ACE Working Group                                           F. Palombini
Internet-Draft                                               Ericsson AB
Intended status: Standards Track                                L. Seitz
Expires: April May 11, 2019                                       RISE SICS AB
                                                             G. Selander
                                                             Ericsson AB
                                                           M. Gunnarsson
                                                            RISE SICS AB
                                                         October 8,
                                                        November 7, 2018

 OSCORE profile of the Authentication and Authorization for Constrained
                         Environments Framework
                    draft-ietf-ace-oscore-profile-04
                    draft-ietf-ace-oscore-profile-05

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

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   This Internet-Draft will expire on April May 11, 2019.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Client-AS Communication . . . . . . . . . . . . . . . . . . .   5
     3.1.  C-to-AS: POST /token  . . . . . to token endpoint . . . . . . . . . . . . .   5   6
     3.2.  AS-to-C: Access Token . . . . . . . . . . . . . . . . . .   7
   4.  Client-RS Communication
       3.2.1.  OSCORE_Security_Context Object  . . . . . . . . . . .  10
   4.  Client-RS Communication . . . . . . . . . . . .  11
     4.1.  C-to-RS: POST /authz-info . . . . . . .  13
     4.1.  C-to-RS: POST to authz-info endpoint  . . . . . . . . . .  12  13
     4.2.  RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . .  12  14
     4.3.  OSCORE Setup  . . . . . . . . . . . . . . . . . . . . . .  13  15
     4.4.  Access rights verification  . . . . . . . . . . . . . . .  15  16
   5.  Secure Communication with AS  . . . . . . . . . . . . . . . .  15  17
   6.  Discarding the Security Context . . . . . . . . . . . . . . .  17
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  18
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  16
   8.  18
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   9.  References  . .  19
     9.1.  ACE OAuth Profile Registry  . . . . . . . . . . . . . . .  19
     9.2.  OSCORE Security Context Parameters Registry . . . . . . .  19
     9.3.  CWT Confirmation Methods Registry .  18
     9.1.  Normative References . . . . . . . . . . .  20
     9.4.  JWT Confirmation Methods Registry . . . . . . .  18
     9.2.  Informative References . . . . .  20
     9.5.  Expert Review Instructions  . . . . . . . . . . . .  19
   Appendix A.  Profile Requirements . . .  20
   10. References  . . . . . . . . . . . . .  19
   Appendix B.  Using the pop-key with EDHOC (EDHOC+OSCORE) . . . .  20
     B.1.  Using Asymmetric Keys . . . . . . . .  21
     10.1.  Normative References . . . . . . . . . .  20
     B.2.  Using Symmetric Keys . . . . . . . .  21
     10.2.  Informative References . . . . . . . . . .  22
     B.3.  Processing . . . . . . .  22
   Appendix A.  Profile Requirements . . . . . . . . . . . . . . . .  24  23
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  25  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26  23

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].

   OSCORE specifies how to use CBOR Object Signing and Encryption (COSE)
   [RFC8152] to secure CoAP messages.  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].

   RESTful terminology follows HTTP [RFC7231].

   Terminology for entities in the architecture is defined in OAuth 2.0
   [RFC6749], 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.

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

2.  Protocol Overview

   This section gives an overview on how to use the ACE Framework
   [I-D.ietf-ace-oauth-authz] to secure the communication between a
   client and a resource server using OSCORE
   [I-D.ietf-core-object-security].  The parameters needed by the client
   to negotiate the use of this profile with the authorization server,
   as well as OSCORE setup process, are described in detail in the
   following sections.

   This profile requires a client to retrieve an access token from the
   AS for the resource it wants to access on a RS, using the token
   resource,
   endpoint, as specified in section 5.6 of [I-D.ietf-ace-oauth-authz].

   To determine the AS in charge of a resource hosted at the RS, the
   client C MAY send an initial Unauthorized Resource Request message to
   the RS.  The RS then denies the request and sends the address of its
   AS back to the client C as specified in section 5.1 of
   [I-D.ietf-ace-oauth-authz].  The access token request and response
   MUST be confidentiality-protected and ensure authenticity.  This
   profile RECOMMENDS the use of OSCORE between client and AS, but TLS
   or DTLS MAY be used additionally or instead.

   Once the client has retrieved the access token, it posts it to the RS
   using the authz-info resource endpoint and mechanisms specified in section 5.8
   of [I-D.ietf-ace-oauth-authz].  If the access token is valid, the RS
   replies to this request with a 2.01 (Created) response, which
   contains a nonce N1.

   After receiving the nonce N1, the client generates a nonce N2,
   concatenates it with N1 and sets the ID Context in its Security
   Context (see section 3 of [I-D.ietf-core-object-security]) to N1
   concatenated with N2.  The client then derives the complete Security
   Context from the ID Context plus the parameters received from the AS.

   Finally, the client sends a request protected with OSCORE to the RS.
   This message contains the ID Context value.  When receiving this
   request after the 2.01 (Created) response, the server extract the ID
   Context from it, verifies that the first part is equal to the nonce
   N1 it previously sent, and if so, sets its own ID Context and derives
   the complete Security Context from it plus the parameters received in
   the AS, following section 3.2 of [I-D.ietf-core-object-security].  If
   the request verifies, then this Security Context is stored in the
   server, and used in the response, and in further communications with
   the client, until token expiration.  Once the client receives a valid
   response, it does not continue to include the ID Context value in
   further requests.

   An overview

   The use of random nonces during the profile flow for exchange prevents the OSCORE profile is given reuse of
   AEAD nonces and keys with different messages, in
   Figure 1.

      C                            RS                   AS
      | [-- case of re-
   derivation of the Security Context both for Clients and Resource Request --->] |                     |
      |                            |                     |
      | [<----- AS Information --] |                     |
      |                            |                     |
      | ----- POST /token  ----------------------------> |
      |                            |                     |
      | <---------------------------- Access Token ----- |
      |                               + RS Information   |
      | ---- POST /authz-info
   Servers from an old non-expired access token, e.g. in case of re-boot
   of either the client or RS.  In fact, by using random nonces as ID
   Context, the request to the authz-info endpoint posting the same
   token results in a different Security Context, since Master Secret,
   Sender ID and Recipient ID are the same but ID Context is different.
   Therefore, the main requirement for the nonces is that they have a
   good amount of randomness.  If random nonces were not used, a node
   re-using a non-expired old token would be susceptible to on-path
   attackers provoking the creation of OSCORE messages using old AEAD
   keys and nonces.

   An overview of the profile flow for the OSCORE profile is given in
   Figure 1.

