



ACE Working Group                                            G. Selander
Internet-Draft                                         J. Preuß Mattsson
Intended status: Standards Track                                Ericsson
Expires: 8 January 2026                                        M. Tiloca
                                                              R. Höglund
                                                                    RISE
                                                             7 July 2025


   Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object Security for
    Constrained Environments (OSCORE) Profile for Authentication and
            Authorization for Constrained Environments (ACE)
                 draft-ietf-ace-edhoc-oscore-profile-08

Abstract

   This document specifies a profile for the Authentication and
   Authorization for Constrained Environments (ACE) framework.  It
   utilizes Ephemeral Diffie-Hellman Over COSE (EDHOC) for achieving
   mutual authentication between an ACE-OAuth client and resource
   server, and it binds an authentication credential of the client to an
   ACE-OAuth access token.  EDHOC also establishes an Object Security
   for Constrained RESTful Environments (OSCORE) Security Context, which
   is used to secure communications between the client and resource
   server when accessing protected resources according to the
   authorization information indicated in the access token.  This
   profile can be used to delegate management of authorization
   information from a resource-constrained server to a trusted host with
   less severe limitations regarding processing power and memory.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-ace-edhoc-oscore-
   profile/.

   Discussion of this document takes place on the Authentication and
   Authorization for Constrained Environments (ace) Working Group
   mailing list (mailto:ace@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/ace/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/ace/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ace-wg/ace-edhoc-oscore-profile.





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Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on 8 January 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Client-AS Communication . . . . . . . . . . . . . . . . . . .  10
     3.1.  C-to-AS: POST to /token endpoint  . . . . . . . . . . . .  11
     3.2.  Token Series  . . . . . . . . . . . . . . . . . . . . . .  14
     3.3.  AS-to-C: Response . . . . . . . . . . . . . . . . . . . .  15
       3.3.1.  Access Token  . . . . . . . . . . . . . . . . . . . .  17
       3.3.2.  Processing at C . . . . . . . . . . . . . . . . . . .  19
       3.3.3.  Update of Access Rights . . . . . . . . . . . . . . .  19
     3.4.  EDHOC_Information . . . . . . . . . . . . . . . . . . . .  20
   4.  Client-RS Communication . . . . . . . . . . . . . . . . . . .  28
     4.1.  EAD items for Access Token and Session Identifier . . . .  28
     4.2.  EDHOC Session . . . . . . . . . . . . . . . . . . . . . .  30
     4.3.  Forward Message Flow  . . . . . . . . . . . . . . . . . .  31



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       4.3.1.  EDHOC message_1 . . . . . . . . . . . . . . . . . . .  32
       4.3.2.  EDHOC message_2 . . . . . . . . . . . . . . . . . . .  32
       4.3.3.  EDHOC message_3 . . . . . . . . . . . . . . . . . . .  32
     4.4.  Reverse Message Flow  . . . . . . . . . . . . . . . . . .  33
       4.4.1.  Trigger Message . . . . . . . . . . . . . . . . . . .  33
       4.4.2.  EDHOC message_1 . . . . . . . . . . . . . . . . . . .  33
       4.4.3.  EDHOC message_2 . . . . . . . . . . . . . . . . . . .  34
       4.4.4.  EDHOC message_3 . . . . . . . . . . . . . . . . . . .  34
       4.4.5.  EDHOC message_4 . . . . . . . . . . . . . . . . . . .  34
     4.5.  OSCORE Security Context . . . . . . . . . . . . . . . . .  35
     4.6.  Update of Access Rights . . . . . . . . . . . . . . . . .  35
       4.6.1.  C-to-RS: POST to /authz-info endpoint . . . . . . . .  36
       4.6.2.  RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . .  37
     4.7.  Discarding the OSCORE Security Context  . . . . . . . . .  37
     4.8.  Establishing a New OSCORE Security Context  . . . . . . .  39
     4.9.  Access Rights Verification  . . . . . . . . . . . . . . .  39
     4.10. Access Token Invalidity . . . . . . . . . . . . . . . . .  40
     4.11. Authentication Credential Invalidity  . . . . . . . . . .  40
     4.12. EDHOC Session Invalidity  . . . . . . . . . . . . . . . .  40
     4.13. Using AS Request Creation Hints . . . . . . . . . . . . .  41
     4.14. Requesting Authentication Credential By Value . . . . . .  42
   5.  Secure Communication with AS  . . . . . . . . . . . . . . . .  43
   6.  CWT Confirmation Methods  . . . . . . . . . . . . . . . . . .  43
     6.1.  Ordered Chain of X.509 Certificates . . . . . . . . . . .  44
     6.2.  Unordered Bag of X.509 Certificates . . . . . . . . . . .  44
     6.3.  Hash of an X.509 Certificate  . . . . . . . . . . . . . .  44
     6.4.  URI Pointing to an Ordered Chain of X.509 Certificates  .  44
     6.5.  Ordered Chain of C509 Certificates  . . . . . . . . . . .  44
     6.6.  Unordered Bag of C509 Certificates  . . . . . . . . . . .  44
     6.7.  Hash of a C509 Certificate  . . . . . . . . . . . . . . .  44
     6.8.  URI Pointing to an Ordered Chain of C509 Certificates . .  45
     6.9.  CWT Containing a COSE_Key . . . . . . . . . . . . . . . .  45
     6.10. CCS Containing a COSE_Key . . . . . . . . . . . . . . . .  45
   7.  JWT Confirmation Methods  . . . . . . . . . . . . . . . . . .  45
     7.1.  Ordered Chain of X.509 Certificates . . . . . . . . . . .  45
     7.2.  Unordered Bag of X.509 Certificates . . . . . . . . . . .  45
     7.3.  Hash of an X.509 Certificate  . . . . . . . . . . . . . .  46
     7.4.  URI Pointing to an Ordered Chain of X.509 Certificates  .  46
     7.5.  Ordered Chain of C509 Certificates  . . . . . . . . . . .  46
     7.6.  Unordered Bag of C509 Certificates  . . . . . . . . . . .  46
     7.7.  Hash of a C09 Certificate . . . . . . . . . . . . . . . .  46
     7.8.  URI Pointing to an Ordered Chain of C509 Certificates . .  47
     7.9.  CWT Containing a COSE_Key . . . . . . . . . . . . . . . .  47
     7.10. CCS Containing a COSE_Key . . . . . . . . . . . . . . . .  47
   8.  EDHOC Endpoint Identity Types . . . . . . . . . . . . . . . .  47
   9.  EDHOC Transports  . . . . . . . . . . . . . . . . . . . . . .  47
   10. EDHOC Trust Anchor Purposes . . . . . . . . . . . . . . . . .  48
   11. EDHOC Trust Anchor Types  . . . . . . . . . . . . . . . . . .  49



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   12. Security Considerations . . . . . . . . . . . . . . . . . . .  50
   13. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  51
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  52
     14.1.  ACE Profiles Registry  . . . . . . . . . . . . . . . . .  52
     14.2.  OAuth Parameters Registry  . . . . . . . . . . . . . . .  52
     14.3.  OAuth Parameters CBOR Mappings Registry  . . . . . . . .  53
     14.4.  JSON Web Token Claims Registry . . . . . . . . . . . . .  53
     14.5.  CBOR Web Token (CWT) Claims Registry . . . . . . . . . .  53
     14.6.  JWT Confirmation Methods Registry  . . . . . . . . . . .  54
     14.7.  CWT Confirmation Methods Registry  . . . . . . . . . . .  56
     14.8.  EDHOC External Authorization Data Registry . . . . . . .  59
     14.9.  EDHOC Information Registry . . . . . . . . . . . . . . .  60
     14.10. EDHOC Endpoint Identity Types Registry . . . . . . . . .  61
     14.11. EDHOC Transports Registry  . . . . . . . . . . . . . . .  62
     14.12. EDHOC Trust Anchor Purposes Registry . . . . . . . . . .  63
     14.13. EDHOC Trust Anchor Types Registry  . . . . . . . . . . .  64
     14.14. Expert Review Instructions . . . . . . . . . . . . . . .  65
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  66
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  66
     15.2.  Informative References . . . . . . . . . . . . . . . . .  70
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  72
     A.1.  Workflow without Optimizations  . . . . . . . . . . . . .  73
     A.2.  Workflow with Optimizations . . . . . . . . . . . . . . .  77
   Appendix B.  Profile Requirements . . . . . . . . . . . . . . . .  79
   Appendix C.  CDDL Model . . . . . . . . . . . . . . . . . . . . .  80
   Appendix D.  Document Updates . . . . . . . . . . . . . . . . . .  82
     D.1.  Version -07 to -08  . . . . . . . . . . . . . . . . . . .  82
     D.2.  Version -06 to -07  . . . . . . . . . . . . . . . . . . .  82
     D.3.  Version -05 to -06  . . . . . . . . . . . . . . . . . . .  83
     D.4.  Version -04 to -05  . . . . . . . . . . . . . . . . . . .  84
     D.5.  Version -03 to -04  . . . . . . . . . . . . . . . . . . .  84
     D.6.  Version -02 to -03  . . . . . . . . . . . . . . . . . . .  84
     D.7.  Version -01 to -02  . . . . . . . . . . . . . . . . . . .  85
     D.8.  Version -00 to -01  . . . . . . . . . . . . . . . . . . .  85
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  85
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  86

1.  Introduction

   This document defines the "coap_edhoc_oscore" profile of the ACE-
   OAuth framework [RFC9200].  This profile addresses a "zero-touch"
   constrained setting where authenticated and authorized operations can
   be performed with low overhead without endpoint specific
   configurations.

   Like in the "coap_oscore" profile [RFC9203], also in this profile a
   client (C) and a resource server (RS) use the Constrained Application
   Protocol (CoAP) [RFC7252] to communicate, and Object Security for



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   Constrained RESTful Environments (OSCORE) [RFC8613] to protect their
   communications.  However, this profile uses the Ephemeral Diffie-
   Hellman Over COSE (EDHOC) protocol [RFC9528] to establish the OSCORE
   Security Context.  The processing of requests for specific protected
   resources is identical to what is defined in the "coap_oscore"
   profile.

   When using this profile, C accesses protected resources hosted at RS
   according to the authorization information specified in an access
   token, which is issued by a trusted authorization server (AS) and is
   bound to an authentication credential of C.  This differs from the
   "coap_oscore" profile, where the access token is bound to a secret
   that is generated by AS and is used to derive the OSCORE Security
   Context.

   Whereas [RFC9200] recommends the use of CBOR Web Tokens (CWTs)
   [RFC8392] as access tokens, this profile requires it (see
   Section 3.3.1).  Furthermore, this profile requires that, for
   messages exchanged between C and AS to request and provide an access
   token, the payload is encoded in CBOR [RFC8949] (see Section 3.1 and
   Section 3.3), which ACE requires if CoAP is used (see Section 5 of
   [RFC9200]) and recommends otherwise (see Section 3 of [RFC9200]).

   An authentication credential can be a raw public key, e.g., encoded
   as a CWT Claims Set (CCS) [RFC8392]; or a public key certificate,
   e.g., an X.509 certificate [RFC5280] or a CBOR-encoded C509
   certificate [I-D.ietf-cose-cbor-encoded-cert]); or a different type
   of data structure containing the public key of the peer in question.

   The ACE framework establishes what those authentication credentials
   are, and may transport the actual authentication credentials by value
   or uniquely refer to them.  If an authentication credential is pre-
   provisioned or can be obtained over less constrained links, then it
   suffices that ACE provides a unique reference such as a certificate
   hash (e.g., by using the COSE header parameter "x5t" [RFC9360]).
   This is in the same spirit as EDHOC, where the authentication
   credentials specified in the ID_CRED_x message fields can be
   transported by value or referred to (see Section 3.5.3 of [RFC9528]).

   In general, AS and RS are likely to have trusted access to each
   other's authentication credentials, since AS acts on behalf of RS as
   per the trust model of ACE.  Also, AS needs to have some information
   about C, including the relevant authentication credential, in order
   to identify C when it requests an access token and to determine what
   access rights it can be granted.  However, the authentication
   credential of C may potentially be conveyed (or uniquely referred to)
   within the request for an access token that C makes to AS.




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   The establishment of an association between RS and AS in an ACE
   ecosystem is out of scope, but one solution is to build on the same
   primitives as used in this document, i.e., EDHOC for authentication
   and OSCORE for communication security, using for example
   [I-D.ietf-lake-authz] for onboarding RS with AS and
   [I-D.ietf-ace-coap-est-oscore] for establishing a trust anchor in RS.
   A similar procedure can also be applied between C and AS for
   registering a client and for the establishment of a trust anchor.

1.1.  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.

   Certain security-related terms such as "authentication",
   "authorization", "confidentiality", "(data) integrity", "Message
   Authentication Code (MAC)", "Hash-based Message Authentication Code
   (HMAC)", and "verify" are taken from [RFC4949].

   RESTful terminology follows HTTP [RFC9110].

   Readers are expected to be familiar with the terms and concepts
   defined in CoAP [RFC7252], OSCORE [RFC8613], and EDHOC [RFC9528].

   Readers are also expected to be familiar with the terms and concepts
   of the ACE framework described in [RFC9200] and in [RFC9201].

   Terminology for entities in the architecture is defined in OAuth 2.0
   [RFC6749], such as the client (C), the resource server (RS), and the
   authorization server (AS).  It is assumed in this document that a
   given resource on a specific RS is associated with a unique AS.

   Note that the term "endpoint" is used here, as in [RFC9200],
   following its OAuth definition, which is to denote resources such as
   /token and /introspect at AS, and /authz-info at RS.  The CoAP
   [RFC7252] definition, which is "An entity participating in the CoAP
   protocol", is not used in this document.

   The authorization information (authz-info) resource refers to the
   authorization information endpoint as specified in [RFC9200].  The
   term "claim" is used in this document with the same semantics as in
   [RFC9200], i.e., it denotes information carried in the access token
   or returned from introspection.





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   Concise Binary Object Representation (CBOR) [RFC8949][RFC8742] and
   Concise Data Definition Language (CDDL) [RFC8610] are used in this
   document.  CDDL predefined type names, especially bstr for CBOR byte
   strings and tstr for CBOR text strings, are used extensively in this
   document.

   Examples throughout this document are expressed in CBOR diagnostic
   notation as defined in Section 8 of [RFC8949] and Appendix G of
   [RFC8610].  Diagnostic notation comments are often used to provide a
   textual representation of the numeric parameter names and values.

   In the CBOR diagnostic notation used in this document, constructs of
   the form e'SOME_NAME' are replaced by the value assigned to SOME_NAME
   in the CDDL model shown in Figure 11 of Appendix C.  For example,
   {e'session_id' : h'01', e'cipher_suites': 3} stands for {0 : h'01', 2
   : 3}.

   Note to RFC Editor: Please delete the paragraph immediately preceding
   this note.  Also, in the CBOR diagnostic notation used in this
   document, please replace the constructs of the form e'SOME_NAME' with
   the value assigned to SOME_NAME in the CDDL model shown in Figure 11
   of Appendix C.  Finally, please delete this note.

2.  Protocol Overview

   This section gives an overview of how to use the ACE framework
   [RFC9200] together with the lightweight authenticated key exchange
   protocol EDHOC [RFC9528].  By doing so, the client (C) and the
   resource server (RS) generate an OSCORE Security Context [RFC8613]
   associated with authorization information, and use that Security
   Context to protect their communications.  The parameters needed by C
   to negotiate the use of this profile with the authorization server
   (AS), as well as the OSCORE setup process, are described in detail in
   the following sections.

   RS maintains a collection of authentication credentials.  These are
   associated with OSCORE Security Contexts and with authorization
   information for all clients that RS is communicating with.  The
   authorization information is used to enforce policies for processing
   requests from those clients.

   The ACE framework describes how integrity protected authorization
   information propagates from AS to RS.  This profile describes how C
   requests from AS an access token specifying authorization information
   for the resources that C wants to access at RS, by sending an access
   token request to the /token endpoint at AS (see Section 5.8 of
   [RFC9200]).




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   If the request is granted, then AS can provide C with an access token
   when sending a response to C, or instead upload the access token
   directly to RS as per the alternative workflow defined in
   [I-D.ietf-ace-workflow-and-params].  The latter option is not
   detailed further in this document.

   After that, C and RS run the EDHOC protocol, with C using the
   authentication credential of RS obtained from AS.  If C has obtained
   an access token from AS, then C specifies the access token within an
   External Authorization Data (EAD) field of an EDHOC message sent
   during the EDHOC session (see Section 3.8 of [RFC9528]).  RS uses the
   authentication credential of C bound to and specified in the access
   token.  How C and RS run EDHOC is detailed in Section 4.2.

   If C and RS successfully complete the EDHOC execution and the
   validation of each other's authentication credential, they are
   mutually authenticated and derive the OSCORE Security Context as per
   Appendix A.1 of [RFC9528].

   Figure 1 outlines an example of the message flow.  A more detailed
   description of the message flow is shown in Appendix A.1.

   From then on and as long as there is a valid access token, C
   effectively gains authorized and secure access to protected resources
   at RS using the established OSCORE Security Context.  When RS
   receives a request from C protected with an OSCORE Security Context
   derived from an EDHOC session implementing this profile, then that
   OSCORE Security Context is used to retrieve the uniquely associated
   access token determining the access rights of C.

   The OSCORE Security Context is discarded when an access token
   (whether the same or a different one) is used to successfully derive
   a new OSCORE Security Context for C.


















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      C                            RS                       AS
      |                            |                         |
      | <==== Mutual authentication and secure channel ====> |
      |                            |                         |
      +-------- POST /token  ------------------------------->|
      |                            |                         |
      |<--------------------------------- Access Token ------+
      |                               + Access Information   |
      |                            |                         |
      +------- POST /edhoc  ------>|                         |
      |     (EDHOC message_1)      |                         |
      |                            |                         |
      |<------ 2.04 Changed -------+                         |
      |     (EDHOC message_2)      |                         |
      |                            |                         |
   / Derivation of OSCORE          |                         |
   Security Context /              |                         |
      |                            |                         |
      +------- POST /edhoc  ------>|                         |
      |   (EDHOC message_3 with    |                         |
      |   access_token in EAD_3)   |                         |
      |                            |                         |
      |                / Derivation of OSCORE                |
      |                  Security Context /                  |
      |                            |                         |
      +----- OSCORE Request ------>|                         |
      |                            |                         |
      |<---- OSCORE Response ------|                         |
      |                            |                         |

      Figure 1: Protocol Outline using the EDHOC Forward Message Flow.

   As long as the OSCORE Security Context and the access token are
   valid, C can contact AS to request an update of its access rights, by
   sending a similar request as described above to the /token endpoint.
   This request also includes a "session identifier" (see Section 3.4)
   provided by AS in the response to the initial access token request,
   which allows AS to retrieve the data that it previously shared with
   C.  The session identifier is assigned by AS and used to identify a
   series of access tokens, called a "token series" (see Section 3.2).

