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Versions: (draft-tiloca-ace-oscoap-joining) 00 01 02 03

ACE Working Group                                              M. Tiloca
Internet-Draft                                                   RISE AB
Intended status: Standards Track                                 J. Park
Expires: January 6, 2020                     Universitaet Duisburg-Essen
                                                            F. Palombini
                                                             Ericsson AB
                                                           July 05, 2019


                Key Management for OSCORE Groups in ACE
               draft-ietf-ace-key-groupcomm-oscore-02

Abstract

   This document describes a method to request and provision keying
   material in group communication scenarios where the group
   communication is based on CoAP and secured with Object Security for
   Constrained RESTful Environments (OSCORE).  The proposed method
   delegates the authentication and authorization of new client nodes
   that join an OSCORE group through a Group Manager server.  This
   approach builds on the ACE framework for Authentication and
   Authorization, and leverages protocol-specific transport profiles of
   ACE to achieve communication security, proof-of-possession and server
   authentication.

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 January 6, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Relation to Other Documents . . . . . . . . . . . . . . .   5
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Overview of the Join Process  . . . . . . . . . . . . . .   7
     2.2.  Overview of the Group Rekeying Process  . . . . . . . . .   8
   3.  Joining Node to Authorization Server  . . . . . . . . . . . .   9
     3.1.  Authorization Request . . . . . . . . . . . . . . . . . .   9
     3.2.  Authorization Response  . . . . . . . . . . . . . . . . .  10
   4.  Joining Node to Group Manager . . . . . . . . . . . . . . . .  11
     4.1.  Token Post  . . . . . . . . . . . . . . . . . . . . . . .  11
     4.2.  Join Request  . . . . . . . . . . . . . . . . . . . . . .  12
     4.3.  Join Response . . . . . . . . . . . . . . . . . . . . . .  13
   5.  Leaving of a Group Member . . . . . . . . . . . . . . . . . .  17
   6.  Public Keys of Joining Nodes  . . . . . . . . . . . . . . . .  18
   7.  Group Rekeying Process  . . . . . . . . . . . . . . . . . . .  20
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     9.1.  ACE Groupcomm Key Registry  . . . . . . . . . . . . . . .  22
     9.2.  OSCORE Security Context Parameters Registry . . . . . . .  23
     9.3.  ACE Groupcomm Profile Registry  . . . . . . . . . . . . .  24
     9.4.  Sequence Number Synchronization Method Registry . . . . .  24
     9.5.  ACE Public Key Encoding Registry  . . . . . . . . . . . .  25
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  25
     10.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Appendix A.  Profile Requirements . . . . . . . . . . . . . . . .  27
   Appendix B.  Document Updates . . . . . . . . . . . . . . . . . .  28
     B.1.  Version -01 to -02  . . . . . . . . . . . . . . . . . . .  28
     B.2.  Version -00 to -01  . . . . . . . . . . . . . . . . . . .  29
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  29
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29







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1.  Introduction

   Object Security for Constrained RESTful Environments (OSCORE)
   [I-D.ietf-core-object-security] is a method for application-layer
   protection of the Constrained Application Protocol (CoAP) [RFC7252],
   using CBOR Object Signing and Encryption (COSE) [RFC8152] and
   enabling end-to-end security of CoAP payload and options.

   As described in [I-D.ietf-core-oscore-groupcomm], OSCORE may be used
   to protect CoAP group communication over IP multicast
   [RFC7390][I-D.dijk-core-groupcomm-bis].  This relies on a Group
   Manager, which is responsible for managing an OSCORE group, where
   members exchange CoAP messages secured with OSCORE.  The Group
   Manager can be responsible for multiple groups, coordinates the join
   process of new group members, and is entrusted with the distribution
   and renewal of group keying material.

   This specification builds on the ACE framework for Authentication and
   Authorization [I-D.ietf-ace-oauth-authz] and defines a method to:

   o  Authorize a node to join an OSCORE group, and provide it with the
      group keying material to communicate with other group members.

   o  Provide updated keying material to group members upon request.

   o  Renew the group keying material and distribute it to the OSCORE
      group (rekeying) upon changes in the group membership.

   A client node joins an OSCORE group through a resource server acting
   as Group Manager for that group.  The join process relies on an
   Access Token, which is bound to a proof-of-possession key and
   authorizes the client to access a specific join resource at the Group
   Manager.

   Messages exchanged among the participants follow the formats defined
   in [I-D.ietf-ace-key-groupcomm] for provisioning and renewing keying
   material in group communication scenarios.

   In order to achieve communication security, proof-of-possession and
   server authentication, the client and the Group Manager leverage
   protocol-specific transport profiles of ACE.  These include also
   possible forthcoming transport profiles that comply with the
   requirements in Appendix C of [I-D.ietf-ace-oauth-authz].








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1.1.  Terminology

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

   Readers are expected to be familiar with the terms and concepts
   described in the ACE framework for authentication and authorization
   [I-D.ietf-ace-oauth-authz].  The terminology for entities in the
   considered architecture is defined in OAuth 2.0 [RFC6749].  In
   particular, this includes Client (C), Resource Server (RS), and
   Authorization Server (AS).

   Readers are expected to be familiar with the terms and concepts
   related to the CoAP protocol described in
   [RFC7252][RFC7390][I-D.dijk-core-groupcomm-bis].  Note that, unless
   otherwise indicated, the term "endpoint" is used here following its
   OAuth definition, aimed at denoting resources such as /token and
   /introspect at the AS and /authz-info at the RS.  This document does
   not use the CoAP definition of "endpoint", which is "An entity
   participating in the CoAP protocol".

   Readers are expected to be familiar with the terms and concepts for
   protection and processing of CoAP messages through OSCORE
   [I-D.ietf-core-object-security] also in group communication scenarios
   [I-D.ietf-core-oscore-groupcomm].  These include the concept of Group
   Manager, as the entity responsible for a set of groups where
   communications are secured with OSCORE.  In this specification, the
   Group Manager acts as Resource Server.

