Key Management for OSCORE Groups in ACE
draft-ietf-ace-key-groupcomm-oscore-16
| Document | Type | Active Internet-Draft (ace WG) | |
|---|---|---|---|
| Authors | Marco Tiloca , Jiye Park , Francesca Palombini | ||
| Last updated | 2023-03-06 | ||
| Replaces | draft-tiloca-ace-oscoap-joining | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Associated WG milestone |
|
||
| Document shepherd | Rikard Höglund | ||
| Shepherd write-up | Show Last changed 2023-02-21 | ||
| IESG | IESG state | Publication Requested | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Paul Wouters | ||
| Send notices to | rikard.hoglund@ri.se |
draft-ietf-ace-key-groupcomm-oscore-16
ACE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track J. Park
Expires: 7 September 2023 Universitaet Duisburg-Essen
F. Palombini
Ericsson AB
6 March 2023
Key Management for OSCORE Groups in ACE
draft-ietf-ace-key-groupcomm-oscore-16
Abstract
This document defines an application profile of the ACE framework for
Authentication and Authorization, to request and provision keying
material in group communication scenarios that are based on CoAP and
are secured with Group Object Security for Constrained RESTful
Environments (Group OSCORE). This application profile delegates the
authentication and authorization of Clients, that join an OSCORE
group through a Resource Server acting as Group Manager for that
group. This application profile leverages protocol-specific
transport profiles of ACE to achieve communication security, server
authentication and proof-of-possession for a key owned by the Client
and bound to an OAuth 2.0 Access Token.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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 7 September 2023.
Copyright Notice
Copyright (c) 2023 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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
3. Format of Scope . . . . . . . . . . . . . . . . . . . . . . . 8
4. Authentication Credentials . . . . . . . . . . . . . . . . . 10
5. Authorization to Join a Group . . . . . . . . . . . . . . . . 12
5.1. Authorization Request . . . . . . . . . . . . . . . . . . 12
5.2. Authorization Response . . . . . . . . . . . . . . . . . 13
5.3. Token Transferring . . . . . . . . . . . . . . . . . . . 14
5.3.1. 'ecdh_info' Parameter . . . . . . . . . . . . . . . . 16
5.3.2. 'kdc_dh_creds' Parameter . . . . . . . . . . . . . . 19
6. Group Joining . . . . . . . . . . . . . . . . . . . . . . . . 20
6.1. Send the Join Request . . . . . . . . . . . . . . . . . . 21
6.1.1. Value of the N_S Challenge . . . . . . . . . . . . . 22
6.2. Receive the Join Request . . . . . . . . . . . . . . . . 23
6.2.1. Follow-up to a 4.00 (Bad Request) Error Response . . 26
6.3. Send the Join Response . . . . . . . . . . . . . . . . . 26
6.4. Receive the Join Response . . . . . . . . . . . . . . . . 33
7. Overview of the Group Rekeying Process . . . . . . . . . . . 35
7.1. Stale OSCORE Sender IDs . . . . . . . . . . . . . . . . . 36
8. Interface at the Group Manager . . . . . . . . . . . . . . . 37
8.1. ace-group/GROUPNAME/active . . . . . . . . . . . . . . . 38
8.1.1. GET Handler . . . . . . . . . . . . . . . . . . . . . 38
8.2. ace-group/GROUPNAME/verif-data . . . . . . . . . . . . . 38
8.2.1. GET Handler . . . . . . . . . . . . . . . . . . . . . 38
8.3. ace-group/GROUPNAME/stale-sids . . . . . . . . . . . . . 39
8.3.1. FETCH Handler . . . . . . . . . . . . . . . . . . . . 39
8.4. Admitted Methods . . . . . . . . . . . . . . . . . . . . 40
8.4.1. Signature Verifiers . . . . . . . . . . . . . . . . . 41
8.5. Operations Supported by Clients . . . . . . . . . . . . . 41
9. Additional Interactions with the Group Manager . . . . . . . 42
9.1. Retrieve Updated Keying Material . . . . . . . . . . . . 42
9.1.1. Get Group Keying Material . . . . . . . . . . . . . . 42
9.1.2. Get Group Keying Material and OSCORE Sender ID . . . 43
9.2. Request to Change Individual Keying Material . . . . . . 43
9.3. Retrieve Authentication Credentials of Group Members . . 45
9.4. Upload a New Authentication Credential . . . . . . . . . 46
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9.5. Retrieve the Group Manager's Authentication Credential . 47
9.6. Retrieve Signature Verification Data . . . . . . . . . . 48
9.7. Retrieve the Group Policies . . . . . . . . . . . . . . . 50
9.8. Retrieve the Keying Material Version . . . . . . . . . . 51
9.9. Retrieve the Group Status . . . . . . . . . . . . . . . . 51
9.10. Retrieve Group Names . . . . . . . . . . . . . . . . . . 52
9.11. Leave the Group . . . . . . . . . . . . . . . . . . . . . 55
10. Removal of a Group Member . . . . . . . . . . . . . . . . . . 55
11. Group Rekeying Process . . . . . . . . . . . . . . . . . . . 57
11.1. Sending Rekeying Messages . . . . . . . . . . . . . . . 59
11.2. Receiving Rekeying Messages . . . . . . . . . . . . . . 61
11.3. Missed Rekeying Instances . . . . . . . . . . . . . . . 62
11.3.1. Retrieve Stale Sender IDs . . . . . . . . . . . . . 64
12. ACE Groupcomm Parameters . . . . . . . . . . . . . . . . . . 66
13. ACE Groupcomm Error Identifiers . . . . . . . . . . . . . . . 68
14. Default Values for Group Configuration Parameters . . . . . . 69
14.1. Common . . . . . . . . . . . . . . . . . . . . . . . . . 70
14.2. Group Mode . . . . . . . . . . . . . . . . . . . . . . . 70
14.3. Pairwise Mode . . . . . . . . . . . . . . . . . . . . . 71
15. Security Considerations . . . . . . . . . . . . . . . . . . . 72
15.1. Management of OSCORE Groups . . . . . . . . . . . . . . 72
15.2. Size of Nonces as Proof-of-Possesion Challenge . . . . . 73
15.3. Reusage of Nonces for Proof-of-Possession Input . . . . 74
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 75
16.1. OAuth Parameters . . . . . . . . . . . . . . . . . . . . 75
16.2. OAuth Parameters CBOR Mappings . . . . . . . . . . . . . 75
16.3. ACE Groupcomm Parameters . . . . . . . . . . . . . . . . 76
16.4. ACE Groupcomm Key Types . . . . . . . . . . . . . . . . 77
16.5. ACE Groupcomm Profiles . . . . . . . . . . . . . . . . . 77
16.6. OSCORE Security Context Parameters . . . . . . . . . . . 78
16.7. TLS Exporter Labels . . . . . . . . . . . . . . . . . . 80
16.8. AIF Media-Type Sub-Parameters . . . . . . . . . . . . . 80
16.9. CoAP Content-Format . . . . . . . . . . . . . . . . . . 80
16.10. Group OSCORE Roles . . . . . . . . . . . . . . . . . . . 81
16.11. CoRE Resource Type . . . . . . . . . . . . . . . . . . . 82
16.12. ACE Groupcomm Errors . . . . . . . . . . . . . . . . . . 82
16.13. Expert Review Instructions . . . . . . . . . . . . . . . 83
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 83
17.1. Normative References . . . . . . . . . . . . . . . . . . 83
17.2. Informative References . . . . . . . . . . . . . . . . . 87
Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 88
A.1. Mandatory-to-Address Requirements . . . . . . . . . . . . 89
A.2. Optional-to-Address Requirements . . . . . . . . . . . . 91
Appendix B. Extensibility for Future COSE Algorithms . . . . . . 93
B.1. Format of 'ecdh_info_entry' . . . . . . . . . . . . . . . 94
B.2. Format of 'key' . . . . . . . . . . . . . . . . . . . . . 95
Appendix C. Document Updates . . . . . . . . . . . . . . . . . . 96
C.1. Version -15 to -16 . . . . . . . . . . . . . . . . . . . 96
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C.2. Version -14 to -15 . . . . . . . . . . . . . . . . . . . 96
C.3. Version -13 to -14 . . . . . . . . . . . . . . . . . . . 96
C.4. Version -12 to -13 . . . . . . . . . . . . . . . . . . . 96
C.5. Version -11 to -12 . . . . . . . . . . . . . . . . . . . 97
C.6. Version -10 to -11 . . . . . . . . . . . . . . . . . . . 97
C.7. Version -09 to -10 . . . . . . . . . . . . . . . . . . . 98
C.8. Version -08 to -09 . . . . . . . . . . . . . . . . . . . 99
C.9. Version -07 to -08 . . . . . . . . . . . . . . . . . . . 100
C.10. Version -06 to -07 . . . . . . . . . . . . . . . . . . . 100
C.11. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 100
C.12. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 101
C.13. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 101
C.14. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 102
C.15. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 102
C.16. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 103
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 104
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 104
1. Introduction
Object Security for Constrained RESTful Environments (OSCORE)
[RFC8613] is a method for application-layer protection of the
Constrained Application Protocol (CoAP) [RFC7252], using CBOR Object
Signing and Encryption (COSE) [RFC9052][RFC9053] and enabling end-to-
end security of CoAP payload and options.
As described in [I-D.ietf-core-oscore-groupcomm], Group OSCORE is
used to protect CoAP group communication
[I-D.ietf-core-groupcomm-bis], which can employ, for example, IP
multicast as underlying data transport. This relies on a Group
Manager, which is responsible for managing an OSCORE group and
enables the group members to exchange CoAP messages secured with
Group OSCORE. The Group Manager can be responsible for multiple
groups, coordinates the joining process of new group members, and is
entrusted with the distribution and renewal of group keying material.
This document is an application profile of
[I-D.ietf-ace-key-groupcomm], which itself builds on the ACE
framework for Authentication and Authorization [RFC9200]. Message
exchanges among the participants as well as message formats and
processing follow what specified in [I-D.ietf-ace-key-groupcomm] for
provisioning and renewing keying material in group communication
scenarios, where Group OSCORE is used to protect CoAP group
communication.
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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 [RFC9200] and in the
Authorization Information Format (AIF) [RFC9237] to express
authorization information. The terminology for entities in the
considered architecture is defined in OAuth 2.0 [RFC6749]. This
includes Client (C), Resource Server (RS), and Authorization
Server (AS).
* The terms and concepts related to the message formats and
processing specified in [I-D.ietf-ace-key-groupcomm], for
provisioning and renewing keying material in group communication
scenarios. These include the abbreviations REQx and OPTx denoting
the numbered mandatory-to-address and optional-to-address
requirements, respectively.
* The terms and concepts described in CBOR [RFC8949] and COSE
[RFC9052][RFC9053].
* The terms and concepts described in CoAP [RFC7252] and group
communication for CoAP [I-D.ietf-core-groupcomm-bis]. 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".
* The terms and concepts for protection and processing of CoAP
messages through OSCORE [RFC8613] and through Group OSCORE
[I-D.ietf-core-oscore-groupcomm] in group communication scenarios.
These especially include:
- Group Manager, as the entity responsible for a set of groups
where communications are secured with Group OSCORE. In this
document, the Group Manager acts as Resource Server.
- Authentication credential, as the set of information associated
with an entity, including that entity's public key and
parameters associated with the public key. Examples of
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authentication credentials are CBOR Web Tokens (CWTs) and CWT
Claims Sets (CCSs) [RFC8392], X.509 certificates [RFC7925] and
C509 certificates [I-D.ietf-cose-cbor-encoded-cert].
Additionally, this document makes use of the following terminology.
* Requester: member of an OSCORE group that sends request messages
to other members of the group.
* 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.
* Monitor: member of an OSCORE 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].
* Signature verifier: entity external to the OSCORE group and
intended to verify the signature of messages exchanged in the
group (see Sections 3.1 and 8.5 of
[I-D.ietf-core-oscore-groupcomm]). An authorized signature
verifier does not join the OSCORE group as an actual member, yet
it can retrieve the authentication credentials of the current
group members from the Group Manager.
* Signature-only group: an OSCORE group that uses only the group
mode (see Section 8 of [I-D.ietf-core-oscore-groupcomm]).
* Pairwise-only group: an OSCORE group that uses only the pairwise
mode (see Section 9 of [I-D.ietf-core-oscore-groupcomm]).
Examples throughout this document are expressed in CBOR diagnostic
notation without the tag and value abbreviations.
2. Protocol Overview
Group communication for CoAP has been enabled in
[I-D.ietf-core-groupcomm-bis] and can be secured with Group Object
Security for Constrained RESTful Environments (Group OSCORE) as
specified 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.
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This document describes how to use [I-D.ietf-ace-key-groupcomm] and
[RFC9200] to perform a number of authentication, authorization and
key distribution actions as overviewed in Section 2 of
[I-D.ietf-ace-key-groupcomm], when the considered group is
specifically an OSCORE group.
With reference to [I-D.ietf-ace-key-groupcomm]:
* The node wishing to join the OSCORE group, i.e., the joining node,
is the Client.
* The Group Manager is the Key Distribution Center (KDC), acting as
a Resource Server.
* The Authorization Server associated with the Group Manager is the
AS.
A node performs the steps described in Sections 3 and 4.3.1.1 of
[I-D.ietf-ace-key-groupcomm] in order to obtain an authorization for
joining an OSCORE group and then to join that group. The format and
processing of messages exchanged during such steps are further
specified in Section 5 and Section 6 of this document.
All communications between the involved entities MUST be secured.
In particular, communications between the Client and the Group
Manager leverage protocol-specific transport profiles of ACE to
achieve communication security, proof-of-possession and server
authentication. It is expected that, in the commonly referred base-
case of this document, the transport profile to use is pre-configured
and well-known to nodes participating in constrained applications.
With respect to what is defined in [I-D.ietf-ace-key-groupcomm]:
* The interface provided by the Group Manager extends the original
interface defined in Section 4.1 of [I-D.ietf-ace-key-groupcomm]
for the KDC, as specified in Section 8 of this document.
* In addition to those defined in Section 8 of
[I-D.ietf-ace-key-groupcomm], additional parameters are defined in
this document and summarized in Section 12.
* In addition to those defined in Section 9 of
[I-D.ietf-ace-key-groupcomm], additional error identifiers are
defined in this document and summarized in Section 13.
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Finally, Appendix A lists the specifications on this application
profile of ACE, based on the requirements defined in Appendix A of
[I-D.ietf-ace-key-groupcomm].
3. Format of Scope
Building on Section 3.1 of [I-D.ietf-ace-key-groupcomm], this section
defines the exact format and encoding of scope used in this profile.
To this end, this profile uses the Authorization Information Format
(AIF) [RFC9237]. With reference to the generic AIF model
AIF-Generic<Toid, Tperm> = [* [Toid, Tperm]]
the value of the CBOR byte string used as scope encodes the CBOR
array [* [Toid, Tperm]], where each [Toid, Tperm] element corresponds
to one scope entry.
Furthermore, this document defines the new AIF specific data model
AIF-OSCORE-GROUPCOMM, that this profile MUST use to format and encode
scope entries.
In particular, the following holds for each scope entry.
* The object identifier ("Toid") is specialized as a CBOR item
specifying the name of the groups pertaining to the scope entry.
* The permission set ("Tperm") is specialized as a CBOR unsigned
integer with value R, specifying the permissions that the Client
wishes to have in the groups indicated by "Toid".
More specifically, the following applies when, as defined in this
document, a scope entry includes as set of permissions the set of
roles to take in an OSCORE group.
* The object identifier ("Toid") is a CBOR text string, specifying
the group name for the scope entry.
* The permission set ("Tperm") is a CBOR unsigned integer with value
R, specifying the role(s) that the Client wishes to take in the
group (REQ1). The value R is computed as follows.
- Each role in the permission set is converted into the
corresponding numeric identifier X from the "Value" column of
the "Group OSCORE Roles" registry, for which this document
defines the entries in Figure 1.
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- The set of N numbers is converted into the single value R, by
taking two to the power of each numeric identifier X_1, X_2,
..., X_N, and then computing the inclusive OR of the binary
representations of all the power values.
+-----------+-------+-------------------------------------------------+
| Name | Value | Description |
+===========+=======+=================================================+
| Reserved | 0 | This value is reserved |
|-----------+-------+-------------------------------------------------+
| Requester | 1 | Send requests; receive responses |
|-----------+-------+-------------------------------------------------+
| Responder | 2 | Send responses; receive requests |
+-----------+-------+-------------------------------------------------+
| Monitor | 3 | Receive requests; never send requests/responses |
|-----------+-------+-------------------------------------------------|
| Verifier | 4 | Verify signature of intercepted messages |
+-----------+-------+-------------------------------------------------+
Figure 1: Numeric identifier of roles in an OSCORE group
The following CDDL [RFC8610] notation defines a scope entry that uses
the AIF-OSCORE-GROUPCOMM data model and expresses a set of Group
OSCORE roles from those in Figure 1.
AIF-OSCORE-GROUPCOMM = AIF-Generic<oscore-gname, oscore-gperm>
oscore-gname = tstr ; Group name
oscore-gperm = uint .bits group-oscore-roles
group-oscore-roles = &(
Requester: 1,
Responder: 2,
Monitor: 3,
Verifier: 4
)
scope_entry = [oscore-gname, oscore-gperm]
Future specifications that define new Group OSCORE roles MUST
register a corresponding numeric identifier in the "Group OSCORE
Roles" registry defined in Section 16.10 of this document.
Note that the value 0 is not available to use as numeric identifier
to specify a Group OSCORE role. It follows that, when expressing
Group OSCORE roles to take in a group as per this document, a scope
entry has the least significant bit of "Tperm" always set to 0.
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This is an explicit feature of the AIF-OSCORE-GROUPCOMM data model.
That is, for each scope entry, the least significant bit of "Tperm"
set to 0 explicitly identifies the scope entry as exactly expressing
a set of Group OSCORE roles ("Tperm"), pertaining to a single group
whose name is specified by the string literal in "Toid".
Instead, by relying on the same AIF-OSCORE-GROUPCOMM data model,
[I-D.ietf-ace-oscore-gm-admin] defines the format of scope entries
for Administrator Clients that wish to access an admin interface at
the Group Manager. In such scope entries, the least significant bit
of "Tperm" is always set to 1.
4. Authentication Credentials
Source authentication of a message sent within the group and
protected with Group OSCORE is ensured by means of a digital
signature embedded in the message (in group mode), or by integrity-
protecting the message with pairwise keying material derived from the
asymmetric keys of sender and recipient (in pairwise mode).
Therefore, group members must be able to retrieve each other's
authentication credential from a trusted 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 authentication credentials
of the group members, and provides those authentication credentials
to group members if requested to. Upon joining an OSCORE group, a
joining node is thus expected to provide its own authentication
credential to the Group Manager.
In particular, the following applies when a node joins an OSCORE
group.
* The joining node is going to join the group exclusively as
monitor, i.e., it is not going to send messages to the group. In
this case, the joining node is not required to provide its own
authentication credential to the Group Manager, which thus does
not have to perform any check related to the format of the
authentication credential, to a signature or ECDH algorithm, and
to possible parameters associated with the algorithm and the
public key. In case the joining node still provides an
authentication credential in the 'client_cred' parameter of the
Join Request (see Section 6.1), the Group Manager silently ignores
that parameter, as well as the related parameters 'cnonce' and
'client_cred_verify'.
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* The Group Manager already acquired the authentication credential
of the joining node during a past joining process. In this case,
the joining node MAY choose not to provide again its own
authentication credential to the Group Manager, in order to limit
the size of the Join Request. The joining node MUST provide its
own authentication credential again if it has provided the Group
Manager with multiple authentication credentials during past
joining processes, intended for different OSCORE groups. If the
joining node provides its own authentication credential, the Group
Manager performs consistency checks as per Section 6.2 and, in
case of success, considers it as the authentication credential
associated with the joining node in the OSCORE group.
* The joining node and the Group Manager use an asymmetric proof-of-
possession key to establish a secure communication association.
Then, two cases can occur.
1. When establishing the secure communication association, the
Group Manager obtained from the joining node the joining
node's authentication credential, in the format used in the
OSCORE group and including the asymmetric proof-of-possession
key as public key. Also, such authentication credential and
the proof-of-possession key are compatible with the signature
or ECDH algorithm, and possible associated parameters used in
the OSCORE group.
In this case, the Group Manager considers the authentication
credential as the one associated with the joining node in the
OSCORE group. If the joining node is aware that the
authentication credential and the public key included thereof
are also valid for the OSCORE group, then the joining node MAY
choose to not provide again its own authentication credential
to the Group Manager.
The joining node MUST provide again its own authentication
credential if it has provided the Group Manager with multiple
authentication credentials during past joining processes,
intended for different OSCORE groups. If the joining node
provides its own authentication credential in the
'client_cred' parameter of the Join Request (see Section 6.1),
the Group Manager performs consistency checks as per
Section 6.2 and, in case of success, considers it as the
authentication credential associated with the joining node in
the OSCORE group.
