en/volunteer.wml (e0f81ea55) - tor-webwml.git

volunteer.wml

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<h2>A few things everyone can do now:</h2>
<ol>
<li>Please consider <a href="<page docs/tor-doc-relay>">running
a relay</a> to help the Tor network grow.</li>
<li>Tell your friends! Get them to run relays. Get them to run hidden
services. Get them to tell their friends.</li>
<li>If you like Tor's goals, please <a href="<page donate>">take a moment
to donate to support further Tor development</a>. We're also looking
for more sponsors &mdash; if you know any companies, NGOs, agencies,
or other organizations that want anonymity / privacy / communications
security, let them know about us.</li>
<li>We're looking for more <a href="<page torusers>">good examples of Tor
users and Tor use cases</a>. If you use Tor for a scenario or purpose not
yet described on that page, and you're comfortable sharing it with us,
we'd love to hear from you.</li>
</ol>

Tor has <a href="<page open-positions>">two open positions</a>.
Please <a href="<page contact>">contact us</a> if you are qualified!

<a id="Documentation"></a>
<h2><a class="anchor" href="#Documentation">Documentation</a></h2>
<ol>
<li>Help translate the web page and documentation into other
languages. See the <a href="<page translation>">translation
guidelines</a> if you want to help out. We especially need Arabic or
Farsi translations, for the many Tor users in censored areas.</li>
<li>Evaluate and document
<a href="https://wiki.torproject.org/wiki/TheOnionRouter/TorifyHOWTO">our
list of programs</a> that can be configured to use Tor.</li>
<li>We have a huge list of <a href="https://wiki.torproject.org/noreply/TheOnionRouter/SupportPrograms">potentially useful
programs that interface to Tor</a>. Which ones are useful in which
situations? Please help us test them out and document your results.</li>
</ol>

<a id="Advocacy"></a>
<h2><a class="anchor" href="#Advocacy">Advocacy</a></h2>
<ol>
<li>Create a <a href="https://wiki.torproject.org/noreply/CommunityLogos">community logo</a> under a Creative Commons license that all can use and modify</li>
<li>Create a presentation that can be used for various user group meetings around the world</li>
<li>Create a video about the positive uses of Tor, what Tor is, or how
to use it. Some have already
started on <a href="http://media.torproject.org/video/">Tor's Media
server</a>, <a
href="http://www.howcast.com/videos/90601-How-To-Circumvent-an-Internet-Proxy">Howcast</a>,
and <a href="http://www.youtube.com/freedom4internet">Youtube</a>.</li> 
<li>Create a poster, or a set of posters, around a theme,
such as "Tor for Freedom!"</li>
</ol>

<a id="Coding"></a>
<a id="Summer"></a>
<a id="Projects"></a>
<h2><a class="anchor" href="#Projects">Good Coding Projects</a></h2>

You may find some of these projects to be good <a href="<page
gsoc>">Google Summer of Code 2010</a> ideas. We have labelled each idea
with how useful it would be to the overall Tor project (priority), how
much work we expect it would be (effort level), how much clue you should
start with (skill level), and which of our <a href="<page
people>#Core">core developers</a> would be good mentors.
If one or more of these ideas looks promising to you, please <a
href="<page contact>">contact us</a> to discuss your plans rather than
sending blind applications. You may also want to propose your own project
idea &mdash; which often results in the best applications.

<ol>

<li>
Tor Browser Bundle for Linux/Mac OS X
 
Priority: High
 
Effort Level: High
 
Skill Level: Medium
 
Likely Mentors: Steven, Erinn, Jacob, Andrew
 
The Tor Browser Bundle incorporates Tor, Firefox, Polipo, and the Vidalia
user interface (and optionally the <a href="http://pidgin.im/">Pidgin</a>
Instant Messaging client). Components are pre-configured to operate in a
secure way, and it has very few dependencies on the installed operating
system. It has therefore become one of the most easy to use, and popular,
ways to use Tor on Windows.
 
