[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
-------------------------------------------------+-------------------------
 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, security, 042-should           |
Parent ID:  #29999                               |         Points:  7
 Reviewer:  dgoulet                              |        Sponsor:
                                                 |  Sponsor27-must
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Comment (by s7r):

 The attacks are quite possible, but also the current replay cache behavior
 can be trivailly gamed so the onion service will rotate intro points more
 often than we would normally want and thus trigger a different sybil type
 attack where eventually the onion service pick a hostile introduction
 point. Both time limit and number of introductions limit are important and
 mitigate different thread models.

 Which is why I think configuring the replay cache to limit on a "hybrid"
 threshold (time + introductions) as described in comment:11 will not
 interfere with the issues and concerns described above. It's just about
 choosing the right variable min and max values so that introduction points
 are not rotated too fast but also cannot send unlimited replays
 (introductions) during their time-based lifetime. A "hybrid" limitation as
 described will simply enhance the current behavior instead of radically
 changing it.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26294#comment:35>
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