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Versions: (draft-seitz-ace-oscoap-profile) 00 01 02 03 04 05 06 07 08 09 10 11

ACE Working Group                                           F. Palombini
Internet-Draft                                               Ericsson AB
Intended status: Standards Track                                L. Seitz
Expires: December 20, 2020                                     Combitech
                                                             G. Selander
                                                             Ericsson AB
                                                           M. Gunnarsson
                                                                    RISE
                                                           June 18, 2020


 OSCORE profile of the Authentication and Authorization for Constrained
                         Environments Framework
                    draft-ietf-ace-oscore-profile-11

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 20, 2020.

Copyright Notice

   Copyright (c) 2020 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.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Client-AS Communication . . . . . . . . . . . . . . . . . . .   6
     3.1.  C-to-AS: POST to token endpoint . . . . . . . . . . . . .   6
     3.2.  AS-to-C: Access Token . . . . . . . . . . . . . . . . . .   8
       3.2.1.  OSCORE_Security_Context Object  . . . . . . . . . . .  13
   4.  Client-RS Communication . . . . . . . . . . . . . . . . . . .  17
     4.1.  C-to-RS: POST to authz-info endpoint  . . . . . . . . . .  18
       4.1.1.  The Nonce 1 Parameter . . . . . . . . . . . . . . . .  19
     4.2.  RS-to-C: 2.01 (Created) . . . . . . . . . . . . . . . . .  19
       4.2.1.  The Nonce 2 Parameter . . . . . . . . . . . . . . . .  21
     4.3.  OSCORE Setup  . . . . . . . . . . . . . . . . . . . . . .  21
     4.4.  Access rights verification  . . . . . . . . . . . . . . .  22
   5.  Secure Communication with AS  . . . . . . . . . . . . . . . .  22
   6.  Discarding the Security Context . . . . . . . . . . . . . . .  23
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  25
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
     9.1.  ACE OAuth Profile Registry  . . . . . . . . . . . . . . .  25
     9.2.  OAuth Parameters Registry . . . . . . . . . . . . . . . .  26
     9.3.  OAuth Parameters CBOR Mappings Registry . . . . . . . . .  26
     9.4.  OSCORE Security Context Parameters Registry . . . . . . .  26
     9.5.  CWT Confirmation Methods Registry . . . . . . . . . . . .  27
     9.6.  JWT Confirmation Methods Registry . . . . . . . . . . . .  28
     9.7.  Expert Review Instructions  . . . . . . . . . . . . . . .  28
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  29
     10.2.  Informative References . . . . . . . . . . . . . . . . .  30
   Appendix A.  Profile Requirements . . . . . . . . . . . . . . . .  30
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

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



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   token, bound to a key (the proof-of-possession key) to authorize its
   access to the resource server.  Note that this profile uses a
   symmetric-crypto-based scheme, where the symmetric secret is used as
   input material for keying material derivation.  In order to provide
   communication security, proof of possession, and server
   authentication the client and resource server use Object Security for
   Constrained RESTful Environments (OSCORE) [RFC8613].  Note that the
   proof of possession is not done by a dedicated protocol element, but
   rather occurs implicitly, based on knowledge of the security keying
   material.

   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", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Certain security-related terms such as "authentication",
   "authorization", "confidentiality", "(data) integrity", "message
   authentication code", 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.

   Concise Data Definition Language (CDDL) [RFC8610] is used in this
   specification.

   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.






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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 [RFC8613].  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.

   The RS maintains a collection of OSCORE Security Contexts with
   associated authorization information for all the clients that it is
   communicating with.  The authorization information is maintained as
   policy that's used as input to processing requests from those
   clients.

   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
   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 other
   protocols (such as TLS or DTLS) can be used as well.

   Once the client has retrieved the access token, it generates a nonce
   N1 and posts both the token and N1 to the RS using the authz-info
   endpoint and mechanisms specified in section 5.8 of
   [I-D.ietf-ace-oauth-authz] and Content-Format = application/ace+cbor.
   Note that, as specified in the ACE framework, the authz-info endpoint
   is not a protected resource, so there is no cryptographic protection
   to this request.

   If the access token is valid, the RS replies to this request with a
   2.01 (Created) response with Content-Format = application/ace+cbor,
   which contains a nonce N2 in a CBOR map.  Moreover, the server
   concatenates the input salt, N1, and N2 to obtain the Master Salt of
   the OSCORE Security Context (see section 3 of [RFC8613]).  The RS
   then derives the complete Security Context associated with the
   received token from it plus the parameters received in the access
   token from the AS, following section 3.2 of [RFC8613].

   After receiving the nonce N2, the client concatenates the input salt,
   N1 and N2 to obtain the Master Salt of the OSCORE Security Context
   (see section 3 of [RFC8613]).  The client then derives the complete




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   Security Context from the nonces plus the parameters received from
   the AS.