However, there is currently no released package for Linux and Mac OS
X, so this project would be to implement Tor Browser Bundle for OS X and
continue work on the Tor Browser Bundle for Linux. This will involve modifications to Vidalia (C++), possibly
Firefox (C) then creating and testing the launcher on a range of
operating system versions and configurations to verify portability.
Some work on this was completed as part of the Google Summer of Code
2009. Another part of this project is to identify all of the traces left
behind by using a Tor Browser Bundle on Mac OS X or Linux. Developing
ways to stop, counter, or remove these traces is a final step.
 
Students should be familiar with application development on one or
preferably both of Linux and Mac OS X, and be comfortable with C/C++
and shell scripting.
 
Part of this project could be usability testing of Tor Browser Bundle,
ideally amongst our target demographic. That would help a lot in knowing
what needs to be done in terms of bug fixes or new features. We get this
informally at the moment, but a more structured process would be better.
</li>

<li>
Help track the overall Tor Network status
 
Priority: Medium to High
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Karsten, Roger
 
It would be great to set up an automated system for tracking network
health over time, graphing it, etc. Part of this project would involve
inventing better metrics for assessing network health and growth. Is the
average uptime of the network increasing? How many relays are qualifying
for Guard status this month compared to last month? What's the turnover
in terms of new relays showing up and relays shutting off? Periodically
people collect brief snapshots, but where it gets really interesting is
when we start tracking data points over time.
 
Data could be collected from the Tor Network Scanners in <a
href="https://svn.torproject.org/svn/torflow/trunk/README">TorFlow</a>, from
the server descriptors that each relay publishes, and from other
sources. Results over time could be integrated into one of the <a
href="https://torstatus.blutmagie.de/">Tor Status</a> web pages, or be
kept separate. Speaking of the Tor Status pages, take a look at Roger's
<a href="http://archives.seul.org/or/talk/Jan-2008/msg00300.html">Tor
Status wish list</a>.
</li>

<li>
Improving Tor's ability to resist censorship
 
Priority: Medium to High
 
Effort Level: Medium
 
Skill Level: High
 
Likely Mentors: Nick, Roger, Steven
 
The Tor 0.2.1.x series makes <a
href="<gitblob>doc/design-paper/blocking.html">significant
improvements</a> in resisting national and organizational censorship.
But Tor still needs better mechanisms for some parts of its
anti-censorship design. For example, current Tors can only listen on a
single address/port combination at a time. There's
<a href="<gitblob>doc/spec/proposals/118-multiple-orports.txt">a
proposal to address this limitation</a> and allow clients to connect
to any given Tor on multiple addresses and ports, but it needs more
work.
 
Another area that needs work is our <a
href="http://gitweb.torproject.org//bridgedb.git?a=tree">bridgedb</a>
service. See e.g. <a
href="http://archives.seul.org/or/dev/Dec-2009/msg00000.html">Roger's
or-dev post</a> from December for details &mdash; lots of design work
remains.
 
This project involves a lot of research and design. One of the big
challenges will be identifying and crafting approaches that can still
resist an adversary even after the adversary knows the design, and
then trading off censorship resistance with usability and robustness.
</li>

<li>
Improving Polipo on Windows
 
Priority: Medium to High
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Chris
 
Help port <a
href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo</a> to
Windows. Example topics to tackle include:
<ol><li> the ability to asynchronously query name servers, find the
system nameservers, and manage netbios and dns queries.</li>
<li> manage events and buffers natively (i.e. in Unix-like OSes,
Polipo defaults to 25% of ram, in Windows it's whatever the config
specifies).</li>
<li> some sort of GUI config and reporting tool, bonus if it has a
systray icon with right clickable menu options. Double bonus if it's
cross-platform compatible.</li>
<li> allow the software to use the Windows Registry and handle proper
Windows directory locations, such as "C:\Program Files\Polipo"</li>
</ol>
</li>

<li>
Tor Controller Status Event Interface for Vidalia
 
Priority: Medium
 
Effort Level: Medium
 
Skill Level: Low to Medium
 
Likely Mentors: Matt
 
There are a number of status changes inside Tor of which the user may need
to be informed. For example, if the user is trying to set up his Tor as a
relay and Tor decides that its ports are not reachable from outside
the user's network, we should alert the user. Currently, all the user
gets is a couple log messages in Vidalia's 'message log' window, which they
likely never see since they don't receive a notification that something
has gone wrong. Even if the user does actually look at the message log,
most of the messages make little sense to the novice user.
 
