ACE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track J. Park
Expires: 13 January 2022 Universitaet Duisburg-Essen
F. Palombini
Ericsson AB
12 July 2021
Key Management for OSCORE Groups in ACE
draft-ietf-ace-key-groupcomm-oscore-11
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
secured with Group Object Security for Constrained RESTful
Environments (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
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Overview of the Joining Process . . . . . . . . . . . . . 7
2.2. Overview of the Group Rekeying Process . . . . . . . . . 7
2.2.1. Stale OSCORE Sender IDs . . . . . . . . . . . . . . . 8
3. Format of Scope . . . . . . . . . . . . . . . . . . . . . . . 10
4. Joining Node to Authorization Server . . . . . . . . . . . . 11
4.1. Authorization Request . . . . . . . . . . . . . . . . . . 12
4.2. Authorization Response . . . . . . . . . . . . . . . . . 12
5. Interface at the Group Manager . . . . . . . . . . . . . . . 12
5.1. ace-group/GROUPNAME/active . . . . . . . . . . . . . . . 13
5.1.1. GET Handler . . . . . . . . . . . . . . . . . . . . . 13
5.2. ace-group/GROUPNAME/gm-pub-key . . . . . . . . . . . . . 14
5.2.1. GET Handler . . . . . . . . . . . . . . . . . . . . . 14
5.3. ace-group/GROUPNAME/verif-data . . . . . . . . . . . . . 14
5.3.1. GET Handler . . . . . . . . . . . . . . . . . . . . . 14
5.4. ace-group/GROUPNAME/stale-sids . . . . . . . . . . . . . 15
5.4.1. FETCH Handler . . . . . . . . . . . . . . . . . . . . 15
5.5. Admitted Methods . . . . . . . . . . . . . . . . . . . . 16
6. Token POST and Group Joining . . . . . . . . . . . . . . . . 17
6.1. Token Post . . . . . . . . . . . . . . . . . . . . . . . 18
6.1.1. 'ecdh_info' Parameter . . . . . . . . . . . . . . . . 20
6.1.2. 'gm_dh_pub_keys' Parameter . . . . . . . . . . . . . 22
6.2. Sending the Joining Request . . . . . . . . . . . . . . . 24
6.2.1. Value of the N_S Challenge . . . . . . . . . . . . . 25
6.3. Receiving the Joining Request . . . . . . . . . . . . . . 26
6.4. Sending the Joining Response . . . . . . . . . . . . . . 29
6.5. Receiving the Joining Response . . . . . . . . . . . . . 35
7. Public Keys of Joining Nodes . . . . . . . . . . . . . . . . 36
8. Retrieval of Updated Keying Material . . . . . . . . . . . . 38
8.1. Retrieval of Group Keying Material . . . . . . . . . . . 38
8.2. Retrieval of Group Keying Material and OSCORE Sender
ID . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
9. Requesting a Change of Keying Material . . . . . . . . . . . 40
10. Retrieval of Public Keys and Roles of Group Members . . . . . 41
11. Update of Public Key . . . . . . . . . . . . . . . . . . . . 42
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12. Retrieval of the Group Manager's Public Key . . . . . . . . . 43
13. Retrieval of Signature Verification Data . . . . . . . . . . 45
14. Retrieval of Group Policies . . . . . . . . . . . . . . . . . 47
15. Retrieval of Keying Material Version . . . . . . . . . . . . 48
16. Retrieval of Group Status . . . . . . . . . . . . . . . . . . 48
17. Retrieval of Group Names and URIs . . . . . . . . . . . . . . 49
18. Request to Leave the Group . . . . . . . . . . . . . . . . . 52
19. Removal of a Group Member . . . . . . . . . . . . . . . . . . 52
20. Group Rekeying Process . . . . . . . . . . . . . . . . . . . 53
20.1. Sending Rekeying Messages . . . . . . . . . . . . . . . 55
20.2. Receiving Rekeying Messages . . . . . . . . . . . . . . 57
20.3. Missed Rekeying Instances . . . . . . . . . . . . . . . 57
20.3.1. Retrieval of Stale Sender IDs . . . . . . . . . . . 60
21. Default Values for Group Configuration Parameters . . . . . . 62
21.1. Common . . . . . . . . . . . . . . . . . . . . . . . . . 62
21.2. Group Mode . . . . . . . . . . . . . . . . . . . . . . . 62
21.3. Pairwise Mode . . . . . . . . . . . . . . . . . . . . . 63
22. Security Considerations . . . . . . . . . . . . . . . . . . . 64
22.1. Management of OSCORE Groups . . . . . . . . . . . . . . 64
22.2. Size of Nonces as Proof-of-Possesion Challenge . . . . . 65
22.3. Reusage of Nonces for Proof-of-Possession Input . . . . 66
23. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 67
23.1. OAuth Parameters Registry . . . . . . . . . . . . . . . 67
23.2. OAuth Parameters CBOR Mappings Registry . . . . . . . . 67
23.3. ACE Groupcomm Parameters Registry . . . . . . . . . . . 68
23.4. ACE Groupcomm Key Registry . . . . . . . . . . . . . . . 69
23.5. ACE Groupcomm Profile Registry . . . . . . . . . . . . . 70
23.6. OSCORE Security Context Parameters Registry . . . . . . 70
23.7. TLS Exporter Label Registry . . . . . . . . . . . . . . 72
23.8. AIF Registry . . . . . . . . . . . . . . . . . . . . . . 73
23.9. Media Type Registrations . . . . . . . . . . . . . . . . 73
23.10. CoAP Content-Format Registry . . . . . . . . . . . . . . 74
23.11. Group OSCORE Roles Registry . . . . . . . . . . . . . . 74
23.12. CoRE Resource Type Registry . . . . . . . . . . . . . . 75
23.13. ACE Scope Semantics Registry . . . . . . . . . . . . . . 75
23.14. ACE Groupcomm Errors . . . . . . . . . . . . . . . . . . 76
23.15. Expert Review Instructions . . . . . . . . . . . . . . . 76
24. References . . . . . . . . . . . . . . . . . . . . . . . . . 77
24.1. Normative References . . . . . . . . . . . . . . . . . . 77
24.2. Informative References . . . . . . . . . . . . . . . . . 81
Appendix A. Profile Requirements . . . . . . . . . . . . . . . . 83
Appendix B. Extensibility for Future COSE Algorithms . . . . . . 86
B.1. Format of 'ecdh_info_entry' . . . . . . . . . . . . . . . 87
B.2. Format of 'key' . . . . . . . . . . . . . . . . . . . . . 87
Appendix C. Document Updates . . . . . . . . . . . . . . . . . . 88
C.1. Version -10 to -11 . . . . . . . . . . . . . . . . . . . 88
C.2. Version -09 to -10 . . . . . . . . . . . . . . . . . . . 89
C.3. Version -08 to -09 . . . . . . . . . . . . . . . . . . . 90
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C.4. Version -07 to -08 . . . . . . . . . . . . . . . . . . . 90
C.5. Version -06 to -07 . . . . . . . . . . . . . . . . . . . 91
C.6. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 91
C.7. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 92
C.8. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 92
C.9. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 93
C.10. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 93
C.11. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 94
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 94
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 95
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)
[I-D.ietf-cose-rfc8152bis-struct][I-D.ietf-cose-rfc8152bis-algs] 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 over IP multicast
[I-D.ietf-core-groupcomm-bis]. 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
[I-D.ietf-ace-oauth-authz]. 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 over IP multicast.
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:
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* The terms and concepts described in the ACE framework for
authentication and authorization [I-D.ietf-ace-oauth-authz] and in
the Authorization Information Format (AIF) [I-D.ietf-ace-aif] to
express authorization information. The terminology for entities
in the considered architecture is defined in OAuth 2.0 [RFC6749].
In particular, this includes Client (C), Resource Server (RS), and
Authorization Server (AS).
* The terms and concept 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.
* The terms and concepts described in CBOR [RFC8949] and COSE
[I-D.ietf-cose-rfc8152bis-struct][I-D.ietf-cose-rfc8152bis-algs].
* 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 include the concept of 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.
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].
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* 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 public keys 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]).
2. Protocol Overview
Group communication for CoAP over IP multicast has been enabled in
[I-D.ietf-core-groupcomm-bis] and can be secured with Group Object
Security for Constrained RESTful Environments (OSCORE) [RFC8613] as
described in [I-D.ietf-core-oscore-groupcomm]. A network node joins
an OSCORE group by interacting with the responsible Group Manager.
Once registered in the group, the new node can securely exchange
messages with other group members.
This document describes how to use [I-D.ietf-ace-key-groupcomm] and
[I-D.ietf-ace-oauth-authz] to perform a number of authentication,
authorization and key distribution actions, as defined in Section 2
of [I-D.ietf-ace-key-groupcomm], for 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 to the Group Manager is the
AS.
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.
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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].
2.1. Overview of the Joining Process
A node performs the steps described in Section 4.3 of
[I-D.ietf-ace-key-groupcomm] in order to join an OSCORE group. The
format and processing of messages exchanged among the participants
are further specified in Section 4 and Section 6 of this document.
2.2. 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 20 of this document. Future application
profiles may define alternative rekeying message formats and group
rekeying schemes, which 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]).
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* A set of stale Sender IDs, which allows each rekeyed node to purge
public keys and Recipient Contexts used in the group and
associated to those Sender IDs. This in turn allows every group
member to rely on owned public keys 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 2.2.1.
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 rekeying 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 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 18), or when the Group Manager forcibly
evicts them from the group, e.g., due to expired or revoked
authorization (see Section 19). 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 public keys of former group members
(see Sections 3.2 and 10.1 of [I-D.ietf-core-oscore-groupcomm]).
* Extension of group lifetime - That is, the group is rekeyed when
the expiration time for the group keying material approaches or
has passed, if it is appropriate to extend the group operation
beyond that.
The Group Manager MAY rekey the group for other reasons, e.g.,
according to an application-dependent rekeying period or scheduling.
2.2.1. Stale OSCORE Sender IDs
Throughout the lifetime of every group, the Group Manager MUST
maintain a collection of stale Sender IDs for that group.
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The collection associated to a group MUST include up to N > 1 ordered
sets of stale OSCORE Sender IDs. It is up to the application to
specify the value of N, possibly on a per-group basis.
The N-th set includes the Sender IDs that have become "stale" under
the current version V of the group keying material. The (N-1)-th set
refers to the immediately previous version (V - 1) of the group
keying material, and so on.
In the following cases, the Group Manager MUST add a new element to
the most recent set X, i.e., the set associated to the current
version V of the group keying material.
* 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), or in case the group member re-joins the group (see
Section 6.2 and Section 6.4), 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 18) or is forcibly evicted from the
group (see Section 19).
The value of N can change throughout the lifetime of the group. If
the new value N' is smaller than N, the Group Manager MUST preserve
the (up to) N' most recent sets in the collection and MUST delete any
possible older set from the collection.
Finally, the Group Manager MUST perform the following actions, when
the group is rekeyed and the group shifts to the next version V' = (V
+ 1) of the group keying material.