   This document refers also to the following terminology.

   o  Joining node: a network node intending to join an OSCORE group,
      where communication is based on CoAP
      [RFC7390][I-D.dijk-core-groupcomm-bis] and secured with OSCORE as
      described in [I-D.ietf-core-oscore-groupcomm].

   o  Join process: the process through which a joining node becomes a
      member of an OSCORE group.  The join process is enforced and
      assisted by the Group Manager responsible for that group.

   o  Join resource: a resource hosted by the Group Manager, associated
      to an OSCORE group under that Group Manager.  A join resource is
      identifiable with the Group Identifier (Gid) of the respective
      group.  A joining node accesses a join resource to start the join




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      process and become a member of that group.  The URI of a join
      resource is fixed.

   o  Join endpoint: an endpoint at the Group Manager associated to a
      join resource.

   o  Requester: member of an OSCORE group that sends request messages
      to other members of the group.

   o  Responder: member of an OSCORE group that receives request
      messages from other members of the group.  A responder may reply
      back, by sending a response message to the requester which has
      sent the request message.

   o  Monitor: member of a group that is configured as responder and
      never replies back to requesters after receiving request messages.
      This corresponds to the term "silent server" used in
      [I-D.ietf-core-oscore-groupcomm].

   o  Group rekeying process: the process through which the Group
      Manager renews the security parameters and group keying material,
      and (re-)distributes them to the OSCORE group members.

1.2.  Relation to Other Documents

   Figure 1 overviews the main documents related to this specification.
   Arrows and asterisk-arrows denote normative references and
   informative refences, respectively.























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                        +---------------------------------------+
                        |                                       |
       +----------------|--------------+                        |
       |                |              |                        |
       |                v              v                 Key Management
    Pub-sub ---> Key Groupcomm ---> ACE Framework <--- for OSCORE Groups
    profile        *  [[WG]]           [[WG]]          [[This document]]
       |           *    *              ^               ^  |     |
       |           *    *              *               *  |     |
       |           *    *              * ***************  |     |
       | ***********    *              * *                |     |
       | *              *              * * +--------------+     |
  ACE  | *              *              * * |                    |
  -----|-*--------------*--------------*-*-|--------------------|-------
  CoRE | *              *              * * |                    |
       v v              v              * * v                    v
      CoRE             CoRE            OSCORE  -------------> OSCORE
     Pubsub          Groupcomm  <*** Groupcomm <************* [[WG]]
     [[WG]]         [[RFC7390]]        [[WG]]

                        Figure 1: Related Documents

2.  Protocol Overview

   Group communication for CoAP over IP multicast has been enabled in
   [RFC7390][I-D.dijk-core-groupcomm-bis] and can be secured with Object
   Security for Constrained RESTful Environments (OSCORE)
   [I-D.ietf-core-object-security] as described in
   [I-D.ietf-core-oscore-groupcomm].  A network node joins an OSCORE
   group by interacting with the responsible Group Manager.  Once
   registered in the group, the new node can securely exchange messages
   with other group members.

   This specification describes how to use the ACE framework for
   authentication and authorization [I-D.ietf-ace-oauth-authz] to:

   o  Enable a node to join an OSCORE group through the Group Manager
      and receive the security parameters and keying material to
      communicate with the other members of the gorup.

   o  Enable members of OSCORE groups to retrieve updated group keying
      material from the Group Manager.

   o  Enable the Group Manager to renew the security parameters and
      group keying material, and to (re-)distribute them to the members
      of the OSCORE group (rekeying).





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   With reference to the ACE framework and the terminology defined in
   OAuth 2.0 [RFC6749]:

   o  The Group Manager acts as Resource Server (RS), and hosts one join
      resource for each OSCORE group it manages.  Each join resource is
      exported by a distinct join endpoint.  During the join process,
      the Group Manager provides joining nodes with the parameters and
      keying material for taking part to secure communications in the
      OSCORE group.  The Group Manager also maintains the group keying
      material and performs the group rekeying process to distribute
      updated keying material to the group members.

   o  The joining node acts as Client (C), and requests to join an
      OSCORE group by accessing the related join endpoint at the Group
      Manager.

   o  The Authorization Server (AS) authorizes joining nodes to join
      OSCORE groups under their respective Group Manager.  Multiple
      Group Managers can be associated to the same AS.  The AS MAY
      release Access Tokens for other purposes than joining OSCORE
      groups under registered Group Managers.  For example, the AS may
      also release Access Tokens for accessing resources hosted by
      members of OSCORE groups.

   All communications between the involved entities rely on the CoAP
   protocol and MUST be secured.

   In particular, communications between the joining node and the Group
   Manager leverage protocol-specific transport profiles of ACE to
   achieve communication security, proof-of-possession and server
   authentication.  To this end, the AS must signal the specific
   transport profile to use, consistently with requirements and
   assumptions defined in the ACE framework [I-D.ietf-ace-oauth-authz].

   With reference to the AS, communications between the joining node and
   the AS (/token endpoint) as well as between the Group Manager and the
   AS (/introspect endpoint) can be secured by different means, for
   instance using DTLS [RFC6347] or OSCORE
   [I-D.ietf-core-object-security].  Further details on how the AS
   secures communications (with the joining node and the Group Manager)
   depend on the specifically used transport profile of ACE, and are out
   of the scope of this specification.

2.1.  Overview of the Join Process

   A node performs the following steps in order to join an OSCORE group.
   Messages exchanged among the participants follow the formats defined
   in [I-D.ietf-ace-key-groupcomm], and are further specified in



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   Section 3 and Section 4 of this document.  The Group Manager acts as
   the Key Distribution Center (KDC) defined in
   [I-D.ietf-ace-key-groupcomm].

   1.  The joining node requests an Access Token from the AS, in order
       to access a join resource on the Group Manager and hence join the
       associated OSCORE group (see Section 3).  The joining node will
       start or continue using a secure communication channel with the
       Group Manager, according to the response from the AS.

   2.  The joining node transfers authentication and authorization
       information to the Group Manager by posting the obtained Access
       Token (see Section 4).  After that, a joining node must have a
       secure communication channel established with the Group Manager,
       before starting to join an OSCORE group under that Group Manager
       (see Section 4).  Possible ways to provide a secure communication
       channel are DTLS [RFC6347] and OSCORE
       [I-D.ietf-core-object-security].

   3.  The joining node starts the join process to become a member of
       the OSCORE group, by accessing the related join resource hosted
       by the Group Manager (see Section 4).

   4.  At the end of the join process, the joining node has received
       from the Group Manager the parameters and keying material to
       securely communicate with the other members of the OSCORE group.

   5.  The joining node and the Group Manager maintain the secure
       channel, to support possible future communications.

   All further communications between the joining node and the Group
   Manager MUST be secured, for instance with the same secure channel
   mentioned in step 2.

2.2.  Overview of the Group Rekeying Process

   If the application requires backward and forward security, the Group
   Manager MUST generate new security parameters and group keying
   material, and distribute them to the group (rekeying) upon membership
   changes.

