wdiff draft-ietf-ace-key-groupcomm-01.txt draft-ietf-ace-key-groupcomm-02.txt

ACE Working Group F. Palombini
Internet-Draft Ericsson AB
Intended status: Standards Track M. Tiloca
Expires: September 9, 2019 January 6, 2020 RISE AB
March 08,
July 05, 2019

Key Provisioning for Group Communication using ACE
draft-ietf-ace-key-groupcomm-01
draft-ietf-ace-key-groupcomm-02

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

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provisions of BCP 78 and BCP 79.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4
3. Authorization to Join a Group . . . . . . . . . . . . . . . . 5 6
3.1. Authorization Request . . . . . . . . . . . . . . . . . . 6 7
3.2. Authorization Response . . . . . . . . . . . . . . . . . 7
3.3. Token Post . . . . . . . . . . . . . . . . . . . . . . . 8
4. Key Distribution . . . . . . . . . . . . . . . . . . . . . . 8 11
4.1. Key Distribution Request . . . . . . . . . . . . . . . . 9 12
4.2. Key Distribution Response . . . . . . . . . . . . . . . . 10 13
5. Removal of a Node from the Group . . . . . . . . . . . . . . 12 16
5.1. Expired Authorization . . . . . . . . . . . . . . . . . . 12 16
5.2. Request to Leave the Group . . . . . . . . . . . . . . . 12 16
6. Retrieval of New or Updated Keying Material . . . . . . . . . . . . 13 17
6.1. Key Re-Distribution Request . . . . . . . . . . . . . . . 14 18
6.2. Key Re-Distribution Response . . . . . . . . . . . . . . 14 19
7. Retrieval of Public Keys for Group Members . . . . . . . . . 15 19
7.1. Public Key Request . . . . . . . . . . . . . . . . . . . 15 20
7.2. Public Key Response . . . . . . . . . . . . . . . . . . . 16 20
8. ACE Groupcomm Parameters . . . . . . . . . . . . . . . . . . 21
9. ACE Groupcomm Request Type . . . . . . . . . . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. 23
10.1. Update of Keying Material . . . . . . . . . . . . . . . 24
10.2. Block-Wise Considerations . . . . . . . . . . . . . . . 24
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9.1. 25
11.1. ACE Authorization Server Request Creation Hints Registry 25
11.2. ACE Public Key Encoding Registry . . . . . . . . . . . . 25
11.3. ACE Groupcomm Parameters Registry . . . . . . . . . . . 26
11.4. Ace Groupcomm Request Type Registry . . . . . . . . . . 26
11.5. ACE Groupcomm Key Registry . . . . . . . . . . . . . . . 16
9.2. 27
11.6. ACE Groupcomm Profile Registry . . . . . . . . . . . . . 17
9.3. 28
11.7. ACE Groupcomm Policy Registry . . . . . . . . . . . . . 28
11.8. Sequence Number Synchronization Method Registry . . . . 29
11.9. Expert Review Instructions . . . . . . . . . . . . . . . 18
10. 29
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. 30
12.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. 30
12.2. Informative References . . . . . . . . . . . . . . . . . 19 31
Appendix A. Requirements on Application Profiles . . . . . . . . 33
Appendix B. Document Updates . . . . . . . . . . . . . . . . . . 20
A.1. 33
B.1. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 34
B.2. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 20 34
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 35

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] [RFC7390][I-D.dijk-core-groupcomm-bis] or on publishing-subscribing publishing-
subscribing [I-D.ietf-core-coap-pubsub].

Profiles that use group communication can build The ACE framework is based
on this document CBOR [RFC7049], so CBOR is the format used in this specification.
However, using JSON [RFC8259] instead of CBOR is possible, using the
conversion method specified in Sections 4.1 and 4.2 of [RFC7049].

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 those addressing
group communication based on multicast [RFC7390]
[RFC7390][I-D.dijk-core-groupcomm-bis] or publishing/
subscribing 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
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).

This document additionally uses the following terminology:

o Transport profile, to indicate a profile of ACE as per
Section 5.6.4.3 of [I-D.ietf-ace-oauth-authz]. That is, a
transport profile specifies the communication protocol and
communication security protocol between an ACE Client and Resource
Server, as well as proof-of-possession methods, if it supports
proof-of-possession access tokens. Tranport profiles of ACE
include, for instance, [I-D.ietf-ace-oscore-profile],
[I-D.ietf-ace-dtls-authorize] and [I-D.ietf-ace-mqtt-tls-profile].

o Application profile, to indicate a profile of ACE that defines how
applications enforce and use supporting security services they
require. These services include, for instance, provisioning,
revocation and (re-)distribution of keying material. An
application profile may define specific procedures and message
formats.

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
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.

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 transport
profile of ACE 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
transport profile of ACE 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
Section 3.2). Communications between the Client and the AS MUST be
secured, and depends on according to the transport profile of ACE used. The
Content-Format used in the messages is the one specified by the used
transport profile of ACE (e.g. application/ace+cbor for the first two
messages and application/cwt for the third message, depending on the
format of the access token).

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', containing the identifier of the specific group (or topic
in the case of pub-sub) that the Client wishes to access, and
optionally the role(s) that 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 'audience', with an identifier of a KDC.

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

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
'scope' of the Authorization Request otherwise), and additionally
other optional parameters that the transport profile of ACE 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 replies with an Authorization Response
including with 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 Section 5.8.1 of [I-D.ietf-ace-oauth-authz].
If the specific ACE transport profile of ACE defines it, the Client MAY
use a different endpoint than /authz-info at the KDC to post the
access token to. After successful verification,

Optionally, the Client is authorized might need to
receive request necessary information
concerning the group keying material from public keys in the KDC group, as well as concerning the
algorithm and join related parameters for computing signatures in the
group.

Note In such a case, the joining node MAY ask for that this step could be merged with information
to the following message from KDC in this same request. To this end, it sends the Client CoAP POST
request to the KDC, namely Key Distribution Request.

4. Key Distribution

This section defines how /authz-info endpoint using the keying material used for group
communication is distributed from Content-Format
"application/ace+cbor" defined in Section 8.14 of
[I-D.ietf-ace-oauth-authz], and includes also the KDC following
parameters:

o 'sign_info' defined in Section 3.3.1, encoding the CBOR simple
value Null, to require information and parameters on the Client, when joining signature
algorithm and on the group as a new member.