1. The Group Manager rekeys the group. This includes also
distributing the set of stale Sender IDs X associated to the old
group keying material with version V (see Section 2.2).
2. After completing the group rekeying, the Group Manager creates a
new empty set X' associated to the new version V' of the newly
established group keying material, i.e., V' = (V + 1).
3. If the current collection of stale Sender IDs has size N, the
Group Manager deletes the oldest set in the collection.
4. The Group Manager adds the new set X' to the collection of stale
Sender IDs, as the most recent set.
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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 to use.
To this end, this profile uses the Authorization Information Format
(AIF) [I-D.ietf-ace-aif], and defines the following AIF specific data
model AIF-OSCORE-GROUPCOMM.
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.
Then, for each scope entry:
* the object identifier ("Toid") is specialized as a CBOR text
string, specifying the group name for the scope entry;
* the permission set ("Tperm") is specialized as a CBOR unsigned
integer with value R, specifying the role(s) that the client
wishes to take in the group (REQ2). 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 table in Figure 1.
- the set of N numbers is converted into the single value R, by
taking each numeric identifier X_1, X_2, ..., X_N to the power
of two, and then computing the inclusive OR of the binary
representations of all the power values.
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+-----------+-------+-------------------------------------------------+
| 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 the OSCORE group
The CDDL [RFC8610] definition of the AIF-OSCORE-GROUPCOMM data model
is as follows:
AIF-OSCORE-GROUPCOMM = AIF_Generic<path, permissions>
path = tstr ; Group name
permissions = uint . bits roles
roles = &(
Requester: 1,
Responder: 2,
Monitor: 3,
Verifier: 4
)
Future specifications that define new roles MUST register a
corresponding numeric identifier in the "Group OSCORE Roles" Registry
defined in Section 23.11 of this document.
4. Joining Node to Authorization Server
This section describes how the joining node interacts with the AS in
order to be authorized to join an OSCORE group under a given Group
Manager. In particular, it considers a joining node that intends to
contact that Group Manager for the first time.
The message exchange between the joining node and the AS consists of
the messages Authorization Request and Authorization Response defined
in Section 3 of [I-D.ietf-ace-key-groupcomm]. Note that what is
defined in [I-D.ietf-ace-key-groupcomm] applies, and only additions
or modifications to that specification are defined here.
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4.1. 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:
- 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. In particular, 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, computed as defined in Section 3 (REQ2)
from the numerical abbreviations defined in Figure 1 for
each requested role (OPT7).
4.2. 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 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 4.1.
Furthermore, if the AS uses the extended format of scope defined in
Section 6 of [I-D.ietf-ace-key-groupcomm] for the 'scope' claim of
the Access Token, the first element of the CBOR sequence [RFC8742]
MUST be the CBOR integer with value SEM_ID_TBD, defined in
Section 23.13 of this document (REQ24). This indicates that the
second element of the CBOR sequence, as conveying the actual access
control information, follows the scope semantics defined for this
application profile in Section 3 of this document.
5. 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 5.1 to Section 5.4 of this document.
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Furthermore, Section 5.5 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 (REQ8).
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]) (REQ1).
The Resource Type (rt=) Link Target Attribute value "core.osc.gm" is
registered in Section 23.12 (REQ7), 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].
5.1. ace-group/GROUPNAME/active
This resource implements a GET handler.
5.1.1. GET Handler
The handler expects a GET request.
The handler verifies that the group name in the /ace-group/GROUPNAME/
active path is a subset of the 'scope' stored in the Access Token
associated to the requesting client.
The handler also verifies that the roles granted to the requesting
client in the group allow it to perform this operation on this
resource (REQ8). If either verification fails, the Group Manager
MUST respond with a 4.01 (Unauthorized) error message.
Additionally, the handler verifies that the requesting client is a
current member of the group. If verification fails, the Group
Manager MUST respond with a 4.01 (Unauthorized) error message. The
response MUST have Content-Format set to application/ace-
groupcomm+cbor and is formatted as defined in Section 4 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 the verifications above succeed, the handler returns a 2.05
(Content) message, specifying the current status of the group, i.e.,
active or inactive. The payload of the response is formatted as
defined in Section 16.
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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].
5.2. ace-group/GROUPNAME/gm-pub-key
This resource implements a GET handler.
5.2.1. GET Handler
The handler expects a GET request.
The handler verifies that the group name in the /ace-group/GROUPNAME/
gm-pub-key path is a subset of the 'scope' stored in the Access Token
associated to the requesting client.
The handler also verifies that the roles granted to the requesting
client allow it to perform this operation on this resource (REQ8).
If either verification fails, the Group Manager MUST respond with a
4.01 (Unauthorized) error message.
If the requesting client is not a current group member and GROUPNAME
denotes a pairwise-only group, the Group Manager MUST respond with a
4.00 (Bad Request) error message. The response MUST have Content-
Format set to application/ace-groupcomm+cbor and is formatted as
defined in Section 4 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 the verifications above succeed, the handler returns a 2.05
(Content) message, specifying the Group Manager's public key together
with a proof-of-possession evidence. 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 12.
5.3. ace-group/GROUPNAME/verif-data
This resource implements a GET handler.
5.3.1. GET Handler
The handler expects a GET request.
The handler verifies that the group name in the /ace-group/GROUPNAME/
verif-data path is a subset of the 'scope' stored in the Access Token
associated to the requesting client.
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The handler also verifies that the roles granted to the requesting
client allow it to perform this operation on this resource (REQ8).
If either verification fails, the Group Manager MUST respond with a
4.01 (Unauthorized) error message.
If the requesting client is a current group member, the Group Manager
MUST respond with a 4.01 (Unauthorized) error message. The response
MUST have Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4 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
respond with a 4.00 (Bad Request) error message. The response MUST
have Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4 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 the verifications above succeed, the handler returns a 2.05
(Content) message, specifying data that allows also a 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 13.
5.4. ace-group/GROUPNAME/stale-sids
This resource implements a FETCH handler.
5.4.1. 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.
The handler verifies that the group name in the /ace-group/GROUPNAME/
stale-sids path is a subset of the 'scope' stored in the Access Token
associated to the requesting client.
The handler also verifies that the roles granted to the requesting
client allow it to perform this operation on this resource (REQ8).
If either verification fails, the Group Manager MUST respond with a
4.01 (Unauthorized) error message.
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Additionally, the handler verifies that the requesting client is a
current member of the group. If verification fails, the Group
Manager MUST respond with a 4.01 (Unauthorized) error message. The
response MUST have Content-Format set to application/ace-
groupcomm+cbor and is formatted as defined in Section 4 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 the verifications above succeed, the handler returns a 2.05
(Content) message, specifying data that allows the requesting client
to delete the Recipient Contexts and public keys associated to 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 20.3.1.
5.5. 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.
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+--------------------------------+--------+-------+-------+-------+
| Resource | Type1 | Type2 | Type3 | Type4 |
+--------------------------------+--------+-------+-------+-------+
| ace-group/ | F | F | F | - |
+--------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/ | G Po | G Po | Po * | Po |
+--------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/active | G | G | - | - |
+--------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/gm-pub-key | G | G | G | - |
+--------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/verif-data | - | - | G | - |
+--------------------------------+--------+-------+-------+-------+
| ace-group/GROUPNAME/pub-key | G F | G F | G F | - |
+--------------------------------+--------+-------+-------+-------+
| 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 | | | | |
+--------------------------------+--------+-------+-------+-------+
Type1 = Member as Requester and/or Responder | G = GET
Type2 = Member as Monitor | F = FETCH
Type3 = Non-member (authorized to be Verifier) | Po = POST
(*) = cannot join the group as Verifier | Pu = PUT
Type4 = Non-member (not authorized to be Verifier) | D = DELETE
Figure 2: Admitted CoAP Methods on the Group Manager Resources
6. Token POST and Group Joining
The rest of this section describes the interactions between the
joining node and the Group Manager, i.e., the sending of the Access
Token and the Request-Response exchange to join the OSCORE group.
The message exchange between the joining node and the Group Manager
consists of the messages defined in Sections 3.3 and 4.3 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 here.
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A signature verifier provides the Group Manager with an Access Token,
as described in Section 6.1, just as any another joining node does.
However, unlike candidate group members, it does not join any OSCORE
group, i.e., it does not perform the joining process defined in
Section 6.2. After successfully posting an Access Token, a signature
verifier is authorized to perform only the operations specified in
Section 10, to retrieve the public keys of group members, and only
for the OSCORE groups specified in the validated Access Token. The
Group Manager MUST respond with a 4.01 (Unauthorized) error message,
in case a signature verifier attempts to access any other endpoint
than /ace-group/GROUPNAME/pub-key at the Group Manager.
6.1. Token Post
The Token post exchange is defined in Section 3.3 of
[I-D.ietf-ace-key-groupcomm].
Additionally to what defined in [I-D.ietf-ace-key-groupcomm], the
following applies.
* The CoAP POST request MAY additionally contain the following
parameters, which, if included, MUST have the corresponding
values:
- 'ecdh_info' defined in Section 6.1.1, encoding the CBOR simple
value Null to require information on the ECDH algorithm, the
ECDH algorithm parameters, the ECDH key parameters and on the
exact encoding of public keys used in the group, in case the
joining node supports the pairwise mode of Group OSCORE
[I-D.ietf-core-oscore-groupcomm].
- 'gm_dh_pub_keys' defined in Section 6.1.2, encoding the CBOR
simple value Null to require the Diffie-Hellman public key of
the Group Manager in the group, 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 a 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 6.2).
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The 'kdcchallenge' parameter MAY be omitted from the 2.01
(Created) response, if the 'scope' of the Access Token specifies
only the role "monitor" or only the role "verifier" or both of
them, 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.
- 'sign_alg' takes value from the "Value" column of the "COSE
Algorithms" Registry [COSE.Algorithms].
- 'sign_parameters' is a CBOR array. Its format and value are
the same 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' is a CBOR array. Its format and value
are the same 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).
- 'pub_key_enc' 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 an
encoding that MUST explicitly provide the full 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 public
key encodings are CWTs [RFC8392], unprotected CWT claim sets
[I-D.ietf-rats-uccs], X.509 certificates [RFC7925] and C509
certificates [I-D.ietf-cose-cbor-encoded-cert]. Further
encodings 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 unprotected CWT claim sets, there is a pending
registration requested by draft-ietf-lake-edhoc. ]
[ As to C509 certificates, there is a pending registration
requested by draft-ietf-cose-cbor-encoded-cert. ]
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This format is consistent with every signature algorithm currently
considered in [I-D.ietf-cose-rfc8152bis-algs], 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.
* If 'ecdh_info' is included in the request, the Group Manager MAY
include in the response the 'ecdh_info' parameter defined in
Section 6.1.1, with the same encoding. Note that the field 'id'
takes as value the group name, or array of group names, for which
the corresponding 'ecdh_info_entry' applies to.
