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<h2>Tor: Research</h2>
<hr />

<p>
Many people around the world are doing research on how to improve the Tor
design, what's going on in the Tor network, and more generally on attacks
and defenses for anonymous communication systems. This page summarizes
the resources we provide to help make your Tor research more effective.
The best way to reach us about research is through the <a href="<page
about/contact>">tor-assistants</a> list.
</p>

<ul>

<li>
<b>Data.</b>
We've been <a href="https://metrics.torproject.org/data.html">collecting
data to learn more about the Tor network</a>: how many relays and
clients there are in the network, what capabilities they have, how
fast the network is, how many clients are connecting via bridges,
what traffic exits the network, etc. We are also developing
tools to process these huge data archives and come up with
<a href="https://metrics.torproject.org/graphs.html">useful
statistics</a>.  For example, we provide a <a
href="https://gitweb.torproject.org//ernie.git?a=blob_plain;f=doc/manual.pdf">tool
called Ernie</a> that can import relay descriptors into a local database
to perform analyses. Let us know what other information you'd like to
see, and we can work with you to help make sure it gets collected
<a href="https://metrics.torproject.org/papers/wecsr10.pdf">safely</a>
and robustly.
</li>

<li>
<b>Analysis.</b>
If you're investigating Tor, or solving a Tor-related problem,
<i>_please_</i> talk to us somewhere along the way &mdash; the earlier
the better. These days we review too many conference paper submissions
that make bad assumptions and end up solving the wrong problem. Since
the Tor protocol and the Tor network are both moving targets, measuring
things without understanding what's going on behind the scenes is going
to result in bad conclusions. In particular, different groups often
unwittingly run a variety of experiments in parallel, and at the same
time we're constantly modifying the design to try new approaches. If
you let us know what you're doing and what you're trying to learn,
we can help you understand what other variables to expect and how to
interpret your results.
</li>

<li>
<b>Measurement and attack tools.</b>
We're building a <a
href="https://metrics.torproject.org/tools.html">repository</a> of tools
that can be used to measure, analyze, or perform attacks on Tor. Many
research groups end up needing to do similar measurements (for example,
change the Tor design in some way and then see if latency improves),
and we hope to help everybody standardize on a few tools and then make
them really good. Also, while there are some really neat Tor attacks
that people have published about, it's hard to track down a copy of
the code they used. Let us know if you have new tools we should list,
or improvements to the existing ones. The more the better, at this stage.
</li>

<li>
<b>We need defenses too &mdash; not just attacks.</b>
Most researchers find it easy and fun to come up with novel attacks on
anonymity systems. We've seen this result lately in terms of improved
congestion attacks, attacks based on remotely measuring latency or
throughput, and so on. Knowing how things can go wrong is important,
and we recognize that the incentives in academia aren't aligned with
spending energy on designing defenses, but it sure would be great to
get more attention to how to address the attacks. We'd love to help
brainstorm about how to make Tor better. As a bonus, your paper might
even end up with a stronger "countermeasures" section.
</li>

<li>
<b>In-person help.</b>
If you're doing interesting and important Tor research and need help
understanding how the Tor network or design works, interpreting your
data, crafting your experiments, etc, we can send a Tor researcher to
your doorstep. As you might expect, we don't have a lot of free time;
but making sure that research is done in a way that's useful to us is
really important. So let us know, and we'll work something out.
</li>

</ul>

<a id="Groups"></a>
<h2><a class="anchor" href="#Groups">Research Groups</a></h2>

<p>Interested to find other anonymity researchers? Here are some
research groups you should take a look at.</p>

<ul>
<li>Ian Goldberg's <a href="http://crysp.uwaterloo.ca/">CrySP</a> group
at Waterloo.
</li>
<li><a href="http://www-users.cs.umn.edu/~hopper/">Nick Hopper</a>'s
group at UMN.
</li>
<li><a href="http://www.hatswitch.org/~nikita/">Nikita Borisov</a>'s
group at Illinois.
</li>
<li>Matt Wright's <a href="http://isec.uta.edu/">iSec</a> group at
UTA.
</li>
</ul>

