Add reference documenting reasons for odd CCM nonce lengths

[selfissued]

Please add a reference to the base document that specified that the odd 13 and 7 byte nonce lengths should be used. There must be a reason for these choices, but the spec currently leaves it a mystery.

[jimsch]

This is covered in RFC 3610 - the description of CCM. There is already a reference to that document here. Not sure why an additional reference to the same document would be useful.

[selfissued]

In JOSE, I was often asked as editor to make references to the specific sections of specs defining particular features that are used. I would think that a reference something like this would be help implementers understand the rationale behind the choices made.

"The nonce length of 13 bytes is used because the Section 2.1 of [RFC3610] specifies a nonce length in octets of N=15-L, where L is the number of octets in the length field, and L=2 in this case."

[jimsch]

This hardly qualifies as a feature being used. If you understand CCM you know about this trade-off. If you don't, then you need to read the CCM specification. I do not believe that this needs to be done

[jimsch]

There is explicit text currently in the document that states there is a trade off between the Nonce length and the message length. This is sufficient documentation for individuals that do not understand the exact trade-off. Understanding the exact trade off involves a full understanding of how CCM works and what it's properties are. This is more than a simple reference to a single equation. That is what the document reference is for.