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Re: [tor-talk] Source code modifying for testing

On Wed, 11 May 2011 10:11:07 +0200
NGUYEN Quoc Viet <quocviet.pfiev@xxxxxxxxx> wrote:

> I'm now researching an attack against Tor.
> *Resume of Attack*: We control exit node and entry node. Upon receiving a
> RELAY BEGIN cell,the exit node will forger  a malicious webpage to client.
> The webpage contains some empty gif files. The entry node will be able to
> detect a distinctive pattern of the connection to that malicious webpage,
> basing on number of relay cells backward and forward.

If you can control both the entry and exit nodes, you don't even need
to perform an active attack -- a purely passive timing attack will
identify the client.  That's why each Tor client selects a few relays
to use as âentry guardsâ -- see
<https://www.torproject.org/docs/faq#EntryGuards> and

> For implementation, it's needed to modify a piece of Tor source code at the
> exit node, to forger a malicious webpage to client. Notice that this is not
> modifying webpage response from the server, but forger attacker's webpage to
> the client. Could some one please give a hint about where I need to modify.


Robert Ransom

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