r26066: {website} TBB design doc: Fix charset and section breakage. (website/trunk/projects/torbrowser/design)
Author: mikeperry Date: 2013-02-25 21:35:57 +0000 (Mon, 25 Feb 2013) New Revision: 26066 Modified: website/trunk/projects/torbrowser/design/index.html.en Log: TBB design doc: Fix charset and section breakage. Modified: website/trunk/projects/torbrowser/design/index.html.en =================================================================== --- website/trunk/projects/torbrowser/design/index.html.en 2013-02-23 04:06:58 UTC (rev 26065) +++ website/trunk/projects/torbrowser/design/index.html.en 2013-02-25 21:35:57 UTC (rev 26066) @@ -1,6 +1,6 @@ <?xml version="1.0" encoding="UTF-8"?> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml"><head><title>The Design and Implementation of the Tor Browser [DRAFT]</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2"/></head><body><div class="article" title="The Design and Implementation of the Tor Browser [DRAFT]"><div class="titlepage"><div><div><h2 class="title"><a id="design"/>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#tor project 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">Feb 23 2013</p></div></div><hr/></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#idp3348944">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="#adversarygoals">3.1. Adversary Goals</a></span></dt><dt><span class="sect2"><a href="#adversarypositioning">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 Identifi er 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="#firefox-patches">4.8. Description of Firefox Patches</a></span></dt></dl></dd><dt><span class="appendix"><a href="#Transparency">A. Towards Transparency in Navigation Tracking</a></span></dt></dl></div><div class="sect1" title="1. Introduction"><div class="titlepage"><div><div><h2 class="title"><a id="idp3348944"/>1. Introduction</h2></div></div></div><p> +<!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 V1.75.2" /></head><body><div class="article" title="The Design and Implementation of the Tor Browser [DRAFT]"><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">Feb 23 2013</p></div></div><hr /></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="#idp1435840">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="#pri vacy">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="#adversarygoals">3.1. Adversary Goals</a></span></dt><dt><span class="sect2"><a href="#adversarypositioning">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="#firefox-patches">4.8. Description of Firefox Patches</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="#idp5757152">A.2. Promising Standards</a></span></dt></dl></dd></dl></div><div class="sect1" title="1. Introduction"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="idp1435840"></a>1. Introduction</h2></div></div></div><p> This document describes the <a class="link" href="#adversary" title="3. Adversary Model">adversary model</a>, <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 2.3.25-4 @@ -13,27 +13,27 @@ against active network adversaries, in addition to the passive forensic local adversary currently addressed by the major browsers. - </p><div class="sect2" title="1.1. Browser Component Overview"><div class="titlepage"><div><div><h3 class="title"><a id="components"/>1.1. Browser Component Overview</h3></div></div></div><p> + </p><div class="sect2" title="1.1. Browser Component Overview"><div class="titlepage"><div><div><h3 class="title"><a id="components"></a>1.1. Browser Component Overview</h3></div></div></div><p> -The Tor Browser is based on <a class="ulink" href="https://www.mozilla.org/en-US/firefox/organizations/">Mozilla's Extended +The Tor Browser is based on <a class="ulink" href="https://www.mozilla.org/en-US/firefox/organizations/" target="_top">Mozilla's Extended Support Release (ESR) Firefox branch</a>. We have a <a class="link" href="#firefox-patches" title="4.8. Description of Firefox Patches">series of patches</a> against this browser to enhance privacy and security. Browser behavior is additionally augmented -through the <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/tree/master">Torbutton +through the <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/tree/master" target="_top">Torbutton extension</a>, though we are in the process of moving this -functionality into direct Firefox patches. We also <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/HEAD:/build-scripts/config/pound_tor.js">change +functionality into direct Firefox patches. We also <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/HEAD:/build-scripts/config..." target="_top">change a number of Firefox preferences</a> from their defaults. </p><p> To help protect against potential Tor Exit Node eavesdroppers, we include -<a class="ulink" href="https://www.eff.org/https-everywhere">HTTPS-Everywhere</a>. To +<a class="ulink" href="https://www.eff.org/https-everywhere" target="_top">HTTPS-Everywhere</a>. To provide users with optional defense-in-depth against Javascript and other -potential exploit vectors, we also include <a class="ulink" href="http://noscript.net/">NoScript</a>. To protect against -PDF-based Tor proxy bypass and to improve usability, we include the <a class="ulink" href="https://addons.mozilla.org/en-us/firefox/addon/pdfjs/">PDF.JS</a> -extension. We also modify <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/HEAD:/build-scripts/config/extension-overrides.js">several +potential exploit vectors, we also include <a class="ulink" href="http://noscript.net/" target="_top">NoScript</a>. To protect against +PDF-based Tor proxy bypass and to improve usability, we include the <a class="ulink" href="https://addons.mozilla.org/en-us/firefox/addon/pdfjs/" target="_top">PDF.JS</a> +extension. We also modify <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/HEAD:/build-scripts/config..." target="_top">several extension preferences</a> from their defaults. - </p></div></div><div class="sect1" title="2. Design Requirements and Philosophy"><div class="titlepage"><div><div><h2 class="title"><a id="DesignRequirements"/>2. Design Requirements and Philosophy</h2></div></div></div><p> + </p></div></div><div class="sect1" title="2. Design Requirements and Philosophy"><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> The Tor Browser Design Requirements are meant to describe the properties of a Private Browsing Mode that defends against both network and local forensic @@ -57,9 +57,9 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in - <a class="ulink" href="https://www.ietf.org/rfc/rfc2119.txt">RFC 2119</a>. + <a class="ulink" href="https://www.ietf.org/rfc/rfc2119.txt" target="_top">RFC 2119</a>. - </p><div class="sect2" title="2.1. Security Requirements"><div class="titlepage"><div><div><h3 class="title"><a id="security"/>2.1. Security Requirements</h3></div></div></div><p> + </p><div class="sect2" title="2.1. Security Requirements"><div class="titlepage"><div><div><h3 class="title"><a id="security"></a>2.1. Security Requirements</h3></div></div></div><p> The security requirements are primarily concerned with ensuring the safe use of Tor. Violations in these properties typically result in serious risk for @@ -67,7 +67,7 @@ respect to browser support, security requirements are the minimum properties in order for Tor to support the use of a particular browser. - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><a class="link" href="#proxy-obedience" title="4.1. Proxy Obedience"><span class="command"><strong>Proxy + </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 Obedience</strong></span></a><p>The browser 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 Separation</strong></span></a><p>The browser MUST NOT provide any stored state to the content window @@ -96,7 +96,7 @@ it out of scope, and/or leave it to the Operating System/platform to implement ephemeral-keyed encrypted swap. -</p></li></ol></div></div><div class="sect2" title="2.2. Privacy Requirements"><div class="titlepage"><div><div><h3 class="title"><a id="privacy"/>2.2. Privacy Requirements</h3></div></div></div><p> +</p></li></ol></div></div><div class="sect2" title="2.2. Privacy Requirements"><div class="titlepage"><div><div><h3 class="title"><a id="privacy"></a>2.2. Privacy Requirements</h3></div></div></div><p> The privacy requirements are primarily concerned with reducing linkability: the ability for a user's activity on one site to be linked with their activity @@ -113,7 +113,7 @@ google.com. Implementations MAY, at their option, restrict the url bar origin to be the entire fully qualified domain name. - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><a class="link" href="#identifier-linkability" title="4.5. Cross-Origin Identifier Unlinkability"><span class="command"><strong>Cross-Origin + </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 Identifier Unlinkability</strong></span></a><p> User activity on one url bar origin MUST NOT be linkable to their activity in @@ -140,12 +140,12 @@ Additionally, the browser SHOULD clear linkable state by default automatically upon browser restart, except at user option. - </p></li></ol></div></div><div class="sect2" title="2.3. Philosophy"><div class="titlepage"><div><div><h3 class="title"><a id="philosophy"/>2.3. Philosophy</h3></div></div></div><p> + </p></li></ol></div></div><div class="sect2" title="2.3. Philosophy"><div class="titlepage"><div><div><h3 class="title"><a id="philosophy"></a>2.3. Philosophy</h3></div></div></div><p> In addition to the above design requirements, the technology decisions about Tor Browser are also guided by some philosophical positions about technology. - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><span class="command"><strong>Preserve existing user