor, Widget, and OS Desktop Resolution</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1362)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1363) Both CSS and Javascript have access to a lot of information about the screen projects/torbrowser/design/index.html.en 1364) resolution, usable desktop size, OS widget size, toolbar size, title bar size,`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1365) and OS desktop widget sizing information that are not at all relevant to`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1366) rendering and serve only to provide information for fingerprinting. Since many projects/torbrowser/design/index.html.en 1367) aspects of desktop widget positioning and size are user configurable, these projects/torbrowser/design/index.html.en 1368) properties yield customized information about the computer, even beyond the projects/torbrowser/design/index.html.en 1369) monitor size.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1370) projects/en/torbrowser/design/index.html.en 1371) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1372) projects/en/torbrowser/design/index.html.en 1373) Our design goal here is to reduce the resolution information down to the bare`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1374) minimum required for properly rendering inside a content window. We intend to`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1375) report all rendering information correctly with respect to the size and projects/en/torbrowser/design/index.html.en 1376) properties of the content window, but report an effective size of 0 for all`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1377) border material, and also report that the desktop is only as big as the inner projects/torbrowser/design/index.html.en 1378) content window. Additionally, new browser windows are sized such that their projects/torbrowser/design/index.html.en 1379) content windows are one of a few fixed sizes based on the user's desktop projects/torbrowser/design/index.html.en 1380) resolution. In addition, to further reduce resolution-based fingerprinting, we projects/torbrowser/design/index.html.en 1381) are <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/7256" target="_top">investigating projects/torbrowser/design/index.html.en 1382) zoom/viewport-based mechanisms</a> that might allow us to always report the projects/torbrowser/design/index.html.en 1383) same desktop resolution regardless of the actual size of the content window, projects/torbrowser/design/index.html.en 1384) and simply scale to make up the difference. Until then, the user should also projects/torbrowser/design/index.html.en 1385) be informed that maximizing their windows can lead to fingerprintability under
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1386) this scheme.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1387) projects/en/torbrowser/design/index.html.en 1388) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1389)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1390) We automatically resize new browser windows to a 200x100 pixel multiple using`
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1391) a window observer <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/tree/src/chrome/content/torbutton.js#n3361" target="_top">based projects/torbrowser/design/index.html.en 1392) on desktop resolution</a>. To minimize the effect of the long tail of large projects/torbrowser/design/index.html.en 1393) monitor sizes, we also cap the window size at 1000 pixels in each direction. projects/torbrowser/design/index.html.en 1394) Additionally, we patch Firefox to use the client content window size <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=bd3b1ed32a9c21fdc92fc35f2ec0a41badc378d5" target="_top">for
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1395) window.screen</a>, and to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=a5648c8d80f396caf294d761cc4a9a76c0b33a9d" target="_top">report projects/torbrowser/design/index.html.en 1396) a window.devicePixelRatio of 1.0</a>. Similarly, we <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=3c02858027634ffcfbd97047dfdf170c19ca29ec" target="_top">patch
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1397) DOM events to return content window relative points</a>.`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1398)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1399) We also force popups to open in new tabs (via`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1400) <span class="command"><strong>browser.link.open_newwindow.restriction</strong></span>), to avoid projects/torbrowser/design/index.html.en 1401) full-screen popups inferring information about the browser resolution. In`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1402) addition, we prevent auto-maximizing on browser start, and inform users that projects/torbrowser/design/index.html.en 1403) maximized windows are detrimental to privacy in this mode.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1404)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1405) </p></li><li class="listitem"><span class="command"><strong>Display Media information</strong></span><p>`
Update design doc to descri... Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1406)`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1407) Beyond simple resolution information, a large amount of so-called "Media" projects/torbrowser/design/index.html.en 1408) information is also exported to content. Even without Javascript, CSS has projects/torbrowser/design/index.html.en 1409) access to a lot of information about the device orientation, system theme`
More fingerprinting clarifi... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1410) colors, and other desktop and display features that are not at all relevant to projects/torbrowser/design/index.html.en 1411) rendering and also user configurable. Most of this`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1412) 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 1413) 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 1414) user and OS theme defined color values</a> to CSS as well.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1415) projects/torbrowser/design/index.html.en 1416) </p><p><span class="command"><strong>Design Goal:</strong></span>`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1417) projects/torbrowser/design/index.html.en 1418) CSS should not be able infer anything that the user has configured about their projects/torbrowser/design/index.html.en 1419) computer. Additionally, it should not be able to infer machine-specific projects/torbrowser/design/index.html.en 1420) details such as screen orientation or type.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1421) projects/torbrowser/design/index.html.en 1422) </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 1423)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1424) We patch`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1425) Firefox to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=cf8956b4460107c5b0053c8fc574e34b0a30ec1e" target="_top">report projects/torbrowser/design/index.html.en 1426) a fixed set of system colors to content window CSS</a>, and <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=bbc138486e0489b0d559343fa0522df4ee3b3533" target="_top">prevent projects/torbrowser/design/index.html.en 1427) detection of font smoothing on OSX</a>. We also always projects/torbrowser/design/index.html.en 1428) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=e17d60442ab0db92664ff68d90fe7bf737374912" target="_top">report
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1429) landscape-primary</a> for the screen orientation.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1430)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1431) </p></li><li class="listitem"><span class="command"><strong>WebGL</strong></span><p>`
Updates to fingerprinting s... Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1432) projects/torbrowser/design/index.html.en 1433) WebGL is fingerprintable both through information that is exposed about the projects/torbrowser/design/index.html.en 1434) underlying driver and optimizations, as well as through performance projects/torbrowser/design/index.html.en 1435) fingerprinting. projects/torbrowser/design/index.html.en 1436) projects/torbrowser/design/index.html.en 1437) </p><p> projects/torbrowser/design/index.html.en 1438) projects/torbrowser/design/index.html.en 1439) 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 1440) vulnerability surface</a>, we deploy a similar strategy against WebGL as projects/torbrowser/design/index.html.en 1441) for plugins. First, WebGL Canvases have click-to-play placeholders (provided projects/torbrowser/design/index.html.en 1442) by NoScript), and do not run until authorized by the user. Second, we projects/torbrowser/design/index.html.en 1443) obfuscate driver information by setting the Firefox preferences projects/torbrowser/design/index.html.en 1444) <span class="command"><strong>webgl.disable-extensions</strong></span> and projects/torbrowser/design/index.html.en 1445) <span class="command"><strong>webgl.min_capability_mode</strong></span>, which reduce the information projects/torbrowser/design/index.html.en 1446) provided by the following WebGL API calls: <span class="command"><strong>getParameter()</strong></span>, projects/torbrowser/design/index.html.en 1447) <span class="command"><strong>getSupportedExtensions()</strong></span>, and projects/torbrowser/design/index.html.en 1448) <span class="command"><strong>getExtension()</strong></span>. projects/torbrowser/design/index.html.en 1449) projects/torbrowser/design/index.html.en 1450) </p><p> projects/torbrowser/design/index.html.en 1451) projects/torbrowser/design/index.html.en 1452) Another option for WebGL might be to use software-only rendering, using a projects/torbrowser/design/index.html.en 1453) library such as <a class="ulink" href="http://www.mesa3d.org/" target="_top">Mesa</a>. The use of projects/torbrowser/design/index.html.en 1454) such a library would avoid hardware-specific rendering differences. projects/torbrowser/design/index.html.en 1455)
