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volunteer.wml

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# Revision: $Revision$

#include "head.wmi" TITLE="Tor: Volunteer"

<h2>Three 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>We are looking for funding and sponsors. If you like Tor's goals, please
 <a href="<page donate>">take a moment to donate to support further
 Tor development</a>. Also, if you know any
 companies, NGOs, agencies, or other organizations that want communications
 security, let them know about us.</li>
</ol>

<a id="Usability"></a>
<h2><a class="anchor" href="#Usability">Supporting Applications</a></h2>
<ol>
<li>We need good 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>Tor can <a
href="https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#ChooseEntryExit">exit
the Tor network from a particular exit node</a>, but we should be able
to specify just a country and have something automatically pick. The
best bet is to fetch Blossom's directory also, and run a local Blossom
client that fetches this directory securely (via Tor and checking its
signature), intercepts <tt>.country.blossom</tt> hostnames, and does
the right thing.</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>
<ol>

<li>
Tor/Polipo/Vidalia Auto-Update Framework
 
Priority: High
 
Effort Level: High
 
Likely Mentors: Matt, others
 
Vidalia already has the ability to notice when the user is running an
outdated or unrecommended version of Tor. Currently, Vidalia simply pops
up a little message box that lets the user know they should manually
upgrade. The goal of this project would be to extend Vidalia with the
ability to also fetch and install the updated Tor software for the
user. Time permitting, we would also like to be able to update other
applications included in the bundled installers, such as Polipo and
Vidalia itself.
 
To complete this project, the student will first need to first investigate
the existing auto-update frameworks (e.g., Sparkle on OS X) to evaluate
their strengths, weaknesses, security properties, and ability to be
integrated into Vidalia. If none are found to be suitable, the student
will design their own auto-update framework, document the design, and
then discuss the design with other developers to assess any security
issues. The student will then implement their framework (or integrate
an existing one) and test it.
 
A student undertaking this project should have good C++ development
experience. Previous experience with Qt is helpful, but not required. The
student should also have a basic understanding of common security
practices, such as package signature verification. Good writing ability
is also important for this project, since a vital step of the project
will be producing a design document for others to review and discuss
with the student prior to implementation.
</li>

<li>
An Improved and More Usable Network Map
 
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 would like to leverage KDE's Marble widget
that 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 might also consider adding 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 foo.com to exit
from here.''
 
This project will first involve the student getting familiar with Vidalia
and the Marble widget's API. The student 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 student undertaking this project should have good C++ development
experience. Previous experience with Qt and CMake is helpful, but not
required.
</li>

<li>
Better Debian Packaging and Debian Packaging Support
 
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
CntrolPort 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 then Vidalia's Tor process will then exit with an error message
the user likely doesn't understand since Tor cannot bind its listening
ports--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 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
making sure it works well with the existing Tor packages. We can also
set up an apt repository to host the new Vidalia packages.
 
A student 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>
Tor Status Event Interface
 
There may are a number of status changes of which the user may need
to be informed. For example, if the user is trying to set up a Tor
relay and Tor decides the user's relay is 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', 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 statuses if they can be corrected by
the user. Of course, this is just an example and the student is free to
suggest another approach.
 
A student undertaking this project should have good UI design and layout
experience and some C++ development experience. Previous experience
with Qt and Qt's Designer will be very helpful, but 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>
A Translation Wiki
 
We require a way to edit and translate sections of the website &mdash;
possibly resulting in a patch for the official svn tree. The current
"cost" of publication of website changes is quite high even for English
language users. They need to check out our template files, translate them
and send us the translation. For a single word change or any type of
minor change, the page may never be corrected or translated. It would
be nice to have a wiki that was specifically geared towards translation
and would somehow track the upstream (English) versions to indicate when
a fresh translation is needed. This seems mostly like a job for a wiki
integrator or wiki software author. Certainly the person would need to
be interested in human languages and translation. They should at least
be minimally familiar with what Tor is but would not have to interact
with the software, only the documentation on the website.
</li>

