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Re: [core] FW: [COSE] draft-ietf-cose-countersign-02 - Secruity problems with COSE_Encrypt and COSE_Encrypt0 with CCM_8

Michael Richardson <mcr+ietf@sandelman.ca> Thu, 13 May 2021 18:01 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: John Mattsson <john.mattsson=40ericsson.com@dmarc.ietf.org>, "core@ietf.org" <core@ietf.org>
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Date: Thu, 13 May 2021 14:01:01 -0400
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Subject: Re: [core] FW: [COSE] draft-ietf-cose-countersign-02 - Secruity problems with COSE_Encrypt and COSE_Encrypt0 with CCM_8
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John Mattsson <john.mattsson=40ericsson.com@dmarc.ietf.org> wrote:
    > Earlier versions of Group OSCORE had these quite significant
    > vulnerabilities. My understanding is that this weakness is addressed in
    > the current version of Group OSCORE by adding more information to the
    > signature external_aad.

    > However, I see no reason to actually use countersignatures in Group
    > OSCORE.

I don't understand the need.  I know that the countersignature use in Group
OSCORE was compatible with RFC8152, but beyond that, I never quite understand
how it was used.

I'd like to ask if there are some slides from ACE that might help illuminate
this?

    > Now when COSE WG is specifying "AEAD" algorithms without integrity
    > protection I think CORE should take the time to modify the signature
    > parts of Group OSCORE from

    > AEAD() || Countersignature( AEAD() )

    > to

    > ENC() || Signature ( MAC( ENC() ) )

Hmm. I see your point, I think.
I don't have the right pieces of OSCORE paged in to understand the impact to
existing protocols, or if they are even far enough along to deal.

But, sometimes, better is the enemy of good enough.

--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide

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