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<title>Tor: an anonymizing overlay network for TCP</title>
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<h1><a href="http://tor.freehaven.net/">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 your workers to check back with your home website while
they're in a foreign country, without notifying everybody nearby that
they're working with your 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 negotiations.
<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 your computer doesn't have a routable IP address or you're using
a modem, you should stay a client. Otherwise, please consider being
a server, to help out the network. (Currently each server uses 20-500
gigabytes of traffic per month, depending on its capacity and its rate
limiting configuration.)</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>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://tor.freehaven.net/dist/">here</a>.</p>
<p>If you got Tor from a tarball, unpack it: <tt>tar xzf
tor-0.0.9.tar.gz; cd tor-0.0.9</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>.
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>Win32 users can use our Tor installer. It will run Tor in a dos window
so you can see its logs and errors. (You can minimize this window, but
do not close it.)
</p>
<p>In any case, see the <a href="#client">next section</a> 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>After installing Tor, 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 privoxy's config file (you can just add it to the
top). Then change your browser to http proxy at localhost port 8118.
(In Mozilla, this is in Edit|Preferences|Advanced|Proxies. In IE, it's
Tools|Internet Options|Connections|LAN Settings|Advanced.)
You should also set your SSL proxy (IE calls it "Secure") to the same
thing, to hide your SSL traffic. Using privoxy is <b>necessary</b> because
<a href="http://tor.freehaven.net/cvs/tor/doc/CLIENTS">Mozilla leaks your
DNS requests when it uses a socks proxy directly</a>. Privoxy also gives
you good html scrubbing.</p>
<p>To test if it's working, 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.
</p>
<p>
If you have a personal firewall, be sure to allow local connections to
port 8118 and port 9050. If your firewall blocks outgoing connections,
punch a hole so it can connect to TCP ports 80, 443, and 9001-9033.
<!--If you're
using Safari as your browser, keep in mind that OS X before 10.3 claims
to support socks but does not. -->
For more troubleshooting suggestions, see <a
href="http://wiki.noreply.org/wiki/TheOnionRouter/TorFAQ">the FAQ</a>.
</p>
<p>To Torify an application that supports http, just point it at
Privoxy. To use socks directly, point it at localhost port 9050. For
applications that support neither socks nor http, 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>
<p>(Windows doesn't have tsocks; instead, you can try
<a
href="http://www.socks.permeo.com/Download/SocksCapDownload/index.asp">SocksCap</a>
or the <a href="http://www.hummingbird.com/products/nc/socks/index.html?cks=y">Hummingbird</a>
SOCKS client.)</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 20 kilobytes/s each way. If you frequently have a
lot of packet loss or really high latency, we can't handle your server
yet. Otherwise, please help out!
</p>
<p>Other things to note:
<ul>
<li>Tor has built-in support for rate limiting; see BandwidthRate
and BandwidthBurst config options. Further, if you have
lots of capacity but don't want to spend that many bytes per
month, check out the Accounting and Hibernation features. See <a
href="http://wiki.noreply.org/wiki/TheOnionRouter/TorFAQ">the FAQ</a>
for details.</li>
<li>It's fine if the server goes offline sometimes. The directories
notice this quickly and stop advertising the server. Just try to make
sure it's not too often, since connections using the server when it
disconnects will break.</li>
<li>We can handle servers with dynamic IPs just fine, as long as the
server itself knows its IP. If your server is behind a NAT and it doesn't
know its public IP (e.g. it has an IP of 192.168.x.y), then we can't use it
as a server yet. (If you want to port forward and set your Address
config option to use dyndns DNS voodoo to get around this, feel free. If
you write a howto, <a href="mailto:tor-volunteer@freehaven.net">even
better</a>.)</li>
<li>Your server will passively estimate and advertise its recent
bandwidth capacity.
Clients choose paths weighted by this capacity, so high-bandwidth
servers will attract more paths than low-bandwidth ones. That's why
having even low-bandwidth servers is useful too.</li>
</ul>
</p>
<p>To set up a Tor server, do the following steps after installing Tor.
