[tor-bugs] #13989 [Tor]: Freak out if we pick too many new guards in too short a time

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#13989: Freak out if we pick too many new guards in too short a time
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 Reporter:  nickm              |          Owner:
     Type:  defect             |         Status:  new
 Priority:  normal             |      Milestone:  Tor: 0.2.6.x-final
Component:  Tor                |        Version:
 Keywords:  tor-client guards  |  Actual Points:
Parent ID:                     |         Points:
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 According to the sniper attack paper, we should never really have to pick
 more than 5 new guards in a 4 week period (I think that's the number).  If
 we do, our network is probably down or filtered or our guards are under
 attack.

 This is going to have some tricky issues.  For example, what should we do
 if we hit this threshold?  We could decline to pick circuits until some
 node we've been willing to use as a guard comes up again, unless the user
 explicitly tells us to, I guess.

 As another issue, we don't currently store exactly when we added a guard,
 but a randomized version of that.  So perhaps we need a fuzzier version of
 this test.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13989>
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