   Finally, the client sends a request protected with OSCORE to the RS.
   If the request verifies, the server stores the complete Security
   Context state that is ready for use in protecting messages, and uses
   it in the response, and in further communications with the client,
   until token expiration.  This Security Context is discarded when a
   token (whether the same or different) is used to successfully derive
   a new Security Context for that client.

   The use of random nonces during the exchange prevents the reuse of an
   AEAD nonces/key pair for two different messages.  This situation
   might occur when client and RS derive a new Security Context from an
   existing (non-expired) access token, as might occur when either party
   has just rebooted.  Instead, by using random nonces as part of the
   Master Salt, the request to the authz-info endpoint posting the same
   token results in a different Security Context, by OSCORE
   construction, since even though the Master Secret, Sender ID and
   Recipient ID are the same, the Master Salt is different (see
   Section 3.2.1 of [RFC8613]).  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.

   After the whole message exchange has taken place, the client can
   contact the AS to request an update of its access rights, sending a
   similar request to the token endpoint that also includes an
   identifier so that the AS can find the correct OSCORE security
   material it has previously shared with the Client.  This specific
   identifier, which [I-D.ietf-ace-oauth-authz] encodes as a bstr, is
   formatted to include two OSCORE identifiers, namely ID context and
   client ID, that are necessary to determine the correct OSCORE
   Security Context.

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













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


                        Figure 1: Protocol Overview

3.  Client-AS Communication

   The following subsections describe the details of the POST request
   and response to the token endpoint between client and AS.
   Section 3.2 of [RFC8613] 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)
   included in the response from the AS MUST be used as master secret in
   OSCORE.

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

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






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

   An example of such a request, with payload 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:
       {
         "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 request
   to the token endpoint a req_cnf object.  The req_cnf MUST include a
   kid field carrying a bstr-wrapped CBOR array object containing the
   client's identifier (assigned as discussed in Section 3.2) and the
   context identifier (if assigned as discussed in Section 3.2).  The
   CBOR array is defined in Figure 3, and follows the notation of
   [RFC8610].  These identifiers, together with other information such
   as audience, can be used by the AS to determine the shared secret
   bound to 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
   key that has 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].












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       kid_arr = [
         clientId,
         ?IdContext
         ]

       kid = bstr .cbor kid_arr


        Figure 3: CDDL Notation of kid for Update of Access Rights

   An example of such a request, with payload in CBOR diagnostic
   notation without the tag and value abbreviations is reported in
   Figure 4

       Header: POST (Code=0.02)
       Uri-Host: "as.example.com"
       Uri-Path: "token"
       Content-Format: "application/ace+cbor"
       Payload:
       {
         "req_aud" : "tempSensor4711",
         "scope" : "write",
         "req_cnf" : {
           "kid" : << ["myclient","contextid1"] >>
        }


   Figure 4: 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 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 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 resource servers for which this
   access token is valid, and follow Section 4.3 to derive the security
   context to run OSCORE.  Usually it is assumed that constrained
   devices will be pre-configured with the necessary profile, so that
   this kind of profile negotiation can be omitted.




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   Moreover, the AS MUST send the following data:

   o  a master secret

   o  a server identifier

   o  a client identifier

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

   o  a context identifier

   o  an AEAD algorithm

   o  an HKDF algorithm

   o  a salt

   o  the OSCORE version number

   The OSCORE_Security_Context is a CBOR map object, defined in
   Section 3.2.1.  This object is transported in the 'cnf' parameter of
   the access token response as defined in Section 3.2 of
   [I-D.ietf-ace-oauth-params], as the value of a field named 'osc',
   registered in Section 9.5 and Section 9.6.  The master secret MUST be
   communicated as the 'ms' field in the 'osc' field in the 'cnf'
   parameter of the access token response as defined in Section 3.2 of
   [I-D.ietf-ace-oauth-params].  The AEAD algorithm may be included as
   the 'alg' parameter in the OSCORE_Security_Context; the HKDF
   algorithm may be included as the 'hkdf' parameter of the
   OSCORE_Security_Context, a salt may be included as the 'salt'
   parameter of the OSCORE_Security_Context, and the OSCORE version
   number may be included as the 'version' parameter of the
   OSCORE_Security_Context.

   The same parameters MUST be included as part 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
   OSCORE_Security_Context structure defined above MUST be placed in the
   'osc' field of the 'cnf' claim of this token.  The access token MUST
   be encrypted, since it will be transferred from the client to the RS
   over an unprotected channel.

   The AS MUST also assign an identifier to the RS (serverId), and to
   the client (clientId), and MAY assign an identifier to the context
   (contextId).  These identifiers are then used as Sender ID, Recipient
   ID and ID Context in the OSCORE context as described in section 3.1



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   of [RFC8613].  Applications need to consider that these identifiers
   are sent in the clear and may reveal information about the endpoints,
   as mentioned in section 12.8 of [RFC8613].  The pair (client
   identifier, context identifier) MUST be unique in the set of all
   clients for a single RS.  Moreover, clientId, serverId and (when
   assigned) contextId MUST be included in the OSCORE_Security_Context,
   as defined in Section 3.2.1.