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2. The authentication credential is not in the format used in the
OSCORE group, or else the authentication credential and the
proof-of-possession key included as public key are not
compatible with the signature or ECDH algorithm, and possible
associated parameters used in the OSCORE group.
In this case, the joining node MUST provide a different
compatible authentication credential and public key included
thereof to the Group Manager in the 'client_cred' parameter of
the Join Request (see Section 6.1). Then, the Group Manager
performs consistency checks on this latest provided
authentication credential as per Section 6.2 and, in case of
success, considers it as the authentication credential
associated with the joining node in the OSCORE group.
* The joining node and the Group Manager use a symmetric proof-of-
possession key to establish a secure communication association.
In this case, upon performing a joining process with that Group
Manager for the first time, the joining node specifies its own
authentication credential in the 'client_cred' parameter of the
Join Request (see Section 6.1).
5. Authorization to Join a Group
This section builds on Section 3 of [I-D.ietf-ace-key-groupcomm] and
is organized as follows.
First, Section 5.1 and Section 5.2 describe how the joining node
interacts with the AS, in order to be authorized to join an OSCORE
group under a given Group Manager and to obtain an Access Token.
Then, Section 5.3 describes how the joining node transfers the
obtained Access Token to the Group Manager. The following considers
a joining node that intends to contact the Group Manager for the
first time.
Note that what is defined in Section 3 of
[I-D.ietf-ace-key-groupcomm] applies, and only additions or
modifications to that specification are defined in this document.
5.1. Authorization Request
The Authorization Request message is as defined in Section 3.1 of
[I-D.ietf-ace-key-groupcomm], with the following additions.
* If the 'scope' parameter is present:
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- The value of the CBOR byte string encodes a CBOR array, whose
format MUST follow the data model AIF-OSCORE-GROUPCOMM defined
in Section 3. For each OSCORE group to join:
o The group name is encoded as a CBOR text string.
o The set of requested roles is expressed as a single CBOR
unsigned integer. This is computed as defined in Section 3,
from the numerical abbreviations of each requested role
defined in the "Group OSCORE Roles" registry, for which this
document defines the entries in Figure 1 (REQ1).
5.2. Authorization Response
The Authorization Response message is as defined in Section 3.2 of
[I-D.ietf-ace-key-groupcomm], with the following additions:
* The AS MUST include the 'expires_in' parameter. Other means for
the AS to specify the lifetime of Access Tokens are out of the
scope of this document.
* The AS MUST include the 'scope' parameter, when the value included
in the Access Token differs from the one specified by the joining
node in the Authorization Request. In such a case, the second
element of each scope entry MUST be present, and specifies the set
of roles that the joining node is actually authorized to take in
the OSCORE group for that scope entry, encoded as specified in
Section 5.1.
Furthermore, the AS MAY use the extended format of scope defined in
Section 7 of [I-D.ietf-ace-key-groupcomm] for the 'scope' claim of
the Access Token. In such a case, the AS MUST use the CBOR tag with
tag number TAG_NUMBER, associated with the CoAP Content-Format CF_ID
for the media type application/aif+cbor registered in Section 16.9 of
this document (REQ28).
Note to RFC Editor: In the previous paragraph, please replace
"TAG_NUMBER" with the CBOR tag number computed as TN(ct) in
Section 4.3 of [RFC9277], where ct is the ID assigned to the CoAP
Content-Format registered in Section 16.9 of this document. Then,
please replace "CF_ID" with the ID assigned to that CoAP Content-
Format. Finally, please delete this paragraph.
This indicates that the binary encoded scope, as conveying the actual
access control information, follows the scope semantics defined for
this application profile in Section 3 of this document.
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5.3. Token Transferring
The exchange of Token Transfer Request and Token Transfer Response is
defined in Section 3.3 of [I-D.ietf-ace-key-groupcomm]. In addition
to that, the following applies.
* The Token Transfer Request MAY additionally contain the following
parameters, which, if included, MUST have the corresponding values
defined below (OPT2):
- 'ecdh_info' defined in Section 5.3.1 of this document, with
value the CBOR simple value "null" (0xf6) to request
information about the ECDH algorithm, the ECDH algorithm
parameters, the ECDH key parameters and the exact format of
authentication credentials used in the groups that the Client
has been authorized to join. This is relevant in case the
joining node supports the pairwise mode of Group OSCORE
[I-D.ietf-core-oscore-groupcomm].
- 'kdc_dh_creds' defined in Section 5.3.2 of this document, with
value the CBOR simple value "null" (0xf6) to request the
Diffie-Hellman authentication credentials of the Group Manager
for the groups that the Client has been authorized to join.
That is, each of such authentication credentials includes a
Diffie-Hellman public key of the Group Manager. This is
relevant in case the joining node supports the pairwise mode of
Group OSCORE [I-D.ietf-core-oscore-groupcomm].
Alternatively, the joining node may retrieve this information by
other means.
* The 'kdcchallenge' parameter contains a dedicated nonce N_S
generated by the Group Manager. For the N_S value, it is
RECOMMENDED to use an 8-byte long random nonce. The joining node
can use this nonce in order to prove the possession of its own
private key, upon joining the group (see Section 6.1).
The 'kdcchallenge' parameter MAY be omitted from the Token
Transfer Response, if the 'scope' of the Access Token specifies
only the role "monitor" or only the role "verifier" or only the
two roles combined, for each and every of the specified groups.
* If the 'sign_info' parameter is present in the response, the
following applies for each element 'sign_info_entry'.
- 'id' MUST NOT refer to OSCORE groups that are pairwise-only
groups.
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- 'sign_alg' takes value from the "Value" column of the "COSE
Algorithms" registry [COSE.Algorithms].
- 'sign_parameters' has the same format and value of the COSE
capabilities array for the algorithm indicated in 'sign_alg',
as specified for that algorithm in the "Capabilities" column of
the "COSE Algorithms" registry [COSE.Algorithms] (REQ4).
- 'sign_key_parameters' has the same format and value of the COSE
capabilities array for the COSE key type of the keys used with
the algorithm indicated in 'sign_alg', as specified for that
key type in the "Capabilities" column of the "COSE Key Types"
registry [COSE.Key.Types] (REQ5).
- 'cred_fmt' takes value from the "Label" column of the "COSE
Header Parameters" registry [COSE.Header.Parameters] (REQ6).
Consistently with Section 2.3 of
[I-D.ietf-core-oscore-groupcomm], acceptable values denote a
format of authentication credential that MUST explicitly
provide the public key as well as the comprehensive set of
information related to the public key algorithm, including,
e.g., the used elliptic curve (when applicable).
At the time of writing this specification, acceptable formats
of authentication credentials are CBOR Web Tokens (CWTs) and
CWT Claims Sets (CCSs) [RFC8392], X.509 certificates [RFC7925]
and C509 certificates [I-D.ietf-cose-cbor-encoded-cert].
Further formats may be available in the future, and would be
acceptable to use as long as they comply with the criteria
defined above.
[ As to CWTs and CCSs, the COSE Header Parameters 'kcwt' and
'kccs' are under pending registration requested by draft-ietf-
lake-edhoc. ]
[ As to C509 certificates, the COSE Header Parameters 'c5b' and
'c5c' are under pending registration requested by draft-ietf-
cose-cbor-encoded-cert. ]
This format is consistent with every signature algorithm currently
considered in [RFC9053], i.e., with algorithms that have only the
COSE key type as their COSE capability. Appendix B of
[I-D.ietf-ace-key-groupcomm] describes how the format of each
'sign_info_entry' can be generalized for possible future
registered algorithms having a different set of COSE capabilities.
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* If 'ecdh_info' is included in the Token Transfer Request, the
Group Manager SHOULD include the 'ecdh_info' parameter in the
Token Transfer Response, as per the format defined in
Section 5.3.1. Note that the field 'id' of each 'ecdh_info_entry'
specifies the name, or array of group names, for which that
'ecdh_info_entry' applies to.
As an exception, the KDC MAY omit the 'ecdh_info' parameter in the
Token Transfer Response even if 'ecdh_info' is included in the
Token Transfer Request, in case all the groups that the Client is
authorized to join are signature-only groups.
* If 'kdc_dh_creds' is included in the Token Transfer Request and
any of the groups that the Client has been authorized to join is a
pairwise-only group, then the Group Manager MUST include the
'kdc_dh_creds' parameter in the Token Transfer Response, as per
the format defined in Section 5.3.2. Otherwise, if 'kdc_dh_creds'
is included in the Token Transfer Request, the Group Manager MAY
include the 'kdc_dh_creds' parameter in the Token Transfer
Response. Note that the field 'id' specifies the group name, or
array of group names, for which the corresponding 'kdc_dh_creds'
applies to.
Note that, other than through the above parameters as defined in
Section 3.3 of [I-D.ietf-ace-key-groupcomm], the joining node may
have obtained such information by alternative means. For example,
information conveyed in the 'sign_info' and 'ecdh_info' parameters
may have been pre-configured, or the joining node may early retrieve
it, e.g., by using the approach described in
[I-D.tiloca-core-oscore-discovery] to discover the OSCORE group and
the link to the associated group-membership resource at the Group
Manager (OPT3).
5.3.1. 'ecdh_info' Parameter
The 'ecdh_info' parameter is an OPTIONAL parameter of the request and
response messages exchanged between the Client and the authz-info
endpoint at the RS (see Section 5.10.1. of [RFC9200]).
This parameter allows the Client and the RS to exchange information
about an ECDH algorithm as well as about the authentication
credentials and public keys to accordingly use for deriving Diffie-
Hellman secrets. Its exact semantics and content are application
specific.
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In this application profile, this parameter is used to exchange
information about the ECDH algorithm as well as about the
authentication credentials and public keys to be used with it, in the
groups indicated by the transferred Access Token as per its 'scope'
claim (see Section 3.2 of [I-D.ietf-ace-key-groupcomm]).
When used in the Token Transfer Request sent to the Group Manager,
the 'ecdh_info' parameter has value the CBOR simple value "null"
(0xf6). This is done to ask for information about the ECDH algorithm
as well as about the authentication credentials and public keys to be
used to compute static-static Diffie-Hellman shared secrets
[NIST-800-56A], in the OSCORE groups that the Client has been
authorized to join and that use the pairwise mode of Group OSCORE
[I-D.ietf-core-oscore-groupcomm].
When used in the following Token Transfer Response from the Group
Manager, the 'ecdh_info' parameter is a CBOR array of one or more
elements. The number of elements is at most the number of OSCORE
groups that the Client has been authorized to join.
Each element contains information about ECDH parameters as well as
about authentication credentials and public keys, for one or more
OSCORE groups that use the pairwise mode of Group OSCORE and that the
Client has been authorized to join. Each element is formatted as
follows.
* The first element 'id' is the group name of the OSCORE group or an
array of group names for the OSCORE groups for which the specified
information applies. In the following, each specified group name
is referred to as 'gname'. The 'id' element MUST NOT refer to
OSCORE groups that are signature-only groups.
* The second element 'ecdh_alg' is a CBOR integer or a CBOR text
string indicating the ECDH algorithm used in the OSCORE group
identified by 'gname'. Values are taken from the "Value" column
of the "COSE Algorithms" registry [COSE.Algorithms].
* The third element 'ecdh_parameters' is a CBOR array indicating the
parameters of the ECDH algorithm used in the OSCORE group
identified by 'gname'. Its format and value are the same of the
COSE capabilities array for the algorithm indicated in 'ecdh_alg',
as specified for that algorithm in the "Capabilities" column of
the "COSE Algorithms" registry [COSE.Algorithms].
* The fourth element 'ecdh_key_parameters' is a CBOR array
indicating the parameters of the keys used with the ECDH algorithm
in the OSCORE group identified by 'gname'. Its content depends on
the value of 'ecdh_alg'. In particular, its format and value are
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the same of the COSE capabilities array for the COSE key type of
the keys used with the algorithm indicated in 'ecdh_alg', as
specified for that key type in the "Capabilities" column of the
"COSE Key Types" registry [COSE.Key.Types].
* The fifth element 'cred_fmt' is a CBOR integer indicating the
format of authentication credentials used in the OSCORE group
identified by 'gname'. It takes value from the "Label" column of
the "COSE Header Parameters" registry [COSE.Header.Parameters]
(REQ6). Acceptable values denote a format that MUST explicitly
provide the public key as well as a comprehensive set of
information related to the public key algorithm. This information
includes, e.g., the used elliptic curve (when applicable). The
same considerations and guidelines for the 'cred_fmt' element of
'sign_info' apply (see Section 5.3).
The CDDL notation [RFC8610] of the 'ecdh_info' parameter is given
below.
ecdh_info = ecdh_info_req / ecdh_info_resp
ecdh_info_req = null ; in the Token Transfer
; Request to the
; Group Manager
ecdh_info_res = [ + ecdh_info_entry ] ; in the Token Transfer
; Response from the
; Group Manager
ecdh_info_entry =
[
id : gname / [ + gname ],
ecdh_alg : int / tstr,
ecdh_parameters : [ any ],
ecdh_key_parameters : [ any ],
cred_fmt : int
]
gname = tstr
This format is consistent with every ECDH algorithm currently defined
in [RFC9053], i.e., with algorithms that have only the COSE key type
as their COSE capability. Appendix B of this document describes how
the format of each 'ecdh_info_entry' can be generalized for possible
future registered algorithms having a different set of COSE
capabilities.
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5.3.2. 'kdc_dh_creds' Parameter
The 'kdc_dh_creds' parameter is an OPTIONAL parameter of the request
and response messages exchanged between the Client and the authz-info
endpoint at the RS (see Section 5.10.1. of [RFC9200]).
This parameter allows the Client to request and retrieve the Diffie-
Hellman authentication credentials of the RS, i.e., authentication
credentials including a Diffie-Hellman public key of the RS.
In this application profile, this parameter is used to request and
retrieve from the Group Manager its Diffie-Hellman authentication
credentials to use, in the OSCORE groups that the Client has been
authorized to join. The Group Manager has a Diffie-Hellman
authentication credential in an OSCORE group if and only if the group
is a pairwise-only group. In this case, the early retrieval of the
Group Manager's authentication credential is necessary in order for
the joining node to prove the possession of its own private key, upon
joining the group (see Section 6.1).
When used in the Token Transfer Request sent to the Group Manager,
the 'kdc_dh_creds' parameter has value the CBOR simple value "null"
(0xf6). This is done to ask for the Diffie-Hellman authentication
credentials that the Group Manager uses in the OSCORE groups that the
Client has been authorized to join.
When used in the following Token Transfer Response from the Group
Manager, the 'kdc_dh_creds' parameter is a CBOR array of one or more
elements. The number of elements is at most the number of OSCORE
groups that the Client has been authorized to join.
Each element 'kdc_dh_creds_entry' contains information about the
Group Manager's Diffie-Hellman authentication credentials, for one or
more OSCORE groups that are pairwise-only groups and that the Client
has been authorized to join. Each element is formatted as follows.
* The first element 'id' is the group name of the OSCORE group or an
array of group names for the OSCORE groups for which the specified
information applies. In particular, 'id' MUST refer exclusively
to OSCORE groups that are pairwise-only groups.
* The second element 'cred_fmt' is a CBOR integer indicating the
format of authentication credentials used in the OSCORE group
identified by 'gname'. It takes value from the "Label" column of
the "COSE Header Parameters" registry [COSE.Header.Parameters]
(REQ6). Acceptable values denote a format that MUST explicitly
provide the public key as well as a comprehensive set of
information related to the public key algorithm. This information
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includes, e.g., the used elliptic curve (when applicable). The
same considerations and guidelines for the 'cred_fmt' element of
'sign_info' apply (see Section 5.3).
* The third element 'cred' is a CBOR byte string, which encodes the
Group Manager's Diffie-Hellman authentication credential in its
original binary representation made available to other endpoints
in the group. That is, the original binary representation
complies with the format specified by the 'cred_fmt' element.
Note that the authentication credential provides the comprehensive
set of information related to its public key algorithm, i.e., the
ECDH algorithm used in the OSCORE group as pairwise key agreement
algorithm.
The CDDL notation [RFC8610] of the 'kdc_dh_creds' parameter is given
below.
kdc_dh_creds = kdc_dh_creds_req / kdc_dh_creds_resp
kdc_dh_creds_req = null ; in the Token Transfer
; Request to the
; Group Manager
kdc_dh_creds_res = [ + kdc_dh_creds_entry ] ; in the Token Transfer
; Response from the
; Group Manager
kdc_dh_creds_entry =
[
id : gname / [ + gname ],
cred_fmt : int,
cred : bstr
]
gname = tstr
6. Group Joining
This section describes the interactions between the joining node and
the Group Manager to join an OSCORE group. The message exchange
between the joining node and the Group Manager consists of the
messages defined in Section 4.3.1.1 of [I-D.ietf-ace-key-groupcomm].
Note that what is defined in [I-D.ietf-ace-key-groupcomm] applies,
and only additions or modifications to that specification are defined
in this document.
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6.1. Send the Join Request
The joining node requests to join the OSCORE group by sending a Join
Request message to the related group-membership resource at the Group
Manager, as per Section 4.3.1.1 of [I-D.ietf-ace-key-groupcomm].
Additionally to what is defined in Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm], the following applies.
* The 'scope' parameter MUST be included. Its value encodes one
scope entry with the format defined in Section 3, indicating the
group name and the role(s) that the joining node wants to take in
the group.
The 'scope' parameter MUST NOT specify any of the following sets
of roles: ("requester", "monitor") and ("responder", "monitor").
Future specifications that define a new role for members of OSCORE
groups MUST define possible sets of roles (including the new role
and existing roles) that are not acceptable to specify in the
'scope' parameter of a Join Request.
* The 'get_creds' parameter is present only if the joining node
wants to retrieve the authentication credentials of the group
members from the Group Manager during the joining process (see
Section 4). Otherwise, this parameter MUST NOT be present.
If this parameter is present and its value is not the CBOR simple
value "null" (0xf6), each element of the inner CBOR array
'role_filter' is encoded as a CBOR unsigned integer, with the same
value of a permission set ("Tperm") indicating that role or
combination of roles in a scope entry, as defined in Section 3.
* 'cnonce' contains a dedicated nonce N_C generated by the joining
node. For the N_C value, it is RECOMMENDED to use an 8-byte long
random nonce.
* The proof-of-possession (PoP) evidence included in
'client_cred_verify' is computed as defined below (REQ14). In
either case, the N_S used to build the PoP input is as defined in
Section 6.1.1.
- If the group is not a pairwise-only group, the PoP evidence
MUST be a signature. The joining node computes the signature
by using the same private key and signature algorithm it
intends to use for signing messages in the OSCORE group.
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- If the group is a pairwise-only group, the PoP evidence MUST be
a MAC computed as follows, by using the HKDF Algorithm HKDF
SHA-256, which consists of composing the HKDF-Extract and HKDF-
Expand steps [RFC5869].
MAC = HKDF(salt, IKM, info, L)
The input parameters of HKDF are as follows.
o salt takes as value the empty byte string.
o IKM is computed as a cofactor Diffie-Hellman shared secret,
see Section 5.7.1.2 of [NIST-800-56A], using the ECDH
algorithm used in the OSCORE group. The joining node uses
its own Diffie-Hellman private key and the Diffie-Hellman
public key of the Group Manager. For X25519 and X448, the
procedure is described in Section 5 of [RFC7748].
o info takes as value the PoP input.
o L is equal to 8, i.e., the size of the MAC, in bytes.
6.1.1. Value of the N_S Challenge
The value of the N_S challenge is determined as follows.
1. If the joining node has provided the Access Token to the Group
Manager by means of a Token Transfer Request to the /authz-info
endpoint as in Section 5.3, then N_S takes the same value of the
most recent 'kdcchallenge' parameter received by the joining node
from the Group Manager. This can be either the one specified in
the Token Transfer Response, or the one possibly specified in a
4.00 (Bad Request) error response to a following Join Request
(see Section 6.2).
2. If the provisioning of the Access Token to the Group Manager has
relied on the DTLS profile of ACE [RFC9202], and the Access Token
was specified:
* in the "psk_identity" field of the ClientKeyExchange message
when using DTLS 1.2 [RFC6347]; or
* in the "identity" field of a PskIdentity within the
PreSharedKeyExtension of the ClientHello message when using
DTLS 1.3 [RFC9147],
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then N_S is an exporter value computed as defined in Section 7.5
of [RFC8446]. Specifically, N_S is exported from the DTLS
session between the joining node and the Group Manager, using an
empty 'context_value', 32 bytes as 'key_length', and the exporter
label "EXPORTER-ACE-Sign-Challenge-coap-group-oscore-app" defined
in Section 16.7 of this document.
It is up to applications to define how N_S is computed in further
alternative settings.
Section 15.3 provides security considerations on the reusage of the
N_S challenge.
6.2. Receive the Join Request
The Group Manager processes the Join Request as defined in
Section 4.3.1 of [I-D.ietf-ace-key-groupcomm], with the following
additions.
