[tor-bugs] #25574 [Core Tor/Tor]: Eliminate "silent-drop" side channels in Tor protocol

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#25574: Eliminate "silent-drop" side channels in Tor protocol
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 Reporter:  mikeperry              |          Owner:  (none)
     Type:  defect                 |         Status:  new
 Priority:  Medium                 |      Milestone:  Tor: unspecified
Component:  Core Tor/Tor           |        Version:
 Severity:  Normal                 |     Resolution:
 Keywords:  guard-discovery-stats  |  Actual Points:
Parent ID:                         |         Points:  10-30
 Reviewer:                         |        Sponsor:  SponsorV-can
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Comment (by cypherpunks):

 there are lots of ways to do it, but the dropmark paper says:

 > We used relay drop cells because they do not raise any log message.


 why is that?

 i found some history:

 Once-upon-a-time DROP cells **were** getting logged. Roger `//`'ed it out
 in '06 cause it was "loud":
 https://gitweb.torproject.org/tor.git/commit/?id=9bc8d69dfc4ddda5a9c8478b1f1e04490845ded0

 (:thinkingface: how was that "loud"? was anything besides attackers
 sending DROP cells in 2006?)

 mikeperry replaced the `//`'ed log line with `return 0` in 2018:
 https://gitweb.torproject.org/tor.git/commit/?id=7be71903daff042e606e7a8445a6359100c9f8f5

 But even if tor had no silent drops relays could still embed timing
 signals like Jann Horn demonstrates here:
 https://var.thejh.net/git/?p=detour.git;a=blob;f=README (what ticket
 number is that?)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25574#comment:7>
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