Tor has the ability to inform Vidalia of many such status changes, and
we recently implemented support for a couple of these events. Still,
there are many more status events the user should be informed of and we
need a better UI for actually displaying them to the user.
 
The goal of this project then is to design and implement a UI for
displaying Tor status events to the user. For example, we might put a
little badge on Vidalia's tray icon that alerts the user to new status
events they should look at. Double-clicking the icon could bring up a
dialog that summarizes recent status events in simple terms and maybe
suggests a remedy for any negative events if they can be corrected by
the user. Of course, this is just an example and one is free to
suggest another approach.
 
A person undertaking this project should have good UI design and layout
and some C++ development experience. Previous experience with Qt and
Qt's Designer will be very helpful, but are not required. Some
English writing ability will also be useful, since this project will
likely involve writing small amounts of help documentation that should
be understandable by non-technical users. Bonus points for some graphic
design/Photoshop fu, since we might want/need some shiny new icons too.
</li>

<li>
Improve our unit testing process
 
Priority: Medium
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Nick, Erinn
 
Tor needs to be far more tested. This is a multi-part effort. To start
with, our unit test coverage should rise substantially, especially in
the areas outside the utility functions. This will require significant
refactoring of some parts of Tor, in order to dissociate as much logic
as possible from globals.
 
Additionally, we need to automate our performance testing. We've got
buildbot to automate our regular integration and compile testing already
(though we need somebody to set it up on Windows),
but we need to get our network simulation tests (as built in <a
href="https://svn.torproject.org/svn/torflow/trunk/README">TorFlow</a>)
updated for more recent versions of Tor, and designed to launch a test
network either on a single machine, or across several, so we can test
changes in performance on machines in different roles automatically.
</li>

<li>
Help with independent Tor client implementations
 
Priority: Medium
 
Effort Level: High
 
Skill Level: Medium to High
 
Likely Mentors: Bruce, Nathan
 
Others are currently working on Tor clients for Java, Android, and Maemo
environments. The first step is to get a handle on the current state of
the project in which you are interested in helping; <a
href="http://github.com/brl/JTor">Tor for Java</a>,
<a href="https://svn.torproject.org/svn/projects/android/trunk/">Android/Orbot</a>
, or Tor for Maemo. Check out the repository and familiarlize yourself
with the source code. Further, support for requesting or even providing
Tor hidden services would be neat, but not required.
 
A prospective developer should be able to understand and write new Java
code, including a Java cryptography API. Being able to read C code would be helpful,
too. One should be willing to read the existing documentation,
implement code based on it, and refine the documentation
when things are underdocumented. This project is mostly about coding and
to a small degree about design.
</li>

<li>
Simulator for slow Internet connections
 
Priority: Medium
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Steven
 
Many users of Tor have poor-quality Internet connections, giving low
bandwidth, high latency, and high packet loss/re-ordering. User
experience is that Tor reacts badly to these conditions, but it is
difficult to improve the situation without being able to repeat the
problems in the lab.
 
This project would be to build a simulation environment which
replicates the poor connectivity so that the effect on Tor performance
can be measured. Other components would be a testing utility to
establish what are the properties of connections available, and to
measure the effect of performance-improving modifications to Tor.
 
