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Message-ID: <20150421031546.GA18623@openwall.com> Date: Tue, 21 Apr 2015 06:15:46 +0300 From: Solar Designer <solar@...nwall.com> To: discussions@...sword-hashing.net Subject: Re: [PHC] enhancing Argon2 (was: Competition process) Dmitry, On Tue, Apr 21, 2015 at 05:33:18AM +0300, Solar Designer wrote: > On Mon, Apr 20, 2015 at 11:08:42PM +0200, Dmitry Khovratovich wrote: > > > To increase the latency of tradeoff attacks, I think BlaMka may be used > > > (along with an un-pwxform chain like this, which serves its different > > > purpose - hardening non-tradeoff latency and providing some anti-GPU). > > > > If using BlaMka, why extra xform chain? Oh, there's one more reason: then you don't need to chain your BlaMka's. BlaMka will be to harden the tradeoff latency only, and the scalar chain will be to harden the non-tradeoff latency only. > Mostly for the anti-GPU. > > Also, in pwxform I tried to maximize the per-bit latency (so that one > round's highest latency output bits are needed by the next round early). > I haven't looked into how optimal or not BLAKE2b's rotate counts happen > to be in this respect (and adjusting them may be bad). > > Finally, I suspect the extra chain might allow for a higher number of > sequential multiplies than BlaMka for the same Argon2 performance. The > instruction issue rate for scalar units may be higher than for SIMD, and > the multiply-hardening rounds may be more closely packed together in > un-pwxform than in BlaMka. (I think TwoCats might have had this sort of > advantage over yescrypt, although this was in part because TwoCats had > only multiplies, and not S-box lookups, on the scalar chain.) Alexander
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