phc-discussions - Re: [PHC] Initial hashing function. Feedback welcome

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Message-ID: <CA+aY-u48TXP4LutbPaAZKRWA4kJYaOXFsPnoF3rG8aMJ84=4TQ@mail.gmail.com>
Date: Sun, 29 Dec 2013 22:50:32 +0000
From: Peter Maxwell <peter@...icient.co.uk>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Initial hashing function. Feedback welcome

On 29 December 2013 22:29, Bill Cox <waywardgeek@...il.com> wrote:

>
> A weakness of the hashing function vs scrypt is that it is a simple
> non-cryptographic hash, rather than script's Salsa20/8.  This is the
> primary reason it runs faster.  If we do not need a strong cryptographic
> hash, there is significant opportunity for improving performance.
>

Afaik, the important property is more that an adversary cannot calculate
what's at each memory location, in a random access model, in less cost than
a memory access.  Or, that the algorithm doesn't create clustered accesses
that can be calculated in a single independent segment.

>
> Is there any reason such a simple hash function should not be used?  I am
> particularly interested in feedback on this point.
>

As far as I know, as long as what you've generated has some fairly basic
properties and would cost more to calculate than the relevant memory
access, you're fine.  I'm open to being corrected though: it's been a
while since I've done any reading on this and I'm not entirely convinced
memory-hard functions are the silver bullet they've been made out to be
anyway.

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