draft-ietf-core-oscore-groupcomm-10.txt   draft-ietf-core-oscore-groupcomm-11.txt 
CoRE Working Group M. Tiloca CoRE Working Group M. Tiloca
Internet-Draft RISE AB Internet-Draft RISE AB
Intended status: Standards Track G. Selander Intended status: Standards Track G. Selander
Expires: May 6, 2021 F. Palombini Expires: August 26, 2021 F. Palombini
J. Mattsson
Ericsson AB Ericsson AB
J. Park J. Park
Universitaet Duisburg-Essen Universitaet Duisburg-Essen
November 02, 2020 February 22, 2021
Group OSCORE - Secure Group Communication for CoAP Group OSCORE - Secure Group Communication for CoAP
draft-ietf-core-oscore-groupcomm-10 draft-ietf-core-oscore-groupcomm-11
Abstract Abstract
This document defines Group Object Security for Constrained RESTful This document defines Group Object Security for Constrained RESTful
Environments (Group OSCORE), providing end-to-end security of CoAP Environments (Group OSCORE), providing end-to-end security of CoAP
messages exchanged between members of a group, e.g. sent over IP messages exchanged between members of a group, e.g. sent over IP
multicast. In particular, the described approach defines how OSCORE multicast. In particular, the described approach defines how OSCORE
is used in a group communication setting to provide source is used in a group communication setting to provide source
authentication for CoAP group requests, sent by a client to multiple authentication for CoAP group requests, sent by a client to multiple
servers, and for protection of the corresponding CoAP responses. servers, and for protection of the corresponding CoAP responses.
skipping to change at page 1, line 40 skipping to change at page 1, line 41
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 6, 2021. This Internet-Draft will expire on August 26, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 21 skipping to change at page 2, line 22
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Security Context . . . . . . . . . . . . . . . . . . . . . . 7 2. Security Context . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Common Context . . . . . . . . . . . . . . . . . . . . . 9 2.1. Common Context . . . . . . . . . . . . . . . . . . . . . 9
2.1.1. ID Context . . . . . . . . . . . . . . . . . . . . . 9 2.1.1. ID Context . . . . . . . . . . . . . . . . . . . . . 9
2.1.2. Counter Signature Algorithm . . . . . . . . . . . . . 9 2.1.2. Counter Signature Algorithm . . . . . . . . . . . . . 9
2.1.3. Counter Signature Parameters . . . . . . . . . . . . 9 2.1.3. Counter Signature Parameters . . . . . . . . . . . . 9
2.1.4. Secret Derivation Algorithm . . . . . . . . . . . . . 10 2.1.4. Secret Derivation Algorithm . . . . . . . . . . . . . 10
2.1.5. Secret Derivation Parameters . . . . . . . . . . . . 10 2.1.5. Secret Derivation Parameters . . . . . . . . . . . . 11
2.2. Sender Context and Recipient Context . . . . . . . . . . 11 2.2. Sender Context and Recipient Context . . . . . . . . . . 11
2.3. Pairwise Keys . . . . . . . . . . . . . . . . . . . . . . 12 2.3. Pairwise Keys . . . . . . . . . . . . . . . . . . . . . . 12
2.3.1. Derivation of Pairwise Keys . . . . . . . . . . . . . 12 2.3.1. Derivation of Pairwise Keys . . . . . . . . . . . . . 12
2.3.2. Usage of Sequence Numbers . . . . . . . . . . . . . . 13 2.3.2. Usage of Sequence Numbers . . . . . . . . . . . . . . 13
2.3.3. Security Context for Pairwise Mode . . . . . . . . . 13 2.3.3. Security Context for Pairwise Mode . . . . . . . . . 14
2.4. Update of Security Context . . . . . . . . . . . . . . . 14 2.4. Update of Security Context . . . . . . . . . . . . . . . 14
2.4.1. Loss of Mutable Security Context . . . . . . . . . . 14 2.4.1. Loss of Mutable Security Context . . . . . . . . . . 15
2.4.2. Exhaustion of Sender Sequence Number . . . . . . . . 15 2.4.2. Exhaustion of Sender Sequence Number . . . . . . . . 16
2.4.3. Retrieving New Security Context Parameters . . . . . 16 2.4.3. Retrieving New Security Context Parameters . . . . . 17
3. The Group Manager . . . . . . . . . . . . . . . . . . . . . . 18 3. The Group Manager . . . . . . . . . . . . . . . . . . . . . . 19
3.1. Management of Group Keying Material . . . . . . . . . . . 19 3.1. Management of Group Keying Material . . . . . . . . . . . 20
3.2. Responsibilities of the Group Manager . . . . . . . . . . 20 3.2. Responsibilities of the Group Manager . . . . . . . . . . 21
4. The COSE Object . . . . . . . . . . . . . . . . . . . . . . . 21 4. The COSE Object . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. Counter Signature . . . . . . . . . . . . . . . . . . . . 21 4.1. Counter Signature . . . . . . . . . . . . . . . . . . . . 23
4.2. The 'kid' and 'kid context' parameters . . . . . . . . . 21 4.2. The 'kid' and 'kid context' parameters . . . . . . . . . 23
4.3. external_aad . . . . . . . . . . . . . . . . . . . . . . 22 4.3. external_aad . . . . . . . . . . . . . . . . . . . . . . 23
4.3.1. external_aad for Encryption . . . . . . . . . . . . . 22 5. OSCORE Header Compression . . . . . . . . . . . . . . . . . . 25
4.3.2. external_aad for Signing . . . . . . . . . . . . . . 23 5.1. Examples of Compressed COSE Objects . . . . . . . . . . . 26
5. OSCORE Header Compression . . . . . . . . . . . . . . . . . . 24 5.1.1. Examples in Group Mode . . . . . . . . . . . . . . . 26
5.1. Examples of Compressed COSE Objects . . . . . . . . . . . 25 5.1.2. Examples in Pairwise Mode . . . . . . . . . . . . . . 27
5.1.1. Examples in Group Mode . . . . . . . . . . . . . . . 25
5.1.2. Examples in Pairwise Mode . . . . . . . . . . . . . . 26
6. Message Binding, Sequence Numbers, Freshness and Replay 6. Message Binding, Sequence Numbers, Freshness and Replay
Protection . . . . . . . . . . . . . . . . . . . . . . . . . 27 Protection . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1. Update of Replay Window . . . . . . . . . . . . . . . . . 27 6.1. Update of Replay Window . . . . . . . . . . . . . . . . . 28
7. Message Reception . . . . . . . . . . . . . . . . . . . . . . 28 6.2. Message Freshness . . . . . . . . . . . . . . . . . . . . 29
8. Message Processing in Group Mode . . . . . . . . . . . . . . 29 7. Message Reception . . . . . . . . . . . . . . . . . . . . . . 29
8.1. Protecting the Request . . . . . . . . . . . . . . . . . 29 8. Message Processing in Group Mode . . . . . . . . . . . . . . 30
8.1.1. Supporting Observe . . . . . . . . . . . . . . . . . 30 8.1. Protecting the Request . . . . . . . . . . . . . . . . . 31
8.2. Verifying the Request . . . . . . . . . . . . . . . . . . 31 8.1.1. Supporting Observe . . . . . . . . . . . . . . . . . 31
8.2.1. Supporting Observe . . . . . . . . . . . . . . . . . 32 8.2. Verifying the Request . . . . . . . . . . . . . . . . . . 32
8.3. Protecting the Response . . . . . . . . . . . . . . . . . 32 8.2.1. Supporting Observe . . . . . . . . . . . . . . . . . 34
8.3.1. Supporting Observe . . . . . . . . . . . . . . . . . 33 8.3. Protecting the Response . . . . . . . . . . . . . . . . . 34
8.4. Verifying the Response . . . . . . . . . . . . . . . . . 34 8.3.1. Supporting Observe . . . . . . . . . . . . . . . . . 35
8.4.1. Supporting Observe . . . . . . . . . . . . . . . . . 34 8.4. Verifying the Response . . . . . . . . . . . . . . . . . 35
9. Message Processing in Pairwise Mode . . . . . . . . . . . . . 35 8.4.1. Supporting Observe . . . . . . . . . . . . . . . . . 36
9.1. Pre-Conditions . . . . . . . . . . . . . . . . . . . . . 36 9. Message Processing in Pairwise Mode . . . . . . . . . . . . . 37
9.2. Protecting the Request . . . . . . . . . . . . . . . . . 36 9.1. Pre-Conditions . . . . . . . . . . . . . . . . . . . . . 38
9.3. Verifying the Request . . . . . . . . . . . . . . . . . . 37 9.2. Main Differences from OSCORE . . . . . . . . . . . . . . 38
9.4. Protecting the Response . . . . . . . . . . . . . . . . . 37 9.3. Protecting the Request . . . . . . . . . . . . . . . . . 39
9.5. Verifying the Response . . . . . . . . . . . . . . . . . 38 9.4. Verifying the Request . . . . . . . . . . . . . . . . . . 39
10. Security Considerations . . . . . . . . . . . . . . . . . . . 38 9.5. Protecting the Response . . . . . . . . . . . . . . . . . 39
10.1. Group-level Security . . . . . . . . . . . . . . . . . . 39 9.6. Verifying the Response . . . . . . . . . . . . . . . . . 40
10.2. Uniqueness of (key, nonce) . . . . . . . . . . . . . . . 40 10. Security Considerations . . . . . . . . . . . . . . . . . . . 40
10.3. Management of Group Keying Material . . . . . . . . . . 40 10.1. Group-level Security . . . . . . . . . . . . . . . . . . 41
10.4. Update of Security Context and Key Rotation . . . . . . 41 10.2. Uniqueness of (key, nonce) . . . . . . . . . . . . . . . 42
10.4.1. Late Update on the Sender . . . . . . . . . . . . . 41 10.3. Management of Group Keying Material . . . . . . . . . . 42
10.4.2. Late Update on the Recipient . . . . . . . . . . . . 42 10.4. Update of Security Context and Key Rotation . . . . . . 43
10.5. Collision of Group Identifiers . . . . . . . . . . . . . 42 10.4.1. Late Update on the Sender . . . . . . . . . . . . . 43
10.6. Cross-group Message Injection . . . . . . . . . . . . . 43 10.4.2. Late Update on the Recipient . . . . . . . . . . . . 44
10.6.1. Attack Description . . . . . . . . . . . . . . . . . 43 10.5. Collision of Group Identifiers . . . . . . . . . . . . . 44
10.6.2. Attack Prevention in Group Mode . . . . . . . . . . 44 10.6. Cross-group Message Injection . . . . . . . . . . . . . 45
10.7. Group OSCORE for Unicast Requests . . . . . . . . . . . 45 10.6.1. Attack Description . . . . . . . . . . . . . . . . . 45
10.8. End-to-end Protection . . . . . . . . . . . . . . . . . 46 10.6.2. Attack Prevention in Group Mode . . . . . . . . . . 46
10.9. Master Secret . . . . . . . . . . . . . . . . . . . . . 46 10.7. Group OSCORE for Unicast Requests . . . . . . . . . . . 47
10.10. Replay Protection . . . . . . . . . . . . . . . . . . . 47 10.8. End-to-end Protection . . . . . . . . . . . . . . . . . 48
10.11. Client Aliveness . . . . . . . . . . . . . . . . . . . . 48 10.9. Master Secret . . . . . . . . . . . . . . . . . . . . . 48
10.12. Cryptographic Considerations . . . . . . . . . . . . . . 48 10.10. Replay Protection . . . . . . . . . . . . . . . . . . . 49
10.13. Message Segmentation . . . . . . . . . . . . . . . . . . 49 10.11. Message Freshness . . . . . . . . . . . . . . . . . . . 49
10.14. Privacy Considerations . . . . . . . . . . . . . . . . . 49 10.12. Client Aliveness . . . . . . . . . . . . . . . . . . . . 50
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 10.13. Cryptographic Considerations . . . . . . . . . . . . . . 50
11.1. OSCORE Flag Bits Registry . . . . . . . . . . . . . . . 50 10.14. Message Segmentation . . . . . . . . . . . . . . . . . . 51
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 50 10.15. Privacy Considerations . . . . . . . . . . . . . . . . . 51
12.1. Normative References . . . . . . . . . . . . . . . . . . 50 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 52
12.2. Informative References . . . . . . . . . . . . . . . . . 52 11.1. OSCORE Flag Bits Registry . . . . . . . . . . . . . . . 52
Appendix A. Assumptions and Security Objectives . . . . . . . . 54 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
A.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 55 12.1. Normative References . . . . . . . . . . . . . . . . . . 52
A.2. Security Objectives . . . . . . . . . . . . . . . . . . . 56 12.2. Informative References . . . . . . . . . . . . . . . . . 54
Appendix B. List of Use Cases . . . . . . . . . . . . . . . . . 57 Appendix A. Assumptions and Security Objectives . . . . . . . . 56
Appendix C. Example of Group Identifier Format . . . . . . . . . 60 A.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 57
Appendix D. Set-up of New Endpoints . . . . . . . . . . . . . . 60 A.2. Security Objectives . . . . . . . . . . . . . . . . . . . 58
Appendix E. Examples of Synchronization Approaches . . . . . . . 61 Appendix B. List of Use Cases . . . . . . . . . . . . . . . . . 59
E.1. Best-Effort Synchronization . . . . . . . . . . . . . . . 61 Appendix C. Example of Group Identifier Format . . . . . . . . . 61
E.2. Baseline Synchronization . . . . . . . . . . . . . . . . 62 Appendix D. Set-up of New Endpoints . . . . . . . . . . . . . . 62
E.3. Challenge-Response Synchronization . . . . . . . . . . . 62 Appendix E. Challenge-Response Synchronization . . . . . . . . . 63
Appendix F. No Verification of Signatures in Group Mode . . . . 65 Appendix F. No Verification of Signatures in Group Mode . . . . 66
Appendix G. Example Values with COSE Capabilities . . . . . . . 66 Appendix G. Example Values with COSE Capabilities . . . . . . . 67
Appendix H. Document Updates . . . . . . . . . . . . . . . . . . 67 Appendix H. Parameter Extensibility for Future COSE Algorithms . 68
H.1. Version -09 to -10 . . . . . . . . . . . . . . . . . . . 67 H.1. Counter Signature Parameters . . . . . . . . . . . . . . 68
H.2. Version -08 to -09 . . . . . . . . . . . . . . . . . . . 68 H.2. Secret Derivation Parameters . . . . . . . . . . . . . . 69
H.3. Version -07 to -08 . . . . . . . . . . . . . . . . . . . 69 H.3. 'par_countersign' in the external_aad . . . . . . . . . . 69
H.4. Version -06 to -07 . . . . . . . . . . . . . . . . . . . 70 Appendix I. Document Updates . . . . . . . . . . . . . . . . . . 71
H.5. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 71 I.1. Version -10 to -11 . . . . . . . . . . . . . . . . . . . 71
H.6. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 72 I.2. Version -09 to -10 . . . . . . . . . . . . . . . . . . . 72
H.7. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 72 I.3. Version -08 to -09 . . . . . . . . . . . . . . . . . . . 72
H.8. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 73 I.4. Version -07 to -08 . . . . . . . . . . . . . . . . . . . 73
H.9. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 74 I.5. Version -06 to -07 . . . . . . . . . . . . . . . . . . . 75
H.10. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 74 I.6. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 75
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 75 I.7. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 76
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 75 I.8. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 76
I.9. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 77
I.10. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 78
I.11. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 79
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 79
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 80
1. Introduction 1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] is a web The Constrained Application Protocol (CoAP) [RFC7252] is a web
transfer protocol specifically designed for constrained devices and transfer protocol specifically designed for constrained devices and
networks [RFC7228]. Group communication for CoAP networks [RFC7228]. Group communication for CoAP
[I-D.ietf-core-groupcomm-bis] addresses use cases where deployed [I-D.ietf-core-groupcomm-bis] addresses use cases where deployed
devices benefit from a group communication model, for example to devices benefit from a group communication model, for example to
reduce latencies, improve performance and reduce bandwidth reduce latencies, improve performance and reduce bandwidth
utilization. Use cases include lighting control, integrated building utilization. Use cases include lighting control, integrated building
skipping to change at page 4, line 39 skipping to change at page 4, line 43
protocol for Group communication for CoAP protocol for Group communication for CoAP
[I-D.ietf-core-groupcomm-bis]. [I-D.ietf-core-groupcomm-bis].
Object Security for Constrained RESTful Environments (OSCORE) Object Security for Constrained RESTful Environments (OSCORE)
[RFC8613] describes a security protocol based on the exchange of [RFC8613] describes a security protocol based on the exchange of
protected CoAP messages. OSCORE builds on CBOR Object Signing and protected CoAP messages. OSCORE builds on CBOR Object Signing and
Encryption (COSE) Encryption (COSE)
[I-D.ietf-cose-rfc8152bis-struct][I-D.ietf-cose-rfc8152bis-algs] and [I-D.ietf-cose-rfc8152bis-struct][I-D.ietf-cose-rfc8152bis-algs] and
provides end-to-end encryption, integrity, replay protection and provides end-to-end encryption, integrity, replay protection and
binding of response to request between a sender and a recipient, binding of response to request between a sender and a recipient,
independent of transport also in the presence of intermediaries. To independent of the transport layer also in the presence of
this end, a CoAP message is protected by including its payload (if intermediaries. To this end, a CoAP message is protected by
any), certain options, and header fields in a COSE object, which including its payload (if any), certain options, and header fields in
replaces the authenticated and encrypted fields in the protected a COSE object, which replaces the authenticated and encrypted fields
message. in the protected message.
This document defines Group OSCORE, providing the same end-to-end This document defines Group OSCORE, providing the same end-to-end
security properties as OSCORE in the case where CoAP requests have security properties as OSCORE in the case where CoAP requests have
multiple recipients. In particular, the described approach defines multiple recipients. In particular, the described approach defines
how OSCORE is used in a group communication setting to provide source how OSCORE is used in a group communication setting to provide source
authentication for CoAP group requests, sent by a client to multiple authentication for CoAP group requests, sent by a client to multiple
servers, and for protection of the corresponding CoAP responses. servers, and for protection of the corresponding CoAP responses.
Just like OSCORE, Group OSCORE is independent of transport layer and Just like OSCORE, Group OSCORE is independent of the transport layer
works wherever CoAP does. Group communication for CoAP and works wherever CoAP does. Group communication for CoAP
[I-D.ietf-core-groupcomm-bis] uses UDP/IP multicast as the underlying [I-D.ietf-core-groupcomm-bis] uses UDP/IP multicast as the underlying
data transport. data transport.
As with OSCORE, it is possible to combine Group OSCORE with As with OSCORE, it is possible to combine Group OSCORE with
communication security on other layers. One example is the use of communication security on other layers. One example is the use of
transport layer security, such as DTLS transport layer security, such as DTLS
[RFC6347][I-D.ietf-tls-dtls13], between one client and one proxy (and [RFC6347][I-D.ietf-tls-dtls13], between one client and one proxy (and
vice versa), or between one proxy and one server (and vice versa), in vice versa), or between one proxy and one server (and vice versa), in
order to protect the routing information of packets from observers. order to protect the routing information of packets from observers.
Note that DTLS does not define how to secure messages sent over IP Note that DTLS does not define how to secure messages sent over IP
skipping to change at page 6, line 26 skipping to change at page 6, line 30
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Readers are expected to be familiar with the terms and concepts Readers are expected to be familiar with the terms and concepts
described in CoAP [RFC7252] including "endpoint", "client", "server", described in CoAP [RFC7252] including "endpoint", "client", "server",
"sender" and "recipient"; group communication for CoAP "sender" and "recipient"; group communication for CoAP
[I-D.ietf-core-groupcomm-bis]; CBOR [I-D.ietf-cbor-7049bis]; COSE [I-D.ietf-core-groupcomm-bis]; CBOR [RFC8949]; COSE
[I-D.ietf-cose-rfc8152bis-struct][I-D.ietf-cose-rfc8152bis-algs] and [I-D.ietf-cose-rfc8152bis-struct][I-D.ietf-cose-rfc8152bis-algs] and
related counter signatures [I-D.ietf-cose-countersign]. related counter signatures [I-D.ietf-cose-countersign].
Readers are also expected to be familiar with the terms and concepts Readers are also expected to be familiar with the terms and concepts
for protection and processing of CoAP messages through OSCORE, such for protection and processing of CoAP messages through OSCORE, such
as "Security Context" and "Master Secret", defined in [RFC8613]. as "Security Context" and "Master Secret", defined in [RFC8613].
Terminology for constrained environments, such as "constrained Terminology for constrained environments, such as "constrained
device" and "constrained-node network", is defined in [RFC7228]. device" and "constrained-node network", is defined in [RFC7228].
This document refers also to the following terminology. This document refers also to the following terminology.
o Keying material: data that is necessary to establish and maintain o Keying material: data that is necessary to establish and maintain
secure communication among endpoints. This includes, for secure communication among endpoints. This includes, for
instance, keys and IVs [RFC4949]. instance, keys and IVs [RFC4949].
o Group: a set of endpoints that share group keying material and o Group: a set of endpoints that share group keying material and
security parameters (Common Context, see Section 2). Unless security parameters (Common Context, see Section 2). That is,
specified otherwise, the term group used in this specification unless otherwise specified, the term group used in this
refers thus to a "security group" (see Section 2.1 of specification refers to a "security group" (see Section 2.1 of
[I-D.ietf-core-groupcomm-bis]), not to be confused with "CoAP [I-D.ietf-core-groupcomm-bis]), not to be confused with "CoAP
group" or "application group". group" or "application group".
o Group Manager: entity responsible for a group. Each endpoint in a o Group Manager: entity responsible for a group. Each endpoint in a
group communicates securely with the respective Group Manager, group communicates securely with the respective Group Manager,
which is neither required to be an actual group member nor to take which is neither required to be an actual group member nor to take
part in the group communication. The full list of part in the group communication. The full list of
responsibilities of the Group Manager is provided in Section 3.2. responsibilities of the Group Manager is provided in Section 3.2.
o Silent server: member of a group that never sends protected o Silent server: member of a group that never sends protected
skipping to change at page 10, line 19 skipping to change at page 10, line 23
[I-D.ietf-cose-rfc8152bis-algs]). [I-D.ietf-cose-rfc8152bis-algs]).
o The second element is the array of COSE capabilities for the COSE o The second element is the array of COSE capabilities for the COSE
key type associated to Counter Signature Algorithm, as specified key type associated to Counter Signature Algorithm, as specified
for that key type in the "Capabilities" column of the "COSE Key for that key type in the "Capabilities" column of the "COSE Key
Types" Registry [COSE.Key.Types] (see Section 8.2 of Types" Registry [COSE.Key.Types] (see Section 8.2 of
[I-D.ietf-cose-rfc8152bis-algs]). [I-D.ietf-cose-rfc8152bis-algs]).
Examples of Counter Signature Parameters are in Appendix G. Examples of Counter Signature Parameters are in Appendix G.
This format is consistent with every counter 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 H describes how Counter Signature Parameters can be
generalized for possible future registered algorithms having a
different set of COSE capabilities.
2.1.4. Secret Derivation Algorithm 2.1.4. Secret Derivation Algorithm
Secret Derivation Algorithm identifies the elliptic curve Diffie- Secret Derivation Algorithm identifies the elliptic curve Diffie-
Hellman algorithm used to derive a static-static Diffie-Hellman Hellman algorithm used to derive a static-static Diffie-Hellman
shared secret, from which pairwise keys are derived (see shared secret, from which pairwise keys are derived (see
Section 2.3.1) to protect messages with the pairwise mode (see Section 2.3.1) to protect messages with the pairwise mode (see
Section 9). Section 9).
This parameter is immutable once the Common Context is established. This parameter is immutable once the Common Context is established.
Secret Derivation Algorithm MUST take value from the "Value" column Secret Derivation Algorithm MUST take value from the "Value" column
skipping to change at page 11, line 16 skipping to change at page 11, line 30
[I-D.ietf-cose-rfc8152bis-algs]). [I-D.ietf-cose-rfc8152bis-algs]).
o The second element is the array of COSE capabilities for the COSE o The second element is the array of COSE capabilities for the COSE
key type associated to Secret Derivation Algorithm, as specified key type associated to Secret Derivation Algorithm, as specified
for that key type in the "Capabilities" column of the "COSE Key for that key type in the "Capabilities" column of the "COSE Key
Types" Registry [COSE.Key.Types] (see Section 8.2 of Types" Registry [COSE.Key.Types] (see Section 8.2 of
[I-D.ietf-cose-rfc8152bis-algs]). [I-D.ietf-cose-rfc8152bis-algs]).