   That is, the group is rekeyed when a node joins the group as a new
   member, or after a current member leaves the group.  By doing so, a
   joining node cannot access communications in the group prior its
   joining, while a leaving node cannot access communications in the
   group after its leaving.





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   Parameters and keying material include a new Group Identifier (Gid)
   for the group and a new Master Secret for the OSCORE Common Security
   Context of that group (see Section 2 of
   [I-D.ietf-core-oscore-groupcomm]).

   The Group Manager MUST support the Group Rekeying Process described
   in Section 7.  Future application profiles may define alternative
   message formats and distribution schemes to perform group rekeying.

3.  Joining Node to Authorization Server

   This section describes how the joining node interacts with the AS in
   order to be authorized to join an OSCORE group under a given Group
   Manager.  In particular, it considers a joining node that intends to
   contact that Group Manager for the first time.

   The message exchange between the joining node and the AS consists of
   the messages Authorization Request and Authorization Response defined
   in Section 3 of [I-D.ietf-ace-key-groupcomm].

   In case the specific AS associated to the Group Manager is unknown to
   the joining node, the latter can rely on mechanisms like the
   Unauthorized Resource Request message described in Section 5.1.1 of
   [I-D.ietf-ace-oauth-authz] to discover the correct AS to contact.

3.1.  Authorization Request

   The joining node contacts the AS, in order to request an Access Token
   for accessing the join resource hosted by the Group Manager and
   associated to the OSCORE group.  The Access Token request sent to the
   /token endpoint follows the format of the Authorization Request
   message defined in Section 3.1 of [I-D.ietf-ace-key-groupcomm].  In
   particular:

   o  The 'scope' parameter MUST be present and MUST include:

      *  in the first element, either the Group Identifier (Gid) of the
         group to join under the Group Manager, or a value from which
         the Group Manager can derive the Gid of the group to join.  It
         is up to the application to define how the Group Manager
         possibly performs the derivation of the full Gid. Appendix C of
         [I-D.ietf-core-oscore-groupcomm] provides an example of
         structured Gid, composed of a fixed part, namely Group Prefix,
         and a variable part, namely Group Epoch.

      *  in the second element, the role (encoded as a text string) or
         CBOR array of roles that the joining node intends to have in
         the group it intends to join.  Accepted values of roles are:



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         "requester", "responder", and "monitor".  Possible combinations
         are: ["requester" , "responder"]; ["requester" , "monitor"].

   o  The 'audience' parameter MUST be present and is set to the
      identifier of the Group Manager.

3.2.  Authorization Response

   The AS is responsible for authorizing the joining node to join
   specific OSCORE groups, according to join policies enforced on behalf
   of the respective Group Manager.

   In case of successful authorization, the AS releases an Access Token
   bound to a proof-of-possession key associated to the joining node.

   Then, the AS provides the joining node with the Access Token as part
   of an Access Token response, which follows the format of the
   Authorization Response message defined in Section 3.2 of
   [I-D.ietf-ace-key-groupcomm].

   The 'exp' parameter MUST be present.  Other means for the AS to
   specify the lifetime of Access Tokens are out of the scope of this
   specification.

   The AS must include the 'scope' parameter in the response when the
   value included in the Access Token differs from the one specified by
   the joining node in the request.  In such a case, the second element
   of 'scope' MUST be present and includes the role or CBOR array of
   roles that the joining node is actually authorized to take in the
   group, encoded as specified in Section 3.1 of this document.

   Also, the 'profile' parameter indicates the specific transport
   profile of ACE to use for securing communications between the joining
   node and the Group Manager (see Section 5.6.4.3 of
   [I-D.ietf-ace-oauth-authz]).

   In particular, if symmetric keys are used, the AS generates a proof-
   of-possession key, binds it to the Access Token, and provides it to
   the joining node in the 'cnf' parameter of the Access Token response.
   Instead, if asymmetric keys are used, the joining node provides its
   own public key to the AS in the 'req_cnf' parameter of the Access
   Token request.  Then, the AS uses it as proof-of-possession key bound
   to the Access Token, and provides the joining node with the Group
   Manager's public key in the 'rs_cnf' parameter of the Access Token
   response.






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4.  Joining Node to Group Manager

   The following subsections describe the interactions between the
   joining node and the Group Manager, i.e. the Access Token post and
   the Request-Response exchange to join the OSCORE group.

4.1.  Token Post

   The joining node posts the Access Token to the /authz-info endpoint
   at the Group Manager, according to the Token post defined in
   Section 3.3 of [I-D.ietf-ace-key-groupcomm].

   At this point in time, the joining node might not have all the
   necessary information concerning the public keys in the OSCORE group,
   as well as concerning the algorithm and related parameters for
   computing countersignatures in the OSCORE group.  In such a case, the
   joining node MAY use the 'sign_info' and 'pub_key_enc' parameters
   defined in Section 3.3 of [I-D.ietf-ace-key-groupcomm] to ask for
   such information.

   Alternatively, the joining node may retrieve this information by
   other means, e.g. by using the approach described in
   [I-D.tiloca-core-oscore-discovery].

   If the Access Token is valid, the Group Manager responds to the POST
   request with a 2.01 (Created) response, according to what is
   specified in the signalled transport profile of ACE.  The Group
   Manager MUST use the Content-Format "application/ace+cbor" defined in
   Section 8.14 of [I-D.ietf-ace-oauth-authz].

   The payload of the 2.01 (Created) response is a CBOR map, which MUST
   include the 'cnonce' parameter defined in section 5.1.2 of
   [I-D.ietf-ace-oauth-authz], and MAY include the 'sign_info' parameter
   as well as the 'pub_key_enc' parameter.

   The 'cnonce' parameter includes a nonce N generated by the Group
   Manager.  The joining node may use this nonce in order to prove the
   possession of its own private key, upon joining the group (see
   Section 4.2).

   If present in the response:

   o  'sign_alg', i.e. the first element of the 'sign_info' parameter,
      takes value from Tables 5 and 6 of [RFC8152].

   o  'sign_parameters', i.e. the second element of the 'sign_info'
      parameter, takes values from the "Counter Signature Parameters"
      Registry (see Section 9.1 of [I-D.ietf-core-oscore-groupcomm]).



