[tor-bugs] #26294 [Core Tor/Tor]: attacker can force intro point rotation by ddos

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#26294: attacker can force intro point rotation by ddos
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 Reporter:  arma                                 |          Owner:  asn
     Type:  defect                               |         Status:
                                                 |  merge_ready
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.4.2.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-hs, tor-dos, network-team-       |  Actual Points:  6
  roadmap-august                                 |
Parent ID:  #29999                               |         Points:  7
 Reviewer:  dgoulet                              |        Sponsor:
                                                 |  Sponsor27-must
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Comment (by asn):

 Replying to [comment:26 nickm]:
 > I think this code looks okay but before we merge it, I think we should
 have a patch for tor-spec that explains the new behavior of the replay
 cache.  We should also have a quick proposal that explains why it's safe
 to allow replays, since I've usually thought of them as a way to mount
 active traffic analysis attacks.

 Here is a torspec patch:
 https://github.com/asn-d6/torspec/commit/f0fbcf3d606b8fb8ec49b1ba8f790607725dbd8b
 https://github.com/asn-d6/torspec/tree/bug26294

 We actually had not heard that replay caches are there to protect against
 traffic analysis attacks. How does the attack work? I considered that
 identical INTRO2 cells could be used as a signal to the HS guard, but
 since they are end-to-end encrypted the singal should not be visible,
 right?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26294#comment:27>
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