phc-discussions - Re: [PHC] winner selection

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Message-ID: <20150413211722.GA12162@bolet.org>
Date: Mon, 13 Apr 2015 23:17:22 +0200
From: Thomas Pornin <pornin@...et.org>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] winner selection

On Mon, Apr 13, 2015 at 03:35:42PM +0000, Gregory Maxwell wrote:
> If I'd offered a Makwa competitor it would have had information
> theoretic security for delegation (in exchange for making some
> tricks/performance worse).

Actually you can. The _definition_ of Makwa is not tied to a specific
delegation mechanism.

Last December, we were discussing these issues in this list with Adam
Back, and he pointed out a method which offered information theoretic
security for delegation. The method described in the Makwa specification
(and implemented in the reference code) is not information-theoretic
secure, but it is also about 12 times faster, which is why I chose it.

However, the beauty of the thing, and the important point here, is that
_both_ methods can be applied to Makwa as it is defined; it is merely an
implementation issue. The function itself, and already computed hashes,
are not impacted in any way by the delegation method you choose.

(I should make an update to the reference code and specification to
include that alternate delegation method. I'll see if I can free up
some time for that job next week-end.)

	--Thomas Pornin