Examples of Secret Derivation Parameters are in Appendix G. Examples of Secret Derivation Parameters are in Appendix G.
This format is consistent with every elliptic curve Diffie-Hellman
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 H describes how Secret Derivation Parameters
can be generalized for possible future registered algorithms having a
different set of COSE capabilities.
2.2. Sender Context and Recipient Context 2.2. Sender Context and Recipient Context
OSCORE specifies the derivation of Sender Context and Recipient OSCORE specifies the derivation of Sender Context and Recipient
Context, specifically of Sender/Recipient Keys and Common IV, from a Context, specifically of Sender/Recipient Keys and Common IV, from a
set of input parameters (see Section 3.2 of [RFC8613]). This set of input parameters (see Section 3.2 of [RFC8613]). This
derivation applies also to Group OSCORE, and the mandatory-to- derivation applies also to Group OSCORE, and the mandatory-to-
implement HKDF and AEAD algorithms are the same as in [RFC8613]. The implement HKDF and AEAD algorithms are the same as in [RFC8613]. The
Sender ID SHALL be unique for each endpoint in a group with a fixed Sender ID SHALL be unique for each endpoint in a group with a fixed
Master Secret, Master Salt and Group Identifier (see Section 3.3 of Master Secret, Master Salt and Group Identifier (see Section 3.3 of
[RFC8613]). [RFC8613]).
For Group OSCORE, the Sender Context and Recipient Context For Group OSCORE, the Sender Context and Recipient Context
additionally contain asymmetric keys, as described previously in additionally contain asymmetric keys, as described previously in
Section 2. The private/public key pair of the sender can, for Section 2. The private/public key pair of the sender can, for
example, be generated by the endpoint or provisioned during example, be generated by the endpoint or provisioned during
manufacturing. manufacturing.
With the exception of the public key of the sender endpoint, a With the exception of the public key of the sender endpoint and the
receiver endpoint can derive a complete Security Context from a possibly associated pairwise keys, a receiver endpoint can derive a
received Group OSCORE message and the Common Context. The public complete Security Context from a received Group OSCORE message and
keys in the Recipient Contexts can be retrieved from the Group the Common Context. The public keys in the Recipient Contexts can be
Manager (see Section 3) upon joining the group. A public key can retrieved from the Group Manager (see Section 3) upon joining the
alternatively be acquired from the Group Manager at a later time, for group. A public key can alternatively be acquired from the Group
example the first time a message is received from a particular Manager at a later time, for example the first time a message is
endpoint in the group (see Section 8.2 and Section 8.4). received from a particular endpoint in the group (see Section 8.2 and
Section 8.4).
For severely constrained devices, it may be not feasible to For severely constrained devices, it may be not feasible to
simultaneously handle the ongoing processing of a recently received simultaneously handle the ongoing processing of a recently received
message in parallel with the retrieval of the sender endpoint's message in parallel with the retrieval of the sender endpoint's
public key. Such devices can be configured to drop a received public key. Such devices can be configured to drop a received
message for which there is no (complete) Recipient Context, and message for which there is no (complete) Recipient Context, and
retrieve the sender endpoint's public key in order to have it retrieve the sender endpoint's public key in order to have it
available to verify subsequent messages from that endpoint. available to verify subsequent messages from that endpoint.
Furthermore, sufficiently large replay windows should be considered, An endpoint admits a maximum amount of Recipient Contexts for a same
to handle Partial IV values moving forward fast. This can happen Security Context, e.g. due to memory limitations. After reaching
when a client engages in frequent or long sequences of one-to-one that limit, the creation of a new Recipient Context results in an
exchanges with servers in the group, such as a large number of block- overflow. When this happens, the endpoint has to delete a current
wise transfers to a single server. When receiving following group Recipient Context to install the new one. It is up to the
requests from that client, other servers in the group may believe to application to define policies for selecting the current Recipient
have lost synchronization with the client's Sender Sequence Number. Context to delete. A newly installed Recipient Context that has
If these servers use an Echo exchange to re-gain synchronization (see required to delete another Recipient Context is initialized with an
Appendix E.3), this in itself may consume a considerable amount of invalid Replay Window, and accordingly requires the endpoint to take
client's Sender Sequence Numbers, hence later resulting in the appropriate actions (see Section 2.4.1.2).
servers possibly performing a new Echo exchange.
2.3. Pairwise Keys 2.3. Pairwise Keys
Certain signature schemes, such as EdDSA and ECDSA, support a secure Certain signature schemes, such as EdDSA and ECDSA, support a secure
combined signature and encryption scheme. This section specifies the combined signature and encryption scheme. This section specifies the
derivation of "pairwise keys", for use in the pairwise mode of Group derivation of "pairwise keys", for use in the pairwise mode defined
OSCORE defined in Section 9. in Section 9.
2.3.1. Derivation of Pairwise Keys 2.3.1. Derivation of Pairwise Keys
Using the Group OSCORE Security Context (see Section 2), a group Using the Group OSCORE Security Context (see Section 2), a group
member can derive AEAD keys to protect point-to-point communication member can derive AEAD keys to protect point-to-point communication
between itself and any other endpoint in the group. The same AEAD between itself and any other endpoint in the group. The same AEAD
algorithm as in the group mode is used. The key derivation of these algorithm as in the group mode is used. The key derivation of these
so-called pairwise keys follows the same construction as in so-called pairwise keys follows the same construction as in
Section 3.2.1 of [RFC8613]: Section 3.2.1 of [RFC8613]:
Pairwise Recipient Key = HKDF(Recipient Key, Shared Secret, info, L)
Pairwise Sender Key = HKDF(Sender Key, Shared Secret, info, L) Pairwise Sender Key = HKDF(Sender Key, Shared Secret, info, L)
Pairwise Recipient Key = HKDF(Recipient Key, Shared Secret, info, L)
where: where:
o The Pairwise Recipient Key is the AEAD key for processing incoming
messages from endpoint X.
o The Pairwise Sender Key is the AEAD key for processing outgoing o The Pairwise Sender Key is the AEAD key for processing outgoing
messages addressed to endpoint X. messages addressed to endpoint X.
o The Pairwise Recipient Key is the AEAD key for processing incoming
messages from endpoint X.
o HKDF is the HKDF algorithm specified by Secret Derivation o HKDF is the HKDF algorithm specified by Secret Derivation
Algorithm from the Common Context (see Section 2.1.4). Algorithm from the Common Context (see Section 2.1.4).
o The Shared Secret is computed as a static-static Diffie-Hellman o The Sender Key and private key are from the Sender Context. The
shared secret [NIST-800-56A], where the endpoint uses its private Sender Key is used as salt in the HKDF, when deriving the Pairwise
key and the public key of the other endpoint X. Sender Key.
o The Recipient Key and the public key are from the Recipient o The Recipient Key and the public key are from the Recipient
Context associated to endpoint X. Context associated to endpoint X. The Recipient Key is used as
salt in the HKDF, when deriving the Pairwise Recipient Key.
o The Sender Key and private key are from the Sender Context. o The Shared Secret is computed as a static-static Diffie-Hellman
shared secret [NIST-800-56A], where the endpoint uses its private
key and the public key of the other endpoint X. The Shared Secret
is used as Input Keying Material (IKM) in the HKDF.
o info and L are defined as in Section 3.2.1 of [RFC8613]. o info and L are as defined in Section 3.2.1 of [RFC8613].
If EdDSA asymmetric keys are used, the Edward coordinates are mapped If EdDSA asymmetric keys are used, the Edward coordinates are mapped
to Montgomery coordinates using the maps defined in Sections 4.1 and to Montgomery coordinates using the maps defined in Sections 4.1 and
4.2 of [RFC7748], before using the X25519 and X448 functions defined 4.2 of [RFC7748], before using the X25519 and X448 functions defined
in Section 5 of [RFC7748]. in Section 5 of [RFC7748].
After establishing a partially or completely new Security Context After establishing a partially or completely new Security Context
(see Section 3.1 and Section 2.4), the old pairwise keys MUST be (see Section 2.4 and Section 3.1), the old pairwise keys MUST be
deleted. Since new Sender/Recipient Keys are derived from the new deleted. Since new Sender/Recipient Keys are derived from the new
group keying material (see Section 2.2), every group member MUST use group keying material (see Section 2.2), every group member MUST use
the new Sender/Recipient Keys when deriving new pairwise keys. the new Sender/Recipient Keys when deriving new pairwise keys.
As long as any two group members preserve the same asymmetric keys, As long as any two group members preserve the same asymmetric keys,
their Diffie-Hellman shared secret does not change across updates of their Diffie-Hellman shared secret does not change across updates of
the group keying material. the group keying material.
2.3.2. Usage of Sequence Numbers 2.3.2. Usage of Sequence Numbers
skipping to change at page 14, line 34 skipping to change at page 15, line 10
On the other hand, the mutable parts of the Security Context are On the other hand, the mutable parts of the Security Context are
updated by the endpoint when executing the security protocol, but may updated by the endpoint when executing the security protocol, but may
nevertheless become outdated, e.g. due to loss of the mutable nevertheless become outdated, e.g. due to loss of the mutable
Security Context (see Section 2.4.1) or exhaustion of Sender Sequence Security Context (see Section 2.4.1) or exhaustion of Sender Sequence
Numbers (see Section 2.4.2). Numbers (see Section 2.4.2).
If it is not feasible or practically possible to store and maintain If it is not feasible or practically possible to store and maintain
up-to-date the mutable part in non-volatile memory (e.g., due to up-to-date the mutable part in non-volatile memory (e.g., due to
limited number of write operations), the endpoint MUST be able to limited number of write operations), the endpoint MUST be able to
detect a loss of the mutable Security Context. detect a loss of the mutable Security Context and MUST accordingly
take the actions defined in Section 2.4.1.
When a loss of mutable Security Context is detected (e.g., following
a reboot), the endpoint MUST NOT protect further messages using this
Security Context to avoid reusing a nonce with the same AEAD key, and
SHOULD instead retrieve new security parameters from the Group
Manager (see Section 2.4.1).
2.4.1. Loss of Mutable Security Context 2.4.1. Loss of Mutable Security Context
An endpoint that has lost its mutable Security Context, e.g. due to a An endpoint may lose its mutable Security Context, e.g. due to a
reboot, needs to prevent the re-use of a nonce with the same AEAD reboot (see Section 2.4.1.1) or to an overflow of Recipient Contexts
key, and to handle incoming replayed messages. (see Section 2.4.1.2).
To this end, after a loss of mutable Security Context, the endpoint In such a case, the endpoint needs to prevent the re-use of a nonce
SHOULD inform the Group Manager, retrieve new Security Context with the same AEAD key, and to handle incoming replayed messages.
parameters from the Group Manager (see Section 2.4.3), and use them
to derive a new Sender Context (see Section 2.2). In particular,
regardless the exact actions taken by the Group Manager, the endpoint
resets its Sender Sequence Number to 0, and derives a new Sender Key.
This is in turn used to possibly derive new Pairwise Sender Keys.
From then on, the endpoint MUST use its latest installed Sender 2.4.1.1. Reboot and Total Loss
Context to protect outgoing messages.
If an endpoint is not able to establish an updated Sender Context, In case a loss of the Sender Context and/or of the Recipient Contexts
e.g. because of lack of connectivity with the Group Manager, the is detected (e.g. following a reboot), the endpoint MUST NOT protect
endpoint MUST NOT protect further messages using the current Security further messages using this Security Context to avoid reusing an AEAD
Context. nonce with the same AEAD key.
In order to handle the update of Replay Window in Recipient Contexts, In particular, before resuming its operations in the group, the
three approaches are discussed in Appendix E. In particular, the endpoint MUST retrieve new Security Context parameters from the Group
approach specified in Appendix E.3 and based on the Echo Option Manager (see Section 2.4.3) and use them to derive a new Sender
[I-D.ietf-core-echo-request-tag] is a variant of the approach defined Context (see Section 2.2). Since this includes a newly derived
in Appendix B.1.2 of [RFC8613] as applicable to Group OSCORE. Sender Key, the server will not reuse the same pair (key, nonce),
even when using the Partial IV of (old re-injected) requests to build
the AEAD nonce for protecting the corresponding responses.
From then on, the endpoint MUST use the latest installed Sender
Context to protect outgoing messages. Also, newly created Recipient
Contexts will have a Replay Window which is initialized as valid.
If not able to establish an updated Sender Context, e.g. because of
lack of connectivity with the Group Manager, the endpoint MUST NOT
protect further messages using the current Security Context and MUST
NOT accept incoming messages from other group members, as currently
unable to detect possible replays.
2.4.1.2. Overflow of Recipient Contexts
After reaching the maximum amount of Recipient Contexts, an endpoint
will experience an overflow when installing a new Recipient Context,
as it requires to first delete an existing one (see Section 2.2).
Every time this happens, the Replay Window of the new Recipient
Context is initialized as not valid. Therefore, the endpoint MUST
take the following actions, before accepting request messages from
the client associated to the new Recipient Context.
If it is not configured as silent server, the endpoint MUST either:
o Retrieve new Security Context parameters from the Group Manager
and derive a new Sender Context, as defined in Section 2.4.1.1; or
o When receiving a first request to process with the new Recipient
Context, use the approach specified in Appendix E and based on the
Echo Option for CoAP [I-D.ietf-core-echo-request-tag], if
supported. In particular, the endpoint MUST use its Partial IV
when generating the AEAD nonce and MUST include the Partial IV in
the response message conveying the Echo Option. If the endpoint
supports the CoAP Echo Option, it is RECOMMENDED to take this
approach.
If it is configured exclusively as silent server, the endpoint MUST
wait for the next group rekeying to occur, in order to derive a new
Security Context and re-initialize the Replay Window of each
Recipient Contexts as valid.
2.4.2. Exhaustion of Sender Sequence Number 2.4.2. Exhaustion of Sender Sequence Number
An endpoint can eventually exhaust the Sender Sequence Number, which An endpoint can eventually exhaust the Sender Sequence Number, which
is incremented for each new outgoing message including a Partial IV. is incremented for each new outgoing message including a Partial IV.
This is the case for group requests, Observe notifications [RFC7641] This is the case for group requests, Observe notifications [RFC7641]
and, optionally, any other response. and, optionally, any other response.
Implementations MUST be able to detect an exhaustion of Sender Implementations MUST be able to detect an exhaustion of Sender
Sequence Number, after the endpoint has consumed the largest usable Sequence Number, after the endpoint has consumed the largest usable
value. If an implementation's integers support wrapping addition, value. If an implementation's integers support wrapping addition,
the implementation MUST treat Sender Sequence Number as exhausted the implementation MUST treat Sender Sequence Number as exhausted
when a wrap-around is detected. when a wrap-around is detected.
Upon exhausting the Sender Sequence Numbers, the endpoint MUST NOT Upon exhausting the Sender Sequence Numbers, the endpoint MUST NOT
use this Security Context to protect further messages including a use this Security Context to protect further messages including a
Partial IV. Partial IV.
The endpoint SHOULD inform the Group Manager, retrieve new Security The endpoint SHOULD inform the Group Manager, retrieve new Security
Context parameters from the Group Manager (see Section 2.4.3), and Context parameters from the Group Manager (see Section 2.4.3), and
use them to derive a new Sender Context (see Section 2.2). In use them to derive a new Sender Context (see Section 2.2).
particular, regardless the exact actions taken by the Group Manager,
the endpoint resets its Sender Sequence Number to 0, and derives a
new Sender Key. This is in turn used to possibly derive new Pairwise
Sender Keys.
From then on, the endpoint MUST use its latest installed Sender From then on, the endpoint MUST use its latest installed Sender
Context to protect outgoing messages. Context to protect outgoing messages.
2.4.3. Retrieving New Security Context Parameters 2.4.3. Retrieving New Security Context Parameters
The Group Manager can assist an endpoint with an incomplete Sender The Group Manager can assist an endpoint with an incomplete Sender
Context to retrieve missing data of the Security Context and thereby Context to retrieve missing data of the Security Context and thereby
become fully operational in the group again. The two main options become fully operational in the group again. The two main options
for the Group Manager are described in this section: i) assignment of for the Group Manager are described in this section: i) assignment of
a new Sender ID to the endpoint (see Section 2.4.3.1); and ii) a new Sender ID to the endpoint (see Section 2.4.3.1); and ii)
establishment of a new Security Context for the group (see establishment of a new Security Context for the group (see
Section 2.4.3.2). Update of Replay Window in Recipient Contexts is Section 2.4.3.2). The update of the Replay Window in each of the
discussed in Section 6.1. Recipient Contexts is discussed in Section 6.1.
As group membership changes, or as group members get new Sender IDs As group membership changes, or as group members get new Sender IDs
(see Section 2.4.3.1) so do the relevant Recipient IDs that the other (see Section 2.4.3.1) so do the relevant Recipient IDs that the other
endpoints need to keep track of. As a consequence, group members may endpoints need to keep track of. As a consequence, group members may
end up retaining stale Recipient Contexts, that are no longer useful end up retaining stale Recipient Contexts, that are no longer useful
to verify incoming secure messages. to verify incoming secure messages.
The Recipient ID ('kid') SHOULD NOT be considered as a persistent and The Recipient ID ('kid') SHOULD NOT be considered as a persistent and
reliable indicator of a group member. Such an indication can be reliable indicator of a group member. Such an indication can be
achieved only by using that member's public key, when verifying achieved only by using that member's public key, when verifying
skipping to change at page 16, line 40 skipping to change at page 17, line 40
(long-)unused Recipient Contexts and reduce the impact on storage (long-)unused Recipient Contexts and reduce the impact on storage
space; as well as ii) check with the Group Manager that a public key space; as well as ii) check with the Group Manager that a public key
is currently the one associated to a 'kid' value, after a number of is currently the one associated to a 'kid' value, after a number of
consecutive failed verifications. consecutive failed verifications.
2.4.3.1. New Sender ID for the Endpoint 2.4.3.1. New Sender ID for the Endpoint
The Group Manager may assign a new Sender ID to an endpoint, while The Group Manager may assign a new Sender ID to an endpoint, while
leaving the Gid, Master Secret and Master Salt unchanged in the leaving the Gid, Master Secret and Master Salt unchanged in the
group. In this case, the Group Manager MUST assign a Sender ID that group. In this case, the Group Manager MUST assign a Sender ID that
has never been assigned before in the group. has never been assigned before in the group under the current Gid
value.
Having retrieved the new Sender ID, and potentially other missing Having retrieved the new Sender ID, and potentially other missing
data of the immutable Security Context, the endpoint can derive a new data of the immutable Security Context, the endpoint can derive a new
Sender Context (see Section 2.2). When doing so, the endpoint re- Sender Context (see Section 2.2). When doing so, the endpoint resets
initilizes the Sender Sequence Number in its Sender Context to 0. the Sender Sequence Number in its Sender Context to 0, and derives a
new Sender Key. This is in turn used to possibly derive new Pairwise
Sender Keys.
From then on, the endpoint MUST use its latest installed Sender From then on, the endpoint MUST use its latest installed Sender
Context to protect outgoing messages. Context to protect outgoing messages.
The assignment of a new Sender ID may be the result of different The assignment of a new Sender ID may be the result of different
processes. The endpoint may request a new Sender ID, e.g. because of processes. The endpoint may request a new Sender ID, e.g. because of
exhaustion of Sender Sequence Numbers (see Section 2.4.2). An exhaustion of Sender Sequence Numbers (see Section 2.4.2). An
endpoint may request to re-join the group, e.g. because of losing its endpoint may request to re-join the group, e.g. because of losing its
mutable Security Context (see Section 2.4.1), and receive as response mutable Security Context (see Section 2.4.1), and is provided with a
a new Sender ID together with the latest immutable Security Context. new Sender ID together with the latest immutable Security Context.
For the other group members, the Recipient Context corresponding to For the other group members, the Recipient Context corresponding to
the old Sender ID becomes stale (see Section 3.1). the old Sender ID becomes stale (see Section 3.1).
2.4.3.2. New Security Context for the Group 2.4.3.2. New Security Context for the Group
The Group Manager may establish a new Security Context for the group The Group Manager may establish a new Security Context for the group
(see Section 3.1). The Group Manager does not necessarily establish (see Section 3.1). The Group Manager does not necessarily establish
a new Security Context for the group if one member has an outdated a new Security Context for the group if one member has an outdated
Security Context (see Section 2.4.3.1), unless that was already Security Context (see Section 2.4.3.1), unless that was already
skipping to change at page 18, line 36 skipping to change at page 19, line 39
interacts with the group members. The responsibilities of the Group interacts with the group members. The responsibilities of the Group
Manager are compiled in Section 3.2. Manager are compiled in Section 3.2.
It is RECOMMENDED to use a Group Manager as described in It is RECOMMENDED to use a Group Manager as described in
[I-D.ietf-ace-key-groupcomm-oscore], where the join process is based [I-D.ietf-ace-key-groupcomm-oscore], where the join process is based
on the ACE framework for authentication and authorization in on the ACE framework for authentication and authorization in
constrained environments [I-D.ietf-ace-oauth-authz]. constrained environments [I-D.ietf-ace-oauth-authz].
The Group Manager assigns unique Group Identifiers (Gids) to The Group Manager assigns unique Group Identifiers (Gids) to
different groups under its control, as well as unique Sender IDs (and different groups under its control, as well as unique Sender IDs (and
thereby Recipient IDs) to the members of those groups. The Group thereby Recipient IDs) to the members of those groups. According to
Manager MUST NOT reassign a Sender ID within the same group, and MUST a hierarchical approach, the Gid value assigned to a group is
NOT reassign a Gid value to the same group. According to a
hierarchical approach, the Gid value assigned to a group is
associated to a dedicated space for the values of Sender ID and associated to a dedicated space for the values of Sender ID and
Recipient ID of the members of that group. Recipient ID of the members of that group.
The Group Manager MUST NOT reassign a Gid value to the same group,
and MUST NOT reassign a Sender ID within the same group under the
same Gid value.
In addition, the Group Manager maintains records of the public keys In addition, the Group Manager maintains records of the public keys
of endpoints in a group, and provides information about the group and of endpoints in a group, and provides information about the group and
its members to other members and selected roles. Upon nodes' its members to other group members and selected roles. Upon nodes'
joining, the Group Manager collects such public keys and MUST verify joining, the Group Manager collects such public keys and MUST verify
proof-of-possession of the respective private key. proof-of-possession of the respective private key.
An endpoint acquires group data such as the Gid and OSCORE input An endpoint acquires group data such as the Gid and OSCORE input
parameters including its own Sender ID from the Group Manager, and parameters including its own Sender ID from the Group Manager, and
provides information about its public key to the Group Manager, for provides information about its public key to the Group Manager, for
example upon joining the group. example upon joining the group.
A group member can retrieve from the Group Manager the public key and A group member can retrieve from the Group Manager the public key and
other information associated to another group member, with which it other information associated to another member of the group, with
can generate the corresponding Recipient Context. An application can which it can generate the corresponding Recipient Context. In
particular, the requested public key is provided together with the
Sender ID of the associated group member. An application can
configure a group member to asynchronously retrieve information about configure a group member to asynchronously retrieve information about
Recipient Contexts, e.g. by Observing [RFC7641] a resource at the Recipient Contexts, e.g. by Observing [RFC7641] a resource at the
Group Manager to get updates on the group membership. Group Manager to get updates on the group membership.
The Group Manager MAY serve additional entities acting as signature The Group Manager MAY serve additional entities acting as signature
checkers, e.g. intermediary gateways. These entities do not join a checkers, e.g. intermediary gateways. These entities do not join a
group as members, but can retrieve public keys of group members from group as members, but can retrieve public keys of group members from
the Group Manager, in order to verify counter signatures of group the Group Manager, in order to verify counter signatures of group
messages. A signature checker MUST be authorized for retrieving messages. A signature checker MUST be authorized for retrieving
public keys of members in a specific group from the Group Manager. public keys of members in a specific group from the Group Manager.
To this end, the same method mentioned above based on the ACE To this end, the same method mentioned above based on the ACE
framework [I-D.ietf-ace-oauth-authz] can be used. framework [I-D.ietf-ace-oauth-authz] can be used.
3.1. Management of Group Keying Material 3.1. Management of Group Keying Material
In order to establish a new Security Context for a group, a new Group In order to establish a new Security Context for a group, a new Group
Identifier (Gid) for that group and a new value for the Master Secret Identifier (Gid) for that group and a new value for the Master Secret
parameter MUST be generated. When distributing the new Gid and parameter MUST be generated. When distributing the new Gid and
Master Secret, the Group Manager MAY distribute also a new value for Master Secret, the Group Manager MAY distribute also a new value for
the Master Salt parameter, and SHOULD preserve the current value of the Master Salt parameter, and should preserve the current value of
the Sender ID of each group member. the Sender ID of each group member.