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1456) </p></li><li class="listitem"><span class="command"><strong>User Agent and HTTP Headers</strong></span><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 1457)`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1458) All Tor Browser users MUST provide websites with an identical user agent and projects/torbrowser/design/index.html.en 1459) HTTP header set for a given request type. We omit the Firefox minor revision, projects/torbrowser/design/index.html.en 1460) and report a popular Windows platform. If the software is kept up to date, projects/torbrowser/design/index.html.en 1461) these headers should remain identical across the population even when updated. projects/torbrowser/design/index.html.en 1462) projects/torbrowser/design/index.html.en 1463) </p><p><span class="command"><strong>Implementation Status:</strong></span>
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1464)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1465) Firefox provides several options for controlling the browser user agent string projects/torbrowser/design/index.html.en 1466) which we leverage. We also set similar prefs for controlling the projects/torbrowser/design/index.html.en 1467) Accept-Language and Accept-Charset headers, which we spoof to English by default. Additionally, we`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1468) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=e9841ee41e7f3f1535be2d605084c41ee9faf6c2" target="_top">remove`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1469) 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 Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1470) used</a> to fingerprint OS, platform, and Firefox minor version. </p></li><li class="listitem"><span class="command"><strong>Locale Fingerprinting</strong></span><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1471) projects/torbrowser/design/index.html.en 1472) In Tor Browser, we provide non-English users the option of concealing their OS projects/torbrowser/design/index.html.en 1473) and browser locale from websites. It is debatable if this should be as high of projects/torbrowser/design/index.html.en 1474) a priority as information specific to the user's computer, but for projects/torbrowser/design/index.html.en 1475) completeness, we attempt to maintain this property. projects/torbrowser/design/index.html.en 1476) projects/torbrowser/design/index.html.en 1477) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/torbrowser/design/index.html.en 1478) projects/torbrowser/design/index.html.en 1479) We set the fallback character set to set to windows-1252 for all locales, via projects/torbrowser/design/index.html.en 1480) <span class="command"><strong>intl.charset.default</strong></span>. We also patch Firefox to allow us to
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1481) <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=4545ecd6dc2ca7d10aefe36b81658547ea97b800" target="_top">instruct`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1482) the JS engine</a> to use en-US as its internal C locale for all Date, Math, projects/torbrowser/design/index.html.en 1483) and exception handling. projects/torbrowser/design/index.html.en 1484)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1485) </p></li><li class="listitem"><span class="command"><strong>Timezone and Clock Offset</strong></span><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1486) projects/torbrowser/design/index.html.en 1487) While the latency in Tor connections varies anywhere from milliseconds to`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1488) a few seconds, it is still possible for the remote site to detect large projects/torbrowser/design/index.html.en 1489) differences between the user's clock and an official reference time source. projects/torbrowser/design/index.html.en 1490)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1491) </p><p><span class="command"><strong>Design Goal:</strong></span>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1492)`
Update TBB design doc with... Mike Perry authored 13 years ago	projects/torbrowser/design/index.html.en 1493) All Tor Browser users MUST report the same timezone to websites. Currently, we projects/torbrowser/design/index.html.en 1494) choose UTC for this purpose, although an equally valid argument could be made projects/torbrowser/design/index.html.en 1495) for EDT/EST due to the large English-speaking population density (coupled with projects/torbrowser/design/index.html.en 1496) the fact that we spoof a US English user agent). Additionally, the Tor projects/torbrowser/design/index.html.en 1497) software should detect if the users clock is significantly divergent from the projects/torbrowser/design/index.html.en 1498) 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 10 years ago	`projects/torbrowser/design/index.html.en 1499) values used in Tor Browser to something reasonably accurate. Alternatively, projects/torbrowser/design/index.html.en 1500) the browser can obtain this clock skew via a mechanism similar to that used in`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1501) <a class="ulink" href="https://github.com/ioerror/tlsdate" target="_top">tlsdate</a>.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1502) projects/en/torbrowser/design/index.html.en 1503) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1504) projects/en/torbrowser/design/index.html.en 1505) We set the timezone using the TZ environment variable, which is supported on`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1506) all platforms.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1507)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1508) </p></li><li class="listitem"><span class="command"><strong>Javascript Performance Fingerprinting</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1509)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1510) <a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf" target="_top">Javascript performance`
Add design doc draft. Mike Perry authored 13 years ago	projects/en/torbrowser/design/index.html.en 1511) fingerprinting</a> is the act of profiling the performance projects/en/torbrowser/design/index.html.en 1512) of various Javascript functions for the purpose of fingerprinting the projects/en/torbrowser/design/index.html.en 1513) Javascript engine and the CPU. projects/en/torbrowser/design/index.html.en 1514) projects/en/torbrowser/design/index.html.en 1515) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1516)
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1517) 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 13 years ago	`projects/en/torbrowser/design/index.html.en 1518) mitigation approaches</a> to reduce the accuracy of performance projects/en/torbrowser/design/index.html.en 1519) fingerprinting without risking too much damage to functionality. Our current projects/en/torbrowser/design/index.html.en 1520) favorite is to reduce the resolution of the Event.timeStamp and the Javascript`
Updates to fingerprinting s... Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1521) Date() object, while also introducing jitter. We believe that Javascript time projects/torbrowser/design/index.html.en 1522) resolution may be reduced all the way up to the second before it seriously projects/torbrowser/design/index.html.en 1523) impacts site operation. Our goal with this quantization is to increase the projects/torbrowser/design/index.html.en 1524) 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 1525) that even with the default precision in most browsers, they required up to 120
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1526) seconds of amortization and repeated trials to get stable results from their projects/en/torbrowser/design/index.html.en 1527) feature set. We intend to work with the research community to establish the`
Updates to fingerprinting s... Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1528) optimum trade-off between quantization+jitter and amortization time, as well projects/torbrowser/design/index.html.en 1529) as identify highly variable Javascript operations. As long as these attacks projects/torbrowser/design/index.html.en 1530) take several seconds or more to execute, they are unlikely to be appealing to projects/torbrowser/design/index.html.en 1531) advertisers, and are also very likely to be noticed if deployed against a projects/torbrowser/design/index.html.en 1532) large number of people.
