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Date: Sun, 5 Jul 2015 09:09:55 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: PHC: Lyra2 on GPU

On Sun, Jul 05, 2015 at 01:42:41AM +0200, magnum wrote:
> On 2015-07-04 19:37, Solar Designer wrote:
> >On Sat, Jul 04, 2015 at 07:26:01PM +0200, Agnieszka Bielec wrote:
> >>2015-07-04 19:19 GMT+02:00 Solar Designer <solar@...nwall.com>:
> >>>Maybe the auto-tuning could be done only once, only in reset()?
> >>
> >>it's only in reset but first reset is called for correctness tests and
> >>after that is called before real password cracking
> >
> >Oh.  This is wasteful, but it makes sense.
> >
> >Ideally, we'd auto-tune for the actual loaded hashes, yet also run
> >self-test with those settings (even if suboptimal for the self-test).
> >But I think there's no easy way to do that currently.
> 
> Something like this perhaps?
> 
> void reset(struct db_main *db)
> {
> 	static int tuned_already;
> 
> 	if (db || (options.flags & FLG_TEST_SET)) {
> 		/* look at db for costs, then autotune here */
> 		tuned_already = 1;
> 	}
> 	else if (!tuned_already) {
> 		/* set a fixed low LWS & GWS here */
> 	}
> }
> 
> So if we're running --test, we'll auto-tune at first call to reset() and 
> not re-tune at second call.
> 
> If running an actual crack, we'll self-test with some low LWS/GWS (eg. 
> 8/64) and then once we get a db (which we can look at to see costs) 
> we'll auto-tune for actual costs.
> 
> It would be slightly safer to self-test using the actual LWS/GWS that 
> will be used later, but iirc this can't be done without changing core.

Yes, right, but you may make or propose specific changes to make this
possible.

Alexander

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