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

   Moreover, implementers of this specification need to be aware that if
   other authentication mechanisms are used to set up OSCORE between the
   same client and RS, that do not rely on AS assigning identifiers,
   collisions may happen and need to be mitigated.  A mitigation example
   would be to use distinct namespaces of identifiers for different
   authentication mechanisms.

   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.

   Figure 5 shows an example of an AS response, with payload in CBOR
   diagnostic notation without the tag and value abbreviations.  The
   access token has been truncated for readability.






















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       Header: Created (Code=2.01)
       Content-Type: "application/ace+cbor"
       Payload:
       {
         "access_token" : h'a5037674656d7053656e73 ...
          (remainder of access token (CWT) omitted for brevity)',
         "profile" : "coap_oscore",
         "expires_in" : "3600",
         "cnf" : {
           "osc" : {
             "alg" : "AES-CCM-16-64-128",
             "clientId" : h'00',
             "serverId" : h'01',
             "ms" : h'f9af838368e353e78888e1426bd94e6f'
           }
         }
       }


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

   Figure 6 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" : {
         "osc" : {
           "alg" : "AES-CCM-16-64-128",
           "clientId" : h'00',
           "serverId" : h'01',
           "ms" : h'f9af838368e353e78888e1426bd94e6f'
       }
     }


               Figure 6: Example CWT with OSCORE parameters.

   The same CWT token as in Figure 6, using the value abbreviations
   defined in [I-D.ietf-ace-oauth-authz] and [RFC8747] and encoded in
   CBOR is shown in Figure 7.






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   NOTE TO THE RFC EDITOR: before publishing, it should be checked (and
   in case fixed) that the values used below (which are not yet
   registered) are the final values registered in IANA.

   A5                                      # map(5)
      03                                   # unsigned(3)
      76                                   # text(22)
         74656D7053656E736F72496E4C6976696E67526F6F6D
                                           # "tempSensorInLivingRoom"
      06                                   # unsigned(6)
      1A 5112D728                          # unsigned(1360189224)
      04                                   # unsigned(4)
      1A 51145DC8                          # unsigned(1360289224)
      09                                   # unsigned(9)
      78 18                                # text(24)
         74656D70657261747572655F67206669726D776172655F70
                                           # "temperature_g firmware_p"
      08                                   # unsigned(8)
      A1                                   # map(1)
         04                                # unsigned(4)
         A4                                # map(4)
            05                             # unsigned(5)
            0A                             # unsigned(10)
            02                             # unsigned(2)
            46                             # bytes(6)
               636C69656E74                # "client"
            03                             # unsigned(3)
            46                             # bytes(6)
               736572766572                # "server"
            01                             # unsigned(1)
            50                             # bytes(16)
               F9AF838368E353E78888E1426BD94E6F
                                           # "\xF9\xAF\x83\x83h\xE3S\xE7
                                              \x88\x88\xE1Bk\xD9No"



               Figure 7: 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 and the context identifier (if it was set and
   included in the initial access token response by the AS) in the 'kid'
   field in the 'cnf' parameter of the token, with the same structure
   defined in Figure 3.  These identifiers need to be included in the
   token in order for the RS to identify the previously generated
   Security Context.



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   Figure 8 shows an example of such an AS response, with payload in
   CBOR diagnostic notation without the tag and value abbreviations.
   The access token has been truncated for readability.

       Header: Created (Code=2.01)
       Content-Type: "application/ace+cbor"
       Payload:
       {
         "access_token" : h'a5037674656d7053656e73 ...
          (remainder of access token (CWT) omitted for brevity)',
         "profile" : "coap_oscore",
         "expires_in" : "3600"
       }


   Figure 8: Example AS-to-C Access Token response with OSCORE profile,
                       for update of access rights.

   Figure 9 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" : h'43814100'
       }
     }


     Figure 9: Example CWT with OSCORE parameters for update of access
                                  rights.

3.2.1.  OSCORE_Security_Context Object

   An OSCORE_Security_Context is an object that represents part or all
   of an OSCORE Security Context, i.e., the local set of information
   elements necessary to carry out the cryptographic operations in
   OSCORE (Section 3.1 of [RFC8613]).  In particular, the
   OSCORE_Security_Context object is defined to be serialized and
   transported between nodes, as specified by this document, but can
   also be used by other specifications if needed.  The
   OSCORE_Security_Context object can either be encoded as a JSON object
   or as a CBOR map.  The set of common parameters that can appear in an
   OSCORE_Security_Context object can be found in the IANA "OSCORE



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   Security Context Parameters" registry (Section 9.4), defined for
   extensibility, and is specified below.  All parameters are optional.
   Table 1 provides a summary of the OSCORE_Security_Context parameters
   defined in this section.















