The tools used would be up to the student, but dummynet (for FreeBSD)
and nistnet (for Linux) are two potential components on which this
project could be built. Students should be experienced with network
programming/debugging and TCP/IP, and preferably familiar with C and a
scripting language.
</li>

<li>
An Improved and More Usable Network Map in Vidalia
 
Priority: Low to Medium
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Matt
 
One of Vidalia's existing features is a network map that shows the user
the approximate geographic location of relays in the Tor network and
plots the paths the user's traffic takes as it is tunneled through the
Tor network. The map is currently not very interactive and has rather
poor graphics. Instead, we implemented KDE's Marble widget such
that it gives us a better quality map and enables improved interactivity,
such as allowing the user to click on individual relays or circuits to
display additional information. We want to add the ability
for users to click on a particular relay or a country containing one or
more Tor exit relays and say, "I want my connections to exit
from here."
 
This project will first involve getting familiar with Vidalia
and the Marble widget's API. One will then integrate the widget
into Vidalia and customize Marble to be better suited for our application,
such as making circuits clickable, storing cached map data in Vidalia's
own data directory, and customizing some of the widget's dialogs.
 
A person undertaking this project should have good C++ development
experience. Previous experience with Qt and CMake is helpful, but not
required.
</li>

<li>
Torbutton equivalent for Thunderbird
 
Priority: Medium
 
Effort Level: High
 
Skill Level: High
 
Likely Mentors: Mike
 
We're hearing from an increasing number of users that they want to use
Thunderbird with Tor. However, there are plenty of application-level
concerns, for example, by default Thunderbird will put your hostname in
the outgoing mail that it sends. At some point we should start a new
push to build a Thunderbird extension similar to Torbutton.
</li>

<li>
Improve Tor Weather
 
Priority: Medium
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Christian, Roger
 
<a href="https://weather.torproject.org/">Tor weather</a> is a tool
that allows signing up to receive notifications via email when the
tracked Tor relay is down. Currently, it isn't really useful for
people who use the hibernation feature of Tor, or for those who
have to shut down their relay regularly. During the project, Tor
weather could be extended to allow more flexible configurations.
Other enhancements are also possible: Weather could send out warnings
when your relay runs an out-of-date version of Tor, or when its
observed bandwith drops below a certain value. It might also be a
nice tool that allows for checking whether your relay has earned
you a <a href="<page tshirt>">T-Shirt</a>, or sending reminders to
directory authorities that
their keys are about to expire. Be creative, and consider how the
above project to track overall network status can help you get your job
done more quickly! See also its
<a href="https://svn.torproject.org/svn/weather/trunk/README">README</a>
and <a href="https://svn.torproject.org/svn/weather/trunk/TODO">TODO</a>.
</li>

<li>
Better Debian/Ubuntu Packaging for Tor+Vidalia
 
Priority: Medium
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Erinn, Peter
 
Vidalia currently doesn't play nicely on Debian and Ubuntu with the
default Tor packages. The current Tor packages automatically start Tor
as a daemon running as the debian-tor user and (sensibly) do not have a
<a href="<gitblob>doc/spec/control-spec.txt">ControlPort</a> defined
in the default torrc. Consequently, Vidalia will try
to start its own Tor process since it could not connect to the existing
Tor, and Vidalia's Tor process will then exit with an error message
the user likely doesn't understand since Tor cannot bind its listening
ports &mdash; they're already in use by the original Tor daemon.
 
The current solution involves either telling the user to stop the
existing Tor daemon and let Vidalia start its own Tor process, or
explaining to the user how to set a control port and password in their
torrc. A better solution on Debian would be to use Tor's ControlSocket,
which allows Vidalia to talk to Tor via a Unix domain socket, and could
possibly be enabled by default in Tor's Debian packages. Vidalia can
then authenticate to Tor using filesystem-based (cookie) authentication
if the user running Vidalia is also in the debian-tor group.
 
This project will first involve adding support for Tor's ControlSocket
to Vidalia. The student will then develop and test Debian and Ubuntu
packages for Vidalia that conform to Debian's packaging standards and
make sure they work well with the existing Tor packages. We can also
set up an apt repository to host the new Vidalia packages.
 
