[tor-relays] The 9001-9051-v0.2.8.9 Gang: 57 relays and counting... // hsdir calc tool?

[teor]

> On 27 Feb 2017, at 23:48, nusenu <nusenu at openmailbox.org> wrote:
> 
> This group is still growing.
> 
> Note that the following table is _not_ sorted by FP.
> 
> The FP links these relays even across ISP, and given the FP column
> pattern it might be obvious what they are after.
> 
> They do not have the hsdir flag yet.
> 
> https://raw.githubusercontent.com/nusenu/tor-network-observations/master/2017-02-24_9001-9051-v0.2.8.9.txt
> 
> Is there a tool out there that tells me which HSDir is/will probably be
> responsible for a given onion address (and at what time)?

There's no tool, unless you can reverse SHA1.
(Or brute-force a set of popular onion addresses.)

In short, it's the first 3 fingerprints following descriptor-id:

permanent-id = H(public-key)[:10]
descriptor-id = H(permanent-id | H(time-period | descriptor-cookie | replica))
where H is SHA1.

The spec is:
https://gitweb.torproject.org/torspec.git/tree/rend-spec.txt#n222
https://gitweb.torproject.org/torspec.git/tree/rend-spec.txt#n505

The implementation is:
https://gitweb.torproject.org/tor.git/tree/src/or/rendcommon.c#n127

As an aside, this attack is not possible with next-generation hidden
services, because the HSDir identities are hashed with the daily
shared random value:
https://gitweb.torproject.org/torspec.git/tree/proposals/224-rend-spec-ng.txt#n791

T

--
Tim Wilson-Brown (teor)

teor2345 at gmail dot com
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