Constrained RESTful Environments M. S. Lenders Internet-Draft TU Dresden Intended status: Informational C. Amsüss Expires: 4 September 2025 T. C. Schmidt HAW Hamburg M. Wählisch TU Dresden & Barkhausen Institut 3 March 2025 ALPN ID Specification for CoAP over DTLS draft-ietf-core-coap-dtls-alpn-02 Abstract This document specifies an Application-Layer Protocol Negotiation (ALPN) ID for transport-layer-secured Constrained Application Protocol (CoAP) services. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://core- wg.github.io/coap-dtls-alpn/draft-ietf-core-coap-dtls-alpn.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-core-coap-dtls-alpn/. Discussion of this document takes place on the Constrained RESTful Environments Working Group mailing list (mailto:core@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/core/. Subscribe at https://www.ietf.org/mailman/listinfo/core/. Source for this draft and an issue tracker can be found at https://github.com/core-wg/coap-dtls-alpn. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Lenders, et al. Expires 4 September 2025 [Page 1] Internet-Draft CoRE ALPN March 2025 Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 4 September 2025. Copyright Notice Copyright (c) 2025 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Application-Layer Protocol Negotiation (ALPN) IDs . . . . . . 3 3. Security Considerations . . . . . . . . . . . . . . . . . . . 3 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 4.1. TLS ALPN for CoAP . . . . . . . . . . . . . . . . . . . . 3 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Normative References . . . . . . . . . . . . . . . . . . 4 5.2. Informative References . . . . . . . . . . . . . . . . . 4 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 4 A.1. Since draft-ietf-core-coap-dtls-alpn-01 . . . . . . . . . 5 A.2. Since draft-ietf-core-coap-dtls-alpn-00 . . . . . . . . . 5 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction Application-Layer Protocol Negotiation (ALPN) enables communicating parties to agree on an application-layer protocol during a Transport Layer Security (TLS) handshake using an ALPN ID [RFC7301]. This ALPN ID can be discovered for services as part of Service Bindings (SVCB) via the DNS, using SVCB resource records with the "alpn" Service Parameter Keys [RFC9460]. As an example, this information can be obtained as part of the discovery of DNS over CoAP (DoC) servers (see Section 3.2 of [I-D.ietf-core-dns-over-coap]) that deploy TLS or Datagram Transport Layer Security (DTLS) to secure their messages. Lenders, et al. Expires 4 September 2025 [Page 2] Internet-Draft CoRE ALPN March 2025 This document specifies an ALPN ID for CoAP services that are secured by transport security using DTLS. An ALPN ID for CoAP services secured by TLS has already been specified in [RFC8323]. 2. Application-Layer Protocol Negotiation (ALPN) IDs For CoAP over TLS, an ALPN ID was defined as "coap" in [RFC8323]. As it is not advisable to re-use the same ALPN ID for a different transport layer, an ALPN for CoAP over DTLS is registered in Section 4.1. ALPN ID values have variable length. For CoAP over DTLS, a short value ("co") is allocated, as this can avoid fragmentation of Client Hello and Server Hello messages in constrained networks with link- layer fragmentation, such as 6LoWPAN [RFC4944]. To discover CoAP services that secure their messages with TLS or DTLS, ALPN IDs "coap" and "co" can be used, respectively, in the same manner as for any other service secured with transport layer security, as described in [RFC9460]. Other authentication mechanisms are currently out of scope. 3. Security Considerations Any security considerations on ALPN (see [RFC7301]) and SVCB resource records (see [RFC9460]), also apply to this document. 4. IANA Considerations // RFC Ed.: throughout this section, please replace RFC-XXXX with the // RFC number of this specification and remove this note. This document has the following actions for IANA. 4.1. TLS ALPN for CoAP The following entry has been added to the "TLS Application-Layer Protocol Negotiation (ALPN) Protocol IDs" registry, which is part of the "Transport Layer Security (TLS) Extensions" registry group. * Protocol: CoAP (over DTLS) * Identification sequence: 0x63 0x6f ("co") * Reference: [RFC7252] and [RFC-XXXX] Lenders, et al. Expires 4 September 2025 [Page 3] Internet-Draft CoRE ALPN March 2025 Note that [RFC7252] does not define the use of the ALPN TLS extension during the DTLS connection handshake. This document does not change this behavior, and thus does not establish any rules like those in Section 8.2 of [RFC8323]. 5. References 5.1. Normative References [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, July 2014, . [RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding and Parameter Specification via the DNS (SVCB and HTTPS Resource Records)", RFC 9460, DOI 10.17487/RFC9460, November 2023, . 5.2. Informative References [I-D.ietf-core-dns-over-coap] Lenders, M. S., Amsüss, C., Gündoğan, C., Schmidt, T. C., and M. Wählisch, "DNS over CoAP (DoC)", Work in Progress, Internet-Draft, draft-ietf-core-dns-over-coap-12, 14 February 2025, . [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, . [RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K., Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets", RFC 8323, DOI 10.17487/RFC8323, February 2018, . Appendix A. Change Log Lenders, et al. Expires 4 September 2025 [Page 4] Internet-Draft CoRE ALPN March 2025 A.1. Since draft-ietf-core-coap-dtls-alpn-01 (https://datatracker.ietf.org/doc/draft-ietf-core-coap-dtls- alpn/01/) * Address review by Esko Dijk * Address review by Marco Tiloca A.2. Since draft-ietf-core-coap-dtls-alpn-00 (https://datatracker.ietf.org/doc/draft-ietf-core-coap-dtls- alpn/00/) * Fix ALPN ID for CoAP over TLS * Change intended status to Informational Acknowledgments We like to thank Rich Salz for the expert review on the "co" ALPN ID allocation. We also like to thank Mohamed Boucadair and Ben Schwartz for their early review before WG adoption of this draft and Esko Dijk, Thomas Fossati, and Marco Tiloca for their feedback and comments. Authors' Addresses Martine Sophie Lenders TUD Dresden University of Technology Helmholtzstr. 10 D-01069 Dresden Germany Email: martine.lenders@tu-dresden.de Christian Amsüss Email: christian@amsuess.com Thomas C. Schmidt HAW Hamburg Berliner Tor 7 D-20099 Hamburg Germany Email: t.schmidt@haw-hamburg.de Lenders, et al. Expires 4 September 2025 [Page 5] Internet-Draft CoRE ALPN March 2025 Matthias Wählisch TUD Dresden University of Technology & Barkhausen Institut Helmholtzstr. 10 D-01069 Dresden Germany Email: m.waehlisch@tu-dresden.de Lenders, et al. Expires 4 September 2025 [Page 6]