* If 'gm_dh_pub_keys' is included in the 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 in the response
the 'gm_dh_pub_keys' parameter defined in Section 6.1.2, with the
same encoding. Otherwise, the Group Manager MAY include the
'gm_dh_pub_keys' parameter. Note that the field 'id' takes as
value the group name, or array of group names, for which the
corresponding 'gm_dh_pub_keys' 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 previously retrieved this information by other means. For
example, information conveyed in the 'sign_info' and 'ecdh_info'
parameters can be obtained 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 (OPT1).
Additionally, if allowed by the used transport profile of ACE, the
joining node may instead provide the Access Token to the Group
Manager by other means, e.g., during a secure session establishment
(see Section 3.3.2 of [I-D.ietf-ace-dtls-authorize]).
6.1.1. 'ecdh_info' Parameter
The 'ecdh_info' parameter is an OPTIONAL parameter of the Token Post
response message defined in Section 5.10.1 of
[I-D.ietf-ace-oauth-authz].
This parameter is used to require and retrieve from the Group Manager
information and parameters about the ECDH algorithm and about the
public keys to be used in the OSCORE group to compute a static-static
Diffie-Hellman shared secret [NIST-800-56A], in case the group uses
the pairwise mode of Group OSCORE [I-D.ietf-core-oscore-groupcomm].
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When used in the request, the 'ecdh_info' parameter encodes the CBOR
simple value Null, to require information and parameters on the ECDH
algorithm and on the public keys to be used to compute Diffie-Hellman
shared secrets in the OSCORE group.
The CDDL notation [RFC8610] of the 'ecdh_info' parameter formatted as
in the request is given below.
ecdh_info_req = nil
The 'ecdh_info' parameter of the 2.01 (Created) response is a CBOR
array of one or more elements. The number of elements is at most the
number of OSCORE groups the client has been authorized to join.
Each element contains information about ECDH parameters and about
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 particular 'id' 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
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 'pub_key_enc' is a CBOR integer indicating the
encoding of public keys used in the OSCORE group identified by
'gname'. It takes value from the "Label" column of the "COSE
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Header Parameters" Registry [COSE.Header.Parameters] (REQ6).
Acceptable values denote an encoding that MUST explicitly provide
the full set of information related to the public key algorithm,
including, e.g., the used elliptic curve (when applicable). The
same considerations and guidelines for the 'pub_key_enc' element
of 'sign_info' (see Section 6.1) apply.
The CDDL notation [RFC8610] of the 'ecdh_info' parameter formatted as
in the response is given below.
ecdh_info_res = [ + ecdh_info_entry ]
ecdh_info_entry =
[
id : gname / [ + gname ],
ecdh_alg : int / tstr,
ecdh_parameters : [ any ],
ecdh_key_parameters : [ any ],
pub_key_enc = int
]
gname = tstr
This format is consistent with every ECDH algorithm currently
considered in [I-D.ietf-cose-rfc8152bis-algs], 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.
6.1.2. 'gm_dh_pub_keys' Parameter
The 'gm_dh_pub_keys' parameter is an OPTIONAL parameter of the Token
Post response message defined in Section 5.10.1 of
[I-D.ietf-ace-oauth-authz].
This parameter is used to require and retrieve from the Group Manager
its Diffie-Hellman public key used in the OSCORE group. The Group
Manager has specifically a Diffie-Hellman public key if and only if
the OSCORE group is a pairwise-only group. In this case, the early
retrieval of the Group Manager's public key is necessary in order for
the joining node to prove the possession of its own private key, upon
joining the group (see Section 6.2).
When used in the request, the 'gm_dh_pub_keys' parameter encodes the
CBOR simple value Null, to require the Diffie-Hellman public key that
the Group Manager uses in the OSCORE group.
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The CDDL notation [RFC8610] of the 'gm_dh_pub_keys' parameter
formatted as in the request is given below.
gm_dh_pub_keys_req = nil
The 'gm_dh_pub_keys' parameter of the 2.01 (Created) response is a
CBOR array of one or more elements. The number of elements is at
most the number of OSCORE groups the client has been authorized to
join.
Each element 'gm_dh_pub_keys_entry' contains information about the
Group Manager's Diffie-Hellman public keys, 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 'pub_key_enc' is a CBOR integer indicating the
encoding of public keys 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 an encoding that MUST explicitly provide
the full set of information related to the public key algorithm,
including, e.g., the used elliptic curve (when applicable). The
same considerations and guidelines for the 'pub_key_enc' element
of 'sign_info' (see Section 6.1) apply.
* The third element 'pub_key' is a CBOR byte string, which encodes
the Group Manager's Diffie-Hellman public key in its original
binary representation made available to other endpoints in the
group. In particular, the original binary representation complies
with the encoding specified by the 'pub_key_enc' parameter. Note
that the public key provides the full 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 'gm_dh_pub_keys' parameter
formatted as in the response is given below.
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gm_dh_pub_keys_res = [ + gm_dh_pub_keys_entry ]
gm_dh_pub_keys_entry =
[
id : gname / [ + gname ],
pub_key_enc = int,
pub_key = bstr
]
gname = tstr
6.2. Sending the Joining Request
The joining node requests to join the OSCORE group by sending a
Joining Request message to the related group-membership resource at
the Group Manager, as per Section 4.3 of
[I-D.ietf-ace-key-groupcomm].
Additionally to what defined in Section 4.1.2.1 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 'get_pub_keys' parameter is present only if the joining node
wants to retrieve the public keys of the group members from the
Group Manager during the joining process (see Section 7).
Otherwise, this parameter MUST NOT be present.
If this parameter is present and its value is non-null, 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 a 8-byte long
random nonce.
* The proof-of-possession (PoP) evidence included in
'client_cred_verify' is computed as defined below (REQ20). In
either case, the N_S used to build the PoP input is as defined in
Section 6.2.1.
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- 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.
- 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.
6.2.1. Value of the N_S Challenge
The value of the N_S challenge is determined as follows.
1. If the joining node has posted the Access Token to the /authz-
info endpoint of the Group Manager as in Section 6.1, 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 2.01 (Created) response to the
Token POST, or the one possibly specified in a 4.00 (Bad Request)
response to a following Joining Request (see Section 6.3).
2. If the Token posting has relied on the DTLS profile of ACE
[I-D.ietf-ace-dtls-authorize] with the Access Token as content of
the "psk_identity" field of the ClientKeyExchange message
[RFC6347], 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 23.7 of this document.
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It is up to applications to define how N_S is computed in further
alternative settings.
Section 22.3 provides security considerations on the reusage of the
N_S challenge.
6.3. Receiving the Joining Request
The Group Manager processes the Joining Request as defined in
Section 4.1.2.1 of [I-D.ietf-ace-key-groupcomm]. Additionally, the
following applies.
* The Group Manager MUST return a 5.03 (Service Unavailable)
response in case the OSCORE group that the joining node has been
trying to join is currently inactive (see Section 5.1). The
response MUST have Content-Format set to application/ace-
groupcomm+cbor and is formatted as defined in Section 4 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST
be set to 9 ("Group currently not active").
* In case the joining node is not going to join the group
exclusively as monitor, the Group Manager MUST return a 5.03
(Service Unavailable) response if there are currently no OSCORE
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 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field MUST
be set to 4 ("No available node identifiers").
* In case the joining node is not going to join the group
exclusively as monitor and the Joining Request does not include
the 'client_cred' parameter, the joining process fails if the
Group Manager either: i) does not store a public key with an
accepted format for the joining node; or ii) stores multiple
public keys with an accepted format for the joining node.
* In order to verify the PoP evidence contained in
'client_cred_verify', the Group Manager proceeds as follows.
- As PoP input, the Group Manager uses the value of the 'scope'
parameter from the Joining 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. In
particular, N_S is determined as described in Section 6.2.1,
while N_C is the nonce provided in the 'cnonce' parameter of
the Joining Request;
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- As public key of the joining node, the Group Manager uses
either the one retrieved from the 'client_cred' parameter of
the Joining Request, or the one already stored as acquired from
previous interactions with the joining node.
- The Group Manager verifies the PoP evidence as defined below.
o 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.
o 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 Joining
Request (see Section 6.2), 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 Joining
Request.
* A 4.00 (Bad Request) 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 7 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]. In
particular, it includes a single element 'sign_info_entry'
pertaining to the OSCORE group that the joining node has tried
to join with the Joining 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 23.3. This parameter has the same
format of 'ecdh_info_res' defined in Section 6.1.1. In
particular, it includes a single element 'ecdh_info_entry'
pertaining to the OSCORE group that the joining node has tried
to join with the Joining Request.
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- If the group is a pairwise-only group, the CBOR map MUST
contain the 'gm_dh_pub_keys' parameter, whose CBOR label is
defined in Section 23.3. This parameter has the same format of
'gm_dh_pub_keys_res' defined in Section 6.1.2. In particular,
it includes a single element 'gm_dh_pub_keys_entry' pertaining
to the OSCORE group that the joining node has tried to join
with the Joining Request.
- The CBOR map MAY include the 'kdcchallenge' parameter, whose
CBOR label is defined in Section 7 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
Joining Request (see Section 6.2). In such a case the Group
Manager MUST store the newly generated value as the
'kdcchallenge' value associated to the joining node, possibly
replacing the currently stored value.
* The Group Manager MUST return a 4.00 (Bad Request) response in
case the 'scope' parameter is not present in the Joining Request,
or if it is present and specifies any set of roles not included in
the following list: "requester", "responder", "monitor",
("requester", "responder"). Future specifications that define a
new role MUST define possible sets of roles including the new one
and existing ones, that are acceptable to specify in the 'scope'
parameter of a Joining Request.
* The Group Manager MUST return a 4.00 (Bad Request) response in
case the Joining Request includes the 'client_cred' parameter but
does not include both the 'cnonce' and 'client_cred_verify'
parameters.
* The Group Manager MUST return a 4.00 (Bad Request) response in
case an eligible public key for the joining node is neither
present in the 'client_cred' parameter nor already stored.
* The Group Manager MAY return a 4.00 (Bad Request) 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 public key of the joining node from the 'client_cred'
parameter:
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o 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
o 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].
This prevents 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 2.3.1 of [I-D.ietf-core-oscore-groupcomm]).
* When receiving a 4.00 (Bad Request) response, the joining node
SHOULD send a new Joining Request to the Group Manager, where:
- The 'cnonce' parameter MUST include a new dedicated nonce N_C
generated by the joining node.
- The 'client_cred' parameter MUST include a public key
compatible with the encoding, signature or ECDH algorithm, and
possible associated parameters indicated by the Group Manager.
- The 'client_cred_verify' parameter MUST include a PoP evidence
computed as described in Section 6.2, by using the public key
indicated 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.
6.4. Sending the Joining Response
If the processing of the Joining Request described in Section 6.3 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 4.1.2.1 of
[I-D.ietf-ace-key-groupcomm].
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 specified in the Access Token (see Section 4.2).
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Consistently with Section 3.1 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 most recent set of stale Sender
IDs, in the collection associated to the group (see
Section 2.2.1).
* The Group Manager stores the association between i) the public key
of the joining node; and ii) the Group Identifier (Gid), i.e., the
OSCORE ID Context, associated to 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 meterial necessary to
participate in the group communication. This success Joining
Response is formatted as defined in Section 4.1.2.1 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 23.4 of
this document.
