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Versions: (draft-seitz-ace-oscoap-profile) 00 01 02 03 04 05

ACE Working Group                                               L. Seitz
Internet-Draft                                              RISE SICS AB
Intended status: Standards Track                            F. Palombini
Expires: December 30, 2018                                   Ericsson AB
                                                           M. Gunnarsson
                                                            RISE SICS AB
                                                             G. Selander
                                                             Ericsson AB
                                                           June 28, 2018


 OSCORE profile of the Authentication and Authorization for Constrained
                         Environments Framework
                    draft-ietf-ace-oscore-profile-02

Abstract

   This memo specifies a profile for the Authentication and
   Authorization for Constrained Environments (ACE) framework.  It
   utilizes Object Security for Constrained RESTful Environments
   (OSCORE) to provide communication security, server authentication,
   and proof-of-possession for a key owned by the client and bound to an
   OAuth 2.0 access token.

Status of This Memo

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

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

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

   This Internet-Draft will expire on December 30, 2018.

Copyright Notice

   Copyright (c) 2018 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



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   (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 and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Client to Resource Server . . . . . . . . . . . . . . . . . .   3
     2.1.  Signaling the use of OSCORE . . . . . . . . . . . . . . .   3
     2.2.  Key establishment for OSCORE  . . . . . . . . . . . . . .   4
   3.  Client to Authorization Server  . . . . . . . . . . . . . . .   8
   4.  Resource Server to Authorization Server . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  Profile Requirements . . . . . . . . . . . . . . . .  11
   Appendix B.  Using the pop-key with EDHOC (EDHOC+OSCORE)  . . . .  12
     B.1.  Using Asymmetric Keys . . . . . . . . . . . . . . . . . .  13
     B.2.  Using Symmetric Keys  . . . . . . . . . . . . . . . . . .  14
     B.3.  Processing  . . . . . . . . . . . . . . . . . . . . . . .  16
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   This memo specifies a profile of the ACE framework
   [I-D.ietf-ace-oauth-authz].  In this profile, a client and a resource
   server use CoAP [RFC7252] to communicate.  The client uses an access
   token, bound to a key (the proof-of-possession key) to authorize its
   access to the resource server.  In order to provide communication
   security, proof of possession, and server authentication they use
   Object Security for Constrained RESTful Environments (OSCORE)
   [I-D.ietf-core-object-security].  Optionally the client and the
   resource server may also use CoAP and OSCORE to communicate with the
   authorization server.

   OSCORE specifies how to use CBOR Object Signing and Encryption (COSE)
   [RFC8152] to secure CoAP messages.  In order to provide replay and
   reordering protection OSCORE also introduces sequence numbers that
   are used together with COSE.



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   Note that OSCORE can be used to secure CoAP messages, as well as HTTP
   and combinations of HTTP and CoAP; a profile of ACE similar to the
   one described in this document, with the difference of using HTTP
   instead of CoAP as communication protocol, could be specified
   analogously to this one.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].  These
   words may also appear in this document in lowercase, absent their
   normative meanings.

   Certain security-related terms such as "authentication",
   "authorization", "confidentiality", "(data) integrity", "message
   authentication code", and "verify" are taken from [RFC4949].

   Since we describe exchanges as RESTful protocol interactions HTTP
   [RFC7231] offers useful terminology.

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

2.  Client to Resource Server

   The use of OSCORE for arbitrary CoAP messages is specified in
   [I-D.ietf-core-object-security].  This section defines the specific
   uses and their purpose for securing the communication between a
   client and a resource server, and the parameters needed to negotiate
   the use of this profile with the token resource at the authorization
   server as specified in section 5.6 of [I-D.ietf-ace-oauth-authz].

2.1.  Signaling the use of OSCORE

   A client requests a token at an AS via the /token resource.  This
   follows the message formats specified in section 5.6.1 of
   [I-D.ietf-ace-oauth-authz].

   The AS responding to a successful access token request as defined in
   section 5.6.2 of [I-D.ietf-ace-oauth-authz] can signal that the use
   of OSCORE is REQUIRED for a specific access token by including the
   "profile" parameter with the value "coap_oscore" in the access token
   response.  This means that the client MUST use OSCORE towards all




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   resource servers for which this access token is valid, and follow
   Section 2.2 to derive the security context to run OSCORE.

   The error response procedures defined in section 5.6.3 of the ACE
   framework are unchanged by this profile.

   Note the the client and the authorization server MAY OPTIONALLY use
   OSCORE to protect the interaction via the /token resource.  See
   Section 3 for details.