   If C has obtained an access token from AS for updating its access
   rights belonging to the same token series, then C transfers the
   access token to RS using the /authz-info endpoint as specified in
   Section 5.10 of [RFC9200], where the exchanged CoAP messages are
   protected by the previously established OSCORE Security Context (see
   Section 4.6).  If the access token is valid, RS replies to the
   request with a 2.01 (Created) response.



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   Upon successful update of access rights, the new issued access token
   effectively becomes the latest in its token series also for RS, but
   the session identifier remains the same.  When the latest access
   token of a token series becomes invalid (e.g., when it expires or
   gets revoked), that token series ends.

   Figure 2 outlines the message flow for updating access rights.

      C                            RS                       AS
      |                            |                         |
      | <====         Existing security context        ====> |
      |                            |                         |
      +-------- POST /token  ------------------------------->|
      |                            |                         |
      |<--------------------------------- Access Token ------+
      |                               + Access Information   |
      |                            |                         |
      +--- POST /authz-info  ----->|                         |
      |  (OSCORE protected with    |                         |
      |   access_token in payload) |                         |
      |                            |                         |
      |               / Updated access rights /              |
      |                            |                         |
      |<------ 2.04 Changed -------+                         |
      |                            |                         |
      |                            |                         |
      +----- OSCORE Request ------>|                         |
      |                            |                         |
      |<---- OSCORE Response ------|                         |
      |                            |                         |

           Figure 2: Protocol Outline for Updating Access Rights.

3.  Client-AS Communication

   The following subsections describe the details of the POST request
   and response to the /token endpoint between C and AS.

   In this exchange, C provides AS with its own authentication
   credential AUTH_CRED_C.  Then, AS issues the access token as securely
   bound to AUTH_CRED_C, by including it or uniquely referring to it in
   the access token.  Together with the access token, AS provides C with
   a set of parameters that enable C to run EDHOC with RS.  In
   particular, these parameters include information about the
   authentication credential AUTH_CRED_RS of RS, which is transported by
   value or uniquely referred to.





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   The request to the /token endpoint and the corresponding response can
   include EDHOC_Information, which is a CBOR map object containing
   information related to an EDHOC implementation (see Section 3.4).
   This object is transported in the "edhoc_info" parameter registered
   in Section 14.2 and Section 14.3.

3.1.  C-to-AS: POST to /token endpoint

   The client-to-AS request is specified in Section 5.8.1 of [RFC9200].

   The client MUST send this POST request to the /token endpoint over a
   secure channel that guarantees authentication, message integrity, and
   confidentiality (see Section 5).

   When using this profile, the payload of the POST request MUST be
   encoded in CBOR [RFC8949], i.e., the request has media-type
   "application/ace+cbor".  In order to reduce the number of libraries
   that C has to support, it is RECOMMENDED that C and AS use CoAP as
   message transfer protocol, OSCORE as security protocol, and EDHOC to
   establish an OSCORE Security Context.

   AUTH_CRED_C is specified in the "req_cnf" parameter [RFC9201] of the
   POST request, either transported by value or uniquely referred to.
   AS could explicitly ask C to provide its authentication credential
   AUTH_CRED_C by value in the Access Token Request, e.g., by relying on
   the method defined in [I-D.ietf-ace-workflow-and-params].

   For AUTH_CRED_C, its authentication credential type MUST be one of
   those supported by EDHOC, e.g., CBOR Web Tokens (CWTs) and CWT Claims
   Sets (CCSs) [RFC8392], X.509 certificates [RFC5280], and C509
   certificates [I-D.ietf-cose-cbor-encoded-cert].  Consequently, the
   "req_cnf" parameter MUST specify a confirmation method suitable for
   the type of AUTH_CRED_C, e.g., "x5chain" or "x5t" when AUTH_CRED_C is
   an X.509 certificate transported by value or referred to,
   respectively.

   Note that EDHOC does not admit the use of "naked" COSE_Keys as
   authentication credentials.  The closest admitted authentication
   credential type is a CCS containing a COSE_Key in a "cnf" claim and
   possibly other claims, which can be transported by value using the
   confirmation method "kccs".  Therefore, the "req_cnf" parameter MUST
   NOT specify the confirmation method "COSE_Key" (CBOR abbreviation:
   1).

   When receiving an Access Token request including the "req_cnf"
   parameter, AS checks whether it is already storing the authentication
   credential of C, namely AUTH_CRED_C, specified in "req_cnf" by value
   or reference.



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   If this is not the case, AS retrieves AUTH_CRED_C, either using the
   "req_cnf" parameter or some other trusted source.  After that, AS
   validates the actual AUTH_CRED_C.

   In either case, the AS also needs to verify that C is in possession
   of the private key corresponding to the public key associated with
   AUTH_CRED_C.  This may already have been accomplished, for example,
   by C authenticating to AS using AUTH_CRED_C as authentication
   credential, or by some other trusted party vouching for C to the AS.
   Alternatively, it is possible to use an approach for achieving proof-
   of-possession similar to that in Section 3.2 of
   [I-D.ietf-ace-group-oscore-profile].

   In case of successful validations, AS stores AUTH_CRED_C as a valid
   authentication credential.  Otherwise, the Client-to-AS request MUST
   be declined.

   An example of client-to-AS request is shown in Figure 3.  In this
   example, C specifies its own authentication credential by reference,
   as the hash of an X.509 certificate carried in the "x5t" field of the
   "req_cnf" parameter.

      Header: POST (Code=0.02)
      Uri-Host: "as.example.com"
      Uri-Path: "token"
      Content-Format: application/ace+cbor
      Payload:
      {
        / audience / 5 : "tempSensor4711",
        / scope /    9 : "read",
        / req_cnf /  4 : {
          e'x5t' : [-15, h'79F2A41B510C1F9B']
        }
      }

   Figure 3: Example of C-to-AS POST /token request for an access token.

   If C wants to update its access rights without changing an existing
   OSCORE Security Context, it MUST specify an EDHOC_Information object
   in the "edhoc_info" parameter of its POST request to the /token
   endpoint.  The EDHOC_Information object MUST include the "session_id"
   field.  This POST request MUST NOT include the "req_cnf" parameter.
   An example of such a request is shown in Figure 4.








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   The identifier "session_id" is assigned by AS as discussed in
   Section 3.2, and identifies an ongoing token series associated with
   the pair (AUTH_CRED_C, AUTH_CRED_RS).  That is, previous access
   tokens in that series were issued by AS to C, as bound to AUTH_CRED_C
   and intended for RS as identified by AUTH_CRED_RS.

   Note that the same "session_id" value might identify multiple ongoing
   token series, e.g., if those are associated with the same client but
   different resource servers.  In this case, AS can use the
   "session_id" value together with other information such as the
   targeted audience (see Section 5.8.1 of [RFC9200]) and the
   authenticated identity of C, in order to determine the exact token
   series to which the new requested access token has to be added.

   If the identifier specified in the "session_id" parameter of the POST
   request identifies multiple, ongoing token series of which C has an
   access token, then C MUST specify the "audience" parameter in the
   POST request.  In particular, the value of the "audience" parameter
   MUST be the same value of the "audience" parameter in the POST
   request that C previously sent to AS, for requesting the first access
   token in the token series to which the new requested access token has
   to be added.

   AS MUST verify that the received "session_id" identifies a token
   series to which a still valid access token issued for C and RS
   belongs.  If that is not the case, the Client-to-AS request MUST be
   declined with the error code "invalid_request" as defined in
   Section 5.8.3 of [RFC9200].

      Header: POST (Code=0.02)
      Uri-Host: "as.example.com"
      Uri-Path: "token"
      Content-Format: application/ace+cbor
      Payload:
      {
        / audience /      5 : "tempSensor4711",
        / scope /         9 : "write",
        e'edhoc_info_param' : {
           e'session_id' : h'01'
        }
      }

       Figure 4: Example of C-to-AS POST /token request for updating
                     access rights to an access token.







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3.2.  Token Series

   This document refers to "token series" as a series of access tokens
   that are sorted in chronological order of release and are
   characterized by the following properties:

   *  Issued by the same AS.

   *  Issued to the same C, and associated with the same authentication
      credential of C.

   *  Issued for the same RS as identified by the same authentication
      credential.

   Upon a successful update of access rights (see Section 3.3.3), the
   new issued access token becomes the latest in its token series.  When
   the latest access token of a token series becomes invalid (e.g., due
   to its expiration or revocation), the token series it belongs to
   ends.

   In this profile, a token series comprises access tokens that are used
   between a given pair (C, RS), are bound to the same authentication
   credential AUTH_CRED_C of C, and specify the same value in the
   "session_id" field of the EDHOC_Information object (see Section 3.4)
   in their "edhoc_info" claim.

   AS assigns the value of "session_id" when issuing the first access
   token of a new series.  That "session_id" value remains fixed
   throughout the series lifetime.

   When assigning the "session_id" value, AS MUST ensure that it was not
   used in a previous series whose access tokens share both the
   following properties with the access tokens of the new series,
   irrespective of the used ACE profile:

   *  issued to the same client C; and

   *  issued for the same RS.

   In case the access token is issued for a group-audience (see
   Section 6.9 of [RFC9200]), what is defined above applies, with the
   difference that the token series is associated with all the RSs in
   the group-audience, as indicated by their respective AUTH_CRED_RS.








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3.3.  AS-to-C: Response

   After verifying the POST request to the /token endpoint and that C is
   authorized to access protected resources at RS, AS responds as
   defined in Section 5.8.2 of [RFC9200], with potential modifications
   as detailed below.

   When using this profile, consistent with what is specified in
   Section 3.1, the payload of the response from AS MUST be encoded in
   CBOR [RFC8949], i.e., the response has media-type "application/
   ace+cbor".

   If the request from C was invalid or not authorized, AS returns an
   error response as described in Section 5.8.3 of [RFC9200].

   AS can signal that the use of EDHOC and OSCORE as per this profile is
   REQUIRED for a specific access token, by including the "ace_profile"
   parameter with the value "coap_edhoc_oscore" in the access token
   response.  This means that C MUST use EDHOC with RS and derive an
   OSCORE Security Context, as specified in Section 4.2.  After that, C
   MUST use the established OSCORE Security Context to protect
   communications with RS, when accessing protected resources at RS
   according to the authorization information indicated in the access
   token.  Usually, it is assumed that constrained devices will be pre-
   configured with the necessary profile, so that this kind of profile
   signaling can be omitted.

   According to this document, the AS provides the access token to C, by
   specifying it in the "access_token" parameter of the access token
   response.  An alternative workflow where the access token is uploaded
   by AS directly to RS is described in
   [I-D.ietf-ace-workflow-and-params].

   When issuing the first access token of a token series, AS MUST
   include the following data in the response to C.

   *  The "edhoc_info" parameter conveying an EDHOC_Information object
      (see Section 3.4).  The EDHOC_Information object MUST include the
      "session_id" field specifying the identifier of the token series
      which the issued access token belongs to.

      The EDHOC_Information object MAY include additional fields (see
      Section 3.4) to convey information about RS.  This information is
      based on knowledge that AS has about RS, e.g., from a previous
      onboarding process, with particular reference to what RS supports
      as EDHOC peer.





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      In case the access token is issued for a group-audience (see
      Section 6.9 of [RFC9200]), the information specified in the
      EDHOC_Information object refers to the group-audience as a whole.
      Therefore, it is appropriate for AS to define group-audiences
      comprising RSs that are all aligned in terms of supported EDHOC
      features and configurations.

   *  A unique identification of the authentication credential of RS,
      AUTH_CRED_RS.  This is specified in the "rs_cnf" parameter defined
      in [RFC9201].  AUTH_CRED_RS can be transported by value or
      referred to by means of an appropriate identifier.  C could
      explicitly ask AS to provide AUTH_CRED_RS by value in the Access
      Token Response, e.g., by relying on the method defined in
      [I-D.ietf-ace-workflow-and-params].

      When issuing the first access token ever to a pair (C, RS) using a
      pair of corresponding authentication credentials (AUTH_CRED_C,
      AUTH_CRED_RS), it is expected that the response to C includes
      AUTH_CRED_RS by value.

      When later issuing further access tokens to the same pair (C, RS)
      using the same AUTH_CRED_RS, it is expected that the response to C
      includes AUTH_CRED_RS by reference.

      For AUTH_CRED_RS, its authentication credential type MUST be one
      of those supported by EDHOC.  Consequently, the "rs_cnf" parameter
      MUST specify a confirmation method suitable for the type of
      AUTH_CRED_RS.  That is, the same considerations about AUTH_CRED_C
      and the "req_cnf" parameter made in Section 3.1 hold for
      AUTH_CRED_RS and the "rs_cnf" parameter.

   When issuing an access token for dynamically updating access rights
   (i.e., the access token is not the first in its token series), the
   response from AS MUST NOT include the "edhoc_info" and "rs_cnf"
   parameters (see Section 3.3.3).

   Figure 5 shows an example of an AS response.  The "rs_cnf" parameter
   specifies the authentication credential of RS, as an X.509
   certificate transported by value in the "x5chain" field.  The access
   token and the authentication credential of RS have been truncated for
   readability.










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      Header: Created (Code=2.01)
         Content-Format: application/ace+cbor
         Payload:
         {
           / access_token / 1 : h'8343a1010aa2044c53...0f6a'
             / remainder of access token (CWT) omitted for brevity /,
           / ace_profile / 38 : e'coap_edhoc_oscore',
           / expires_in /   2 : 3600,
           / rs_cnf /      41 : {
             e'x5chain' : h'3081ee3081a1a00302...77bc'
               / remainder of the credential omitted for brevity /
           }
           e'edhoc_info_param' : {
             e'session_id'    : h'01',
             e'methods'       : [0, 1, 2, 3],
             e'cipher_suites' : 0
           }
         }

     Figure 5: Example of AS-to-C Access Token response with EDHOC and
                              OSCORE profile.

3.3.1.  Access Token

   To avoid the complexity of different encodings, an access token of
   this profile SHALL be a CBOR Web Token (CWT) [RFC8392].

   When issuing any access token of a token series, AS MUST include the
   following claims in the access token:

   *  The "edhoc_info" claim defined in Section 14.5 and conveying an
      EDHOC_Information object (see Section 3.4).

      The EDHOC_Information object MUST include the "session_id" field
      specifying the identifier of the token series which the issued
      access token belongs to.  The "session_id" value is the same one
      included in the EDHOC_Information object of the response to C from
      the /token endpoint (see Section 3.3), when providing C with the
      first access token in the series.

   *  The "cnf" claim, specifying the authentication credential
      AUTH_CRED_C that C specified in its POST request to the /token
      endpoint, when requesting the first access token in the series
      which the issued access token belongs to (see Section 3.1).

      In the access token, AUTH_CRED_C can be transported by value or
      uniquely referred to by means of an appropriate identifier.  Yet,
      consistent with the considerations about AUTH_CRED_C and the



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      "req_cnf" parameter made in Section 3.1, the "cnf" claim of the
      access token MUST specify a confirmation method suitable for the
      type of AUTH_CRED_C.

      When issuing the first access token of a token series, the
      confirmation method used in the "cnf" claim MUST be the same one
      used in the "req_cnf" parameter of the corresponding POST request
      from C to the /token endpoint.

      When issuing the first access token ever to a pair (C, RS) using a
      pair of corresponding authentication credentials (AUTH_CRED_C,
      AUTH_CRED_RS), it is expected that AUTH_CRED_C is included by
      value in the "cnf" claim of the access token.

      When later issuing further access tokens to the same pair (C, RS)
      using the same AUTH_CRED_C, it is expected that AUTH_CRED_C is
      identified by reference in the "cnf" claim of the access token.

   When issuing the first access token of a token series, AS MAY include
   additional fields in the EDHOC_Information object (see Section 3.4)
   specified in the "edhoc_info" claim of the access token.

   The access token needs to be protected for various reasons.  To
   prevent manipulation of the content, it needs to be integrity
   protected.  Also, RS has to be able to verify that the access token
   is issued by a trusted AS, by achieving source authentication.
   Depending on the use case and deployment, the access token may need
   to be confidentiality protected, for example due to privacy reasons.

   AS protects the access token using a COSE method [RFC9052] as
   specified in [RFC8392].  Depending on the audience, there can be
   different ways to most appropriately ensure the confidentiality of an
   access token.  For an audience comprising a single RS, the CWT Claims
   Set may be wrapped in COSE_Encrypt / COSE_Encrypt0.  Instead, if the
   access token needs to be read by multiple RSs, then the CWT Claims
   Set may be wrapped in COSE_Sign / COSE_Sign1 and confidentiality
   protection is applied during transport, by including the access token
   in the EAD_3 field of EDHOC message_3 sent by C to RS, when using the
   EDHOC forward message flow (see Section 4.2).

   Figure 6 shows an example of CWT Claims Set, including the relevant
   EDHOC parameters in the "edhoc_info" claim.  The "cnf" claim
   specifies the authentication credential of C, as an X.509 certificate
   transported by value in the "x5chain" field.  The authentication
   credential of C has been truncated for readability.






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      {
       / aud /   3 : "tempSensorInLivingRoom",
       / iat /   6 : 1563451500,
       / exp /   4 : 1563453000,
       / scope / 9 :  "temperature_g firmware_p",
       / cnf /   8 : {
         e'x5chain' : h'3081ee3081a1a00302...77bc'
           / remainder of the credential omitted for brevity /
       }
       e'edhoc_info_claim' : {
         e'session_id'    : h'01',
         e'methods'       : [0, 1, 2, 3],
         e'cipher_suites' : 0
       }
     }

         Figure 6: Example of CWT Claims Set with EDHOC parameters.

3.3.2.  Processing at C

   When receiving an access token response including the "rs_cnf"
   parameter, C checks whether it is already storing the authentication
   credential of RS, namely AUTH_CRED_RS, specified in "rs_cnf" by value
   or reference.

   If this is not the case, C retrieves AUTH_CRED_RS, either using the
   "rs_cnf" parameter or some other trusted source.  After that, C
   validates the actual AUTH_CRED_RS.  In case of successful validation,
   C stores AUTH_CRED_RS as a valid authentication credential.
   Otherwise, C MUST delete the access token.

3.3.3.  Update of Access Rights

   If C has a valid OSCORE Security Context associated with a valid
   access token, then C can send a request to AS for updating its access
   rights while preserving the same OSCORE Security Context.

   If the request is granted, then AS generates a new access token,
   where the EDHOC_Information object specified in the "edhoc_info"
   claim MUST include only the "session_id" field.  The access token is
   provisioned to RS either via C as specified in this document, or
   directly as described in [I-D.ietf-ace-workflow-and-params].  In
   either case, the access token response from AS to C MUST NOT include
   the "edhoc_info" and "rs_cnf" parameters.

   As defined in Section 3.3.1, the "session_id" field is included in
   the EDHOC_Information object specified in the "edhoc_info" claim of
   the new access token.  This allows RS to identify the old access



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   token to supersede, as well as the OSCORE Security Context already
   shared between C and RS and to be associated with the new access
   token.

