Internet-Draft CoRE DNR July 2024
Lenders, et al. Expires 10 January 2025 [Page]
Workgroup:
Constrained RESTful Environments
Internet-Draft:
draft-lenders-core-dnr-03
Published:
Intended Status:
Informational
Expires:
Authors:
M. S. Lenders
TU Dresden
C. Amsüss
T. C. Schmidt
HAW Hamburg
M. Wählisch
TU Dresden & Barkhausen Institut

Discovery of Network-designated OSCORE-based Resolvers: Problem Statement

Abstract

This document states problems when designing DNS SVCB records to discover endpoints that communicate over Object Security for Constrained RESTful Environments (OSCORE) [RFC8613]. As a consequence of learning about OSCORE, this discovery will allow a host to learn both CoAP servers and DNS over CoAP resolvers that use OSCORE to encrypt messages and Ephemeral Diffie-Hellman Over COSE (EDHOC) [RFC9528] for key exchange. Challenges arise because SVCB records are not meant to be used to exchange security contexts, which is required in OSCORE scenarios.

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-lenders-core-dnr/draft-lenders-core-dnr.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-lenders-core-dnr/.

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-lenders-core-dnr.

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 10 January 2025.

Table of Contents

1. Introduction

The discovery of Internet services can be facilitated by the Domain Name System (DNS). To discover services of the constrained Internet of Things (IoT) using the DNS, two challenges must be solved. First, the discovery of a DNS resolver that supports DNS resolution based on secure, IoT-friendly protocols—otherwise the subsequent discovery of IoT-tailored services would be limited to resolution protocols conflicting with constrained resources. Second, the discovery of an IoT-friendly service beyond the DNS resolution.

[RFC9460] specifies the "SVCB" ("Service Binding") DNS resource record to lookup information needed to connect to a network service. Service Parameters (SvcParams) carry that information within the SVCB record.

The discovery of DNS resolvers can be enabled by the DNS itself [RFC9461], [RFC9462] or, in a local network, by Router Advertisements and DHCP [RFC9463]. In all theses cases, the SvcParams is used, but supports only DNS transfer based on Transport Layer Security (TLS), namely DNS over TLS (DoT) [RFC7858], DNS over HTTPS (DoH) [RFC8484], and DNS over Dedicated QUIC (DoQ) [RFC9250]. The use of DoT, DoH, or DoQ, however, is not recommended in IoT scenarios.

DNS over CoAP [I-D.ietf-core-dns-over-coap] provides a solution for encrypted DNS in constrained environments. The Constrained Application Protocol (CoAP) [RFC7252] is mostly agnostic to the transport layer CoAP can be transported over UDP, TCP, or WebSockets [RFC8323], and even less common transports such as Bluetooth GATT [I-D.amsuess-core-coap-over-gatt] or SMS [lwm2m] are discussed. [I-D.ietf-core-transport-indication] covers the selection of different CoAP transports using SVCB records.

CoAP offers three security modes:

The SVCB-based discovery of a CoAP service in mode "no security" is covered in [I-D.ietf-core-transport-indication], and a CoAP service in the mode "transport security" in [I-D.lenders-core-coap-dtls-svcb]. The discovery of CoAP services in mode "object security" is not specified. To guide future specifications, this document clarifies aspects when using SVCB in the context of CoAP and object security.

2. Terminology

The terms "DoC server" and "DoC client" are used as defined in [I-D.ietf-core-dns-over-coap].

The terms "constrained node" and "constrained network" are used as defined in [RFC7228].

SvcParams denotes the field in either DNS SVCB/HTTPS records as defined in [RFC9460], or DHCP and RA messages as defined in [RFC9463]. SvcParamKeys are used as defined in [RFC9460].

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Problem Space

The first and most important point of discussion for the discoverability of CoAP is if and what new SvcParamKeys need to be defined and what is already there.

[RFC9460] defines the "alpn" key, which is used to identify the protocol suite of a service binding using its Application-Layer Protocol Negotiation (ALPN) ID [RFC7301]. While this is useful to identify classic transport layer security, the question is raised if this is needed or even helpful for when there is only object security. There is an ALPN ID for CoAP over TLS that is defined in [RFC8323]. As using the same ALPN ID for different transport layers is not recommended, another ALPN ID for CoAP over DTLS is introduced in [I-D.lenders-core-coap-dtls-svcb]. Object security may be selected in addition to transport layer security or without it. Additionally, different CoAP transports can be selected, which may be orthogonal to the transport security. For instance, DTLS can be used over transports other than UDP. The selection of CoAP transport protocols will be covered in future versions of [I-D.ietf-core-transport-indication]. Defining an ALPN ID for each combination of object security, mode of transport layer security, and transport protocol might not be viable or scalable. For some ways of setting up object security, additional information is needed, such as an establishment options for an encryption context with EDHOC or an authentication server (AS) with ACE.

Beyond the SvcParamKeys, there is the question of what the field values of the Encrypted DNS Options defined in [RFC9463] might be with EDHOC or ACE EDHOC. While most fields map, "authentication-domain-name" (ADN) and its corresponding ADN length field may not matter when authentication is driven by Authorization for Constrained Environments (ACE) [RFC9203] [I-D.ietf-ace-edhoc-oscore-profile].

