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#include "head.wmi" TITLE="Tor: Volunteer" CHARSET="UTF-8"
<div id="content" class="clearfix">
  <div id="breadcrumbs">
    <a href="<page index>">Home &raquo; </a>
    <a href="<page getinvolved/volunteer>">Volunteer</a>
  </div>
  <div id="maincol">
    <!-- PUT CONTENT AFTER THIS TAG -->
    <h1>A few things everyone can do now:</h1>
    <ol>
    <li>Please consider <a href="<page docs/tor-doc-relay>">running
    a relay</a> to help the Tor network grow.</li>
    <li>Do you have an Amazon account? Are you willing to spend up to $3 a
    month? Then spin up your own Tor <a href="<page
    docs/bridges>">bridge</a> in less than 10 minutes with <a
    href="https://cloud.torproject.org/">tor cloud</a>!</li>
    <li>Tell your friends! Get them to run relays. Get them to run hidden
    services. Get them to tell their friends.</li>
    <li>If you like Tor's goals, please <a href="<page donate/donate>">take a moment
    to donate to support further Tor development</a>. We're also looking
    for more sponsors &mdash; if you know any companies, NGOs, agencies,
    or other organizations that want anonymity / privacy / communications
    security, let them know about us.</li>
    <li>We're looking for more <a href="<page about/torusers>">good examples of Tor
    users and Tor use cases</a>. If you use Tor for a scenario or purpose not
    yet described on that page, and you're comfortable sharing it with us,
    we'd love to hear from you.</li>
    </ol>

    <a id="Documentation"></a>
    <h2><a class="anchor" href="#Documentation">Documentation</a></h2>
    <ol>
    <li>Help translate the
<!-- web page and -->
    documentation into other
    languages. See the <a href="<page getinvolved/translation>">translation
    guidelines</a> if you want to help out. We especially need Arabic or
    Farsi translations, for the many Tor users in censored areas.</li>
    <li>Evaluate and document
    <a href="<wiki>doc/TorifyHOWTO">our
    list of programs</a> that can be configured to use Tor.</li>
    <li>We have a huge list of <a
    href="<wiki>doc/SupportPrograms">potentially useful
    programs that interface to Tor</a>. Which ones are useful in which
    situations? Please help us test them out and document your results.</li>
    </ol>

    <a id="Advocacy"></a>
    <h2><a class="anchor" href="#Advocacy">Advocacy</a></h2>
    <ol>
    <li>Create a presentation that can be used for various user group
meetings around the world.</li>
    <li>Create a video about the positive uses of Tor, what Tor is,
    or how to use it.  Some have already started on <a
    href="https://media.torproject.org/video/">Tor's Media server</a>,
    <a
    href="http://www.howcast.com/videos/90601-How-To-Circumvent-an-Internet-Proxy">Howcast</a>,
    and <a href="http://www.youtube.com/thetorproject">YouTube</a>.</li>
    <li>Create a poster, or a set of posters, around a theme,
    such as "Tor for Freedom!"</li>
    <li>Create a t-shirt design that incorporates "<a
    href="https://check.torproject.org/">Congratulations! You are using
    Tor!</a>" in any language.</li>
    </ol>

<!--
    <a id="gsoc"></a>
    <h2><a class="anchor" href="#gsoc">Google Summer of Code</a></h2>

    <p>
    Tor is also taking part in this year's <a
    href="https://www.google-melange.com/gsoc/homepage/google/gsoc2013">Google
    Summer of Code</a>! The criteria for this is a little different - either
    gender can apply but you need to be either <a
    href="https://www.google-melange.com/gsoc/document/show/gsoc_program/google/gsoc2013/help_page#2._Whos_eligible_to_participate_as_a">a
    present student or just graduated</a>.
    </p>

    <p>
    As mentioned above if you're eligible for either program then please apply
    for both! Google Summer of Code is a far, far larger program for us than
    OPW so your chances of being applied that way are considerably better.
    </p>

    <p>
    <b>See our page for <a href="<page about/gsoc>">Google Summer of Code</a>
    for more information.</b>
    </p>
-->

    <a id="Projects"></a>
    <h2><a class="anchor" href="#Projects">Projects</a></h2>

    <p>
    Below are a list of Tor related projects we're developing and/or
    maintaining. Most discussions happen on IRC so if you're interested in any
    of these (or you have a project idea of your own), then please <a
    href="<page about/contact>#irc">join us in #tor-dev</a>. Don't be shy
    to ask questions, and don't hesitate to ask even if the main contributors
    aren't active at that moment.
    </p>

    <p>
    For a presentation summarizing many of these projects see...
    </p>

    <div id="ecosystem_presentation">
      <a href="https://media.torproject.org/video/2013-11-t3am-damian-johnson.mp4">Tor Ecosystem</a> (<a href="https://svn.torproject.org/svn/projects/presentations/2013-11-t3am-tor-ecosystem.pdf">slides</a>)
    </div>

    <br /></br />

    <table id="projects">
      <tr>
        <th>Name</th>
        <th>Category</th>
        <th>Language</th>
        <th>Activity</th>
        <th>Contributors</th>
      </tr>

      <tr>
        <td><a href="#project-tor">Tor</a></td>
        <td>Core</td>
        <td>C</td>
        <td>Heavy</td>
        <td>nickm, athena, arma</td>
      </tr>

      <tr>
        <td>*<a href="#project-orchid">Orchid</a></td>
        <td>Core</td>
        <td>Java</td>
        <td>Moderate</td>
        <td>bleidl</td>
      </tr>

      <tr>
        <td><a href="#project-torbrowser">Tor Browser</a></td>
        <td>Bundle</td>
        <td>C, Scripting</td>
        <td>Moderate</td>
        <td>mikeperry, Erinn</td>
      </tr>

      <tr>
        <td><a href="#project-torbutton">Torbutton</a></td>
        <td>Browser Add-on</td>
        <td>Javascript</td>
        <td>Moderate</td>
        <td>mikeperry</td>
      </tr>

      <tr>
        <td><a href="#project-httpseverywhere">HTTPS Everywhere</a></td>
        <td>Browser Add-on</td>
        <td>Javascript</td>
        <td>Heavy</td>
        <td>pde, mikeperry</td>
      </tr>

      <tr>
        <td><a href="#project-vidalia">Vidalia</a></td>
        <td>User Interface</td>
        <td>C++, Qt</td>
        <td>None</td>
        <td>chiiph</td>
      </tr>

      <tr>
        <td><a href="#project-arm">Arm</a></td>
        <td>User Interface</td>
        <td>Python, Curses</td>
        <td>Light</td>
        <td>atagar</td>
      </tr>

