[tor-bugs] #30172 [Core Tor/Tor]: Always send PADDING_NEGOTIATE if middle supports it

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#30172: Always send PADDING_NEGOTIATE if middle supports it
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     Reporter:           |      Owner:  (none)
  mikeperry              |
         Type:           |     Status:  new
  enhancement            |
     Priority:  Medium   |  Milestone:
    Component:  Core     |    Version:
  Tor/Tor                |   Keywords:  wtf-pad, tor-relay, tor-cell,
     Severity:  Normal   |  padding, 041-proposed
Actual Points:           |  Parent ID:  #28634
       Points:           |   Reviewer:
      Sponsor:           |
  Sponsor2-can           |
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 We should define some kind of NULL machine for whatever hop is most common
 in our padding machine list, and always negotiate that machine.

 Similarly, this NULL machine should (maybe) set should_negotiate_end and
 send a PADDING_NEGOTIATE at circuit close.

 We need to do this so that there isn't an obvious PADDING_NEGOTIATE cell
 request/response pair with obvious timings that it went to the middle node
 (ie the response will come faster than all other responses on the
 circuit). See also #30092 for similar motivating reasoning.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30172>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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