3.4.  EDHOC_Information

   EDHOC_Information is an object including information that guides two
   peers towards executing the EDHOC protocol.  In particular, the
   EDHOC_Information is defined to be serialized and transported between
   nodes, as specified by this document, but it can also be used by
   other specifications.

   In the "coap_edhoc_oscore" profile of the ACE-OAuth framework, which
   is specified in this document, the EDHOC_Information object MUST be
   encoded as CBOR.  However, for easy applicability to other contexts,
   we define also the JSON encoding.

   The EDHOC_Information can be encoded either as a JSON object or as a
   CBOR map.  The set of common fields that can appear in an
   EDHOC_Information can be found in the IANA "EDHOC Information"
   registry defined in Section 14.9 for extensibility.

   All EDHOC_Information parameters are optional.  The initial set of
   parameters defined in this document is summarized in Table 1 and is
   specified below.

   EDHOC_Information parameters are also categorized, i.e., each has one
   of two possible types, namely prescriptive or non-prescriptive:

   *  A prescriptive parameter is used to provide an authoritative
      statement about how an execution of EDHOC has to be performed.  An
      example is the "message_4" parameter indicating whether the use of
      EDHOC message_4 in an EDHOC session is mandatory or not.

   *  A non-prescriptive parameter is used to provide convenient
      information to consider when executing EDHOC, e.g., in terms of
      features supported by other peers.  Such information is not
      necessarily exhaustive.  An example is the "methods" parameter
      indicating a set of supported EDHOC methods.

   This categorization helps coordinate the use of EDHOC application
   profiles Section 3.9 of [RFC9528] in a robust way, e.g., by using the
   means defined in [I-D.ietf-lake-app-profiles].








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   +===============+=====+=====+================+================+====+
   | Name          |CBOR |CBOR | Registry       | Description    |Type|
   |               |label|type |                |                |    |
   +===============+=====+=====+================+================+====+
   | session_id    |0    |bstr |                | Identifier of  |P   |
   |               |     |     |                | a session      |    |
   +---------------+-----+-----+----------------+----------------+----+
   | methods       |1    |int  | EDHOC Method   | Set of         |NP  |
   |               |     |or   | Type registry  | supported      |    |
   |               |     |array|                | EDHOC methods  |    |
   +---------------+-----+-----+----------------+----------------+----+
   | cipher_suites |2    |int  | EDHOC Cipher   | Set of         |NP  |
   |               |     |or   | Suites         | supported      |    |
   |               |     |array| registry       | EDHOC cipher   |    |
   |               |     |     |                | suites         |    |
   +---------------+-----+-----+----------------+----------------+----+
   | message_4     |3    |True |                | Mandatory use  |P   |
   |               |     |or   |                | of EDHOC       |    |
   |               |     |False|                | message_4      |    |
   +---------------+-----+-----+----------------+----------------+----+
   | comb_req      |4    |True |                | Support for    |NP  |
   |               |     |or   |                | the EDHOC +    |    |
   |               |     |False|                | OSCORE         |    |
   |               |     |     |                | combined       |    |
   |               |     |     |                | request        |    |
   +---------------+-----+-----+----------------+----------------+----+
   | uri_path      |5    |tstr |                | URI-path of    |P   |
   |               |     |     |                | the EDHOC      |    |
   |               |     |     |                | resource       |    |
   +---------------+-----+-----+----------------+----------------+----+
   | cred_types    |6    |int  | EDHOC          | Set of         |NP  |
   |               |     |or   | Authentication | supported      |    |
   |               |     |array| Credential     | types of       |    |
   |               |     |     | Types registry | authentication |    |
   |               |     |     |                | credentials    |    |
   |               |     |     |                | for EDHOC      |    |
   +---------------+-----+-----+----------------+----------------+----+
   | id_cred_types |7    |int  | COSE Header    | Set of         |NP  |
   |               |     |or   | Parameters     | supported      |    |
   |               |     |tstr | registry       | types of       |    |
   |               |     |or   |                | authentication |    |
   |               |     |array|                | credential     |    |
   |               |     |     |                | identifiers    |    |
   |               |     |     |                | for EDHOC      |    |
   +---------------+-----+-----+----------------+----------------+----+
   | eads          |8    |uint | EDHOC External | Set of         |NP  |
   |               |     |or   | Authorization  | supported      |    |
   |               |     |array| Data registry  | EDHOC External |    |



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   |               |     |     |                | Authorization  |    |
   |               |     |     |                | Data (EAD)     |    |
   |               |     |     |                | items          |    |
   +---------------+-----+-----+----------------+----------------+----+
   | initiator     |9    |True |                | Support for    |NP  |
   |               |     |or   |                | the EDHOC      |    |
   |               |     |False|                | Initiator role |    |
   +---------------+-----+-----+----------------+----------------+----+
   | responder     |10   |True |                | Support for    |NP  |
   |               |     |or   |                | the EDHOC      |    |
   |               |     |False|                | Responder role |    |
   +---------------+-----+-----+----------------+----------------+----+
   | max_msgsize   |11   |uint |                | Maximum size   |P   |
   |               |     |     |                | of EDHOC       |    |
   |               |     |     |                | messages in    |    |
   |               |     |     |                | bytes          |    |
   +---------------+-----+-----+----------------+----------------+----+
   | coap_ct       |12   |True |                | Mandatory use  |P   |
   |               |     |of   |                | of the CoAP    |    |
   |               |     |False|                | Content-Format |    |
   |               |     |     |                | Option in CoAP |    |
   |               |     |     |                | messages whose |    |
   |               |     |     |                | payload        |    |
   |               |     |     |                | includes       |    |
   |               |     |     |                | exclusively an |    |
   |               |     |     |                | EDHOC message, |    |
   |               |     |     |                | possibly       |    |
   |               |     |     |                | prepended by   |    |
   |               |     |     |                | an EDHOC       |    |
   |               |     |     |                | connection     |    |
   |               |     |     |                | identifier     |    |
   +---------------+-----+-----+----------------+----------------+----+
   | ep_id_types   |13   |int  | EDHOC Endpoint | Set of         |NP  |
   |               |     |or   | Identity Types | supported      |    |
   |               |     |array| registry       | types of       |    |
   |               |     |     |                | endpoint       |    |
   |               |     |     |                | identities for |    |
   |               |     |     |                | EDHOC          |    |
   +---------------+-----+-----+----------------+----------------+----+
   | transports    |14   |int  | EDHOC          | Set of         |NP  |
   |               |     |or   | Transports     | supported      |    |
   |               |     |array| registry       | means for      |    |
   |               |     |     |                | transporting   |    |
   |               |     |     |                | EDHOC messages |    |
   +---------------+-----+-----+----------------+----------------+----+
   | trust_anchors |15   |map  | EDHOC Trust    | Set of         |NP  |
   |               |     |     | Anchor         | supported      |    |
   |               |     |     | Purposes       | trust anchors  |    |



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   |               |     |     | registry and   |                |    |
   |               |     |     | EDHOC Trust    |                |    |
   |               |     |     | Anchor Types   |                |    |
   |               |     |     | registry       |                |    |
   +---------------+-----+-----+----------------+----------------+----+

     Table 1: EDHOC_Information Parameters.  Types: P (Prescriptive),
                          NP (Non- Prescriptive)

   *  session_id: This parameter identifies a 'session' which the EDHOC
      information is associated with, but does not necessarily identify
      a specific EDHOC session.  In this document, "session_id"
      identifies a token series.  In JSON, the "session_id" value is a
      Base64 encoded byte string.  In CBOR, the "session_id" type is a
      byte string, and has label 0.

   *  methods: This parameter specifies a set of supported EDHOC methods
      (see Section 3.2 of [RFC9528]).  If the set is composed of a
      single EDHOC method, this is encoded as an integer.  Otherwise,
      the set is encoded as an array of integers, where each array
      element encodes one EDHOC method.  In JSON, the "methods" value is
      an integer or an array of integers.  In CBOR, the "methods" is an
      integer or an array of integers, and has label 1.

   *  cipher_suites: This parameter specifies a set of supported EDHOC
      cipher suites (see Section 3.6 of [RFC9528]).  If the set is
      composed of a single EDHOC cipher suite, this is encoded as an
      integer.  Otherwise, the set is encoded as an array of integers,
      where each array element encodes one EDHOC cipher suite.  In JSON,
      the "cipher_suites" value is an integer or an array of integers.
      In CBOR, the "cipher_suites" is an integer or an array of
      integers, and has label 2.

   *  message_4: This parameter indicates whether the EDHOC message_4
      (see Section 5.5 of [RFC9528]) is supported.  In JSON, the
      "message_4" value is a boolean.  In CBOR, "message_4" is the
      simple value true (0xf5) or false (0xf4), and has label 4.

   *  comb_req: This parameter indicates whether the combined EDHOC +
      OSCORE request defined in [RFC9668]) is supported.  In JSON, the
      "comb_req" value is a boolean.  In CBOR, "comb_req" is the simple
      value true (0xf5) or false (0xf4), and has label 5.

   *  uri_path: This parameter specifies the path component of the URI
      of the EDHOC resource where EDHOC messages have to be sent as
      requests.  In JSON, the "uri_path" value is a string.  In CBOR,
      "uri_path" is a text string, and has label 6.




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   *  cred_types: This parameter specifies a set of supported types of
      authentication credentials for EDHOC (see Section 3.5.2 of
      [RFC9528]).  If the set is composed of a single type of
      authentication credential, this is encoded as an integer.
      Otherwise, the set is encoded as an array of integers, where each
      array element encodes one type of authentication credential.  In
      JSON, the "cred_types" value is an integer or an array of
      integers.  In CBOR, "cred_types" is an integer or an array of
      integers, and has label 6.  The integer values are taken from the
      "EDHOC Authentication Credential Types" registry defined in
      [RFC9668].

   *  id_cred_types: This parameter specifies a set of supported types
      of authentication credential identifiers for EDHOC (see
      Section 3.5.3 of [RFC9528]).  If the set is composed of a single
      type of authentication credential identifier, this is encoded as
      an integer or a text string.  Otherwise, the set is encoded as an
      array, where each array element encodes one type of authentication
      credential identifier, as an integer or a text string.  In JSON,
      the "id_cred_types" value is an integer, or a text string, or an
      array of integers and text strings.  In CBOR, "id_cred_types" is
      an integer or a text string, or an array of integers and text
      strings, and has label 7.  The integer or text string values are
      taken from the 'Label' column of the "COSE Header Parameters"
      registry [COSE.Header.Parameters].

   *  eads: This parameter specifies a set of supported EDHOC External
      Authorization Data (EAD) items, identified by their ead_label (see
      Section 3.8 of [RFC9528]).  If the set is composed of a single
      ead_label, this is encoded as an unsigned integer.  Otherwise, the
      set is encoded as an array of unsigned integers, where each array
      element encodes one ead_label.  In JSON, the "eads" value is an
      unsigned integer or an array of unsigned integers.  In CBOR,
      "eads" is an unsigned integer or an array of unsigned integers,
      and has label 8.  The unsigned integer values are taken from the
      'Label' column of the "EDHOC External Authorization Data" registry
      defined in [RFC9528].

   *  initiator: This parameter specifies whether the EDHOC Initiator
      role is supported.  In JSON, the "initiator" value is a boolean.
      In CBOR, "initiator" is the simple value true (0xf5) or false
      (0xf4), and has label 9.

   *  responder: This parameter specifies whether the EDHOC Responder
      role is supported.  In JSON, the "responder" value is a boolean.
      In CBOR, "responder" is the simple value true (0xf5) or false
      (0xf4), and has label 10.




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   *  max_msgsize: This parameter specifies the admitted maximum size of
      EDHOC messages in bytes.  In JSON, the "max_msgsize" value is an
      unsigned integer.  In CBOR, "max_msgsize" is an unsigned integer
      and has label 11.

   *  coap_cf: This parameter specifies whether it is required that CoAP
      messages include the CoAP Content-Format Option with value 64
      (application/edhoc+cbor-seq) or 65 (application/cid-edhoc+cbor-
      seq) as appropriate, when the message payload includes exclusively
      an EDHOC message possibly prepended by an EDHOC connection
      identifier (see Sections 3.4.1 and A.2 of [RFC9528]).  In JSON,
      the "coap_cf" value is a boolean.  In CBOR, "coap_cf" is the
      simple value true (0xf5) or false (0xf4), and has label 12.

   *  ep_id_types: This parameter specifies a set of supported types of
      endpoint identities for EDHOC.  If the set is composed of a single
      type of endpoint identity, this is encoded as an integer.
      Otherwise, the set is encoded as an array, where each array
      element encodes one type of endpoint identity as an integer.  In
      JSON, the "ep_id_types" value is an integer or an array of
      integers.  In CBOR, "ep_id_types" is an integer or an array of
      integers, and has label 13.  The integer values are taken from the
      'CBOR Label' column of the "EDHOC Endpoint Identity Types"
      registry defined in Section 14.10 of this document.

   *  transports: This parameter specifies a set of supported means for
      transporting EDHOC messages.  If the set is composed of a single
      means for transporting EDHOC messages, this is encoded as an
      integer.  Otherwise, the set is encoded as an array, where each
      array element encodes one means for transporting EDHOC messages as
      an integer.  In JSON, the "transports" value is an integer or an
      array of integers.  In CBOR, "transports" is an integer or an
      array of integers, and has label 14.  The integer values are taken
      from the 'Transport ID' column of the "EDHOC Transports" Registry
      defined in Section 14.11 of this document.

   *  trust_anchors: This parameter specifies a collection of supported
      trust anchors for performing authentication.  According to what is
      specified within the collection, these trust anchors are used for
      different purposes, e.g., for verifying authentication credentials
      of other EDHOC peers in EDHOC sessions.

      More in detail, the collection of trust anchors is composed of one
      or more sets.  Each set includes one or more trust anchors to use
      for one specific purpose associated with that set.






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      In particular, each set is composed of pairs, each of which
      specifies a trust anchor type and an identifier of a trust anchor
      of that type.  If the set is composed of a single pair, this pair
      is specified as a single item.  If the set is composed of multiple
      pairs, these pairs are specified as elements of an array.

      Trust anchor purposes are selected from the "EDHOC Trust Anchor
      Purposes" registry defined in Section 14.12 of this document.
      Trust anchor types are selected from the "EDHOC Trust Anchor
      Types" registry defined in Section 14.13 of this document.

      In JSON, the "trust_anchors" value is an object with one or more
      outer entries, each of which is associated with a trust anchor
      purpose.  The following applies for each outer entry:

      -  The outer entry's key specifies the associated trust anchor
         purpose taken from the 'Name' column' of the "EDHOC Trust
         Anchor Purposes" registry.

      -  The outer entry's value is an object or an array of at least
         two objects.  Each object includes one inner entry, specifying
         the pair for a trust anchor TA of type TYPE.  The inner entry
         is formatted as follows:

         o  The inner entry's key specifies the TA's type TYPE taken
            from the 'Name' column of the "EDHOC Trust Anchor Types"
            registry.

         o  The inner entry's value is the identifier of TA, whose
            encoding depends on TYPE.  Such an encoding is what results
            from applying the conversion in Section 6.1 of [RFC8949] to
            the CBOR encoding of the identifier of TA when
            "trust_anchors" is encoded in CBOR (see below).

      In CBOR, the "trust_anchors" value is a map and has label 15.  The
      map includes one or more outer entries, each of which is
      associated with a trust anchor purpose.  The following applies for
      each outer entry:

      -  The outer entry's key specifies the associated trust anchor
         purpose encoded as a CBOR integer, with integer value taken
         from the 'CBOR label' column of the "EDHOC Trust Anchor
         Purposes" registry.

      -  The outer entry's value is a map or an array of at least two
         maps.  Each map includes one inner entry, specifying the pair
         for a trust anchor TA of type TYPE.  The inner entry is
         formatted as follows:



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         o  The inner entry's key specifies the TA's type TYPE encoded
            as a CBOR integer, with integer value taken from the 'CBOR
            label' column of the "EDHOC Trust Anchor Types" registry.

         o  The inner entry's value specifies the identifier of TA,
            whose encoding depends on TYPE and is specified by the
            'Value type' column of the "EDHOC Trust Anchor Types"
            registry, for the registry entry that has TYPE as value of
            the 'Name' column.

   An example of JSON EDHOC_Information is given in Figure 7.

      "edhoc_info" : {
          "session_id"    : b64'AQ==',
          "methods"       : 1,
          "cipher_suites" : 0,
          "trust_anchors" : {
            "edhoc_cred" : [
              { "c5u" : "coap://certs.c509.example" },
              { "x5u" : "coap://certs.x509.example" }
            ]
          }
      }

                Figure 7: Example of JSON EDHOC_Information

   An example of CBOR EDHOC_Information is given in Figure 8.

      e'edhoc_info_param'  : {
        e'session_id'    : h'01',
        e'methods'       : 1,
        e'cipher_suites' : 0,
        e'trust_anchors' : {
          e'edhoc_cred' : [
            { e'c5t_ta_type' : [-15, h'81DC2F32CB87E163'] },
            { e'c5u_ta_type' : "coap://certs.c509.example" },
            { e'x5t_ta_type' : [-15, h'79F2A41B510C1F9B'] },
            { e'x5u_ta_type' : "coap://certs.x509.example" }
          ]
        }
      }

                Figure 8: Example of CBOR EDHOC_Information

   The CDDL grammar describing the CBOR EDHOC_Information is:






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   EDHOC_Information = {
     ?  0 => bstr,                   ; id
     ?  1 => int / array,            ; methods
     ?  2 => int / array,            ; cipher_suites
     ?  3 => true / false,           ; message_4
     ?  4 => true / false,           ; comb_req
     ?  5 => tstr,                   ; uri_path
     ?  6 => int / array,            ; cred_types
     ?  7 => int / tstr / array,     ; id_cred_types
     ?  8 => uint / array,           ; eads
     ?  9 => true / false,           ; initiator
     ? 10 => true / false,           ; responder
     ? 11 => uint,                   ; max_msgsize
     ? 12 => true / false,           ; coap_ct
     ? 13 => int / array,            ; ep_id_types
     ? 14 => int / array,            ; transports
     ? 15 => map,                    ; trust_anchors
     * int / tstr => any
   }

4.  Client-RS Communication

   This section describes the exchange between C and RS, including the
   execution of the EDHOC protocol and the uploading of the access token
   from C to RS.  The alternative workflow, where AS uploads the access
   token directly to RS, is described in
   [I-D.ietf-ace-workflow-and-params].

   C and RS run the EDHOC protocol (see Section 4.2), and C uploads the
   access token in an EAD field (see Section 4.1) of an EDHOC message.
   Once successfully completed the EDHOC session, C and RS derive an
   OSCORE Security Context (see Section 4.5).  After that, OSCORE is
   used for protecting communications when C accesses resources at RS,
   as per the access rights specified in the access token (see
   Section 4.9).

