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List:       tor-talk
Subject:    Re: [tor-talk] I have a quick question about security of tor with 3 nodes
From:       Mirimir <mirimir () riseup ! net>
Date:       2014-08-31 22:10:20
Message-ID: 54039D4C.7090009 () riseup ! net
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On 08/31/2014 02:22 PM, Juan wrote:
> On Fri, 29 Aug 2014 18:59:19 -0600 Mirimir <mirimir@riseup.net>
> wrote:

<SNIP>

>> Even the NSA, with global intercepts, is apparently not doing 
>> full-network traffic correlation among Tor relays.
> 
> And you know that how, exactly?

I said "apparently not" because there's been no mention so far in the
Snowden stuff, and also because it's a very hard problem. But I have no
more hard evidence than you do. I keep emailing support@nsa.gov but I
haven't ever received a reply ;)

From "Tor Metrics: Users"[0], I get that there are typically about two
million simultaneous Tor users. If each has three active circuits, there
are about six million concurrent circuits.

Tracing a particular Tor circuit would entail correlating traffic from
one intercept (presumably starting with an exit relay, or an entry
guard) with several million traffic intercepts from at most a few
thousand other relays. That would be trivial for a global adversary,
given the intercepts.

By "full-network traffic correlation", I meant cross correlating in real
time all of the several million concurrent traffic intercepts from all
Tor relays. That would yield a database of conversations, with such data
fields as user IP, entry guard ID, exit ID and destination site.

That would arguably involve on the order of 10^13 comparisons for each
snapshot, with snapshots perhaps every few minutes. Can the NSA manage
that? Shall we take a poll?

[0] https://metrics.torproject.org/users.html

<SNIP>
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