add the value type 'bstr' to counter signature

[fpalombini]

We propose to give the choice between the whole COSE_Signature structure or only the bstr 'signature' as "counter signature" value type. In CDDL, that would give:

Generic_Headers = (
...
? 7 => COSE_Signature / bstr, ; Counter signature
...
)

on section 3.1 and in Table 2.
If we only send the btstr 'signature', we assume that the alg for the counter signature is also pre-established between nodes and is included in the "alg" parameter.

[jimsch]

Per discussion on the list, this has been changed from a request to modify the current existing counter signature attribute to defining a new one. The reason for the change in the request is that the input for the new counter signature computation process should reflect the ToBeSigned structure of the COSE_Sign1 rather than the full COSE_Sign structure. This better reflects the circumstances that it is being designed for.

[selfissued]

It's not clear to me why another way of doing this is being requested. Are both really needed?

[fpalombini]

Hi Mike, the goal behind this is again to reduce the size of the COSE message: instead of using a COSE_Signature structure (which itself contains headers and bstr signature value), we would like to use the simple bstr signature value directly. This would reduce the size of 3B: 1 for the array, 1 for the unprotected header and 1 for the protected header.

(the discussion about this in the mailing list is [here]([COSE] Issue - add the value type 'bstr' to counter signature)).