phc-discussions - Re: [PHC] PHC: survey and benchmarks

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Message-ID: <20150406214456.GA17227@openwall.com>
Date: Tue, 7 Apr 2015 00:44:56 +0300
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] PHC: survey and benchmarks

Steve - I think you haven't yet posted a clarification on my concerns
below, yet now this table made its way into Milan's revised report.

Please clarify what exactly you meant by "t_cost for 2x".  Thanks!

On Wed, Apr 01, 2015 at 04:33:54PM +0300, Solar Designer wrote:
> Steve,
> 
> On Mon, Mar 23, 2015 at 09:33:28PM -0500, Steve Thomas wrote:
> > Name       | t_cost for 2x | t_cost for 3x | t_cost for 4x | t_cost for 5x
> > -----------+---------------+---------------+---------------+---------------
> > Argon      | 2             | 3             | 4             | 5
> > battcrypt  | 0             | 1             | 3             | -
> > Catena     | 2             | 3             | 4             | 5
> > Lyra2      | 2             | 3             | 4             | 5
> > POMELO     | 1             | -             | 2             | -
> > Pufferfish | -             | 0             | -             | 1
> > yescrypt   | 3             | 4             | 5             | 6
> 
> For yescrypt it's t = 2 to have it perform 2x the number of read-writes
> compared to the total number of blocks.  t = 0 means 4/3, t = 1 means
> 5/3, and t = 2 means 2.  Then it's just whole numbers.
> 
> So if I understood you right, all of the numbers for yescrypt in the
> table above should be decreased by 1.
> 
> ... or are you only counting memory accesses starting with the point
> where the memory is filled, and not counting the initial accesses
> during memory filling (which often involves reads of previously-written
> blocks, and thus contributes to the attacker's area-time product too)?
> If so, your table is correct (for yescrypt; I didn't verify the rest).
> 
> Alexander