If not previously established, public keys used in the Client and group.

o 'pub_key_enc' defined in Section 3.3.2, encoding the KDC MUST first
establish a pairwise secure communication channel using ACE. The
exchange CBOR simple
value Null, to require information on the exact encoding of Key Distribution Request-Response MUST occur over that
secure channel. public
keys used in the group.

The Client CDDL notation of the 'sign_info' and 'pub_key_enc' parameters
formatted as in the KDC MAY use that same secure
channel to protect further pairwise communications, that MUST be
secured.

During request is given below.

sign_info_req = nil

pub_key_enc_req = nil

Alternatively, the joining node may retrieve this exchange, information by
other means.

After successful verification, the Client sends a request is authorized to the AS,
specifying receive
the group it wishes to join (see Section 4.1). Then, keying material from the KDC verifies the access token and that the Client is authorized to join that group; if so, it provides the Client with group. In
particular, the keying
material KDC replies to securely communicate with the member of the group (see
Section 4.2).

Figure 4 gives an overview of the exchange described above. Client KDC
| |
|---- Key Distribution Request: POST /group-id --->|
| |
|<--- Key Distribution Response: with a 2.01 (Created) ---|
| |

Figure 4: Message Flow
response, using Content-Format "application/ace+cbor" defined in
Section 8.14 of Key Distribution to a New Group Member [I-D.ietf-ace-oauth-authz].

The same set payload of message can also be used for the following cases,
when the Client 2.01 response is already a group member:

o The Client wishes to (re-)get CBOR map, which MUST include a
nonce N generated by 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 KDC. The Client wishes to (re-)get may use this nonce for
proving the public keys of other group
members, e.g. if it is aware possession of new nodes joining its own private key (see the group after
itself. This is further discussed
'client_cred_verify' parameter in Section 7.

Additionally, 4).

Optionally, if they were included in the format of request, the payload of AS MAY include
the Key Distribution
Response (Section 4.2) can be reused for messages sent by 'sign_info' parameter as well as the KDC to
distribute updated group keying material, 'pub_key_enc' parameter
defined in case Section 3.3.1 and Section 3.3.2 of a new node
joining this specification,
respectively.

The 'sign_info' parameter MUST be present if the group or of a current member leaving POST request
included the group. The key
management scheme used to send such messages could rely on, e.g.,
multicast in case 'sign_info' parameter with value Null. If present, the
'sign_info' parameter of the 2.01 (Created) response is a new node joining CBOR array
formatted as follows.

o The first element 'sign_alg' is an integer or unicast in case of a node
leaving text string,
indicating the signature algorithm used in the group.

Note that proof-of-possession to bind It is
required of the access token application profiles to define specific values for
this parameter.

o The second element 'sign_parameters' indicates the Client parameters of
the signature algorithm. Its structure depends on the value of
'sign_alg'. It is performed by using required of the proof-of-possession key bound application profiles to the access
token define
specific values for establishing secure communication between this parameter. If no parameters of 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
signature algorithm are specified, 'sign_parameters' MUST be
encoding the 'scope' CBOR simple value of the Authorization Request/
Response. Null.

o The payload of this request is a CBOR Map which MAY
contain third element 'sign_key_parameters' indicates the following fields, which, if included, MUST have parameters
of the
corresponding values:

o 'scope', key used with value the specific resource that signature algorithm. Its structure
depends on the Client value of 'sign_alg'. It is
authorized to access (i.e. group or topic identifier) and role(s),
encoded as in Section 3.1.

o 'get_pub_keys', if required of the Client wishes
application profiles to receive the public keys define specific values for this parameter.
If no parameters of the other nodes in key used with the group from signature algorithm are
specified, 'sign_key_parameters' MUST be encoding the KDC. The value is an empty CBOR Array. This simple
value Null.

The 'pub_key_enc' parameter may MUST be present if the KDC stores the
public keys of POST request
included the nodes in 'pub_key_enc' parameter with value Null. If present,
the group and distributes them to 'pub_key_enc' parameter of the
Client; it 2.01 (Created) response is useless to have here if a CBOR
integer, indicating the set encoding of public keys of used in the members group.
The values of the group is known this field are registered in another way, e.g. it was
provided by the AS.

o 'client_cred', with value the public key or certificate "ACE Public Key
Encoding" Registry, defined in Section 11.2. It is required of the
Client. If the KDC is managing (collecting from/distributing
application profiles to
the Client) the public keys define specific values to use for this
parameter.

The CDDL notation of the group members, this field
contains the public key of 'sign_info' and 'pub_key_enc' parameters
formatted as in the Client.

o 'pub_keys_repos', can be present if a certificate response is present in given below.

sign_info_res = [
sign_alg : int / tstr,
sign_parameters : any / nil,
sign_key_parameters : any / nil
]

pub_key_enc_res = int

Note that the 'client_cred' field, with value a list CBOR map specified as payload of public key
repositories storing the certificate 2.01 (Created)
response may include further parameters, e.g. according to the
signalled transport profile of ACE.

Note that this step could be merged with the Client.

4.2. following message from
the Client to the KDC, namely Key Distribution Response Request.

3.3.1. 'sign_info' Parameter

The KDC verifies 'sign_info' parameter is an OPTIONAL parameter of the 'scope' received AS Request
Creation Hints message defined in Section 5.1.2. of
[I-D.ietf-ace-oauth-authz]. This parameter contains information and
parameters about the Key Distribution
Request, if present, against signature algorithm and the 'scope' stored public keys to be
used between the Client and the RS. Its exact content is application
specific.

3.3.2. 'pub_key_enc' Parameter

The 'pub_key_enc' parameter is an OPTIONAL parameter of the AS
Request Creation Hints message defined in Section 5.1.2. of
[I-D.ietf-ace-oauth-authz]. This parameter contains information
about the access token
associated exact encoding of public keys to this client. If verification fails, be used between the KDC MUST
respond with a 4.01 (Unauthorized) error message. If Client
and the RS. Its exact content is application specific.

