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Date: Thu, 23 Jul 2015 03:43:05 +0200
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Cc: Taylor Hornby <havoc@...use.ca>
Subject: Re: [PHC] Argon2 improvement thread

On Thu, Jul 23, 2015 at 02:09:58AM +0100, Samuel Neves wrote:
> On 22-07-2015 22:12, Jean-Philippe Aumasson wrote:
> > @Bill, Solar (and others): blamka and maxform, respectively in Argon2i and
> > 2d, is that what you have in mind, of maxform in both?
> 
> I would like to see a concrete specification of MAXFORM before this is settled. I understand that this is some variant
> of yescrypt's pwxform using MUL-ADD-XOR plus S-box lookups, but I haven't found an actual description of it.

It's a subset of pwxform, with:

PWXsimple = 1
PWXgather = 1

PWXrounds and Swidth are to be agreed upon / tuned specifically for
Argon2d integration.  I had submitted a patch for Argon2d in here, along
with benchmarks showing that there's very little performance impact, and
it used specific sane values.  Optimized implementations will have the
PWXrounds loop fully unrolled with cpp macros, to make the compiler
intermix it with instructions coming from Blake2b rounds.  (The patch I
posted in here did that.)

Do you think we should produce a specification of MAXFORM on its own,
not merely referring to yescrypt's specification of pwxform with the
above two parameters fixed at 1, before we decide on accepting it for
Argon2 tweak?  I'd think the above would be sufficient for the
decision-making, with the concrete specification of MAXFORM on its own
only needed as part of a revision of the tweaked Argon2 specification.

I won't have time to produce a specification of MAXFORM on its own very
soon, but maybe Taylor (CC'ed) would be willing to help?  (Taylor is
working on a hopefully better specification of yescrypt.)

Alexander

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