The Group Manager verifies the PoP evidence contained in
'client_cred_verify' as follows:
* As PoP input, the Group Manager uses the value of the 'scope'
parameter from the Join Request as a CBOR byte string,
concatenated with N_S encoded as a CBOR byte string, concatenated
with N_C encoded as a CBOR byte string. The value of N_S is
determined as described in Section 6.1.1, while N_C is the nonce
provided in the 'cnonce' parameter of the Join Request.
* As public key of the joining node, the Group Manager uses either
the one included in the authentication credential retrieved from
the 'client_cred' parameter of the Join Request, or the one from
the already stored authentication credential as acquired from
previous interactions with the joining node (see Section 4).
* If the group is not a pairwise-only group, the PoP evidence is a
signature. The Group Manager verifies it by using the public key
of the joining node, as well as the signature algorithm used in
the OSCORE group and possible corresponding parameters.
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* If the group is a pairwise-only group, the PoP evidence is a MAC.
The Group Manager recomputes the MAC through the same process
taken by the joining node when preparing the value of the
'client_cred_verify' parameter for the Join Request (see
Section 6.1), with the difference that the Group Manager uses its
own Diffie-Hellman private key and the Diffie-Hellman public key
of the joining node. The verification succeeds if and only if the
recomputed MAC is equal to the MAC conveyed as PoP evidence in the
Join Request.
The Group Manager MUST reply with a 5.03 (Service Unavailable) error
response in the following cases:
* There are currently no OSCORE Sender IDs available to assign in
the OSCORE group and, at the same time, the joining node is not
going to join the group exclusively as monitor. The response MUST
have Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST
be set to 4 ("No available node identifiers").
* The OSCORE group that the joining node has been trying to join is
currently inactive (see Section 8.1). The response MUST have
Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST
be set to 9 ("Group currently not active").
The Group Manager MUST reply with a 4.00 (Bad Request) error response
in the following cases:
* The 'client_cred' parameter is present in the Join Request and its
value is not an eligible authentication credential (e.g., it is
not of the format accepted in the group).
* The 'client_cred' parameter is not present in the Join Request
while the joining node is not going to join the group exclusively
as monitor, and any of the following conditions holds:
- The Group Manager does not store an eligible authentication
credential (e.g., of the format accepted in the group) for the
joining node.
- The Group Manager stores multiple eligible authentication
credentials (e.g., of the format accepted in the group) for the
joining node.
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* The 'scope' parameter is not present in the Join Request, or it is
present and specifies any of the following sets of roles:
("requester", "monitor") and ("responder", "monitor").
* The Join Request includes the 'client_cred' parameter but does not
include both the 'cnonce' and 'client_cred_verify' parameters.
In order to prevent the acceptance of Ed25519 and Ed448 public keys
that cannot be successfully converted to Montgomery coordinates, and
thus cannot be used for the derivation of pairwise keys (see
Section 2.4.1 of [I-D.ietf-core-oscore-groupcomm]), the Group Manager
MAY reply with a 4.00 (Bad Request) error response in case all the
following conditions hold:
* The OSCORE group uses the pairwise mode of Group OSCORE.
* The OSCORE group uses EdDSA public keys [RFC8032].
* The authentication credential of the joining node from the
'client_cred' parameter includes a public key which:
- Is for the elliptic curve Ed25519 and has its Y coordinate
equal to -1 or 1 (mod p), with p = (2^255 - 19), see
Section 4.1 of [RFC7748]; or
- Is for the elliptic curve Ed448 and has its Y coordinate equal
to -1 or 1 (mod p), with p = (2^448 - 2^224 - 1), see
Section 4.2 of [RFC7748].
A 4.00 (Bad Request) error response from the Group Manager to the
joining node MUST have content format application/ace-groupcomm+cbor.
The response payload is a CBOR map formatted as follows:
* If the group uses (also) the group mode of Group OSCORE, the CBOR
map MUST contain the 'sign_info' parameter, whose CBOR label is
defined in Section 8 of [I-D.ietf-ace-key-groupcomm]. This
parameter has the same format of 'sign_info_res' defined in
Section 3.3.1 of [I-D.ietf-ace-key-groupcomm] and includes a
single element 'sign_info_entry', pertaining to the OSCORE group
that the joining node has tried to join with the Join Request.
* If the group uses (also) the pairwise mode of Group OSCORE, the
CBOR map MUST contain the 'ecdh_info' parameter, whose CBOR label
is defined in Section 16.3. This parameter has the same format of
'ecdh_info_res' defined in Section 5.3.1 and includes a single
element 'ecdh_info_entry', pertaining to the OSCORE group that the
joining node has tried to join with the Join Request.
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* If the group is a pairwise-only group, the CBOR map MUST contain
the 'kdc_dh_creds' parameter, whose CBOR label is defined in
Section 16.3. This parameter has the same format of
'kdc_dh_creds_res' defined in Section 5.3.2 and includes a single
element 'kdc_dh_creds_entry', pertaining to the OSCORE group that
the joining node has tried to join with the Join Request.
* The CBOR map MAY include the 'kdcchallenge' parameter, whose CBOR
label is defined in Section 8 of [I-D.ietf-ace-key-groupcomm]. If
present, this parameter is a CBOR byte string, which encodes a
newly generated 'kdcchallenge' value that the Client can use when
preparing a Join Request (see Section 6.1). In such a case the
Group Manager MUST store the newly generated value as the
'kdcchallenge' value associated with the joining node, replacing
the currently stored value (if any).
6.2.1. Follow-up to a 4.00 (Bad Request) Error Response
When receiving a 4.00 (Bad Request) error response, the joining node
MAY send a new Join Request to the Group Manager. In such a case:
* The 'cnonce' parameter MUST include a new dedicated nonce N_C
generated by the joining node.
* The 'client_cred' parameter MUST include an authentication
credential in the format indicated by the Group Manager. Also,
the authentication credential as well as the included public key
MUST be compatible with the signature or ECDH algorithm, and
possible associated parameters.
* The 'client_cred_verify' parameter MUST include a PoP evidence
computed as described in Section 6.1, by using the private key
associated with the authentication credential specified in the
current 'client_cred' parameter, with the signature or ECDH
algorithm, and possible associated parameters indicated by the
Group Manager. If the error response from the Group Manager
includes the 'kdcchallenge' parameter, the joining node MUST use
its content as new N_S challenge to compute the PoP evidence.
6.3. Send the Join Response
If the processing of the Join Request described in Section 6.2 is
successful, the Group Manager updates the group membership by
registering the joining node NODENAME as a new member of the OSCORE
group GROUPNAME, as described in Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm].
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If the joining node has not taken exclusively the role of monitor,
the Group Manager performs also the following actions.
* The Group Manager selects an available OSCORE Sender ID in the
OSCORE group, and exclusively assigns it to the joining node. The
Group Manager MUST NOT assign an OSCORE Sender ID to the joining
node if this joins the group exclusively with the role of monitor,
according to what is specified in the Access Token (see
Section 5.2).
Consistently with Section 3.2.1 of
[I-D.ietf-core-oscore-groupcomm], the Group Manager MUST assign an
OSCORE Sender ID that has not been used in the OSCORE group since
the latest time when the current Gid value was assigned to the
group.
If the joining node is recognized as a current group member, e.g.,
through the ongoing secure communication association, the
following also applies.
- The Group Manager MUST assign a new OSCORE Sender ID different
than the one currently used by the joining node in the OSCORE
group.
- The Group Manager MUST add the old, relinquished OSCORE Sender
ID of the joining node to the set of stale Sender IDs
associated with the current version of the group keying
material for the group (see Section 7.1).
* The Group Manager stores the association between i) the
authentication credential of the joining node; and ii) the Group
Identifier (Gid), i.e., the OSCORE ID Context, associated with the
OSCORE group together with the OSCORE Sender ID assigned to the
joining node in the group. The Group Manager MUST keep this
association updated over time.
Then, the Group Manager replies to the joining node, providing the
updated security parameters and keying material necessary to
participate in the group communication. This success Join Response
is formatted as defined in Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm], with the following additions:
* The 'gkty' parameter identifies a key of type
"Group_OSCORE_Input_Material object", defined in Section 16.4 of
this document.
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* The 'key' parameter includes what the joining node needs in order
to set up the Group OSCORE Security Context as per Section 2 of
[I-D.ietf-core-oscore-groupcomm].
This parameter has as value a Group_OSCORE_Input_Material object,
which is defined in this document and extends the
OSCORE_Input_Material object encoded in CBOR as defined in
Section 3.2.1 of [RFC9203]. In particular, it contains the
additional parameters 'group_senderId', 'cred_fmt',
'sign_enc_alg', 'sign_alg', 'sign_params', 'ecdh_alg' and
'ecdh_params' defined in Section 16.6 of this document.
More specifically, the 'key' parameter is composed as follows.
- The 'hkdf' parameter, if present, specifies the HKDF Algorithm
used in the OSCORE group. The HKDF Algorithm is specified by
the HMAC Algorithm value. This parameter MAY be omitted, if
the HKDF Algorithm used in the group is HKDF SHA-256.
Otherwise, this parameter MUST be present.
- The 'salt' parameter, if present, has as value the OSCORE
Master Salt used in the OSCORE group. This parameter MAY be
omitted, if the Master Salt used in the group is the empty byte
string. Otherwise, this parameter MUST be present.
- The 'ms' parameter includes the OSCORE Master Secret value used
in the OSCORE group. This parameter MUST be present.
- The 'contextId' parameter has as value the Group Identifier
(Gid), i.e., the OSCORE ID Context of the OSCORE group. This
parameter MUST be present.
- The 'group_senderId' parameter has as value the OSCORE Sender
ID assigned to the joining node by the Group Manager, as
described above. This parameter MUST be present if and only if
the node does not join the OSCORE group exclusively with the
role of monitor, according to what is specified in the Access
Token (see Section 5.2).
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- The 'cred_fmt' parameter specifies the format of authentication
credentials used in the OSCORE group. This parameter MUST be
present and it takes value from the "Label" column of the "COSE
Header Parameters" registry [COSE.Header.Parameters] (REQ6).
Consistently with Section 2.3 of
[I-D.ietf-core-oscore-groupcomm], acceptable values denote a
format that MUST explicitly provide the public key as well as a
comprehensive set of information related to the public key
algorithm. This information includes, e.g., the used elliptic
curve (when applicable).
At the time of writing this specification, acceptable formats
of authentication credentials are CBOR Web Tokens (CWTs) and
CWT Claims Sets (CCSs) [RFC8392], X.509 certificates [RFC7925]
and C509 certificates [I-D.ietf-cose-cbor-encoded-cert].
Further formats may be available in the future, and would be
acceptable to use as long as they comply with the criteria
defined above.
[ As to CWTs and CCSs, the COSE Header Parameters 'kcwt' and
'kccs' are under pending registration requested by draft-ietf-
lake-edhoc. ]
[ As to C509 certificates, the COSE Header Parameters 'c5b' and
'c5c' are under pending registration requested by draft-ietf-
cose-cbor-encoded-cert. ]
The 'key' parameter MUST also include the following parameters, if
and only if the OSCORE group is not a pairwise-only group.
- The 'sign_enc_alg' parameter, specifying the Signature
Encryption Algorithm used in the OSCORE group to encrypt
messages protected with the group mode. This parameter takes
values from the "Value" column of the "COSE Algorithms"
registry [COSE.Algorithms].
- The 'sign_alg' parameter, specifying the Signature Algorithm
used to sign messages in the OSCORE group. This parameter
takes values from the "Value" column of the "COSE Algorithms"
registry [COSE.Algorithms].
- The 'sign_params' parameter, specifying the parameters of the
Signature Algorithm. This parameter is a CBOR array, which
includes the following two elements:
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o 'sign_alg_capab': a CBOR array, with the same format and
value of the COSE capabilities array for the Signature
Algorithm indicated in 'sign_alg', as specified for that
algorithm in the "Capabilities" column of the "COSE
Algorithms" registry [COSE.Algorithms].
o 'sign_key_type_capab': a CBOR array, with the same format
and value of the COSE capabilities array for the COSE key
type of the keys used with the Signature Algorithm indicated
in 'sign_alg', as specified for that key type in the
"Capabilities" column of the "COSE Key Types" registry
[COSE.Key.Types].
The 'key' parameter MUST also include the following parameters, if
and only if the OSCORE group is not a signature-only group.
- The 'alg' parameter, specifying the AEAD Algorithm used in the
OSCORE group to encrypt messages protected with the pairwise
mode.
- The 'ecdh_alg' parameter, specifying the Pairwise Key Agreement
Algorithm used in the OSCORE group. This parameter takes
values from the "Value" column of the "COSE Algorithms"
registry [COSE.Algorithms].
- The 'ecdh_params' parameter, specifying the parameters of the
Pairwise Key Agreement Algorithm. This parameter is a CBOR
array, which includes the following two elements:
o 'ecdh_alg_capab': a CBOR array, with the same format and
value of the COSE capabilities array for the algorithm
indicated in 'ecdh_alg', as specified for that algorithm in
the "Capabilities" column of the "COSE Algorithms" registry
[COSE.Algorithms].
o 'ecdh_key_type_capab': a CBOR array, with the same format
and value of the COSE capabilities array for the COSE key
type of the keys used with the algorithm indicated in
'ecdh_alg', as specified for that key type in the
"Capabilities" column of the "COSE Key Types" registry
[COSE.Key.Types].
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The format of 'key' defined above is consistent with every
signature algorithm and ECDH algorithm currently considered in
[RFC9053], i.e., with algorithms that have only the COSE key type
as their COSE capability. Appendix B of this document describes
how the format of the 'key' parameter can be generalized for
possible future registered algorithms having a different set of
COSE capabilities.
Furthermore, the following applies.
* The 'exp' parameter MUST be present.
* The 'ace_groupcomm_profile' parameter MUST be present and has
value coap_group_oscore_app (PROFILE_TBD), which is defined in
Section 16.5 of this document.
* The 'creds' parameter, if present, includes the authentication
credentials requested by the joining node by means of the
'get_creds' parameter in the Join Request.
If the joining node has asked for the authentication credentials
of all the group members, i.e., 'get_creds' had value the CBOR
simple value "null" (0xf6) in the Join Request, then the Group
Manager provides only the authentication credentials of the group
members that are relevant to the joining node. That is, in such a
case, 'creds' includes only: i) the authentication credentials of
the responders currently in the OSCORE group, in case the joining
node is configured (also) as requester; and ii) the authentication
credentials of the requesters currently in the OSCORE group, in
case the joining node is configured (also) as responder or
monitor.
* The 'peer_identifiers' parameter includes the OSCORE Sender ID of
each group member whose authentication credential is specified in
the 'creds' parameter. That is, a group member's Sender ID is
used as identifier for that group member (REQ25).
* The 'group_policies' parameter SHOULD be present, and SHOULD
include the following elements:
- "Key Update Check Interval" defined in Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm], with default value 3600;
- "Expiration Delta" defined in Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm], with default value 0.
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* The 'kdc_cred' parameter MUST be present, specifying the Group
Manager's authentication credential in its original binary
representation (REQ8). The Group Manager's authentication
credential MUST be in the format used in the OSCORE group. Also,
the authentication credential as well as the included public key
MUST be compatible with the signature or ECDH algorithm, and
possible associated parameters used in the OSCORE group.
* The 'kdc_nonce' parameter MUST be present, specifying the
dedicated nonce N_KDC generated by the Group Manager. For N_KDC,
it is RECOMMENDED to use an 8-byte long random nonce.
* The 'kdc_cred_verify' parameter MUST be present, specifying the
proof-of-possession (PoP) evidence computed by the Group Manager.
The PoP evidence is computed over the nonce N_KDC, which is
specified in the 'kdc_nonce' parameter and taken as PoP input.
The PoP evidence is computed as defined below (REQ21).
- If the group is not a pairwise-only group, the PoP evidence
MUST be a signature. The Group Manager computes the signature
by using the signature algorithm used in the OSCORE group, as
well as its own private key associated with the authentication
credential specified in the 'kdc_cred' parameter.
- If the group is a pairwise-only group, the PoP evidence MUST be
a MAC computed as follows, by using the HKDF Algorithm HKDF
SHA-256, which consists of composing the HKDF-Extract and HKDF-
Expand steps [RFC5869].
MAC = HKDF(salt, IKM, info, L)
The input parameters of HKDF are as follows.
o salt takes as value the empty byte string.
o IKM is computed as a cofactor Diffie-Hellman shared secret,
see Section 5.7.1.2 of [NIST-800-56A], using the ECDH
algorithm used in the OSCORE group. The Group Manager uses
its own Diffie-Hellman private key and the Diffie-Hellman
public key of the joining node. For X25519 and X448, the
procedure is described in Section 5 of [RFC7748].
o info takes as value the PoP input.
o L is equal to 8, i.e., the size of the MAC, in bytes.
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* The 'group_rekeying' parameter MAY be omitted, if the Group
Manager uses the "Point-to-Point" group rekeying scheme registered
in Section 11.12 of [I-D.ietf-ace-key-groupcomm] as rekeying
scheme in the OSCORE group (OPT9). Its detailed use for this
profile is defined in Section 11 of this document. In any other
case, the 'group_rekeying' parameter MUST be included.
As a last action, if the Group Manager reassigns Gid values during
the group's lifetime (see Section 3.2.1.1 of
[I-D.ietf-core-oscore-groupcomm]), then the Group Manager MUST store
the Gid specified in the 'contextId' parameter of the 'key'
parameter, as the Birth Gid of the joining node in the joined group
(see Section 3 of [I-D.ietf-core-oscore-groupcomm]). This applies
also in case the joining node is in fact re-joining the group; in
such a case, the newly determined Birth Gid overwrites the one
currently stored.
6.4. Receive the Join Response
Upon receiving the Join Response, the joining node retrieves the
Group Manager's authentication credential from the 'kdc_cred'
parameter. The joining node MUST verify the proof-of-possession
(PoP) evidence specified in the 'kdc_cred_verify' parameter of the
Join Response as defined below (REQ21).
* If the group is not a pairwise-only group, the PoP evidence is a
signature. The joining node verifies it by using the public key
of the Group Manager from the received authentication credential,
as well as the signature algorithm used in the OSCORE group and
possible corresponding parameters.
* If the group is a pairwise-only group, the PoP evidence is a MAC.
The joining node recomputes the MAC through the same process taken
by the Group Manager when computing the value of the
'kdc_cred_verify' parameter (see Section 6.3), with the difference
that the joining node uses its own Diffie-Hellman private key and
the Diffie-Hellman public key of the Group Manager from the
received authentication credential. The verification succeeds if
and only if the recomputed MAC is equal to the MAC conveyed as PoP
evidence in the Join Response.
In case of failed verification of the PoP evidence, the joining node
MUST stop processing the Join Response and MAY send a new Join
Request to the Group Manager (see Section 6.1).
In case of successful verification of the PoP evidence, the joining
node uses the information received in the Join Response to set up the
Group OSCORE Security Context, as described in Section 2 of
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[I-D.ietf-core-oscore-groupcomm]. If the following parameters were
not included in the 'key' parameter of the Join Response, the joining
node considers the default values specified below, consistently with
Section 3.2 of [RFC8613].
* Absent the 'hkdf' parameter, the joining node considers HKDF
SHA-256 as HKDF Algorithm to use in the OSCORE group.
* Absent the 'salt' parameter, the joining node considers the empty
byte string as Master Salt to use in the OSCORE group.
* Absent the 'group_rekeying' parameter, the joining node considers
the "Point-to-Point" group rekeying scheme registered in
Section 11.12 of [I-D.ietf-ace-key-groupcomm] as the rekeying
scheme used in the group (OPT9). Its detailed use for this
profile is defined in Section 11 of this document.
In addition, the joining node maintains an association between each
authentication credential retrieved from the 'creds' parameter and
the role(s) that the corresponding group member has in the OSCORE
group.
From then on, the joining node can exchange group messages secured
with Group OSCORE as described in [I-D.ietf-core-oscore-groupcomm].
When doing so:
* The joining node MUST NOT process an incoming request message, if
protected by a group member whose authentication credential is not
associated with the role "Requester".
* The joining node MUST NOT process an incoming response message, if
protected by a group member whose authentication credential is not
associated with the role "Responder".
* The joining node MUST NOT use the pairwise mode of Group OSCORE to
process messages in the group, if the Join Response did not
include the 'ecdh_alg' parameter.
If the application requires backward security, the Group Manager MUST
generate updated security parameters and group keying material, and
provide it to the current group members, upon the new node's joining
(see Section 11). In such a case, the joining node is not able to
access secure communication in the OSCORE group that occurred prior
to its joining.
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7. Overview of the Group Rekeying Process
In a number of cases, the Group Manager has to generate new keying
material and distribute it to the group (rekeying), as also discussed
in Section 3.2 of [I-D.ietf-core-oscore-groupcomm].
