Date: Wed, 19 Apr 2017 10:04:03 -0700
From: Bill Cox <waywardgeek@...il.com>
To: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>
Subject: Re: [PHC] Fwd: memory-hard password hashing

I wrote a GPU-focused memory-hard proof-of-work algorithm with fast
verification I call GPU Hog.  Basically, it hashes the input key material
to init a CPRNG that selects several 4 KiB blocks from a multi-GiB pool of
pseudo-random data.  It hashes the selected blocks together, and if the
result has enough leading zeros, then you've proven you have done enough
work.

It requires a modern GPU with high GDRAM bandwidth since it is memory
bandwidth limited.  For mining, you need all of the pseudo-random data in
memory to mine efficiently, but for verification, you only need to generate
the several pseudo-random blocks and hash them together.  Verification is
faster than a typical public key operation, so it would not be the
bottleneck in verifying a block-chain.

Is this similar to what you had in mind, or are you specifically looking
for GPU based password hashing?  I think that password hashing on mobile
phones and tablets could be considerably strengthened using their graphics
processors.

Bill

On Wed, Apr 19, 2017 at 9:38 AM, Dean Pierce <pierce403@...il.com> wrote:

> Personally I think "GPU friendly" is not a great thing for passwords,
> since GPUs are asymmetrically more popular with attackers, but you might be
> interested in checking out the "Vertcoin" project: https://vertcoin.org/
>
> It's a cryptocoin, similar to Bitcoin, with the gimmick that they have
> always tried to target the GPU mining audience.  Their proof of work
> started out with an adaptive N scrypt algorithm, but when KnC released
> scrypt ASICs, they pivoted to a modified Lyra2, at which point a large
> botnet took control of most of the mining power, and they pivoted again
> with a Lyra2 more finely tuned for modern GPUs.
>
> I think the ideal goal for password algorithms is CPU friendly, where the
> most efficient machinery for calculating the hash is a commodity CPU.  At
> that point, you could roll your own ASICs, but they wouldn't be much better
> than what you could just pick up at Best Buy, and you'd lose out on the
> economies of scale that CPU vendors have.
>
>   - DEAN
>
> On Wed, Apr 19, 2017 at 9:07 AM, Erik Aronesty <erik@....com> wrote:
>
>> There is a focus on memory-hard algorithms in password hashing, since
>> that renders them ASIC/GPU resistant.
>>
>> However, it is /possible/ for an ASIC to be tightly coupled with DRAM in
>> ways that can exceed PC memory performance.
>>
>> Instead, is there an algorithm that is "very GPU friendly"?
>>
>> GPU's are cheap, common and highly optimized for certain operations in
>> ways that make the construction of ASICs that beat them at what they are
>> best at very unlikely.   They are, essentially, "floating point matrix
>> operation ASICs".
>>
>> Yes, this means that servers using such a mechanism may want to have GPUs
>> installed to reduce hashing times and allow a larger number of operations
>> to increase hashing security.   But I think this is a reasonable request
>> for many applications.
>>
>> If it takes 10 milliseconds to compute a single hash with highly parallel
>> FLOPs on a modern GPU, that affords a massive amount of security for a hash
>> - ASIC resistant in ways that memory-hard algorithms cannot be.
>>
>> Is there an algorithm that already lends itself to this kind of
>> application?
>>
>>
>

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