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Versions: (draft-palombini-ace-key-groupcomm) 00 01 02 03

ACE Working Group                                           F. Palombini
Internet-Draft                                               Ericsson AB
Intended status: Standards Track                               M. Tiloca
Expires: June 23, 2019                                           RISE AB
                                                       December 20, 2018


           Key Provisioning for Group Communication using ACE
                    draft-ietf-ace-key-groupcomm-00

Abstract

   This document defines message formats and procedures for requesting
   and distributing group keying material using the ACE framework, to
   protect communications between group members.

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 June 23, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Authorization to Join a Group . . . . . . . . . . . . . . . .   5
     3.1.  Authorization Request . . . . . . . . . . . . . . . . . .   6
     3.2.  Authorization Response  . . . . . . . . . . . . . . . . .   7
     3.3.  Token Post  . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Key Distribution  . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Key Distribution Request  . . . . . . . . . . . . . . . .   9
     4.2.  Key Distribution Response . . . . . . . . . . . . . . . .  10
   5.  Removal of a Node from the Group  . . . . . . . . . . . . . .  12
     5.1.  Expired Authorization . . . . . . . . . . . . . . . . . .  12
     5.2.  Request to Leave the Group  . . . . . . . . . . . . . . .  12
   6.  Retrieval of Updated Keying Material  . . . . . . . . . . . .  13
     6.1.  Key Re-Distribution Request . . . . . . . . . . . . . . .  13
     6.2.  Key Re-Distribution Response  . . . . . . . . . . . . . .  13
   7.  Retrieval of Public Keys for Group Members  . . . . . . . . .  13
     7.1.  Public Key Request  . . . . . . . . . . . . . . . . . . .  14
     7.2.  Public Key Response . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   This document expands the ACE framework [I-D.ietf-ace-oauth-authz] to
   define the format of messages used to request, distribute and renew
   the keying material in a group communication scenario, e.g. based on
   multicast [RFC7390] or on publishing-subscribing
   [I-D.ietf-core-coap-pubsub].

   Profiles that use group communication can build on this document to
   specify the selection of the message parameters defined in this
   document to use and their values.  Known applications that can
   benefit from this document would be, for example, profiles addressing
   group communication based on multicast [RFC7390] or publishing/
   subscribing [I-D.ietf-core-coap-pubsub] in ACE.

   If the application requires backward and forward security, updated
   keying material is generated and distributed to the group members
   (rekeying), when membership changes.  A key management scheme
   performs the actual distribution of the updated keying material to



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   the group.  In particular, the key management scheme rekeys the
   current group members when a new node joins the group, and the
   remaining group members when a node leaves the group.  This document
   provides a message format for group rekeying that allows to fulfill
   these requirements.  Rekeying mechanisms can be based on [RFC2093],
   [RFC2094] and [RFC2627].

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.

   Readers are expected to be familiar with the terms and concepts
   described in [I-D.ietf-ace-oauth-authz] and [RFC8152], such as
   Authorization Server (AS) and Resource Server (RS).

2.  Overview

       +------------+                  +-----------+
       |     AS     |                  |    KDC    |
       |            |        .-------->|           |
       +------------+       /          +-----------+
             ^             /
             |            /
             v           /                           +-----------+
       +------------+   /      +------------+        |+-----------+
       |   Client   |<-'       | Dispatcher |        ||+-----------+
       |            |<-------->|    (RS)    |<------->||   Group   |
       +------------+          +------------+         +|  members  |
                                                       +-----------+

                  Figure 1: Key Distribution Participants

   The following participants (see Figure 1) take part in the
   authorization and key distribution.

   o  Client (C): node that wants to join the group communication.  It
      can request write and/or read rights.

   o  Authorization Server (AS): same as AS in the ACE Framework; it
      enforces access policies, and knows if a node is allowed to join
      the group with write and/or read rights.

   o  Key Distribution Center (KDC): maintains the keying material to
      protect group communications, and provides it to Clients



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      authorized to join the group.  During the first part of the
      exchange (Section 3), it takes the role of the RS in the ACE
      Framework.  During the second part (Section 4), which is not based
      on the ACE Framework, it distributes the keying material.  In
      addition, it provides the latest keying material to group members
      when requested.  If required by the application, the KDC renews
      and re-distributes the keying material in the group when
      membership changes.

   o  Dispatcher: entity through which the Clients communicate with the
      group and which distributes messages to the group members.
      Examples of dispatchers are: the Broker node in a pub-sub setting;
      a relayer node for group communication that delivers group
      messages as multiple unicast messages to all group members; an
      implicit entity as in a multicast communication setting, where
      messages are transmitted to a multicast IP address and delivered
      on the transport channel.

