Re: Patch: cprng_fast performance - please review.

[darkstar%city-net.com@localhost]

> I would still suggest Salsa20 or ChaCha.  My measurements with naive C
> code suggest that, if you buffer the output for short outputs, these
> take on average 40-50 Ivy Bridge cycles per request.  (If you don't
> buffer the output, it's 300 cycles.)  Long requests get ~4 cpb.  In
> contrast, libc random(3) takes on average 50-60 Ivy Bridge cycles per
> request, and long requests get ~13 cpb.

  It is also possible to used reduced round versions of these; I believe
the best known attacks are still on 8 rounds of Salsa20 and 7 of ChaCha
and the default is 20 rounds.  20, 12, and 8 are the suggested numbers
of rounds.  It may well be safer to use ChaCha/8 than some other
algorithm (the known attacks on Salsa20/8 and ChaCha/7 are not that
good).

-Matt