The Group Manager MUST NOT reassign a Gid value to the same group. The Group Manager MUST NOT reassign a Gid value to the same group.
That is, each group can have a given Gid at most once during its That is, every group can have a given Gid at most once during its
lifetime. An example of Gid format supporting this operation is lifetime. An example of Gid format supporting this operation is
provided in Appendix C. provided in Appendix C.
The Group Manager MUST NOT reassign a previously used Sender ID The Group Manager MUST NOT reassign a previously used Sender ID
('kid') with the same Gid, Master Secret and Master Salt. Even if ('kid') with the same Gid, Master Secret and Master Salt. That is,
Gid and Master Secret are renewed as described in this section, the the Group Manager MUST NOT reassign a Sender ID value within a same
Group Manager MUST NOT reassign an endpoint's Sender ID ('kid') group under the same Gid value (see Section 2.4.3.1). Within this
within a same group (see Section 2.4.3.1). restriction, the Group Manager can assign a Sender ID used under an
old Gid value, thus avoiding Sender ID values to irrecoverably grow
in size.
Even when an endpoint joining a group is recognized as a current
member of that group, e.g. through the ongoing secure communication
association, the Group Manager MUST assign a new Sender ID different
than the one currently used by the endpoint in the group, unless the
group is rekeyed first and a new Gid value is established.
Figure 2 overviews the different keying material components,
considering their relation and possible reuse across group rekeying.
Components changed in lockstep * Changing a kid does not
upon a group rekeying need changing the Group ID
+----------------------------+
| | * A kid is not reassigned
| Master Group |<--> kid1 under the same Group ID
| Secret <---> o <---> ID |
| ^ |<--> kid2 * Upon changing the Group ID,
| | | every current kid should
| | |<--> kid3 be preserved for efficient
| v | key rollover
| Master Salt | ... ...
| (optional) | * After changing Group ID, an
| | unused kid can be assigned
+----------------------------+
Figure 2: Relations among keying material components.
If required by the application (see Appendix A.1), it is RECOMMENDED If required by the application (see Appendix A.1), it is RECOMMENDED
to adopt a group key management scheme, and securely distribute a new to adopt a group key management scheme, and securely distribute a new
value for the Gid and for the Master Secret parameter of the group's value for the Gid and for the Master Secret parameter of the group's
Security Context, before a new joining endpoint is added to the group Security Context, before a new joining endpoint is added to the group
or after a currently present endpoint leaves the group. This is or after a currently present endpoint leaves the group. This is
necessary to preserve backward security and forward security in the necessary to preserve backward security and forward security in the
group, if the application requires it. group, if the application requires it.
The specific approach used to distribute new group data is out of the The specific approach used to distribute new group data is out of the
skipping to change at page 20, line 24 skipping to change at page 22, line 11
2. Defining policies for authorizing the joining of its OSCORE 2. Defining policies for authorizing the joining of its OSCORE
groups. groups.
3. Handling the join process to add new endpoints as group members. 3. Handling the join process to add new endpoints as group members.
4. Establishing the Common Context part of the Security Context, 4. Establishing the Common Context part of the Security Context,
and providing it to authorized group members during the join and providing it to authorized group members during the join
process, together with the corresponding Sender Context. process, together with the corresponding Sender Context.
5. Generating and managing Sender IDs within its OSCORE groups, as 5. Updating the Gid of its OSCORE groups, upon renewing the
respective Security Context. This includes ensuring that the
same Gid value is not reassigned to the same group.
6. Generating and managing Sender IDs within its OSCORE groups, as
well as assigning and providing them to new endpoints during the well as assigning and providing them to new endpoints during the
join process, or to current group members upon request of join process, or to current group members upon request of
renewal. This includes ensuring that each Sender ID is unique renewal or re-joining.
within each of the OSCORE groups, and that it is not reassigned
within the same group.
6. Defining communication policies for each of its OSCORE groups, This includes ensuring that each Sender ID: is unique within
and signalling them to new endpoints during the join process. each of the OSCORE groups; and is not reassigned within the same
group under the same Gid value, i.e. not even to a current group
member re-joining the same group without a rekeying happening
first.
7. Renewing the Security Context of an OSCORE group upon membership 7. Defining communication policies for each of its OSCORE groups,
and signaling them to new endpoints during the join process.
8. Renewing the Security Context of an OSCORE group upon membership
change, by revoking and renewing common security parameters and change, by revoking and renewing common security parameters and
keying material (rekeying). keying material (rekeying).
8. Providing the management keying material that a new endpoint 9. Providing the management keying material that a new endpoint
requires to participate in the rekeying process, consistently requires to participate in the rekeying process, consistently
with the key management scheme used in the group joined by the with the key management scheme used in the group joined by the
new endpoint. new endpoint.
9. Updating the Gid of its OSCORE groups, upon renewing the
respective Security Context. This includes ensuring that the
same Gid value is not reassigned to the same group.
10. Acting as key repository, in order to handle the public keys of 10. Acting as key repository, in order to handle the public keys of
the members of its OSCORE groups, and providing such public keys the members of its OSCORE groups, and providing such public keys
to other members of the same group upon request. The actual to other members of the same group upon request. The actual
storage of public keys may be entrusted to a separate secure storage of public keys may be entrusted to a separate secure
storage device or service. storage device or service.
11. Validating that the format and parameters of public keys of 11. Validating that the format and parameters of public keys of
group members are consistent with the countersignature algorithm group members are consistent with the countersignature algorithm
and related parameters used in the respective OSCORE group. and related parameters used in the respective OSCORE group.
skipping to change at page 21, line 24 skipping to change at page 23, line 17
Building on Section 5 of [RFC8613], this section defines how to use Building on Section 5 of [RFC8613], this section defines how to use
COSE [I-D.ietf-cose-rfc8152bis-struct] to wrap and protect data in COSE [I-D.ietf-cose-rfc8152bis-struct] to wrap and protect data in
the original message. OSCORE uses the untagged COSE_Encrypt0 the original message. OSCORE uses the untagged COSE_Encrypt0
structure with an Authenticated Encryption with Associated Data structure with an Authenticated Encryption with Associated Data
(AEAD) algorithm. Unless otherwise specified, the following (AEAD) algorithm. Unless otherwise specified, the following
modifications apply for both the group mode and the pairwise mode of modifications apply for both the group mode and the pairwise mode of
Group OSCORE. Group OSCORE.
4.1. Counter Signature 4.1. Counter Signature
For the group mode only, the 'unprotected' field MUST additionally When protecting a message in group mode, the 'unprotected' field MUST
include the following parameter: additionally include the following parameter:
o COSE_CounterSignature0: its value is set to the counter signature o COSE_CounterSignature0: its value is set to the counter signature
of the COSE object, computed by the sender as described in of the COSE object, computed by the sender as described in
Sections 3.2 and 3.3 of [I-D.ietf-cose-countersign], by using its Sections 3.2 and 3.3 of [I-D.ietf-cose-countersign], by using its
private key and according to the Counter Signature Algorithm and private key and according to the Counter Signature Algorithm and
Counter Signature Parameters in the Security Context. Counter Signature Parameters in the Security Context.
In particular, the Countersign_structure contains the context text In particular, the Countersign_structure contains the context text
string "CounterSignature0", the external_aad as defined in string "CounterSignature0", the external_aad as defined in
Section 4.3.2 of this specification, and the ciphertext of the Section 4.3 of this specification, and the ciphertext of the COSE
COSE object as payload. object as payload.
4.2. The 'kid' and 'kid context' parameters 4.2. The 'kid' and 'kid context' parameters
The value of the 'kid' parameter in the 'unprotected' field of The value of the 'kid' parameter in the 'unprotected' field of
response messages MUST be set to the Sender ID of the endpoint response messages MUST be set to the Sender ID of the endpoint
transmitting the message. That is, unlike in [RFC8613], the 'kid' transmitting the message, if the request was protected in group mode.
parameter is always present in all messages, both requests and That is, unlike in [RFC8613], the 'kid' parameter is always present
responses. in responses to a request that was protected in group mode.
The value of the 'kid context' parameter in the 'unprotected' field The value of the 'kid context' parameter in the 'unprotected' field
of requests messages MUST be set to the ID Context, i.e. the Group of requests messages MUST be set to the ID Context, i.e. the Group
Identifier value (Gid) of the group. That is, unlike in [RFC8613], Identifier value (Gid) of the group. That is, unlike in [RFC8613],
the 'kid context' parameter is always present in requests. the 'kid context' parameter is always present in requests.
4.3. external_aad 4.3. external_aad
The external_aad of the Additional Authenticated Data (AAD) is The external_aad of the Additional Authenticated Data (AAD) is
different compared to OSCORE. In particular, there is one different compared to OSCORE, and is defined in this section.
external_aad used for encryption (both in group mode and pairwise
mode), and another external_aad used for signing (only in group
mode).
4.3.1. external_aad for Encryption The same external_aad structure is used in group mode and pairwise
mode for encryption (see Section 5.3 of
[I-D.ietf-cose-rfc8152bis-struct]), as well as in group mode for
signing (see Section 4.4 of [I-D.ietf-cose-rfc8152bis-struct]).
The external_aad for encryption (see Section 4.3 of In particular, the external_aad includes also the counter signature
[I-D.ietf-cose-rfc8152bis-struct]), used both in group mode and algorithm and related signature parameters, the value of the 'kid
pairwise mode, includes also the counter signature algorithm and context' in the COSE object of the request, and the OSCORE option of
related signature parameters, as well as the value of the 'kid the protected message.
context' in the COSE object of the request (see Figure 2).
external_aad = bstr .cbor aad_array external_aad = bstr .cbor aad_array
aad_array = [ aad_array = [
oscore_version : uint, oscore_version : uint,
algorithms : [alg_aead : int / tstr, algorithms : [alg_aead : int / tstr,
alg_countersign : int / tstr, alg_countersign : int / tstr,
par_countersign : [countersign_alg_capab, par_countersign : [countersign_alg_capab,
countersign_key_type_capab], countersign_key_type_capab]],
par_countersign_key : countersign_key_type_capab], request_kid : bstr,
request_kid : bstr, request_piv : bstr,
request_piv : bstr, options : bstr,
options : bstr, request_kid_context : bstr,
request_kid_context : bstr OSCORE_option: bstr
] ]
Figure 2: external_aad for Encryption Figure 3: external_aad
Compared with Section 5.4 of [RFC8613], the aad_array has the Compared with Section 5.4 of [RFC8613], the aad_array has the
following differences. following differences.
o The 'algorithms' array in the aad_array additionally includes: o The 'algorithms' array additionally includes:
* 'alg_countersign', which specifies Counter Signature Algorithm * 'alg_countersign', which specifies Counter Signature Algorithm
from the Common Context (see Section 2.1.2). This parameter from the Common Context (see Section 2.1.2). This parameter
MUST encode the value of Counter Signature Algorithm as a CBOR MUST encode the value of Counter Signature Algorithm as a CBOR
integer or text string, consistently with the "Value" field in integer or text string, consistently with the "Value" field in
the "COSE Algorithms" Registry for this counter signature the "COSE Algorithms" Registry for this counter signature
algorithm. algorithm.
* 'par_countersign', which specifies the CBOR array Counter * 'par_countersign', which specifies the CBOR array Counter
Signature Parameters from the Common Context (see Signature Parameters from the Common Context (see
skipping to change at page 23, line 16 skipping to change at page 25, line 5
for the countersignature algorithm indicated in for the countersignature algorithm indicated in
'alg_countersign'. This is the first element of the CBOR 'alg_countersign'. This is the first element of the CBOR
array Counter Signature Parameters from the Common Context. array Counter Signature Parameters from the Common Context.
+ 'countersign_key_type_capab' is the array of COSE + 'countersign_key_type_capab' is the array of COSE
capabilities for the COSE key type used by the capabilities for the COSE key type used by the
countersignature algorithm indicated in 'alg_countersign'. countersignature algorithm indicated in 'alg_countersign'.
This is the second element of the CBOR array Counter This is the second element of the CBOR array Counter
Signature Parameters from the Common Context. Signature Parameters from the Common Context.
* 'par_countersign_key', which specifies the parameters This format is consistent with every counter signature
associated to the keys used with the countersignature algorithm algorithm currently considered in
indicated in 'alg_countersign'. These parameters are encoded [I-D.ietf-cose-rfc8152bis-algs], i.e. with algorithms that have
as a CBOR array 'countersign_key_type_capab', whose exact only the COSE key type as their COSE capability. Appendix H
structure and value depend on the value of 'alg_countersign'. describes how 'par_countersign' can be generalized for possible
future registered algorithms having a different set of COSE
In particular, 'countersign_key_type_capab' is the array of capabilities.
COSE capabilities for the COSE key type of the keys used with
the countersignature algorithm. This is the second element of
the CBOR array Counter Signature Parameters from the Common
Context.
Examples of 'par_countersign_key' are in Appendix G.
o The new element 'request_kid_context' contains the value of the o The new element 'request_kid_context' contains the value of the
'kid context' in the COSE object of the request (see Section 4.2). 'kid context' in the COSE object of the request (see Section 4.2).
4.3.2. external_aad for Signing In case Observe [RFC7641] is used, this enables endpoints to
safely keep an observation active beyond a possible change of Gid,
The external_aad for signing (see Section 4.3 of i.e. of ID Context, following a group rekeying (see Section 3.1).
[I-D.ietf-cose-rfc8152bis-struct]) used in group mode is identical to In fact, it ensures that every notification cryptographically
the external_aad for encryption (see Section 4.3.1) with the addition matches with only one observation request, rather than with
of the OSCORE option (see Figure 3). multiple ones that were protected with different keying material
but share the same 'request_kid' and 'request_piv' values.
external_aad = bstr .cbor aad_array
aad_array = [
oscore_version : uint,
algorithms : [alg_aead : int / tstr,
alg_countersign : int / tstr,
par_countersign : [countersign_alg_capab,
countersign_key_type_capab],
par_countersign_key : countersign_key_type_capab],
request_kid : bstr,
request_piv : bstr,
options : bstr,
request_kid_context : bstr,
OSCORE_option: bstr
]
Figure 3: external_aad for Signing
Compared with Section 5.4 of [RFC8613] the aad_array additionally
includes:
o the 'algorithms' array, as defined in the external_aad for
encryption (see Section 4.3.1);
o the 'request_kid_context' element, as defined in the external_aad
for encryption (see Section 4.3.1);
o the value of the OSCORE Option present in the protected message, o The new element 'OSCORE_option', containing the value of the
encoded as a binary string. OSCORE Option present in the protected message, encoded as a
binary string. This prevents the attack described in Section 10.6
when using the group mode, as further explained in Section 10.6.2.
Note for implementation: this construction requires the OSCORE option Note for implementation: this construction requires the OSCORE
of the message to be generated before calculating the signature. option of the message to be generated and finalized before
Also, the aad_array needs to be large enough to contain the largest computing the ciphertext of the COSE_Encrypt0 object (when using
possible OSCORE option. the group mode or the pairwise mode) and before calculating the
counter signature (when using the group mode). Also, the
aad_array needs to be large enough to contain the largest possible
OSCORE option.
5. OSCORE Header Compression 5. OSCORE Header Compression
The OSCORE header compression defined in Section 6 of [RFC8613] is The OSCORE header compression defined in Section 6 of [RFC8613] is
used, with the following differences. used, with the following differences.
o The payload of the OSCORE message SHALL encode the ciphertext of o The payload of the OSCORE message SHALL encode the ciphertext of
the COSE_Encrypt0 object. In the group mode, the ciphertext above the COSE_Encrypt0 object. In the group mode, the ciphertext above
is concatenated with the value of the COSE_CounterSignature0 of is concatenated with the value of the COSE_CounterSignature0 of
the COSE object, computed as described in Section 4.1. the COSE object, computed as described in Section 4.1.
o This specification defines the usage of the sixth least o This specification defines the usage of the sixth least
significant bit, called the "Group Flag", in the first byte of the significant bit, called "Group Flag", in the first byte of the
OSCORE option containing the OSCORE flag bits. This flag bit is OSCORE option containing the OSCORE flag bits. This flag bit is
specified in Section 11.1. specified in Section 11.1.
o The Group Flag MUST be set to 1 if the OSCORE message is protected o The Group Flag MUST be set to 1 if the OSCORE message is protected
using the group mode (see Section 8). using the group mode (see Section 8).
o The Group Flag MUST be set to 0 if the OSCORE message is protected o The Group Flag MUST be set to 0 if the OSCORE message is protected
using the pairwise mode (see Section 9). The Group Flag MUST also using the pairwise mode (see Section 9). The Group Flag MUST also
be set to 0 for ordinary OSCORE messages processed according to be set to 0 for ordinary OSCORE messages processed according to
[RFC8613]. [RFC8613].
skipping to change at page 25, line 33 skipping to change at page 26, line 31
examples do not include the full CoAP unprotected message or the full examples do not include the full CoAP unprotected message or the full
Security Context, but only the input necessary to the compression Security Context, but only the input necessary to the compression
mechanism, i.e. the COSE_Encrypt0 object. The output is the mechanism, i.e. the COSE_Encrypt0 object. The output is the
compressed COSE object as defined in Section 5 and divided into two compressed COSE object as defined in Section 5 and divided into two
parts, since the object is transported in two CoAP fields: OSCORE parts, since the object is transported in two CoAP fields: OSCORE
option and payload. option and payload.
The examples assume that the plaintext (see Section 5.3 of [RFC8613]) The examples assume that the plaintext (see Section 5.3 of [RFC8613])
is 6 bytes long, and that the AEAD tag is 8 bytes long, hence is 6 bytes long, and that the AEAD tag is 8 bytes long, hence
resulting in a ciphertext which is 14 bytes long. When using the resulting in a ciphertext which is 14 bytes long. When using the
group mode, COUNTERSIGN denotes the COSE_CounterSignature0 byte group mode, the COSE_CounterSignature0 byte string as described in
string as described in Section 4, and is 64 bytes long. Section 4 is assumed to be 64 bytes long.
5.1.1. Examples in Group Mode 5.1.1. Examples in Group Mode
o Request with ciphertext = 0xaea0155667924dff8a24e4cb35b9, kid = o Request with ciphertext = 0xaea0155667924dff8a24e4cb35b9, kid =
0x25, Partial IV = 5 and kid context = 0x44616c 0x25, Partial IV = 5 and kid context = 0x44616c.
Before compression (96 bytes): * Before compression (96 bytes):
[ [
h'', h'',
{ 4:h'25', 6:h'05', 10:h'44616c', 11:COUNTERSIGN }, { 4:h'25', 6:h'05', 10:h'44616c', 11:h'de9e ... f1' },
h'aea0155667924dff8a24e4cb35b9' h'aea0155667924dff8a24e4cb35b9'
] ]
After compression (85 bytes):
Flag byte: 0b00111001 = 0x39 * After compression (85 bytes):
Option Value: 39 05 03 44 61 6c 25 (7 bytes) Flag byte: 0b00111001 = 0x39 (1 byte)
Payload: ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 COUNTERSIGN Option Value: 0x39 05 03 44 61 6c 25 (7 bytes)
(14 bytes + size of COUNTERSIGN)
Payload: 0xaea0155667924dff8a24e4cb35b9 de9e ... f1
(14 bytes + size of the counter signature)
o Response with ciphertext = 0x60b035059d9ef5667c5a0710823b, kid = o Response with ciphertext = 0x60b035059d9ef5667c5a0710823b, kid =
0x52 and no Partial IV. 0x52 and no Partial IV.
Before compression (88 bytes): * Before compression (88 bytes):
[ [
h'', h'',
{ 4:h'52', 11:COUNTERSIGN }, { 4:h'52', 11:h'ca1e ... b3' },
h'60b035059d9ef5667c5a0710823b' h'60b035059d9ef5667c5a0710823b'
] ]
After compression (80 bytes): * After compression (80 bytes):
Flag byte: 0b00101000 = 0x28 Flag byte: 0b00101000 = 0x28 (1 byte)
Option Value: 28 52 (2 bytes) Option Value: 0x28 52 (2 bytes)
Payload: 60 b0 35 05 9d 9e f5 66 7c 5a 07 10 82 3b COUNTERSIGN Payload: 0x60b035059d9ef5667c5a0710823b ca1e ... b3
(14 bytes + size of COUNTERSIGN) (14 bytes + size of the counter signature)
5.1.2. Examples in Pairwise Mode 5.1.2. Examples in Pairwise Mode
o Request with ciphertext = 0xaea0155667924dff8a24e4cb35b9, kid = o Request with ciphertext = 0xaea0155667924dff8a24e4cb35b9, kid =
0x25, Partial IV = 5 and kid context = 0x44616c 0x25, Partial IV = 5 and kid context = 0x44616c.
Before compression (32 bytes): * Before compression (29 bytes):
[ [
h'', h'',
{ 4:h'25', 6:h'05', 10:h'44616c' }, { 4:h'25', 6:h'05', 10:h'44616c' },
h'aea0155667924dff8a24e4cb35b9' h'aea0155667924dff8a24e4cb35b9'
] ]
After compression (21 bytes):
Flag byte: 0b00011001 = 0x19 * After compression (21 bytes):
Option Value: 19 05 03 44 61 6c 25 (7 bytes) Flag byte: 0b00011001 = 0x19 (1 byte)
Payload: ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9 (14 bytes) Option Value: 0x19 05 03 44 61 6c 25 (7 bytes)
o Response with ciphertext = 0x60b035059d9ef5667c5a0710823b, kid = Payload: 0xaea0155667924dff8a24e4cb35b9 (14 bytes)
0x52 and no Partial IV.
Before compression (24 bytes): o Response with ciphertext = 0x60b035059d9ef5667c5a0710823b and no
Partial IV.
[ * Before compression (18 bytes):
h'',
{ 4:h'52'},
h'60b035059d9ef5667c5a0710823b'
]
After compression (16 bytes): [
h'',
{},
h'60b035059d9ef5667c5a0710823b'
]
Flag byte: 0b00001000 = 0x08 * After compression (14 bytes):
Option Value: 08 52 (2 bytes) Flag byte: 0b00000000 = 0x00 (1 byte)
Payload: 60 b0 35 05 9d 9e f5 66 7c 5a 07 10 82 3b (14 bytes) Option Value: 0x (0 bytes)
Payload: 0x60b035059d9ef5667c5a0710823b (14 bytes)
6. Message Binding, Sequence Numbers, Freshness and Replay Protection 6. Message Binding, Sequence Numbers, Freshness and Replay Protection
The requirements and properties described in Section 7 of [RFC8613] The requirements and properties described in Section 7 of [RFC8613]
also apply to OSCORE used in group communication. In particular, also apply to Group OSCORE. In particular, Group OSCORE provides
Group OSCORE provides message binding of responses to requests, which message binding of responses to requests, which enables absolute
enables absolute freshness of responses that are not notifications, freshness of responses that are not notifications, relative freshness
relative freshness of requests and notification responses, and replay of requests and notification responses, and replay protection of
protection of requests. requests. In addition, the following holds for Group OSCORE.
6.1. Update of Replay Window 6.1. Update of Replay Window
A new server joining a group may not be aware of the current Partial Sender Sequence Numbers seen by a server as Partial IV values in
IVs (Sender Sequence Numbers of the clients). Hence, when receiving request messages can spontaneously increase at a fast pace, for
a request from a particular client for the first time, the new server example when a client exchanges unicast messages with other servers
is not able to verify if that request is a replay. The same holds using the Group OSCORE Security Context. As in OSCORE [RFC8613], a
when a server loses its mutable Security Context (see Section 2.4.1), server always needs to accept such increases and accordingly updates
for instance after a device reboot. the Replay Window in each of its Recipient Contexts.
The exact way to address this issue is application specific, and As discussed in Section 2.4.1, a newly created Recipient Context
depends on the particular use case and its replay requirements. The would have an invalid Replay Window, if its installation has required
list of methods to handle the update of a Replay Window is part of to delete another Recipient Context. Hence, the server is not able
the group communication policy, and different servers can use to verify if a request from the client associated to the new
different methods. Appendix E describes three possible approaches Recipient Context is a replay. When this happens, the server MUST
that can be considered to address the issue discussed above. validate the Replay Window of the new Recipient Context, before
accepting messages from the associated client (see Section 2.4.1).