* 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 [I-D.ietf-ace-oscore-profile]. In particular, it
contains the additional parameters 'group_senderId',
'pub_key_enc', 'sign_enc_alg', 'sign_alg', 'sign_params',
'ecdh_alg' and 'ecdh_params' defined in Section 23.6 of this
document.
More specifically, the 'key' parameter is composed as follows.
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- The 'hkdf' parameter, if present, has as value the HKDF
Algorithm used in the OSCORE group. 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 MUST be present and 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, if present, has as value the
OSCORE Sender ID assigned to the joining node by the Group
Manager, as described above. This parameter MUST NOT be
present if the node joins the OSCORE group exclusively with the
role of monitor, according to what specified in the Access
Token (see Section 4.2). In any other case, this parameter
MUST be present.
- The 'pub_key_enc' parameter MUST be present and specifies the
encoding of public keys used in the OSCORE group. 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 an encoding that MUST explicitly provide the full
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 public
key encodings are CWTs [RFC8392], unprotected CWT claim sets
[I-D.ietf-rats-uccs], X.509 certificates [RFC7925] and C509
certificates [I-D.ietf-cose-cbor-encoded-cert]. Further
encodings 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 unprotected CWT claim sets, there is a pending
registration requested by draft-ietf-lake-edhoc. ]
[ As to C509 certificates, there is a pending registration
requested by draft-ietf-cose-cbor-encoded-cert. ]
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- The 'sign_enc_alg' parameter MUST NOT be present if the OSCORE
group is a pairwise-only group. Otherwise, it MUST be present
and specifies 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 MUST NOT be present if the OSCORE
group is a pairwise-only group. Otherwise, it MUST be present
and specifies 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 MUST NOT be present if the OSCORE
group is a pairwise-only group. Otherwise, it MUST be present
and specifies the parameters of the Signature Algorithm. This
parameter is a CBOR array, which includes the following two
elements:
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 'alg' parameter MUST NOT be present if the OSCORE group is
a signature-only group. Otherwise, it MUST be present and
specifies the AEAD Algorithm used in the OSCORE group to
encrypt messages protected with the pairwise mode.
- The 'ecdh_alg' parameter MUST NOT be present if the OSCORE
group is a signature-only group. Otherwise, it MUST be present
and specifies 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 MUST NOT be present if the OSCORE
group is a signature-only group. Otherwise, it MUST be present
and specifies the parameters of the Pairwise Key Agreement
Algorithm. This parameter is a CBOR array, which includes the
following two elements:
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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].
The format of 'key' defined above is consistent with every
signature algorithm and ECDH algorithm currently considered in
[I-D.ietf-cose-rfc8152bis-algs], 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.
* 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 23.5 of this document.
* The 'pub_keys' parameter, if present, includes the public keys
requested by the joining node by means of the 'get_pub_keys'
parameter in the Joining Request.
If the joining node has asked for the public keys of all the group
members, i.e., 'get_pub_keys' had value Null in the Joining
Request, then the Group Manager provides only the public keys of
the group members that are relevant to the joining node. That is,
in such a case, 'pub_keys' includes only: i) the public keys of
the responders currently in the OSCORE group, in case the joining
node is configured (also) as requester; and ii) the public keys 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 public key is specified in the 'pub_keys'
parameter. That is, a group member's Sender ID is used as
identifier for that group member (REQ12).
* The 'group_policies' parameter SHOULD be present, and SHOULD
include the following elements:
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- "Key Update Check Interval" defined in Section 4.1.2.1 of
[I-D.ietf-ace-key-groupcomm], with default value 3600;
- "Expiration Delta" defined in Section 4.1.2.1 of
[I-D.ietf-ace-key-groupcomm], with default value 0.
Furthermore, the CBOR map in the payload of the Joining Response MUST
also include the following new parameters, defined in Section 23.3 of
this document.
* The 'kdc_nonce' parameter, which is a CBOR byte string encoding a
dedicated nonce N_KDC generated by the Group Manager. For N_KDC,
it is RECOMMENDED to use a 8-byte long random nonce.
* The 'kdc_cred' parameter, which is a CBOR byte string encoding the
Group Manager's public key in its original binary representation.
The Group Manager's public key MUST be compatible with the
encoding, signature or ECDH algorithm, and possible associated
parameters used in the OSCORE group.
* The 'kdc_cred_verify' parameter, which is a CBOR byte string
encoding a 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.
- 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 to the public key
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.
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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.
As a last action, 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 3.1 of
[I-D.ietf-core-oscore-groupcomm]). This applies also in case the
node is in fact re-joining the group; in such a case, the newly
determined Birth Gid overwrites the one currently stored.
6.5. Receiving the Joining Response
Upon receiving the Joining Response, the joining node retrieves the
Group Manager's public key 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 Joining Response
as defined below.
* 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, 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 6.4), with the difference
that the joining node uses its own Diffie-Hellman private key and
the Diffie-Hellman public key of the Group Manager. The
verification succeeds if and only if the recomputed MAC is equal
to the MAC conveyed as PoP evidence in the Joining Response.
In case of failed verification of the PoP evidence, the joining node
MUST stop processing the Joining Response and MAY send a new Joining
Request to the Group Manager (see Section 6.2).
In case of successful verification of the PoP evidence, the joining
node uses the information received in the Joining Response to set up
the Group OSCORE Security Context, as described in Section 2 of
[I-D.ietf-core-oscore-groupcomm]. If the following parameters were
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not included in the 'key' parameter of the Joining Response, the
joining node considers the following default values, 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.
In addition, the joining node maintains an association between each
public key retrieved from the 'pub_keys' 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 public key is not associated to
the role "Requester".
* The joining node MUST NOT process an incoming response message, if
protected by a group member whose public key is not associated to
the role "Responder".
* The joining node MUST NOT use the pairwise mode of Group OSCORE to
process messages in the group, if the Joining 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 20). As a consequence, the joining node is not able to
access secure communication in the OSCORE group occurred prior its
joining.
7. Public Keys of Joining Nodes
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 public
key from a trusted key repository, in order to verify source
authenticity of incoming group messages.
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As also discussed in [I-D.ietf-core-oscore-groupcomm], the Group
Manager acts as trusted repository of the public keys of the group
members, and provides those public keys to group members if requested
to. Upon joining an OSCORE group, a joining node is thus expected to
provide its own public key to the Group Manager.
In particular, one of the following four cases can occur when a new
node joins an OSCORE group.
* 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
public key to the Group Manager, which thus does not have to
perform any check related to the public key encoding, to a
signature or ECDH algorithm, and to possible associated
parameters. In case that joining node still provides a public key
in the 'client_cred' parameter of the Joining Request (see
Section 6.2), the Group Manager silently ignores that parameter,
as well as the related parameters 'cnonce' and
'client_cred_verify'.
* The Group Manager already acquired the public key of the joining
node during a past joining process. In this case, the joining
node MAY choose not to provide again its own public key to the
Group Manager, in order to limit the size of the Joining Request.
The joining node MUST provide its own public key again if it has
provided the Group Manager with multiple public keys during past
joining processes, intended for different OSCORE groups. If the
joining node provides its own public key, the Group Manager
performs consistency checks as per Section 6.3 and, in case of
success, considers it as the public key associated to 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. The proof-of-possession key is compatible with the encoding,
as well as with the signature or ECDH algorithm, and with
possible associated parameters used in the OSCORE group.
Then, the Group Manager considers the proof-of-possession key
as the public key associated to the joining node in the OSCORE
group. If the joining node is aware that the proof-of-
possession key is also valid for the OSCORE group, it MAY not
provide it again as its own public key to the Group Manager.
The joining node MUST provide its own public key again if it
has provided the Group Manager with multiple public keys
during past joining processes, intended for different OSCORE
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groups. If the joining node provides its own public key in
the 'client_cred' parameter of the Joining Request (see
Section 6.2), the Group Manager performs consistency checks as
per Section 6.3 and, in case of success, considers it as the
public key associated to the joining node in the OSCORE group.
2. The proof-of-possession key is not compatible with the
encoding, or with the signature or algorithm, and with
possible associated parameters used in the OSCORE group. In
this case, the joining node MUST provide a different
compatible public key to the Group Manager in the
'client_cred' parameter of the Joining Request (see
Section 6.2). Then, the Group Manager performs consistency
checks on this latest provided public key as per Section 6.3
and, in case of success, considers it as the public key
associated to 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
public key in the 'client_cred' parameter of the Joining Request
targeting the group-membership endpoint (see Section 6.2).
8. Retrieval of 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 Joining 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.
8.1. Retrieval of 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.
In particular, 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 4.1.2.2 of [I-D.ietf-ace-key-groupcomm]. The Key
Distribution Response is formatted as defined in Section 4.1.2.2 of
[I-D.ietf-ace-key-groupcomm]. In addition:
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* The 'key' parameter is formatted as defined in Section 6.4 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].
8.2. Retrieval of 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.
In particular, 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 4.1.6.2 of [I-D.ietf-ace-key-groupcomm]. The Key
Distribution Response is formatted as defined in Section 4.1.6.2 of
[I-D.ietf-ace-key-groupcomm]. In addition:
* The 'key' parameter is formatted as defined in Section 6.4 of this
document. In particular, if the requesting group member has
exclusively the role of monitor, no 'group_SenderId' is specified
within the 'key' parameter.
Note that, in any other case, the current Sender ID of the group
member is not specified as a separate parameter, but rather
specified as '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].
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9. Requesting a Change of Keying Material
As discussed in Section 2.4.2 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 4.5 of
[I-D.ietf-ace-key-groupcomm]. In particular, 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 4.1.6.1 of [I-D.ietf-ace-key-groupcomm],
with the following additions.
The Group Manager MUST return a 5.03 (Service Unavailable) response
in case the OSCORE group identified by GROUPNAME is currently
inactive (see Section 5.1). The response MUST have Content-Format
set to application/ace-groupcomm+cbor and is formatted as defined in
Section 4 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 4.01 (Unauthorized)
error response. The response MUST have Content-Format set to
application/ace-groupcomm+cbor and is formatted as defined in
Section 4 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 20), and replies to the group member with a group
rekeying message as defined in Section 20, providing the new
group keying material. Then, the Group Manager rekeys the
rest of the OSCORE group, as discussed in Section 20.
The Group Manager SHOULD perform a group rekeying only if
already scheduled to occur shortly, e.g., according to an
application-dependent 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 (OPT8).
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* 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 4.1.6.1 of
[I-D.ietf-ace-key-groupcomm]. In particular, the CBOR Map in
the response payload includes a single parameter
'group_SenderId' defined in Section 23.3 of this document,
specifying the new Sender ID of the group member encoded as a
CBOR byte string.
Consistently with Section 2.4.3.1 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.
Furthermore, the Group Manager MUST add the old, relinquished
Sender ID of the group member to the most recent set of stale
Sender IDs, in the collection associated to the group (see
Section 2.2.1).
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 of
[I-D.ietf-ace-key-groupcomm]. The value of the 'error' field
MUST be set to 4 ("No available node identifiers").
