From: COSE <cose-boun...@ietf.org> On Behalf Of Laurence Lundblade Sent: Monday, August 10, 2020 1:25 PM To: Ace Wg <ace@ietf.org>; cose <c...@ietf.org> Subject: [COSE] Gap in registration of application/cwt? It doesn’t seem clear what the CBOR tagging requirements are when application/cwt is used to indicate a message is a CWT. This is the text that I think it missing: The CBOR CWT tag (61) must NOT be used. It is unnecessary because the media type already indicates it is a CWT. The COSE type indicating tag MUST be present. It is necessary to determine whether what the COSE type is, whether it is COSE_Sign1, COSE_Mac0... Another solution could be a MIME parameter added to the application/cwt indicating the COSE type. [JLS] Yes that would have been an alternative that would work – However this option would require either that you use text content types for CoAP or you allocate N different integer content types one for each possible set of options that could be placed there. The current solution is cleaner and smaller. Step 3 in section 7.2 also seems wrong. It doesn’t make it an error for the COSE type tag to be absent when the CBOR CWT tag is present. This is all based on my understanding that the surrounding protocol for must specify exactly when CBOR tags are to be used and when they are not to be used and that the surrounding protocol must not leave it as an optional implementation choice. In this case application/cwt is the supporting protocol. [JLS] What is the text that says that this is true. This would be a surprising statement for me. Jim LL
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