[tor-bugs] #29004 [Core Tor/Tor]: PrivCount proof of concept: implement check counters

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#29004: PrivCount proof of concept: implement check counters
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     Reporter:  teor          |      Owner:  teor
         Type:  defect        |     Status:  assigned
     Priority:  Medium        |  Milestone:  Tor: 0.4.0.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  privcount
Actual Points:                |  Parent ID:  #27908
       Points:                |   Reviewer:
      Sponsor:                |
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 We can start building a PrivCount proof of concept with 3 check counters:
 * ZeroCount - all Data Collectors (DCs) store zero in this counter. If
 aggregation succeeds, the result is zero. Otherwise, all aggregated
 results for this round are meaningless.
 * DataCollectorCount - all Data Collectors (DCs) store one in this
 counter. If aggregation succeeds, the result is the number of DCs that
 reported results.
 * SampledNoiseAmount - all Data Collectors (DCs) store some noise in this
 counter, using their standard processes for generating noise, including
 noise weighting, sampling, and rounding (if needed). If aggregation
 succeeds, and the standard deviation is large enough, the result will
 almost always be non-zero, and almost always be within a few standard
 deviations of zero. We need this counter, because bugs in noise generation
 may not be obvious in the results.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29004>
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