Classification: UNCLASSIFIED

I realize publication has been requested for this draft, but I have a few 
comments that the author might want to address, if still possible.

1. The draft says that if none of the PSKs provided by the client are 
acceptable to the server, then the extension must be omitted from the 
ServerHello message.  Nothing is said about how the client should behave if it 
receives this: continue or abort with what error code?

2. It can be detected if two PSK identifiers sent in the same ClientHello have 
the same PSK value by observing the binder values.  Granted, I can't think why 
this would occur, but it might be important to point this out in the Security 
Considerations in order for implementers to be clear about security guarantees.

3. Section 4, paragraph 3 states that "If none of the external
   PSKs in the list provided by the client is acceptable to the server,
   then the "tls_cert_with_extern_psk" extension is omitted from the
   ServerHello message."

Section 5 has a similar statement but using the word "MUST": "If none of the
   offered external PSKs in the list provided by the client are
   acceptable to the server, then the "tls_cert_with_extern_psk"
   extension MUST be omitted from the ServerHello message."

These statements should be consistent in the requirement language.

4. Section 5, paragraph starting with "The identities are a list of external 
PSK identities...": s/identities may be know to other parties/identities may be 
known to other parties


Best regards,
Jonathan

--
Jonathan Hammell
Canadian Centre for Cyber Security
[email protected]



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