4. Key Distribution Request

This section defines how the keying material used for group
communication is not formatted correctly (e.g. no 'scope'
field present while expected, or unknown fields present), distributed from the KDC
MUST respond with 4.00 (Bad Request) error message. to the Client, when joining
the group as a new member.

If verification succeeds, not previously established, the Client and the KDC sends MUST first
establish a pairwise secure communication channel using ACE. The
exchange of Key Distribution success
Response to the Client. Request-Response MUST occur over that
secure channel. The Key Distribution success Response
corresponds Client and the KDC MAY use that same secure
channel to a 2.01 Created message. The payload of protect further pairwise communications, that MUST be
secured.

During this response
is exchange, the Client sends a CBOR map, which MUST contain:

o 'kty', identifying request to the key type of AS,
specifying the 'key' parameter. The set
of values can be found in group it wishes to join (see Section 4.1). Then, the "Key Type" column of
KDC verifies the "ACE
Groupcomm Key" Registry. Implementations MUST verify access token and that the key
type matches the profile being used, Client is authorized to
join that group; if present, as registered in so, it provides the "ACE Groupcomm Key" registry.

o 'key', containing Client with the keying
material for the group communication,
or information required to derive it.

The exact format of securely communicate with the 'key' value MUST be defined in applications member of this specification. Additionally, documents specifying the key
format MUST register it group (see
Section 4.2). The Content-Format used in the "ACE Groupcomm Key" registry,
including its name, type and profile messages is set to be used with, as defined in
application/cbor.

Figure 4 gives an overview of the "ACE Groupcomm Key" registry, defined in Section 9.1.

+----------+----------------+---------+-------------------------+ exchange described above.

Client KDC
| Name |
|---- Key Type Value | Profile | Description |
+----------+----------------+---------+-------------------------+
| Reserved Distribution Request: POST /group-id --->|
| 0 |
|<--- Key Distribution Response: 2.01 (Created) ---|
| This value is reserved |
+----------+----------------+---------+-------------------------+

Figure 5: Key Type Values

Optionally, the 4: Message Flow of Key Distribution Response MAY contain the following
parameters, which, if included, MUST have the corresponding values:

o 'profile', with value an identifier that MUST be used to uniquely
identify itself. a New Group Member

The identifier MUST same set of message can also be registered in used for the "ACE
Groupcomm Profile" Registry.

o 'exp', with value following cases,
when the expiration time of Client is already a group member:

o The Client wishes to (re-)get the current keying material material, for
the group communication, encoded
cases such as a CBOR unsigned integer expiration, loss or
floating-point number.

o 'pub_keys', may only be present if 'get_pub_keys' was present in
the Key Distribution Request. suspected mismatch, due to e.g.
reboot or missed group rekeying. This parameter is a CBOR Byte
String, which encodes further discussed in
Section 6.

o The Client wishes to (re-)get the public keys of all the other group members
paired with the respective member identifiers. In case public
keys in
members, e.g. if it is aware of new nodes joining the group are represented as COSE Keys, the CBOR Byte
String encodes a COSE_KeySet (see [RFC8152]), which contains after
itself. This is further discussed in Section 7.

Additionally, the
public keys format of all the members payload of the group. In particular, each
COSE Key in the COSE_KeySet includes Distribution
Response (Section 4.2) can be reused for messages sent by the identifier KDC to
distribute updated group keying material, in case of a new node
joining the
corresponding group member as value or of its 'kid' a current member leaving the group. The key parameter.
Alternative specific encodings
management scheme used to send such messages could rely on, e.g.,
multicast in case of this parameter MUST be defined a new node joining or unicast in applications case of this specification.

o 'group_policies', with value a list of parameters indicating how node
leaving 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 group.

Note that proof-of-possession to bind the profile.

o 'mgt_key_material', with value the administrative keying material access token to participate in the group rekeying Client
is performed by using 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 proof-of-possession key bound to specify how exactly the keying material is
used to protect access
token for establishing secure communication between the group communication. Client and
the KDC.

If the application requires backward security, the KDC SHALL generate
new group keying material and securely distribute it to all the
current group members, using the message format defined in this
section. Application profiles may define alternative message
formats.

5. Removal of

4.1. Key Distribution Request

The Client sends a Node from Key Distribution Request to the Group KDC. This section describes at a high level how
corresponds to a node can be removed from
the group.

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

5.1. Expired Authorization

If the node KDC is not authorized anymore, the AS can directly
communicate that
associated to the KDC. Alternatively, 'scope' value of the access token might
have expired. If Token introspection Authorization Request/
Response. The payload of this request is provided by the AS, a CBOR map which MUST
contain the KDC
can use it following fields:

o 'type', encoded as per Section 5.7 of [I-D.ietf-ace-oauth-authz], in order
to verify that a CBOR int, with value 1 ("key distribution").

Additionally, the access token is still valid.

Either case, once aware that a node is not authorized anymore, the
KDC has to remove CBOR map in the unauthorized node from payload MAY contain the list of group
members, following
fields, which, 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. The client MUST use the protected channel established
with ACE, mentioned in Section 4.

To request to leave a group, the client included, MUST send a CoAP POST request
to the endpoint in the KDC associated to have the group to leave (same
endpoint used in Section 4.1 for Key Distribution requests). The
payload of this Leave Request is a CBOR Map which MUST contain:

o 'leave', with value an empty CBOR array. corresponding values:

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

Additionally, the Leave request MAY contain the following parameters,
which, if included, MUST have the corresponding values:

o 'client_cred', with value 'get_pub_keys', if the identifier of Client wishes to receive the public key or
certificate keys of
the Client. This field other nodes in the group from the KDC. The value is used an empty
CBOR array. This parameter may be present if the KDC is
managing (collecting from/distributing to the Client) stores the
public keys of the nodes in the group members.

Note that and distributes them to the 'role' field
Client; it is omitted since such a request should
only be used useless to leave a group altogether. If have here if the leaving node wants
to be part set of a public keys of
the members of the group with fewer roles, is known in another way, e.g. it does not need to
communicate that to was
provided by the KDC, and can simply stop acting according to
such roles.

