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Re: [TLS] Singular or multiple NamedGroup(s) in the "HelloRetryRequest"

Henrik Grubbström <grubba@gmail.com> Fri, 16 January 2015 16:44 UTC

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Date: Fri, 16 Jan 2015 17:44:08 +0100
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From: Henrik Grubbström <grubba@gmail.com>
To: "Dang, Quynh" <quynh.dang@nist.gov>
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Subject: Re: [TLS] Singular or multiple NamedGroup(s) in the "HelloRetryRequest"
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On Fri, Jan 16, 2015 at 4:51 PM, Dang, Quynh <quynh.dang@nist.gov> wrote:
> If a client offers all of the options it supports and a server sends back
> one group out of these options, it would guarantee a failure.

It seems you've misunderstood; the client announces all named groups
that it supports in the named_group extension, but usually only
provides a subset of these in its ClientKeyShare message. Thus the
server can ask for a named group that the client supports but hasn't
provided a key share for in its HelloRetry.

/grubba

-- 
Henrik Grubbström                                       grubba@grubba.org
Roxen Internet Software AB                              grubba@roxen.com

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