On Tue, May 30, 2017 at 1:03 PM, Martin Rex <m...@sap.com> wrote: > Eric Rescorla wrote: >> On Tue, May 23, 2017 at 9:34 PM, Martin Rex <m...@sap.com> wrote: >>> >>> 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. > > The suggestion to accept a recognized TLSv1.2 cipher suite code point > as an alternative indicator for the highest client-supported protocol > version is not really a "mechanism". It's efficient (with 0-bytes on > the wire), intuitive and extremely backwards-compatible (will not upset > old servers, neither version-intolerant as the Win2008/2012 servers, > nor extension-intolerant servers.
It's a substantial change made after WG last call. That alone makes it improper. If you want to get WG consensus for such a change, go ahead. But don't try making this in the dead of night. > > >> >>> 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. > > > It's worse -- there are still TLS servers out there which choke on > TLS extensions (and TLS server which choke on extension ordering). TLS 1.2 demands extensions work. Sending a TLS 1.2 hello without extensions is going to make it impossible to implement many features TLS 1.2 security relies on. > > Sending TLS extensions is therefore a negotiation scheme that we > can not ship as patch into the installed base, because we *KNOW* > that it will break a few existing usage scenarios. Stuff that needs > TLS extensions is therefore an opt-in only scheme -- and even when > making it opt-in, we may have to additonally provide a TLS extension > exclusion list of hostnames. > > It seems that there are others facing the same issue: > > https://support.microsoft.com/en-us/help/3140245/update-to-enable-tls-1.1-and-tls-1.2-as-a-default-secure-protocols-in-winhttp-in-windows > > and defer enabling to explicit customer opt-in. > > > Really, a very compatible and extremely robust and useful approach would > be to allow implied client protocol version indication through presence of > TLSv1.2-only cipher suite codepoints and this would allow large parts > of the installed base to quickly start using TLSv1.2--without breaking > existing usage scenarios and without the hazzle for users having to opt-in > and test stuff. The people who have these problems are not "large parts" of the install base. They are large parts of *your* install base. Don't confuse these two. > > > -Martin > > _______________________________________________ > TLS mailing list > TLS@ietf.org > https://www.ietf.org/mailman/listinfo/tls -- "Man is born free, but everywhere he is in chains". --Rousseau. _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