If AS.

o 'client_cred', with value the Leave Request is not formatted correctly (e.g. no 'scope'
field present, public key or unknown fields present), certificate of the KDC MUST respond with
Client, encoded as a 4.00 (Bad Request) error message. Otherwise, CBOR byte string. If the KDC MUST remove is managing
(collecting from/distributing to the leaving node from Client) the list public keys of
the group members, if this field contains the KDC keeps
track public key of that.

Note that, after having left the group, a node may wish to join it
again. Then, as long as the node
Client. The default encoding for public keys is still authorized to join the
group, i.e. it has COSE Keys.
Alternative specific encodings of this parameter MAY be defined in
applications of this specification.

o 'client_cred_verify', encoded as a still valid access token, it can re-request to
join CBOR byte string. This
parameter contains a signature computed by the group directly to Client over the KDC without needing to retrieve a new
access token
nonce N received from the AS. This means that the KDC needs in the 2.01 (Created) response to keep
track of nodes with valid access tokens, before deleting all
information about
the leaving node.

6. Retrieval of Updated Keying Material

A node stops using token POST request (see Section 3.3). The Client computes the group keying material upon
signature by using its expiration,
according to the 'exp' parameter own private key, whose corresponding public
key is either directly specified in the retained COSE Key.
Then, if it wants to continue participating 'client_cred' parameter or
included in the group
communication, the node has to request new updated keying material to
the KDC.

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

Note that policies 'client_cred'
parameter is present.

o 'pub_keys_repos', can be set up so that the Client sends present if a request
to certificate is present in
the KDC only after 'client_cred' field, with value a given number list of unsuccessfully decrypted
incoming messages.

Alternatively, public key
repositories storing the re-distribution certificate of keying material can be
initiated by the KDC, which e.g.:

o Can maintain an Observable resource to send notifications to
Clients when the keying material Client. This
parameter is updated. Such a notification
would have the same payload encoded as a CBOR array of CBOR text strings, each of
which specifies the URI of a key repository.

4.2. Key Re-Distribution Distribution Response
defined in Section 6.2.

o Can send

The KDC verifies that the payload of 'scope' received in the Key Re-Distribution Response in Distribution
Request, if present, is a
multicast request to the members subset of the group.

o Can send unicast requests 'scope' stored in the access
token associated to each Client over a secure channel, this client. If verification fails, the KDC MUST
respond with a 4.01 (Unauthorized) error message.

If the Key Re-Distribution Response as payload.

o Can act as a publisher in a pub-sub scenario, and update the
keying material by publishing on a specific topic on a broker,
which all the members of the group are subscribed to.

Note that these methods of KDC-initiated key re-distribution have
different security properties and require different security
associations.

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.

If that is not the case, i.e. it does not store the token or the
token is not valid for that client for the scope requested, the KDC
MUST respond with a 4.01 (Unauthorized) error message. Analogously
to Section 4.2, if the Key Re-Distribution Request is not formatted correctly (e.g. no
'scope' field present, present while expected, or unknown fields present), the
KDC MUST respond with a 4.00 (Bad Request) error message.

Otherwise,

If verification succeeds, the KDC replies to the Client with sends a Key Distribution
Response, which MUST include success
Response to the 'kty' and 'key' parameters specified
in Section 4.2. Client. The Key Distribution success Response MAY also include the
'profile', 'exp', 'group_policies' and 'mgt_key_material' parameters
specified in Section 4.2.

Note that
corresponds to a 2.01 Created message. The payload of this response might simply re-provide
is a CBOR map, which MUST contain:

o 'kty', identifying the same keying
material currently owned by key type of the Client, if it has not been renewed.

7. Retrieval 'key' parameter. The set
of Public Keys for Group Members

In case the KDC maintains values can be found in the public keys "Key Type" column of group members, a node the "ACE
Groupcomm Key" Registry. Implementations MUST verify that the key
type matches the application profile being used, if present, as
registered in the group can contact "ACE Groupcomm Key" registry.

o 'key', containing the keying material for the KDC to request public keys of either all group members communication,
or a specified subset, using information required to derive it.

The exact format of the messages 'key' value MUST be defined
below.

Figure 6 gives an overview in applications
of this specification. Additionally, documents specifying the exchange described above.

Client KDC key
format MUST register it in the "ACE Groupcomm Key" registry,
including its name, type and application profile to be used with, as
defined in the "ACE Groupcomm Key" registry, defined in Section 11.5.

+----------+----------------+---------+-------------------------+
| Name |
|---- Public Key Request: POST /group-id --->| Type Value | Profile | Description |
|<--- Public Key Response: 2.01 (Created) ---|
+----------+----------------+---------+-------------------------+
| Reserved | 0 | | This value is reserved |
+----------+----------------+---------+-------------------------+

Figure 6: Message Flow of Public 5: Key Request-Response

Note Type Values

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

o 'profile', with value a CBOR integer that these messages can MUST be combined with used to uniquely
identify the Key Re-Distribution
messages application profile for group communication. The
value MUST be registered in Section 6, to request at the same "ACE Groupcomm Profile" Registry.

o 'exp', with value the expiration time of the keying material and for
the public keys. In this case, either group communication, encoded as a new endpoint at
the KDC may be used, CBOR unsigned integer or additional information needs to be sent in
floating-point number. This field contains a numeric value
representing the request payload, to distinguish these combined messages number of seconds from 1970-01-01T00:00:00Z UTC
until the
Public Key messages described below, since they would specified UTC date/time, ignoring leap seconds,
analogous to what specified in Section 2 of [RFC7519].

o 'pub_keys', may only be identical
otherwise.

7.1. Public Key Request

To request public keys, present if 'get_pub_keys' was present in
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 Request. This parameter is a CBOR array including either:

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

* N elements, each of which is the identifier of a group member,
in order to request members
paired with the respective member identifiers. The default
encoding for 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 keys is
not present.

7.2. Public Key Response

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

o 'pub_keys', is a CBOR byte string wrapping a COSE_KeySet (see
[RFC8152]), which contains either:

* the public keys of all the members of
the group, if group. In particular, each COSE Key in the
'get_pub_keys' parameter COSE_KeySet
includes the identifier of the corresponding group member as value
of its 'kid' key parameter. Alternative specific encodings of
this parameter MAY be defined in applications of this
specification.

o 'group_policies', with value a CBOR map, whose entries specify how
the group handles specific management aspects. These include, for
instance, approaches to achieve synchronization of sequence
numbers among group members. The elements of this field are
registered in the "ACE Groupcomm Policy" Registry. This
specification defines the two elements "Sequence Number
Synchronization Method" and "Key Update Check Interval", which are
summarized in Figure 6. Application profiles that build on this
document MUST specify the exact content format of included map
entries.

