draft-ietf-lake-edhoc-08.txt   draft-ietf-lake-edhoc-09.txt 
Network Working Group G. Selander Network Working Group G. Selander
Internet-Draft J. Mattsson Internet-Draft J. Preuß Mattsson
Intended status: Standards Track F. Palombini Intended status: Standards Track F. Palombini
Expires: January 13, 2022 Ericsson AB Expires: 24 February 2022 Ericsson
July 12, 2021 23 August 2021
Ephemeral Diffie-Hellman Over COSE (EDHOC) Ephemeral Diffie-Hellman Over COSE (EDHOC)
draft-ietf-lake-edhoc-08 draft-ietf-lake-edhoc-09
Abstract Abstract
This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a
very compact and lightweight authenticated Diffie-Hellman key very compact and lightweight authenticated Diffie-Hellman key
exchange with ephemeral keys. EDHOC provides mutual authentication, exchange with ephemeral keys. EDHOC provides mutual authentication,
perfect forward secrecy, and identity protection. EDHOC is intended forward secrecy, and identity protection. EDHOC is intended for
for usage in constrained scenarios and a main use case is to usage in constrained scenarios and a main use case is to establish an
establish an OSCORE security context. By reusing COSE for OSCORE security context. By reusing COSE for cryptography, CBOR for
cryptography, CBOR for encoding, and CoAP for transport, the encoding, and CoAP for transport, the additional code size can be
additional code size can be kept very low. kept very low.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 January 13, 2022. This Internet-Draft will expire on 24 February 2022.
Copyright Notice Copyright Notice
Copyright (c) 2021 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/
(https://trustee.ietf.org/license-info) in effect on the date of license-info) in effect on the date of publication of this document.
publication of this document. Please review these documents Please review these documents carefully, as they describe your rights
carefully, as they describe your rights and restrictions with respect and restrictions with respect to this document. Code Components
to this document. Code Components extracted from this document must extracted from this document must include Simplified BSD License text
include Simplified BSD License text as described in Section 4.e of as described in Section 4.e of the Trust Legal Provisions and are
the Trust Legal Provisions and are provided without warranty as provided without warranty as described in the Simplified BSD License.
described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Use of EDHOC . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Use of EDHOC . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Message Size Examples . . . . . . . . . . . . . . . . . . 5 1.3. Message Size Examples . . . . . . . . . . . . . . . . . . 5
1.4. Document Structure . . . . . . . . . . . . . . . . . . . 6 1.4. Document Structure . . . . . . . . . . . . . . . . . . . 6
1.5. Terminology and Requirements Language . . . . . . . . . . 6 1.5. Terminology and Requirements Language . . . . . . . . . . 6
2. EDHOC Outline . . . . . . . . . . . . . . . . . . . . . . . . 6 2. EDHOC Outline . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 8 3. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 9
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Method . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Method . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Connection Identifiers . . . . . . . . . . . . . . . . . 9 3.3. Connection Identifiers . . . . . . . . . . . . . . . . . 10
3.4. Transport . . . . . . . . . . . . . . . . . . . . . . . . 11 3.4. Transport . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5. Authentication Parameters . . . . . . . . . . . . . . . . 11 3.5. Authentication Parameters . . . . . . . . . . . . . . . . 12
3.6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 16 3.6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 18
3.7. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 18 3.7. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 20
3.8. External Authorization Data . . . . . . . . . . . . . . . 18 3.8. External Authorization Data (EAD) . . . . . . . . . . . . 20
3.9. Applicability Statement . . . . . . . . . . . . . . . . . 19 3.9. Applicability Statement . . . . . . . . . . . . . . . . . 21
4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . 21 4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. EDHOC-Exporter Interface . . . . . . . . . . . . . . . . 23 4.1. Extract . . . . . . . . . . . . . . . . . . . . . . . . . 23
5. Message Formatting and Processing . . . . . . . . . . . . . . 24 4.2. Expand . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.1. Message Processing Outline . . . . . . . . . . . . . . . 24 4.3. EDHOC-Exporter . . . . . . . . . . . . . . . . . . . . . 26
5.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 25 4.4. EDHOC-KeyUpdate . . . . . . . . . . . . . . . . . . . . . 27
5.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 27 5. Message Formatting and Processing . . . . . . . . . . . . . . 27
5.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 30 5.1. Message Processing Outline . . . . . . . . . . . . . . . 27
5.5. EDHOC Message 4 . . . . . . . . . . . . . . . . . . . . . 33 5.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 28
6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 35 5.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 30
6.1. Success . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 32
6.2. Unspecified . . . . . . . . . . . . . . . . . . . . . . . 36 5.5. EDHOC Message 4 . . . . . . . . . . . . . . . . . . . . . 36
6.3. Wrong Selected Cipher Suite . . . . . . . . . . . . . . . 36 6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 37
7. Security Considerations . . . . . . . . . . . . . . . . . . . 38 6.1. Success . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.1. Security Properties . . . . . . . . . . . . . . . . . . . 38 6.2. Unspecified . . . . . . . . . . . . . . . . . . . . . . . 39
7.2. Cryptographic Considerations . . . . . . . . . . . . . . 40 6.3. Wrong Selected Cipher Suite . . . . . . . . . . . . . . . 39
7.3. Cipher Suites and Cryptographic Algorithms . . . . . . . 41 7. Security Considerations . . . . . . . . . . . . . . . . . . . 41
7.4. Unprotected Data . . . . . . . . . . . . . . . . . . . . 42 7.1. Security Properties . . . . . . . . . . . . . . . . . . . 41
7.5. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 42 7.2. Cryptographic Considerations . . . . . . . . . . . . . . 44
7.6. Implementation Considerations . . . . . . . . . . . . . . 43 7.3. Cipher Suites and Cryptographic Algorithms . . . . . . . 45
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 7.4. Unprotected Data . . . . . . . . . . . . . . . . . . . . 45
8.1. EDHOC Exporter Label . . . . . . . . . . . . . . . . . . 44 7.5. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 46
8.2. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 45 7.6. Implementation Considerations . . . . . . . . . . . . . . 46
8.3. EDHOC Method Type Registry . . . . . . . . . . . . . . . 47 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48
8.4. EDHOC Error Codes Registry . . . . . . . . . . . . . . . 47 8.1. EDHOC Exporter Label . . . . . . . . . . . . . . . . . . 48
8.5. COSE Header Parameters Registry . . . . . . . . . . . . . 47 8.2. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 48
8.6. COSE Header Parameters Registry . . . . . . . . . . . . . 47 8.3. EDHOC Method Type Registry . . . . . . . . . . . . . . . 50
8.7. COSE Key Common Parameters Registry . . . . . . . . . . . 48 8.4. EDHOC Error Codes Registry . . . . . . . . . . . . . . . 50
8.8. The Well-Known URI Registry . . . . . . . . . . . . . . . 48 8.5. COSE Header Parameters Registry . . . . . . . . . . . . . 50
8.9. Media Types Registry . . . . . . . . . . . . . . . . . . 48 8.6. COSE Header Parameters Registry . . . . . . . . . . . . . 51
8.10. CoAP Content-Formats Registry . . . . . . . . . . . . . . 49 8.7. COSE Key Common Parameters Registry . . . . . . . . . . . 51
8.11. EDHOC External Authorization Data . . . . . . . . . . . . 49 8.8. The Well-Known URI Registry . . . . . . . . . . . . . . . 51
8.12. Expert Review Instructions . . . . . . . . . . . . . . . 50 8.9. Media Types Registry . . . . . . . . . . . . . . . . . . 52
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 50 8.10. CoAP Content-Formats Registry . . . . . . . . . . . . . . 53
9.1. Normative References . . . . . . . . . . . . . . . . . . 50 8.11. EDHOC External Authorization Data . . . . . . . . . . . . 53
9.2. Informative References . . . . . . . . . . . . . . . . . 53 8.12. Expert Review Instructions . . . . . . . . . . . . . . . 53
Appendix A. Use with OSCORE and Transfer over CoAP . . . . . . . 55 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 54
A.1. Selecting EDHOC Connection Identifier . . . . . . . . . . 55 9.1. Normative References . . . . . . . . . . . . . . . . . . 54
A.2. Deriving the OSCORE Security Context . . . . . . . . . . 56 9.2. Informative References . . . . . . . . . . . . . . . . . 56
A.3. Transferring EDHOC over CoAP . . . . . . . . . . . . . . 57 Appendix A. Use with OSCORE and Transfer over CoAP . . . . . . . 59
Appendix B. Compact Representation . . . . . . . . . . . . . . . 60 A.1. Selecting EDHOC Connection Identifier . . . . . . . . . . 59
Appendix C. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 60 A.2. Deriving the OSCORE Security Context . . . . . . . . . . 60
C.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 60 A.3. Transferring EDHOC over CoAP . . . . . . . . . . . . . . 61
C.2. CDDL Definitions . . . . . . . . . . . . . . . . . . . . 61 Appendix B. Compact Representation . . . . . . . . . . . . . . . 64
C.3. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Appendix C. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 65
Appendix D. Test Vectors . . . . . . . . . . . . . . . . . . . . 63 C.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 65
D.1. Test Vectors for EDHOC Authenticated with Signature Keys C.2. CDDL Definitions . . . . . . . . . . . . . . . . . . . . 66
(x5t) . . . . . . . . . . . . . . . . . . . . . . . . . . 63 C.3. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 68
D.2. Test Vectors for EDHOC Authenticated with Static Diffie- Appendix D. Test Vectors . . . . . . . . . . . . . . . . . . . . 68
Hellman Keys . . . . . . . . . . . . . . . . . . . . . . 81 Appendix E. Applicability Template . . . . . . . . . . . . . . . 68
Appendix E. Applicability Template . . . . . . . . . . . . . . . 96 Appendix F. EDHOC Message Deduplication . . . . . . . . . . . . 69
Appendix F. EDHOC Message Deduplication . . . . . . . . . . . . 96 Appendix G. Transports Not Natively Providing Correlation . . . 70
Appendix G. Transports Not Natively Providing Correlation . . . 97 Appendix H. Change Log . . . . . . . . . . . . . . . . . . . . . 70
Appendix H. Change Log . . . . . . . . . . . . . . . . . . . . . 98 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 75
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 75
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 101
1. Introduction 1. Introduction
1.1. Motivation 1.1. Motivation
Many Internet of Things (IoT) deployments require technologies which Many Internet of Things (IoT) deployments require technologies which
are highly performant in constrained environments [RFC7228]. IoT are highly performant in constrained environments [RFC7228]. IoT
devices may be constrained in various ways, including memory, devices may be constrained in various ways, including memory,
storage, processing capacity, and power. The connectivity for these storage, processing capacity, and power. The connectivity for these
settings may also exhibit constraints such as unreliable and lossy settings may also exhibit constraints such as unreliable and lossy
skipping to change at page 4, line 34 skipping to change at page 4, line 34
protocols such as COSE and OSCORE, the two endpoints may run an protocols such as COSE and OSCORE, the two endpoints may run an
authenticated Diffie-Hellman key exchange protocol, from which shared authenticated Diffie-Hellman key exchange protocol, from which shared
secret key material can be derived. Such a key exchange protocol secret key material can be derived. Such a key exchange protocol
should also be lightweight; to prevent bad performance in case of should also be lightweight; to prevent bad performance in case of
repeated use, e.g., due to device rebooting or frequent rekeying for repeated use, e.g., due to device rebooting or frequent rekeying for
security reasons; or to avoid latencies in a network formation security reasons; or to avoid latencies in a network formation
setting with many devices authenticating at the same time. setting with many devices authenticating at the same time.
This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a
lightweight authenticated key exchange protocol providing good lightweight authenticated key exchange protocol providing good
security properties including perfect forward secrecy, identity security properties including forward secrecy, identity protection,
protection, and cipher suite negotiation. Authentication can be and cipher suite negotiation. Authentication can be based on raw
based on raw public keys (RPK) or public key certificates, and public keys (RPK) or public key certificates and requires the
requires the application to provide input on how to verify that application to provide input on how to verify that endpoints are
endpoints are trusted. This specification focuses on referencing trusted. This specification focuses on referencing instead of
instead of transporting credentials to reduce message overhead. transporting credentials to reduce message overhead. EDHOC does
currently not support pre-shared key (PSK) authentication as
authentication with static Diffie-Hellman public keys by reference
produces equally small message sizes but with much simpler key
distribution.
EDHOC makes use of known protocol constructions, such as SIGMA EDHOC makes use of known protocol constructions, such as SIGMA
[SIGMA] and Extract-and-Expand [RFC5869]. COSE also provides crypto [SIGMA] and Extract-and-Expand [RFC5869]. COSE also provides crypto
agility and enables the use of future algorithms targeting IoT. agility and enables the use of future algorithms targeting IoT.
1.2. Use of EDHOC 1.2. Use of EDHOC
EDHOC is designed for highly constrained settings making it EDHOC is designed for highly constrained settings making it
especially suitable for low-power wide area networks [RFC8376] such especially suitable for low-power wide area networks [RFC8376] such
as Cellular IoT, 6TiSCH, and LoRaWAN. A main objective for EDHOC is as Cellular IoT, 6TiSCH, and LoRaWAN. A main objective for EDHOC is
to be a lightweight authenticated key exchange for OSCORE, i.e. to to be a lightweight authenticated key exchange for OSCORE, i.e., to
provide authentication and session key establishment for IoT use provide authentication and session key establishment for IoT use
cases such as those built on CoAP [RFC7252]. CoAP is a specialized cases such as those built on CoAP [RFC7252]. CoAP is a specialized
web transfer protocol for use with constrained nodes and networks, web transfer protocol for use with constrained nodes and networks,
providing a request/response interaction model between application providing a request/response interaction model between application
endpoints. As such, EDHOC is targeting a large variety of use cases endpoints. As such, EDHOC is targeting a large variety of use cases
involving 'things' with embedded microcontrollers, sensors, and involving 'things' with embedded microcontrollers, sensors, and
actuators. actuators.
A typical setting is when one of the endpoints is constrained or in a A typical setting is when one of the endpoints is constrained or in a
constrained network, and the other endpoint is a node on the Internet constrained network, and the other endpoint is a node on the Internet
(such as a mobile phone) or at the edge of the constrained network (such as a mobile phone) or at the edge of the constrained network
(such as a gateway). Thing-to-thing interactions over constrained (such as a gateway). Thing-to-thing interactions over constrained
networks are also relevant since both endpoints would then benefit networks are also relevant since both endpoints would then benefit
from the lightweight properties of the protocol. EDHOC could e.g. be from the lightweight properties of the protocol. EDHOC could e.g.,
run when a device connects for the first time, or to establish fresh be run when a device connects for the first time, or to establish
keys which are not revealed by a later compromise of the long-term fresh keys which are not revealed by a later compromise of the long-
keys. Further security properties are described in Section 7.1. term keys. Further security properties are described in Section 7.1.
EDHOC enables the reuse of the same lightweight primitives as OSCORE: EDHOC enables the reuse of the same lightweight primitives as OSCORE:
CBOR for encoding, COSE for cryptography, and CoAP for transport. By CBOR for encoding, COSE for cryptography, and CoAP for transport. By
reusing existing libraries the additional code size can be kept very reusing existing libraries, the additional code size can be kept very
low. Note that, while CBOR and COSE primitives are built into the low. Note that, while CBOR and COSE primitives are built into the
protocol messages, EDHOC is not bound to a particular transport. protocol messages, EDHOC is not bound to a particular transport.
However, it is recommended to transfer EDHOC messages in CoAP Transfer of EDHOC messages in CoAP payloads is detailed in
payloads as is detailed in Appendix A.3. Appendix A.3.
1.3. Message Size Examples 1.3. Message Size Examples
Compared to the DTLS 1.3 handshake [I-D.ietf-tls-dtls13] with ECDHE Compared to the DTLS 1.3 handshake [I-D.ietf-tls-dtls13] with ECDHE
and connection ID, the number of bytes in EDHOC + CoAP can be less and connection ID, the number of bytes in EDHOC + CoAP can be less
than 1/6 when RPK authentication is used, see than 1/6 when RPK authentication is used, see
[I-D.ietf-lwig-security-protocol-comparison]. Figure 1 shows two [I-D.ietf-lwig-security-protocol-comparison]. Figure 1 shows two
examples of message sizes for EDHOC with different kinds of examples of message sizes for EDHOC with different kinds of
authentication keys and different COSE header parameters for authentication keys and different COSE header parameters for
identification: static Diffie-Hellman keys identified by 'kid' identification: static Diffie-Hellman keys identified by 'kid'
[I-D.ietf-cose-rfc8152bis-struct], and X.509 signature certificates [I-D.ietf-cose-rfc8152bis-struct], and X.509 signature certificates
identified by a hash value using 'x5t' [I-D.ietf-cose-x509]. identified by a hash value using 'x5t' [I-D.ietf-cose-x509].
================================= =================================
kid x5t kid x5t
--------------------------------- ---------------------------------
message_1 37 37 message_1 37 37
message_2 45 116 message_2 45 116
message_3 20 91 message_3 19 90
--------------------------------- ---------------------------------
Total 103 245 Total 101 243
================================= =================================
Figure 1: Example of message sizes in bytes. Figure 1: Example of message sizes in bytes.
1.4. Document Structure 1.4. Document Structure
The remainder of the document is organized as follows: Section 2 The remainder of the document is organized as follows: Section 2
outlines EDHOC authenticated with digital signatures, Section 3 outlines EDHOC authenticated with digital signatures, Section 3
describes the protocol elements of EDHOC, including message flow, and describes the protocol elements of EDHOC, including formatting of the
formatting of the ephemeral public keys, Section 4 describes the key ephemeral public keys, Section 4 specifies the key derivation,
derivation, Section 5 specifies EDHOC with authentication based on Section 5 specifies message processing for EDHOC authenticated with
signature keys or static Diffie-Hellman keys, Section 6 specifies the signature keys or static Diffie-Hellman keys, Section 6 describes the
EDHOC error message, and Appendix A describes how EDHOC can be error messages, and Appendix A shows how to transfer EDHOC with CoAP
transferred in CoAP and used to establish an OSCORE security context. and establish an OSCORE security context.