   This document specifies the message flows and formats for:

   o  Authorizing a new node to join the group (Section 3), and
      providing it with the group keying material to communicate with
      the other group members (Section 4).

   o  Removing of a current member from the group (Section 5).

   o  Retrieving keying material as a current group member (Section 6
      and Section 7).

   o  Renewing and re-distributing the group keying material (rekeying)
      upon a membership change in the group (Section 4.2 and Section 5).

   Figure 2 provides a high level overview of the message flow for a
   node joining a group communication setting.

















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  C                              AS     KDC   Dispatcher          Group
  |                              |       |        |               Member
  |                              |       |        | \               |
  |     Authorization Request    |       |        | | Defined       |
  |----------------------------->|       |        | | in the ACE    |
  |                              |       |        | | framework     |
  |     Authorization Response   |       |        | |               |
  |<-----------------------------|       |        | |               |
  |                              |       |        | |               |
  |--------- Token Post ---------------->|        | /               |
  |                                      |        |                 |
  |---- Key Distribution Request ------->|        |                 |
  |                                      |        |                 |
  |<--- Key Distribution Response ------ | --- Group Rekeying ----->|
  |                                               |                 |
  |<================== Protected communication ===|================>|
  |                                               |                 |

              Figure 2: Message Flow Upon New Node's Joining

   The exchange of Authorization Request and Authorization Response
   between Client and AS MUST be secured, as specified by the ACE
   profile used between Client and KDC.

   The exchange of Key Distribution Request and Key Distribution
   Response between Client and KDC MUST be secured, as a result of the
   ACE profile used between Client and KDC.

   All further communications between the Client and the KDC MUST be
   secured, for instance with the same security mechanism used for the
   Key Distribution exchange.

   All further communications between a Client and the other group
   members MUST be secured using the keying material provided in
   Section 4.

3.  Authorization to Join a Group

   This section describes in detail the format of messages exchanged by
   the participants when a node requests access to a group.  The first
   part of the exchange is based on ACE [I-D.ietf-ace-oauth-authz].

   As defined in [I-D.ietf-ace-oauth-authz], the Client requests from
   the AS an authorization to join the group through the KDC (see
   Section 3.1).  If the request is approved and authorization is
   granted, the AS provides the Client with a proof-of-possession access
   token and parameters to securely communicate with the KDC (see




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   Section 3.2).  Communications between the Client and the AS MUST be
   secured, and depends on the profile of ACE used.

   Figure 3 gives an overview of the exchange described above.

         Client                                            AS  KDC
            |                                               |   |
            |---- Authorization Request: POST /token ------>|   |
            |                                               |   |
            |<--- Authorization Response: 2.01 (Created) ---|   |
            |                                               |   |
            |----- POST Token: POST /authz-info --------------->|
            |                                                   |

               Figure 3: Message Flow of Join Authorization

3.1.  Authorization Request

   The Authorization Request sent from the Client to the AS is as
   defined in Section 5.6.1 of [I-D.ietf-ace-oauth-authz] and MUST
   contain the following parameters:

   o  'grant_type', with value "client_credentials".

   Additionally, the Authorization Request MAY contain the following
   parameters, which, if included, MUST have the corresponding values:

   o  'scope', with value the identifier of the specific group or topic
      the Client wishes to access, and optionally the role(s) the Client
      wishes to take.  This value is a CBOR array encoded as a byte
      string, which contains:

      *  As first element, the identifier of the specific group or
         topic.

      *  Optionally, as second element, the role (or CBOR array of
         roles) the Client wishes to take in the group.

      The encoding of the group or topic identifier and of the role
      identifiers is application specific.

   o  'req_aud', as defined in Section 3.1 of
      [I-D.ietf-ace-oauth-params], with value an identifier of the KDC.

   o  'req_cnf', as defined in Section 3.1 of
      [I-D.ietf-ace-oauth-params], optionally containing the public key
      or the certificate of the Client, if it wishes to communicate that
      to the AS.



