[tor-bugs] #22963 [Core Tor/Tor]: Make relay integrity digests harder to guess by padding cells with random bytes

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#22963: Make relay integrity digests harder to guess by padding cells with random
bytes
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     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  security
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 The tor spec says we should put random bytes in padding cells:
 https://gitweb.torproject.org/torspec.git/tree/tor-spec.txt#n1534

 But we don't currently do this (see #22948).
 And we don't put random bytes in other cells.

 This makes it easier to guess the circuit integrity digest, which makes
 some DoS and malleability attacks easier.

 Should we pad all cells with random bytes?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22963>
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