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Date: Thu, 18 Sep 2014 13:41:09 +1000
From: Rade Vuckovac <rade.vuckovac@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Schvrch is broken

Hi Bill



Please find schvrch2prelim.h attached.



Memory cost attempt:

- write to the memstate is done by state stir stream

- read is done by getting index of current carry modulo memstate array size
and reading memstate element with that index

- read result modifies mixer

- until next read, stir is run to produce a new current carry (it runs
statelen times but that can be fine tuned)

- hash is just a partial final state (every 8th word provides one byte =
256 bits)



Never done programming professionally (although have cs formal education,
MAG entry to eStream was my honours thesis).

Happpy to do work with you too if Schvrch makes to the next stage.



Regards, Rade

On Wed, Sep 17, 2014 at 9:29 AM, Bill Cox <waywardgeek@...hershed.org>
wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 09/16/2014 07:19 PM, Rade Vuckovac wrote:
> > My err, lapsus ... apologies ... I keep forgetting that.
>
> No problem.  There is zero reason for you to apologize, while I have
> several.  Thanks for introducing me to Wolfram's Rule 30 :-)
>
> > The solution is simple with reintroducing mixer with value
> > 010101... instead of 000000... (was there in the first place to
> > nullify above mentioned xor properties) Mixer addition is actually
> > the only difference between stir and revolve and it was dropped
> > (long time ago) for the performance sake believing it was safe
> > thing to do.
>
> I did my best to attack your stir function, and failed.  I believe it
> mixes securely, if slowly.
>
> > On the positive side the 117 lines of code will shrink considerably
> > (less chance for bugs) and the algorithm will become significantly
> > simpler (will be posted in near future).
>
> I look forward to it.  My preference for implementing Wolfram's Rule
> 30 is this loop:
>
> static uint128_t updateState(uint128_t a) {
>     uint128_t lsb = a & 1;
>     uint128_t msb = a >> 127;
>     return ((a << 1) | msb) ^ (a | (a >> 1) | (lsb << 127));
> }
>
> This would work well in our SIMD uints, and mixes reasonably fast.
> Keccak combined this with moving lot's of data around to get near and
> far data mixing, similar to what Blake2b seems to do.  This whole
> AND-XOR-ROTATE thing is cool, and not that I know much about this
> stuff, but I only learned about because I reviewed your code, and
> eventually read your paper.  It is very cool stuff.
>
> I do get the feeling that you are not a programmer by trade.  I happen
> to be an old code-monkey.  If you would like, I would be happy to work
> with you on a revised version so we can clean up some of the holes
> before letting Steve have a crack at it :-)
>
> Bill
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