2.2.  Key establishment for OSCORE

   Section 3.2 of [I-D.ietf-core-object-security] defines how to derive
   a security context based on a shared master secret and a set of other
   parameters, established between client and server.  The proof-of-
   possession key (pop-key) provisioned from the AS MAY, in case of pre-
   shared keys, be used directly as master secret in OSCORE.

   If OSCORE is used directly with the symmetric pop-key as master
   secret, then the AS MUST provision the following data, in response to
   the access token request:

   o  a master secret

   o  the sender identifier

   o  the recipient identifier

   Additionally, the AS MAY provision the following data, in the same
   response.  In case these parameters are omitted, the default values
   are used as described in section 3.2 of
   [I-D.ietf-core-object-security].

   o  an AEAD algorithm

   o  a KDF algorithm

   o  a salt

   o  a replay window type and size

   The master secret MUST be communicated as COSE_Key in the 'cnf'
   parameter of the access token response as defined in Section 5.6.4.5
   of [I-D.ietf-ace-oauth-authz].  The AEAD algorithm MAY be included as
   the 'alg' parameter in the COSE_Key; the KDF algorithm MAY be
   included as the 'kdf' parameter of the COSE_Key and the salt MAY be
   included as the 'slt' parameter of the COSE_Key as defined in table
   1.



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   The same parameters MUST be included as metadata of the access token;
   if the token is a CWT [RFC8392], the same COSE_Key structure MUST be
   placed in the 'cnf' claim of this token.  If a CWT is used it MUST be
   encrypted, since the token is transferred from the client to the RS
   over an unprotected channel.

   The AS MUST also assign identifiers to both client and RS, which are
   then used as Sender ID and Recipient ID in the OSCORE context as
   described in section 3.1 of [I-D.ietf-core-object-security].  These
   identifiers MUST be unique in the set of all clients and RS
   identifiers for a certain AS.  Moreover, these MUST be included in
   the COSE_Key as header parameters, as defined in table 1.

   We assume in this document that a resource is associated to one
   single AS, which makes it possible to assume unique identifiers for
   each client requesting a particular resource to a RS.  If this is not
   the case, collisions of identifiers may appear in the RS, in which
   case the RS needs to have a mechanism in place to disambiguate
   identifiers or mitigate their effect.

   Note that C should set the Sender ID of its security context to the
   clientId value received and the Recipient ID to the serverId value,
   and RS should do the opposite.




























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   +----------+-------+--------------+------------+-------------------+
   | name     | label | CBOR type    | registry   | description       |
   +----------+-------+--------------+------------+-------------------+
   | clientId | TBD1  | bstr         |            | Identifies the    |
   |          |       |              |            | client in an      |
   |          |       |              |            | OSCORE context    |
   |          |       |              |            | using this key    |
   |          |       |              |            |                   |
   | serverId | TBD2  | bstr         |            | Identifies the    |
   |          |       |              |            | server in an      |
   |          |       |              |            | OSCORE context    |
   |          |       |              |            | using this key    |
   |          |       |              |            |                   |
   | kdf      | TBD3  | bstr         |            | Identifies the    |
   |          |       |              |            | KDF algorithm in  |
   |          |       |              |            | an OSCORE context |
   |          |       |              |            | using this key    |
   |          |       |              |            |                   |
   | slt      | TBD4  | bstr         |            | Identifies the    |
   |          |       |              |            | master salt in    |
   |          |       |              |            | an OSCORE context |
   |          |       |              |            | using this key    |
   +----------+-------+--------------+------------+-------------------+
       Table 1: Additional COSE_Key Common Parameters


   Figure 1 shows an example of such an AS response, in CBOR diagnostic
   notation without the tag and value abbreviations.























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       Header: Created (Code=2.01)
       Content-Type: "application/cose+cbor"
       Payload:
       {
         "access_token" : b64'SlAV32hkKG ...
          (remainder of access token omitted for brevity)',
         "profile" : "coap_oscore",
         "expires_in" : "3600",
         "cnf" : {
           "COSE_Key" : {
             "kty" : "Symmetric",
             "alg" : "AES-CCM-16-64-128",
             "clientId" : b64'qA',
             "serverId" : b64'Qg',
             "k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
           }
         }
       }

       Figure 1: Example AS response with OSCORE parameters.

   Figure 2 shows an example CWT, containing the necessary OSCORE
   parameters in the 'cnf' claim, in CBOR diagnostic notation without
   tag and value abbreviations.