To this end the Group Manager MUST support the Group Rekeying Process
described in Section 11 of this document, as an instance of the
"Point-to-Point" rekeying scheme defined in Section 6.1 of
[I-D.ietf-ace-key-groupcomm] and registered in Section 11.12 of
[I-D.ietf-ace-key-groupcomm]. Future documents may define the use of
alternative group rekeying schemes for this application profile,
together with the corresponding rekeying message formats. The
resulting group rekeying process MUST comply with the functional
steps defined in Section 3.2 of [I-D.ietf-core-oscore-groupcomm].
Upon generating the new group keying material and before starting its
distribution, the Group Manager MUST increment the version number of
the group keying material. When rekeying a group, the Group Manager
MUST preserve the current value of the OSCORE Sender ID of each
member in that group.
The data distributed to a group through a rekeying MUST include:
* The new version number of the group keying material for the group.
* A new Group Identifier (Gid) for the group as introduced in
[I-D.ietf-ace-key-groupcomm], used as ID Context parameter of the
Group OSCORE Common Security Context of that group (see Section 2
of [I-D.ietf-core-oscore-groupcomm]).
Note that the Gid differs from the group name also introduced in
[I-D.ietf-ace-key-groupcomm], which is a plain, stable and
invariant identifier, with no cryptographic relevance and meaning.
* A new value for the Master Secret parameter of the Group OSCORE
Common Security Context of the group (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]).
* A set of stale Sender IDs, which allows each rekeyed node to purge
authentication credentials and Recipient Contexts used in the
group and associated with those Sender IDs. This in turn allows
every group member to rely on stored authentication credentials,
in order to confidently assert the group membership of other
sender nodes, when receiving protected messages in the group (see
Section 3.2 of [I-D.ietf-core-oscore-groupcomm]). More details on
the maintenance of stale Sender IDs are provided in Section 7.1.
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Also, the data distributed through a group rekeying MAY include a new
value for the Master Salt parameter of the Group OSCORE Common
Security Context of that group.
The Group Manager MUST rekey the group in the following cases.
* The application requires backward security - In this case, the
group is rekeyed when a node joins the group as a new member.
Therefore, a joining node cannot access communications in the
group prior to its joining.
* One or more nodes leave the group - That is, the group is rekeyed
when one or more current members spontaneously request to leave
the group (see Section 9.11), or when the Group Manager forcibly
evicts them from the group, e.g., due to expired or revoked
authorization (see Section 10). Therefore, a leaving node cannot
access communications in the group after its leaving, thus
ensuring forward security in the group.
Due to the set of stale Sender IDs distributed through the
rekeying, this ensures that a node owning the latest group keying
material does not store the authentication credentials of former
group members (see Sections 3.2 and 12.1 of
[I-D.ietf-core-oscore-groupcomm]).
When the expiration time for the group keying material approaches or
has passed, the Group Manager may want to extend the secure group
operation, as considered appropriate. If the Group Manager does so,
the Group Manager MUST rekey the group.
The Group Manager MAY rekey the group for other reasons, e.g.,
according to an application-specific rekeying period or scheduling.
7.1. Stale OSCORE Sender IDs
For each OSCORE group, the Group Manager MUST maintain N > 1 sets of
"stale" OSCORE Sender IDs. It is up to the application to specify
the value of N, possibly on a per-group basis.
Each set is uniquely associated with one version of the group keying
material, and includes the OSCORE Sender IDs that have become "stale"
in the OSCORE group under that version of the group keying material.
In the following cases, the Group Manager MUST add an element to the
set X associated with the current version of the group keying
material.
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* When a current group member obtains a new Sender ID, its old
Sender ID is added to X. This happens when the Group Manager
assigns a new Sender ID upon request from the group member (see
Section 9.2), or in case the group member re-joins the group (see
Section 6.1 and Section 6.3), thus also obtaining a new Sender ID.
* When a current group member leaves the group, its current Sender
ID is added to X. This happens when a group member requests to
leave the group (see Section 9.11) or is forcibly evicted from the
group (see Section 10).
The value of N can change during the lifetime of the group. If the
new value N' is smaller than N, the Group Manager MUST preserve the
sets associated with the (up to) N' most recent versions of the group
keying material.
When performing a group rekeying (see Section 11) for switching from
an old version V to a new version V' = (V + 1) of the group keying
material, the Group Manager MUST perform the following actions.
* Before creating the new group keying material with version V', if
the number of sets of stale Sender IDs for the group is equal to
N, then the Group Manager deletes the oldest set.
* The Group Manager rekeys the group. This includes also
distributing the set of stale Sender IDs associated with the
version V of the group keying material (see Section 7).
* After completing the group rekeying, the Group Manager creates an
empty set of stale Sender IDs, as associated with the version V'
of the group keying material.
8. Interface at the Group Manager
The Group Manager provides the interface defined in Section 4.1 of
[I-D.ietf-ace-key-groupcomm], with the additional sub-resources
defined from Section 8.1 to Section 8.3 of this document.
Furthermore, Section 8.4 provides a summary of the CoAP methods
admitted to access different resources at the Group Manager, for
nodes with different roles in the group or as non members (REQ11).
The GROUPNAME segment of the URI path MUST match with the group name
specified in the scope entry of the Access Token scope (i.e., 'gname'
in Section 3.1 of [I-D.ietf-ace-key-groupcomm]) (REQ7).
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The Resource Type (rt=) Link Target Attribute value "core.osc.gm" is
registered in Section 16.11 (REQ10), and can be used to describe
group-membership resources and its sub-resources at a Group Manager,
e.g., by using a link-format document [RFC6690].
Applications can use this common resource type to discover links to
group-membership resources for joining OSCORE groups, e.g., by using
the approach described in [I-D.tiloca-core-oscore-discovery].
8.1. ace-group/GROUPNAME/active
This resource implements a GET handler.
8.1.1. GET Handler
The handler expects a GET request.
In addition to what is defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm], the handler verifies that the
requesting Client is a current member of the group. If the
verification fails, the KDC MUST reply with a 4.03 (Forbidden) error
response. The response MUST have Content-Format set to application/
ace-groupcomm+cbor and is formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST be
set to 0 ("Operation permitted only to group members").
If all verifications succeed, the handler replies with a 2.05
(Content) response, specifying the current status of the group, i.e.,
active or inactive. The payload of the response is formatted as
defined in Section 9.9.
The method to set the current group status is out of the scope of
this document, and is defined for the administrator interface of the
Group Manager specified in [I-D.ietf-ace-oscore-gm-admin].
8.2. ace-group/GROUPNAME/verif-data
This resource implements a GET handler.
8.2.1. GET Handler
The handler expects a GET request.
In addition to what is defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm], the Group Manager performs the
following checks.
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If the requesting Client is a current group member, the Group Manager
MUST reply with a 4.03 (Forbidden) error response. The response MUST
have Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST be
set to 8 ("Operation permitted only to signature verifiers").
If GROUPNAME denotes a pairwise-only group, the Group Manager MUST
reply with a 4.00 (Bad Request) error response. The response MUST
have Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST be
set to 7 ("Signatures not used in the group").
If all verifications succeed, the handler replies with a 2.05
(Content) response, specifying data that allow also an external
signature verifier to verify signatures of messages protected with
the group mode and sent to the group (see Sections 3.1 and 8.5 of
[I-D.ietf-core-oscore-groupcomm]). The response MUST have Content-
Format set to application/ace-groupcomm+cbor. The payload of the
response is a CBOR map, which is formatted as defined in Section 9.6.
8.3. ace-group/GROUPNAME/stale-sids
This resource implements a FETCH handler.
8.3.1. FETCH Handler
The handler expects a FETCH request, whose payload specifies a
version number of the group keying material, encoded as an unsigned
CBOR integer.
In addition to what is defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm], the handler verifies that the
requesting Client is a current member of the group. If the
verification fails, the Group Manager MUST reply with a 4.03
(Forbidden) error response. The response MUST have Content-Format
set to application/ace-groupcomm+cbor and is formatted as defined in
Section 4.1.2 of [I-D.ietf-ace-key-groupcomm]. The value of the
'error' field MUST be set to 0 ("Operation permitted only to group
members").
If all verifications succeed, the handler replies with a 2.05
(Content) response, specifying data that allow the requesting Client
to delete the Recipient Contexts and authentication credentials
associated with former members of the group (see Section 3.2 of
[I-D.ietf-core-oscore-groupcomm]. The payload of the response is
formatted as defined in Section 11.3.1.
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8.4. Admitted Methods
The table in Figure 2 summarizes the CoAP methods admitted to access
different resources at the Group Manager, for (non-)members of a
group with group name GROUPNAME, and considering different roles.
The last two rows of the table apply to a node with node name
NODENAME.
+---------------------------------+--------+-------+-------+-------+
| Resource | Type1 | Type2 | Type3 | Type4 |
+---------------------------------+--------+-------+-------+-------+
| ace-group/ | F | F | F | F |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/ | G Po | G Po | Po * | Po |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/active | G | G | - | - |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/verif-data | - | - | G | - |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/creds | G F | G F | G F | - |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/kdc-cred | G | G | G | - |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/stale-sids | F | F | - | - |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/policies | G | G | - | - |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/num | G | G | - | - |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/nodes/ | G Pu D | G D | - | - |
| NODENAME | | | | |
+---------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/nodes/ | Po | - | - | - |
| NODENAME/pub-key | | | | |
+---------------------------------+--------+-------+-------+-------+
CoAP methods: G = GET; F = FETCH; Po = POST; Pu = PUT; D = DELETE
Type1 = Member as Requester and/or Responder
Type2 = Member as Monitor
Type3 = Non-member (authorized to be signature verifier)
(*) = cannot join the group as signature verifier
Type4 = Non-member (not authorized to be signature verifier)
Figure 2: Admitted CoAP Methods on the Group Manager Resources
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8.4.1. Signature Verifiers
Just like any candidate group member, a signature verifier provides
the Group Manager with an Access Token, as described in Section 5.3.
However, unlike candidate group members, it does not join any OSCORE
group, i.e., it does not perform the joining process defined in
Section 6.
After successfully transferring an Access Token to the Group Manager,
a signature verifier is allowed to perform only some operations as
non-member of a group, and only for the OSCORE groups specified in
the validated Access Token. These are the operations specified in
Section 9.3, Section 9.5, Section 9.6 and Section 9.10.
Consistently, in case a node is not a member of the group with group
name GROUPNAME and is authorized to be only signature verifier for
that group, the Group Manager MUST reply with a 4.03 (Forbidden)
error response if that node attempts to access any other endpoint
than: /ace-group; ace-group/GROUPNAME/verif-data; /ace-
group/GROUPNAME/creds; and ace-group/GROUPNAME/kdc-cred.
8.5. Operations Supported by Clients
Building on what is defined in Section 4.1.1 of
[I-D.ietf-ace-key-groupcomm], and with reference to the resources at
the Group Manager newly defined earlier in Section 8 of this
document, it is expected that a Client minimally supports also the
following set of operations and corresponding interactions with the
Group Manager (REQ12).
* GET request to ace-group/GROUPNAME/active, in order to check the
current status of the group.
* GET request to ace-group/GROUPNAME/verif-data, in order for a
signature verifier to retrieve data required to verify signatures
of messages protected with the group mode of Group OSCORE and sent
to a group (see Sections 3.1 and 8.5 of
[I-D.ietf-core-oscore-groupcomm]). Note that this operation is
relevant to support only to signature verifiers.
* FETCH request to ace-group/GROUPNAME/stale-sids, in order to
retrieve from the Group Manager the data required to delete some
of the stored group members' authentication credentials and
associated Recipient Contexts (see Section 8.3.1). This data is
provided as an aggregated set of stale Sender IDs, which are used
as specified in Section 11.3.
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9. Additional Interactions with the Group Manager
This section defines the possible interactions with the Group
Manager, in addition to the group joining specified in Section 6.
9.1. Retrieve Updated Keying Material
At some point, a group member considers the Group OSCORE Security
Context invalid and to be renewed. This happens, for instance, after
a number of unsuccessful security processing of incoming messages
from other group members, or when the Security Context expires as
specified by the 'exp' parameter of the Join Response.
When this happens, the group member retrieves updated security
parameters and group keying material. This can occur in the two
different ways described below.
9.1.1. Get Group Keying Material
If the group member wants to retrieve only the latest group keying
material, it sends a Key Distribution Request to the Group Manager.
That is, it sends a CoAP GET request to the endpoint /ace-group/
GROUPNAME at the Group Manager.
The Group Manager processes the Key Distribution Request according to
Section 4.3.2 of [I-D.ietf-ace-key-groupcomm]. The Key Distribution
Response is formatted as defined in Section 4.3.2 of
[I-D.ietf-ace-key-groupcomm], with the following additions.
* The 'key' parameter is formatted as defined in Section 6.3 of this
document, with the difference that it does not include the
'group_SenderId' parameter.
* The 'exp' parameter MUST be present.
* The 'ace_groupcomm_profile' parameter MUST be present and has
value coap_group_oscore_app.
Upon receiving the Key Distribution Response, the group member
retrieves the updated security parameters and group keying material,
and, if they differ from the current ones, uses them to set up the
new Group OSCORE Security Context as described in Section 2 of
[I-D.ietf-core-oscore-groupcomm].
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9.1.2. Get Group Keying Material and OSCORE Sender ID
If the group member wants to retrieve the latest group keying
material as well as the OSCORE Sender ID that it has in the OSCORE
group, it sends a Key Distribution Request to the Group Manager.
That is, it sends a CoAP GET request to the endpoint /ace-
group/GROUPNAME/nodes/NODENAME at the Group Manager.
The Group Manager processes the Key Distribution Request according to
Section 4.8.1 of [I-D.ietf-ace-key-groupcomm]. The Key Distribution
Response is formatted as defined in Section 4.8.1 of
[I-D.ietf-ace-key-groupcomm], with the following additions.
* The 'key' parameter is formatted as defined in Section 6.3 of this
document. If the requesting group member has exclusively the role
of monitor, then the 'key' parameter does not include the
'group_SenderId'.
Note that, in any other case, the current Sender ID of the group
member is not specified as a separate parameter, but rather
specified by 'group_SenderId' within the 'key' parameter.
* The 'exp' parameter MUST be present.
Upon receiving the Key Distribution Response, the group member
retrieves the updated security parameters, group keying material and
Sender ID, and, if they differ from the current ones, uses them to
set up the new Group OSCORE Security Context as described in
Section 2 of [I-D.ietf-core-oscore-groupcomm].
9.2. Request to Change Individual Keying Material
As discussed in Section 2.5.2 of [I-D.ietf-core-oscore-groupcomm], a
group member may at some point exhaust its Sender Sequence Numbers in
the OSCORE group.
When this happens, the group member MUST send a Key Renewal Request
message to the Group Manager, as per Section 4.8.2.1 of
[I-D.ietf-ace-key-groupcomm]. That is, it sends a CoAP PUT request
to the endpoint /ace-group/GROUPNAME/nodes/NODENAME at the Group
Manager.
Upon receiving the Key Renewal Request, the Group Manager processes
it as defined in Section 4.8.2 of [I-D.ietf-ace-key-groupcomm], with
the following additions.
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The Group Manager MUST return a 5.03 (Service Unavailable) response
in case the OSCORE group identified by GROUPNAME is currently
inactive (see Section 8.1). The response MUST have Content-Format
set to application/ace-groupcomm+cbor and is formatted as defined in
Section 4.1.2 of [I-D.ietf-ace-key-groupcomm]. The value of the
'error' field MUST be set to 9 ("Group currently not active").
Otherwise, the Group Manager performs one of the following actions.
1. If the requesting group member has exclusively the role of
monitor, the Group Manager replies with a 4.03 (Forbidden) error
response. The response MUST have Content-Format set to
application/ace-groupcomm+cbor and is formatted as defined in
Section 4.1.2 of [I-D.ietf-ace-key-groupcomm]. The value of the
'error' field MUST be set to 1 ("Request inconsistent with the
current roles").
2. Otherwise, the Group Manager takes one of the following actions.
* The Group Manager rekeys the OSCORE group. That is, the Group
Manager generates new group keying material for that group
(see Section 11), and replies to the group member with a group
rekeying message as defined in Section 11, providing the new
group keying material. Then, the Group Manager rekeys the
rest of the OSCORE group, as discussed in Section 11.
The Group Manager SHOULD perform a group rekeying only if
already scheduled to occur shortly, e.g., according to an
application-specific rekeying period or scheduling, or as a
reaction to a recent change in the group membership. In any
other case, the Group Manager SHOULD NOT rekey the OSCORE
group when receiving a Key Renewal Request (OPT12).
* The Group Manager determines and assigns a new OSCORE Sender
ID for that group member, and replies with a Key Renewal
Response formatted as defined in Section 4.8.2 of
[I-D.ietf-ace-key-groupcomm]. The CBOR Map in the response
payload includes a single parameter 'group_SenderId' defined
in Section 16.3 of this document, specifying the new Sender ID
of the group member encoded as a CBOR byte string.
Consistently with Section 2.5.3.1 of
[I-D.ietf-core-oscore-groupcomm], the Group Manager MUST
assign a new Sender ID that has not been used in the OSCORE
group since the latest time when the current Gid value was
assigned to the group.
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Furthermore, the Group Manager MUST add the old, relinquished
Sender ID of the group member to the most recent set of stale
Sender IDs for the group (see Section 7.1).
The Group Manager MUST return a 5.03 (Service Unavailable)
response in case there are currently no Sender IDs available
to assign in the OSCORE group. The response MUST have
Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field
MUST be set to 4 ("No available node identifiers").
9.3. Retrieve Authentication Credentials of Group Members
A group member or a signature verifier may need to retrieve the
authentication credentials of (other) group members. To this end,
the group member or signature verifier sends an Authentication
Credential Request message to the Group Manager, as per Sections
4.4.1.1 and 4.4.2.1 of [I-D.ietf-ace-key-groupcomm]. That is, it
sends the request to the endpoint /ace-group/GROUPNAME/creds at the
Group Manager.
If the Authentication Credential Request uses the method FETCH, the
Authentication Credential Request is formatted as defined in
Section 4.4.1 of [I-D.ietf-ace-key-groupcomm]. That is:
* Each element (if any) of the inner CBOR array 'role_filter' is
formatted as in the inner CBOR array 'role_filter' of the
'get_creds' parameter of the Join Request when the parameter value
is not the CBOR simple value "null" (0xf6) (see Section 6.1).
* Each element (if any) of the inner CBOR array 'id_filter' is a
CBOR byte string, which encodes the OSCORE Sender ID of the group
member for which the associated authentication credential is
requested (REQ25).
Upon receiving the Authentication Credential Request, the Group
Manager processes it as per Section 4.4.1 or Section 4.4.2 of
[I-D.ietf-ace-key-groupcomm], depending on the request method being
FETCH or GET, respectively. Additionally, if the Authentication
Credential Request uses the method FETCH, the Group Manager silently
ignores node identifiers included in the 'get_creds' parameter of the
request that are not associated with any current group member
(REQ26).
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The success Authentication Credential Response is formatted as
defined in Section 4.4.1 or Section 4.4.2 of
[I-D.ietf-ace-key-groupcomm], depending on the request method being
FETCH or GET, respectively.
9.4. Upload a New Authentication Credential
A group member may need to provide the Group Manager with its new
authentication credential to use in the group from then on, hence
replacing the current one. This can be the case, for instance, if
the signature or ECDH algorithm and possible associated parameters
used in the OSCORE group have been changed, and the current
authentication credential is not compatible with them.
To this end, the group member sends an Authentication Credential
Update Request message to the Group Manager, as per Section 4.9.1.1
of [I-D.ietf-ace-key-groupcomm], with the following addition.
* The group member computes the proof-of-possession (PoP) evidence
included in 'client_cred_verify' in the same way taken when
preparing a Join Request for the OSCORE group in question, as
defined in Section 6.1 (REQ14).
That is, the group member sends a CoAP POST request to the endpoint
/ace-group/GROUPNAME/nodes/NODENAME/cred at the Group Manager.
Upon receiving the Authentication Credential Update Request, the
Group Manager processes it as per Section 4.9.1 of
[I-D.ietf-ace-key-groupcomm], with the following additions.
* The N_S challenge used to build the proof-of-possession input is
computed as defined in Section 6.1.1 (REQ15).
* The Group Manager verifies the PoP challenge included in
'client_cred_verify' in the same way as when processing a Join
Request for the OSCORE group in question, as defined in
Section 6.2 (REQ14).
* The Group Manager MUST return a 5.03 (Service Unavailable)
response in case the OSCORE group identified by GROUPNAME is
currently inactive (see Section 8.1). The response MUST have
Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST
be set to 9 ("Group currently not active").
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* If the requesting group member has exclusively the role of
monitor, the Group Manager replies with a 4.00 (Bad request) error
response. The response MUST have Content-Format set to
application/ace-groupcomm+cbor and is formatted as defined in
Section 4.1.2 of [I-D.ietf-ace-key-groupcomm]. The value of the
'error' field MUST be set to 1 ("Request inconsistent with the
current roles").