1.5. Terminology and Requirements Language 1.5. Terminology and Requirements Language
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 CBOR [RFC8949], CBOR Sequences [RFC8742], COSE described in CBOR [RFC8949], CBOR Sequences [RFC8742], COSE
structures and process [I-D.ietf-cose-rfc8152bis-struct], COSE structures and process [I-D.ietf-cose-rfc8152bis-struct], COSE
algorithms [I-D.ietf-cose-rfc8152bis-algs], and CDDL [RFC8610]. The algorithms [I-D.ietf-cose-rfc8152bis-algs], and CDDL [RFC8610]. The
Concise Data Definition Language (CDDL) is used to express CBOR data Concise Data Definition Language (CDDL) is used to express CBOR data
structures [RFC8949]. Examples of CBOR and CDDL are provided in structures [RFC8949]. Examples of CBOR and CDDL are provided in
Appendix C.1. When referring to CBOR, this specification always Appendix C.1. When referring to CBOR, this specification always
refer to Deterministically Encoded CBOR as specified in Sections refers to Deterministically Encoded CBOR as specified in Sections
4.2.1 and 4.2.2 of [RFC8949]. 4.2.1 and 4.2.2 of [RFC8949].
The single output from authenticated encryption (including the The single output from authenticated encryption (including the
authentication tag) is called 'ciphertext', following [RFC5116]. authentication tag) is called "ciphertext", following [RFC5116].
We use the term Unprotected CWT Claims Set (UCCS) just as in
[I-D.ietf-rats-uccs] to denote a CBOR Web Token [RFC8392] without
wrapping it into a COSE object, i.e., a CBOR map consisting of
claims.
Editor's note: If [I-D.ietf-rats-uccs] completes before this draft,
make it a normative reference.
2. EDHOC Outline 2. EDHOC Outline
EDHOC specifies different authentication methods of the Diffie- EDHOC specifies different authentication methods of the Diffie-
Hellman key exchange: digital signatures and static Diffie-Hellman Hellman key exchange: digital signatures and static Diffie-Hellman
keys. This section outlines the digital signature based method. keys. This section outlines the digital signature-based method.
Further details of protocol elements and other authentication methods Further details of protocol elements and other authentication methods
are provided in the remainder of this document. are provided in the remainder of this document.
SIGMA (SIGn-and-MAc) is a family of theoretical protocols with a SIGMA (SIGn-and-MAc) is a family of theoretical protocols with a
large number of variants [SIGMA]. Like IKEv2 [RFC7296] and (D)TLS large number of variants [SIGMA]. Like IKEv2 [RFC7296] and (D)TLS
1.3 [RFC8446], EDHOC authenticated with digital signatures is built 1.3 [RFC8446], EDHOC authenticated with digital signatures is built
on a variant of the SIGMA protocol which provides identity protection on a variant of the SIGMA protocol which provides identity protection
of the initiator (SIGMA-I), and like IKEv2 [RFC7296], EDHOC of the initiator (SIGMA-I), and like IKEv2 [RFC7296], EDHOC
implements the SIGMA-I variant as MAC-then-Sign. The SIGMA-I implements the SIGMA-I variant as MAC-then-Sign. The SIGMA-I
protocol using an authenticated encryption algorithm is shown in protocol using an authenticated encryption algorithm is shown in
Figure 2. Figure 2.
Initiator Responder Initiator Responder
| G_X | | G_X |
+-------------------------------------------------------->| +-------------------------------------------------------->|
| | | |
| G_Y, AEAD( K_2; ID_CRED_R, Sig(R; CRED_R, G_X, G_Y) ) | | G_Y, AEAD( K_2; ID_CRED_R, Sig(R; CRED_R, G_X, G_Y) ) |
|<--------------------------------------------------------+ |<--------------------------------------------------------+
| | | |
| AEAD( K_3; ID_CRED_I, Sig(I; CRED_I, G_Y, G_X) ) | | AEAD( K_3; ID_CRED_I, Sig(I; CRED_I, G_Y, G_X) ) |
+-------------------------------------------------------->| +-------------------------------------------------------->|
| | | |
Figure 2: Authenticated encryption variant of the SIGMA-I protocol. Figure 2: Authenticated encryption variant of the SIGMA-I protocol.
The parties exchanging messages are called Initiator (I) and The parties exchanging messages are called Initiator (I) and
Responder (R). They exchange ephemeral public keys, compute a shared Responder (R). They exchange ephemeral public keys, compute a shared
secret, and derive symmetric application keys used to protect secret, and derive symmetric application keys used to protect
application data. application data.
o G_X and G_Y are the ECDH ephemeral public keys of I and R, * G_X and G_Y are the ECDH ephemeral public keys of I and R,
respectively. respectively.
o CRED_I and CRED_R are the credentials containing the public * CRED_I and CRED_R are the credentials containing the public
authentication keys of I and R, respectively. authentication keys of I and R, respectively.
o ID_CRED_I and ID_CRED_R are credential identifiers enabling the * ID_CRED_I and ID_CRED_R are credential identifiers enabling the
recipient party to retrieve the credential of I and R, recipient party to retrieve the credential of I and R,
respectively. respectively.
o Sig(I; . ) and Sig(R; . ) denote signatures made with the private * Sig(I; . ) and Sig(R; . ) denote signatures made with the private
authentication key of I and R, respectively. authentication key of I and R, respectively.
o AEAD(K; . ) denotes authenticated encryption with additional data * AEAD(K; . ) denotes authenticated encryption with additional data
using a key K derived from the shared secret. using a key K derived from the shared secret.
In order to create a "full-fledged" protocol some additional protocol In order to create a "full-fledged" protocol some additional protocol
elements are needed. EDHOC adds: elements are needed. EDHOC adds:
o Transcript hashes (hashes of message data) TH_2, TH_3, TH_4 used * Transcript hashes (hashes of message data) TH_2, TH_3, TH_4 used
for key derivation and as additional authenticated data. for key derivation and as additional authenticated data.
o Computationally independent keys derived from the ECDH shared * Computationally independent keys derived from the ECDH shared
secret and used for authenticated encryption of different secret and used for authenticated encryption of different
messages. messages.
o An optional fourth message giving explicit key confirmation to I * An optional fourth message giving explicit key confirmation to I
in deployments where no protected application data is sent from R in deployments where no protected application data is sent from R
to I. to I.
o A key material exporter and a key update function enabling * A key material exporter and a key update function enabling forward
frequent forward secrecy. secrecy.
o Verification of a common preferred cipher suite: * Verification of a common preferred cipher suite:
* The Initiator lists supported cipher suites in order of - The Initiator lists supported cipher suites in order of
preference preference
* The Responder verifies that the selected cipher suite is the - The Responder verifies that the selected cipher suite is the
first supported cipher suite (or else rejects and states first supported cipher suite (or else rejects and states
supported cipher suites). supported cipher suites).
o Method types and error handling. * Method types and error handling.
o Selection of connection identifiers C_I and C_R which may be used * Selection of connection identifiers C_I and C_R which may be used
to identify established keys or protocol state. to identify established keys or protocol state.
o Transport of external authorization data. * Transport of external authorization data.
EDHOC is designed to encrypt and integrity protect as much EDHOC is designed to encrypt and integrity protect as much
information as possible, and all symmetric keys are derived using as information as possible, and all symmetric keys are derived using as
much previous information as possible. EDHOC is furthermore designed much previous information as possible. EDHOC is furthermore designed
to be as compact and lightweight as possible, in terms of message to be as compact and lightweight as possible, in terms of message
sizes, processing, and the ability to reuse already existing CBOR, sizes, processing, and the ability to reuse already existing CBOR,
COSE, and CoAP libraries. COSE, and CoAP libraries.
To simplify for implementors, the use of CBOR and COSE in EDHOC is To simplify for implementors, the use of CBOR and COSE in EDHOC is
summarized in Appendix C and test vectors including CBOR diagnostic summarized in Appendix C and test vectors including CBOR diagnostic
notation are given in Appendix D. notation are given in Appendix D.
3. Protocol Elements 3. Protocol Elements
3.1. General 3.1. General
An EDHOC message flow consists of three mandatory messages The EDHOC protocol consists of three mandatory messages (message_1,
(message_1, message_2, message_3) between Initiator and Responder, an message_2, message_3) between Initiator and Responder, an optional
optional fourth message (message_4), plus an EDHOC error message. fourth message (message_4), plus an error message. EDHOC messages
EDHOC messages are CBOR Sequences [RFC8742], see Figure 3. The are CBOR Sequences [RFC8742], see Figure 3. The protocol elements in
protocol elements in the figure are introduced in the following the figure are introduced in the following sections. Message
sections. Message formatting and processing is specified in formatting and processing is specified in Section 5 and Section 6.
Section 5 and Section 6. An implementation may support only An implementation may support only Initiator or only Responder.
Initiator or only Responder.
Application data is protected using the agreed application algorithms Application data is protected using the agreed application algorithms
(AEAD, hash) in the selected cipher suite (see Section 3.6) and the (AEAD, hash) in the selected cipher suite (see Section 3.6) and the
application can make use of the established connection identifiers application can make use of the established connection identifiers
C_I and C_R (see Section 3.3). EDHOC may be used with the media type C_I and C_R (see Section 3.3). EDHOC may be used with the media type
application/edhoc defined in Section 8. application/edhoc defined in Section 8.
The Initiator can derive symmetric application keys after creating The Initiator can derive symmetric application keys after creating
EDHOC message_3, see Section 4.1. Application protected data can EDHOC message_3, see Section 4.3. Protected application data can
therefore be sent in parallel or together with EDHOC message_3. therefore be sent in parallel or together with EDHOC message_3.
Initiator Responder Initiator Responder
| METHOD, SUITES_I, G_X, C_I, EAD_1 | | METHOD, SUITES_I, G_X, C_I, EAD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
| | | |
| G_Y, C_R, Enc(ID_CRED_R, Signature_or_MAC_2, EAD_2) | | G_Y, Enc(ID_CRED_R, Signature_or_MAC_2, EAD_2), C_R |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| message_2 | | message_2 |
| | | |
| AEAD(K_3ae; ID_CRED_I, Signature_or_MAC_3, EAD_3) | | AEAD(K_3ae; ID_CRED_I, Signature_or_MAC_3, EAD_3) |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_3 | | message_3 |
Figure 3: EDHOC Message Flow Figure 3: EDHOC Message Flow
3.2. Method 3.2. Method
The data item METHOD in message_1 (see Section 5.2.1), is an integer The data item METHOD in message_1 (see Section 5.2.1), is an integer
specifying the authentication method. EDHOC supports authentication specifying the authentication method. EDHOC supports authentication
with signature or static Diffie-Hellman keys, as defined in the four with signature or static Diffie-Hellman keys, as defined in the four
authentication methods: 0, 1, 2, and 3, see Figure 4. (Method 0 authentication methods: 0, 1, 2, and 3, see Figure 4. (Method 0
corresponds to the case outlined in Section 2 where both Initiator corresponds to the case outlined in Section 2 where both Initiator
and Responder authenticate with signature keys.) and Responder authenticate with signature keys.)
skipping to change at page 9, line 46 skipping to change at page 10, line 27
+-------+-------------------+-------------------+-------------------+ +-------+-------------------+-------------------+-------------------+
| Value | Initiator | Responder | Reference | | Value | Initiator | Responder | Reference |
+-------+-------------------+-------------------+-------------------+ +-------+-------------------+-------------------+-------------------+
| 0 | Signature Key | Signature Key | [[this document]] | | 0 | Signature Key | Signature Key | [[this document]] |
| 1 | Signature Key | Static DH Key | [[this document]] | | 1 | Signature Key | Static DH Key | [[this document]] |
| 2 | Static DH Key | Signature Key | [[this document]] | | 2 | Static DH Key | Signature Key | [[this document]] |
| 3 | Static DH Key | Static DH Key | [[this document]] | | 3 | Static DH Key | Static DH Key | [[this document]] |
+-------+-------------------+-------------------+-------------------+ +-------+-------------------+-------------------+-------------------+
Figure 4: Method Types Figure 4: Method Types
3.3. Connection Identifiers 3.3. Connection Identifiers
EDHOC includes the selection of connection identifiers (C_I, C_R) EDHOC includes the selection of connection identifiers (C_I, C_R)
identifying a connection for which keys are agreed. Connection identifying a connection for which keys are agreed. Connection
identifiers may be used in the ongoing EDHOC protocol (see identifiers may be used in the ongoing EDHOC protocol (see
Section 3.3.2) or in a subsequent application protocol, e.g., OSCORE Section 3.3.2) or in a subsequent application protocol, e.g., OSCORE
(see Section 3.3.3). The connection identifiers do not have any (see Section 3.3.3). The connection identifiers do not have any
cryptographic purpose in EDHOC. cryptographic purpose in EDHOC.
Connection identifiers in EDHOC are byte strings or integers, encoded Connection identifiers in EDHOC are byte strings or integers, encoded
in CBOR. One byte connection identifiers (the integers -24 to 23 and in CBOR. One byte connection identifiers (the integers -24 to 23 and
the empty bytestring h'') are realistic in many scenarios as most the empty byte string h'') are realistic in many scenarios as most
constrained devices only have a few connections. constrained devices only have a few connections.
3.3.1. Selection of Connection Identifiers 3.3.1. Selection of Connection Identifiers
C_I and C_R are chosen by I and R, respectively. The Initiator C_I and C_R are chosen by I and R, respectively. The Initiator
selects C_I and sends it in message_1 for the Responder to use as a selects C_I and sends it in message_1 for the Responder to use as a
reference to the connection in communications with the Initiator. reference to the connection in communications with the Initiator.
The Responder selects C_R and sends in message_2 for the Initiator to The Responder selects C_R and sends in message_2 for the Initiator to
use as a reference to the connection in communications with the use as a reference to the connection in communications with the
Responder. Responder.
If connection identifiers are used by an application protocol for If connection identifiers are used by an application protocol for
which EDHOC establishes keys then the selected connection identifiers which EDHOC establishes keys then the selected connection identifiers
SHALL adhere to the requirements for that protocol, see Section 3.3.3 SHALL adhere to the requirements for that protocol, see Section 3.3.3
for an example. for an example.
3.3.2. Use of Connection Identifiers in EDHOC 3.3.2. Use of Connection Identifiers with EDHOC
Connection identifiers may be used to correlate EDHOC messages and Connection identifiers may be used to correlate EDHOC messages and
facilitate the retrieval of protocol state during EDHOC protocol facilitate the retrieval of protocol state during EDHOC protocol
execution. EDHOC transports that do not inherently provide execution. EDHOC transports that do not inherently provide
correlation across all messages of an exchange can send connection correlation across all messages of an exchange can send connection
identifiers along with EDHOC messages to gain that required identifiers along with EDHOC messages to gain that required
capability, see Section 3.4. For an example when CoAP is used as capability, see Section 3.4. For an example of using connection
transport, see Appendix A.3. identifiers when CoAP is used as transport, see Appendix A.3.
3.3.3. Use of Connection Identifiers in OSCORE 3.3.3. Use of Connection Identifiers with OSCORE
For OSCORE, the choice of a connection identifier results in the For OSCORE, the choice of a connection identifier results in the
endpoint selecting its Recipient ID, see Section 3.1 of [RFC8613]), endpoint selecting its Recipient ID, see Section 3.1 of [RFC8613],
for which certain uniqueness requirements apply, see Section 3.3 of for which certain uniqueness requirements apply, see Section 3.3 of
[RFC8613]). Therefore the Initiator and the Responder MUST NOT [RFC8613]. Therefore, the Initiator and the Responder MUST NOT
select connection identifiers such that it results in same OSCORE select connection identifiers such that it results in same OSCORE
Recipient ID. Since the Recipient ID is a byte string and a EDHOC Recipient ID. Since the Recipient ID is a byte string and a EDHOC
connection identifier is either a CBOR byte string or a CBOR integer, connection identifier is either a CBOR byte string or a CBOR integer,
care must be taken when selecting the connection identifiers and care must be taken when selecting the connection identifiers and
converting them to Recipient IDs. A mapping from EDHOC connection converting them to Recipient IDs. A mapping from EDHOC connection
identifier to OSCORE Recipient ID is specified in Appendix A.1. identifier to OSCORE Recipient ID is specified in Appendix A.1.
3.4. Transport 3.4. Transport
Cryptographically, EDHOC does not put requirements on the lower Cryptographically, EDHOC does not put requirements on the lower
layers. EDHOC is not bound to a particular transport layer, and can layers. EDHOC is not bound to a particular transport layer and can
even be used in environments without IP. The transport is even be used in environments without IP. The transport is
responsible, where necessary, to handle: responsible, where necessary, to handle:
o message loss, * message loss,
o message reordering, * message reordering,
o message duplication, * message duplication,
o fragmentation, * fragmentation,
o demultiplex EDHOC messages from other types of messages, and * demultiplex EDHOC messages from other types of messages, and
o denial of service protection. * denial-of-service protection.
Besides these common transport oriented properties, EDHOC transport Besides these common transport-oriented properties, EDHOC transport
additionally needs to support the correlation between EDHOC messages, additionally needs to support the correlation between EDHOC messages,
including an indication of a message being message_1. The including an indication of a message being message_1. The
correlation may reuse existing mechanisms in the transport protocol. correlation may reuse existing mechanisms in the transport protocol.
For example, the CoAP Token may be used to correlate EDHOC messages For example, the CoAP Token may be used to correlate EDHOC messages
in a CoAP response and an associated CoAP request. In the absense of in a CoAP response and an associated CoAP request. In the absence of
correlation between a message received and a message previously sent correlation between a message received and a message previously sent
inherent to the transport, the EDHOC connection identifiers may be inherent to the transport, the EDHOC connection identifiers may be
added, e.g. by prepending the appropriate connection identifier (when added, e.g., by prepending the appropriate connection identifier
available from the EDHOC protocol) to the EDHOC message. Transport (when available from the EDHOC protocol) to the EDHOC message.
of EDHOC in CoAP payloads is described in Appendix A.3, which also Transport of EDHOC in CoAP payloads is described in Appendix A.3,
shows how to use connection identifiers and message_1 indication with which also shows how to use connection identifiers and message_1
CoAP. indication with CoAP.
The Initiator and the Responder need to have agreed on a transport to The Initiator and the Responder need to have agreed on a transport to
be used for EDHOC, see Section 3.9. be used for EDHOC, see Section 3.9.
3.5. Authentication Parameters 3.5. Authentication Parameters
EDHOC enables public-key based authentication and supports various
settings for how the other endpoint's public key is transported,
identified, and trusted.
The authentication key (i.e., the public key) appears in different
functions:
1. as part of the authentication credential CRED_x included in the
integrity calculation
2. for verification of the Signature_or_MAC field in message_2 and
message_3 (see Section 5.3.2 and Section 5.4.2)
3. in the key derivation (in case of a static Diffie-Hellman key,
see Section 4).
