[tor-bugs] #18318 [Tor]: Make sure keys and IP:Ports are unique in a consensus

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#18318: Make sure keys and IP:Ports are unique in a consensus
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     Reporter:  teor       |      Owner:
         Type:  defect     |     Status:  new
     Priority:  Very High  |  Milestone:  Tor: 0.2.7.x-final
    Component:  Tor        |    Version:
     Severity:  Blocker    |   Keywords:  TorCoreTeam201602
Actual Points:             |  Parent ID:  #17668
       Points:             |    Sponsor:
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 When voting for RSA / Ed25519 key combinations, each RSA key must be
 unique in the vote, and and each Ed key must be unique in the vote:
 * authorities must vote using the most recent descriptor signed by a RSA
 key, as the signature proves ownership of that key, and ignore earlier
 descriptors signed by that key;
 * authorities must vote using the most recent descriptor signed by both a
 RSA and an Ed key, as the signatures prove ownership of both keys, and
 ignore earlier descriptors signed by either key.

 When voting for RSA key / IPv4:Port combinations, there can only be one
 Running instance of each RSA key, and one Running instance of each
 IPv4:Port, in the vote:
 * authorities must vote Running for only one IPv4:Port per RSA key, and
 only one RSA key per IPv4:Port. The IPv4:Port and RSA key must be the
 latest RSA key proven by reachability test to that IPv4:Port from that
 authority;
 * authorities may vote for RSA keys that have signed a descriptor
 specifying an IPv4:Port, but which haven't been reachability tested, or
 which have been superseded by a later reachability test. (This helps us
 deduce internal authority state from votes.) But authorities must not vote
 Running for these additional RSA key or IPv4:Port instances.

 Whether or not authorities can perform IPv6 reachability tests, there can
 only be one Running instance of each IPv6:Port in the vote:
 * authorities must vote Running for at most one IPv6:Port per RSA key, and
 only one RSA key per IPv6:Port. The IPv6:Port and RSA key must be the
 latest RSA key proven by reachability test to that IPv6:Port from that
 authority;
 * authorities that aren't on IPv6 must vote Running for at most one
 IPv6:Port per RSA key, and only one RSA key per IPv6:Port. If multiple RSA
 keys claim an IPv6:Port, the RSA key voted Running must be the one with
 the latest reachable IPv4:Port.
 * authorities may include additional IPv6:Port instances, but must not
 vote them running.

 When we transition to Ed25519 proofs via authenticate cells in
 reachability tests, similar uniqueness constraints will apply. But that's
 out of scope for this ticket.

 Since consensuses only include Running relays, and the Running flag is
 assigned by a majority vote, each RSA key, Ed key, IPv4:Port, and
 IPv6:Port must be unique in the consensus.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18318>
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