model</strong></span><p> + </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Preserve existing user model</strong></span><p> The existing way that the user expects to use a browser must be preserved. If the user has to maintain a different mental model of how the sites they are @@ -156,7 +156,7 @@ </p><p> -User model breakage was one of the <a class="ulink" href="https://blog.torproject.org/blog/toggle-or-not-toggle-end-torbutton">failures +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 of Torbutton</a>: Even if users managed to install everything properly, the toggle model was too hard for the average user to understand, especially in the face of accumulating tabs from multiple states crossed with the current @@ -188,16 +188,16 @@ </p></li><li class="listitem"><span class="command"><strong>Minimize Global Privacy Options</strong></span><p> -<a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3100">Another +<a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3100" target="_top">Another failure of Torbutton</a> was the options panel. Each option that detectably alters browser behavior can be used as a fingerprinting tool. -Similarly, all extensions <a class="ulink" href="http://blog.chromium.org/2010/06/extensions-in-incognito.html">SHOULD be +Similarly, all extensions <a class="ulink" href="http://blog.chromium.org/2010/06/extensions-in-incognito.html" target="_top">SHOULD be disabled in the mode</a> except as an opt-in basis. We SHOULD NOT load system-wide and/or Operating System provided addons or plugins. </p><p> Instead of global browser privacy options, privacy decisions SHOULD be made -<a class="ulink" href="https://wiki.mozilla.org/Privacy/Features/Site-based_data_management_UI">per +<a class="ulink" href="https://wiki.mozilla.org/Privacy/Features/Site-based_data_management_UI" target="_top">per url bar origin</a> to eliminate the possibility of linkability between domains. For example, when a plugin object (or a Javascript access of window.plugins) is present in a page, the user should be given the choice of @@ -209,9 +209,9 @@ permissions can be written to disk. Otherwise, they MUST remain memory-only. </p></li><li class="listitem"><span class="command"><strong>No filters</strong></span><p> -Site-specific or filter-based addons such as <a class="ulink" href="https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/">AdBlock -Plus</a>, <a class="ulink" href="http://requestpolicy.com/">Request Policy</a>, -<a class="ulink" href="http://www.ghostery.com/about">Ghostery</a>, <a class="ulink" href="http://priv3.icsi.berkeley.edu/">Priv3</a>, and <a class="ulink" href="http://sharemenot.cs.washington.edu/">Sharemenot</a> are to be +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 +Plus</a>, <a class="ulink" href="http://requestpolicy.com/" target="_top">Request Policy</a>, +<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 avoided. We believe that these addons do not add any real privacy to a proper <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 should be focused on general solutions that prevent tracking by all @@ -238,13 +238,13 @@ technologies, we cannot hope to substantially influence or be involved in their proper deployment or privacy realization. However, we will likely disable high-risk features pending analysis, audit, and mitigation. - </p></li></ol></div></div></div><div class="sect1" title="3. Adversary Model"><div class="titlepage"><div><div><h2 class="title"><a id="adversary"/>3. Adversary Model</h2></div></div></div><p> + </p></li></ol></div></div></div><div class="sect1" title="3. Adversary Model"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="adversary"></a>3. Adversary Model</h2></div></div></div><p> A Tor web browser adversary has a number of goals, capabilities, and attack types that can be used to illustrate the design requirements for the Tor Browser. Let's start with the goals. - </p><div class="sect2" title="3.1. Adversary Goals"><div class="titlepage"><div><div><h3 class="title"><a id="adversarygoals"/>3.1. Adversary Goals</h3></div></div></div><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><span class="command"><strong>Bypassing proxy settings</strong></span><p>The adversary's primary goal is direct compromise and bypass of + </p><div class="sect2" title="3.1. Adversary Goals"><div class="titlepage"><div><div><h3 class="title"><a id="adversarygoals"></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 Tor, causing the user to directly connect to an IP of the adversary's 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 happily settle for the ability to correlate something a user did via Tor with @@ -283,10 +283,10 @@ seizing the computers of all Tor users in an area (especially after narrowing the field by the above two pieces of information). History records and cache data are the primary goals here. - </p></li></ol></div></div><div class="sect2" title="3.2. Adversary Capabilities - Positioning"><div class="titlepage"><div><div><h3 class="title"><a id="adversarypositioning"/>3.2. Adversary Capabilities - Positioning</h3></div></div></div><p> + </p></li></ol></div></div><div class="sect2" title="3.2. Adversary Capabilities - Positioning"><div class="titlepage"><div><div><h3 class="title"><a id="adversarypositioning"></a>3.2. Adversary Capabilities - Positioning</h3></div></div></div><p> The adversary can position themselves at a number of different locations in order to execute their attacks. - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><span class="command"><strong>Exit Node or Upstream Router</strong></span><p> + </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Exit Node or Upstream Router</strong></span><p> The adversary can run exit nodes, or alternatively, they may control routers upstream of exit nodes. Both of these scenarios have been observed in the wild. @@ -306,7 +306,7 @@ countries where simply using tools like Tor is illegal, users may face confiscation of their computer equipment for excessive Tor usage or just general suspicion. - </p></li></ol></div></div><div class="sect2" title="3.3. Adversary Capabilities - Attacks"><div class="titlepage"><div><div><h3 class="title"><a id="attacks"/>3.3. Adversary Capabilities - Attacks</h3></div></div></div><p> + </p></li></ol></div></div><div class="sect2" title="3.3. Adversary Capabilities - Attacks"><div class="titlepage"><div><div><h3 class="title"><a id="attacks"></a>3.3. Adversary Capabilities - Attacks</h3></div></div></div><p> The adversary can perform the following attacks from a number of different positions to accomplish various aspects of their goals. It should be noted @@ -316,7 +316,7 @@ correlate users' activity across different IP addresses, and still others are performed by malicious agents on the Tor network and at national firewalls. - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><span class="command"><strong>Read and insert identifiers</strong></span><p> + </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><span class="command"><strong>Read and insert identifiers</strong></span><p> The browser contains multiple facilities for storing identifiers that the adversary creates for the purposes of tracking users. These identifiers are @@ -329,7 +329,7 @@ An adversary in a position to perform MITM content alteration can inject document content elements to both read and inject cookies for arbitrary domains. In fact, even many "SSL secured" websites are vulnerable to this sort of -<a class="ulink" href="http://seclists.org/bugtraq/2007/Aug/0070.html">active +<a class="ulink" href="http://seclists.org/bugtraq/2007/Aug/0070.html" target="_top">active sidejacking</a>. In addition, the ad networks of course perform tracking with cookies as well. @@ -337,7 +337,7 @@ 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 Unlikability</a> design requirements. - </p></li><li class="listitem"><a id="fingerprinting"/><span class="command"><strong>Fingerprint users based on browser + </p></li><li class="listitem"><a id="fingerprinting"></a><span class="command"><strong>Fingerprint users based on browser attributes</strong></span><p> There is an absurd amount of information available to websites via attributes @@ -356,10 +356,10 @@ </p><p> -The <a class="ulink" href="https://panopticlick.eff.org/about.php">Panopticlick study -done</a> by the EFF uses the <a class="ulink" href="https://en.wikipedia.org/wiki/Entropy_%28information_theory%29">Shannon +The <a class="ulink" href="https://panopticlick.eff.org/about.php" target="_top">Panopticlick study +done</a> by the EFF uses the <a class="ulink" href="https://en.wikipedia.org/wiki/Entropy_%28information_theory%29" target="_top">Shannon entropy</a> - the number of identifying bits of information encoded in -browser properties - as this metric. Their <a class="ulink" href="https://wiki.mozilla.org/Fingerprinting#Data">result data</a> is +browser properties - as this metric. Their <a class="ulink" href="https://wiki.mozilla.org/Fingerprinting#Data" target="_top">result data</a> is definitely useful, and the metric is probably the appropriate one for determining how identifying a particular browser property is. However, some quirks of their study means that they do not extract as much information as @@ -375,7 +375,7 @@ Despite the uncertainty, all fingerprinting attacks leverage the following attack vectors: - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><span class="command"><strong>Observing Request Behavior</strong></span><p> + </p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><span class="command"><strong>Observing Request Behavior</strong></span><p> Properties of the user's request behavior comprise the bulk of low-hanging fingerprinting targets. These include: User agent, Accept-* headers, pipeline @@ -390,11 +390,11 @@ about the useragent. Also, Javascript can be used to