* If the request is successfully processed, the Group Manager stores
the association between i) the new authentication credential of
the group member; and ii) the Group Identifier (Gid), i.e., the
OSCORE ID Context, associated with the OSCORE group together with
the OSCORE Sender ID assigned to the group member in the group.
The Group Manager MUST keep this association updated over time.
9.5. Retrieve the Group Manager's Authentication Credential
A group member or a signature verifier may need to retrieve the
authentication credential of the Group Manager. To this end, the
requesting Client sends a KDC Authentication Credential Request
message to the Group Manager.
That is, it sends a CoAP GET request to the endpoint /ace-
group/GROUPNAME/kdc-cred at the Group Manager defined in
Section 4.5.1.1 of [I-D.ietf-ace-key-groupcomm], where GROUPNAME is
the name of the OSCORE group.
In addition to what is defined in Section 4.5.1 of
[I-D.ietf-ace-key-groupcomm], the Group Manager MUST respond with a
4.00 (Bad Request) error response, if the requesting Client is not a
current group member and GROUPNAME denotes a pairwise-only group.
The response MUST have Content-Format set to application/ace-
groupcomm+cbor and is formatted as defined in Section 4.1.2 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST be
set to 7 ("Signatures not used in the group").
The payload of the 2.05 (Content) KDC Authentication Credential
Response is a CBOR map, which is formatted as defined in
Section 4.5.1 of [I-D.ietf-ace-key-groupcomm]. The Group Manager
specifies the parameters 'kdc_cred', 'kdc_nonce' and 'kdc_challenge'
as defined for the Join Response in Section 6.3 of this document.
This especially applies to the computing of the proof-of-possession
(PoP) evidence included in 'kdc_cred_verify' (REQ21).
Upon receiving a 2.05 (Content) KDC Authentication Credential
Response, the requesting Client retrieves the Group Manager's
authentication credential from the 'kdc_cred' parameter, and proceeds
as defined in Section 4.5.1.1 of [I-D.ietf-ace-key-groupcomm]. The
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requesting Client verifies the PoP evidence included in
'kdc_cred_verify' by means of the same method used when processing
the Join Response, as defined in Section 6.3 of this document
(REQ21).
Note that a signature verifier would not receive a successful
response from the Group Manager, in case GROUPNAME denotes a
pairwise-only group.
9.6. Retrieve Signature Verification Data
A signature verifier may need to retrieve data required to verify
signatures of messages protected with the group mode and sent to a
group (see Sections 3.1 and 8.5 of [I-D.ietf-core-oscore-groupcomm]).
To this end, the signature verifier sends a Signature Verification
Data Request message to the Group Manager.
That is, it sends a CoAP GET request to the endpoint /ace-
group/GROUPNAME/verif-data at the Group Manager defined in
Section 8.2 of this document, where GROUPNAME is the name of the
OSCORE group.
The payload of the 2.05 (Content) Signature Verification Data
Response is a CBOR map, which has the format used for the Join
Response message in Section 6.3, with the following differences.
* From the Join Response message, only the parameters 'gkty', 'key',
'num', 'exp' and 'ace_groupcomm_profile' are present. The 'key'
parameter includes only the following data.
- The parameters 'hkdf', 'contextId', 'cred_fmt', 'sign_enc_alg',
'sign_alg', 'sign_params'. These parameters MUST be present.
- The parameters 'alg' and 'ecdh_alg'. These parameters MUST NOT
be present if the group is a signature-only group. Otherwise,
they MUST be present.
* The parameter 'group_enc_key' is also included, with CBOR label
defined in Section 16.3. This parameter specifies the Group
Encryption Key of the OSCORE Group, encoded as a CBOR byte string.
The Group Manager derives the Group Encryption Key from the group
keying material, as per Section 2.1.6 of
[I-D.ietf-core-oscore-groupcomm]. This parameter MUST be present.
In order to verify signatures in the group (see Section 8.5 of
[I-D.ietf-core-oscore-groupcomm]), the signature verifier relies on:
the data retrieved from the 2.05 (Content) Signature Verification
Data Response; the public keys of the group members signing the
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messages to verify, retrieved from those members' authentication
credentials that can be obtained as defined in Section 9.3; and the
public key of the Group Manager, retrieved from the Group Manager's
authentication credential that can be obtained as defined in
Section 9.5.
Figure 3 gives an overview of the exchange described above, while
Figure 4 shows an example of Signature Verification Data Request-
Response.
Signature Group
Verifier Manager
| |
| Signature Verification Data Request |
|------------------------------------------------------------>|
| GET ace-group/GROUPNAME/verif-data |
| |
|<--- Signature Verification Data Response: 2.05 (Content) ---|
| |
Figure 3: Message Flow of Signature Verification Data Request-
Response
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Request:
Header: GET (Code=0.01)
Uri-Host: "kdc.example.com"
Uri-Path: "ace-group"
Uri-Path: "g1"
Uri-Path: "verif-data"
Payload: -
Response:
Header: Content (Code=2.05)
Content-Format: "application/ace-groupcomm+cbor"
Payload (in CBOR diagnostic notation, with GROUPCOMM_KEY_TBD
and PROFILE_TBD being CBOR integers, while GROUP_ENC_KEY
being a CBOR byte string):
{
"gkty": GROUPCOMM_KEY_TBD,
"key": {
"hkdf": 5, ; HMAC 256/256
"contextId": h'37fc',
"cred_fmt": 33, ; x5chain
"sign_enc_alg": 10, ; AES-CCM-16-64-128
"sign_alg": -8, ; EdDSA
"sign_params": [[1], [1, 6]] ; [[OKP], [OKP, Ed25519]]
},
"num": 12,
"exp": 1609459200,
"ace_groupcomm_profile": PROFILE_TBD,
"group_enc_key": GROUP_ENC_KEY
}
Figure 4: Example of Signature Verification Data Request-Response
9.7. Retrieve the Group Policies
A group member may request the current policies used in the OSCORE
group. To this end, the group member sends a Policies Request, as
per Section 4.6.1.1 of [I-D.ietf-ace-key-groupcomm]. That is, it
sends a CoAP GET request to the endpoint /ace-group/GROUPNAME/
policies at the Group Manager, where GROUPNAME is the name of the
OSCORE group.
Upon receiving the Policies Request, the Group Manager processes it
as per Section 4.6.1 of [I-D.ietf-ace-key-groupcomm]. The success
Policies Response is formatted as defined in Section 4.6.1 of
[I-D.ietf-ace-key-groupcomm].
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9.8. Retrieve the Keying Material Version
A group member may request the current version of the keying material
used in the OSCORE group. To this end, the group member sends a
Version Request, as per Section 4.7.1.1 of
[I-D.ietf-ace-key-groupcomm]. That is, it sends a CoAP GET request
to the endpoint /ace-group/GROUPNAME/num at the Group Manager, where
GROUPNAME is the name of the OSCORE group.
Upon receiving the Version Request, the Group Manager processes it as
per Section 4.7.1 of [I-D.ietf-ace-key-groupcomm]. The success
Version Response is formatted as defined in Section 4.7.1 of
[I-D.ietf-ace-key-groupcomm].
9.9. Retrieve the Group Status
A group member may request the current status of the OSCORE group,
i.e., active or inactive. To this end, the group member sends a
Group Status Request to the Group Manager.
That is, the group member sends a CoAP GET request to the endpoint
/ace-group/GROUPNAME/active at the Group Manager defined in
Section 8.1 of this document, where GROUPNAME is the name of the
OSCORE group.
The payload of the 2.05 (Content) Group Status Response includes the
CBOR simple value "true" (0xf5) if the group is currently active, or
the CBOR simple value "false" (0xf4) otherwise. The group is
considered active if it is set to allow new members to join, and if
communication within the group is fine to happen.
Upon learning from a 2.05 (Content) response that the group is
currently inactive, the group member SHOULD stop taking part in
communications within the group, until it becomes active again.
Upon learning from a 2.05 (Content) response that the group has
become active again, the group member can resume taking part in
communications within the group.
Figure 5 gives an overview of the exchange described above, while
Figure 6 shows an example of Group Status Request-Response.
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Group Group
Member Manager
| |
|--- Group Status Request: GET ace-group/GROUPNAME/active --->|
| |
|<---------- Group Status Response: 2.05 (Content) -----------|
| |
Figure 5: Message Flow of Group Status Request-Response
Request:
Header: GET (Code=0.01)
Uri-Host: "kdc.example.com"
Uri-Path: "ace-group"
Uri-Path: "g1"
Uri-Path: "active"
Payload: -
Response:
Header: Content (Code=2.05)
Payload (in CBOR diagnostic notation):
true
Figure 6: Example of Group Status Request-Response
9.10. Retrieve Group Names
A node may want to retrieve from the Group Manager the group name and
the URI of the group-membership resource of a group. This is
relevant in the following cases.
* Before joining a group, a joining node may know only the current
Group Identifier (Gid) of that group, but not the group name and
the URI to the group-membership resource.
* As current group member in several groups, the node has missed a
previous group rekeying in one of them (see Section 11). Hence,
it retains stale keying material and fails to decrypt received
messages exchanged in that group.
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Such messages do not provide a direct hint to the correct group
name, that the node would need in order to retrieve the latest
keying material and authentication credentials from the Group
Manager (see Section 9.1.1, Section 9.1.2 and Section 9.3).
However, such messages may specify the current Gid of the group,
as value of the 'kid_context' field of the OSCORE CoAP option (see
Section 6.1 of [RFC8613] and Section 4.2 of
[I-D.ietf-core-oscore-groupcomm]).
* As signature verifier, the node also refers to a group name for
retrieving the required authentication credentials from the Group
Manager (see Section 9.3). As discussed above, intercepted
messages do not provide a direct hint to the correct group name,
while they may specify the current Gid of the group, as value of
the 'kid_context' field of the OSCORE CoAP option. In such a
case, upon intercepting a message in the group, the node requires
to correctly map the Gid currently used in the group with the
invariant group name.
Furthermore, since it is not a group member, the node does not
take part to a possible group rekeying. Thus, following a group
rekeying and the consequent change of Gid in a group, the node
would retain the old Gid value and cannot correctly associate
intercepted messages to the right group, especially if acting as
signature verifier in several groups. This in turn prevents the
efficient verification of signatures, and especially the retrieval
of required, new authentication credentials from the Group
Manager.
In either case, the node only knows the current Gid of the group, as
learned from received or intercepted messages exchanged in the group.
As detailed below, the node can contact the Group Manager, and
request the group name and URI to the group-membership resource
corresponding to that Gid. Then, it can use that information to join
the group, or get the latest keying material as a current group
member, or retrieve authentication credentials used in the group as a
signature verifier. To this end, the node sends a Group Name and URI
Retrieval Request, as per Section 4.2.1.1 of
[I-D.ietf-ace-key-groupcomm].
That is, the node sends a CoAP FETCH request to the endpoint /ace-
group at the Group Manager formatted as defined in Section 4.2.1 of
[I-D.ietf-ace-key-groupcomm]. Each element of the CBOR array 'gid'
is a CBOR byte string (REQ13), which encodes the Gid of the group for
which the group name and the URI to the group-membership resource are
requested.
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Upon receiving the Group Name and URI Retrieval Request, the Group
Manager processes it as per Section 4.2.1 of
[I-D.ietf-ace-key-groupcomm]. The success Group Name and URI
Retrieval Response is formatted as defined in Section 4.2.1 of
[I-D.ietf-ace-key-groupcomm]. Each element of the CBOR array 'gid'
is a CBOR byte string (REQ13), which encodes the Gid of the group for
which the group name and the URI to the group-membership resource are
provided.
For each of its groups, the Group Manager maintains an association
between the group name and the URI to the group-membership resource
on one hand, and only the current Gid for that group on the other
hand. That is, the Group Manager does not maintain an association
between the former pair and any other Gid for that group than the
current, most recent one.
Figure 7 gives an overview of the exchanges described above, while
Figure 8 shows an example of Group Name and URI Retrieval Request-
Response.
Group
Node Manager
| |
|---- Group Name and URI Retrieval Request: FETCH ace-group/ --->|
| |
|<--- Group Name and URI Retrieval Response: 2.05 (Content) -----|
| |
Figure 7: Message Flow of Group Name and URI Retrieval Request-
Response
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Request:
Header: FETCH (Code=0.05)
Uri-Host: "kdc.example.com"
Uri-Path: "ace-group"
Content-Format: "application/ace-groupcomm+cbor"
Payload (in CBOR diagnostic notation):
{
"gid": [h'37fc', h'84bd']
}
Response:
Header: Content (Code=2.05)
Content-Format: "application/ace-groupcomm+cbor"
Payload (in CBOR diagnostic notation):
{
"gid": [h'37fc', h'84bd'],
"gname": ["g1", "g2"],
"guri": ["ace-group/g1", "ace-group/g2"]
}
Figure 8: Example of Group Name and URI Retrieval Request-Response
9.11. Leave the Group
A group member may request to leave the OSCORE group. To this end,
the group member sends a Group Leaving Request, as per
Section 4.8.3.1 of [I-D.ietf-ace-key-groupcomm]. That is, it sends a
CoAP DELETE request to the endpoint /ace-group/GROUPNAME/nodes/
NODENAME at the Group Manager.
Upon receiving the Group Leaving Request, the Group Manager processes
it as per Section 4.8.3 of [I-D.ietf-ace-key-groupcomm]. Then, the
Group Manager performs the follow-up actions defined in Section 10 of
this document.
10. Removal of a Group Member
Other than after a spontaneous request to the Group Manager as
described in Section 9.11, a node may be forcibly removed from the
OSCORE group, e.g., due to expired or revoked authorization.
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In either case, if the Group Manager reassigns Gid values during the
group's lifetime (see Section 3.2.1.1 of
[I-D.ietf-core-oscore-groupcomm]), the Group Manager "forgets" the
Birth Gid currently associated with the leaving node in the OSCORE
group. This was stored following the Join Response sent to that
node, after its latest (re-)joining of the OSCORE group (see
Section 6.3).
If any of the two conditions below holds, the Group Manager MUST
inform the leaving node of its eviction as follows. If both
conditions hold, the Group Manager MUST inform the leaving node by
using only the method corresponding to one of either conditions.
* If, upon joining the group (see Section 6.1), the leaving node
specified a URI in the 'control_uri' parameter defined in
Section 4.3.1 of [I-D.ietf-ace-key-groupcomm], the Group Manager
sends a DELETE request targeting the URI specified in the
'control_uri' parameter (OPT7).
* If the leaving node has been observing the associated resource at
ace-group/GROUPNAME/nodes/NODENAME, the Group Manager sends an
unsolicited 4.04 (Not Found) error response to the leaving node,
as specified in Section 4.3.2 of [I-D.ietf-ace-key-groupcomm].
Furthermore, the Group Manager might intend to evict all the current
group members from the group at once. In such a case, if the Join
Responses sent by the Group Manager to nodes joining the group (see
Section 6.3) specify a URI in the 'control_group_uri' parameter
defined in Section 4.3.1 of [I-D.ietf-ace-key-groupcomm], then the
Group Manager MUST additionally send a DELETE request targeting the
URI specified in the 'control_group_uri' parameter (OPT10).
If the leaving node has not exclusively the role of monitor, the
Group Manager performs the following actions.
* The Group Manager frees the OSCORE Sender ID value of the leaving
node. This value MUST NOT become available for possible upcoming
joining nodes in the same group, until the group has been rekeyed
and assigned a new Group Identifier (Gid).
* The Group Manager MUST add the relinquished Sender ID of the
leaving node to the most recent set of stale Sender IDs for the
group (see Section 7.1).
* The Group Manager cancels the association between, on one hand,
the authentication credential of the leaving node and, on the
other hand, the Gid associated with the OSCORE group together with
the freed Sender ID value. The Group Manager deletes the
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authentication credential of the leaving node, if that
authentication credential has no remaining association with any
pair (Gid, Sender ID).
Then, the Group Manager MUST generate updated security parameters and
group keying material, and provide it to the remaining group members
(see Section 11). As a consequence, the leaving node is not able to
acquire the new security parameters and group keying material
distributed after its leaving.
The same considerations from Section 5 of
[I-D.ietf-ace-key-groupcomm] apply here as well, considering the
Group Manager acting as KDC.
11. Group Rekeying Process
In order to rekey the OSCORE group, the Group Manager distributes a
new Group Identifier (Gid), i.e., a new OSCORE ID Context; a new
OSCORE Master Secret; and, optionally, a new OSCORE Master Salt for
that group. When doing so, the Group Manager MUST increment the
version number of the group keying material, before starting its
distribution.
As per Section 3.2.1.1 of [I-D.ietf-core-oscore-groupcomm], the Group
Manager MAY reassign a Gid to the same group over that group's
lifetime, e.g., once the whole space of Gid values has been used for
the group in question. If the Group Manager supports reassignment of
Gid values and performs it in a group, then the Group Manager
additionally takes the following actions.
* Before rekeying the group, the Group Manager MUST check if the new
Gid to be distributed coincides with the Birth Gid of any of the
current group members (see Section 6.3).
* If any of such "elder members" is found in the group, the Group
Manager MUST evict them from the group. That is, the Group
Manager MUST terminate their membership and MUST rekey the group
in such a way that the new keying material is not provided to
those evicted elder members. This also includes adding their
relinquished Sender IDs to the most recent set of stale Sender IDs
for the group (see Section 7.1), before rekeying the group.
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Until a further following group rekeying, the Group Manager MUST
store the list of those latest-evicted elder members. If any of
those nodes re-joins the group before a further following group
rekeying occurs, the Group Manager MUST NOT rekey the group upon
their re-joining. When one of those nodes re-joins the group, the
Group Manager can rely, e.g., on the ongoing secure communication
association to recognize the node as included in the stored list.
Across the rekeying execution, the Group Manager MUST preserve the
same unchanged OSCORE Sender IDs for all group members intended to
remain in the group. This avoids affecting the retrieval of
authentication credentials from the Group Manager and the
verification of group messages.
The Group Manager MUST support the "Point-to-Point" group rekeying
scheme registered in Section 11.12 of [I-D.ietf-ace-key-groupcomm],
as per the detailed use defined in Section 11.1 of this document.
Future specifications may define how this application profile can use
alternative group rekeying schemes, which MUST comply with the
functional steps defined in Section 3.2 of
[I-D.ietf-core-oscore-groupcomm]. The Group Manager MUST indicate
the use of such an alternative group rekeying scheme to joining
nodes, by means of the 'group_rekeying' parameter included in Join
Response messages (see Section 6.3).
It is RECOMMENDED that the Group Manager gets confirmation of
successful distribution from the group members, and admits a maximum
number of individual retransmissions to non-confirming group members.
Once completed the group rekeying process, the Group Manager creates
a new empty set of stale Sender IDs associated with the version of
the newly distributed group keying material (see Section 7.1).
In case the rekeying terminates and some group members have not
received the new keying material, they will not be able to correctly
process following secured messages exchanged in the group. These
group members will eventually contact the Group Manager, in order to
retrieve the current keying material and its version.
Some of these group members may be in multiple groups, each
associated with a different Group Manager. When failing to correctly
process messages secured with the new keying material, these group
members may not have sufficient information to determine which exact
Group Manager they should contact, in order to retrieve the current
keying material they are missing.
If the Gid is formatted as described in Appendix C of
[I-D.ietf-core-oscore-groupcomm], the Group Prefix can be used as a
hint to determine the right Group Manager, as long as no collisions
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among Group Prefixes are experienced. Otherwise, a group member
needs to contact the Group Manager of each group, e.g., by first
requesting only the version of the current group keying material (see
Section 9.8) and then possibly requesting the current keying material
(see Section 9.1.1).
Furthermore, some of these group members can be in multiple groups,
all of which are associated with the same Group Manager. In this
case, these group members may also not have sufficient information to
determine which exact group they should refer to, when contacting the
right Group Manager. Hence, they need to contact a Group Manager
multiple times, i.e., separately for each group they belong to and
associated with that Group Manager.
Section 11.2 defines the actions performed by a group member upon
receiving the new group keying material. Section 11.3 discusses how
a group member can realize that it has missed one or more rekeying
instances, and the actions it is accordingly required to take.
11.1. Sending Rekeying Messages
When using the "Point-to-Point" group rekeying scheme, the group
rekeying messages MUST have Content-Format set to application/ace-
groupcomm+cbor and have the same format used for the Join Response
message in Section 6.3, with the following differences. Note that
this extends the minimal content of a rekeying message as defined in
Section 6 of [I-D.ietf-ace-key-groupcomm] (OPT14).
* From the Join Response, only the parameters 'gkty', 'key', 'num',
'exp', and 'ace_groupcomm_profile' are present. The 'key'
parameter includes only the following data.
- The 'ms' parameter, specifying the new OSCORE Master Secret
value. This parameter MUST be present.
- The 'contextId' parameter, specifying the new Gid to use as
OSCORE ID Context value. This parameter MUST be present.
- The 'salt' value, specifying the new OSCORE Master Salt value.
This parameter MAY be present.
