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.
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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