[tor-bugs] #2628 [Tor Client]: Be smarter about launching connections to authorities to learn about clock skew

[Tor Bug Tracker & Wiki]

#2628: Be smarter about launching connections to authorities to learn about clock
skew
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 Reporter:  nickm        |          Owner:                  
     Type:  enhancement  |         Status:  new             
 Priority:  normal       |      Milestone:  Tor: unspecified
Component:  Tor Client   |        Version:                  
 Keywords:  easy         |         Parent:                  
   Points:               |   Actualpoints:                  
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 While applying altf4's code related to bug1074, some possible enhancements
 came up.  They wouldn't be too hard to do.

 Right now, we notice clock skew for two reasons: a time from a netinfo
 cell is different from ours, and a time in an HTTP response header is
 different from ours.  In the netinfo case, if the skew came from an
 authority, we believe it.  If not, and we haven't gotten a netinfo from an
 authority, we launch an OR connection to an authority.

 In fact, we should be a bit more sophisticated:

  * Any authenticated time from an authority should count as "hearing the
 time from an authority".  This includes not only netinfo cells but also
 authenticated directory connections.
  * Maybe, skew information from regular HTTP responses should also count
 as "hearing that we are skewed from a non-authority".
  * Instead of keeping track  of *whether* we've heard the correct time
 from an authority, we should keep track of *when* we heard from the
 authority.  In other words, if we last heard about the correct time from
 an authority an hour ago and somebody else disagrees with them, the
 authority is probably right.  But if we last heard about the correct time
 a week ago, we might want to ask again.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2628>
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