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      Its structure depends on the value of 'sign_alg'.  If no
      parameters of the counter signature algorithm are specified,
      'sign_parameters' MUST be encoding the CBOR simple value Null.

   o  'sign_key_parameters', i.e. the third element of the 'sign_info'
      parameter, takes values from the "Counter Signature Key
      Parameters" Registry (see Section 9.2 of
      [I-D.ietf-core-oscore-groupcomm]).  Its structure depends on the
      value of 'sign_alg'.  If no parameters of the key used with the
      counter signature algorithm are specified, 'sign_key_parameters'
      MUST be encoding the CBOR simple value Null.

   o  'pub_key_enc' takes value from Figure 2, as a public key encoding
      in the "ACE Public Key Encoding" Registry (see Section 11.2 of
      [I-D.ietf-ace-key-groupcomm]).

    +----------+-------+--------------------------------+-------------+
    | Name     | Value |          Description           |  Reference  |
    +----------+-------+--------------------------------+-------------+
    | COSE_Key |   1   | Public key encoded as COSE Key | {{RFC8152}} |
    +----------+-------+--------------------------------+-------------+

                 Figure 2: ACE Public Key Encoding Values

   Note that the CBOR map specified as payload of the 2.01 (Created)
   response may include further parameters, e.g. according to the
   signalled transport profile of ACE.

   Finally, the joining node establishes a secure channel with the Group
   Manager, according to what is specified in the Access Token response
   and the signalled transport profile of ACE.

4.2.  Join Request

   Once a secure communication channel with the Group Manager has been
   established, the joining node requests to join the OSCORE group, by
   accessing the related join resource at the Group Manager.

   In particular, the joining node sends to the Group Manager a
   confirmable CoAP request, using the method POST and targeting the
   join endpoint associated to that group.  This Join Request follows
   the format and processing of the Key Distribution Request message
   defined in Section 4.1 of [I-D.ietf-ace-key-groupcomm].  In
   particular:

   o  The 'type' parameter is set to 1 ("key distribution").





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   o  The 'get_pub_keys' parameter is present only if the joining node
      wants to retrieve the public keys of the group members from the
      Group Manager during the join process (see Section 6).  Otherwise,
      this parameter MUST NOT be present.

   o  The 'client_cred' parameter, if present, includes the public key
      of the joining node.  In case the joining node knows the encoding
      of public keys in the OSCORE group, as well as the
      countersignature algorithm and possible associated parameters used
      in the OSCORE group, the included public key MUST be in a
      consistent format.  This parameter MAY be omitted if: i) the
      joining node is asking to access the group exclusively as monitor;
      or ii) the Group Manager already acquired this information, for
      instance during a past join process.  In any other case, this
      parameter MUST be present.

   Furthermore, the CBOR map specified as payload of the Join Request
   MAY also include the following additional parameter, which MUST be
   present if the 'client_cred' parameter is present.

   o  The 'client_cred_verify' parameter, which is encoded as a CBOR
      byte string and contains a signature computed by the joining node,
      in order to prove possession of its own private key.  The
      signature is computed over the nonce N received in the 2.01
      (Created) response to the Token POST (see Section 4.1).  In
      particular, the joining node MUST use the COSE_CounterSignature0
      object [RFC8152], with the Sig_structure containing the nonce N as
      payload; and an empty external_aad.  The joining node computes the
      signature by using the same private key and countersignature
      algorithm it intends to use for signing messages in the OSCORE
      group.

4.3.  Join Response

   The Group Manager processes the Join Request according to
   [I-D.ietf-ace-oauth-authz] and Section 4.2 of
   [I-D.ietf-ace-key-groupcomm].  Also, the Group Manager MUST return a
   4.00 (Bad Request) response in case the Join Request includes the
   'client_cred' parameter but does not include the 'client_cred_verify'
   parameter.

   If the request processing yields a positive outcome, the Group
   Manager performs the further following checks.

   o  In case the Join Request includes the 'client_cred' parameter, the
      Group Manager checks that the public key of the joining node has
      an accepted format.  That is, the public key has to be encoded as
      expected in the OSCORE group, and has to be consistent with the



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      counter signature algorithm and possible associated parameters
      used in the OSCORE group.  The join process fails if the public
      key of the joining node does not have an accepted format.

   o  In case the Join Request does not include the 'client_cred'
      parameter, the Group Manager checks whether it is storing a public
      key for the joining node, which is consistent with the encoding,
      counter signature algorithm and possible associated parameters
      used in the OSCORE group.  The join process fails if the Group
      Manager either: i) does not store a public key with an accepted
      format for the joining node; or ii) stores multiple public keys
      with an accepted format for the joining node.

   o  In case the Join Request includes the 'client_cred_verify'
      parameter, the Group Manager verifies the signature contained in
      the parameter.  To this end, it considers: i) as signed value, the
      nonce N previously provided in the 2.01 (Created) response to the
      Token POST (see Section 4.1); ii) the countersignature algorithm
      used in the OSCORE group; and iii) the public key of the joining
      node, either retrieved from the 'client_cred' parameter, or as
      stored from a past join process.  The join process fails if the
      Group Manager does not successfully verify the signature.

   If the join process has failed, the Group Manager MUST reply to the
   joining node with a 4.00 (Bad Request) response.  The payload of this
   response is a CBOR map, which includes a 'sign_info' parameter and a
   'pub_key_enc' parameter, formatted as in the Token POST response in
   Section 4.1.

   Upon receiving this response, the joining node SHOULD send a new Join
   Request to the Group Manager, which contains:

   o  The 'client_cred' parameter, including a public key in a format
      consistent with the encoding, countersignature algorithm and
      possible associated parameters indicated by the Group Manager.

   o  The 'client_cred_verify' parameter, including a signature computed
      as described in Section 4.2, by using the public key indicated in
      the current 'client_cred' parameter, with the countersignature
      algorithm and possible associated parameters indicated by the
      Group Manager.

   Otherwise, in case of success, the Group Manager updates the group
   membership by registering the joining node as a new member of the
   OSCORE group.

   Then, the Group Manager replies to the joining node providing the
   updated security parameters and keying meterial necessary to



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   participate in the group communication.  This Join Response follows
   the format and processing of the Key Distribution success Response
   message defined in Section 4.2 of [I-D.ietf-ace-key-groupcomm].  In
   particular:

   o  The 'kty' parameter identifies a key of type
      "Group_OSCORE_Security_Context object", defined in Section 9.1 of
      this specification.

   o  The 'key' parameter includes what the joining node needs in order
      to set up the OSCORE Security Context as per Section 2 of
      [I-D.ietf-core-oscore-groupcomm].  This parameter has as value a
      Group_OSCORE_Security_Context object, which is defined in this
      specification and extends the OSCORE_Security_Context object
      encoded in CBOR as defined in Section 3.2.1 of
      [I-D.ietf-ace-oscore-profile].  In particular, it contains the
      additional parameters 'cs_alg', 'cs_params', 'cs_key_params' and
      'cs_key_enc' defined in Section 9.2 of this specification.  More
      specifically, the 'key' parameter is composed as follows.