      <tr>
        <td><a href="#project-orbot">Orbot</a></td>
        <td>User Interface</td>
        <td>Java</td>
        <td>Light</td>
        <td>n8fr8</td>
      </tr>

      <tr>
        <td><a href="#project-tails">Tails</a></td>
        <td>OS image</td>
        <td>Sys Admin</td>
        <td>Heavy</td>
        <td><a href="https://tails.boum.org/">#tails</a></td>
      </tr>

      <tr>
        <td><a href="#project-torramdisk">tor-ramdisk</a></td>
        <td>OS image</td>
        <td>Sys Admin</td>
        <td>None</td>
        <td>blueness</td>
      </tr>

      <tr>
        <td>*<a href="#project-torouter">Torouter</a></td>
        <td>OS image</td>
        <td>Sys Admin</td>
        <td>None</td>
        <td>ioerror</td>
      </tr>

      <tr>
        <td><a href="#project-torsocks">Torsocks</a></td>
        <td>Usability</td>
        <td>C</td>
        <td>Light</td>
        <td>ioerror, nickm</td>
      </tr>

      <tr>
        <td><a href="#project-torbirdy">TorBirdy</a></td>
        <td>Browser Add-on</td>
        <td>JavaScript</td>
        <td>Heavy</td>
        <td>Sukhbir (sukhe)</td>
      </tr>

      <tr>
        <td><a href="#project-obfsproxy">Obfsproxy</a></td>
        <td>Client Add-on</td>
        <td>Python</td>
        <td>Moderate</td>
        <td>asn</td>
      </tr>

      <tr>
        <td><a href="#project-flash-proxy">Flash Proxy</a></td>
        <td>Client Add-on</td>
        <td>Python, JavaScript, Go</td>
        <td>Heavy</td>
        <td>dcf, aallai, jct</td>
      </tr>

      <tr>
        <td><a href="#project-shadow">Shadow</a></td>
        <td>Simulator</td>
        <td>C, Python</td>
        <td>Heavy</td>
        <td>robgjansen</td>
      </tr>

      <tr>
        <td><a href="#project-stem">Stem</a></td>
        <td>Library</td>
        <td>Python</td>
        <td>Heavy</td>
        <td>atagar</td>
      </tr>

      <tr>
        <td><a href="#project-txtorcon">Txtorcon</a></td>
        <td>Library</td>
        <td>Python, Twisted</td>
        <td>Moderate</td>
        <td>meejah</td>
      </tr>

      <tr>
        <td><a href="#project-tlsdate">Tlsdate</a></td>
        <td>Utility</td>
        <td>C</td>
        <td>Moderate</td>
        <td>ioerror</td>
      </tr>

      <tr>
        <td><a href="#project-metrics">Metrics</a></td>
        <td>Client Service</td>
        <td>Java</td>
        <td>Moderate</td>
        <td>karsten</td>
      </tr>

      <tr>
        <td><a href="#project-atlas">Atlas</a></td>
        <td>Client Service</td>
        <td>JavaScript</td>
        <td>Light</td>
        <td>hellais, karsten</td>
      </tr>

      <tr>
        <td><a href="#project-globe">Globe</a></td>
        <td>Client Service</td>
        <td>JavaScript</td>
        <td>Heavy</td>
        <td>Christian</td>
      </tr>

      <tr>
        <td><a href="#project-compass">Compass</a></td>
        <td>Client Service</td>
        <td>Python</td>
        <td>Light</td>
        <td>gsathya, karsten, cwacek</td>
      </tr>

      <tr>
        <td><a href="#project-onionoo">Onionoo</a></td>
        <td>Backend Service</td>
        <td>Java, Python</td>
        <td>Moderate</td>
        <td>karsten, gsathya</td>
      </tr>

      <tr>
        <td><a href="#project-doctor">DocTor</a></td>
        <td>Backend Service</td>
        <td>Python</td>
        <td>Light</td>
        <td>atagar</td>
      </tr>

      <tr>
        <td><a href="#project-weather">Weather</a></td>
        <td>Client Service</td>
        <td>Python</td>
        <td>None</td>
        <td>kaner</td>
      </tr>

      <tr>
        <td><a href="#project-gettor">GetTor</a></td>
        <td>Client Service</td>
        <td>Python</td>
        <td>None</td>
        <td>kaner</td>
      </tr>

      <tr>
        <td><a href="#project-torcheck">TorCheck</a></td>
        <td>Client Service</td>
        <td>Go</td>
        <td>Moderate</td>
        <td>Arlo</td>
      </tr>

      <tr>
        <td><a href="#project-bridgedb">BridgeDB</a></td>
        <td>Backend Service</td>
        <td>Python</td>
        <td>Light</td>
        <td>kaner, nickm</td>
      </tr>

      <tr>
        <td><a href="#project-ooni-probe">Ooni Probe</a></td>
        <td>Scanner</td>
        <td>Python</td>
        <td>Moderate</td>
        <td>hellais, isis, ioerror</td>
      </tr>

      <tr>
        <td><a href="#project-torps">TorPS</a></td>
        <td>Backend Service</td>
        <td>Python</td>
        <td>Light</td>
        <td>Aaron Johnson</td>
      </tr>

      <tr>
        <td><a href="#project-torflow">TorFlow</a></td>
        <td>Backend Service</td>
        <td>Python</td>
        <td>None</td>
        <td>aagbsn, mikeperry</td>
      </tr>

      <tr>
        <td>*<a href="#project-torbel">TorBEL</a></td>
        <td>Backend Service</td>
        <td>Python</td>
        <td>None</td>
        <td>Sebastian</td>
      </tr>

      <tr>
        <td><a href="#project-tor2web">Tor2web</a></td>
        <td>Client Service</td>
        <td>Python</td>
        <td>Moderate</td>
        <td>evilaliv3, hellais</td>
      </tr>

      <tr>
        <td><a href="#project-anonbib">Anonbib</a></td>
        <td>Website</td>
        <td>Python</td>
        <td>Light</td>
        <td>arma, nickm</td>
      </tr>

    </table>

    <sub>
    * Project is still in an alpha state.
    </sub>

    <br /><br />

    <a id="project-tor"></a>
    <h3>Tor (<a href="https://gitweb.torproject.org/tor.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/report/12">bug
    tracker</a>)</h3>

    <p>
    Central project, providing the core software for using and participating in
    the Tor network. Numerous people contribute to the project to varying
    extents, but the chief architects are Nick Mathewson and Roger Dingledine.
    </p>

