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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>

<a id="Usability"></a>
<h2><a class="anchor" href="#Usability">Supporting Applications</a></h2>
<ol>
<li>We need more and better ways to intercept DNS requests so they don't "leak" their
request to a local observer while we're trying to be anonymous. (This
happens because the application does the DNS resolve before going to
the SOCKS proxy.)</li>
<li>Tsocks/dsocks items:
<ul>
<li>We need to <a
href="https://wiki.torproject.org/noreply/TheOnionRouter/TSocksPatches">apply
all our tsocks patches</a> and maintain a new fork. We'll host it if
you want.</li>
<li>We should patch Dug Song's "dsocks" program 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.</li>
<li>We need to make our torify script detect which of tsocks 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>
</ul>
</li>
<li>People running relays tell us they want to have one BandwidthRate
during some part of the day, and a different BandwidthRate at other
parts of the day. Rather than coding this inside Tor, we should have a
little script that speaks via the <a href="<page gui/index>">Tor
Controller Interface</a>, and does a setconf to change the bandwidth
rate. There is one for Unix and Mac already (it uses bash and cron),
but Windows users still need a solution.
</li>
<li>Speaking of geolocation data, somebody should draw a map of the Earth
with a pin-point for each Tor relay. Bonus points if it updates as the
network grows and changes. Unfortunately, the easy ways to do this involve
sending all the data to Google and having them draw the map for you. How
much does this impact privacy, and do we have any other good options?</li>
</ol>

<a id="Documentation"></a>
<h2><a class="anchor" href="#Documentation">Documentation</a></h2>
<ol>
<li>Please help Matt Edman with the documentation and how-tos for his
Tor controller,
<a href="http://vidalia-project.net/">Vidalia</a>.</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 need better documentation for dynamically intercepting
connections and sending them through Tor. tsocks (Linux), dsocks (BSD),
and freecap (Windows) seem to be good candidates, as would better
use of our new TransPort feature.</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>
<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>
</ol>

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

Here is a list of ideas that are proposed for the <a href="<page gsoc>">Google Summer of Code 2009</a>
Some of the <a href="<svnsandbox>doc/spec/proposals/">current proposals</a> 
might also be short on developers. If you think you can help out, <a href="<page contact>"> let us know!</a>

<ol>

<li>
Help track the overall Tor Network status
 
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
 
The Tor 0.2.0.x series makes <a
href="<svnsandbox>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="<svnsandbox>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 anti-censorship project (far more difficult) is to try
to make Tor more scanning-resistant. Right now, an adversary can identify
<a href="<svnsandbox>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="<svnsandbox>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.
 
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>
Tor Controller Status Event Interface
 
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>
Tuneup Tor!
 
Right now, Tor relays measure and report their own bandwidth, and Tor
clients choose which relays to use in part based on that bandwidth.
This approach is vulnerable to
<a href="http://freehaven.net/anonbib/#bauer:wpes2007">attacks where
relays lie about their bandwidth</a>;
to address this, Tor currently caps the maximum bandwidth
it's willing to believe any relay provides. This is a limited fix, and
a waste of bandwidth capacity to boot. Instead,
Tor should possibly measure bandwidth in a more distributed way, perhaps
as described in the
<a href="http://freehaven.net/anonbib/author.html#snader08">"A Tune-up for
Tor"</a> paper
by Snader and Borisov. One could use current testing code to
double-check this paper's findings and verify the extent to which they
dovetail with Tor as deployed in the wild, and determine good ways to
incorporate them into their suggestions Tor network without adding too
much communications overhead between relays and directory
authorities.
</li>

<li>
Improve our unit testing process
 
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 revive an independent Tor client implementation
 
Reanimate one of the approaches to implement a Tor client in Java,
e.g. the <a href="http://onioncoffee.sourceforge.net/">OnionCoffee
project</a>, and make it run on <a
href="http://code.google.com/android/">Android</a>. The first step
would be to port the existing code and execute it in an Android
environment. Next, the code should be updated to support the newer Tor
protocol versions like the <a href="<svnsandbox>doc/spec/dir-spec.txt">v3
directory protocol</a>. 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>
Bring moniTor to life
 
Implement a <a href="http://www.ss64.com/bash/top.html">top-like</a>
management tool for Tor relays. The purpose of such a tool would be
to monitor a local Tor relay via its control port and include useful
system information of the underlying machine. When running this tool, it
would dynamically update its content like top does for Linux processes.
<a href="http://archives.seul.org/or/dev/Jan-2008/msg00005.html">This
or-dev post</a> might be a good first read.
 
