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395 lines
17 KiB
HTML
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<title>Tor: an anonymizing overlay network for TCP</title>
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<meta name="Author" content="Roger Dingledine">
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<link rel="stylesheet" type="text/css" href="tor-doc.css">
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<h1><a href="http://tor.freehaven.net/">Tor</a> documentation</h1>
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<p>The simple version: Tor provides a distributed network of servers
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("onion routers"). Users bounce their TCP streams (web traffic, FTP, SSH,
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etc.) around the routers. This makes it hard for recipients, observers, and
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even the onion routers themselves to track the source of the stream.</p>
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<p>The complex version: Onion Routing is a connection-oriented anonymizing
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communication service. Users choose a source-routed path through a set of
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nodes, and negotiate a "virtual circuit" through the network, in which
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each node knows its predecessor and successor, but no others. Traffic
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flowing down the circuit is unwrapped by a symmetric key at each node,
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which reveals the downstream node.</p>
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<a name="why"></a>
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<h2>Why should I use Tor?</h2>
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<p>Individuals need Tor for privacy:
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<ul>
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<li>Privacy in web browsing -- both from the remote website (so it can't
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track and sell your behavior), and similarly from your local ISP.
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<li>Safety in web browsing: if your local government doesn't approve
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of its citizens visiting certain websites, they may monitor the sites
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and put readers on a list of suspicious persons.
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<li>Circumvention of local censorship: connect to resources (news
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sites, instant messaging, etc) that are restricted from your
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ISP/school/company/government.
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<li>Socially sensitive communication: chat rooms and web forums for
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rape and abuse survivors, or people with illnesses.
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</ul>
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<p>Journalists and NGOs need Tor for safety:
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<ul>
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<li>Allowing dissidents and whistleblowers to communicate more safely.
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<li>Censorship-resistant publication, such as making available your
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home-made movie anonymously via a Tor <a href="#hidden-service">hidden
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service</a>; and reading, e.g. of news sites not permitted in some
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countries.
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<li>Allowing your workers to check back with your home website while
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they're in a foreign country, without notifying everybody nearby that
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they're working with your organization.
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</ul>
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<p>Companies need Tor for business security:
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<ul>
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<li>Competitive analysis: browse the competition's website safely.
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<li>Protecting collaborations of sensitive business units or partners.
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<li>Protecting procurement suppliers or patterns.
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<li>Putting the "P" back in "VPN": traditional VPNs reveal the exact
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amount and frequency of communication. Which locations have employees
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working late? Which locations have employees consulting job-hunting
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websites? Which research groups are communicating with your company's
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patent lawyers?
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</ul>
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<p>Governments need Tor for traffic-analysis-resistant communication:
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<ul>
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<li>Open source intelligence gathering (hiding individual analysts is
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not enough -- the organization itself may be sensitive).
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<li>Defense in depth on open <em>and classified</em> networks -- networks
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with a million users (even if they're all cleared) can't be made safe just
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by hardening them to external threat.
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<li>Dynamic and semi-trusted international coalitions: the network can
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be shared without revealing the existence or amount of communication
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between all parties.
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<li>Networks partially under known hostile control: to block
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communications, the enemy must take down the whole network.
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<li>Politically sensitive negotiations.
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<li>Road warriors.
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<li>Protecting procurement patterns.
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<li>Anonymous tips.
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</ul>
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<p>Law enforcement needs Tor for safety:
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<ul>
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<li>Allowing anonymous tips or crime reporting
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<li>Allowing agents to observe websites without notifying them that
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they're being observed (or, more broadly, without having it be an
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official visit from law enforcement).
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<li>Surveillance and honeypots (sting operations)
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</ul>
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<p>Does the idea of sharing the Tor network with
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all of these groups bother you? It shouldn't -- <a
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href="http://freehaven.net/doc/fc03/econymics.pdf">you need them for
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your security</a>.</p>
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<a name="client-or-server"></a>
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<h2>Should I run a client or a server?</h2>
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<p>You can run Tor in either client mode or server mode. By default,
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everybody is a <i>client</i>. This means you don't relay traffic for
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anybody but yourself.</p>
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<p>If your computer doesn't have a routable IP address or you're using
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a modem, you should stay a client. Otherwise, please consider being
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a server, to help out the network. (Currently each server uses 20-500
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gigabytes of traffic per month, depending on its capacity and its rate
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limiting configuration.)</p>
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<p>Note that you can be a server without allowing users to make
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connections from your computer to the outside world. This is called being
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a middleman server.</p>
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<p> Benefits of running a server include:
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<ul>
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<li>You may get stronger anonymity, since your destination can't know
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whether connections relayed through your computer originated at your
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computer or not.