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   +-----------+-------+----------------+--------------+---------------+
   | name      | CBOR  | CBOR type      | registry     | description   |
   |           | label |                |              |               |
   +-----------+-------+----------------+--------------+---------------+
   | version   | 0     | int            |              | OSCORE        |
   |           |       |                |              | Version       |
   |           |       |                |              |               |
   | ms        | 1     | bstr           |              | OSCORE Master |
   |           |       |                |              | Secret value  |
   |           |       |                |              |               |
   | clientId  | 2     | bstr           |              | OSCORE Sender |
   |           |       |                |              | ID value of   |
   |           |       |                |              | the client,   |
   |           |       |                |              | OSCORE        |
   |           |       |                |              | Recipient ID  |
   |           |       |                |              | value of the  |
   |           |       |                |              | server        |
   |           |       |                |              |               |
   | serverId  | 3     | bstr           |              | OSCORE Sender |
   |           |       |                |              | ID value of   |
   |           |       |                |              | the server,   |
   |           |       |                |              | OSCORE        |
   |           |       |                |              | Recipient ID  |
   |           |       |                |              | value of the  |
   |           |       |                |              | client        |
   |           |       |                |              |               |
   | hkdf      | 4     | tstr / 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    |
   |           |       |                |              |               |
   | contextId | 7     | bstr           |              | OSCORE ID     |
   |           |       |                |              | Context value |
   +-----------+-------+----------------+--------------+---------------+

                Table 1: OSCORE_Security_Context Parameters

   version:  This parameter identifies the OSCORE Version number, which
      is an int.  For more information about this field, see section 5.4




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      of [RFC8613].  In JSON, the "version" value is an integer.  In
      CBOR, the "version" type is int, and has label 0.

   ms:  This parameter identifies the OSCORE Master Secret value, which
      is a byte string.  For more information about this field, see
      section 3.1 of [RFC8613].  In JSON, the "ms" value is a Base64
      encoded byte string.  In CBOR, the "ms" type is 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
      and OSCORE Recipient ID in the server.  For more information about
      this field, see section 3.1 of [RFC8613].  In JSON, the "clientId"
      value is a Base64 encoded byte string.  In CBOR, the "clientId"
      type is bstr, and has label 2.

   serverId:  This parameter identifies a server identifier as a byte
      string.  This identifier is used as OSCORE Sender ID in the server
      and OSCORE Recipient ID in the client.  For more information about
      this field, see section 3.1 of [RFC8613].  In JSON, the "serverId"
      value is a Base64 encoded byte string.  In CBOR, the "serverId"
      type is bstr, and has label 3.

   hkdf:  This parameter identifies the OSCORE HKDF Algorithm.  For more
      information about this field, see section 3.1 of [RFC8613].  The
      values used MUST be registered in the IANA "COSE Algorithms"
      registry and MUST be HMAC-based HKDF algorithms.  The value can
      either be the integer or the text string value of the HMAC-based
      HKDF algorithm in the "COSE Algorithms" registry.  In JSON, the
      "hkdf" value is a case-sensitive ASCII string or an integer.  In
      CBOR, the "hkdf" type is tstr or int, and has label 4.

   alg:  This parameter identifies the OSCORE AEAD Algorithm.  For more
      information about this field, see section 3.1 of [RFC8613] The
      values used MUST be registered in the IANA "COSE Algorithms"
      registry and MUST be AEAD algorithms.  The value can either be the
      integer or the text string value of the HMAC-based HKDF algorithm
      in the "COSE Algorithms" registry.  In JSON, the "alg" value is a
      case-sensitive ASCII string or an integer.  In CBOR, the "alg"
      type is tstr or int, and has label 5.

   salt:  This parameter identifies the OSCORE Master Salt value, which
      is a byte string.  For more information about this field, see
      section 3.1 of [RFC8613].  In JSON, the "salt" value is a Base64
      encoded byte string.  In CBOR, the "salt" type is bstr, and has
      label 6.





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   contextId:  This parameter identifies the security context as a byte
      string.  This identifier is used as OSCORE ID Context.  For more
      information about this field, see section 3.1 of [RFC8613].  In
      JSON, the "contextID" value is a Base64 encoded byte string.  In
      CBOR, the "contextID" type is bstr, and has label 7.

   An example of JSON OSCORE_Security_Context is given in Figure 10.

           "osc" : {
             "alg" : "AES-CCM-16-64-128",
             "clientId" : b64'AA',
             "serverId" : b64'AQ',
             "ms" : b64'+a+Dg2jjU+eIiOFCa9lObw'
           }


          Figure 10: Example JSON OSCORE_Security_Context object

   The CDDL grammar describing the CBOR OSCORE_Security_Context object
   is:

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

4.  Client-RS Communication

   The following subsections describe the details of the POST request
   and response to the authz-info endpoint between client and RS.  The
   client generates a nonce N1, and posts it together with the token
   that includes the materials (e.g., OSCORE parameters) received from
   the AS to the RS.  The RS then generates a nonce N2, and uses
   Section 3.2 of [RFC8613] to derive a security context based on a
   shared master secret and the two nonces, established between client
   and server.  The nonces are encoded as CBOR bstr if CBOR is used, and
   as Base64 string if JSON is used.  This security context is used to
   protect all future communication between client and RS using OSCORE,
   as long as the access token is valid.





