exit node and circuit

[Roger Dingledine]

On Mon, Oct 04, 2010 at 07:43:33PM +0800, Trystero Lot wrote:
> running tor as exit node and client inthe same pc, is there possiblity
> that my exit node will be included in the client circuit? or do i have
> to use the excludenode string to make sure it never ever happen?

If you have two Tor processes (one an exit relay, one a client) running
on one computer, then yes, the client might sometimes end up exiting from
the exit relay. The Tor client won't automatically exclude relays with a
"similar" address.

But for anonymity, I would argue that you shouldn't exclude your own
relay. Imagine you're using Tor to contact some destination site over
time. If that destination site suspects you're running an exit relay,
and it notices that you tend to connect from everywhere except for one
exit relay... it could guess that the exit relay you're trying to avoid
is related to you.

If your exit relay is tiny, the probability of reaching this conclusion
is probably pretty low. If your exit relay is huge, the probability is
pretty high.

On the other hand, if the destination doesn't understand anything about
Tor, then you may be better off never having your IP address show up
in his logs. That might work, but you should ask yourself how hard it
would be for your adversary to get smarter.

Hope this helps,
--Roger