10. Retrieval of Public Keys and Roles of Group Members
A group member or a signature verifier may need to retrieve the
public keys of (other) group members. To this end, the group member
or signature verifier sends a Public Key Request message to the Group
Manager, as per Section 4.6 of [I-D.ietf-ace-key-groupcomm]. In
particular, it sends the request to the endpoint /ace-
group/GROUPNAME/pub-key at the Group Manager.
If the Public Key Request uses the method FETCH, the Public Key
Request is formatted as defined in Section 4.1.3.1 of
[I-D.ietf-ace-key-groupcomm]. In particular:
* Each element (if any) of the inner CBOR array 'role_filter' is
formatted as in the inner CBOR array 'role_filter' of the
'get_pub_keys' parameter of the Joining Request when the parameter
value is non-null (see Section 6.2).
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* 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 public key is requested (REQ12).
Upon receiving the Public Key Request, the Group Manager processes it
as per Section 4.1.3.1 or Section 4.1.3.2 of
[I-D.ietf-ace-key-groupcomm], depending on the request method being
FETCH or GET, respectively. Additionally, if the Public Key Request
uses the method FETCH, the Group Manager silently ignores node
identifiers included in the 'get_pub_keys' parameter of the request
that are not associated to any current group member.
The success Public Key Response is formatted as defined in
Section 4.1.3.1 or Section 4.1.3.2 of [I-D.ietf-ace-key-groupcomm],
depending on the request method being FETCH or GET, respectively.
11. Update of Public Key
A group member may need to provide the Group Manager with its new
public key 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 public key is not compatible
with them.
To this end, the group member sends a Public Key Update Request
message to the Group Manager, as per Section 4.7 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 Joining Request for the OSCORE group in question, as
defined in Section 6.2 (REQ20).
In particular, the group member sends a CoAP POST request to the
endpoint /ace-group/GROUPNAME/nodes/NODENAME/pub-key at the Group
Manager.
Upon receiving the Public Key Update Request, the Group Manager
processes it as per Section 4.1.7.1 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 per point (1) in Section 6.2.1 (REQ21).
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* The Group Manager verifies the PoP challenge included in
'client_cred_verify' in the same way taken when processing a
Joining Request for the OSCORE group in question, as defined in
Section 6.3 (REQ20).
* The Group Manager MUST return a 5.03 (Service Unavailable)
response in case the OSCORE group identified by GROUPNAME is
currently inactive (see Section 5.1). The response MUST have
Content-Format set to application/ace-groupcomm+cbor and is
formatted as defined in Section 4 of [I-D.ietf-ace-key-groupcomm].
The value of the 'error' field MUST be set to 9 ("Group currently
not active").
* 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 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 public key of the group member;
and ii) the Group Identifier (Gid), i.e., the OSCORE ID Context,
associated to 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.
12. Retrieval of the Group Manager's Public Key
A group member or a signature verifier may need to retrieve the
public key of the Group Manager. To this end, the group member or
signature verifier sends a Group Manager Public Key Request message
to the Group Manager.
In particular, it sends a CoAP GET request to the endpoint /ace-
group/GROUPNAME/gm-pub-key at the Group Manager defined in
Section 5.2 of this document, where GROUPNAME is the name of the
OSCORE group.
The payload of the 2.05 (Content) Group Manager Public Key Response
is a CBOR map, which MUST contain the following parameters defined in
Section 23.3.
* The 'kdc_nonce' parameter, specifying a nonce generated by the
Group Manager. This parameter is encoded like the 'kdc_nonce'
parameter in the Joining Response (see Section 6.4).
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* The 'kdc_cred' parameter, specifying the Group Manager's public
key. This parameter is encoded like the 'kdc_cred' parameter in
the Joining Response (see Section 6.4).
* The 'kdc_cred_verify' parameter, specifying a proof-of-possession
(PoP) evidence computed by the Group Manager. This parameter is
encoded like the 'kdc_cred_verify' parameter in the Joining
Response (see Section 6.4).
The PoP evidence is computed over the nonce specified in the
'kdc_nonce' parameter and taken as PoP input, by means of the same
method used when preparing the Joining Response (see Section 6.4).
In particular, if the group is a pairwise-only group, the Group
Manager computes IKM by using its own Diffie-Hellman private key
as well as the Diffie-Hellman public key of the requesting client.
Upon receiving a 2.05 (Content) Group Manager Public Key Response,
the group member or signature verifier retrieves the Group Manager's
public key from the 'kdc_cred' parameter, and MUST verify the proof-
of-possession (PoP) evidence specified in the 'kdc_cred_verify'
parameter. That is:
* A group member verifies the PoP evidence by means of the same
method used when processing the Joining Response (see
Section 6.4). In particular, if the group is a pairwise-only
group, the group member computes IKM by using its own Diffie-
Hellman private key as well as the Diffie-Hellman public key of
the Group Manager.
* A signature verifier verifies the PoP evidence as a signature, by
using the public key of the Group Manager, as well as the
signature algorithm used in the OSCORE group and possible
corresponding parameters. Note that a signature verifier would
not receive a successful response from the Group Manager, in case
GROUPNAME denotes a pairwise-only group.
In case of successful verification of the PoP evidence, the group
member or signature verifier MUST store the obtained Group Manager's
public key, possibly replacing the currently stored one.
Figure 3 gives an overview of the exchange described above, while
Figure 4 shows an example.
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Group Group
Member Manager
| |
| Group Manager Public Key Request |
|------------------------------------------------------------>|
| GET ace-group/GROUPNAME/gm-pub-key |
| |
|<---- Group Manager Public Key Response: 2.05 (Content) -----|
| |
Figure 3: Message Flow of Group Manager Public Key Request-Response
Request:
Header: GET (Code=0.01)
Uri-Host: "kdc.example.com"
Uri-Path: "ace-group"
Uri-Path: "g1"
Uri-Path: "gm-pub-key"
Payload: -
Response:
Header: Content (Code=2.05)
Content-Format: "application/ace-groupcomm+cbor"
Payload (in CBOR diagnostic notation, with PUB_KEY_GM
and POP_EVIDENCE being CBOR byte strings):
{
"kdc_nonce": h'25a8991cd700ac01',
"kdc_cred": PUB_KEY_GM,
"kdc_cred_verify": POP_EVIDENCE
}
Figure 4: Example of Group Manager Public Key Request-Response
13. Retrieval of 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.
In particular, it sends a CoAP GET request to the endpoint /ace-
group/GROUPNAME/verif-data at the Group Manager defined in
Section 5.3 of this document, where GROUPNAME is the name of the
OSCORE group.
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The payload of the 2.05 (Content) Signature Verification Data
Response is a CBOR map, which has the format used for the Joining
Response message in Section 6.4, with the following differences.
* From the Joining Response message, only the parameters 'gkty',
'key', 'num', 'exp' and 'ace-groupcomm-profile' are present. In
particular, the 'key' parameter includes only the following data.
- The parameters 'hkdf', 'contextId', 'pub_key_enc',
'sign_enc_alg', 'sign_alg', 'sign_params'. These parameters
MUST be present.
- The parameters 'alg' and 'ecdh_alg'. These parameter 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 23.3. 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
messages to verify, that can be retrieved as defined in Section 10;
and the public key of the Group Manager, which can be retrieved as
defined in Section 12.
Figure 5 gives an overview of the exchange described above, while
Figure 6 shows an example.
Signature Group
Verifier Manager
| |
| Signature Verification Data Request |
|------------------------------------------------------------>|
| GET ace-group/GROUPNAME/verif-data |
| |
|<--- Signature Verification Data Response: 2.05 (Content) ---|
| |
Figure 5: 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': -10, ; HKDF SHA-256
'contextId': h'37fc',
'pub_key_enc': 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 6: Example of Signature Verification Data Request-Response
14. Retrieval of 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 4.8 of [I-D.ietf-ace-key-groupcomm]. In particular, 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 4.1.4.1 of [I-D.ietf-ace-key-groupcomm]. The success
Policies Response is formatted as defined in Section 4.1.4.1 of
[I-D.ietf-ace-key-groupcomm].
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15. Retrieval of 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 4.9 of [I-D.ietf-ace-key-groupcomm].
In particular, 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 4.1.5.1 of [I-D.ietf-ace-key-groupcomm]. The success
Version Response is formatted as defined in Section 4.1.5.1 of
[I-D.ietf-ace-key-groupcomm].
16. Retrieval of Group Status
A group member may request the current status of the the OSCORE
group, i.e., active or inactive. To this end, the group member sends
a Group Status Request to the Group Manager.
In particular, the group member sends a CoAP GET request to the
endpoint /ace-group/GROUPNAME/active at the Group Manager defined in
Section 5.1 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 if the group is currently active, or the CBOR
simple value False 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 7 gives an overview of the exchange described above, while
Figure 8 shows an example.
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Group Group
Member Manager
| |
|--- Group Status Request: GET ace-group/GROUPNAME/active --->|
| |
|<---------- Group Status Response: 2.05 (Content) -----------|
| |
Figure 7: 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 8: Example of Group Status Request-Response
17. Retrieval of Group Names and URIs
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 20). 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 public keys from the Group Manager (see
Section 8.1, Section 8.2 and Section 10). 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 public keys from the Group Manager (see
Section 10). 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 public keys 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
either join the group as a candidate group member, get the latest
keying material as a current group member, or retrieve public keys
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 of
[I-D.ietf-ace-key-groupcomm].
In particular, the node sends a CoAP FETCH request to the endpoint
/ace-group at the Group Manager formatted as defined in
Section 4.1.1.1 of [I-D.ietf-ace-key-groupcomm]. Each element of the
CBOR array 'gid' is a CBOR byte string (REQ9), which encodes the Gid
of the group for which the group name and the URI to the group-
membership resource are requested.
Upon receiving the Group Name and URI Retrieval Request, the Group
Manager processes it as per Section 4.1.1.1 of
[I-D.ietf-ace-key-groupcomm]. The success Group Name and URI
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Retrieval Response is formatted as defined in Section 4.1.1.1 of
[I-D.ietf-ace-key-groupcomm]. In particular, each element of the
CBOR array 'gid' is a CBOR byte string (REQ9), 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 MUST NOT maintain an association
between the former pair and any other Gid for that group than the
current, most recent one.
Figure 9 gives an overview of the exchanges described above, while
Figure 10 shows an example.
Group
Node Manager
| |
|---- Group Name and URI Retrieval Request: FETCH ace-group/ --->|
| |
|<--- Group Name and URI Retrieval Response: 2.05 (Content) -----|
| |
Figure 9: Message Flow of Group Name and URI Retrieval Request-
Response
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"]
}
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Figure 10: Example of Group Name and URI Retrieval Request-Response
18. Request to 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 4.10
of [I-D.ietf-ace-key-groupcomm]. In particular, 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 4.1.6.3 of [I-D.ietf-ace-key-groupcomm].
19. Removal of a Group Member
Other than after a spontaneous request to the Group Manager as
described in Section 18, a node may be forcibly removed from the
OSCORE group, e.g., due to expired or revoked authorization.