     {
       "aud" : "tempSensorInLivingRoom",
       "iat" : "1360189224",
       "exp" : "1360289224",
       "scope" :  "temperature_g firmware_p",
       "cnf" : {
         "COSE_Key" : {
           "kty" : "Symmetric",
           "alg" : "AES-CCM-16-64-128",
           "clientId" : b64'Qg',
           "serverId" : b64'qA',
           "k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
       }
     }

        Figure 2: Example CWT with OSCORE parameters.

   Note that the proof-of-possession required to bind the access token
   to the client is implicitly performed by generating the shared OSCORE
   context using the pop-key as master secret, both on the client and RS
   side.  An attacker using a stolen token will not be able to generate
   a valid OSCORE context and thus not be able to prove possession of
   the pop-key.



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3.  Client to Authorization Server

   As specified in the ACE framework (section 5.6 of
   [I-D.ietf-ace-oauth-authz]), the Client and AS can also use CoAP
   instead of HTTP to communicate via the token resource.  This section
   specifies how to use OSCORE between Client and AS together with CoAP.
   The use of OSCORE for this communication is OPTIONAL in this profile,
   other security protocols (such as DTLS) MAY be used instead.

   The client and the AS are expected to have pre-established security
   contexts in place.  How these security contexts are established is
   out of scope for this profile.  Furthermore the client and the AS
   communicate using OSCORE ([I-D.ietf-core-object-security]) through
   the introspection resource as specified in section 5.7 of
   [I-D.ietf-ace-oauth-authz].

4.  Resource Server to Authorization Server

   As specified in the ACE framework (section 5.7 of
   [I-D.ietf-ace-oauth-authz]), the RS and AS can also use CoAP instead
   of HTTP to communicate via the introspection resource.  This section
   specifies how to use OSCORE between RS and AS.  The use of OSCORE for
   this communication is OPTIONAL in this profile, other security
   protocols (such as DTLS) MAY be used instead.

   The RS and the AS are expected to have pre-established security
   contexts in place.  How these security contexts are established is
   out of scope for this profile.  Furthermore the RS and the AS
   communicate using OSCORE ([I-D.ietf-core-object-security]) through
   the introspection resource as specified in section 5.7 of
   [I-D.ietf-ace-oauth-authz].

5.  Security Considerations

   This document specifies a profile for the Authentication and
   Authorization for Constrained Environments (ACE) framework
   [I-D.ietf-ace-oauth-authz].  Thus the general security considerations
   from the framework also apply to this profile.

   Furthermore the general security considerations of OSCORE
   [I-D.ietf-core-object-security] also apply to this specific use of
   the OSCORE protocol.

   OSCORE is designed to secure point-to-point communication, providing
   a secure binding between the request and the response(s).  Thus the
   basic OSCORE protocol is not intended for use in point-to-multipoint
   communication (e.g. multicast, publish-subscribe).  Implementers of
   this profile should make sure that their usecase corresponds to the



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   expected use of OSCORE, to prevent weakening the security assurances
   provided by OSCORE.

6.  Privacy Considerations

   TBD.

7.  IANA Considerations

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

   The following registration is done for the ACE OAuth Profile Registry
   following the procedure specified in section 8.6 of
   [I-D.ietf-ace-oauth-authz]:

   o  Profile name: coap_oscore
   o  Profile Description: Profile for using OSCORE to secure
      communication between constrained nodes using the Authentication
      and Authorization for Constrained Environments framework.
   o  Profile ID: TBD (value between 1 and 255)
   o  Change Controller: IESG
   o  Specification Document(s): [[this specification]]

   The following registrations are done for the COSE Key Common
   Parameter Registry specified in section 16.5 of [RFC8152]:

   o  Name: clientId
   o  Label: TBD1 (value between 1 and 255)
   o  CBOR Type: bstr
   o  Value Registry: N/A
   o  Description: Identifies the client in an OSCORE context
   o  Reference: [[this specification]]

   o  Name: serverId
   o  Label: TBD2 (value between 1 and 255)
   o  Value Type: bstr
   o  Value Registry: N/A
   o  Description: Identifies the server in an OSCORE context
   o  Reference: [[this specification]]

   o  Name: kdf
   o  Label: TBD3 (value between 1 and 255)
   o  Value Type: bstr
   o  Value Registry: COSE Algorithms registry
   o  Description: Identifies the KDF algorithm to be used in an OSCORE
      context



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   o  Reference: [[this specification]]

   o  Name: slt
   o  Label: TBD4 (value between 1 and 255)
   o  Value Type: bstr
   o  Value Registry: N/A
   o  Description: Identifies the master salt of to be used in an OSCORE
      context
   o  Reference: [[this specification]]

8.  References

8.1.  Normative References

   [I-D.ietf-ace-oauth-authz]
              Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
              H. Tschofenig, "Authentication and Authorization for
              Constrained Environments (ACE) using the OAuth 2.0
              Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-12
              (work in progress), May 2018.

