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Date: Sun, 5 Jul 2015 10:44:27 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: PHC: Lyra2 on GPU

Agnieszka,

On Sat, Jul 04, 2015 at 07:22:08PM +0300, Solar Designer wrote:
> By the way, while your current choice of:
> 
> > >> Speed for cost 1 (t) of 8, cost 2 (m) of 8, cost 3 (c) of 256, cost 4 (p) of 2
> 
> is fine for testing, I think for all of the PHC finalists we need to
> tune parameters to a level comparable with defensive use of bcrypt at
> cost 5, using this as our baseline.
> 
> When used defensively and running an efficient implementation, bcrypt at
> cost 5 achieves about 541*8 = ~4330 c/s on i7-4770K:
> 
> solar@...l:~/crypt_blowfish-1.2-notest$ ./crypt_test_threads 
> 602.8 c/s real, 602.8 c/s virtual
> 0: 540.4 c/s real
> 1: 542.4 c/s real
> 2: 542.4 c/s real
> 3: 542.6 c/s real
> 4: 540.4 c/s real
> 5: 540.4 c/s real
> 6: 542.4 c/s real
> 7: 540.4 c/s real
> 
> So you'd need to tune the PHC finalists to achieve the same defensive
> use performance for their most optimal implementations on "well", and
> these will be the settings you'd use for attacking them on GPU.  You'd
> set t_cost to the lowest supported value, parallelism to 1 (no thread
> level parallelism within one instance), the rest of parameters as
> recommended by the PHC finalist designers, and tune m_cost to achieve
> the defensive speed above.

Just to make it clear: this is important and high priority, for all of 
your PHC finalist formats.

Also, please add an output line showing the per-instance memory size, as
derived from the cost settings being benchmarked.  E.g., this would have
printed "192 KiB" (or the equivalent in bytes) for your Lyra2 benchmarks.

> As an extra test, you'd set t_cost higher and m_cost lower, still for
> the same defensive speed.  But it's just an extra.  The main test should
> use the lowest supported t_cost.

Alexander

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