      C                            RS                   AS
      | [-- Resource Request --->] |                     |
      |                            |                     |
      | [<----- AS Information --] |                     |
      |                            |                     |
      | ----- POST /token  ----------------------------> |
      |                            |                     |
      | <---------------------------- Access Token ----- |
      |                               + RS Information   |
      | ---- POST /authz-info ---> |                     |
      |                            |                     |
      | <--- 2.01 Created (N1) --- |                     |
      |                            |                     |
    /Sec Context Derivation/       |                     |
      |                            |                     |
      | ---- OSCORE Request -----> |                     |
      |         (N1, N2)           |                     |
      |                            |                     |
      |               /Sec Context Derivation/           |
      |                            |                     |
      | <--- OSCORE Response ----- |                     |
      |                            |                     |
      | ---- OSCORE Request -----> |                     |
      |                            |                     |
      | <--- OSCORE Response ----- |                     |
      |           ...              |                     |

                        Figure 1: Protocol Overview

3.  Client-AS Communication

   The following subsections describe the details of the POST /token request
   and response to the token endpoint between client and AS.
   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, which the client
   receives from the AS in this exchange.  The proof-of-possession key
   (pop-key) provisioned from the AS MUST be used as master secret in
   OSCORE.

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

   The client-to-AS request is specified in Section 5.6.1 of
   [I-D.ietf-ace-oauth-authz].

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

   An example of such a request, in CBOR diagnostic notation without the
   tag and value abbreviations is reported in Figure 2

       Header: POST (Code=0.02)
       Uri-Host: "as.example.com"
       Uri-Path: "token"
       Content-Format: "application/ace+cbor"
       Payload:
       {
         "grant_type" : "client_credentials",
         "client_id" : "myclient",
         "req_aud" : "tempSensor4711",
         "scope" : "read"
        }

     Figure 2: Example C-to-AS POST /token request for an access token
                         bound to a symmetric key.

   If the client wants to update its access rights without changing an
   existing OSCORE Security Context, it MUST include in its POST /token request
   to the token endpoint a req_cnf object carrying the client's
   identifier (that was assigned in section Section 3.2) in the kid
   field.  This identifier can be used by the AS to determine the shared
   secret to construct the proof-of-possession token and therefore MUST
   identify a symmetric key that was previously generated by the AS as a
   shared secret for the communication between the client and the RS.
   The AS MUST verify that the received value identifies a proof-of-possession proof-of-
   possession key and token that have previously been issued to the
   requesting client.  If that is not the case, the Client-to-AS request
   MUST be declined with the error code 'invalid_request' as defined in
   Section 5.6.3 of [I-D.ietf-ace-oauth-authz].

   An example of such a request, in CBOR diagnostic notation without the
   tag and value abbreviations is reported in Figure 3
       Header: POST (Code=0.02)
       Uri-Host: "as.example.com"
       Uri-Path: "token"
       Content-Format: "application/ace+cbor"
       Payload:
       {
         "grant_type" : "client_credentials",
         "client_id" : "myclient",
         "req_aud" : "tempSensor4711",
         "scope" : "write",
         "req_cnf" : {
           "kid" : b64'Qg'
        }

   Figure 3: Example C-to-AS POST /token request for updating rights to
                 an access token bound to a symmetric key.

3.2.  AS-to-C: Access Token

   After verifying the POST /token request to the token endpoint and that the
   client is authorized to obtain an access token corresponding to its
   access token request, the AS responds as defined in section 5.6.2 of
   [I-D.ietf-ace-oauth-authz].  If the client request was invalid, or
   not authorized, the AS returns an error response as described in
   section 5.6.3 of [I-D.ietf-ace-oauth-authz].

   The AS signals 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 resource servers for which this
   access token is valid, and follow Section 4.3 to derive the security
   context to run OSCORE.

   Moreover, the AS MUST provision the following data:

   o  a master secret

   o  a client identifier

   o  a server identifier

   Additionally, the AS MAY provision the following data, in the same
   response.

   o  an AEAD algorithm

   o  an HKDF algorithm
   o  a salt

   o  a replay window type and size

   The master secret MUST be communicated as COSE_Key the 'ms' field in the
   OSCORE_Security_Context in the 'cnf' parameter of the access token
   response as defined in Section 3.2 of [I-D.ietf-ace-oauth-params].
   The OSCORE_Security_Context is a CBOR map object, defined in
   Section 3.2.1.  The AEAD algorithm MAY be included as the 'alg'
   parameter in the COSE_Key; OSCORE_Security_Context; the HKDF algorithm MAY be
   included as the 'hkdf' parameter of the COSE_Key and OSCORE_Security_Context, the
   salt MAY be included as the 'slt' 'salt' parameter of the COSE_Key
   COSCORE_Security_Context and the replay window type and size MAY be
   included as the 'rpl' of the OSCORE_Security_Context, as defined in
   Figure 4.
   Section 3.2.1.

   The same parameters MUST be included as metadata of the access token.
   This profile RECOMMENDS the use of CBOR web token (CWT) as specified
   in [RFC8392].  If the token is a CWT, the same COSE_Key
   OSCORE_Security_Context structure defined above MUST be placed in the
   'cnf' claim of this token.

   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  The
   client identifiers MUST be unique in the set of all clients on a
   single RS, and RS identifiers MUST be unique in the set of all RS for a certain AS.
   any given client.  Moreover, these MUST be included in the COSE_Key as header parameters,
   OSCORE_Security_Context, as defined in Figure 4. Section 3.2.1.

   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 in Section 4.3 C sets the Sender ID of its Security Context
   to the clientId value received and the Recipient ID to the serverId
   value, and RS does the opposite.

   +----------+-------+--------------+------------+-------------------+
   | 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    |
   |          |       |              |            |                   |
   | hkdf     | 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    |
   +----------+-------+--------------+------------+-------------------+

              Figure 4: Additional COSE_Key Common Parameters

   Figure 5 shows an example of such an AS response, in

   Figure 4 shows an example of such an AS response, in CBOR diagnostic
   notation without the tag and value abbreviations.

       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"
           "OSCORE_Security_Context" : {
             "kty" : "Symmetric",
             "alg" : "AES-CCM-16-64-128",
             "clientId" : b64'qA',
             "serverId" : b64'Qg',
             "k"
             "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw'
           }
         }
       }

   Figure 5: 4: Example AS-to-C Access Token response with OSCORE profile.

