[tor-bugs] #24366 [Core Tor/Tor]: compare_vote_rs() could check more fields for better SHA1 collision resistance

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#24366: compare_vote_rs() could check more fields for better SHA1 collision
resistance
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  (none)
     Type:  defect                               |         Status:  new
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.3.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-dirauth, possible-consensus-     |  Actual Points:
  failure, needs-proposal                        |
Parent ID:                                       |         Points:  2
 Reviewer:                                       |        Sponsor:
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Changes (by teor):

 * keywords:  tor-dirauth, possible-consensus-failure, needs-proposal? =>
     tor-dirauth, possible-consensus-failure, needs-proposal


Comment:

 The votes already include a better hash of the microdescriptor, but that's
 probably not enough. (And they contain *multiple* microdesc hashes.)

 So yes, I think the right thing to do is to:
 * add a sha-best (are we at SHA3-256 now?) descriptor hash to votes
 * define a new consensus method
 * when using that new consensus method, use this hash as the tie-breaker

 I think this lets us remove all the other tie-breaker fields.

 Maybe we could just get away with comparing the sha3-256 hash, but let's
 stick with the existing two hashes, and the sha3, so we don't accidentally
 *reduce* security.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24366#comment:3>
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