* The parameter 'stale_node_ids' MUST also be included, with CBOR
label defined in Section 16.3. This parameter is encoded as a
CBOR array, where each element is encoded as a CBOR byte string.
The order of elements in the CBOR array is irrelevant. The
parameter is populated as follows.
- The Group Manager creates an empty CBOR array ARRAY.
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- The Group Manager considers the most recent set of stale Sender
IDs for the group (see Section 7.1), i.e., the set X associated
with the current version of the group keying material about to
be relinquished.
- For each Sender ID in X, the Group Manager encodes it as a CBOR
byte string and adds the result to ARRAY.
- The parameter 'stale_node_ids' takes ARRAY as value.
* The parameters 'creds', 'peer_roles' and 'peer_identifiers' SHOULD
be present, if the group rekeying is performed due to one or
multiple Clients that have requested to join the group. Following
the same semantics used in the Join Response message (see
Section 6.3), the three parameters specify the authentication
credential, roles in the group and node identifier of each of the
Clients that have requested to join the group. The Group Manager
MUST NOT include a non-empty subset of these three parameters.
The Group Manager separately sends a group rekeying message formatted
as defined above to each group member to be rekeyed.
Each rekeying message MUST be secured with the pairwise secure
communication association between the Group Manager and the group
member used during the joining process. Each rekeying message can
target the 'control_uri' URI path defined in Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm] (OPT7), if provided by the intended
recipient upon joining the group (see Section 6.1).
This distribution approach requires group members to act (also) as
servers, in order to correctly handle unsolicited group rekeying
messages from the Group Manager. If a group member and the Group
Manager use OSCORE [RFC8613] 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 [RFC9203].
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Group members and the Group Manager SHOULD additionally support
alternative distribution 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]. In particular, a group
member may use CoAP Observe [RFC7641] and subscribe for updates to
the group-membership resource of the group, at the endpoint /ace-
group/GROUPNAME/ of the Group Manager (see Section 6.1 of
[I-D.ietf-ace-key-groupcomm]). Alternatively, a full-fledged Pub-Sub
model can be considered [I-D.ietf-core-coap-pubsub], where the Group
Manager publishes to a rekeying topic hosted at a Broker, while the
group members subscribe to such topic (see Section 6.2 of
[I-D.ietf-ace-key-groupcomm]).
11.2. Receiving Rekeying Messages
After having received the new group keying material, a group member
proceeds as follows. Unless otherwise specified, the following is
independent of the specifically used group rekeying scheme.
The group member considers the stale Sender IDs received from the
Group Manager. If the "Point-to-Point" group rekeying scheme as
detailed in Section 11.1 is used, the stale Sender IDs are specified
by the 'stale_node_ids' parameter.
After that, as per Section 3.2 of [I-D.ietf-core-oscore-groupcomm],
the group member MUST remove every authentication credential
associated with a stale Sender ID from its list of group members'
authentication credentials used in the group, and MUST delete each of
its Recipient Contexts used in the group whose corresponding
Recipient ID is a stale Sender ID.
Then, the following cases can occur, based on the version number V'
of the new group keying material distributed through the rekeying
process. If the "Point-to-Point" group rekeying scheme as detailed
in Section 11.1 is used, this information is specified by the 'num'
parameter.
* The group member has not missed any group rekeying. That is, the
old keying material stored by the group member has version number
V, while the received new keying material has version number V' =
(V + 1). In such a case, the group member simply installs the new
keying material and derives the corresponding new Security
Context.
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* The group member has missed one or more group rekeying instances.
That is, the old keying material stored by the group member has
version number V, while the received new keying material has
version number V' > (V + 1). In such a case, the group member
MUST proceed as defined in Section 11.3.
* The group member has received keying material not newer than the
stored one. That is, the old keying material stored by the group
member has version number V, while the received keying material
has version number V' < (V + 1). In such a case, the group member
MUST ignore the received rekeying messages and MUST NOT install
the received keying material.
11.3. Missed Rekeying Instances
A group member can realize to have missed one or more rekeying
instances in one of the ways discussed below. In the following, V
denotes the version number of the old keying material stored by the
group member, while V' denotes the version number of the latest,
possibly just distributed, keying material.
a. The group member has participated to a rekeying process that has
distributed new keying material with version number V' > (V + 1), as
discussed in Section 11.2.
b. The group member has obtained the latest keying material from the
Group Manager, as a response to a Key Distribution Request (see
Section 9.1.1) or to a Join Request when re-joining the group (see
Section 6.1). That is, V is different than V' specified by the 'num'
parameter in the response.
c. The group member has obtained the authentication credentials of
other group members, through an Authentication Credential Request-
Response exchange with the Group Manager (see Section 9.3). That is,
V is different than V' specified by the 'num' parameter in the
response.
d. The group member has performed a Version Request-Response
exchange with the Group Manager (see Section 9.8). That is, V is
different than V' specified by the 'num' parameter in the response.
In either case, the group member MUST delete the stored keying
material with version number V.
If case (a) or case (b) applies, the group member MUST perform the
following actions.
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1. The group member MUST NOT install the latest keying material yet,
in case that was already obtained.
2. The group member sends a Stale Sender IDs Request to the Group
Manager (see Section 11.3.1), specifying the version number V as
payload of the request.
If the Stale Sender IDs Response from the Group Manager has no
payload, the group member MUST remove all the authentication
credentials from its list of group members' authentication
credentials used in the group, and MUST delete all its Recipient
Contexts used in the group.
Otherwise, the group member considers the stale Sender IDs
specified in the Stale Sender IDs Response from the Group
Manager. Then, the group member MUST remove every authentication
credential associated with a stale Sender ID from its list of
group members' authentication credentials used in the group, and
MUST delete each of its Recipient Contexts used in the group
whose corresponding Recipient ID is a stale Sender ID.
3. The group member installs the latest keying material with version
number V' and derives the corresponding new Security Context.
If case (c) or case (d) applies, the group member SHOULD perform the
following actions.
1. The group member sends a Stale Sender IDs Request to the Group
Manager (see Section 11.3.1), specifying the version number V as
payload of the request.
If the Stale Sender IDs Response from the Group Manager has no
payload, the group member MUST remove all the authentication
credentials from its list of group members' authentication
credentials used in the group, and MUST delete all its Recipient
Contexts used in the group.
Otherwise, the group member considers the stale Sender IDs
specified in the Stale Sender IDs Response from the Group
Manager. Then, the group member MUST remove every authentication
credential associated with a stale Sender ID from its list of
group members' authentication credentials used in the group, and
MUST delete each of its Recipient Contexts used in the group
whose corresponding Recipient ID is a stale Sender ID.
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2. The group member obtains the latest keying material with version
number V' from the Group Manager. This can happen by sending a
Key Distribution Request to the Group Manager (see Section 9.1.1)
and Section 9.1.2).
3. The group member installs the latest keying material with version
number V' and derives the corresponding new Security Context.
If case (c) or case (d) applies, the group member can alternatively
perform the following actions.
1. The group member re-joins the group (see Section 6.1). When
doing so, the group member MUST re-join with the same roles it
currently has in the group, and MUST request from the Group
Manager the authentication credentials of all the current group
members. That is, the 'get_creds' parameter of the Join Request
MUST be present and MUST be set to the CBOR simple value "null"
(0xf6).
2. When receiving the Join Response (see Section 6.4 and
Section 6.4), the group member retrieves the set Z of
authentication credentials specified in the 'creds' parameter.
Then, the group member MUST remove every authentication
credential which is not in Z from its list of group members'
authentication credentials used in the group, and MUST delete
each of its Recipient Contexts used in the group that does not
include any of the authentication credentials in Z.
3. The group member installs the latest keying material with version
number V' and derives the corresponding new Security Context.
11.3.1. Retrieve Stale Sender IDs
When realizing to have missed one or more group rekeying instances
(see Section 11.3), a node needs to retrieve from the Group Manager
the data required to delete some of its stored group members'
authentication credentials and Recipient Contexts (see
Section 8.3.1). These data is provided as an aggregated set of stale
Sender IDs, which are used as specified in Section 11.3.
That is, the node sends a CoAP FETCH request to the endpoint /ace-
group/GROUPNAME/stale-sids at the Group Manager defined in
Section 8.3 of this document, where GROUPNAME is the name of the
OSCORE group.
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The payload of the Stale Sender IDs Request MUST include a CBOR
unsigned integer. This encodes the version number V of the most
recent group keying material stored and installed by the requesting
Client, which is older than the latest, possibly just distributed,
keying material with version number V'.
The handler MUST reply with a 4.00 (Bad Request) error response, if
the request is not formatted correctly. Also, the handler MUST
respond with a 4.00 (Bad Request) error response, if the specified
version number V is greater or equal than the version number V'
associated with the latest keying material in the group, i.e., in
case V >= V'.
Otherwise, the handler responds with a 2.05 (Content) Stale Sender
IDs Response. The payload of the response is formatted as defined
below, where SKEW = (V' - V + 1).
* The Group Manager considers ITEMS as the current number of sets of
stale Sender IDs for the group (see Section 7.1).
* If SKEW > ITEMS, the Stale Sender IDs Response MUST NOT have a
payload.
* Otherwise, the payload of the Stale Sender IDs Response MUST
include a CBOR array, where each element is encoded as a CBOR byte
string. The order of elements in the CBOR array is irrelevant.
The Group Manager populates the CBOR array as follows.
- The Group Manager creates an empty CBOR array ARRAY and an
empty set X.
- The Group Manager considers the SKEW most recent sets of stale
Sender IDs for the group. Note that the most recent set is the
one associated with the latest version of the group keying
material.
- The Group Manager copies all the Sender IDs from the selected
sets into X. When doing so, the Group Manager MUST discard
duplicates. That is, the same Sender ID MUST NOT be present
more than once in the final content of X.
- For each Sender ID in X, the Group Manager encodes it as a CBOR
byte string and adds the result to ARRAY.
- Finally, ARRAY is specified as payload of the Stale Sender IDs
Response. Note that ARRAY might result in the empty CBOR
array.
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Figure 9 gives an overview of the exchange described above, while
Figure 10 shows an example of Stale Sender IDs Request-Response.
Group
Node Manager
| |
| Stale Sender IDs Request |
|------------------------------------------------------------>|
| FETCH ace-group/GROUPNAME/stale-sids |
| |
|<---------- Stale Sender IDs Response: 2.05 (Content) -------|
| |
Figure 9: Message Flow of Stale Sender IDs Request-Response
Request:
Header: FETCH (Code=0.05)
Uri-Host: "kdc.example.com"
Uri-Path: "ace-group"
Uri-Path: "g1"
Uri-Path: "stale-sids"
Payload (in CBOR diagnostic notation):
42
Response:
Header: Content (Code=2.05)
Payload (in CBOR diagnostic notation):
[h'01', h'fc', h'12ab', h'de44', h'ff']
Figure 10: Example of Stale Sender IDs Request-Response
12. ACE Groupcomm Parameters
In addition to those defined in Section 8 of
[I-D.ietf-ace-key-groupcomm], this application profile defines
additional parameters used during the second part of the message
exchange with the Group Manager, i.e., after the exchange of Token
Transfer Request and Response (see Section 5.3). The table below
summarizes them and specifies the CBOR key to use instead of the full
descriptive name.
Note that the media type application/ace-groupcomm+cbor MUST be used
when these parameters are transported in the respective message
fields.
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+----------------+------+-------+------------+
| Name | CBOR | CBOR | Reference |
| | Key | Type | |
+----------------+------+-------+------------+
| group_senderId | TBD | bstr | [RFC-XXXX] |
+----------------+------+-------+------------+
| ecdh_info | TBD | array | [RFC-XXXX] |
+----------------+------+-------+------------+
| kdc_dh_creds | TBD | array | [RFC-XXXX] |
+----------------+------+-------+------------+
| group_enc_key | TBD | bstr | [RFC-XXXX] |
+----------------+------+-------+------------+
| stale_node_ids | TBD | array | [RFC-XXXX] |
+----------------+------+-------+------------+
Figure 11: ACE Groupcomm Parameters
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
The Group Manager is expected to support all the parameters above.
Instead, a Client is required to support the new parameters defined
in this application profile as specified below (REQ29).
* 'group_senderId' MUST be supported by a Client that intends to
join an OSCORE group with the role of Requester and/or Responder.
* 'ecdh_info' MUST be supported by a Client that intends to join a
group which uses the pairwise mode of Group OSCORE.
* 'kdc_dh_creds' MUST be supported by a Client that intends to join
a group which uses the pairwise mode of Group OSCORE and that does
not plan to or cannot rely on an early retrieval of the Group
Manager's Diffie-Hellman authentication credential.
* 'group_enc_key' MUST be supported by a Client that intends to join
a group which uses the group mode of Group OSCORE or to be
signature verifier for that group.
* 'stale_node_ids' MUST be supported.
When the conditional parameters defined in Section 8 of
[I-D.ietf-ace-key-groupcomm] are used with this application profile,
a Client must, should or may support them as specified below (REQ30).
* 'client_cred', 'cnonce', 'client_cred_verify'. A Client that has
an own authentication credential to use in a group MUST support
these parameters.
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* 'kdcchallenge'. A Client that has an own authentication
credential to use in a group and that provides the Access Token to
the Group Manager through a Token Transfer Request (see
Section 5.3) MUST support this parameter.
* 'creds_repo'. This parameter is not relevant for this application
profile, since the Group Manager always acts as repository of the
group members' authentication credentials.
* 'group_policies'. A Client that is interested in the specific
policies used in a group, but that does not know them or cannot
become aware of them before joining that group, SHOULD support
this parameter.
* 'peer_roles'. A Client MUST support this parameter, since in this
application profile it is relevant for Clients to know the roles
of the group member associated with each authentication
credential.
* 'kdc_nonce', 'kdc_cred' and 'kdc_cred_verify'. A Client MUST
support these parameters, since the Group Manager's authentication
credential is required to process messages protected with Group
OSCORE (see Section 4.3 of [I-D.ietf-core-oscore-groupcomm]).
* 'mgt_key_material'. A Client that supports an advanced rekeying
scheme possibly used in the group, such as based on one-to-many
rekeying messages sent by the Group Manager (e.g., over IP
multicast), MUST support this parameter.
* 'control_group_uri'. A Client that supports the hosting of local
resources each associated with a group (hence acting as CoAP
server) and the reception of one-to-many requests sent to those
resources by the Group Manager (e.g., over IP multicast) MUST
support this parameter.
13. ACE Groupcomm Error Identifiers
In addition to those defined in Section 9 of
[I-D.ietf-ace-key-groupcomm], this application profile defines new
values that the Group Manager can include as error identifiers, in
the 'error' field of an error response with Content-Format
application/ace-groupcomm+cbor.
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+-------+-------------------------------------------------+
| Value | Description |
+-------+-------------------------------------------------+
| 7 | Signatures not used in the group |
+-------+-------------------------------------------------+
| 8 | Operation permitted only to signature verifiers |
+-------+-------------------------------------------------+
| 9 | Group currently not active |
+-------+-------------------------------------------------+
Figure 12: ACE Groupcomm Error Identifiers
A Client supporting the 'error' parameter (see Sections 4.1.2 and 8
of [I-D.ietf-ace-key-groupcomm]) and able to understand the specified
error may use that information to determine what actions to take
next. If it is included in the error response and supported by the
Client, the 'error_description' parameter may provide additional
context. The following guidelines apply.
* In case of error 7, the Client should stop sending the request in
question to the Group Manager. In this application profile, this
error is relevant only for a signature verifier, in case it tries
to access resources related to a pairwise-only group.
* In case of error 8, the Client should stop sending the request in
question to the Group Manager.
* In case of error 9, the Client should wait for a certain (pre-
configured) amount of time, before trying to re-send its request
to the Group Manager.
14. Default Values for Group Configuration Parameters
This section defines the default values that the Group Manager
assumes for the configuration parameters of an OSCORE group, unless
differently specified when creating and configuring the group. This
can be achieved as specified in [I-D.ietf-ace-oscore-gm-admin].
A possible reason for the Group Manager to consider default values
different from those recommended in this section is to ensure that
each of those are consistent with what the Group Manager supports,
e.g., in terms of signature algorithm and format of authentication
credentials used in the OSCORE group.
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This ensures that the Group Manager is able to perform the operations
defined in this document, e.g., to achieve proof-of-possession of a
joining node's private key (see Section 6.2), as well as to provide a
joining node with its own authentication credential and the
associated proof-of-possession challenge (see Section 6.3).
14.1. Common
This section always applies, as related to common configuration
parameters.
* For the HKDF Algorithm 'hkdf', the Group Manager SHOULD use HKDF
SHA-256, defined as default in Section 3.2 of [RFC8613]. In the
'hkdf' parameter, this HKDF Algorithm is specified by the HMAC
Algorithm HMAC 256/256 (COSE algorithm encoding: 5).
* For the format 'cred_fmt' used for the authentication credentials
in the group, the Group Manager SHOULD use CBOR Web Token (CWT) or
CWT Claims Set (CCS) [RFC8392], i.e., the COSE Header Parameter
'kcwt' and 'kccs', respectively.
[ These COSE Header Parameters are under pending registration
requested by draft-ietf-lake-edhoc. ]
* For 'max_stale_sets', the Group Manager SHOULD consider N = 3 as
the maximum number of stored sets of stale Sender IDs for the
group (see Section 7.1).
14.2. Group Mode
This section applies if the group uses (also) the group mode of Group
OSCORE.
* For the Signature Encryption Algorithm 'sign_enc_alg' used to
encrypt messages protected with the group mode, the Group Manager
SHOULD use AES-CCM-16-64-128 (COSE algorithm encoding: 10) as
default value.
The Group Manager SHOULD use the following default values for the
Signature Algorithm 'sign_alg' and related parameters 'sign_params',
consistently with the "COSE Algorithms" registry [COSE.Algorithms],
the "COSE Key Types" registry [COSE.Key.Types] and the "COSE Elliptic
Curves" registry [COSE.Elliptic.Curves].
* For the Signature Algorithm 'sign_alg' used to sign messages
protected with the group mode, the signature algorithm EdDSA
[RFC8032].
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* For the parameters 'sign_params' of the Signature Algorithm:
- The array [[OKP], [OKP, Ed25519]], in case EdDSA is assumed or
specified for 'sign_alg'. This indicates to use the COSE key
type OKP and the elliptic curve Ed25519 [RFC8032].
- The array [[EC2], [EC2, P-256]], in case ES256 [RFC6979] is
specified for 'sign_alg'. This indicates to use the COSE key
type EC2 and the elliptic curve P-256.
- The array [[EC2], [EC2, P-384]], in case ES384 [RFC6979] is
specified for 'sign_alg'. This indicates to use the COSE key
type EC2 and the elliptic curve P-384.
- The array [[EC2], [EC2, P-521]], in case ES512 [RFC6979] is
specified for 'sign_alg'. This indicates to use the COSE key
type EC2 and the elliptic curve P-521.
- The array [[RSA], [RSA]], in case PS256, PS384 or PS512
[RFC8017] is specified for 'sign_alg'. This indicates to use
the COSE key type RSA.
14.3. Pairwise Mode
This section applies if the group uses (also) the pairwise mode of
Group OSCORE.
For the AEAD Algorithm 'alg' used to encrypt messages protected with
the pairwise mode, the Group Manager SHOULD use the same default
value defined in Section 3.2 of [RFC8613], i.e., AES-CCM-16-64-128
(COSE algorithm encoding: 10).
For the Pairwise Key Agreement Algorithm 'ecdh_alg' and related
parameters 'ecdh_params', the Group Manager SHOULD use the following
default values, consistently with the "COSE Algorithms" registry
[COSE.Algorithms], the "COSE Key Types" registry [COSE.Key.Types] and
the "COSE Elliptic Curves" registry [COSE.Elliptic.Curves].
* For the Pairwise Key Agreement Algorithm 'ecdh_alg' used to
compute static-static Diffie-Hellman shared secrets, the ECDH
algorithm ECDH-SS + HKDF-256 specified in Section 6.3.1 of
[RFC9053].
* For the parameters 'ecdh_params' of the Pairwise Key Agreement
Algorithm:
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- The array [[OKP], [OKP, X25519]], in case EdDSA is assumed or
specified for 'sign_alg', or in case the group is a pairwise-
only group. This indicates to use the COSE key type OKP and
the elliptic curve X25519 [RFC8032].
- The array [[EC2], [EC2, P-256]], in case ES256 [RFC6979] is
specified for 'sign_alg'. This indicates to use the COSE key
type EC2 and the elliptic curve P-256.
- The array [[EC2], [EC2, P-384]], in case ES384 [RFC6979] is
specified for 'sign_alg'. This indicates to use the COSE key
type EC2 and the elliptic curve P-384.
- The array [[EC2], [EC2, P-521]], in case ES512 [RFC6979] is
specified for 'sign_alg'. This indicates to use the COSE key
type EC2 and the elliptic curve P-521.
