Internet DRAFT - draft-tiloca-ace-authcred-dtls-profile

draft-tiloca-ace-authcred-dtls-profile







ACE Working Group                                              M. Tiloca
Internet-Draft                                                   RISE AB
Updates: 9202 (if approved)                               J. P. Mattsson
Intended status: Standards Track                             Ericsson AB
Expires: 13 July 2024                                    10 January 2024


   Additional Formats of Authentication Credentials for the Datagram
     Transport Layer Security (DTLS) Profile for Authentication and
            Authorization for Constrained Environments (ACE)
               draft-tiloca-ace-authcred-dtls-profile-01

Abstract

   This document updates the Datagram Transport Layer Security (DTLS)
   Profile for Authentication and Authorization for Constrained
   Environments (ACE).  In particular, it specifies the use of
   additional formats of authentication credentials for establishing a
   DTLS session, when peer authentication is based on asymmetric
   cryptography.  Therefore, this document updates RFC 9202.  What is
   defined in this document is seamlessly applicable also if the profile
   uses Transport Layer Security (TLS) instead, as defined in RFC 9430.

Discussion Venues

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

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

   Source for this draft and an issue tracker can be found at
   https://gitlab.com/crimson84/draft-tiloca-ace-authcred-dtls-profile.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.







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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 13 July 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Updates to the RPK Mode . . . . . . . . . . . . . . . . . . .   5
   3.  Certificate Mode  . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  Examples with Hybrid Settings  . . . . . . . . . . .  14
     A.1.  RPK Mode (Raw Public Keys of Different Formats) . . . . .  14
     A.2.  Certificate Mode (Certificates of Different Formats)  . .  14
     A.3.  Combination of RPK Mode and Certificate Mode  . . . . . .  14
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The Authentication and Authorization for Constrained Environments
   (ACE) framework [RFC9200] defines an architecture to enforce access
   control for constrained devices.  A Client (C) requests an evidence
   of granted permissions from an Authorization Server (AS) in the form
   of an access token, then uploads the access token to the target
   Resource Server (RS), and finally accesses protected resources at RS
   according to what is specified in the access token.



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   The framework has as main building blocks the OAuth 2.0 framework
   [RFC6749], the Constrained Application Protocol (CoAP) [RFC7252] for
   message transfer, CBOR [RFC8949] for compact encoding, and COSE
   [RFC9052][RFC9053] for self-contained protection of access tokens.

   Separate profile documents define in detail how the participants in
   the ACE architecture communicate, especially as to the security
   protocols that they use.  In particular, the ACE profile defined in
   [RFC9202] specifies how Datagram Transport Layer Security (DTLS)
   [RFC6347][RFC9147] is used to protect communications with transport-
   layer security in the ACE architecture.  The profile has also been
   extended in [RFC9430], in order to allow the alternative use of
   Transport Layer Security (TLS) [RFC8446] when CoAP is transported
   over TCP or WebSockets [RFC8323].

   The DTLS profile [RFC9202] allows C and RS to establish a DTLS
   session with peer authentication based on symmetric or asymmetric
   cryptography.  For the latter case, the profile defines an RPK mode
   (see Section 3.2 of [RFC9202]), where authentication relies on the
   public keys of the two peers as raw public keys [RFC7250].

   That is, C specifies its public key to the AS when requesting an
   access token, and the AS provides such public key to the target RS as
   included in the issued access token.  Upon issuing the access token,
   the AS also provides C with the public key of RS.  Then, C and RS use
   their asymmetric keys when performing the DTLS handshake, as defined
   in [RFC7250].

   Per [RFC9202], the DTLS profile admits only a COSE Key object
   [RFC9052] as the format of authentication credentials to use for
   transporting the public keys of C and RS, as raw public keys.
   However, it is desirable to enable additional types of authentication
   credentials, as enhanced raw public keys or as public certificates.

   This document enables such additional formats, by defining how the
   public keys of C and RS can be specified as CBOR Web Token (CWT)
   Claims Sets (CCSs) [RFC8392], or X.509 certificates [RFC5280], or
   C509 certificates [I-D.ietf-cose-cbor-encoded-cert].  In particular,
   this document updates [RFC9202] as follows.

   *  It extends the RPK mode defined in Section 3.2 of [RFC9202], by
      enabling the use of CCSs to transport the raw public keys of C and
      RS (see Section 2).