Furthermore, when the Group Manager establishes a new Security Furthermore, when the Group Manager establishes a new Security
Context for the group (see Section 2.4.3.2), every server re- Context for the group (see Section 2.4.3.2), every server re-
initializes the Replay Window in each of its Recipient Contexts. initializes the Replay Window in each of its Recipient Contexts.
6.2. Message Freshness
When receiving a request from a client for the first time, the server
is not synchronized with the client's Sender Sequence Number, i.e. it
is not able to verify if that request is fresh. This applies to a
server that has just joined the group, with respect to already
present clients, and recurs as new clients are added as group
members.
During its operations in the group, the server may also lose
synchronization with a client's Sender Sequence Number. This can
happen, for instance, if the server has rebooted or has deleted its
previously synchronized version of the Recipient Context for that
client (see Section 2.4.1).
If the application requires message freshness, e.g. according to
time- or event-based policies, the server has to (re-)synchronize
with a client's Sender Sequence Number before delivering request
messages from that client to the application. To this end, the
server can use the approach in Appendix E based on the Echo Option
for CoAP [I-D.ietf-core-echo-request-tag], as a variant of the
approach defined in Appendix B.1.2 of [RFC8613] applicable to Group
OSCORE.
7. Message Reception 7. Message Reception
Upon receiving a protected message, a recipient endpoint retrieves a Upon receiving a protected message, a recipient endpoint retrieves a
Security Context as in [RFC8613]. An endpoint MUST be able to Security Context as in [RFC8613]. An endpoint MUST be able to
distinguish between a Security Context to process OSCORE messages as distinguish between a Security Context to process OSCORE messages as
in [RFC8613] and a Security Context to process Group OSCORE messages in [RFC8613] and a Group OSCORE Security Context to process Group
as defined in this specification. OSCORE messages as defined in this specification.
To this end, an endpoint can take into account the different To this end, an endpoint can take into account the different
structure of the Security Context defined in Section 2, for example structure of the Security Context defined in Section 2, for example
based on the presence of Counter Signature Algorithm in the Common based on the presence of Counter Signature Algorithm in the Common
Context. Alternatively implementations can use an additional Context. Alternatively implementations can use an additional
parameter in the Security Context, to explicitly signal that it is parameter in the Security Context, to explicitly signal that it is
intended for processing Group OSCORE messages. intended for processing Group OSCORE messages.
If either of the following two conditions holds, a recipient endpoint If either of the following two conditions holds, a recipient endpoint
MUST discard the incoming protected message: MUST discard the incoming protected message:
o The Group Flag is set to 1, and the recipient endpoint can not
retrieve a Security Context which is both valid to process the
message and also associated to an OSCORE group.
o The Group Flag is set to 0, and the recipient endpoint retrieves a o The Group Flag is set to 0, and the recipient endpoint retrieves a
Security Context which is both valid to process the message and Security Context which is both valid to process the message and
also associated to an OSCORE group, but the endpoint does not also associated to an OSCORE group, but the endpoint does not
support the pairwise mode. support the pairwise mode.
o The Group Flag is set to 1, and the recipient endpoint can not
retrieve a Security Context which is both valid to process the
message and also associated to an OSCORE group.
As per Section 6.1 of [RFC8613], this holds also when retrieving a
Security Context which is valid but not associated to an OSCORE
group. Future specifications may define how to process incoming
messages protected with a Security Contexts as in [RFC8613], when
the Group Flag bit is set to 1.
Otherwise, if a Security Context associated to an OSCORE group and Otherwise, if a Security Context associated to an OSCORE group and
valid to process the message is retrieved, the recipient endpoint valid to process the message is retrieved, the recipient endpoint
processes the message with Group OSCORE, using the group mode (see processes the message with Group OSCORE, using the group mode (see
Section 8) if the Group Flag is set to 1, or the pairwise mode (see Section 8) if the Group Flag is set to 1, or the pairwise mode (see
Section 9) if the Group Flag is set to 0. Section 9) if the Group Flag is set to 0.
Note that, if the Group Flag is set to 0, and the recipient endpoint Note that, if the Group Flag is set to 0, and the recipient endpoint
retrieves a Security Context which is valid to process the message retrieves a Security Context which is valid to process the message
but is not associated to an OSCORE group, then the message is but is not associated to an OSCORE group, then the message is
processed according to [RFC8613]. processed according to [RFC8613].
skipping to change at page 29, line 27 skipping to change at page 31, line 8
The group mode MUST be used to protect group requests intended for The group mode MUST be used to protect group requests intended for
multiple recipients or for the whole group. This includes both multiple recipients or for the whole group. This includes both
requests directly addressed to multiple recipients, e.g. sent by the requests directly addressed to multiple recipients, e.g. sent by the
client over multicast, as well as requests sent by the client over client over multicast, as well as requests sent by the client over
unicast to a proxy, that forwards them to the intended recipients unicast to a proxy, that forwards them to the intended recipients
over multicast [I-D.ietf-core-groupcomm-bis]. over multicast [I-D.ietf-core-groupcomm-bis].
As per [RFC7252][I-D.ietf-core-groupcomm-bis], group requests sent As per [RFC7252][I-D.ietf-core-groupcomm-bis], group requests sent
over multicast MUST be Non-Confirmable, and thus are not over multicast MUST be Non-Confirmable, and thus are not
retransmitted by the CoAP messaging layer. Instead, applications retransmitted by the CoAP messaging layer. Instead, applications
should store such outgoing messages for a pre-defined, sufficient should store such outgoing messages for a predefined, sufficient
amount of time, in order to correctly perform possible amount of time, in order to correctly perform possible
retransmissions at the application layer. According to Section 5.2.3 retransmissions at the application layer. According to Section 5.2.3
of [RFC7252], responses to Non-Confirmable group requests SHOULD also of [RFC7252], responses to Non-Confirmable group requests SHOULD also
be Non-Confirmable, but endpoints MUST be prepared to receive be Non-Confirmable, but endpoints MUST be prepared to receive
Confirmable responses in reply to a Non-Confirmable group request. Confirmable responses in reply to a Non-Confirmable group request.
Confirmable group requests are acknowledged in non-multicast Confirmable group requests are acknowledged in non-multicast
environments, as specified in [RFC7252]. environments, as specified in [RFC7252].
Furthermore, endpoints in the group locally perform error handling Furthermore, endpoints in the group locally perform error handling
and processing of invalid messages according to the same principles and processing of invalid messages according to the same principles
adopted in [RFC8613]. However, a recipient MUST stop processing and adopted in [RFC8613]. However, a recipient MUST stop processing and
silently reject any message which is malformed and does not follow silently reject any message which is malformed and does not follow
the format specified in Section 4, or which is not cryptographically the format specified in Section 4 of this specification, or which is
validated in a successful way. In either case, it is RECOMMENDED not cryptographically validated in a successful way. In either case,
that the recipient does not send back any error message. This it is RECOMMENDED that the recipient does not send back any error
prevents servers from replying with multiple error messages to a message. This prevents servers from replying with multiple error
client sending a group request, so avoiding the risk of flooding and messages to a client sending a group request, so avoiding the risk of
possibly congesting the network. flooding and possibly congesting the network.
8.1. Protecting the Request 8.1. Protecting the Request
A client transmits a secure group request as described in Section 8.1 A client transmits a secure group request as described in Section 8.1
of [RFC8613], with the following modifications. of [RFC8613], with the following modifications.
o In step 2, the Additional Authenticated Data is modified as o In step 2, the Additional Authenticated Data is modified as
described in Section 4 of this document. described in Section 4 of this document.
o In step 4, the encryption of the COSE object is modified as o In step 4, the encryption of the COSE object is modified as
skipping to change at page 30, line 39 skipping to change at page 32, line 18
update the stored value associated to a particular Observe update the stored value associated to a particular Observe
request. request.
o If the client intends to keep the observation active beyond a o If the client intends to keep the observation active beyond a
possible change of ID Context following a group rekeying (see possible change of ID Context following a group rekeying (see
Section 3.1), then the following applies. Section 3.1), then the following applies.
* The client MUST store the value of the 'kid context' parameter * The client MUST store the value of the 'kid context' parameter
from the original Observe request, and retain it for the whole from the original Observe request, and retain it for the whole
duration of the observation. Upon establishing a new Security duration of the observation. Upon establishing a new Security
Context with a new ID Context as Gid (see Section 2.4.3.2), the Context with a new Gid as ID Context (see Section 2.4.3.2), the
client MUST NOT update the stored value associated to a client MUST NOT update the stored value associated to a
particular Observe request. particular Observe request.
* The client MUST store an invariant identifier of the group, * The client MUST store an invariant identifier of the group,
which is immutable even in case the Security Context of the which is immutable even in case the Security Context of the
group is re-established. For example, this invariant group is re-established. For example, this invariant
identifier can be the "group name" in identifier can be the "group name" in
[I-D.ietf-ace-key-groupcomm-oscore], where it is used for [I-D.ietf-ace-key-groupcomm-oscore], where it is used for
joining the group and retrieving the current group keying joining the group and retrieving the current group keying
material from the Group Manager. material from the Group Manager.
skipping to change at page 31, line 20 skipping to change at page 32, line 48
Upon receiving a secure group request with the Group Flag set to 1, Upon receiving a secure group request with the Group Flag set to 1,
following the procedure in Section 7, a server proceeds as described following the procedure in Section 7, a server proceeds as described
in Section 8.2 of [RFC8613], with the following modifications. in Section 8.2 of [RFC8613], with the following modifications.
o In step 2, the decoding of the compressed COSE object follows o In step 2, the decoding of the compressed COSE object follows
Section 5 of this document. In particular: Section 5 of this document. In particular:
* If the server discards the request due to not retrieving a * If the server discards the request due to not retrieving a
Security Context associated to the OSCORE group, the server MAY Security Context associated to the OSCORE group, the server MAY
respond with a 4.02 (Bad Option) error. When doing so, the respond with a 4.01 (Unauthorized) error message. When doing
server MAY set an Outer Max-Age option with value zero, and MAY so, the server MAY set an Outer Max-Age option with value zero,
include a descriptive string as diagnostic payload. and MAY include a descriptive string as diagnostic payload.
* If the received 'kid context' matches an existing ID Context * If the received 'kid context' matches an existing ID Context
(Gid) but the received 'kid' does not match any Recipient ID in (Gid) but the received 'kid' does not match any Recipient ID in
this Security Context, then the server MAY create a new this Security Context, then the server MAY create a new
Recipient Context for this Recipient ID and initialize it Recipient Context for this Recipient ID and initialize it
according to Section 3 of [RFC8613], and also retrieve the according to Section 3 of [RFC8613], and also retrieve the
associated public key. Such a configuration is application associated public key. Such a configuration is application
specific. If the application does not specify dynamic specific. If the application does not specify dynamic
derivation of new Recipient Contexts, then the server SHALL derivation of new Recipient Contexts, then the server SHALL
stop processing the request. stop processing the request.
skipping to change at page 32, line 4 skipping to change at page 33, line 33
the server MUST stop processing the request and MAY respond the server MUST stop processing the request and MAY respond
with a 5.03 (Service Unavailable) response. The response MAY with a 5.03 (Service Unavailable) response. The response MAY
include a Max-Age Option, indicating to the client the number include a Max-Age Option, indicating to the client the number
of seconds after which to retry. If the Max-Age Option is not of seconds after which to retry. If the Max-Age Option is not
present, a retry time of 60 seconds will be assumed by the present, a retry time of 60 seconds will be assumed by the
client, as default value defined in Section 5.10.5 of client, as default value defined in Section 5.10.5 of
[RFC7252]. [RFC7252].
* If the signature verification fails, the server SHALL stop * If the signature verification fails, the server SHALL stop
processing the request and MAY respond with a 4.00 (Bad processing the request and MAY respond with a 4.00 (Bad
Request) response. If the verification fails, the same steps Request) response. The server MAY set an Outer Max-Age option
are taken as if the decryption had failed. In particular, the with value zero. The diagnostic payload MAY contain a string,
Replay Window is only updated if both the signature which, if present, MUST be "Decryption failed" as if the
verification and the decryption succeed. decryption had failed. Furthermore, the Replay Window MUST be
updated only if both the signature verification and the
decryption succeed.
o Additionally, if the used Recipient Context was created upon o Additionally, if the used Recipient Context was created upon
receiving this group request and the message is not verified receiving this group request and the message is not verified
successfully, the server MAY delete that Recipient Context. Such successfully, the server MAY delete that Recipient Context. Such
a configuration, which is specified by the application, mitigates a configuration, which is specified by the application, mitigates
attacks that aim at overloading the server's storage. attacks that aim at overloading the server's storage.
A server SHOULD NOT process a request if the received Recipient ID A server SHOULD NOT process a request if the received Recipient ID
('kid') is equal to its own Sender ID in its own Sender Context. For ('kid') is equal to its own Sender ID in its own Sender Context. For
an example where this is not fulfilled, see Section 6.2.1 in an example where this is not fulfilled, see Section 7.2.1 in
[I-D.tiloca-core-observe-multicast-notifications]. [I-D.tiloca-core-observe-multicast-notifications].
8.2.1. Supporting Observe 8.2.1. Supporting Observe
If Observe [RFC7641] is supported, the following holds for each newly If Observe [RFC7641] is supported, the following holds for each newly
started observation. started observation.
o The server MUST store the value of the 'kid' parameter from the o The server MUST store the value of the 'kid' parameter from the
original Observe request, and retain it for the whole duration of original Observe request, and retain it for the whole duration of
the observation. The server MUST NOT update the stored value of a the observation. The server MUST NOT update the stored value of a
'kid' parameter associated to a particular Observe request, even 'kid' parameter associated to a particular Observe request, even
in case the observer client is individually rekeyed and starts in case the observer client is individually rekeyed and starts
using a new Sender ID received from the Group Manager (see using a new Sender ID received from the Group Manager (see
Section 2.4.3.1). Section 2.4.3.1).
o The server MUST store the value of the 'kid context' parameter o The server MUST store the value of the 'kid context' parameter
from the original Observe request, and retain it for the whole from the original Observe request, and retain it for the whole
duration of the observation, beyond a possible change of ID duration of the observation, beyond a possible change of ID
Context following a group rekeying (see Section 3.1). That is, Context following a group rekeying (see Section 3.1). That is,
upon establishing a new Security Context with a new ID Context as upon establishing a new Security Context with a new Gid as ID
Gid (see Section 2.4.3.2), the server MUST NOT update the stored Context (see Section 2.4.3.2), the server MUST NOT update the
value associated to the ongoing observation. stored value associated to the ongoing observation.
8.3. Protecting the Response 8.3. Protecting the Response
If a server generates a CoAP message in response to a Group OSCORE If a server generates a CoAP message in response to a Group OSCORE
request, then the server SHALL follow the description in Section 8.3 request, then the server SHALL follow the description in Section 8.3
of [RFC8613], with the modifications described in this section. of [RFC8613], with the modifications described in this section.
Note that the server always protects a response with the Sender Note that the server always protects a response with the Sender
Context from its latest Security Context, and that establishing a new Context from its latest Security Context, and that establishing a new
Security Context resets the Sender Sequence Number to 0 (see Security Context resets the Sender Sequence Number to 0 (see
skipping to change at page 33, line 36 skipping to change at page 35, line 19
document. In particular, the payload of the OSCORE message document. In particular, the payload of the OSCORE message
includes also the counter signature. includes also the counter signature.
8.3.1. Supporting Observe 8.3.1. Supporting Observe
If Observe [RFC7641] is supported, the following holds when If Observe [RFC7641] is supported, the following holds when
protecting notifications for an ongoing observation. protecting notifications for an ongoing observation.
o The server MUST use the stored value of the 'kid' parameter from o The server MUST use the stored value of the 'kid' parameter from
the original Observe request (see Section 8.2.1), as value for the the original Observe request (see Section 8.2.1), as value for the
'request_kid' parameter in the two external_aad structures (see 'request_kid' parameter in the external_aad structure (see
Section 4.3.1 and Section 4.3.2). Section 4.3).
o The server MUST use the stored value of the 'kid context' o The server MUST use the stored value of the 'kid context'
parameter from the original Observe request (see Section 8.2.1), parameter from the original Observe request (see Section 8.2.1),
as value for the 'request_kid_context' parameter in the two as value for the 'request_kid_context' parameter in the
external_aad structures (see Section 4.3.1 and Section 4.3.2). external_aad structure (see Section 4.3).
Furthermore, the server may have ongoing observations started by Furthermore, the server may have ongoing observations started by
Observe requests protected with an old Security Context. After Observe requests protected with an old Security Context. After
completing the establishment of a new Security Context, the server completing the establishment of a new Security Context, the server
MUST protect the following notifications with the Sender Context of MUST protect the following notifications with the Sender Context of
the new Security Context. the new Security Context.
For each ongoing observation, the server MUST include in the first For each ongoing observation, the server can help the client to
notification protected with the new Security Context also the 'kid synchronize, by including also the 'kid context' parameter in
context' parameter, which is set to the ID Context (Gid) of the new notifications following a group rekeying, with value set to the ID
Security Context. It is OPTIONAL for the server to include the ID Context (Gid) of the new Security Context.
Context (Gid) in the 'kid context' parameter also in further
following notifications for those observations. If there is a known upper limit to the duration of a group rekeying,
the server SHOULD include the 'kid context' parameter during that
time. Otherwise, the server SHOULD include it until the Max-Age has
expired for the last notification sent before the installation of the
new Security Context.
8.4. Verifying the Response 8.4. Verifying the Response
Upon receiving a secure response message with the Group Flag set to Upon receiving a secure response message with the Group Flag set to
1, following the procedure in Section 7, the client proceeds as 1, following the procedure in Section 7, the client proceeds as
described in Section 8.4 of [RFC8613], with the following described in Section 8.4 of [RFC8613], with the following
modifications. modifications.
Note that a client may receive a response protected with a Security Note that a client may receive a response protected with a Security
Context different from the one used to protect the corresponding Context different from the one used to protect the corresponding
group request, and that, upon the establishment of a new Security group request, and that, upon the establishment of a new Security
Context, the client re-initializes its replay windows in its Context, the client re-initializes its Replay Windows in its
Recipient Contexts (see Section 3.1). Recipient Contexts (see Section 3.1).
o In step 2, the decoding of the compressed COSE object is modified o In step 2, the decoding of the compressed COSE object is modified
as described in Section 5 of this document. If the received 'kid as described in Section 5 of this document. In particular, a
context' matches an existing ID Context (Gid) but the received 'kid' may not be present, if the response is a reply to a request
'kid' does not match any Recipient ID in this Security Context, protected in pairwise mode. In such a case, the client assumes
then the client MAY create a new Recipient Context for this the response 'kid' to be exactly the one of the server to which
Recipient ID and initialize it according to Section 3 of the request protected in pairwise mode was intended for.
[RFC8613], and also retrieve the associated public key. If the
application does not specify dynamic derivation of new Recipient If the response 'kid context' matches an existing ID Context (Gid)
Contexts, then the client SHALL stop processing the response. but the received/assumed 'kid' does not match any Recipient ID in
this Security Context, then the client MAY create a new Recipient
Context for this Recipient ID and initialize it according to
Section 3 of [RFC8613], and also retrieve the associated public
key. If the application does not specify dynamic derivation of
new Recipient Contexts, then the client SHALL stop processing the
response.
o In step 3, the Additional Authenticated Data is modified as o In step 3, the Additional Authenticated Data is modified as
described in Section 4 of this document. described in Section 4 of this document.
o In step 5, the client also verifies the counter signature using o In step 5, the client also verifies the counter signature using
the public key of the server from the associated Recipient the public key of the server from the associated Recipient
Context. If the verification fails, the same steps are taken as Context. If the verification fails, the same steps are taken as
if the decryption had failed. if the decryption had failed.
o Additionally, if the used Recipient Context was created upon o Additionally, if the used Recipient Context was created upon
skipping to change at page 35, line 4 skipping to change at page 36, line 48
a configuration, which is specified by the application, mitigates a configuration, which is specified by the application, mitigates
attacks that aim at overloading the client's storage. attacks that aim at overloading the client's storage.
8.4.1. Supporting Observe 8.4.1. Supporting Observe
If Observe [RFC7641] is supported, the following holds when verifying If Observe [RFC7641] is supported, the following holds when verifying
notifications for an ongoing observation. notifications for an ongoing observation.
o The client MUST use the stored value of the 'kid' parameter from o The client MUST use the stored value of the 'kid' parameter from
the original Observe request (see Section 8.1.1), as value for the the original Observe request (see Section 8.1.1), as value for the
'request_kid' parameter in the two external_aad structures (see 'request_kid' parameter in the external_aad structure (see
Section 4.3.1 and Section 4.3.2). Section 4.3).
o The client MUST use the stored value of the 'kid context' o The client MUST use the stored value of the 'kid context'
parameter from the original Observe request (see Section 8.1.1), parameter from the original Observe request (see Section 8.1.1),
as value for the 'request_kid_context' parameter in the two as value for the 'request_kid_context' parameter in the
external_aad structures (see Section 4.3.1 and Section 4.3.2). external_aad structure (see Section 4.3).
This ensures that the client can correctly verify notifications, even This ensures that the client can correctly verify notifications, even
in case it is individually rekeyed and starts using a new Sender ID in case it is individually rekeyed and starts using a new Sender ID
received from the Group Manager (see Section 2.4.3.1), as well as received from the Group Manager (see Section 2.4.3.1), as well as
when it establishes a new Security Context with a new ID Context when it installs a new Security Context with a new ID Context (Gid)
(Gid) following a group rekeying (see Section 3.1). following a group rekeying (see Section 3.1).
9. Message Processing in Pairwise Mode 9. Message Processing in Pairwise Mode
When using the pairwise mode of Group OSCORE, messages are protected When using the pairwise mode of Group OSCORE, messages are protected
and processed as in Section 8, with the modifications described in and processed as in [RFC8613], with the modifications described in
this section. The security objectives of the pairwise mode are this section. The security objectives of the pairwise mode are
discussed in Appendix A.2. discussed in Appendix A.2.
The pairwise mode takes advantage of an existing Security Context for The pairwise mode takes advantage of an existing Security Context for
the group mode to establish a Security Context shared exclusively the group mode to establish a Security Context shared exclusively
with any other member. In order to use the pairwise mode, the with any other member. In order to use the pairwise mode, the
signature scheme of the group mode MUST support a combined signature signature scheme of the group mode MUST support a combined signature
and encryption scheme. This can be, for example, signature using and encryption scheme. This can be, for example, signature using
ECDSA, and encryption using AES-CCM with a key derived with ECDH. ECDSA, and encryption using AES-CCM with a key derived with ECDH.
skipping to change at page 35, line 44 skipping to change at page 37, line 39
messages, such as intermediary gateways (see Section 3). messages, such as intermediary gateways (see Section 3).
The pairwise mode MAY be supported. An endpoint implementing only a The pairwise mode MAY be supported. An endpoint implementing only a
silent server does not support the pairwise mode. silent server does not support the pairwise mode.
If the signature algorithm used in the group supports ECDH (e.g., If the signature algorithm used in the group supports ECDH (e.g.,
ECDSA, EdDSA), the pairwise mode MUST be supported by endpoints that ECDSA, EdDSA), the pairwise mode MUST be supported by endpoints that
use the CoAP Echo Option [I-D.ietf-core-echo-request-tag] and/or use the CoAP Echo Option [I-D.ietf-core-echo-request-tag] and/or
block-wise transfers [RFC7959], for instance for responses after the block-wise transfers [RFC7959], for instance for responses after the
first block-wise request, which possibly targets all servers in the first block-wise request, which possibly targets all servers in the
group and includes the CoAP Block2 option (see Section 2.3.6 of group and includes the CoAP Block2 option (see Section 3.7 of
[I-D.ietf-core-groupcomm-bis]). This prevents the attack described [I-D.ietf-core-groupcomm-bis]). This prevents the attack described
in Section 10.7, which leverages requests sent over unicast to a in Section 10.7, which leverages requests sent over unicast to a
single group member and protected with the group mode. single group member and protected with the group mode.
The pairwise mode protects messages between two members of a group, Senders cannot use the pairwise mode to protect a message intended
essentially following [RFC8613], but with the following notable for multiple recipients. In fact, the pairwise mode is defined only
differences: between two endpoints and the keying material is thus only available
to one recipient.
o The 'kid' and 'kid context' parameters of the COSE object are used
as defined in Section 4.2 of this document.
o The external_aad defined in Section 4.3.1 of this document is used
for the encryption process.
o The Pairwise Sender/Recipient Keys used as Sender/Recipient keys
are derived as defined in Section 2.3 of this document.