The choice of authentication key has an impact on the message size
(see Section 3.5.1), and even more so the choice of authentication
credential (see Section 3.5.2) in case it is transported within the
protocol (see Section 3.5.4). EDHOC supports authentication
credentials for which COSE header parameters are defined, including:
* X.509 v3 certificate [RFC5280]
* C509 certificate [I-D.ietf-cose-cbor-encoded-cert]
* CBOR Web Token (CWT, [RFC8392])
* Unprotected CWT Claims Set (UCCS, see Section 1.5)
For CWT and UCCS, the authentication key is represented with a 'cnf'
claim [RFC8747] containing a COSE_Key
[I-D.ietf-cose-rfc8152bis-struct]. UCCS can be seen as a generic
representation of a raw public key, see Section 3.5.2 for an example.
COSE_Key is omitted from the list above because of limitations to
represent the identity (see Section 3.5.3) and because it can easily
be embedded in a UCCS.
Identical authentication credentials need to be established in both
endpoints to accomplish item 1 above (see Section 3.5.2) but for many
settings it is not necessary to transport the authentication
credential over constrained links. It may, for example, be pre-
provisioned or acquired out-of-band over less constrained links.
ID_CRED_x coincides with the authentication credential CRED_x in case
it is transported, or else contains a reference to the authentication
credential to facilitate its retrieval (see Section 3.5.4).
The choice of authentication credential also depends on the trust
model. For example, a certificate or CWT may rely on a trusted third
party, whereas a UCCS may be used when trust in the public key can be
achieved by other means, or in the case of trust-on-first-use. A
UCCS as authentication credential provides essentially the same
trustworthiness as a self-signed certificate or CWT but has smaller
size.
More details are provided in the following subsections.
3.5.1. Authentication Keys 3.5.1. Authentication Keys
The authentication key MUST be a signature key or static Diffie- The authentication key MUST be a signature key or static Diffie-
Hellman key. The Initiator and the Responder MAY use different types Hellman key. The Initiator and the Responder MAY use different types
of authentication keys, e.g. one uses a signature key and the other of authentication keys, e.g., one uses a signature key and the other
uses a static Diffie-Hellman key. When using a signature key, the uses a static Diffie-Hellman key. When using a signature key, the
authentication is provided by a signature. When using a static authentication is provided by a signature. When using a static
Diffie-Hellman key the authentication is provided by a Message Diffie-Hellman key the authentication is provided by a Message
Authentication Code (MAC) computed from an ephemeral-static ECDH Authentication Code (MAC) computed from an ephemeral-static ECDH
shared secret which enables significant reductions in message sizes. shared secret which enables significant reductions in message sizes.
When using static Diffie-Hellman keys the Initiator's and Responder's
private authentication keys are called I and R, respectively, and the
public authentication keys are called G_I and G_R, respectively.
The MAC is implemented with an AEAD algorithm. When using static The authentication key algorithm needs to be specified with enough
Diffie-Hellman keys the Initiator's and Responder's private
authentication keys are called I and R, respectively, and the public
authentication keys are called G_I and G_R, respectively. The
authentication key algorithm needs to specified with enough
parameters to make it completely determined. Note that for most parameters to make it completely determined. Note that for most
signature algorithms, the signature is determined by the signature signature algorithms, the signature is determined jointly by the
algorithm and the authentication key algorithm together. For signature algorithm and the authentication key algorithm. For
example, the curve used in the signature is typically determined by example, the curve used in the signature is typically determined by
the authentication key parameters. the authentication key parameters.
o Only the Responder SHALL have access to the Responder's private * Only the Responder SHALL have access to the Responder's private
authentication key. authentication key.
o Only the Initiator SHALL have access to the Initiator's private * Only the Initiator SHALL have access to the Initiator's private
authentication key. authentication key.
3.5.2. Identities 3.5.2. Authentication Credentials
EDHOC assumes the existence of mechanisms (certification authority,
trusted third party, manual distribution, etc.) for specifying and
distributing authentication keys and identities. Policies are set
based on the identity of the other party, and parties typically only
allow connections from a specific identity or a small restricted set
of identities. For example, in the case of a device connecting to a
network, the network may only allow connections from devices which
authenticate with certificates having a particular range of serial
numbers in the subject field and signed by a particular CA. On the
other side, the device may only be allowed to connect to a network
which authenticates with a particular public key (information of
which may be provisioned, e.g., out of band or in the external
authorization data, see Section 3.8).
The EDHOC implementation must be able to receive and enforce
information from the application about what is the intended endpoint,
and in particular whether it is a specific identity or a set of
identities.
o When a Public Key Infrastructure (PKI) is used, the trust anchor
is a Certification Authority (CA) certificate, and the identity is
the subject whose unique name (e.g. a domain name, NAI, or EUI) is
included in the endpoint's certificate. Before running EDHOC each
party needs at least one CA public key certificate, or just the
public key, and a specific identity or set of identities it is
allowed to communicate with. Only validated public-key
certificates with an allowed subject name, as specified by the
application, are to be accepted. EDHOC provides proof that the
other party possesses the private authentication key corresponding
to the public authentication key in its certificate. The
certification path provides proof that the subject of the
certificate owns the public key in the certificate.
o When public keys are used but not with a PKI (RPK, self-signed
certificate), the trust anchor is the public authentication key of
the other party. In this case, the identity is typically directly
associated to the public authentication key of the other party.
For example, the name of the subject may be a canonical
representation of the public key. Alternatively, if identities
can be expressed in the form of unique subject names assigned to
public keys, then a binding to identity can be achieved by
including both public key and associated subject name in the
protocol message computation: CRED_I or CRED_R may be a self-
signed certificate or COSE_Key containing the public
authentication key and the subject name, see Section 3.5.3.
Before running EDHOC, each endpoint needs a specific public
authentication key/unique associated subject name, or a set of
public authentication keys/unique associated subject names, which
it is allowed to communicate with. EDHOC provides proof that the
other party possesses the private authentication key corresponding
to the public authentication key.
3.5.3. Authentication Credentials
The authentication credentials, CRED_I and CRED_R, contain the public The authentication credentials, CRED_I and CRED_R, contain the public
authentication key of the Initiator and the Responder, respectively. authentication key of the Initiator and the Responder, respectively.
The Initiator and the Responder MAY use different types of The Initiator and the Responder MAY use different types of
credentials, e.g. one uses an RPK and the other uses a public key credentials, e.g., one uses an UCCS and the other uses an X.509
certificate. certificate.
The credentials CRED_I and CRED_R are signed or MAC:ed (depending on The credentials CRED_I and CRED_R are MACed by the Initiator and the
method) by the Initiator and the Responder, respectively, see Responder, respectively, see Section 5.4.2 and Section 5.3.2, and
Section 5.4 and Section 5.3. thus included in the message integrity calculation.
When the credential is a certificate, CRED_x is an end-entity
certificate (i.e. not the certificate chain) encoded as a CBOR bstr.
In X.509 certificates, signature keys typically have key usage
"digitalSignature" and Diffie-Hellman keys typically have key usage
"keyAgreement".
To prevent misbinding attacks in systems where an attacker can To prevent misbinding attacks in systems where an attacker can
register public keys without proving knowledge of the private key, register public keys without proving knowledge of the private key,
SIGMA [SIGMA] enforces a MAC to be calculated over the "Identity", SIGMA [SIGMA] enforces a MAC to be calculated over the "identity".
which in case of a X.509 certificate would be the 'subject' and EDHOC follows SIGMA by calculating a MAC over the whole credential,
'subjectAltName' fields. EDHOC follows SIGMA by calculating a MAC which in case of a X.509 or C509 certificate includes the "subject"
over the whole certificate. While the SIGMA paper only focuses on and "subjectAltName" fields, and in the case of CWT or UCCS includes
the identity, the same principle is true for any information such as the "sub" claim, see Section 3.5.3. While the SIGMA paper only
policies connected to the public key. focuses on the identity, the same principle is true for any
information such as policies connected to the public key.
When the credential is a COSE_Key, CRED_x is a CBOR map only When the credential is a certificate, CRED_x is an end-entity
containing specific fields from the COSE_Key identifying the public certificate (i.e., not the certificate chain). In X.509 and C509
key, and optionally the "Identity". CRED_x needs to be defined such certificates, signature keys typically have key usage
that it is identical when generated by Initiator or Responder. The "digitalSignature" and Diffie-Hellman public keys typically have key
parameters SHALL be encoded in bytewise lexicographic order of their usage "keyAgreement".
deterministic encodings as specified in Section 4.2.1 of [RFC8949].
If the parties have agreed on an identity besides the public key, the In case of elliptic curve based credential the claims set for CWT or
identity is included in the CBOR map with the label "subject name", UCCS includes:
otherwise the subject name is the empty text string. The public key
parameters depend on key type.
o For COSE_Keys of type OKP the CBOR map SHALL, except for subject * the 'cnf' claim with value COSE_Key, see [RFC8747], where the
name, only include the parameters 1 (kty), -1 (crv), and -2 public key parameters depend on key type:
(x-coordinate).
o For COSE_Keys of type EC2 the CBOR map SHALL, except for subject - for OKP the CBOR map typically includes the parameters 1 (kty),
name, only include the parameters 1 (kty), -1 (crv), -2 -1 (crv), and -2 (x-coordinate)
(x-coordinate), and -3 (y-coordinate).
An example of CRED_x when the RPK contains an X25519 static Diffie- - for EC2 the CBOR map typically includes the parameters 1 (kty),
Hellman key and the parties have agreed on an EUI-64 identity is -1 (crv), -2 (x-coordinate), and -3 (y-coordinate)
shown below:
CRED_x = { * the 'sub' (subject) claim containing the "identity", if the
1: 1, parties have agreed on an identity besides the public key.
-1: 4,
-2: h'b1a3e89460e88d3a8d54211dc95f0b90 CRED_x needs to be defined such that it is identical when generated
3ff205eb71912d6db8f4af980d2db83a', by Initiator or Responder, see Section 3.9. The parameters SHALL be
"subject name" : "42-50-31-FF-EF-37-32-39" encoded in bytewise lexicographic order of their deterministic
encodings as specified in Section 4.2.1 of [RFC8949].
An example of CRED_x being a UCCS in bytewise lexicographic order
containing an X25519 static Diffie-Hellman key and where the parties
have agreed on an EUI-64 identity is shown below:
{ /UCCS/
2 : "42-50-31-FF-EF-37-32-39", /sub/
8 : { /cnf/
1 : { /COSE_Key/
1 : 1, /kty/
-1 : 4, /crv/
-2 : h'b1a3e89460e88d3a8d54211dc95f0b90 /x/
3ff205eb71912d6db8f4af980d2db83a'
}
}
} }
3.5.3. Identities
EDHOC assumes the existence of mechanisms (certification authority,
trusted third party, pre-provisioning, etc.) for specifying and
distributing authentication keys and identities. Policies are
typically set based on the identity of the other party, and parties
typically only allow connections from a specific identity or a small
restricted set of identities. For example, in the case of a device
connecting to a network, the network may only allow connections from
devices which authenticate with certificates having a particular
range of serial numbers in the subject field and signed by a
particular CA. On the other side, the device may only be allowed to
connect to a network which authenticates with a particular public key
(information of which may be provisioned, e.g., out of band or in the
external authorization data, see Section 3.8).
The EDHOC implementation or the application must enforce information
about the intended endpoint, and in particular whether it is a
specific identity or a set of identities. Either EDHOC passes
information about identity to the application for a decision, or
EDHOC needs to have access to relevant information and makes the
decision on its own.
* When a Public Key Infrastructure (PKI) is used with certificates,
the trust anchor is a Certification Authority (CA) certificate,
and the identity is the subject whose unique name (e.g. a domain
name, NAI, or EUI) is included in the endpoint's certificate.
Before running EDHOC each party needs at least one CA public key
certificate, or just the public key, and a specific identity or
set of identities it is allowed to communicate with. Only
validated public-key certificates with an allowed subject name, as
specified by the application, are to be accepted. EDHOC provides
proof that the other party possesses the private authentication
key corresponding to the public authentication key in its
certificate. The certification path provides proof that the
subject of the certificate owns the public key in the certificate.
* Similarly, when a PKI is used with CWTs, each party needs to have
a trusted third party self-signed CWT, or just the UCCS/raw public
key, to verify the CWTs, and a specific identity or set of
identities in the 'sub'(subject) claim of the CWT to determine if
it is allowed to communicate with.
* When public keys are used but not with a PKI (UCCS, self-signed
certificate/CWT), the trust anchor is the authentication key of
the other party. In this case, the identity is typically directly
associated to the authentication key of the other party. For
example, the name of the subject may be a canonical representation
of the public key. Alternatively, if identities can be expressed
in the form of unique subject names assigned to public keys, then
a binding to identity can be achieved by including both public key
and associated subject name in the protocol message computation:
CRED_I or CRED_R may be a self-signed certificate/CWT or UCCS
containing the authentication key and the subject name, see
Section 3.5.2. Before running EDHOC, each endpoint needs a
specific authentication key/unique associated subject name, or a
set of public authentication keys/unique associated subject names,
which it is allowed to communicate with. EDHOC provides proof
that the other party possesses the private authentication key
corresponding to the public authentication key.
3.5.4. Identification of Credentials 3.5.4. Identification of Credentials
ID_CRED_I and ID_CRED_R are used to identify and optionally transport ID_CRED_I and ID_CRED_R are used to identify and optionally transport
the public authentication keys of the Initiator and the Responder, the public authentication keys of the Initiator and the Responder,
respectively. ID_CRED_I and ID_CRED_R do not have any cryptographic respectively. ID_CRED_I and ID_CRED_R do not have any cryptographic
purpose in EDHOC. purpose in EDHOC.
o ID_CRED_R is intended to facilitate for the Initiator to retrieve * ID_CRED_R is intended to facilitate for the Initiator to retrieve
the Responder's public authentication key. the Responder's public authentication key.
o ID_CRED_I is intended to facilitate for the Responder to retrieve * ID_CRED_I is intended to facilitate for the Responder to retrieve
the Initiator's public authentication key. the Initiator's public authentication key.
The identifiers ID_CRED_I and ID_CRED_R are COSE header_maps, i.e. The identifiers ID_CRED_I and ID_CRED_R are registered in the "COSE
CBOR maps containing Common COSE Header Parameters, see Section 3.1 Header Parameters" IANA registry. As such, ID_CRED_I and ID_CRED_R
of [I-D.ietf-cose-rfc8152bis-struct]). In the following we give some typically also provide information about the format of authentication
examples of COSE header_maps. credential, CRED_I and CRED_R, respectively. ID_CRED_I and ID_CRED_R
MAY be of different types.
Raw public keys are most optimally stored as COSE_Key objects and Public key certificates can be identified in different ways. COSE
identified with a 'kid2' parameter (see Section 8.6 and Section 8.7): header parameters for identifying X.509 or C509 certificates are
defined in [I-D.ietf-cose-x509] and
[I-D.ietf-cose-cbor-encoded-cert], for example:
o ID_CRED_x = { 4 : kid_x }, where kid_x : bstr / int, for x = I or * by a hash value with the 'x5t' or 'c5t' parameters, respectively:
R.
Note that the integers -24 to 23 and the empty bytestring h'' are - ID_CRED_x = { 34 : COSE_CertHash }, for x = I or R,
encoded as one byte.
Public key certificates can be identified in different ways. Header - ID_CRED_x = { TBD3 : COSE_CertHash }, for x = I or R;
parameters for identifying C509 certificates and X.509 certificates
are defined in [I-D.ietf-cose-cbor-encoded-cert] and
[I-D.ietf-cose-x509], for example:
o by a hash value with the 'c5t' or 'x5t' parameters; * or by a URI with the 'x5u' or 'c5u' parameters, respectively:
* ID_CRED_x = { 34 : COSE_CertHash }, for x = I or R, - ID_CRED_x = { 35 : uri }, for x = I or R,
* ID_CRED_x = { TDB3 : COSE_CertHash }, for x = I or R, - ID_CRED_x = { TBD4 : uri }, for x = I or R.
o by a URI with the 'c5u' or 'x5u' parameters; ID_CRED_x MAY contain the actual credential used for authentication,
CRED_x. For example, a certificate chain can be transported in
ID_CRED_x with COSE header parameter c5c or x5chain, defined in
[I-D.ietf-cose-cbor-encoded-cert] and [I-D.ietf-cose-x509].
* ID_CRED_x = { 35 : uri }, for x = I or R, Credentials of type CWT and UCCS are transported with the COSE header
parameter registered in Section 8.5:
* ID_CRED_x = { TBD4 : uri }, for x = I or R, * ID_CRED_x = { TBD1 : CWT }, for x = I or R,
o ID_CRED_x MAY contain the actual credential used for * ID_CRED_x = { TBD1 : UCCS }, for x = I or R.
authentication, CRED_x. For example, a certificate chain can be
transported in ID_CRED_x with COSE header parameter c5c or
x5chain, defined in [I-D.ietf-cose-cbor-encoded-cert] and
[I-D.ietf-cose-x509].
It is RECOMMENDED that ID_CRED_x uniquely identify the public It is RECOMMENDED that ID_CRED_x uniquely identify the public
authentication key as the recipient may otherwise have to try several authentication key as the recipient may otherwise have to try several
keys. ID_CRED_I and ID_CRED_R are transported in the 'ciphertext', keys. ID_CRED_I and ID_CRED_R are transported in the 'ciphertext',
see Section 5.4 and Section 5.3. see Section 5.4.2 and Section 5.3.2.
When ID_CRED_x does not contain the actual credential it may be very When ID_CRED_x does not contain the actual credential, it may be very
short. One byte credential identifiers are realistic in many short, e.g., if the endpoints have agreed to use a key identifier
scenarios as most constrained devices only have a few keys. In cases parameter 'kid':
where a node only has one key, the identifier may even be the empty
byte string. * ID_CRED_x = { 4 : key_id_x }, where key_id_x : kid, for x = I or
R.
Note that 'kid' is extended to support int values to allow more one-
byte identifiers (see Section 8.6 and Section 8.7) which may be
useful in many scenarios since constrained devices only have a few
keys.
