Subject: [COSE] How COSE items are identified

From: "Jim Schaad" <[email-masked]>
Date: Sun, 15 Nov 2015 23:12:30 -0800

We seem to have a potential problem for how COSE items are identified.

Initially, we used an integer inside of the structure to identify it.  That
is how the current ACE documents are written. This uses a single byte.

At the request of Carsten, we moved from doing this to using a tag at the
front of the structure.  Carsten believes that this can be done with a tag
that is in the two byte range when encoded (tag, length=1, tag value).  Part
of the reason that I agreed was that this was not really being used at the
time by the ACE documents.  

If one is almost always doing encrypted, then one could encode that
structure w/o the tag and do the other three structures with the tag.  This
would probably be ok as it would mostly use the smallest tagging (none) when
needed the most and use larger tagging (2 bytes) for the rest of the
structures.

Alternatively, we could modify the document to request the assignment of
tags in the one byte range for the most common structures and two bytes for
the less common structures (and have arguments about which is which).

Alternatively, we could revert back to putting an integer tag inside of the
array structure.

Comments on this are requested.

Jim

---

From: Justin Richer <[email-masked]>
Date: Mon, 16 Nov 2015 09:17:02 -0600

I think it’s premature to assume one structure is used “most of the time” as opposed to other structures and to optimize COSE for that case. Though if we take a cue from JOSE, it’s asymmetric signing, then MAC. Those might be reversed as I don’t have concrete numbers on this. Public keys are probably next. Encryption is far behind in my experience with JOSE.

My point is that I don’t think we can pick any one structure as “most common” yet as we’re extrapolating from exactly zero real-world examples.

 — Justin (as non-chair)

> On Nov 16, 2015, at 1:12 AM, Jim Schaad <[email-masked]> wrote:
> 
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