   Figure 6 5 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"
         "OSCORE_Security_Context" : {
           "kty" : "Symmetric",
           "alg" : "AES-CCM-16-64-128",
           "clientId" : b64'Qg',
           "serverId" : b64'qA',
           "k"
           "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw'
       }
     }

               Figure 6: 5: Example CWT with OSCORE parameters.

   If the client has requested an update to its access rights using the
   same OSCORE Security Context, which is valid and authorized, the AS
   MUST omit the 'cnf' parameter in the response, and MUST carry the
   client identifier in the 'kid' field in the 'cnf' parameter of the
   token.  The client identifier needs to be provisioned, in order for
   the RS to identify the previously generated Security Context.

   Figure 7 6 shows an example of such an AS response, in CBOR diagnostic
   notation without the tag and value abbreviations.

       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"
       }

   Figure 7: 6: Example AS-to-C Access Token response with OSCORE profile,
                       for update of access rights.

   Figure 8 7 shows an example CWT, containing the necessary OSCORE
   parameters in the 'cnf' claim for update of access rights, in CBOR
   diagnostic notation without tag and value abbreviations.

     {
       "aud" : "tempSensorInLivingRoom",
       "iat" : "1360189224",
       "exp" : "1360289224",
       "scope" :  "temperature_h",
       "cnf" : {
         "kid" : b64'Qg'
       }
     }

     Figure 8: 7: Example CWT with OSCORE parameters for update of access
                                  rights.

4.  Client-RS Communication

3.2.1.  OSCORE_Security_Context Object

   An OSCORE_Security_Context is an object that represents part or all
   of an OSCORE Security Context (Section 3.1 of
   [I-D.ietf-core-object-security]).  The following subsections describe OSCORE_Security_Context object
   can either be encoded as JSON or as CBOR.  In both cases, the details set of
   common parameters that can appear in an OSCORE_Security_Context
   object can be found in the POST /authz-
   info request and response between client IANA "OSCORE Security Context Parameters"
   registry (Section Section 9.2) and RS.  The client posts is defined below.  All parameters
   are optional.  Table 1 provides a summary of the token that includes the materials provisioned by the AS to the
   RS, which can then use Section 3.2 of [I-D.ietf-core-object-security]
   to derive a security context based on a shared master secret and a
   set
   OSCORE_Security_Context parameters defined in this section.

   +----------+-------+----------------+--------------+----------------+
   | name     | CBOR  | CBOR type      | registry     | description    |
   |          | label |                |              |                |
   +----------+-------+----------------+--------------+----------------+
   | ms       | 1     | bstr           |              | OSCORE Master  |
   |          |       |                |              | Secret value   |
   |          |       |                |              |                |
   | clientId | 2     | bstr           |              | OSCORE Sender  |
   |          |       |                |              | ID value of other parameters, established between client and server.

   Note that the proof-of-possession required to bind the access token
   to    |
   |          |       |                |              | the client is implicitly performed by generating client,    |
   |          |       |                |              | OSCORE         |
   |          |       |                |              | Recipient ID   |
   |          |       |                |              | value of the shared   |
   |          |       |                |              | server         |
   |          |       |                |              |                |
   | serverId | 3     | bstr           |              | OSCORE
   Security Context using Sender  |
   |          |       |                |              | ID value of    |
   |          |       |                |              | the pop-key as master secret, for both client
   and RS.  An attacker using a stolen token will not be able to
   generate a valid server,    |
   |          |       |                |              | OSCORE context and thus not be able to prove
   possession         |
   |          |       |                |              | Recipient ID   |
   |          |       |                |              | value of the pop-key.

4.1.  C-to-RS: POST /authz-info

   The client MUST use CoAP   |
   |          |       |                |              | client         |
   |          |       |                |              |                |
   | hkdf     | 4     | bstr / int     | COSE         | OSCORE HKDF    |
   |          |       |                | Algorithm    | value          |
   |          |       |                | Values       |                |
   |          |       |                | (HMAC-based) |                |
   |          |       |                |              |                |
   | alg      | 5     | tstr / int     | COSE         | OSCORE AEAD    |
   |          |       |                | Algorithm    | Algorithm      |
   |          |       |                | Values       | value          |
   |          |       |                | (AEAD)       |                |
   |          |       |                |              |                |
   | salt     | 6     | bstr           |              | OSCORE Master  |
   |          |       |                |              | Salt value     |
   |          |       |                |              |                |
   | rpl      | 7     | bstr / int     |              | OSCORE Replay  |
   |          |       |                |              | Window Type    |
   |          |       |                |              | and Size       |
   +----------+-------+----------------+--------------+----------------+

                Table 1: OSCORE_Security_Context Parameters

   ms:  This parameter identifies the Authorization Information resource
   as described in OSCORE Master Secret value, which
      is a byte string.  For more information about this field, see
      section 5.8.1 3.1 of [I-D.ietf-ace-oauth-authz] to
   transport the token to [I-D.ietf-core-object-security].  In JSON, the RS.

   The authz-info resource "ms"
      value is not protected, nor are a Base64 encoded byte string.  In CBOR, the responses from
   this resource.

   The access token MUST be encrypted, since it "ms" type is transferred from
      bstr, and has label 1.

   clientId:  This parameter identifies a client identifier as a byte
      string.  This identifier is used as OSCORE Sender ID in the client to
      and OSCORE Recipient ID in the RS over an unprotected channel.

   Note that server.  For more information about
      this field, see section 3.1 of [I-D.ietf-core-object-security].
      In JSON, the "clientID" value is a client may be required to re-POST Base64 encoded byte string.  In
      CBOR, the access token, since
   an RS may delete "clientID" type is bstr, and has label 2.

   serverId:  This parameter identifies a stored access token, due to lack of memory.

   Figure 9 shows an example server identifier as a byte
      string.  This identifier is used as OSCORE Sender ID in the client
      and OSCORE Recipient ID in the server.  For more information about
      this field, see section 3.1 of [I-D.ietf-core-object-security].
      In JSON, the request sent from "serverID" value is a Base64 encoded byte string.  In
      CBOR, the client to "serverID" type is bstr, and has label 3.

   hkdf:  This parameter identifies the
   RS.