In either case, the Group Manager "forgets" the Birth Gid currently
associated to the leaving node in the OSCORE group. This was stored
following the Joining Response sent to that node, after its latest
(re-)joining of the OSCORE group (see Section 6.4).
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 only
once, using either of the corresponding methods.
* If, upon joining the group (see Section 6.2), the leaving node
specified a URI in the 'control_uri' parameter defined in
Section 4.1.2.1 of [I-D.ietf-ace-key-groupcomm], the Group Manager
sends a DELETE request targeting the URI specified in the
'control_uri' parameter (OPT9).
* 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) response to the leaving node, as
specified in 4.1.6.2 of [I-D.ietf-ace-key-groupcomm].
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).
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* The Group Manager MUST add the relinquished Sender ID of the
leaving node to the most recent set of stale Sender IDs, in the
collection associated to the group (see Section 2.2.1).
* The Group Manager cancels the association between, on one hand,
the public key of the leaving node and, on the other hand, the Gid
associated to the OSCORE group together with the freed Sender ID
value. The Group Manager deletes the public key of the leaving
node, if that public key 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 20). As a consequence, the leaving node is not able to
acquire the new security parameters and group keying material
distributed after its leaving.
Same considerations in Section 5 of [I-D.ietf-ace-key-groupcomm]
apply here as well, considering the Group Manager acting as KDC.
20. 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.
Consistently with Section 3.1 of [I-D.ietf-core-oscore-groupcomm]:
* The Group Manager can 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.
* 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 6.4). 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, in the collection associated
to the group (see Section 2.2.1), 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 public
keys from the Group Manager and the verification of group messages.
The Group Manager MUST support at least the group rekeying scheme
defined in Section 20.1. Future application profiles may define
alternative message formats and group rekeying schemes, which MUST
comply with the functional steps defined in Section 3.2 of
[I-D.ietf-core-oscore-groupcomm].
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 X' of stale Sender IDs associated to the version of
the newly distributed group keying material. Then, the Group Manager
MUST add the set X' to the collection of stale Sender IDs associated
to the group (see Section 2.2.1).
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 to 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.
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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
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 15) and then possibly requesting the current keying material
(see Section 8.1).
Furthermore, some of these group members can be in multiple groups,
all of which associated to 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 to that Group Manager.
Finally, Section 20.3 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.
20.1. Sending Rekeying Messages
The Group Manager MUST support at least the group rekeying scheme
defined in this section.
The group rekeying messages MUST have Content-Format set to
application/ace-groupcomm+cbor and have the same format used for the
Joining Response message in Section 6.4, with the following
differences.
* From the Joining Response, only the parameters 'gkty', 'key',
'num', 'exp', and 'ace-groupcomm-profile' are present. In
particular, 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.
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* The parameter 'stale_node_ids' MUST also be included, with CBOR
label defined in Section 23.3. This parameter is encoded as a
CBOR array, where each element is encoded as a CBOR byte string.
The CBOR array has to be intended as a set, i.e., the order of its
elements is irrelevant. The parameter is populated as follows.
- The Group Manager creates an empty CBOR array ARRAY.
- The Group Manager considers the collection of stale Sender IDs
associated to the group (see Section 2.2.1), and takes the most
recent set X, i.e., the set associated to 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 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 channel between the Group Manager and the group member
used during the joining process. In particular, each rekeying
message can target the 'control_uri' URI path defined in
Section 4.1.2.1 of [I-D.ietf-ace-key-groupcomm] (OPT9), if provided
by the intended recipient upon joining the group (see Section 6.2).
This distribution approach requires group members to act (also) as
servers, in order to correctly handle unsolicited group rekeying
messages from the Group Manager. In particular, if a group member
and the Group Manager use OSCORE [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
[I-D.ietf-ace-oscore-profile].
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 4.4 of [I-D.ietf-ace-key-groupcomm]. In particular, a group
member may subscribe for updates to the group-membership resource of
the group, at the endpoint /ace-group/GROUPNAME/ of the Group
Manager. This can rely on CoAP Observe [RFC7641] or on a full-
fledged Pub-Sub model [I-D.ietf-core-coap-pubsub] with the Group
Manager acting as Broker.
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20.2. Receiving Rekeying Messages
Once received the new group keying material, a group member proceeds
as follows.
The group member considers the stale Sender IDs received from the
Group Manager. If the group rekeying scheme defined in Section 20.1
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 public key associated to a stale
Sender ID from its list of group members' public keys 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 group rekeying scheme defined in Section 20.1 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 owned 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.
* The group member has missed one or more group rekeying instances.
That is, the old keying material owned 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 20.3.
* The group member has received keying material not newer than the
stored one. That is, the stored keying material owned 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.
20.3. 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.
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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 20.2.
b. The group member has obtained the latest keying material from the
Group Manager, as a response to a Key Distribution Request (see
Section 8.1) or to a Joining Request when re-joining the group (see
Section 6.2). In particular, V is different than V' specified by the
'num' parameter in the response.
c. The group member has obtained the public keys of other group
members, through a Public Key Request-Response exchange with the
Group Manager (see Section 10). In particular, 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 15). In particular, 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.
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 20.3.1), 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 public keys from
its list of group members' public keys 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 public key
associated to a stale Sender ID from its list of group members'
public keys 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.
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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 20.3.1), 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 public keys from
its list of group members' public keys 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 public key
associated to a stale Sender ID from its list of group members'
public keys 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.
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 8.1),
or by re-joining the group (see Section 6.2).
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 6.2). When
doing so, the group member MUST re-join with the same roles it
currently has in the group, and MUST request the Group Manager
for the public keys of all the current group members. That is,
the 'get_pub_keys' parameter of the Joining Request MUST be
present and MUST be set to the CBOR simple value Null.
2. When receiving the Joining Response (see Section 6.5 and
Section 6.5), the group member retrieves the set Z of public keys
specified in the 'pub_keys' parameter.
Then, the group member MUST remove every public key which is not
in Z from its list of group members' public keys used in the
group, and MUST delete each of its Recipient Contexts used in the
group that does not include any of the public keys in Z.
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3. The group member installs the latest keying material with version
number V' and derives the corresponding new Security Context.
20.3.1. Retrieval of Stale Sender IDs
When realizing to have missed one or more group rekeying instances
(see Section 20.3), a node needs to retrieve from the Group Manager
the data required to delete some of its stored group members' public
keys and Recipient Contexts (see Section 5.4.1). This data is
provided as an aggregated set of stale Sender IDs, which are used as
specified in Section 20.3.
In particular, the node sends a CoAP FETCH request to the endpoint
/ace-group/GROUPNAME/stale-sids at the Group Manager defined in
Section 5.4 of this document, where GROUPNAME is the name of the
OSCORE group.
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 owned and installed by the requesting
client, which is older than the latest, possibly just distributed,
keying material with version number V'.
The handler MUST respond with a 4.00 (Bad Request) response, if the
request is not formatted correctly. Also, the handler MUST respond
with a 4.00 (Bad Request) response, if the specified version number V
is greater or equal than the version number V' associated to the
latest keying material in the group, i.e., if 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
stored in the collection of stale Sender IDs associated to the
group (see Section 2.2.1).
* 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 CBOR array has to be intended as a set, i.e., the
order of its elements 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.
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- The Group Manager considers the SKEW most recent sets stored in
the collection of stale Sender IDs associated to the group.
Note that the most recent set is the one associate to 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.
Figure 11 gives an overview of the exchange described above, while
Figure 12 shows an example.
Group
Node Manager
| |
| Stale Sender IDs Request |
|------------------------------------------------------------>|
| FETCH ace-group/GROUPNAME/stale-sids |
| |
|<---------- Stale Sender IDs Response: 2.05 (Content) -------|
| |
Figure 11: 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']
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Figure 12: Example of Stale Sender IDs Request-Response
21. 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].
21.1. Common
This section always applies, as related to common configuration
parameters.
* For the HKDF Algorithm 'hkdf', the Group Manager SHOULD use the
same default value defined in Section 3.2 of [RFC8613], i.e., HKDF
SHA-256 (COSE algorithm encoding: -10).
* For the format 'pub_key_enc' used to encode the public keys in the
group, the Group Manager SHOULD use a CBOR Web Token
(CWT)[RFC8392] or an unprotected CWT Claim Set
[I-D.ietf-rats-uccs].
[ This is a 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 in the
collection associated to the group (see Section 2.2.1).
21.2. 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
encrypted 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].
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* For the Signature Algorithm 'sign_alg' used to sign messages
protected with the group mode, the signature algorithm EdDSA
[RFC8032].
* For the parameters 'sign_params' of the Signature Algorithm:
- The array [[OKP], [OKP, Ed25519]], in case EdDSA is assumed or
specified for 'sign_alg'. In particular, 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'. In particular, 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'. In particular, 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'. In particular, 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'. In particular, this
indicates to use the COSE key type RSA.
21.3. 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
[I-D.ietf-cose-rfc8152bis-algs].
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* For the parameters 'ecdh_params' of the Pairwise Key Agreement
Algorithm:
- The array [[OKP], [OKP, X25519]], in case EdDSA is assumed or
specified for 'sign_alg'. In particular, 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'. In particular, 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'. In particular, 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'. In particular, this indicates to use
the COSE key type EC2 and the elliptic curve P-521.
22. Security Considerations
Security considerations for this profile are inherited from
[I-D.ietf-ace-key-groupcomm], the ACE framework for Authentication
and Authorization [I-D.ietf-ace-oauth-authz], and the specific
transport profile of ACE signalled by the AS, such as
[I-D.ietf-ace-dtls-authorize] and [I-D.ietf-ace-oscore-profile].
The following security considerations also apply for this profile.
22.1. 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 3.1 of
[I-D.ietf-core-oscore-groupcomm]). The Group Manager is
responsible for the renewal and re-distribution of the keying
material in the groups of its competence (rekeying). According to
the specific application requirements, this can include rekeying
the group upon changes in its membership. In particular, renewing
the group keying material is required upon a new node's joining or
a current node's leaving, in case backward security and forward
security have to be preserved, respectively.
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* Provisioning and retrieval of public keys (see Section 2 of
[I-D.ietf-core-oscore-groupcomm]). The Group Manager acts as key
repository of public keys of group members, and provides them upon
request.
* Synchronization of sequence numbers (see Section 6.2 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 Joining 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, the joining
node can use its own public key as asymmetric proof-of-possession key
to establish a secure channel with the Group Manager, e.g., as in
Section 3.2.2 of [I-D.ietf-ace-dtls-authorize]. However, this
requires such proof-of-possession key to be compatible with the
encoding, as well as with the signature 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.
22.2. Size of Nonces as Proof-of-Possesion Challenge
With reference to the Joining Request message in Section 6.2, 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 a 8-byte long random
nonce. Furthermore, N_C is always conveyed in the 'cnonce' parameter
of the Joining Request, which is always sent over the secure
communication channel between the joining node and the Group Manager.
As defined in Section 6.2.1, 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.
