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Date: Fri, 4 Apr 2014 04:56:11 -0400
From: Bill Cox <waywardgeek@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Some Schvrch issues

On Thu, Apr 3, 2014 at 6:19 PM, Rade Vuckovac <rade.vuckovac@...il.com> wrote:
> The evolve function is an attempt to emulate Wolfram's rule 30 (random
> number generator in Wolfram's Mathematica).
>
> What is behind the randomness of rule 30 and how it is related to the evolve
> function in terms of cyclomatic complexity is presented in the paper (see
> submission Appendix).

I'm afraid this scheme doesn't work as you're expecting it to.  For
example, if you fix line 107, but comment out both calls to the stir
function, and run with t_cost = 1000, and m_cost = 1000, here's what I
get:

./phs-schvrch 1000 1000 1
type: d
count: 8
numbit: 32
2341707444
2341707404
4294967279
4294967295
32
0
2341707436
2341707404

This resulting hash is not at all random.  Revolve and evolve simply
don't mix the data significantly, no matter how long they run.  The
XORing with memstate also does essentially no real mixing.  The only
two function calls that do any significant mixing are the two calls to
stir, and each can be reversed in 2^64 guesses of carry, so guessing
them both at the same time should not take more than 2^128 guesses.

Bill

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