The next challenge would be to find an intuitive usable way for Vidalia
to be able to change Tor's configuration (torrc) even though it is
located in <code>/etc/tor/torrc</code> and thus immutable. The best
idea we've come up with so far is to feed Tor a new configuration via
the ControlSocket when Vidalia starts, but that's bad because Tor starts
each boot with a different configuration than the user wants. The second
best idea
we've come up with is for Vidalia to write out a temporary torrc file
and ask the user to manually move it to <code>/etc/tor/torrc</code>,
but that's bad because users shouldn't have to mess with files directly.
 
A person undertaking this project should have prior knowledge of
Debian package management and some C++ development experience. Previous
experience with Qt is helpful, but not required.
</li>

<li>
Improving the Tor QA process: Continuous Integration for builds
 
Priority: Medium
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: Erinn
 
It would be useful to have automated build processes for Windows and
probably other platforms. The purpose of having a continuous integration
build environment is to ensure that Windows isn't left behind for any of
the software projects used in the Tor project or its accompanying. 
Buildbot may be a good choice for this as it appears to support all of
the platforms Tor does. See the
<a href="http://en.wikipedia.org/wiki/BuildBot">wikipedia entry for
buildbot</a>. 
There may be better options and the person undertaking this task should
evaluate other options. Any person working on this automatic build
process should have experience or be willing to learn how to build all
of the respective Tor related code bases from scratch. Furthermore, the
person should have some experience building software in Windows
environments as this is the target audience we want to ensure we do not
leave behind. It would require close work with the Tor source code but
probably only in the form of building, not authoring. 
Additionally, we need to automate our performance testing for all platforms.
We've got buildbot (except on Windows &mdash; as noted above) to automate
our regular integration and compile testing already,
but we need to get our network simulation tests (as built in torflow)
updated for more recent versions of Tor, and designed to launch a test
network either on a single machine, or across several, so we can test
changes in performance on machines in different roles automatically.
</li>

<li>
An authenticating IRC proxy
 
Priority: Medium
 
Effort Level: Medium to High
 
Skill Level: Medium to High
 
Likely Mentors: Sebastian, Weasel, Roger
 
The world needs an authenticating irc proxy. As we're periodically
reminded from the Penny Arcade web comic, "Internet user + anonymity =
jerk". With respect to websites we're actually doing ok, since websites
can make their users log in and use other application-level authentication
approaches. But IRC servers are much worse off, because most IRC server
code is poorly written: hard to maintain, and harder to modify. Many
IRC networks now block connections from Tor, and we're basically down to
two holdouts (OFTC and Freenode). This state of affairs means that a lot
of people around the world are thinking "I told you so" about anonymity
online, when in fact the problem is simply lack of technology to make the
problem manageable. We need some way to let the IRC networks distinguish
which users have developed a reputation as not being jerks, so they can
treat the two groups separately. There are some really cool research
designs like <a href="http://www.cs.dartmouth.edu/~nymble/">Nymble</a>,
which aim to let websites blacklist users without needing to learn who
they are. But Nymble is designed around web interactions. We need to
build the glue around the IRC protocol that would let us plug in a project
like Nymble (or a simpler one to start, as a proof-of-concept). One way
to do that would be to build an IRC proxy that knows how to hear from
IRC clients, knows how to talk to IRC servers, and has an additional
layer that requires the users to authenticate.
</li>

<li>
Make torsocks/dsocks work on OS X
 
Priority: Medium
 
Effort Level: Medium
 
Skill Level: Medium
 
Likely Mentors: ?
 
<a href="http://code.google.com/p/torsocks/">Torsocks</a> and <a
href="http://code.google.com/p/dsocks/">dsocks</a> are wrappers that will
run applications, intercept their outgoing network connections, and push
those connections through Tor. The goal is to handle applications that
don't support proxies (or don't supporting them well). To get it right,
they need to intercept many system calls. The syscalls you need to
intercept on Linux differ dramatically from those on BSD. So Torsocks
works fine on Linux, dsocks works ok on BSD (though it may be less
maintained and thus might miss more syscalls), and nothing works well
on both. First, we should patch dsocks to use Tor's mapaddress
commands from the controller interface, so we don't waste a whole
round-trip inside Tor doing the resolve before connecting. Second,
we should make our torify script detect which of torsocks or
dsocks is installed, and call them appropriately. This probably means
unifying their interfaces, and might involve sharing code between them
or discarding one entirely.
</li>

<li>
Bring up new ideas!
 
