Re: [Cbor] [EXTERNAL EMAIL] Re: Private tag numbers

[Carsten Bormann <[e-mail]>]

On 2023-04-24, at 13:27, Tony Putman <[e-mail]> wrote:
> 
> It looks like a mixed approach is the way to go if the contents schema is changing often. 

If “mixed approach” is combining a tag allocation with some internal (number-/)namespace, here is an example for how we tend to do this:

CWT (RFC 8392) has CBOR tag 61 for indicating the overall data item (Section 9.4 [1]).
(Alternatively, this can be indicated using transfer protocol mechanisms such as Content-Type in HTTP or Content-Format in CoAP (Section 9.2, 9.3 [2]).)

Within CWT, we have a namespace of numbers for the individual claims (“Claim Keys”), e.g., number 4 for expiration time (“exp”) [3].  This namespace (and not the tag number space) is augmented by further standards contributing to CWT, e.g. number 8 for the confirmation claim (“cnf”) defined in RFC 8747 [4].

Note that RFC 8747 in turn defines a nested internal name space for sub-items of the confirmation claim [5] such as 3 for “kid” or 1 for “COSE_Key”.

Grüße, Carsten


[1]: https://www.rfc-editor.org/rfc/rfc8392#section-9.4
[2]: https://www.rfc-editor.org/rfc/rfc8392#section-9.2
[3]: https://www.rfc-editor.org/rfc/rfc8392#section-9.1.2
[4]: https://www.rfc-editor.org/rfc/rfc8747#section-7.1
[5]: https://www.rfc-editor.org/rfc/rfc8747#section-7.2.2