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

Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Mon, 20 July 2015 11:39 UTC

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Date: Mon, 20 Jul 2015 14:39:03 +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 12:55:37PM +0200, Hubert Kario wrote:
> On Tuesday 14 July 2015 17:23:44 Simon Josefsson wrote:
> >
> > Compare how we "reuse" the ECDHE ciphersuite values to refer to
> > Curve25519 (instead of defining new ciphersuites for Curve25519), and
> > how we are "reusing" the "uncompressed" code point to refer to
> > Curve25519-compressed code points (instead of defining new
> > ECPointFormat).
> 
> the point is, that if Ed25519 for signatures is defined, an implementation 
> that doesn't understand it[1] can't advertise that fact

Are you thinking about 1.0/1.1? In 1.2 it can: signature_algorithms
(I'm not confident new signature algorithm would work without either
that nor new ciphersuites).


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.



-Ilari