   Detailed examples are given in Appendix A.

4.1.  EAD items for Access Token and Session Identifier

   This document defines EAD items (see Section 3.8 of [RFC9528]) for
   transporting an access token or a session identifier in EDHOC.

   *  EAD_ACCESS_TOKEN = (ead_label, ead_value), where:

      -  ead_label is the integer value TBD registered in Section 14.8.





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      -  ead_value is a CBOR byte string equal to the value of the
         "access_token" field of the access token response from AS (see
         Section 3.3).

      This EAD item is critical, i.e., it is used only with the negative
      value of its ead_label, indicating that the receiving RS must
      progress the protocol using the received access token, or else
      abort the EDHOC session (see Section 3.8 of [RFC9528]).  A client
      or resource server supporting the profile of ACE defined in this
      document MUST support this EAD item.

      EAD_ACCESS_TOKEN is used only when uploading the first access
      token of a token series, but not for the update of access rights
      (see Section 4.6).

      Editor's note: Add example.

   *  EAD_SESSION_ID = (ead_label, ead_value), where:

      -  ead_label is the integer value TBD registered in Section 14.8.

      -  ead_value is a CBOR byte string equal to the value of the
         "session_id" field within the EDHOC_Information object
         specified by AS in the "edhoc_info" parameter of the response
         from the /token endpoint, when issuing the first access token
         of a token series (see Section 3.3).

      This EAD item is critical, i.e., it is used only with the negative
      value of its ead_label, indicating that the receiving RS must
      progress the protocol using the access token associated with the
      identifier specified in "ead_value" and with the AUTH_CRED_C used
      in the EDHOC session, or else abort the EDHOC session (see
      Section 3.8 of [RFC9528]).  A client or resource server supporting
      the profile of ACE defined in this document MUST support this EAD
      item.

      EAD_SESSION_ID is used only if the access token has been
      provisioned to RS and is valid, but there is a need to establish a
      (new) OSCORE Security Context between C and RS through EDHOC.

      Editor's note: Add example.










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4.2.  EDHOC Session

   In order to mutually authenticate and establish secure communication
   for authorized access according to the profile described in this
   document, C and RS run the EDHOC protocol augmented with an access
   token.  During the EDHOC session, C specifies the access token to RS
   by value as conveyed in EAD item EAD_ACCESS_TOKEN, or by reference
   through a session identifier SESSION_ID conveyed in the EAD item
   EAD_SESSION_ID (see Section 4.1).

   As per Appendix A.2 of [RFC9528], EDHOC can be transferred over CoAP
   using either the forward or the reverse message flow, thus
   manifesting the two possible mappings between the ACE roles (client
   and resource server) and the EDHOC roles (Initiator and Responder),
   whereas the CoAP roles (client and server) remain the same.  The
   choice of message flow and corresponding mapping depends on the
   deployment setting and in particular on which identity to protect the
   most, since EDHOC protects the identity of the Initiator against
   active attackers.

   In case the EDHOC forward message flow is used (see Section 4.3), C
   acts as EDHOC Initiator, and the access token MUST be specified by
   value or by reference in the EAD_3 field of EDHOC message_3.  In case
   the EDHOC reverse message flow is used (see Section 4.4), C acts as
   EDHOC Responder, and the access token MUST be specified by value or
   by reference either in the EAD_2 field of EDHOC message_2 or in the
   EAD_4 field of EDHOC message_4.  By doing so, the access token or the
   associated session identifier gets at least the same confidentiality
   protection by EDHOC as provided to the authentication credential used
   by C in the EDHOC session (see Section 9.1 of [RFC9528]).

   When RS processes the EAD item EAD_ACCESS_TOKEN or EAD_SESSION_ID, RS
   MUST verify that the authentication credential AUTH_CRED_C that C
   specifies in the ID_CRED_X field during the EDHOC session is the same
   authentication credential correlated with the EAD item.  If such a
   verification fails, RS MUST abort the EDHOC session.  Note that:

   *  The ID_CRED_X field in question is the ID_CRED_I or ID_CRED_R
      field, when using the EDHOC forward or reverse message flow,
      respectively.

   *  If the processed EAD item is EAD_ACCESS_TOKEN, then the
      authentication credential correlated with the EAD item is
      specified in the 'cnf' claim of the access token conveyed in the
      EAD item.






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   *  If the processed EAD item is EAD_SESSION_ID, then the
      authentication credential correlated with the EAD item is
      specified in the 'cnf' claim of an access token stored at the RS,
      which is associated with the authentication credential specified
      by ID_CRED_X and with the SESSION_ID conveyed in the EAD item.

   RS MUST have successfully validated the access token before
   completing the EDHOC session.  If completed successfully, then the
   EDHOC session is associated with both the access token and the pair
   (SESSION_ID, AUTH_CRED_C).  If the EAD item used in the EDHOC session
   is EAD_ACCESS_TOKEN, then SESSION_ID is specified by the "session_id"
   field, within the EDHOC_Information object specified by the "cnf"
   claim of the access token.

   Any previous EDHOC session associated with the same access token and
   with the same pair (SESSION_ID, AUTH_CRED_C) MUST be deleted.  The
   OSCORE Security Context derived from that EDHOC session MUST also be
   deleted.

   Depending on the message flow used, the EDHOC messages will be
   carried either in CoAP POST requests or in CoAP 2.04 (Changed)
   responses, as detailed in Appendix A.2 of [RFC9528].

   C MUST target the EDHOC resource at RS with the URI path specified in
   the "uri_path" field (if present) of the EDHOC_Information object
   within the access token response received from AS, through which C
   obtained the first access token of the token series (see
   Section 3.1).  If the "uri_path" field is not present in that
   EDHOC_Information object, C assumes the target resource at RS to be
   the well-known EDHOC resource at the path /.well-known/edhoc.

   RS has to ensure that no requests can be performed on an EDHOC
   resource other than for running the EDHOC protocol.  Specifically, it
   SHOULD NOT be possible to perform any other operation than POST on an
   EDHOC resource.

4.3.  Forward Message Flow

   This section details the case where the EDHOC forward message flow is
   used (see Appendix A.2.1 of [RFC9528]), i.e., where C acts as the
   Initiator I and RS acts as the Responder R.

   Consistently with the EDHOC forward message flow, C sends EDHOC
   message_1 and EDHOC message_3 to an EDHOC resource at RS, as CoAP
   POST requests.  RS sends EDHOC message_2 and (optionally) EDHOC
   message_4 as CoAP 2.04 (Changed) responses.





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4.3.1.  EDHOC message_1

   The processing of EDHOC message_1 is specified in Section 5.2 of
   [RFC9528], with the following additions:

   *  The EDHOC method MUST be one of the EDHOC methods specified in the
      "methods" field (if present) of the EDHOC_Information object
      within the access token response received from AS, through which C
      obtained the first access token of the token series (see
      Section 3.1)

   *  The selected cipher suite MUST be an EDHOC cipher suite specified
      in the "cipher_suites" field (if present) of the EDHOC_Information
      object within the access token response received from AS, through
      which C obtained the first access token of the token series (see
      Section 3.1)

4.3.2.  EDHOC message_2

   The processing of EDHOC message_2 is specified in Section 5.3 of
   [RFC9528], with the following additions:

   *  The authentication credential CRED_R specified by the message
      field ID_CRED_R is AUTH_CRED_RS.

4.3.3.  EDHOC message_3

   The processing of EDHOC message_3 is specified in Section 5.4 of
   [RFC9528], with the following additions:

   *  The authentication credential CRED_I specified by the message
      field ID_CRED_I is AUTH_CRED_C.

   *  Exactly one of the EAD items EAD_ACCESS_TOKEN or EAD_SESSION_ID
      MUST be included in the EAD_3 field.  If this is not the case, RS
      MUST abort the EDHOC session.

   *  If the EAD_3 field includes the EAD item EAD_ACCESS_TOKEN, then RS
      MUST ensure that the access token specified in the EAD item is
      valid.  If the EAD_3 field includes the EAD item EAD_SESSION_ID,
      then RS MUST ensure that the access token associated with the
      session identifier SESSION_ID specified in the EAD item and with
      the AUTH_CRED_C used in the EDHOC session is valid.

      The validation follows the procedure specified in Section 4.6.2.
      If such validation fails, RS MUST reply to C with an EDHOC error
      message with ERR_CODE = 1 (see Section 6 of [RFC9528]) and it MUST
      abort the EDHOC session.



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      Editor's note: Instead of ERR_CODE = 1, consider to use ERR_CODE =
      3 "Access Denied" defined in draft-ietf-lake-authz

4.4.  Reverse Message Flow

   This section details the case where the EDHOC reverse message flow is
   used (see Appendix A.2.2 of [RFC9528]), i.e., where C acts as the
   Responder R and RS acts as the Initiator I.

   Consistently with the EDHOC reverse message flow, C sends a trigger
   message, EDHOC message_2, and (optionally) EDHOC message_4 to RS as
   CoAP POST requests.  RS sends EDHOC message_1 and EDHOC message_3 as
   CoAP 2.04 (Changed) responses.

   In this profile of ACE, if RS implements the EDHOC reverse message
   flow, then RS MUST implement EDHOC message_4.

   Exactly one of the EAD items EAD_ACCESS_TOKEN or EAD_SESSION_ID MUST
   be included in either the EAD_2 field of EDHOC message_2 or the EAD_4
   field of EDHOC message_4.  If this is not the case, RS MUST abort the
   EDHOC session.

   Specific instructions for the different messages are provided in the
   following subsections.

4.4.1.  Trigger Message

   As specified in Appendix A.2.2 of [RFC9528], the trigger message is
   an empty POST request that C sends to the EDHOC resource at RS, as
   intended to trigger a response conveying EDHOC message_1.

   In case the access token is issued for a group-audience (see
   Section 6.9 of [RFC9200]), then C can perform an EDHOC "roll call",
   by sending the trigger message as a group request over IP multicast
   [I-D.ietf-core-groupcomm-bis].  For the sake of efficiency, it is
   expected that the group-audience is appropriately associated with a
   CoAP group and/or application group (see Section 2 of
   [I-D.ietf-core-groupcomm-bis]), so that only the RSs belonging to the
   group-audience receive the trigger message.  After that, C can
   receive a different EDHOC message_1 from each of the targeted RSs and
   separately progresses the corresponding EDHOC sessions, by sending a
   different EDHOC message_2 to each RS that has replied with an EDHOC
   message_1.

4.4.2.  EDHOC message_1

   The processing of EDHOC message_1 is specified in Section 5.2 of
   [RFC9528].



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4.4.3.  EDHOC message_2

   The processing of EDHOC message_2 is specified in Section 5.3 of
   [RFC9528], with the following additions:

   *  The authentication credential CRED_R specified by the message
      field ID_CRED_R is AUTH_CRED_C.

   *  If the EAD_2 field includes the EAD item EAD_ACCESS_TOKEN, then RS
      MUST ensure that the access token specified in the EAD item is
      valid.  If the EAD_2 field includes the EAD item EAD_SESSION_ID,
      then RS MUST ensure that the access token associated with the
      session identifier SESSION_ID specified in the EAD item and with
      the AUTH_CRED_C used in the EDHOC session is valid.

   Note that in this case C uploads the Access Token or session ID
   before RS is authenticated, since C will not learn about the identity
   of RS until having verified message_3.  In particular, in the case of
   a group-audience, when there may be multiple legitimate RS, C does
   not yet know which member of the group-audience it communicates with
   (if any).

   The validation follows the procedure specified in Section 4.6.2.  If
   such validation fails, RS MUST reply to C with an EDHOC error message
   with ERR_CODE = 1 (see Section 6 of [RFC9528]) and it MUST abort the
   EDHOC session.

   Editor's note: Instead of ERR_CODE = 1, consider to use ERR_CODE = 3
   "Access Denied" defined in draft-ietf-lake-authz

4.4.4.  EDHOC message_3

   The processing of EDHOC message_3 is specified in Section 5.4 of
   [RFC9528], with the following additions:

   *  The authentication credential CRED_I specified by the message
      field ID_CRED_I is AUTH_CRED_RS.

4.4.5.  EDHOC message_4

   The processing of EDHOC message_4 is specified in Section 5.5 of
   [RFC9528], with the following additions:









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   *  If the EAD_4 field includes the EAD item EAD_ACCESS_TOKEN, then RS
      MUST ensure that the access token specified in the EAD item is
      valid.  If the EAD_4 field includes the EAD item EAD_SESSION_ID,
      then RS MUST ensure that the access token associated with the
      session identifier SESSION_ID specified in the EAD item and with
      the AUTH_CRED_C used in the EDHOC session is valid.

      The validation follows the procedure specified in Section 4.6.2.
      If such validation fails, RS MUST reply to C with an EDHOC error
      message with ERR_CODE = 1 (see Section 6 of [RFC9528]) and it MUST
      abort the EDHOC session.

      Editor's note: Instead of ERR_CODE = 1, consider to use ERR_CODE =
      3 "Access Denied" defined in draft-ietf-lake-authz

4.5.  OSCORE Security Context

   Once successfully completed the EDHOC session, C and RS derive an
   OSCORE Security Context as defined in Appendix A.1 of [RFC9528].

   In addition, RS associates the latest EDHOC session and the derived
   OSCORE Security Context with the stored access token, which is bound
   to the authentication credential AUTH_CRED_C used in the EDHOC
   session.  The access token is also associated with the pair
   (SESSION_ID, AUTH_CRED_C), where SESSION_ID is the identifier of the
   token series to which the access token belongs.

   If supported by C, C MAY use the EDHOC + OSCORE combined request
   defined in [RFC9668], unless the EDHOC_Information object specified
   by the "edhoc_info" parameter of the access token response included
   the "comb_req" field encoding the CBOR simple value false (0xf4).

   In the combined request, both EDHOC message_3 and the first OSCORE-
   protected application request are combined together in a single
   OSCORE-protected CoAP request, thus saving one round trip.  This
   requires C to derive the OSCORE Security Context with RS already
   after having successfully processed the received EDHOC message_2 and
   before sending EDHOC message_3.  An example is provided in
   Appendix A.2.

4.6.  Update of Access Rights

   If C has a valid OSCORE Security Context associated with a valid
   access token at RS, then C can request from AS an update of the
   access rights as described in Section 3.1.






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   If the request is granted, then AS generates a new access token
   containing updated access rights for C (see Section 3.3.3), in the
   same token series of the current access token (see Section 3.2).

   According to this document, AS provides the new access token to C
   (see Section 3.3) for further uploading to RS.  Alternatively, the
   new access token can be uploaded by AS directly to RS, as described
   in [I-D.ietf-ace-workflow-and-params].

   If all validations are successful, C can access protected resources
   at RS according to the updated access rights, using the previously
   established OSCORE Security Context.

   The rest of this section describes the message exchange for the
   uploading of the new access token from C to RS.

4.6.1.  C-to-RS: POST to /authz-info endpoint

   C can update its access rights by uploading the updated access token
   to RS using CoAP [RFC7252] and the Authorization Information endpoint
   as described in Section 5.10.1 of [RFC9200].

   That is, C sends a POST request to the /authz-info endpoint at RS,
   with the request payload containing the access token without any CBOR
   wrapping.  As per Section 5.10.1 of [RFC9200], the Content-Format of
   the POST request MUST be "application/cwt" to reflect the format of
   the transported access token.

   C MUST protect the POST request using the current OSCORE Security
   Context shared with RS.

   Upon receiving an access token from C, RS MUST follow the procedures
   defined in Section 5.10.1 of [RFC9200].  That is, RS MUST verify the
   validity of the access token.  RS MAY make an introspection request
   (see Section 5.9.1 of [RFC9200]) to validate the access token at AS.

   RS MUST check the following conditions:

   *  RS checks whether it stores an access token T_OLD, such that the
      "session_id" field of the EDHOC_Information object specified by
      the "cnf" claim matches the "session_id" field of the
      EDHOC_Information object specified by the "cnf" claim of the new
      access token T_NEW.

   *  RS checks whether the OSCORE Security Context CTX used to protect
      the request matches the OSCORE Security Context associated with
      the stored access token T_OLD.




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   If both the conditions above hold, RS MUST supersede the old access
   token T_OLD by replacing the corresponding authorization information
   with the one specified in the new access token T_NEW, and MUST
   associate T_NEW with the OSCORE Security Context CTX.

   Note that C and RS do not execute the EDHOC protocol, they do not
   establish a new OSCORE Security Context, and AUTH_CRED_C remains the
   same.

4.6.2.  RS-to-C: 2.01 (Created)

   If all validations are successful, RS stores the new access token in
   such a way that it is possible to retrieve it based on the pair
   (SESSION_ID, AUTH_CRED_C), where SESSION_ID is the identifier of the
   token series to which the access token belongs.  Note that SESSION_ID
   is specified in the "session_id" field of the EDHOC_Information
   object, within the "cnf" claim of the access token.

   Then, RS MUST reply to the POST request by sending a 2.01 (Created)
   response with no payload.  The response is protected with the same
   OSCORE Security Context used to protect the corresponding request.
   After that, C can access protected resources at RS according to the
   updated access rights, using the previously established OSCORE
   Security Context.

   Instead, if any validation fails, RS MUST respond with a 4.01
   (Unauthorized) error response.  RS MAY provide additional information
   in the payload of the error response, in order to clarify what went
   wrong.

   As specified in Section 5.10.1 of [RFC9200], when receiving a valid
   access token with updated authorization information from C (see
   Section 4.6.1), it is recommended that RS overwrites the previous
   access token.  That is, only the latest authorization information in
   the access token received by RS is valid.  This simplifies the
   process needed by RS to keep track of authorization information for a
   given client.

4.7.  Discarding the OSCORE Security Context

   There are a number of cases where C or RS have to discard the OSCORE
   Security Context that they share, and may establish a new one (see
   Section 4.8).

   C MUST discard the current OSCORE Security Context shared with RS
   when any of the following occurs.

   *  The OSCORE Sender Sequence Number space of C is exhausted.



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   *  The access token associated with the OSCORE Security Context
      becomes invalid, for example, due to expiration or revocation.

   *  C receives a number of unprotected 4.01 (Unauthorized) responses
      to OSCORE-protected requests, which are sent to RS and protected
      using the same OSCORE Security Context.  The exact number of such
      received responses needs to be specified by the application.  This
      can happen, for example, due to lack of storage at RS, which then
      sends the "AS Request Creation Hints" message (see Section 5.3 of
      [RFC9200]).

   *  The authentication credential of C (of RS) becomes invalid, e.g.,
      due to expiration or revocation, and it was used as AUTH_CRED_C
      (AUTH_CRED_RS) in the EDHOC session to establish the OSCORE
      Security Context.

   RS MUST discard the current OSCORE Security Context shared with C
   when any of the following occurs:

   *  The OSCORE Sender Sequence Number space of RS is exhausted.