    <p>
    <b>Project Ideas:</b><br />
    <i><a href="#torCleanup">Tor Codebase Cleanup</a></i><br />
    <i><a href="#httpsImpersonation">HTTPS Server Impersonation</a></i><br />
    <i><a href="#chutneyExpansion">Make Chutney Do More, More Reliably</a></i>
    </p>

    <a id="project-orchid"></a>
    <h3><a href="https://github.com/subgraph/Orchid">Orchid</a> (<a
    href="https://github.com/subgraph/Orchid">code</a>, <a
    href="https://github.com/subgraph/Orchid/issues">bug
    tracker</a>)</h3>

    <p>
    Java implementation of Tor and successor to <a href="http://onioncoffee.sourceforge.net/">OnionCoffee</a>.
    </p>

    <a id="project-torbrowser"></a>
    <h3><a href="<page projects/torbrowser>">Tor Browser Bundle</a> (<a
    href="https://gitweb.torproject.org/torbrowser.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Tor+bundles/installation&order=priority">bug
    tracker</a>, <a href="https://www.torproject.org/projects/torbrowser/design/">design doc</a>)</h3>

    <p>
    The Tor Browser Bundle is an easy-to-use portable package of Tor, Vidalia,
    Torbutton, and a Firefox fork preconfigured to work together out of
    the box. It contains a modified copy of Firefox that aims to resolve the
    privacy and security issues in mainline version.
    </p>

    <a id="project-torbutton"></a>
    <h3><a href="<page torbutton/index>">Torbutton</a> (<a
    href="https://gitweb.torproject.org/torbutton.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Torbutton&order=priority">bug
    tracker</a>)</h3>

    <p>
    Firefox addon that addresses many of the client-side threats to browsing
    the Internet anonymously. Mike has since continued to adapt it to new
    threats, updated versions of Firefox, and possibly <a
    href="https://blog.torproject.org/blog/google-chrome-incognito-mode-tor-and-fingerprinting">Chrome
    as well</a>.
    </p>

    <a id="project-httpseverywhere"></a>
    <h3><a href="https://www.eff.org/https-everywhere">HTTPS Everywhere</a> (<a
    href="https://gitweb.torproject.org/https-everywhere.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/report/19">bug
    tracker</a>)</h3>

    <p>
    HTTPS Everywhere is a Firefox and Chrome extension that encrypts
    your communications with many major websites, making your browsing
    more secure.
    </p>

    <a id="project-vidalia"></a>
    <h3><a href="<page projects/vidalia>">Vidalia</a> (<a
    href="https://gitweb.torproject.org/vidalia.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Vidalia&order=priority">bug
    tracker</a>)</h3>

    <p>
    The most commonly used user interface for Tor. Matt Edman started the
    project in 2006 and brought it to its current stable state. Development
    slowed for several years, though Tomás Touceda has since taken the
    lead with pushing the project forward.
    </p>

    <a id="project-arm"></a>
    <h3><a href="https://www.atagar.com/arm/">Arm</a> (<a
    href="https://gitweb.torproject.org/arm.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=arm&order=priority">bug
    tracker</a>)</h3>

    <p>
    The anonymizing relay monitor (arm) is a terminal status monitor for Tor,
    intended for command-line aficionados, ssh connections, and anyone with a
    tty terminal. This works much like top does for system usage, providing
    real time statistics for bandwidth, resource usage, connections, and quite
    a bit more.
    </p>

    <a id="project-orbot"></a>
    <h3><a href="https://guardianproject.info/apps/orbot/">Orbot</a> (<a
    href="https://gitweb.torproject.org/orbot.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Orbot&order=priority">bug
    tracker</a>)</h3>

    <p>
    Provides Tor on the Android platform. This was under very active
    development up through Fall 2010, after which things have been quiet.
    </p>

    <a id="project-tails"></a>
    <h3><a href="https://tails.boum.org/">The Amnesic Incognito Live System</a> (<a
    href="https://git-tails.immerda.ch/tails/">code</a>, <a
    href="https://labs.riseup.net/code/projects/tails">bug
    tracker</a>)</h3>

    <p>
    The Amnesic Incognito Live System is a live CD/USB distribution
    preconfigured so that everything is safely routed through Tor and leaves no
    trace on the local system. This is a merger of the Amnesia and <a
    href="http://www.anonymityanywhere.com/incognito/">Incognito</a> projects,
    and still under very active development.
    </p>

    <a id="project-torramdisk"></a>
    <h3><a href="http://opensource.dyc.edu/tor-ramdisk">Tor-ramdisk</a> (<a
    href="https://gitweb.torproject.org/tor-ramdisk.git">code</a>, <a
    href="http://opensource.dyc.edu/tor-ramdisk-documentation">documentation</a>)</h3>

    <p>
    Tor-ramdisk is a uClibc-based micro Linux distribution whose sole
    purpose is to securely host a Tor server purely in RAM.
    </p>

    <a id="project-torouter"></a>
    <h3><a
    href="<wiki>doc/Torouter">Torouter</a> (<a
    href="https://gitweb.torproject.org/torouter.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Torouter&order=priority">bug
    tracker</a>)</h3>

    <p>
    Project to provide an easy-to-use, embedded Tor instance for routers. This
    had high activity in late 2010, but has since been rather quiet.
    </p>

    <a id="project-torsocks"></a>
    <h3>Torsocks (<a
    href="https://gitweb.torproject.org/torsocks.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Torify&order=priority">bug
    tracker</a>)</h3>

    <p>
    Utility for adapting other applications to work with Tor. Development has
    slowed and compatibility issues remain with some platforms, but it's
    otherwise feature complete.
    </p>

    <a id="project-torbirdy"></a>
    <h3>TorBirdy (<a
    href="https://github.com/ioerror/torbirdy">code</a>, <a
    href="https://trac.torproject.org/projects/tor/wiki/torbirdy/dev">bug
    tracker</a>)</h3>

    <p>
    TorBirdy is Torbutton for Thunderbird and related Mozilla mail clients.
    </p>

    <a id="project-obfsproxy"></a>
    <h3><a href="<page projects/obfsproxy>">Obfsproxy</a> (<a
    href="https://gitweb.torproject.org/pluggable-transports/obfsproxy.git">code</a>,
    <a href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Pluggable+transport&order=priority">bug
    tracker</a>)</h3>

    <p>
    A proxy that shapes Tor traffic, making it harder for censors to detect and
    block Tor. This has both a C and python implementation.
    </p>

