[tor-bugs] #26871 [Core Tor/Tor]: prop289: randomize the unused part of relay payloads

Tor Bug Tracker & Wiki blackhole at torproject.org
Thu Jul 19 06:03:11 UTC 2018


#26871: prop289: randomize the unused part of relay payloads
-------------------------------------------------+-------------------------
 Reporter:  teor                                 |          Owner:  dgoulet
     Type:  enhancement                          |         Status:
                                                 |  assigned
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.5.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  prop289, 035-roadmap-master, 035     |  Actual Points:
  -triaged-in-20180711                           |
Parent ID:  #26288                               |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by arma):

 Replying to [comment:3 teor]:
 > Here's an attack on exits with expensive PRNGs:

 (a) don't just worry about exits; clients also will fill relay payloads.

 (b) if this is actually a practical issue, I could get behind a design
 where we randomize only the first byte of the unused part of the relay
 payload. That would serve my purposes. But I bet we'd be forever
 explaining to people why we cut that corner.

 (c) For added efficiency, let's only *sometimes* randomize that first
 byte. We can flip a coin to figure out whether we will, thus saving the
 prng that extra call to -- oh. :)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26871#comment:4>
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