      *  The 'ms' parameter MUST be present and includes the OSCORE
         Master Secret value.

      *  The 'clientId' parameter, if present, has as value the OSCORE
         Sender ID assigned to the joining node by the Group Manager.
         This parameter is not present if the node joins the group
         exclusively as monitor, according to what specified in the
         Access Token (see Section 3.2).  In any other case, this
         parameter MUST be present.

      *  The 'hkdf' parameter, if present, has as value the KDF
         algorithm used in the group.

      *  The 'alg' parameter, if present, has as value the AEAD
         algorithm used in the group.

      *  The 'salt' parameter, if present, has as value the OSCORE
         Master Salt.

      *  The 'contextId' parameter MUST be present and has as value the
         Group Identifier (Gid) associated to the OSCORE group.

      *  The 'rpl' parameter, if present, specifies the OSCORE Replay
         Window Size and Type value.

      *  The 'cs_alg' parameter MUST be present and specifies the
         algorithm used to countersign messages in the group.  This
         parameter takes values from Tables 5 and 6 of [RFC8152].



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      *  The 'cs_params' parameter MAY be present and specifies the
         additional parameters for the counter signature algorithm.
         This parameter is a CBOR map whose content depends on the
         counter signature algorithm, as specified in Section 2 and
         Section 9.1 of [I-D.ietf-core-oscore-groupcomm].

      *  The 'cs_key_params' parameter MAY be present and specifies the
         additional parameters for the key used with the counter
         signature algorithm.  This parameter is a CBOR map whose
         content depends on the counter signature algorithm, as
         specified in Section 2 and Section 9.2 of
         [I-D.ietf-core-oscore-groupcomm].

      *  The 'cs_key_enc' parameter MAY be present and specifies the
         encoding of the public keys of the group members.  This
         parameter is a CBOR integer, whose value is taken from
         Figure 2, as a public key encoding in the "ACE Public Key
         Encoding" Registry (see Section 11.2 of
         [I-D.ietf-ace-key-groupcomm]).  If this parameter is not
         present, COSE_Key (1) MUST be assumed as default value.

   o  The 'profile' parameter MUST be present and has value
      coap_group_oscore_app (TBD), which is defined in Section 9.3 of
      this specification.

   o  The 'exp' parameter MUST be present and specifies the expiration
      time in seconds after which the OSCORE Security Context derived
      from the 'key' parameter is not valid anymore.

   o  The 'pub_keys' parameter is present only if the 'get_pub_keys'
      parameter was present in the Join Request.  If present, this
      parameter includes the public keys of the group members that are
      relevant to the joining node.  That is, it includes: i) the public
      keys of the responders currently in the group, in case the joining
      node is configured (also) as requester; and ii) the public keys of
      the requesters currently in the group, in case the joining node is
      configured (also) as responder or monitor.

   o  The 'group_policies' parameter SHOULD be present and includes a
      list of parameters indicating particular policies enforced in the
      group.  For instance, its field "Sequence Number Synchronization
      Method" can indicate the method to achieve synchronization of
      sequence numbers among group members (see Appendix E of
      [I-D.ietf-core-oscore-groupcomm]), as indicated by the
      corresponding value from the "Sequence Number Synchronization
      Method" Registry defined in Section 11.8 of
      [I-D.ietf-ace-key-groupcomm].




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   Finally, the joining node uses the information received in the Join
   Response to set up the OSCORE Security Context, as described in
   Section 2 of [I-D.ietf-core-oscore-groupcomm].  From then on, the
   joining node can exchange group messages secured with OSCORE as
   described in [I-D.ietf-core-oscore-groupcomm].

   If the application requires backward security, the Group Manager
   SHALL generate updated security parameters and group keying material,
   and provide it to all the current group members (see Section 7).

   When the OSCORE Security Context expires, as specified by the 'exp'
   parameter of the Join Response, the node considers it invalid and to
   be renewed.  Then, the node retrieves updated security parameters and
   keying material, by exchanging with the Group Manager a shortened
   Join Request sent to the same Join Resource with the 'type' parameter
   set to 3 ("update key") and a shortened Join Response message,
   according to the approach defined in Section 6 of
   [I-D.ietf-ace-key-groupcomm].  Finally, the node uses the updated
   security parameters and keying material to set up the new OSCORE
   Security Context as described in Section 2 of
   [I-D.ietf-core-oscore-groupcomm].

   Furthermore, as discussed in Section 2.2 of
   [I-D.ietf-core-oscore-groupcomm], the node may at some point
   experience a wrap-around of its own Sender Sequence Number in the
   group.  When this happens, the node MUST send to the Group Manager a
   shortened Join Request message to the same Join Resource, with the
   'type' parameter set to 4 ("new").  Upon receiving this request
   message, the Group Manager either rekeys the whole OSCORE group as
   discussed in Section 7, or generates a new Sender ID for that node
   and replies with a shortened Join Response message where:

   o  Only the parameters 'type', 'kty', 'key', 'profile' and 'exp' are
      present.

   o  The 'clientId' parameter of the 'key' parameter specifies the new
      Sender ID of the node.

5.  Leaving of a Group Member

   A node may be removed from the OSCORE group, due to expired or
   revoked authorization, or after its own request to the Group Manager.

   If the application requires forward security, the Group Manager SHALL
   generate updated security parameters and group keying material, and
   provide it to the remaining group members (see Section 7).  The
   leaving node must not be able to acquire the new security parameters
   and group keying material distributed after its leaving.



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   Same considerations in Section 5 of [I-D.ietf-ace-key-groupcomm]
   apply here as well, considering the Group Manager acting as KDC.  In
   particular, a node requests to leave the OSCORE group as described in
   Section 5.2 of [I-D.ietf-ace-key-groupcomm], i.e. by sending to the
   Group Manager a request to the same Join Resource with the 'type'
   parameter set to 2 ("leave").