    <p>
    <b>Project Ideas:</b><br />
    <i><a href="#betterPluggableTransports">Build Better Pluggable Transports</a></i>
    </p>

    <a id="project-flash-proxy"></a>
    <h3><a href="https://crypto.stanford.edu/flashproxy/">Flash Proxy</a> (<a
    href="https://gitweb.torproject.org/flashproxy.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_information&status=needs_review&status=needs_revision&status=new&status=reopened&component=Flashproxy">bug
    tracker</a>)</h3>

    <p>
    Pluggable transport using proxies running in web browsers to defeat
    address-based blocking.
    </p>

    <a id="project-shadow"></a>
    <h3><a href="https://shadow.cs.umn.edu/">Shadow</a> (<a
    href="https://github.com/shadow">code</a>, <a
    href="https://github.com/shadow/shadow/issues">bug
    tracker</a>)</h3>

    <p>
    Shadow is a discrete-event network simulator that runs the real
    Tor software as a plug-in. Shadow is open-source software that enables
    accurate, efficient, controlled, and repeatable Tor experimentation.
    For another simulator, see <a
    href="http://crysp.uwaterloo.ca/software/exptor/">ExperimenTor</a>.
    </p>

    <a id="project-stem"></a>
    <h3><a href="https://stem.torproject.org/">Stem</a> (<a
    href="https://gitweb.torproject.org/stem.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/wiki/doc/stem/bugs">bug
    tracker</a>)</h3>

    <p>
    Python controller library for scripts and controller applications using
    Tor.
    </p>

    <p>
    <b>Project Ideas:</b><br />
    <i><a href="#txtorcon-stemIntegration">Txtorcon/Stem Integration</a></i><br />
    </p>

    <a id="project-txtorcon"></a>
    <h3><a href="https://txtorcon.readthedocs.org">Txtorcon</a> (<a
    href="https://github.com/meejah/txtorcon">code</a>, <a
    href="https://github.com/meejah/txtorcon/issues">bug tracker</a>)</h3>

    <p>
    Twisted-based asynchronous Tor control protocol implementation. Includes
    unit-tests, examples, state-tracking code and configuration abstraction.
    Used by OONI and APAF.
    </p>

    <p>
    <b>Project Ideas:</b><br />
    <i><a href="#txtorcon-stemIntegration">Txtorcon/Stem Integration</a></i>
    </p>

    <a id="project-tlsdate"></a>
    <h3>Tlsdate (<a href="https://github.com/ioerror/tlsdate">code</a>)</h3>

    <p>
    tlsdate: secure parasitic rdate replacement
    </p>

    <p>
    tlsdate sets the local clock by securely connecting with TLS to remote
    servers and extracting the remote time out of the secure handshake. Unlike
    ntpdate, tlsdate uses TCP, for instance connecting to a remote HTTPS or TLS
    enabled service, and provides some protection against adversaries that try
    to feed you malicious time information.
    </p>

    <a id="project-metrics"></a>
    <h3><a href="https://metrics.torproject.org/">Metrics</a> (code: <a
    href="https://gitweb.torproject.org/metrics-db.git">db</a>, <a
    href="https://gitweb.torproject.org/metrics-utils.git">utils</a>, <a
    href="https://gitweb.torproject.org/metrics-web.git">web</a>)</h3>

    <p>
    Processing and analytics of consensus data, provided to users via the
    metrics portal. This has been under active development for several years by
    Karsten Loesing. See also <a
    href="https://gitweb.torproject.org/torperf.git">TorPerf</a>.
    </p>

    <a id="project-atlas"></a>
    <h3><a href="https://atlas.torproject.org/">Atlas</a> (<a
    href="https://gitweb.torproject.org/atlas.git">code</a>)</h3>

    <p>
    Atlas is a web application to discover Tor relays and bridges. It provides
    useful information on how relays are configured along with graphics about
    their past usage.
    </p>

    <p>
    This is the spiritual successor to <a
    href="https://gitweb.torproject.org/torstatus.git">TorStatus</a>, the <a
    href="https://svn.torproject.org/svn/torstatus/trunk/">original
    codebase</a> for which was written in PHP, and rewritten by students from
    Wesleyan as Django.
    </p>

    <a id="project-globe"></a>
    <h3><a href="http://globe.rndm.de/">Globe</a> (<a
    href="https://github.com/makepanic/globe">code</a>, <a
    href="https://github.com/makepanic/globe/issues">bug tracker</a>)</h3>

    <p>
    Globe is a web application that allows you to search for Tor relays and
    bridges. It gives you a detailed overview of properties and configurations
    of a relay or bridge.
    </p>

    <a id="project-compass"></a>
    <h3><a href="https://compass.torproject.org/">Compass</a> (<a
    href="https://gitweb.torproject.org/compass.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Compass&order=priority">bug
    tracker</a>)</h3>

    <p>
    Compass is a web and command line application that filters and
    aggregates the Tor relays based on various attributes.
    </p>

    <a id="project-onionoo"></a>
    <h3><a href="<page projects/onionoo>">Onionoo</a> (<a
    href="https://gitweb.torproject.org/onionoo.git">java codebase</a>, <a
    href="https://gitweb.torproject.org/pyonionoo.git">python
    codebase</a>, <a href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Onionoo&order=priority">bug tracker</a>)</h3>

    <p>
    Onionoo is a JSON based protocol to learn information about currently
    running Tor relays and bridges.
    </p>

    <a id="project-doctor"></a>
    <h3>DocTor (<a
    href="https://gitweb.torproject.org/doctor.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=DocTor&order=priority">bug
    tracker</a>)</h3>

    <p>
    DocTor is a notification service that monitors newly published descriptor
    information for issues. This is primarily a service to help the tor
    directory authority operators, but it also checks for a handful of other
    issues like sybil attacks.
    </p>

    <a id="project-weather"></a>
    <h3><a href="https://trac.torproject.org/projects/tor/wiki/org/roadmaps/Weather">Weather</a> (<a
    href="https://gitweb.torproject.org/weather.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Tor+Weather&order=priority">bug
    tracker</a>)</h3>

    <p>
    Provides automatic notification to subscribed relay operators when their
    relay's unreachable. This underwent a rewrite by the <a
    href="http://hfoss.wesleyan.edu/">Wesleyan HFOSS team</a>, which went live
    in early 2011.
    </p>

    <a id="project-gettor"></a>
    <h3><a href="https://trac.torproject.org/projects/tor/wiki/org/roadmaps/GetTor">GetTor</a> (<a
    href="https://gitweb.torproject.org/gettor.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=GetTor&order=priority">bug
    tracker</a>)</h3>

