Subject: [Cose] Issue: Create separate MAC structure

From: "Jim Schaad" <[email-masked]>
Date: Tue, 21 Apr 2015 21:04:41 -0700

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.

Jim

---

From: Stephen Farrell <[email-masked]>
Date: Wed, 22 Apr 2015 07:57:36 +0100

> *  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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From: Paul Hoffman <[email-masked]>
Date: Wed, 22 Apr 2015 07:03:01 -0700

> be supported by a device/application.

+1. The fact that they were conflated on JOSE is not relevant here. Even if someone was going to create a JOSE<->COSE translator, COSE separating them will not significantly hinder such a translator. Just to be clear, I don't care about such translators: COSE's use case is different than JOSE's.

--Paul Hoffman

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From: ⌘ Matt Miller <[email-masked]>
Date: Wed, 22 Apr 2015 08:37:05 -0600

On 4/22/15 8:03 AM, Paul Hoffman wrote:
> +1. The fact that they were conflated on JOSE is not relevant here.
> Even if someone was going to create a JOSE<->COSE translator, COSE
> separating them will not significantly hinder such a translator.
> Just to be clear, I don't care about such translators: COSE's use
> case is different than JOSE's.
> 

+1 on separating MACs from signatures.

- -- 
- - m&m

Matt Miller < [email-masked] >
Cisco Systems, Inc.

---

From: Samuel Erdtman <[email-masked]>
Date: Wed, 22 Apr 2015 18:12:16 +0200

+1 for separating,

And a question is there a point in translating JOSE<->COSE? If I understod
tings correctly a translation would break signatures. I could se a server
lib that would like to be able to output both COSE and JOSE signatures, but
I cannot se any problem with the separation.

Best Regards
//Samuel Erdtman

On Wed, Apr 22, 2015 at 4:03 PM, Paul Hoffman <[email-masked]> wrote:

> +1. The fact that they were conflated on JOSE is not relevant here. Even
> if someone was going to create a JOSE<->COSE translator, COSE separating
> them will not significantly hinder such a translator. Just to be clear, I
> don't care about such translators: COSE's use case is different than JOSE's.
>
> --Paul Hoffman

---

From: Derek Atkins <[email-masked]>
Date: Wed, 22 Apr 2015 12:16:14 -0400

> be supported by a device/application.

I agree, too.  We should separate MAC from Signature.

> S.

-derek
-- 
       Derek Atkins                 617-623-3745
       [email-masked]             www.ihtfp.com
       Computer and Internet Security Consultant