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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