Re: [TLS] Call for WG adoption draft-josefsson-tls-curve25519

Yoav Nir <ynir.ietf@gmail.com> Sat, 30 May 2015 08:23 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Sat, 30 May 2015 11:23:43 +0300
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To: Simon Josefsson <simon@josefsson.org>
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Subject: Re: [TLS] Call for WG adoption draft-josefsson-tls-curve25519
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> On May 30, 2015, at 12:01 AM, Simon Josefsson <simon@josefsson.org>; wrote:
> 
> Yoav Nir <ynir.ietf@gmail.com>; writes:
> 
>> Me too.
>> 
>> I notice that while the draft doesn’t say that explicitly, it uses
>> existing *_ECDHE_* ciphersuites, so that no new ciphersuites are
>> required, despite the fact that this ECDHE has different point formats
>> and different back-end math than the existing ECDHE.  I wonder if we
>> can also get away with using *ECDSA* ciphersuites for EdDSA
>> signatures.
> 
> This is an interesting idea, thanks for mentioning that.  It would ugly
> for "ECDSA" in a cipher suite name to not actually mean that ECDSA is
> used, but it is a valid engineering tradeoff to sometimes prefer ugly
> things that simplify over beautiful things that complicate.

It’s based on Elliptic Curves; it’s a Digital Signature; it’s an Algorithm. The “ECDSA” label seems to still fit.

If we wanted to be really radical while losing backward compatibility, we could call the ciphersuite SIG_with_DHE, and use point formats for supporting RSA, DSA, ECDSA and EdDSA for signatures and DHE,ECDHE and Curve25519 for key agreement.

But since we do want backward compatibility, I think lumping all kinds of elliptic curve ephemeral D-H on “_ECDHE_” and all kinds of elliptic curve signatures on “_ECDSA_” is fine, even though ANSI X9.62 has labeled only the particular signature scheme used with P-256 as “ECDSA”.

Yoav