query the user's timezone via the -<code class="function">Date()</code> object, <a class="ulink" href="https://www.khronos.org/registry/webgl/specs/1.0/#5.13">WebGL</a> can +<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 reveal information about the video card in use, and high precision timing -information can be used to <a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf">fingerprint the CPU and +information can be used to <a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf" target="_top">fingerprint the CPU and interpreter speed</a>. In the future, new JavaScript features such as -<a class="ulink" href="http://w3c-test.org/webperf/specs/ResourceTiming/">Resource +<a class="ulink" href="http://w3c-test.org/webperf/specs/ResourceTiming/" target="_top">Resource Timing</a> may leak an unknown amount of network timing related information. @@ -408,7 +408,7 @@ interface addresses, and other machine information that is beyond what the browser would normally provide to content. In addition, plugins can be used to store unique identifiers that are more difficult to clear than standard -cookies. <a class="ulink" href="http://epic.org/privacy/cookies/flash.html">Flash-based +cookies. <a class="ulink" href="http://epic.org/privacy/cookies/flash.html" target="_top">Flash-based cookies</a> fall into this category, but there are likely numerous other examples. Beyond fingerprinting, plugins are also abysmal at obeying the proxy settings of the browser. @@ -416,7 +416,7 @@ </p></li><li class="listitem"><span class="command"><strong>Inserting CSS</strong></span><p> -<a class="ulink" href="https://developer.mozilla.org/En/CSS/Media_queries">CSS media +<a class="ulink" href="https://developer.mozilla.org/En/CSS/Media_queries" target="_top">CSS media queries</a> can be inserted to gather information about the desktop size, widget size, display type, DPI, user agent type, and other information that was formerly available only to Javascript. @@ -429,11 +429,11 @@ install malware and surveillance software. An adversary with physical access can perform similar actions. Regrettably, this last attack capability is outside of the browser's ability to defend against, but it is worth mentioning -for completeness. In fact, <a class="ulink" href="http://tails.boum.org/contribute/design/">The Tails system</a> can +for completeness. In fact, <a class="ulink" href="http://tails.boum.org/contribute/design/" target="_top">The Tails system</a> can provide some defense against this adversary, and it does include the Tor Browser. - </p></li></ol></div></div></div><div class="sect1" title="4. Implementation"><div class="titlepage"><div><div><h2 class="title"><a id="Implementation"/>4. Implementation</h2></div></div></div><p> + </p></li></ol></div></div></div><div class="sect1" title="4. Implementation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="Implementation"></a>4. Implementation</h2></div></div></div><p> The Implementation section is divided into subsections, each of which corresponds to a <a class="link" href="#DesignRequirements" title="2. Design Requirements and Philosophy">Design Requirement</a>. @@ -446,15 +446,15 @@ way (for example, by disabling features). In rare cases, there may be no implementation at all. Both of these cases are denoted by differentiating between the <span class="command"><strong>Design Goal</strong></span> and the <span class="command"><strong>Implementation -Status</strong></span> for each property. Corresponding bugs in the <a class="ulink" href="https://trac.torproject.org/projects/tor/report">Tor bug tracker</a> +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> are typically linked for these cases. - </p><div class="sect2" title="4.1. Proxy Obedience"><div class="titlepage"><div><div><h3 class="title"><a id="proxy-obedience"/>4.1. Proxy Obedience</h3></div></div></div><p> + </p><div class="sect2" title="4.1. Proxy Obedience"><div class="titlepage"><div><div><h3 class="title"><a id="proxy-obedience"></a>4.1. Proxy Obedience</h3></div></div></div><p> Proxy obedience is assured through the following: - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem">Firefox proxy settings, patches, and build flags + </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Firefox proxy settings, patches, and build flags <p> -Our <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/HEAD:/build-scripts/config/pound_tor.js">Firefox +Our <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/HEAD:/build-scripts/config..." target="_top">Firefox preferences file</a> sets the Firefox proxy settings to use Tor directly as a SOCKS proxy. It sets <span class="command"><strong>network.proxy.socks_remote_dns</strong></span>, <span class="command"><strong>network.proxy.socks_version</strong></span>, @@ -462,10 +462,10 @@ <span class="command"><strong>network.dns.disablePrefetch</strong></span>. </p><p> -We also patch Firefox in order to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0016-Prevent-WebSocket-DNS-leak.patch">prevent +We also patch Firefox in order to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">prevent a DNS leak due to a WebSocket rate-limiting check</a>. As stated in the patch, we believe the direct DNS resolution performed by this check is in -violation of the W3C standard, but <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=751465">this DNS proxy leak +violation of the W3C standard, but <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=751465" target="_top">this DNS proxy leak remains present in stock Firefox releases</a>. </p><p> @@ -491,11 +491,11 @@ </p><p> Numerous other third parties have also reviewed and tested the proxy settings -and have provided test cases based on their work. See in particular <a class="ulink" href="http://decloak.net/">decloak.net</a>. +and have provided test cases based on their work. See in particular <a class="ulink" href="http://decloak.net/" target="_top">decloak.net</a>. </p></li><li class="listitem">Disabling plugins - <p>Plugins have the ability to make arbitrary OS system calls and <a class="ulink" href="http://decloak.net/">bypass proxy settings</a>. This includes + <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 the ability to make UDP sockets and send arbitrary data independent of the browser proxy settings. </p><p> @@ -510,7 +510,7 @@ </p><p> In addition, to reduce any unproxied activity by arbitrary plugins at load time, and to reduce the fingerprintability of the installed plugin list, we -also patch the Firefox source code to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0005-Block-all-plugins-except-flash.patch">prevent the load of any plugins except +also patch the Firefox source code to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">prevent the load of any plugins except for Flash and Gnash</a>. </p></li><li class="listitem">External App Blocking @@ -518,7 +518,7 @@ External apps, if launched automatically, can be induced to load files that perform network activity. In order to prevent this, Torbutton installs a component to -<a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob_plain/HEAD:/src/components/external-app-blocker.js"> +<a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob_plain/HEAD:/src/components/..." target="_top"> provide the user with a popup</a> whenever the browser attempts to launch a helper app. @@ -526,30 +526,30 @@ filtered by this component. Unity was pre-fetching URLs without using the browser's proxy settings during a drag action, even if the drop was ultimately canceled by the user. A similar issue was discovered on Mac OS. - </p></li></ol></div></div><div class="sect2" title="4.2. State Separation"><div class="titlepage"><div><div><h3 class="title"><a id="state-separation"/>4.2. State Separation</h3></div></div></div><p> + </p></li></ol></div></div><div class="sect2" title="4.2. State Separation"><div class="titlepage"><div><div><h3 class="title"><a id="state-separation"></a>4.2. State Separation</h3></div></div></div><p> Tor Browser State is separated from existing browser state through use of a custom Firefox profile. Furthermore, plugins are disabled, which prevents Flash cookies from leaking from a pre-existing Flash directory. - </p></div><div class="sect2" title="4.3. Disk Avoidance"><div class="titlepage"><div><div><h3 class="title"><a id="disk-avoidance"/>4.3. Disk Avoidance</h3></div></div></div><div class="sect3" title="Design Goal:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5523344"/>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"> + </p></div><div class="sect2" title="4.3. Disk Avoidance"><div class="titlepage"><div><div><h3 class="title"><a id="disk-avoidance"></a>4.3. Disk Avoidance</h3></div></div></div><div class="sect3" title="Design Goal:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5528304"></a>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"> The User Agent MUST (at user option) prevent all disk records of browser activity. The user should be able to optionally enable URL history and other history features if they so desire. - </blockquote></div></div><div class="sect3" title="Implementation Status:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5524704"/>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"> + </blockquote></div></div><div class="sect3" title="Implementation Status:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5529664"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"> We achieve this goal through several mechanisms. First, we set the Firefox Private Browsing preference <span class="command"><strong>browser.privatebrowsing.autostart</strong></span>. In addition, four Firefox patches are needed to prevent disk writes, even if Private Browsing Mode is enabled. We need to -<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0002-Make-Permissions-Manager-memory-only.patch">prevent +<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">prevent the permissions manager from recording HTTPS STS state</a>, -<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0003-Make-Intermediate-Cert-Store-memory-only.patch">prevent +<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">prevent intermediate SSL certificates from being recorded</a>, -<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0013-Make-Download-manager-memory-only.patch">prevent +<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">prevent download history from being recorded</a>, and -<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0006-Make-content-pref-service-memory-only-clearable.patch">prevent +<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">prevent the content preferences service from recording site zoom</a>. For more details on these patches, <a class="link" href="#firefox-patches" title="4.8. Description of Firefox Patches">see the @@ -558,7 +558,7 @@ </blockquote></div><div class="blockquote"><blockquote class="blockquote"> As an additional defense-in-depth measure, we set the following preferences: -<span class="command"><strong/></span>, +<span class="command"><strong></strong></span>, <span class="command"><strong>browser.cache.disk.enable</strong></span>, <span class="command"><strong>browser.cache.offline.enable</strong></span>, <span class="command"><strong>dom.indexedDB.enabled</strong></span>, @@ -574,11 +574,11 @@ </blockquote></div><div class="blockquote"><blockquote class="blockquote"> -Torbutton also <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob/HEAD:/src/components/tbSessionStore.js">contains +Torbutton also <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob/HEAD:/src/components/tbSess..." target="_top">contains code</a> to prevent the Firefox session store from writing to disk. </blockquote></div><div class="blockquote"><blockquote class="blockquote"> -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">tbb-disk-leak tag in our bugtracker</a></blockquote></div></div></div><div class="sect2" title="4.4. Application Data Isolation"><div class="titlepage"><div><div><h3 class="title"><a id="app-data-isolation"/>4.4. Application Data Isolation</h3></div></div></div><p> +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" title="4.4. Application Data Isolation"><div class="titlepage"><div><div><h3 class="title"><a id="app-data-isolation"></a>4.4. Application Data Isolation</h3></div></div></div><p> Tor Browser Bundle MUST NOT cause any information to be written outside of the bundle directory. This is to ensure that the user is able to completely and @@ -592,7 +592,7 @@ <span class="command"><strong>browser.shell.checkDefaultBrowser</strong></span>, and <span class="command"><strong>browser.download.manager.addToRecentDocs</strong></span>. We also set the $HOME environment variable to be the TBB extraction directory. - </p></div><div class="sect2" title="4.5. Cross-Origin Identifier Unlinkability"><div class="titlepage"><div><div><h3 class="title"><a id="identifier-linkability"/>4.5. Cross-Origin Identifier Unlinkability</h3></div></div></div><p> + </p></div><div class="sect2" title="4.5. Cross-Origin Identifier Unlinkability"><div class="titlepage"><div><div><h3 class="title"><a id="identifier-linkability"></a>4.5. Cross-Origin Identifier Unlinkability</h3></div></div></div><p> The Tor Browser MUST prevent a user's activity on one site from being linked to their activity on another site. When this goal cannot yet be met with an @@ -616,7 +616,7 @@ context-menu option to drill down into specific types of state or permissions. An example of this simplification can be seen in Figure 1. - </p><div class="figure"><a id="idp5548704"/><p class="title"><b>Figure 1. Improving the Privacy UI</b></p><div class="figure-contents"><div class="mediaobject" style="text-align: center"><img src="NewCookieManager.png" style="text-align: middle" alt="Improving the Privacy UI"/></div><div class="caption"><p/> + </p><div class="figure"><a id="idp5553664"></a><p class="title"><b>Figure 1. Improving the Privacy UI</b></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> This example UI is a mock-up of how isolating identifiers to the URL bar origin can simplify the privacy UI for all data - not just cookies. Once @@ -624,11 +624,11 @@ privacy window can represent browsing history, DOM Storage, HTTP Auth, search form history, login values, and so on within a context menu for each site. -</div></div></div><br class="figure-break"/><div class="orderedlist"><ol class="orderedlist"><li class="listitem">Cookies +</div></div></div><br class="figure-break" /><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Cookies <p><span class="command"><strong>Design Goal:</strong></span> All cookies MUST be double-keyed to the url bar origin and third-party -origin. There exists a <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=565965">Mozilla bug</a> +origin. There exists a <a class="ulink" href="https://bugzilla.mozilla.org/show_bug.cgi?id=565965" target="_top">Mozilla bug</a> that contains a prototype patch, but it lacks UI, and does not apply to modern Firefoxes. @@ -644,17 +644,17 @@ <p> Cache is isolated to the url bar origin by using a technique pioneered by -Colin Jackson et al, via their work on <a class="ulink" href="http://www.safecache.com/">SafeCache</a>. The technique re-uses the -<a class="ulink" href="https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsICachingChannel">nsICachingChannel.cacheKey</a> +Colin Jackson et al, via their work on <a class="ulink" href="http://www.safecache.com/" target="_top">SafeCache</a>. The technique re-uses the +<a class="ulink" href="https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsICachingChannel" target="_top">nsICachingChannel.cacheKey</a> attribute that Firefox uses internally to prevent improper caching and reuse of HTTP POST data. </p><p> -However, to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3666">increase the -security of the isolation</a> and to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3754">solve conflicts +However, to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3666" target="_top">increase the +security of the isolation</a> and to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3754" target="_top">solve conflicts with OCSP relying the cacheKey property for reuse of POST requests</a>, we -had to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0004-Add-a-string-based-cacheKey.patch">patch +had to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">patch Firefox to provide a cacheDomain cache attribute</a>. We use the fully qualified url bar domain as input to this field. @@ -669,9 +669,9 @@ </p><p> -Therefore, <a class="ulink" href="http://crypto.stanford.edu/sameorigin/safecachetest.html">the original +Therefore, <a class="ulink" href="http://crypto.stanford.edu/sameorigin/safecachetest.html" target="_top">the original Stanford test cases</a> are expected to fail. Functionality can still be -verified by navigating to <a class="ulink" href="about:cache">about:cache</a> and +verified by navigating to <a class="ulink" href="about:cache" target="_top">about:cache</a> and viewing the key used for each cache entry. Each third party element should have an additional "domain=string" property prepended, which will list the FQDN that was used to source the third party element. @@ -679,22 +679,22 @@ </p><p> Additionally, because the image cache is a separate entity from the content -cache, we had to patch Firefox to also <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0024-Isolate-the-Image-Cache-per-url-bar-domain.patch">isolate +cache, we had to patch Firefox to also <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">isolate this cache per url bar domain</a>. </p></li><li class="listitem">HTTP Auth <p> HTTP authentication tokens are removed for third party elements using the -<a class="ulink" href="https://developer.mozilla.org/en/Setting_HTTP_request_headers#Observers">http-on-modify-request -observer</a> to remove the Authorization headers to prevent <a class="ulink" href="http://jeremiahgrossman.blogspot.com/2007/04/tracking-users-without-cookies.html">silent +<a class="ulink" href="https://developer.mozilla.org/en/Setting_HTTP_request_headers#Observers" target="_top">http-on-modify-request +observer</a> to remove the Authorization headers to prevent <a class="ulink" href="http://jeremiahgrossman.blogspot.com/2007/04/tracking-users-without-cookies...." target="_top">silent linkability between domains</a>. </p></li><li class="listitem">DOM Storage <p> DOM storage for third party domains MUST be isolated to the url bar origin, to prevent linkability between sites. This functionality is provided through a -<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0026-Isolate-DOM-storage-to-first-party-URI.patch">patch +<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">patch to Firefox</a>. </p></li><li class="listitem">Flash cookies @@ -702,12 +702,12 @@ Users should be able to click-to-play flash objects from trusted sites. To make this behavior unlinkable, we wish to include a settings file for all platforms that disables flash -cookies using the <a class="ulink" href="http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager03.html">Flash +cookies using the <a class="ulink" href="http://www.macromedia.com/support/documentation/en/flashplayer/help/settings..." target="_top">Flash settings manager</a>. </p><p><span class="command"><strong>Implementation Status:</strong></span> -We are currently <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3974">having +We are currently <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3974" target="_top">having difficulties</a> causing Flash