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<li>You can also get stronger anonymity by configuring your Tor clients
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to use your Tor server for entry or for exit.
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<li>You're helping me with development and scalability testing.
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<li>You're helping your fellow Internet users by providing a larger
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network. Also, having servers in many different pieces of the Internet
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gives users more robustness against curious telcos and brute force
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attacks.
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</ul>
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<p>You can read more about setting up Tor as a
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server <a href="#server">below</a>.</p>
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<a name="installing"></a>
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<h2>Installing Tor</h2>
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<p>You can get the latest releases <a
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href="http://tor.freehaven.net/dist/">here</a>.</p>
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<p>If you got Tor from a tarball, unpack it: <tt>tar xzf
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tor-0.0.9.tar.gz; cd tor-0.0.9</tt>. Run <tt>./configure</tt>, then
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<tt>make</tt>, and then <tt>make install</tt> (as root if necessary). Then
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you can launch tor from the command-line by running <tt>tor</tt>.
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Otherwise, if you got it prepackaged (e.g. in the <a
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href="http://packages.debian.org/tor">Debian package</a> or <a
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href="http://packages.gentoo.org/packages/?category=net-misc;name=tor">Gentoo
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package</a>), these steps are already done for you, and you may
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even already have Tor started in the background (logging to
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/var/log/something).</p>
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<p>Win32 users can use our Tor installer. It will run Tor in a dos window
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so you can see its logs and errors. (You can minimize this window, but
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do not close it.)
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</p>
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<p>In any case, see the <a href="#client">next section</a> for what to
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<i>do</i> with it now that you've got it running.</p>
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<a name="client"></a>
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<h2>Configuring a client</h2>
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<p>Tor comes configured as a client by default. It uses a built-in
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default configuration file, and most people won't need to change any of
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the settings.</p>
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<!--
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<p>The only setting you might need to change is "SocksBindAddress".
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By default, your Tor client only listens for applications that connect
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from localhost. Connections from other computers are refused. If you
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want to torify applications on different computers than the Tor client,
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you should copy torrc.sample to torrc (it's installed by default
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to /usr/local/etc/tor/), change the SocksBindAddress line to
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0.0.0.0, and then hup or restart Tor.</p>
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-->
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<p>After installing Tor, you should install <a
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href="http://www.privoxy.org/">privoxy</a>, which is a filtering web
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proxy that integrates well with Tor. Add the line <br>
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<tt>forward-socks4a / localhost:9050 .</tt><br>
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(don't forget the dot) to privoxy's config file (you can just add it to the
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top). Then change your browser to http proxy at localhost port 8118.
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(In Mozilla, this is in Edit|Preferences|Advanced|Proxies. In IE, it's
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Tools|Internet Options|Connections|LAN Settings|Advanced.)
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You should also set your SSL proxy (IE calls it "Secure") to the same
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thing, to hide your SSL traffic. Using privoxy is <b>necessary</b> because
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<a href="http://tor.freehaven.net/cvs/tor/doc/CLIENTS">Mozilla leaks your
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DNS requests when it uses a socks proxy directly</a>. Privoxy also gives
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you good html scrubbing.</p>
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<p>To test if it's working, go to <a
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href="http://www.junkbusters.com/cgi-bin/privacy">http://www.junkbusters.com/cgi-bin/privacy</a>
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and see what IP it says you're coming from.
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</p>
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<p>
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If you have a personal firewall, be sure to allow local connections to
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port 8118 and port 9050. If your firewall blocks outgoing connections,
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punch a hole so it can connect to TCP ports 80, 443, and 9001-9033.
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<!--If you're
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using Safari as your browser, keep in mind that OS X before 10.3 claims
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to support socks but does not. -->
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For more troubleshooting suggestions, see <a
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href="http://wiki.noreply.org/wiki/TheOnionRouter/TorFAQ">the FAQ</a>.