<li>
Improvements on our active browser configuration tester - 
<a href="https://check.torproject.org">https://check.torproject.org</a>
 
We currently have a functional web page to detect if Tor is working. It
is has a few places where it falls short. It requires improvements with
regard to default languages and functionality. It currently only responds
in English. In addition, it is a hack of a perl script that should have
never seen the light of day. It should probably be rewritten in python
with multi-lingual support in mind. It currently uses the Tor DNS exit
list and should continue to do so in the future. It may result in certain
false positives and these should be discovered, documented, and fixed
where possible. Anyone working on this project should be interested in
DNS, basic perl or preferably python programming skills and will have
to interact minimally with Tor to test their code.
</li>

<li>
Improvements on our DNS Exit List service - 
<a href="http://exitlist.torproject.org">http://exitlist.torproject.org</a>
 
The exitlist software is written by our fabulous anonymous
contributer Tup. It's a DNS server written in Haskell that supports part of our <a
href="https://www.torproject.org/svn/trunk/doc/contrib/torel-design.txt">exitlist
design document</a>. Currently, it's functional and it is used by
check.torproject.org and other users. The issues that are outstanding
are mostly aesthetic. This wonderful service could use a much better
website using the common Tor theme. It would be best served with better
documentation for common services that use an RBL. It could use more
publicity. A person working on this project should be interested in DNS,
basic RBL configuration for popular services, and writing documentation.
The person would require minimal Tor interaction &mdash; testing their
own documentation at the very least. Furthermore, it would be useful
if they were interested in Haskell and wanted to implement more of the
torel-design.txt suggestions.
</li>

<li>
Testing integration of Tor with web browsers for our end users
 
The Tor project currently lacks a solid test to ensure that a
user has a properly configured web browser. It should test for as
many known issues as possible. It should attempt to decloak the
user in any way possible. Two current webpages that track these
kinds of issues are run by Greg and HD Moore. Greg keeps a nice <a
href="http://pseudo-flaw.net/tor/torbutton/">list of issues along
with their proof of concept code, bug issues, etc</a>. HD Moore runs
the <a href="http://metasploit.com/research/misc/decloak/">metasploit
decloak website</a>. A person interested in attacking Tor could start
by collecting as many workable and known methods for decloaking a
Tor user. The person should be familiar with the common pitfalls but
possibly have new methods in mind for implementing decloaking issues. The
website should ensure that it tells a user what their problem is. It
should help them to fix the problem or direct them to the proper support
channels. The person should be closely familiar with using Tor and how
to prevent Tor leakage.
</li>

<li>
Improving our ability to be resistant to censorship
 
Tor needs even better censorship resistance mechanisms. There are
several mechanisms that can help. Tor should be able listen on multiple
addresses and ports, and allow clients to connect to all of them.
Tor should be able to appear like a webserver (HTTP or HTTPS) when
contacted by port-scanning tools.
</li>

<li>
Libevent and Tor integration improvements
 
Tor should make better use of the more recent features of Niels Provos's
Libevent library. Libevent already provides HTTP and socket buffers;
Tor's code for those could be replaced. We'll need to improve libevent's
code as needed; particularly, to add good openssl support on top of
libevent's buffer abstraction.
</li>

<li>
Tuneup Tor!
 
Tor should possibly measure bandwidth in a distributed way, as in the
<a href="http://freehaven.net/anonbib/">"A Tuneup for Tor"</a> paper
by Snader and Borisov. A student could use current testing code to
double-check this paper's findings and verify the extent to which they
dovetail with Tor in the wild, and determine good ways to incorporate them
into the Tor network without adding undesirable n^2 traffic properties
at the directory authorities.
</li>

<li>
Improving the Tor QA process: Continuous Integration for Windows builds
 
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>
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 (except on Windows &mdash; see 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>
Help revive the Java community around Tor
 
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. The
student 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. The student should be willing to read the existing documentation,
implement code based on it, and, if required, refine the documentation
if things are underdocumented. This project is mostly about coding and
to a small degree about design.
</li>