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* If the Access Token is not explicitly posted to the /authz-info
endpoint of the Group Manager, then N_S is computed as a 32-byte
long challenge. For an example, see point (2) of Section 6.2.1.
* If the Access Token has been explicitly posted to the /authz-info
endpoint of the Group Manager, 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 6.2.1. This is
provided either in the 2.01 response to the Token Post (see
Section 6.1), or in a 4.00 response to a following Joining Request
(see Section 6.3). In either case, it is RECOMMENDED to use a
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 posted Access Tokens, while the average collision for N_C
will happen after 2^32 new Joining Requests. This amounts to
considerably more token provisionings than the expected new
joinings of 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 [I-D.ietf-ace-oscore-profile] 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.
22.3. Reusage of Nonces for Proof-of-Possession Input
As long as the Group Manager preserves the same N_S value currently
associated to 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 Joining Requests to that Group Manager.
In particular, the Client can reuse the same N_C value for every
Joining 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 Joining Requests.
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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 to
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.
23. IANA Considerations
Note to RFC Editor: Please replace all occurrences of "[[This
document]]" with the RFC number of this specification and delete this
paragraph.
This document has the following actions for IANA.
23.1. OAuth Parameters Registry
The following registrations are done for the OAuth Parameters
Registry following 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): [[This specification]]
* Parameter name: gm_dh_pub_keys
* Parameter usage location: client-rs request, rs-client response
* Change Controller: IESG
* Specification Document(s): [[This specification]]
23.2. OAuth Parameters CBOR Mappings Registry
The following registrations are done for the OAuth Parameters CBOR
Mappings Registry following the procedure specified in Section 8.10
of [I-D.ietf-ace-oauth-authz].
* Name: ecdh_info
* CBOR Key: TBD (range -256 to 255)
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* Value Type: Simple value Null / array
* Reference: [[This specification]]
* Name: gm_dh_pub_keys
* CBOR Key: TBD (range -256 to 255)
* Value Type: Simple value Null / array
* Reference: [[This specification]]
23.3. ACE Groupcomm Parameters Registry
IANA is asked to register the following entry to the "ACE Groupcomm
Parameters" Registry defined in Section 10.5 of
[I-D.ietf-ace-key-groupcomm].
* Name: group_senderId
* CBOR Key: TBD
* CBOR Type: Byte string
* Reference: [[This document]] (Section 9)
* Name: kdc_nonce
* CBOR Key: TBD
* CBOR Type: Byte string
* Reference: [[This document]] (Section 6.4)
* Name: kdc_cred
* CBOR Key: TBD
* CBOR Type: Byte string
* Reference: [[This document]] (Section 6.4)
* Name: kdc_cred_verify
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* CBOR Key: TBD
* CBOR Type: Byte string
* Reference: [[This document]] (Section 6.4)
* Name: ecdh_info
* CBOR Key: TBD
* CBOR Type: Array
* Reference: [[This document]] (Section 6.3)
* Name: gm_dh_pub_keys
* CBOR Key: TBD
* CBOR Type: Array
* Reference: [[This document]] (Section 6.3)
* Name: group_enc_key
* CBOR Key: TBD
* CBOR Type: Byte String
* Reference: [[This document]] (Section 5.3.1)
* Name: stale_node_ids
* CBOR Key: TBD
* CBOR Type: Array
* Reference: [[This document]] (Section 20)
23.4. ACE Groupcomm Key Registry
IANA is asked to register the following entry to the "ACE Groupcomm
Key" Registry defined in Section 10.6 of
[I-D.ietf-ace-key-groupcomm].
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* Name: Group_OSCORE_Input_Material object
* Key Type Value: GROUPCOMM_KEY_TBD
* Profile: "coap_group_oscore_app", defined in Section 23.5 of this
document.
* Description: A Group_OSCORE_Input_Material object encoded as
described in Section 6.4 of this document.
* Reference: [[This document]] (Section 6.4)
23.5. ACE Groupcomm Profile Registry
IANA is asked to register the following entry to the "ACE Groupcomm
Profile" Registry defined in Section 10.7 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
* Reference: [[This document]] (Section 6.4)
23.6. OSCORE Security Context Parameters Registry
IANA is asked to register the following entries in the "OSCORE
Security Context Parameters" Registry defined in Section 9.4 of
[I-D.ietf-ace-oscore-profile].
* Name: group_SenderId
* CBOR Label: TBD
* CBOR Type: bstr
* Registry: -
* Description: OSCORE Sender ID assigned to a member of an OSCORE
group
* Reference: [[This document]] (Section 6.4)
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* Name: pub_key_enc
* CBOR Label: TBD
* CBOR Type: integer
* Registry: COSE Header Parameters
* Description: Encoding of Public Keys to be used in the OSCORE
group
* Reference: [[This document]] (Section 6.4)
* Name: sign_enc_alg
* CBOR Label: TBD
* CBOR Type: tstr / int
* Registry: COSE Algorithms
* Description: OSCORE Signature Encryption Algorithm Value
* Reference: [[This document]] (Section 6.4)
* Name: sign_alg
* CBOR Label: TBD
* CBOR Type: tstr / int
* Registry: COSE Algorithms
* Description: OSCORE Signature Algorithm Value
* Reference: [[This document]] (Section 6.4)
* Name: sign_params
* CBOR Label: TBD
* CBOR Type: array
* Registry: COSE Algorithms, COSE Key Types, COSE Elliptic Curves
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* Description: OSCORE Signature Algorithm Parameters
* Reference: [[This document]] (Section 6.4)
* Name: ecdh_alg
* CBOR Label: TBD
* CBOR Type: tstr / int
* Registry: COSE Algorithms
* Description: OSCORE Pairwise Key Agreement Algorithm Value
* Reference: [[This document]] (Section 6.4)
* 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
* Reference: [[This document]] (Section 6.4)
23.7. TLS Exporter Label Registry
IANA is asked to register the following entry to the "TLS Exporter
Label" 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: [[This document]] (Section 6.2.1)
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23.8. AIF Registry
IANA is asked to register the following entry to the "Toid" sub-
registry of the "AIF" Registry defined in Section 5.2 of
[I-D.ietf-ace-aif].
* Name: oscore-group-name
* Description/Specification: group name of the OSCORE group, as
specified in [[This document]].
IANA is asked to register the following entry to the "Tperm" sub-
Registry of the "AIF" Registry defined in Section 5.2 of
[I-D.ietf-ace-aif].
* Name: oscore-group-roles
* Description/Specification: role(s) of the member of the OSCORE
group, as specified in [[This document]].
23.9. Media Type Registrations
This document registers the 'application/aif-groupcomm-oscore+cbor'
media type for the AIF specific data model AIF-OSCORE-GROUPCOMM
defined in Section 3 of [[This document]]. This registration follows
the procedures specified in [RFC6838].
These media type has parameters for specifying the object identifier
("Toid") and set of permissions ("Tperm") defined for the AIF-generic
model in [I-D.ietf-ace-aif]; default values are the values "oscore-
group-name" for "Toid" and "oscore-group-roles" for "Tperm".
Type name: application
Subtype name: aif-groupcomm-oscore+cbor
Required parameters: "Toid", "Tperm"
Optional parameters: N/A
Encoding considerations: Must be encoded as a CBOR array, each
element of which is an array [Toid, Tperm] as defined in Section 3 of
[[This document]].
Security considerations: See Section 22 of [[This document]].
Interoperability considerations: N/A
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Published specification: [[This document]]
Applications that use this media type: The type is used by
applications that want to express authorization information about
joining OSCORE groups, as specified in [[This document]].
Fragment identifier considerations: N/A
Additional information: N/A
Person & email address to contact for further information:
iesg@ietf.org (mailto:iesg@ietf.org)
Intended usage: COMMON
Restrictions on usage: None
Author: Marco Tiloca marco.tiloca@ri.se (mailto:marco.tiloca@ri.se)
Change controller: IESG
Provisional registration? No
23.10. CoAP Content-Format Registry
IANA is asked to register the following entry to the "CoAP Content-
Formats" registry, within the "CoRE Parameters" registry:
Media Type: application/aif-groupcomm-oscore+cbor;Toid="oscore-group-
name",Tperm"oscore-group-roles"
Encoding: -
ID: TBD
Reference: [[This document]]
23.11. Group OSCORE Roles Registry
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 23.15.
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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 [[This
document]].
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.
The Reference column for all of these entries will be [[This
document]].
23.12. CoRE Resource Type Registry
IANA is asked to register a new Resource Type (rt=) Link Target
Attribute in the "Resource Type (rt=) Link Target Attribute Values"
subregistry under the "Constrained Restful Environments (CoRE)
Parameters" [CORE.Parameters] registry.
* Value: "core.osc.gm"
* Description: Group-membership resource of an OSCORE Group Manager.
* Reference: [[This document]]
23.13. ACE Scope Semantics Registry
IANA is asked to register the following entry in the "ACE Scope
Semantics" registry defined in Section 10.12 of
[I-D.ietf-ace-key-groupcomm].
* Value: SEM_ID_TBD
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* Description: Access to OSCORE groups through the ACE Group
Manager.
* Reference: [[This document]]
23.14. ACE Groupcomm Errors
IANA is asked to register the following entry in the "ACE Groupcomm
Errors" registry defined in Section 10.13 of
[I-D.ietf-ace-key-groupcomm].
* Value: 7
* Description: Signatures not used in the group.
* Reference: [[This document]]
* Value: 8
* Description: Operation permitted only to signature verifiers.
* Reference: [[This document]]
* Value: 9
* Description: Group currently not active.
* Reference: [[This document]]
23.15. 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:
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* 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. Expert 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 objective 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 assignment. 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.
24. References
24.1. Normative References
[CORE.Parameters]
IANA, "Constrained RESTful Environments (CoRE)
Parameters", <https://www.iana.org/assignments/core-
parameters/core-parameters.xhtml>.
[COSE.Algorithms]
IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>.
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[COSE.Elliptic.Curves]
IANA, "COSE Elliptic Curves",
<https://www.iana.org/assignments/cose/
cose.xhtml#elliptic-curves>.
[]
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-aif]
Bormann, C., "An Authorization Information Format (AIF)
for ACE", Work in Progress, Internet-Draft, draft-ietf-
ace-aif-03, 24 June 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-aif-
03.txt>.
[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-13, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-key-
groupcomm-13.txt>.
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", Work in Progress, Internet-Draft,
draft-ietf-ace-oauth-authz-43, 10 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-oauth-
authz-43.txt>.
[I-D.ietf-ace-oscore-profile]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"OSCORE Profile of the Authentication and Authorization
for Constrained Environments Framework", Work in Progress,
Internet-Draft, draft-ietf-ace-oscore-profile-19, 6 May
2021, <https://www.ietf.org/archive/id/draft-ietf-ace-
oscore-profile-19.txt>.
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[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-12, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-core-oscore-
groupcomm-12.txt>.
[I-D.ietf-cose-rfc8152bis-algs]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", Work in Progress, Internet-Draft,
draft-ietf-cose-rfc8152bis-algs-12, 24 September 2020,
<https://www.ietf.org/archive/id/draft-ietf-cose-
rfc8152bis-algs-12.txt>.