3.6. Cipher Suites 3.6. Cipher Suites
An EDHOC cipher suite consists of an ordered set of algorithms from An EDHOC cipher suite consists of an ordered set of algorithms from
the "COSE Algorithms" and "COSE Elliptic Curves" registries. the "COSE Algorithms" and "COSE Elliptic Curves" registries as well
Algorithms need to be specified with enough parameters to make them as the EDHOC MAC length. Algorithms need to be specified with enough
completely determined. Currently, none of the algorithms require parameters to make them completely determined. Currently, none of
parameters. EDHOC is only specified for use with key exchange the algorithms require parameters. EDHOC is only specified for use
algorithms of type ECDH curves. Use with other types of key exchange with key exchange algorithms of type ECDH curves. Use with other
algorithms would likely require a specification updating EDHOC. Note types of key exchange algorithms would likely require a specification
that for most signature algorithms, the signature is determined by updating EDHOC. Note that for most signature algorithms, the
the signature algorithm and the authentication key algorithm signature is determined by the signature algorithm and the
together, see Section 3.5.1. authentication key algorithm together, see Section 3.5.1.
o EDHOC AEAD algorithm * EDHOC AEAD algorithm
o EDHOC hash algorithm * EDHOC hash algorithm
o EDHOC key exchange algorithm (ECDH curve) * EDHOC MAC length in bytes (Static DH)
o EDHOC signature algorithm * EDHOC key exchange algorithm (ECDH curve)
o Application AEAD algorithm * EDHOC signature algorithm
o Application hash algorithm * Application AEAD algorithm
* Application hash algorithm
Each cipher suite is identified with a pre-defined int label. Each cipher suite is identified with a pre-defined int label.
EDHOC can be used with all algorithms and curves defined for COSE. EDHOC can be used with all algorithms and curves defined for COSE.
Implementation can either use one of the pre-defined cipher suites Implementation can either use one of the pre-defined cipher suites
(Section 8.2) or use any combination of COSE algorithms and (Section 8.2) or use any combination of COSE algorithms and
parameters to define their own private cipher suite. Private cipher parameters to define their own private cipher suite. Private cipher
suites can be identified with any of the four values -24, -23, -22, suites can be identified with any of the four values -24, -23, -22,
-21. -21.
The following CCM cipher suites are for constrained IoT where message The following CCM cipher suites are for constrained IoT where message
overhead is a very important factor. Cipher suites 1 and 3 use a overhead is a very important factor. Cipher suites 1 and 3 use a
larger tag length (128-bit) in the EDHOC AEAD algorithm than the larger tag length (128-bit) in the EDHOC AEAD algorithm than the
Application AEAD algorithm (64-bit): Application AEAD algorithm (64-bit):
0. ( 10, -16, 4, -8, 10, -16 ) 0. ( 10, -16, 8, 4, -8, 10, -16 )
(AES-CCM-16-64-128, SHA-256, X25519, EdDSA, (AES-CCM-16-64-128, SHA-256, 8, X25519, EdDSA,
AES-CCM-16-64-128, SHA-256) AES-CCM-16-64-128, SHA-256)
1. ( 30, -16, 4, -8, 10, -16 ) 1. ( 30, -16, 16, 4, -8, 10, -16 )
(AES-CCM-16-128-128, SHA-256, X25519, EdDSA, (AES-CCM-16-128-128, SHA-256, 16, X25519, EdDSA,
AES-CCM-16-64-128, SHA-256) AES-CCM-16-64-128, SHA-256)
2. ( 10, -16, 1, -7, 10, -16 ) 2. ( 10, -16, 8, 1, -7, 10, -16 )
(AES-CCM-16-64-128, SHA-256, P-256, ES256, (AES-CCM-16-64-128, SHA-256, 8, P-256, ES256,
AES-CCM-16-64-128, SHA-256) AES-CCM-16-64-128, SHA-256)
3. ( 30, -16, 1, -7, 10, -16 ) 3. ( 30, -16, 16, 1, -7, 10, -16 )
(AES-CCM-16-128-128, SHA-256, P-256, ES256, (AES-CCM-16-128-128, SHA-256, 16, P-256, ES256,
AES-CCM-16-64-128, SHA-256) AES-CCM-16-64-128, SHA-256)
The following ChaCha20 cipher suites are for less constrained The following ChaCha20 cipher suites are for less constrained
applications and only use 128-bit tag lengths. applications and only use 128-bit tag lengths.
4. ( 24, -16, 4, -8, 24, -16 ) 4. ( 24, -16, 16, 4, -8, 24, -16 )
(ChaCha20/Poly1305, SHA-256, X25519, EdDSA, (ChaCha20/Poly1305, SHA-256, 16, X25519, EdDSA,
ChaCha20/Poly1305, SHA-256) ChaCha20/Poly1305, SHA-256)
5. ( 24, -16, 1, -7, 24, -16 ) 5. ( 24, -16, 16, 1, -7, 24, -16 )
(ChaCha20/Poly1305, SHA-256, P-256, ES256, (ChaCha20/Poly1305, SHA-256, 16, P-256, ES256,
ChaCha20/Poly1305, SHA-256) ChaCha20/Poly1305, SHA-256)
The following GCM cipher suite is for general non-constrained The following GCM cipher suite is for general non-constrained
applications. It uses high performance algorithms that are widely applications. It uses high performance algorithms that are widely
supported: supported:
6. ( 1, -16, 4, -7, 1, -16 ) 6. ( 1, -16, 16, 4, -7, 1, -16 )
(A128GCM, SHA-256, X25519, ES256, (A128GCM, SHA-256, 16, X25519, ES256,
A128GCM, SHA-256) A128GCM, SHA-256)
The following two cipher suites are for high security application The following two cipher suites are for high security application
such as government use and financial applications. The two cipher such as government use and financial applications. The two cipher
suites do not share any algorithms. The first of the two cipher suites do not share any algorithms. The first of the two cipher
suites is compatible with the CNSA suite [CNSA]. suites is compatible with the CNSA suite [CNSA].
24. ( 3, -43, 2, -35, 3, -43 ) 24. ( 3, -43, 16, 2, -35, 3, -43 )
(A256GCM, SHA-384, P-384, ES384, (A256GCM, SHA-384, 16, P-384, ES384,
A256GCM, SHA-384) A256GCM, SHA-384)
25. ( 24, -45, 5, -8, 24, -45 ) 25. ( 24, -45, 16, 5, -8, 24, -45 )
(ChaCha20/Poly1305, SHAKE256, X448, EdDSA, (ChaCha20/Poly1305, SHAKE256, 16, X448, EdDSA,
ChaCha20/Poly1305, SHAKE256) ChaCha20/Poly1305, SHAKE256)
The different methods use the same cipher suites, but some algorithms The different methods use the same cipher suites, but some algorithms
are not used in some methods. The EDHOC signature algorithm is not are not used in some methods. The EDHOC signature algorithm is not
used in methods without signature authentication. used in methods without signature authentication.
The Initiator needs to have a list of cipher suites it supports in The Initiator needs to have a list of cipher suites it supports in
order of preference. The Responder needs to have a list of cipher order of preference. The Responder needs to have a list of cipher
suites it supports. SUITES_I is a CBOR array containing cipher suites it supports. SUITES_I is a CBOR array containing cipher
suites that the Initiator supports. SUITES_I is formatted and suites that the Initiator supports. SUITES_I is formatted and
skipping to change at page 18, line 30 skipping to change at page 20, line 30
see Appendix B. In COSE compact representation is achieved by see Appendix B. In COSE compact representation is achieved by
formatting the ECDH ephemeral public keys as COSE_Keys of type EC2 or formatting the ECDH ephemeral public keys as COSE_Keys of type EC2 or
OKP according to Sections 7.1 and 7.2 of OKP according to Sections 7.1 and 7.2 of
[I-D.ietf-cose-rfc8152bis-algs], but only including the 'x' parameter [I-D.ietf-cose-rfc8152bis-algs], but only including the 'x' parameter
in G_X and G_Y. For Elliptic Curve Keys of type EC2, compact in G_X and G_Y. For Elliptic Curve Keys of type EC2, compact
representation MAY be used also in the COSE_Key. If the COSE representation MAY be used also in the COSE_Key. If the COSE
implementation requires an 'y' parameter, the value y = false SHALL implementation requires an 'y' parameter, the value y = false SHALL
be used. COSE always use compact output for Elliptic Curve Keys of be used. COSE always use compact output for Elliptic Curve Keys of
type EC2. type EC2.
3.8. External Authorization Data 3.8. External Authorization Data (EAD)
In order to reduce round trips and number of messages or to simplify In order to reduce round trips and number of messages or to simplify
processing, external security applications may be integrated into processing, external security applications may be integrated into
EDHOC by transporting authorization related data together with the EDHOC by transporting authorization related data in the messages.
messages. One example is the transport third-party identity and One example is third-party identity and authorization information
authorization information protected out of scope of EDHOC protected out of scope of EDHOC [I-D.selander-ace-ake-authz].
[I-D.selander-ace-ake-authz]. Another example is the embedding of a Another example is a certificate enrolment request or the resulting
certificate enrolment request or a newly issued certificate. issued certificate.
EDHOC allows opaque external authorization data (EAD) to be sent in EDHOC allows opaque external authorization data (EAD) to be sent in
the EDHOC messages. External authorization data sent in message_1 the EDHOC messages. External authorization data sent in message_1
(EAD_1) or message_2 (EAD_2) must be considered unprotected by EDHOC, (EAD_1) or message_2 (EAD_2) must be considered unprotected by EDHOC,
see Section 7.4. External authorization data sent in message_3 see Section 7.4. External authorization data sent in message_3
(EAD_3) or message_4 (EAD_4) is protected between Initiator and (EAD_3) or message_4 (EAD_4) is protected between Initiator and
Responder. Responder.
External authorization data is a CBOR sequence (see Appendix C.1) as External authorization data is a CBOR sequence (see Appendix C.1)
defined below: consisting of one or more (type, ext_authz_data) pairs as defined
below:
EAD = ( ead = 1* (
type : int, type : int,
1* ext_authz_data : any, ext_authz_data : any,
) )
where type is an int and is followed by one or more ext_authz_data where ext_authz_data is authorization related data defined in a
depending on type as defined in a separate specification. separate specification and its type is an int. Different types of
ext_authz_data are registered in Section 8.11.
The EAD fields of EDHOC are not intended for generic application The EAD fields of EDHOC are not intended for generic application
data. Since data carried in EAD_1 and EAD_2 fields may not be data. Since data carried in EAD_1 and EAD_2 fields may not be
protected, special considerations need to be made such that a) it protected, special considerations need to be made such that it does
does not violate security, privacy etc. requirements of the service not violate security and privacy requirements of the service which
which uses this data, and b) it does not violate the security uses this data. Moreover, the content in an EAD field may impact the
properties of EDHOC. Security applications making use of the EAD security properties provided by EDHOC. Security applications making
fields must perform the necessary security analysis. use of the EAD fields must perform the necessary security analysis.
3.9. Applicability Statement 3.9. Applicability Statement
EDHOC requires certain parameters to be agreed upon between Initiator EDHOC requires certain parameters to be agreed upon between Initiator
and Responder. Some parameters can be agreed through the protocol and Responder. Some parameters can be agreed through the protocol
execution (specifically cipher suite negotiation, see Section 3.6) execution (specifically cipher suite negotiation, see Section 3.6)
but other parameters may need to be known out-of-band (e.g., which but other parameters may need to be known out-of-band (e.g., which
authentication method is used, see Section 3.2). authentication method is used, see Section 3.2).
The purpose of the applicability statement is describe the intended The purpose of the applicability statement is to describe the
use of EDHOC to allow for the relevant processing and verifications intended use of EDHOC to allow for the relevant processing and
to be made, including things like: verifications to be made, including things like:
1. How the endpoint detects that an EDHOC message is received. This 1. How the endpoint detects that an EDHOC message is received. This
includes how EDHOC messages are transported, for example in the includes how EDHOC messages are transported, for example in the
payload of a CoAP message with a certain Uri-Path or Content- payload of a CoAP message with a certain Uri-Path or Content-
Format; see Appendix A.3. * The method of transporting EDHOC Format; see Appendix A.3.
messages may also describe data carried along with the messages
that are needed for the transport to satisfy the requirements of * The method of transporting EDHOC messages may also describe
Section 3.4, e.g., connection identifiers used with certain data carried along with the messages that are needed for the
messages, see Appendix A.3. transport to satisfy the requirements of Section 3.4, e.g.,
connection identifiers used with certain messages, see
Appendix A.3.
2. Authentication method (METHOD; see Section 3.2). 2. Authentication method (METHOD; see Section 3.2).
3. Profile for authentication credentials (CRED_I, CRED_R; see 3. Profile for authentication credentials (CRED_I, CRED_R; see
Section 3.5.3), e.g., profile for certificate or COSE_key, Section 3.5.2), e.g., profile for certificate or UCCS, including
including supported authentication key algorithms (subject public supported authentication key algorithms (subject public key
key algorithm in X.509 certificate). algorithm in X.509 or C509 certificate).
4. Type used to identify authentication credentials (ID_CRED_I, 4. Type used to identify authentication credentials (ID_CRED_I,
ID_CRED_R; see Section 3.5.4). ID_CRED_R; see Section 3.5.4).
5. Use and type of external authorization data (EAD_1, EAD_2, EAD_3, 5. Use and type of external authorization data (EAD_1, EAD_2, EAD_3,
EAD_4; see Section 3.8). EAD_4; see Section 3.8).
6. Identifier used as identity of endpoint; see Section 3.5.2. 6. Identifier used as identity of endpoint; see Section 3.5.3.
7. If message_4 shall be sent/expected, and if not, how to ensure a 7. If message_4 shall be sent/expected, and if not, how to ensure a
protected application message is sent from the Responder to the protected application message is sent from the Responder to the
Initiator; see Section 5.5. Initiator; see Section 5.5.
The applicability statement may also contain information about The applicability statement may also contain information about
supported cipher suites. The procedure for selecting and verifying supported cipher suites. The procedure for selecting and verifying
cipher suite is still performed as specified by the protocol, but it cipher suite is still performed as specified by the protocol, but it
may become simplified by this knowledge. may become simplified by this knowledge.
skipping to change at page 20, line 31 skipping to change at page 22, line 34
For some parameters, like METHOD, ID_CRED_x, type of EAD, the For some parameters, like METHOD, ID_CRED_x, type of EAD, the
receiver is able to verify compliance with applicability statement, receiver is able to verify compliance with applicability statement,
and if it needs to fail because of incompliance, to infer the reason and if it needs to fail because of incompliance, to infer the reason
why the protocol failed. why the protocol failed.
For other parameters, like CRED_x in the case that it is not For other parameters, like CRED_x in the case that it is not
transported, it may not be possible to verify that incompliance with transported, it may not be possible to verify that incompliance with
applicability statement was the reason for failure: Integrity applicability statement was the reason for failure: Integrity
verification in message_2 or message_3 may fail not only because of verification in message_2 or message_3 may fail not only because of
wrong authentication credential. For example, in case the Initiator wrong authentication credential. For example, in case the Initiator
uses public key certificate by reference (i.e. not transported within uses public key certificate by reference (i.e., not transported
the protocol) then both endpoints need to use an identical data within the protocol) then both endpoints need to use an identical
structure as CRED_I or else the integrity verification will fail. data structure as CRED_I or else the integrity verification will
fail.
Note that it is not necessary for the endpoints to specify a single Note that it is not necessary for the endpoints to specify a single
transport for the EDHOC messages. For example, a mix of CoAP and transport for the EDHOC messages. For example, a mix of CoAP and
HTTP may be used along the path, and this may still allow correlation HTTP may be used along the path, and this may still allow correlation
between messages. between messages.
The applicability statement may be dependent on the identity of the The applicability statement may be dependent on the identity of the
other endpoint, but this applies only to the later phases of the other endpoint, or other information carried in an EDHOC message, but
protocol when identities are known. (Initiator does not know it then applies only to the later phases of the protocol when such
identity of Responder before having verified message_2, and Responder information is known. (The Initiator does not know identity of
does not know identity of Initiator before having verified Responder before having verified message_2, and the Responder does
message_3.) not know identity of the Initiator before having verified message_3.)
Other conditions may be part of the applicability statement, such as Other conditions may be part of the applicability statement, such as
target application or use (if there is more than one application/use) target application or use (if there is more than one application/use)
to the extent that EDHOC can distinguish between them. In case to the extent that EDHOC can distinguish between them. In case
multiple applicability statements are used, the receiver needs to be multiple applicability statements are used, the receiver needs to be
able to determine which is applicable for a given session, for able to determine which is applicable for a given session, for
example based on URI or external authorization data type. example based on URI or external authorization data type.
4. Key Derivation 4. Key Derivation
EDHOC uses Extract-and-Expand [RFC5869] with the EDHOC hash algorithm EDHOC uses Extract-and-Expand [RFC5869] with the EDHOC hash algorithm
in the selected cipher suite to derive keys used in EDHOC and in the in the selected cipher suite to derive keys used in EDHOC and in the
application. Extract is used to derive fixed-length uniformly application. Extract is used to derive fixed-length uniformly
pseudorandom keys (PRK) from ECDH shared secrets. Expand is used to pseudorandom keys (PRK) from ECDH shared secrets. Expand is used to
derive additional output keying material (OKM) from the PRKs. The derive additional output keying material (OKM) from the PRKs.
PRKs are derived using Extract.
This section defines Extract, Expand and other key derivation
functions based on these: Expand is used to define EDHOC-KDF and in
turn EDHOC-Exporter, whereas Extract is used to define EDHOC-
KeyUpdate.
4.1. Extract
The pseudorandom keys (PRKs) are derived using Extract.
PRK = Extract( salt, IKM ) PRK = Extract( salt, IKM )
If the EDHOC hash algorithm is SHA-2, then Extract( salt, IKM ) = where the input keying material (IKM) and salt are defined for each
HKDF-Extract( salt, IKM ) [RFC5869]. If the EDHOC hash algorithm is PRK below.
SHAKE128, then Extract( salt, IKM ) = KMAC128( salt, IKM, 256, "" ).
If the EDHOC hash algorithm is SHAKE256, then Extract( salt, IKM ) =
KMAC256( salt, IKM, 512, "" ).
PRK_2e is used to derive a keystream to encrypt message_2. PRK_3e2m The definition of Extract depends on the EDHOC hash algorithm of the
is used to derive keys and IVs to produce a MAC in message_2 and to selected cipher suite:
encrypt message_3. PRK_4x3m is used to derive keys and IVs to
produce a MAC in message_3 and to derive application specific data.