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1533) projects/en/torbrowser/design/index.html.en 1534) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1535)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1536) Currently, our mitigation against performance fingerprinting is to`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1537) 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 1538) Timing</a> through the Firefox preference`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1539) <span class="command"><strong>dom.enable_performance</strong></span>, and to disable the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Web/API/HTMLVideoElement#Gecko-specific_properties" target="_top">Mozilla projects/torbrowser/design/index.html.en 1540) Video Statistics</a> API extensions via the preference projects/torbrowser/design/index.html.en 1541) <span class="command"><strong>media.video_stats.enabled</strong></span>.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1542)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1543) </p></li><li class="listitem"><span class="command"><strong>Keystroke Fingerprinting</strong></span><p>`
Add design doc draft. Mike Perry authored 13 years ago	projects/en/torbrowser/design/index.html.en 1544) projects/en/torbrowser/design/index.html.en 1545) Keystroke fingerprinting is the act of measuring key strike time and key projects/en/torbrowser/design/index.html.en 1546) flight time. It is seeing increasing use as a biometric. projects/en/torbrowser/design/index.html.en 1547) projects/en/torbrowser/design/index.html.en 1548) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/en/torbrowser/design/index.html.en 1549) projects/en/torbrowser/design/index.html.en 1550) We intend to rely on the same mechanisms for defeating Javascript performance projects/en/torbrowser/design/index.html.en 1551) fingerprinting: timestamp quantization and jitter. projects/en/torbrowser/design/index.html.en 1552) projects/en/torbrowser/design/index.html.en 1553) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/en/torbrowser/design/index.html.en 1554) We have no implementation as of yet.
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1555) </p></li><li class="listitem"><span class="command"><strong>Operating System Type Fingerprinting</strong></span><p>`
Describe OS type fingerprin... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1556) projects/torbrowser/design/index.html.en 1557) As we mentioned in the introduction of this section, OS type fingerprinting is projects/torbrowser/design/index.html.en 1558) currently considered a lower priority, due simply to the numerous ways that`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1559) characteristics of the operating system type may leak into content, and the`
Describe OS type fingerprin... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1560) comparatively low contribution of OS to overall entropy. In particular, there projects/torbrowser/design/index.html.en 1561) are likely to be many ways to measure the differences in widget size, projects/torbrowser/design/index.html.en 1562) scrollbar size, and other rendered details on a page. Also, directly exported`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1563) OS routines (such as those from the standard C math library) expose projects/torbrowser/design/index.html.en 1564) differences in their implementations through their return values.`
Describe OS type fingerprin... Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1565) projects/torbrowser/design/index.html.en 1566) </p><p><span class="command"><strong>Design Goal:</strong></span> projects/torbrowser/design/index.html.en 1567) projects/torbrowser/design/index.html.en 1568) We intend to reduce or eliminate OS type fingerprinting to the best extent projects/torbrowser/design/index.html.en 1569) possible, but recognize that the effort for reward on this item is not as high projects/torbrowser/design/index.html.en 1570) as other areas. The entropy on the current OS distribution is somewhere around projects/torbrowser/design/index.html.en 1571) 2 bits, which is much lower than other vectors which can also be used to
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1572) fingerprint configuration and user-specific information. You can see the projects/torbrowser/design/index.html.en 1573) 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 1574) tag on our bug tracker</a>.`
Describe OS type fingerprin... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1575) projects/torbrowser/design/index.html.en 1576) </p><p><span class="command"><strong>Implementation Status:</strong></span> projects/torbrowser/design/index.html.en 1577)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1578) At least three HTML5 features have different implementation status across the projects/torbrowser/design/index.html.en 1579) major OS vendors and/or the underlying hardware: 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 1580) API</a>, 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 1581) Connection API</a>, and the <a class="ulink" href="https://wiki.mozilla.org/Sensor_API" target="_top">Sensor API</a>. We disable these APIs through the Firefox preferences projects/torbrowser/design/index.html.en 1582) <span class="command"><strong>dom.battery.enabled</strong></span>, projects/torbrowser/design/index.html.en 1583) <span class="command"><strong>dom.network.enabled</strong></span>, and
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1584) <span class="command"><strong>device.sensors.enabled</strong></span>.`
Describe OS type fingerprin... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1585)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1586) </p></li></ol></div><p>`
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1587) 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 Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1588) </p></div></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 13 years ago	`projects/en/torbrowser/design/index.html.en 1589)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1590) In order to avoid long-term linkability, we provide a "New Identity" context projects/torbrowser/design/index.html.en 1591) menu option in Torbutton. This context menu option is active if Torbutton can projects/torbrowser/design/index.html.en 1592) read the environment variables $TOR_CONTROL_PASSWD and $TOR_CONTROL_PORT.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1593)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1594) </p><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp56156768"></a>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote">`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1595)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1596) All linkable identifiers and browser state MUST be cleared by this feature.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1597)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1598) </blockquote></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp56158016"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1599)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1600) 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 1601) 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 1602) 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 1603) 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 1604) 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 1605) <span class="command"><strong>browser.zoom.siteSpecific</strong></span>, and clear the GeoIP wifi token URL projects/torbrowser/design/index.html.en 1606) <span class="command"><strong>geo.wifi.access_token</strong></span> and the last opened URL prefs (if projects/torbrowser/design/index.html.en 1607) they exist). Each tab is then closed.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1608)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1609) </p><p>`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1610)`
TBB design doc: More review... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1611) 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 1612) (which instructs addons and various Firefox components to clear their session projects/torbrowser/design/index.html.en 1613) state), and then manually clear the following state: searchbox and findbox projects/torbrowser/design/index.html.en 1614) text, HTTP auth, SSL state, OCSP state, site-specific content preferences
