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Date: Thu, 27 Mar 2014 10:07:34 -0700
From: Jeremi Gosney <epixoip@...dshell.nl>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] pufferfish

On 3/27/2014 9:55 AM, Solar Designer wrote:
> Jeremi,
>
> On Tue, Mar 25, 2014 at 01:39:58AM +0400, Solar Designer wrote:
>> OK, maybe it makes sense to apply this approach to L2, despite of the
>> inefficiency.  Or maybe not.  Typical L2 is 256 KB/core (it has actually
>> decreased in size when L3 was introduced), meaning 64 KB/thread may be
>> "safe" to use.  At this size, my guess is you give advantage to some GPU
>> attackers vs. your typical defender, for the reason explained above.
> I did some testing with escrypt's S-boxes, and things are reasonably
> good.  For the first few doublings of S-box size, beyond L1 cache size
> but still fitting in L2 cache, there's only a ~10% performance hit per
> doubling on Sandy Bridge-EP.  It's not worse than that in part because
> escrypt also does some L2/L3/RAM accesses anyway, so there's some L1
> cache thrashing going on anyway.  For pufferfish, the slowdown per
> doubling of S-box size might be a bit higher (although I guess it'd
> start only with 16 -> 32 KiB), but perhaps not terribly so.  1 MiB total
> memory, 2 threads/core, slowdown by S-box size:
> [...]
> I stopped this at 128 KiB since going beyond 256 KiB combined for the
> two threads is "unsafe" for many CPUs, so higher values are probably not
> reasonable due to higher risk of incurring unacceptable slowdowns after
> migrations to other/future systems.  Indeed, we could test them anyway.
>
> This is for AVX builds of current development escrypt.  The random
> lookups are 128-bit wide, made with AVX instructions.  They're uniformly
> distributed over the S-boxes of the sizes given above.

Thanks, this is helpful. Is your code for escrypt public yet?

Also, I added a jtr patch for the reference implementation of pufferfish
to my github repository:

https://raw.githubusercontent.com/epixoip/pufferfish/master/jtr/pufferfish-ref.diff

I'm working on an optimized version now, and hopefully if time permits,
a GPU version.

Jeremi

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