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- <title>Tor: an anonymizing overlay network for TCP</title>
- <meta name="Author" content="Roger Dingledine">
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- <h1><a href="http://freehaven.net/tor/">Tor</a> documentation</h1>
- <p>The simple version: Tor provides a distributed network of servers
- ("onion routers"). Users bounce their TCP streams (web traffic, FTP, SSH,
- etc.) around the routers. This makes it hard for recipients, observers, and
- even the onion routers themselves to track the source of the stream.</p>
- <p>The complex version: Onion Routing is a connection-oriented anonymizing
- communication service. Users choose a source-routed path through a set of
- nodes, and negotiate a "virtual circuit" through the network, in which
- each node knows its predecessor and successor, but no others. Traffic
- flowing down the circuit is unwrapped by a symmetric key at each node,
- which reveals the downstream node.</p>
- <a name="why"></a>
- <h2>Why should I use Tor?</h2>
- <p>Individuals need Tor for privacy:
- <ul>
- <li>Privacy in web browsing -- both from the remote website (so it can't
- track and sell your behavior), and similarly from your local ISP.
- <li>Safety in web browsing: if your local government doesn't approve
- of its citizens visiting certain websites, they may monitor the sites
- and put readers on a list of suspicious persons.
- <li>Circumvention of local censorship: connect to resources (news
- sites, instant messaging, etc) that are restricted from your
- ISP/school/company/government.
- <li>Socially sensitive communication: chat rooms and web forums for
- rape and abuse survivors, or people with illnesses.
- </ul>
- <p>Journalists and NGOs need Tor for safety:
- <ul>
- <li>Allowing dissidents and whistleblowers to communicate more safely.
- <li>Censorship-resistant publication, such as making available your
- home-made movie anonymously via a Tor <a href="#hidden-service">hidden
- service</a>; and reading, e.g. of news sites not permitted in some
- countries.
- <li>Allowing their workers to check back with their home website while
- they're in a foreign country, without notifying everybody nearby that
- they're working with that organization.
- </ul>
- <p>Companies need Tor for business security:
- <ul>
- <li>Competitive analysis: browse the competition's website safely.
- <li>Protecting collaborations of sensitive business units or partners.
- <li>Protecting procurement suppliers or patterns.
- <li>Putting the "P" back in "VPN": traditional VPNs reveal the exact
- amount and frequency of communication. Which locations have employees
- working late? Which locations have employees consulting job-hunting
- websites? Which research groups are communicating with your company's
- patent lawyers?
- </ul>
- <p>Governments need Tor for traffic-analysis-resistant communication:
- <ul>
- <li>Open source intelligence gathering (hiding individual analysts is
- not enough -- the organization itself may be sensitive).
- <li>Defense in depth on open <em>and classified</em> networks -- networks
- with a million users (even if they're all cleared) can't be made safe just
- by hardening them to external threat.
- <li>Dynamic and semi-trusted international coalitions: the network can
- be shared without revealing the existence or amount of communication
- between all parties.
- <li>Networks partially under known hostile control: to block
- communications, the enemy must take down the whole network.
- <li>Politically sensitive negotations.
- <li>Road warriors.
- <li>Protecting procurement patterns.
- <li>Anonymous tips.
- </ul>
- <p>Law enforcement needs Tor for safety:
- <ul>
- <li>Allowing anonymous tips or crime reporting
- <li>Allowing agents to observe websites without notifying them that
- they're being observed (or, more broadly, without having it be an
- official visit from law enforcement).
- <li>Surveillance and honeypots (sting operations)
- </ul>
- <p>Does the idea of sharing the Tor network with
- all of these groups bother you? It shouldn't -- <a
- href="http://freehaven.net/doc/fc03/econymics.pdf">you need them for
- your security</a>.</p>
- <a name="client-or-server"></a>
- <h2>Should I run a client or a server?</h2>
- <p>You can run Tor in either client mode or server mode. By default,
- everybody is a <i>client</i>. This means you don't relay traffic for
- anybody but yourself.</p>
- <p>If you have less than 1Mbit in both directions, you should stay
- a client. Otherwise, please consider being a server, to help out the
- network. (Currently each server uses 20-30 gigabytes of traffic
- per month; but that may go up.)</p>
- <p>Note that you can be a server without allowing users to make
- connections from your computer to the outside world. This is called being
- a middleman server.</p>
- <p> Benefits of running a server include:
- <ul>
- <li>Clients are generally limited to 100KB/s, whereas servers can inject
- or receive as much traffic as they want.
- <li>You may get stronger anonymity, since your destination can't know
- whether connections relayed through your computer originated at your
- computer or not.
- <li>You can also get stronger anonymity by configuring your Tor clients
- to use your Tor server for entry or for exit.
- <li>You're helping me with development and scalability testing.
- <li>You're helping your fellow Internet users by providing a larger
- network. Also, having servers in many different pieces of the Internet
- gives users more robustness against curious telcos and brute force
- attacks.