Senders MUST NOT use the pairwise mode to protect a message intended However, a sender can use the pairwise mode to protect a message sent
for multiple recipients. The pairwise mode is defined only between to (but not intended for) multiple recipients, if interested in a
two endpoints and the keying material is thus only available to one response from only one of them. For instance, this is useful to
recipient. support the address discovery service defined in Section 9.1, when a
single 'kid' value is indicated in the payload of a request sent to
multiple recipients, e.g. over multicast.
The Group Manager MAY indicate that the group uses also the pairwise The Group Manager MAY indicate that the group uses also the pairwise
mode, as part of the group data provided to candidate group members mode, as part of the group data provided to candidate group members
when joining the group. when joining the group.
9.1. Pre-Conditions 9.1. Pre-Conditions
In order to protect an outgoing message in pairwise mode, the sender In order to protect an outgoing message in pairwise mode, the sender
needs to know the public key and the Recipient ID for the recipient needs to know the public key and the Recipient ID for the recipient
endpoint, as stored in the Recipient Context associated to that endpoint, as stored in the Recipient Context associated to that
endpoint (see Pairwise Sender Context of Section 2.3.3). endpoint (see Section 2.3.3).
Furthermore, the sender needs to know the individual address of the Furthermore, the sender needs to know the individual address of the
recipient endpoint. This information may not be known at any given recipient endpoint. This information may not be known at any given
point in time. For instance, right after having joined the group, a point in time. For instance, right after having joined the group, a
client may know the public key and Recipient ID for a given server, client may know the public key and Recipient ID for a given server,
but not the addressing information required to reach it with an but not the addressing information required to reach it with an
individual, one-to-one request. individual, one-to-one request.
To make addressing information of individual endpoints available, To make addressing information of individual endpoints available,
servers in the group MAY expose a resource to which a client can send servers in the group MAY expose a resource to which a client can send
a group request targeting a server or a set of servers, identified by a group request targeting a set of servers, identified by their 'kid'
their 'kid' value(s). The specified set may be empty, hence values specified in the request payload. The specified set may be
identifying all the servers in the group. Further details of such an empty, hence identifying all the servers in the group. Further
interface are out of scope for this document. details of such an interface are out of scope for this document.
9.2. Protecting the Request 9.2. Main Differences from OSCORE
When using the pairwise mode, the request is protected as defined in The pairwise mode protects messages between two members of a group,
Section 8.1, with the following differences. essentially following [RFC8613], but with the following notable
differences.
o The Group Flag MUST be set to 0. o The 'kid' and 'kid context' parameters of the COSE object are used
as defined in Section 4.2 of this document.
o The used Sender Key is the Pairwise Sender Key (see Section 2.3). o The external_aad defined in Section 4.3 of this document is used
for the encryption process.
o The counter signature is not computed and therefore not included o The Pairwise Sender/Recipient Keys used as Sender/Recipient keys
in the message. The payload of the protected request thus are derived as defined in Section 2.3 of this document.
terminates with the encoded ciphertext of the COSE object, just
like in [RFC8613].
Note that, like in the group mode, the external_aad for encryption is 9.3. Protecting the Request
generated as in Section 4.3.1, and the Partial IV is the current
fresh value of the client's Sender Sequence Number (see
Section 2.3.2).
9.3. Verifying the Request When using the pairwise mode, the request is protected as defined in
Section 8.1 of [RFC8613], with the differences summarized in
Section 9.2 of this document. The following difference also applies.
o If Observe [RFC7641] is supported, what defined in Section 8.1.1
of this document holds.
9.4. Verifying the Request
Upon receiving a request with the Group Flag set to 0, following the Upon receiving a request with the Group Flag set to 0, following the
procedure in Section 7, the server MUST process it as defined in procedure in Section 7, the server MUST process it as defined in
Section 8.2, with the following differences. Section 8.2 of [RFC8613], with the differences summarized in
Section 9.2 of this document. The following differences also apply.
o If the server discards the request due to not retrieving a o If the server discards the request due to not retrieving a
Security Context associated to the OSCORE group or to not Security Context associated to the OSCORE group or to not
supporting the pairwise mode, the server MAY respond with a 4.02 supporting the pairwise mode, the server MAY respond with a 4.01
(Bad Option) error. When doing so, the server MAY set an Outer (Unauthorized) error message or a 4.02 (Bad Option) error message,
Max-Age option with value zero, and MAY include a descriptive respectively. When doing so, the server MAY set an Outer Max-Age
string as diagnostic payload. option with value zero, and MAY include a descriptive string as
diagnostic payload.
o If a new Recipient Context is created for this Recipient ID, new o If a new Recipient Context is created for this Recipient ID, new
Pairwise Sender/Recipient Keys are also derived (see Pairwise Sender/Recipient Keys are also derived (see
Section 2.3.1). The new Pairwise Sender/Recipient Keys are Section 2.3.1). The new Pairwise Sender/Recipient Keys are
deleted if the Recipient Context is deleted as a result of the deleted if the Recipient Context is deleted as a result of the
message not being successfully verified. message not being successfully verified.
o The used Recipient Key is the Pairwise Recipient Key (see o If Observe [RFC7641] is supported, what defined in Section 8.2.1
Section 2.3). of this document holds.
o No verification of counter signature occurs, as there is none
included in the message.
9.4. Protecting the Response 9.5. Protecting the Response
When using the pairwise mode, a response is protected as defined in When using the pairwise mode, a response is protected as defined in
Section 8.3, with the following differences. Section 8.3 of [RFC8613], with the differences summarized in
Section 9.2 of this document. The following differences also apply.
o The Group Flag MUST be set to 0. o As discussed in Section 2.4.3.1, the server can obtain a new
Sender ID from the Group Manager. In such a case, the server can
help the client to synchronize, by including the 'kid' parameter
in a response protected in pairwise mode, even when the request
was also protected in pairwise mode.
o The used Sender Key is the Pairwise Sender Key (see Section 2.3). That is, when responding to a request protected in pairwise mode,
the server SHOULD include the 'kid' parameter in a response
protected in pairwise mode, if it is replying to that client for
the first time since the assignment of its new Sender ID.
o The counter signature is not computed and therefore not included o If Observe [RFC7641] is supported, what defined in Section 8.3.1
in the message. The payload of the protected response thus of this document holds.
terminates with the encoded ciphertext of the COSE object, just
like in [RFC8613].
9.5. Verifying the Response 9.6. Verifying the Response
Upon receiving a response with the Group Flag set to 0, following the Upon receiving a response with the Group Flag set to 0, following the
procedure in Section 7, the client MUST process it as defined in procedure in Section 7, the client MUST process it as defined in
Section 8.4, with the following differences. Section 8.4 of [RFC8613], with the differences summarized in
Section 9.2 of this document. The following differences also apply.
o If a new Recipient Context is created for this Recipient ID, new o If a new Recipient Context is created for this Recipient ID, new
Pairwise Sender/Recipient Keys are also derived (see Pairwise Sender/Recipient Keys are also derived (see
Section 2.3.1). The new Pairwise Sender/Recipient Keys are Section 2.3.1). The new Pairwise Sender/Recipient Keys are
deleted if the Recipient Context is deleted as a result of the deleted if the Recipient Context is deleted as a result of the
message not being successfully verified. message not being successfully verified.
o The used Recipient Key is the Pairwise Recipient Key (see o If Observe [RFC7641] is supported, what defined in Section 8.4.1
Section 2.3). of this document holds.
o No verification of counter signature occurs, as there is none
included in the message.
10. Security Considerations 10. Security Considerations
The same threat model discussed for OSCORE in Appendix D.1 of The same threat model discussed for OSCORE in Appendix D.1 of
[RFC8613] holds for Group OSCORE. In addition, when using the group [RFC8613] holds for Group OSCORE. In addition, when using the group
mode, source authentication of messages is explicitly ensured by mode, source authentication of messages is explicitly ensured by
means of counter signatures, as discussed in Section 10.1. means of counter signatures, as discussed in Section 10.1.
The same considerations on supporting Proxy operations discussed for The same considerations on supporting Proxy operations discussed for
OSCORE in Appendix D.2 of [RFC8613] hold for Group OSCORE. OSCORE in Appendix D.2 of [RFC8613] hold for Group OSCORE.
The same considerations on protected message fields for OSCORE The same considerations on protected message fields for OSCORE
discussed in Appendix D.3 of [RFC8613] hold for Group OSCORE. discussed in Appendix D.3 of [RFC8613] hold for Group OSCORE.
The same considerations on uniqueness of (key, nonce) pairs for The same considerations on uniqueness of (key, nonce) pairs for
OSCORE discussed in Appendix D.4 of [RFC8613] hold for Group OSCORE. OSCORE discussed in Appendix D.4 of [RFC8613] hold for Group OSCORE.
This is further discussed in Section 10.2 of this document. This is further discussed in Section 10.2 of this document.
The same considerations on unprotected message fields for OSCORE The same considerations on unprotected message fields for OSCORE
discussed in Appendix D.5 of [RFC8613] hold for Group OSCORE, with discussed in Appendix D.5 of [RFC8613] hold for Group OSCORE, with
the following difference. The counter signature included in a Group the following differences. First, the 'kid context' of request
OSCORE message protected in group mode is computed also over the messages is part of the Additional Authenticated Data, thus safely
value of the OSCORE option, which is part of the Additional enabling to keep observations active beyond a possible change of ID
Authenticated Data used in the signing process. This is further Context (Gid), following a group rekeying (see Section 4.3). Second,
discussed in Section 10.6 of this document. the counter signature included in a Group OSCORE message protected in
group mode is computed also over the value of the OSCORE option,
which is also part of the Additional Authenticated Data used in the
signing process. This is further discussed in Section 10.6 of this
document.
As discussed in Section 6.2.3 of [I-D.ietf-core-groupcomm-bis], Group As discussed in Section 6.2.3 of [I-D.ietf-core-groupcomm-bis], Group
OSCORE addresses security attacks against CoAP listed in Sections OSCORE addresses security attacks against CoAP listed in Sections
11.2-11.6 of [RFC7252], especially when run over IP multicast. 11.2-11.6 of [RFC7252], especially when run over IP multicast.
The rest of this section first discusses security aspects to be taken The rest of this section first discusses security aspects to be taken
into account when using Group OSCORE. Then it goes through aspects into account when using Group OSCORE. Then it goes through aspects
covered in the security considerations of OSCORE (see Section 12 of covered in the security considerations of OSCORE (see Section 12 of
[RFC8613]), and discusses how they hold when Group OSCORE is used. [RFC8613]), and discusses how they hold when Group OSCORE is used.
skipping to change at page 39, line 32 skipping to change at page 41, line 38
ensures that a message sent to a group has been sent by a member ensures that a message sent to a group has been sent by a member
of that group, but not necessarily by the alleged sender. This is of that group, but not necessarily by the alleged sender. This is
why source authentication of messages sent to a group is ensured why source authentication of messages sent to a group is ensured
through a counter signature, which is computed by the sender using through a counter signature, which is computed by the sender using
its own private key and then appended to the message payload. its own private key and then appended to the message payload.
Instead, the pairwise mode described in Section 9 protects messages Instead, the pairwise mode described in Section 9 protects messages
by using pairwise symmetric keys, derived from the static-static by using pairwise symmetric keys, derived from the static-static
Diffie-Hellman shared secret computed from the asymmetric keys of the Diffie-Hellman shared secret computed from the asymmetric keys of the
sender and recipient endpoint (see Section 2.3). Therefore, in the sender and recipient endpoint (see Section 2.3). Therefore, in the
parwise mode, the AEAD algorithm provides both pairwise data- pairwise mode, the AEAD algorithm provides both pairwise data-
confidentiality and source authentication of messages, without using confidentiality and source authentication of messages, without using
counter signatures. counter signatures.
The long-term storing of the Diffie-Hellman shared secret is a The long-term storing of the Diffie-Hellman shared secret is a
potential security issue. In fact, if the shared secret of two group potential security issue. In fact, if the shared secret of two group
members is leaked, a third group member can exploit it to impersonate members is leaked, a third group member can exploit it to impersonate
any of those two group members, by deriving and using their pairwise any of those two group members, by deriving and using their pairwise
key. The possibility of such leakage should be contemplated, as more key. The possibility of such leakage should be contemplated, as more
likely to happen than the leakage of a private key, which could be likely to happen than the leakage of a private key, which could be
rather protected at a significantly higher level than generic memory, rather protected at a significantly higher level than generic memory,
skipping to change at page 40, line 15 skipping to change at page 42, line 22
case of misbehaving. case of misbehaving.
10.2. Uniqueness of (key, nonce) 10.2. Uniqueness of (key, nonce)
The proof for uniqueness of (key, nonce) pairs in Appendix D.4 of The proof for uniqueness of (key, nonce) pairs in Appendix D.4 of
[RFC8613] is also valid in group communication scenarios. That is, [RFC8613] is also valid in group communication scenarios. That is,
given an OSCORE group: given an OSCORE group:
o Uniqueness of Sender IDs within the group is enforced by the Group o Uniqueness of Sender IDs within the group is enforced by the Group
Manager, which never reassigns the same Sender ID within the same Manager, which never reassigns the same Sender ID within the same
group. group under the same Gid value.
o The case A in Appendix D.4 of [RFC8613] concerns all group o The case A in Appendix D.4 of [RFC8613] concerns all group
requests and responses including a Partial IV (e.g. Observe requests and responses including a Partial IV (e.g. Observe
notifications). In this case, same considerations from [RFC8613] notifications). In this case, same considerations from [RFC8613]
apply here as well. apply here as well.
o The case B in Appendix D.4 of [RFC8613] concerns responses not o The case B in Appendix D.4 of [RFC8613] concerns responses not
including a Partial IV (e.g. single response to a group request). including a Partial IV (e.g. single response to a group request).
In this case, same considerations from [RFC8613] apply here as In this case, same considerations from [RFC8613] apply here as
well. well.
skipping to change at page 41, line 12 skipping to change at page 43, line 14
join and leave at any time, in order to limit the impact on join and leave at any time, in order to limit the impact on
performance due to the Security Context and keying material update. performance due to the Security Context and keying material update.
10.4. Update of Security Context and Key Rotation 10.4. Update of Security Context and Key Rotation
A group member can receive a message shortly after the group has been A group member can receive a message shortly after the group has been
rekeyed, and new security parameters and keying material have been rekeyed, and new security parameters and keying material have been
distributed by the Group Manager. distributed by the Group Manager.
This may result in a client using an old Security Context to protect This may result in a client using an old Security Context to protect
a group request, and a server using a different new Security Context a request, and a server using a different new Security Context to
to protect a corresponding response. As a consequence, clients may protect a corresponding response. As a consequence, clients may
receive a response protected with a Security Context different from receive a response protected with a Security Context different from
the one used to protect the corresponding group request. the one used to protect the corresponding request.
In particular, a server may first get a group request protected with In particular, a server may first get a request protected with the
the old Security Context, then install the new Security Context, and old Security Context, then install the new Security Context, and only
only after that produce a response to send back to the client. In after that produce a response to send back to the client. In such a
such a case, as specified in Section 8.3, the server MUST protect the case, as specified in Section 8.3, the server MUST protect the
potential response using the new Security Context. Specifically, the potential response using the new Security Context. Specifically, the
server MUST include its Sender Sequence Number as Partial IV in the server MUST include its Sender Sequence Number as Partial IV in the
response and use it to build the AEAD nonce to protect the response. response and use it to build the AEAD nonce to protect the response.
This prevents the AEAD nonce from the request from being reused with This prevents the AEAD nonce from the request from being reused with
the new Security Context. the new Security Context.
The client will process that response using the new Security Context, The client will process that response using the new Security Context,
provided that it has installed the new security parameters and keying provided that it has installed the new security parameters and keying
material before the message processing. material before the message processing.
skipping to change at page 41, line 48 skipping to change at page 43, line 50
10.4.1. Late Update on the Sender 10.4.1. Late Update on the Sender
In this case, the sender protects a message using the old Security In this case, the sender protects a message using the old Security
Context, i.e. before having installed the new Security Context. Context, i.e. before having installed the new Security Context.
However, the recipient receives the message after having installed However, the recipient receives the message after having installed
the new Security Context, and is thus unable to correctly process it. the new Security Context, and is thus unable to correctly process it.
A possible way to ameliorate this issue is to preserve the old, A possible way to ameliorate this issue is to preserve the old,
recent, Security Context for a maximum amount of time defined by the recent, Security Context for a maximum amount of time defined by the
application. By doing so, the recipient can still try to process the application. By doing so, the recipient can still try to process the
received message using the old retained Security Context as second received message using the old retained Security Context as a second
attempt. This makes particular sense when the recipient is a client, attempt. This makes particular sense when the recipient is a client,
that would hence be able to process incoming responses protected with that would hence be able to process incoming responses protected with
the old, recent, Security Context used to protect the associated the old, recent, Security Context used to protect the associated
group request. Instead, a recipient server would better and more group request. Instead, a recipient server would better and more
simply discard an incoming group request which is not successfully simply discard an incoming group request which is not successfully
processed with the new Security Context. processed with the new Security Context.
This tolerance preserves the processing of secure messages throughout This tolerance preserves the processing of secure messages throughout
a long-lasting key rotation, as group rekeying processes may likely a long-lasting key rotation, as group rekeying processes may likely
take a long time to complete, especially in large scale groups. On take a long time to complete, especially in large scale groups. On
skipping to change at page 43, line 21 skipping to change at page 45, line 21
When a sender endpoint sends a message protected in pairwise mode to When a sender endpoint sends a message protected in pairwise mode to
a recipient endpoint in an OSCORE group, a malicious group member may a recipient endpoint in an OSCORE group, a malicious group member may
attempt to inject the message to a different OSCORE group also attempt to inject the message to a different OSCORE group also
including the same endpoints (see Section 10.6.1). including the same endpoints (see Section 10.6.1).
This practically relies on altering the content of the OSCORE option, This practically relies on altering the content of the OSCORE option,
and having the same MAC in the ciphertext still correctly validating, and having the same MAC in the ciphertext still correctly validating,
which has a success probability depending on the size of the MAC. which has a success probability depending on the size of the MAC.
As discussed in Section 10.6.2, the attack is practically infeasible As discussed in Section 10.6.2, the attack is practically infeasible
if the message is protected in group mode, since the counter if the message is protected in group mode, thanks to the counter
signature is bound also to the OSCORE option, through the Additional signature also bound to the OSCORE option through the Additional
Authenticated Data used in the signing process (see Section 4.3.2). Authenticated Data used in the signing process (see Section 4.3).
10.6.1. Attack Description 10.6.1. Attack Description
Let us consider: Let us consider:
o Two OSCORE groups G1 and G2, with ID Context (Group ID) Gid1 and o Two OSCORE groups G1 and G2, with ID Context (Group ID) Gid1 and
Gid2, respectively. Both G1 and G2 use the AEAD cipher AES-CCM- Gid2, respectively. Both G1 and G2 use the AEAD cipher AES-CCM-
16-64-128, i.e. the MAC of the ciphertext is 8 bytes in size. 16-64-128, i.e. the MAC of the ciphertext is 8 bytes in size.
o A sender endpoint X which is member of both G1 and G2, and uses o A sender endpoint X which is member of both G1 and G2, and uses
skipping to change at page 43, line 46 skipping to change at page 45, line 46
(Sid1, Gid1) and (Sid2, Gid2) identify the same public key of X in (Sid1, Gid1) and (Sid2, Gid2) identify the same public key of X in
G1 and G2, respectively. G1 and G2, respectively.
o A recipient endpoint Y which is member of both G1 and G2, and uses o A recipient endpoint Y which is member of both G1 and G2, and uses
the same public/private key pair in both groups. The endpoint Y the same public/private key pair in both groups. The endpoint Y
has Sender ID Sid3 in G1 and Sender ID Sid4 in G2. The pairs has Sender ID Sid3 in G1 and Sender ID Sid4 in G2. The pairs
(Sid3, Gid1) and (Sid4, Gid2) identify the same public key of Y in (Sid3, Gid1) and (Sid4, Gid2) identify the same public key of Y in
G1 and G2, respectively. G1 and G2, respectively.
o A malicious endpoint Z is also member of both G1 and G2. Hence, Z o A malicious endpoint Z is also member of both G1 and G2. Hence, Z
is able to derive the symmetric keys associated to X in G1 and G2. is able to derive the Sender Keys used by X in G1 and G2.
When X sends a message M1 addressed to Y in G1 and protected in When X sends a message M1 addressed to Y in G1 and protected in
pairwise mode, Z can intercept M1, and forge a valid message M2 to be pairwise mode, Z can intercept M1, and attempt to forge a valid
injected in G2, making it appear as still sent by X to Y and valid to message M2 to be injected in G2, making it appear as still sent by X
be accepted. to Y and valid to be accepted.
More in detail, Z intercepts and stops message M1, and forges a More in detail, Z intercepts and stops message M1, and forges a
message M2 by changing the value of the OSCORE option from M1 as message M2 by changing the value of the OSCORE option from M1 as
follows: the 'kid context' is changed from G1 to G2; and the 'kid' is follows: the 'kid context' is set to G2 (rather than G1); and the
changed from Sid1 to Sid2. Then, Z injects message M2 as addressed 'kid' is set to Sid2 (rather than Sid1). Then, Z injects message M2
to Y in G2. as addressed to Y in G2.
Upon receiving M2, there is a probability equal to 2^-64 that Y Upon receiving M2, there is a probability equal to 2^-64 that Y
successfully verifies the same unchanged MAC by using Sid2 as successfully verifies the same unchanged MAC by using the Pairwise
'request_kid' and using the Pairwise Recipient Key associated to X in Recipient Key associated to X in G2.
G2.
Note that Z does not know the pairwise keys of X and Y, since it does Note that Z does not know the pairwise keys of X and Y, since it does
not know and is not able to compute their shared Diffie-Hellman not know and is not able to compute their shared Diffie-Hellman
secret. Therefore, Z is not able to check offline if a performed secret. Therefore, Z is not able to check offline if a performed
forgery is actually valid, before sending the forged message to G2. forgery is actually valid, before sending the forged message to G2.
10.6.2. Attack Prevention in Group Mode 10.6.2. Attack Prevention in Group Mode
When a Group OSCORE message is protected with the group mode, the When a Group OSCORE message is protected with the group mode, the
counter signature is computed also over the value of the OSCORE counter signature is computed also over the value of the OSCORE
option, which is part of the Additional Authenticated Data used in option, which is part of the Additional Authenticated Data used in
the signing process (see Section 4.3.2). the signing process (see Section 4.3).
That is, the countersignature is computed also over: the ID Context That is, other than over the ciphertext, the countersignature is
(Group ID) and the Partial IV, which are always present in group computed over: the ID Context (Gid) and the Partial IV, which are
requests; as well as the Sender ID of the message originator, which always present in group requests; as well as the Sender ID of the
is always present in all group requests and responses. message originator, which is always present in group requests as well
as in responses to requests protected in group mode.
Since the signing process takes as input also the ciphertext of the Since the signing process takes as input also the ciphertext of the
COSE_Encrypt0 object, the countersignature is bound not only to the COSE_Encrypt0 object, the countersignature is bound not only to the
intended OSCORE group, hence to the triplet (Master Secret, Master intended OSCORE group, hence to the triplet (Master Secret, Master
Salt, ID Context), but also to a specific Sender ID in that group and Salt, ID Context), but also to a specific Sender ID in that group and
to its specific symmetric key used for AEAD encryption, hence to the to its specific symmetric key used for AEAD encryption, hence to the
quartet (Master Secret, Master Salt, ID Context, Sender ID). quartet (Master Secret, Master Salt, ID Context, Sender ID).
This makes it practically infeasible to perform the attack described This makes it practically infeasible to perform the attack described
in Section 10.6.1, since it would require the adversary to in Section 10.6.1, since it would require the adversary to
additionally forge a valid countersignature that replaces the additionally forge a valid countersignature that replaces the
original one in the forged message M2. original one in the forged message M2.
If the countersignature did not cover the OSCORE option, the attack If the countersignature did not cover the OSCORE option, the attack
would be possible also in group mode, since the same unchanged would still be possible against response messages protected in group
countersignature from messsage M1 would be also valid in message M2. mode, since the same unchanged countersignature from message M1 would
be also valid in message M2.
Also, the following attack simplifications would hold, since Z is Also, the following attack simplifications would hold, since Z is
able to derive the Sender/Recipient Keys of X and Y in G1 and G2. able to derive the Sender/Recipient Keys of X and Y in G1 and G2.
