Re: [Ace] WGLC for draft-ietf-ace-coap-est - optimization for embedded devices

Michael Richardson <mcr@sandelman.ca> Thu, 24 January 2019 02:26 UTC

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From: Michael Richardson <mcr@sandelman.ca>
To: Esko Dijk <esko.dijk@iotconsultancy.nl>
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Date: Wed, 23 Jan 2019 21:26:47 -0500
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Subject: Re: [Ace] WGLC for draft-ietf-ace-coap-est - optimization for embedded devices
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Esko Dijk <esko.dijk@iotconsultancy.nl> wrote:
    > My main comment on this draft is based on recent experience with an
    > embedded implementation. In the draft, the content format
    > "application/pkcs7-mime;smime-type=certs-only" is used to transport a
    > single certificate back to the client. However, in the embedded
    > implementation crypto library there is no support for parsing this
    > format, but there is support for parsing X.509v3
    > (application/pkix-cert). See
    > e.g. https://tls.mbed.org/api/group__x509__module.html for an embedded
    > API that can parse CSR and certs, but not PKCS#7.

    > Therefore the X.509 format seems better to use; also given that
    > 1) the signing of data that the PKCS#7 S/MIME envelope provides is useless because the DTLS session is already end-to-end protected and the certificate is already signed; and
    > 2) RFC 7030 requires that only one certificate, the  generated one, is
    > carried in the /simple(re)enroll response so that a container format
    > for multiple certificates is not really needed here.

    > So to reduce code size for embedded implementations it would be very
    > beneficial if the EST Server would support an additional content
    > format:
    > application/pkix-cert  (see RFC 5280)

I think that this is a reasonable thing to do.
The client can easily say what it wants and I think the two formats are
relatively easy to swap.

What about if we went further, and went to:
             Concise Identities
             draft-birkholz-core-coid-01

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