+-----------------+-------+----------|--------------------|------------+
| Name | CBOR | CBOR | Description | Reference |
| | label | type | | |
|-----------------+-------+----------|--------------------|------------|
| Sequence Number | TBD1 | tstr/int | Method for a re- | [[this |
| Synchronization | | | cipient node to | document]] |
| Method | | | synchronize with | |
| | | | sequence numbers | |
| | | | of a sender node. | |
| | | | Its value is taken | |
| | | | from the 'Value' | |
| | | | column of the | |
| | | | Sequence Number | |
| | | | Synchronization | |
| | | | Method registry | |
| | | | | |
| Key Update | TBD2 | int | Polling interval | [[this |
| Check Interval | | | in seconds, to | document]] |
| | | | check for new | |
| | | | keying material at | |
| | | | the KDC | |
+-----------------+-------+----------|--------------------|------------+

Figure 6: ACE Groupcomm Policies

o 'mgt_key_material', encoded as a CBOR byte string and containing
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 application profile.

Specific application profiles that build on this document need to
specify how exactly the keying material is used to protect the group
communication.

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 AS provides Token introspection (see Section 5.7 of
[I-D.ietf-ace-oauth-authz]), the KDC can optionally use and check
whether:

o the node is not authorized anymore;

o the access token is still valid, upon its expiration.

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

To request to leave a group, the client MUST send a CoAP POST request
to the endpoint in the KDC associated to the group to leave (same
endpoint used in Section 4.1 for Key Distribution requests). The
payload of this Leave Request is a CBOR map which MUST contain:

o 'type', encoded as a CBOR int, with value 2 ("leave").

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

Note that the 'role' field is omitted since such a request should
only be used to leave a group altogether. If the leaving node wants
to be part of a group with fewer roles, it does not need to
communicate that to the KDC, and can simply stop acting according to
such roles.

If the Leave Request is such that the KDC cannot extract all the
necessary information to understand and process it correctly (e.g. no
'scope' field present), the KDC MUST respond with a 4.00 (Bad
Request) error message. Otherwise, the KDC MUST 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.

6. Retrieval of New or 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. In this case, and depending on what part of the keying
material is expired, the client may need to communicate to the KDC
its need for that part to be renewed: for example, if the Client uses
an individual key to protect outgoing traffic and has to renew it,
the node may request a new one, or new input material to derive it,
without renewing the whole group keying material.

The Client may perform the same request to the KDC also upon
receiving messages from other group members without being able to
retrieve the material 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. It is application dependent and pertaining to the
particular message exchange (e.g. [I-D.ietf-core-oscore-groupcomm])
to set up policies that instruct clients to retain unsuccessfully
decrypted messages and for how long, so that they can be decrypted
after getting updated keying material, rather than just considered
non valid messages to discard right away.

The same request could also be sent by the client without being
triggered by a failed decryption of a message, if the client wants to
confirm that it has the latest group keying material. If that is the
case, the client will receive from the KDC the same group keying
material it has in memory.

Note that the difference between the keying material renewal request
and the keying material update request is that the first one triggers
the KDC to produce new keying material for that node, while the
second one only triggers distribution (the renewal might have
happened independently, because of expiration). Once a node receives
new individual keying material, other group members may need to use
the update keying material request to retrieve it.

Alternatively, the re-distribution of keying material can be
initiated by the KDC, which e.g.:

o Can maintain an Observable resource to send notifications to
Clients when the keying material is updated. Such a notification
would have the same payload as the Key Re-Distribution Response
defined in Section 6.2.

o Can send the payload of the Key Re-Distribution Response as one or
multiple multicast requests to the members of the group, using
secure rekeying schemes such as [RFC2093][RFC2094][RFC2627].

o Can send unicast requests to each Client over a secure channel,
with the Key Re-Distribution Response as payload.

o Can act as a publisher in a pub-sub scenario, and update the
keying material by publishing on a specific topic on a broker,
which all the members of the group are subscribed to.

Note that these methods of KDC-initiated key re-distribution have
different security properties and require different security
associations.

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 the following fields:

o 'type', encoded as a CBOR int, with value 3 ("update key") if the
request is intended to retrieve updated group keying material, and
4 ("new") if the request is intended for the KDC to produce and
provide new individual keying material for the Client.

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.

If that is not the case, i.e. it does not store the token or the
token is not valid for that client for the scope requested, the KDC
MUST respond with a 4.01 (Unauthorized) error message. Analogously
to Section 4.2, if the Key Re-Distribution Request is not formatted
correctly (e.g. no 'scope' field present, or unknown fields present),
the KDC MUST respond with a 4.00 (Bad Request) error message.

Otherwise, the KDC replies to the Client with a Key Distribution
Response, which MUST include the 'kty', 'key' and 'exp' parameters
specified in Section 4.2. The Key Distribution Response MAY also
include the 'profile', 'group_policies' and 'mgt_key_material'
parameters 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.

Figure 7 gives an overview of the exchange described above.

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

Figure 7: 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 'type', encoded as a CBOR int, with value 5 ("pub keys").

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
encoded as a CBOR byte string, 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:

* 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 may enforce one of the following policies, in order to handle
possible identifiers that are included in the 'get_pub_keys'
parameter of the Public Key request but are not associated to any
current group member.

o The KDC silently ignores those identifiers.

o The KDC retains public keys of group members for a given amount of
time after their leaving, before discarding them. As long as such
public keys are retained, the KDC provides them to a requesting
Client.

Either case, a node that has left the group should not expect any of
its outgoing messages to be successfully processed, if received after
its leaving, due to a possible group rekeying occurred before the
message reception.

8. ACE Groupcomm Parameters

This specification defines a number of fields used during the message
exchange. The table below summarizes them, and specifies the CBOR
key to use instead of the full descriptive name.

