[TLS] Ben Campbell's Yes on draft-ietf-tls-tls13-26: (with COMMENT)

Ben Campbell <ben@nostrum.com> Tue, 06 March 2018 17:27 UTC

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From: Ben Campbell <ben@nostrum.com>
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Date: Tue, 06 Mar 2018 09:27:42 -0800
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Subject: [TLS] Ben Campbell's Yes on draft-ietf-tls-tls13-26: (with COMMENT)
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Ben Campbell has entered the following ballot position for
draft-ietf-tls-tls13-26: Yes

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There has clearly been a lot of work put into this. It's a surprisingly
understandable document, given its length and the complexity of the subject. I
am balloting yes, but I have a few minor comments and nits. None of these are
showstoppers, so please do with them as you will.

*** Substantive Comments:

§4.1.2, first paragraph: " When a client first connects to a server, it is
REQUIRED to send the
   ClientHello as its first message. "

Is that intended to prohibit the use of STARTTLS or similar application layer
patterns? (To be clear, this is not an objection, just a clarification request.)

§4.1.2, legacy_compression_methods: "Note that TLS 1.3 servers might receive
TLS 1.2 or prior
      ClientHellos which contain other compression methods and MUST
      follow the procedures for the appropriate prior version of TLS."

Is that intended to require TLS 1.3 servers to always be willing and able to
negotiate 1.2? §4.2.1 has a similar assertion:

"If this extension is not present, servers which are compliant with
   this specification MUST negotiate TLS 1.2 or prior as specified in
   [RFC5246], even if ClientHello.legacy_version is 0x0304 or later."

But §4.2.3 says:

 "Note that TLS 1.2 defines this extension differently.  TLS 1.3
   implementations willing to negotiate TLS 1.2 MUST behave in
   accordance with the requirements of [RFC5246] when negotiating that

... which seems inconsistent (noting that this paragraph talks about
"implementations" rather than "servers", so perhaps there's a subtle difference?

§ The section is marked for removal. Do you expect that RFC
implementations will ever need to interop with draft implementations? If so,
the information in this section may continue to be useful for some time.

§D.5: This section has a lot of normative requirements that seem important. I
wonder why it has been relegated to an appendix.

*** Editorial Comments and nits:

§2: "If (EC)DHE key establishment
   is in use, then the ServerHello contains a "key_share" extension with
   the server’s ephemeral Diffie-Hellman share which MUST be in the same
   group as one of the client’s shares. "

missing comma prior to "which".

§4.1.1: "Note that if the PSK can be used without (EC)DHE then non-
   overlap in the "supported_groups" parameters need not be fatal, as it
   is in the non-PSK case discussed in the previous paragraph."

I read "need not be fatal" to mean that it may still be fatal at times. Is that
the intent?

§11: The IANA considerations have a number of constructions similar to "SHALL
update/has updated". Is that text expected to collapse to "has updated" at some

§E.2.1: [BDFKPPRSZZ16]  : Best citation anchor evar