   *  It defines a new certificate mode, which enables the transport of
      the public keys of C and RS as X.509 or C509 certificates (see
      Section 3).




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   When using the updated RPK mode, the raw public keys of C and RS do
   not have to be of the same type.  That is, it is possible to have
   both public keys as a COSE Key object or as a CCS, or instead one as
   a COSE Key object while the other one as a CCS.

   When using the certificate mode, the certificates of C and RS do not
   have to be of the same type.  That is, it is possible to have both as
   X.509 certificates, or both as C509 certificates, or one as an X.509
   certificate while the other one as a C509 certificate.

   Also, the RPK mode and the certificate mode can be combined.  That
   is, it is possible that one of the two authentication credentials is
   a certificate, while the other one is a raw public key.

   When using the formats introduced in this document, authentication
   credentials are transported by means of the CWT Confirmation Methods
   "kccs", "x5bag", "x5chain", "c5b", and "c5c", which are defined in
   [I-D.ietf-ace-edhoc-oscore-profile].

   What is defined in this document is seamlessly applicable if TLS is
   used instead, as defined in [RFC9430].

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.

   Readers are expected to be familiar with the terms and concepts
   described in the ACE framework for Authentication and Authorization
   [RFC9200][RFC9201] and its DTLS profile [RFC9202], as well as with
   terms and concepts related to CBOR Web Tokens (CWTs) [RFC8392] and
   CWT Confirmation Methods [RFC8747].

   The terminology for entities in the considered architecture is
   defined in OAuth 2.0 [RFC6749].  In particular, this includes Client
   (C), Resource Server (RS), and Authorization Server (AS).

   Readers are also expected to be familiar with the terms and concepts
   related to the CoAP protocol [RFC7252], CBOR [RFC8949], COSE
   [RFC9052][RFC9053], the DTLS protocol suite [RFC6347][RFC9147], and
   the use of raw public keys in DTLS [RFC7250].







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   Note that, unless otherwise indicated, the term "endpoint" is used
   here following its OAuth definition, aimed at denoting resources such
   as /token and /introspect at the AS, and /authz-info at RS.  This
   document does not use the CoAP definition of "endpoint", which is "An
   entity participating in the CoAP protocol."

   This document also refers to the term "authentication credential",
   which denotes the information associated with an entity, including
   that entity's public key and parameters associated with the public
   key.  Examples of authentication credentials are CWT Claims Sets
   (CCSs) [RFC8392], X.509 certificates [RFC5280], and C509 certificates
   [I-D.ietf-cose-cbor-encoded-cert].

   Examples throughout this document are expressed in CBOR diagnostic
   notation without the tag and value abbreviations.

2.  Updates to the RPK Mode

   This section updates the RPK mode defined in Section 3.2 of
   [RFC9202], by defining how the raw public key of C and RS can be
   transported as a CCS [RFC8392], instead of as a COSE Key object
   [RFC9052].  Note that only the differences from [RFC9202] are
   compiled below.

   If the raw public key of C is transported as a CCS, the following
   applies.

   *  The payload of the Access Token Request (see Section 5.8.1 of
      [RFC9200]) is as defined in Section 3.2.1 of [RFC9202], with the
      difference that the "req_cnf" parameter [RFC9201] MUST specify a
      "kccs" structure, with value a CCS specifying the public key of C.

   *  The content of the access token that the AS provides to C in the
      Access Token Response (see Section 5.8.2 of [RFC9200]) is as
      defined in Section 3.2.1 of [RFC9202], with the difference that
      the "cnf" claim of the access token MUST specify a "kccs"
      structure, with value a CCS specifying the public key of C.

   If the raw public key of RS is transported as a CCS, the following
   applies.

   *  The payload of the Access Token Response is as defined in
      Section 3.2.1 of [RFC9202], with the difference that the "rs_cnf"
      parameter [RFC9201] MUST specify a "kccs" structure, with value a
      CCS [RFC8392] specifying the public key of RS.






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   For the "req_cnf" parameter of the Access Token Request, the "rs_cnf"
   parameter of the Access Token Response, and the "cnf" claim of the
   access token, the Confirmation Method "kccs" structure and its
   identifier are defined in [I-D.ietf-ace-edhoc-oscore-profile].

