[tor-bugs] #15935 [Tor]: Implement a kill switch / exponential backoff for old clients

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#15935: Implement a kill switch / exponential backoff for old clients
--------------------------------+------------------------------------
 Reporter:  teor                |          Owner:
     Type:  defect              |         Status:  new
 Priority:  normal              |      Milestone:  Tor: 0.2.7.x-final
Component:  Tor                 |        Version:  Tor: unspecified
 Keywords:  SponsorS, SponsorU  |  Actual Points:
Parent ID:  #15228              |         Points:
--------------------------------+------------------------------------
 In #15233, we want to kill off 0.2.2 and 0.2.3 clients, but we want to
 make sure they won't increase their request rate to the directory
 authorities if we stop answering them.

 We face this issue every time we kill off old client versions.

 #15228 will change the scope of this issue, as it may affect the fallback
 directories, as well as the directory authorities.

 We don't want to have many of our best directories overloaded with rapid
 requests from obsolete clients.

 I suggest, at a minimum:
 1. A kill switch for old client versions should be part of a valid, signed
 consensus:
 * a permitted-but-not-recommended client versions list, and every version
 not on that list is banned? The problem with this is that new dev versions
 and custom versions would be banned.
 * an obsoleted client version list, every version on that list banned? It
 would be a long list, and custom versions wouldn't be banned.
 2. Every request in tor should be random-exponential-backoff, which would
 resolve repeated-connection overloading issues in general.
 3. How do we deal with botnets that don't use the full tor code? They need
 not obey the consensus, or use exponential backoff.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15935>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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