Re: [Cose] Issue: Create separate MAC structure

On 22/04/15 05:04, Jim Schaad wrote:
> Question:  Should we separate out MACs from Signatures?
> 
> Discussion:
> 
> I have a number of reasons that I would support this change:
> 
> .  It is easier to talk about the security properties of signatures and MACs
> if they are not combined into a single structure.  The security properties
> of the two items are very different and conflating them does not make for
> good decisions by people who are using the message format.
> 
> * It is problematic to do recipient key management if they are in the same
> structure.  The fact that signers and recipients have different structures,
> means that overlapping them can lead to implementation errors if a recipient
> structure is used when a signer structure is called for.  One way that has
> been conceived to do the recipient management can be found in
> http://datatracker.ietf.org/doc/draft-jones-jose-key-managed-json-web-signat
> ure. 
> 
> *  Having MAC different from Signatures allows for the ability to do a clean
> separation of MAC and signature code implementations when only one of them
> is needed.
> 
> Why it should not be done:
> 
> *  There might be confusion of people moving from JOSE to COSE.

You gotta choose who to confuse:-)

I agree with you - I'd prefer separating MACs and signatures at
as high a level as possible. Consuming code needs to know the
difference and should have a smaller footprint if these concepts
are not conflated and if only one of MACs or signature needs to
be supported by a device/application.

S.

> 
> Jim
> 
> 
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