   *  The access token associated with the OSCORE Security Context
      becomes invalid, for example, due to expiration or revocation.

   *  The authentication credential of C (of RS) becomes invalid (e.g.,
      due to expiration or revocation), and it was used as AUTH_CRED_C
      (AUTH_CRED_RS) in the EDHOC session to establish the OSCORE
      Security Context.

   After a new access token is successfully uploaded to RS and a new
   OSCORE Security Context is established between C and RS, messages
   still in transit that were protected with the previous OSCORE
   Security Context might not be successfully verified by the recipient,
   since the old OSCORE Security Context might have been discarded.
   This means that messages sent shortly before C has uploaded the new
   access token to RS might not be successfully accepted by the
   recipient.

   Furthermore, implementations may want to cancel CoAP observations at
   RS, if registered before the new OSCORE Security Context has been
   established.  Alternatively, applications need to implement a
   mechanism to ensure that, from then on, messages exchanged within
   those observations are going to be protected with the newly derived
   OSCORE Security Context.







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4.8.  Establishing a New OSCORE Security Context

   The procedure of provisioning a new access token to RS specified in
   this section applies to various cases when an OSCORE Security Context
   shared between C and RS has been deleted, for example as described in
   Section 4.7.

   Another exceptional case is when there is still a valid OSCORE
   Security Context but it needs to be updated, e.g., due to a policy
   limiting its use in terms of time or amount of processed data, or to
   the imminent exhaustion of the OSCORE Sender Sequence Number space.
   In this case, C and RS MAY alternatively attempt to run a key update
   protocol that they both support.  One lightweight example is KUDOS
   [I-D.ietf-core-oscore-key-update], which is independent of ACE and
   EDHOC and does not require the uploading of an access token.  If C
   and RS does not support a common key update protocol to use for
   updating their still valid OSCORE Security Context, then C and RS
   fall back to EDHOC as outlined above.

   In either case, C and RS establish a new OSCORE Security Context that
   replaces the old one and will be used for protecting their
   communications from then on.  In particular, RS MUST associate the
   new OSCORE Security Context with the current (potentially re-
   uploaded) access token.  Furthermore, the SESSION_ID identifying the
   token series to which the access token belongs to remains unchanged,
   even if C and RS have established a new EDHOC session.  Unless C and
   RS re-run the EDHOC protocol, they preserve their OSCORE identifiers,
   i.e., their OSCORE Sender/Recipient IDs.

4.9.  Access Rights Verification

   RS MUST follow the procedures defined in Section 5.10.2 of [RFC9200].
   That is, if RS receives an OSCORE-protected request targeting a
   protected resource from C, then RS processes the request according to
   [RFC8613].

   If OSCORE verification succeeds and the target resource requires
   authorization, RS retrieves the authorization information using the
   access token associated with the OSCORE Security Context.  Then, RS
   MUST verify that the authorization information covers the target
   resource and the action intended by C on it.










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4.10.  Access Token Invalidity

   When an access token becomes invalid (e.g., due to its expiration or
   revocation), RS MUST delete the access token and the associated
   OSCORE Security Context, and MUST notify C with an error response
   with code 4.01 (Unauthorized) for any long running request, as
   specified in Section 5.8.3 of [RFC9200].

4.11.  Authentication Credential Invalidity

   If an authentication credential AUTH_CRED_C of C is invalidated
   (e.g., it expires), then the following applies:

   *  RS MUST delete all the stored access tokens that specify
      AUTH_CRED_C in the "cnf" claim.

   *  C MUST delete every stored access token such that C obtained the
      first access token of the same series through the response to an
      access token request specifying AUTH_CRED_C, e.g., in the
      "req_cnf" parameter (see Section 3.1).

   *  RS and C MUST abort and purge all the EDHOC sessions that used
      AUTH_CRED_C and successfully completed, as well as the OSCORE
      Security Context derived from those sessions (see Section 4.7).

   If an authentication credential AUTH_CRED_RS of RS is invalidated
   (e.g., it expires), then the following applies:

   *  C MUST delete every stored access token such that C obtained the
      first access token of the same series through an access token
      response specifying AUTH_CRED_RS, e.g., in the 'rs_cnf' parameter
      (see Section 3.3).

   *  C MUST delete every stored access token that C specified (by value
      or be reference) during an EDHOC session that used AUTH_CRED_RS
      and successfully completed.

   *  RS and C MUST abort and purge all the EDHOC sessions that used
      AUTH_CRED_RS and successfully completed, as well as the OSCORE
      Security Context derived from those sessions (see Section 4.7).

4.12.  EDHOC Session Invalidity

   If an EDHOC session is aborted and purged for other reasons than
   those in Section 4.11, then RS and C that established the session
   MUST delete the OSCORE Security Context derived from that session
   (see Section 4.7).




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4.13.  Using AS Request Creation Hints

   When replying to an unauthorized resource request message from a
   client, RS can send an unprotected AS Request Creation Hints message
   as a 4.01 (Unauthorized) error response (see Section 5.3 of
   [RFC9200]).

   The message payload can specify a number of parameters that help the
   sender client acquire a valid access token from AS.  These parameters
   include "audience" and "scope".

   When using this profile and running EDHOC per its reverse message
   flow (see Section 4.4), RS acts as EDHOC Initiator.  A compelling
   reason to do so is the wish to protect the identity of RS against
   active attackers, consistently with the EDHOC security properties.

   However, the identity protection achieved through EDHOC can be
   defeated if RS exposes information such as audience and scope, when
   specifying the corresponding parameters in an unprotected AS Request
   Creation Hints message.

   Therefore, if RS supports the EDHOC reverse message flow and sends an
   AS Request Creation Hints, the following applies:

   *  The message payload MUST NOT include the "audience" parameter.

   *  The message payload SHOULD NOT include the "scope" parameter,
      unless its value cannot contribute to expose the identity of RS.

   AS Request Creation Hints may also be requested and retrieved through
   a new EAD item defined here, see Figure 9.

   ead_label = TBD
   ? ead_value = bstr .cbor AS_request_creation_hints

   AS_request_creation_hints : map

               Figure 9: EAD item AS Request Creation Hints.

   The AS_request_creation_hints is a CBOR map with keys defined in the
   IANA registry "ACE Authorization Server Request Creation Hints".

   This EAD item is intended to be used in EAD fields of EDHOC messages
   exchanged between C and RS: in the forward message flow in EAD_1 and
   EAD_2, and in the reverse message flow in EAD_2 and EAD_3.  In the
   first EDHOC message from C to RS, an EAD item with ead_label = TBD
   with no ead_value asks the RS to include in the next EDHOC message
   the same EAD item with ead_value encoding the



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   AS_request_creation_hints map.  This EAD item is non-critical, i.e.,
   it can be ignored by the receiving peer.  It is OPTIONAL to
   implement.

   Since C has not made an actual request targeting a specific
   application resource, the RS may not know what resource C is
   interested in accessing.  Moreover, such information needs to be
   matched against the privacy policy of the application.  Since EDHOC
   message_2 is only protected against passive attackers, the
   AS_request_creation_hints map SHOULD NOT include "audience" and
   "scope" when present in the EAD item conveyed in the EAD_2 field.

4.14.  Requesting Authentication Credential By Value

   EDHOC peers need access to each other's authentication credentials to
   complete the protocol.  However, to reduce unnecessary overhead, the
   EDHOC protocol enables credential references to be sent instead of
   authentication credentials.  The ACE protocol includes the initial
   transport of authentication credentials of C and RS and thus matches
   the use of credential references in EDHOC.

   However, if one of the parties has deleted the other party's
   authentication credential from its local storage, then there should
   be a way to restore it without requesting a new access token.

   Consider first the EDHOC forward message flow.  If the ACE Client /
   EDHOC Initiator sends a credential by reference in message_3, then
   Responder may return error code 3, Unknown credential referenced.
   This enables the Initiator to restart the protocol using some other
   ID_CRED, typically the authentication credential by value thereby
   resolving the issue.  However, in case the ACE Resource Server /
   EDHOC Responder sends a credential by reference in message_2, then
   returning a code 3 EDHOC error message does not automatically solve
   the problem.  Having aborted the protocol, the Responder has no
   reliable way to act differently in a following EDHOC session since it
   never authenticated the Initiator.

   In order to remediate this situation, this section specifies a new
   EAD item for requesting the peer's authentication credential by
   value, see Figure 10.

   ead_label = TBD

     Figure 10: EAD item Requesting Authentication Credential By Value.

   This EAD item has no ead_value.  When present in EAD_1, it requests
   the Responder's authentication credential by value in ID_CRED_R of
   message_2.  When present in EAD_2, it requests the the Initiator's



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   authentication credential by value in ID_CRED_I of message_3.  The
   EAD item is non-critical, i.e., it can be ignored by the receiving
   peer.  It is OPTIONAL to implement.

   Also in the EDHOC reverse message flow this EAD item can be applied
   for better control of the use of credential by value.

   Note that in the reverse flow both C and RS may recover from error
   code 3, but at the cost of more round trips which can be avoided by
   the use of the EAD item.

   *  In case the ACE Client / EDHOC Responder sends a credential by
      reference in message_2 and receives a code 3 error message, then
      it can trigger a new EDHOC session and send credential by value
      this time.

   *  In case the ACE Resource Server / EDHOC Initiator sends a
      credential by reference in message_3 and receives a code 3 error
      message, then since the RS has authenticated C, it can store the
      authentication credential of C, and in the next session with C,
      the RS can send its credential by value.

5.  Secure Communication with AS

   As specified in the ACE framework (see Sections 5.8 and 5.9 of
   [RFC9200]), the requesting entity (RS and/or C) and AS communicates
   via the /token or /introspect endpoint.  When using this profile, the
   use of CoAP [RFC7252] and OSCORE [RFC8613] for this communication is
   RECOMMENDED.  Other protocols fulfilling the security requirements
   defined in Section 5 of [RFC9200] (such as HTTP and DTLS [RFC9147] or
   TLS [RFC8446]) MAY be used instead.

   If OSCORE is used, the requesting entity and AS need to have an
   OSCORE Security Context in place.  While this can be pre-installed,
   the requesting entity and AS can establish such an OSCORE Security
   Context, for example, by running the EDHOC protocol, as shown between
   C and AS by the examples in Appendix A.1 and Appendix A.2.  This also
   applies for communication between RS and AS, for example to protect
   the upload of access tokens from AS directly to RS as described in
   [I-D.ietf-ace-workflow-and-params].

6.  CWT Confirmation Methods

   This document defines a number of new CWT confirmation methods, which
   are registered in Section 14.7.  The semantics of each confirmation
   method is defined below.





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6.1.  Ordered Chain of X.509 Certificates

   The confirmation method "x5chain" specifies an ordered array of X.509
   certificates [RFC5280].  The semantics of "x5chain" is like that of
   the "x5chain" COSE Header Parameter specified in [RFC9360].

6.2.  Unordered Bag of X.509 Certificates

   The confirmation method "x5bag" specifies a bag of X.509 certificates
   [RFC5280].  The semantics of "x5bag" is like that of the "x5bag" COSE
   Header Parameter specified in [RFC9360].

6.3.  Hash of an X.509 Certificate

   The confirmation method "x5t" specifies the hash value of the end-
   entity X.509 certificate [RFC5280].  The semantics of "x5t" is like
   that of the "x5t" COSE Header Parameter specified in [RFC9360].

6.4.  URI Pointing to an Ordered Chain of X.509 Certificates

   The confirmation method "x5u" specifies the URI [RFC3986] of an
   ordered chain of X.509 certificates [RFC5280].  The semantics of
   "x5u" is like that of the "x5u" COSE Header Parameter specified in
   [RFC9360].

6.5.  Ordered Chain of C509 Certificates

   The confirmation method "c5c" specifies an ordered array of C509
   certificates [I-D.ietf-cose-cbor-encoded-cert].  The semantics of
   "c5c" is like that of the "c5c" COSE Header Parameter specified in
   [I-D.ietf-cose-cbor-encoded-cert].

6.6.  Unordered Bag of C509 Certificates

   The confirmation method "c5b" specifies a bag of C509 certificates
   [I-D.ietf-cose-cbor-encoded-cert].  The semantics of "c5b" is like
   that of the "c5b" COSE Header Parameter specified in
   [I-D.ietf-cose-cbor-encoded-cert].

6.7.  Hash of a C509 Certificate

   The confirmation method "c5t" specifies the hash value of the end-
   entity C509 certificate [I-D.ietf-cose-cbor-encoded-cert].  The
   semantics of "c5t" is like that of the "c5t" COSE Header Parameter
   specified in [I-D.ietf-cose-cbor-encoded-cert].






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6.8.  URI Pointing to an Ordered Chain of C509 Certificates

   The confirmation method "c5u" specifies the URI [RFC3986] of a
   COSE_C509 containing an ordered chain of C509 certificates
   [I-D.ietf-cose-cbor-encoded-cert].  COSE_C509 is defined in
   [I-D.ietf-cose-cbor-encoded-cert].  The semantics of "c5u" is like
   that of the "c5u" COSE Header Parameter specified in
   [I-D.ietf-cose-cbor-encoded-cert].

6.9.  CWT Containing a COSE_Key

   The confirmation method "kcwt" specifies a CBOR Web Token (CWT)
   [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and
   possibly other claims.  The semantics of "kcwt" is like that of the
   "kcwt" COSE Header Parameter specified in [RFC9528].

6.10.  CCS Containing a COSE_Key

   The confirmation method "kccs" specifies a CWT Claims Set (CCS)
   [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and
   possibly other claims.  The semantics of "kccs" is like that of the
   "kccs" COSE Header Parameter specified in [RFC9528].

7.  JWT Confirmation Methods

   This document defines a number of new JWT confirmation methods, which
   are registered in Section 14.6.  The semantics of each confirmation
   method is defined below.

7.1.  Ordered Chain of X.509 Certificates

   The confirmation method "x5c" specifies an ordered array of X.509
   certificates [RFC5280].  The semantics of "x5c" is like that of the
   "x5c" JSON Web Signature and Encryption Header Parameter specified in
   [RFC7515], with the following difference.  The public key contained
   in the first certificate is the proof-of-possession key and does not
   have to correspond to a key used to digitally sign the JWS.

7.2.  Unordered Bag of X.509 Certificates

   The confirmation method "x5b" specifies a bag of X.509 certificates
   [RFC5280].  The semantics of the "x5b" is like that of the "x5c" JWT
   confirmation method defined in Section 7.1, with the following
   differences.  First, the set of certificates is unordered and may
   contain self-signed certificates.  Second, the composition and
   processing of "x5b" are like for the "x5bag" COSE Header Parameter
   defined in [RFC9360].




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7.3.  Hash of an X.509 Certificate

   The confirmation method "x5t" specifies the hash value of the end-
   entity X.509 certificate [RFC5280].  The semantics of "x5t" is like
   that of the "x5t" JSON Web Signature and Encryption Header Parameter
   specified in [RFC7515].

7.4.  URI Pointing to an Ordered Chain of X.509 Certificates

   The confirmation method "x5u" specifies the URI [RFC3986] of an
   ordered chain of X.509 certificates [RFC5280].  The semantics of
   "x5u" is like that of the "x5u" COSE Header Parameter specified in
   [RFC9360], with the following difference.  The public key contained
   in the first certificate is the proof-of-possession key and does not
   have to correspond to a key used to digitally sign the JWS.

7.5.  Ordered Chain of C509 Certificates

   The confirmation method "c5c" specifies an ordered array of C509
   certificates [I-D.ietf-cose-cbor-encoded-cert].  The semantics of
   "c5c" is like that of the "x5c" JWT confirmation method defined in
   Section 7.1, with the following difference.  Each string in the JSON
   array is a base64-encoded (Section 4 of [RFC4648] - not base64url-
   encoded) C509 certificate.

7.6.  Unordered Bag of C509 Certificates

   The confirmation method "c5b" specifies a bag of C509 certificates
   [I-D.ietf-cose-cbor-encoded-cert].  The semantics of "c5b" is like
   that of the "c5c" JWT confirmation method defined in Section 7.5,
   with the following differences.  First, the set of certificates is
   unordered and may contain self-signed certificates.  Second, the
   composition and processing of "c5b" is like for the "c5b" COSE Header
   Parameter defined in [I-D.ietf-cose-cbor-encoded-cert].

7.7.  Hash of a C09 Certificate

   The confirmation method "c5t" specifies the hash value of the end-
   entity C509 certificate [I-D.ietf-cose-cbor-encoded-cert].  The
   semantics of "c5t" is like that of the "x5t" JWT confirmation method
   defined in Section 7.3, with the following differences.  First, the
   base64url-encoded SHA-1 thumbprint is computed over the C509
   certificate.  Second, the public key contained in the C509
   certificate does not have to correspond to a key used to digitally
   sign the JWS.






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7.8.  URI Pointing to an Ordered Chain of C509 Certificates

   The confirmation method "c5u" specifies the URI [RFC3986] of
   COSE_C509 containing an ordered chain of C509 certificates
   [I-D.ietf-cose-cbor-encoded-cert].  COSE_C509 is defined in
   [I-D.ietf-cose-cbor-encoded-cert].  The semantics of "c5u" is like
   that of the "x5u" JWT confirmation method defined in Section 7.4,
   with the following differences.  First, the URI refers to a resource
   for the C509 certificate chain.  Second, the public key contained in
   one of the C509 certificates and acting as proof-of-possession key
   does not have to correspond to a key used to digitally sign the JWS.

7.9.  CWT Containing a COSE_Key

   The confirmation method "kcwt" specifies a CBOR Web Token (CWT)
   [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and
   possibly other claims.  The format of "kcwt" is the base64url-encoded
   serialization of the CWT.

7.10.  CCS Containing a COSE_Key

   The confirmation method "kccs" specifies a CWT Claims Set (CCS)
   [RFC8392] containing a COSE_Key [RFC9053] in a 'cnf' claim and
   possibly other claims.  The format of "kcwt" is the base64url-encoded
   serialization of the CWT.

8.  EDHOC Endpoint Identity Types

   This document defines the following identifier of type of endpoint
   identity for EDHOC.

   Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
   with the RFC number of this specification and delete this paragraph.

    +========+============+====================+=====================+
    | Name   | CBOR label | Description        | Reference           |
    +========+============+====================+=====================+
    | EUI-64 | 0          | An EUI-64 identity | [RFC-XXXX][RFC4291] |
    +--------+------------+--------------------+---------------------+

                  Table 2: EDHOC Endpoint Identity Types

9.  EDHOC Transports

   This document defines the following identifiers of means for
   transporting EDHOC messages.





