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Re: Timing attacks from a user's point of view

I guess the approach will not be quite useful.

1. Delay is a big enemy of Tor. Read http://www.cs.uml.edu/%7Exinwenfu/paper/IPDPS08_Fu.pdf. How much delay is a problem too.

2. An attack can be dynamic against your mechanism by varying the parameters of the attack. We already tested the impact of using various batching and reordering on attacks. Read http://www.cs.uml.edu/%7Exinwenfu/paper/SP07_Fu.pdf. Basically, it is of not much use.

3. Many people still talk about reordering. Reordering cannot be used for TCP at all. It kills the performance. Read http://www.cs.uml.edu/%7Exinwenfu/paper/MixPerf_Fu.pdf.


Xinwen Fu

On Wed, Nov 25, 2009 at 3:54 PM, Just A. User <just_a_user@xxxxxxxxxxxxx> wrote:

As the recent (and not so recent) research shows [1, 2], it is quite
possible for a low-bandwidth adversary controlling the exit node or
destination server to identify all the nodes in a circuit. If the victim
is unlucky, the further deanonymization may use a malicious entry node.
Otherwise, the attacker can measure the RTT distance between the victim
and entry node and benefit from that somehow [3].

One of the obvious methods (of yet unclear efficiency) to mitigate the
issue is introducing of high variance random delays at the routers. As I
can understand, however, the Developers want to keep net delays low.
They have their reasons (the lower the delays, the larger the net and
the stronger anonymity). Nevertheless, a user is able to randomly delay
her traffic before the first router of a circuit. Does this make any

a. the user tries to decrease the reliability of the attack from [2];
she hopes that there will be more false positives and all the
measurements become less significant or take more time.

b. using the attack from [2], the adversary can make a chosen router
delay some cells for quite a long time (tens of seconds). Since such
delay variances are hardly tolerable, e.g. for web surfing, the user is
very limited in her ability to simulate a false positive.

c. the user will have an unusual delay pattern, which could suffice for
pseudonymity requirements only.

[1] Murdoch, Danezis. Low-cost traffic analysis of Tor.
[2] Evans, Dingledine, Grothoff. A practical congestion attack on Tor
using long paths.
[3] Hopper, Vasserman, Chan-Tin. How much anonymity does network latency

Thanks in advance.

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