[tor-bugs] #25753 [Core Tor/Tor]: Check/enforce path restrictions for each path position

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#25753: Check/enforce path restrictions for each path position
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     Reporter:  mikeperry     |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  034-roadmap-subtask
Actual Points:                |  Parent ID:  #25546
       Points:                |   Reviewer:
      Sponsor:                |
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 For the vanguard torrc options, we may want to check that each layer has
 at least one node from a different /16 and different node family than
 others in that layer, to ensure that a path can always be built using the
 vanguard set.

 We may also want to do the same thing for Tor's Primary Guard set from
 Prop271, to ensure that an adversary can't force the user to pick guards
 randomly from Sampled Guards.

 Doing both of these things at once should allow us to drop #24487.

 See also: https://gitweb.torproject.org/torspec.git/tree/proposals/291
 -two-guard-nodes.txt#n33

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25753>
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