   [I-D.ietf-core-object-security]
              Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security for Constrained RESTful Environments
              (OSCORE)", draft-ietf-core-object-security-13 (work in
              progress), June 2018.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [RFC8152]  Schaad, J., "CBOR Object Signing and Encryption (COSE)",
              RFC 8152, DOI 10.17487/RFC8152, July 2017,
              <https://www.rfc-editor.org/info/rfc8152>.

   [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/info/rfc8392>.







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8.2.  Informative References

   [I-D.gerdes-ace-dcaf-authorize]
              Gerdes, S., Bergmann, O., and C. Bormann, "Delegated CoAP
              Authentication and Authorization Framework (DCAF)", draft-
              gerdes-ace-dcaf-authorize-04 (work in progress), October
              2015.

   [I-D.ietf-ace-actors]
              Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
              architecture for authorization in constrained
              environments", draft-ietf-ace-actors-06 (work in
              progress), November 2017.

   [I-D.selander-ace-cose-ecdhe]
              Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
              Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace-
              cose-ecdhe-08 (work in progress), March 2018.

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

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

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

Appendix A.  Profile Requirements

   This section lists the specifications on this profile based on the
   requirements on the framework, as requested in Appendix C of
   [I-D.ietf-ace-oauth-authz].

   o  (Optional) discovery process of how the client finds the right AS
      for an RS it wants to send a request to: Not specified
   o  communication protocol the client and the RS must use: CoAP
   o  security protocol the client and RS must use: OSCORE
   o  how the client and the RS mutually authenticate: Implicitly by
      possession of a common OSCORE security context



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   o  Content-format of the protocol messages: "application/cose+cbor"
   o  proof-of-possession protocol(s) and how to select one; which key
      types (e.g. symmetric/asymmetric) supported: OSCORE algorithms;
      pre-established symmetric keys
   o  profile identifier: coap_oscore
   o  (Optional) how the RS talks to the AS for introspection: HTTP/CoAP
      (+ TLS/DTLS/OSCORE)
   o  how the client talks to the AS for requesting a token: HTTP/CoAP
      (+ TLS/DTLS/OSCORE)
   o  how/if the /authz-info endpoint is protected: Security protocol
      above
   o  (Optional)other methods of token transport than the /authz-info
      endpoint: no

Appendix B.  Using the pop-key with EDHOC (EDHOC+OSCORE)

   EDHOC specifies an authenticated Diffie-Hellman protocol that allows
   two parties to use CBOR [RFC7049] and COSE in order to establish a
   shared secret key with perfect forward secrecy.  The use of Ephemeral
   Diffie-Hellman Over COSE (EDHOC) [I-D.selander-ace-cose-ecdhe] in
   this profile in addition to OSCORE, provides perfect forward secrecy
   (PFS) and the initial proof-of-possession, which ties the proof-of-
   possession key to an OSCORE security context.

   If EDHOC is used together with OSCORE, and the pop-key (symmetric or
   asymmetric) is used to authenticate the messages in EDHOC, then the
   AS MUST provision the following data, in response to the access token
   request:

   o  a symmetric or public key (associated to the RS)
   o  a key identifier;

   How these parameters are communicated depends on the type of key
   (asymmetric or symmetric).  Moreover, the AS MUST signal the use of
   OSCORE + EDHOC with the 'profile' parameter set to
   "coap_oscore_edhoc" and follow Appendix B to derive the security
   context to run OSCORE.

   Note that in the case described in this section, the 'expires_in'
   parameter, defined in Section 4.2.2. of [RFC6749] defines the
   lifetime in seconds of both the access token and the shared secret.
   After expiration, C MUST acquire a new access token from the AS, and
   run EDHOC again, as specified in this section








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B.1.  Using Asymmetric Keys

   In case of an asymmetric key, C MUST communicate its own asymmetric
   key to the AS in the 'cnf' parameter of the access token request, as
   specified in Section 5.6.1 of [I-D.ietf-ace-oauth-authz]; the AS MUST
   communicate the RS's public key to C in the response, in the 'rs_cnf'
   parameter, as specified in Section 5.6.1 of
   [I-D.ietf-ace-oauth-authz].  Note that the RS's public key MUST
   include a 'kid' parameter, and that the value of the 'kid' MUST be
   included in the access token, to let the RS know which of its public
   keys C used.  If the access token is a CWT [RFC8392], the key
   identifier MUST be placed directly in the 'cnf' structure (if the key
   is only referenced).