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1615) (including HSTS state), content and image cache, offline cache, offline projects/torbrowser/design/index.html.en 1616) storage, Cookies, crypto tokens, DOM storage, the safe browsing key, and the`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1617) Google wifi geolocation token (if it exists). We also clear NoScript's site`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1618) and temporary permissions, and all other browser site permissions.`
Add design doc draft. Mike Perry authored 13 years ago	`projects/en/torbrowser/design/index.html.en 1619)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1620) </p><p>`
Update TBB design doc based... Mike Perry authored 13 years ago	`projects/torbrowser/design/index.html.en 1621)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1622) After the state is cleared, we then close all remaining HTTP keep-alive projects/torbrowser/design/index.html.en 1623) connections and then send the NEWNYM signal to the Tor control port to cause a projects/torbrowser/design/index.html.en 1624) new circuit to be created. projects/torbrowser/design/index.html.en 1625) </p><p>`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1626)`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1627) Finally, a fresh browser window is opened, and the current browser window is`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1628) closed (this does not spawn a new Firefox process, only a new window). Upon projects/torbrowser/design/index.html.en 1629) the close of the final window, an unload handler is fired to invoke the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIDOMWindowUtils#garbageCollect%28%29" target="_top">garbage projects/torbrowser/design/index.html.en 1630) collector</a>, which has the effect of immediately purging any blob:UUID projects/torbrowser/design/index.html.en 1631) URLs that were created by website content via <a class="ulink" href="https://developer.mozilla.org/en-US/docs/Web/API/URL/createObjectURL" target="_top">URL.createObjectURL</a>. projects/torbrowser/design/index.html.en 1632)
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1633) </p></blockquote></div><div class="blockquote"><blockquote class="blockquote"> projects/torbrowser/design/index.html.en 1634) If the user chose to "protect" any cookies by using the Torbutton Cookie projects/torbrowser/design/index.html.en 1635) Protections UI, those cookies are not cleared as part of the above.`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1636) </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 1637) projects/torbrowser/design/index.html.en 1638) In addition to the above mechanisms that are devoted to preserving privacy projects/torbrowser/design/index.html.en 1639) while browsing, we also have a number of technical mechanisms to address other projects/torbrowser/design/index.html.en 1640) privacy and security issues. projects/torbrowser/design/index.html.en 1641)`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1642) </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 1643) projects/torbrowser/design/index.html.en 1644) In order to provide vulnerability surface reduction for users that need high`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1645) security, we have implemented a "Security Slider" to allow users to make a projects/torbrowser/design/index.html.en 1646) tradeoff between usability and security while minimizing the total number of projects/torbrowser/design/index.html.en 1647) choices (to reduce fingerprinting). Using metrics collected from projects/torbrowser/design/index.html.en 1648) Mozilla's bug tracker, we analyzed the vulnerability counts of core projects/torbrowser/design/index.html.en 1649) components, and used <a class="ulink" href="https://github.com/iSECPartners/publications/tree/master/reports/Tor%20Browser%20Bundle" target="_top">information
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1650) gathered from a study performed by iSec Partners</a> to inform which projects/torbrowser/design/index.html.en 1651) features should be disabled at which security levels. projects/torbrowser/design/index.html.en 1652) projects/torbrowser/design/index.html.en 1653) </p><p> projects/torbrowser/design/index.html.en 1654)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1655) The Security Slider consists of four positions: projects/torbrowser/design/index.html.en 1656) projects/torbrowser/design/index.html.en 1657) </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="command"><strong>Low</strong></span><p> projects/torbrowser/design/index.html.en 1658) projects/torbrowser/design/index.html.en 1659) At this security level, the preferences are the Tor Browser defaults. projects/torbrowser/design/index.html.en 1660) projects/torbrowser/design/index.html.en 1661) </p></li><li class="listitem"><span class="command"><strong>Medium-Low</strong></span><p> projects/torbrowser/design/index.html.en 1662) projects/torbrowser/design/index.html.en 1663) At this security level, we disable the ION JIT projects/torbrowser/design/index.html.en 1664) (<span class="command"><strong>javascript.options.ion.content</strong></span>), TypeInference JIT projects/torbrowser/design/index.html.en 1665) (<span class="command"><strong>javascript.options.typeinference</strong></span>), ASM.JS projects/torbrowser/design/index.html.en 1666) (<span class="command"><strong>javascript.options.asmjs</strong></span>), WebAudio projects/torbrowser/design/index.html.en 1667) (<span class="command"><strong>media.webaudio.enabled</strong></span>), MathML projects/torbrowser/design/index.html.en 1668) (<span class="command"><strong>mathml.disabled</strong></span>), block remote JAR files projects/torbrowser/design/index.html.en 1669) (<span class="command"><strong>network.jar.block-remote-files</strong></span>), and make HTML5 audio and projects/torbrowser/design/index.html.en 1670) video click-to-play via NoScript (<span class="command"><strong>noscript.forbidMedia</strong></span>). projects/torbrowser/design/index.html.en 1671) projects/torbrowser/design/index.html.en 1672) </p></li><li class="listitem"><span class="command"><strong>Medium-High</strong></span><p> projects/torbrowser/design/index.html.en 1673) projects/torbrowser/design/index.html.en 1674) This security level inherits the preferences from the Medium-Low level, and projects/torbrowser/design/index.html.en 1675) additionally disables the baseline JIT
Update Tor Browser design doc. Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1676) (<span class="command"><strong>javascript.options.baselinejit.content</strong></span>), disables Graphite projects/torbrowser/design/index.html.en 1677) (<span class="command"><strong>gfx.font_rendering.graphite.enabled</strong></span>) and SVG OpenType font projects/torbrowser/design/index.html.en 1678) rendering (<span class="command"><strong>gfx.font_rendering.opentype_svg.enabled</strong></span>) and only projects/torbrowser/design/index.html.en 1679) allows Javascript to run if it is loaded over HTTPS and the URL bar is HTTPS projects/torbrowser/design/index.html.en 1680) (by setting <span class="command"><strong>noscript.global</strong></span> to false and
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1681) <span class="command"><strong>noscript.globalHttpsWhitelist</strong></span> to true). projects/torbrowser/design/index.html.en 1682) projects/torbrowser/design/index.html.en 1683) </p></li><li class="listitem"><span class="command"><strong>High</strong></span><p> projects/torbrowser/design/index.html.en 1684) projects/torbrowser/design/index.html.en 1685) This security level inherits the preferences from the Medium-Low and projects/torbrowser/design/index.html.en 1686) Medium-High levels, and additionally disables remote fonts projects/torbrowser/design/index.html.en 1687) (<span class="command"><strong>noscript.forbidFonts</strong></span>), completely disables Javascript (by projects/torbrowser/design/index.html.en 1688) unsetting <span class="command"><strong>noscript.globalHttpsWhitelist</strong></span>), and disables SVG projects/torbrowser/design/index.html.en 1689) images (<span class="command"><strong>svg.in-content.enabled</strong></span>). projects/torbrowser/design/index.html.en 1690) projects/torbrowser/design/index.html.en 1691) </p></li></ul></div></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 1692) projects/torbrowser/design/index.html.en 1693) <a class="link" href="#website-traffic-fingerprinting">Website Traffic projects/torbrowser/design/index.html.en 1694) Fingerprinting</a> is a statistical attack to attempt to recognize specific projects/torbrowser/design/index.html.en 1695) encrypted website