6.  Public Keys of Joining Nodes

   Source authentication of OSCORE messages exchanged within the group
   is ensured by means of digital counter signatures (see Sections 2 and
   3 of [I-D.ietf-core-oscore-groupcomm]).  Therefore, group members
   must be able to retrieve each other's public key from a trusted key
   repository, in order to verify source authenticity of incoming group
   messages.

   As also discussed in [I-D.ietf-core-oscore-groupcomm], the Group
   Manager acts as trusted repository of the public keys of the group
   members, and provides those public keys to group members if requested
   to.  Upon joining an OSCORE group, a joining node is thus expected to
   provide its own public key to the Group Manager.

   In particular, one of the following four cases can occur when a new
   node joins an OSCORE group.

   o  The joining node is going to join the group exclusively as
      monitor.  That is, it is not going to send messages to the group,
      and hence to produce signatures with its own private key.  In this
      case, the joining node is not required to provide its own public
      key to the Group Manager, which thus does not have to perform any
      check related to the public key encoding, or to a countersignature
      algorithm and possible associated parameters for that joining
      node.

   o  The Group Manager already acquired the public key of the joining
      node during a past join process.  In this case, the joining node
      MAY not provide again its own public key to the Group Manager, in
      order to limit the size of the Join Request.  The joining node
      MUST provide its own public key again if it has provided the Group
      Manager with multiple public keys during past join processes,
      intended for different OSCORE groups.  If the joining node
      provides its own public key, the Group Manager performs
      consistency checks as in Section 4.3 and, in case of success,
      considers it as the public key associated to the joining node in
      the OSCORE group.






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   o  The joining node and the Group Manager use an asymmetric proof-of-
      possession key to establish a secure communication channel.  Then,
      two cases can occur.

      1.  The proof-of-possession key is consistent with the encoding as
          well as with the counter signature algorithm and possible
          associated parameters used in the OSCORE group.  Then, the
          Group Manager considers the proof-of-possession key as the
          public key associated to the joining node in the OSCORE group.
          If the joining node is aware that the proof-of-possession key
          is also valid for the OSCORE group, it MAY not provide it
          again as its own public key to the Group Manager.  The joining
          node MUST provide its own public key again if it has provided
          the Group Manager with multiple public keys during past join
          processes, intended for different OSCORE groups.  If the
          joining node provides its own public key in the 'client_cred'
          parameter of the Join Request (see Section 4.2), the Group
          Manager performs consistency checks as in Section 4.3 and, in
          case of success, considers it as the public key associated to
          the joining node in the OSCORE group.

      2.  The proof-of-possession key is not consistent with the
          encoding or with the counter signature algorithm and possible
          associated parameters used in the OSCORE group.  In this case,
          the joining node MUST provide a different consistent public
          key to the Group Manager in the 'client_cred' parameter of the
          Join Request (see Section 4.2).  Then, the Group Manager
          performs consistency checks on this latest provided public key
          as in Section 4.3 and, in case of success, considers it as the
          public key associated to the joining node in the OSCORE group.

   o  The joining node and the Group Manager use a symmetric proof-of-
      possession key to establish a secure communication channel.  In
      this case, upon performing a join process with that Group Manager
      for the first time, the joining node specifies its own public key
      in the 'client_cred' parameter of the Join Request targeting the
      join endpoint (see Section 4.2).

   Furthermore, as described in Section 4.2, the joining node may have
   explicitly requested the Group Manager to retrieve the public keys of
   the current group members, i.e. by including the 'get_pub_keys'
   parameter in the Join Request.  In this case, the Group Manager
   includes also such public keys in the 'pub_keys' parameter of the
   Join Response (see Section 4.3).

   Later on as a group member, the node may need to retrieve the public
   keys of other group members.  The node can do that by exchanging with
   the Group Manager a shortened Join Request sent to the same Join



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   Resource with the 'type' parameter set to 5 ("pub keys") and a
   shortened Join Response, according to the approach defined in
   Section 7 of [I-D.ietf-ace-key-groupcomm].

7.  Group Rekeying Process

   In order to rekey the OSCORE group, the Group Manager distributes a
   new Group ID of the group and a new OSCORE Master Secret for that
   group.  When doing so, the Group Manager MAY take a best effort to
   preserve the same unchanged Sender IDs for all group members.  This
   avoids affecting the retrieval of public keys from the Group Manager
   as well as the verification of message countersignatures.

   The Group Manager MUST support at least the following group rekeying
   scheme.  Future application profiles may define alternative message
   formats and distribution schemes.

   The Group Manager uses the same format of the Join Response message
   in Section 4.3.  In particular:

   o  Only the parameters 'type', 'kty', 'key', 'profile' and 'exp' are
      present.

   o  The 'ms' parameter of the 'key' parameter specifies the new OSCORE
      Master Secret value.

   o  The 'contextId' parameter of the 'key' parameter specifies the new
      Group ID.

   The Group Manager separately sends a group rekeying message to each
   group member to be rekeyed.  Each rekeying message MUST be secured
   with the pairwise secure communication channel between the Group
   Manager and the group member used during the join process.

   This approach requires group members to act (also) as servers, in
   order to correctly handle unsolicited group rekeying messages from
   the Group Manager.  In particular, if a group member and the Group
   Manager use OSCORE [I-D.ietf-core-object-security] to secure their
   pairwise communications, the group member MUST create a Replay Window
   in its own Recipient Context upon establishing the OSCORE Security
   Context with the Group Manager, e.g. by means of the OSCORE profile
   of ACE [I-D.ietf-ace-oscore-profile].

   Group members and the Group Manager SHOULD additionally support
   alternative rekeying approaches that do not require group members to
   act (also) as servers.  A number of such approaches are defined in
   Section 6 of [I-D.ietf-ace-key-groupcomm], and are based on the
   following rationale:



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   o  A group member queries the Group Manager for updated group keying
      material, by sending a dedicated request to the same Join Resource
      targeted when joining the group.  Like for the case discussed in
      Section 4.3 where the OSCORE Security Context expires, the group
      member exchanges with the Group Manager a shortened Join Request
      sent to the same Join Resource with the 'type' parameter set to 3
      ("update key") and a shortened Join Response message, according to
      the approach defined in Section 6 of [I-D.ietf-ace-key-groupcomm].

   o  A group member subscribes for updates to the join resource and its
      associated group keying material on the Group Manager.  This can
      rely on CoAP Observe [RFC7641] or on a full-fledged Pub-Sub model
      [I-D.ietf-core-coap-pubsub] with the Group Manager acting as
      Broker.

