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

Michael Richardson <mcr+ietf@sandelman.ca> Wed, 06 June 2018 23:32 UTC

Return-Path: <mcr+ietf@sandelman.ca>
X-Original-To: ace@ietfa.amsl.com
Delivered-To: ace@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id D349F130E04 for <ace@ietfa.amsl.com>; Wed, 6 Jun 2018 16:32:53 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.201
X-Spam-Level:
X-Spam-Status: No, score=-4.201 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id KrdhoTuGse3M for <ace@ietfa.amsl.com>; Wed, 6 Jun 2018 16:32:50 -0700 (PDT)
Received: from tuna.sandelman.ca (tuna.sandelman.ca [209.87.249.19]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id D9C6A130DFF for <ace@ietf.org>; Wed, 6 Jun 2018 16:32:49 -0700 (PDT)
Received: from sandelman.ca (obiwan.sandelman.ca [209.87.249.21]) by tuna.sandelman.ca (Postfix) with ESMTP id D3B4C20090 for <ace@ietf.org>; Wed, 6 Jun 2018 19:46:16 -0400 (EDT)
Received: by sandelman.ca (Postfix, from userid 179) id 4AC0D74; Wed, 6 Jun 2018 19:32:13 -0400 (EDT)
Received: from sandelman.ca (localhost [127.0.0.1]) by sandelman.ca (Postfix) with ESMTP id 485973F for <ace@ietf.org>; Wed, 6 Jun 2018 19:32:13 -0400 (EDT)
From: Michael Richardson <mcr+ietf@sandelman.ca>
To: ace@ietf.org
X-Attribution: mcr
X-Mailer: MH-E 8.6; nmh 1.7+dev; GNU Emacs 24.5.1
X-Face: $\n1pF)h^`}$H>Hk{L"x@)JS7<%Az}5RyS@k9X%29-lHB$Ti.V>2bi.~ehC0; <'$9xN5Ub# z!G,p`nR&p7Fz@^UXIn156S8.~^@MJ*mMsD7=QFeq%AL4m<nPbLgmtKK-5dC@#:k
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha1; protocol="application/pgp-signature"
Date: Wed, 06 Jun 2018 19:32:13 -0400
Message-ID: <13635.1528327933@localhost>
Archived-At: <https://mailarchive.ietf.org/arch/msg/ace/-YirmW3WsqDuCLez71DlLXjnhXY>
Subject: [Ace] How to specify DTLS MTI in COAP-EST
X-BeenThere: ace@ietf.org
X-Mailman-Version: 2.1.26
Precedence: list
List-Id: "Authentication and Authorization for Constrained Environments \(ace\)" <ace.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ace>, <mailto:ace-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ace/>
List-Post: <mailto:ace@ietf.org>
List-Help: <mailto:ace-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ace>, <mailto:ace-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 06 Jun 2018 23:32:54 -0000

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    [