phc-discussions - Re: Security of these two hash functions?

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Date: Sat, 22 Feb 2014 09:00:21 -0500
From: Bill Cox <waywardgeek@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: Security of these two hash functions?

On Fri, Feb 21, 2014 at 5:32 PM, Bill Cox <waywardgeek@...il.com> wrote:
> TigerKDF, as I'm calling the successor to NoelKDF, uses two hash
> functions.  The first is a multiplication intensive compute-hardened
> loop that is hard to speed up even in custom hardware.  It hashes 256
> bits of state in a long permutation, with applications of Blake2s
> after every "block", which is typically 4000 iterations long:
>
> // Do low memory-bandwidth multiplication hashing.
> static void multHash(uint32_t hash[8], uint32_t numblocks, uint32_t repetitions,
>         uint32_t *multHashes, uint32_t multipliesPerBlock, uint32_t
> parallelism) {
>     uint32_t state[8];
>     hashWithSalt(state, hash, parallelism);
>     for(uint32_t i = 0; i < numblocks*2; i++) {
>         for(uint32_t j = 0; j < multipliesPerBlock * repetitions; j++) {
>             // This is reversible, and will not lose entropy
>             state[j&7] = (state[j&7]*(state[(j+1)&7] | 1)) ^
> (state[(j+2)&7] >> 1);
>         }
>         // Apply a crypt-strength hash to the state and broadcast the result
>         hashStateWithSalt(state, i);
>         memcpy(multHashes + 8*i, state, 32);
>     }
> }

I'm having to rewrite this function, so please don't waste time
analyzing it.  I messed up the data dependencies, and it is 8-way
parallelizable when I intended for there to be a single multiplication
chain.

Bill