PRK_2e is derived with the following input: * if the EDHOC hash algorithm is SHA-2, then Extract( salt, IKM ) =
HKDF-Extract( salt, IKM ) [RFC5869]
o The salt SHALL be the empty byte string. Note that [RFC5869] * if the EDHOC hash algorithm is SHAKE128, then Extract( salt, IKM )
= KMAC128( salt, IKM, 256, "" )
* if the EDHOC hash algorithm is SHAKE256, then Extract( salt, IKM )
= KMAC256( salt, IKM, 512, "" )
4.1.1. PRK_2e
PRK_2e is used to derive a keystream to encrypt message_2. PRK_2e is
derived with the following input:
* The salt SHALL be the empty byte string. Note that [RFC5869]
specifies that if the salt is not provided, it is set to a string specifies that if the salt is not provided, it is set to a string
of zeros (see Section 2.2 of [RFC5869]). For implementation of zeros (see Section 2.2 of [RFC5869]). For implementation
purposes, not providing the salt is the same as setting the salt purposes, not providing the salt is the same as setting the salt
to the empty byte string. to the empty byte string.
o The input keying material (IKM) SHALL be the ECDH shared secret * The IKM SHALL be the ECDH shared secret G_XY (calculated from G_X
G_XY (calculated from G_X and Y or G_Y and X) as defined in and Y or G_Y and X) as defined in Section 6.3.1 of
Section 6.3.1 of [I-D.ietf-cose-rfc8152bis-algs]. [I-D.ietf-cose-rfc8152bis-algs].
Example: Assuming the use of curve25519, the ECDH shared secret G_XY
is the output of the X25519 function [RFC7748]:
G_XY = X25519( Y, G_X ) = X25519( X, G_Y )
Example: Assuming the use of SHA-256 the extract phase of HKDF Example: Assuming the use of SHA-256 the extract phase of HKDF
produces PRK_2e as follows: produces PRK_2e as follows:
PRK_2e = HMAC-SHA-256( salt, G_XY ) PRK_2e = HMAC-SHA-256( salt, G_XY )
where salt = 0x (the empty byte string). where salt = 0x (the empty byte string).
The pseudorandom keys PRK_3e2m and PRK_4x3m are defined as follow: 4.1.2. PRK_3e2m
o If the Responder authenticates with a static Diffie-Hellman key, PRK_3e2m is used to produce a MAC in message_2 and to encrypt
then PRK_3e2m = Extract( PRK_2e, G_RX ), where G_RX is the ECDH message_3. PRK_3e2m is derived as follows:
shared secret calculated from G_R and X, or G_X and R, else
PRK_3e2m = PRK_2e.
o If the Initiator authenticates with a static Diffie-Hellman key, If the Responder authenticates with a static Diffie-Hellman key, then
then PRK_4x3m = Extract( PRK_3e2m, G_IY ), where G_IY is the ECDH PRK_3e2m = Extract( PRK_2e, G_RX ), where G_RX is the ECDH shared
shared secret calculated from G_I and Y, or G_Y and I, else secret calculated from G_R and X, or G_X and R, else PRK_3e2m =
PRK_4x3m = PRK_3e2m. PRK_2e.
Example: Assuming the use of curve25519, the ECDH shared secrets 4.1.3. PRK_4x3m
G_XY, G_RX, and G_IY are the outputs of the X25519 function
[RFC7748]:
G_XY = X25519( Y, G_X ) = X25519( X, G_Y ) PRK_4x3m is used to produce a MAC in message_3, to encrypt message_4,
and to derive application specific data. PRK_4x3m is derived as
follows:
The keys and IVs used in EDHOC are derived from PRKs using Expand If the Initiator authenticates with a static Diffie-Hellman key, then
[RFC5869] where the EDHOC-KDF is instantiated with the EDHOC AEAD PRK_4x3m = Extract( PRK_3e2m, G_IY ), where G_IY is the ECDH shared
algorithm in the selected cipher suite. secret calculated from G_I and Y, or G_Y and I, else PRK_4x3m =
PRK_3e2m.
OKM = EDHOC-KDF( PRK, transcript_hash, label, length ) 4.2. Expand
The keys, IVs and MACs used in EDHOC are derived from the PRKs using
Expand, and instantiated with the EDHOC AEAD algorithm in the
selected cipher suite.
OKM = EDHOC-KDF( PRK, transcript_hash, label, context, length )
= Expand( PRK, info, length ) = Expand( PRK, info, length )
where info is the CBOR encoding of where info is the CBOR encoding of
info = [ info = [
edhoc_aead_id : int / tstr, edhoc_aead_id : int / tstr,
transcript_hash : bstr, transcript_hash : bstr,
label : tstr, label : tstr,
length : uint * context : any,
length : uint,
] ]
where where
o edhoc_aead_id is an int or tstr containing the algorithm * edhoc_aead_id is an int or tstr containing the algorithm
identifier of the EDHOC AEAD algorithm in the selected cipher identifier of the EDHOC AEAD algorithm in the selected cipher
suite encoded as defined in [I-D.ietf-cose-rfc8152bis-algs]. Note suite encoded as defined in [I-D.ietf-cose-rfc8152bis-algs]. Note
that a single fixed edhoc_aead_id is used in all invocations of that a single fixed edhoc_aead_id is used in all invocations of
EDHOC-KDF, including the derivation of KEYSTREAM_2 and invocations EDHOC-KDF, including the derivation of KEYSTREAM_2 and invocations
of the EDHOC-Exporter. of the EDHOC-Exporter (see Section 4.3).
o transcript_hash is a bstr set to one of the transcript hashes * transcript_hash is a bstr set to one of the transcript hashes
TH_2, TH_3, or TH_4 as defined in Sections 5.3.1, 5.4.1, and 4.1. TH_2, TH_3, or TH_4 as defined in Sections 5.3.1, 5.4.1, and 4.3.
o label is a tstr set to the name of the derived key or IV, i.e. * label is a tstr set to the name of the derived key, IV or MAC;
"K_2m", "IV_2m", "KEYSTREAM_2", "K_3m", "IV_3m", "K_3ae", or i.e., "KEYSTREAM_2", "MAC_2", "K_3ae", "IV_3ae", or "MAC_3".
"IV_3ae".
o length is the length of output keying material (OKM) in bytes * context is a CBOR sequence, i.e., zero or more encoded CBOR data
items
If the EDHOC hash algorithm is SHA-2, then Expand( PRK, info, length * length is the length of output keying material (OKM) in bytes
) = HKDF-Expand( PRK, info, length ) [RFC5869]. If the EDHOC hash
algorithm is SHAKE128, then Expand( PRK, info, length ) = KMAC128(
PRK, info, L, "" ). If the EDHOC hash algorithm is SHAKE256, then
Expand( PRK, info, length ) = KMAC256( PRK, info, L, "" ).
KEYSTREAM_2 are derived using the transcript hash TH_2 and the The definition of Expand depends on the EDHOC hash algorithm of the
pseudorandom key PRK_2e. K_2m and IV_2m are derived using the selected cipher suite:
transcript hash TH_2 and the pseudorandom key PRK_3e2m. K_3ae and
IV_3ae are derived using the transcript hash TH_3 and the
pseudorandom key PRK_3e2m. K_3m and IV_3m are derived using the
transcript hash TH_3 and the pseudorandom key PRK_4x3m. IVs are only
used if the EDHOC AEAD algorithm uses IVs.
4.1. EDHOC-Exporter Interface * if the EDHOC hash algorithm is SHA-2, then Expand( PRK, info,
length ) = HKDF-Expand( PRK, info, length ) [RFC5869]
* if the EDHOC hash algorithm is SHAKE128, then Expand( PRK, info,
length ) = KMAC128( PRK, info, L, "" )
* if the EDHOC hash algorithm is SHAKE256, then Expand( PRK, info,
length ) = KMAC256( PRK, info, L, "" )
where L = 8*length, the output length in bits.
The keys, IVs and MACs are derived as follows:
* KEYSTREAM_2 is derived using the transcript hash TH_2 and the
pseudorandom key PRK_2e.
* MAC_2 is derived using the transcript hash TH_2 and the
pseudorandom key PRK_3e2m.
* K_3ae and IV_3ae are derived using the transcript hash TH_3 and
the pseudorandom key PRK_3e2m. IVs are only used if the EDHOC
AEAD algorithm uses IVs.
* MAC_3 is derived using the transcript hash TH_3 and the
pseudorandom key PRK_4x3m.
KEYSTREAM_2, K_3ae, and IV_3ae do not use a context. MAC_2 and MAC_3
use context as defined in Section 5.3.2 and Section 5.4.2,
respectively.
4.3. EDHOC-Exporter
Application keys and other application specific data can be derived Application keys and other application specific data can be derived
using the EDHOC-Exporter interface defined as: using the EDHOC-Exporter interface defined as:
EDHOC-Exporter(label, context, length) EDHOC-Exporter(label, context, length)
= EDHOC-KDF(PRK_4x3m, TH_4, label_context, length) = EDHOC-KDF(PRK_4x3m, TH_4, label, context, length)
label_context is a CBOR sequence:
label_context = (
label : tstr,
context : bstr,
)
where label is a registered tstr from the EDHOC Exporter Label where label is a registered tstr from the EDHOC Exporter Label
registry (Section 8.1), context is a bstr defined by the application, registry (Section 8.1), context is a CBOR sequence defined by the
and length is a uint defined by the application. The (label, application, and length is a uint defined by the application. The
context) pair must be unique, i.e. a (label, context) MUST NOT be (label, context) pair must be unique, i.e., a (label, context) MUST
used for two different purposes. However an application can re- NOT be used for two different purposes. However an application can
derive the same key several times as long as it is done in a secure re-derive the same key several times as long as it is done in a
way. For example, in most encryption algorithms the same (key, secure way. For example, in most encryption algorithms the same
nonce) pair must not be reused. (key, nonce) pair must not be reused. The context can for example be
the empty (zero-length) sequence or a single CBOR byte string.
The transcript hash TH_4 is a CBOR encoded bstr and the input to the The transcript hash TH_4 is a CBOR encoded bstr and the input to the
hash function is a CBOR Sequence. hash function is a CBOR Sequence.
TH_4 = H( TH_3, CIPHERTEXT_3 ) TH_4 = H( TH_3, CIPHERTEXT_3 )
where H() is the hash function in the selected cipher suite. where H() is the hash function in the selected cipher suite.
Examples of use of the EDHOC-Exporter are given in Section 5.5.2 and Examples of use of the EDHOC-Exporter are given in Section 5.5.2 and
Appendix A. Appendix A.
4.4. EDHOC-KeyUpdate
To provide forward secrecy in an even more efficient way than re- To provide forward secrecy in an even more efficient way than re-
running EDHOC, EDHOC provides the function EDHOC-KeyUpdate. When running EDHOC, EDHOC provides the function EDHOC-KeyUpdate. When
EDHOC-KeyUpdate is called the old PRK_4x3m is deleted and the new EDHOC-KeyUpdate is called the old PRK_4x3m is deleted and the new
PRK_4x3m is calculated as a "hash" of the old key using the Extract PRK_4x3m is calculated as a "hash" of the old key using the Extract
function as illustrated by the following pseudocode: function as illustrated by the following pseudocode:
EDHOC-KeyUpdate( nonce ): EDHOC-KeyUpdate( nonce ):
PRK_4x3m = Extract( nonce, PRK_4x3m ) PRK_4x3m = Extract( nonce, PRK_4x3m )
The EDHOC-KeyUpdate takes a nonce as input to guarantee that there
are no short cycles. The Initiator and the Responder need to agree
on the nonce, which can e.g., be a counter or a random number. While
the KeyUpdate method provides forward secrecy it does not give as
strong security properties as re-running EDHOC, see Section 7.
5. Message Formatting and Processing 5. Message Formatting and Processing
This section specifies formatting of the messages and processing This section specifies formatting of the messages and processing
steps. Error messages are specified in Section 6. steps. Error messages are specified in Section 6.
An EDHOC message is encoded as a sequence of CBOR data (CBOR An EDHOC message is encoded as a sequence of CBOR data (CBOR
Sequence, [RFC8742]). Additional optimizations are made to reduce Sequence, [RFC8742]). Additional optimizations are made to reduce
message overhead. message overhead.
While EDHOC uses the COSE_Key, COSE_Sign1, and COSE_Encrypt0 While EDHOC uses the COSE_Key, COSE_Sign1, and COSE_Encrypt0
structures, only a subset of the parameters is included in the EDHOC structures, only a subset of the parameters is included in the EDHOC
messages. The unprotected COSE header in COSE_Sign1, and messages, see Appendix C.3. The unprotected COSE header in
COSE_Encrypt0 (not included in the EDHOC message) MAY contain COSE_Sign1, and COSE_Encrypt0 (not included in the EDHOC message) MAY
parameters (e.g. 'alg'). contain parameters (e.g., 'alg').
5.1. Message Processing Outline 5.1. Message Processing Outline
This section outlines the message processing of EDHOC. This section outlines the message processing of EDHOC.
For each session, the endpoints are assumed to keep an associated For each session, the endpoints are assumed to keep an associated
protocol state containing identifiers, keys, etc. used for subsequent protocol state containing identifiers, keys, etc. used for subsequent
processing of protocol related data. The protocol state is assumed processing of protocol related data. The protocol state is assumed
to be associated to an applicability statement (Section 3.9) which to be associated to an applicability statement (Section 3.9) which
provides the context for how messages are transported, identified and provides the context for how messages are transported, identified,
processed. and processed.
EDHOC messages SHALL be processed according to the current protocol EDHOC messages SHALL be processed according to the current protocol
state. The following steps are expected to be performed at reception state. The following steps are expected to be performed at reception
of an EDHOC message: of an EDHOC message:
1. Detect that an EDHOC message has been received, for example by 1. Detect that an EDHOC message has been received, for example by
means of port number, URI, or media type (Section 3.9). means of port number, URI, or media type (Section 3.9).
2. Retrieve the protocol state according to the message correlation 2. Retrieve the protocol state according to the message correlation
provided by the transport, see Section 3.4. If there is no provided by the transport, see Section 3.4. If there is no
protocol state, in the case of message_1, a new protocol state is protocol state, in the case of message_1, a new protocol state is
created. The Responder endpoint needs to make use of available created. The Responder endpoint needs to make use of available
Denial-of-Service mitigation (Section 7.5). Denial-of-Service mitigation (Section 7.5).
3. If the message received is an error message then process 3. If the message received is an error message, then process
according to Section 6, else process as the expected next message according to Section 6, else process as the expected next message
according to the protocol state. according to the protocol state.
If the processing fails, then the protocol is discontinued, an error If the processing fails for some reason then, typically, an error
message sent, and the protocol state erased. Further details are message is sent, the protocol is discontinued, and the protocol state
provided in the following subsections. erased. Further details are provided in the following subsections
and in Section 6.
Different instances of the same message MUST NOT be processed in one Different instances of the same message MUST NOT be processed in one
session. Note that processing will fail if the same message appears session. Note that processing will fail if the same message appears
a second time for EDHOC processing because the state of the protocol a second time for EDHOC processing because the state of the protocol
has moved on and now expects something else. This assumes that has moved on and now expects something else. This assumes that
message duplication due to re-transmissions is handled by the message duplication due to re-transmissions is handled by the
transport protocol, see Section 3.4. The case when the transport transport protocol, see Section 3.4. The case when the transport
does not support message deduplication is addressed in Appendix F. does not support message deduplication is addressed in Appendix F.
5.2. EDHOC Message 1 5.2. EDHOC Message 1
skipping to change at page 25, line 29 skipping to change at page 28, line 43
5.2.1. Formatting of Message 1 5.2.1. Formatting of Message 1
message_1 SHALL be a CBOR Sequence (see Appendix C.1) as defined message_1 SHALL be a CBOR Sequence (see Appendix C.1) as defined
below below
message_1 = ( message_1 = (
METHOD : int, METHOD : int,
SUITES_I : [ selected : suite, supported : 2* suite ] / suite, SUITES_I : [ selected : suite, supported : 2* suite ] / suite,
G_X : bstr, G_X : bstr,
C_I : bstr / int, C_I : bstr / int,
? EAD ; EAD_1 ? EAD_1 : ead,
) )
suite = int suite = int
where: where:
o METHOD = 0, 1, 2, or 3 (see Figure 4). * METHOD = 0, 1, 2, or 3 (see Figure 4).
o SUITES_I - cipher suites which the Initiator supports in order of * SUITES_I - cipher suites which the Initiator supports in order of
(decreasing) preference. The list of supported cipher suites can (decreasing) preference. The list of supported cipher suites can
be truncated at the end, as is detailed in the processing steps be truncated at the end, as is detailed in the processing steps
below and Section 6.3. One of the supported cipher suites is below and Section 6.3. One of the supported cipher suites is
selected. The selected suite is the first suite in the SUITES_I selected. The selected suite is the first suite in the SUITES_I
CBOR array. If a single supported cipher suite is conveyed then CBOR array. If a single supported cipher suite is conveyed, then
that cipher suite is selected and SUITES_I is encoded as an int that cipher suite is selected and SUITES_I is encoded as an int
instead of an array. instead of an array.
o G_X - the ephemeral public key of the Initiator * G_X - the ephemeral public key of the Initiator
o C_I - variable length connection identifier * C_I - variable length connection identifier
o EAD_1 - unprotected external authorization data, see Section 3.8. * EAD_1 - unprotected external authorization data, see Section 3.8.
5.2.2. Initiator Processing of Message 1 5.2.2. Initiator Processing of Message 1
The Initiator SHALL compose message_1 as follows: The Initiator SHALL compose message_1 as follows:
o The supported cipher suites and the order of preference MUST NOT * The supported cipher suites and the order of preference MUST NOT
be changed based on previous error messages. However, the list be changed based on previous error messages. However, the list
SUITES_I sent to the Responder MAY be truncated such that cipher SUITES_I sent to the Responder MAY be truncated such that cipher
suites which are the least preferred are omitted. The amount of suites which are the least preferred are omitted. The amount of
truncation MAY be changed between sessions, e.g. based on previous truncation MAY be changed between sessions, e.g., based on
error messages (see next bullet), but all cipher suites which are previous error messages (see next bullet), but all cipher suites
more preferred than the least preferred cipher suite in the list which are more preferred than the least preferred cipher suite in
MUST be included in the list. the list MUST be included in the list.
o The Initiator MUST select its most preferred cipher suite, * The Initiator MUST select its most preferred cipher suite,
conditioned on what it can assume to be supported by the conditioned on what it can assume to be supported by the
Responder. If the Initiator previously received from the Responder. If the Initiator previously received from the
Responder an error message with error code 2 (see Section 6.3) Responder an error message with error code 2 (see Section 6.3)
indicating cipher suites supported by the Responder which also are indicating cipher suites supported by the Responder which also are
supported by the Initiator, then the Initiator SHOULD select the supported by the Initiator, then the Initiator SHOULD select the
most preferred cipher suite of those (note that error messages are most preferred cipher suite of those (note that error messages are
not authenticated and may be forged). not authenticated and may be forged).
o Generate an ephemeral ECDH key pair using the curve in the * Generate an ephemeral ECDH key pair using the curve in the
selected cipher suite and format it as a COSE_Key. Let G_X be the selected cipher suite and format it as a COSE_Key. Let G_X be the
'x' parameter of the COSE_Key. 'x' parameter of the COSE_Key.
o Choose a connection identifier C_I and store it for the length of * Choose a connection identifier C_I and store it for the length of
the protocol. the protocol.
o Encode message_1 as a sequence of CBOR encoded data items as * Encode message_1 as a sequence of CBOR encoded data items as
specified in Section 5.2.1 specified in Section 5.2.1
5.2.3. Responder Processing of Message 1 5.2.3. Responder Processing of Message 1
The Responder SHALL process message_1 as follows: The Responder SHALL process message_1 as follows:
o Decode message_1 (see Appendix C.1). * Decode message_1 (see Appendix C.1).
o Verify that the selected cipher suite is supported and that no * Verify that the selected cipher suite is supported and that no
prior cipher suite in SUITES_I is supported. prior cipher suite in SUITES_I is supported.
o Pass EAD_1 to the security application. * Pass EAD_1 to the security application.
