



Internet Engineering Task Force (IETF)                       O. Bergmann
Request for Comments: 9430                                           TZI
Updates: 9202                                          J. Preuß Mattsson
Category: Standards Track                                    G. Selander
ISSN: 2070-1721                                                 Ericsson
                                                               July 2023


 Extension of the Datagram Transport Layer Security (DTLS) Profile for
 Authentication and Authorization for Constrained Environments (ACE) to
                     Transport Layer Security (TLS)

Abstract

   This document updates "Datagram Transport Layer Security (DTLS)
   Profile for Authentication and Authorization for Constrained
   Environments (ACE)" (RFC 9202) by specifying that the profile applies
   to TLS as well as DTLS.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9430.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Specific Changes to RFC 9202
   4.  Connection Establishment
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   The Authentication and Authorization for Constrained Environments
   (ACE) framework [RFC9200] defines an architecture for lightweight
   authentication between the Client, Resource Server (RS), and
   Authorization Server (AS), where the Client and RS may be
   constrained.  "Datagram Transport Layer Security (DTLS) Profile for
   Authentication and Authorization for Constrained Environments (ACE)"
   [RFC9202] only specifies the use of DTLS [RFC9147] for transport
   layer security between the nodes in the ACE architecture but works
   equally well for Transport Layer Security (TLS) [RFC8446].  For many
   constrained implementations, the Constrained Application Protocol
   (CoAP) over UDP [RFC7252] is the first choice, but when deploying ACE
   in networks controlled by other entities (such as the Internet), UDP
   might be blocked on the path between the Client and the Resource
   Server, and the Client might have to fall back to CoAP over TCP
   [RFC8323] for NAT or firewall traversal.  This dual support for
   security over TCP as well as UDP is already supported by the Object
   Security for Constrained RESTful Environments (OSCORE) profile
   [RFC9203].

   This document updates [RFC9202] by specifying that the profile
   applies to TLS as well as DTLS.  It only impacts the transport layer
   security channel between the Client and Resource Server.  The same
   access rights are valid in case transport layer security is provided
   by either DTLS or TLS.  The same access token can be used by either
   DTLS or TLS between a given (Client, RS) pair.  Therefore, the value
   coap_dtls in the ace_profile parameter of an Authorization Server to
   Client (AS-to-Client) response or in the ace_profile claim of an
   access token indicates that either DTLS or TLS can be used for
   transport layer security.

2.  Terminology

   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.

   Readers are expected to be familiar with the terms and concepts
   described in [RFC9200] and [RFC9202].

3.  Specific Changes to RFC 9202

   The main changes to [RFC9202] specified in this document are limited
   to replacing "DTLS" with "DTLS/TLS" throughout the document.  This
   essentially impacts the use of secure transport, as described in
   Sections 3.2.2, 3.3.2, 4, and 5.

   In addition to this, the Client and Resource Server behavior is
   updated to describe the case where either or both DTLS and TLS may be
   available, as described in the following section.

4.  Connection Establishment

   Following the procedures defined in [RFC9202], a Client can retrieve
   an access token from an Authorization Server in order to establish a
   security association with a specific Resource Server.  The
   ace_profile parameter in the Client-to-AS request and AS-to-Client
   response is used to determine the ACE profile that the Client uses
   towards the Resource Server.

   The ace_profile parameter indicates the use of the DTLS profile for
   ACE, as defined in [RFC9202].  Therefore, the Client typically first
   tries using DTLS to connect to the Resource Server.  If this fails,
   the Client MAY try to connect to the Resource Server via TLS.

   As resource-constrained devices are not expected to support both
   transport layer security mechanisms, Clients and Resource Servers
   SHOULD support DTLS and MAY support TLS.  A Client that implements
   either TLS or DTLS but not both might fail in establishing a secure
   communication channel with the Resource Server altogether.
   Nonconstrained Clients and Resource Servers SHOULD support both TLS
   and DTLS.

   Note that a communication setup with an a priori unknown Resource
   Server typically employs an initial unauthorized resource request, as
   illustrated in Section 2 of [RFC9202].  If this message exchange
   succeeds, the Client SHOULD first use the same underlying transport
   protocol for the establishment of the security association to the
   Resource Server (i.e., DTLS for UDP, and TLS for TCP).

   As a consequence, the selection of the transport protocol used for
   the initial unauthorized resource request also depends on the
   transport layer security mechanism supported by the Client.  Clients
   that support either DTLS or TLS but not both SHOULD use the transport
   protocol underlying the supported transport layer security mechanism
   for an initial unauthorized resource request to the Resource Server,
   as in Section 2 of [RFC9202].

5.  IANA Considerations

   In the "ACE Profiles" registry, the Description and Reference fields
   have been updated as follows for coap_dtls:

   Name:  coap_dtls

   Description:  Profile for delegating client Authentication and
      Authorization for Constrained Environments by establishing a
      Datagram Transport Layer Security (DTLS) or Transport Layer
      Security (TLS) channel between resource-constrained nodes.

   CBOR Value:  1

   Reference:  [RFC9202], RFC 9430

6.  Security Considerations

   The security consideration and requirements in [RFC9202], TLS 1.3
   [RFC8446], and BCP 195 [RFC8996] [RFC9325] also apply to this
   document.

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, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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,
              <https://www.rfc-editor.org/info/rfc8323>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/info/rfc9147>.

   [RFC9200]  Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authentication and Authorization for
              Constrained Environments Using the OAuth 2.0 Framework
              (ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
              <https://www.rfc-editor.org/info/rfc9200>.

   [RFC9202]  Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
              L. Seitz, "Datagram Transport Layer Security (DTLS)
              Profile for Authentication and Authorization for
              Constrained Environments (ACE)", RFC 9202,
              DOI 10.17487/RFC9202, August 2022,
              <https://www.rfc-editor.org/info/rfc9202>.

7.2.  Informative References

   [RFC8996]  Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
              1.1", BCP 195, RFC 8996, DOI 10.17487/RFC8996, March 2021,
              <https://www.rfc-editor.org/info/rfc8996>.

   [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, August 2022,
              <https://www.rfc-editor.org/info/rfc9203>.

   [RFC9325]  Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/info/rfc9325>.

Acknowledgments

   The authors would like to thank Marco Tiloca for reviewing this
   specification.

Authors' Addresses

   Olaf Bergmann
   Universität Bremen TZI
   D-28359 Bremen
   Germany
   Email: bergmann@tzi.org


   John Preuß Mattsson
   Ericsson AB
   SE-164 80 Stockholm
   Sweden
   Email: john.mattsson@ericsson.com


   Göran Selander
   Ericsson AB
   SE-164 80 Stockholm
   Sweden
   Email: goran.selander@ericsson.com
