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Date: Tue, 05 May 2015 14:59:35 +0000
From: Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Argon2

To clarify: I'd talk of optimizations rather than tweaks, after we've
selected the winner. I'm not planning another round of tweaks and
evaluations that would delay the process. If the panel selects some Argon2
variant as a winner, the final version may be optimized jointly with the
authors. A bit like Keccak/SHA3 was optimized after being selected by NIST.

On Tue, May 5, 2015 at 3:50 PM Solar Designer <solar@...nwall.com> wrote:

> On Tue, May 05, 2015 at 01:06:56PM +0200, Dmitry Khovratovich wrote:
> > We appreciate the panel's decision.
> >
> > Argon2 will become even better. We plan to add new features and
> > security enhancements in a post-PHC tweak. The tweak will contain:
>
> I think PHC should accept tweaks to finalists, now including to Argon2.
> Otherwise, expecting post-PHC tweaks to the same schemes is a (minor?)
> reason for PHC not to select those schemes as winners, as we'd expect
> fragmentation (e.g., "Argon2 is a PHC winner, but the Argon2 team now
> recommends Argon2+tweaks for actual use").
>
> I hope the PHC panel will agree to accept tweaks, or better yet will
> request specific tweaks from designers, so we won't have to discriminate
> against post-PHC-tweaks-expected finalists.
>
> >  - new indexing function, that makes the memory access pattern more
> > uniform and also strengthens the TMTO resistance. We are currently
> > working out the best solution by
> > calculating the penalties for various existing (Bill's distancecubed,
> > Solar's sliding window) and our own indexing functions using the
> > improved version of the ranking tradeoff algorithm.
>
> Sounds good.
>
> >  - new internal permutation that uses integer multiplication for
> > hardening and chains the subblocks in the way that maximizes the
> > non-tradeoff latency.
>
> Will it also include bcrypt-like rapid lookups?
>
> Will the chaining of sub-blocks be tunable?
>
> I think my suggested MAXFORM chain was almost ready for inclusion, with
> only S-box initialization and overwrites needing to be added.
> It'd avoid the need for you to chain the sub-blocks, so would be more
> scalable (when that parallelism is eventually needed on future CPUs,
> it'd be right there - just decrease the MAXFORM chain length to reduce
> the latency bottleneck and use the parallelism).
>
> > We plan to finish these ideas by the end of the month. The design
> > rationale will be published, as usual.
>
> Sounds great.  Especially the timing.
>
> > Today, however, we are proud to announce a feature for Argon2, that
> > makes it suitable for cryptocurrencies. Namely, it enables fast,
> > memoryless verification in a non-interactive way. In a concrete
> > example, a proof for running 3-pass Argon2 using 2 GB of RAM is only
> > 500 KB in size and the verifier has to just hash (with Blake2) the
> > string of about the same size, i.e. this takes milliseconds.
> >
> > The full paper is available here
> > https://www.cryptolux.org/images/9/95/Fast_memory_hard.pdf , and this
> > new feature is described in Section 8. You do not need to know many
> > details about Argon2 to read it.
>
> Interesting.  I'll plan to take a look when I have time.
>
> Thank you!
>
> Alexander
>

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