If any processing step fails, the Responder SHOULD send an EDHOC If any processing step fails, the Responder SHOULD send an EDHOC
error message back, formatted as defined in Section 6, and the error message back, formatted as defined in Section 6, and the
session MUST be discontinued. Sending error messages is essential session MUST be discontinued. Sending error messages is essential
for debugging but MAY e.g. be skipped due to denial of service for debugging but MAY e.g., be skipped due to denial-of-service
reasons, see Section 7. reasons, see Section 7.
5.3. EDHOC Message 2 5.3. EDHOC Message 2
5.3.1. Formatting of Message 2 5.3.1. Formatting of Message 2
message_2 and data_2 SHALL be CBOR Sequences (see Appendix C.1) as message_2 SHALL be a CBOR Sequence (see Appendix C.1) as defined
defined below below
message_2 = ( message_2 = (
data_2, G_Y_CIPHERTEXT_2 : bstr,
CIPHERTEXT_2 : bstr,
)
data_2 = (
G_Y : bstr,
C_R : bstr / int, C_R : bstr / int,
) )
where: where:
o G_Y - the ephemeral public key of the Responder * G_Y_CIPHERTEXT_2 - the concatenation of G_Y, the ephemeral public
key of the Responder, and CIPHERTEXT_2
o C_R - variable length connection identifier * C_R - variable length connection identifier
5.3.2. Responder Processing of Message 2 5.3.2. Responder Processing of Message 2
The Responder SHALL compose message_2 as follows: The Responder SHALL compose message_2 as follows:
o Generate an ephemeral ECDH key pair using the curve in the * Generate an ephemeral ECDH key pair using the curve in the
selected cipher suite and format it as a COSE_Key. Let G_Y be the selected cipher suite and format it as a COSE_Key. Let G_Y be the
'x' parameter of the COSE_Key. 'x' parameter of the COSE_Key.
o Choose a connection identifier C_R and store it for the length of * Choose a connection identifier C_R and store it for the length of
the protocol. the protocol.
o Compute the transcript hash TH_2 = H( H(message_1), data_2 ) where * Compute the transcript hash TH_2 = H( H(message_1), G_Y, C_R )
H() is the hash function in the selected cipher suite. The where H() is the hash function in the selected cipher suite. The
transcript hash TH_2 is a CBOR encoded bstr and the input to the transcript hash TH_2 is a CBOR encoded bstr and the input to the
hash function is a CBOR Sequence. Note that H(message_1) can be hash function is a CBOR Sequence. Note that H(message_1) can be
computed and cached already in the processing of message_1. computed and cached already in the processing of message_1.
o Compute an inner COSE_Encrypt0 as defined in Section 5.3 of * Compute MAC_2 = EDHOC-KDF( PRK_3e2m, TH_2, "MAC_2", ( ID_CRED_R,
[I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm CRED_R, ? EAD_2 ), mac_length ). If the Responder authenticates
in the selected cipher suite, K_2m, IV_2m, and the following with a static Diffie-Hellman key (method equals 1 or 3), then
parameters: mac_length is the EDHOC MAC length given by the cipher suite. If
the Responder authenticates with a signature key (method equals 0
* protected = << ID_CRED_R >> or 2), then mac_length is equal to the output size of the EDHOC
+ ID_CRED_R - identifier to facilitate retrieval of CRED_R, hash algorithm given by the cipher suite.
see Section 3.5.4
* external_aad = << TH_2, CRED_R, ? EAD_2 >>
+ CRED_R - bstr containing the credential of the Responder,
see Section 3.5.4
+ EAD_2 = unprotected external authorization data, see
Section 3.8
* plaintext = h''
COSE constructs the input to the AEAD [RFC5116] as follows:
* Key K = EDHOC-KDF( PRK_3e2m, TH_2, "K_2m", length )
* Nonce N = EDHOC-KDF( PRK_3e2m, TH_2, "IV_2m", length )
* Plaintext P = 0x (the empty string)
* Associated data A = - ID_CRED_R - identifier to facilitate retrieval of CRED_R, see
Section 3.5.4
[ "Encrypt0", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >> ] - CRED_R - CBOR item containing the credential of the Responder,
see Section 3.5.4
MAC_2 is the 'ciphertext' of the inner COSE_Encrypt0. - EAD_2 = unprotected external authorization data, see
Section 3.8
o If the Responder authenticates with a static Diffie-Hellman key * If the Responder authenticates with a static Diffie-Hellman key
(method equals 1 or 3), then Signature_or_MAC_2 is MAC_2. If the (method equals 1 or 3), then Signature_or_MAC_2 is MAC_2. If the
Responder authenticates with a signature key (method equals 0 or Responder authenticates with a signature key (method equals 0 or
2), then Signature_or_MAC_2 is the 'signature' of a COSE_Sign1 2), then Signature_or_MAC_2 is the 'signature' of a COSE_Sign1
object as defined in Section 4.4 of object as defined in Section 4.4 of
[I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm in [I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm in
the selected cipher suite, the private authentication key of the the selected cipher suite, the private authentication key of the
Responder, and the following parameters: Responder, and the following parameters:
* protected = << ID_CRED_R >> - protected = << ID_CRED_R >>
* external_aad = << TH_2, CRED_R, ? EAD_2 >> - external_aad = << TH_2, CRED_R, ? EAD_2 >>
* payload = MAC_2 - payload = MAC_2
COSE constructs the input to the Signature Algorithm as: COSE constructs the input to the Signature Algorithm as:
* The key is the private authentication key of the Responder. - The key is the private authentication key of the Responder.
* The message M to be signed = - The message M to be signed =
[ "Signature1", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >>, [ "Signature1", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >>,
MAC_2 ] MAC_2 ]
o CIPHERTEXT_2 is encrypted by using the Expand function as a binary * CIPHERTEXT_2 is encrypted by using the Expand function as a binary
additive stream cipher. additive stream cipher.
* plaintext = ( ID_CRED_R / bstr / int, Signature_or_MAC_2, ? - plaintext = ( ID_CRED_R / bstr / int, Signature_or_MAC_2, ?
EAD_2 ) EAD_2 )
+ Note that if ID_CRED_R contains a single 'kid2' parameter, o Note that if ID_CRED_R contains a single 'kid' parameter,
i.e., ID_CRED_R = { 4 : kid_R }, only the byte string or i.e., ID_CRED_R = { 4 : kid_R }, only the byte string or
integer kid_R is conveyed in the plaintext encoded as a bstr integer kid_R is conveyed in the plaintext encoded as a bstr
/ int. or int.
* CIPHERTEXT_2 = plaintext XOR KEYSTREAM_2 - CIPHERTEXT_2 = plaintext XOR KEYSTREAM_2
o Encode message_2 as a sequence of CBOR encoded data items as * Encode message_2 as a sequence of CBOR encoded data items as
specified in Section 5.3.1. specified in Section 5.3.1.
5.3.3. Initiator Processing of Message 2 5.3.3. Initiator Processing of Message 2
The Initiator SHALL process message_2 as follows: The Initiator SHALL process message_2 as follows:
o Decode message_2 (see Appendix C.1). * Decode message_2 (see Appendix C.1).
o Retrieve the protocol state using the message correlation provided * Retrieve the protocol state using the message correlation provided
by the transport (e.g., the CoAP Token and the 5-tuple as a by the transport (e.g., the CoAP Token and the 5-tuple as a
client, or the prepended C_I as a server). client, or the prepended C_I as a server).
o Decrypt CIPHERTEXT_2, see Section 5.3.2. * Decrypt CIPHERTEXT_2, see Section 5.3.2.
o Pass EAD_2 to the security application. * Pass EAD_2 to the security application.
o Verify that the identity of the Responder is an allowed identity * Verify that the identity of the Responder is an allowed identity
for this connection, see Section 3.5. for this connection, see Section 3.5.
o Verify Signature_or_MAC_2 using the algorithm in the selected * Verify Signature_or_MAC_2 using the algorithm in the selected
cipher suite. The verification process depends on the method, see cipher suite. The verification process depends on the method, see
Section 5.3.2. Section 5.3.2.
If any processing step fails, the Initiator SHOULD send an EDHOC If any processing step fails, the Initiator SHOULD send an EDHOC
error message back, formatted as defined in Section 6. Sending error error message back, formatted as defined in Section 6. Sending error
messages is essential for debugging but MAY e.g.be skipped if a messages is essential for debugging but MAY e.g., be skipped if a
session cannot be found or due to denial of service reasons, see session cannot be found or due to denial-of-service reasons, see
Section 7. If an error message is sent, the session MUST be Section 7. If an error message is sent, the session MUST be
discontinued. discontinued.
5.4. EDHOC Message 3 5.4. EDHOC Message 3
5.4.1. Formatting of Message 3 5.4.1. Formatting of Message 3
message_3 SHALL be a CBOR Sequence (see Appendix C.1) as defined message_3 SHALL be a CBOR Sequence (see Appendix C.1) as defined
below below
message_3 = ( message_3 = (
CIPHERTEXT_3 : bstr, CIPHERTEXT_3 : bstr,
) )
5.4.2. Initiator Processing of Message 3 5.4.2. Initiator Processing of Message 3
skipping to change at page 30, line 20 skipping to change at page 33, line 17
below below
message_3 = ( message_3 = (
CIPHERTEXT_3 : bstr, CIPHERTEXT_3 : bstr,
) )
5.4.2. Initiator Processing of Message 3 5.4.2. Initiator Processing of Message 3
The Initiator SHALL compose message_3 as follows: The Initiator SHALL compose message_3 as follows:
o Compute the transcript hash TH_3 = H(TH_2, CIPHERTEXT_2) where H() * Compute the transcript hash TH_3 = H(TH_2, CIPHERTEXT_2) where H()
is the hash function in the selected cipher suite. The transcript is the hash function in the selected cipher suite. The transcript
hash TH_3 is a CBOR encoded bstr and the input to the hash hash TH_3 is a CBOR encoded bstr and the input to the hash
function is a CBOR Sequence. Note that H(TH_2, CIPHERTEXT_2) can function is a CBOR Sequence. Note that H(TH_2, CIPHERTEXT_2) can
be computed and cached already in the processing of message_2. be computed and cached already in the processing of message_2.
o Compute an inner COSE_Encrypt0 as defined in Section 5.3 of * Compute MAC_3 = EDHOC-KDF( PRK_4x3m, TH_3, "MAC_3", ( ID_CRED_I,
[I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm CRED_I, ? EAD_3 ), mac_length ). If the Initiator authenticates
in the selected cipher suite, K_3m, IV_3m, and the following with a static Diffie-Hellman key (method equals 2 or 3), then
parameters: mac_length is the EDHOC MAC length given by the cipher suite. If
the Initiator authenticates with a signature key (method equals 0
* protected = << ID_CRED_I >> or 1), then mac_length is equal to the output size of the EDHOC
hash algorithm given by the cipher suite.
+ ID_CRED_I - identifier to facilitate retrieval of CRED_I,
see Section 3.5.4
* external_aad = << TH_3, CRED_I, ? EAD_3 >>
+ CRED_I - bstr containing the credential of the Initiator,
see Section 3.5.4.
+ EAD_3 = protected external authorization data, see
Section 3.8
* plaintext = h''
COSE constructs the input to the AEAD [RFC5116] as follows:
* Key K = EDHOC-KDF( PRK_4x3m, TH_3, "K_3m", length )
* Nonce N = EDHOC-KDF( PRK_4x3m, TH_3, "IV_3m", length )
* Plaintext P = 0x (the empty string) - ID_CRED_I - identifier to facilitate retrieval of CRED_I, see
* Associated data A = Section 3.5.4
[ "Encrypt0", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >> ] - CRED_I - CBOR item containing the credential of the Initiator,
see Section 3.5.4
MAC_3 is the 'ciphertext' of the inner COSE_Encrypt0. - EAD_3 = protected external authorization data, see Section 3.8
o If the Initiator authenticates with a static Diffie-Hellman key * If the Initiator authenticates with a static Diffie-Hellman key
(method equals 2 or 3), then Signature_or_MAC_3 is MAC_3. If the (method equals 2 or 3), then Signature_or_MAC_3 is MAC_3. If the
Initiator authenticates with a signature key (method equals 0 or Initiator authenticates with a signature key (method equals 0 or
1), then Signature_or_MAC_3 is the 'signature' of a COSE_Sign1 1), then Signature_or_MAC_3 is the 'signature' of a COSE_Sign1
object as defined in Section 4.4 of object as defined in Section 4.4 of
[I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm in [I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm in
the selected cipher suite, the private authentication key of the the selected cipher suite, the private authentication key of the
Initiator, and the following parameters: Initiator, and the following parameters:
* protected = << ID_CRED_I >> - protected = << ID_CRED_I >>
* external_aad = << TH_3, CRED_I, ? EAD_3 >>
* payload = MAC_3 - external_aad = << TH_3, CRED_I, ? EAD_3 >>
- payload = MAC_3
COSE constructs the input to the Signature Algorithm as: COSE constructs the input to the Signature Algorithm as:
* The key is the private authentication key of the Initiator. - The key is the private authentication key of the Initiator.
* The message M to be signed = - The message M to be signed =
[ "Signature1", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >>, [ "Signature1", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >>,
MAC_3 ] MAC_3 ]
o Compute an outer COSE_Encrypt0 as defined in Section 5.3 of * Compute an outer COSE_Encrypt0 as defined in Section 5.3 of
[I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm
in the selected cipher suite, K_3ae, IV_3ae, and the following in the selected cipher suite, K_3ae, IV_3ae, and the following
parameters. The protected header SHALL be empty. parameters. The protected header SHALL be empty.
* external_aad = TH_3 - external_aad = TH_3
* plaintext = ( ID_CRED_I / bstr / int, Signature_or_MAC_3, ? - plaintext = ( ID_CRED_I / bstr / int, Signature_or_MAC_3, ?
EAD_3 ) EAD_3 )
+ Note that if ID_CRED_I contains a single 'kid2' parameter, o Note that if ID_CRED_I contains a single 'kid' parameter,
i.e., ID_CRED_I = { 4 : kid_I }, only the byte string or i.e., ID_CRED_I = { 4 : kid_I }, only the byte string or
integer kid_I is conveyed in the plaintext encoded as a bstr integer kid_I is conveyed in the plaintext encoded as a bstr
or int. or int.
COSE constructs the input to the AEAD [RFC5116] as follows: COSE constructs the input to the AEAD [RFC5116] as follows:
* Key K = EDHOC-KDF( PRK_3e2m, TH_3, "K_3ae", length ) - Key K = EDHOC-KDF( PRK_3e2m, TH_3, "K_3ae", length )
* Nonce N = EDHOC-KDF( PRK_3e2m, TH_3, "IV_3ae", length )
* Plaintext P = ( ID_CRED_I / bstr / int, Signature_or_MAC_3, ? - Nonce N = EDHOC-KDF( PRK_3e2m, TH_3, "IV_3ae", length )
- Plaintext P = ( ID_CRED_I / bstr / int, Signature_or_MAC_3, ?
EAD_3 ) EAD_3 )
* Associated data A = [ "Encrypt0", h'', TH_3 ] - Associated data A = [ "Encrypt0", h'', TH_3 ]
CIPHERTEXT_3 is the 'ciphertext' of the outer COSE_Encrypt0. CIPHERTEXT_3 is the 'ciphertext' of the outer COSE_Encrypt0.
o Encode message_3 as a sequence of CBOR encoded data items as * Encode message_3 as a sequence of CBOR encoded data items as
specified in Section 5.4.1. specified in Section 5.4.1.
Pass the connection identifiers (C_I, C_R) and the application Pass the connection identifiers (C_I, C_R) and the application
algorithms in the selected cipher suite to the application. The algorithms in the selected cipher suite to the application. The
application can now derive application keys using the EDHOC-Exporter application can now derive application keys using the EDHOC-Exporter
interface. interface, see Section 4.3.
After sending message_3, the Initiator is assured that no other party After sending message_3, the Initiator is assured that no other party
than the Responder can compute the key PRK_4x3m (implicit key than the Responder can compute the key PRK_4x3m (implicit key
authentication). The Initiator can securely derive application keys authentication). The Initiator can securely derive application keys
and send protected application data. However, the Initiator does not and send protected application data. However, the Initiator does not
know that the Responder has actually computed the key PRK_4x3m and know that the Responder has actually computed the key PRK_4x3m and
therefore the Initiator SHOULD NOT permanently store the keying therefore the Initiator SHOULD NOT permanently store the keying
material PRK_4x3m and TH_4, or derived application keys, until the material PRK_4x3m and TH_4, or derived application keys, until the
Initiator is assured that the Responder has actually computed the key Initiator is assured that the Responder has actually computed the key
PRK_4x3m (explicit key confirmation). This is similar to waiting for PRK_4x3m (explicit key confirmation). This is similar to waiting for
acknowledgement (ACK) in a transport protocol. Explicit key acknowledgement (ACK) in a transport protocol. Explicit key
confirmation is e.g. assured when the Initiator has verified an confirmation is e.g., assured when the Initiator has verified an
OSCORE message or message_4 from the Responder. OSCORE message or message_4 from the Responder.