   Either case, the Group Manager provides the (updated) group keying
   material as specified above in this section.

8.  Security Considerations

   The method described in this document leverages the following
   management aspects related to OSCORE groups and discussed in the
   sections of [I-D.ietf-core-oscore-groupcomm] referred below.

   o  Management of group keying material (see Section 2.1 of
      [I-D.ietf-core-oscore-groupcomm]).  The Group Manager is
      responsible for the renewal and re-distribution of the keying
      material in the groups of its competence (rekeying).  According to
      the specific application requirements, this can include rekeying
      the group upon changes in its membership.  In particular, renewing
      the keying material is required upon a new node's joining or a
      current node's leaving, in case backward security and forward
      security have to be preserved, respectively.

   o  Provisioning and retrieval of public keys (see Section 2 of
      [I-D.ietf-core-oscore-groupcomm]).  The Group Manager acts as key
      repository of public keys of group members, and provides them upon
      request.

   o  Synchronization of sequence numbers (see Section 5 of
      [I-D.ietf-core-oscore-groupcomm]).  This concerns how a responder
      node that has just joined an OSCORE group can synchronize with the
      sequence number of requesters in the same group.

   Before sending the Join Response, the Group Manager MUST verify that
   the joining node actually owns the associated private key.  To this
   end, the Group Manager can rely on the proof-of-possession challenge-
   response defined in Section 4.  Alternatively, the joining node can



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   use its own public key as asymmetric proof-of-possession key to
   establish a secure channel with the Group Manager, e.g. as in
   Section 3.2 of [I-D.ietf-ace-dtls-authorize].  However, this requires
   such proof-of-possession key to be consistent with the encoding as
   well as with the countersignature algorithm and possible associated
   parameters used in the OSCORE group.

   A node may have joined multiple OSCORE groups under different non-
   synchronized Group Managers.  Therefore, it can happen that those
   OSCORE groups have the same Group Identifier (Gid).  It follows that,
   upon receiving a Group OSCORE message addressed to one of those
   groups, the node would have multiple Security Contexts matching with
   the Gid in the incoming message.  It is up to the application to
   decide how to handle such collisions of Group Identifiers, e.g. by
   trying to process the incoming message using one Security Context at
   the time until the right one is found.

   Further security considerations are inherited from
   [I-D.ietf-ace-key-groupcomm], the ACE framework for Authentication
   and Authorization [I-D.ietf-ace-oauth-authz], and the specific
   transport profile of ACE signalled by the AS, such as
   [I-D.ietf-ace-dtls-authorize] and [I-D.ietf-ace-oscore-profile].

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.

   This document has the following actions for IANA.

9.1.  ACE Groupcomm Key Registry

   IANA is asked to register the following entry in the "ACE Groupcomm
   Key" Registry defined in Section 11.5 of
   [I-D.ietf-ace-key-groupcomm].

   o  Name: Group_OSCORE_Security_Context object

   o  Key Type Value: TBD

   o  Profile: "coap_group_oscore_app", defined in Section 9.3 of this
      specification.

   o  Description: A Group_OSCORE_Security_Context object encoded as
      described in Section 4.3 of this specification.

   o  Reference: [[This specification]]



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9.2.  OSCORE Security Context Parameters Registry

   IANA is asked to register the following entries in the "OSCORE
   Security Context Parameters" Registry defined in Section 9.2 of
   [I-D.ietf-ace-oscore-profile].

   o  Name: cs_alg

   o  CBOR Label: TBD

   o  CBOR Type: tstr / int

   o  Registry: COSE Algorithm Values (ECDSA, EdDSA)

   o  Description: OSCORE Counter Signature Algorithm Value

   o  Reference: [[This specification]]

   o  Name: cs_params

   o  CBOR Label: TBD

   o  CBOR Type: map

   o  Registry: Counter Signatures Parameters

   o  Description: OSCORE Counter Signature Algorithm Additional
      Parameters

   o  Reference: [[This specification]]

   o  Name: cs_key_params

   o  CBOR Label: TBD

   o  CBOR Type: map

   o  Registry: Counter Signatures Key Parameters

   o  Description: OSCORE Counter Signature Key Additional Parameters

   o  Reference: [[This specification]]

   o  Name: cs_key_enc

   o  CBOR Label: TBD

   o  CBOR Type: integer



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   o  Registry: ACE Public Key Encoding

   o  Description: Encoding of Public Keys to be used with the OSCORE
      Counter Signature Algorithm

   o  Reference: [[This specification]]

9.3.  ACE Groupcomm Profile Registry

   IANA is asked to register the following entry in the "ACE Groupcomm
   Profile" Registry defined in Section 11.6 of
   [I-D.ietf-ace-key-groupcomm].

   o  Name: coap_group_oscore_app

   o  Description: Application profile to provision keying material for
      participating in group communication protected with Group OSCORE
      as per [I-D.ietf-core-oscore-groupcomm].

   o  CBOR Value: TBD

   o  Reference: [[This specification]]

9.4.  Sequence Number Synchronization Method Registry

   IANA is asked to register the following entries in the "Sequence
   Number Synchronization Method" Registry defined in Section 11.8 of
   [I-D.ietf-ace-key-groupcomm].

   o  Name: Best effort

   o  Value: 1

   o  Description: No action is taken.

   o  Reference: [I-D.ietf-core-oscore-groupcomm] (Appendix E.1).

   o  Name: Baseline

   o  Value: 2

   o  Description: The first received request sets the baseline
      reference point, and is discarded with no delivery to the
      application.

   o  Reference: [I-D.ietf-core-oscore-groupcomm] (Appendix E.2).

   o  Name: Echo challenge-response



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   o  Value: 3

   o  Description: Challenge response using the Echo Option for CoAP
      from [I-D.ietf-core-echo-request-tag].

   o  Reference: [I-D.ietf-core-oscore-groupcomm] (Appendix E.3).

9.5.  ACE Public Key Encoding Registry

   This specification registers the value defined in Figure 2 in the
   "ACE Public Key Encoding" IANA Registry.

10.  References

10.1.  Normative References

   [I-D.ietf-ace-key-groupcomm]
              Palombini, F. and M. Tiloca, "Key Provisioning for Group
              Communication using ACE", draft-ietf-ace-key-groupcomm-02
              (work in progress), July 2019.

   [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-24
              (work in progress), March 2019.

   [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-07 (work in progress), February 2019.

   [I-D.ietf-core-object-security]
              Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security for Constrained RESTful Environments
              (OSCORE)", draft-ietf-core-object-security-16 (work in
              progress), March 2019.