That is, Z can also set a convenient Partial IV in the response,
until the same unchanged MAC is successfully verified by using G2 as
'request_kid_context', Sid2 as 'request_kid', and the symmetric key
associated to X in G2.
o If M2 is used as a request, Z can check offline if a performed Since the Partial IV is 5 bytes in size, this requires 2^40
forgery is actually valid before sending the forged message to G2. operations to test all the Partial IVs, which can be done in real-
time. The probability that a single given message M1 can be used to
That is, this attack would have a complexity of 2^64 offline forge a response M2 for a given request would be equal to 2^-24,
calculations. since there are more MAC values (8 bytes in size) than Partial IV
values (5 bytes in size).
o If M2 is used as a response, Z can also change the response
Partial IV, until the same unchanged MAC is successfully verified
by using Sid2 as 'request_kid' and the symmetric key associated to
X in G2. Since the Partial IV is 5 bytes in size, this requires
2^40 operations to test all the Partial IVs, which can be done in
real-time. Also, the probability that a single given message M1
can be used to forge a response M2 for a given request would be
equal to 2^-24, since there are more MAC values (8 bytes in size)
than Partial IV values (5 bytes in size).
Note that, by changing the Partial IV as discussed above, any Note that, by changing the Partial IV as discussed above, any member
member of G1 would also be able to forge a valid signed response of G1 would also be able to forge a valid signed response message M2
message M2 to be injected in G1. to be injected in the same group G1.
10.7. Group OSCORE for Unicast Requests 10.7. Group OSCORE for Unicast Requests
If a request is intended to be sent over unicast as addressed to a If a request is intended to be sent over unicast as addressed to a
single group member, it is NOT RECOMMENDED for the client to protect single group member, it is NOT RECOMMENDED for the client to protect
the request by using the group mode as defined in Section 8.1. the request by using the group mode as defined in Section 8.1.
This does not include the case where the client sends a request over This does not include the case where the client sends a request over
unicast to a proxy, to be forwarded to multiple intended recipients unicast to a proxy, to be forwarded to multiple intended recipients
over multicast [I-D.ietf-core-groupcomm-bis]. In this case, the over multicast [I-D.ietf-core-groupcomm-bis]. In this case, the
skipping to change at page 46, line 15 skipping to change at page 48, line 11
The impact of such an attack depends especially on the REST method of The impact of such an attack depends especially on the REST method of
the request, i.e. the Inner CoAP Code of the OSCORE request message. the request, i.e. the Inner CoAP Code of the OSCORE request message.
In particular, safe methods such as GET and FETCH would trigger In particular, safe methods such as GET and FETCH would trigger
(several) unintended responses from the targeted server(s), while not (several) unintended responses from the targeted server(s), while not
resulting in destructive behavior. On the other hand, non safe resulting in destructive behavior. On the other hand, non safe
methods such as PUT, POST and PATCH/iPATCH would result in the target methods such as PUT, POST and PATCH/iPATCH would result in the target
server(s) taking active actions on their resources and possible server(s) taking active actions on their resources and possible
cyber-physical environment, with the risk of destructive consequences cyber-physical environment, with the risk of destructive consequences
and possible implications for safety. and possible implications for safety.
A client can instead use the pairwise mode as defined in Section 9.2, A client can instead use the pairwise mode as defined in Section 9.3,
in order to protect a request sent to a single group member by using in order to protect a request sent to a single group member by using
pairwise keying material (see Section 2.3). This prevents the attack pairwise keying material (see Section 2.3). This prevents the attack
discussed above by construction, as only the intended server is able discussed above by construction, as only the intended server is able
to derive the pairwise keying material used by the client to protect to derive the pairwise keying material used by the client to protect
the request. A client supporting the pairwise mode SHOULD use it to the request. A client supporting the pairwise mode SHOULD use it to
protect requests sent to a single group member over unicast, instead protect requests sent to a single group member over unicast, instead
of using the group mode. For an example where this is not fulfilled, of using the group mode. For an example where this is not fulfilled,
see Section 6.2.1 in see Section 7.2.1 in
[I-D.tiloca-core-observe-multicast-notifications]. [I-D.tiloca-core-observe-multicast-notifications].
With particular reference to block-wise transfers [RFC7959], With particular reference to block-wise transfers [RFC7959],
Section 2.3.6 of [I-D.ietf-core-groupcomm-bis] points out that, while Section 3.7 of [I-D.ietf-core-groupcomm-bis] points out that, while
an initial request including the CoAP Block2 option can be sent over an initial request including the CoAP Block2 option can be sent over
multicast, any other request in a transfer has to occur over unicast, multicast, any other request in a transfer has to occur over unicast,
individually addressing the servers in the group. individually addressing the servers in the group.
Additional considerations are discussed in Appendix E.3, with respect Additional considerations are discussed in Appendix E, with respect
to requests including a CoAP Echo Option to requests including a CoAP Echo Option
[I-D.ietf-core-echo-request-tag] that has to be sent over unicast, as [I-D.ietf-core-echo-request-tag] that has to be sent over unicast, as
a challenge-response method for servers to achieve synchronization of a challenge-response method for servers to achieve synchronization of
clients' Sender Sequence Number. clients' Sender Sequence Number.
10.8. End-to-end Protection 10.8. End-to-end Protection
The same considerations from Section 12.1 of [RFC8613] hold for Group The same considerations from Section 12.1 of [RFC8613] hold for Group
OSCORE. OSCORE.
skipping to change at page 47, line 18 skipping to change at page 49, line 16
kept secret among the members of the respective OSCORE group and the kept secret among the members of the respective OSCORE group and the
Group Manager responsible for that group. Also, the Master Secret Group Manager responsible for that group. Also, the Master Secret
must have a good amount of randomness, and the Group Manager can must have a good amount of randomness, and the Group Manager can
generate it offline using a good random number generator. This generate it offline using a good random number generator. This
includes the case where the Group Manager rekeys the group by includes the case where the Group Manager rekeys the group by
generating and distributing a new Master Secret. Randomness generating and distributing a new Master Secret. Randomness
requirements for security are described in [RFC4086]. requirements for security are described in [RFC4086].
10.10. Replay Protection 10.10. Replay Protection
As in OSCORE, also Group OSCORE relies on sender sequence numbers As in OSCORE [RFC8613], also Group OSCORE relies on Sender Sequence
included in the COSE message field 'Partial IV' and used to build Numbers included in the COSE message field 'Partial IV' and used to
AEAD nonces. build AEAD nonces.
Note that the Partial IV of an endpoint does not necessarily grow Note that the Partial IV of an endpoint does not necessarily grow
monotonically. For instance, upon exhaustion of the endpoint Sender monotonically. For instance, upon exhaustion of the endpoint Sender
Sequence Number, the Partial IV also gets exhausted. As discussed in Sequence Number, the Partial IV also gets exhausted. As discussed in
Section 2.4.3, this results either in the endpoint being individually Section 2.4.3, this results either in the endpoint being individually
rekeyed and getting a new Sender ID, or in the establishment of a new rekeyed and getting a new Sender ID, or in the establishment of a new
Security Context in the group. Therefore, uniqueness of (key, nonce) Security Context in the group. Therefore, uniqueness of (key, nonce)
pairs (see Section 10.2) is preserved also when a new Security pairs (see Section 10.2) is preserved also when a new Security
Context is established. Context is established.
As discussed in Section 6.1, an endpoint that has just joined a group Since one-to-many communication such as multicast usually involves
is exposed to replay attack, as it is not aware of the Sender unreliable transports, the simplification of the Replay Window to a
Sequence Numbers currently used by other group members. Appendix E size of 1 suggested in Section 7.4 of [RFC8613] is not viable with
describes how endpoints can synchronize with others' Sender Sequence Group OSCORE, unless exchanges in the group rely only on unicast
Number. messages.
Unless exchanges in a group rely only on unicast messages, Group As discussed in Section 6.1, a Replay Window may be initialized as
OSCORE cannot be used with reliable transport. Thus, unless only not valid, following the loss of mutable Security Context
unicast messages are sent in the group, it cannot be defined that Section 2.4.1. In particular, Section 2.4.1.1 and Section 2.4.1.2
only messages with sequence numbers that are equal to the previous define measures that endpoints need to take in such a situation,
sequence number + 1 are accepted. before resuming to accept incoming messages from other group members.
The processing of response messages described in Section 2.3.1 of 10.11. Message Freshness
[I-D.ietf-core-groupcomm-bis] also ensures that a client accepts a
single valid response to a given request from each replying server,
unless CoAP observation is used.
10.11. Client Aliveness As discussed in Section 6.2, a server may not be able to assert
whether an incoming request is fresh, in case it does not have or has
lost synchronization with the client's Sender Sequence Number.
As discussed in Section 12.5 of [RFC8613], a server may use the CoAP If freshness is relevant for the application, the server may
Echo Option [I-D.ietf-core-echo-request-tag] to verify the aliveness (re-)synchronize with the client's Sender Sequence Number at any
of the client that originated a received request. This would also time, by using the approach described in Appendix E and based on the
allow the server to (re-)synchronize with the client's Sender CoAP Echo Option [I-D.ietf-core-echo-request-tag], as a variant of
Sequence Number, as well as to ensure that the request is fresh and the approach defined in Appendix B.1.2 of [RFC8613] applicable to
has not been replayed or (purposely) delayed, if it is the first one Group OSCORE.
received from that client after having joined the group or rebooted
(see Appendix E.3).
10.12. Cryptographic Considerations 10.12. Client Aliveness
Building on Section 12.5 of [RFC8613], a server may use the CoAP Echo
Option [I-D.ietf-core-echo-request-tag] to verify the aliveness of
the client that originated a received request, by using the approach
described in Appendix E of this specification.
10.13. Cryptographic Considerations
The same considerations from Section 12.6 of [RFC8613] about the The same considerations from Section 12.6 of [RFC8613] about the
maximum Sender Sequence Number hold for Group OSCORE. maximum Sender Sequence Number hold for Group OSCORE.
As discussed in Section 2.4.2, an endpoint that experiences an As discussed in Section 2.4.2, an endpoint that experiences an
exhaustion of its own Sender Sequence Numbers MUST NOT protect exhaustion of its own Sender Sequence Numbers MUST NOT protect
further messages including a Partial IV, until it has derived a new further messages including a Partial IV, until it has derived a new
Sender Context. This prevents the endpoint to reuse the same AEAD Sender Context. This prevents the endpoint to reuse the same AEAD
nonces with the same Sender Key. nonces with the same Sender Key.
skipping to change at page 49, line 13 skipping to change at page 51, line 8
consequence, some deployments using, for instance, ECDSA with NIST consequence, some deployments using, for instance, ECDSA with NIST
P-256 may not support the mandatory signature algorithm but that P-256 may not support the mandatory signature algorithm but that
should not be an issue for local deployments. should not be an issue for local deployments.
The derivation of pairwise keys defined in Section 2.3.1 is The derivation of pairwise keys defined in Section 2.3.1 is
compatible with ECDSA and EdDSA asymmetric keys, but is not compatible with ECDSA and EdDSA asymmetric keys, but is not
compatible with RSA asymmetric keys. The security of using the same compatible with RSA asymmetric keys. The security of using the same
key pair for Diffie-Hellman and for signing is demonstrated in key pair for Diffie-Hellman and for signing is demonstrated in
[Degabriele]. [Degabriele].
10.13. Message Segmentation 10.14. Message Segmentation
The same considerations from Section 12.7 of [RFC8613] hold for Group The same considerations from Section 12.7 of [RFC8613] hold for Group
OSCORE. OSCORE.
10.14. Privacy Considerations 10.15. Privacy Considerations
Group OSCORE ensures end-to-end integrity protection and encryption Group OSCORE ensures end-to-end integrity protection and encryption
of the message payload and all options that are not used for proxy of the message payload and all options that are not used for proxy
operations. In particular, options are processed according to the operations. In particular, options are processed according to the
same class U/I/E that they have for OSCORE. Therefore, the same same class U/I/E that they have for OSCORE. Therefore, the same
privacy considerations from Section 12.8 of [RFC8613] hold for Group privacy considerations from Section 12.8 of [RFC8613] hold for Group
OSCORE. OSCORE.
Furthermore, the following privacy considerations hold, about the Furthermore, the following privacy considerations hold about the
OSCORE option that may reveal information on the communicating OSCORE option, which may reveal information on the communicating
endpoints. endpoints.
o The 'kid' parameter, which is intended to help a recipient o The 'kid' parameter, which is intended to help a recipient
endpoint to find the right Recipient Context, may reveal endpoint to find the right Recipient Context, may reveal
information about the Sender Endpoint. Since both requests and information about the Sender Endpoint. When both a request and
responses always include the 'kid' parameter, this may reveal the corresponding responses include the 'kid' parameter, this may
information about both a client sending a group request and all reveal information about both a client sending a request and all
the possibly replying servers sending their own individual the possibly replying servers sending their own individual
response. response.
o The 'kid context' parameter, which is intended to help a recipient o The 'kid context' parameter, which is intended to help a recipient
endpoint to find the right Security Context, reveals information endpoint to find the right Security Context, reveals information
about the sender endpoint. In particular, it reveals that the about the sender endpoint. In particular, it reveals that the
sender endpoint is a member of a particular OSCORE group, whose sender endpoint is a member of a particular OSCORE group, whose
current Group ID is indicated in the 'kid context' parameter. current Group ID is indicated in the 'kid context' parameter.
When receiving a group request, each of the recipient endpoints can When receiving a group request, each of the recipient endpoints can
reply with a response that includes its Sender ID as 'kid' parameter. reply with a response that includes its Sender ID as 'kid' parameter.
All these responses will be matchable with the request through the All these responses will be matchable with the request through the
Token. Thus, even if these responses do not include a 'kid context' Token. Thus, even if these responses do not include a 'kid context'
parameter, it becomes possible to understand that the responder parameter, it becomes possible to understand that the responder
endpoints are in the same group of the requester endpoint. endpoints are in the same group of the requester endpoint.
Furthermore, using the mechanisms described in Appendix E.3 to Furthermore, using the mechanisms described in Appendix E to achieve
achieve sequence number synchronization with a client may reveal when Sender Sequence Number synchronization with a client may reveal when
a server device goes through a reboot. This can be mitigated by the a server device goes through a reboot. This can be mitigated by the
server device storing the precise state of the replay window of each server device storing the precise state of the Replay Window of each
known client on a clean shutdown. known client on a clean shutdown.
Finally, the mechanism described in Section 10.5 to prevent Finally, the mechanism described in Section 10.5 to prevent
collisions of Group Identifiers from different Group Managers may collisions of Group Identifiers from different Group Managers may
reveal information about events in the respective OSCORE groups. In reveal information about events in the respective OSCORE groups. In
particular, a Group Identifier changes when the corresponding group particular, a Group Identifier changes when the corresponding group
is rekeyed. Thus, Group Managers might use the shared list of Group is rekeyed. Thus, Group Managers might use the shared list of Group
Identifiers to infer the rate and patterns of group membership Identifiers to infer the rate and patterns of group membership
changes triggering a group rekeying, e.g. due to newly joined members changes triggering a group rekeying, e.g. due to newly joined members
or evicted (compromised) members. In order to alleviate this privacy or evicted (compromised) members. In order to alleviate this privacy
concern, it should be hidden from the Group Managers which exact concern, it should be hidden from the Group Managers which exact
Group Manager has currently assigned which Group Identifiers in its Group Manager has currently assigned which Group Identifiers in its
OSCORE groups. OSCORE groups.
11. IANA Considerations 11. IANA Considerations
Note to RFC Editor: Please replace all occurrences of "[This Note to RFC Editor: Please replace "[This Document]" with the RFC
Document]" with the RFC number of this specification and delete this number of this specification and delete this paragraph.
paragraph.
This document has the following actions for IANA. This document has the following actions for IANA.
11.1. OSCORE Flag Bits Registry 11.1. OSCORE Flag Bits Registry
IANA is asked to add the following value entry to the "OSCORE Flag IANA is asked to add the following value entry to the "OSCORE Flag
Bits" subregistry defined in Section 13.7 of [RFC8613] as part of the Bits" subregistry defined in Section 13.7 of [RFC8613] as part of the
"CoRE Parameters" registry. "CoRE Parameters" registry.
+--------------+------------+----------------------------+-----------+ +--------------+------------+-----------------------------+-----------+
| Bit Position | Name | Description | Reference | | Bit Position | Name | Description | Reference |
+--------------+------------+----------------------------+-----------+ +--------------+------------+-----------------------------+-----------+
| 2 | Group Flag | Set to 1 if the message is | [This | | 2 | Group Flag | For using a Group OSCORE | [This |
| | | protected with the group | Document] | | | | Security Context, set to 1 | Document] |
| | | mode of Group OSCORE | | | | | if the message is protected | |
+--------------+------------+----------------------------+-----------+ | | | with the group mode | |
+--------------+------------+-----------------------------+-----------+
12. References 12. References
12.1. Normative References 12.1. Normative References
[COSE.Algorithms] [COSE.Algorithms]
IANA, "COSE Algorithms", IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/ <https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>. cose.xhtml#algorithms>.
[COSE.Key.Types] [COSE.Key.Types]
IANA, "COSE Key Types", IANA, "COSE Key Types",
<https://www.iana.org/assignments/cose/cose.xhtml#key- <https://www.iana.org/assignments/cose/cose.xhtml#key-
type>. type>.
[I-D.ietf-cbor-7049bis]
Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", draft-ietf-cbor-7049bis-16 (work
in progress), September 2020.
[I-D.ietf-core-groupcomm-bis] [I-D.ietf-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", draft- for the Constrained Application Protocol (CoAP)", draft-
ietf-core-groupcomm-bis-02 (work in progress), November ietf-core-groupcomm-bis-03 (work in progress), February
2020. 2021.
[I-D.ietf-cose-countersign] [I-D.ietf-cose-countersign]
Schaad, J. and R. Housley, "CBOR Object Signing and Schaad, J. and R. Housley, "CBOR Object Signing and
Encryption (COSE): Countersignatures", draft-ietf-cose- Encryption (COSE): Countersignatures", draft-ietf-cose-
countersign-01 (work in progress), October 2020. countersign-02 (work in progress), December 2020.
[I-D.ietf-cose-rfc8152bis-algs] [I-D.ietf-cose-rfc8152bis-algs]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", draft-ietf-cose-rfc8152bis-algs-12 Initial Algorithms", draft-ietf-cose-rfc8152bis-algs-12
(work in progress), September 2020. (work in progress), September 2020.
[I-D.ietf-cose-rfc8152bis-struct] [I-D.ietf-cose-rfc8152bis-struct]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", draft-ietf-cose-rfc8152bis- Structures and Process", draft-ietf-cose-rfc8152bis-
struct-14 (work in progress), September 2020. struct-15 (work in progress), February 2021.
[NIST-800-56A] [NIST-800-56A]
Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R. Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
Davis, "Recommendation for Pair-Wise Key-Establishment Davis, "Recommendation for Pair-Wise Key-Establishment
Schemes Using Discrete Logarithm Cryptography - NIST Schemes Using Discrete Logarithm Cryptography - NIST
Special Publication 800-56A, Revision 3", April 2018, Special Publication 800-56A, Revision 3", April 2018,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/ <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-56Ar3.pdf>. NIST.SP.800-56Ar3.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 52, line 28 skipping to change at page 54, line 19
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments "Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>. <https://www.rfc-editor.org/info/rfc8613>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
12.2. Informative References 12.2. Informative References
[Degabriele] [Degabriele]
Degabriele, J., Lehmann, A., Paterson, K., Smart, N., and Degabriele, J., Lehmann, A., Paterson, K., Smart, N., and
M. Strefler, "On the Joint Security of Encryption and M. Strefler, "On the Joint Security of Encryption and
Signature in EMV", December 2011, Signature in EMV", December 2011,
<https://eprint.iacr.org/2011/615>. <https://eprint.iacr.org/2011/615>.
[I-D.ietf-ace-key-groupcomm] [I-D.ietf-ace-key-groupcomm]
Palombini, F. and M. Tiloca, "Key Provisioning for Group Palombini, F. and M. Tiloca, "Key Provisioning for Group
Communication using ACE", draft-ietf-ace-key-groupcomm-10 Communication using ACE", draft-ietf-ace-key-groupcomm-11
(work in progress), November 2020. (work in progress), February 2021.
[I-D.ietf-ace-key-groupcomm-oscore] [I-D.ietf-ace-key-groupcomm-oscore]
Tiloca, M., Park, J., and F. Palombini, "Key Management Tiloca, M., Park, J., and F. Palombini, "Key Management
for OSCORE Groups in ACE", draft-ietf-ace-key-groupcomm- for OSCORE Groups in ACE", draft-ietf-ace-key-groupcomm-
oscore-09 (work in progress), November 2020. oscore-10 (work in progress), February 2021.
[I-D.ietf-ace-oauth-authz] [I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0 Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-35 Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-37
(work in progress), June 2020. (work in progress), February 2021.
[I-D.ietf-core-echo-request-tag] [I-D.ietf-core-echo-request-tag]
Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo, Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo,
Request-Tag, and Token Processing", draft-ietf-core-echo- Request-Tag, and Token Processing", draft-ietf-core-echo-
request-tag-10 (work in progress), July 2020. request-tag-12 (work in progress), January 2021.
[I-D.ietf-lwig-curve-representations] [I-D.ietf-lwig-curve-representations]
Struik, R., "Alternative Elliptic Curve Representations", Struik, R., "Alternative Elliptic Curve Representations",
draft-ietf-lwig-curve-representations-12 (work in draft-ietf-lwig-curve-representations-20 (work in
progress), August 2020. progress), February 2021.
[I-D.ietf-lwig-security-protocol-comparison] [I-D.ietf-lwig-security-protocol-comparison]
Mattsson, J., Palombini, F., and M. Vucinic, "Comparison Mattsson, J., Palombini, F., and M. Vucinic, "Comparison
of CoAP Security Protocols", draft-ietf-lwig-security- of CoAP Security Protocols", draft-ietf-lwig-security-
protocol-comparison-04 (work in progress), March 2020. protocol-comparison-05 (work in progress), November 2020.
[I-D.ietf-tls-dtls13] [I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-38 (work in progress), May 1.3", draft-ietf-tls-dtls13-41 (work in progress),
2020. February 2021.
[I-D.mattsson-cfrg-det-sigs-with-noise] [I-D.mattsson-cfrg-det-sigs-with-noise]
Mattsson, J., Thormarker, E., and S. Ruohomaa, Mattsson, J., Thormarker, E., and S. Ruohomaa,
"Deterministic ECDSA and EdDSA Signatures with Additional "Deterministic ECDSA and EdDSA Signatures with Additional
Randomness", draft-mattsson-cfrg-det-sigs-with-noise-02 Randomness", draft-mattsson-cfrg-det-sigs-with-noise-02
(work in progress), March 2020. (work in progress), March 2020.
[I-D.somaraju-ace-multicast] [I-D.somaraju-ace-multicast]
Somaraju, A., Kumar, S., Tschofenig, H., and W. Werner, Somaraju, A., Kumar, S., Tschofenig, H., and W. Werner,
"Security for Low-Latency Group Communication", draft- "Security for Low-Latency Group Communication", draft-
somaraju-ace-multicast-02 (work in progress), October somaraju-ace-multicast-02 (work in progress), October
2016. 2016.
[I-D.tiloca-core-observe-multicast-notifications] [I-D.tiloca-core-observe-multicast-notifications]
Tiloca, M., Hoeglund, R., Amsuess, C., and F. Palombini, Tiloca, M., Hoeglund, R., Amsuess, C., and F. Palombini,
"Observe Notifications as CoAP Multicast Responses", "Observe Notifications as CoAP Multicast Responses",
draft-tiloca-core-observe-multicast-notifications-04 (work draft-tiloca-core-observe-multicast-notifications-05 (work
in progress), November 2020. in progress), February 2021.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4 "Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>. <https://www.rfc-editor.org/info/rfc4944>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>. <https://www.rfc-editor.org/info/rfc4949>.
skipping to change at page 54, line 42 skipping to change at page 56, line 37
for the approach described in this document. The rest of this for the approach described in this document. The rest of this
section refers to three types of groups: section refers to three types of groups:
o Application group, i.e. a set of CoAP endpoints that share a o Application group, i.e. a set of CoAP endpoints that share a
common pool of resources. common pool of resources.
o Security group, as defined in Section 1.1 of this specification. o Security group, as defined in Section 1.1 of this specification.