player to use this settings file on Windows, so Flash remains difficult to enable. @@ -723,10 +723,10 @@ We currently clear SSL Session IDs upon <a class="link" href="#new-identity" title="4.7. Long-Term Unlinkability via "New Identity" button">New Identity</a>, we disable TLS Session Tickets via the Firefox Pref <span class="command"><strong>security.enable_tls_session_tickets</strong></span>. We disable SSL Session -IDs via a <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0008-Disable-SSL-Session-ID-tracking.patch">patch +IDs via a <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">patch to Firefox</a>. To compensate for the increased round trip latency from disabling these performance optimizations, we also enable -<a class="ulink" href="https://tools.ietf.org/html/draft-bmoeller-tls-falsestart-00">TLS +<a class="ulink" href="https://tools.ietf.org/html/draft-bmoeller-tls-falsestart-00" target="_top">TLS False Start</a> via the Firefox Pref <span class="command"><strong>security.ssl.enable_false_start</strong></span>. </p><p> @@ -761,16 +761,16 @@ </p><p><span class="command"><strong>Implementation status:</strong></span> There are numerous ways for the user to be redirected, and the Firefox API -support to detect each of them is poor. We have a <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3600">trac bug +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 open</a> to implement what we can. </p></li><li class="listitem">window.name <p> -<a class="ulink" href="https://developer.mozilla.org/En/DOM/Window.name">window.name</a> is +<a class="ulink" href="https://developer.mozilla.org/En/DOM/Window.name" target="_top">window.name</a> is a magical DOM property that for some reason is allowed to retain a persistent value for the lifespan of a browser tab. It is possible to utilize this property for -<a class="ulink" href="http://www.thomasfrank.se/sessionvars.html">identifier +<a class="ulink" href="http://www.thomasfrank.se/sessionvars.html" target="_top">identifier storage</a>. </p><p> @@ -788,7 +788,7 @@ We disable the password saving functionality in the browser as part of our <a class="link" href="#disk-avoidance" title="4.3. Disk Avoidance">Disk Avoidance</a> requirement. However, since users may decide to re-enable disk history records and password saving, -we also set the <a class="ulink" href="http://kb.mozillazine.org/Signon.autofillForms">signon.autofillForms</a> +we also set the <a class="ulink" href="http://kb.mozillazine.org/Signon.autofillForms" target="_top">signon.autofillForms</a> preference to false to prevent saved values from immediately populating fields upon page load. Since Javascript can read these values as soon as they appear, setting this preference prevents automatic linkability from stored passwords. @@ -796,7 +796,7 @@ </p></li><li class="listitem">HSTS supercookies <p> -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">HSTS +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-..." target="_top">HSTS supercookies</a>. Since HSTS effectively stores one bit of information per domain name, an adversary in possession of numerous domains can use them to construct cookies based on stored HSTS state. @@ -823,17 +823,17 @@ </p><p><span class="command"><strong>Implementation Status:</strong></span> The Tor feature that supports this ability only exists in the 0.2.3.x-alpha -series. <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3455">Ticket +series. <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3455" target="_top">Ticket #3455</a> is the Torbutton ticket to make use of the new Tor functionality. </p></li></ol></div><p> -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">tbb-linkability tag in our bugtracker</a> - </p></div><div class="sect2" title="4.6. Cross-Origin Fingerprinting Unlinkability"><div class="titlepage"><div><div><h3 class="title"><a id="fingerprinting-linkability"/>4.6. Cross-Origin Fingerprinting Unlinkability</h3></div></div></div><p> +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> + </p></div><div class="sect2" title="4.6. Cross-Origin Fingerprinting Unlinkability"><div class="titlepage"><div><div><h3 class="title"><a id="fingerprinting-linkability"></a>4.6. Cross-Origin Fingerprinting Unlinkability</h3></div></div></div><p> In order to properly address the fingerprinting adversary on a technical level, we need a metric to measure linkability of the various browser -properties beyond any stored origin-related state. <a class="ulink" href="https://panopticlick.eff.org/about.php">The Panopticlick Project</a> +properties beyond any stored origin-related state. <a class="ulink" href="https://panopticlick.eff.org/about.php" target="_top">The Panopticlick Project</a> by the EFF provides us with a prototype of such a metric. The researchers conducted a survey of volunteers who were asked to visit an experiment page that harvested many of the above components. They then computed the Shannon @@ -858,11 +858,11 @@ years, any fingerprinting defenses attempted by browsers today are very likely to cause Panopticlick to report an <span class="emphasis"><em>increase</em></span> in fingerprintability and entropy, because those defenses will stand out in sharp -contrast to historical data. We have been <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/6119">working to convince +contrast to historical data. We have been <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/6119" target="_top">working to convince the EFF</a> that it is worthwhile to release the source code to Panopticlick to allow us to run our own version for this reason. - </p><div class="sect3" title="Fingerprinting defenses in the Tor Browser"><div class="titlepage"><div><div><h4 class="title"><a id="fingerprinting-defenses"/>Fingerprinting defenses in the Tor Browser</h4></div></div></div><div class="orderedlist"><ol class="orderedlist"><li class="listitem">Plugins + </p><div class="sect3" title="Fingerprinting defenses in the Tor Browser"><div class="titlepage"><div><div><h4 class="title"><a id="fingerprinting-defenses"></a>Fingerprinting defenses in the Tor Browser</h4></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Plugins <p> Plugins add to fingerprinting risk via two main vectors: their mere presence in @@ -874,7 +874,7 @@ disabled. To reduce linkability potential, even sandboxed plugins should not be allowed to load objects until the user has clicked through a click-to-play barrier. Additionally, version information should be reduced or obfuscated -until the plugin object is loaded. For flash, we wish to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3974">provide a +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 settings.sol file</a> to disable Flash cookies, and to restrict P2P features that are likely to bypass proxy settings. @@ -884,7 +884,7 @@ compromise due to the popularity of Flash, we allow users to re-enable Flash, and flash objects are blocked behind a click-to-play barrier that is available only after the user has specifically enabled plugins. Flash is the only plugin -available, the rest are <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0005-Block-all-plugins-except-flash.patch">entirely +available, the rest are <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">entirely blocked from loading by a Firefox patch</a>. We also set the Firefox preference <span class="command"><strong>plugin.expose_full_path</strong></span> to false, to avoid leaking plugin installation information. @@ -892,11 +892,11 @@ </p></li><li class="listitem">HTML5 Canvas Image Extraction <p> -The <a class="ulink" href="https://developer.mozilla.org/en-US/docs/HTML/Canvas">HTML5 +The <a class="ulink" href="https://developer.mozilla.org/en-US/docs/HTML/Canvas" target="_top">HTML5 Canvas</a> is a feature that has been added to major browsers after the EFF developed their Panopticlick study. After plugins and plugin-provided information, we believe that the HTML5 Canvas is the single largest -fingerprinting threat browsers face today. <a class="ulink" href="http://www.w2spconf.com/2012/papers/w2sp12-final4.pdf">Initial +fingerprinting threat browsers face today. <a class="ulink" href="http://www.w2spconf.com/2012/papers/w2sp12-final4.pdf" target="_top">Initial studies</a> show that the Canvas can provide an easy-access fingerprinting target: The adversary simply renders WebGL, font, and named color data to a Canvas element, extracts the image buffer, and computes a hash of that image @@ -907,7 +907,7 @@ </p><p> -To reduce the threat from this vector, we have patched Firefox to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0020-Add-canvas-image-extraction-prompt.patch">prompt +To reduce the threat from this vector, we have patched Firefox to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">prompt before returning valid image data</a> to the Canvas APIs. If the user hasn't previously allowed the site in the URL bar to access Canvas image data, pure white image data is returned to the Javascript APIs. @@ -921,7 +921,7 @@ </p><p> -Because of the large amount of potential fingerprinting vectors and the <a class="ulink" href="http://www.contextis.com/resources/blog/webgl/">previously unexposed +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 vulnerability surface</a>, we deploy a similar strategy against WebGL as for plugins. First, WebGL Canvases have click-to-play placeholders (provided by NoScript), and do not run until authorized by the user. Second, we @@ -947,7 +947,7 @@ The sure-fire way to address font linkability is to ship the browser with a font for every language, typeface, and style in use in the world, and to only use those fonts at the exclusion of system fonts. However, this set may be -impractically large. It is possible that a smaller <a