4. Objectives

SVCB records are not meant and should not be used to exchange security contexts, so this eliminates scenarios that use pre-shared keys with OSCORE. This leaves 2 base scenarios for OSCORE, which may occur in combination, with scenarios using transport security, or alternative transport protocols:

We mostly need to answer the question for additional SvcParamKeys. [RFC9460] defines the keys "mandatory", "alpn", "no-default-alpn", "port", "ipv4hint", and "ipv6hint". Additionally, [I-D.ietf-core-dns-over-coap] defines "docpath" which carries the path for the DNS resource at the DoC server as a CBOR sequence.

Since "alpn" is needed for transport layer security, the type of object security (OSCORE using EDHOC, OSCORE using ACE, OSCORE using EDHOC using ACE), needs to be conveyed in a different SvcParamKey. The semantics and necessacity of the authenticator-domain-name field in [RFC9463] needs to be evaluated in each case.

When using ACE, more SvcParamKeys might be needed, such as the OAuth audience, the scope or the authentication server URI.

Defining these SvcParamKeys, including their value formats and spaces, as well as the behavior definition for authenticator-domain-name field, shall be part of future work.

5. Security Considerations

TODO Security

6. IANA Considerations

This document has no IANA considerations.

7. References

7.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[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>.
[RFC9461]
Schwartz, B., "Service Binding Mapping for DNS Servers", RFC 9461, DOI 10.17487/RFC9461, , <https://www.rfc-editor.org/rfc/rfc9461>.
[RFC9462]
Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T. Jensen, "Discovery of Designated Resolvers", RFC 9462, DOI 10.17487/RFC9462, , <https://www.rfc-editor.org/rfc/rfc9462>.
[RFC9463]
Boucadair, M., Ed., Reddy.K, T., Ed., Wing, D., Cook, N., and T. Jensen, "DHCP and Router Advertisement Options for the Discovery of Network-designated Resolvers (DNR)", RFC 9463, DOI 10.17487/RFC9463, , <https://www.rfc-editor.org/rfc/rfc9463>.

7.2. Informative References

[I-D.amsuess-core-coap-over-gatt]
Amsüss, C., "CoAP over GATT (Bluetooth Low Energy Generic Attributes)", Work in Progress, Internet-Draft, draft-amsuess-core-coap-over-gatt-06, , <https://datatracker.ietf.org/doc/html/draft-amsuess-core-coap-over-gatt-06>.
[I-D.ietf-ace-edhoc-oscore-profile]
Selander, G., Mattsson, J. P., Tiloca, M., and R. Höglund, "Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object Security for Constrained Environments (OSCORE) Profile for Authentication and Authorization for Constrained Environments (ACE)", Work in Progress, Internet-Draft, draft-ietf-ace-edhoc-oscore-profile-05, , <https://datatracker.ietf.org/doc/html/draft-ietf-ace-edhoc-oscore-profile-05>.
[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>.
[I-D.ietf-core-transport-indication]
Amsüss, C. and M. S. Lenders, "CoAP Transport Indication", Work in Progress, Internet-Draft, draft-ietf-core-transport-indication-06, , <https://datatracker.ietf.org/doc/html/draft-ietf-core-transport-indication-06>.
[I-D.lenders-core-coap-dtls-svcb]
Lenders, M. S., Amsüss, C., Schmidt, T. C., and M. Wählisch, "Service Binding and Parameter Specification for CoAP over (D)TLS", Work in Progress, Internet-Draft, draft-lenders-core-coap-dtls-svcb-00, , <https://datatracker.ietf.org/doc/html/draft-lenders-core-coap-dtls-svcb-00>.
[lwm2m]
OMA SpecWorks, "White Paper – Lightweight M2M 1.1", , <https://omaspecworks.org/white-paper-lightweight-m2m-1-1/>.
[RFC7228]
Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, , <https://www.rfc-editor.org/rfc/rfc7228>.
[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>.
[RFC7858]
Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., and P. Hoffman, "Specification for DNS over Transport Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, , <https://www.rfc-editor.org/rfc/rfc7858>.
[RFC7959]
Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, , <https://www.rfc-editor.org/rfc/rfc7959>.
[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>.
[RFC8484]
Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, , <https://www.rfc-editor.org/rfc/rfc8484>.
[RFC8613]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, , <https://www.rfc-editor.org/rfc/rfc8613>.
[RFC9203]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson, "The Object Security for Constrained RESTful Environments (OSCORE) Profile of the Authentication and Authorization for Constrained Environments (ACE) Framework", RFC 9203, DOI 10.17487/RFC9203, , <https://www.rfc-editor.org/rfc/rfc9203>.
[RFC9250]
Huitema, C., Dickinson, S., and A. Mankin, "DNS over Dedicated QUIC Connections", RFC 9250, DOI 10.17487/RFC9250, , <https://www.rfc-editor.org/rfc/rfc9250>.
[RFC9528]
Selander, G., Preuß Mattsson, J., and F. Palombini, "Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528, DOI 10.17487/RFC9528, , <https://www.rfc-editor.org/rfc/rfc9528>.

Appendix A. Change Log

A.1. Since draft-lenders-core-dnr-02

A.2. Since draft-lenders-core-dnr-01

A.3. Since draft-lenders-core-dnr-00

  • IANA has processed the "co" ALPN and it is now added to the registry

Acknowledgments

TODO acknowledge.

Authors' Addresses

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