[tor-bugs] #15918 [Tor]: Investigate using the EVP interface for non-oneshot hash calls.

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#15918: Investigate using the EVP interface for non-oneshot hash calls.
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 Reporter:  yawning                              |          Owner:
     Type:  enhancement                          |         Status:  new
 Priority:  minor                                |      Milestone:  Tor:
Component:  Tor                                  |  unspecified
 Keywords:  tor-core, tor-crypto, openssl, evp,  |        Version:  Tor:
  lorax                                          |  unspecified
Parent ID:                                       |  Actual Points:
                                                 |         Points:
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 People have recently asked about VIA PadLock and cryptdev (#15503/some
 random tor-relays@ post).  Both of these things in theory can do
 SHA1/SHA256 in hardware (though in the case of cryptdev, performance is
 likely to be worse).

 Since it can be a decent gain (at least PadLock will be), we should
 consider switching over the `crypto_digest_t` routines to use the EVP
 interface (People that try to use cryptdev for hashes and suffer a
 performance decrease did not read the documentation, and thus get what
 they deserve).

 Minor (very low priority) because:
  * cryptdev's hash performance will probably suck.
  * OpenSSL does not support PadLock SHA acceleration.
  * The only hardware SHA implementation that's actually relevant to a
 significant sized userbase (ARMv8) is supported via the raw `SHA*`
 routines.

 So this is mostly for future-proofing and code cleanup purposes.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15918>
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