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    +===========+============+===================+====================+
    | Transport | Name       | Description       | Reference          |
    | ID        |            |                   |                    |
    +===========+============+===================+====================+
    | 0         | CoAP over  | EDHOC messages    | [RFC7252],         |
    |           | UDP        | are transported   | Appendix A.2 of    |
    |           |            | as payload of     | [RFC9528]          |
    |           |            | CoAP messages, in |                    |
    |           |            | turn transported  |                    |
    |           |            | over UDP          |                    |
    +-----------+------------+-------------------+--------------------+
    | 1         | CoAP over  | EDHOC messages    | [RFC7252][RFC8323] |
    |           | TCP        | are transported   |                    |
    |           |            | as payload of     |                    |
    |           |            | CoAP messages, in |                    |
    |           |            | turn transported  |                    |
    |           |            | over TCP          |                    |
    +-----------+------------+-------------------+--------------------+
    | 2         | CoAP over  | EDHOC messages    | [RFC7252][RFC8323] |
    |           | WebSockets | are transported   |                    |
    |           |            | as payload of     |                    |
    |           |            | CoAP messages, in |                    |
    |           |            | turn transported  |                    |
    |           |            | over WebSockets   |                    |
    +-----------+------------+-------------------+--------------------+

                         Table 3: EDHOC Transports

10.  EDHOC Trust Anchor Purposes

   This document defines the following EDHOC trust anchor purpose.

   Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
   with the RFC number of this specification and delete this paragraph.

     +============+=======+===================+=====================+
     | Name       | CBOR  | Description       | Reference           |
     |            | label |                   |                     |
     +============+=======+===================+=====================+
     | edhoc_cred | 0     | Verifying         | [RFC-XXXX][RFC9528] |
     |            |       | authentication    |                     |
     |            |       | credentials of    |                     |
     |            |       | other EDHOC peers |                     |
     |            |       | in EDHOC sessions |                     |
     +------------+-------+-------------------+---------------------+

                   Table 4: EDHOC Trust Anchor Purposes




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   Trust anchors with purpose "edhoc_cred" are used for verifying
   authentication credentials of other EDHOC peers in an EDHOC session,
   and they typically are authentication credentials of Certificate
   Authorities (CAs).

11.  EDHOC Trust Anchor Types

   This document defines the following EDHOC trust anchor types.

   Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
   with the RFC number of this specification and delete this paragraph.

   +======+=======+===============+=================+=================+
   | Name | CBOR  | Value type    | Description     | Reference       |
   |      | label |               |                 |                 |
   +======+=======+===============+=================+=================+
   | uuid | 0     | #6.37(bstr)   | Binary CBOR-    | [RFC-           |
   |      |       |               | encoded UUID    | XXXX][RFC9562]  |
   +------+-------+---------------+-----------------+-----------------+
   | kid  | 4     | bstr          | Key identifier  | [RFC-           |
   |      |       |               |                 | XXXX][RFC9052]  |
   +------+-------+---------------+-----------------+-----------------+
   | c5t  | 22    | COSE_CertHash | Hash of a C509  | [RFC-           |
   |      |       |               | certificate     | XXXX][draft-    |
   |      |       |               |                 | ietf-cose-cbor- |
   |      |       |               |                 | encoded-cert]   |
   +------+-------+---------------+-----------------+-----------------+
   | c5u  | 23    | uri           | URI pointing to | [RFC-           |
   |      |       |               | a COSE_C509     | XXXX][draft-    |
   |      |       |               | containing a    | ietf-cose-cbor- |
   |      |       |               | ordered chain   | encoded-cert]   |
   |      |       |               | of certificates |                 |
   +------+-------+---------------+-----------------+-----------------+
   | x5t  | 34    | COSE_CertHash | Hash of an      | [RFC-           |
   |      |       |               | X.509           | XXXX][RFC9360]  |
   |      |       |               | certificate     |                 |
   +------+-------+---------------+-----------------+-----------------+
   | x5u  | 35    | uri           | URI pointing to | [RFC-           |
   |      |       |               | an X.509        | XXXX][RFC9360]  |
   |      |       |               | certificate     |                 |
   +------+-------+---------------+-----------------+-----------------+

                    Table 5: EDHOC Trust Anchor Types








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12.  Security Considerations

   This document specifies a profile for the Authentication and
   Authorization for Constrained Environments (ACE) framework [RFC9200].
   Thus, the general security considerations from the ACE framework also
   apply to this profile.

   Furthermore, the security considerations from OSCORE [RFC8613] and
   from EDHOC [RFC9528] also apply to this specific use of the OSCORE
   and EDHOC protocols.

   As previously stated, once completed the EDHOC session, C and RS are
   mutually authenticated through their respective authentication
   credentials, whose retrieval has been facilitated by AS.  Also, once
   completed the EDHOC session, C and RS have established a long-term
   secret key PRK_out enjoying forward secrecy.  This is in turn used by
   C and RS to establish an OSCORE Security Context.

   Furthermore, RS achieves confirmation that C has PRK_out (proof-of-
   possession) when completing the EDHOC session.  Instead, C achieves
   confirmation that RS has PRK_out (proof-of-possession) either when
   receiving the optional EDHOC message_4 from RS, or when successfully
   verifying a response from RS protected with the established OSCORE
   Security Context.

   OSCORE is designed to secure point-to-point communication, providing
   a secure binding between a request and the corresponding response(s).
   Thus, the basic OSCORE protocol is not intended for use in point-to-
   multipoint communication (e.g., enforced via multicast or a publish-
   subscribe model).  Implementers of this profile should make sure that
   their use case of OSCORE corresponds to the expected one, in order to
   prevent weakening the security assurances provided by OSCORE.

   When using this profile, it is RECOMMENDED that RS stores only one
   access token per client.  The use of multiple access tokens for a
   single client increases the strain on RS, since it must consider
   every access token associated with the client and calculate the
   actual permissions that client has.  Also, access tokens indicating
   different or disjoint permissions from each other may lead RS to
   enforce wrong permissions.  If one of the access tokens expires
   earlier than others, the resulting permissions may offer insufficient
   protection.  Developers SHOULD avoid using multiple access tokens for
   a same client.  Furthermore, RS MUST NOT store more than one access
   token per client per PoP-key (i.e., per client's authentication
   credential).






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   This profile defines the confirmation methods "kcwt" and "kccs"
   corresponding to the use of CBOR Web Tokens (CWTs) and CWT Claims Set
   (CCSs), respectively.  Security considerations of CWTs and CCSs, and
   of COSE header parameters "kcwt" and "kccs" are given in Section 9.8
   of [RFC9528], and apply also to confirmation methods.  In particular,
   the contents of the CWT or CCS must be processed as untrusted input.
   The application needs to define a trust-establishment mechanism and
   identify the relevant trust anchors.

13.  Privacy Considerations

   This document specifies a profile for the Authentication and
   Authorization for Constrained Environments (ACE) framework [RFC9200].
   Thus, the general privacy considerations from the ACE framework also
   apply to this profile.

   Furthermore, the privacy considerations from OSCORE [RFC8613] and
   from EDHOC [RFC9528] also apply to this specific use of the OSCORE
   and EDHOC protocols.

   An unprotected response to an unauthorized request may disclose
   information about RS and/or its existing relationship with C.  It is
   advisable to include as little information as possible in an
   unencrypted response (see also Section 4.13).  When an OSCORE
   Security Context already exists between C and RS, more detailed
   information may be included.

   The (encrypted) access token is never sent in an unprotected POST
   request to the /authz-info endpoint at RS.  Thus, even if C uses the
   same single access token from multiple locations, the access token's
   value does not contribute to the risk of C being tracked.

   The identifiers used in OSCORE, i.e., the OSCORE Sender/Recipient
   IDs, are negotiated by C and RS during the EDHOC session.  When using
   the EDHOC forward (reverse) message flow:

   *  The EDHOC Connection Identifier C_I (C_R) of C is going to be the
      OSCORE Recipient ID of C, i.e., the OSCORE Sender ID of RS.

   *  The EDHOC Connection Identifier C_R (C_I) of RS is going to be the
      OSCORE Recipient ID of RS, i.e., the OSCORE Sender ID of C.










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   These OSCORE identifiers are privacy sensitive (see Section 12.8 of
   [RFC8613]).  In particular, they could reveal information about C, or
   may be used for correlating different requests from C, e.g., across
   different networks that C has joined and left over time.  This can be
   mitigated if C and RS dynamically update their OSCORE identifiers,
   e.g., by using the method defined in
   [I-D.ietf-core-oscore-id-update].

14.  IANA Considerations

   This document has the following actions for IANA.

   Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
   with the RFC number of this specification and delete this paragraph.

14.1.  ACE Profiles Registry

   IANA is asked to add the following entry to the "ACE Profiles"
   registry, following the procedure specified in [RFC9200].

   *  Name: coap_edhoc_oscore

   *  Description: Profile for delegating client authentication and
      authorization in a constrained environment by establishing an
      OSCORE Security Context [RFC8613] between resource-constrained
      nodes, through the execution of the lightweight authenticated key
      exchange protocol EDHOC [RFC9528].

   *  CBOR Value: TBD (value between 1 and 23)

   *  Reference: [RFC-XXXX]

14.2.  OAuth Parameters Registry

   IANA is asked to add the following entry to the "OAuth Parameters"
   registry.

   *  Name: edhoc_info

   *  Parameter Usage Location: token request and token response

   *  Change Controller: IETF

   *  Reference: [RFC-XXXX]







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14.3.  OAuth Parameters CBOR Mappings Registry

   IANA is asked to add the following entry to the "OAuth Parameters
   CBOR Mappings" registry, following the procedure specified in
   [RFC9200].

   *  Name: edhoc_info

   *  CBOR Key: TBD (value between 1 and 255)

   *  Value Type: map

   *  Reference: [RFC-XXXX]

   *  Original Specification: [RFC-XXXX]

14.4.  JSON Web Token Claims Registry

   IANA is asked to add the following entries to the "JSON Web Token
   Claims" registry, following the procedure specified in [RFC7519].

   *  Claim Name: edhoc_info

   *  Claim Description: Information for EDHOC session

   *  Change Controller: IETF

   *  Reference: [RFC-XXXX]

14.5.  CBOR Web Token (CWT) Claims Registry

   IANA is asked to add the following entries to the "CBOR Web Token
   (CWT) Claims" registry, following the procedure specified in
   [RFC8392].

   *  Claim Name: edhoc_info

   *  Claim Description: Information for EDHOC session

   *  JWT Claim Name: edhoc_info

   *  Claim Key: TBD (value between 1 and 255)

   *  Claim Value Type: map

   *  Change Controller: IETF

   *  Reference: [RFC-XXXX]



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14.6.  JWT Confirmation Methods Registry

   IANA is asked to add the following entries to the "JWT Confirmation
   Methods" registry, following the procedure specified in [RFC7800].

   *  Confirmation Method Value: x5c

   *  Confirmation Method Description: An ordered chain of X.509
      certificates

   *  Change Controller: IETF

   *  Reference: Section 7.1 of [RFC-XXXX]



   *  Confirmation Method Value: x5b

   *  Confirmation Method Description: An unordered bag of X.509
      certificates

   *  Change Controller: IETF

   *  Reference: Section 7.2 of [RFC-XXXX]



   *  Confirmation Method Value: x5t

   *  Confirmation Method Description: Hash of an X.509 certificate

   *  Change Controller: IETF

   *  Reference: Section 7.3 of [RFC-XXXX]



   *  Confirmation Method Value: x5u

   *  Confirmation Method Description: URI pointing to an ordered chain
      of X.509 certificates

   *  Change Controller: IETF

   *  Reference: Section 7.4 of [RFC-XXXX]






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   *  Confirmation Method Value: c5c

   *  Confirmation Method Description: An ordered chain of C509
      certificates

   *  Change Controller: IETF

   *  Reference: Section 7.5 of [RFC-XXXX]



   *  Confirmation Method Value: c5b

   *  Confirmation Method Description: An unordered bag of C509
      certificates

   *  Change Controller: IETF

   *  Reference: Section 7.6 of [RFC-XXXX]



   *  Confirmation Method Value: c5t

   *  Confirmation Method Description: Hash of a C509 certificate

   *  Change Controller: IETF

   *  Reference: Section 7.7 of [RFC-XXXX]



   *  Confirmation Method Value: c5u

   *  Confirmation Method Description: URI pointing to a COSE_C509
      containing an ordered chain of C509 certificates

   *  Change Controller: IETF

   *  Reference: Section 7.8 of [RFC-XXXX]



   *  Confirmation Method Value: kcwt

   *  Confirmation Method Description: A CBOR Web Token (CWT) containing
      a COSE_Key in a 'cnf' claim and possibly other claims




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   *  Change Controller: IETF

   *  Reference: Section 7.9 of [RFC-XXXX]



   *  Confirmation Method Value: kccs

   *  Confirmation Method Description: A CWT Claims Set (CCS) containing
      a COSE_Key in a 'cnf' claim and possibly other claims

   *  Change Controller: IETF

   *  Reference: Section 7.10 of [RFC-XXXX]

14.7.  CWT Confirmation Methods Registry

   IANA is asked to add the following entries to the "CWT Confirmation
   Methods" registry, following the procedure specified in [RFC8747].

   *  Confirmation Method Name: x5chain

   *  Confirmation Method Description: An ordered chain of X.509
      certificates

   *  JWT Confirmation Method Name: x5c

   *  Confirmation Key: TBD (value between 24 and 255)

   *  Confirmation Value Type: COSE_X509

   *  Change Controller: IETF

   *  Reference: Section 6.1 of [RFC-XXXX]



   *  Confirmation Method Name: x5bag

   *  Confirmation Method Description: An unordered bag of X.509
      certificates

   *  JWT Confirmation Method Name: x5b

   *  Confirmation Key: TBD (value between 24 and 255)

   *  Confirmation Value Type: COSE_X509




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   *  Change Controller: IETF

   *  Reference: Section 6.2 of [RFC-XXXX]



   *  Confirmation Method Name: x5t

   *  Confirmation Method Description: Hash of an X.509 certificate

   *  JWT Confirmation Method Name: x5t

   *  Confirmation Key: TBD (value between 1 and 23)

   *  Confirmation Value Type: COSE_CertHash

   *  Change Controller: IETF

   *  Reference: Section 6.3 of [RFC-XXXX]



   *  Confirmation Method Name: x5u

   *  Confirmation Method Description: URI pointing to an ordered chain
      of X.509 certificates

   *  JWT Confirmation Method Name: x5u

   *  Confirmation Key: TBD (value between 1 and 23)

   *  Confirmation Value Type: uri

   *  Change Controller: IETF

   *  Reference: Section 6.4 of [RFC-XXXX]



   *  Confirmation Method Name: c5c

   *  Confirmation Method Description: An ordered chain of C509
      certificates

   *  JWT Confirmation Method Name: c5c

   *  Confirmation Key: TBD (value between 24 and 255)




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   *  Confirmation Value Type: COSE_C509

   *  Change Controller: IETF

   *  Reference: Section 6.5 of [RFC-XXXX]



   *  Confirmation Method Name: c5b

   *  Confirmation Method Description: An unordered bag of C509
      certificates

   *  JWT Confirmation Method Name: c5b

   *  Confirmation Key: TBD (value between 24 and 255)

   *  Confirmation Value Type: COSE_C509

   *  Change Controller: IETF

   *  Reference: Section 6.6 of [RFC-XXXX]



   *  Confirmation Method Name: c5t

   *  Confirmation Method Description: Hash of a C509 certificate

   *  JWT Confirmation Method Name: c5t

   *  Confirmation Key: TBD (value between 1 and 23)

   *  Confirmation Value Type: COSE_CertHash

   *  Change Controller: IETF

   *  Reference: Section 6.7 of [RFC-XXXX]



   *  Confirmation Method Name: c5u

   *  Confirmation Method Description: URI pointing to a COSE_C509
      containing an ordered chain of C509 certificates

   *  JWT Confirmation Method Name: c5u




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   *  Confirmation Key: TBD (value between 1 and 23)

   *  Confirmation Value Type: uri

   *  Change Controller: IETF

   *  Reference: Section 6.8 of [RFC-XXXX]



   *  Confirmation Method Name: kcwt

   *  Confirmation Method Description: A CBOR Web Token (CWT) containing
      a COSE_Key in a 'cnf' claim and possibly other claims

   *  JWT Confirmation Method Name: kcwt

   *  Confirmation Key: TBD (value between 1 and 23)

   *  Confirmation Value Type: COSE_Messages

   *  Change Controller: IETF

   *  Reference: Section 6.9 of [RFC-XXXX]



   *  Confirmation Method Name: kccs

   *  Confirmation Method Description: A CWT Claims Set (CCS) containing
      a COSE_Key in a 'cnf' claim and possibly other claims

   *  JWT Confirmation Method Name: kccs

   *  Confirmation Key: TBD (value between 1 and 23)

   *  Confirmation Value Type: map / #6(map)

   *  Change Controller: IETF

   *  Reference: Section 6.10 of [RFC-XXXX]

14.8.  EDHOC External Authorization Data Registry

   IANA is asked to add the following entries to the "EDHOC External
   Authorization Data" registry defined in Section 10.5 of [RFC9528].

   *  Name: ACE-OAuth Access Token



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   *  Label: TBD (value between 24 and 255)

   *  Description: An Access Token as used in the ACE-OAuth framework
      [RFC9200]

   *  Reference: [RFC-XXXX], Section 4.1



   *  Name: Session ID

   *  Label: TBD (value between 1 and 23)

   *  Description: The identifier of an EDHOC session

   *  Reference: [RFC-XXXX], Section 4.1

14.9.  EDHOC Information Registry

   IANA is requested to create a new "EDHOC Information" registry within
   the "Ephemeral Diffie-Hellman Over COSE (EDHOC)" registry group
   defined in [RFC9528].

   The registration policy is either "Private Use", "Standards Action
   with Expert Review", "Specification Required" per Section 4.6 of
   [RFC8126], or "Expert Review" per Section 4.5 of [RFC8126].  "Expert
   Review" guidelines are provided in Section 14.14.

   All assignments according to "Standards Action with Expert Review"
   are made on a "Standards Action" basis per Section 4.9 of [RFC8126],
   with Expert Review additionally required per Section 4.5 of
   [RFC8126].  The procedure for early IANA allocation of Standards
   Track code points defined in [RFC7120] also applies.  When such a
   procedure is used, review and approval by the designated expert are
   also required, in order for the WG chairs to determine that the
   conditions for early allocation are met (see step 2 in Section 3.1 of
   [RFC7120]).

   The columns of the registry are:

   *  Name: A descriptive name that enables easier reference to this
      item.  Because a core goal of this document is for the resulting
      representations to be compact, it is RECOMMENDED that the name be
      short.







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      This name is case sensitive.  Names may not match other registered
      names in a case-insensitive manner unless the Designated Experts
      determine that there is a compelling reason to allow an exception.
      The name is not used in the CBOR encoding.

   *  CBOR label: The value to be used as CBOR abbreviation of the item.

      The value MUST be unique.  The value can be a positive integer, a
      negative integer, or a string.  Integer values between -256 and
      255 and strings of length 1 are designated as "Standards Action
      with Expert Review".  Integer values from -65536 to -257 and from
      256 to 65535 and strings of maximum length 2 are designated as
      "Specification Required".  Integer values greater than 65535 and
      strings of length greater than 2 are designated as "Expert
      Review".  Integer values less than -65536 are marked as "Private
      Use".