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   Note that the RS and client authenticates themselves by generating
   the shared OSCORE Security Context using the pop-key as master
   secret.  An attacker posting a valid token to the RS will not be able
   to generate a valid OSCORE context and thus not be able to prove
   possession of the pop-key.

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

   The client MUST generate a nonce value very unlikely to have been
   previously used with the same input keying material.  This profile
   RECOMMENDS to use a 64-bit long random number as nonce's value.  The
   client MUST store the nonce N1 as long as the response from the RS is
   not received and the access token related to it is still valid.  The
   client MUST use CoAP and the Authorization Information resource as
   described in section 5.8.1 of [I-D.ietf-ace-oauth-authz] to transport
   the token and N1 to the RS.

   Note that the use of the payload and the Content-Format is different
   from what described in section 5.8.1 of [I-D.ietf-ace-oauth-authz],
   which only transports the token without any CBOR wrapping.  In this
   profile, the client MUST wrap the token and N1 in a CBOR map.  The
   client MUST use the Content-Format "application/ace+cbor" defined in
   section 8.14 of [I-D.ietf-ace-oauth-authz].  The client MUST include
   the access token using the "access_token" parameter and N1 using the
   'nonce1' parameter defined in Section 4.1.1.

   The authz-info endpoint is not protected, nor are the responses from
   this resource.

   The access token MUST be encrypted, since it is transferred from the
   client to the RS over an unprotected channel.

   Note that a client may be required to re-POST the access token in
   order to complete a request, since an RS may delete a stored access
   token (and associated Security Context) at any time, for example due
   to all storage space being consumed.  This situation is detected by
   the client when it receives an AS Request Creation Hints response.
   Reposting the same access token will result in deriving a new OSCORE
   Security Context to be used with the RS, as different nonces will be
   used.

   Figure 11 shows an example of the request sent from the client to the
   RS, with payload in CBOR diagnostic notation without the tag and
   value abbreviations.  The access token has been truncated for
   readability.






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         Header: POST (Code=0.02)
         Uri-Host: "rs.example.com"
         Uri-Path: "authz-info"
         Content-Format: "application/ace+cbor"
         Payload:
           {
             "access_token": h'a5037674656d7053656e73 ...
          (remainder of access token (CWT) omitted for brevity)',
             "nonce1": h'018a278f7faab55a'
           }


       Figure 11: Example C-to-RS POST /authz-info request using CWT

   If the client has already posted a valid token, has already
   established a security association with the RS, and wants to update
   its access rights, the client can do so by posting the new token
   (retrieved from the AS and containing the update of access rights) to
   the /authz-info endpoint.  The client MUST protect the request using
   the OSCORE Security Context established during the first token
   exchange.  The client MUST only send the access token in the payload,
   no nonce is sent.  After proper verification (see Section 4.2), the
   RS will replace the old token with the new one, maintaining the same
   Security Context.

4.1.1.  The Nonce 1 Parameter

   This parameter MUST be sent from the client to the RS, together with
   the access token, if the ace profile used is coap_oscore.  The
   parameter is encoded as a byte string for CBOR-based interactions,
   and as a string (Base64 encoded binary) for JSON-based interactions.
   This parameter is registered in Section 9.2.

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

   The RS MUST follow the procedures defined in section 5.8.1 of
   [I-D.ietf-ace-oauth-authz]: the RS must verify the validity of the
   token.  If the token is valid, the RS must respond to the POST
   request with 2.01 (Created).  If the token is valid but is associated
   to claims that the RS cannot process (e.g., an unknown scope), or if
   any of the expected parameters in the 'osc' is missing (e.g., any of
   the mandatory parameters from the AS), or if any parameters received
   in the 'osc' is unrecognized, the RS must respond with an error
   response code equivalent to the CoAP code 4.00 (Bad Request).  In the
   latter two cases, the RS may provide additional information 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 endpoint.



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   Additionally, the RS MUST generate a nonce N2 very unlikely to have
   been previously used with the same input keying material, and send it
   within the 2.01 (Created) response.  The payload of the 2.01
   (Created) response MUST be a CBOR map containing the 'nonce2'
   parameter defined in Section 4.2.1, set to N2.  This profile
   RECOMMENDS to use a 64-bit long random number as nonce's value.  The
   RS MUST use the Content-Format "application/ace+cbor" defined in
   section 8.14 of [I-D.ietf-ace-oauth-authz].

   Figure 12 shows an example of the response sent from the RS to the
   client, with payload in CBOR diagnostic notation without the tag and
   value abbreviations.

         Header: Created (Code=2.01)
         Content-Format: "application/ace+cbor"
         Payload:
           {
             "nonce2": h'25a8991cd700ac01'
           }


            Figure 12: Example RS-to-C 2.01 (Created) response

   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.