Don't like any of these? Look at the <a
href="<gitblob>doc/roadmaps/2008-12-19-roadmap-full.pdf">Tor development
roadmap</a> for more ideas, or just try out Tor, Vidalia, and Torbutton,
and find out what you think needs fixing.
Some of the <a href="<gittree>doc/spec/proposals">current proposals</a>
might also be short on developers.
</li>

</ol>

<a id="OtherCoding"></a>
<h2><a class="anchor" href="#OtherCoding">Other Coding and Design related ideas</a></h2>
<ol>
<li>Tor relays don't work well on Windows XP. On
Windows, Tor uses the standard <tt>select()</tt> system
call, which uses space in the non-page pool. This means
that a medium sized Tor relay will empty the non-page pool, <a
href="https://wiki.torproject.org/noreply/TheOnionRouter/WindowsBufferProblems">causing
havoc and system crashes</a>. We should probably be using overlapped IO
instead. One solution would be to teach <a
href="http://www.monkey.org/~provos/libevent/">libevent</a> how to use
overlapped IO rather than select() on Windows, and then adapt Tor to
the new libevent interface. Christian King made a
<a href="https://svn.torproject.org/svn/libevent-urz/trunk/">good
start</a> on this in the summer of 2007.</li>

<li>We need to actually start building our <a href="<page
documentation>#DesignDoc">blocking-resistance design</a>. This involves
fleshing out the design, modifying many different pieces of Tor, adapting
<a href="<page vidalia/index>">Vidalia</a> so it supports the
new features, and planning for deployment.</li>

<li>We need a flexible simulator framework for studying end-to-end
traffic confirmation attacks. Many researchers have whipped up ad hoc
simulators to support their intuition either that the attacks work
really well or that some defense works great. Can we build a simulator
that's clearly documented and open enough that everybody knows it's
giving a reasonable answer? This will spur a lot of new research.
See the entry <a href="#Research">below</a> on confirmation attacks for
details on the research side of this task &mdash; who knows, when it's
done maybe you can help write a paper or three also.</li>

<li>Tor 0.1.1.x and later include support for hardware crypto accelerators
via OpenSSL. It has been lightly tested and is possibly very buggy. We're looking for more rigorous testing, performance analysis, and optimally, code fixes to openssl and Tor if needed.</li>

<li>Perform a security analysis of Tor with <a
href="http://en.wikipedia.org/wiki/Fuzz_testing">"fuzz"</a>. Determine
if there are good fuzzing libraries out there for what we want. Win fame by
getting credit when we put out a new release because of you!</li>

<li>Tor uses TCP for transport and TLS for link
encryption. This is nice and simple, but it means all cells
on a link are delayed when a single packet gets dropped, and
it means we can only reasonably support TCP streams. We have a <a
href="https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#TransportIPnotTCP">list
of reasons why we haven't shifted to UDP transport</a>, but it would
be great to see that list get shorter. We also have a proposed <a
href="<gitblob>doc/spec/proposals/100-tor-spec-udp.txt">specification
for Tor and
UDP</a> &mdash; please let us know what's wrong with it.</li>

<li>We're not that far from having IPv6 support for destination addresses
(at exit nodes). If you care strongly about IPv6, that's probably the
first place to start.</li>

<li>We need a way to generate the website diagrams (for example, the "How
Tor Works" pictures on the <a href="<page overview>">overview page</a>
from source, so we can translate them as UTF-8 text rather than edit
them by hand with Gimp. We might want to
integrate this as an wml file so translations are easy and images are
generated in multiple languages whenever we build the website.</li>

<li>How can we make the various LiveCD/USB systems easier
to maintain, improve, and document? Some examples are <a
href="http://amnesia.boum.org/">amnesia LiveCD/USB</a> and the <a
href="http://anonymityanywhere.com/incognito/">Incognito LiveCD</a>
</li>

