[tor-bugs] #2693 [Tor Relay]: Design and implement improved algorithm for choosing consensus method

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#2693: Design and implement improved algorithm for choosing consensus method
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 Reporter:  nickm        |          Owner:                    
     Type:  enhancement  |         Status:  new               
 Priority:  normal       |      Milestone:  Tor: 0.2.3.x-final
Component:  Tor Relay    |        Version:                    
 Keywords:               |         Parent:  #2664             
   Points:               |   Actualpoints:                    
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 Our current algorithm for picking a consenus method is, "Pick the highest
 method supported by more than 2/3 of the authorities currently voting."
 This can sometimes result in an insufficiently signed consensus.  Instead,
 it should be something like, "Pick the highest method supported by more
 than 2/3 of the authorities currently voting, UNLESS the number of
 authorities supporting that method is less than the threshold needed to
 sign a valid consensus.  In that case, pick the highest method supported
 by enough authorities to sign a valid consensus."

 Alternatively, the algorithm could be something like, "Pick the highest
 method supported by enough authorities to sign a valid consensus", which I
 believe is mathematically identical to the above (more obviously safe)
 formulation.

 This change would make some attacks harder for a hostile authority, and
 some attacks easier.  It needs a design proposal and some analysis.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/2693>
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