+--------------+----------+---------------+
| Name | CBOR Key | CBOR Type |
+--------------+----------+---------------+
| scope | TBD | array |
+--------------+----------+---------------+
| get_pub_keys | TBD | array |
+--------------+----------+---------------+
| client_cred | TBD | byte string |
+--------------+----------+---------------+
| client_cred_ | TBD | byte string |
| verify | | |
+--------------+----------+---------------+
| pub_keys_ | TBD | array |
| repos | | |
+--------------+----------+---------------+
| kty | TBD | int / byte |
| | | string |
+--------------+----------+---------------+
| key | TBD | see "ACE |
| | | Groupcomm |
| | | Key" Registry |
+--------------+----------+---------------+
| profile | TBD | int |
+--------------+----------+---------------+
| exp | TBD | int / float |
+--------------+----------+---------------+
| pub_keys | TBD | byte string |
+--------------+----------+---------------+
| group_ | TBD | map |
| policies | | |
+--------------+----------+---------------+
| mgt_key_ | TBD | byte string |
| material | | |
+--------------+----------+---------------+
| type | TBD | int |
+--------------+----------+---------------+

9. ACE Groupcomm Request Type

This specification defines a number of types of requests. The table
below summarizes them.

+------------------+----------+
| Name | Value |
+------------------+----------+
| key distribution | 1 |
+------------------+----------+
| leave | 2 |
+------------------+----------+
| update key | 3 |
+------------------+----------+
| new | 4 |
+------------------+----------+
| pub keys | 5 |
+------------------+----------+

10. Security Considerations

When a Client receives a message from a sender for the first time, it
needs to have a mechanism in place to avoid replay, e.g.
Appendix B.2 of [I-D.ietf-core-object-security].

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.

The KDC may enforce a rekeying policy that takes into account the
overall time required to rekey the group, as well as the expected
rate of changes in the group membership.

That is, the KDC may not rekey the group at every membership change,
for instance if members' joining and leaving occur frequently and
performing a group rekeying takes too long. Instead, the KDC may
rekey the group after a minum number of group members have joined or
left within a given time interval, or during predictable network
inactivity periods.

However, this would result in the KDC not constantly preserving
backward and forward security. In fact, newly joining group members
could be able to access the keying material used before their
joining, and thus could access past group communications. Also,
until the KDC performs a group rekeying, the newly leaving nodes
would still be able to access upcoming group communications that are
protected with the keying material that has not yet been updated.

10.1. Update of Keying Material

A group member can receive a message shortly after the group has been
rekeyed, and new keying material has been distributed by the KDC. In
the following two cases, this may result in misaligned keying
material between the group members.

In the first case, the sender protects a message using the old keying
material. However, the recipient receives the message after having
received the new keying material, hence not being able to correctly
process it. A possible way to ameliorate this issue is to preserve
the old, recent, keying material for a maximum amount of time defined
by the application. By doing so, the recipient can still try to
process the received message using the old retained keying material
as second attempt. Note that a former (compromised) group member can
take advantage of this by sending messages protected with the old
retained keying material. Therefore, a conservative application
policy should not admit the storage of old keying material.

In the second case, the sender protects a message using the new
keying material, but the recipient receives that request before
having received the new keying material. Therefore, the recipient
would not be able to correctly process the request and hence discards
it. If the recipient receives the new keying material shortly after
that and the sender endpoint uses CoAP retransmissions, the former
will still be able to receive and correctly process the message. In
any case, the recipient should actively ask the KDC for an updated
keying material according to an application-defined policy, for
instance after a given number of unsuccessfully decrypted incoming
messages.

10.2. Block-Wise Considerations

If the block-wise options [RFC7959] are used, and the keying material
is updated in the middle of a block-wise transfer, the sender of the
blocks just changes the keying material to the updated one and
continues the transfer. As long as both sides get the new keying
material, updating the keying material in the middle of a transfer
will not cause any issue. Otherwise, the sender will have to
transmit the message again, when receiving an error message from the
recipient.

Compared to a scenario where the transfer does not use block-wise,
depending on how fast the keying material is changed, the nodes might
consume a larger amount of the network resending the blocks again and
again, which might be problematic.

11. IANA Considerations

This document has the following actions for IANA.

11.1. ACE Authorization Server Request Creation Hints Registry

IANA is asked to register the following entries in the "ACE
Authorization Server Request Creation Hints" Registry defined in
Section 8.1 of [I-D.ietf-ace-oauth-authz].

o Name: sign_info

o CBOR Key: TBD (range -256 to 255)

o Value Type: any

o Reference: [[This specification]]

o Name: pub_key_enc

o CBOR Key: TBD (range -256 to 255)

o Value Type: integer

o Reference: [[This specification]]

11.2. ACE Public Key Encoding Registry

This specification establishes the "ACE Public Key Encoding" IANA
Registry. The Registry has been created to use the "Expert Review
Required" registration procedure [RFC8126]. Expert review guidelines
are provided in Section 11.9. It should be noted that, in addition
to the expert review, some portions of the Registry require a
specification, potentially a Standards Track RFC, be supplied as
well.

The columns of this Registry are:

o Name: This is a descriptive name that enables easier reference to
the item. The name MUST be unique. It is not used in the
encoding.

o Value: The value to be used to identify this public key encoding.
This value MUST be unique. The value can be a positive or a
negative integer. Integer values between 0 and 255 are designated
as Standards Track Document required. Integer values from 256 to
65535 are designated as Specification Required. Integer values of
greater than 65535 are designated as expert review. Integer
values less than -65536 are marked as private use.

o Description: This field contains a brief description for this
public key encoding.

o Reference: This field contains a pointer to the public
specification providing the public key encoding, if one exists.

The value 0 is to be marked as "Reserved".

11.3. ACE Groupcomm Parameters Registry

This specification establishes the "ACE Groupcomm Parameters" IANA
Registry. The Registry has been created to use the "Expert Review
Required" registration procedure [RFC8126]. Expert review guidelines
are provided in Section 11.9.