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   o  Other additional parameters as defined in
      [I-D.ietf-ace-oauth-authz], if necessary.

3.2.  Authorization Response

   The Authorization Response sent from the AS to the Client is as
   defined in Section 5.6.2 of [I-D.ietf-ace-oauth-authz] and MUST
   contain the following parameters:

   o  'access_token', containing the proof-of-possession access token.

   o  'cnf' if symmetric keys are used, not present if asymmetric keys
      are used.  This parameter is defined in Section 3.2 of
      [I-D.ietf-ace-oauth-params] and contains the symmetric proof-of-
      possession key that the Client is supposed to use with the KDC.

   o  'rs_cnf' if asymmetric keys are used, not present if symmetric
      keys are used.  This parameter is as defined in Section 3.2 of
      [I-D.ietf-ace-oauth-params] and contains information about the
      public key of the KDC.

   o  'exp', contains the lifetime in seconds of the access token.  This
      parameter MAY be omitted if the application defines how the
      expiration time is communicated to the Client via other means, or
      if it establishes a default value.

   Additionally, the Authorization Response MAY contain the following
   parameters, which, if included, MUST have the corresponding values:

   o  'scope', which mirrors the 'scope' parameter in the Authorization
      Request (see Section 3.1).  Its value is a CBOR array encoded as a
      byte string, containing:

      *  As first element, the identifier of the specific group or topic
         the Client is authorized to access.

      *  Optionally, as second element, the role (or CBOR array of
         roles) the Client is authorized to take in the group.

      The encoding of the group or topic identifier and of the role
      identifiers is application specific.

   o  Other additional parameters as defined in
      [I-D.ietf-ace-oauth-authz], if necessary.

   The access token MUST contain all the parameters defined above
   (including the same 'scope' as in this message, if present, or the




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   'scope' of the Authorization Request otherwise), and additionally
   other optional parameters the profile requires.

   When receiving an Authorization Request from a Client that was
   previously authorized, and which still owns a valid non expired
   access token, the AS can simply reply with an Authorization Response
   including a new access token.

3.3.  Token Post

   The Client sends a CoAP POST request including the access token to
   the KDC, as specified in section 5.8.1 of [I-D.ietf-ace-oauth-authz].
   If the specific ACE profile defines it, the Client MAY use a
   different endpoint than /authz-info at the KDC to post the access
   token to.  After successful verification, the Client is authorized to
   receive the group keying material from the KDC and join the group.

   Note that this step could be merged with the following message from
   the Client to the KDC, namely Key Distribution Request.

4.  Key Distribution

   This section defines how the keying material used for group
   communication is distributed from the KDC to the Client, when joining
   the group as a new member.

   If not previously established, the Client and the KDC MUST first
   establish a pairwise secure communication channel using ACE.  The
   exchange of Key Distribution Request-Response MUST occur over that
   secure channel.  The Client and the KDC MAY use that same secure
   channel to protect further pairwise communications, that MUST be
   secured.

   During this exchange, the Client sends a request to the AS,
   specifying the group it wishes to join (see Section 4.1).  Then, the
   KDC verifies the access token and that the Client is authorized to
   join that group; if so, it provides the Client with the keying
   material to securely communicate with the member of the group (see
   Section 4.2).

   Figure 4 gives an overview of the exchange described above.










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         Client                                               KDC
            |                                                  |
            |---- Key Distribution Request: POST /group-id --->|
            |                                                  |
            |<--- Key Distribution Response: 2.01 (Created) ---|
            |                                                  |

     Figure 4: Message Flow of Key Distribution to a New Group Member

   The same set of message can also be used for the following cases,
   when the Client is already a group member:

   o  The Client wishes to (re-)get the current keying material, for
      cases such as expiration, loss or suspected mismatch, due to e.g.
      reboot or missed group rekeying.  This is further discussed in
      Section 6.

   o  The Client wishes to (re-)get the public keys of other group
      members, e.g. if it is aware of new nodes joining the group after
      itself.  This is further discussed in Section 7.