   It is not required that both public keys are transported as a CCS.
   That is, one of the two authentication credentials can be a CCS,
   while the other one can be a COSE Key object as per Section 3.2 of
   [RFC9202].

   Figure 1 shows an example of Access Token Request from C to the AS.

      POST coaps://as.example.com/token
      Content-Format: application/ace+cbor
      Payload:
      {
        "grant_type" : 2,
        "audience" : "tempSensor4711",
        "req_cnf" : {
          "kccs" : {
            "sub" : "42-50-31-FF-EF-37-32-39",
            "cnf" : {
              "COSE_Key" : {
                "kty" : 2,
                "crv" : 1,
                "x" : h'd7cc072de2205bdc1537a543d53c60a6
                        acb62eccd890c7fa27c9e354089bbe13',
                "y" : h'f95e1d4b851a2cc80fff87d8e23f22af
                        b725d535e515d020731e79a3b4e47120'
              }
            }
          }
        }
      }

       Figure 1: Access Token Request Example for RPK Mode, with the
           Public Key of C Transported as a CCS within "req_cnf"

   Figure 2 shows an example of Access Token Response from the AS to C.












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      2.01 Created
      Content-Format: application/ace+cbor
      Max-Age: 3560
      Payload:
      {
        "access_token" : b64'SlAV32hk'/...
         (remainder of CWT omitted for brevity;
         CWT contains the client's RPK in the cnf claim)/,
        "expires_in" : 3600,
        "rs_cnf" : {
          "kccs" : {
            "sub" : "AA-BB-CC-00-01-02-03-04",
            "cnf" : {
              "COSE_Key" : {
                "kty" : 2,
                "crv" : 1,
                "x" : h'bbc34960526ea4d32e940cad2a234148
                        ddc21791a12afbcbac93622046dd44f0',
                "y" : h'4519e257236b2a0ce2023f0931f1f386
                        ca7afda64fcde0108c224c51eabf6072'
              }
            }
          }
        }
      }

       Figure 2: Access Token Response Example for RPK Mode, with the
           Public Key of RS Transported as a CCS within "rs_cnf"

3.  Certificate Mode

   This section defines a new certificate mode of the DTLS profile,
   which enables the transport of the public keys of C and RS as public
   certificates.

   Compared to the RPK mode defined in Section 3.2 of [RFC9202] and
   extended in Section 2 of this document, the certificate mode displays
   the following differences.

   *  The authentication credential of C and/or RS is a public
      certificate, i.e., an X.509 certificate [RFC5280] or a C509
      certificate [I-D.ietf-cose-cbor-encoded-cert].  The CWT
      Confirmation Methods "x5chain", "x5bag", "c5c", and "c5b" defined
      in [I-D.ietf-ace-edhoc-oscore-profile] are used to transport such
      authentication credentials.

   *  If the authentication credential AUTH_CRED_C of C is a public
      certificate, the following applies.



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      -  The "req_cnf" parameter [RFC9201] of the Access Token Request
         (see Section 5.8.1 of [RFC9200]) specifies AUTH_CRED_C as
         follows.

         o  If AUTH_CRED_C is an X.509 certificate, the "req_cnf"
            parameter MUST specify an "x5chain" or "x5bag" structure, in
            case AUTH_CRED_C is conveyed in a certificate chain or in a
            certificate bag, respectively.

         o  If AUTH_CRED_C is a C509 certificate, the "req_cnf"
            parameter MUST specify a "c5c" or "c5b" structure, in case
            AUTH_CRED_C is conveyed in a certificate chain or in a
            certificate bag, respectively.

      -  The "cnf" claim of the access token that the AS provides to C
         in the Access Token Response (see Section 5.8.2 of [RFC9200])
         specifies AUTH_CRED_C as follows.

         o  If AUTH_CRED_C is an X.509 certificate, the "cnf" claim MUST
            specify an "x5chain" or "x5bag" structure, in case
            AUTH_CRED_C is conveyed in a certificate chain or in a
            certificate bag, respectively.

         o  If AUTH_CRED_C is a C509 certificate, the "cnf" claim MUST
            specify a "c5c" or "c5b" structure, in case AUTH_CRED_C is
            conveyed in a certificate chain or in a certificate bag,
            respectively.

   *  If the authentication credential AUTH_CRED_RS of RS is a public
      certificate, the following applies.

