phc-discussions - Re: [PHC] multiply-hardening (Re: NoelKDF ready for submission)

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Message-ID: <20140210025703.GA17198@openwall.com>
Date: Mon, 10 Feb 2014 06:57:03 +0400
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] multiply-hardening (Re: NoelKDF ready for submission)

On Mon, Feb 10, 2014 at 06:46:46AM +0400, Solar Designer wrote:
> PMULLW is 8 packed 16x16->16.  I felt that if we go for 16x16, we
> probably want to take the upper 16 bits of result (so PMULHW or PMULHUW
> or PMULHRSW), not lower, although this does make the signedness matter.
> 
> We'd need to compare ASIC circuit sizes for lower vs. upper 16 bits.

Actually, mostly not sizes, but number of levels, as you've nicely
illustrated by your examples of multiplying by a constant.

Alexander