phc-discussions - Re: [PHC] Re: Some KDF stumbling blocks, plus Common

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Message-ID: <20141217112613.GA6968@bolet.org>
Date: Wed, 17 Dec 2014 12:26:13 +0100
From: Thomas Pornin <pornin@...et.org>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Re: Some KDF stumbling blocks, plus Common

On Wed, Dec 17, 2014 at 09:57:15AM +0800, Ben Harris wrote:
> A naive question based on my limited knowledge of cool terms like abelian
> groups - if you did this using elliptic curves could you not worry about
> the security of pq? And just suffer the once off work to calculate y. Or
> does the math not carry over to elliptic curves?

The math does not carry over to elliptic curves (or, at least, I did not
find a way to), unless you do something like generating a curve of order
n where n = pq with p and q unknown (in which case you gained nothing).

Generally speaking, algorithms that have an EC equivalent are algorithms
that work with multiplications only, modulo a big prime (like DSA or
ElGamal).

	--Thomas Pornin