   Figure 3 shows an example of such a request in CBOR diagnostic
   notation without tag and value abbreviations.

   Header: POST (Code=0.02)
   Uri-Host: "server.example.com"
   Uri-Path: "token"
   Content-Type: "application/cose+cbor"
   Payload:
   {
    "grant_type" : "client_credentials",
    "cnf" : {
      "COSE_Key" : {
        "kid" : "client_key"
        "kty" : "EC",
        "crv" : "P-256",
        "x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
        "y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
      }
    }
   }

   Figure 3: Example access token request (OSCORE+EDHOC, asymmetric).

   Figure 4 shows an example of a corresponding response in CBOR
   diagnostic notation without tag and value abbreviations.












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     Header: Created (Code=2.01)
     Content-Type: "application/cose+cbor"
     Payload:
     {
       "access_token" : b64'SlAV32hkKG ...
        (contains "kid" : "client_key")',
       "profile" : "coap_oscore_edhoc",
       "expires_in" : "3600",
       "cnf" : {
         "COSE_Key" : {
           "kid" : "server_key"
           "kty" : "EC",
           "crv" : "P-256",
           "x" : b64'cGJ90UiglWiGahtagnv8usWxHK2PmfnHKwXPS54m0kT',
           "y" : b64'reASjpkttcsz+1rb7btKLv8EX4IBOL+C3BttVivg+lS'
        }
       }
     }

   Figure 4: Example AS response (EDHOC+OSCORE, asymmetric).

B.2.  Using Symmetric Keys

   In the case of a symmetric key, the AS MUST communicate the key to
   the client in the 'cnf' parameter of the access token response, as
   specified in Section 5.6.2. of [I-D.ietf-ace-oauth-authz].  AS MUST
   also select a key identifier, that MUST be included as the 'kid'
   parameter either directly in the 'cnf' structure, as in figure 4 of
   [I-D.ietf-ace-oauth-authz], or as the 'kid' parameter of the
   COSE_key, as in figure 6 of [I-D.ietf-ace-oauth-authz].

   Figure 5 shows an example of the necessary parameters in the AS
   response to the access token request when EDHOC is used.  The example
   uses CBOR diagnostic notation without tag and value abbreviations.

















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     Header: Created (Code=2.01)
     Content-Type: "application/cose+cbor"
     Payload:
     {
       "access_token" : b64'SlAV32hkKG ...
        (remainder of access token omitted for brevity)',
       "profile" : "coap_oscore_edhoc",
       "expires_in" : "3600",
       "cnf" : {
         "COSE_Key" : {
           "kty" : "Symmetric",
           "kid" : b64'5tOS+h42dkw',
           "k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
         }
       }
     }

   Figure 5: Example AS response (EDHOC+OSCORE, symmetric).

   In both cases, the AS MUST also include the same key identifier as
   'kid' parameter in the access token metadata.  If the access token is
   a CWT [RFC8392], the key identifier MUST be placed inside the 'cnf'
   claim as 'kid' parameter of the COSE_Key or directly in the 'cnf'
   structure (if the key is only referenced).

   Figure 6 shows an example CWT containing the necessary EDHOC+OSCORE
   parameters in the 'cnf' claim, in CBOR diagnostic notation without
   tag and value abbreviations.

   {
     "aud" : "tempSensorInLivingRoom",
     "iat" : "1360189224",
     "exp" : "1360289224",
     "scope" :  "temperature_g firmware_p",
     "cnf" : {
       "COSE_Key" : {
         "kty" : "Symmetric",
         "kid" : b64'5tOS+h42dkw',
         "k" : b64'+a+Dg2jjU+eIiOFCa9lObw'
     }
   }

     Figure 6: Example CWT with EDHOC+OSCORE, symmetric case.

   All other parameters defining OSCORE security context are derived
   from EDHOC message exchange, including the master secret (see
   Appendix C.2 of [I-D.selander-ace-cose-ecdhe]).