class="ulink" href="https://secure.wikimedia.org/wikipedia/en/wiki/Unicode_typeface#List_of_Unicode_fonts">common +impractically large. It is possible that a smaller <a class="ulink" href="https://secure.wikimedia.org/wikipedia/en/wiki/Unicode_typeface#List_of_Unic..." target="_top">common subset</a> may be found that provides total coverage. However, we believe that with strong url bar origin identifier isolation, a simpler approach can reduce the number of bits available to the adversary while avoiding the rendering and @@ -957,7 +957,7 @@ We disable plugins, which prevents font enumeration. Additionally, we limit both the number of font queries from CSS, as well as the total number of -fonts that can be used in a document <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0011-Limit-the-number-of-fonts-per-document.patch">with +fonts that can be used in a document <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">with a Firefox patch</a>. We create two prefs, <span class="command"><strong>browser.display.max_font_attempts</strong></span> and <span class="command"><strong>browser.display.max_font_count</strong></span> for this purpose. Once these @@ -967,7 +967,7 @@ </p><p> -To improve rendering, we exempt remote <a class="ulink" href="https://developer.mozilla.org/en-US/docs/CSS/@font-face">@font-face +To improve rendering, we exempt remote <a class="ulink" href="https://developer.mozilla.org/en-US/docs/CSS/@font-face" target="_top">@font-face fonts</a> from these counts, and if a font-family CSS rule lists a remote font (in any order), we use that font instead of any of the named local fonts. @@ -992,13 +992,13 @@ </p><p><span class="command"><strong>Implementation Status:</strong></span> -We have implemented the above strategy using a window observer to <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob/HEAD:/src/chrome/content/torbutton.js#l2004">resize +We have implemented the above strategy using a window observer to <a class="ulink" href="https://gitweb.torproject.org/torbutton.git/blob/HEAD:/src/chrome/content/to..." target="_top">resize new windows based on desktop resolution</a>. Additionally, we patch -Firefox to use the client content window size <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0022-Do-not-expose-physical-screen-info.-via-window-and-w.patch">for -window.screen</a> and <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0010-Limit-device-and-system-specific-CSS-Media-Queries.patch">for -CSS Media Queries</a>. Similarly, we <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0021-Return-client-window-coordinates-for-mouse-event-scr.patch">patch +Firefox to use the client content window size <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">for +window.screen</a> and <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">for +CSS Media Queries</a>. Similarly, we <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">patch DOM events to return content window relative points</a>. We also patch -Firefox to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0023-Do-not-expose-system-colors-to-CSS-or-canvas.patch">report +Firefox to <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">report a fixed set of system colors to content window CSS</a>. </p></li><li class="listitem">User Agent and HTTP Headers @@ -1014,8 +1014,8 @@ Firefox provides several options for controlling the browser user agent string which we leverage. We also set similar prefs for controlling the Accept-Language and Accept-Charset headers, which we spoof to English by default. Additionally, we -<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0001-Block-Components.interfaces-from-content.patch">remove -content script access</a> to Components.interfaces, which <a class="ulink" href="http://pseudo-flaw.net/tor/torbutton/fingerprint-firefox.html">can be +<a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">remove +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 used</a> to fingerprint OS, platform, and Firefox minor version. </p></li><li class="listitem">Timezone and clock offset <p><span class="command"><strong>Design Goal:</strong></span> @@ -1030,26 +1030,26 @@ </p><p><span class="command"><strong>Implementation Status:</strong></span> We set the timezone using the TZ environment variable, which is supported on -all platforms. Additionally, we plan to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3652">obtain a clock +all platforms. Additionally, we plan to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3652" target="_top">obtain a clock offset from Tor</a>, but this won't be available until Tor 0.2.3.x is in use. </p></li><li class="listitem">Javascript performance fingerprinting <p> -<a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf">Javascript performance +<a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf" target="_top">Javascript performance fingerprinting</a> is the act of profiling the performance of various Javascript functions for the purpose of fingerprinting the Javascript engine and the CPU. </p><p><span class="command"><strong>Design Goal:</strong></span> -We have <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3059">several potential +We have <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3059" target="_top">several potential mitigation approaches</a> to reduce the accuracy of performance fingerprinting without risking too much damage to functionality. Our current favorite is to reduce the resolution of the Event.timeStamp and the Javascript Date() object, while also introducing jitter. Our goal is to increase the -amount of time it takes to mount a successful attack. <a class="ulink" href="http://w2spconf.com/2011/papers/jspriv.pdf">Mowery et al</a> found that +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 that even with the default precision in most browsers, they required up to 120 seconds of amortization and repeated trials to get stable results from their feature set. We intend to work with the research community to establish the @@ -1059,7 +1059,7 @@ </p><p><span class="command"><strong>Implementation Status:</strong></span> Currently, the only mitigation against performance fingerprinting is to -disable <a class="ulink" href="http://www.w3.org/TR/navigation-timing/">Navigation +disable <a class="ulink" href="http://www.w3.org/TR/navigation-timing/" target="_top">Navigation Timing</a> through the Firefox preference <span class="command"><strong>dom.enable_performance</strong></span>. @@ -1067,8 +1067,8 @@ <p> At least two HTML5 features have different implementation status across the -major OS vendors: the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/DOM/window.navigator.battery">Battery -API</a> and the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/DOM/window.navigator.connection">Network +major OS vendors: the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/DOM/window.navigator.battery" target="_top">Battery +API</a> and the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/DOM/window.navigator.connection" target="_top">Network Connection API</a>. We disable these APIs through the Firefox preferences <span class="command"><strong>dom.battery.enabled</strong></span> and <span class="command"><strong>dom.network.enabled</strong></span>. @@ -1087,23 +1087,23 @@ </p><p><span class="command"><strong>Implementation Status:</strong></span> We have no implementation as of yet. </p></li></ol></div></div><p> -For more details on identifier linkability bugs and enhancements, see the <a class="ulink" href="https://trac.torproject.org/projects/tor/query?keywords=~tbb-fingerprinting&status=!closed">tbb-fingerprinting tag in our bugtracker</a> - </p></div><div class="sect2" title="4.7. Long-Term Unlinkability via "New Identity" button"><div class="titlepage"><div><div><h3 class="title"><a id="new-identity"/>4.7. Long-Term Unlinkability via "New Identity" button</h3></div></div></div><p> +For more details on identifier linkability 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 bugtracker</a> + </p></div><div class="sect2" title="4.7. Long-Term Unlinkability via "New Identity" button"><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> In order to avoid long-term linkability, we provide a "New Identity" context menu option in Torbutton. This context menu option is active if Torbutton can read the environment variables $TOR_CONTROL_PASSWD and $TOR_CONTROL_PORT. - </p><div class="sect3" title="Design Goal:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5665856"/>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"> + </p><div class="sect3" title="Design Goal:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5670816"></a>Design Goal:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"> All linkable identifiers and browser state MUST be cleared by this feature. - </blockquote></div></div><div class="sect3" title="Implementation Status:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5667104"/>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"><p> + </blockquote></div></div><div class="sect3" title="Implementation Status:"><div class="titlepage"><div><div><h4 class="title"><a id="idp5672064"></a>Implementation Status:</h4></div></div></div><div class="blockquote"><blockquote class="blockquote"><p> First, Torbutton disables Javascript in all open tabs and windows by using -both the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIDocShell#Attributes">browser.docShell.allowJavascript</a> -attribute as well as <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIDOMWindowUtils#suppressEventHandling%28%29">nsIDOMWindowUtil.suppressEventHandling()</a>. -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">browser.webNavigation.stop(nsIWebNavigation.STOP_ALL)</a>. +both the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIDocShe..." target="_top">browser.docShell.allowJavascript</a> +attribute