[tor-bugs] #3122 [Tor Client]: Write and use constant-time comparison functions

[Tor Bug Tracker & Wiki]

#3122: Write and use constant-time comparison functions
-------------------------+--------------------------------------------------
 Reporter:  rransom      |          Owner:  ioerror           
     Type:  enhancement  |         Status:  new               
 Priority:  major        |      Milestone:  Tor: 0.2.1.x-final
Component:  Tor Client   |        Version:                    
 Keywords:               |         Parent:                    
   Points:               |   Actualpoints:                    
-------------------------+--------------------------------------------------

Comment(by rransom):

 Replying to [comment:8 nickm]:
 > III. Other things
 >
 > We need to look for other kinds of operations that alter control flow
 based on sensitive information.  This includes at minimum auditing hash
 tables and lookup functions.  This will be an ongoing thing.

 The solution here is to ''never'' use a secret string as a lookup key in
 an associative data structure.  One easy way to do this is to HMAC the
 secret lookup key with an ephemeral secret HMAC key; the result is not so
 secret, although we would still use our constant-time comparison functions
 within the data structure's implementation purely for performance reasons.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3122#comment:11>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online