Hello Cose ML! (Sorry for the late reply, I didn't see the replies the same day; then I was on holidays)
Jim: thanks for the suggestion. Indeed I think I will go for this option to keep the solution non-homebrew. I will borrow from the CoAP Content-Formats (application/cose-key : 101) and put this in the protected headers. I think this solution will be 3 bytes (1B content-type label + 2B to represent "101") instead of 1 byte of the hypothetical CBOR Tag for COSE-Key (19 or 20 looked nice). Carsten: I am using CoAP (..for now) but I want the least possible COSE metadata on the CoAP header; to make the COSE message as agnostic as possible of the transport (maybe we will transport this message over-foo). In my particular case, I simply use the CoAP Content-format 60 to indicate that this is an "application/cbor" payload. Then I use the CBOR-Tag 16 (COSE_Encrypt0), because indeed that is what this CBOR message is. So even if I use CoAP metadata for COSE I should indicate this message as "application/cose; cose-type="cose-encrypt0" (16). My 'problem' arose when, once decrypted; the plaintext part of the COSE_Encrypt0 contains , in some cases, a COSE_Key object; and I simply wanted to indicate that with a 1-byte tag . Jim's suggestions of content-type in protected header solves my problem indeed. So maybe the question I want to ask to the ML is: why you discarded defining the COSE_Key/COSE_KeySet CBOR tag? ( I see the pretty tags 19 and 20 unassigned) Carsten, I really agree with your opinion from 2015 : >I'd propose this rule: >If there is a media type, there should be a CBOR tag for those >environments that don't benefit from media types. In the end, it's a matter of 2 bytes, 1 byte tag, vs 3 byte protected header content-type. The COSE messages are around 52 Bytes, so It's a matter of 4% longer Messages/Energy. I found it strange not to find a CBOR tag for a mayor COSE type. These are my 2 cents, Thank you for your quick reply Jim and Carsten! Renzo On Fri, Apr 7, 2017 at 6:14 PM, Carsten Bormann <[email protected]> wrote: > Hi Renzo, > > where would you put such a tag? > > Starting the encoded CBOR with a tag would amount to a magic number unless > the media type already indicates that this is CBOR-encoded. But then it > could indicate that this is a application/cose-key in the first place > (Content-Format 101): > > https://www.iana.org/assignments/core-parameters/core-parameters.xhtml#content-formats > > Grüße, Carsten > _______________________________________________ COSE mailing list [email protected] https://www.ietf.org/mailman/listinfo/cose
