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Commit c9398e89 authored by Damian Johnson's avatar Damian Johnson
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Drop volunteer page footer idea blob 

This is an antique, horribly unreadable wad of text as denser than a legal
footer. We should invest effort in making project ideas readable or not have
them at all. Actually, this section predates me (meaning it's over six years
old) and never been maintained in that time. Guess it's so dense even we
ignored it. :P

If we want to resurrect any of these then it should be done so as tickets.
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......@@ -1556,216 +1556,6 @@ implementation.
</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="<wiki>doc/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 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>Write a <a
href="https://secure.wikimedia.org/wikipedia/en/wiki/Fuzz_testing">fuzzer</a>
for Tor to discover security vulnerabilities. Determine if there
are good fuzzing frameworks 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="<page docs/faq>#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="<specblob>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 about/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? One example is <a
href="https://tails.boum.org/">The Amnesic Incognito Live
System</a>.
</li>
<li>
Another anti-censorship project is to try to make Tor
more scanning-resistant. Right now, an adversary can identify <a
href="<specblob>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="<svnprojects>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 "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/index.php/hpn-ssh/638">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="<svnprojects>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 docs/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>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>
<p>
<a href="<page about/contact>">Let us know</a> if you've made progress on any
of these!
</p>
</div>
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