The columns of this Registry are:

o Name: This is a descriptive name that enables easier reference to
the item. The name MUST be unique. It is not used in the
encoding.

o CBOR Key: This is the value used as CBOR key of the item. These
values MUST be unique. The value can be a positive integer, a
negative integer, or a string.

o CBOR Type: This contains the CBOR type of the item, or a pointer
to the registry that defines its type, when that depends on
another item.

o Reference: This contains a pointer to the public specification for
the format of the item, if one exists.

This Registry has been initially populated by the values in
Section 8. The specification column for all of these entries will be
this document.

11.4. Ace Groupcomm Request Type Registry

This specification establishes the "ACE Groupcomm Request Type" IANA
Registry. The Registry has been created to use the "Expert Review
Required" registration procedure [RFC8126]. Expert review guidelines
are provided in Section 11.9.

The columns of this Registry are:

o Name: This is a descriptive name that enables easier reference to
the item. The name MUST be unique. It is not used in the
encoding.

o Value: This is the value used to identify the request. These
values MUST be unique. The value must be a positive integer.

o Reference: This contains a pointer to the public specification for
the format of the item, if one exists.

This Registry has been initially populated by the values in
Section 9. The reference column for all of these entries will be
this document. The value 0 is to be marked as "Reserved".

11.5. ACE Groupcomm Key Registry

This specification establishes the "ACE Groupcomm Key" IANA Registry.
The Registry has been created to use the "Expert Review Required"
registration procedure [RFC8126]. Expert review guidelines are
provided in Section 11.9.

The columns of this Registry are:

o Name: This is a descriptive name that enables easier reference to
the item. The name MUST be unique. It is not used in the
encoding.

o Key Type Value: This is the value used to identify the keying
material. These values MUST be unique. The value can be a
positive integer, a negative integer, or a string.

o Profile: This field may contain one or more descriptive strings of
application profiles to be used with this item. The values should
be taken from the Name column of the Public Key request was an empty
array; or

* "ACE Groupcomm Profile"
Registry.

o Description: This field contains a brief description of the keying
material.

o References: This contains a pointer to the public keys specification
for the format of the group members with keying material, if one exists.

This Registry has been initially populated by the identifiers
specified values in the 'get_pub_keys' parameter Figure 5.
The specification column for all of these entries will be this
document.

11.6. ACE Groupcomm Profile Registry

This specification establishes the Public Key
request. "ACE Groupcomm Profile" IANA
Registry. The KDC ignores possible identifiers included Registry has been created to use the "Expert Review
Required" registration procedure [RFC8126]. Expert review guidelines
are provided in Section 11.9. It should be noted that, in addition
to the 'get_pub_keys'
parameter expert review, some portions of the Public Key request if they are not associated to any
current group member.

8. Security Considerations Registry require a
specification, potentially a Standards Track RFC, be supplied as
well.

The KDC must renew the group keying material upon its expiration. columns of this Registry are:

o Name: The KDC should renew name of the keying material upon group membership
change, and should provide it application profile, to be used as value of
the current group members through profile attribute.

o Description: Text giving an overview of the rekeying scheme used in application profile
and the group.

When a Client receives a message context it is developed for.

o CBOR Value: CBOR abbreviation for the name of this application
profile. Different ranges of values use different registration
policies [RFC8126]. Integer values from -256 to 255 are
designated as Standards Action. Integer values from a sender for the first time, it
needs -65536 to have
-257 and from 256 to 65535 are designated as Specification
Required. Integer values greater than 65535 are designated as
Expert Review. Integer values less than -65536 are marked as
Private Use.

o Reference: This contains a mechanism in place pointer to avoid replay, e.g.
Appendix B.2 the public specification of [I-D.ietf-core-object-security].

9. IANA Considerations

This document has
the following actions abbreviation for IANA.

9.1. this application profile, if one exists.

11.7. ACE Groupcomm Key Policy Registry

This specification establishes the IANA "ACE Groupcomm Key" Policy" IANA
Registry. The Registry has been created to use the "Expert Review
Required" registration procedure [RFC8126]. Expert review guidelines
are provided in Section 9.3. 11.9. It should be noted that, in addition
to the expert review, some portions of the Registry require a
specification, potentially a Standards Track RFC, be supplied as
well.

The columns of this Registry are:

o Name: This is a descriptive name that enables easier reference to
the item. The name MUST be unique. It is not used in of the
encoding. group communication policy.

o Key Type Value: This is the CBOR label: The value to be used to identify the keying
material. These values this group
communication policy. Key map labels MUST be unique. The value label
can be a positive integer, a negative integer, integer or a string.

o Profile: This field may contain a descriptive string
Integer values between 0 and 255 and strings of a profile length 1 are
designated as Standards Track Document required. Integer values
from 256 to be 65535 and strings of length 2 are designated as
Specification Required. Integer values of greater than 65535 and
strings of length greater than 2 are designated as expert review.
Integer values less than -65536 are marked as private use.

o CBOR type: the CBOR type used with this item. This should be a value that is in to encode the
Name column value of the "ACE Groupcomm Profile" Registry. this group
communication policy.

o Description: This field contains a brief description of the keying
material. for this
group communication policy.

o References: Reference: This field contains a pointer to the public
specification
for providing the format of the keying material, group communication
policy, if one exists.

This Registry has been registry will be initially populated by the values in Figure 5.
The specification column for all of these entries will be this
document.

9.2. ACE Groupcomm Profile 6.

11.8. Sequence Number Synchronization Method Registry

This specification establishes the "Sequence Number Synchronization
Method" IANA "ACE Groupcomm Profile" Registry. The Registry has been created to use the
"Expert Review Required" registration procedure [RFC8126]. Expert
review guidelines are provided in Section 9.3. 11.9. It should be noted
that, in addition to the expert review, some portions of the Registry
require a specification, potentially a Standards Track RFC, be
supplied as well.

The columns of this Registry are:

o Name: The name of the profile, sequence number synchronization method.

o Value: The value to be used as value of the profile
attribute. to identify this sequence number
synchronization method.

o Description: Text giving an overview of the profile and the
context it is developed for.

o CBOR Value: CBOR abbreviation This field contains a brief description for this profile name. Different
ranges of values use different registration policies [RFC8126].
Integer values from -256 to 255 are designated as Standards
Action. Integer values from -65536 to -257 and from 256 to 65535
are designated as Specification Required. Integer values greater
than 65535 are designated as Expert Review. Integer values less
than -65536 are marked as Private Use.
sequence number synchronization method.

o Reference: This field contains a pointer to the public
specification of describing the profile abbreviation, if one exists.