5.4.3. Responder Processing of Message 3 5.4.3. Responder Processing of Message 3
The Responder SHALL process message_3 as follows: The Responder SHALL process message_3 as follows:
o Decode message_3 (see Appendix C.1). * Decode message_3 (see Appendix C.1).
o Retrieve the protocol state using the message correlation provided * Retrieve the protocol state using the message correlation provided
by the transport (e.g., the CoAP Token and the 5-tuple as a by the transport (e.g., the CoAP Token and the 5-tuple as a
client, or the prepended C_R as a server). client, or the prepended C_R as a server).
o Decrypt and verify the outer COSE_Encrypt0 as defined in * Decrypt and verify the outer COSE_Encrypt0 as defined in
Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC
AEAD algorithm in the selected cipher suite, K_3ae, and IV_3ae. AEAD algorithm in the selected cipher suite, K_3ae, and IV_3ae.
o Pass EAD_3 to the security application. * Pass EAD_3 to the security application.
o Verify that the identity of the Initiator is an allowed identity * Verify that the identity of the Initiator is an allowed identity
for this connection, see Section 3.5. for this connection, see Section 3.5.
o Verify Signature_or_MAC_3 using the algorithm in the selected * Verify Signature_or_MAC_3 using the algorithm in the selected
cipher suite. The verification process depends on the method, see cipher suite. The verification process depends on the method, see
Section 5.4.2. Section 5.4.2.
o Pass the connection identifiers (C_I, C_R), and the application * Pass the connection identifiers (C_I, C_R), and the application
algorithms in the selected cipher suite to the security algorithms in the selected cipher suite to the security
application. The application can now derive application keys application. The application can now derive application keys
using the EDHOC-Exporter interface. using the EDHOC-Exporter interface.
If any processing step fails, the Responder SHOULD send an EDHOC If any processing step fails, the Responder SHOULD send an EDHOC
error message back, formatted as defined in Section 6. Sending error error message back, formatted as defined in Section 6. Sending error
messages is essential for debugging but MAY e.g.be skipped if a messages is essential for debugging but MAY e.g., be skipped if a
session cannot be found or due to denial of service reasons, see session cannot be found or due to denial-of-service reasons, see
Section 7. If an error message is sent, the session MUST be Section 7. If an error message is sent, the session MUST be
discontinued. discontinued.
After verifying message_3, the Responder is assured that the After verifying message_3, the Responder is assured that the
Initiator has calculated the key PRK_4x3m (explicit key confirmation) Initiator has calculated the key PRK_4x3m (explicit key confirmation)
and that no other party than the Responder can compute the key. The and that no other party than the Responder can compute the key. The
Responder can securely send protected application data and store the Responder can securely send protected application data and store the
keying material PRK_4x3m and TH_4. keying material PRK_4x3m and TH_4.
5.5. EDHOC Message 4 5.5. EDHOC Message 4
skipping to change at page 34, line 9 skipping to change at page 36, line 42
below below
message_4 = ( message_4 = (
CIPHERTEXT_4 : bstr, CIPHERTEXT_4 : bstr,
) )
5.5.2. Responder Processing of Message 4 5.5.2. Responder Processing of Message 4
The Responder SHALL compose message_4 as follows: The Responder SHALL compose message_4 as follows:
o Compute a COSE_Encrypt0 as defined in Section 5.3 of * Compute a COSE_Encrypt0 as defined in Section 5.3 of
[I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm
in the selected cipher suite, and the following parameters. The in the selected cipher suite, and the following parameters. The
protected header SHALL be empty. protected header SHALL be empty.
* protected = h'' - protected = h''
* external_aad = TH_4
* plaintext = ( ? EAD_4 ) - external_aad = TH_4
- plaintext = ( ? EAD_4 )
where EAD_4 is protected external authorization data, see where EAD_4 is protected external authorization data, see
Section 3.8. COSE constructs the input to the AEAD [RFC5116] as Section 3.8. COSE constructs the input to the AEAD [RFC5116] as
follows: follows:
* Key K = EDHOC-Exporter( "EDHOC_message_4_Key", h'', length ) - Key K = EDHOC-Exporter( "EDHOC_message_4_Key", , length )
* Nonce N = EDHOC-Exporter( "EDHOC_message_4_Nonce", h'', length - Nonce N = EDHOC-Exporter( "EDHOC_message_4_Nonce", , length )
)
* Plaintext P = ( ? EAD_4 ) - Plaintext P = ( ? EAD_4 )
* Associated data A = [ "Encrypt0", h'', TH_4 ] - Associated data A = [ "Encrypt0", h'', TH_4 ]
CIPHERTEXT_4 is the 'ciphertext' of the COSE_Encrypt0. CIPHERTEXT_4 is the ciphertext of the COSE_Encrypt0.
o Encode message_4 as a sequence of CBOR encoded data items as * Encode message_4 as a sequence of CBOR encoded data items as
specified in Section 5.5.1. specified in Section 5.5.1.
5.5.3. Initiator Processing of Message 4 5.5.3. Initiator Processing of Message 4
The Initiator SHALL process message_4 as follows: The Initiator SHALL process message_4 as follows:
o Decode message_4 (see Appendix C.1). * Decode message_4 (see Appendix C.1).
o Retrieve the protocol state using the message correlation provided * Retrieve the protocol state using the message correlation provided
by the transport (e.g., the CoAP Token and the 5-tuple as a by the transport (e.g., the CoAP Token and the 5-tuple as a
client, or the prepended C_I as a server). client, or the prepended C_I as a server).
o Decrypt and verify the outer COSE_Encrypt0 as defined in * Decrypt and verify the outer COSE_Encrypt0 as defined in
Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC
AEAD algorithm in the selected cipher suite, and the parameters AEAD algorithm in the selected cipher suite, and the parameters
defined in Section 5.5.2. defined in Section 5.5.2.
o Pass EAD_4 to the security application. * Pass EAD_4 to the security application.
If any verification step fails the Initiator MUST send an EDHOC error If any processing step fails, the Responder SHOULD send an EDHOC
message back, formatted as defined in Section 6, and the session MUST error message back, formatted as defined in Section 6. Sending error
be discontinued. messages is essential for debugging but MAY e.g., be skipped if a
session cannot be found or due to denial-of-service reasons, see
Section 7. If an error message is sent, the session MUST be
discontinued.
6. Error Handling 6. Error Handling
This section defines the format for error messages. This section defines the format for error messages.
An EDHOC error message can be sent by either endpoint as a reply to An EDHOC error message can be sent by either endpoint as a reply to
any non-error EDHOC message. How errors at the EDHOC layer are any non-error EDHOC message. How errors at the EDHOC layer are
transported depends on lower layers, which need to enable error transported depends on lower layers, which need to enable error
messages to be sent and processed as intended. messages to be sent and processed as intended.
skipping to change at page 35, line 32 skipping to change at page 38, line 22
error message as an indication that the other party likely has error message as an indication that the other party likely has
discontinued the protocol. But as the error message is not discontinued the protocol. But as the error message is not
authenticated, a received error message might also have been sent by authenticated, a received error message might also have been sent by
an attacker and the receiver MAY therefore try to continue the an attacker and the receiver MAY therefore try to continue the
protocol. protocol.
error SHALL be a CBOR Sequence (see Appendix C.1) as defined below error SHALL be a CBOR Sequence (see Appendix C.1) as defined below
error = ( error = (
ERR_CODE : int, ERR_CODE : int,
ERR_INFO : any ERR_INFO : any,
) )
Figure 5: EDHOC Error Message Figure 5: EDHOC Error Message
where: where:
o ERR_CODE - error code encoded as an integer. The value 0 is used * ERR_CODE - error code encoded as an integer. The value 0 is used
for success, all other values (negative or positive) indicate for success, all other values (negative or positive) indicate
errors. errors.
o ERR_INFO - error information. Content and encoding depend on * ERR_INFO - error information. Content and encoding depend on
error code. error code.
The remainder of this section specifies the currently defined error The remainder of this section specifies the currently defined error
codes, see Figure 6. Error codes 1 and 2 MUST be supported. codes, see Figure 6. Error codes 1 and 2 MUST be supported.
Additional error codes and corresponding error information may be Additional error codes and corresponding error information may be
specified. specified.
+----------+---------------+----------------------------------------+ +----------+---------------+----------------------------------------+
| ERR_CODE | ERR_INFO Type | Description | | ERR_CODE | ERR_INFO Type | Description |
+==========+===============+========================================+ +==========+===============+========================================+
skipping to change at page 36, line 20 skipping to change at page 39, line 8
| 1 | tstr | Unspecified | | 1 | tstr | Unspecified |
+----------+---------------+----------------------------------------+ +----------+---------------+----------------------------------------+
| 2 | SUITES_R | Wrong selected cipher suite | | 2 | SUITES_R | Wrong selected cipher suite |
+----------+---------------+----------------------------------------+ +----------+---------------+----------------------------------------+
Figure 6: Error Codes and Error Information Figure 6: Error Codes and Error Information
6.1. Success 6.1. Success
Error code 0 MAY be used internally in an application to indicate Error code 0 MAY be used internally in an application to indicate
success, e.g. in log files. ERR_INFO can contain any type of CBOR success, e.g., in log files. ERR_INFO can contain any type of CBOR
item. Error code 0 MUST NOT be used as part of the EDHOC message item. Error code 0 MUST NOT be used as part of the EDHOC message
exchange flow. exchange flow.
6.2. Unspecified 6.2. Unspecified
Error code 1 is used for errors that do not have a specific error Error code 1 is used for errors that do not have a specific error
code defined. ERR_INFO MUST be a text string containing a human- code defined. ERR_INFO MUST be a text string containing a human-
readable diagnostic message written in English. The diagnostic text readable diagnostic message written in English. The diagnostic text
message is mainly intended for software engineers that during message is mainly intended for software engineers that during
debugging need to interpret it in the context of the EDHOC debugging need to interpret it in the context of the EDHOC
skipping to change at page 37, line 43 skipping to change at page 40, line 29
| message_1 | | message_1 |
| | | |
| DIAG_MSG, SUITES_R = 6 | | DIAG_MSG, SUITES_R = 6 |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| error | | error |
| | | |
| METHOD, SUITES_I = [6, 5, 6], G_X, C_I, EAD_1 | | METHOD, SUITES_I = [6, 5, 6], G_X, C_I, EAD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
Figure 7: Example of Responder supporting suite 6 but not suite 5. Figure 7: Example of Responder supporting suite 6 but not suite 5.
In the second example (Figure 8), the Responder supports cipher In the second example (Figure 8), the Responder supports cipher
suites 8 and 9 but not the more preferred (by the Initiator) cipher suites 8 and 9 but not the more preferred (by the Initiator) cipher
suites 5, 6 or 7. To illustrate the negotiation mechanics we let the suites 5, 6 or 7. To illustrate the negotiation mechanics we let the
Initiator first make a guess that the Responder supports suite 6 but Initiator first make a guess that the Responder supports suite 6 but
not suite 5. Since the Responder supports neither 5 nor 6, it not suite 5. Since the Responder supports neither 5 nor 6, it
responds with an error and SUITES_R, after which the Initiator responds with an error and SUITES_R, after which the Initiator
selects its most preferred supported suite. The order of cipher selects its most preferred supported suite. The order of cipher
suites in SUITES_R does not matter. (If the Responder had supported suites in SUITES_R does not matter. (If the Responder had supported
suite 5, it would include it in SUITES_R of the response, and it suite 5, it would include it in SUITES_R of the response, and it
skipping to change at page 38, line 21 skipping to change at page 41, line 17
| message_1 | | message_1 |
| | | |
| DIAG_MSG, SUITES_R = [9, 8] | | DIAG_MSG, SUITES_R = [9, 8] |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| error | | error |
| | | |
| METHOD, SUITES_I = [8, 5, 6, 7, 8], G_X, C_I, EAD_1 | | METHOD, SUITES_I = [8, 5, 6, 7, 8], G_X, C_I, EAD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
Figure 8: Example of Responder supporting suites 8 and 9 but not 5, 6 Figure 8: Example of Responder supporting suites 8 and 9 but not
or 7. 5, 6 or 7.
Note that the Initiator's list of supported cipher suites and order Note that the Initiator's list of supported cipher suites and order
of preference is fixed (see Section 5.2.1 and Section 5.2.2). of preference is fixed (see Section 5.2.1 and Section 5.2.2).
Furthermore, the Responder shall only accept message_1 if the Furthermore, the Responder shall only accept message_1 if the
selected cipher suite is the first cipher suite in SUITES_I that the selected cipher suite is the first cipher suite in SUITES_I that the
Responder supports (see Section 5.2.3). Following this procedure Responder supports (see Section 5.2.3). Following this procedure
ensures that the selected cipher suite is the most preferred (by the ensures that the selected cipher suite is the most preferred (by the
Initiator) cipher suite supported by both parties. Initiator) cipher suite supported by both parties.
If the selected cipher suite is not the first cipher suite which the If the selected cipher suite is not the first cipher suite which the
Responder supports in SUITES_I received in message_1, then Responder Responder supports in SUITES_I received in message_1, then Responder
MUST discontinue the protocol, see Section 5.2.3. If SUITES_I in MUST discontinue the protocol, see Section 5.2.3. If SUITES_I in
message_1 is manipulated then the integrity verification of message_2 message_1 is manipulated, then the integrity verification of
containing the transcript hash TH_2 will fail and the Initiator will message_2 containing the transcript hash TH_2 will fail and the
discontinue the protocol. Initiator will discontinue the protocol.
7. Security Considerations 7. Security Considerations
7.1. Security Properties 7.1. Security Properties
EDHOC inherits its security properties from the theoretical SIGMA-I EDHOC inherits its security properties from the theoretical SIGMA-I
protocol [SIGMA]. Using the terminology from [SIGMA], EDHOC provides protocol [SIGMA]. Using the terminology from [SIGMA], EDHOC provides
perfect forward secrecy, mutual authentication with aliveness, forward secrecy, mutual authentication with aliveness, consistency,
consistency, and peer awareness. As described in [SIGMA], peer and peer awareness. As described in [SIGMA], peer awareness is
awareness is provided to the Responder, but not to the Initiator. provided to the Responder, but not to the Initiator.
EDHOC protects the credential identifier of the Initiator against EDHOC protects the credential identifier of the Initiator against
active attacks and the credential identifier of the Responder against active attacks and the credential identifier of the Responder against
passive attacks. The roles should be assigned to protect the most passive attacks. The roles should be assigned to protect the most
sensitive identity/identifier, typically that which is not possible sensitive identity/identifier, typically that which is not possible
to infer from routing information in the lower layers. to infer from routing information in the lower layers.
Compared to [SIGMA], EDHOC adds an explicit method type and expands Compared to [SIGMA], EDHOC adds an explicit method type and expands
the message authentication coverage to additional elements such as the message authentication coverage to additional elements such as
algorithms, external authorization data, and previous messages. This algorithms, external authorization data, and previous messages. This
protects against an attacker replaying messages or injecting messages protects against an attacker replaying messages or injecting messages
from another session. from another session.
EDHOC also adds selection of connection identifiers and downgrade EDHOC also adds selection of connection identifiers and downgrade
protected negotiation of cryptographic parameters, i.e. an attacker protected negotiation of cryptographic parameters, i.e., an attacker
cannot affect the negotiated parameters. A single session of EDHOC cannot affect the negotiated parameters. A single session of EDHOC
does not include negotiation of cipher suites, but it enables the does not include negotiation of cipher suites, but it enables the
Responder to verify that the selected cipher suite is the most Responder to verify that the selected cipher suite is the most
preferred cipher suite by the Initiator which is supported by both preferred cipher suite by the Initiator which is supported by both
the Initiator and the Responder. the Initiator and the Responder.
As required by [RFC7258], IETF protocols need to mitigate pervasive As required by [RFC7258], IETF protocols need to mitigate pervasive
monitoring when possible. One way to mitigate pervasive monitoring monitoring when possible. EDHOC therefore only supports methods with
is to use a key exchange that provides perfect forward secrecy. ephemeral Diffie-Hellman and provides a KeyUpdate function for
EDHOC therefore only supports methods with perfect forward secrecy. lightweight application protocol rekeying with forward secrecy, in
the sense that compromise of the private authentication keys does not
compromise past session keys, and compromise of a session key does
not compromise past session keys.
While the KeyUpdate method can be used to meet cryptographic limits
and provide partial protection against key leakage, it provides
significantly weaker security properties than re-running EDHOC with
ephemeral Diffie-Hellman. Even with frequent use of KeyUpdate,
compromise of one session key compromises all future session keys,
and an attacker therefore only needs to perform static key
exfiltration [RFC7624]. Frequently re-running EDHOC with ephemeral
Diffie-Hellman forces attackers to perform dynamic key exfiltration
instead of static key exfiltration [RFC7624]. In the dynamic case,
the attacker must have continuous interactions with the collaborator,
which is more complicated and has a higher risk profile than the
static case.
To limit the effect of breaches, it is important to limit the use of To limit the effect of breaches, it is important to limit the use of
symmetrical group keys for bootstrapping. EDHOC therefore strives to symmetrical group keys for bootstrapping. EDHOC therefore strives to
make the additional cost of using raw public keys and self-signed make the additional cost of using raw public keys and self-signed
certificates as small as possible. Raw public keys and self-signed certificates as small as possible. Raw public keys and self-signed
certificates are not a replacement for a public key infrastructure, certificates are not a replacement for a public key infrastructure
but SHOULD be used instead of symmetrical group keys for but SHOULD be used instead of symmetrical group keys for
bootstrapping. bootstrapping.
Compromise of the long-term keys (private signature or static DH Compromise of the long-term keys (private signature or static DH
keys) does not compromise the security of completed EDHOC exchanges. keys) does not compromise the security of completed EDHOC exchanges.
Compromising the private authentication keys of one party lets an Compromising the private authentication keys of one party lets an
active attacker impersonate that compromised party in EDHOC exchanges active attacker impersonate that compromised party in EDHOC exchanges
with other parties, but does not let the attacker impersonate other with other parties but does not let the attacker impersonate other
parties in EDHOC exchanges with the compromised party. Compromise of parties in EDHOC exchanges with the compromised party. Compromise of
the long-term keys does not enable a passive attacker to compromise the long-term keys does not enable a passive attacker to compromise
future session keys. Compromise of the HDKF input parameters (ECDH future session keys. Compromise of the HDKF input parameters (ECDH
shared secret) leads to compromise of all session keys derived from shared secret) leads to compromise of all session keys derived from
that compromised shared secret. Compromise of one session key does that compromised shared secret. Compromise of one session key does
not compromise other session keys. Compromise of PRK_4x3m leads to not compromise other session keys. Compromise of PRK_4x3m leads to
compromise of all exported keying material derived after the last compromise of all exported keying material derived after the last
invocation of the EDHOC-KeyUpdate function. invocation of the EDHOC-KeyUpdate function.
