[tor-bugs] #3652 [Tor Client]: Export clock skew opinion as getinfo command

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#3652: Export clock skew opinion as getinfo command
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 Reporter:  mikeperry    |          Owner:  nickm             
     Type:  enhancement  |         Status:  assigned          
 Priority:  major        |      Milestone:  Tor: 0.2.3.x-final
Component:  Tor Client   |        Version:                    
 Keywords:               |         Parent:                    
   Points:               |   Actualpoints:                    
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Comment(by rransom):

 Replying to [comment:6 mikeperry]:
 > Replying to [comment:4 nickm]:
 > > I started doing some work here in a branch called "skew_estimate".
 Needs some attention and review for sanity.
 >
 > In command_process_netinfo_cell(), why do you only set apparent_skew if
 conn->handshake_state->sent_versions_at was within 180 seconds? Is it
 possible that the dirauth just won't respond in any reasonable amount of
 time here?

 The SSL handshake itself is our only assurance that we are actually
 talking to the server we think we are talking to in something like 'real
 time'.  After the handshake completes, an active attacker can delay the
 NETINFO and VERSIONS cells for arbitrarily long periods of time.  We
 should probably decrease the 180-second window to around 30 seconds or
 less.

 > In router_set_networkstatus_v2() and
 networkstatus_set_current_consensus(), you use the published/valid_after
 time. This is probably too low of a resolution to bother to record it to
 report for TBB. We care about precision down to the second (possibly even
 sub-second)... Recording this value will just cause all TBB users to all
 have weird, messed up clocks. If we want that property, we can get it
 other ways than through the control port command...

 The timestamp on a published consensus is only used as a lower bound on
 the current time.  Tor reports this timestamp to its clock skew reporting
 system so that it can complain if the system clock is ''definitely''
 skewed.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3652#comment:8>
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