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340 lines
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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://freehaven.net/tor/">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 their agents to check back with their 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 that 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 negotations.
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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 you have less than 768kbit in both directions, you should stay
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a client. Otherwise, please consider being a server, to help out the
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network. (Currently each server uses 20-30 gigabytes of traffic
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per month; but that may go up.)</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>Clients are generally limited to 100KB/s, whereas servers can inject
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or receive as much traffic as they want.
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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://freehaven.net/tor/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-0.0.7.tar.gz; cd tor-0.0.7</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>.</p>
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<p>If you got Tor from the Win32 .exe file, you
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can just click-click it (you may need to install <a
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href="http://www.slproweb.com/products/Win32OpenSSL.html">OpenSSL
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0.9.7</a> first, if you get an error about missing
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libeay32.dll.) You might also want to run Tor in a dos window,
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so you can see its logs, and see its error messages if it
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crashes. If you don't want the default configuration, fetch the <a
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href="http://freehaven.net/tor/doc/torrc.sample">torrc</a>, edit it,
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and use <tt>tor.exe -f torrc</tt>.</p>
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<p>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>In any case, see the next section for what to <i>do</i> with it now that
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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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<p>The only setting you might need to change is "SocksAddress".
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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 SocksAddress line to
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0.0.0.0, and then restart Tor.</p>
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<p>To test if it's working, point your browser
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to socks4 or socks5 proxy at localhost port 9050. In
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Mozilla, this is in edit|preferences|advanced|proxies. 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. (If you have a personal
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firewall, be sure to allow local connections to port 9050. If your
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firewall blocks outgoing connections, punch a hole so it can connect to
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TCP *:9001-9004 and *:9030-9033. If you're using Safari as your browser,
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keep in mind that OS X before 10.3 claims to support socks but does
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not.)</p>
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<p>Once you've tested that it works, 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 its
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config file. Then change your mozilla to http proxy at localhost port 8118
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(and no socks proxy). This step will give you good html scrubbing as well.
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(See <a href="http://freehaven.net/tor/cvs/doc/CLIENTS">this explanation</a>
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for why direct socks gives you less anonymity.)</p>
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<p>You might want to use Tor with an application that doesn't
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support socks directly. In this case, 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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<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 768kbit each way. Currently we don't use all of that,
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but we want it available for burst traffic.</p>
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<p>The Tor server doesn't need to be run as root, and doesn't
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need any special system permissions or kernel mods. If you're
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the paranoid sort, feel free to put it into a chroot jail (<a
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href="http://archives.seul.org/or/dev/Jun-2004/msg00001.html">some
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hints</a>), etc.</p>
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<p>First, copy torrc.sample to torrc (by default it's in
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/usr/local/etc/tor/), and edit the middle part. Create the DataDirectory,
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and make sure it's owned by whoever will be running tor. Fix your system
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clock so it's not too far off. Make sure name resolution works. Open a
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hole in your firewall so outsiders can connect to your ORPort.</p>
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<p>Then run tor to generate keys: <tt>tor</tt>. One of the files generated
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in your DataDirectory is your 'fingerprint' file. Mail it to
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tor-ops@freehaven.net.</p>
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<p>In that mail, be sure to tell us who you are, so we know whom to contact
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if there's any problem. Also describe what kind of connectivity the new
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server will have. If possible, PGP sign your mail.</p>
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<p>NOTE: You won't be able to use tor as a client or server
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in this configuration until you've been added to the directory
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and can authenticate to the other nodes.</p>
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<p>Once your fingerprint has been approved, you can click <a
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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
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running-routers line to see if your server is part of the network.</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 bottom 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 change the tarball so it points to your directory
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servers rather than the default ones.
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<ul>
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<li>1: Grab the latest release.
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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, DataDirectory, and Nickname
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defined.
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<li>2b: Set "DirPort" to the intended port for serving directories.
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<li>2c: Set "RecommendedVersions" to a comma-separated list of acceptable
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versions of the code for clients and servers to be running (see step
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4c below).
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<!-- <li>2d: Create a file called approved-routers in your DataDirectory:
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<tt>touch approved-routers</tt>. It will be empty for now. We'll fill it in
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step 5. -->
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<li>2d: Create an empty dirservers file (<tt>touch dirservers</tt>). Point
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RouterFile at it in your torrc.
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<li>2e: Run it: <tt>tor -f torrc</tt>. This will generate your keys and a
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router.desc (router descriptor) file. It will then exit with a complaint
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that it can't open the fingerprint file; that's fine.
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</ul>
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<li>3: Create the new dirservers file. You do this by concatenating the
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"router.desc" files from each dirserver's DataDirectory: <tt>cat router1.desc
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router2.desc ... > dirservers</tt>
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<li>4: Now you need to teach clients and servers to use the new
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dirservers file. First, check out the tor cvs repository (instructions <a
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href="http://freehaven.net/tor/">here</a> -- be sure to check out the
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tag that matches the version of the code you intend to use; and note that
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the latest cvs version may not compile or work right). Then:
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<ul>
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<li>4a: Edit src/or/config.c and change the default_dirservers_string array
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so that it reflects the contents of the new dirservers file instead
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of the old one. Be sure to get the quotes and newlines and semicolons
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right. (This step sucks. Please suggest a better way to handle this
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step. ;)
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<li>4b: Replace the dirservers file in your sandbox (in src/config/)
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with the one from step 3.
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<li>4c: edit configure.in, change the AM_INIT_AUTOMAKE(tor, 0.0.6)
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line so that it specifies a version that is specific to you, such as
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0.0.6-arma. This will help you keep from being confused later. Be sure
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to update the RecommendedVersions lines to include this version.
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<li>4d: run <tt>./autogen.sh</tt> (you'll need a new enough set of auto* tools),
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then <tt>make dist</tt>.
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</ul>
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<li>5: Create a file called approved-routers in the DataDirectory
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of each directory server. Collect the 'fingerprint' lines from the
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DataDirectory of each server (including directory servers), and include
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them (one per line) in each approved-routers file. You can hup the tor
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process for each directory server to reload the approved-routers file
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(so you don't 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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