[tor-dev] automatically detect many new identical/similar bridges

nusenu nusenu at openmailbox.org
Wed Dec 14 22:26:00 UTC 2016

>> I'm not sure I understand what you mean by brute-forcing in this case
>> since I would not suggest any deterministic algorithm (like a hash) that
>> takes an ASname and a timestamp and produces a string but just a
>> AS number -> random id
>> mapping, stored for a day or an hour and deleted after that.
>> Another way an attacker could take advantage of this:
>> unique AS sign-up rate patterns
>> "everyday there are about x new bridges in AS y" so it doesn't help much
>> if we change the random AS id daily.
> If an adversary submits a bridge descriptor from every (popular) AS
> (in every hour of) every day, they know which AS each bridge is from.

Understood, that is what I meant with:

Note: This introduces a confirmation opportunity, where attackers can
learn the AS in which a new bridge is added if they added a bridge in
the same AS on the same day. To reduce this problem it could be a hourly
generated identifier.

> Or, alternately, if they submit a bridge descriptor from an AS they
> are watching, then they know all the bridges in that AS.
> And they don't actually need to be in the AS to submit a descriptor
> with an IP address from that AS.

Ok that makes it bad to a point where it is pointless. I'm surprised
that you can get bridge auth to distribute fake bridges for arbitrary
IPs - I assume that is not actually the case.

Anyway as I said, no need to pursue this any further, but thanks for the

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