[tor-bugs] #11203 [Obfsproxy]: ScrambleSuit CSPRNG for Probability Distributions

Tor Bug Tracker & Wiki blackhole at torproject.org
Fri Mar 14 03:26:11 UTC 2014


#11203: ScrambleSuit CSPRNG for Probability Distributions
-------------------------------------------------+-------------------------
 Reporter:  yawning                              |          Owner:  asn
     Type:  enhancement                          |         Status:  new
 Priority:  normal                               |      Milestone:
Component:  Obfsproxy                            |        Version:
 Keywords:  scramblesuit, probability            |  Actual Points:
  distribution, random number generator          |         Points:
Parent ID:                                       |
-------------------------------------------------+-------------------------
 As discussed in #10893, ScrambleSuit should use a CSPRNG when
 generating/sampling the probability distributions for the packet length
 and inter packet arrival times.

 I have went ahead and implemented this in a branch at
 https://github.com/yawning/obfsproxy/tree/ctr_drbg

 It appears to work though packet distributions for existing bridges will
 change when they update to use the new PRNG (for obvious reasons).  There
 also are some unit tests that use the NIST AES CTR test vectors to make
 sure that the bytes that are expected to come out with a given key/initial
 counter do.

 phw said I should be doing development vs the scramblesuit repo, but since
 the plan is to fold the repo with history into obfsproxy, I did it the
 other way.  If needed, I will move the ctr_drbg module into
 scramblesuit/transports and make a scramblesuit branch for this, but since
 it's not a critical thing, merging this can wait till after the repo
 madness is done.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11203>
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