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Date: Wed, 25 Mar 2015 07:49:15 +0300
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Another PHC candidates "mechanical" tests (ROUND2)

On Tue, Mar 24, 2015 at 11:50:44PM +0100, Milan Broz wrote:
> The updated test report (draft) is here
> 
>   https://github.com/mbroz/PHCtest/blob/master/output/phc_round2.pdf

Thank you!

I think you should include more info on your two test platforms.  Most
notably, the specific CPU types and clock rate.

The charts showing real memory usage and real time vs. the cost
parameter values might be useful, but it would also be useful to see a
cross-chart of real memory usage vs. real time (with the lowest time cost
setting supported by each scheme) and with growing memory cost setting
(this is how you'd control the real time).

> - battcrypt, MAKWA, Parallel and yescrypt produces the same output on big-endian system.
>   All other candidates are broken there (probably quite easy fixes possible).

To other candidate authors: I may provide SSH access to a FreeBSD/mips64
toy machine (64-bit big-endian) that I use for testing.  It's just like
this one: http://rtfm.net/FreeBSD/ERL/  Please e-mail me off-list if
interested.

> - I added some test case for my intended use (KDF for LUKS) for few functions.

Lyra2 is surprisingly fast.  That's nice.  Your table does not give
exact numbers for candidates meeting your requirements, though - maybe
you can add that (for their lowest supported t_cost)?

As to yescrypt taking 1.3s for 1 GB, I'd say that consuming 1 GB isn't a
goal per se.  The goal is attack resistance.  Quite possibly yescrypt's
6 sequential pwxform rounds (each with two S-box lookups and one
multiply) per sub-block provide more attack resistance in the time
factor of the area-time product than Lyra2's higher memory filling speed
does in the area factor (if you measured these two at the same running
time, so with different memory usage).  Besides, yescrypt tries not to
bump into the memory bandwidth prematurely, thereby letting you use
multiple threads to a greater advantage.  If you do not intend to use
multiple threads and want to maximize the memory filling speed by your
one thread (even if at expense of possibly reducing the attacker's
area-time product, via the potentially much lower time factor), you may
reduce yescrypt's pwxform round count from 6 to 1 as Bill suggested.  In
yescrypt-simd.c, simply delete 5 of the 6 repetitions of PWXFORM_ROUND
in the PWXFORM cpp macro.  I got to make this runtime tunable (easy),
even if just to show that yescrypt is (more) competitive. ;-)

Thanks again,

Alexander

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