There can be a one-to-one or a one-to-many relation between There can be a one-to-one or a one-to-many relation between
security groups and application groups, and vice versa. security groups and application groups, and vice versa.
o CoAP group, as defined in [I-D.ietf-core-groupcomm-bis] i.e. a set o CoAP group, i.e. a set of CoAP endpoints where each endpoint is
of CoAP endpoints, where each endpoint is configured to receive configured to receive one-to-many CoAP requests, e.g. sent to the
CoAP multicast requests that are sent to the group's associated IP group's associated IP multicast address and UDP port as defined in
multicast address and UDP port. An endpoint may be a member of [I-D.ietf-core-groupcomm-bis]. An endpoint may be a member of
multiple CoAP groups. There can be a one-to-one or a one-to-many multiple CoAP groups. There can be a one-to-one or a one-to-many
relation between application groups and CoAP groups. Note that a relation between application groups and CoAP groups. Note that a
device sending a CoAP request to a CoAP group is not necessarily device sending a CoAP request to a CoAP group is not necessarily
itself a member of that group: it is a member only if it also has itself a member of that group: it is a member only if it also has
a CoAP server endpoint listening to requests for this CoAP group, a CoAP server endpoint listening to requests for this CoAP group,
sent to the associated IP multicast address and port. In order to sent to the associated IP multicast address and port. In order to
provide secure group communication, all members of a CoAP group as provide secure group communication, all members of a CoAP group as
well as all further endpoints configured only as clients sending well as all further endpoints configured only as clients sending
CoAP (multicast) requests to the CoAP group have to be member of a CoAP (multicast) requests to the CoAP group have to be member of a
security group. There can be a one-to-one or a one-to-many security group. There can be a one-to-one or a one-to-many
relation between security groups and CoAP groups, and vice versa. relation between security groups and CoAP groups, and vice versa.
A.1. Assumptions A.1. Assumptions
The following assumptions are assumed to be already addressed and are The following points are assumed to be already addressed and are out
out of the scope of this document. of the scope of this document.
o Multicast communication topology: this document considers both o Multicast communication topology: this document considers both
1-to-N (one sender and multiple recipients) and M-to-N (multiple 1-to-N (one sender and multiple recipients) and M-to-N (multiple
senders and multiple recipients) communication topologies. The senders and multiple recipients) communication topologies. The
1-to-N communication topology is the simplest group communication 1-to-N communication topology is the simplest group communication
scenario that would serve the needs of a typical Low-power and scenario that would serve the needs of a typical Low-power and
Lossy Network (LLN). Examples of use cases that benefit from Lossy Network (LLN). Examples of use cases that benefit from
secure group communication are provided in Appendix B. secure group communication are provided in Appendix B.
In a 1-to-N communication model, only a single client transmits In a 1-to-N communication model, only a single client transmits
data to the CoAP group, in the form of request messages; in an data to the CoAP group, in the form of request messages; in an
M-to-N communication model (where M and N do not necessarily have M-to-N communication model (where M and N do not necessarily have
the same value), M clients transmit data to the CoAP group. the same value), M clients transmit data to the CoAP group.
According to [I-D.ietf-core-groupcomm-bis], any possible proxy According to [I-D.ietf-core-groupcomm-bis], any possible proxy
entity is supposed to know about the clients and to not perform entity is supposed to know about the clients. Also, every client
aggregation of response messages from multiple servers. Also, expects and is able to handle multiple response messages
every client expects and is able to handle multiple response associated to a same request sent to the CoAP group.
messages associated to a same request sent to the CoAP group.
o Group size: security solutions for group communication should be o Group size: security solutions for group communication should be
able to adequately support different and possibly large security able to adequately support different and possibly large security
groups. The group size is the current number of members in a groups. The group size is the current number of members in a
security group. In the use cases mentioned in this document, the security group. In the use cases mentioned in this document, the
number of clients (normally the controlling devices) is expected number of clients (normally the controlling devices) is expected
to be much smaller than the number of servers (i.e. the controlled to be much smaller than the number of servers (i.e. the controlled
devices). A security solution for group communication that devices). A security solution for group communication that
supports 1 to 50 clients would be able to properly cover the group supports 1 to 50 clients would be able to properly cover the group
sizes required for most use cases that are relevant for this sizes required for most use cases that are relevant for this
skipping to change at page 57, line 50 skipping to change at page 59, line 44
use cases that benefit from secure group communication, and refers to use cases that benefit from secure group communication, and refers to
the three types of groups from Appendix A. Specific security the three types of groups from Appendix A. Specific security
requirements for these use cases are discussed in Appendix A. requirements for these use cases are discussed in Appendix A.
o Lighting control: consider a building equipped with IP-connected o Lighting control: consider a building equipped with IP-connected
lighting devices, switches, and border routers. The lighting lighting devices, switches, and border routers. The lighting
devices acting as servers are organized into application groups devices acting as servers are organized into application groups
and CoAP groups, according to their physical location in the and CoAP groups, according to their physical location in the
building. For instance, lighting devices in a room or corridor building. For instance, lighting devices in a room or corridor
can be configured as members of a single application group and can be configured as members of a single application group and
corresponding CoAP group. Those ligthing devices together with corresponding CoAP group. Those lighting devices together with
the switches acting as clients in the same room or corridor can be the switches acting as clients in the same room or corridor can be
configured as members of the corresponding security group. configured as members of the corresponding security group.
Switches are then used to control the lighting devices by sending Switches are then used to control the lighting devices by sending
on/off/dimming commands to all lighting devices in the CoAP group, on/off/dimming commands to all lighting devices in the CoAP group,
while border routers connected to an IP network backbone (which is while border routers connected to an IP network backbone (which is
also multicast-enabled) can be used to interconnect routers in the also multicast-enabled) can be used to interconnect routers in the
building. Consequently, this would also enable logical groups to building. Consequently, this would also enable logical groups to
be formed even if devices with a role in the lighting application be formed even if devices with a role in the lighting application
may be physically in different subnets (e.g. on wired and wireless may be physically in different subnets (e.g. on wired and wireless
networks). Connectivity between lighting devices may be realized, networks). Connectivity between lighting devices may be realized,
skipping to change at page 58, line 36 skipping to change at page 60, line 30
responsible for sending commands to a set of lighting devices. In responsible for sending commands to a set of lighting devices. In
more advanced lighting control use cases, a M-to-N communication more advanced lighting control use cases, a M-to-N communication
topology would be required, for instance in case multiple sensors topology would be required, for instance in case multiple sensors
(presence or day-light) are responsible to trigger events to a set (presence or day-light) are responsible to trigger events to a set
of lighting devices. Especially in professional lighting of lighting devices. Especially in professional lighting
scenarios, the roles of client and server are configured by the scenarios, the roles of client and server are configured by the
lighting commissioner, and devices strictly follow those roles. lighting commissioner, and devices strictly follow those roles.
o Integrated building control: enabling Building Automation and o Integrated building control: enabling Building Automation and
Control Systems (BACSs) to control multiple heating, ventilation Control Systems (BACSs) to control multiple heating, ventilation
and air-conditioning units to pre-defined presets. Controlled and air-conditioning units to predefined presets. Controlled
units can be organized into application groups and CoAP groups in units can be organized into application groups and CoAP groups in
order to reflect their physical position in the building, e.g. order to reflect their physical position in the building, e.g.
devices in the same room can be configured as members of a single devices in the same room can be configured as members of a single
application group and corresponding CoAP group. As a practical application group and corresponding CoAP group. As a practical
guideline, events within intervals of seconds are typically guideline, events within intervals of seconds are typically
acceptable. Controlled units are expected to possibly reply back acceptable. Controlled units are expected to possibly reply back
to the BACS issuing control commands, in order to report about the to the BACS issuing control commands, in order to report about the
execution of the requested operation (e.g. OK, failure, error) execution of the requested operation (e.g. OK, failure, error)
and their current operational status. and their current operational status.
skipping to change at page 60, line 31 skipping to change at page 62, line 21
Context (see Section 3.1). Context (see Section 3.1).
As an example, a 3-byte Gid can be composed of: i) a 1-byte Group As an example, a 3-byte Gid can be composed of: i) a 1-byte Group
Prefix '0xb1' interpreted as a raw byte string; and ii) a 2-byte Prefix '0xb1' interpreted as a raw byte string; and ii) a 2-byte
Group Epoch interpreted as an unsigned integer ranging from 0 to Group Epoch interpreted as an unsigned integer ranging from 0 to
65535. Then, after having established the Common Context 61532 times 65535. Then, after having established the Common Context 61532 times
in the group, its Gid will assume value '0xb1f05c'. in the group, its Gid will assume value '0xb1f05c'.
Using an immutable Group Prefix for a group assumes that enough time Using an immutable Group Prefix for a group assumes that enough time
elapses before all possible Group Epoch values are used, since the elapses before all possible Group Epoch values are used, since the
Group Manager does not reassign the same Gid to the same group. Group Manager never reassigns the same Gid to the same group. Thus,
Thus, the expected highest rate for addition/removal of group members the expected highest rate for addition/removal of group members and
and consequent group rekeying should be taken into account for a consequent group rekeying should be taken into account for a proper
proper dimensioning of the Group Epoch size. dimensioning of the Group Epoch size.
As discussed in Section 10.5, if endpoints are deployed in multiple As discussed in Section 10.5, if endpoints are deployed in multiple
groups managed by different non-synchronized Group Managers, it is groups managed by different non-synchronized Group Managers, it is
possible that Group Identifiers of different groups coincide at some possible that Group Identifiers of different groups coincide at some
point in time. In this case, a recipient has to handle coinciding point in time. In this case, a recipient has to handle coinciding
Group Identifiers, and has to try using different Security Contexts Group Identifiers, and has to try using different Security Contexts
to process an incoming message, until the right one is found and the to process an incoming message, until the right one is found and the
message is correctly verified. Therefore, it is favourable that message is correctly verified. Therefore, it is favorable that Group
Group Identifiers from different Group Managers have a size that Identifiers from different Group Managers have a size that result in
result in a small probability of collision. How small this a small probability of collision. How small this probability should
probability should be is up to system designers. be is up to system designers.
Appendix D. Set-up of New Endpoints Appendix D. Set-up of New Endpoints
An endpoint joins a group by explicitly interacting with the An endpoint joins a group by explicitly interacting with the
responsible Group Manager. When becoming members of a group, responsible Group Manager. When becoming members of a group,
endpoints are not required to know how many and what endpoints are in endpoints are not required to know how many and what endpoints are in
the same group. the same group.
Communications between a joining endpoint and the Group Manager rely Communications between a joining endpoint and the Group Manager rely
on the CoAP protocol and must be secured. Specific details on how to on the CoAP protocol and must be secured. Specific details on how to
skipping to change at page 61, line 29 skipping to change at page 63, line 20
Manager provides the joining endpoint with the keying material and Manager provides the joining endpoint with the keying material and
parameters to initialize the Security Context (see Section 2). The parameters to initialize the Security Context (see Section 2). The
actual provisioning of keying material and parameters to the joining actual provisioning of keying material and parameters to the joining
endpoint is out of the scope of this document. endpoint is out of the scope of this document.
It is RECOMMENDED that the join process adopts the approach described It is RECOMMENDED that the join process adopts the approach described
in [I-D.ietf-ace-key-groupcomm-oscore] and based on the ACE framework in [I-D.ietf-ace-key-groupcomm-oscore] and based on the ACE framework
for Authentication and Authorization in constrained environments for Authentication and Authorization in constrained environments
[I-D.ietf-ace-oauth-authz]. [I-D.ietf-ace-oauth-authz].
Appendix E. Examples of Synchronization Approaches Appendix E. Challenge-Response Synchronization
This section describes three possible approaches that can be
considered by server endpoints to synchronize with Sender Sequence
Numbers of client endpoints sending group requests.
The Group Manager MAY indicate which of such approaches are used in
the group, as part of the group communication policies signalled to
candidate group members upon their group joining.
If a server has recently lost the mutable Security Context, e.g. due
to a reboot, the server has also to establish an updated Security
Context before resuming to send protected messages to the group (see
Section 2.4.1). Since this results in deriving a new Sender Key for
its Sender Context, the server does not reuse the same pair (key,
nonce), even when using the Partial IV of (old re-injected) requests
to build the AEAD nonce for protecting the corresponding responses.
E.1. Best-Effort Synchronization
Upon receiving a group request from a client, a server does not take
any action to synchronize with the Sender Sequence Number of that
client. This provides no assurance at all as to message freshness,
which can be acceptable in non-critical use cases.
With the notable exception of Observe notifications and responses
following a group rekeying, it is optional for the server to use its
Sender Sequence Number as Partial IV when protecting a response.
Instead, for efficiency reasons, the server may rather use the
request's Partial IV when protecting a response to that request.
E.2. Baseline Synchronization
Upon receiving a group request from a given client for the first
time, a server initializes the last-seen Sender Sequence Number
associated to that client in its corresponding Recipient Context.
The server may also drop the group request without delivering it to
the application. This method provides a reference point to identify
if future group requests from the same client are fresher than the
last one received.
A replay time interval exists, between when a possibly replayed or
delayed message is originally transmitted by a given client and the
first authentic fresh message from that same client is received.
This can be acceptable for use cases where servers admit such a
trade-off between performance and assurance of message freshness.
With the notable exception of Observe notifications and responses
following a group rekeying, it is optional for the server to use its
Sender Sequence Number as Partial IV when protecting a response.
Instead, for efficiency reasons, the server may rather use the
request's Partial IV when protecting a response to that request.
E.3. Challenge-Response Synchronization
A server performs a challenge-response exchange with a client, by This section describes a possible approach that a server endpoint can
using the Echo Option for CoAP described in Section 2 of use to synchronize with Sender Sequence Numbers of client endpoints
[I-D.ietf-core-echo-request-tag] and according to Appendix B.1.2 of in the group. In particular, the server performs a challenge-
[RFC8613]. response exchange with a client, by using the Echo Option for CoAP
described in Section 2 of [I-D.ietf-core-echo-request-tag] and
according to Appendix B.1.2 of [RFC8613].
That is, upon receiving a group request from a particular client for That is, upon receiving a request from a particular client for the
the first time, the server processes the message as described in this first time, the server processes the message as described in this
specification, but, even if valid, does not deliver it to the specification, but, even if valid, does not deliver it to the
application. Instead, the server replies to the client with an application. Instead, the server replies to the client with an
OSCORE protected 4.01 (Unauthorized) response message, including only OSCORE protected 4.01 (Unauthorized) response message, including only
the Echo Option and no diagnostic payload. The server MUST NOT set the Echo Option and no diagnostic payload. The Echo option value
the Echo Option to a value which is both predictable and reusable. SHOULD NOT be reused; when it is reused, it MUST be highly unlikely
Since this response is protected with the Security Context used in to have been used with this client recently. Since this response is
the group, the client will consider the response valid upon protected with the Security Context used in the group, the client
successfully decrypting and verifying it. will consider the response valid upon successfully decrypting and
verifying it.
The server stores the Echo Option value included therein, together The server stores the Echo Option value included therein, together
with the pair (gid,kid), where 'gid' is the Group Identifier of the with the pair (gid,kid), where 'gid' is the Group Identifier of the
OSCORE group and 'kid' is the Sender ID of the client in the group, OSCORE group and 'kid' is the Sender ID of the client in the group,
as specified in the 'kid context' and 'kid' fields of the OSCORE as specified in the 'kid context' and 'kid' fields of the OSCORE
Option of the group request, respectively. After a group rekeying Option of the request, respectively. After a group rekeying has been
has been completed and a new Security Context has been established in completed and a new Security Context has been established in the
the group, which results also in a new Group Identifier (see group, which results also in a new Group Identifier (see
Section 3.1), the server MUST delete all the stored Echo values Section 3.1), the server MUST delete all the stored Echo values
associated to members of that group. associated to members of that group.
Upon receiving a 4.01 (Unauthorized) response that includes an Echo Upon receiving a 4.01 (Unauthorized) response that includes an Echo
Option and originates from a verified group member, a client sends a Option and originates from a verified group member, the client sends
request as a unicast message addressed to the same server, echoing a request as a unicast message addressed to the same server, echoing
the Echo Option value. The client MUST NOT send the request the Echo Option value. The client MUST NOT send the request
including the Echo Option over multicast. including the Echo Option over multicast.
In particular, the client does not necessarily resend the same group If the signature algorithm used in the group supports ECDH (e.g.
request, but can instead send a more recent one, if the application ECDSA, EdDSA), the client MUST use the pairwise mode of Group OSCORE
permits it. This makes it possible for the client to not retain to protect the request, as described in Section 9.3. Note that, as
previously sent group requests for full retransmission, unless the defined in Section 9, members of such a group and that use the Echo
application explicitly requires otherwise. In either case, the Option MUST support the pairwise mode.
client uses a fresh Sender Sequence Number value from its own Sender
Context. If the client stores group requests for possible The client does not necessarily resend the same group request, but
retransmission with the Echo Option, it should not store a given can instead send a more recent one, if the application permits it.
request for longer than a pre-configured time interval. Note that This makes it possible for the client to not retain previously sent
the unicast request echoing the Echo Option is correctly treated and group requests for full retransmission, unless the application
processed as a message, since the 'kid context' field including the explicitly requires otherwise. In either case, the client uses a
Group Identifier of the OSCORE group is still present in the OSCORE fresh Sender Sequence Number value from its own Sender Context. If
Option as part of the COSE object (see Section 4). the client stores group requests for possible retransmission with the
Echo Option, it should not store a given request for longer than a
preconfigured time interval. Note that the unicast request echoing
the Echo Option is correctly treated and processed as a message,
since the 'kid context' field including the Group Identifier of the
OSCORE group is still present in the OSCORE Option as part of the
COSE object (see Section 4).
Upon receiving the unicast request including the Echo Option, the Upon receiving the unicast request including the Echo Option, the
server performs the following verifications. server performs the following verifications.
o If the server does not store an Echo Option value for the pair o If the server does not store an Echo Option value for the pair
(gid,kid), it considers: i) the time t1 when it has established (gid,kid), it considers: i) the time t1 when it has established
the Security Context used to protect the received request; and ii) the Security Context used to protect the received request; and ii)
the time t2 when the request has been received. Since a valid the time t2 when the request has been received. Since a valid
request cannot be older than the Security Context used to protect request cannot be older than the Security Context used to protect
it, the server verifies that (t2 - t1) is less than the largest it, the server verifies that (t2 - t1) is less than the largest
skipping to change at page 64, line 5 skipping to change at page 64, line 51
o If the server stores an Echo Option value for the pair (gid,kid) o If the server stores an Echo Option value for the pair (gid,kid)
associated to that same client in the same group, the server associated to that same client in the same group, the server
verifies that the option value equals that same stored value verifies that the option value equals that same stored value
previously sent to that client. previously sent to that client.
If the verifications above fail, the server MUST NOT process the If the verifications above fail, the server MUST NOT process the
request further and MAY send a 4.01 (Unauthorized) response including request further and MAY send a 4.01 (Unauthorized) response including
an Echo Option. an Echo Option.
In case of positive verification, the request is further processed If the verifications above are successful and the Replay Window has
and verified. Finally, the server updates the Recipient Context not been set yet, the server updates its Replay Window to mark the
associated to that client, by setting the Replay Window according to current Sender Sequence Number from the latest received request as
the Sender Sequence Number from the unicast request conveying the seen (but all newer ones as new), and delivers the message as fresh
Echo Option. The server either delivers the request to the to the application. Otherwise, it discards the verification result
application if it is an actual retransmission of the original one, or and treats the message as fresh or as a replay, according to the
discards it otherwise. Mechanisms to signal whether the resent existing Replay Window.
request is a full retransmission of the original one are out of the
scope of this specification.
A server should not deliver group requests from a given client to the A server should not deliver requests from a given client to the
application until one valid request from that same client has been application until one valid request from that same client has been
verified as fresh, as conveying an echoed Echo Option verified as fresh, as conveying an echoed Echo Option
[I-D.ietf-core-echo-request-tag]. Also, a server may perform the [I-D.ietf-core-echo-request-tag]. Also, a server may perform the
challenge-response described above at any time, if synchronization challenge-response described above at any time, if synchronization
with Sender Sequence Numbers of clients is (believed to be) lost, for with Sender Sequence Numbers of clients is lost, for instance after a
instance after a device reboot. A client has to be always ready to device reboot. A client has to be always ready to perform the
perform the challenge-response based on the Echo Option in case a challenge-response based on the Echo Option in case a server starts
server starts it. it.
It is the role of the server application to define under what It is the role of the server application to define under what
circumstances Sender Sequence Numbers lose synchronization. This can circumstances Sender Sequence Numbers lose synchronization. This can
include experiencing a "large enough" gap D = (SN2 - SN1), between include experiencing a "large enough" gap D = (SN2 - SN1), between
the Sender Sequence Number SN1 of the latest accepted group request the Sender Sequence Number SN1 of the latest accepted group request
from a client and the Sender Sequence Number SN2 of a group request from a client and the Sender Sequence Number SN2 of a group request
just received from that client. However, a client may send several just received from that client. However, a client may send several
unicast requests to different group members as protected with the unicast requests to different group members as protected with the
pairwise mode (see Section 9.2), which may result in the server pairwise mode (see Section 9.3), which may result in the server
experiencing the gap D in a relatively short time. This would induce experiencing the gap D in a relatively short time. This would induce
the server to perform more challenge-response exchanges than actually the server to perform more challenge-response exchanges than actually
needed. needed.
To ameliorate this, the server may rather rely on a trade-off between To ameliorate this, the server may rather rely on a trade-off between
the Sender Sequence Number gap D and a time gap T = (t2 - t1), where the Sender Sequence Number gap D and a time gap T = (t2 - t1), where
t1 is the time when the latest group request from a client was t1 is the time when the latest group request from a client was
accepted and t2 is the time when the latest group request from that accepted and t2 is the time when the latest group request from that
client has been received, respectively. Then, the server can start a client has been received, respectively. Then, the server can start a
challenge-response when experiencing a time gap T larger than a challenge-response when experiencing a time gap T larger than a
given, pre-configured threshold. Also, the server can start a given, preconfigured threshold. Also, the server can start a
challenge-response when experiencing a Sender Sequence Number gap D challenge-response when experiencing a Sender Sequence Number gap D
greater than a different threshold, computed as a monotonically greater than a different threshold, computed as a monotonically
increasing function of the currently experienced time gap T. increasing function of the currently experienced time gap T.
The challenge-response approach described in this appendix provides The challenge-response approach described in this appendix provides
an assurance of absolute message freshness. However, it can result an assurance of absolute message freshness. However, it can result
in an impact on performance which is undesirable or unbearable, in an impact on performance which is undesirable or unbearable,
especially in large groups where many endpoints at the same time especially in large groups where many endpoints at the same time
might join as new members or lose synchronization. might join as new members or lose synchronization.
skipping to change at page 65, line 18 skipping to change at page 66, line 14
client. Therefore, silent servers should adopt alternative client. Therefore, silent servers should adopt alternative
approaches to achieve and maintain synchronization with sender approaches to achieve and maintain synchronization with sender
sequence numbers of clients. sequence numbers of clients.
Since requests including the Echo Option are sent over unicast, a Since requests including the Echo Option are sent over unicast, a
server can be a victim of the attack discussed in Section 10.7, when server can be a victim of the attack discussed in Section 10.7, when
such requests are protected with the group mode of Group OSCORE, as such requests are protected with the group mode of Group OSCORE, as
described in Section 8.1. described in Section 8.1.
Instead, protecting requests with the Echo Option by using the Instead, protecting requests with the Echo Option by using the
pairwise mode of Group OSCORE as described in Section 9.2 prevents pairwise mode of Group OSCORE as described in Section 9.3 prevents
the attack in Section 10.7. In fact, only the exact server involved the attack in Section 10.7. In fact, only the exact server involved
in the Echo exchange is able to derive the correct pairwise key used in the Echo exchange is able to derive the correct pairwise key used
by the client to protect the request including the Echo Option. by the client to protect the request including the Echo Option.
In either case, an internal on-path adversary would not be able to In either case, an internal on-path adversary would not be able to
mix up the Echo Option value of two different unicast requests, sent mix up the Echo Option value of two different unicast requests, sent
by a same client to any two different servers in the group. In fact, by a same client to any two different servers in the group. In fact,
if the group mode was used, this would require the adversary to forge if the group mode was used, this would require the adversary to forge
the client's counter signature in both such requests. As a the client's countersignature in both such requests. As a
consequence, each of the two servers remains able to selectively consequence, each of the two servers remains able to selectively
accept a request with the Echo Option only if it is waiting for that accept a request with the Echo Option only if it is waiting for that
exact integrity-protected Echo Option value, and is thus the intended exact integrity-protected Echo Option value, and is thus the intended
recipient. recipient.
