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

Thu Jul 19 05:24:10 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 teor):

 I hope our PRNG is cheap.

 Here's an attack on exits with expensive PRNGs:
 * make a client you control connect to a site you control
 * feed the exit one byte at a time

 The exit then creates ~500 bytes of random padding per byte sent by the
 remote site.
 (This would be a devastating attack if we used /dev/random directly, on an
 OS that thinks entropy is subtractive, like Linux.)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26871#comment:3>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online