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Date: Sun, 18 Nov 2012 15:38:40 +0400
From: Solar Designer <solar@...nwall.com>
To: Colin Percival <cperciva@...snap.com>
Cc: scrypt@...snap.com, crypt-dev@...ts.openwall.com
Subject: Re: scrypt time-memory tradeoff

On Sun, Nov 18, 2012 at 03:23:31AM -0800, Colin Percival wrote:
> You get a 2x cost reduction by trading increased time for reduced area (as
> in a previous email) and another 2x reduction by ignoring the initial setup
> (practically speaking)

Yes, that's what I was thinking.  The initial setup time becomes
negligible compared to that of the second phase - or it can even be
fully removed, but that's not optimal in practice because the Salsa20
core has some area cost too.

> but I never intended to include the setup in my
> area-time bound.

Oh, that's nice.

In other words, you could have killed this trade-off (by slightly
different design) and then claim 4x or 2x higher costs (depending on
whether the trade-off was accounted for in the costs or not).

Alexander

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