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Date: Tue, 21 Jul 2015 12:50:52 -0700
From: Bill Cox <>
To: "" <>
Subject: Re: [PHC] Argon2 improvement thread

On Tue, Jul 21, 2015 at 12:45 PM, Solar Designer <> wrote:

> On Tue, Jul 21, 2015 at 12:24:00PM -0700, Bill Cox wrote:
> > If Alexander proposed to integrate his PWXFORM (I don't know what MAXFORM
> > is), then I would be for it.  This would satisfy my request for improved
> > GPU resistance, and also my request for multiplication-chain computation
> > time hardening.
> MAXFORM is the scalar equivalent to (and subset of) pwxform.  It's
> neither parallel, nor wide, but is otherwise the same.
> It would co-exist with Argon2's existing SIMD code.

Nice!  I was getting excellent multiplication-chain hardening with a
similar approach.  The scalar pipeline has a faster multiplier.

> > There are only two really outstanding SIMD-optimized mixing functions
> which
> > were used in this competition, IMO.  The choices are the reduced-Blake2
> > with or without it's multiplication modification, and PWXFORM.  I suspect
> > between Samuel Neves, Alexander, and the Argon2 team, they could figure
> out
> > the best solution.
> Switching Argon2 to use pwxform would be too much of a change - not
> code-wise, but design-wise.  If we were to do that, then it'd be better
> to go with (simplified) yescrypt or the like instead, which we already
> have separately (just not as the PHC winner).
> Alexander

Got it.  In that case, I'm for the MAXFORM upgrade.  I agree that
Bcrypt-like GPU resistance is a critical defense.  For example, without it,
I would have to use Yescrypt in the PoW systems I've been playing with
rather than Argon2.  With MAXFORM, would Argon2's GPU resistance be as
strong as Yescrypt's?


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