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Message-ID: <50A8C596.6080406@tarsnap.com>
Date: Sun, 18 Nov 2012 03:25:10 -0800
From: Colin Percival <cperciva@...snap.com>
To: Solar Designer <solar@...nwall.com>
CC: scrypt@...snap.com, crypt-dev@...ts.openwall.com
Subject: Re: scrypt time-memory tradeoff
On 11/18/12 03:19, Solar Designer wrote:
> On Sun, Nov 18, 2012 at 03:07:54AM -0800, Colin Percival wrote:
>> This is correct, and gives you asymptotically a 2x reduction in area-time
>> cost during the second phase.
>
> Yes, but that's 4x for scrypt overall.
Right, by ignoring the setup phase.
>> Which falls within the definition of "constant
>> factor", and was taken into account in the cost estimates in the paper.
>
> Was it? That's good news. IIRC, when I tried repeating your cost
> calculations ~2 years ago, I managed to arrive at numbers in your paper
> without taking this trade-off into account. So it must be one of: I
> made an error back then, I do not recall correctly, or you did not
> actually take this into account. Should we verify those numbers now?
I was certainly aware of these factors, and intended to take them into account
in my estimates. But I'm not so brave as to claim that I definitely didn't
lose a factor of 2 when I was doing my calculations. :-)
--
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid
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