Re: [TLS] I-D Action: draft-ietf-tls-curve25519-01.txt

Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Mon, 20 July 2015 13:03 UTC

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Date: Mon, 20 Jul 2015 16:02:54 +0300
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
To: Hubert Kario <hkario@redhat.com>
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Cc: Simon Josefsson <simon@josefsson.org>, tls@ietf.org
Subject: Re: [TLS] I-D Action: draft-ietf-tls-curve25519-01.txt
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On Mon, Jul 20, 2015 at 01:42:01PM +0200, Hubert Kario wrote:
> On Monday 20 July 2015 14:39:03 Ilari Liusvaara wrote:
> > On Mon, Jul 20, 2015 at 12:55:37PM +0200, Hubert Kario wrote:
> > 
> > There are other shortcomings tho:
> > - If Ed25519 is supported, one also needs to support Curve25519.
> > - If Ed25519 and Curve448 are supported, one needs to support
> >   Curve25519 and Ed448.
> > - And the cross case from previous.
> > 
> > So with the same, in TLS 1.2, the following combinations would
> > be possible:
> > - None at all.
> > - Curve25519
> > - Curve448
> > - Curve25519 & Curve448
> > - Curve25519 & Ed25519
> > - Curve448 & Ed448
> > - Curve25519 & Curve448 & Ed25519 & Ed448.
> 
> if we define separate codepoints for Curve25519 and Ed25519, yes

That list was assuming the following:
- TLS at least 1.2 (I don't see much point with bothering with
  lesser versions here).
- Unified 255/448 bit signature algorithm as one of SignatureAlgorithm
  codepoints, using ECDSA ciphersuites.
- The same codepoint used for both 25519 kex and sig curve (and the
  same for 448).

Breaking any of those three assumptions changes things here.


-Ilari