   Additionally, the format of the payload of the Key Distribution
   Response (Section 4.2) can be reused for messages sent by the KDC to
   distribute updated group keying material, in case of a new node
   joining the group or of a current member leaving the group.  The key
   management scheme used to send such messages could rely on, e.g.,
   multicast in case of a new node joining or unicast in case of a node
   leaving the group.

   Note that proof-of-possession to bind the access token to the Client
   is performed by using the proof-of-possession key bound to the access
   token for establishing secure communication between the Client and
   the KDC.

4.1.  Key Distribution Request

   The Client sends a Key Distribution request to the KDC.  This
   corresponds to a CoAP POST request to the endpoint in the KDC
   associated to the group to join.  The endpoint in the KDC is
   associated to the 'scope' value of the Authorization Request/
   Response.  The payload of this request is a CBOR Map which MAY
   contain the following fields, which, if included, MUST have the
   corresponding values:

   o  'scope', with value the specific resource that the Client is
      authorized to access (i.e. group or topic identifier) and role(s),
      encoded as in Section 3.1.




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   o  'get_pub_keys', if the Client wishes to receive the public keys of
      the other nodes in the group from the KDC.  The value is an empty
      CBOR Array.  This parameter may be present if the KDC stores the
      public keys of the nodes in the group and distributes them to the
      Client; it is useless to have here if the set of public keys of
      the members of the group is known in another way, e.g. it was
      provided by the AS.

   o  'client_cred', with value the public key or certificate of the
      Client.  If the KDC is managing (collecting from/distributing to
      the Client) the public keys of the group members, this field
      contains the public key of the Client.

   o  'pub_keys_repos', can be present if a certificate is present in
      the 'client_cred' field, with value a list of public key
      repositories storing the certificate of the Client.

4.2.  Key Distribution Response

   The KDC verifies the access token and, if verification succeeds,
   sends a Key Distribution success Response to the Client.  This
   corresponds to a 2.01 Created message.  The payload of this response
   is a CBOR Map which MUST contain the following fields:

   o  'key', used to send the keying material to the Client, as a
      COSE_Key ([RFC8152]) containing the following parameters:

      *  'kty', as defined in [RFC8152].

      *  'k', as defined in [RFC8152].

      *  'exp' (optionally), as defined below.  This parameter is
         RECOMMENDED to be included in the COSE_Key.  If omitted, the
         authorization server SHOULD provide the expiration time via
         other means or document the default value.

      *  'alg' (optionally), as defined in [RFC8152].

      *  'kid' (optionally), as defined in [RFC8152].

      *  'base iv' (optionally), as defined in [RFC8152].

      *  'clientID' (optionally), as defined in
         [I-D.ietf-ace-oscore-profile].

      *  'serverID' (optionally), as defined in
         [I-D.ietf-ace-oscore-profile].




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      *  'kdf' (optionally), as defined in
         [I-D.ietf-ace-oscore-profile].

      *  'slt' (optionally), as defined in
         [I-D.ietf-ace-oscore-profile].

      *  'cs_alg' (optionally), containing the algorithm value to
         countersign the message, taken from Table 5 and 6 of [RFC8152].

   The parameter 'exp' identifies the expiration time in seconds after
   which the COSE_Key is not valid anymore for secure communication in
   the group.  A summary of 'exp' can be found in Figure 5.

     +------+-------+----------------+------------+-----------------+
     | Name | Label | CBOR Type      | Value      | Description     |
     |      |       |                | Registry   |                 |
     +------+-------+----------------+------------+-----------------+
     | exp  | TBD   | Integer or     | COSE Key   | Expiration time |
     |      |       | floating-point | Common     | in seconds      |
     |      |       | number         | Parameters |                 |
     +------+-------+----------------+------------+-----------------+

             Figure 5: COSE Key Common Header Parameter 'exp'

   Optionally, the Key Distribution Response MAY contain the following
   parameters, which, if included, MUST have the corresponding values:

   o  'pub_keys', may only be present if 'get_pub_keys' was present in
      the Key Distribution Request; this parameter is a COSE_KeySet (see
      [RFC8152]), which contains the public keys of all the members of
      the group.

   o  'group_policies', with value a list of parameters indicating how
      the group handles specific management aspects.  This includes, for
      instance, approaches to achieve synchronization of sequence
      numbers among group members.  The exact format of this parameter
      is specific to the profile.

   o  'mgt_key_material', with value the administrative keying material
      to participate in the group rekeying performed by the KDC.  The
      exact format and content depend on the specific rekeying scheme
      used in the group, which may be specified in the profile.

