Re: [Cfrg] RGLC on draft-irtf-cfrg-chacha20-poly1305-01.txt

David Leon Gil <coruus@gmail.com> Tue, 07 October 2014 16:54 UTC

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From: David Leon Gil <coruus@gmail.com>
Date: Tue, 7 Oct 2014 12:54:25 -0400
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To: Ted Krovetz <ted@krovetz.net>
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Subject: Re: [Cfrg] RGLC on draft-irtf-cfrg-chacha20-poly1305-01.txt
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On Tue, Oct 7, 2014 at 11:47 AM, Ted Krovetz <ted@krovetz.net> wrote:
> If one views the chacha core as a PRF from 384 bits to 512 bits, then there are all sorts of ways to increase the lengths of the internal counter and/or external nonce.

Is there a reason not to define an "XChaCha" by analogy with XSalsa?
See http://cr.yp.to/snuffle/xsalsa-20110204.pdf

(The situation seems trickier for narrow PRPs, but ChaCha and Salsa
are both PRFs of the form you describe.)