[tor-bugs] #26228 [Core Tor/Tor]: Clarify/determine specification for padding bytes, (formerly also PADDING cell)

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#26228: Clarify/determine specification for padding bytes, (formerly also PADDING
cell)
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 Reporter:  dmr           |          Owner:  dmr
     Type:  defect        |         Status:  needs_revision
 Priority:  Medium        |      Milestone:  Tor: 0.3.5.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  tor-spec      |  Actual Points:
Parent ID:  #26869        |         Points:
 Reviewer:                |        Sponsor:
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Comment (by dmr):

 Replying to [comment:12 teor]:
 > Oops. VERSIONS cells can't have (more than 1 byte of) random padding,
 because it will be interpreted as an extra version.

 Actually, well-formed VERSIONS cells can't have //any// (fully) random
 padding.

 The spec [[https://gitweb.torproject.org/torspec.git/tree/tor-
 spec.txt?id=ce1d4a8b7e1e5eb714068a8cf44fdc5ae24460d9#n556|says]]:
 > Either party MUST close the connection if the versions cell is not well-
 formed (for example, if it contains an odd number of bytes).

 It's unclear in the spec if you can pad VERSIONS cells by repeating (pairs
 of) version bytes. The algorithms described in the spec make it sound
 possible, but "not well-formed" is a bit loosely defined.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26228#comment:14>
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