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Date: Tue, 22 Apr 2014 14:53:40 +0200
From: Dmitry Khovratovich <khovratovich@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] Any other authores ready for benchmarking? (was [PHC] Lyra2
 initial review)

Hi Bill,

Please feel free to benchmark the optimized Argon with 4/8/16 threads.

Regarding the memory bandwidth, Argon with default parameters accesses each
memory location 12 times for reading and 11 times for writing on average
(Section 6.4 of the submission document). If I understand your metrics
correctly, this gives 23x multiplier on the speed that is around 9 cycles
per byte for 1 GB of RAM used (330 MB/sec on a 3 GHz CPU).

Best regards,
Dmitry


On Fri, Apr 18, 2014 at 8:34 PM, Bill Cox <waywardgeek@...il.com> wrote:

> Yesterday, I had some fun benchmarking Lyra2, TwoCats, and Yescrypt.  Are
> there any other authors who would like their algorithms benchmarked?  I'd
> be happy to start tabulating data on all the entries that are ready for
> benchmarking.  After yesterday's hack-fest, I don't feel simply running the
> PHS routines without the involvement of the author is likely to generate
> useful data, so I'm only going to do benchmarking the authors request for
> now.
>
> We should discuss what to measure and how to report it.  Is there a better
> place than posting it here?
>
> I think we maybe we need three memory size categories, where PHC entries
> can be benchmarked in any or all of them.  Basically, the 3 memory sizes
> correspond to:
>
> - L1 cache bound:  how about 8KiB?
> - Cache bound: how about 8MiB?
> - External DRAM bound: how about 2GiB?
>
> Also, some are not memory bound, for PBKDF2-like entries.  It's best if we
> stick to powers of two for memory size, as some entries require that.
>
> The simplest thing to report is how long a algorithm takes to run to hash
> for a given amount of memory, so I think we should report that.  However,
> it needs to be interpreted based on what the algorithm is doing.  Assuming
> the algorithm is linear in runtime for the range of memory in the category
> (for example, heavily external DRAM bound), then we can can convert runtime
> to now many MiB or GiB would be hashed in a 1 second runtime, by dividing
> the memory hashed by the runtime.  This let's us compare the memory*time
> cost for a 1 second runtime, and obviously higher is better.
>
> An important modification to the GiB/s hashed is the expected "average"
> memory usage for a 1 second run.  Several entries call malloc or a similar
> function to allocate uninitialized memory, and in a first loop they fill
> that memory.  Linux does not allocate physical memory to malloc-ed address
> space until it is accessed, so memory usage increases roughly linearly for
> the first memory filling loop.  TwoCats fills memory and is done, so it's
> average memory usage is only 1/2 of the total.  Others mostly write to
> memory more than once, and so they reach peak memory early in the
> algorithm.  For example Scrypt would be expected to have around a 75%
> average memory usage relative to the total used, since it fills memory
> linearly in the first loop and hashes it once in the second loop.
>
> Finally, there's memory bandwidth, which should be in terms of MiB or GiB
> per second read/write to DRAM or cache.  Memory bandwidth is the primary
> runtime defense for a lot of the entries, so having high bandwidth is very
> important.  We can estimate memory bandwidth by the total memory hashed
> divided by runtime, times the number of memory accesses on average.  Cache
> adds a complication when estimating external DRAM bandwidth, but so far
> we've been able to guestimate which reads are most likely cached, and
> discount them for external DRAM bandwidth.  For example, for TwoCats, I
> estimate each DRAM location is written on average once, and read on average
> once, the same as Scrypt.
>
> Are these the right metrics?
>
> Bill
>



-- 
Best regards,
Dmitry Khovratovich

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