    <p>
    E-mail autoresponder providing Tor's packages over SMTP. This has been
    relatively unchanged for quite a while.
    </p>

    <a id="project-torcheck"></a>
    <h3><a href="https://trac.torproject.org/projects/tor/wiki/org/roadmaps/TorCheck">TorCheck</a> (<a
    href="https://gitweb.torproject.org/check.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Tor+Check&order=priority">bug
    tracker</a>)</h3>

    <p>
    Site for determining if the visitor is using Tor or not.
    </p>

    <a id="project-bridgedb"></a>
    <h3><a href="https://trac.torproject.org/projects/tor/wiki/org/roadmaps/BridgeDB">BridgeDB</a> (<a
    href="https://gitweb.torproject.org/bridgedb.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=BridgeDB&order=priority">bug
    tracker</a>)</h3>

    <p>
    Backend bridge distributor, handling the various pools they're distributed
    in. This was actively developed until Fall of 2010.
    </p>

    <a id="project-ooni-probe"></a>
    <h3><a href="https://ooni.torproject.org/">Ooni Probe</a> (<a
    href="https://gitweb.torproject.org/ooni-probe.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Ooni&order=priority">bug
    tracker</a>)</h3>

    <p>
    Censorship scanner, checking your local connection for blocked or modified
    content.
    </p>

    <p>
    <b>Project Ideas:</b><br />
    <i><a href="#censorshipAnalyzer">Develop a Censorship Analyzer</a></i>
    </p>

    <a id="project-torps"></a>
    <h3>TorPS</a> (<a href="https://github.com/torps/torps">code</a>)</h3>

    <p>
    The Tor Path Simulator (TorPS) is a tool for efficiently simulating
    path selection in Tor. It chooses circuits and assigns user streams to
    those circuits in the same way that Tor does. TorPS is fast enough to
    perform thousands of simulations over periods of months.
    </p>

    <a id="project-torflow"></a>
    <h3><a href="https://trac.torproject.org/projects/tor/wiki/org/roadmaps/TorFlow">TorFlow</a> (<a
    href="https://gitweb.torproject.org/torflow.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=Torflow&order=priority">bug
    tracker</a>)</h3>

    <p>
    Library and collection of services for actively monitoring the Tor network.
    These include the Bandwidth Scanners (measuring throughput of relays) and
    SoaT (scans for malicious or misconfigured exit nodes). SoaT was last
    actively developed in the Summer of 2010, and the Bandwidth Scanners a few
    months later. Both have been under active use since then, but development
    has stopped.
    </p>

    <a id="project-torbel"></a>
    <h3><a
    href="https://blog.torproject.org/blog/torbel-tor-bulk-exit-list-tools">TorBEL</a> (<a
    href="https://gitweb.torproject.org/torbel.git">code</a>, <a
    href="https://trac.torproject.org/projects/tor/query?status=accepted&status=assigned&status=needs_review&status=new&status=reopened&component=TorDNSEL/TorBEL&order=priority">bug
    tracker</a>)</h3>

    <p>
    The Tor Bulk Exitlist provides a method of identifying if IPs belong to
    exit nodes or not. This is a replacement for TorDNSEL which is a stable
    (though unmaintained) Haskell application for this purpose. The initial
    version of TorBEL was started in GSOC 2010 but since then the project has
    been inactive.
    </p>

    <a id="project-tor2web"></a>
    <h3><a
    href="http://wiki.tor2web.org/index.php/Main_Page">Tor2web</a> (<a
    href="https://github.com/globaleaks/tor2web-3.0/wiki">code</a>)</h3>

    <p>
    Tor2web allows Internet users to browse websites running in <a
    href="<page docs/hidden-services>">Tor hidden services</a>. It trades
    user anonymity for usability by allowing anonymous content to be
    distributed to non-anonymous users.
    </p>

    <a id="project-anonbib"></a>
    <h3><a
    href="http://freehaven.net/anonbib/">Anonymity Bibliography</a> (<a
    href="https://gitweb.torproject.org/anonbib.git">code</a>)</h3>

    <p>
    Anonbib is a list of important papers in the field of anonymity. It's
    also a set of scripts to generate the website from Latex (bibtex). If
    we're missing any important papers, please let us know!
    </p>

    <a id="Coding"></a>
    <a id="Summer"></a>
    <h2><a class="anchor" href="#Coding">Project Ideas</a></h2>

    <p>
    You may find some of these projects to be good ideas for <a href="<page
    about/gsoc>">Google Summer of Code</a> and the <a
    href="https://live.gnome.org/OutreachProgramForWomen">Outreach Program for
    Women</a>. We have labelled each idea with how much work we expect it would
    be (effort level), how much clue you should start with (skill level),
    and which of our <a href="<page about/corepeople>">core developers</a>
    would be good mentors. If one or more of these ideas looks promising to
    you, please <a href="<page about/contact>">contact us</a> to discuss your
    plans rather than sending blind applications. You may also want to propose
    your own project idea &mdash; which often results in the best applications.
    </p>

    <ol>

    <a id="txtorcon-stemIntegration"></a>
    <li>
    <b>Txtorcon/Stem Integration</b>
    <br>
    Effort Level: <i>Medium</i>
    <br>
    Skill Level: <i>Medium</i>
    <br>
    Likely Mentors: <i>meejah, Damian (atagar)</i>
    <p>Txtorcon is a Twisted-based Python controller library, and Stem is a
    synchronous (threaded) one, also in Python. There is no need to have
    two implementations of (at least) the protocol parsing code. This
    project would entail eliminating duplication by leveraging Stem's
    parsing in txtorcon while keeping txtorcon's API the same (or at least
    close).</p>
    <p>Besides this you should identify some additional tasks to improve our
    controller space across these two libraries. Some ideas are...</p>
    <ul>
      <li>Write a tutorial for <a
      href="https://stem.torproject.org/tutorials.html">stem's tutorial
      page</a> demonstrating cross txtorcon/stem usage.</li>
      <li>Expand the txtorcon API to include functionality of <a
      href="https://gitweb.torproject.org/stem.git/blob/HEAD:/stem/control.py">stem's
      controller</a> that would be of interest to twisted users. All additions
      should include tests!</li>
      <li>Come up with some ideas of your own! We'd love to discuss them with
      you.</li>
    </ul>
    <p>This would very likely involve changes to both libraries, although
    most would be expected to be in txtorcon. meejah is available to
    mentor txtorcon changes, and Damian (atagar) can help with Stem.</p>
    <p>It would help if you're already familiar with event-based programming,
    bonus points if it's Twisted.</p>
    </li>

