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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 "SocksAddress".
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 SocksAddress 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 ... &gt; 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> -->
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