<a id="Ideas"></a>
<h2><a class="anchor" href="#Ideas">Research Ideas</a></h2>

<p>
If you're interested in anonymity research, you must make it to the
<a href="http://petsymposium.org/">Privacy Enhancing Technologies
Symposium</a>. Everybody who's anybody in the anonymity research world
will be there. Stipends are generally available for people whose presence
will benefit the community.
</p>

<p>To get up to speed on anonymity research, read <a
href="http://freehaven.net/anonbib/">these papers</a> (especially the
ones in boxes).</p>

<p>We need people to attack the system, quantify defenses,
etc. Here are some example projects:</p>

<ul>

<li>What algorithm should we use to assign Guard flags such that a)
we assign the flag to as many relays as possible, yet b) we minimize
the chance that Alice will use an attacker's node as a guard? See the
<a href="<blog>/research-problem-better-guard-rotation-parameters">blog
post</a> for details.
</li>

<li>For various diversity metrics, how has the diversity of
the Tor network changed over time? How robust is it to change or
attack? These results can help us make better design decisions. See the <a
href="<blog>/research-problem-measuring-safety-tor-network">blog post</a>
for details.
</li>

<li>If we prevent the really loud users from using too much of the Tor
network, how much can it help? We've instrumented Tor's entry relays
so they can rate-limit connections from users, and we've instrumented
the directory authorities so they can change the rate-limiting
parameters globally across the network. Which parameter values improve
performance for the Tor network as a whole? How should relays adapt
their rate-limiting parameters based on their capacity and based on
the network load they see, and what rate-limiting algorithms will work
best? See the <a
href="<blog>/research-problem-adaptive-throttling-tor-clients-entry-guards">blog
post</a> for details.
</li>

<li>Right now Tor clients are willing to reuse a given circuit for ten
minutes after it's first used. The goal is to avoid loading down the
network with too many circuit creations, yet to also avoid having
clients use the same circuit for so long that the exit node can build a
useful pseudonymous profile of them. Alas, ten minutes is probably way
too long, especially if connections from multiple protocols (e.g. IM and
web browsing) are put on the same circuit. If we keep fixed the overall
number of circuit extends that the network needs to do, are there more
efficient and/or safer ways for clients to allocate streams to circuits,
or for clients to build preemptive circuits? Perhaps this research item
needs to start with gathering some traces of what requests typical
clients try to launch, so you have something realistic to try to optimize.
</li>

<li>The "website fingerprinting attack": make a list of a few
hundred popular websites, download their pages, and make a set of
"signatures" for each site. Then observe a Tor client's traffic. As
you watch him receive data, you quickly approach a guess about which
(if any) of those sites he is visiting. First, how effective is
this attack on the deployed Tor design? The problem with all the
previous attack papers is that they look at timing and counting of
IP packets on the wire. But OpenSSL's TLS records, plus Tor's use of
TCP pushback to do rate limiting, means that tracing by IP packets
produces very poor results. The right approach is to realize that
Tor uses OpenSSL, look inside the TLS record at the TLS headers, and
figure out how many 512-byte cells are being sent or received. Then
start exploring defenses: for example, we could change Tor's cell
size from 512 bytes to 1024 bytes, we could employ padding techniques
like <a href="http://freehaven.net/anonbib/#timing-fc2004">defensive
dropping</a>, or we could add traffic delays. How much of an impact do
these have, and how much usability impact (using some suitable metric)
is there from a successful defense in each case?</li>

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<li>
Path selection algorithms, directory fetching schedules for Tor-on-mobile
that are compatible anonymity-wise with our current approaches.
</li>

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<li>More coming soon. See also the "Research" section of the <a
href="<page getinvolved/volunteer>#Research">volunteer</a> page for
other topics.
</li>

</ul>

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