[tor-dev] "Trawling for Tor Hidden Services: Detection, Measurement, Deanonymization"

Mike Perry mikeperry at torproject.org
Wed May 29 06:20:18 UTC 2013

Tom Ritter:

> On 28 May 2013 16:33, Mike Perry <mikeperry at torproject.org> wrote:
> > Additionally, as far as I can see, if you can control the introduction
> > points using the attack from the first part of the paper, you could also
> > perform this attack against a *user* as well (which is the threat model
> > strongbox really tries to address). A captured Introduction Point could
> > repeatedly fail circuits, forcing the user to reconnect on new ones
> > until their Guard node is discovered.

I misspoke above. While it might be possible to capture the Introduction
Point using some other attack, the more direct route to attack clients
is to use the /HSDir/ nodes you control from the paper's methods, and
fail client circuits who are asking for the HSdesc you're interested in.

In that case, it would take about an hour to locate the Guard nodes of
persistent clients, and then you would have to coerce the Guard nodes
into surveilling further (or just giving you their identity key, so you
can MITM their TLS connections remotely without their further assistance
or knowledge).

Still, less practical than attacking the service side unless you have a
client that continues to connect to the target service for long enough
for you to find the Guard, compromise it, and then watch their traffic.

> > Of course, most users will probably give up trying to use the service
> > long before the hour is up, but if the attack could be optimized in any
> > other way, it could mean trouble..
> They won't give up if they are irssi trying to reconnect to a server.
> Or a VPN trying to auto-reconnect. Or any manner of non-human
> auto-retrying applications talking to a Hidden Service.

Absolutely correct. Hopefully Strongbox doesn't keep retrying for you in
the background or anything like that.

Mike Perry
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