    <a id="httpsImpersonation"></a>
    <li>
    <b>HTTPS Server Impersonation</b>
    <br>
    Effort Level: <i>Medium to High</i>
    <br>
    Skill Level: <i>Medium to High</i>
    <br>
    Likely Mentors: <i>Nick (nickm)</i>
    <p>
    We have an open proposal for a way to make Tor bridges avoid censorship by
    impersonating an HTTPS server.  Specifically, we need to hack some popular
    SSL "reverse proxy" (your choice) so that it relays regular web connections
    to an HTTP server, but certain connections to a local Tor process.  <a
    href="https://gitweb.torproject.org/torspec.git/blob_plain/HEAD:/proposals/203-https-frontend.txt">Proposal
    203</a> has a general design sketch.
    </p>

    <p>
    <b>This project is likely trickier than it looks. You should avoid applying
    for this if you're uncertain about being able to complete it.</b>
    </p>
    </li>
    </li>

    <a id="chutneyExpansion"></a>
    <li>
    <b>Make Chutney Do More, More Reliably</b>
    <br>
    Effort Level: <i>Medium to High, depending on scope of project</i>
    <br>
    Skill Level: <i>Medium</i>
    <br>
    Likely Mentors: <i>Nick (nickm)</i>
    <p>
    We have a little Python tool called <a
    href="https://gitweb.torproject.org/nickm/chutney.git">Chutney</a> for
    making small local test networks.  It's small, not widely used, and not as
    automated as it could be.
    </p>

    <p>
    It would be great to see chutney extended and a set of supporting tests
    built to the point where we could use Chutney to exercise various Tor
    features as an automated integration test.
    </p>

    <p>
    <b>As part of your application for this project please submit a patch that
    expands Chutney.</b>
    </p>

    </li>

    <a id="torCleanup"></a>
    <li>
    <b>Tor Codebase Cleanup</b>
    <br>
    Effort Level: <i>Low to High, depending on subproject chosen</i>
    <br>
    Skill Level: <i>Medium to High</i>
    <br>
    Likely Mentors: <i>Nick (nickm)</i>
    <p>
    The Tor code is almost 10 years old in places, and we haven't always had
    enough time or wisdom to write things as well as we could have.  Our unit
    test coverage is shamefully low, and the dependency graph of our modules is
    shamefully convoluted . We could use refactoring and unit tests!  Please
    look through the Tor source code and look for ugly or tricky code or
    dependencies -- the uglier and trickier the better -- and think about how
    you could make the code look better, read better, and (subject to testing)
    work better.
    </p>

    <p>
    If this is for a fun side-project, it would be great for you to work on
    anything that can be made better and more tested.  For an internship-level
    position, we'd hope that you could find a number of particularly tricky or
    knotty piece of the code to clean up, and aim for resolving the ugliest
    problems, not necessarily the easiest.
    </p>

    <p>
    For a big project here, it would be great to pick one of the major
    "submodules" of Tor -- path selection, node discovery, directory authority
    operations, directory service -- and refactor its interface completely, to
    minify and codify its points of contact with the rest of Tor.
    </p>

    <p>
    <b>As part of your application for this project please identify one of the
    thorniest Tor functions and submit a patch refactoring it to be better. If
    you find this to be difficult then this likely isn't the project for
    you.</b>
    </p>
    </li>

    <a id="betterPluggableTransports"></a>
    <li>
    <b>Build Better Pluggable Transports</b>
    <br>
    Effort Level: <i>Medium to High</i>
    <br>
    Skill Level: <i>Medium</i>
    <br>
    Likely Mentors: <i>Steven (sjmurdoch), George (asn)</i>
    <p>
    For Tor users in censored countries, we currently offer <a
    href="https://www.torproject.org/projects/obfsproxy.html.en">obfsproxy</a>
    bridges, which disguise Tor traffic by making it look random. This works
    for many users, but it has disadvantages: firstly it does not disguise
    packet size and secondly it looks like no real protocol. These weaknesses
    may result in obfsproxy being blocked.
    </p>

    <p>
    The goal for this project will be to implement new pluggable transports,
    which resolve these weaknesses and so can be deployed if/when obfsproxy is
    blocked. Ideas for doing so include:
      <ul>
        <li>Impersonate a voice-over-IP protocol</li>
        <li>Impersonate HTTP sufficiently well that traffic will go through a HTTP-only proxy</li>
        <li>Implement <a href="http://cacr.uwaterloo.ca/techreports/2011/cacr2011-21.pdf">scanning resistance</a></a>
      </ul>
    </p>

    <a id="profileUDPTransport"></a>
    <li>
    <b>Profile UDP transport protocols</b>
    <br>
    Effort Level: <i>Medium to High</i>
    <br>
    Skill Level: <i>High</i>
    <br>
    Likely Mentors: <i>Steven (sjmurdoch)</i>
    <p>
    There are <a
    href="https://research.torproject.org/techreports/datagram-comparison-2011-11-07.pdf">lots
    of options</a> as to how Tor could send its data over UDP rather than TCP,
    and some will likely perform significantly better than others. This project
    will evaluate these options, so as to decide which should be used in future
    versions of Tor. A first step will be to benchmark the various transport
    protocols being considered, in terms of performance and also code quality,
    including userspace TCP, <a
    href="https://github.com/bittorrent/libutp">&mu;TP</a>, <a
    href="http://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocol">SCTP</a>
    and <a href="http://curvecp.org/">CurveCP</a>. Initially these transport
    protocols will be examined in isolation, but if the project progresses well
    one or more could be integrated in Tor.
    </p>
    </li>

    <a id="httpsEverywhereRulesetTesting"></a>
    <li>
    <b>Incorporate Ruleset Testing into the HTTPS Everywhere release process</b>
    <br>
    Effort Level: <i>Medium</i>
    <br>
    Skill Level: <i>Medium</i>
    <br>
    Likely Mentors: <i>Peter Eckersley (pde), Micah Lee</i>
    <p>
Ondrej Mikle has implemented a codebase for testing HTTPS Everywhere rulesets
by crawling pages that are affected by the ruleset (<a href="https://github.com/hiviah/https-everywhere-checker">repository</a>).
    </p>

    <p>
This codebase still has some rough edges that need to be smoothed over, but
once those are done it should be incorporated into the HTTPS Everywhere build
process, in order to improve the quality of our releases.
    </p>
    </li>