   If the RS receives the token in a OSCORE protected message, it means
   that the client is requesting an update of access rights.  The RS
   MUST discard any nonce in the request, if any was sent.  The RS MUST
   check that the "kid" of the "cnf" parameter of the new access token
   matches the OSCORE Security Context used to protect the message.  If
   that's the case, the RS MUST discard the old token and associate the
   new token to the Security Context identified by "kid".  The RS MUST
   respond with a 2.01 (Created) response protected with the same
   Security Context, with no payload.  If any verification fails, the RS
   MUST respond with a 4.01 (Unauthorized) error response.

   As specified in section 5.8.1 of [I-D.ietf-ace-oauth-authz], when
   receiving an updated access token with updated authorization
   information from the client (see 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.





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4.2.1.  The Nonce 2 Parameter

   This parameter MUST be sent from the RS to the Client if the ace
   profile used is coap_oscore.  The parameter is encoded as a byte
   string for CBOR-based interactions, and as a string (Base64 encoded
   binary) for JSON-based interactions.  This parameter is registered in
   Section 9.2

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 CBOR
   bstr nonce N2 from the 'nonce2' parameter in the CBOR map in the
   payload of the response.  Then, the client MUST set the Master Salt
   of the Security Context created to communicate with the RS to the
   concatenation of salt, N1, and N2, in this order: Master Salt =
   salt | N1 | N2, where | denotes byte string concatenation, where salt
   was received from the AS in Section 3.2, and where N1 and N2 are the
   two nonces encoded as CBOR bstr.  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, ID
   Context, HKDF, and OSCORE Version from the parameters received from
   the AS in Section 3.2, if present.  In case these parameters are
   omitted, the default values are used as described in sections 3.2 and
   5.4 of [RFC8613].  After that, the client MUST derive the complete
   Security Context following section 3.2.1 of [RFC8613].  From this
   point on, the client MUST use this Security Context to communicate
   with the RS when accessing the resources as specified by the
   authorization information.

   If any of the expected parameters is missing (e.g., any of the
   mandatory parameters from the AS, the client MUST stop the exchange,
   and MUST NOT derive the Security Context.  The client MAY restart the
   exchange, to get the correct security material.

   The client then uses this Security Context to send requests to RS
   using OSCORE.

   After sending the 2.01 (Created) response, the RS MUST set the Master
   Salt of the Security Context created to communicate with the client
   to the concatenation of salt, N1, and N2, in this order: Master Salt
   = salt | N1 | N2, where | denotes byte string concatenation, where
   salt was received from the AS in Section 4.2, and where N1 and N2 are
   the two nonces encoded as CBOR bstr.  The RS MUST set the Master
   Secret, Sender ID and Recipient ID from the parameters, received from
   the AS and forwarded by the client in the access token in Section 4.1
   after validation of the token as specified in Section 4.2.  The RS
   MUST set the AEAD Algorithm, ID Context, HKDF, and OSCORE Version



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   from the parameters received from the AS and forwarded by the client
   in the access token in Section 4.1 after validation of the token as
   specified in Section 4.2, if present.  In case these parameters are
   omitted, the default values are used as described in sections 3.2 and
   5.4 of [RFC8613].  After that, the RS MUST derive the complete
   Security Context following section 3.2.1 of [RFC8613], and MUST
   associate this Security Context with the authorization information
   from the access token.

   The RS then uses this Security Context to verify requests and send
   responses to C using OSCORE.  If OSCORE verification fails, error
   responses are used, as specified in section 8 of [RFC8613].
   Additionally, if OSCORE verification succeeds, the verification of
   access rights is performed as described in section Section 4.4.  The
   RS MUST NOT use the Security Context after the related token has
   expired, and MUST respond with a unprotected 4.01 (Unauthorized)
   error message to requests received that correspond to a Security
   Context with an expired token.

4.4.  Access rights verification

   The RS MUST follow 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 the RS processes it according to
   [RFC8613].  If OSCORE verification succeeds, and the target resource
   requires authorization, the RS retrieves the authorization
   information using the access token associated to the Security
   Context.  The RS then must verify that the authorization information
   covers the resource and the action requested.

   The response code must be 4.01 (Unauthorized) in case the client has
   a valid token associated with that Security Context, but the Security
   Context has not been used before, as the proof-of-possession in this
   profile is performed by both parties verifying that they have
   established the same Security Context.

5.  Secure Communication with AS

   As specified in the ACE framework (section 5.7 of
   [I-D.ietf-ace-oauth-authz]), the requesting entity (RS and/or client)
   and the AS communicates via the introspection or token endpoint.  The
   use of CoAP and OSCORE ([RFC8613]) for this communication is
   RECOMMENDED in 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 to
   have pre-established security contexts in place.  How these security
   contexts are established is out of scope for this profile.



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   Furthermore the requesting entity and the AS communicate through the
   introspection endpoint as specified in section 5.7 of
   [I-D.ietf-ace-oauth-authz] and through the token endpoint as
   specified in section 5.6 of [I-D.ietf-ace-oauth-authz].

