phc-discussions - Re: [PHC] Added "lanes" and 3 hash functions as inputs

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Date: Wed, 19 Mar 2014 13:45:47 +0400
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Added "lanes" and 3 hash functions as inputs

On Tue, Mar 18, 2014 at 07:46:29PM -0400, Bill Cox wrote:
> I'm still making last-minute upgrades.  I added a "lanes" parameter to
> the "extended" interface which normally is set to the number of 32-bit
> ints in the hash function in use.  For SHA256 and Blake2s, it is 8,
> and for SHA512 and Blake2b, it's16.  This was meant to match the SIMD
> units on high-end CPUs, but it works against low-end CPUs.  Instead of
> calculating 8 or 16 lanes in parallel, a low-end CPU can now do just
> one, if it has no SIMD unit.
> 
> The architecture had a pluggable hash function architecture before,
> but Blake2s was the only option.  I've added three more: Blake2s,
> SHA256, and SHA512.  Naturally it took some work to make it really
> easy to add new ones.

Having the number of lanes tunable is great.  Having it depend on the
chosen underlying crypto primitive is not great.

> I still feel like a pluggable large memory block hash function would
> be a good thing, but if mine's the only one to do such a thing,
> there's not really much point.

Doesn't escrypt have a large block multi-lane hash function like this?
It's not pluggable, but I'm not sure it needs to be.  For now, it can be
part of a password hashing scheme.  And yes, I'm still working on
improving this component in escrypt, and it still needs a name...
although most likely I'll call it pwxform, for "parallel wide
transformation", even though it may be scaled down to one 64-bit lane.

Alexander