as well as <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIDOMWin..." target="_top">nsIDOMWindowUtil.suppressEventHandling()</a>. +We then stop all page activity for each tab using <a class="ulink" href="https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIWebNav..." target="_top">browser.webNavigation.stop(nsIWebNavigation.STOP_ALL)</a>. We then clear the site-specific Zoom by temporarily disabling the preference <span class="command"><strong>browser.zoom.siteSpecific</strong></span>, and clear the GeoIP wiki token URL and the last opened URL prefs (if they exist). Each tab is then closed. @@ -1127,29 +1127,29 @@ </p></blockquote></div><div class="blockquote"><blockquote class="blockquote"> If the user chose to "protect" any cookies by using the Torbutton Cookie Protections UI, those cookies are not cleared as part of the above. - </blockquote></div></div></div><div class="sect2" title="4.8. Description of Firefox Patches"><div class="titlepage"><div><div><h3 class="title"><a id="firefox-patches"/>4.8. Description of Firefox Patches</h3></div></div></div><p> + </blockquote></div></div></div><div class="sect2" title="4.8. Description of Firefox Patches"><div class="titlepage"><div><div><h3 class="title"><a id="firefox-patches"></a>4.8. Description of Firefox Patches</h3></div></div></div><p> -The set of patches we have against Firefox can be found in the <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/tree/maint-2.4:/src/current-patches/firefox">current-patches directory of the torbrowser git repository</a>. They are: +The set of patches we have against Firefox can be found in the <a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/tree/maint-2.4:/src/current-pat..." target="_top">current-patches directory of the torbrowser git repository</a>. They are: - </p><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0001-Block-Components.interfaces-from-content.patch">Block + </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Block Components.interfaces</a><p> In order to reduce fingerprinting, we block access to this interface from content script. Components.interfaces can be used for fingerprinting the platform, OS, and Firebox version, but not much else. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0002-Make-Permissions-Manager-memory-only.patch">Make + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Make Permissions Manager memory only</a><p> This patch exposes a pref 'permissions.memory_only' that properly isolates the permissions manager to memory, which is responsible for all user specified -site permissions, as well as stored <a class="ulink" href="https://secure.wikimedia.org/wikipedia/en/wiki/HTTP_Strict_Transport_Security">HSTS</a> +site permissions, as well as stored <a class="ulink" href="https://secure.wikimedia.org/wikipedia/en/wiki/HTTP_Strict_Transport_Securit..." target="_top">HSTS</a> policy from visited sites. The pref does successfully clear the permissions manager memory if toggled. It does not need to be set in prefs.js, and can be handled by Torbutton. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0003-Make-Intermediate-Cert-Store-memory-only.patch">Make + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Make Intermediate Cert Store memory-only</a><p> The intermediate certificate store records the intermediate SSL certificates @@ -1164,28 +1164,28 @@ information to be cleared from memory. The implementation does not currently allow this. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0004-Add-a-string-based-cacheKey.patch">Add + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Add a string-based cacheKey property for domain isolation</a><p> -To <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3666">increase the -security of cache isolation</a> and to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3754">solve strange and +To <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3666" target="_top">increase the +security of cache isolation</a> and to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3754" target="_top">solve strange and unknown conflicts with OCSP</a>, we had to patch Firefox to provide a cacheDomain cache attribute. We use the url bar FQDN as input to this field. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0005-Block-all-plugins-except-flash.patch">Block + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Block all plugins except flash</a><p> -We cannot use the <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/components/@mozilla.org/extensions/blocklist%3B1"> +We cannot use the <a class="ulink" href="http://www.oxymoronical.com/experiments/xpcomref/applications/Firefox/3.5/co..." target="_top"> @mozilla.org/extensions/blocklist;1</a> service, because we actually want to stop plugins from ever entering the browser's process space and/or executing code (for example, AV plugins that collect statistics/analyze URLs, magical toolbars that phone home or "help" the user, Skype buttons that ruin our day, and censorship filters). Hence we rolled our own. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0006-Make-content-pref-service-memory-only-clearable.patch">Make content-prefs service memory only</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Make content-prefs service memory only</a><p> This patch prevents random URLs from being inserted into content-prefs.sqlite in the profile directory as content prefs change (includes site-zoom and perhaps other site prefs?). - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0007-Make-Tor-Browser-exit-when-not-launched-from-Vidalia.patch">Make Tor Browser exit when not launched from Vidalia</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Make Tor Browser exit when not launched from Vidalia</a><p> It turns out that on Windows 7 and later systems, the Taskbar attempts to automatically learn the most frequent apps used by the user, and it recognizes @@ -1195,118 +1195,118 @@ connect directly without using Tor. This patch is a simple hack to cause Tor Browser to immediately exit in this case. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0008-Disable-SSL-Session-ID-tracking.patch">Disable SSL Session ID tracking</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Disable SSL Session ID tracking</a><p> This patch is a simple 1-line hack to prevent SSL connections from caching (and then later transmitting) their Session IDs. There was no preference to govern this behavior, so we had to hack it by altering the SSL new connection defaults. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0009-Provide-an-observer-event-to-close-persistent-connec.patch">Provide an observer event to close persistent connections</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Provide an observer event to close persistent connections</a><p> This patch creates an observer event in the HTTP connection manager to close all keep-alive connections that still happen to be open. This event is emitted by the <a class="link" href="#new-identity" title="4.7. Long-Term Unlinkability via "New Identity" button">New Identity</a> button. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0010-Limit-device-and-system-specific-CSS-Media-Queries.patch">Limit Device and System Specific Media Queries</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Limit Device and System Specific Media Queries</a><p> -<a class="ulink" href="https://developer.mozilla.org/en-US/docs/CSS/Media_queries">CSS +<a class="ulink" href="https://developer.mozilla.org/en-US/docs/CSS/Media_queries" target="_top">CSS Media Queries</a> have a fingerprinting capability approaching that of Javascript. This patch causes such Media Queries to evaluate as if the device resolution was equal to the content window resolution. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0011-Limit-the-number-of-fonts-per-document.patch">Limit the number of fonts per document</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Limit the number of fonts per document</a><p> -Font availability can be <a class="ulink" href="http://flippingtypical.com/">queried by +Font availability can be <a class="ulink" href="http://flippingtypical.com/" target="_top">queried by CSS and Javascript</a> and is a fingerprinting vector. This patch limits the number of times CSS and Javascript can cause font-family rules to evaluate. Remote @font-face fonts are exempt from the limits imposed by this patch, and remote fonts are given priority over local fonts whenever both appear in the same font-family rule. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0012-Rebrand-Firefox-to-TorBrowser.patch">Rebrand Firefox to Tor Browser</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Rebrand Firefox to Tor Browser</a><p> This patch updates our branding in compliance with Mozilla's trademark policy. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0013-Make-Download-manager-memory-only.patch">Make Download Manager Memory Only</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Make Download Manager Memory Only</a><p> This patch prevents disk leaks from the download manager. The original behavior is to write the download history to disk and then delete it, even if you disable download history from your Firefox preferences. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0014-Add-DDG-and-StartPage-to-Omnibox.patch">Add DDG and StartPage to Omnibox</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Add DDG and StartPage to Omnibox</a><p> This patch adds DuckDuckGo and StartPage to the Search Box, and sets our default search engine to StartPage. We deployed this patch due to excessive Captchas and complete 403 bans from Google. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0015-Make-nsICacheService.EvictEntries-synchronous.patch">Make nsICacheService.EvictEntries() Synchronous</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Make nsICacheService.EvictEntries() Synchronous</a><p> This patch eliminates a race condition with "New Identity". Without it, cache-based Evercookies survive for up to a minute after clearing the cache on some platforms. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0016-Prevent-WebSocket-DNS-leak.patch">Prevent WebSockets DNS Leak</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Prevent WebSockets DNS Leak</a><p> This patch prevents a DNS leak when using WebSockets. It also prevents other similar types of DNS leaks. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0017-Randomize-HTTP-request-order-and-pipeline-depth.patch">Randomize HTTP pipeline order and depth</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Randomize HTTP pipeline order and depth</a><p> As an -<a class="ulink" href="https://blog.torproject.org/blog/experimental-defense-website-traffic-fingerprinting">experimental +<a class="ulink" href="https://blog.torproject.org/blog/experimental-defense-website-traffic-finger..." target="_top">experimental defense against Website Traffic Fingerprinting</a>, we patch the standard HTTP pipelining code to randomize the number of requests in a pipeline, as well as their order. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0018-Adapt-Steven-Michaud-s-Mac-crashfix-patch.patch">Adapt Steve Michaud's Mac crashfix patch</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Adapt Steve Michaud's Mac crashfix patch</a><p> This patch allows us to block Drag and Drop without causing crashes on Mac OS. We need to block Drag and Drop because Mac OS and Ubuntu both immediately load any URLs they find in your drag buffer before you even drop them (without using your browser's proxy settings, of course). - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0019-Add-mozIThirdPartyUtil.getFirstPartyURI-API.patch">Add mozIThirdPartyUtil.getFirstPartyURI() API</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Add mozIThirdPartyUtil.getFirstPartyURI() API</a><p> This patch provides an API that allows us to more easily isolate identifiers to the URL bar domain. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0020-Add-canvas-image-extraction-prompt.patch">Add canvas image extraction prompt</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Add canvas image extraction prompt</a><p> This patch prompts the user before returning canvas image data. Canvas image data can be used to create an extremely stable, high-entropy fingerprint based on the unique rendering behavior of video cards, OpenGL behavior, system fonts, and supporting library versions. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0021-Return-client-window-coordinates-for-mouse-event-scr.patch">Return client window coordinates for mouse events</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Return client window coordinates for mouse events</a><p> This patch causes mouse events to return coordinates relative to the content window instead of the desktop. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0022-Do-not-expose-physical-screen-info.-via-window-and-w.patch">Do not expose physical screen info to window.screen</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Do not expose physical screen info to window.screen</a><p> This patch causes window.screen to return the display resolution size of the content window instead of the desktop resolution size. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0023-Do-not-expose-system-colors-to-CSS-or-canvas.patch">Do not expose system colors to CSS or canvas</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Do not expose system colors to CSS or canvas</a><p> This patch prevents CSS and Javascript from discovering your desktop color scheme and/or theme. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0024-Isolate-the-Image-Cache-per-url-bar-domain.patch">Isolate the Image Cache per url bar domain</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Isolate the Image Cache per url bar domain</a><p> This patch prevents cached images from being used to store third party tracking identifiers. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0025-nsIHTTPChannel.redirectTo-API.patch">nsIHTTPChannel.redirectTo() API</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">nsIHTTPChannel.redirectTo() API</a><p> This patch provides HTTPS-Everywhere with an API to perform redirections more securely and without addon conflicts. - </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-patches/firefox/0026-Isolate-DOM-storage-to-first-party-URI.patch">Isolate DOM Storage to first party URI</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://gitweb.torproject.org/torbrowser.git/blob/maint-2.4:/src/current-pat..." target="_top">Isolate DOM Storage to first party URI</a><p> This patch prevents DOM Storage from being used to store third party tracking identifiers. - </p></li></ol></div></div></div><div class="appendix" title="A. Towards Transparency in Navigation Tracking"><h2 class="title"><a id="Transparency"/>A. Towards Transparency in Navigation Tracking</h2><p> + </p></li></ol></div></div></div><div class="appendix" title="A. Towards Transparency in Navigation Tracking"><h2 class="title" style="clear: both"><a id="Transparency"></a>A. Towards Transparency in Navigation Tracking</h2><p> The <a class="link" href="#privacy" title="2.2. Privacy Requirements">privacy properties</a> of Tor Browser are based upon the assumption that link-click navigation indicates user consent to @@ -1338,7 +1338,7 @@ preserve this functionality while still providing transparency when tracking is occurring. -</p><div class="sect2" title="A.1. Deprecation Wishlist"><div class="titlepage"><div><div><h3 class="title"><a id="deprecate"/>A.1. Deprecation Wishlist</h3></div></div></div><div class="orderedlist"><ol class="orderedlist"><li class="listitem">The Referer Header +</p><div class="sect1" title="A.1. Deprecation Wishlist"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="deprecate"></a>A.1. Deprecation Wishlist</h2></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">The Referer Header <p> We haven't disabled or restricted the referer ourselves because of the @@ -1353,7 +1353,7 @@ Because of the availability of these other explicit vectors, we believe the main risk of the referer header is through inadvertent and/or covert data -leakage. In fact, <a class="ulink" href="http://www2.research.att.com/~bala/papers/wosn09.pdf">a great deal of +leakage. In fact, <a class="ulink" href="http://www2.research.att.com/~bala/papers/wosn09.pdf" target="_top">a great deal of personal data</a> is inadvertently leaked to third parties through the source URL parameters. @@ -1366,15 +1366,15 @@ agent to inform the user if they are about to click on a link that will transmit referer information (perhaps through something as subtle as a different color for the destination URL). This same UI notification can also -be used for links with the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/HTML/Element/a#Attributes">"ping"</a> +be used for links with the <a class="ulink" href="https://developer.mozilla.org/en-US/docs/HTML/Element/a#Attributes" target="_top">"ping"</a> attribute. </p></li><li class="listitem">window.name <p> -<a class="ulink" href="https://developer.mozilla.org/En/DOM/Window.name">window.name</a> is +<a class="ulink" href="https://developer.mozilla.org/En/DOM/Window.name" target="_top">window.name</a> is a DOM property that for some reason is allowed to retain a persistent value for the lifespan of a browser tab. It is possible to utilize this property for -<a class="ulink" href="http://www.thomasfrank.se/sessionvars.html">identifier +<a class="ulink" href="http://www.thomasfrank.se/sessionvars.html" target="_top">identifier storage</a> during click navigation. This is sometimes used for additional XSRF protection and federated login. </p><p> @@ -1397,18 +1397,18 @@ </p><p> Automated cross-origin redirects are one form of this behavior that is -possible for us to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3600">address +possible for us to <a class="ulink" href="https://trac.torproject.org/projects/tor/ticket/3600" target="_top">address ourselves</a>, as they are comparatively rare and can be handled with site permissions. - </p></li></ol></div></div><div class="sect2" title="A.2. Promising Standards"><div class="titlepage"><div><div><h3 class="title"><a id="idp5752304"/>A.2. Promising Standards</h3></div></div></div><div class="orderedlist"><ol class="orderedlist"><li class="listitem"><a class="ulink" href="http://web-send.org">Web-Send Introducer</a><p> + </p></li></ol></div></div><div class="sect1" title="A.2. Promising Standards"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="idp5757152"></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> Web-Send is a browser-based link sharing and federated login widget that is designed to operate without relying on third-party tracking or abusing other -cross-origin link-click side channels. It has a compelling list of <a class="ulink" href="http://web-send.org/features.html">privacy and security features</a>, +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>, especially if used as a "Like button" replacement. - </p></li><li class="listitem"><a class="ulink" href="https://developer.mozilla.org/en-US/docs/Persona">Mozilla Persona</a><p> + </p></li><li class="listitem"><a class="ulink" href="https://developer.mozilla.org/en-US/docs/Persona" target="_top">Mozilla Persona</a><p> Mozilla's Persona is designed to provide decentralized, cryptographically authenticated federated login in a way that does not expose the user to third
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Mike Perry