6.  Discarding the Security Context

   There are a number of scenarios where a client or RS needs to discard
   the OSCORE security context, and acquire a new one.

   The client MUST discard the current Security Context associated with
   an RS when:

   o  the Sequence Number space ends.

   o  the access token associated with the context expires.

   o  the client receives a number of 4.01 Unauthorized responses to
      OSCORE requests using the same Security Context.  The exact number
      needs to be specified by the application.

   o  the 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 existing
      context.

   The RS MUST discard the current Security Context associated with a
   client when:

   o  the Sequence Number space ends.

   o  the access token associated with the context expires.

   o  the client has successfully replaced the current security context
      with a newer one by posting an access token to the unprotected
      /authz-info endpoint at the RS, e.g., by re-posting the same
      token, as specified in Section 4.1.

   Whenever one more access token is successfully posted to the RS, and
   a new Security Context is derived between the client and RS, messages
   in transit that were protected with the previous Security Context
   might not pass verification, as the old context is discarded.  That
   means that messages sent shortly before the client posts one more
   access token to the RS might not successfully reach the destination.
   Analogously, implementations may want to cancel CoAP observations at
   the RS registered before the Security Context is replaced, or
   conversely they will need to implement a mechanism to ensure that




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   those observation are to be protected with the newly derived Security
   Context.

7.  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 [RFC8613]
   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
   expected use of OSCORE, to prevent weakening the security assurances
   provided by OSCORE.

   Since the use of nonces in the exchange guarantees uniqueness of AEAD
   keys and nonces, it is REQUIRED that nonces are not reused with the
   same input keying material even in case of re-boots.  This document
   RECOMMENDS the use of 64 bit random nonces.  Considering the birthday
   paradox, the average collision for each nonce will happen after 2^32
   messages, which is considerably more token provisionings than
   expected for intended applications.  If applications use something
   else, such as a counter, they need to guarantee that reboot and loss
   of state on either node does not provoke re-use.  If that is not
   guaranteed, nodes are susceptible to re-use of AEAD (nonces, keys)
   pairs, especially since an on-path attacker can cause the client to
   use an arbitrary nonce for Security Context establishment by
   replaying client-to-server messages.

   This profile recommends that the RS maintains a single access token
   for a client.  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 indicating different or disjoint permissions from each
   other 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.







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8.  Privacy 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 privacy considerations
   from the framework also apply to this profile.

   As this document uses OSCORE, thus the privacy considerations from
   [RFC8613] 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.

   Although encrypted, the token is sent in the clear to the authz-info
   endpoint, so if a client uses the same single token from multiple
   locations with multiple Resource Servers, it can risk being tracked
   by the token's value.

   The nonces exchanged in the request and response to the authz-info
   endpoint are also sent in the clear, so using random nonces is best
   for privacy (as opposed to, e.g., a counter, that might leak some
   information about the client).

   The AS is the party tasked of assigning the identifiers used in
   OSCORE, which are privacy sensitive (see Section 12.8 of [RFC8613]),
   and which could reveal information about the client, or may be used
   for correlating requests from one client.

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

9.  IANA Considerations

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

9.1.  ACE OAuth Profile Registry

   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]:




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   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]]

9.2.  OAuth Parameters Registry

   The following registrations are done for the OAuth Parameters
   Registry following the procedure specified in section 11.2 of
   [RFC6749]:

   o  Parameter name: nonce1
   o  Parameter usage location: token request
   o  Change Controller: IESG
   o  Specification Document(s): [[this specification]]

   o  Parameter name: nonce2
   o  Parameter usage location: token response
   o  Change Controller: IESG
   o  Specification Document(s): [[this specification]]

9.3.  OAuth Parameters CBOR Mappings Registry

   The following registrations are done for the OAuth Parameters CBOR
   Mappings Registry following the procedure specified in section 8.9 of
   [I-D.ietf-ace-oauth-authz]:

   o  Name: nonce1
   o  CBOR Key: TBD1
   o  Value Type: bstr
   o  Reference: [[this specification]]

   o  Name: nonce2
   o  CBOR Key: TBD2
   o  Value Type: IESG
   o  Reference: [[this specification]]

9.4.  OSCORE Security Context Parameters Registry

   It is requested that IANA create a new registry entitled "OSCORE
   Security Context Parameters" registry.  The registry is to be created
   as Expert Review Required.  Guidelines for the experts is provided
   Section 9.7.  It should be noted that in addition to the expert
   review, some portions of the registry require a specification,
   potentially on standards track, be supplied as well.