<li>
Become the PuppeTor Master
 
Write a tool that runs automatic system tests in addition
to the existing unit tests. The Java-based Tor simulator <a
href="https://tor-svn.freehaven.net/svn/puppetor/trunk/">PuppeTor</a>
might be a good start for starting up a private Tor network, using it
for a while, and verifying that at least parts of it are working. This
project requires to conceive a blueprint for performing system tests
of private Tor networks, before starting to code. Typical types of
tests range from performing single requests over the private network to
manipulating exchanged messages and see if nodes handle corrupt messages
appropriately. The student should be able to obtain a good understanding
of how Tor works and what problems and bugs could arise to design good
test cases. Understanding the existing Tor code and documentation is
vital. If PuppeTor is used, the student should also be able to understand
and possibly extend an existing Java application. This project is partly
about design and partly about coding.
</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. The student 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 for the one part about identifying requirements to such a
tool and designing its interface; but on the other part, the project
also requires a lot of coding.
</li>

<li>
TorFlow improvements
 
Help Mike Perry on his <a
href="https://www.torproject.org/svn/torflow/">TorFlow</a>
library (<a href="https://www.torproject.org/svn/torflow/TODO">TODO</a>):
it's a python library that uses the <a
href="https://www.torproject.org/svn/torctl/doc/howto.txt">Tor controller
protocol</a> to instruct Tor to build circuits in a variety of ways,
and then it measures performance and tries to detect anomalies.
Help detect bad relays and automatically get that
info to the directory authorities for realtime blacklisting.

<li>
Help track the overall Tor Network status
Torstatus. Set up an automated system for tracking network health
over time, graphing it, etc. Better metrics for assessing network
health and growth. Make it short and simple. Unbloated and easy to audit.
</li>

<li>vidalia and upnp</li>
<li>nymble</li>

<li>
Porting Polipo to Windows
 
Help port <a
href="http://www.pps.jussieu.fr/~jch/software/polipo/">Polipo</a> to
Windows. 1) handle spaces in path names and understand the filesystem
namespace &mdash; namespace meaning 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>

<li>
Make our diagrams beautiful and automated
 
a way to generate the website diagrams from source, so we can translate
them as utf-8 text rather than with gimp. (svg? or imagemagick?)
integrate this with a wml file so translations are easy and images are
generated in multiple languages at web publish
</li>

<li>
Improve the LiveCD offerings for the Tor community
 
How can we make the <a
href="http://anonymityanywhere.com/incognito/">Incognito LiveCD</a>
easier to maintain, improve, and document?</li>
<li>We need a distributed testing framework. We have unit tests,
but it would be great to have a script that starts up a Tor network, uses
it for a while, and verifies that at least parts of it are working.</li>

<li>
Bring up new ideas!
 
Don't like any of these? Look at the <a
href="<svnsandbox>doc/design-paper/roadmap-future.pdf">Tor development
roadmap</a> for more ideas. 
Don't see your idea here? We probably need it anyway! Contact
us and find out.</li>
</ol>

<h2><a class="anchor" href="#Coding">Coding and Design</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://tor-svn.freehaven.net/svn/libevent-urz/trunk/">good
start</a> on this last summer.</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>
</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>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>To let dissidents in remote countries use Tor without being blocked
at their country's firewall, we need a way to get tens of thousands of
relays, not just a few hundred. We can imagine a Tor client GUI that
has a "Tor for Freedom" button at the top that opens a port and relays a
few KB/s of traffic into the Tor network. (A few KB/s shouldn't be too
much hassle, and there are few abuse issues since they're not being exit
nodes.) But how do we distribute a list of these volunteer clients to the
good dissidents in an automated way that doesn't let the country-level
firewalls intercept and enumerate them? Probably needs to work on a
human-trust level. See our <a href="<page documentation>#DesignDoc">early
blocking-resistance design document</a> and our
<a
href="https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#BlockingResistance">FAQ
entry</a> on this, and then read the <a
href="http://freehaven.net/anonbib/topic.html#Communications_20Censorship">censorship
resistance section of anonbib</a>.</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>
</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

Added a small number of improvements that will be added to each entry.