[tor-talk] Tor spying

Mike Perry mikeperry at fscked.org
Thu Sep 8 07:05:31 UTC 2011

Thus spake Greg Kalitnikoff (kalitnikoff at privatdemail.net):

> Andrew Lewman <andrew at torproject.org> wrote:
> > Moxie is a smart guy, his answer to the CA issues, and therefore his own 
> > sslsniff/sslstrip attack is currently http://convergence.io/. I think Moxie's 
> > on the list, he can reply as well.
> Do you consider including Convergence (or similar extension -
> Perspectives http://www.networknotary.org/firefox.html) to official
> TorBrowser? I think the idea of distributed notaries is something that
> ssl security would evolve to.

Yes. We haven't included Perspectives and related pre-Convergence
addons because the Firefox APIs are not sophisticated enough to notify
the user of SSL MITM before your browser sent authentication data. They
expect to improve them soon, but confusion still remains:

IIRC, Moxie's Convergence bypasses the API problem by creating a
synthetic proxy that MITMs you and re-signs your HTTPS certificates as
either "good" or "bad" internally (after notary verification) to
prevent the authentication transmission. It also makes use of OpenSSL
functions for certificate inspection through js-ctypes, which adds a
little more complexity into the mix.

While functional, this approach needs to be reviewed and digested a
bit by the security community before we jump right on board and toss
it in. It will also require some testing and auditing to ensure it
properly behaves with Tor's proxy in all cases. 

We don't have to do this testing ourselves (indeed, it is not high
priority right now - we don't even have a trac ticket for it), but
we'd like an external audit to be well documented and thorough if we
were to rely on it. The audit should also be done with Tor Browser

AFAIK, Tor Browser Bundle users should be able to install his XPI and
use it now, but beware that doing so will reduce your anonymity set to
exit node observers (due to the presumably low adoption rate of
Convergence today).

Mike Perry
Mad Computer Scientist
fscked.org evil labs
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