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</p>
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<p>To Torify an application that supports http, just point it at
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Privoxy. To use socks directly, point it at localhost port 9050. For
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applications that support neither socks nor http, you should look at
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using <a href="http://tsocks.sourceforge.net/">tsocks</a>
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to dynamically replace the system calls in your program to
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route through Tor. If you want to use socks4a, consider using <a
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href="http://www.dest-unreach.org/socat/">socat</a> (specific instructions
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are on <a href="http://6sxoyfb3h2nvok2d.onion/tor/SocatHelp">this hidden
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service url</a>).</p>
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<p>(Windows doesn't have tsocks; instead, you can try
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<a
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href="http://www.socks.permeo.com/Download/SocksCapDownload/index.asp">SocksCap</a>
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or the <a href="http://www.hummingbird.com/products/nc/socks/index.html?cks=y">Hummingbird</a>
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SOCKS client.)</p>
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<a name="server"></a>
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<h2>Configuring a server</h2>
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<p>We're looking for people with reasonably reliable Internet connections,
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that have at least 20 kilobytes/s each way. If you frequently have a
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lot of packet loss or really high latency, we can't handle your server
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yet. Otherwise, please help out!
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</p>
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<p>Other things to note:
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<ul>
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<li>Tor has built-in support for rate limiting; see BandwidthRate
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and BandwidthBurst config options. Further, if you have
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lots of capacity but don't want to spend that many bytes per
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month, check out the Accounting and Hibernation features. See <a
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href="http://wiki.noreply.org/wiki/TheOnionRouter/TorFAQ">the FAQ</a>
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for details.</li>
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<li>It's fine if the server goes offline sometimes. The directories
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notice this quickly and stop advertising the server. Just try to make
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sure it's not too often, since connections using the server when it
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disconnects will break.</li>
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<li>We can handle servers with dynamic IPs just fine, as long as the
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server itself knows its IP. If your server is behind a NAT and it doesn't
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know its public IP (e.g. it has an IP of 192.168.x.y), then we can't use it
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as a server yet. (If you want to port forward and set your Address
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config option to use dyndns DNS voodoo to get around this, feel free. If
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you write a howto, <a href="mailto:tor-volunteer@freehaven.net">even
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better</a>.)</li>
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<li>Your server will passively estimate and advertise its recent
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bandwidth capacity.
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Clients choose paths weighted by this capacity, so high-bandwidth
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servers will attract more paths than low-bandwidth ones. That's why
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having even low-bandwidth servers is useful too.</li>
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</ul>
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</p>
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<p>To set up a Tor server, do the following steps after installing Tor.
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(These instructions are Unix-centric; if you're excited about working
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with us to get a Tor server working on Windows, let us know and we'll
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work with you to fix whatever bugs come up.)
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</p>
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<ul>
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<li>1. Copy torrc.sample to torrc (in the default configuration this
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means copy /usr/local/etc/tor/torrc.sample to /usr/local/etc/tor/torrc),
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and edit the bottom part. Create the DataDirectory, and make sure it's
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owned by the uid/gid that will be running tor. Fix your system clock so
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it's not too far off. Make sure name resolution works.
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<!--Make sure each
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process can get to 1024 file descriptors (this should be already done
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for everybody but some BSD folks). -->
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<li>2. Run tor to generate keys and then exit: <tt>tor
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--list-fingerprint</tt>. Send mail to tor-ops@freehaven.net including
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a) this key fingerprint, b) who you are, so we know whom to contact if
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there's any problem, and c) what kind of connectivity the new server
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will have. If possible, PGP sign your mail.
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<li>3. If you are using a firewall, open a hole in your firewall so
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incoming connections can reach the ports you configured (i.e. ORPort,
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plus DirPort if you enabled it). Make sure outgoing connections can reach
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at least ports 80, 443, and 9001-9033 (to get to other onion routers),
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plus any other addresses or ports your exit policy allows.
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<li>4. Start your server: <tt>tor</tt>. If it logs any warnings,
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address them.
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</ul>
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<p>
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Optionally, we recommend the following steps as well:
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</p>
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<ul>
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<li>1. Make a separate user to run the server. If you
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installed the deb or the rpm, this is already done. Otherwise,
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you can do it by hand. (The Tor server doesn't need to be run as
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root, so it's good practice to not run it as root. Running as a
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'tor' user avoids issues with identd and other services that
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detect user name. If you're the paranoid sort, feel free to <a
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href="http://wiki.noreply.org/wiki/TheOnionRouter/TorInChroot">put Tor
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into a chroot jail</a>.)
