Re: Reducing relays = reducing anonymity ? Tortunnel.

[Sebastian Hahn <mail@xxxxxxxxxxxxxxxxx>]

Hi Niklas,

On May 19, 2010, at 6:06 PM, Attac Heidenheim wrote:
> Hi everybody,
> I just tried a little tool called "Tortunnel" which allows a user to
> "tunnel" Tor via Privoxy/Polipo to any selected exitnode. Just one hop
> instead of three relays.

This works by pretending to the exit relay that you've already come
through the Tor network. This is considered abusing the resources
made available to the Tor network by volunteers, and effectively
entirely breaks your anonymity.

> Of course, if the exitnode ist evil, you're lost, but it really speeds
> up the whole thing on the other hand.

The only goal of tortunnel is speed. Remember, though, that most
nodes on the Tor network aren't exits, so even for the network as a
whole tortunnel, is a bad idea as exit capacity is tapped by more
people (assuming the people who use tortunnel would otherwise
find something else that offers speed but no anonymity).

Remember that not only the exit node, but also people who might
want to threaten/watch the exit node or its operator are perfectly
able to track you down and analyze all your traffic as much as
they want.

> My questions:
> Does anybody use tortunnel ?

Yes, quite many people do, unfortunately. We have implemented
a patch to detect people who abuse Tor in this way, and exit node
operators using the development version can already opt to deny
handling traffic for tortunnel users. As this option gets more testing
it will propagate into the stable versions and probably be turned
on by default before too long.

> Is tortunnel evil since it maybe hacks Tor-cirucits to reduce the  
> number
> of relays ?

Yes, unfortunately quite a few people use it.
It hurts the network by endangering exit node operators, and
by completely ignoring any of the load balancing that happens
in normal Tor.

> Where is the security/anonymity reduction since tortunnel also uses
> Tor ?

Anonymity is entirely gone.

> Can Tor itself reduce the number of relays (like tortunnel) ?

No, because Tor itself identifies as a client to the first hop. This
means that the first hop knows that you are a client, and
disallows exiting.

> Greetings,
> Niklas

One thing you fail to consider is how secure tortunnel itself is.
Others have reported it is doing some dubious things, and it
wouldn't come as a big surprise if there were a nice bugdoor
somewhere.

Sebastian
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