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   The columns of the registry are:

   name  The JSON name requested (e.g., "ms").  Because a core goal of
      this specification is for the resulting representations to be
      compact, it is RECOMMENDED that the name be short.  This name is
      case sensitive.  Names may not match other registered names in a
      case-insensitive manner unless the Designated Experts determine
      that there is a compelling reason to allow an exception.  The name
      is not used in the CBOR encoding.
   CBOR label  The value to be used to identify this algorithm.  Map key
      labels MUST be unique.  The label can be a positive integer, a
      negative integer or a string.  Integer values between -256 and 255
      and strings of length 1 are designated as Standards Track Document
      required.  Integer values from -65536 to -257 and from 256 to
      65535 and strings of length 2 are designated as Specification
      Required.  Integer values greater than 65535 and strings of length
      greater than 2 are designated as expert review.  Integer values
      less than -65536 are marked as private use.
   CBOR Type  This field contains the CBOR type for the 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 public specification
      for the field if one exists

   This registry will be initially populated by the values in Table 1.
   The specification column for all of these entries will be this
   document and [RFC8613].

9.5.  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
   [RFC8747]:

   o  Confirmation Method Name: "osc"
   o  Confirmation Method Description: OSCORE_Security_Context carrying
      the parameters for using OSCORE per-message security with implicit
      key confirmation
   o  Confirmation Key: TBD (value between 4 and 255)
   o  Confirmation Value Type(s): map
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.2.1 of [[this specification]]








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9.6.  JWT Confirmation Methods Registry

   The following registration is done for the JWT Confirmation Methods
   Registry following the procedure specified in section 6.2.1 of
   [RFC7800]:

   o  Confirmation Method Value: "osc"
   o  Confirmation Method Description: OSCORE_Security_Context carrying
      the parameters for using OSCORE per-message security with implicit
      key confirmation
   o  Change Controller: IESG
   o  Specification Document(s): Section 3.2.1 of [[this specification]]

9.7.  Expert Review Instructions

   The IANA registry established in this document is defined to use the
   Expert Review registration policy.  This section gives some general
   guidelines for what the experts should be looking for, but they are
   being designated as experts for a reason so they should be given
   substantial latitude.

   Expert reviewers should take into consideration the following points:

   o  Point squatting should be discouraged.  Reviewers are encouraged
      to get sufficient information for registration requests to ensure
      that the usage is not going to duplicate one that is already
      registered and that the point is likely to be used in deployments.
      The zones tagged as private use are intended for testing purposes
      and closed environments.  Code points in other ranges should not
      be assigned for testing.
   o  Specifications are required for the 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 closed environments in an interoperable way.
      When specifications are not provided, the description provided
      needs to have sufficient information to identify what the 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 on, and the number of code points left that encode to that
      size.




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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 OAuth 2.0
              Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-33
              (work in progress), February 2020.

   [I-D.ietf-ace-oauth-params]
              Seitz, L., "Additional OAuth Parameters for Authorization
              in Constrained Environments (ACE)", draft-ietf-ace-oauth-
              params-13 (work in progress), April 2020.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

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

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



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10.2.  Informative References

   [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 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>.

   [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>.

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

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  Optionally define new methods for the client to discover the
      necessary permissions and AS for accessing a resource, different
      from the one proposed in: Not specified
   o  Optionally specify new grant types: Not specified
   o  Optionally define the use of client certificates as client
      credential type: Not specified
   o  Specify the communication protocol the client and RS the must use:
      CoAP
   o  Specify the security protocol the client and RS must use to
      protect their communication: OSCORE
   o  Specify how the client and the RS mutually authenticate:
      Implicitly by possession of a common OSCORE security context
   o  Specify the proof-of-possession protocol(s) and how to select one,
      if several are available.  Also specify which key types (e.g.,
      symmetric/asymmetric) are supported by a specific proof-of-
      possession protocol: OSCORE algorithms; pre-established symmetric
      keys



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   o  Specify a unique ace_profile identifier: coap_oscore
   o  If introspection is supported: Specify the communication and
      security protocol for introspection: HTTP/CoAP (+ TLS/DTLS/OSCORE)
   o  Specify the communication and security protocol for interactions
      between client and AS: HTTP/CoAP (+ TLS/DTLS/OSCORE)
   o  Specify how/if the authz-info endpoint is protected, including how
      error responses are protected: Not protected.
   o  Optionally define other methods of token transport than the authz-
      info endpoint: Not defined

Acknowledgments

   The authors wish to thank Jim Schaad and Marco Tiloca for the input
   on this memo.  Special thanks to the responsible area director
   Benjamin Kaduk for his extensive review and contributed text.  Ludwig
   Seitz worked on this document as part of the CelticNext projects
   CyberWI, and CRITISEC with funding from Vinnova.

Authors' Addresses

   Francesca Palombini
   Ericsson AB

   Email: francesca.palombini@ericsson.com


   Ludwig Seitz
   Combitech
   Djaeknegatan 31
   Malmoe  211 35
   Sweden

   Email: ludwig.seitz@combitech.se


   Goeran Selander
   Ericsson AB

   Email: goran.selander@ericsson.com


   Martin Gunnarsson
   RISE
   Scheelevagen 17
   Lund  22370
   Sweden

   Email: martin.gunnarsson@ri.se



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