[tor-bugs] #22460 [Core Tor/Tor]: Received a bad CERTS cell: Link certificate does not match TLS certificate

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#22460: Received a bad CERTS cell: Link certificate does not match TLS certificate
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 Reporter:  teor                                 |          Owner:
     Type:  defect                               |         Status:  new
 Priority:  High                                 |      Milestone:  Tor:
                                                 |  0.3.1.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Major                                |     Resolution:
 Keywords:  tor-relay certs handshake ed25519    |  Actual Points:
  needs-analysis 030-backport                    |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by nickm):

 BINGO.  I have a diagnosis for at least part of the bug.  Specifically,
 this would explain the "At least one Ed25519 certificate was badly signed"
 case.

 In load_ed_keys(), and in generate_ed_link_cert(), we check to see whether
 our SIGNING->AUTH certificate and our SIGNING->LINK certificate have a
 signed key that matches our current key... but we don't make sure that the
 _signing_ key matches the current _signing_ key.  So when the _signing
 key_ is updated, we'll keep serving certificates signed with the old
 signing key.

 Furthermore, in rotate_x509_certificate_callback(), we don't call
 generate_ed_link_cert(), which means that our link cert will remain
 outdated for a while.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22460#comment:23>
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