[tor-bugs] #33129 [Core Tor]: Tor node that is not part of the consensus should not be used as rendezvous point with the onion service

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#33129: Tor node that is not part of the consensus should not be used as rendezvous
point with the onion service
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 Reporter:  cypherpunks     |          Owner:  (none)
     Type:  defect          |         Status:  needs_information
 Priority:  Very High       |      Milestone:
Component:  Core Tor        |        Version:
 Severity:  Critical        |     Resolution:
 Keywords:  onion services  |  Actual Points:
Parent ID:                  |         Points:
 Reviewer:                  |        Sponsor:
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Comment (by s7r):

 I agree with you. It is actually bad for performance if we want to request
 that the RP point should be part of the consensus (for the onion service
 server view of the network). Onion service client and onion service server
 can have (and will often have) different views over the network.

 If we change this, it will be incompatible with Nick's walking onions
 vision (which I really think is the way to go for the really really long
 term).

 Also, it gives us only downsides. Because it doesn't actually fix
 anything. The attack is still possible exactly the same (not even with
 slight additional effort from the attacker), because the RP is selected by
 the onion service CLIENT (which we should always assume it's an attacker)
 thus it's trivial to spin in some malicious middle relays (cheap to setup,
 not even required to have the Guard flag), wait for the first consensus
 and use them to carry on this attack just fine.

 I indicated this back in 2016, and wrote a proposal attempt:
 https://lists.torproject.org/pipermail/tor-dev/2016-January/010291.html

 mikeperry considered it and implemented it as part of the vanguards
 defense as `Rendguard`. If we change something, this should be a default
 from my perspective, regardless to layer 2 and layer 3 guards for onion
 service server. Because as opposite to layer 2 and layer 3 guards, the
 rendguard subsystem doesn't face the load-balancing and fingerprinting
 potential problems.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33129#comment:2>
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