         Header: POST (Code=0.02)
         Uri-Host: "rs.example.com"
         Uri-Path: "authz-info"
         Content-Format: "application/cwt"
         Payload:
          b64'SlAV32hkKG ...
            (remainder OSCORE HKDF Algorithm.  For more
      information about this field, see section 3.1 of access token omitted for brevity)',

       Figure 9: Example C-to-RS POST /authz-info request using CWT

4.2.  RS-to-C: 2.01 (Created)
      [I-D.ietf-core-object-security].  The RS values used MUST follow the procedures defined be
      registered in section 5.8.1 of
   [I-D.ietf-ace-oauth-authz]: the RS IANA "COSE Algorithms" registry and MUST verify the validity of be
      HMAC-based HKDF algorithms.  The value can either be the
   token.  If integer
      or the token is valid, text string value of the RS MUST respond to HMAC-based HKDF algorithm in the POST
   request with 2.01 (Created).  If
      "COSE Algorithms" registry.  In JSON, the token "hkdf" value is valid but a case-
      sensitive ASCII string or an integer.  In CBOR, the "hkdf" type is associated
   to claims that
      tstr or int, and has label 4.

   alg:  This parameter identifies the RS cannot process (e.g., an unknown scope) OSCORE AEAD Algorithm.  For more
      information about this field, see section 3.1 of
      [I-D.ietf-core-object-security] The values used MUST be registered
      in the RS IANA "COSE Algorithms" registry and MUST respond with a response code equivalent to be AEAD
      algorithms.  The value can either be the CoAP code 4.00
   (Bad Request).  In integer or the latter case text
      string value of the RS MAY provide additional
   information HMAC-based HKDF algorithm in the error response, in order to clarify what went
   wrong.  The RS MAY make an introspection request to validate the
   token before responding to the POST request to the authz-info
   resource.

   Additionally, "COSE
      Algorithms" registry.  In JSON, the RS MUST generate a nonce (N1) with "alg" value is a good amount of
   randomness, case-
      sensitive ASCII string or an integer.  In CBOR, the "alg" type is
      tstr or int, and include it in has label 5.

   salt:  This parameter identifies the payload OSCORE Master Salt value, which
      is a byte string.  For more information about this field, see
      section 3.1 of [I-D.ietf-core-object-security].  In JSON, the 2.01 (Created)
   response as
      "salt" value is a CBOR Base64 encoded byte string.  In CBOR, the "salt"
      type is bstr, and has label 6.

   repl:  This profile RECOMMENDS parameter is used to use a
   nonce of 64 bits.  The RS MUST store this nonce as long carry the OSCORE value, encoded as a
      bstr.  This parameter identifies the access
   token related to it OSCORE Replay Window Size and
      Type value, which is still valid.

   Note that, when using a byte string.  For more information about
      this profile, an identifier field, see section 3.1 of [I-D.ietf-core-object-security].
      In JSON, the token (e.g.,
   the cti for a CWT) "repl" value is not transported in a Base64 encoded byte string.  In
      CBOR, the payload of this request,
   as section 5.8.1 "repl" type is bstr, and has label 7.

   An example of [I-D.ietf-ace-oauth-authz] allows. JSON OSCORE_Security_Context is given in Figure 10 shows an example 8.

           "OSCORE_Security_Context" : {
             "alg" : "AES-CCM-16-64-128",
             "clientId" : b64'qA',
             "serverId" : b64'Qg',
             "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw'
           }

           Figure 8: Example JSON OSCORE_Security_Context object

   The CDDL grammar describing the CBOR OSCORE_Security_Context object
   is:

   OSCORE_Security_Context = {
       ? 1 => bstr,              ; ms
       ? 2 => bstr,              ; clientId
       ? 3 => bstr,              ; serverId
       ? 4 => tstr / int,        ; hkdf
       ? 5 => tstr / int,        ; alg
       ? 6 => bstr,              ; salt
       ? 7 => bstr / tstr        ; rpl
   }

4.  Client-RS Communication

   The following subsections describe the details of the POST request
   and response sent from the RS to the
   client.

         Header: Created (Code=2.01)
         Content-Format: "application/cbor"
         Payload:
          h'018a278f7faab55a',

            Figure 10: Example RS-to-C 2.01 (Created) response

   When receiving an updated access token with updated authorization
   information from the authz-info endpoint between client (see section Section 3.1), it is
   RECOMMENDED that the RS overwrites and RS.  The
   client posts the previous token, token that is only
   the latest authorization information in includes the token received materials provisioned by the RS
   is valid.  This simplifies for the RS
   AS to keep track the RS, which can then use Section 3.2 of authorization
   information for
   [I-D.ietf-core-object-security] to derive a given client.

   As specified in section 5.8.3 security context based on
   a shared master secret and a set of [I-D.ietf-ace-oauth-authz], the RS
   MUST notify the other parameters, established
   between client with an error response with code 4.01
   (Unauthorized) for any long running request before terminating and server.

   Note that the
   session, when proof-of-possession required to bind the access token expires.

4.3.  OSCORE Setup

   Once receiving the 2.01 (Created) response from the RS, following the
   POST /authz-info request,
   to the client MUST extract the nonce N1 from
   the CBOR byte string in is implicitly performed by generating the payload of shared OSCORE
   Security Context using the response.  The pop-key as master secret, for both client MUST
   generate itself a nonce (N2) with
   and RS.  An attacker using a good amount of randomness.  This
   profile RECOMMENDS stolen token will not be able to use
   generate a nonce valid OSCORE context and thus not be able to prove
   possession of 64 bits.  Then, the pop-key.

4.1.  C-to-RS: POST to authz-info endpoint

   The client MUST
   set use CoAP and the ID Context Authorization Information resource
   as described in section 5.8.1 of the Security Context created [I-D.ietf-ace-oauth-authz] to communicate
   with
   transport the RS token to the concatenation of N1 and N2, in RS.

   The authz-info endpoint is not protected, nor are the responses from
   this order: ID
   Context = N1 | N2, where | denotes byte string concatenation. resource.

   The
   client access token MUST set the Master Secret, Sender ID and Recipient ID be encrypted, since it is transferred from the parameters received from
   client to the AS in Section 3.2.  The RS over an unprotected channel.

   Note that a client MUST
   set may be required to re-POST the AEAD Algorithm, Master Salt, HKDF and Replay Window from access token, since
   an RS may delete a stored access token, due to lack of memory.

   Figure 9 shows an example of the
   parameters received request sent from the AS in Section 3.2, if present.  In case
   these parameters are omitted, client to the default values are used as
   described in section 3.2
   RS.

