[tor-bugs] #3890 [Tor bundles/installation]: Applications should start using optimistic data

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#3890: Applications should start using optimistic data
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 Reporter:  nickm                     |          Owner:  erinn
     Type:  enhancement               |         Status:  new  
 Priority:  major                     |      Milestone:       
Component:  Tor bundles/installation  |        Version:       
 Keywords:                            |         Parent:  #5456
   Points:                            |   Actualpoints:       
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Changes (by mikeperry):

  * priority:  normal => major
 * cc: rransom, arma (added)
  * parent:  => #5456


Comment:

 While staring at my circuit window fretting about #5456, I realized that
 the Tor client behavior of retrying stream stages prior to RELAY_CONNECTED
 allows an active exit node attacker to embed an arbitrarily long timing
 signature transparently during stream setup. Because this phase is still
 transparent to the user, the circuit still can be closed at this step if
 the timing signature is not detected on a colluding malicious guard,
 allowing for resource amplification. It's not as much amplification as
 tagging via cipher malleability, because you don't get to do it at both
 ends, but it's still amplification.

 But if we deploy optimistic data, we remove the amplification property
 because if the stream does not succeed in that first round trip, the app
 will actually experience failure instead of the Tor client transparently
 retrying until a signature can be added.

 So it turns out this performance feature is actually a security
 improvement as well.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3890#comment:5>
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