On Tue, May 23, 2017 at 9:34 PM, Martin Rex <m...@sap.com> wrote: > Eric Rescorla wrote: > > draft-ietf-tls-ecdhe-psk-aead-04: Discuss > > > > ---------------------------------------------------------------------- > > DISCUSS: > > ---------------------------------------------------------------------- > > > > The following text appears to have been added in -04 > > > > A server receiving a ClientHello and a client_version indicating > > (3,1) "TLS 1.0" or (3,2) "TLS 1.1" and any of the cipher suites from > > this document in ClientHello.cipher_suites can safely assume that > > the > > client supports TLS 1.2 and is willing to use it. The server MUST > > NOT negotiate these cipher suites with TLS protocol versions earlier > > than TLS 1.2. Not requiring clients to indicate their support for > > TLS 1.2 cipher suites exclusively through ClientHello.client_hello > > improves the interoperability in the installed base and use of TLS > > 1.2 AEAD cipher suites without upsetting the installed base of > > version-intolerant TLS servers, results in more TLS handshakes > > succeeding and obviates fallback mechanisms. > > > > This is a major technical change from -03, which, AFAIK, prohibited > > the server from negotiating these algorithms with TLS 1.1 and below > > and maintained the usual TLS version 1.2 negotiation rules. > > This change _still_ prohibits the server from negotiating these algorithms > with TLSv1.1 and below.
> Could you elaborate a little on where and why you see a problem with this? > For starters, TLS 1.3 has already designed a completely independent mechanism for doing version negotiation outside of ClientHello.version, so doing another seems pretty odd. In any case, it's not something you do between IETF-LC and IESG approval. As this changes tries to explain, had such a text been used for all > TLSv1.2 AEAD cipher suite code points, then browsers would have never > needed any "downgrade dance" fallbacks, POODLE would have never > existed as a browser problem, and the TLS_FALLBACK_SCSV band-aid > would not been needed, either. > I'm not sure this is true, because there were also servers which did not understand extensions. -Ekr > -Martin >
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