         Header: POST (Code=0.02)
         Uri-Host: "rs.example.com"
         Uri-Path: "authz-info"
         Content-Format: "application/cwt"
         Payload:
          b64'SlAV32hkKG ...
            (remainder of [I-D.ietf-core-object-security].  After
   that, the client access token omitted for brevity)',

       Figure 9: Example C-to-RS POST /authz-info request using CWT

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

   The RS MUST derive follow the complete Security Context following procedures defined in section 3.2.1 5.8.1 of [I-D.ietf-core-object-security].  From this point
   on,
   [I-D.ietf-ace-oauth-authz]: the client RS MUST use this Security Context to communicate with verify the
   RS when accessing validity of the resources as specified by
   token.  If the token is valid, the authorization
   information.

   The client then uses this Security Context to send requests to RS
   using OSCORE.  In MUST respond to the first POST
   request sent with 2.01 (Created).  If the token is valid but is associated
   to claims that the RS, RS cannot process (e.g., an unknown scope) the client RS
   MUST
   include the kid context, with value ID Context, i.e. N1 concatenated respond with N2.  The client needs to make sure the RS receives the kid
   context, possibly adding the kid context to later requests, until it
   receives a valid OSCORE response from code equivalent to the RS using CoAP code 4.00
   (Bad Request).  In the same Security
   Context.

   When latter case the RS receives this first OSCORE-protected request, it MUST
   extract the kid context from MAY provide additional
   information in the message first.  Then, it needs error response, in order to
   verify that clarify what went
   wrong.  The RS MAY make an introspection request to validate the first part of
   token before responding to the kid context corresponds POST request to the authz-info
   endpoint.

   Additionally, the RS MUST generate a nonce N1 it previously sent, (N1) with a good amount of
   randomness, and that include it is followed by in the payload of the 2.01 (Created)
   response as a non-zero-
   length CBOR byte string.  If that is verified, the  This profile RECOMMENDS to use a
   nonce of 64 bits.  The RS MUST set store this nonce as long as the ID
   Context access
   token related to it is still valid.

   Note that, when using this profile, an identifier of the kid context value.  Then, token (e.g.,
   the RS MUST set cti for a CWT) is not transported in the Master
   Secret, Sender ID and Recipient ID from payload of this request,
   as section 5.8.1 of [I-D.ietf-ace-oauth-authz] allows.

   Figure 10 shows an example of the parameters received response sent from the client in RS to the
   client.

         Header: Created (Code=2.01)
         Content-Format: "application/cbor"
         Payload:
          h'018a278f7faab55a',

            Figure 10: Example RS-to-C 2.01 (Created) response

   When receiving an updated access token in Section 4.1.  The RS with updated authorization
   information from the client (see section Section 3.1), it is
   RECOMMENDED that the RS overwrites the previous token, that is only
   the latest authorization information in the token received by the RS
   is valid.  This simplifies for the RS to keep track of authorization
   information for a given client.

   As specified in section 5.8.3 of [I-D.ietf-ace-oauth-authz], the RS
   MUST notify the client with an error response with code 4.01
   (Unauthorized) for any long running request before terminating the
   session, when the access token expires.

4.3.  OSCORE Setup

   Once receiving the 2.01 (Created) response from the RS, following the
   POST request to authz-info endpoint, the client MUST extract the
   nonce N1 from the CBOR byte string in the payload of the response.
   The client MUST generate itself a nonce (N2) with a good amount of
   randomness.  This profile RECOMMENDS to use a nonce of 64 bits.
   Then, the client MUST set the ID Context of the Security Context
   created to communicate with the RS to the concatenation of N1 and N2,
   in this order: ID Context = N1 | N2, where | denotes byte string
   concatenation.  The client MUST set the Master Secret, Sender ID and
   Recipient ID from the parameters received from the AS in Section 3.2.
   The client MUST set the AEAD Algorithm, Master Salt, HKDF and Replay
   Window from the parameters received from the client in the access token AS in Section 4.1, 3.2, if
   present.  In case these parameters are omitted, the default values
   are used as described in section 3.2 of
   [I-D.ietf-core-object-security].  After that, the RS client MUST derive
   the complete Security Context following section 3.2.1 of
   [I-D.ietf-core-object-security], and MUST associate
   [I-D.ietf-core-object-security].  From this Security
   Context with the authorization information from the access token.
   Then, point on, the RS client MUST delete the nonce N1 from memory.

   The RS then uses
   use this Security Context to verify communicate with the request and send
   responses to RS using OSCORE.  If OSCORE verification fails, error
   responses are used, when accessing
   the resources as specified in section 8 of
   [I-D.ietf-core-object-security].  Additionally, if OSCORE
   verification succeeds, by the verification of access rights is performed
   as described in section Section 4.4. authorization information.

   The RS MUST NOT use the client then uses this Security Context after to send requests to RS
   using OSCORE.  In the related token has expired, and first request sent to the RS, the client MUST
   respond
   include the kid context, with a unprotected 4.01 (Unauthorized) error message.

4.4.  Access rights verification value ID Context, i.e. N1 concatenated
   with N2.  The RS MUST follow client needs to make sure the procedures defined in section 5.8.2 of
   [I-D.ietf-ace-oauth-authz]: if an RS receives an OSCORE-protected
   request from a client, then it processes according to
   [I-D.ietf-core-object-security].  If OSCORE verification succeeds,
   and the target resource requires authorization, the RS retrieves kid
   context, possibly adding the
   authorization information kid context to later requests, until it
   receives a valid OSCORE response from the access token associated to RS using the same Security
   Context.  The

   When the RS then receives this first OSCORE-protected request, it MUST
   extract the kid context from the message first.  Then, it needs to
   verify that the authorization
   information covers first part of the resource kid context corresponds to the
   nonce N1 it previously sent, and that it is followed by a non-zero-
   length byte string.  If that is verified, the action requested.

   The response code RS MUST be 4.01 (Unauthorized) in case the client has
   not used set the Security ID
   Context associated with to the access token, or if
   RS has no valid access token for kid context value.  Then, the client.  If RS has an access
   token for MUST set the Master
   Secret, Sender ID and Recipient ID from the parameters received from
   the client but not for in the resource that was requested, access token in Section 4.1.  The RS MUST reject set the request with a 4.03 (Forbidden).  If RS has an access
   token for
   AEAD Algorithm, Master Salt, HKDF and Replay Window from the
   parameters received from the client but it does not cover in the action that was
   requested on access token in
   Section 4.1, if present.  In case these parameters are omitted, the
   default values are used as described in section 3.2 of
   [I-D.ietf-core-object-security].  After that, the resource, RS MUST reject derive the request with a 4.05
   (Method Not Allowed).