      -  The "rs_cnf" parameter [RFC9201] of the Access Token Response
         specifies AUTH_CRED_RS as follows.

         o  If AUTH_CRED_RS is an X.509 certificate, the "rs_cnf"
            parameter MUST specify an "x5chain" or "x5bag" structure, in
            case AUTH_CRED_RS is conveyed in a certificate chain or in a
            certificate bag, respectively.

         o  If AUTH_CRED_RS is a C509 certificate, the "rs_cnf"
            parameter MUST specify a "c5c" or "c5b" structure, in case
            AUTH_CRED_RS is conveyed in a certificate chain or in a
            certificate bag, respectively.

   For the "req_cnf" parameter of the Access Token Request, the "rs_cnf"
   parameter of the Access Token Response, and the "cnf" claim of the
   access token, the Confirmation Method "c5c" and "c5b" structures and
   their identifiers are defined in [I-D.ietf-ace-edhoc-oscore-profile].



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   When using either of the structures "x5chain", "x5bag", "c5c", and
   "c5b", i.e., either a chain or a bag of certificates, the specified
   authentication credential is just the end entity X.509 or C509
   certificate.

   As per [RFC6347][RFC9147], a public certificate is specified in the
   Certificate message of the DTLS handshake.  For X.509 certificates,
   the TLS Certificate Type is "X509", as defined in [RFC6091].  For
   C509 certificates, the TLS certificate type is "C509 Certificate", as
   defined in [I-D.ietf-cose-cbor-encoded-cert].

   It is not required that AUTH_CRED_C and AUTH_CRED_RS are both X.509
   certificates or both C509 certificates.

   Also, one of the two authentication credentials can be a public
   certificate, while the other one can be a raw public key.  This is
   consistent with the admitted, combined use of raw public keys and
   certificates, as discussed in Section 5.3 of [RFC7250].

   Figure 3 shows an example of Access Token Request from C to the AS.
   In the example, C specifies its authentication credential by means of
   an "x5chain" structure, including only its own X.509 certificate.

      POST coaps://as.example.com/token
      Content-Format: application/ace+cbor
      Payload:
      {
        "grant_type" : 2,
        "audience" : "tempSensor4711",
        "req_cnf" : {
          "x5chain" : h'3081ee3081a1a003020102020462319ec430
                        0506032b6570301d311b301906035504030c
                        124544484f4320526f6f7420456432353531
                        39301e170d3232303331363038323433365a
                        170d3239313233313233303030305a302231
                        20301e06035504030c174544484f43205265
                        73706f6e6465722045643235353139302a30
                        0506032b6570032100a1db47b95184854ad1
                        2a0c1a354e418aace33aa0f2c662c00b3ac5
                        5de92f9359300506032b6570034100b723bc
                        01eab0928e8b2b6c98de19cc3823d46e7d69
                        87b032478fecfaf14537a1af14cc8be829c6
                        b73044101837eb4abc949565d86dce51cfae
                        52ab82c152cb02'
        }
      }





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      Figure 3: Access Token Request Example for Certificate Mode with
         an X.509 Certificate as Authentication Credential of C and
                        Transported within "req_cnf"

   Figure 4 shows an example of Access Token Response from the AS to C.
   In the example, the AS specifies the authentication credential of RS
   by means of an "x5chain" structure, including only the X.509
   certificate of RS.

      2.01 Created
      Content-Format: application/ace+cbor
      Max-Age: 3560
      Payload:
      {
        "access_token" : b64'SlAV32hk'/...
         (remainder of CWT omitted for brevity;
         CWT contains the client's X.509 certificate in the cnf claim)/,
        "expires_in" : 3600,
        "rs_cnf" : {
          "x5chain" : h'3081ee3081a1a003020102020462319ea030
                        0506032b6570301d311b301906035504030c
                        124544484f4320526f6f7420456432353531
                        39301e170d3232303331363038323430305a
                        170d3239313233313233303030305a302231
                        20301e06035504030c174544484f4320496e
                        69746961746f722045643235353139302a30
                        0506032b6570032100ed06a8ae61a829ba5f
                        a54525c9d07f48dd44a302f43e0f23d8cc20
                        b73085141e300506032b6570034100521241
                        d8b3a770996bcfc9b9ead4e7e0a1c0db353a
                        3bdf2910b39275ae48b756015981850d27db
                        6734e37f67212267dd05eeff27b9e7a813fa
                        574b72a00b430b'
        }
      }

     Figure 4: Access Token Response Example for Certificate Mode with
        an X.509 Certificate as Authentication Credential of RS and
                        Transported within "rs_cnf"

4.  Security Considerations

   The security considerations from [RFC9200] and [RFC9202] apply to
   this document as well.

