[tor-bugs] #4900 [Tor]: Use a more randomized hash function for our hash tables

[Tor Bug Tracker & Wiki]

#4900: Use a more randomized hash function for our hash tables
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     Reporter:  nickm        |      Owner:
         Type:  enhancement  |     Status:  needs_review
     Priority:  major        |  Milestone:  Tor: 0.2.5.x-final
    Component:  Tor          |    Version:
   Resolution:               |   Keywords:  dos security tor-relay
Actual Points:               |  Parent ID:
       Points:               |
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Changes (by nickm):

 * status:  new => needs_review


Comment:

 My branch bug4900_siphash_v2 is where it's at.  Please review.

 Before this branch:
 {{{
 digestmap_set: 43.14 ns per element
 digestmap_get: 32.29 ns per element
 }}}

 preliminary performance results with this branch:
 {{{
 digestmap_set: 64.79 ns per element
 digestmap_get: 54.71 ns per element
 }}}

 IMO, that's not a terrible price to pay for acceptable DoS resistance
 here.  If we find some place where it actually matters for Tor
 performance, we can optimize that or look at other data structures.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4900#comment:13>
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