Re: [Ace] How to specify DTLS MTI in COAP-EST

Michael Richardson <mcr+ietf@sandelman.ca> Thu, 07 June 2018 17:15 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Russ Housley <housley@vigilsec.com>
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Date: Thu, 07 Jun 2018 13:14:40 -0400
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Subject: Re: [Ace] How to specify DTLS MTI in COAP-EST
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Russ Housley <housley@vigilsec.com>; wrote:
    > These words were first used by IPsec; see RFC 4307.  They have gained
    > broader acceptance.  I see no problem just using them here.

Yes, but they aren't in an RFC2119-like document that we can simply cite, and I'm
not sure if the TLS reviewers will like them.  Ben doesn't like them for instance.

I would probably just write:
  SHOULD+/SHOULD-/MUST- are used in the same way as in RFC8247




    >> On Jun 6, 2018, at 7:32 PM, Michael Richardson <mcr+ietf@sandelman.ca>; wrote:
    >> 
    >> 
    >> In draft-ietf-ace-coap-est, we would like to specify some mandatory to
    >> implement algorithms for DTLS.
    >> 
    >> We write:
    >> The mandatory cipher suite for DTLS in EST-coaps is
    >> TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 defined in [RFC7251] which is the
    >> mandatory-to-implement cipher suite in CoAP.
    >> 
    >> Additionally, the curve secp256r1 MUST be supported [RFC4492]; this curve
    >> is equivalent to the NIST P-256 curve.
    >> 
    >> And this is fine for now, but we'd like to signal that Curve25519 should be
    >> considered as an alternative, but we don't want to make it a MUST *today*,
    >> and we don't want to force implementations 15 years down the road that have
    >> it to include secp256r1.
    >> 
    >> IPsec(ME) has published things like: https://datatracker.ietf.org/doc/rfc8247/
    >> which include language like:
    >> 
    >> SHOULD+   This term means the same as SHOULD.  However, it is likely
    >> that an algorithm marked as SHOULD+ will be promoted at
    >> some future time to be a MUST.
    >> 
    >> SHOULD-   This term means the same as SHOULD.  However, an algorithm
    >> marked as SHOULD- may be deprecated to a MAY in a future
    >> version of this document.
    >> 
    >> MUST-     This term means the same as MUST.  However, it is expected
    >> at some point that this algorithm will no longer be a MUST
    >> in a future document.  Although its status will be
    >> determined at a later time, it is reasonable to expect that
    >> if a future revision of a document alters the status of a
    >> MUST- algorithm, it will remain at least a SHOULD or a
    >> SHOULD- level.
    >> 
    >> I don't think TLS has done this... maybe TLS plans to.
    >> We think that we'd like to use SHOULD+ for Curve25519 and MUST- for
    >> secp256r1, but we aren't sure that the WG will like us to use so many
    >> words as IPsec to say so.
    >> 
    >> --
    >> ]               Never tell me the odds!                 | ipv6 mesh networks [
    >> ]   Michael Richardson, Sandelman Software Works        | network architect  [
    >> ]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on rails    [
    >> 
    >> 
    >> _______________________________________________
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    >> Ace@ietf.org
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-- 
Michael Richardson <mcr+IETF@sandelman.ca>;, Sandelman Software Works
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