   When using public certificates as authentication credentials, the
   security considerations from Appendix C.2 of [RFC8446] apply.




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   When using X.509 certificates as authentication credentials, the
   security considerations from [RFC5280], [RFC6818], [RFC8398], and
   [RFC8399] apply.

   When using C509 certificates as authentication credentials, the
   security considerations from [I-D.ietf-cose-cbor-encoded-cert] apply.

5.  IANA Considerations

   This document has no actions for IANA.

6.  References

6.1.  Normative References

   [I-D.ietf-ace-edhoc-oscore-profile]
              Selander, G., Mattsson, J. P., Tiloca, M., and R. Höglund,
              "Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object
              Security for Constrained Environments (OSCORE) Profile for
              Authentication and Authorization for Constrained
              Environments (ACE)", Work in Progress, Internet-Draft,
              draft-ietf-ace-edhoc-oscore-profile-03, 23 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ace-
              edhoc-oscore-profile-03>.

   [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-07, 20 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-cose-
              cbor-encoded-cert-07>.

   [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>.

   [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>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/rfc/rfc6347>.




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   [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>.

   [RFC6818]  Yee, P., "Updates to the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 6818, DOI 10.17487/RFC6818, January
              2013, <https://www.rfc-editor.org/rfc/rfc6818>.

   [RFC7250]  Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
              Weiler, S., and T. Kivinen, "Using Raw Public Keys in
              Transport Layer Security (TLS) and Datagram Transport
              Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
              June 2014, <https://www.rfc-editor.org/rfc/rfc7250>.

   [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>.

   [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>.

   [RFC8398]  Melnikov, A., Ed. and W. Chuang, Ed., "Internationalized
              Email Addresses in X.509 Certificates", RFC 8398,
              DOI 10.17487/RFC8398, May 2018,
              <https://www.rfc-editor.org/rfc/rfc8398>.

   [RFC8399]  Housley, R., "Internationalization Updates to RFC 5280",
              RFC 8399, DOI 10.17487/RFC8399, May 2018,
              <https://www.rfc-editor.org/rfc/rfc8399>.

   [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>.





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   [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>.

   [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>.

   [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>.

   [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>.

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

   [RFC9430]  Bergmann, O., Preuß Mattsson, J., and G. Selander,
              "Extension of the Datagram Transport Layer Security (DTLS)
              Profile for Authentication and Authorization for
              Constrained Environments (ACE) to Transport Layer Security
              (TLS)", RFC 9430, DOI 10.17487/RFC9430, July 2023,
              <https://www.rfc-editor.org/rfc/rfc9430>.



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6.2.  Informative References

   [RFC6091]  Mavrogiannopoulos, N. and D. Gillmor, "Using OpenPGP Keys
              for Transport Layer Security (TLS) Authentication",
              RFC 6091, DOI 10.17487/RFC6091, February 2011,
              <https://www.rfc-editor.org/rfc/rfc6091>.

Appendix A.  Examples with Hybrid Settings

   This section provides additional examples where, within the same ACE
   execution workflow, C and RS use different formats of raw public keys
   (see Appendix A.1), or different formats of certificates (see
   Appendix A.2), or a combination of the RPK mode and certificate mode
   (see Appendix A.3).

A.1.  RPK Mode (Raw Public Keys of Different Formats)

   TBD

A.2.  Certificate Mode (Certificates of Different Formats)

   TBD

A.3.  Combination of RPK Mode and Certificate Mode

   TBD

Acknowledgments

   The authors sincerely thank Rikard Höglund and Göran Selander for
   their comments and feedback.  The work on this document has been
   partly supported by the H2020 project SIFIS-Home (Grant agreement
   952652).

Authors' Addresses

   Marco Tiloca
   RISE AB
   Isafjordsgatan 22
   SE-16440 Kista
   Sweden
   Email: marco.tiloca@ri.se









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   John Preuß Mattsson
   Ericsson AB
   Torshamnsgatan 23
   SE-16440 Stockholm Kista
   Sweden
   Email: john.mattsson@ericsson.com













































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