Appendix F. No Verification of Signatures in Group Mode Appendix F. No Verification of Signatures in Group Mode
There are some application scenarios using group communication that There are some application scenarios using group communication that
have particularly strict requirements. One example of this is the have particularly strict requirements. One example of this is the
requirement of low message latency in non-emergency lighting requirement of low message latency in non-emergency lighting
skipping to change at page 66, line 31 skipping to change at page 67, line 28
The table below provides examples of values for Counter Signature The table below provides examples of values for Counter Signature
Parameters in the Common Context (see Section 2.1.3), for different Parameters in the Common Context (see Section 2.1.3), for different
values of Counter Signature Algorithm. values of Counter Signature Algorithm.
+-------------------+---------------------------------------------+ +-------------------+---------------------------------------------+
| Counter Signature | Example Values for Counter | | Counter Signature | Example Values for Counter |
| Algorithm | Signature Parameters | | Algorithm | Signature Parameters |
+-------------------+---------------------------------------------+ +-------------------+---------------------------------------------+
| (-8) // EdDSA | [1], [1, 6] // 1: OKP ; 1: OKP, 6: Ed25519 | | (-8) // EdDSA | [1], [1, 6] // 1: OKP ; 1: OKP, 6: Ed25519 |
| (-8) // EdDSA | [1], [1, 6] // 1: OKP ; 1: OKP, 7: Ed448 | | (-8) // EdDSA | [1], [1, 7] // 1: OKP ; 1: OKP, 7: Ed448 |
| (-7) // ES256 | [2], [2, 1] // 2: EC2 ; 2: EC2, 1: P-256 | | (-7) // ES256 | [2], [2, 1] // 2: EC2 ; 2: EC2, 1: P-256 |
| (-35) // ES384 | [2], [2, 2] // 2: EC2 ; 2: EC2, 2: P-384 | | (-35) // ES384 | [2], [2, 2] // 2: EC2 ; 2: EC2, 2: P-384 |
| (-36) // ES512 | [2], [2, 3] // 2: EC2 ; 2: EC2, 3: P-512 | | (-36) // ES512 | [2], [2, 3] // 2: EC2 ; 2: EC2, 3: P-521 |
| (-37) // PS256 | [], [3] // empty ; 3: RSA | | (-37) // PS256 | [3], [3] // 3: RSA ; 3: RSA |
| (-38) // PS384 | [], [3] // empty ; 3: RSA | | (-38) // PS384 | [3], [3] // 3: RSA ; 3: RSA |
| (-39) // PS512 | [], [3] // empty ; 3: RSA | | (-39) // PS512 | [3], [3] // 3: RSA ; 3: RSA |
+-------------------+---------------------------------------------+ +-------------------+---------------------------------------------+
Figure 4: Examples of Counter Signature Parameters Figure 4: Examples of Counter Signature Parameters
The table below provides examples of values for Secret Derivation The table below provides examples of values for Secret Derivation
Parameters in the Common Context (see Section 2.1.5), for different Parameters in the Common Context (see Section 2.1.5), for different
values of Secret Derivation Algorithm. values of Secret Derivation Algorithm.
+-----------------------+--------------------------------------------+ +-----------------------+--------------------------------------------+
| Secret Derivation | Example Values for Secret | | Secret Derivation | Example Values for Secret |
| Algorithm | Derivation Parameters | | Algorithm | Derivation Parameters |
+-----------------------+--------------------------------------------+ +-----------------------+--------------------------------------------+
| (-27) // ECDH-SS | [1], [1, 6] // 1: OKP ; 1: OKP, 4: X25519 | | (-27) // ECDH-SS | [1], [1, 4] // 1: OKP ; 1: OKP, 4: X25519 |
| // + HKDF-256 | | | // + HKDF-256 | |
| (-27) // ECDH-SS | [1], [1, 6] // 1: OKP ; 1: OKP, 5: X448 | | (-27) // ECDH-SS | [1], [1, 5] // 1: OKP ; 1: OKP, 5: X448 |
| // + HKDF-256 | | | // + HKDF-256 | |
| (-27) // ECDH-SS | [2], [2, 1] // 2: EC2 ; 2: EC2, 1: P-256 | | (-27) // ECDH-SS | [2], [2, 1] // 2: EC2 ; 2: EC2, 1: P-256 |
| // + HKDF-256 | | | // + HKDF-256 | |
| (-27) // ECDH-SS | [2], [2, 2] // 2: EC2 ; 2: EC2, 2: P-384 | | (-27) // ECDH-SS | [2], [2, 2] // 2: EC2 ; 2: EC2, 2: P-384 |
| // + HKDF-256 | | | // + HKDF-256 | |
| (-27) // ECDH-SS | [2], [2, 3] // 2: EC2 ; 2: EC2, 3: P-512 | | (-27) // ECDH-SS | [2], [2, 3] // 2: EC2 ; 2: EC2, 3: P-512 |
| // + HKDF-256 | | | // + HKDF-256 | |
+-----------------------+--------------------------------------------+ +-----------------------+--------------------------------------------+
Figure 5: Examples of Secret Derivation Parameters Figure 5: Examples of Secret Derivation Parameters
The table below provides examples of values for the Appendix H. Parameter Extensibility for Future COSE Algorithms
'par_countersign_key' element of the 'algorithms' array used in the
two external_aad structures (see Section 4.3.1 and Section 4.3.2),
for different values of Counter Signature Algorithm.
+-------------------+---------------------------------+ As defined in Section 8.1 of [I-D.ietf-cose-rfc8152bis-algs], future
| Counter Signature | Example Values for | algorithms can be registered in the "COSE Algorithms" Registry
| Algorithm | 'par_countersign_key' | [COSE.Algorithms] as specifying none or multiple COSE capabilities.
+-------------------+---------------------------------+
| (-8) // EdDSA | [1, 6] // 1: OKP , 6: Ed25519 |
| (-8) // EdDSA | [1, 6] // 1: OKP , 7: Ed448 |
| (-7) // ES256 | [2, 1] // 2: EC2 , 1: P-256 |
| (-35) // ES384 | [2, 2] // 2: EC2 , 2: P-384 |
| (-36) // ES512 | [2, 3] // 2: EC2 , 3: P-512 |
| (-37) // PS256 | [3] // 3: RSA |
| (-38) // PS384 | [3] // 3: RSA |
| (-39) // PS512 | [3] // 3: RSA |
+-------------------+---------------------------------+
Figure 6: Examples of 'par_countersign_key' To enable the seamless use of such future registered algorithms, this
section defines a general, agile format for parameters of the
Security Context (see Section 2.1.3 and Section 2.1.5) and for
related elements of the external_aad structure (see Section 4.3).
Appendix H. Document Updates 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.
H.1. Counter Signature Parameters
The definition of Counter Signature Parameters in the Common Context
(see Section 2.1.3) is generalized as follows.
Counter Signature Parameters is a CBOR array CS_PARAMS including N+1
elements, whose exact structure and value depend on the value of
Counter Signature Algorithm.
o The first element, i.e. CS_PARAMS[0], is the array of the N COSE
capabilities for Counter 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]).
o Each following element CS_PARAMS[i], i.e. with index i > 0, is the
array of COSE capabilities for the algorithm capability specified
in CS_PARAMS[0][i-1].
For example, if CS_PARAMS[0][0] specifies the key type as
capability of the algorithm, then CS_PARAMS[1] is the array of
COSE capabilities for the COSE key type associated to Counter
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]).
H.2. Secret Derivation Parameters
The definition of Secret Derivation Parameters in the Common Context
(see Section 2.1.5) is generalized as follows.
Secret Derivation Parameters is a CBOR array SD_PARAMS including N+1
elements, whose exact structure and value depend on the value of
Secret Derivation Algorithm.
o The first element, i.e. SD_PARAMS[0], is the array of the N COSE
capabilities for Secret Derivation 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]).
o Each following element SD_PARAMS[i], i.e. with index i > 0, is the
array of COSE capabilities for the algorithm capability specified
in SD_PARAMS[0][i-1].
For example, if SD_PARAMS[0][0] specifies the key type as
capability of the algorithm, then SD_PARAMS[1] is the array of
COSE capabilities for the COSE key type associated to Secret
Derivation 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]).
H.3. 'par_countersign' in the external_aad
The definition of the 'par_countersign' element in the 'algorithms'
array of the external_aad structure (see Section 4.3) is generalized
as follows.
The 'par_countersign' element takes the CBOR array CS_PARAMS
specified by Counter Signature Parameters in the Common Context (see
Section 2.1.3), considering the format generalization in Appendix H.
In particular:
o The first element 'countersign_alg_capab' is the array of COSE
capabilities for the countersignature algorithm indicated in
'alg_countersign'. This is CS_PARAMS[0], i.e. the first element
of the CBOR array CS_PARAMS specified by Counter Signature
Parameters in the Common Context.
o Each following element 'countersign_capab_i' (i = 1, ..., N) is
the array of COSE capabilities for the algorithm capability
specified in 'countersign_alg_capab'[i-1]. This algorithm
capability is the element CS_PARAMS[0][i-1] of the CBOR array
CS_PARAMS specified by Counter Signature Parameters in the Common
Context.
For example, if 'countersign_alg_capab'[i-1] specifies the key
type as capability of the algorithm, then 'countersign_capab_i' is
the array of COSE capabilities for the COSE key type associated to
Counter 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]).
external_aad = bstr .cbor aad_array
aad_array = [
oscore_version : uint,
algorithms : [alg_aead : int / tstr,
alg_countersign : int / tstr,
par_countersign : [countersign_alg_capab,
countersign_capab_1,
countersign_capab_2,
...,
countersign__capab_N]],
request_kid : bstr,
request_piv : bstr,
options : bstr,
request_kid_context : bstr,
OSCORE_option: bstr
]
countersign_alg_capab : [c_1 : any, c_2 : any, ..., c_N : any]
Figure 6: external_aad with general 'par_countersign'
Appendix I. Document Updates
RFC EDITOR: PLEASE REMOVE THIS SECTION. RFC EDITOR: PLEASE REMOVE THIS SECTION.
H.1. Version -09 to -10 I.1. Version -10 to -11
o Loss of Recipient Contexts due to their overflow.
o Added diagram on keying material components and their relation.
o Distinction between anti-replay and freshness.
o Preservation of Sender IDs over rekeying.
o Clearer cause-effect about reset of SSN.
o The GM provides public keys of group members with associated
Sender IDs.
o Removed 'par_countersign_key' from the external_aad.
o One single format for the external_aad, both for encryption and
signing.
o Presence of 'kid' in responses to requests protected with the
pairwise mode.
o Inclusion of 'kid_context' in notifications following a group
rekeying.
o Pairwise mode presented with OSCORE as baseline.
o Revised examples with signature values.
o Decoupled growth of clients' Sender Sequence Numbers and loss of
synchronization for server.
o Sender IDs not recycled in the group under the same Gid.
o Processing and description of the Group Flag bit in the OSCORE
option.
o Usage of the pairwise mode for multicast requests.
o Clarifications on synchronization using the Echo option.
o General format of context parameters and external_aad elements,
supporting future registered COSE algorithms (new Appendix).
o Fixes and editorial improvements.
I.2. Version -09 to -10
o Removed 'Counter Signature Key Parameters' from the Common o Removed 'Counter Signature Key Parameters' from the Common
Context. Context.
o New parameters in the Common Context covering the DH secret o New parameters in the Common Context covering the DH secret
derivation. derivation.
o New counter signature header parameter from draft-ietf-cose- o New counter signature header parameter from draft-ietf-cose-
countersign. countersign.
skipping to change at page 68, line 38 skipping to change at page 72, line 45
o The server uses a fresh PIV if protecting the response with a o The server uses a fresh PIV if protecting the response with a
Security Context different from the one used to protect the Security Context different from the one used to protect the
request. request.
o Clarifications on MTI algorithms and curves. o Clarifications on MTI algorithms and curves.
o Removed optimized requests. o Removed optimized requests.
o Overall clarifications and editorial revision. o Overall clarifications and editorial revision.
H.2. Version -08 to -09 I.3. Version -08 to -09
o Pairwise keys are discarded after group rekeying. o Pairwise keys are discarded after group rekeying.
o Signature mode renamed to group mode. o Signature mode renamed to group mode.
o The parameters for countersignatures use the updated COSE o The parameters for countersignatures use the updated COSE
registries. Newly defined IANA registries have been removed. registries. Newly defined IANA registries have been removed.
o Pairwise Flag bit renamed as Group Flag bit, set to 1 in group o Pairwise Flag bit renamed as Group Flag bit, set to 1 in group
mode and set to 0 in pairwise mode. mode and set to 0 in pairwise mode.
skipping to change at page 69, line 29 skipping to change at page 73, line 34
o Normative support for the signature and pairwise mode. o Normative support for the signature and pairwise mode.
o Revised methods for synchronization with clients' sender sequence o Revised methods for synchronization with clients' sender sequence
number. number.
o Appendix with example values of parameters for countersignatures. o Appendix with example values of parameters for countersignatures.
o Clarifications and editorial improvements. o Clarifications and editorial improvements.
H.3. Version -07 to -08 I.4. Version -07 to -08
o Clarified relation between pairwise mode and group communication o Clarified relation between pairwise mode and group communication
(Section 1). (Section 1).
o Improved definition of "silent server" (Section 1.1). o Improved definition of "silent server" (Section 1.1).
o Clarified when a Recipient Context is needed (Section 2). o Clarified when a Recipient Context is needed (Section 2).
o Signature checkers as entities supported by the Group Manager o Signature checkers as entities supported by the Group Manager
(Section 2.3). (Section 2.3).
skipping to change at page 70, line 44 skipping to change at page 75, line 5
(Section 10.15). (Section 10.15).
o Updates to the methods for synchronizing with clients' sequence o Updates to the methods for synchronizing with clients' sequence
number (Appendix E). number (Appendix E).
o Simplified text on discovery services supporting the pairwise mode o Simplified text on discovery services supporting the pairwise mode
(Appendix G.1). (Appendix G.1).
o Editorial improvements. o Editorial improvements.
H.4. Version -06 to -07 I.5. Version -06 to -07
o Updated abstract and introduction. o Updated abstract and introduction.
o Clarifications of what pertains a group rekeying. o Clarifications of what pertains a group rekeying.
o Derivation of pairwise keying material. o Derivation of pairwise keying material.
o Content re-organization for COSE Object and OSCORE header o Content re-organization for COSE Object and OSCORE header
compression. compression.
skipping to change at page 71, line 29 skipping to change at page 75, line 37
o Security considerations on Group OSCORE for unicast requests, also o Security considerations on Group OSCORE for unicast requests, also
as affecting the usage of the Echo option. as affecting the usage of the Echo option.
o Clarification on different types of groups considered o Clarification on different types of groups considered
(application/security/CoAP). (application/security/CoAP).
o New pairwise mode, using pairwise keying material for both o New pairwise mode, using pairwise keying material for both
requests and responses. requests and responses.
H.5. Version -05 to -06 I.6. Version -05 to -06
o Group IDs mandated to be unique under the same Group Manager. o Group IDs mandated to be unique under the same Group Manager.
o Clarifications on parameter update upon group rekeying. o Clarifications on parameter update upon group rekeying.
o Updated external_aad structures. o Updated external_aad structures.
o Dynamic derivation of Recipient Contexts made optional and o Dynamic derivation of Recipient Contexts made optional and
application specific. application specific.
skipping to change at page 72, line 9 skipping to change at page 76, line 16
rekeying. rekeying.
o Added Group Manager responsibility on validating public keys. o Added Group Manager responsibility on validating public keys.
o Updates IANA registries. o Updates IANA registries.
o Reference to RFC 8613. o Reference to RFC 8613.
o Editorial improvements. o Editorial improvements.
H.6. Version -04 to -05 I.7. Version -04 to -05
o Added references to draft-dijk-core-groupcomm-bis. o Added references to draft-dijk-core-groupcomm-bis.
o New parameter Counter Signature Key Parameters (Section 2). o New parameter Counter Signature Key Parameters (Section 2).
o Clarification about Recipient Contexts (Section 2). o Clarification about Recipient Contexts (Section 2).
o Two different external_aad for encrypting and signing o Two different external_aad for encrypting and signing
(Section 3.1). (Section 3.1).
o Updated response verification to handle Observe notifications o Updated response verification to handle Observe notifications
(Section 6.4). (Section 6.4).
o Extended Security Considerations (Section 8). o Extended Security Considerations (Section 8).
o New "Counter Signature Key Parameters" IANA Registry o New "Counter Signature Key Parameters" IANA Registry
(Section 9.2). (Section 9.2).
H.7. Version -03 to -04 I.8. Version -03 to -04
o Added the new "Counter Signature Parameters" in the Common Context o Added the new "Counter Signature Parameters" in the Common Context
(see Section 2). (see Section 2).
o Added recommendation on using "deterministic ECDSA" if ECDSA is o Added recommendation on using "deterministic ECDSA" if ECDSA is
used as counter signature algorithm (see Section 2). used as counter signature algorithm (see Section 2).
o Clarified possible asynchronous retrieval of keying material from o Clarified possible asynchronous retrieval of keying material from
the Group Manager, in order to process incoming messages (see the Group Manager, in order to process incoming messages (see
Section 2). Section 2).
skipping to change at page 73, line 12 skipping to change at page 77, line 21
o The former signature bit in the Flag Byte of the OSCORE option o The former signature bit in the Flag Byte of the OSCORE option
value is reverted to reserved (see Section 4.1). value is reverted to reserved (see Section 4.1).
o Updated examples of compressed COSE object, now with the sixth o Updated examples of compressed COSE object, now with the sixth
less significant bit in the Flag Byte of the OSCORE option value less significant bit in the Flag Byte of the OSCORE option value
set to 0 (see Section 4.3). set to 0 (see Section 4.3).
o Relaxed statements on sending error messages (see Section 6). o Relaxed statements on sending error messages (see Section 6).
o Added explicit step on computing the counter signature for o Added explicit step on computing the counter signature for
outgoing messages (see Setions 6.1 and 6.3). outgoing messages (see Sections 6.1 and 6.3).
o Handling of just created Recipient Contexts in case of o Handling of just created Recipient Contexts in case of
unsuccessful message verification (see Sections 6.2 and 6.4). unsuccessful message verification (see Sections 6.2 and 6.4).
o Handling of replied/repeated responses on the client (see o Handling of replied/repeated responses on the client (see
Section 6.4). Section 6.4).
o New IANA Registry "Counter Signature Parameters" (see o New IANA Registry "Counter Signature Parameters" (see
Section 9.1). Section 9.1).
H.8. Version -02 to -03 I.9. Version -02 to -03
o Revised structure and phrasing for improved readability and better o Revised structure and phrasing for improved readability and better
alignment with draft-ietf-core-object-security. alignment with draft-ietf-core-object-security.
o Added discussion on wrap-Around of Partial IVs (see Section 2.2). o Added discussion on wrap-Around of Partial IVs (see Section 2.2).
o Separate sections for the COSE Object (Section 3) and the OSCORE o Separate sections for the COSE Object (Section 3) and the OSCORE
Header Compression (Section 4). Header Compression (Section 4).
o The countersignature is now appended to the encrypted payload of o The countersignature is now appended to the encrypted payload of
skipping to change at page 74, line 8 skipping to change at page 78, line 19
Section 7. Section 7.
o Revised and extended security considerations in Section 8. o Revised and extended security considerations in Section 8.
o Added IANA considerations for the OSCORE Flag Bits Registry in o Added IANA considerations for the OSCORE Flag Bits Registry in
Section 9. Section 9.
o Revised Appendix D, now giving a short high-level description of a o Revised Appendix D, now giving a short high-level description of a
new endpoint set-up. new endpoint set-up.
H.9. Version -01 to -02 I.10. Version -01 to -02
o Terminology has been made more aligned with RFC7252 and draft- o Terminology has been made more aligned with RFC7252 and draft-
ietf-core-object-security: i) "client" and "server" replace the ietf-core-object-security: i) "client" and "server" replace the
old "multicaster" and "listener", respectively; ii) "silent old "multicaster" and "listener", respectively; ii) "silent
server" replaces the old "pure listener". server" replaces the old "pure listener".
o Section 2 has been updated to have the Group Identifier stored in o Section 2 has been updated to have the Group Identifier stored in
the 'ID Context' parameter defined in draft-ietf-core-object- the 'ID Context' parameter defined in draft-ietf-core-object-
security. security.
skipping to change at page 74, line 43 skipping to change at page 79, line 5
implications of possible collisions of group identifiers. implications of possible collisions of group identifiers.
o Updated Appendix D.2, adding a pointer to draft-palombini-ace-key- o Updated Appendix D.2, adding a pointer to draft-palombini-ace-key-
groupcomm about retrieval of nodes' public keys through the Group groupcomm about retrieval of nodes' public keys through the Group
Manager. Manager.
o Minor updates to Appendix E.3 about Challenge-Response o Minor updates to Appendix E.3 about Challenge-Response
synchronization of sequence numbers based on the Echo option from synchronization of sequence numbers based on the Echo option from
draft-ietf-core-echo-request-tag. draft-ietf-core-echo-request-tag.
H.10. Version -00 to -01 I.11. Version -00 to -01
o Section 1.1 has been updated with the definition of group as o Section 1.1 has been updated with the definition of group as
"security group". "security group".
o Section 2 has been updated with: o Section 2 has been updated with:
* Clarifications on etablishment/derivation of Security Contexts. * Clarifications on establishment/derivation of Security
Contexts.
* A table summarizing the the additional context elements * A table summarizing the the additional context elements
compared to OSCORE. compared to OSCORE.
o Section 3 has been updated with: o Section 3 has been updated with:
* Examples of request and response messages. * Examples of request and response messages.
* Use of CounterSignature0 rather than CounterSignature. * Use of CounterSignature0 rather than CounterSignature.
skipping to change at page 75, line 34 skipping to change at page 79, line 44
o Added Appendix C, providing an example of Group Identifier format. o Added Appendix C, providing an example of Group Identifier format.
o Appendix D has been updated to be aligned with draft-palombini- o Appendix D has been updated to be aligned with draft-palombini-
ace-key-groupcomm. ace-key-groupcomm.
Acknowledgments Acknowledgments
The authors sincerely thank Christian Amsuess, Stefan Beck, Rolf The authors sincerely thank Christian Amsuess, Stefan Beck, Rolf
Blom, Carsten Bormann, Esko Dijk, Klaus Hartke, Rikard Hoeglund, Blom, Carsten Bormann, Esko Dijk, Klaus Hartke, Rikard Hoeglund,
Richard Kelsey, John Mattsson, Dave Robin, Jim Schaad, Ludwig Seitz, Richard Kelsey, Dave Robin, Jim Schaad, Ludwig Seitz, Peter van der
Peter van der Stok and Erik Thormarker for their feedback and Stok and Erik Thormarker for their feedback and comments.
comments.
The work on this document has been partly supported by VINNOVA and The work on this document has been partly supported by VINNOVA and
the Celtic-Next project CRITISEC; the H2020 project SIFIS-Home (Grant the Celtic-Next project CRITISEC; the H2020 project SIFIS-Home (Grant
agreement 952652); the SSF project SEC4Factory under the grant agreement 952652); the SSF project SEC4Factory under the grant
RIT17-0032; and the EIT-Digital High Impact Initiative ACTIVE. RIT17-0032; and the EIT-Digital High Impact Initiative ACTIVE.
Authors' Addresses Authors' Addresses
Marco Tiloca Marco Tiloca
RISE AB RISE AB
skipping to change at page 76, line 20 skipping to change at page 80, line 31
Email: goran.selander@ericsson.com Email: goran.selander@ericsson.com
Francesca Palombini Francesca Palombini
Ericsson AB Ericsson AB
Torshamnsgatan 23 Torshamnsgatan 23
Kista SE-16440 Stockholm Kista SE-16440 Stockholm
Sweden Sweden
Email: francesca.palombini@ericsson.com Email: francesca.palombini@ericsson.com
John Preuss Mattsson
Ericsson AB
Torshamnsgatan 23
Kista SE-16440 Stockholm
Sweden
Email: john.mattsson@ericsson.com
Jiye Park Jiye Park
Universitaet Duisburg-Essen Universitaet Duisburg-Essen
Schuetzenbahn 70 Schuetzenbahn 70
Essen 45127 Essen 45127
Germany Germany
Email: ji-ye.park@uni-due.de Email: ji-ye.park@uni-due.de
 End of changes. 231 change blocks. 
749 lines changed or deleted 971 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/