(These instructions are Unix-centric; if you're excited about working
with us to get a Tor server working on Windows, let us know and we'll
work with you to fix whatever bugs come up.)
</p>
<ul>
<li>1. Copy torrc.sample to torrc (in the default configuration this
means copy /usr/local/etc/tor/torrc.sample to /usr/local/etc/tor/torrc),
and edit the bottom part. Create the DataDirectory, and make sure it's
owned by the uid/gid that will be running tor. Fix your system clock so
it's not too far off. Make sure name resolution works.
<!--Make sure each
process can get to 1024 file descriptors (this should be already done
for everybody but some BSD folks). -->
<li>2. Run tor to generate keys and then exit: <tt>tor
--list-fingerprint</tt>. Send mail to tor-ops@freehaven.net including
a) this key fingerprint, b) who you are, so we know whom to contact if
there's any problem, and c) what kind of connectivity the new server
will have. If possible, PGP sign your mail.
<li>3. If you are using a firewall, open a hole in your firewall so
incoming connections can reach the ports you configured (i.e. ORPort,
plus DirPort if you enabled it). Make sure outgoing connections can reach
at least ports 80, 443, and 9001-9033 (to get to other onion routers),
plus any other addresses or ports your exit policy allows.
<li>4. Start your server: <tt>tor</tt>. If it logs any warnings,
address them.
</ul>
<p>
Optionally, we recommend the following steps as well:
</p>
<ul>
<li>1. Make a separate user to run the server. If you
installed the deb or the rpm, this is already done. Otherwise,
you can do it by hand. (The Tor server doesn't need to be run as
root, so it's good practice to not run it as root. Running as a
'tor' user avoids issues with identd and other services that
detect user name. If you're the paranoid sort, feel free to <a
href="http://wiki.noreply.org/wiki/TheOnionRouter/TorInChroot">put Tor
into a chroot jail</a>.)
<li>2. Decide what exit policy you want. By default your server allows
access to many popular services, but we restrict some (such as port 25)
due to abuse potential. You might want an exit policy that is either
less restrictive or more restrictive; edit your torrc appropriately.
If you choose a particularly open exit policy, you might want to make
sure your upstream or ISP is ok with that choice.
<li>3. You may find the initscripts in contrib/tor.sh or
contrib/torctl useful if you want to set up Tor to start at boot. Let
us know which script you find more useful.
<li>4. Consider setting your hostname to 'anonymous' or
'proxy' or 'tor-proxy' if you can, so when other people see the address
in their web logs or whatever, they will more quickly understand what's
going on.
<li>5. If you're not running anything else on port 80 or port
443, please consider setting up port-forwarding and advertising these
low-numbered ports as your Tor server. This will help allow users behind
particularly restrictive firewalls to access the Tor network. See section
4 of <a href="http://wiki.noreply.org/wiki/TheOnionRouter_2fTorFAQ">the
FAQ</a> for details of how to set this up.
</ul>
<p>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 router-status
line to see if your server is part of the network. It will be listed by
nickname once we have added your server to the list of known servers;
otherwise it is listed only by its fingerprint.</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 middle 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 configure each client and server so it knows
about your directory servers rather than the default ones.
<ul>
<li>1: Grab the latest release. Use at least 0.0.9.
<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, DirPort, DataDirectory, and Nickname
defined. Set "AuthoritativeDirectory 1".
<li>2b: Set "RecommendedVersions" to a comma-separated list of acceptable
versions of the code for clients and servers to be running.
<li>2c: Run it: <tt>tor --list-fingerprint</tt> if your torrc is in
the default place, or <tt>tor -f torrc --list-fingerprint</tt> to
specify one. This will generate your keys and output a fingerprint
line.
</ul>
<li>3: Now you need to teach clients and servers to use the new
dirservers. For each fingerprint, add a line like<br>
<tt>DirServer 18.244.0.114:80 719B E45D E224 B607 C537 07D0 E214 3E2D 423E 74CF</tt><br>
to the torrc of each client and server who will be using your network.
<li>4: Create a file called approved-routers in the DataDirectory
of each directory server. Collect the 'fingerprint' lines from
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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