phc-discussions - Re: [PHC] multiply-hardening (Re: NoelKDF ready for submission)

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Date: Sat, 8 Feb 2014 12:31:06 +0400
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] multiply-hardening (Re: NoelKDF ready for submission)

Bill,

On Sat, Feb 08, 2014 at 12:00:30PM +0400, Solar Designer wrote:
> As an option, you might want to reuse the operations and the constant
> used in Mersenne twister's initialization:
> 
> #define NEXT_STATE(x, i) \
> 	(x) = 1812433253U * ((x) ^ ((x) >> 30)) + (i);
> 
> where "x" is the current state (32-bit) and "i" is the iteration number.

As a less conservative option, you may keep the non-linear operations
from MT, but replace the constant with your "mem[] | 3" or similar.

If you need to reference two memory locations on each iteration, like
you currently do, then maybe take this construction from init_by_array()
from mt19937ar.c:

        mt[i] = (mt[i] ^ ((mt[i-1] ^ (mt[i-1] >> 30)) * 1664525UL))
          + init_key[j] + j; /* non linear */

and modify it as follows:

        value = ((value ^ (value >> 30)) * (mem[prevAddr + i] | 3))
          + mem[fromAddr + i] + i;

(totally untested).

Alexander