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Re: [Cfrg] revised requirements for new curves

Manuel Pégourié-Gonnard <mpg@elzevir.fr> Mon, 08 September 2014 14:30 UTC

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Date: Mon, 08 Sep 2014 16:30:21 +0200
From: Manuel Pégourié-Gonnard <mpg@elzevir.fr>
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To: William Whyte <wwhyte@securityinnovation.com>, "Paterson, Kenny" <Kenny.Paterson@rhul.ac.uk>, cfrg@irtf.org
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Subject: Re: [Cfrg] revised requirements for new curves
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On 08/09/2014 15:49, William Whyte wrote:
> IN1: I don't understand how a curve could be incompatible with a TLS RFC. A
> new curve would be a new ciphersuite: to support a new curve, you reserve a
> ciphersuite identifier and define behavior for that ciphersuite identifier.

I guess you mean a NamedCurve identifier (RFC 4492 sec. 5.1.1) rather than a
ciphersuite identifier. Currently, ciphersuites only specify the high-level
mechanism (ECDH(E), ECDSA), not the specific curve(s) used by this mechanism.
(There is a draft for including curve selection in the ciphersuite identifier,
but for now it's only a draft). And possibly some new ECPointFormat (sec 5.1.2)
in addition, if the new curves support other representations than short
Weierstrass, and the decision is made to allow those representations on the wire
(rather than to force conversion to short Weierstrass).

By the way, the TLS curve/point negotiation doesn't allow peers to negotiate the
use of different point formats for different curves. That's probably something
to bear in mind when discussing point formats.

Manuel.

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