   [I-D.ietf-core-oscore-groupcomm]
              Tiloca, M., Selander, G., Palombini, F., and J. Park,
              "Group OSCORE - Secure Group Communication for CoAP",
              draft-ietf-core-oscore-groupcomm-05 (work in progress),
              July 2019.






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   [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>.

10.2.  Informative References

   [I-D.dijk-core-groupcomm-bis]
              Dijk, E., Wang, C., and M. Tiloca, "Group Communication
              for the Constrained Application Protocol (CoAP)", draft-
              dijk-core-groupcomm-bis-00 (work in progress), March 2019.

   [I-D.ietf-ace-dtls-authorize]
              Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
              L. Seitz, "Datagram Transport Layer Security (DTLS)
              Profile for Authentication and Authorization for
              Constrained Environments (ACE)", draft-ietf-ace-dtls-
              authorize-08 (work in progress), April 2019.

   [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-08 (work in
              progress), March 2019.

   [I-D.ietf-core-echo-request-tag]
              Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo,
              Request-Tag, and Token Processing", draft-ietf-core-echo-
              request-tag-05 (work in progress), May 2019.

   [I-D.tiloca-core-oscore-discovery]
              Tiloca, M., Amsuess, C., and P. Stok, "Discovery of OSCORE
              Groups with the CoRE Resource Directory", draft-tiloca-
              core-oscore-discovery-02 (work in progress), March 2019.




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

   [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>.

   [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>.

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,
              <https://www.rfc-editor.org/info/rfc7641>.

Appendix A.  Profile Requirements

   This appendix lists the specifications on this application profile of
   ACE, based on the requiremens defined in Appendix A of
   [I-D.ietf-ace-key-groupcomm].

   o  Communication protocol that the members of the group must use:
      CoAP, possibly over IP multicast.

   o  Security protocols that the group members must use to protect
      their communication: Group OSCORE.

   o  Specify the encoding and value of the identifier of group and role
      of 'scope': see Section 3.1.

   o  Profile identifier: coap_group_oscore_app

   o  Acceptable values of 'kty': Group_OSCORE_Security_Context object

   o  Specify the format and content of 'group_policies' entries: three
      values are defined and registered, as content of the entry
      "Sequence Number Synchronization Method" (see Section 9.4).

   o  (Optional) specify the format and content of 'mgt_key_material':
      no.

   o  (Optional) specify the transport profile of ACE
      [I-D.ietf-ace-oauth-authz] to use between Client and Group
      Manager: any transport profile of ACE that complies with the
      requirements in Appendix C of [I-D.ietf-ace-oauth-authz].



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   o  (Optional) specify the encoding of public keys, of 'client_cred',
      and of 'pub_keys' if COSE_Keys are not used: no.

   o  (Optional) specify the acceptable values for parameters related to
      signature algorithm and signature keys: 'sign_alg' takes value
      from Tables 5 and 6 of [RFC8152]; 'sign_parameters' takes values
      from the "Counter Signature Parameters" Registry (see Section 9.1
      of [I-D.ietf-core-oscore-groupcomm]); 'sign_key_parameters' takes
      values from the "Counter Signature Key Parameters" Registry (see
      Section 9.2 of [I-D.ietf-core-oscore-groupcomm]); 'pub_key_enc'
      takes value from Figure 2 in Section 4.1.

   o  (Optional) specify the negotiation of parameter values for
      signature algorithm and signature keys, if 'sign_info' and
      'pub_key_enc' are not used: pre-knowledge by using the approach
      based on the CoRE Resource Directory described in
      [I-D.tiloca-core-oscore-discovery].

Appendix B.  Document Updates

   RFC EDITOR: PLEASE REMOVE THIS SECTION.

B.1.  Version -01 to -02

   o  Editorial fixes.

   o  Changed: "listener" to "responder"; "pure listener" to "monitor".

   o  Changed profile name to "coap_group_oscore_app", to reflect it is
      an application profile.

   o  Added the 'type' parameter for all requests to a Join Resource.

   o  Added parameters to indicate the encoding of public keys.

   o  Challenge-response for proof-of-possession of signature keys
      (Section 4).

   o  Renamed 'key_info' parameter to 'sign_info'; updated its format;
      extended to include also parameters of the countersignature key
      (Section 4.1).

   o  Code 4.00 (Bad request), in responses to joining nodes providing
      an invalid public key (Section 4.3).

   o  Clarifications on provisioning and checking of public keys
      (Sections 4 and 6).




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   o  Extended discussion on group rekeying and possible different
      approaches (Section 7).

   o  Extended security considerations: proof-of-possession of signature
      keys; collision of OSCORE Group Identifiers (Section 8).

   o  Registered three entries in the IANA Registry "Sequence Number
      Synchronization Method Registry" (Section 9).

   o  Registered one public key encoding in the "ACE Public Key
      Encoding" IANA Registry (Section 9).

B.2.  Version -00 to -01

   o  Changed name of 'req_aud' to 'audience' in the Authorization
      Request (Section 3.1).

   o  Added negotiation of countersignature algorithm/parameters between
      Client and Group Manager (Section 4).

   o  Updated format of the Key Distribution Response as a whole
      (Section 4.3).

   o  Added parameter 'cs_params' in the 'key' parameter of the Key
      Distribution Response (Section 4.3).

   o  New IANA registrations in the "ACE Authorization Server Request
      Creation Hints" Registry, "ACE Groupcomm Key" Registry, "OSCORE
      Security Context Parameters" Registry and "ACE Groupcomm Profile"
      Registry (Section 9).

Acknowledgments

   The authors sincerely thank Santiago Aragon, Stefan Beck, Martin
   Gunnarsson, Rikard Hoeglund, Jim Schaad, Ludwig Seitz, Goeran
   Selander and Peter van der Stok for their comments and feedback.

   The work on this document has been partly supported by VINNOVA and
   the Celtic-Next project CRITISEC; and by the EIT-Digital High Impact
   Initiative ACTIVE.

Authors' Addresses









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   Marco Tiloca
   RISE AB
   Isafjordsgatan 22
   Kista  SE-164 29 Stockholm
   Sweden

   Email: marco.tiloca@ri.se


   Jiye Park
   Universitaet Duisburg-Essen
   Schuetzenbahn 70
   Essen  45127
   Germany

   Email: ji-ye.park@uni-due.de


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

   Email: francesca.palombini@ericsson.com


























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