activity. projects/torbrowser/design/index.html.en 1696)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1697) </p><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp56192352"></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 1698)`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1699) 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 1700) for classification. This mechanism would either impact the true and false`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1701) positive accuracy rates, <span class="emphasis"><em>or</em></span> reduce the number of web pages`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1702) that could be classified at a given accuracy rate. projects/torbrowser/design/index.html.en 1703) projects/torbrowser/design/index.html.en 1704) </p><p> projects/torbrowser/design/index.html.en 1705) projects/torbrowser/design/index.html.en 1706) Ideally, this mechanism would be as light-weight as possible, and would be projects/torbrowser/design/index.html.en 1707) tunable in terms of overhead. We suspect that it may even be possible to projects/torbrowser/design/index.html.en 1708) deploy a mechanism that reduces feature extraction resolution without any projects/torbrowser/design/index.html.en 1709) 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 1710) <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 1711) use of HTTP pipelining and/or SPDY</a>. projects/torbrowser/design/index.html.en 1712) In the tunable/low-overhead`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1713) category, we have <a class="ulink" href="http://freehaven.net/anonbib/cache/ShWa-Timing06.pdf" target="_top">Adaptive projects/torbrowser/design/index.html.en 1714) Padding</a> and <a class="ulink" href="http://www.cs.sunysb.edu/~xcai/fp.pdf" target="_top"> projects/torbrowser/design/index.html.en 1715) 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 1716) 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 1717) network, making them also effectively no-overhead.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1718)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1719) </p></blockquote></div></div><div class="sect3"><div class="titlepage"><div><div><h4 class="title"><a id="idp56199248"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"><p>`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1720) Currently, we patch Firefox to <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=20a59cec9886cf2575b1fd8e92b43e31ba053fbd" target="_top">randomize`
Update TBB design doc based... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 1721) pipeline order and depth</a>. Unfortunately, pipelining is very fragile. projects/torbrowser/design/index.html.en 1722) Many sites do not support it, and even sites that advertise support for projects/torbrowser/design/index.html.en 1723) pipelining may simply return error codes for successive requests, effectively projects/torbrowser/design/index.html.en 1724) forcing the browser into non-pipelined behavior. Firefox also has code to back projects/torbrowser/design/index.html.en 1725) off and reduce or eliminate the pipeline if this happens. These projects/torbrowser/design/index.html.en 1726) shortcomings and fallback behaviors are the primary reason that Google
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1727) developed SPDY as opposed to simply extending HTTP to improve pipelining. It`
TBB Design Doc: Mention use... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1728) turns out that we could actually deploy exit-side proxies that allow us to`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1729) <a class="ulink" href="https://gitweb.torproject.org/torspec.git/tree/proposals/ideas/xxx-using-spdy.txt" target="_top">use`
TBB Design Doc: Mention use... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1730) SPDY from the client to the exit node</a>. This would make our defense not projects/torbrowser/design/index.html.en 1731) 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 1732) projects/torbrowser/design/index.html.en 1733) </p><p> projects/torbrowser/design/index.html.en 1734)`
TBB design doc: Clarify web... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1735) 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 1736) 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 1737) case with full server support. Unfortunately, the bias in favor of compelling projects/torbrowser/design/index.html.en 1738) attack papers has caused academia to ignore this request thus far, instead projects/torbrowser/design/index.html.en 1739) publishing only cursory (yet "devastating") evaluations that fail to provide projects/torbrowser/design/index.html.en 1740) even simple statistics such as the rates of actual pipeline utilization during projects/torbrowser/design/index.html.en 1741) 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 1742) accept that our defense might fail to work as well as others (in fact we projects/torbrowser/design/index.html.en 1743) expect it), but unfortunately the very same shortcuts that provide excellent projects/torbrowser/design/index.html.en 1744) attack results also allow the conclusion that all defenses are broken forever. projects/torbrowser/design/index.html.en 1745) 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 1746) projects/torbrowser/design/index.html.en 1747) </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 1748) projects/torbrowser/design/index.html.en 1749) 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 1750) 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 1751) 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 1752) and searches that version list for the current value for the local preference projects/torbrowser/design/index.html.en 1753) <span class="command"><strong>torbrowser.version</strong></span>. If the value from our preference is projects/torbrowser/design/index.html.en 1754) present in the recommended version list, the check is considered to have projects/torbrowser/design/index.html.en 1755) succeeded and the user is up to date. If not, it is considered to have failed projects/torbrowser/design/index.html.en 1756) and an update is needed. The check is triggered upon browser launch, new projects/torbrowser/design/index.html.en 1757) window, and new tab, but is rate limited so as to happen no more frequently projects/torbrowser/design/index.html.en 1758) than once every 1.5 hours. projects/torbrowser/design/index.html.en 1759) projects/torbrowser/design/index.html.en 1760) </p><p> projects/torbrowser/design/index.html.en 1761) projects/torbrowser/design/index.html.en 1762) If the check fails, we cache this fact, and update the Torbutton graphic to projects/torbrowser/design/index.html.en 1763) display a flashing warning icon and insert a menu option that provides a link projects/torbrowser/design/index.html.en 1764) to our download page. Additionally, we reset the value for the browser projects/torbrowser/design/index.html.en 1765) 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 1766) informs the user</a> that their browser is out of projects/torbrowser/design/index.html.en 1767) date. projects/torbrowser/design/index.html.en 1768)
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1769) </p><p> projects/torbrowser/design/index.html.en 1770)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1771) We also make use of the in-browser Mozilla updater, and have <a class="ulink" href="https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-31.6.0esr-4.5-1&id=bcf51aae541fc28de251924ce9394224bd2b814c" target="_top">patched`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1772) the updater</a> to avoid sending OS and Kernel version information as part projects/torbrowser/design/index.html.en 1773) of its update pings. projects/torbrowser/design/index.html.en 1774)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1775) </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 1776)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1777) 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 1778) believe</a> it is impossible to expect to keep a single build machine or projects/torbrowser/design/index.html.en 1779) software signing key secure, given the class of adversaries that Tor has to projects/torbrowser/design/index.html.en 1780) contend with. For this reason, we have deployed a build system projects/torbrowser/design/index.html.en 1781) that allows anyone to use our source code to reproduce byte-for-byte identical projects/torbrowser/design/index.html.en 1782) binary packages to the ones that we distribute.