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B.3.  Processing

   To provide forward secrecy and mutual authentication in the case of
   pre-shared keys, pre-established raw public keys or with X.509
   certificates it is RECOMMENDED to use EDHOC
   [I-D.selander-ace-cose-ecdhe] to generate the keying material.  EDHOC
   MUST be used as defined in Appendix C of
   [I-D.selander-ace-cose-ecdhe], with the following additions and
   modifications.

   The first EDHOC message is sent after the access token is posted to
   the /authz-info resource of the RS as specified in Section 5.8.1 of
   [I-D.ietf-ace-oauth-authz].  Then the EDHOC message_1 is sent and the
   EDHOC protocol is initiated [I-D.selander-ace-cose-ecdhe]).

   Before the RS continues with the EDHOC protocol and responds to this
   token submission request, additional verifications on the access
   token are done: the RS SHALL process the access token according to
   [I-D.ietf-ace-oauth-authz].  If the token is valid then the RS
   continues processing EDHOC following Appendix C of
   [I-D.selander-ace-cose-ecdhe], otherwise it discontinues EDHOC and
   responds with the error code as specified in
   [I-D.ietf-ace-oauth-authz].

   o  In case the EDHOC verification fails, the RS MUST return an error
      response to the client with code 4.01 (Unauthorized).
   o  If RS has an access token for C but not for the resource that C
      has requested, RS MUST reject the request with a 4.03 (Forbidden).
   o  If RS has an access token for C but it does not cover the action C
      requested on the resource, RS MUST reject the request with a 4.05
      (Method Not Allowed).
   o  If all verifications above succeeds, further communication between
      client and RS is protected with OSCORE, including the RS response
      to the OSCORE request.

   In the case of EDHOC being used with symmetric keys, the protocol in
   Section 5 of [I-D.selander-ace-cose-ecdhe] MUST be used.  If the key
   is asymmetric, the RS MUST also use an asymmetric key for
   authentication.  This key is known to the client through the access
   token response (see Section 5.6.2 of [I-D.ietf-ace-oauth-authz]).  In
   this case the protocol in Section 4 of [I-D.selander-ace-cose-ecdhe]
   MUST be used.

   Figure 7 illustrates the message exchanges for using OSCORE+EDHOC
   (step C in figure 1 of [I-D.ietf-ace-oauth-authz]).






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                    Resource
           Client    Server
           |          |
           |          |
           +--------->| Header: POST (Code=0.02)
           | POST     | Uri-Path:"authz-info"
           |          | Content-Type: application/cbor
           |          | Payload: access token
           |          |
           |          |
           +--------->| Header: POST (Code=0.02)
           |   POST   | Uri-Path: "/.well-known/edhoc"
           |          | Content-Type: application/edhoc
           |          | Payload: EDHOC message_1
           |          |
           |<---------+ Header: 2.04 Changed
           |   2.04   | Content-Type: application/edhoc
           |          | Payload: EDHOC message_2
           |          |
           +--------->| Header: POST (Code=0.02)
           |   POST   | Uri-Path: "/.well-known/edhoc"
           |          | Content-Type: application/edhoc
           |          | Payload: EDHOC message_3
           |          |
           |<---------+ Header: 2.04 Changed
           |   2.04   |
           |          |
    start of protected communication
           |          |
           +--------->| CoAP request +
           |  OSCORE  | Object-Security option
           | request  |
           |          |
           |<---------+ CoAP response +
           |  OSCORE  | Object-Security option
           | response |
           |          |

   Figure 7: Access token and key establishment with EDHOC

Acknowledgments

   The authors wish to thank Jim Schaad, Goeran Selander and Marco
   Tiloca for the input on this memo.  The error responses specified in
   Appendix B.3 were originally specified by Gerdes et al. in
   [I-D.gerdes-ace-dcaf-authorize].





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Authors' Addresses

   Ludwig Seitz
   RISE SICS AB
   Scheelevagen 17
   Lund  22370
   Sweden

   Email: ludwig.seitz@ri.se


   Francesca Palombini
   Ericsson AB
   Farogatan 6
   Kista  SE-16480 Stockholm
   Sweden

   Email: francesca.palombini@ericsson.com


   Martin Gunnarsson
   RISE SICS AB
   Scheelevagen 17
   Lund  22370
   Sweden

   Email: martin.gunnarsson@ri.se


   Goeran Selander
   Ericsson AB
   Farogatan 6
   Kista  SE-16480 Stockholm
   Sweden

   Email: goran.selander@ericsson.com















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