- </ul>
- <p>You can read more about setting up Tor as a
- server <a href="#server">below</a>.</p>
- <a name="installing"></a>
- <h2>Installing Tor</h2>
- <p>You can get the latest releases <a
- href="http://freehaven.net/tor/dist/">here</a>.</p>
- <p>If you got Tor from a tarball, unpack it: <tt>tar xzf
- tor-0.0.7.tar.gz; cd tor-0.0.7</tt>. Run <tt>./configure</tt>, then
- <tt>make</tt>, and then <tt>make install</tt> (as root if necessary). Then
- you can launch tor from the command-line by running <tt>tor</tt>.</p>
- <p>If you got Tor from the Win32 .exe file, you
- can just click-click it (you may need to install <a
- href="http://www.slproweb.com/products/Win32OpenSSL.html">OpenSSL
- 0.9.7</a> first, if you get an error about missing
- libeay32.dll.) You might also want to run Tor in a dos window,
- so you can see its logs, and see its error messages if it
- crashes. If you don't want the default configuration, fetch the <a
- href="http://freehaven.net/tor/doc/torrc.sample">torrc</a>, edit it,
- and use <tt>tor.exe -f torrc</tt>.</p>
- <p>Otherwise, if you got it prepackaged (e.g. in the <a
- href="http://packages.debian.org/tor">Debian package</a> or <a
- href="http://packages.gentoo.org/packages/?category=net-misc;name=tor">Gentoo
- package</a>), these steps are already done for you, and you may
- even already have Tor started in the background (logging to
- /var/log/something).</p>
- <p>In any case, see the next section for what to <i>do</i> with it now that
- you've got it running.</p>
- <a name="client"></a>
- <h2>Configuring a client</h2>
- <p>Tor comes configured as a client by default. It uses a built-in
- default configuration file, and most people won't need to change any of
- the settings.</p>
- <p>The only setting you might need to change is "SocksBindAddress".
- By default, your Tor client only listens for applications that connect
- from localhost. Connections from other computers are refused. If you
- want to torify applications on different computers than the Tor client,
- you should copy torrc.sample to torrc (it's installed by default
- to /usr/local/etc/tor/), change the SocksBindAddress line to
- 0.0.0.0, and then hup or restart Tor.</p>
- <p>To test if it's working, point your browser
- to socks4 or socks5 proxy at localhost port 9050. In
- Mozilla, this is in edit|preferences|advanced|proxies. Go to <a
- href="http://www.junkbusters.com/cgi-bin/privacy">http://www.junkbusters.com/cgi-bin/privacy</a>
- and see what IP it says you're coming from. (If you have a personal
- firewall, be sure to allow local connections to port 9050. If your
- firewall blocks outgoing connections, punch a hole so it can connect to
- TCP *:9001-9004 and *:9030-9033. If you're using Safari as your browser,
- keep in mind that OS X before 10.3 claims to support socks but does
- not.)</p>
- <p>Once you've tested that it works, you should install <a
- href="http://www.privoxy.org/">privoxy</a>, which is a filtering web
- proxy that integrates well with Tor. Add the line <br>
- <tt>forward-socks4a / localhost:9050 .</tt><br>
- (don't forget the dot) to its
- config file. Then change your mozilla to http proxy at localhost port 8118
- (and no socks proxy). You should also set your SSL proxy to the same
- thing, to hide your https traffic. Using privoxy is necessary because
- <a href="http://freehaven.net/tor/cvs/doc/CLIENTS">Mozilla leaks your
- DNS requests when it uses a socks proxy directly</a>. Privoxy also gives
- you good html scrubbing.</p>
- <p>You might want to use Tor with an application that doesn't
- support socks directly. In this case, you should look at
- using <a href="http://tsocks.sourceforge.net/">tsocks</a>
- to dynamically replace the system calls in your program to
- route through Tor. If you want to use socks4a, consider using <a
- href="http://www.dest-unreach.org/socat/">socat</a> (specific instructions
- are on <a href="http://6sxoyfb3h2nvok2d.onion/tor/SocatHelp">this hidden
- service url</a>).</p>
- <a name="server"></a>
- <h2>Configuring a server</h2>
- <p>We're looking for people with reasonably reliable Internet connections,
- that have at least 1Mbit each way. Currently we don't use all of that,
- but we want it available for burst traffic.</p>
- <p>(The Tor server doesn't need to be run as root, and doesn't
- need any special system permissions or kernel mods. If you're
- the paranoid sort, feel free to <a
- href="http://wiki.noreply.org/wiki/TheOnionRouter/TorInChroot">put it
- into a chroot jail</a>.)</p>
- <p>First, copy torrc.sample to torrc (by default it's in
- /usr/local/etc/tor/), and edit the middle part. Create the DataDirectory,
- and make sure it's owned by whoever will be running tor. Fix your system
- clock so it's not too far off. Make sure name resolution works. Open a
- hole in your firewall so outsiders can connect to your ORPort.</p>
- <p>Then run tor to generate keys: <tt>tor</tt>. One of the files generated
- in your DataDirectory is your 'fingerprint' file. Mail it to
- tor-ops@freehaven.net.</p>