Update TBB design doc. Mike Perry authored 12 years ago	`projects/torbrowser/design/index.html.en 1783)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1784) </p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="idp56215504"></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 1785)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1786) The GNU toolchain has been working on providing reproducible builds for some projects/torbrowser/design/index.html.en 1787) time, however a large software project such as Firefox typically ends up projects/torbrowser/design/index.html.en 1788) embedding a large number of details about the machine it was built on, both projects/torbrowser/design/index.html.en 1789) intentionally and inadvertently. Additionally, manual changes to the build projects/torbrowser/design/index.html.en 1790) machine configuration can accumulate over time and are difficult for others to projects/torbrowser/design/index.html.en 1791) 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 1792)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1793) </p><p> projects/torbrowser/design/index.html.en 1794) 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 1795) Gitian is a wrapper around Ubuntu's virtualization tools that allows you to projects/torbrowser/design/index.html.en 1796) specify an Ubuntu version, architecture, a set of additional packages, a set projects/torbrowser/design/index.html.en 1797) of input files, and a bash build scriptlet in an YAML document called a projects/torbrowser/design/index.html.en 1798) "Gitian Descriptor". This document is used to install a qemu-kvm image, and projects/torbrowser/design/index.html.en 1799) execute your build scriptlet inside it. projects/torbrowser/design/index.html.en 1800) </p><p>
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1801)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1802) 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 1803) of wrapper scripts</a> around Gitian to automate dependency download and projects/torbrowser/design/index.html.en 1804) authentication, as well as transfer intermediate build outputs between the projects/torbrowser/design/index.html.en 1805) stages of the build process. Because Gitian creates an Ubuntu build projects/torbrowser/design/index.html.en 1806) environment, we must use cross-compilation to create packages for Windows and projects/torbrowser/design/index.html.en 1807) Mac OS. For Windows, we use mingw-w64 as our cross compiler. For Mac OS, we
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1808) 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 10 years ago	`projects/torbrowser/design/index.html.en 1809) SDK.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1810)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1811) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1812)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1813) The use of the Gitian system eliminates build non-determinism by normalizing projects/torbrowser/design/index.html.en 1814) the build environment's hostname, username, build path, uname output, projects/torbrowser/design/index.html.en 1815) toolchain versions, and time. On top of what Gitian provides, we also had to projects/torbrowser/design/index.html.en 1816) 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 1817)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1818) </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Filesystem and archive reordering</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1819)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1820) The most prevalent source of non-determinism in the components of Tor Browser projects/torbrowser/design/index.html.en 1821) by far was various ways that archives (such as zip, tar, jar/ja, DMG, and projects/torbrowser/design/index.html.en 1822) Firefox manifest lists) could be reordered. Many file archivers walk the`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1823) file system in inode structure order by default, which will result in ordering`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1824) differences between two different archive invocations, especially on machines projects/torbrowser/design/index.html.en 1825) of different disk and hardware configurations.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1826)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1827) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1828)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1829) The fix for this is to perform an additional sorting step on the input list projects/torbrowser/design/index.html.en 1830) for archives, but care must be taken to instruct libc and other sorting routines projects/torbrowser/design/index.html.en 1831) to use a fixed locale to determine lexicographic ordering, or machines with projects/torbrowser/design/index.html.en 1832) different locale settings will produce different sort results. We chose the`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1833) 'C' locale for this purpose. We created wrapper scripts for <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/gitian/build-helpers/dtar.sh" target="_top">tar</a>, projects/torbrowser/design/index.html.en 1834) <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/gitian/build-helpers/dzip.sh" target="_top">zip</a>, projects/torbrowser/design/index.html.en 1835) and <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/gitian/build-helpers/ddmg.sh" target="_top">DMG</a>
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1836) to aid in reproducible archive creation. projects/torbrowser/design/index.html.en 1837)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1838) </p></li><li class="listitem"><span class="command"><strong>Uninitialized memory in toolchain/archivers</strong></span><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1839) projects/torbrowser/design/index.html.en 1840) We ran into difficulties with both binutils and the DMG archive script using projects/torbrowser/design/index.html.en 1841) uninitialized memory in certain data structures that ended up written to disk. projects/torbrowser/design/index.html.en 1842) Our binutils fixes were merged upstream, but the DMG archive fix remains an`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1843) <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/gitian/patches/libdmg.patch" target="_top">independent`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1844) patch</a>. projects/torbrowser/design/index.html.en 1845)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1846) </p></li><li class="listitem"><span class="command"><strong>Fine-grained timestamps and timezone leaks</strong></span><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1847) projects/torbrowser/design/index.html.en 1848) The standard way of controlling timestamps in Gitian is to use libfaketime, projects/torbrowser/design/index.html.en 1849) which hooks time-related library calls to provide a fixed timestamp. However,`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1850) due to our use of wine to run py2exe for python-based pluggable transports,`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1851) pyc timestamps had to be addressed with an additional <a class="ulink" href="https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/gitian/build-helpers/pyc-timestamp.sh" target="_top">helper`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1852) script</a>. The timezone leaks were addressed by setting the projects/torbrowser/design/index.html.en 1853) <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 1854)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1855) </p></li><li class="listitem"><span class="command"><strong>Deliberately generated entropy</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1856)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1857) In two circumstances, deliberately generated entropy was introduced in various projects/torbrowser/design/index.html.en 1858) components of the build process. First, the BuildID Debuginfo identifier projects/torbrowser/design/index.html.en 1859) (which associates detached debug files with their corresponding stripped projects/torbrowser/design/index.html.en 1860) executables) was introducing entropy from some unknown source. We removed this projects/torbrowser/design/index.html.en 1861) header using objcopy invocations in our build scriptlets, and opted to use GNU projects/torbrowser/design/index.html.en 1862) DebugLink instead of BuildID for this association.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1863)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1864) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1865)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1866) Second, on Linux, Firefox builds detached signatures of its cryptographic projects/torbrowser/design/index.html.en 1867) libraries using a temporary key for FIPS-140 certification. A rather insane projects/torbrowser/design/index.html.en 1868) subsection of the FIPS-140 certification standard requires that you distribute projects/torbrowser/design/index.html.en 1869) signatures for all of your cryptographic libraries. The Firefox build process projects/torbrowser/design/index.html.en 1870) meets this requirement by generating a temporary key, using it to sign the projects/torbrowser/design/index.html.en 1871) libraries, and discarding the private portion of that key. Because there are projects/torbrowser/design/index.html.en 1872) many other ways to intercept the crypto outside of modifying the actual DLL projects/torbrowser/design/index.html.en 1873) images, we opted to simply remove these signature files from distribution. projects/torbrowser/design/index.html.en 1874) There simply is no way to verify code integrity on a running system without projects/torbrowser/design/index.html.en 1875) both OS and co-processor assistance. Download package signatures make sense of projects/torbrowser/design/index.html.en 1876) 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 1877) projects/torbrowser/design/index.html.en 1878)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1879) </p></li><li class="listitem"><span class="command"><strong>LXC-specific leaks</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1880)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1881) Gitian provides an option to use LXC containers instead of full qemu-kvm projects/torbrowser/design/index.html.en 1882) virtualization. Unfortunately, these containers can allow additional details projects/torbrowser/design/index.html.en 1883) about the host OS to leak. In particular, umask settings as well as the projects/torbrowser/design/index.html.en 1884) hostname and Linux kernel version can leak from the host OS into the LXC projects/torbrowser/design/index.html.en 1885) container. We addressed umask by setting it explicitly in our Gitian projects/torbrowser/design/index.html.en 1886) descriptor scriptlet, and addressed the hostname and kernel version leaks by projects/torbrowser/design/index.html.en 1887) directly patching the aspects of the Firefox build process that included this
