[tor-bugs] #15503 [Tor]: VIA PadLock suupport does not work.

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#15503: VIA PadLock suupport does not work.
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     Reporter:  toyboy  |      Owner:
         Type:  defect  |     Status:  new
     Priority:  normal  |  Milestone:  Tor: 0.2.???
    Component:  Tor     |    Version:  Tor: unspecified
   Resolution:          |   Keywords:  VIA PadLock, lorax
Actual Points:          |  Parent ID:
       Points:          |
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Comment (by anon):

 For SHA, and getting access to state before finalization, see this
 undocumented behavior:

 "On VIA Nano and later, you can perform partial hashes by setting EAX to
 FFFFFFFF before executing the REP XSHA1/256 instruction - and the CPU
 won't perform the final padding (so you can simply feed the chunks into
 the hash, just as you usually do with hashing functions). On older models
 (up to C7), such a possibility is not present, EAX has to be set to zero
 before the hash instruction, and a full hash (i.e. including the final
 padding) is performed." - http://stackoverflow.com/questions/21526677
 /streaming-sha-calculation-using-vias-padlock-hashing-engine

 They link to the VIA Padlock SDK which contains examples of this usage.

 Prior to all bits high option, you could trigger a bus error like
 exception during call, which left the state un-finalized. The performance
 hit of this method may make it useful to avoid side channels in software
 impls but gain nothing or very small in terms of performance.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15503#comment:4>
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