   *  CBOR type: The CBOR type of the item, or a pointer to the registry
      that defines its type, when that depends on another item.

   *  Registry: The registry that values of the item may come from, if
      one exists.

   *  Description: A brief description of the item.

   *  Type: The category of the item, i.e., P if prescriptive or NP if
      Non-Prescriptive.

   *  Specification: A pointer to the public specification for the item,
      if one exists.

   This registry will be initially populated by the values in Table 1.
   In the "Specification" column, the value for all of these entries
   will be [RFC-XXXX] and [RFC9528].

14.10.  EDHOC Endpoint Identity Types Registry

   IANA is requested to create a new "EDHOC Endpoint Identity Types"
   registry within the "Ephemeral Diffie-Hellman Over COSE (EDHOC)"
   registry group defined in [RFC9528].

   The registration policy is either "Private Use", "Standards Action
   with Expert Review", or "Specification Required" per Section 4.6 of
   [RFC8126].  "Expert Review" guidelines are provided in Section 14.14.

   All assignments according to "Standards Action with Expert Review"
   are made on a "Standards Action" basis per Section 4.9 of [RFC8126],
   with Expert Review additionally required per Section 4.5 of



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   [RFC8126].  The procedure for early IANA allocation of Standards
   Track code points defined in [RFC7120] also applies.  When such a
   procedure is used, IANA will ask the designated expert(s) to approve
   the early allocation before registration.  In addition, WG chairs are
   encouraged to consult the expert(s) early during the process outlined
   in Section 3.1 of [RFC7120].

   The columns of this registry are:

   *  Name: This field contains the name of the EDHOC endpoint identity
      type.

   *  CBOR label: The value to be used to identify this EDHOC endpoint
      identity type.  These values MUST be unique.  The value can be a
      positive integer or a negative integer.  Different ranges of
      values use different registration policies [RFC8126].  Integer
      values from -24 to 23 are designated as "Standards Action with
      Expert Review".  Integer values from -65536 to -25 and from 24 to
      65535 are designated as "Specification Required".  Integer values
      smaller than -65536 and greater than 65535 are marked as "Private
      Use".

   *  Description: This field contains a short description of the EDHOC
      endpoint identity type.

   *  Reference: This field contains a pointer to the public
      specification for the EDHOC endpoint identity type.

   This registry has been initially populated with the values in
   Table 2.

14.11.  EDHOC Transports Registry

   IANA is requested to create a new "EDHOC Transports" registry within
   the "Ephemeral Diffie-Hellman Over COSE (EDHOC)" registry group
   defined in [RFC9528].

   The registration policy is either "Private Use", "Standards Action
   with Expert Review", or "Specification Required" per Section 4.6 of
   [RFC8126].  "Expert Review" guidelines are provided in Section 14.14.











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   All assignments according to "Standards Action with Expert Review"
   are made on a "Standards Action" basis per Section 4.9 of [RFC8126],
   with Expert Review additionally required per Section 4.5 of
   [RFC8126].  The procedure for early IANA allocation of Standards
   Track code points defined in [RFC7120] also applies.  When such a
   procedure is used, IANA will ask the designated expert(s) to approve
   the early allocation before registration.  In addition, WG chairs are
   encouraged to consult the expert(s) early during the process outlined
   in Section 3.1 of [RFC7120].

   The columns of this registry are:

   *  Transport ID: The value to be used to identify this means for
      transporting EDHOC messages.  These values MUST be unique.  The
      value can be a positive integer or a negative integer.  Different
      ranges of values use different registration policies [RFC8126].
      Integer values from -24 to 23 are designated as "Standards Action
      with Expert Review".  Integer values from -65536 to -25 and from
      24 to 65535 are designated as "Specification Required".  Integer
      values smaller than -65536 and greater than 65535 are marked as
      "Private Use".

   *  Name: This field contains the name of the means for transporting
      EDHOC messages.

   *  Description: This field contains a short description of the means
      used for transporting EDHOC messages.

   *  Reference: This field contains a pointer to the public
      specification for the means used for transporting EDHOC messages.

   This registry has been initially populated with the values in
   Table 3.

14.12.  EDHOC Trust Anchor Purposes Registry

   IANA is requested to create a new "EDHOC Trust Anchor Purposes"
   registry within the "Ephemeral Diffie-Hellman Over COSE (EDHOC)"
   registry group defined in [RFC9528].

   The registration policy is either "Private Use", "Standards Action
   with Expert Review", or "Specification Required" per Section 4.6 of
   [RFC8126].  "Expert Review" guidelines are provided in Section 14.14.

   All assignments according to "Standards Action with Expert Review"
   are made on a "Standards Action" basis per Section 4.9 of [RFC8126],
   with Expert Review additionally required per Section 4.5 of
   [RFC8126].  The procedure for early IANA allocation of Standards



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   Track code points defined in [RFC7120] also applies.  When such a
   procedure is used, IANA will ask the designated expert(s) to approve
   the early allocation before registration.  In addition, WG chairs are
   encouraged to consult the expert(s) early during the process outlined
   in Section 3.1 of [RFC7120].

   The columns of this registry are:

   *  Name: This field contains the descriptive name of the trust anchor
      purpose, to enable easier reference to the item.  These names MUST
      be unique.

   *  CBOR label: This field contains the value used to identify the
      trust anchor purpose.  These values MUST be unique.  The value can
      be an unsigned integer or a negative integer.  Different ranges of
      values use different registration policies:

      -  Integer values from -24 to 23 are designated as "Standards
         Action with Expert Review".

      -  Integer values from -65536 to -25 and from 24 to 65535 are
         designated as "Specification Required".

      -  Integer values smaller than -65536 and greater than 65535 are
         marked as "Private Use".

   *  Description: This field contains a short description of the trust
      anchor purpose.

   *  Reference: This field contains a pointer to the public
      specification for the trust anchor purpose.

   This registry has been initially populated with the values in
   Section 10.

14.13.  EDHOC Trust Anchor Types Registry

   IANA is requested to create a new "EDHOC Trust Anchor Types" registry
   within the "Ephemeral Diffie-Hellman Over COSE (EDHOC)" registry
   group defined in [RFC9528].

   The registration policy is either "Private Use", "Standards Action
   with Expert Review", or "Specification Required" per Section 4.6 of
   [RFC8126].  "Expert Review" guidelines are provided in Section 14.14.

   All assignments according to "Standards Action with Expert Review"
   are made on a "Standards Action" basis per Section 4.9 of [RFC8126],
   with Expert Review additionally required per Section 4.5 of



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   [RFC8126].  The procedure for early IANA allocation of Standards
   Track code points defined in [RFC7120] also applies.  When such a
   procedure is used, IANA will ask the designated expert(s) to approve
   the early allocation before registration.  In addition, WG chairs are
   encouraged to consult the expert(s) early during the process outlined
   in Section 3.1 of [RFC7120].

   The columns of this registry are:

   *  Name: This field contains the descriptive name of the type of
      trust anchor, to enable easier reference to the item.  These names
      MUST be unique.

   *  CBOR label: This field contains the value used to identify the
      type of trust anchor.  These values MUST be unique.  The value can
      be an unsigned integer or a negative integer.  Different ranges of
      values use different registration policies:

      -  Integer values from -24 to 23 are designated as "Standards
         Action with Expert Review".

      -  Integer values from -65536 to -25 and from 24 to 65535 are
         designated as "Specification Required".

      -  Integer values smaller than -65536 and greater than 65535 are
         marked as "Private Use".

   *  Value type: This field contains the CBOR type for the value
      portion of the label.

   *  Description: This field contains a short description of the type
      of trust anchor.

   *  Reference: This field contains a pointer to the public
      specification for the type of trust anchor.

   This registry has been initially populated with the values in
   Table 5.

14.14.  Expert Review Instructions

   "Standards Action with Expert Review", "Specification Required", and
   "Expert Review" are three of the registration policies defined for
   the IANA registries established in this document.  This section gives
   some general guidelines for what the experts should be looking for,
   but they are being designated as experts for a reason so they should
   be given substantial latitude.




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   Expert reviewers should take into consideration the following points:

   *  Clarity and correctness of registrations.  Experts are expected to
      check the clarity of purpose and use of the requested entries.
      Experts need to make sure that the object of registration is
      clearly defined in the corresponding specification.  Entries that
      do not meet these objective of clarity and completeness must not
      be registered.

   *  Point squatting should be discouraged.  Reviewers are encouraged
      to get sufficient information for registration requests to ensure
      that the usage is not going to duplicate one that is already
      registered and that the point is likely to be used in deployments.
      The zones tagged as "Private Use" are intended for testing
      purposes and closed environments.  Code points in other ranges
      should not be assigned for testing.

   *  Specifications are required for the "Standards Action with Expert
      Review" range of point assignment.  Specifications should exist
      for "Specification Required" ranges, but early assignment before a
      specification is available is considered to be permissible.  When
      specifications are not provided, the description provided needs to
      have sufficient information to identify what the point is being
      used for.

   *  Experts should take into account the expected usage of fields when
      approving point assignment.  Documents published via Standards
      Action can also register points outside the Standards Action
      range.  The length of the encoded value should be weighed against
      how many code points of that length are left, the size of device
      it will be used on, and the number of code points left that encode
      to that size.

15.  References

15.1.  Normative References

   [COSE.Header.Parameters]
              IANA, "COSE Header Parameters",
              <https://www.iana.org/assignments/cose/cose.xhtml#header-
              parameters>.










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   [I-D.ietf-cose-cbor-encoded-cert]
              Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
              M. Furuhed, "CBOR Encoded X.509 Certificates (C509
              Certificates)", Work in Progress, Internet-Draft, draft-
              ietf-cose-cbor-encoded-cert-14, 23 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-cose-
              cbor-encoded-cert-14>.

   [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/rfc/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/rfc/rfc4291>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/rfc/rfc4648>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/rfc/rfc5280>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/rfc/rfc6749>.

   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <https://www.rfc-editor.org/rfc/rfc7120>.

   [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/rfc/rfc7252>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/rfc/rfc7515>.



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   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7519>.

   [RFC7800]  Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
              Possession Key Semantics for JSON Web Tokens (JWTs)",
              RFC 7800, DOI 10.17487/RFC7800, April 2016,
              <https://www.rfc-editor.org/rfc/rfc7800>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/rfc/rfc8126>.

   [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/rfc/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/rfc/rfc8323>.

   [RFC8392]  Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.

   [RFC8613]  Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security for Constrained RESTful Environments
              (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
              <https://www.rfc-editor.org/rfc/rfc8613>.

   [RFC8742]  Bormann, C., "Concise Binary Object Representation (CBOR)
              Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
              <https://www.rfc-editor.org/rfc/rfc8742>.

   [RFC8747]  Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
              Tschofenig, "Proof-of-Possession Key Semantics for CBOR
              Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
              2020, <https://www.rfc-editor.org/rfc/rfc8747>.




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   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/rfc/rfc8949>.

   [RFC9052]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", STD 96, RFC 9052,
              DOI 10.17487/RFC9052, August 2022,
              <https://www.rfc-editor.org/rfc/rfc9052>.

   [RFC9053]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
              August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.

   [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/rfc/rfc9200>.

   [RFC9201]  Seitz, L., "Additional OAuth Parameters for Authentication
              and Authorization for Constrained Environments (ACE)",
              RFC 9201, DOI 10.17487/RFC9201, August 2022,
              <https://www.rfc-editor.org/rfc/rfc9201>.

   [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/rfc/rfc9203>.

   [RFC9360]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Header Parameters for Carrying and Referencing X.509
              Certificates", RFC 9360, DOI 10.17487/RFC9360, February
              2023, <https://www.rfc-editor.org/rfc/rfc9360>.

   [RFC9528]  Selander, G., Preuß Mattsson, J., and F. Palombini,
              "Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528,
              DOI 10.17487/RFC9528, March 2024,
              <https://www.rfc-editor.org/rfc/rfc9528>.

   [RFC9562]  Davis, K., Peabody, B., and P. Leach, "Universally Unique
              IDentifiers (UUIDs)", RFC 9562, DOI 10.17487/RFC9562, May
              2024, <https://www.rfc-editor.org/rfc/rfc9562>.






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   [RFC9668]  Palombini, F., Tiloca, M., Höglund, R., Hristozov, S., and
              G. Selander, "Using Ephemeral Diffie-Hellman Over COSE
              (EDHOC) with the Constrained Application Protocol (CoAP)
              and Object Security for Constrained RESTful Environments
              (OSCORE)", RFC 9668, DOI 10.17487/RFC9668, November 2024,
              <https://www.rfc-editor.org/rfc/rfc9668>.

15.2.  Informative References

   [I-D.ietf-ace-coap-est-oscore]
              Selander, G., Raza, S., Furuhed, M., Vučinić, M., and T.
              Claeys, "Protecting EST Payloads with OSCORE", Work in
              Progress, Internet-Draft, draft-ietf-ace-coap-est-oscore-
              07, 3 March 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-ace-coap-est-oscore-07>.

   [I-D.ietf-ace-group-oscore-profile]
              Tiloca, M., Höglund, R., and F. Palombini, "The Group
              Object Security for Constrained RESTful Environments
              (Group OSCORE) Profile of the Authentication and
              Authorization for Constrained Environments (ACE)
              Framework", Work in Progress, Internet-Draft, draft-ietf-
              ace-group-oscore-profile-04, 3 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ace-
              group-oscore-profile-04>.

   [I-D.ietf-ace-workflow-and-params]
              Tiloca, M. and G. Selander, "Short Distribution Chain
              (SDC) Workflow and New OAuth Parameters for the
              Authentication and Authorization for Constrained
              Environments (ACE) Framework", Work in Progress, Internet-
              Draft, draft-ietf-ace-workflow-and-params-04, 3 March
              2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
              ace-workflow-and-params-04>.

   [I-D.ietf-core-groupcomm-bis]
              Dijk, E. and M. Tiloca, "Group Communication for the
              Constrained Application Protocol (CoAP)", Work in
              Progress, Internet-Draft, draft-ietf-core-groupcomm-bis-
              14, 2 July 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-core-groupcomm-bis-14>.

   [I-D.ietf-core-oscore-id-update]
              Höglund, R. and M. Tiloca, "Identifier Update for OSCORE",
              Work in Progress, Internet-Draft, draft-ietf-core-oscore-
              id-update-02, 8 January 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-core-
              oscore-id-update-02>.



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   [I-D.ietf-core-oscore-key-update]
              Höglund, R. and M. Tiloca, "Key Update for OSCORE
              (KUDOS)", Work in Progress, Internet-Draft, draft-ietf-
              core-oscore-key-update-10, 3 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-core-
              oscore-key-update-10>.

   [I-D.ietf-lake-app-profiles]
              Tiloca, M. and R. Höglund, "Coordinating the Use of
              Application Profiles for Ephemeral Diffie-Hellman Over
              COSE (EDHOC)", Work in Progress, Internet-Draft, draft-
              ietf-lake-app-profiles-01, 3 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lake-
              app-profiles-01>.

   [I-D.ietf-lake-authz]
              Selander, G., Mattsson, J. P., Vučinić, M., Fedrecheski,
              G., and M. Richardson, "Lightweight Authorization using
              Ephemeral Diffie-Hellman Over COSE (ELA)", Work in
              Progress, Internet-Draft, draft-ietf-lake-authz-04, 3
              March 2025, <https://datatracker.ietf.org/doc/html/draft-
              ietf-lake-authz-04>.

   [I-D.serafin-lake-ta-hint]
              Serafin, M. and G. Selander, "Trust Anchor Hints in
              Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in
              Progress, Internet-Draft, draft-serafin-lake-ta-hint-00,
              21 October 2024, <https://datatracker.ietf.org/doc/html/
              draft-serafin-lake-ta-hint-00>.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
              <https://www.rfc-editor.org/rfc/rfc4949>.

   [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/rfc/rfc8446>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [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/rfc/rfc9147>.




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Appendix A.  Examples

   This appendix provides examples where this profile of ACE is used.
   In particular:

   *  Appendix A.1 does not make use of use of any optimization.

   *  Appendix A.2 makes use of the optimizations defined in [RFC9668],
      hence reducing the roundtrips of the interactions between C and
      RS.

   All these examples build on the following assumptions, as relying on
   expected early procedures performed at AS.  These include the
   registration of resource servers by the respective resource owners as
   well as the registrations of clients authorized to request access
   tokens for those resource servers.

   *  AS knows the authentication credential AUTH_CRED_C of C.

   *  C knows the authentication credential AUTH_CRED_AS of AS.

   *  AS knows the authentication credential AUTH_CRED_RS of RS.

   *  RS knows the authentication credential AUTH_CRED_AS of AS.

      This is relevant in case AS and RS actually require a secure
      association (e.g., for RS to perform token introspection at AS, or
      for AS to upload an access token to RS on behalf of C as described
      in [I-D.ietf-ace-workflow-and-params]).

   As a result of the assumptions above, it is possible to limit the
   transport of AUTH_CRED_C and AUTH_CRED_RS by value only to the
   following two cases, and only when C requests an access token for RS
   for the first time when considering the pair (AUTH_CRED_C,
   AUTH_CRED_RS).

   *  In the access token response from AS to C, where AUTH_CRED_RS is
      specified by the "rs_cnf" parameter.

   *  In the access token, where AUTH_CRED_C is specified by the "cnf"
      claim.

   Note that, even under the circumstances mentioned above, AUTH_CRED_C
   might rather be identified by reference.  This is possible if RS can
   effectively use such a reference from the access token to retrieve
   AUTH_CRED_C (e.g., from a trusted repository of authentication
   credentials reachable through a non-constrained link), and if AS is
   in turn aware of that.



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   In any other case, it is otherwise possible to identify both
   AUTH_CRED_C and AUTH_CRED_RS by reference, when performing the ACE
   access control workflow as well as later on when C and RS run EDHOC.

A.1.  Workflow without Optimizations

   The example below shows a simple interaction between C and RS: C and
   RS run EDHOC wherein C uploads the access token to RS, and then
   accesses a protected resource at RS.

