[tor-bugs] #17188 [Tor]: Tor should warn users when traveling backwards through time

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#17188: Tor should warn users when traveling backwards through time
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 Reporter:  hdevalence   |          Owner:
     Type:  enhancement  |         Status:  new
 Priority:  normal       |      Milestone:
Component:  Tor          |        Version:
 Keywords:  security     |  Actual Points:
Parent ID:               |         Points:
  Sponsor:               |
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 An attacker can do evil things by rewinding a user's clock, without having
 to own their machine (e.g., NTP attacks).

 Tor maintains a monotonic clock to prevent rewinding attacks while Tor is
 running.  Tor also keeps some persistent information about the user's time
 in the state file, in the LastWritten field.

 On launch, if Tor sees that the system time has been rewound to before the
 LastWritten time, it should warn the user that something strange is
 happening. However, Tor should not update the monotonic clock or fail to
 launch, since the user may have changed the time deliberately.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17188>
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