[I-D.ietf-cose-rfc8152bis-struct]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", Work in Progress, Internet-Draft,
draft-ietf-cose-rfc8152bis-struct-15, 1 February 2021,
<https://www.ietf.org/archive/id/draft-ietf-cose-
rfc8152bis-struct-15.txt>.
[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>.
[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>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[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>.
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[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>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
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[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>.
[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>.
24.2. Informative References
[I-D.ietf-ace-dtls-authorize]
Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
L. Seitz, "Datagram Transport Layer Security (DTLS)
Profile for Authentication and Authorization for
Constrained Environments (ACE)", Work in Progress,
Internet-Draft, draft-ietf-ace-dtls-authorize-18, 4 June
2021, <https://www.ietf.org/archive/id/draft-ietf-ace-
dtls-authorize-18.txt>.
[I-D.ietf-ace-oscore-gm-admin]
Tiloca, M., Hoeglund, R., Stok, P. V. D., Palombini, F.,
and K. Hartke, "Admin Interface for the OSCORE Group
Manager", Work in Progress, Internet-Draft, draft-ietf-
ace-oscore-gm-admin-03, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-oscore-gm-
admin-03.txt>.
[I-D.ietf-core-coap-pubsub]
Koster, M., Keranen, A., and J. Jimenez, "Publish-
Subscribe Broker for the Constrained Application Protocol
(CoAP)", Work in Progress, Internet-Draft, draft-ietf-
core-coap-pubsub-09, 30 September 2019,
<https://www.ietf.org/archive/id/draft-ietf-core-coap-
pubsub-09.txt>.
[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-
04, 12 July 2021, <https://www.ietf.org/archive/id/
draft-ietf-core-groupcomm-bis-04.txt>.
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[I-D.ietf-cose-cbor-encoded-cert]
Raza, S., Hoeglund, J., Selander, G., Mattsson, J. P.,
and M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", Work in Progress, Internet-Draft, draft-
ietf-cose-cbor-encoded-cert-01, 25 May 2021,
<https://www.ietf.org/archive/id/draft-ietf-cose-cbor-
encoded-cert-01.txt>.
[I-D.ietf-rats-uccs]
Birkholz, H., O'Donoghue, J., Cam-Winget, N., and C.
Bormann, "A CBOR Tag for Unprotected CWT Claims Sets",
Work in Progress, Internet-Draft, draft-ietf-rats-uccs-00,
19 May 2021, <https://www.ietf.org/archive/id/draft-ietf-
rats-uccs-00.txt>.
[I-D.tiloca-core-oscore-discovery]
Tiloca, M., Amsuess, C., and P. V. D. Stok, "Discovery of
OSCORE Groups with the CoRE Resource Directory", Work in
Progress, Internet-Draft, draft-tiloca-core-oscore-
discovery-09, 12 July 2021,
<https://www.ietf.org/archive/id/draft-tiloca-core-oscore-
discovery-09.txt>.
[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>.
[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>.
[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>.
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[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 appendix lists the specifications on this application profile of
ACE, based on the requirements defined in Appendix A of
[I-D.ietf-ace-key-groupcomm].
* REQ1 - 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]) do not match, specify the mechanism
to map the GROUPNAME value in the URI to the group name: not
applicable, since a match is required.
* REQ2 - Specify the encoding and value of roles, for scope entries
of 'scope': see Section 3 and Section 4.1.
* 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 encoding public keys
and, if used, the acceptable values for 'pub_key_enc': acceptable
formats explicitly provide the full set of information related to
the public key algorithm (see Section 6.1 and Section 6.4).
Consistent acceptable values for 'pub_key_enc' are taken from the
"Label" column of the "COSE Header Parameters" Registry
[COSE.Header.Parameters].
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* REQ7 - 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 23.12.
* REQ8 - Define what operations (e.g., CoAP methods) are allowed on
each resource, for each role defined in REQ2: see Section 5.5.
* REQ9 - Specify the exact encoding of group identifier (see
Section 4.1.1.1 of [I-D.ietf-ace-key-groupcomm]): CBOR byte string
(see Section 17).
* REQ10 - Format of the 'key' value: see Section 6.4.
* REQ11 - Acceptable values of 'gkty': Group_OSCORE_Input_Material
object (see Section 6.4).
* REQ12 - Specify the format of the identifiers of group members:
the Sender ID used in the OSCORE group (see Section 6.4 and
Section 10).
* REQ13 - Specify the communication protocol that the members of the
group must use: CoAP [RFC7252], possibly over IP multicast
[I-D.ietf-core-groupcomm-bis].
* REQ14 - Specify the security protocols that the group members must
use to protect their communication: Group OSCORE
[I-D.ietf-core-oscore-groupcomm].
* REQ15 - Specify and register the application profile identifier:
coap_group_oscore_app (see Section 23.5).
* REQ16 - Specify policies at the KDC to handle member ids that are
not included in 'get_pub_keys': see Section 10.
* REQ17 - If used, specify the format and content of
'group_policies' and its entries: see Section 6.4.
* REQ18 - 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.
* REQ19 - Specify how the communication is secured between the
Client and KDC: by means of any transport profile of ACE
[I-D.ietf-ace-oauth-authz] between Client and Group Manager that
complies with the requirements in Appendix C of
[I-D.ietf-ace-oauth-authz].
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* REQ20 - Specify the exact 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 6.2 and
Section 6.3.
* REQ21 - Specify how the nonce N_S is generated, if the token is
not being posted (e.g., if it is used directly to validate TLS
instead): see Section 6.2.1.
* REQ22 - Specify if 'mgt_key_material' is used, and if yes specify
its format and content: not used in this version of the profile.
* REQ23 - 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].
* REQ24 - Specify and register the identifier of newly defined
semantics for binary scopes: see Section 23.13.
* OPT1 (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].
* OPT2 (Optional) - Specify additional parameters used in the Token
Post exchange: 'ecdh_info', to negotiate the ECDH algorithm, ECDH
algorithm parameters, ECDH key parameters and exact encoding of
public keys used in the group, in case the joining node supports
the pairwise mode of Group OSCORE.
* OPT3 (Optional) - Specify the encoding of 'pub_keys_repos' if the
default is not used: no.
* OPT4 (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.
* OPT5 (Optional) - Specify possible or required payload formats for
specific error cases: send a 4.00 (Bad Request) response to a
Joining Request (see Section 6.3).
* OPT6 (Optional) - Specify the behavior of the handler in case of
failure to retrieve a public key for the specific node: send a
4.00 (Bad Request) response to a Joining Request (see
Section 6.3).
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* OPT7 (Optional) - Specify CBOR values to use for abbreviating
identifiers of roles in the group or topic: see Section 4.1.
* OPT8 (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).
* OPT9 (Optional) - Specify the functionalities implemented at the
'control_uri' resource hosted at the Client, including message
exchange encoding and other details (see Section 4.1.2.1 of
[I-D.ietf-ace-key-groupcomm]): see Section 19 for the eviction of
a group member; see Section 20 for the group rekeying process.
* OPT10 (Optional) - Specify how the identifier of the sender's
public key is included in the group request: no.
* OPT11 (Optional) - Specify additional identifiers of error types,
as values of the 'error' field in an error response from the KDC:
see Section 23.14.
Appendix B. Extensibility for Future COSE Algorithms
As defined in Section 8.1 of [I-D.ietf-cose-rfc8152bis-algs], 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
Post response, see Section 6.1 and Section 6.1.1;
* The 'sign_params' and 'ecdh_params' parameters within the 'key'
parameter, see Section 6.4, as part of the response payloads used
in Section 6.4, Section 8.1, Section 8.2 and Section 20.
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 Post response, see Section 6.1.
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.
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B.1. Format of 'ecdh_info_entry'
The format of each 'ecdh_info_entry' (see Section 6.1 and
Section 6.1.1) 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].
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 ],
pub_key_enc = int / nil
]
gname = tstr
Figure 13: 'ecdh_info_entry' with general format
B.2. Format of 'key'
The format of 'key' (see Section 6.4) 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
[I-D.ietf-cose-rfc8152bis-algs]).
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- 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 to 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
[I-D.ietf-cose-rfc8152bis-algs]).
* 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
[I-D.ietf-cose-rfc8152bis-algs]).
- 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 to 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 [I-D.ietf-cose-rfc8152bis-algs]).
Appendix C. Document Updates
RFC EDITOR: PLEASE REMOVE THIS SECTION.
C.1. Version -10 to -11
* Removed redundancy of key type capabilities, from 'sign_info',
'ecdh_info' and 'key'.
* New resource to retrieve the Group Manager's public key.
* New resource to retrieve material for Signature Verifiers.
* New parameter 'sign_enc_alg' related to the group mode.
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* 'pub_key_enc' takes value from the COSE Header Parameters
registry.
* Improved alignment of the Joining 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
Joining 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.2. Version -09 to -10
* Updated non-recycling policy of Sender IDs.
* Removed policies about Sender Sequence Number synchronization.
* '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.
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* Registered semantics identifier for extended scope format.
* Extended error handling, with error type specified in some error
responses.
* Renumbered requirements.
C.3. 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.
C.4. Version -07 to -08
* AIF specific data model to express scope entries.
* A set of roles is checked as valid when processing the Joining
Request.
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* Updated format of 'get_pub_keys' in the Joining Request.
* Payload format and default values of group policies in the Joining
Response.
* Updated payload format of the FETCH request to retrieve public
keys.
* Default values for group configuration parameters.
* IANA registrations to support the AIF specific data model.
C.5. Version -06 to -07
* Alignments with draft-ietf-core-oscore-groupcomm.
* New format of 'sign_info', using the COSE capabilities.
* New format of Joining Response parameters, using the COSE
capabilities.
* Considerations on group rekeying.
* Editorial revision.
C.6. 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.
* Scope not mandatory to include in the Joining Request.
* Group policy about supporting Group OSCORE in pairwise mode.
* Possible individual rekeying of a single requesting node combined
with a group rekeying.
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* Security considerations on reusage of signature challenges.
* Addressing optional requirement OPT8 from draft-ietf-ace-key-
groupcomm
* Editorial improvements.
C.7. Version -04 to -05
* Nonce N_S also in error responses to the Joining 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 public key 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.8. Version -03 to -04
* New abstract.
* 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).
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* 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.9. 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.10. Version -01 to -02
* Editorial fixes.
* Changed: "listener" to "responder"; "pure listener" to "monitor".
* 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 public keys.
* Challenge-response for proof-of-possession of signature keys
(Section 4).
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* 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 public key (Section 4.3).
* Clarifications on provisioning and checking of public keys
(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 Registry" (Section 9).
* Registered one public key encoding in the "ACE Public Key
Encoding" IANA Registry (Section 9).
C.11. 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).
* 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 Amsuess, Santiago Aragon,
Stefan Beck, Carsten Bormann, Martin Gunnarsson, Rikard Hoeglund,
Daniel Migault, Jim Schaad, Ludwig Seitz, Goeran Selander and Peter
van der Stok for their comments and feedback.
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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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