     C                                 AS                             RS
     |                                  |                              |
     |  EDHOC message_1 to /edhoc       |                              |
 M01 +--------------------------------->|                              |
     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_2                 |                              |
 M02 |<---------------------------------+                              |
     |  ID_CRED_R identifies            |                              |
     |     CRED_R = AUTH_CRED_AS        |                              |
     |     by reference                 |                              |
     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_3 to /edhoc       |                              |
 M03 +--------------------------------->|                              |
     |  ID_CRED_I identifies            |                              |
     |     CRED_I = AUTH_CRED_C         |                              |
     |     by reference                 |                              |
     |                                  |                              |
     |                                  |                              |
     |  Token request to /token         |                              |
     |  (OSCORE-protected message)      |                              |
 M04 +--------------------------------->|                              |
     |  "req_cnf" identifies            |                              |
     |     AUTH_CRED_C by reference     |                              |
     |                                  |                              |
     |                                  |                              |
     |  Token response                  |                              |
     |  (OSCORE-protected message)      |                              |
 M05 |<---------------------------------+                              |
     |  "rs_cnf" specifies              |                              |
     |     AUTH_CRED_RS by value        |                              |
     |                                  |                              |
     |  "ace_profile" specifies the     |                              |
     |  ACE profile "coap_edhoc_oscore" |                              |
     |                                  |                              |
     |  "edhoc_info" specifies:         |                              |
     |     {                            |                              |



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     |       e'session_id' : h'01',     |                              |
     |       e'cipher_suites' : 2,      |                              |
     |       e'methods' : 3,            |                              |
     |       e'uri_path' : "/edhoc"     |                              |
     |     }                            |                              |
     |                                  |                              |
     |  In the access token:            |                              |
     |  - the "cnf" claim specifies     |                              |
     |    AUTH_CRED_C by value          |                              |
     |  - the "edhoc_info" claim        |                              |
     |    specifies the same as         |                              |
     |    "edhoc_info" above            |                              |
     |                                  |                              |

      Possibly after chain verification, C adds AUTH_CRED_RS
      to the set of its trusted peer authentication credentials,
      relying on AS as trusted provider

     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_1 to /edhoc       |                              |
     |  (no access control is enforced) |                              |
 M06 +---------------------------------------------------------------->|
     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_2                 |                              |
 M07 |<----------------------------------------------------------------+
     |  ID_CRED_R identifies            |                              |
     |     CRED_R = AUTH_CRED_RS        |                              |
     |     by reference                 |                              |
     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_3 to /edhoc       |                              |
     |  (no access control is enforced) |                              |
 M08 +---------------------------------------------------------------->|
     |      EAD_3 contains access token |                              |
     |  ID_CRED_I identifies            |                              |
     |     CRED_I = AUTH_CRED_C         |                              |
     |     by reference                 |                              |
     |                                  |                              |

      Possibly after chain verification, RS adds AUTH_CRED_C
      to the set of its trusted peer authentication credentials,
      relying on AS as trusted provider

     |                                  |                              |
     |                                  |                              |
     |  Access to protected resource    |                              |



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     |  (OSCORE-protected message)      |                              |
     |  (access control is enforced)    |                              |
 M08 +---------------------------------------------------------------->|
     |                                  |                              |
     |  Response                        |                              |
     |  (OSCORE-protected message)      |                              |
 M10 |<----------------------------------------------------------------+
     |                                  |                              |

      Later on, the access token expires ...

       - C and RS delete their OSCORE Security Context and purge
         the EDHOC session used to derive it (unless the same
         session is also used for other reasons).
       - RS retains AUTH_CRED_C as still valid,
         and AS knows about it.
       - The Client retains AUTH_CRED_RS as still valid,
         and AS knows about it.

     |                                  |                              |
     |                                  |                              |

      Time passes ...

     |                                  |                              |
     |                                  |                              |

      C asks for a new access token; now all the
      authentication credentials can be identifies by reference

      The price to pay is on AS, about remembering that at least
      one access token has been issued for the pair (Client, RS)
      and considering the pair (AUTH_CRED_C, AUTH_CRED_RS)

     |                                  |                              |
     |                                  |                              |
     |  Token request to /token         |                              |
     |  (OSCORE-protected message)      |                              |
 M11 +--------------------------------->|                              |
     |  "req_cnf" identifies            |                              |
     |     CRED_I = AUTH_CRED_C         |                              |
     |     by reference                 |                              |
     |                                  |                              |
     |                                  |                              |
     |  Token response                  |                              |
     |  (OSCORE-protected message)      |                              |
 M12 |<---------------------------------+                              |
     |  "rs_cnf" identifies             |                              |



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     |     AUTH_CRED_RS by reference    |                              |
     |                                  |                              |
     |  "ace_profile" specifies the     |                              |
     |  ACE profile "coap_edhoc_oscore" |                              |
     |                                  |                              |
     |  "edhoc_info" specifies:         |                              |
     |     {                            |                              |
     |       e'session_id' : h'05',     |                              |
     |       e'cipher_suites' : 2,      |                              |
     |       e'methods' : 3,            |                              |
     |       e'uri_path' : "/edhoc"     |                              |
     |     }                            |                              |
     |                                  |                              |
     |  In the access token:            |                              |
     |  - the "cnf" claim identifies    |                              |
     |    AUTH_CRED_C by reference      |                              |
     |  - the "edhoc_info" claim        |                              |
     |    specifies the same as         |                              |
     |    "edhoc_info" above            |                              |
     |                                  |                              |
     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_1 to /edhoc       |                              |
     |  (no access control is enforced) |                              |
 M13 +---------------------------------------------------------------->|
     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_2                 |                              |
     |  (no access control is enforced) |                              |
 M14 |<----------------------------------------------------------------+
     |  ID_CRED_R identifies            |                              |
     |     CRED_R = AUTH_CRED_RS        |                              |
     |     by reference                 |                              |
     |                                  |                              |
     |                                  |                              |
     |  EDHOC message_3 to /edhoc       |                              |
     |  (no access control is enforced) |                              |
 M15 +---------------------------------------------------------------->|
     |      EAD_3 contains access token |                              |
     |  ID_CRED_I identifies            |                              |
     |     CRED_I = AUTH_CRED_C         |                              |
     |     by reference                 |                              |
     |                                  |                              |
     |                                  |                              |
     |  Access to protected resource /r |                              |
     |  (OSCORE-protected message)      |                              |
     |  (access control is enforced)    |                              |
 M16 +---------------------------------------------------------------->|



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     |                                  |                              |
     |                                  |                              |
     |  Response                        |                              |
     |  (OSCORE-protected message)      |                              |
 M17 |<----------------------------------------------------------------+
     |                                  |                              |

A.2.  Workflow with Optimizations

   The example below builds on the example in Appendix A.1, while
   additionally using the EDHOC + OSCORE request defined in [RFC9668]
   when running EDHOC both with AS and with RS.

   This interaction between C and RS consists of only two roundtrips to
   upload the access token, run EDHOC, and access the protected resource
   at RS.

     C                                   AS                           RS
     |                                    |                            |
     |  EDHOC message_1 to /edhoc         |                            |
 M01 +----------------------------------->|                            |
     |                                    |                            |
     |                                    |                            |
     |  EDHOC message_2                   |                            |
 M02 |<-----------------------------------+                            |
     |  ID_CRED_R identifies              |                            |
     |     CRED_R = AUTH_CRED_AS          |                            |
     |     by reference                   |                            |
     |                                    |                            |
     |                                    |                            |
     |  EDHOC + OSCORE request to /token  |                            |
 M03 +----------------------------------->|                            |
     |  - EDHOC message_3                 |                            |
     |      ID_CRED_I identifies          |                            |
     |         CRED_I = AUTH_CRED_C       |                            |
     |         by reference               |                            |
     |  --- --- ---                       |                            |
     |  - OSCORE-protected part           |                            |
     |      Token request                 |                            |
     |         "req_cnf" identifies       |                            |
     |         AUTH_CRED_C by reference   |                            |
     |                                    |                            |
     |                                    |                            |
     |  Token response                    |                            |
     |  (OSCORE-protected message)        |                            |
 M04 |<-----------------------------------+                            |
     |  "rs_cnf" specifies                |                            |
     |     AUTH_CRED_RS by value          |                            |



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     |                                    |                            |
     |  "ace_profile" specifies the       |                            |
     |  ACE profile "coap_edhoc_oscore"   |                            |
     |                                    |                            |
     |  "edhoc_info" specifies:           |                            |
     |     {                              |                            |
     |       e'session_id' : h'01',       |                            |
     |       e'cipher_suites' : 2,        |                            |
     |       e'methods' : 3,              |                            |
     |       e'uri_path' : "/edhoc"       |                            |
     |     }                              |                            |
     |                                    |                            |
     |  In the access token:              |                            |
     |  - the "cnf" claim specifies       |                            |
     |    AUTH_CRED_C by value            |                            |
     |  - the "edhoc_info" claim          |                            |
     |    specifies the same as           |                            |
     |    "edhoc_info" above              |                            |
     |                                    |                            |

      Possibly after chain verification, C adds AUTH_CRED_RS
      to the set of its trusted peer authentication credentials,
      relying on AS as trusted provider

     |                                    |                            |
     |  EDHOC message_1 to /edhoc         |                            |
     |  (no access control is enforced)   |                            |
 M05 +---------------------------------------------------------------->|
     |                                    |                            |

      Possibly after chain verification, RS adds AUTH_CRED_C
      to the set of its trusted peer authentication credentials,
      relying on AS as trusted provider

     |                                    |                            |
     |                                    |                            |
     |  EDHOC message_2                   |                            |
 M06 |<----------------------------------------------------------------+
     |  ID_CRED_R identifies              |                            |
     |     CRED_R = AUTH_CRED_RS          |                            |
     |     by reference                   |                            |
     |                                    |                            |
     |                                    |                            |
     |  EDHOC + OSCORE request to /r      |                            |
 M07 +---------------------------------------------------------------->|
     |  - EDHOC message_3                 |                            |
     |      EAD_3 contains access token   |                            |
     |      ID_CRED_I identifies          |                            |



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     |         CRED_I = AUTH_CRED_C       |                            |
     |         by reference               |                            |
     |  --- --- ---                       |                            |
     |  - OSCORE-protected part           |                            |
     |      Application request to /r     |                            |
     |                                    |                            |

      After the EDHOC processing is completed, access control
      is enforced on the rebuilt OSCORE-protected request,
      like if it had been sent stand-alone

     |                                    |                            |
     |                                    |                            |
     |  Response                          |                            |
     |  (OSCORE-protected message)        |                            |
 M08 |<----------------------------------------------------------------+
     |                                    |                            |

Appendix B.  Profile Requirements

   This section lists the specifications of this profile based on the
   requirements of the framework, as requested in Appendix C of
   [RFC9200].

   *  Optionally, define new methods for the client to discover the
      necessary permissions and AS for accessing a resource, different
      from the one proposed in [RFC9200]: Not specified

   *  Optionally, specify new grant types: Not specified

   *  Optionally, define the use of client certificates as client
      credential type: C can use authentication credentials of any type
      admitted by the EDHOC protocol, including public key certificates
      such as X.509 and C509 certificates.

   *  Specify the communication protocol the client and RS must use:
      CoAP

   *  Specify the security protocol the client and RS must use to
      protect their communication: OSCORE

   *  Specify how the client and RS mutually authenticate: Explicitly,
      by successfully executing the EDHOC protocol, after which a common
      OSCORE Security Context is exported from the EDHOC session.  As
      per the EDHOC authentication method used during the EDHOC session,
      authentication is provided by digital signatures, or by Message
      Authentication Codes (MACs) computed from an ephemeral-static ECDH
      shared secret.



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   *  Specify the proof-of-possession protocol(s) and how to select one,
      if several are available.  Also specify which key types (e.g.,
      symmetric/asymmetric) are supported by a specific proof-of-
      possession protocol: proof-of-possession is first achieved by RS
      when successfully processing EDHOC message_3 during the EDHOC
      session with C, through EDHOC algorithms and symmetric EDHOC
      session keys.  Also, proof-of-possession is later achieved by C
      when receiving from RS: i) the optional EDHOC message_4 during the
      EDHOC session with RS, through EDHOC algorithms and symmetric
      EDHOC session keys; or ii) the first response protected with the
      OSCORE Security Context established after the EDHOC session with
      RS, through OSCORE algorithms and OSCORE symmetric keys derived
      from the completed EDHOC session.

   *  Specify a unique ace_profile identifier: coap_edhoc_oscore

   *  If introspection is supported, specify the communication and
      security protocol for introspection: HTTP/CoAP (+ TLS/DTLS/OSCORE)

   *  Specify the communication and security protocol for interactions
      between client and AS: HTTP/CoAP (+ TLS/DTLS/OSCORE)

   *  Specify if/how the authz-info endpoint is protected, including how
      error responses are protected: Not protected

   *  Optionally, define methods of token transport other than the
      authz-info endpoint: C can upload the access token when executing
      EDHOC with RS, by including the access token in the EAD_3 field of
      EDHOC message_3 (see Section 4.2).

Appendix C.  CDDL Model

   This section is to be removed before publishing as an RFC.


















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   ; ACE Profiles
   coap_edhoc_oscore = 4

   ; OAuth Parameters CBOR Mappings
   edhoc_info_param = 47

   ; CBOR Web Token (CWT) Claims
   edhoc_info_claim = 41

   ; CWT Confirmation Methods
   x5t = 6
   x5u = 7
   c5t = 8
   c5u = 9
   kcwt = 10
   kccs = 11
   x5chain = 24
   x5bag = 25
   c5c = 26
   c5b = 27

   ; EDHOC Information
   session_id = 0
   methods = 1
   cipher_suites = 2
   message_4 = 3
   comb_req = 4
   uri_path = 5
   cred_types = 6
   id_cred_types = 7
   eads = 8
   initiator = 9
   responder = 10
   max_msgsize = 11
   coap_ct = 12
   ep_id_types = 13
   transports = 14
   trust_anchors = 15

   ; EDHOC Trust Anchor Purposes
   edhoc_cred = 0

   ; EDHOC Trust Anchor Types
   c5t_ta_type = 22
   c5u_ta_type = 23
   x5t_ta_type = 34
   x5u_ta_type = 35




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                           Figure 11: CDDL model

Appendix D.  Document Updates

   This section is to be removed before publishing as an RFC.

D.1.  Version -07 to -08

   *  KUDOS is just an example of protocol to use for optional key
      update.

   *  message_4 is mandatory to support for an RS that supports the
      reverse message flow.

   *  Method in -workflow-and-params as example for coordinating the
      exchange of authentication credentials by value or reference.

   *  Revised initial set of EDHOC_Information parameters.

   *  Defined categorization of EDHOC_Information parameters.

   *  New EAD item for C to retrieve Request Creation Hints information
      from RS.

   *  New EAD item for requesting authentication credential by value.

   *  Means for the AS to achive proof-of-possession of C's private key.

   *  Editorial improvements.

D.2.  Version -06 to -07

   *  Renamed id_ep_types as ep_id_types.

   *  Revised rules for the AS to assign session ID values.

   *  Added explicit validation of AUTH_CRED_C at AS.

   *  "edhoc_info" only in AS-to-C response for first token in a series.

   *  With a group-audience, "edhoc_info" refers to the whole audience.

   *  Defined parameters for the EDHOC_Information object:

      -  Parameters moved here from draft-ietf-lake-app-profiles.

      -  New parameter "trust_anchors".




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   *  Access Token Request/Response messages must be encoded in CBOR.

   *  Explicit statement on admitted confirmation methods.

   *  First token in a series: the "cnf" claim uses the same
      confirmation method of the "req_cnf" request to /token.

   *  Revised examples in CBOR diagnostic notation.

   *  With a group-audience, the reverse message flow can use a roll
      call.

   *  Matching authentication credentials from ID_CRED_X and EAD item.

   *  Handling authentication credentials and EDHOC session that become
      invalid.

   *  Limited use of ACE Request Creation Hints when supporting the
      EDHOC reverse message flow.

   *  Changed CBOR abbreviations to not collide with existing
      codepoints.

   *  Updates and fixes in the IANA considerations.

   *  Updated references.

   *  Clarifications and editorial improvements.

D.3.  Version -05 to -06

   *  The access token can be uploaded through EDHOC in EAD_3, EAD_2, or
      EAD_4.

   *  Ruled out the upload of the access token to the /authz-info
      endpoint over an unprotected channel.

   *  Defined an EDHOC EAD item for transporting a Session ID.

   *  Provided more details and added example of dynamic update of
      access rights.

   *  Defined in detail the use of the EDHOC reverse message flow.

   *  Provided details on access token invalidity.

   *  Revised examples with message exchanges.




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   *  Clarifications and editorial improvements.

D.4.  Version -04 to -05

   *  CBOR diagnostic notation uses placeholders from a CDDL model.

   *  Only CWTs are supported as access tokens in this profile.

   *  The alternative workflow of ACE is only mentioned as an example.

   *  Clarified that both the EDHOC forward and reverse message flows
      are possible.

   *  Consistent with the used EDHOC message flow, the access token can
      be in the EAD item of any EDHOC message.

   *  Explicit registration policies for the new IANA registry.

   *  Fixes in the IANA considerations.

   *  Editorial fixes and improvements.

D.5.  Version -03 to -04

   *  Fixed column name and prefilling of the "EDHOC Information"
      registry.

   *  Added EDHOC_Information Parameters originally in draft-tiloca-
      lake-app-profiles-00.

   *  Removed the case of transporting access token in EAD_1

   *  Removed redundant normative text

   *  Clarifications of association between access token, session_id,
      EDHOC session and OSCORE security context

   *  Updated references.

   *  Editorial fixes and improvements.

D.6.  Version -02 to -03

   *  Restructured presentation of content.

   *  Simplified description of the use of EDHOC_Information.





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   *  Merged the concepts of EDHOC "session_id" and identifier of token
      series.

   *  Enabled the transport of the access token also in EDHOC EAD_3.

   *  Defined semantics of the newly defined CWT/JWT Confirmation
      Methods.

   *  Clarifications and editorial improvements.

D.7.  Version -01 to -02

   *  Removed use of EDHOC_KeyUpdate.

   *  The Security Context is updated either by KUDOS or a rerun of
      EDHOC.

   *  The alternative workflow (AS token posting) is specified in
      separate draft.

   *  Fixed and updated examples.

   *  Editorial improvements.

D.8.  Version -00 to -01

   *  Fixed semantics of the ead_value for transporting an Access Token
      in the EAD_1 field.

   *  Error handling aligned with EDHOC.

   *  Precise characterization of the EDHOC execution considered for
      EDHOC-KeyUpdate.

   *  Fixed message exchange examples.

   *  Added appendix with profile requirements.

   *  Updated references.

   *  Clarifications and editorial improvements.

Acknowledgments

   The authors sincerely thank Christian Amsüss and Carsten Bormann for
   their comments and feedback.





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   The parameter "trust_anchors" for specifying supported trust anchors
   builds on a proposal originally described in
   [I-D.serafin-lake-ta-hint].

   This work was supported by the Sweden's Innovation Agency VINNOVA
   within the EUREKA CELTIC-NEXT project CYPRESS; and by the H2020
   project SIFIS-Home (Grant agreement 952652).

Authors' Addresses

   Göran Selander
   Ericsson
   Email: goran.selander@ericsson.com


   John Preuß Mattsson
   Ericsson
   Email: john.mattsson@ericsson.com


   Marco Tiloca
   RISE
   Email: marco.tiloca@ri.se


   Rikard Höglund
   RISE
   Email: rikard.hoglund@ri.se























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