5.  Secure Communication
   complete Security Context following section 3.2.1 of
   [I-D.ietf-core-object-security], and MUST associate this Security
   Context with AS

   As specified in the ACE framework (section 5.7 of
   [I-D.ietf-ace-oauth-authz]), authorization information from the requesting entity (RS and/or client)
   and access token.
   Then, the AS communicates via RS MUST delete the introspection or token resource. nonce N1 from memory.

   The
   use of CoAP and OSCORE for this communication is RECOMMENDED in RS then uses this
   profile, other protocols (such as HTTP and DTLS or TLS) MAY be used
   instead.

   If OSCORE is used, the requesting entity and the AS are expected Security Context to
   have pre-established security contexts in place.  How these security
   contexts are established is out of scope for this profile.
   Furthermore verify the requesting entity request and the AS communicate send
   responses to RS using OSCORE.  If OSCORE
   ([I-D.ietf-core-object-security]) through the introspection resource verification fails, error
   responses are used, as specified in section 5.7 8 of [I-D.ietf-ace-oauth-authz] and through
   the token resource
   [I-D.ietf-core-object-security].  Additionally, if OSCORE
   verification succeeds, the verification of access rights is performed
   as specified described in section 5.6 of
   [I-D.ietf-ace-oauth-authz].

6. Section 4.4.  The RS MUST NOT use the
   Security Considerations

   This document specifies a profile for Context after the Authentication related token has expired, 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 MUST
   respond with a unprotected 4.01 (Unauthorized) error message.

4.4.  Access rights verification

   The RS MUST follow the general security considerations procedures defined in section 5.8.2 of OSCORE
   [I-D.ietf-core-object-security] also apply
   [I-D.ietf-ace-oauth-authz]: if an RS receives an OSCORE-protected
   request from a client, then it processes according to this specific use of
   the OSCORE protocol.
   [I-D.ietf-core-object-security].  If OSCORE is designed to secure point-to-point communication, providing
   a secure binding between the request verification succeeds,
   and the response(s).  Thus target resource requires authorization, 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 RS retrieves the
   expected use of OSCORE,
   authorization information from the access token associated to prevent weakening the security assurances
   provided by OSCORE.
   Security Context.  The use of nonces during RS then MUST verify that the OSCORE Setup Section 4.3 prevents authorization
   information covers the
   reuse of AEAD nonces in resource and the RS Security Context, action requested.

   The response code MUST be 4.01 (Unauthorized) in case the RS loses client has
   not used the Security Context associated with a client (e.g. in case of
   unplanned reboot) and receives a replayed the access token.  In fact, by
   using random nonces as ID Context, token, or if
   RS has no valid access token for the POST /auth-info request
   results in a different Security Context, since Master Secret, Sender
   ID and Recipient ID are client.  If RS has an access
   token for the same client but ID Context is different.
   Therefore, the main requirement not for the nonces is resource that they have was requested, RS
   MUST reject the request with a
   good amount of randomness.  Moreover, 4.03 (Forbidden).  If RS has an access
   token for the client echoes but it does not cover the nonce
   created by action that was
   requested on the RS, which verifies it before deriving resource, RS MUST reject the Security
   Context, and this protects against an adversary acting as request with a Man-in-
   the-Middle and substituting the nonce 4.05
   (Method Not Allowed).

5.  Secure Communication with AS

   As specified in transit from client to RS to
   provoke the creation ACE framework (section 5.7 of different Security Contexts in
   [I-D.ietf-ace-oauth-authz]), the client requesting entity (RS and/or client)
   and
   RS.

   This profiles recommends that the RS maintains a single access AS communicates via the introspection or token
   for a client. endpoint.  The
   use of multiple access tokens for a single client
   increases the strain on the resource server as it must consider every
   access token and calculate the actual permissions of the client.
   Also, tokens may contradict each other which may lead the server 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 client.

7.  Privacy Considerations

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

   As this document uses OSCORE, thus the privacy considerations from
   [I-D.ietf-core-object-security] apply here as well.

   An unprotected response to an unauthorized request may disclose
   information about the resource server and/or its existing
   relationship with the client.  It is advisable to include as little
   information as possible in an unencrypted response.  When an OSCORE
   Security Context already exists between the client and the resource
   server, more detailed information may be included.

   Note that some information might still leak after OSCORE is
   established, due to observable message sizes, the source, and the
   destination addresses.

8.  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 8.7 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 is RECOMMENDED in an OSCORE context
   o  Reference: [[this specification]]

   o  Name: hkdf
   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

   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]]

9.  References

9.1.  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-15
              (work in progress), September 2018.

   [I-D.ietf-ace-oauth-params]
              Seitz, L., "Additional OAuth Parameters for Authorization
              in Constrained Environments (ACE)", draft-ietf-ace-oauth-
              params-00 (work in progress), September 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-15 (work in
              progress), August 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>.

9.2.  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.selander-ace-cose-ecdhe]
              Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
              Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace-
              cose-ecdhe-10 (work in progress), September 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. this
   profile, other protocols (such as HTTP and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics DTLS or TLS) MAY be used
   instead.

   If OSCORE is used, the requesting entity 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 AS are expected to
   have pre-established security contexts in place.  How these security
   contexts are established is out of scope for this profile based on profile.
   Furthermore the
   requirements on requesting entity and the framework, AS communicate using OSCORE
   ([I-D.ietf-core-object-security]) through the introspection endpoint
   as requested specified in Appendix C section 5.7 of
   [I-D.ietf-ace-oauth-authz].

   o  (Optional) discovery process [I-D.ietf-ace-oauth-authz] and through
   the token endpoint as specified in section 5.6 of how
   [I-D.ietf-ace-oauth-authz].

6.  Discarding the Security Context

   There are a number of scenarios where a client finds the right AS
      for an or RS it wants needs to send a request to: Not specified
   o  communication protocol discard
   the client OSCORE security context, and acquire a new one.

   The client MUST discard the current security context associated with
   an RS must use: CoAP when:

   o  security protocol  the client and RS must use: OSCORE Sequence Number space ends.

   o  how  the client and access token associated with the RS mutually authenticate: Implicitly by
      possession of a common OSCORE security context expires.

   o  Content-format of  the protocol messages: "application/cose+cbor"
   o  proof-of-possession protocol(s) and how client receives a number of 4.01 Unauthorized responses 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 requests using the RS talks same security context.  The exact number
      needs to be specified by the AS for introspection: HTTP/CoAP
      (+ TLS/DTLS/OSCORE) application.

   o  how  the client talks client receives a new nonce in the 2.01 Created response (see
      Section 4.2) to a POST request to the authz-info endpoint, when
      re-posting a non-expired token associated to the AS for requesting existing context.

