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

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#3122: Write and use constant-time comparison functions
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 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:                    
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Comment(by nickm):

 I threw together some quick and dirty timing code at
 http://www.wangafu.net/~nickm/volatile/memcmp_timing.gitbundle , based on
 rransom's repo.  The emphasis is on *dirty*: either i am testing it wrong,
 or I am doing the stats wrong on the output, or something.

 Things to check: Did I get the T-value calculation about right?  Should I
 just be piping the results to R to do my stats instead?

 Does the way that I make a change to the n'th position between calling
 memcmp (to prevent the compiler from caring that memcmp is
 __attribute__((pure, const)) ) affect cacheing?

 Suggestive datum: The reported T values are high even for the function
 do_nothing_at_all, which doesn't actually do anything but add all the
 bytes in its inputs and return the results.  This suggests a bug in the
 harness or in the analysis.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/3122#comment:18>
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