    <a id="censorshipAnalyzer"></a>
    <li>
    <b>Develop a Censorship Analyzer</b>
    <br>
    Effort Level: <i>Medium</i>
    <br>
    Skill Level: <i>Medium to High (depends on the implemented tests)</i>
    <br>
    Likely Mentors: <i>Philipp (phw)</i>
    <p>
Tor is documented to be blocked in <a
href="https://censorshipwiki.torproject.org">several countries</a>. Analyzing
these censorship incidents can be a tedious task; especially without access to
machines inside the censoring networks. To make analysis easier, it would be
great to have a lightweight analysis tool which can be run by censored users.
This tool would conduct a number of networking tests and figure out if and how
Tor could be blocked. The tool's final report should then somehow make it back
to the Tor project.
    </p>

    <p>
The theory behind this tool is already <a
href="http://www.cs.kau.se/philwint/pdf/foci2013.pdf">documented
in a research paper</a>. What we now need is code! Implementing it would first
mean getting familiar with <a href="https://ooni.torproject.org">OONI</a> and
<a href="http://twistedmatrix.com/trac/">Twisted</a>. After that, the tool
should be implemented as a number of OONI-specific networking tests.
    </p>
    </li>

    <li>
    <b>Bring up new ideas!</b>
    <br>
    Don't like any of these? Look at the <a
    href="/press/presskit/2008-12-19-roadmap-full.pdf">Tor development
    roadmap</a> for more ideas, or just try out Tor, Vidalia, and Torbutton,
    and find out what you think needs fixing.
    Some of the <a href="<spectree>proposals">current proposals</a>
    might also be short on developers.
    </li>

    </ol>

    <a id="OtherCoding"></a>
    <h2><a class="anchor" href="#OtherCoding">Other Coding and Design related ideas</a></h2>
    <ol>
    <li>Tor relays don't work well on Windows XP. On
    Windows, Tor uses the standard <tt>select()</tt> system
    call, which uses space in the non-page pool. This means
    that a medium sized Tor relay will empty the non-page pool, <a
    href="<wiki>doc/WindowsBufferProblems">causing
    havoc and system crashes</a>. We should probably be using overlapped IO
    instead. One solution would be to teach <a
    href="http://www.monkey.org/~provos/libevent/">libevent</a> how to use
    overlapped IO rather than select() on Windows, and then adapt Tor to
    the new libevent interface. Christian King made a
    <a href="https://svn.torproject.org/svn/libevent-urz/trunk/">good
    start</a> on this in the summer of 2007.</li>

    <li>We need to actually start building our <a href="<page
    docs/documentation>#DesignDoc">blocking-resistance design</a>. This involves
    fleshing out the design, modifying many different pieces of Tor, adapting
    <a href="<page projects/vidalia>">Vidalia</a> so it supports the
    new features, and planning for deployment.</li>

    <li>We need a flexible simulator framework for studying end-to-end
    traffic confirmation attacks. Many researchers have whipped up ad hoc
    simulators to support their intuition either that the attacks work
    really well or that some defense works great. Can we build a simulator
    that's clearly documented and open enough that everybody knows it's
    giving a reasonable answer? This will spur a lot of new research.
    See the entry <a href="#Research">below</a> on confirmation attacks for
    details on the research side of this task &mdash; who knows, when it's
    done maybe you can help write a paper or three also.</li>

    <li>Tor 0.1.1.x and later include support for hardware crypto
    accelerators via OpenSSL. It has been lightly tested and is
    possibly very buggy.  We're looking for more rigorous testing,
    performance analysis, and optimally, code fixes to OpenSSL and
    Tor if needed.</li>

    <li>Write a <a
    href="https://secure.wikimedia.org/wikipedia/en/wiki/Fuzz_testing">fuzzer</a>
    for Tor to discover security vulnerabilities. Determine if there
    are good fuzzing frameworks out there for what we want. Win fame by
    getting credit when we put out a new release because of you!</li>

    <li>Tor uses TCP for transport and TLS for link
    encryption. This is nice and simple, but it means all cells
    on a link are delayed when a single packet gets dropped, and
    it means we can only reasonably support TCP streams. We have a <a
    href="<page docs/faq>#TransportIPnotTCP">list
    of reasons why we haven't shifted to UDP transport</a>, but it would
    be great to see that list get shorter. We also have a proposed <a
    href="<specblob>proposals/100-tor-spec-udp.txt">specification
    for Tor and
    UDP</a> &mdash; please let us know what's wrong with it.</li>

    <li>We're not that far from having IPv6 support for destination addresses
    (at exit nodes). If you care strongly about IPv6, that's probably the
    first place to start.</li>

    <li>We need a way to generate the website diagrams (for example, the "How
    Tor Works" pictures on the <a href="<page about/overview>">overview page</a>
    from source, so we can translate them as UTF-8 text rather than edit
    them by hand with Gimp. We might want to
    integrate this as an wml file so translations are easy and images are
    generated in multiple languages whenever we build the website.</li>

    <li>How can we make the various LiveCD/USB systems easier
    to maintain, improve, and document?  One example is <a
    href="https://tails.boum.org/">The Amnesic Incognito Live
    System</a>.
    </li>

    <li>
    Another anti-censorship project is to try to make Tor
    more scanning-resistant.  Right now, an adversary can identify <a
    href="<specblob>proposals/125-bridges.txt">Tor bridges</a>
    just by trying to connect to them, following the Tor protocol,
    and seeing if they respond.  To solve this, bridges could <a
    href="<svnprojects>design-paper/blocking.html#tth_sEc9.3">act like
    webservers</a> (HTTP or HTTPS) when contacted by port-scanning tools,
    and not act like bridges until the user provides a bridge-specific key.
    To start, check out Shane Pope's <a
    href="http://dl.dropbox.com/u/37735/index.html">thesis and prototype</a>.
    </li>

