Re: [TLS] A la carte handshake negotiation

Viktor Dukhovni <ietf-dane@dukhovni.org> Fri, 12 June 2015 17:22 UTC

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Date: Fri, 12 Jun 2015 17:22:00 +0000
From: Viktor Dukhovni <ietf-dane@dukhovni.org>
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Subject: Re: [TLS] A la carte handshake negotiation
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On Fri, Jun 12, 2015 at 01:09:26PM -0400, Dave Garrett wrote:

> On Friday, June 12, 2015 12:55:59 pm Viktor Dukhovni wrote:
> > I still don't understand preclude as a matter of principle negotiation
> > of ECDH_anon with AEAD if DH_anon with the same bulk cipher would
> > be allowed.  Once we have separate negotiation of the key exchange,
> > surely ECDH_anon can be one of the supported key exchange variants,
> > and then take advantage of all the available bulk ciphersuites.
> 
> EC/FF may be negotiated separately, but a suite still needs to be selected.
> Anon cannot be negotiated via an ECDHE_ECDSA suite, as the signatures
> extension explicitly prohibits proposing anon alongside actual signatures.
> One way or another, anon needs its own suites to be used.

The extension definition can presumably be updated in a way that
allows peers that support additional code-points to treat one of
those as being "anon".  Is the current definition really a serious
obstacle to solving the problem in a properly orthogonal way.

> > Or does this proposal simply compress the client HELLO message,
> > but the server is still ultimately selecting the same all-in-one
> > ciphersuite (thus requiring Nico's new code points for ECDH_anon
> > with AEAD)?
> 
> The server still needs to select a suite. If it selects an ECDHE_ECDSA
> suite, then it can negotiate EC/FF and RSA,DSA,ECDSA with extensions. It
> cannot negotiate anon. To do so would require either an ECDH_anon or
> DH_anon suite be negotiated. Yes, the preferred route is to require Nico's
> ECDH_anon codepoints for AEAD ciphers. With an ECDH_anon suite, the groups
> extension can be used to negotiate EC/FF. What I was stating earlier is
> that we could theoretically do so with DH_anon if we wanted to, but I
> would much rather the ECDH_anon draft be resurrected and passed as it
> would avoid confusion and the appearance of contradiction.

So be it I guess.  I wish it were simpler...

-- 
	Viktor.