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1888) information into the build. It also turns out that some libraries (in projects/torbrowser/design/index.html.en 1889) particular: libgmp) attempt to detect the current CPU to determine which projects/torbrowser/design/index.html.en 1890) optimizations to compile in. This CPU type is uniform on our KVM instances,`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1891) but differs under LXC. We are also investigating currently`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1892) <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/12240" target="_top">oddities related to projects/torbrowser/design/index.html.en 1893) time-based dependency tracking</a> that only appear in LXC containers. projects/torbrowser/design/index.html.en 1894)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1895) </p></li></ol></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="idp56237264"></a>5.2. Package Signatures and Verification</h3></div></div></div><p>`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1896)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1897) The build process generates a single sha256sums.txt file that contains a sorted`
Update design document base... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1898) 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 10 years ago	`projects/torbrowser/design/index.html.en 1899) official builder uploads this file and a GPG signature of it to a directory projects/torbrowser/design/index.html.en 1900) on a Tor Project's web server. The build scripts have an optional matching projects/torbrowser/design/index.html.en 1901) step that downloads these signatures, verifies them, and ensures that the projects/torbrowser/design/index.html.en 1902) local builds match this file.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1903)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1904) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1905)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1906) When builds are published officially, the single sha256sums.txt file is projects/torbrowser/design/index.html.en 1907) accompanied by a detached GPG signature from each official builder that projects/torbrowser/design/index.html.en 1908) produced a matching build. The packages are additionally signed with detached projects/torbrowser/design/index.html.en 1909) GPG signatures from an official signing key.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1910)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1911) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1912)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1913) The fact that the entire set of packages for a given version can be projects/torbrowser/design/index.html.en 1914) authenticated by a single hash of the sha256sums.txt file will also allow us projects/torbrowser/design/index.html.en 1915) to create a number of auxiliary authentication mechanisms for our packages, projects/torbrowser/design/index.html.en 1916) beyond just trusting a single offline build machine and a single cryptographic projects/torbrowser/design/index.html.en 1917) key's integrity. Interesting examples include providing multiple independent projects/torbrowser/design/index.html.en 1918) cryptographic signatures for packages, listing the package hashes in the Tor projects/torbrowser/design/index.html.en 1919) 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 1920)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1921) </p><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1922)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	projects/torbrowser/design/index.html.en 1923) The Windows releases are also signed by a hardware token provided by Digicert. projects/torbrowser/design/index.html.en 1924) In order to verify package integrity, the signature must be stripped off using projects/torbrowser/design/index.html.en 1925) the osslsigncode tool, as described on the <a class="ulink" href="https://www.torproject.org/docs/verifying-signatures.html.en#BuildVerification" target="_top">Signature projects/torbrowser/design/index.html.en 1926) Verification</a> page.
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1927)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1928) </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="idp56241792"></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 1929)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1930) Due to the fact that bit-identical packages can be produced by anyone, the projects/torbrowser/design/index.html.en 1931) security of this build system extends beyond the security of the official projects/torbrowser/design/index.html.en 1932) build machines. In fact, it is still possible for build integrity to be`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1933) 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 1934)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1935) </p><p>`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1936)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 1937) By default, all tor-specific dependencies and inputs to the build process are projects/torbrowser/design/index.html.en 1938) downloaded over Tor, which allows build verifiers to remain anonymous and projects/torbrowser/design/index.html.en 1939) hidden. Because of this, any individual can use our anonymity network to projects/torbrowser/design/index.html.en 1940) privately download our source code, verify it against public signed, audited, projects/torbrowser/design/index.html.en 1941) and mirrored git repositories, and reproduce our builds exactly, without being projects/torbrowser/design/index.html.en 1942) subject to targeted attacks. If they notice any differences, they can alert projects/torbrowser/design/index.html.en 1943) the public builders/signers, hopefully using a pseudonym or our anonymous
Updates to fingerprinting s... Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1944) bug tracker account, to avoid revealing the fact that they are a build`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1945) verifier.`
Update TBB design doc based... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1946)`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1947) </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="update-safety"></a>5.4. Update Safety</h3></div></div></div><p> projects/torbrowser/design/index.html.en 1948) projects/torbrowser/design/index.html.en 1949) We make use of the Firefox updater in order to provide automatic updates to`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1950) users. We make use of certificate pinning to ensure that update checks cannot`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1951) be tampered with, and we sign the individual MAR update files with an offline projects/torbrowser/design/index.html.en 1952) signing key. projects/torbrowser/design/index.html.en 1953) projects/torbrowser/design/index.html.en 1954) </p><p> projects/torbrowser/design/index.html.en 1955) projects/torbrowser/design/index.html.en 1956) The Firefox updater also has code to ensure that it can reliably access the`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1957) update server to prevent availability attacks, and complains to the user after 48`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1958) hours go by without a successful response from the server. Additionally, we projects/torbrowser/design/index.html.en 1959) use Tor's SOCKS username and password isolation to ensure that every new`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1960) request to the updater (provided the former got issued more than 10 minutes ago) projects/torbrowser/design/index.html.en 1961) traverses a separate circuit, to avoid holdback attacks by exit nodes.`
Update Tor Browser Design D... Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1962)`
