[tor-bugs] #29266 [Core Tor/Tor]: PrivCount proof of concept: round results to hide usage over time

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#29266: PrivCount proof of concept: round results to hide usage over time
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     Reporter:  teor     |      Owner:  (none)
         Type:  defect   |     Status:  new
     Priority:  Medium   |  Milestone:  Tor: 0.4.1.x-final
    Component:  Core     |    Version:
  Tor/Tor                |   Keywords:  privcount, 040-unreached-20190109,
     Severity:  Normal   |  041-accepted-20190115
Actual Points:           |  Parent ID:  #27908
       Points:           |   Reviewer:
      Sponsor:           |
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 We need to round the results to hide usage over time. We should work out
 how much to round each result, and how to implement the rounding.

 Here is one possible scheme:
 * we want to round the result to the closest multiple of N
 * each tally reporter rounds their blinded subtotal to the closest
 multiple of N
 * the final un-blinded result is rounded to the nearest multiple of N
 (plus an arbitrary value between 0 and N, due to the unblinding), as long
 as at least one Tally Reporter is honest

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29266>
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