   Specific profiles need to specify how exactly the keying material is
   used to protect the group communication.

   If the application requires backward security, the KDC SHALL generate
   new group keying material and securely distribute it to all the



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   current group members, using the message format defined in this
   section.  Application profiles may define alternative message
   formats.

   TBD: define for verification failure

5.  Removal of a Node from the Group

   This section describes at a high level how a node can be removed from
   the group.

   If the application requires forward security, the KDC SHALL generate
   new group keying material and securely distribute it to all the
   current group members but the leaving node, using the message format
   defined in Section 4.2.  Application profiles may define alternative
   message formats.

5.1.  Expired Authorization

   If the node is not authorized anymore, the AS can directly
   communicate that to the KDC.  Alternatively, the access token might
   have expired.  If Token introspection is provided by the AS, the KDC
   can use it as per Section 5.7 of [I-D.ietf-ace-oauth-authz], in order
   to verify that the access token is still valid.

   Either case, once aware that a node is not authorized anymore, the
   KDC has to remove the unauthorized node from the list of group
   members, if the KDC keeps track of that.

5.2.  Request to Leave the Group

   A node can actively request to leave the group.  In this case, the
   Client can send a request formatted as follows to the KDC, to abandon
   the group.

   TBD: Format of the message to leave the group

   The KDC should then remove the leaving node from the list of group
   members, if the KDC keeps track of that.

   Note that, after having left the group, a node may wish to join it
   again.  Then, as long as the node is still authorized to join the
   group, i.e. it has a still valid access token, it can re-request to
   join the group directly to the KDC without needing to retrieve a new
   access token from the AS.  This means that the KDC needs to keep
   track of nodes with valid access tokens, before deleting all
   information about the leaving node.




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6.  Retrieval of Updated Keying Material

   A node stops using the group keying material upon its expiration,
   according to the 'exp' parameter specified in the retained COSE Key.
   Then, if it wants to continue participating in the group
   communication, the node has to request new updated keying material to
   the KDC.

   The Client may perform the same request to the KDC also upon
   receiving messages from other group members without being able to
   correctly decrypt them.  This may be due to a previous update of the
   group keying material (rekeying) triggered by the KDC, that the
   Client was not able to receive or decrypt.

   Note that policies can be set up so that the Client sends a request
   to the KDC only after a given number of unsuccessfully decrypted
   incoming messages.

6.1.  Key Re-Distribution Request

   To request a re-distribution of keying material, the Client sends a
   shortened Key Distribution Request to the KDC (Section 4.1),
   formatted as follows.  The payload MUST contain only the following
   field:

   o  'scope', which contains only the identifier of the specific group
      or topic, encoded as in Section 3.1.  That is, the role field is
      not present.

6.2.  Key Re-Distribution Response

   The KDC receiving a Key Re-Distribution Request MUST check that it is
   storing a valid access token from that client for that scope.

   TODO: defines error response if it does not have it / is not valid.

   The KDC replies to the Client with a Key Distribution Response
   containing the 'key' parameter, and optionally 'group_policies' and
   'mgt_key_material', as specified in Section 4.2.  Note that this
   response might simply re-provide the same keying material currently
   owned by the Client, if it has not been renewed.

7.  Retrieval of Public Keys for Group Members

   In case the KDC maintains the public keys of group members, a node in
   the group can contact the KDC to request public keys of either all
   group members or a specified subset, using the messages defined
   below.



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   Figure 6 gives an overview of the exchange described above.

            Client                                         KDC
               |                                            |
               |---- Public Key Request: POST /group-id --->|
               |                                            |
               |<--- Public Key Response: 2.01 (Created) ---|
               |                                            |

           Figure 6: Message Flow of Public Key Request-Response

   Note that these messages can be combined with the Key Re-Distribution
   messages in Section 6, to request at the same time the keying
   material and the public keys.  In this case, either a new endpoint at
   the KDC may be used, or additional information needs to be sent in
   the request payload, to distinguish these combined messages from the
   Public Key messages described below, since they would be identical
   otherwise.