15. Security Considerations
Security considerations for this profile are inherited from
[I-D.ietf-ace-key-groupcomm], the ACE framework for Authentication
and Authorization [RFC9200], and the specific transport profile of
ACE signalled by the AS, such as [RFC9202] and [RFC9203].
The following security considerations also apply for this profile.
15.1. Management of OSCORE Groups
This profile leverages the following management aspects related to
OSCORE groups and discussed in the sections of
[I-D.ietf-core-oscore-groupcomm] referred below.
* Management of group keying material (see Section 3.2 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).
The Group Manager performs a rekeying when one or more members
leave the group, thus preserving forward security and ensuring
that the security properties of Group OSCORE are fulfilled.
According to the specific application requirements, the Group
Manager can also rekey the group upon a new node's joining, in
case backward security has also to be preserved.
* Provisioning and retrieval of authentication credentials (see
Section 3 of [I-D.ietf-core-oscore-groupcomm]). The Group Manager
acts as repository of authentication credentials of group members,
and provides them upon request.
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* Synchronization of sequence numbers (see Section 6.3 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 6.
Alternatively, when establishing a secure communication association
with the Group Manager, the joining node can provide the Group
Manager with its own authentication credential, and use the public
key included thereof as asymmetric proof-of-possession key. For
example, this is the case when the joining node relies on
Section 3.2.2 of [RFC9202] and authenticates itself during the DTLS
handshake with the Group Manager. However, this requires the
authentication credential to be in the format used in the OSCORE
group, and that both the authentication credential of the joining
node and the included public key are compatible with the signature or
ECDH 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.
15.2. Size of Nonces as Proof-of-Possesion Challenge
With reference to the Join Request message in Section 6.1, the proof-
of-possession (PoP) evidence included in 'client_cred_verify' is
computed over an input including also N_C | N_S, where | denotes
concatenation.
For the N_C challenge, it is RECOMMENDED to use an 8-byte long random
nonce. Furthermore, N_C is always conveyed in the 'cnonce' parameter
of the Join Request, which is always sent over the secure
communication association between the joining node and the Group
Manager.
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As defined in Section 6.1.1, the way the N_S value is computed
depends on the particular way the joining node provides the Group
Manager with the Access Token, as well as on following interactions
between the two.
* If the Access Token has not been provided to the Group Manager by
means of a Token Transfer Request to the /authz-info endpoint as
in Section 5.3, then N_S is computed as a 32-byte long challenge.
For an example, see point (2) of Section 6.1.1.
* If the Access Token has been provided to the Group Manager by
means of a Token Transfer Request to the /authz-info endpoint as
in Section 5.3, then N_S takes the most recent value provided to
the Client by the Group Manager in the 'kdcchallenge' parameter,
as specified in point (1) of Section 6.1.1. This value is
provided either in the Token Transfer Response (see Section 5.3),
or in a 4.00 (Bad Request) error response to a following Join
Request (see Section 6.2). In either case, it is RECOMMENDED to
use an 8-byte long random challenge as value for N_S.
If we consider both N_C and N_S to take 8-byte long values, the
following considerations hold.
* Let us consider both N_C and N_S as taking random values, and the
Group Manager to never change the value of the N_S provided to a
Client during the lifetime of an Access Token. Then, as per the
birthday paradox, the average collision for N_S will happen after
2^32 new transferred Access Tokens, while the average collision
for N_C will happen after 2^32 new Join Requests. This amounts to
considerably more token provisionings than the expected new
joinings to OSCORE groups under a same Group Manager, as well as
to considerably more requests to join OSCORE groups from a same
Client using a same Access Token under a same Group Manager.
* Section 7 of [RFC9203] as well Appendix B.2 of [RFC8613] recommend
the use of 8-byte random values as well. Unlike in those cases,
the values of N_C and N_S considered in this document are not used
for as sensitive operations as the derivation of a Security
Context, and thus do not have possible implications in the
security of AEAD ciphers.
15.3. Reusage of Nonces for Proof-of-Possession Input
As long as the Group Manager preserves the same N_S value currently
associated with an Access Token, i.e., the latest value provided to a
Client in a 'kdcchallenge' parameter, the Client is able to
successfully reuse the same proof-of-possession (PoP) input for
multiple Join Requests to that Group Manager.
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In particular, the Client can reuse the same N_C value for every Join
Request to the Group Manager, and combine it with the same unchanged
N_S value. This results in reusing the same PoP input for producing
the PoP evidence to include in the 'client_cred_verify' parameter of
the Join Requests.
Unless the Group Manager maintains a list of N_C values already used
by that Client since the latest update to the N_S value associated
with the Access Token, the Group Manager can be forced to falsely
believe that the Client possesses its own private key at that point
in time, upon verifying the PoP evidence in the 'client_cred_verify'
parameter.
16. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
16.1. OAuth Parameters
IANA is asked to register the following entries to the "OAuth
Parameters" registry, as per the procedure specified in Section 11.2
of [RFC6749].
* Parameter name: ecdh_info
* Parameter usage location: client-rs request, rs-client response
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
* Parameter name: kdc_dh_creds
* Parameter usage location: client-rs request, rs-client response
* Change Controller: IESG
* Specification Document(s): [RFC-XXXX]
16.2. OAuth Parameters CBOR Mappings
IANA is asked to register the following entries to the "OAuth
Parameters CBOR Mappings" registry, as per the procedure specified in
Section 8.10 of [RFC9200].
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* Name: ecdh_info
* CBOR Key: TBD (range -256 to 255)
* Value Type: Simple value "null" / Array
* Reference: [RFC-XXXX]
* Name: kdc_dh_creds
* CBOR Key: TBD (range -256 to 255)
* Value Type: Simple value "null" / Array
* Reference: [RFC-XXXX]
16.3. ACE Groupcomm Parameters
IANA is asked to register the following entries to the "ACE Groupcomm
Parameters" registry defined in Section 11.6 of
[I-D.ietf-ace-key-groupcomm].
* Name: group_senderId
* CBOR Key: TBD
* CBOR Type: Byte string
* Reference: [RFC-XXXX] (Section 9.2)
* Name: ecdh_info
* CBOR Key: TBD
* CBOR Type: Array
* Reference: [RFC-XXXX] (Section 6.2)
* Name: kdc_dh_creds
* CBOR Key: TBD
* CBOR Type: Array
* Reference: [RFC-XXXX] (Section 6.2)
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* Name: group_enc_key
* CBOR Key: TBD
* CBOR Type: Byte string
* Reference: [RFC-XXXX] (Section 8.2.1)
* Name: stale_node_ids
* CBOR Key: TBD
* CBOR Type: Array
* Reference: [RFC-XXXX] (Section 11)
16.4. ACE Groupcomm Key Types
IANA is asked to register the following entry to the "ACE Groupcomm
Key Types" registry defined in Section 11.7 of
[I-D.ietf-ace-key-groupcomm].
* Name: Group_OSCORE_Input_Material object
* Key Type Value: GROUPCOMM_KEY_TBD
* Profile: "coap_group_oscore_app", defined in Section 16.5 of this
document.
* Description: A Group_OSCORE_Input_Material object encoded as
described in Section 6.3 of this document.
* Reference: [RFC-XXXX] (Section 6.3)
16.5. ACE Groupcomm Profiles
IANA is asked to register the following entry to the "ACE Groupcomm
Profiles" registry defined in Section 11.8 of
[I-D.ietf-ace-key-groupcomm].
* Name: coap_group_oscore_app
* Description: Application profile to provision keying material for
participating in group communication protected with Group OSCORE
as per [I-D.ietf-core-oscore-groupcomm].
* CBOR Value: PROFILE_TBD
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* Reference: [RFC-XXXX] (Section 6.3)
16.6. OSCORE Security Context Parameters
IANA is asked to register the following entries in the "OSCORE
Security Context Parameters" registry defined in Section 9.4 of
[RFC9203].
* Name: group_SenderId
* CBOR Label: TBD
* CBOR Type: Byte string
* Registry: -
* Description: OSCORE Sender ID assigned to a member of an OSCORE
group
* Reference: [RFC-XXXX] (Section 6.3)
* Name: cred_fmt
* CBOR Label: TBD
* CBOR Type: Integer
* Registry: COSE Header Parameters
* Description: Format of authentication credentials to be used in
the OSCORE group
* Reference: [RFC-XXXX] (Section 6.3)
* Name: sign_enc_alg
* CBOR Label: TBD
* CBOR Type: Text string / Integer
* Registry: COSE Algorithms
* Description: OSCORE Signature Encryption Algorithm Value
* Reference: [RFC-XXXX] (Section 6.3)
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* Name: sign_alg
* CBOR Label: TBD
* CBOR Type: Text string / Integer
* Registry: COSE Algorithms
* Description: OSCORE Signature Algorithm Value
* Reference: [RFC-XXXX] (Section 6.3)
* Name: sign_params
* CBOR Label: TBD
* CBOR Type: Array
* Registry: COSE Algorithms, COSE Key Types, COSE Elliptic Curves
* Description: OSCORE Signature Algorithm Parameters
* Reference: [RFC-XXXX] (Section 6.3)
* Name: ecdh_alg
* CBOR Label: TBD
* CBOR Type: Text string / Integer
* Registry: COSE Algorithms
* Description: OSCORE Pairwise Key Agreement Algorithm Value
* Reference: [RFC-XXXX] (Section 6.3)
* Name: ecdh_params
* CBOR Label: TBD
* CBOR Type: Array
* Registry: COSE Algorithms, COSE Key Types, COSE Elliptic Curves
* Description: OSCORE Pairwise Key Agreement Algorithm Parameters
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* Reference: [RFC-XXXX] (Section 6.3)
16.7. TLS Exporter Labels
IANA is asked to register the following entry to the "TLS Exporter
Labels" registry defined in Section 6 of [RFC5705] and updated in
Section 12 of [RFC8447].
* Value: EXPORTER-ACE-Sign-Challenge-coap-group-oscore-app
* DTLS-OK: Y
* Recommended: N
* Reference: [RFC-XXXX] (Section 6.1.1)
16.8. AIF Media-Type Sub-Parameters
For the media-types application/aif+cbor and application/aif+json
defined in Section 5.1 of [RFC9237], IANA is requested to register
the following entries for the two media-type parameters Toid and
Tperm, in the respective sub-registry defined in Section 5.2 of
[RFC9237] within the "MIME Media Type Sub-Parameter" registry group.
* Parameter: Toid
* Name: oscore-gname
* Description/Specification: OSCORE group name
* Reference: [RFC-XXXX]
* Parameter: Tperm
* Name: oscore-gperm
* Description/Specification: permissions pertaining OSCORE groups
* Reference: [RFC-XXXX]
16.9. CoAP Content-Format
IANA is asked to register the following entries to the "CoAP Content-
Formats" registry within the "Constrained RESTful Environments (CoRE)
Parameters" registry group.
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* Media Type: application/aif+cbor;Toid="oscore-
gname",Tperm="oscore-gperm"
* Encoding: -
* ID: 292 (suggested)
* Reference: [RFC-XXXX]
* Media Type: application/aif+json;Toid="oscore-
gname",Tperm="oscore-gperm"
* Encoding: -
* ID: 293 (suggested)
* Reference: [RFC-XXXX]
16.10. Group OSCORE Roles
This document establishes the IANA "Group OSCORE Roles" registry.
The registry has been created to use the "Expert Review" registration
procedure [RFC8126]. Expert review guidelines are provided in
Section 16.13.
This registry includes the possible roles that nodes can take in an
OSCORE group, each in combination with a numeric identifier. These
numeric identifiers are used to express authorization information
about joining OSCORE groups, as specified in Section 3 of [RFC-XXXX].
The columns of this registry are:
* Name: A value that can be used in documents for easier
comprehension, to identify a possible role that nodes can take in
an OSCORE group.
* Value: The numeric identifier for this role. Integer values
greater than 65535 are marked as "Private Use", all other values
use the registration policy "Expert Review" [RFC8126].
* Description: This field contains a brief description of the role.
* Reference: This contains a pointer to the public specification for
the role.
This registry will be initially populated by the values in Figure 1.
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The Reference column for all of these entries will be [RFC-XXXX].
16.11. CoRE Resource Type
IANA is asked to register the following entry in the "Resource Type
(rt=) Link Target Attribute Values" registry within the "Constrained
Restful Environments (CoRE) Parameters" registry group.
* Value: "core.osc.gm"
* Description: Group-membership resource of an OSCORE Group Manager.
* Reference: [RFC-XXXX]
Client applications can use this resource type to discover a group
membership resource at an OSCORE Group Manager, where to send a
request for joining the corresponding OSCORE group.
16.12. ACE Groupcomm Errors
IANA is asked to register the following entries in the "ACE Groupcomm
Errors" registry defined in Section 11.11 of
[I-D.ietf-ace-key-groupcomm].
* Value: 7
* Description: Signatures not used in the group.
* Reference: [RFC-XXXX]
* Value: 8
* Description: Operation permitted only to signature verifiers.
* Reference: [RFC-XXXX]
* Value: 9
* Description: Group currently not active.
* Reference: [RFC-XXXX]
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16.13. Expert Review Instructions
The IANA registry established in this document is 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:
* Clarity and correctness of registrations. Experts are expected to
check the clarity of purpose and use of the requested entries.
Experts should inspect the entry for the considered role, to
verify the correctness of its description against the role as
intended in the specification that defined it. Experts should
consider requesting an opinion on the correctness of registered
parameters from the Authentication and Authorization for
Constrained Environments (ACE) Working Group and the Constrained
RESTful Environments (CoRE) Working Group.
Entries that do not meet these objectives of clarity and
completeness should not be registered.
* Duplicated registration and 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.
* Experts should take into account the expected usage of roles when
approving point assignments. Given a 'Value' V as code point, the
length of the encoding of (2^(V+1) - 1) should be weighed against
the usage of the entry, considering the resources and capabilities
of devices it will be used on. Additionally, given a 'Value' V as
code point, the length of the encoding of (2^(V+1) - 1) should be
weighed against how many code points resulting in that encoding
length are left, and the resources and capabilities of devices it
will be used on.
* Specifications are recommended. When specifications are not
provided, the description provided needs to have sufficient
information to verify the points above.
17. References
17.1. Normative References
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[COSE.Algorithms]
IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>.
[COSE.Elliptic.Curves]
IANA, "COSE Elliptic Curves",
<https://www.iana.org/assignments/cose/
cose.xhtml#elliptic-curves>.
[COSE.Header.Parameters]
IANA, "COSE Header Parameters",
<https://www.iana.org/assignments/cose/cose.xhtml#header-
parameters>.
[COSE.Key.Types]
IANA, "COSE Key Types",
<https://www.iana.org/assignments/cose/cose.xhtml#key-
type>.
[I-D.ietf-ace-key-groupcomm]
Palombini, F. and M. Tiloca, "Key Provisioning for Group
Communication using ACE", Work in Progress, Internet-
Draft, draft-ietf-ace-key-groupcomm-16, 5 September 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-key-
groupcomm-16>.
[I-D.ietf-core-oscore-groupcomm]
Tiloca, M., Selander, G., Palombini, F., Mattsson, J. P.,
and J. Park, "Group OSCORE - Secure Group Communication
for CoAP", Work in Progress, Internet-Draft, draft-ietf-
core-oscore-groupcomm-17, 20 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
oscore-groupcomm-17>.
[NIST-800-56A]
Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
Davis, "Recommendation for Pair-Wise Key-Establishment
Schemes Using Discrete Logarithm Cryptography - NIST
Special Publication 800-56A, Revision 3", April 2018,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-56Ar3.pdf>.
[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>.
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[RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
March 2010, <https://www.rfc-editor.org/info/rfc5705>.
[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>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
2013, <https://www.rfc-editor.org/info/rfc6979>.
[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>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/info/rfc8017>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
[RFC8126] Cotton, M., Leiba, B., and 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>.
[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>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/info/rfc8447>.
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[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/info/rfc9052>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/info/rfc9053>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments Using the OAuth 2.0 Framework
(ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
<https://www.rfc-editor.org/info/rfc9200>.
[RFC9202] 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)", RFC 9202,
DOI 10.17487/RFC9202, August 2022,
<https://www.rfc-editor.org/info/rfc9202>.
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[RFC9203] Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"The Object Security for Constrained RESTful Environments
(OSCORE) Profile of the Authentication and Authorization
for Constrained Environments (ACE) Framework", RFC 9203,
DOI 10.17487/RFC9203, August 2022,
<https://www.rfc-editor.org/info/rfc9203>.
[RFC9237] Bormann, C., "An Authorization Information Format (AIF)
for Authentication and Authorization for Constrained
Environments (ACE)", RFC 9237, DOI 10.17487/RFC9237,
August 2022, <https://www.rfc-editor.org/info/rfc9237>.
[RFC9277] Richardson, M. and C. Bormann, "On Stable Storage for
Items in Concise Binary Object Representation (CBOR)",
RFC 9277, DOI 10.17487/RFC9277, August 2022,
<https://www.rfc-editor.org/info/rfc9277>.
17.2. Informative References
[I-D.ietf-ace-oscore-gm-admin]
Tiloca, M., Höglund, R., Van der Stok, P., and F.
Palombini, "Admin Interface for the OSCORE Group Manager",
Work in Progress, Internet-Draft, draft-ietf-ace-oscore-
gm-admin-07, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
oscore-gm-admin-07>.
[I-D.ietf-core-coap-pubsub]
Koster, M., Keränen, A., and J. Jimenez, "Publish-
Subscribe Broker for the Constrained Application Protocol
(CoAP)", Work in Progress, Internet-Draft, draft-ietf-
core-coap-pubsub-11, 7 November 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
coap-pubsub-11>.
[I-D.ietf-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", Work in
Progress, Internet-Draft, draft-ietf-core-groupcomm-bis-
08, 11 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
groupcomm-bis-08>.
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[I-D.ietf-cose-cbor-encoded-cert]
Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", Work in Progress, Internet-Draft, draft-
ietf-cose-cbor-encoded-cert-05, 10 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
cbor-encoded-cert-05>.
[I-D.tiloca-core-oscore-discovery]
Tiloca, M., Amsüss, C., and P. Van der Stok, "Discovery of
OSCORE Groups with the CoRE Resource Directory", Work in
Progress, Internet-Draft, draft-tiloca-core-oscore-
discovery-12, 5 September 2022,
<https://datatracker.ietf.org/doc/html/draft-tiloca-core-
oscore-discovery-12>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[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>.
[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>.
[RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer
Security (TLS) / Datagram Transport Layer Security (DTLS)
Profiles for the Internet of Things", RFC 7925,
DOI 10.17487/RFC7925, July 2016,
<https://www.rfc-editor.org/info/rfc7925>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
Appendix A. Profile Requirements
This section lists how this application profile of ACE addresses the
requirements defined in Appendix A of [I-D.ietf-ace-key-groupcomm].
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A.1. Mandatory-to-Address Requirements
* REQ1 - Specify the format and encoding of 'scope'. This includes
defining the set of possible roles and their identifiers, as well
as the corresponding encoding to use in the scope entries
according to the used scope format: see Section 3 and Section 5.1.
* REQ2 - If the AIF format of 'scope' is used, register its specific
instance of "Toid" and "Tperm" as Media Type parameters and a
corresponding Content-Format, as per the guidelines in [RFC9237]:
see Section 16.8 and Section 16.9.
* REQ3 - if used, specify the acceptable values for 'sign_alg':
values from the "Value" column of the "COSE Algorithms" registry
[COSE.Algorithms].
* REQ4 - If used, specify the acceptable values for
'sign_parameters': format and values from the COSE algorithm
capabilities as specified in the "COSE Algorithms" registry
[COSE.Algorithms].
* REQ5 - If used, specify the acceptable values for
'sign_key_parameters': format and values from the COSE key type
capabilities as specified in the "COSE Key Types" registry
[COSE.Key.Types].
* REQ6 - Specify the acceptable formats for authentication
credentials and, if used, the acceptable values for 'cred_fmt':
acceptable formats explicitly provide the public key as well as
the comprehensive set of information related to the public key
algorithm (see Section 5.3 and Section 6.3). Consistent
acceptable values for 'cred_fmt' are taken from the "Label" column
of the "COSE Header Parameters" registry [COSE.Header.Parameters].
* REQ7 - If the value of the GROUPNAME URI path and the group name
in the Access Token scope (gname in Section 3.1 of
[I-D.ietf-ace-key-groupcomm]) are not required to coincide,
specify the mechanism to map the GROUPNAME value in the URI to the
group name: not applicable, since a perfect matching is required.
* REQ8 - Define whether the KDC has an authentication credential and
if this has to be provided through the 'kdc_cred' parameter, see
Section 4.1 of [I-D.ietf-ace-key-groupcomm]: yes, as required by
the Group OSCORE protocol [I-D.ietf-core-oscore-groupcomm], see
Section 6.3 of this document.
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* REQ9 - Specify if any part of the KDC interface as defined in
Section 4.1 of [I-D.ietf-ace-key-groupcomm] is not supported by
the KDC: not applicable.