   The RS MUST discard the current security context associated with a token: HTTP/CoAP
      (+ TLS/DTLS/OSCORE)
   client when:

   o  how/if the /authz-info endpoint is protected: Security protocol
      above  Sequence Number space ends.

   o  (Optional)other methods of  Access token transport than the /authz-info
      endpoint: no

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

   EDHOC the context expires.

7.  Security Considerations

   This document 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) for the Authentication and
   Authorization for Constrained Environments (ACE) framework
   [I-D.ietf-ace-oauth-authz].  Thus the initial proof-of-possession, which ties general security considerations
   from the proof-of-
   possession key framework also apply to an OSCORE this profile.

   Furthermore the general security context.

   If EDHOC is used together with OSCORE, and considerations of OSCORE
   [I-D.ietf-core-object-security] also apply to this specific use of
   the pop-key (symmetric or
   asymmetric) OSCORE protocol.

   OSCORE is used designed to authenticate secure point-to-point communication, providing
   a secure binding between the messages in EDHOC, then request and the
   AS MUST provision response(s).  Thus the following data,
   basic OSCORE protocol is not intended for use in response point-to-multipoint
   communication (e.g. multicast, publish-subscribe).  Implementers of
   this profile should make sure that their usecase corresponds to the access token
   request:

   o  a symmetric or public key (associated
   expected use of OSCORE, to prevent weakening the RS)
   o  a key identifier;

   How these parameters are communicated depends on security assurances
   provided by OSCORE.

   Since the type use of key
   (asymmetric or symmetric).  Moreover, nonces in the AS MUST signal exchange guarantees uniqueness of AEAD
   keys and nonces even in case of re-boots, a good amount of randomness
   is required.  If that is not guaranteed, nodes are still susceptible
   to re-using nonces and keys, in case the Security Context is lost,
   and on-path attacker replaying messages.

   This profiles recommends that the RS maintains a single access token
   for a client.  The use of
   OSCORE + EDHOC with multiple access tokens for a single client
   increases the 'profile' parameter set to
   "coap_oscore_edhoc".

   Note that in strain on the case described in this section, resource server as it must consider every
   access token and calculate the 'expires_in'
   parameter, defined in Section 4.2.2. actual permissions of [RFC6749] defines the
   lifetime in seconds client.
   Also, tokens may contradict each other which may lead the server to
   enforce wrong permissions.  If one of both the access token and tokens expires
   earlier than others, the shared secret.
   After expiration, C MUST acquire a new resulting permissions may offer insufficient
   protection.  Developers should avoid using multiple access token from tokens for
   a client.

8.  Privacy Considerations

   This document specifies a profile for the AS, Authentication and
   run EDHOC again, as specified in this section

B.1.  Using Asymmetric Keys

   In case of an asymmetric key, C MUST communicate its own asymmetric
   key to
   Authorization for Constrained Environments (ACE) framework
   [I-D.ietf-ace-oauth-authz].  Thus the AS in general privacy considerations
   from the 'req_cnf' parameter of framework also apply to this profile.

   As this document uses OSCORE, thus the access token request, privacy considerations from
   [I-D.ietf-core-object-security] apply here as specified in Section 3.1 of [I-D.ietf-ace-oauth-params]; well.

   An unprotected response to an unauthorized request may disclose
   information about the AS
   MUST communicate resource server and/or its existing
   relationship with the RS's public key client.  It is advisable to C include as little
   information as possible in an unencrypted response.  When an OSCORE
   Security Context already exists between the response, in client and the
   'rs_cnf' parameter, as specified in Section 3.2 of
   [I-D.ietf-ace-oauth-params]. resource
   server, more detailed information may be included.

   Note that some information might still leak after OSCORE is
   established, due to observable message sizes, the RS's public key MUST
   include a 'kid' parameter, source, and that the value of the 'kid' MUST be
   included in the access token,
   destination addresses.

9.  IANA Considerations

   Note to let the RS know which RFC Editor: Please replace all occurrences of its public
   keys C used.  If "[[this
   specification]]" with the access token RFC number of this specification and delete
   this paragraph.

9.1.  ACE OAuth Profile Registry

   The following registration is a CWT [RFC8392], the key
   identifier MUST be placed directly in done for the 'cnf' structure (if ACE OAuth Profile Registry
   following the key
   is only referenced).

   Figure 3 shows an example of such a request procedure specified 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",
    "req_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 section 8.7 of a corresponding response in CBOR
   diagnostic notation without tag and value abbreviations.

     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
   [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 case of 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]]

9.2.  OSCORE Security Context Parameters Registry

   It is requested that IANA create a symmetric key, the AS MUST communicate the key new registry entitled "OSCORE
   Security Context Parameters" registry.  The registry is to be created
   as Expert Review Required.  Guidelines for the client experts is provided
   Section 9.5.  It should be noted that in additional to the 'cnf' parameter expert
   review, some portions of the access token response, registry require a specification,
   potentially on standards track, be supplied as
   specified in Section 3.2. of [I-D.ietf-ace-oauth-params]. well.

   The AS
   MUST also select columns of the registry are:

   name  This is a key identifier, descriptive name that enables easier reference to the
      item.  It is not used in the CBOR encoding.
   CBOR label  The value to be used to identify this algorithm.  Key map
      labels MUST be included unique.  The label can be a positive integer, a
      negative integer or a string.  Integer values between 0 and 255
      and strings of length 1 are designated as the 'kid'
   parameter Standards Track Document
      required.  Integer values from 256 to 65535 and strings of the COSE_key, length
      2 are designated as in figure 9 Specification Required.  Integer values of
   [I-D.ietf-ace-oauth-authz].

   Figure 5 shows an example
      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  This field contains the necessary parameters in CBOR type for the AS
   response field.
   registry  This field denotes the registry that values may come from,
      if one exists.
   description  This field contains a brief description for the field.
   specification  This contains a pointer to the access token request when EDHOC is used. public specification
      for the field if one exists

   This registry will be initially populated by the values in Table 1.
   The example
   uses CBOR diagnostic notation without tag specification column for all of these entries will be this
   document.

9.3.  CWT Confirmation Methods Registry

   The following registration is done for the CWT Confirmation Methods
   Registry following the procedure specified in section 7.2.1 of
   [I-D.ietf-ace-cwt-proof-of-possession]:

   o  Confirmation Method Name: "OSCORE_Security_Context"
   o  Confirmation Method Description: OSCORE_Security_Context carrying
      the OSCORE Security Context parameters
   o  Confirmation Key: TBD (value between 4 and value abbreviations.

