[tor-bugs] #16824 [Tor]: coexistence of client and relay processing on same thread poses traffic confirmation risk

[Tor Bug Tracker & Wiki]

#16824: coexistence of client and relay processing on same thread poses traffic
confirmation risk
---------------------------+--------------------------------
     Reporter:  starlight  |      Owner:
         Type:  defect     |     Status:  new
     Priority:  normal     |  Milestone:  Tor: 0.2.7.x-final
    Component:  Tor        |    Version:  Tor: 0.2.6.10
   Resolution:             |   Keywords:  PostFreeze027
Actual Points:             |  Parent ID:
       Points:             |
---------------------------+--------------------------------

Comment (by mikeperry):

 While serious, the side channel in #16585 doesn't fully differentiate all
 client and relay traffic. It only lets you know that a client circuit
 setup is happening, not if or when an existing circuit is being used for
 client traffic. As far as I can tell, it also doesn't directly disclose
 the volume of client traffic relative to relay traffic, either. Nor does
 it expose when client circuits are actually closed.

 This means that significantly less information is available to an
 adversary who is monitoring a relay (that is also used as a client) than
 is available to an adversary who is watching a machine that has a separate
 relay tor instance and a client tor instance, even with the side channel.

 I do believe that #16585 is serious and should be fixed, especially since
 it seems like it could also be a vector for other side channels as well,
 and potentially even in client-only scenarios. However, shouting
 confusing, nuanced, and/or partially correct information at users in our
 loglines isn't the right stopgap in the meantime, IMO.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16824#comment:9>
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