phc-discussions - Re: [Cryptography] [OT] Improvement to Momentum PoW

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Message-ID: <CAOU__fyR+OM=X16uFBgQC2QpiHRKgR+H1H+Z8Nfrisr=ShaKPg@mail.gmail.com>
Date: Mon, 27 Jul 2015 15:46:37 -0400
From: John Tromp <john.tromp@...il.com>
To: Bill Cox <waywardgeek@...il.com>
Cc: "discussions@...sword-hashing.net" <discussions@...sword-hashing.net>, 
	"cryptography@...zdowd.com" <cryptography@...zdowd.com>
Subject: Re: [Cryptography] [OT] Improvement to Momentum PoW

On Mon, Jul 27, 2015 at 2:29 PM, Bill Cox <waywardgeek@...il.com> wrote:
> A problem with Momentum as currently implemented is that it can be run with
> reduced memory, enabling efficient GPU attacks.

Dave Andersen's latest remarks on his GPU code:
https://bitcointalk.org/index.php?topic=826901.msg11944049#msg11944049
You can ask him what he thinks is a faster implementation.

Fore reduced memory, you can find all collisions in 8MB,
using Cuckoo Cycle's algorithm for finding 2 cycles in bipartite graphs.

>  I think we can get around
> this problem simply by changing the parameters it uses.

> If instead, we run with n == 26, and Hb's output also being 26 bits, then we
> get around 2^26 collisions.

To me, that's a completely different beast.
I would no longer call that Momentum...

-John