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[TLS] Simpler backward compatibility rules for 0-RTT

Martin Thomson <martin.thomson@gmail.com> Tue, 21 June 2016 01:15 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Tue, 21 Jun 2016 11:15:39 +1000
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Subject: [TLS] Simpler backward compatibility rules for 0-RTT
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David Benjamin wrote our section on 0-RTT backward compatibility to be
a little bit lenient about server deployment.  On consideration, I
think that a simpler set of rules are better:

1. If the server advertises support for 0-RTT, then it implies a
commitment to support TLS 1.3 for the duration of that advertisement.
2. Therefore, if the client attempts 0-RTT, then it should reject a
ServerHello with TLS 1.2 or older.

https://github.com/tlswg/tls13-spec/pull/502

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