* REQ10 - Register a Resource Type for the root url-path, which is
used to discover the correct url to access at the KDC (see
Section 4.1 of [I-D.ietf-ace-key-groupcomm]): the Resource Type
(rt=) Link Target Attribute value "core.osc.gm" is registered in
Section 16.11.
* REQ11 - Define what specific actions (e.g., CoAP methods) are
allowed on each resource provided by the KDC interface, depending
on whether the Client is a current group member; the roles that a
Client is authorized to take as per the obtained access token; and
the roles that the Client has as current group member: see
Section 8.4.
* REQ12 - Categorize possible newly defined operations for Clients
into primary operations expected to be minimally supported and
secondary operations, and provide accompanying considerations: see
Section 8.5.
* REQ13 - Specify the encoding of group identifier (see
Section 4.2.1 of [I-D.ietf-ace-key-groupcomm]): CBOR byte string
(see Section 9.10).
* REQ14 - Specify the approaches used to compute and verify the PoP
evidence to include in 'client_cred_verify', and which of those
approaches is used in which case: see Section 6.1 and Section 6.2.
* REQ15 - Specify how the nonce N_S is generated, if the token is
not provided to the KDC through the Token Transfer Request to the
authz-info endpoint (e.g., if it is used directly to validate TLS
instead): see Section 6.1.1.
* REQ16 - Define the initial value of the 'num' parameter: the
initial value MUST be set to 0 when creating the OSCORE group,
e.g., as in [I-D.ietf-ace-oscore-gm-admin].
* REQ17 - Specify the format of the 'key' parameter: see
Section 6.3.
* REQ18 - Specify acceptable values of the 'gkty' parameter:
Group_OSCORE_Input_Material object (see Section 6.3).
* REQ19 - Specify and register the application profile identifier:
coap_group_oscore_app (see Section 16.5).
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* REQ20 - If used, specify the format and content of
'group_policies' and its entries: see Section 6.3.
* REQ21 - Specify the approaches used to compute and verify the PoP
evidence to include in 'kdc_cred_verify', and which of those
approaches is used in which case: see Section 6.3, Section 6.4 and
Section 9.5.
* REQ22 - Specify the communication protocol that the members of the
group must use: CoAP [RFC7252], also for group communication
[I-D.ietf-core-groupcomm-bis].
* REQ23 - Specify the security protocols that the group members must
use to protect their communication: Group OSCORE
[I-D.ietf-core-oscore-groupcomm].
* REQ24 - Specify how the communication is secured between the
Client and KDC: by means of any transport profile of ACE [RFC9200]
between Client and Group Manager that complies with the
requirements in Appendix C of [RFC9200].
* REQ25 - Specify the format of the identifiers of group members:
the Sender ID used in the OSCORE group (see Section 6.3 and
Section 9.3).
* REQ26 - Specify policies at the KDC to handle member ids that are
not included in 'get_creds': see Section 9.3.
* REQ27 - Specify the format of newly-generated individual keying
material for group members, or of the information to derive it,
and corresponding CBOR label: see Section 9.2.
* REQ28 - Specify which CBOR tag is used for identifying the
semantics of binary scopes, or register a new CBOR tag if a
suitable one does not exist already: see Section 5.2.
* REQ29 - Categorize newly defined parameters according to the same
criteria of Section 8 of [I-D.ietf-ace-key-groupcomm]: see
Section 12.
* REQ30 - Define whether Clients must, should or may support the
conditional parameters defined in Section 8 of
[I-D.ietf-ace-key-groupcomm], and under which circumstances: see
Section 12.
A.2. Optional-to-Address Requirements
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* OPT1 (Optional) - If the textual format of 'scope' is used,
specify CBOR values to use for abbreviating the role identifiers
in the group: not applicable.
* OPT2 (Optional) - Specify additional parameters used in the
exchange of Token Transfer Request and Response:
- 'ecdh_info', to negotiate the ECDH algorithm, ECDH algorithm
parameters, ECDH key parameters and exact format of
authentication credentials used in the group, in case the
joining node supports the pairwise mode of Group OSCORE (see
Section 5.3).
- 'kdc_dh_creds', to ask for and retrieve the Group Manager's
Diffie-Hellman authentication credentials, in case the joining
node supports the pairwise mode of Group OSCORE and the Access
Token authorizes to join parwise-only groups (see Section 5.3).
* OPT3 (Optional) - Specify the negotiation of parameter values for
signature algorithm and signature keys, if 'sign_info' is not
used: possible early discovery by using the approach based on the
CoRE Resource Directory described in
[I-D.tiloca-core-oscore-discovery].
* OPT4 (Optional) - Specify possible or required payload formats for
specific error cases: send a 4.00 (Bad Request) error response to
a Join Request (see Section 6.2).
* OPT5 (Optional) - Specify additional identifiers of error types,
as values of the 'error' field in an error response from the KDC:
see Section 16.12.
* OPT6 (Optional) - Specify the encoding of 'creds_repo' if the
default is not used: no.
* OPT7 (Optional) - Specify the functionalities implemented at the
'control_uri' resource hosted at the Client, including message
exchange encoding and other details (see Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm]): see Section 10 for the eviction of
a group member; see Section 11 for the group rekeying process.
* OPT8 (Optional) - Specify the behavior of the handler in case of
failure to retrieve an authentication credential for the specific
node: send a 4.00 (Bad Request) error response to a Join Request
(see Section 6.2).
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* OPT9 (Optional) - Define a default group rekeying scheme, to refer
to in case the 'rekeying_scheme' parameter is not included in the
Join Response (see Section 4.3.1.1 of
[I-D.ietf-ace-key-groupcomm]): the "Point-to-Point" rekeying
scheme registered in Section 11.12 of
[I-D.ietf-ace-key-groupcomm], whose detailed use for this profile
is defined in Section 11 of this document.
* OPT10 (Optional) - Specify the functionalities implemented at the
'control_group_uri' resource hosted at the Client, including
message exchange encoding and other details (see Section 4.3.1 of
[I-D.ietf-ace-key-groupcomm]): see Section 10 for the eviction of
multiple group members.
* OPT11 (Optional) - Specify policies that instruct Clients to
retain unsuccessfully decrypted messages and for how long, so that
they can be decrypted after getting updated keying material: no.
* OPT12 (Optional) - Specify for the KDC to perform group rekeying
(together or instead of renewing individual keying material) when
receiving a Key Renewal Request: the Group Manager SHOULD NOT
perform a group rekeying, unless already scheduled to occur
shortly (see Section 9.2).
* OPT13 (Optional) - Specify how the identifier of a group members's
authentication credential is included in requests sent to other
group members: no.
* OPT14 (Optional) - Specify additional information to include in
rekeying messages for the "Point-to-Point" group rekeying scheme
(see Section 6.1 of [I-D.ietf-ace-key-groupcomm]): see
Section 11.1.
* OPT15 (Optional) - Specify if Clients must or should support any
of the parameters defined as optional in Section 8 of
[I-D.ietf-ace-key-groupcomm]: no.
Appendix B. Extensibility for Future COSE Algorithms
As defined in Section 8.1 of [RFC9053], future algorithms can be
registered in the "COSE Algorithms" registry [COSE.Algorithms] as
specifying none or multiple COSE capabilities.
To enable the seamless use of such future registered algorithms, this
section defines a general, agile format for:
* Each 'ecdh_info_entry' of the 'ecdh_info' parameter in the Token
Transfer Response (see Section 5.3 and Section 5.3.1);
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* The 'sign_params' and 'ecdh_params' parameters within the 'key'
parameter (see Section 6.3), as part of the response payloads used
in Section 6.3, Section 9.1.1, Section 9.1.2 and Section 11.
Appendix B of [I-D.ietf-ace-key-groupcomm] describes the analogous
general format for 'sign_info_entry' of the 'sign_info' parameter in
the Token Transfer Response (see Section 5.3 of this document).
If any of the currently registered COSE algorithms is considered,
using this general format yields the same structure defined in this
document for the items above, thus ensuring retro-compatibility.
B.1. Format of 'ecdh_info_entry'
The format of each 'ecdh_info_entry' (see Section 5.3 and
Section 5.3.1) is generalized as follows. Given N the number of
elements of the 'ecdh_parameters' array, i.e., the number of COSE
capabilities of the ECDH algorithm, then:
* 'ecdh_key_parameters' is replaced by N elements 'ecdh_capab_i',
each of which is a CBOR array.
* The i-th array following 'ecdh_parameters', i.e., 'ecdh_capab_i'
(i = 0, ..., N-1), is the array of COSE capabilities for the
algorithm capability specified in 'ecdh_parameters'[i].
The CDDL notation [RFC8610] of the 'ecdh_info_entry' parameter is
given below.
ecdh_info_entry =
[
id : gname / [ + gname ],
ecdh_alg : int / tstr,
ecdh_parameters : [ alg_capab_1 : any,
alg_capab_2 : any,
...,
alg_capab_N : any],
ecdh_capab_1 : [ any ],
ecdh_capab_2 : [ any ],
...,
ecdh_capab_N : [ any ],
cred_fmt : int / null
]
gname = tstr
Figure 13: 'ecdh_info_entry' with general format
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B.2. Format of 'key'
The format of 'key' (see Section 6.3) is generalized as follows.
* The 'sign_params' array includes N+1 elements, whose exact
structure and value depend on the value of the signature algorithm
specified in 'sign_alg'.
- The first element, i.e., 'sign_params'[0], is the array of the
N COSE capabilities for the signature algorithm, as specified
for that algorithm in the "Capabilities" column of the "COSE
Algorithms" registry [COSE.Algorithms] (see Section 8.1 of
[RFC9053]).
- Each following element 'sign_params'[i], i.e., with index i >
0, is the array of COSE capabilities for the algorithm
capability specified in 'sign_params'[0][i-1].
For example, if 'sign_params'[0][0] specifies the key type as
capability of the algorithm, then 'sign_params'[1] is the array of
COSE capabilities for the COSE key type associated with the
signature algorithm, as specified for that key type in the
"Capabilities" column of the "COSE Key Types" registry
[COSE.Key.Types] (see Section 8.2 of [RFC9053]).
* The 'ecdh_params' array includes M+1 elements, whose exact
structure and value depend on the value of the ECDH algorithm
specified in 'ecdh_alg'.
- The first element, i.e., 'ecdh_params'[0], is the array of the
M COSE capabilities for the ECDH algorithm, as specified for
that algorithm in the "Capabilities" column of the "COSE
Algorithms" registry [COSE.Algorithms] (see Section 8.1 of
[RFC9053]).
- Each following element 'ecdh_params'[i], i.e., with index i >
0, is the array of COSE capabilities for the algorithm
capability specified in 'ecdh_params'[0][i-1].
For example, if 'ecdh_params'[0][0] specifies the key type as
capability of the algorithm, then 'ecdh_params'[1] is the array of
COSE capabilities for the COSE key type associated with the ECDH
algorithm, as specified for that key type in the "Capabilities"
column of the "COSE Key Types" registry [COSE.Key.Types] (see
Section 8.2 of [RFC9053]).
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Appendix C. Document Updates
RFC EDITOR: PLEASE REMOVE THIS SECTION.
C.1. Version -15 to -16
* Early mentioning of invalid combinations of roles.
* Revised presentation of handling of stale Sender IDs.
* Fixed CDDL notation.
* Fixed diagnostic notation in examples.
* Possible reason to deviate from default parameter values.
* Clarifications and editorial fixes.
C.2. Version -14 to -15
* Alignment with renaming in draft-ietf-ace-key-groupcomm.
* Updated signaling of semantics for binary encoded scopes.
* Considered the upload of Access Tokens in the DTLS 1.3 Handshake.
* Fixes in IANA registrations.
* Editorial fixes.
C.3. Version -13 to -14
* Major reordering of the document sections.
* The HKDF Algorithm is specified by the HMAC Algorithm.
* Group communication does not necessarily use IP multicast.
* Generalized AIF data model, also for draft-ace-oscore-gm-admin.
* Clarifications and editorial improvements.
C.4. Version -12 to -13
* Renamed parameters about authentication credentials.
* It is optional for the Group Manager to reassign Gids by tracking
"Birth Gids".
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* Distinction between authentication credentials and public keys.
* Updated IANA considerations related to AIF.
* Updated textual description of registered ACE Scope Semantics
value.
C.5. Version -11 to -12
* Clarified semantics of 'ecdh_info' and 'kdc_dh_creds'.
* Definition of /ace-group/GROUPNAME/kdc-pub-key moved to draft-
ietf-ace-key-groupcomm.
* ace-group/ accessible also to non-members that are not Verifiers.
* Clarified what resources are accessible to Verifiers.
* Revised error handling for the newly defined resources.
* Revised use of CoAP error codes.
* Use of "Token Tranfer Request" and "Token Transfer Response".
* New parameter 'rekeying_scheme'.
* Categorization of new parameters and inherited conditional
parameters.
* Clarifications on what to do in case of enhanced error responses.
* Changed UCCS to CCS.
* Authentication credentials of just joined Clients can be in
rekeying messages.
* Revised names of new IANA registries.
* Clarified meaning of registered CoRE resource type.
* Alignment to new requirements from draft-ietf-ace-key-groupcomm.
* Fixes and editorial improvements.
C.6. Version -10 to -11
* Removed redundancy of key type capabilities, from 'sign_info',
'ecdh_info' and 'key'.
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* New resource to retrieve the Group Manager's authentication
credential.
* New resource to retrieve material for Signature Verifiers.
* New parameter 'sign_enc_alg' related to the group mode.
* 'cred_fmt' takes value from the COSE Header Parameters registry.
* Improved alignment of the Join Response payload with the Group
OSCORE Security Context parameters.
* Recycling Group IDs by tracking "Birth GIDs".
* Error handling in case of non available Sender IDs upon joining.
* Error handling in case EdDSA public keys with invalid Y coordinate
when the pairwise mode of Group OSCORE is supported.
* Generalized proof-of-possession (PoP) for the joining node's
private key; defined Diffie-Hellman based PoP for OSCORE groups
using only the pairwise mode.
* Proof-of-possession of the Group Manager's private key in the Join
Response.
* Always use 'peer_identifiers' to convey Sender IDs as node
identifiers.
* Stale Sender IDs provided when rekeying the group.
* New resource for late retrieval of stale Sender IDs.
* Added examples of message exchanges.
* Revised default values of group configuration parameters.
* Fixes to IANA registrations.
* General format of parameters related to COSE capabilities,
supporting future registered COSE algorithms (new Appendix).
C.7. Version -09 to -10
* Updated non-recycling policy of Sender IDs.
* Removed policies about Sender Sequence Number synchronization.
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* 'control_path' renamed to 'control_uri'.
* Format of 'get_pub_keys' aligned with draft-ietf-ace-key-
groupcomm.
* Additional way to inform of group eviction.
* Registered semantics identifier for extended scope format.
* Extended error handling, with error type specified in some error
responses.
* Renumbered requirements.
C.8. Version -08 to -09
* The url-path "ace-group" is used.
* Added overview of admitted methods on the Group Manager resources.
* Added exchange of parameters relevant for the pairwise mode of
Group OSCORE.
* The signed value for 'client_cred_verify' includes also the scope.
* Renamed the key material object as Group_OSCORE_Input_Material
object.
* Replaced 'clientId' with 'group_SenderId'.
* Added message exchange for Group Names request-response.
* No reassignment of Sender ID and Gid in the same OSCORE group.
* Updates on group rekeying contextual with request of new Sender
ID.
* Signature verifiers can also retrieve Group Names and URIs.
* Removed group policy about supporting Group OSCORE in pairwise
mode.
* Registration of the resource type rt="core.osc.gm".
* Update list of requirements.
* Clarifications and editorial revision.
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C.9. Version -07 to -08
* AIF specific data model to express scope entries.
* A set of roles is checked as valid when processing the Join
Request.
* Updated format of 'get_pub_keys' in the Join Request.
* Payload format and default values of group policies in the Join
Response.
* Updated payload format of the FETCH request to retrieve
authentication credentials.
* Default values for group configuration parameters.
* IANA registrations to support the AIF specific data model.
C.10. Version -06 to -07
* Alignments with draft-ietf-core-oscore-groupcomm.
* New format of 'sign_info', using the COSE capabilities.
* New format of Join Response parameters, using the COSE
capabilities.
* Considerations on group rekeying.
* Editorial revision.
C.11. Version -05 to -06
* Added role of external signature verifier.
* Parameter 'rsnonce' renamed to 'kdcchallenge'.
* Parameter 'kdcchallenge' may be omitted in some cases.
* Clarified difference between group name and OSCORE Gid.
* Removed the role combination ["requester", "monitor"].
* Admit implicit scope and audience in the Authorization Request.
* New format for the 'sign_info' parameter.
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* Scope not mandatory to include in the Join Request.
* Group policy about supporting Group OSCORE in pairwise mode.
* Possible individual rekeying of a single requesting node combined
with a group rekeying.
* Security considerations on reusage of signature challenges.
* Addressing optional requirement OPT12 from draft-ietf-ace-key-
groupcomm
* Editorial improvements.
C.12. Version -04 to -05
* Nonce N_S also in error responses to the Join Requests.
* Supporting single Access Token for multiple groups/topics.
* Supporting legal requesters/responders using the 'peer_roles'
parameter.
* Registered and used dedicated label for TLS Exporter.
* Added method for uploading a new authentication credential to the
Group Manager.
* Added resource and method for retrieving the current group status.
* Fixed inconsistency in retrieving group keying material only.
* Clarified retrieval of keying material for monitor-only members.
* Clarification on incrementing version number when rekeying the
group.
* Clarification on what is re-distributed with the group rekeying.
* Security considerations on the size of the nonces used for the
signature challenge.
* Added CBOR values to abbreviate role identifiers in the group.
C.13. Version -03 to -04
* New abstract.
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* Moved general content to draft-ietf-ace-key-groupcomm
* Terminology: node name; node resource.
* Creation and pointing at node resource.
* Updated Group Manager API (REST methods and offered services).
* Size of challenges 'cnonce' and 'rsnonce'.
* Value of 'rsnonce' for reused or non-traditionally-posted tokens.
* Removed reference to RFC 7390.
* New requirements from draft-ietf-ace-key-groupcomm
* Editorial improvements.
C.14. Version -02 to -03
* New sections, aligned with the interface of ace-key-groupcomm .
* Exchange of information on the signature algorithm and related
parameters, during the Token POST (Section 4.1).
* Nonce 'rsnonce' from the Group Manager to the Client
(Section 4.1).
* Client PoP signature in the Key Distribution Request upon joining
(Section 4.2).
* Local actions on the Group Manager, upon a new node's joining
(Section 4.2).
* Local actions on the Group Manager, upon a node's leaving
(Section 12).
* IANA registration in ACE Groupcomm Parameters registry.
* More fulfilled profile requirements (Appendix A).
C.15. Version -01 to -02
* Editorial fixes.
* Changed: "listener" to "responder"; "pure listener" to "monitor".
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* Changed profile name to "coap_group_oscore_app", to reflect it is
an application profile.
* Added the 'type' parameter for all requests to a Join Resource.
* Added parameters to indicate the encoding of authentication
credentials.
* Challenge-response for proof-of-possession of signature keys
(Section 4).
* Renamed 'key_info' parameter to 'sign_info'; updated its format;
extended to include also parameters of the signature key
(Section 4.1).
* Code 4.00 (Bad request), in responses to joining nodes providing
an invalid authentication credential (Section 4.3).
* Clarifications on provisioning and checking of authentication
credentials (Sections 4 and 6).
* Extended discussion on group rekeying and possible different
approaches (Section 7).
* Extended security considerations: proof-of-possession of signature
keys; collision of OSCORE Group Identifiers (Section 8).
* Registered three entries in the IANA registry "Sequence Number
Synchronization Method" (Section 9).
* Registered one public key encoding in the "ACE Public Key
Encoding" IANA registry (Section 9).
C.16. Version -00 to -01
* Changed name of 'req_aud' to 'audience' in the Authorization
Request (Section 3.1).
* Added negotiation of signature algorithm/parameters between Client
and Group Manager (Section 4).
* Updated format of the Key Distribution Response as a whole
(Section 4.3).
* Added parameter 'cs_params' in the 'key' parameter of the Key
Distribution Response (Section 4.3).
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* 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 Christian Amsüss, Santiago Aragón, Stefan
Beck, Carsten Bormann, Martin Gunnarsson, Rikard Höglund, Watson
Ladd, Daniel Migault, Jim Schaad, Ludwig Seitz, Göran 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; by the H2020 project SIFIS-Home
(Grant agreement 952652); and by the EIT-Digital High Impact
Initiative ACTIVE.
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-164 29 Stockholm Kista
Sweden
Email: marco.tiloca@ri.se
Jiye Park
Universitaet Duisburg-Essen
Schuetzenbahn 70
45127 Essen
Germany
Email: ji-ye.park@uni-due.de
Francesca Palombini
Ericsson AB
Torshamnsgatan 23
SE-16440 Stockholm Kista
Sweden
Email: francesca.palombini@ericsson.com
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