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Re: [TLS] Curve25519 in TLS and Additional Curves in TLS

Rob Stradling <rob.stradling@comodo.com> Wed, 22 January 2014 18:07 UTC

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Date: Wed, 22 Jan 2014 18:07:25 +0000
From: Rob Stradling <rob.stradling@comodo.com>
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To: Simon Josefsson <simon@josefsson.org>, tls@ietf.org
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Subject: Re: [TLS] Curve25519 in TLS and Additional Curves in TLS
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On 22/01/14 16:18, Simon Josefsson wrote:
<snip>
> 1) Curve25519 for TLS.  This was the original scope of the draft.  The
> URL is: <http://tools.ietf.org/html/draft-josefsson-tls-curve25519>.  As
> far as I know, there are no outstanding issues, and it is possible to
> implement and deploy Curve25519 in TLS following the draft.  Please
> prove me wrong with comments or preferrably patches to the draft.

Simon, Section 2.1 says:
   "Since Curve25519 are not designed to be used in signatures, clients
    who offer ECDHE_ECDSA ciphersuites and advertise support for
    Curve25519 in the elliptic_curves ClientHello extension SHOULD also
    advertise support for at least one other curve, suitable for ECDSA.
    Servers MUST NOT select an ECDHE_ECDSA ciphersuite if the only common
    curve is Curve25519."

Why is that "SHOULD" not a MUST?

<snip>

-- 
Rob Stradling
Senior Research & Development Scientist
COMODO - Creating Trust Online

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