[core] ALPN "coap" for DTLS

Christian Amsüss <christian@amsuess.com> Sun, 26 March 2023 10:24 UTC

Return-Path: <christian@amsuess.com>
X-Original-To: core@ietfa.amsl.com
Delivered-To: core@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 45B26C14CE53; Sun, 26 Mar 2023 03:24:45 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.597
X-Spam-Level:
X-Spam-Status: No, score=-2.597 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_ZEN_BLOCKED_OPENDNS=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_DBL_BLOCKED_OPENDNS=0.001, URIBL_ZEN_BLOCKED_OPENDNS=0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([50.223.129.194]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id eDXNT2z39gIx; Sun, 26 Mar 2023 03:24:41 -0700 (PDT)
Received: from smtp.akis.at (smtp.akis.at [IPv6:2a02:b18:500:a515::f455]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 9E7B9C14CE31; Sun, 26 Mar 2023 03:24:33 -0700 (PDT)
Received: from poseidon-mailhub.amsuess.com (095129206250.cust.akis.net [95.129.206.250]) by smtp.akis.at (8.17.1/8.17.1) with ESMTPS id 32QAOUQN035846 (version=TLSv1.2 cipher=ECDHE-ECDSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sun, 26 Mar 2023 12:24:30 +0200 (CEST) (envelope-from christian@amsuess.com)
X-Authentication-Warning: smtp.akis.at: Host 095129206250.cust.akis.net [95.129.206.250] claimed to be poseidon-mailhub.amsuess.com
Received: from poseidon-mailbox.amsuess.com (poseidon-mailbox.amsuess.com [IPv6:2a02:b18:c13b:8010:a800:ff:fede:b1bf]) by poseidon-mailhub.amsuess.com (Postfix) with ESMTP id 264351D99B; Sun, 26 Mar 2023 12:24:30 +0200 (CEST)
Received: from hephaistos.amsuess.com (hephaistos.amsuess.com [IPv6:2a02:b18:c13b:8010::aa6]) by poseidon-mailbox.amsuess.com (Postfix) with ESMTPSA id CC7C02002E; Sun, 26 Mar 2023 12:24:29 +0200 (CEST)
Received: (nullmailer pid 7890 invoked by uid 1000); Sun, 26 Mar 2023 10:24:29 -0000
Date: Sun, 26 Mar 2023 12:24:29 +0200
From: Christian Amsüss <christian@amsuess.com>
To: core@ietf.org
Cc: draft-ietf-core-dns-over-coap@ietf.org
Message-ID: <ZCAdXXuvkqmn5eFB@hephaistos.amsuess.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="hnF18WaGaJVjV4Qx"
Content-Disposition: inline
Archived-At: <https://mailarchive.ietf.org/arch/msg/core/I_vkEz046qEWQKGh6dOE1WobIM4>
Subject: [core] ALPN "coap" for DTLS
X-BeenThere: core@ietf.org
X-Mailman-Version: 2.1.39
Precedence: list
List-Id: "Constrained RESTful Environments \(CoRE\) Working Group list" <core.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/core>, <mailto:core-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/core/>
List-Post: <mailto:core@ietf.org>
List-Help: <mailto:core-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/core>, <mailto:core-request@ietf.org?subject=subscribe>
X-List-Received-Date: Sun, 26 Mar 2023 10:24:45 -0000

Hi DTLS experts in CoRE,

processing reviews for DNS-over-CoAP[1] showed that while we do have an
ALPN and usage guidance for CoAP-over-TLS (ALPN "coap"), there is no
referencable text on whether and how CoAP-over-DTLS can be disambiguated
in an ALPN. While the general specification situation is a bit dire on
mixing DTLS with ALPNs[^2], it appears to be readily used[3].

Having an ALPN sounds like a prerequisite to announcing DNS-over-CoAP
through the DNR mechanism[4]. Can we Simply™ use the ALPN defined for
CoAP-over-TCP over there, or would that need a dedicated document that
says something along the lines of "The 'coap' ALPN can be used both with
TLS and DTLS (there is no confusion as they don't mix); unlike on TLS
where it has been a requirement from the start, its use stays optional
with DTLS"?

BR
c

[1]: https://datatracker.ietf.org/doc/draft-ietf-core-dns-over-coap/
[^2]: The only update to the DTLS-unaware ALPN RFC 7031 is 8447, which
  mentions DTLS, but not in the context of ALPNs.
[3]: https://www.rfc-editor.org/rfc/rfc8833.html
[4]: https://datatracker.ietf.org/doc/draft-ietf-add-dnr/

PS. This is exactly the footnote 2 of
https://mailarchive.ietf.org/arch/msg/core/yFHfHUHDDwh0HANDJEqj_TmkiMc
-- starting the work on OSCORE/EDHOC in SVCBs is yet another task.

-- 
This may seem a bit weird, but that's okay, because it is weird.
  -- perldata(1) about perl variables