[TLS] Remove 0-RTT client auth

Martin Thomson <martin.thomson@gmail.com> Sun, 21 February 2016 19:31 UTC

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Date: Sun, 21 Feb 2016 11:31:04 -0800
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From: Martin Thomson <martin.thomson@gmail.com>
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Subject: [TLS] Remove 0-RTT client auth
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I'm sitting here in TRON listening to Karthik describe all the various
ways in which client authentication in 0-RTT is bad.  I'm particularly
sympathetic to the perpetual impersonation attack that arises when the
client's ephemeral key is compromised.

We originally thought that we might want to do this for
WebRTC/real-time.  As it so happens, we have an alternative design
that doesn't need this, so...

I propose that we remove client authentication from 0-RTT.

This should simplify the protocol considerably.

https://github.com/tlswg/tls13-spec/issues/420

[1] Compromising the server's long term key has the same impact, but
that's interesting for other, worse reasons.