     Header: Created (Code=2.01)
     Content-Type: "application/cose+cbor"
     Payload:
     {
       "access_token" : b64'SlAV32hkKG ...
        (remainder 255)
   o  Confirmation Value Type(s): map
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.2.1 of access token omitted [[this specification]]

9.4.  JWT Confirmation Methods Registry

   The following registration is done 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 JWT Confirmation Methods
   Registry following the same key identifier as
   'kid' parameter procedure specified in section 6.2.1 of
   [RFC7800]:

   o  Confirmation Method Value: "osc"
   o  Confirmation Method Description: OSCORE_Security_Context carrying
      the access token metadata.  If the access token OSCORE Security Context parameters
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.2.1 of [[this specification]]

9.5.  Expert Review Instructions

   The IANA registry established in this document is
   a CWT [RFC8392], defined as expert
   review.  This section gives some general guidelines for what the key identifier MUST
   experts should be placed inside the 'cnf'
   claim looking for, but they are being designated as 'kid' parameter of the COSE_Key or directly in
   experts for a reason so they should be given substantial latitude.

   Expert reviewers should take into consideration the 'cnf'
   structure (if following points:

   o  Point squatting should be discouraged.  Reviewers are encouraged
      to get sufficient information for registration requests to ensure
      that the key usage is only referenced).

   Figure 6 shows an example CWT containing the necessary EDHOC+OSCORE
   parameters in not going to duplicate one that is already
      registered and that the 'cnf' claim, point is likely to be used in CBOR diagnostic notation without
   tag deployments.
      The zones tagged as private use are intended for testing purposes
      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 closed environments, code points in other parameters defining OSCORE security context ranges should not be
      assigned for testing.
   o  Specifications are derived
   from EDHOC message exchange, including required for the master secret (see
   Appendix D.2 standards track range of point
      assignment.  Specifications should exist for specification
      required ranges, but early assignment before a specification is
      available is considered to be permissible.  Specifications are
      needed for the first-come, first-serve range if they are expected
      to be used outside of [I-D.selander-ace-cose-ecdhe]).

B.3.  Processing

   To provide forward secrecy and mutual authentication closed environments in an interoperable way.
      When specifications are not provided, the case of
   pre-shared keys, pre-established raw public keys or with X.509
   certificates it is RECOMMENDED description provided
      needs to use EDHOC
   [I-D.selander-ace-cose-ecdhe] have sufficient information to generate identify what the keying material.  EDHOC
   MUST point is
      being used for.
   o  Experts should take into account the expected usage of fields when
      approving point assignment.  The fact that there is a range for
      standards track documents does not mean that a standards track
      document cannot have points assigned outside of that 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 as defined in Appendix D on, and the number of
   [I-D.selander-ace-cose-ecdhe], with code points left that encode to that
      size.

10.  References

10.1.  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 following additions OAuth 2.0
              Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-16
              (work in progress), October 2018.

   [I-D.ietf-ace-oauth-params]
              Seitz, L., "Additional OAuth Parameters for Authorization
              in Constrained Environments (ACE)", draft-ietf-ace-oauth-
              params-00 (work in progress), September 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-15 (work in
              progress), August 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>.

10.2.  Informative References

   [I-D.ietf-ace-cwt-proof-of-possession]
              Jones, M., Seitz, L., Selander, G., Erdtman, S., and
   modifications.

   The first EDHOC message is sent after the access token is posted to
   the /authz-info resource of the RS as specified H.
              Tschofenig, "Proof-of-Possession Key Semantics for CBOR
              Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of-
              possession-04 (work in Section 5.8.1 of
   [I-D.ietf-ace-oauth-authz].  Then the EDHOC message_1 is sent progress), November 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>.

   [RFC7231]  Fielding, R., Ed. and the
   EDHOC protocol is initiated [I-D.selander-ace-cose-ecdhe]).

   Before the RS continues with the EDHOC protocol J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and responds to Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [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/info/rfc7800>.

Appendix A.  Profile Requirements

   This section lists the specifications on this
   token submission request, additional verifications profile based 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 D of
   [I-D.selander-ace-cose-ecdhe], otherwise it discontinues EDHOC and
   responds with
   requirements on the error code framework, as specified requested in Appendix C of
   [I-D.ietf-ace-oauth-authz].

   o  In case the EDHOC verification fails, the RS MUST return an error
      response to  (Optional) discovery process of how 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 finds the request with a 4.03 (Forbidden).
   o  If RS has an access token right AS
      for C but it does not cover the action C
      requested on the resource, an RS MUST reject the request with it wants to send a 4.05
      (Method request to: Not Allowed). specified
   o  If all verifications above succeeds, further  communication between protocol the client and RS is protected with OSCORE, including the RS response
      to must use: CoAP
   o  security protocol the client and RS must use: OSCORE request.

   In
   o  how the case of EDHOC being used with symmetric keys, client and the protocol in
   Section 5 RS mutually authenticate: Implicitly by
      possession of a common OSCORE security context
   o  Content-format of [I-D.selander-ace-cose-ecdhe] MUST be used.  If the protocol messages: "application/cose+cbor"
   o  proof-of-possession protocol(s) and how to select one; which key
   is asymmetric,
      types (e.g. symmetric/asymmetric) supported: OSCORE algorithms;
      pre-established symmetric keys
   o  profile identifier: coap_oscore
   o  (Optional) how the RS MUST also use an asymmetric key for
   authentication.  This key is known talks to the AS for introspection: HTTP/CoAP
      (+ TLS/DTLS/OSCORE)
   o  how the client through talks to the access
   token response (see Section 5.6.2 of [I-D.ietf-ace-oauth-authz]).  In
   this case AS for requesting a token: HTTP/CoAP
      (+ TLS/DTLS/OSCORE)
   o  how/if the authz-info endpoint is protected: Security 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]).

                    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
      above
   o  (Optional)other methods 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 transport than the authz-info
      endpoint: no

Acknowledgments

   The authors wish to thank Jim Schaad and Marco Tiloca for the input
   on this memo.

Authors' Addresses

   Francesca Palombini
   Ericsson AB

   Email: francesca.palombini@ericsson.com

   Ludwig Seitz
   RISE SICS AB
   Scheelevagen 17
   Lund  22370
   Sweden

   Email: ludwig.seitz@ri.se
   Goeran Selander
   Ericsson AB

   Email: goran.selander@ericsson.com

   Martin Gunnarsson
   RISE SICS AB
   Scheelevagen 17
   Lund  22370
   Sweden

   Email: martin.gunnarsson@ri.se