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

Hannes Tschofenig <> Thu, 07 June 2018 16:30 UTC

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From: Hannes Tschofenig <>
To: Russ Housley <>, Michael Richardson <>
CC: "" <>
Thread-Topic: [Ace] How to specify DTLS MTI in COAP-EST
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Date: Thu, 07 Jun 2018 16:30:08 +0000
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Subject: Re: [Ace] How to specify DTLS MTI in COAP-EST
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Hi Russ, Hi Michael,

why don't you just reference

I am not a big fan of making all sorts of different crypto recommendations in our specs that differ slightly.


PS: Next time someone suggests the use of a new crypto algorithm I will demand that they also implement one themselves.

-----Original Message-----
From: Ace [] On Behalf Of Russ Housley
Sent: 07 June 2018 15:55
To: Michael Richardson
Subject: Re: [Ace] How to specify DTLS MTI in COAP-EST


These words were first used by IPsec; see RFC 4307.  They have gained broader acceptance.  I see no problem just using them here.


> On Jun 6, 2018, at 7:32 PM, Michael Richardson <> 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:
> 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  [
> ]        |   ruby on rails    [
> _______________________________________________
> Ace mailing list

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