<li>
Another anti-censorship project is to try to make Tor
more scanning-resistant. Right now, an adversary can identify <a
href="<gitblob>doc/spec/proposals/125-bridges.txt">Tor bridges</a>
just by trying to connect to them, following the Tor protocol,
and seeing if they respond. To solve this, bridges could <a
href="<gitblob>doc/design-paper/blocking.html#tth_sEc9.3">act like
webservers</a> (HTTP or HTTPS) when contacted by port-scanning tools,
and not act like bridges until the user provides a bridge-specific key.
To start, check out Shane Pope's <a
href="http://dl.dropbox.com/u/37735/index.html">thesis and prototype</a>.
</li>

</ol>

<a id="Research"></a>
<h2><a class="anchor" href="#Research">Research</a></h2>
<ol>
<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 codebase? 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>
<li>The "end-to-end traffic confirmation attack":
by watching traffic at Alice and at Bob, we can <a
href="http://freehaven.net/anonbib/#danezis:pet2004">compare
traffic signatures and become convinced that we're watching the same
stream</a>. So far Tor accepts this as a fact of life and assumes this
attack is trivial in all cases. First of all, is that actually true? How
much traffic of what sort of distribution is needed before the adversary
is confident he has won? Are there scenarios (e.g. not transmitting much)
that slow down the attack? Do some traffic padding or traffic shaping
schemes work better than others?</li>
<li>A related question is: Does running a relay/bridge provide additional
protection against these timing attacks? Can an external adversary that can't
see inside TLS links still recognize individual streams reliably?
Does the amount of traffic carried degrade this ability any? What if the
client-relay deliberately delayed upstream relayed traffic to create a queue
that could be used to mimic timings of client downstream traffic to make it
look like it was also relayed? This same queue could also be used for masking
timings in client upstream traffic with the techniques from <a
href="http://www.freehaven.net/anonbib/#ShWa-Timing06">adaptive padding</a>,
but without the need for additional traffic. Would such an interleaving of
client upstream traffic obscure timings for external adversaries? Would the
strategies need to be adjusted for asymmetric links? For example, on
asymmetric links, is it actually possible to differentiate client traffic from
natural bursts due to their asymmetric capacity? Or is it easier than
symmetric links for some other reason?</li>
<li>Repeat Murdoch and Danezis's <a
href="http://www.cl.cam.ac.uk/~sjm217/projects/anon/#torta">attack from
Oakland 05</a> on the current Tor network. See if you can learn why it
works well on some nodes and not well on others. (My theory is that the
fast nodes with spare capacity resist the attack better.) If that's true,
then experiment with the RelayBandwidthRate and RelayBandwidthBurst
options to run a relay that is used as a client while relaying the
attacker's traffic: as we crank down the RelayBandwidthRate, does the
attack get harder? What's the right ratio of RelayBandwidthRate to
actually capacity? Or is it a ratio at all? While we're at it, does a
much larger set of candidate relays increase the false positive rate
or other complexity for the attack? (The Tor network is now almost two
orders of magnitude larger than it was when they wrote their paper.) Be
sure to read <a href="http://freehaven.net/anonbib/#clog-the-queue">Don't
Clog the Queue</a> too.</li>
<li>The "routing zones attack": most of the literature thinks of
the network path between Alice and her entry node (and between the
exit node and Bob) as a single link on some graph. In practice,
though, the path traverses many autonomous systems (ASes), and <a
href="http://freehaven.net/anonbib/#feamster:wpes2004">it's not uncommon
that the same AS appears on both the entry path and the exit path</a>.
Unfortunately, to accurately predict whether a given Alice, entry,
exit, Bob quad will be dangerous, we need to download an entire Internet
routing zone and perform expensive operations on it. Are there practical
approximations, such as avoiding IP addresses in the same /8 network?</li>
<li>Other research questions regarding geographic diversity consider
the tradeoff between choosing an efficient circuit and choosing a random
circuit. Look at Stephen Rollyson's <a
href="http://swiki.cc.gatech.edu:8080/ugResearch/uploads/7/ImprovingTor.pdf">position
paper</a> on how to discard particularly slow choices without hurting
