[tor-talk] End-to-end correlation for fun and profit

[Maxim Kammerer]

On Sat, Aug 25, 2012 at 1:12 AM, Mike Perry <mikeperry at torproject.org> wrote:
> The Raccoon has made a believer out of me, but there are some limits to
> both of his/her proofs.. The full proofs can still be found here:
> http://web.archive.org/web/20100416150300/http://archives.seul.org/or/dev/Sep-2008/msg00016.html

Wrt. the first proof, it seems to me that the assumed correlation
accuracy rate of 99.9% is incredibly low, and I think that the Raccoon
recognized that by referring to sampling and retention at the end of
his post. With the targeted attack that's similar to bExample 3b in
Raccoon's post that I described in my previous comment here, where one
analyzes all exit traffic without missing packets, I would expect the
correlation accuracy (and as a result, match confidence) to
exponentially approach 100% very quickly with the number of relevant
packets seen, and extremely quickly if the traffic is interactive
(i.e., browsing).

Actually, c/n of 30% in bExample 3b is close to the 25% that's
discussed in the OP here, so let's redo the example with c/n=25% and
different correlation accuracies (leaving the other numbers intact):

(using bbc -lb)
ca  = 0.999
pm  = (1/5000) * (0.25)^2
ca*pm / (pm*ca + (1-pm)*(1-ca))

ca  = 0.999
.01233363786760166917
ca = 0.9999
.11110246894375430565
ca = 0.99999
.55555617284636495961
ca = 0.999999
.92592671467910125759
ca = 0.9999999
.99206358969515668554
ca = 0.99999999
.99920064946444143613
ca = 0.999999999
.99992000739924807495

So reducing correlation accuracy error to 10^-9 will give you 99.99%
confidence in end-to-end correlation match. I suspect that a few
seconds of interactive traffic will give you a correlation accuracy
that's much better than a 10^-9 error.

-- 
Maxim Kammerer
LibertC) Linux: http://dee.su/liberte
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