Internet-Draft CoRE ALPN September 2024
Lenders, et al. Expires 9 March 2025 [Page]
Workgroup:
Constrained RESTful Environments
Internet-Draft:
draft-ietf-core-coap-dtls-alpn-latest
Published:
Intended Status:
Standards Track
Expires:
Authors:
M. S. Lenders
TU Dresden
C. Amsüss
T. C. Schmidt
HAW Hamburg
M. Wählisch
TU Dresden & Barkhausen Institut

ALPN ID Specification for CoAP over DTLS

Abstract

This document specifies an Application-Layer Protocol Negotiation (ALPN) ID for transport-layer-secured 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://anr-bmbf-pivot.github.io/draft-ietf-core-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/anr-bmbf-pivot/draft-ietf-core-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/.

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 9 March 2025.

Table of Contents

1. Introduction

Application-Layer Protocol Negotiation (ALPN) enable communicating parties to agree on an application-layer protocol during a Transport Layer Security (TLS) handshake using an ALPN ID. 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. As an example, this information can be obtained as part of the discovery of DNS over CoAP (DoC) servers (see [I-D.ietf-core-dns-over-coap]) that deploy TLS or DTLS to secure their messages. This document specifies an ALPN ID for CoAP services that are secured by transport security using DTLS. An ALPN ID for CoAP service 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 "coaps" 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.

ALPN ID values have variable length. Here, a short value ("co") is allocated for CoAP over DTLS, 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 "coaps" 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

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" group.

  • Protocol: CoAP (over DTLS)

  • Identification sequence: 0x63 0x6f ("co")

  • Reference: [RFC7252] and [this document]

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, , <https://www.rfc-editor.org/rfc/rfc7252>.
[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, , <https://www.rfc-editor.org/rfc/rfc7301>.
[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, , <https://www.rfc-editor.org/rfc/rfc9460>.

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-07, , <https://datatracker.ietf.org/doc/html/draft-ietf-core-dns-over-coap-07>.
[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, , <https://www.rfc-editor.org/rfc/rfc4944>.
[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, , <https://www.rfc-editor.org/rfc/rfc8323>.

Appendix A. Change Log

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.

Authors' Addresses

Martine Sophie Lenders
TUD Dresden University of Technology
Helmholtzstr. 10
D-01069 Dresden
Germany
Christian Amsüss
Thomas C. Schmidt
HAW Hamburg
Berliner Tor 7
D-20099 Hamburg
Germany
Matthias Wählisch
TUD Dresden University of Technology & Barkhausen Institut
Helmholtzstr. 10
D-01069 Dresden
Germany