7.1.  Public Key Request

   To request public keys, the Client sends a shortened Key Distribution
   Request to the KDC (Section 4.1), formatted as follows.  The payload
   of this request MUST contain the following fields:

   o  'get_pub_keys', which has as value a CBOR array including either:

      *  no elements, i.e. an empty array, in order to request the
         public key of all current group members; or

      *  N elements, each of which is the identifier of a group member,
         in order to request the public key of the specified nodes.

   o  'scope', which contains only the identifier of the specific group
      or topic, encoded as in Section 3.1.  That is, the role field is
      not present.

7.2.  Public Key Response

   The KDC replies to the Client with a Key Distribution Response
   containing only the 'pub_keys' parameter, as specified in
   Section 4.2.  The payload of this response contains the following
   field:

   o  'pub_keys', which contains either:






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      *  the public keys of all the members of the group, if the
         'get_pub_keys' parameter of the Public Key request was an empty
         array; or

      *  the public keys of the group members with the identifiers
         specified in the 'get_pub_keys' parameter of the Public Key
         request.

   The KDC ignores possible identifiers included in the 'get_pub_keys'
   parameter of the Public Key request if they are not associated to any
   current group member.

8.  Security Considerations

   The KDC must renew the group keying material upon its expiration.

   The KDC should renew the keying material upon group membership
   change, and should provide it to the current group members through
   the rekeying scheme used in the group.

9.  IANA Considerations

   The following registration is required for the COSE Key Common
   Parameter Registry specified in Section 16.5 of [RFC8152]:

   o  Name: exp

   o  Label: TBD

   o  CBOR Type: Integer or floating-point number

   o  Value Registry: COSE Key Common Parameters

   o  Description: Identifies the expiration time in seconds of the COSE
      Key

   o  Reference: [[this specification]]

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-17
              (work in progress), November 2018.



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   [I-D.ietf-ace-oauth-params]
              Seitz, L., "Additional OAuth Parameters for Authorization
              in Constrained Environments (ACE)", draft-ietf-ace-oauth-
              params-01 (work in progress), November 2018.

   [I-D.ietf-ace-oscore-profile]
              Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
              "OSCORE profile of the Authentication and Authorization
              for Constrained Environments Framework", draft-ietf-ace-
              oscore-profile-05 (work in progress), November 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>.

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

10.2.  Informative References

   [I-D.ietf-core-coap-pubsub]
              Koster, M., Keranen, A., and J. Jimenez, "Publish-
              Subscribe Broker for the Constrained Application Protocol
              (CoAP)", draft-ietf-core-coap-pubsub-05 (work in
              progress), July 2018.

   [RFC2093]  Harney, H. and C. Muckenhirn, "Group Key Management
              Protocol (GKMP) Specification", RFC 2093,
              DOI 10.17487/RFC2093, July 1997,
              <https://www.rfc-editor.org/info/rfc2093>.

   [RFC2094]  Harney, H. and C. Muckenhirn, "Group Key Management
              Protocol (GKMP) Architecture", RFC 2094,
              DOI 10.17487/RFC2094, July 1997,
              <https://www.rfc-editor.org/info/rfc2094>.

   [RFC2627]  Wallner, D., Harder, E., and R. Agee, "Key Management for
              Multicast: Issues and Architectures", RFC 2627,
              DOI 10.17487/RFC2627, June 1999,
              <https://www.rfc-editor.org/info/rfc2627>.

   [RFC7390]  Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
              the Constrained Application Protocol (CoAP)", RFC 7390,
              DOI 10.17487/RFC7390, October 2014,
              <https://www.rfc-editor.org/info/rfc7390>.




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Acknowledgments

   The following individuals were helpful in shaping this document: Ben
   Kaduk, John Mattsson, Jim Schaad, Ludwig Seitz, Goeran Selander and
   Peter van der Stok.

   The work on this document has been partly supported by the EIT-
   Digital High Impact Initiative ACTIVE.

Authors' Addresses

   Francesca Palombini
   Ericsson AB
   Torshamnsgatan 23
   Kista  SE-16440 Stockholm
   Sweden

   Email: francesca.palombini@ericsson.com


   Marco Tiloca
   RISE AB
   Isafjordsgatan 22
   Kista  SE-16440 Stockholm
   Sweden

   Email: marco.tiloca@ri.se
























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