Update design doc for TBB 4.0. Mike Perry authored 10 years ago	`projects/torbrowser/design/index.html.en 1963) </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 1964) projects/torbrowser/design/index.html.en 1965) 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 1966) upon the assumption that link-click navigation indicates user consent to projects/torbrowser/design/index.html.en 1967) tracking between the linking site and the destination site. While this projects/torbrowser/design/index.html.en 1968) definition is sufficient to allow us to eliminate cross-site third party projects/torbrowser/design/index.html.en 1969) tracking with only minimal site breakage, it is our long-term goal to further projects/torbrowser/design/index.html.en 1970) reduce cross-origin click navigation tracking to mechanisms that are projects/torbrowser/design/index.html.en 1971) detectable by attentive users, so they can alert the general public if projects/torbrowser/design/index.html.en 1972) cross-origin click navigation tracking is happening where it should not be. projects/torbrowser/design/index.html.en 1973) projects/torbrowser/design/index.html.en 1974) </p><p> projects/torbrowser/design/index.html.en 1975) projects/torbrowser/design/index.html.en 1976) In an ideal world, the mechanisms of tracking that can be employed during a projects/torbrowser/design/index.html.en 1977) link click would be limited to the contents of URL parameters and other projects/torbrowser/design/index.html.en 1978) properties that are fully visible to the user before they click. However, the projects/torbrowser/design/index.html.en 1979) entrenched nature of certain archaic web features make it impossible for us to projects/torbrowser/design/index.html.en 1980) achieve this transparency goal by ourselves without substantial site breakage. projects/torbrowser/design/index.html.en 1981) So, instead we maintain a <a class="link" href="#deprecate" title="A.1. Deprecation Wishlist">Deprecation projects/torbrowser/design/index.html.en 1982) Wishlist</a> of archaic web technologies that are currently being (ab)used projects/torbrowser/design/index.html.en 1983) to facilitate federated login and other legitimate click-driven cross-domain projects/torbrowser/design/index.html.en 1984) activity but that can one day be replaced with more privacy friendly, projects/torbrowser/design/index.html.en 1985) auditable alternatives. projects/torbrowser/design/index.html.en 1986) projects/torbrowser/design/index.html.en 1987) </p><p> projects/torbrowser/design/index.html.en 1988) projects/torbrowser/design/index.html.en 1989) Because the total elimination of side channels during cross-origin navigation projects/torbrowser/design/index.html.en 1990) will undoubtedly break federated login as well as destroy ad revenue, we projects/torbrowser/design/index.html.en 1991) also describe auditable alternatives and promising web draft standards that would projects/torbrowser/design/index.html.en 1992) preserve this functionality while still providing transparency when tracking is projects/torbrowser/design/index.html.en 1993) occurring. projects/torbrowser/design/index.html.en 1994)
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 1995) </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"><span class="command"><strong>The Referer Header</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1996)`
TBB design doc: More review... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 1997) We haven't disabled or restricted the Referer ourselves because of the projects/torbrowser/design/index.html.en 1998) 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 1999) image requests and deep-link navigation on their sites. Furthermore, there projects/torbrowser/design/index.html.en 2000) 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 2001) vacuum, because many sites have begun encoding Referer URL information into`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 2002) GET parameters when they need it to cross HTTP to HTTPS scheme transitions.`
Update design doc with FF17... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 2003) Google's +1 buttons are the best example of this activity. projects/torbrowser/design/index.html.en 2004) projects/torbrowser/design/index.html.en 2005) </p><p> projects/torbrowser/design/index.html.en 2006) projects/torbrowser/design/index.html.en 2007) 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 2008) 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 2009) 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 2010) personal data</a> is inadvertently leaked to third parties through the projects/torbrowser/design/index.html.en 2011) source URL parameters. projects/torbrowser/design/index.html.en 2012) projects/torbrowser/design/index.html.en 2013) </p><p> projects/torbrowser/design/index.html.en 2014)`
Update design document base... Mike Perry authored 10 years ago	projects/torbrowser/design/index.html.en 2015) We believe the Referer header should be made explicit, and believe that CSP projects/torbrowser/design/index.html.en 2016) 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 2017) direction</a>. If a site wishes to transmit its URL to third party content projects/torbrowser/design/index.html.en 2018) elements during load or during link-click, it should have to specify this as a projects/torbrowser/design/index.html.en 2019) property of the associated HTML tag or CSP policy. With an explicit property projects/torbrowser/design/index.html.en 2020) or policy, it would then be possible for the user agent to inform the user if projects/torbrowser/design/index.html.en 2021) they are about to click on a link that will transmit Referer information projects/torbrowser/design/index.html.en 2022) (perhaps through something as subtle as a different color in the lower toolbar projects/torbrowser/design/index.html.en 2023) for the destination URL). This same UI notification can also be used for links projects/torbrowser/design/index.html.en 2024) 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 2025) attribute. projects/torbrowser/design/index.html.en 2026)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 2027) </p></li><li class="listitem"><span class="command"><strong>window.name</strong></span><p>`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 2028) <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 2029) a DOM property that for some reason is allowed to retain a persistent value projects/torbrowser/design/index.html.en 2030) 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 2031) <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 2032) storage</a> during click navigation. This is sometimes used for additional projects/torbrowser/design/index.html.en 2033) XSRF protection and federated login. projects/torbrowser/design/index.html.en 2034) </p><p> projects/torbrowser/design/index.html.en 2035) projects/torbrowser/design/index.html.en 2036) It's our opinion that the contents of window.name should not be preserved for projects/torbrowser/design/index.html.en 2037) cross-origin navigation, but doing so may break federated login for some sites. projects/torbrowser/design/index.html.en 2038)
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 2039) </p></li><li class="listitem"><span class="command"><strong>Javascript link rewriting</strong></span><p>`
Update design doc with FF17... Mike Perry authored 11 years ago	projects/torbrowser/design/index.html.en 2040) projects/torbrowser/design/index.html.en 2041) In general, it should not be possible for onclick handlers to alter the projects/torbrowser/design/index.html.en 2042) navigation destination of 'a' tags, silently transform them into POST projects/torbrowser/design/index.html.en 2043) requests, or otherwise create situations where a user believes they are projects/torbrowser/design/index.html.en 2044) clicking on a link leading to one URL that ends up on another. This projects/torbrowser/design/index.html.en 2045) functionality is deceptive and is frequently a vector for malware and phishing projects/torbrowser/design/index.html.en 2046) attacks. Unfortunately, many legitimate sites also employ such transparent projects/torbrowser/design/index.html.en 2047) link rewriting, and blanket disabling this functionality ourselves will simply projects/torbrowser/design/index.html.en 2048) cause Tor Browser to fail to navigate properly on these sites. projects/torbrowser/design/index.html.en 2049) projects/torbrowser/design/index.html.en 2050) </p><p> projects/torbrowser/design/index.html.en 2051) projects/torbrowser/design/index.html.en 2052) 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 2053) 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 2054) ourselves</a>, as they are comparatively rare and can be handled with site projects/torbrowser/design/index.html.en 2055) permissions. projects/torbrowser/design/index.html.en 2056)`
Update Tor Browser design doc. Mike Perry authored 9 years ago	`projects/torbrowser/design/index.html.en 2057) </p></li></ol></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="idp56278768"></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 2058) projects/torbrowser/design/index.html.en 2059) Web-Send is a browser-based link sharing and federated login widget that is projects/torbrowser/design/index.html.en 2060) 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 2061) 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 2062) especially if used as a "Like button" replacement. projects/torbrowser/design/index.html.en 2063)`
TBB design doc: Fix charset... Mike Perry authored 11 years ago	`projects/torbrowser/design/index.html.en 2064) </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 2065) projects/torbrowser/design/index.html.en 2066) Mozilla's Persona is designed to provide decentralized, cryptographically projects/torbrowser/design/index.html.en 2067) authenticated federated login in a way that does not expose the user to third projects/torbrowser/design/index.html.en 2068) party tracking or require browser redirects or side channels. While it does projects/torbrowser/design/index.html.en 2069) not directly provide the link sharing capabilities that Web-Send does, it is a projects/torbrowser/design/index.html.en 2070) better solution to the privacy issues associated with federated login than projects/torbrowser/design/index.html.en 2071) Web-Send is. projects/torbrowser/design/index.html.en 2072)