A person interested in this should be familiar
with or willing to learn about administering a Tor relay and configuring
it via its control port. As an initial prototype is written in Python,
some knowledge about writing Python code would be helpful, too. This
project is one part about identifying requirements to such a
tool and designing its interface, and one part lots of coding.
</li>

<li>
Porting Polipo to Windows
 
Help port <a
href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo</a> to
Windows. Example topics to tackle include:
1) handle spaces in path names and understand the filesystem
namespace &mdash; that is, where application data, personal data,
and program data typically reside in various versions of Windows. 2) the
ability to handle ipv6 communications. 3) the ability to asynchronously
query name servers, find the system nameservers, and manage netbios
and dns queries. 4) use native regex capabilities of Windows, rather
than using 3rd party GNU regex libraries. 5) 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). 6) 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>

<!-- Is Blossom development still happening?
<li>
Rework and extend Blossom
 
Rework and extend Blossom (a tool for monitoring and
selecting appropriate Tor circuits based upon exit node requirements
specified by the user) to gather data in a self-contained way, with
parameters easily configurable by the user. Blossom is presently
implemented as a single Python script that interfaces with Tor using the
Controller interface and depends upon metadata about Tor nodes obtained
via external processes, such as a webpage indicating status of the nodes
plus publically available data from DNS, whois, etc. This project has
two parts: (1) Determine which additional metadata may be useful and
rework Blossom so that it cleanly obtains the metadata on its own rather
than depend upon external scripts (this may, for example, involve
additional threads or inter-process communication), and (2) develop a
means by which the user can easily configure Blossom, starting with a
configuration file and possibly working up to a web configuration engine.
Knowledge of Tor and Python are important; knowledge of
TCP, interprocess communication, and Perl will also be helpful. An
interest in network neutrality is important as well, since the
principles of evaluating and understanding internet inconsistency are at
the core of the Blossom effort.
</li>

<li>
Improve Blossom: Allow users to qualitatively describe exit nodes they desire
 
Develop and implement a means of affording Blossom
users the ability to qualitatively describe the exit node that they
want. The Internet is an inconsistent place: some Tor exit nodes see
the world differently than others. As presently implemented, Blossom (a
tool for monitoring and selecting appropriate Tor circuits based upon
exit node requirements specified by the user) lacks a sufficiently rich
language to describe how the different vantage points are different.
For example, some exit nodes may have an upstream network that filters
certain kinds of traffic or certain websites. Other exit nodes may
provide access to special content as a result of their location, perhaps
as a result of discrimination on the part of the content providers
themselves. This project has two parts: (1) develop a language for
describing characteristics of networks in which exit nodes reside, and
(2) incorporate this language into Blossom so that users can select Tor
paths based upon the description.
Knowledge of Tor and Python are important; knowledge of
TCP, interprocess communication, and Perl will also be helpful. An
interest in network neutrality is important as well, since the
principles of evaluating and understanding internet inconsistency are at
the core of the Blossom effort.
</li>
-->

<li>
Implement a torrent-based scheme for downloading Thandy packages
 
<a
href="http://git.torproject.org/checkout/thandy/master/specs/thandy-spec.txt">Thandy</a>
is a relatively new software to allow automatic updates of Tor and related
software. Currently, there are very few users, but we expect Thandy to be
used by almost every Tor user in the future. To avoid crashing servers on
the day of a Tor update, we need new ways to distribute new packages
efficiently, and using libtorrent seems to be a possible solution. If you
think of other good ideas, great - please do let us know! 
We also need to investigate how to include our mirrors better. If possible,
there should be an easy way for them to help distributing the packages.
</li>

<li>
Torbutton equivalent for Thunderbird
 
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>
New Torbutton Features
 
There are several <a
href="https://bugs.torproject.org/flyspray/index.php?tasks=all&project=5&type=2">good
feature requests</a> on the Torbutton Flyspray section. In particular, <a
href="https://bugs.torproject.org/flyspray/index.php?do=details&id=523">Integrating
'New Identity' with Vidalia</a>, 
<a href="https://bugs.torproject.org/flyspray/index.php?do=details&id=940">ways of
managing multiple cookie jars/identities</a>, <a
href="https://bugs.torproject.org/flyspray/index.php?do=details&id=637">preserving
specific cookies</a> when
cookies are cleared, 
<a
href="https://bugs.torproject.org/flyspray/index.php?do=details&id=524">better
referrer spoofing</a>, <a
href="https://bugs.torproject.org/flyspray/index.php?do=details&id=564">correct
Tor status reporting</a>, and <a
href="https://bugs.torproject.org/flyspray/index.php?do=details&id=462">"tor://"
and "tors://" urls</a> are all interesting
features that could be added.
 
This work would be independent coding in Javascript and the fun world of <a
href="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">XUL</a>,
with not too much involvement in the Tor internals.
</li>

<li>
Usability testing of Tor
 
Especially the 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>
Bring up new ideas!
 
Don't like any of these? Look at the <a
href="<svnsandbox>doc/roadmaps/2008-12-19-roadmap-full.pdf">Tor development
roadmap</a> for more ideas.
</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="http://vidalia-project.net/">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. Nobody has ever tested it, though. Does somebody want to get
a card and let us know how it goes?</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="<svnsandbox>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 <a
href="http://anonymityanywhere.com/incognito/">Incognito LiveCD</a>
easier to maintain, improve, and document?</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="<svnsandbox>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

Add new torbutton features section to volunteer page.