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Re: [TLS] Remove DH-based 0-RTT

Martin Thomson <martin.thomson@gmail.com> Wed, 24 February 2016 15:54 UTC

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Date: Wed, 24 Feb 2016 07:54:27 -0800
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From: Martin Thomson <martin.thomson@gmail.com>
To: Subodh Iyengar <subodh@fb.com>
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Subject: Re: [TLS] Remove DH-based 0-RTT
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On 24 February 2016 at 07:44, Subodh Iyengar <subodh@fb.com> wrote:
> Unless we add a way for the client to require a server authentication during
> PSK resumption.

I have been arguing for this now for a while.  If there is an
incentive to do "PSK resumption" (there is), and that does not provide
the client a way to verify server certificates, then clients are
forced to make a choice between performance and checking that the
server holds the private key for the certificate.  I'd like to see a
mode where 0-RTT is grafted on to a full handshake with DHE and
signing.  Unfortunately, that gives us an almost full matrix of
options:

PSK only
PSK + DHE
PSK + DHE + signing
DHE + signing

But at least we can remove "DH0RTT + DHE + signing" and maybe other
combinations (though which ones we have currently isn't 100% clear to
me).

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