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Re: [tor-bugs] #16389 [Tor]: Redesign the HS client descriptor cache

#16389: Redesign the HS client descriptor cache
-------------------------+-------------------------------------------------
     Reporter:  dgoulet  |      Owner:
         Type:  defect   |     Status:  reopened
     Priority:  major    |  Milestone:  Tor: 0.2.7.x-final
    Component:  Tor      |    Version:
   Resolution:           |   Keywords:  SponsorR, tor-hs, TorCoreTeam201508
Actual Points:           |  Parent ID:  #16381
       Points:           |
-------------------------+-------------------------------------------------

Comment (by arma):

 Did everybody just assume I picked the perfect number "5 minutes", or has
 anybody thought through the time period required here?

 Basically, any time interval is suboptimal, in that waiting a long time
 will result in more instances of unhappy users who can't reach their HS,
 and waiting a short time will result in duplicate attempts.

 It seems like we want a nonce in the hidden service descriptor, and in the
 cache we tag which descriptor we had when we tried it, and then expire --
 no, that wouldn't work either, since the hidden service doesn't need to
 publish a new version of its descriptor if it's just reusing all its old
 intro points. So there isn't any explicit signal by the HS that it was
 gone for a while and has now returned so maybe you want to retry.

 In sum: with this patch are we still going to have cases where Alice tries
 to visit a hidden service, finds it unavailable, then the HS goes back
 online and tells her to try again, and for five minutes she fails?

 Maybe this argues for hidden services putting the nonce into their HS
 descs anyway, and publishing an updated HS desc every time they lose
 contact with their intro points, to give clients a way to recognize when
 the HS has acknowledged that things changed? Yuck.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16389#comment:16>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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