    </ol>

    <a id="Research"></a>
    <h2><a class="anchor" href="#Research">Research</a></h2>
    <ol>
    <li>The "end-to-end traffic confirmation attack":
    by watching traffic at Alice and at Bob, we can <a
    href="http://freehaven.net/anonbib/#danezis:pet2004">compare
    traffic signatures and become convinced that we're watching the same
    stream</a>. So far Tor accepts this as a fact of life and assumes this
    attack is trivial in all cases. First of all, is that actually true? How
    much traffic of what sort of distribution is needed before the adversary
    is confident he has won? Are there scenarios (e.g. not transmitting much)
    that slow down the attack? Do some traffic padding or traffic shaping
    schemes work better than others?</li>
    <li>A related question is: Does running a relay/bridge provide additional
    protection against these timing attacks? Can an external adversary that can't
    see inside TLS links still recognize individual streams reliably?
    Does the amount of traffic carried degrade this ability any? What if the
    client-relay deliberately delayed upstream relayed traffic to create a queue
    that could be used to mimic timings of client downstream traffic to make it
    look like it was also relayed? This same queue could also be used for masking
    timings in client upstream traffic with the techniques from <a
    href="http://www.freehaven.net/anonbib/#ShWa-Timing06">adaptive padding</a>,
    but without the need for additional traffic. Would such an interleaving of
    client upstream traffic obscure timings for external adversaries? Would the
    strategies need to be adjusted for asymmetric links? For example, on
    asymmetric links, is it actually possible to differentiate client traffic from
    natural bursts due to their asymmetric capacity? Or is it easier than
    symmetric links for some other reason?</li>
    <li>Repeat Murdoch and Danezis's <a
    href="http://www.cl.cam.ac.uk/~sjm217/projects/anon/#torta">attack from
    Oakland 05</a> on the current Tor network. See if you can learn why it
    works well on some nodes and not well on others. (My theory is that the
    fast nodes with spare capacity resist the attack better.) If that's true,
    then experiment with the RelayBandwidthRate and RelayBandwidthBurst
    options to run a relay that is used as a client while relaying the
    attacker's traffic: as we crank down the RelayBandwidthRate, does the
    attack get harder? What's the right ratio of RelayBandwidthRate to
    actually capacity? Or is it a ratio at all? While we're at it, does a
    much larger set of candidate relays increase the false positive rate
    or other complexity for the attack? (The Tor network is now almost two
    orders of magnitude larger than it was when they wrote their paper.) Be
    sure to read <a href="http://freehaven.net/anonbib/#clog-the-queue">Don't
    Clog the Queue</a> too.</li>
    <li>The "routing zones attack": most of the literature thinks of
    the network path between Alice and her entry node (and between the
    exit node and Bob) as a single link on some graph. In practice,
    though, the path traverses many autonomous systems (ASes), and <a
    href="http://freehaven.net/anonbib/#feamster:wpes2004">it's not uncommon
    that the same AS appears on both the entry path and the exit path</a>.
    Unfortunately, to accurately predict whether a given Alice, entry,
    exit, Bob quad will be dangerous, we need to download an entire Internet
    routing zone and perform expensive operations on it. Are there practical
    approximations, such as avoiding IP addresses in the same /8 network?</li>
    <li>Other research questions regarding geographic diversity consider
    the tradeoff between choosing an efficient circuit and choosing a random
    circuit. Look at Stephen Rollyson's <a
    href="http://swiki.cc.gatech.edu:8080/ugResearch/uploads/7/ImprovingTor.pdf">position
    paper</a> on how to discard particularly slow choices without hurting
    anonymity "too much". This line of reasoning needs more work and more
    thinking, but it looks very promising.</li>
    <li>Tor doesn't work very well when relays have asymmetric bandwidth
    (e.g. cable or DSL). Because Tor has separate TCP connections between
    each hop, if the incoming bytes are arriving just fine and the outgoing
    bytes are all getting dropped on the floor, the TCP push-back mechanisms
    don't really transmit this information back to the incoming streams.
    Perhaps Tor should detect when it's dropping a lot of outgoing packets,
    and rate-limit incoming streams to regulate this itself? I can imagine
    a build-up and drop-off scheme where we pick a conservative rate-limit,
    slowly increase it until we get lost packets, back off, repeat. We
    need somebody who's good with networks to simulate this and help design
    solutions; and/or we need to understand the extent of the performance
    degradation, and use this as motivation to reconsider UDP transport.</li>
    <li>A related topic is congestion control. Is our
    current design sufficient once we have heavy use? Maybe
    we should experiment with variable-sized windows rather
    than fixed-size windows? That seemed to go well in an <a
    href="http://www.psc.edu/index.php/hpn-ssh/638">ssh
    throughput experiment</a>. We'll need to measure and tweak, and maybe
    overhaul if the results are good.</li>
    <li>Our censorship-resistance goals include preventing
    an attacker who's looking at Tor traffic on the wire from <a
    href="<svnprojects>design-paper/blocking.html#sec:network-fingerprint">distinguishing
    it from normal SSL traffic</a>. Obviously we can't achieve perfect
    steganography and still remain usable, but for a first step we'd like to
    block any attacks that can win by observing only a few packets. One of
    the remaining attacks we haven't examined much is that Tor cells are 512
    bytes, so the traffic on the wire may well be a multiple of 512 bytes.
    How much does the batching and overhead in TLS records blur this on the
    wire? Do different buffer flushing strategies in Tor affect this? Could
    a bit of padding help a lot, or is this an attack we must accept?</li>
    <li>Tor circuits are built one hop at a time, so in theory we have the
    ability to make some streams exit from the second hop, some from the
    third, and so on. This seems nice because it breaks up the set of exiting
    streams that a given relay can see. But if we want each stream to be safe,
    the "shortest" path should be at least 3 hops long by our current logic, so
    the rest will be even longer. We need to examine this performance / security
    tradeoff.</li>
    <li>It's not that hard to DoS Tor relays or directory authorities. Are client
    puzzles the right answer? What other practical approaches are there? Bonus
    if they're backward-compatible with the current Tor protocol.</li>
    <li>Programs like <a
    href="<page torbutton/index>">Torbutton</a> aim to hide
    your browser's UserAgent string by replacing it with a uniform answer for
    every Tor user. That way the attacker can't splinter Tor's anonymity set
    by looking at that header. It tries to pick a string that is commonly used
    by non-Tor users too, so it doesn't stand out. Question one: how badly
    do we hurt ourselves by periodically updating the version of Firefox
    that Torbutton claims to be? If we update it too often, we splinter the
    anonymity sets ourselves. If we don't update it often enough, then all the
    Tor users stand out because they claim to be running a quite old version
    of Firefox. The answer here probably depends on the Firefox versions seen
    in the wild. Question two: periodically people ask us to cycle through N
    UserAgent strings rather than stick with one. Does this approach help,
    hurt, or not matter? Consider: cookies and recognizing Torbutton users
    by their rotating UserAgents; malicious websites who only attack certain
    browsers; and whether the answers to question one impact this answer.
    </li>
    <li>How many bridge relays do you need to know to maintain
    reachability? We should measure the churn in our bridges. If there is
    lots of churn, are there ways to keep bridge users more likely to stay
    connected?
    </li>
    </ol>

    <p>
    <a href="<page about/contact>">Let us know</a> if you've made progress on any
    of these!
    </p>
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