9.3. sequence number synchronization
method.

11.9. Expert Review Instructions

The IANA Registries established in this document are defined as
expert review. This section gives some general guidelines for what
the experts should be looking for, but they are being designated as
experts for a reason so they should be given substantial latitude.

Expert reviewers should take into consideration the following points:

o Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already
registered and that the point is likely to be used in deployments.
The zones tagged as private use are intended for testing purposes
and closed environments, code points in other ranges should not be
assigned for testing.

o Specifications are required for the standards track range of point
assignment. Specifications should exist for specification
required ranges, but early assignment before a specification is
available is considered to be permissible. Specifications are
needed for the first-come, first-serve range if they are expected
to be used outside of closed environments in an interoperable way.
When specifications are not provided, the description provided
needs to have sufficient information to identify what the point is
being used for.

o Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for
standards track documents does not mean that a standards track
document cannot have points assigned outside of that range. The
length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be
used on, and the number of code points left that encode to that
size.

10.

12. References

10.1.

12.1. 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-22 draft-ietf-ace-oauth-authz-24
(work in progress), March 2019.

[I-D.ietf-ace-oauth-params]
Seitz, L., "Additional OAuth Parameters for Authorization
in Constrained Environments (ACE)", draft-ietf-ace-oauth-
params-04
params-05 (work in progress), February 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.

[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>.

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

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

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

12.2. 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-ace-mqtt-tls-profile]
Sengul, C., Kirby, A., and P. Fremantle, "MQTT-TLS profile
of ACE", draft-ietf-ace-mqtt-tls-profile-00 (work in
progress), May 2019.

[I-D.ietf-ace-oscore-profile]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"OSCORE profile of the Authentication and Authorization
for
Writing an IANA Considerations Section Constrained Environments Framework", draft-ietf-ace-
oscore-profile-07 (work in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[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 progress), February 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-06 draft-ietf-core-coap-pubsub-08 (work in
progress), January March 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.

[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 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>.

[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.

[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.

[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.

Appendix A. Requirements on Application Profiles

This section lists the requirements on application profiles of this
specification,for the convenience of application profile designers.

o Specify the communication protocol the members of the group must
use (e.g., multicast CoAP).

o Specify the security protocol the group members must use to
protect their communication (e.g., group OSCORE). This must
provide encryption, integrity and replay protection.

o Specify the encoding and value of the identifier of group or topic
and role of 'scope' (see Section 3.1).

o Specify and register the application profile identifier (see
Section 4.1).

o Specify the acceptable values of 'kty' (see Section 4.2).

o Specify the format and content of 'group_policies' entries (see
Section 4.2).

o Optionally, specify the format and content of 'mgt_key_material'
(see Section 4.2).

o Optionally, specify tranport profile of ACE
[I-D.ietf-ace-oauth-authz] to use between Client and KDC.

o Optionally, specify the encoding of public keys, of 'client_cred',
and of 'pub_keys' if COSE_Keys are not used (see Section 4.2).

o Optionally, specify the acceptable values for parameters related
to signature algorithm and signature keys: 'sign_alg',
'sign_parameters', 'sign_key_parameters', 'pub_key_enc' (see
Section 3.3).

o Optionally, specify the negotiation of parameter values for
Multicast: Issues
signature algorithm and Architectures", RFC 2627,
DOI 10.17487/RFC2627, June 1999,
<https://www.rfc-editor.org/info/rfc2627>.

[RFC7390] Rahman, A., Ed. signature keys, if 'sign_info' 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>.
'pub_key_enc' are not used (see Section 3.3).

Appendix A. B. Document Updates

RFC EDITOR: PLEASE REMOVE THIS SECTION.

A.1.

B.1. Version -01 to -02

o Editorial fixes.

o Distinction between transport profile and application profile
(Section 1.1).

o New parameters 'sign_info' and 'pub_key_enc' to negotiate
parameter values for signature algorithm and signature keys
(Section 3.3).

o New parameter 'type' to distinguish different Key Distribution
Request messages (Section 4.1).

o New parameter 'client_cred_verify' in the Key Distribution Request
to convey a Client signature (Section 4.1).

o Encoding of 'pub_keys_repos' (Section 4.1).

o Encoding of 'mgt_key_material' (Section 4.1).

o Improved description on retrieval of new or updated keying
material (Section 6).

o Encoding of 'get_pub_keys' in Public Key Request (Section 7.1).

o Extended security considerations (Sections 10.1 and 10.2).

o New "ACE Public Key Encoding" IANA Registry (Section 11.2).

o New "ACE Groupcomm Parameters" IANA Registry (Section 11.3),
populated with the entries in Section 8.

o New "Ace Groupcomm Request Type" IANA Registry (Section 11.4),
populated with the values in Section 9.

o New "ACE Groupcomm Policy" IANA Registry (Section 11.7) populated
with two entries "Sequence Number Synchronization Method" and "Key
Update Check Interval" (Section 4.2).

o Improved list of requirements for application profiles
(Appendix A).

B.2. Version -00 to -01

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

o Defined error handling on the KDC (Sections 4.2 and 6.2).

o Updated format of the Key Distribution Response as a whole
(Section 4.2).

o Generalized format of 'pub_keys' in the Key Distribution Response
(Section 4.2).

o Defined format for the message to request leaving the group
(Section 5.2).

o Mentioned Renewal of individual keying material and methods for group
rekeying initiated by the KDC (Section 6).

o CBOR type for node identifiers in 'get_pub_keys' (Section 7.1).

o Added security consideration section on replay protection parameter identifiers and their CBOR keys
(Section 8).

o Added request types for requests to a Join Response (Section 9).

o Extended security considerations (Section 10).

o New IANA registries "ACE Groupcomm Key Registry" and Registry", "ACE Groupcomm
Profile Registry", "ACE Groupcomm Policy Registry" and "Sequence
Number Synchronization Method Registry" (Section 9). 11).

o Added appendix about requirements for application profiles of ACE
on group communication (Appendix A).

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 VINNOVA and
the Celtic-Next project CRITISEC; and 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