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<li>2. Decide what exit policy you want. By default your server allows
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access to many popular services, but we restrict some (such as port 25)
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due to abuse potential. You might want an exit policy that is either
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less restrictive or more restrictive; edit your torrc appropriately.
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If you choose a particularly open exit policy, you might want to make
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sure your upstream or ISP is ok with that choice.
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<li>3. You may find the initscripts in contrib/tor.sh or
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contrib/torctl useful if you want to set up Tor to start at boot. Let
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us know which script you find more useful.
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<li>4. Consider setting your hostname to 'anonymous' or
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'proxy' or 'tor-proxy' if you can, so when other people see the address
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in their web logs or whatever, they will more quickly understand what's
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going on.
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<li>5. If you're not running anything else on port 80 or port
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443, please consider setting up port-forwarding and advertising these
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low-numbered ports as your Tor server. This will help allow users behind
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particularly restrictive firewalls to access the Tor network. See section
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4 of <a href="http://wiki.noreply.org/wiki/TheOnionRouter_2fTorFAQ">the
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FAQ</a> for details of how to set this up.
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</ul>
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<p>You can click <a href="http://moria.seul.org:9031/">here</a> or <a
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href="http://62.116.124.106:9030/">here</a> and look at the router-status
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line to see if your server is part of the network. It will be listed by
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nickname once we have added your server to the list of known servers;
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otherwise it is listed only by its fingerprint.</p>
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<a name="hidden-service"></a>
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<h2>Configuring a hidden service</h2>
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<p>Tor allows clients and servers to offer <em>hidden services</em>. That
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is, you can offer an apache, sshd, etc, without revealing your IP to its
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users. This works via Tor's rendezvous point design: both sides build
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a Tor circuit out, and they meet in the middle.</p>
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<p>If you're using Tor and <a href="http://www.privoxy.org/">Privoxy</a>,
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you can <a href="http://6sxoyfb3h2nvok2d.onion/">go to the hidden wiki</a>
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to see hidden services in action.</p>
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<p>To set up a hidden service, copy torrc.sample to torrc (by default it's
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in /usr/local/etc/tor/), and edit the middle part. Then run Tor. It will
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create each HiddenServiceDir you have configured, and it will create a
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'hostname' file which specifies the url (xyz.onion) for that service. You
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can tell people the url, and they can connect to it via their Tor client,
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assuming they're using a proxy (such as Privoxy) that speaks socks4a.</p>
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<a name="own-network"></a>
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<h2>Setting up your own network</h2>
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<p>
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If you want to experiment locally with your own network, or you're cut
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off from the Internet and want to be able to mess with Tor still, then
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you may want to set up your own separate Tor network.
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<p>
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To set up your own Tor network, you need to run your own directory
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servers, and you need to configure each client and server so it knows
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about your directory servers rather than the default ones.
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<ul>
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<li>1: Grab the latest release. Use at least 0.0.9.
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<li>2: For each directory server you want,
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<ul>
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<li>2a: Set it up as a server (see <a href="#server">"setting up a
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server"</a> above), with a least ORPort, DirPort, DataDirectory, and Nickname
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defined. Set "AuthoritativeDirectory 1".
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<li>2b: Set "RecommendedVersions" to a comma-separated list of acceptable
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versions of the code for clients and servers to be running.
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<li>2c: Run it: <tt>tor --list-fingerprint</tt> if your torrc is in
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the default place, or <tt>tor -f torrc --list-fingerprint</tt> to
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specify one. This will generate your keys and output a fingerprint
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line.
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</ul>
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<li>3: Now you need to teach clients and servers to use the new
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dirservers. For each fingerprint, add a line like<br>
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<tt>DirServer 18.244.0.114:80 719B E45D E224 B607 C537 07D0 E214 3E2D 423E 74CF</tt><br>
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to the torrc of each client and server who will be using your network.
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<li>4: Create a file called approved-routers in the DataDirectory
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of each directory server. Collect the 'fingerprint' lines from
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each server (including directory servers), and include them (one per
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line) in each approved-routers file. You can hup the tor process for
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each directory server to reload the approved-routers file (so you don't
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have to restart the process).
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</ul>
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<!--<h2>Other doc resources</h2>
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<ul>
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<li>Design paper
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<li>Spec and rend-spec
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<li>others
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</ul> -->
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</body>
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</html>
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