anonymity "too much". This line of reasoning needs more work and more
thinking, but it looks very promising.</li>
<li>Tor doesn't work very well when relays have asymmetric bandwidth
(e.g. cable or DSL). Because Tor has separate TCP connections between
each hop, if the incoming bytes are arriving just fine and the outgoing
bytes are all getting dropped on the floor, the TCP push-back mechanisms
don't really transmit this information back to the incoming streams.
Perhaps Tor should detect when it's dropping a lot of outgoing packets,
and rate-limit incoming streams to regulate this itself? I can imagine
a build-up and drop-off scheme where we pick a conservative rate-limit,
slowly increase it until we get lost packets, back off, repeat. We
need somebody who's good with networks to simulate this and help design
solutions; and/or we need to understand the extent of the performance
degradation, and use this as motivation to reconsider UDP transport.</li>
<li>A related topic is congestion control. Is our
current design sufficient once we have heavy use? Maybe
we should experiment with variable-sized windows rather
than fixed-size windows? That seemed to go well in an <a
href="http://www.psc.edu/networking/projects/hpn-ssh/theory.php">ssh
throughput experiment</a>. We'll need to measure and tweak, and maybe
overhaul if the results are good.</li>
<li>Our censorship-resistance goals include preventing
an attacker who's looking at Tor traffic on the wire from <a
href="<gitblob>doc/design-paper/blocking.html#sec:network-fingerprint">distinguishing
it from normal SSL traffic</a>. Obviously we can't achieve perfect
steganography and still remain usable, but for a first step we'd like to
block any attacks that can win by observing only a few packets. One of
the remaining attacks we haven't examined much is that Tor cells are 512
bytes, so the traffic on the wire may well be a multiple of 512 bytes.
How much does the batching and overhead in TLS records blur this on the
wire? Do different buffer flushing strategies in Tor affect this? Could
a bit of padding help a lot, or is this an attack we must accept?</li>
<li>Tor circuits are built one hop at a time, so in theory we have the
ability to make some streams exit from the second hop, some from the
third, and so on. This seems nice because it breaks up the set of exiting
streams that a given relay can see. But if we want each stream to be safe,
the "shortest" path should be at least 3 hops long by our current logic, so
the rest will be even longer. We need to examine this performance / security
tradeoff.</li>
<li>It's not that hard to DoS Tor relays or directory authorities. Are client
puzzles the right answer? What other practical approaches are there? Bonus
if they're backward-compatible with the current Tor protocol.</li>
<li>Programs like <a
href="<page torbutton/index>">Torbutton</a> aim to hide
your browser's UserAgent string by replacing it with a uniform answer for
every Tor user. That way the attacker can't splinter Tor's anonymity set
by looking at that header. It tries to pick a string that is commonly used
by non-Tor users too, so it doesn't stand out. Question one: how badly
do we hurt ourselves by periodically updating the version of Firefox
that Torbutton claims to be? If we update it too often, we splinter the
anonymity sets ourselves. If we don't update it often enough, then all the
Tor users stand out because they claim to be running a quite old version
of Firefox. The answer here probably depends on the Firefox versions seen
in the wild. Question two: periodically people ask us to cycle through N
UserAgent strings rather than stick with one. Does this approach help,
hurt, or not matter? Consider: cookies and recognizing Torbutton users
by their rotating UserAgents; malicious websites who only attack certain
browsers; and whether the answers to question one impact this answer.
</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 extend operations, 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 connections typical
clients try to launch, so you have something realistic to try to optimize.
</li>
<li>How many bridge relays do you need to know to maintain
reachability? We should measure the churn in our bridges. If there is
lots of churn, are there ways to keep bridge users more likely to stay
connected?
</li>
</ol>

<a href="<page contact>">Let us know</a> if you've made progress on any
of these!

</div>

#include <foot.wmi>

tor-webwml.git

some more cleanups on the ideas list