Re: [COSE] MAC with no recipient structures

What I'm hearing from this thread is a lot of support for plain MAC 
structures, including several documented use cases. Not the least of 
which is mapping to JOSE's HS* algorithm suite in JWS, one of the two 
most-used and most-successful portions of JOSE to date.

Consequently, I'm not seeing any consensus to drop plain MAC support in 
favor of any other method. I'm also not seeing opposition to defining 
AEAD structures in addition to MAC structures in COSE and allowing 
applications to choose.

Therefore, we'll keep MAC in place until there's sufficient consensus to 
remove the capability from COSE.

Thank you,
  -- Justin, your COSE chair.

On 11/7/2015 5:39 PM, Jim Schaad wrote:
> People keep telling me that they want to have a version of MACs that do not
> have a set of recipient information attached so that they can do direct
> MACs.  I keep asking for a use case where this makes sense.  In all of the
> use cases that I have been presented so far, a better answer is going to be
> to do an AEAD encrypted item rather than a MACed item.
>
> The scenario that wants this is going to be:
>
> Alice sends data to Bob in such a way that Bob can authenticate the data.
> Eve needs to be able to read the data in transit, without knowing if the
> message contains data or misinformation and will act on the message as if it
> were data.
>
> The difference in message size between MAC and Encryption is going to be
> minimal, at most a few bytes.  The execution difference is going to be a few
> extra encryption operations.
>
> What use cases exist for this where encryption is not a better security
> answer anyway.
>
> Jim
>
>
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