[tor-talk] on the topic of tor's weaknesses

[Ralf-Philipp Weinmann]

On Feb 29, 2012, at 11:17 AM, grarpamp wrote:

>> The main problem, besides the overhead, is that padding doesn't work
>> if an adversary can do something as trivial as very briefly delaying
>> It is too easy for an adversary to put a traffic signature on a
>> circuit in one place, and look for it elsewhere. If he owns, e.g., the
>> first node and any of the last node, the link to the destination, or
>> the destination it won't matter what kind of padding is done. There's
>> lots of published work showing this in various ways. Some already
>> alluded to in this thread. If nothing else the adversary can just kill
>> the connection at the first node and see which connection exiting the
>> network dies.
> 
> Doesn't this mean bad news for users of hidden services, and to a
> lesser extent clearnet services (since they're not as 'illegal' and thus
> maybe lesser hot targets for snagging users). IE:
> 
> Sting runs a HS and an entry. Thus Sting has full packets, timing,
> cleartext and logs of anyone that builds: clientA <> entry <---> HS
> 
> There may even be these additional structures to the left of clientA's
> entry, for which the role of entry may switch to relay or exit, but for
> which entry may be still able to discriminate among on its left...
> clientB
> clientC <> relay
> clientD [...] <> relay <> relay [...]
> 
> It may take a while for a clientA to use said entry but when they do it seems
> it would be quite easy to time/count correlate or munge the HS traffic of
> clientA. And only require two nodes (hs, entry) and no GPA taps to do so.

That's why guards were introduced: They will not completely eliminate the above class of attacks, but at least make it statistically much less likely; since you will only use 3 out of 800 or so guard nodes per month.

Cheers,
Ralf