- <p>In that mail, be sure to tell us who you are, so we know whom to contact
- if there's any problem. Also describe what kind of connectivity the new
- server will have. If possible, PGP sign your mail.</p>
- <p>NOTE: You won't be able to use tor as a client or server
- in this configuration until you've been added to the directory
- and can authenticate to the other nodes. (This is no longer the case
- for 0.0.8 and after.)</p>
- <p>Once your fingerprint has been approved, you can click <a
- href="http://moria.seul.org:9031/">here</a> or <a
- href="http://62.116.124.106:9030/">here</a> and look at the
- running-routers line to see if your server is part of the network.</p>
- <a name="hidden-service"></a>
- <h2>Configuring a hidden service</h2>
- <p>Tor allows clients and servers to offer <em>hidden services</em>. That
- is, you can offer an apache, sshd, etc, without revealing your IP to its
- users. This works via Tor's rendezvous point design: both sides build
- a Tor circuit out, and they meet in the middle.</p>
- <p>If you're using Tor and <a href="http://www.privoxy.org/">Privoxy</a>,
- you can <a href="http://6sxoyfb3h2nvok2d.onion/">go to the hidden wiki</a>
- to see hidden services in action.</p>
- <p>To set up a hidden service, copy torrc.sample to torrc (by default it's
- in /usr/local/etc/tor/), and edit the bottom part. Then run Tor. It will
- create each HiddenServiceDir you have configured, and it will create a
- 'hostname' file which specifies the url (xyz.onion) for that service. You
- can tell people the url, and they can connect to it via their Tor client,
- assuming they're using a proxy (such as Privoxy) that speaks socks4a.</p>
- <a name="own-network"></a>
- <h2>Setting up your own network</h2>
- <p>
- If you want to experiment locally with your own network, or you're cut
- off from the Internet and want to be able to mess with Tor still, then
- you may want to set up your own separate Tor network.
- <p>
- To set up your own Tor network, you need to run your own directory
- servers, and you need to change the tarball so it points to your directory
- servers rather than the default ones.
- <ul>
- <li>1: Grab the latest release.
- <li>2: For each directory server you want,
- <ul>
- <li>2a: Set it up as a server (see <a href="#server">"setting up a
- server"</a> above), with a least ORPort, DataDirectory, and Nickname
- defined.
- <li>2b: Set "DirPort" to the intended port for serving directories.
- <li>2c: Set "RecommendedVersions" to a comma-separated list of acceptable
- versions of the code for clients and servers to be running (see step
- 4c below).
- <!-- <li>2d: Create a file called approved-routers in your DataDirectory:
- <tt>touch approved-routers</tt>. It will be empty for now. We'll fill it in
- step 5. -->
- <li>2d: Create an empty dirservers file (<tt>touch dirservers</tt>). Point
- RouterFile at it in your torrc.
- <li>2e: Run it: <tt>tor -f torrc</tt>. This will generate your keys and a
- router.desc (router descriptor) file. It will then exit with a complaint
- that it can't open the fingerprint file; that's fine.
- </ul>
- <li>3: Create the new dirservers file. You do this by concatenating the
- "router.desc" files from each dirserver's DataDirectory: <tt>cat router1.desc
- router2.desc ... > dirservers</tt>
- <li>4: Now you need to teach clients and servers to use the new
- dirservers file. First, check out the tor cvs repository (instructions <a
- href="http://freehaven.net/tor/">here</a> -- be sure to check out the
- tag that matches the version of the code you intend to use; and note that
- the latest cvs version may not compile or work right). Then:
- <ul>
- <li>4a: Edit src/or/config.c and change the default_dirservers_string array
- so that it reflects the contents of the new dirservers file instead
- of the old one. Be sure to get the quotes and newlines and semicolons
- right. (This step sucks. We plan to have it solved by the release of 0.0.8.)
- <li>4b: Replace the dirservers file in your sandbox (in src/config/)
- with the one from step 3.
- <li>4c: edit configure.in, change the AM_INIT_AUTOMAKE(tor, 0.0.8)
- line so that it specifies a version that is specific to you, such as
- 0.0.8-arma. This will help you keep from being confused later. Be sure
- to update the RecommendedVersions lines to include this version.
- <li>4d: run <tt>./autogen.sh</tt> (you'll need a new enough set of auto* tools),
- then <tt>make dist</tt>.
- </ul>
- <li>5: Create a file called approved-routers in the DataDirectory
- of each directory server. Collect the 'fingerprint' lines from the
- DataDirectory of each server (including directory servers), and include
- them (one per line) in each approved-routers file. You can hup the tor
- process for each directory server to reload the approved-routers file
- (so you don't have to restart the process).
- </ul>
- <!--<h2>Other doc resources</h2>
- <ul>
- <li>Design paper
- <li>Spec and rend-spec
- <li>others
- </ul> -->
- </body>
- </html>
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