EDHOC provides a minimum of 64-bit security against online brute EDHOC provides a minimum of 64-bit security against online brute
skipping to change at page 40, line 15 skipping to change at page 43, line 28
which is infeasible in constrained IoT radio technologies. which is infeasible in constrained IoT radio technologies.
After sending message_3, the Initiator is assured that no other party After sending message_3, the Initiator is assured that no other party
than the Responder can compute the key PRK_4x3m (implicit key than the Responder can compute the key PRK_4x3m (implicit key
authentication). The Initiator does however not know that the authentication). The Initiator does however not know that the
Responder has actually computed the key PRK_4x3m. While the Responder has actually computed the key PRK_4x3m. While the
Initiator can securely send protected application data, the Initiator Initiator can securely send protected application data, the Initiator
SHOULD NOT permanently store the keying material PRK_4x3m and TH_4 SHOULD NOT permanently store the keying material PRK_4x3m and TH_4
until the Initiator is assured that the Responder has actually until the Initiator is assured that the Responder has actually
computed the key PRK_4x3m (explicit key confirmation). Explicit key computed the key PRK_4x3m (explicit key confirmation). Explicit key
confirmation is e.g. assured when the Initiator has verified an confirmation is e.g., assured when the Initiator has verified an
OSCORE message or message_4 from the Responder. After verifying OSCORE message or message_4 from the Responder. After verifying
message_3, the Responder is assured that the Initiator has calculated message_3, the Responder is assured that the Initiator has calculated
the key PRK_4x3m (explicit key confirmation) and that no other party the key PRK_4x3m (explicit key confirmation) and that no other party
than the Responder can compute the key. The Responder can securely than the Responder can compute the key. The Responder can securely
send protected application data and store the keying material send protected application data and store the keying material
PRK_4x3m and TH_4. PRK_4x3m and TH_4.
Key compromise impersonation (KCI): In EDHOC authenticated with Key compromise impersonation (KCI): In EDHOC authenticated with
signature keys, EDHOC provides KCI protection against an attacker signature keys, EDHOC provides KCI protection against an attacker
having access to the long term key or the ephemeral secret key. With having access to the long-term key or the ephemeral secret key. With
static Diffie-Hellman key authentication, KCI protection would be static Diffie-Hellman key authentication, KCI protection would be
provided against an attacker having access to the long-term Diffie- provided against an attacker having access to the long-term Diffie-
Hellman key, but not to an attacker having access to the ephemeral Hellman key, but not to an attacker having access to the ephemeral
secret key. Note that the term KCI has typically been used for secret key. Note that the term KCI has typically been used for
compromise of long-term keys, and that an attacker with access to the compromise of long-term keys, and that an attacker with access to the
ephemeral secret key can only attack that specific protocol run. ephemeral secret key can only attack that specific protocol run.
Repudiation: In EDHOC authenticated with signature keys, the Repudiation: In EDHOC authenticated with signature keys, the
Initiator could theoretically prove that the Responder performed a Initiator could theoretically prove that the Responder performed a
run of the protocol by presenting the private ephemeral key, and vice run of the protocol by presenting the private ephemeral key, and vice
skipping to change at page 40, line 47 skipping to change at page 44, line 19
protocol requirements. With static Diffie-Hellman key protocol requirements. With static Diffie-Hellman key
authentication, both parties can always deny having participated in authentication, both parties can always deny having participated in
the protocol. the protocol.
Two earlier versions of EDHOC have been formally analyzed [Norrman20] Two earlier versions of EDHOC have been formally analyzed [Norrman20]
[Bruni18] and the specification has been updated based on the [Bruni18] and the specification has been updated based on the
analysis. analysis.
7.2. Cryptographic Considerations 7.2. Cryptographic Considerations
The security of the SIGMA protocol requires the MAC to be bound to The SIGMA protocol requires that the encryption of message_3 provides
the identity of the signer. Hence the message authenticating confidentiality against active attackers and EDHOC message_4 relies
functionality of the authenticated encryption in EDHOC is critical: on the use of authenticated encryption. Hence the message
authenticated encryption MUST NOT be replaced by plain encryption authenticating functionality of the authenticated encryption in EDHOC
only, even if authentication is provided at another level or through is critical: authenticated encryption MUST NOT be replaced by plain
a different mechanism. EDHOC implements SIGMA-I using a MAC-then- encryption only, even if authentication is provided at another level
Sign approach. or through a different mechanism.
To reduce message overhead EDHOC does not use explicit nonces and To reduce message overhead EDHOC does not use explicit nonces and
instead rely on the ephemeral public keys to provide randomness to instead rely on the ephemeral public keys to provide randomness to
each session. A good amount of randomness is important for the key each session. A good amount of randomness is important for the key
generation, to provide liveness, and to protect against interleaving generation, to provide liveness, and to protect against interleaving
attacks. For this reason, the ephemeral keys MUST NOT be reused, and attacks. For this reason, the ephemeral keys MUST NOT be reused, and
both parties SHALL generate fresh random ephemeral key pairs. both parties SHALL generate fresh random ephemeral key pairs.
As discussed the [SIGMA], the encryption of message_2 does only need As discussed, the [SIGMA], the encryption of message_2 does only need
to protect against passive attacker as active attackers can always to protect against passive attacker as active attackers can always
get the Responders identity by sending their own message_1. EDHOC get the Responders identity by sending their own message_1. EDHOC
uses the Expand function (typically HKDF-Expand) as a binary additive uses the Expand function (typically HKDF-Expand) as a binary additive
stream cipher. HKDF-Expand provides better confidentiality than AES- stream cipher. HKDF-Expand provides better confidentiality than AES-
CTR but is not often used as it is slow on long messages, and most CTR but is not often used as it is slow on long messages, and most
applications require both IND-CCA confidentiality as well as applications require both IND-CCA confidentiality as well as
integrity protection. For the encryption of message_2, any speed integrity protection. For the encryption of message_2, any speed
difference is negligible, IND-CCA does not increase security, and difference is negligible, IND-CCA does not increase security, and
integrity is provided by the inner MAC (and signature depending on integrity is provided by the inner MAC (and signature depending on
method). method).
The data rates in many IoT deployments are very limited. Given that
the application keys are protected as well as the long-term
authentication keys they can often be used for years or even decades
before the cryptographic limits are reached. If the application keys
established through EDHOC need to be renewed, the communicating
parties can derive application keys with other labels or run EDHOC
again.
Requirement for how to securely generate, validate, and process the Requirement for how to securely generate, validate, and process the
ephermeral public keys depend on the elliptic curve. For X25519 and ephemeral public keys depend on the elliptic curve. For X25519 and
X448, the requirements are defined in [RFC7748]. For secp256r1, X448, the requirements are defined in [RFC7748]. For secp256r1,
secp384r1, and secp521r1, the requirements are defined in Section 5 secp384r1, and secp521r1, the requirements are defined in Section 5
of [SP-800-56A]. For secp256r1, secp384r1, and secp521r1, at least of [SP-800-56A]. For secp256r1, secp384r1, and secp521r1, at least
partial public-key validation MUST be done. partial public-key validation MUST be done.
7.3. Cipher Suites and Cryptographic Algorithms 7.3. Cipher Suites and Cryptographic Algorithms
For many constrained IoT devices it is problematic to support more For many constrained IoT devices it is problematic to support more
than one cipher suite. Existing devices can be expected to support than one cipher suite. Existing devices can be expected to support
either ECDSA or EdDSA. To enable as much interoperability as we can either ECDSA or EdDSA. To enable as much interoperability as we can
skipping to change at page 42, line 47 skipping to change at page 46, line 19
attacker may cause the Responder to allocate state, perform attacker may cause the Responder to allocate state, perform
cryptographic operations, and amplify messages. To mitigate such cryptographic operations, and amplify messages. To mitigate such
attacks, an implementation SHOULD rely on lower layer mechanisms such attacks, an implementation SHOULD rely on lower layer mechanisms such
as the Echo option in CoAP [I-D.ietf-core-echo-request-tag] that as the Echo option in CoAP [I-D.ietf-core-echo-request-tag] that
forces the initiator to demonstrate reachability at its apparent forces the initiator to demonstrate reachability at its apparent
network address. network address.
An attacker can also send faked message_2, message_3, message_4, or An attacker can also send faked message_2, message_3, message_4, or
error in an attempt to trick the receiving party to send an error error in an attempt to trick the receiving party to send an error
message and discontinue the session. EDHOC implementations MAY message and discontinue the session. EDHOC implementations MAY
evaluate if a received message is likely to have be forged by and evaluate if a received message is likely to have been forged by and
attacker and ignore it without sending an error message or attacker and ignore it without sending an error message or
discontinuing the session. discontinuing the session.
7.6. Implementation Considerations 7.6. Implementation Considerations
The availability of a secure random number generator is essential for The availability of a secure random number generator is essential for
the security of EDHOC. If no true random number generator is the security of EDHOC. If no true random number generator is
available, a truly random seed MUST be provided from an external available, a truly random seed MUST be provided from an external
source and used with a cryptographically secure pseudorandom number source and used with a cryptographically secure pseudorandom number
generator. As each pseudorandom number must only be used once, an generator. As each pseudorandom number must only be used once, an
implementation need to get a new truly random seed after reboot, or implementation needs to get a new truly random seed after reboot, or
continuously store state in nonvolatile memory, see ([RFC8613], continuously store state in nonvolatile memory, see ([RFC8613],
Appendix B.1.1) for issues and solution approaches for writing to Appendix B.1.1) for issues and solution approaches for writing to
nonvolatile memory. Intentionally or unintentionally weak or nonvolatile memory. Intentionally or unintentionally weak or
predictable pseudorandom number generators can be abused or exploited predictable pseudorandom number generators can be abused or exploited
for malicious purposes. [RFC8937] describes a way for security for malicious purposes. [RFC8937] describes a way for security
protocol implementations to augment their (pseudo)random number protocol implementations to augment their (pseudo)random number
generators using a long-term private keys and a deterministic generators using a long-term private key and a deterministic
signature function. This improves randomness from broken or signature function. This improves randomness from broken or
otherwise subverted random number generators. The same idea can be otherwise subverted random number generators. The same idea can be
used with other secrets and functions such as a Diffie-Hellman used with other secrets and functions such as a Diffie-Hellman
function or a symmetric secret and a PRF like HMAC or KMAC. It is function or a symmetric secret and a PRF like HMAC or KMAC. It is
RECOMMENDED to not trust a single source of randomness and to not put RECOMMENDED to not trust a single source of randomness and to not put
unaugmented random numbers on the wire. unaugmented random numbers on the wire.
If ECDSA is supported, "deterministic ECDSA" as specified in If ECDSA is supported, "deterministic ECDSA" as specified in
[RFC6979] MAY be used. Pure deterministic elliptic-curve signatures [RFC6979] MAY be used. Pure deterministic elliptic-curve signatures
such as deterministic ECDSA and EdDSA have gained popularity over such as deterministic ECDSA and EdDSA have gained popularity over
randomized ECDSA as their security do not depend on a source of high- randomized ECDSA as their security do not depend on a source of high-
quality randomness. Recent research has however found that quality randomness. Recent research has however found that
implementations of these signature algorithms may be vulnerable to implementations of these signature algorithms may be vulnerable to
certain side-channel and fault injection attacks due to their certain side-channel and fault injection attacks due to their
determinism. See e.g. Section 1 of determinism. See e.g., Section 1 of
[I-D.mattsson-cfrg-det-sigs-with-noise] for a list of attack papers. [I-D.mattsson-cfrg-det-sigs-with-noise] for a list of attack papers.
As suggested in Section 6.1.2 of [I-D.ietf-cose-rfc8152bis-algs] this As suggested in Section 6.1.2 of [I-D.ietf-cose-rfc8152bis-algs] this
can be addressed by combining randomness and determinism. can be addressed by combining randomness and determinism.
All private keys, symmetric keys, and IVs MUST be secret. All private keys, symmetric keys, and IVs MUST be secret.
Implementations should provide countermeasures to side-channel Implementations should provide countermeasures to side-channel
attacks such as timing attacks. Intermediate computed values such as attacks such as timing attacks. Intermediate computed values such as
ephemeral ECDH keys and ECDH shared secrets MUST be deleted after key ephemeral ECDH keys and ECDH shared secrets MUST be deleted after key
derivation is completed. derivation is completed.
The Initiator and the Responder are responsible for verifying the The Initiator and the Responder are responsible for verifying the
integrity of certificates. The selection of trusted CAs should be integrity of certificates. The selection of trusted CAs should be
done very carefully and certificate revocation should be supported. done very carefully and certificate revocation should be supported.
The private authentication keys MUST be kept secret. The private authentication keys MUST be kept secret.
The Initiator and the Responder are allowed to select the connection The Initiator and the Responder are allowed to select the connection
identifiers C_I and C_R, respectively, for the other party to use in identifiers C_I and C_R, respectively, for the other party to use in
the ongoing EDHOC protocol as well as in a subsequent application the ongoing EDHOC protocol as well as in a subsequent application
protocol (e.g. OSCORE [RFC8613]). The choice of connection protocol (e.g., OSCORE [RFC8613]). The choice of connection
identifier is not security critical in EDHOC but intended to simplify identifier is not security critical in EDHOC but intended to simplify
the retrieval of the right security context in combination with using the retrieval of the right security context in combination with using
short identifiers. If the wrong connection identifier of the other short identifiers. If the wrong connection identifier of the other
party is used in a protocol message it will result in the receiving party is used in a protocol message it will result in the receiving
party not being able to retrieve a security context (which will party not being able to retrieve a security context (which will
terminate the protocol) or retrieve the wrong security context (which terminate the protocol) or retrieve the wrong security context (which
also terminates the protocol as the message cannot be verified). also terminates the protocol as the message cannot be verified).
If two nodes unintentionally initiate two simultaneous EDHOC message If two nodes unintentionally initiate two simultaneous EDHOC message
exchanges with each other even if they only want to complete a single exchanges with each other even if they only want to complete a single
skipping to change at page 44, line 26 skipping to change at page 47, line 45
lexicographically smallest G_X. If the two G_X values are equal, the lexicographically smallest G_X. If the two G_X values are equal, the
received message_1 MUST be discarded to mitigate reflection attacks. received message_1 MUST be discarded to mitigate reflection attacks.
Note that in the case of two simultaneous EDHOC exchanges where the Note that in the case of two simultaneous EDHOC exchanges where the
nodes only complete one and where the nodes have different preferred nodes only complete one and where the nodes have different preferred
cipher suites, an attacker can affect which of the two nodes' cipher suites, an attacker can affect which of the two nodes'
preferred cipher suites will be used by blocking the other exchange. preferred cipher suites will be used by blocking the other exchange.
If supported by the device, it is RECOMMENDED that at least the long- If supported by the device, it is RECOMMENDED that at least the long-
term private keys are stored in a Trusted Execution Environment (TEE) term private keys are stored in a Trusted Execution Environment (TEE)
and that sensitive operations using these keys are performed inside and that sensitive operations using these keys are performed inside
the TEE. To achieve even higher security it is RECOMMENDED that in the TEE. To achieve even higher security, it is RECOMMENDED that in
additional operations such as ephemeral key generation, all additional operations such as ephemeral key generation, all
computations of shared secrets, and storage of the pseudorandom keys computations of shared secrets, and storage of the pseudorandom keys
(PRK) can be done inside the TEE. The use of a TEE enforces that (PRK) can be done inside the TEE. The use of a TEE enforces that
code within that environment cannot be tampered with, and that any code within that environment cannot be tampered with, and that any
data used by such code cannot be read or tampered with by code data used by such code cannot be read or tampered with by code
outside that environment. Note that non-EDHOC code inside the TEE outside that environment. Note that non-EDHOC code inside the TEE
might still be able to read EDHOC data and tamper with EDHOC code, to might still be able to read EDHOC data and tamper with EDHOC code, to
protect against such attacks EDHOC needs to be in its own zone. To protect against such attacks EDHOC needs to be in its own zone. To
provide better protection against some forms of physical attacks, provide better protection against some forms of physical attacks,
sensitive EDHOC data should be stored inside the SoC or encrypted and sensitive EDHOC data should be stored inside the SoC or encrypted and
integrity protected when sent on a data bus (e.g. between the CPU and integrity protected when sent on a data bus (e.g., between the CPU
RAM or Flash). Secure boot can be used to increase the security of and RAM or Flash). Secure boot can be used to increase the security
code and data in the Rich Execution Environment (REE) by validating of code and data in the Rich Execution Environment (REE) by
the REE image. validating the REE image.
8. IANA Considerations 8. IANA Considerations
8.1. EDHOC Exporter Label 8.1. EDHOC Exporter Label
IANA has created a new registry titled "EDHOC Exporter Label" under IANA has created a new registry titled "EDHOC Exporter Label" under
the new heading "EDHOC". The registration procedure is "Expert the new heading "EDHOC". The registration procedure is "Expert
Review". The columns of the registry are Label, Description, and Review". The columns of the registry are Label, Description, and
Reference. All columns are text strings. The initial contents of Reference. All columns are text strings. The initial contents of
the registry are: the registry are:
skipping to change at page 47, line 16 skipping to change at page 50, line 34
Desc: ChaCha20/Poly1305, SHAKE256, X448, EdDSA, Desc: ChaCha20/Poly1305, SHAKE256, X448, EdDSA,
ChaCha20/Poly1305, SHAKE256 ChaCha20/Poly1305, SHAKE256
Reference: [[this document]] Reference: [[this document]]
8.3. EDHOC Method Type Registry 8.3. EDHOC Method Type Registry
IANA has created a new registry entitled "EDHOC Method Type" under IANA has created a new registry entitled "EDHOC Method Type" under
the new heading "EDHOC". The registration procedure is "Expert the new heading "EDHOC". The registration procedure is "Expert
Review". The columns of the registry are Value, Description, and Review". The columns of the registry are Value, Description, and
Reference, where Value is an integer and the other columns are text Reference, where Value is an integer and the other columns are text
strings. The initial contents of the registry is shown in Figure 4. strings. The initial contents of the registry are shown in Figure 4.
8.4. EDHOC Error Codes Registry 8.4. EDHOC Error Codes Registry
IANA has created a new registry entitled "EDHOC Error Codes" under IANA has created a new registry entitled "EDHOC Error Codes" under
the new heading "EDHOC". The registration procedure is the new heading "EDHOC". The registration procedure is
"Specification Required". The columns of the registry are ERR_CODE, "Specification Required". The columns of the registry are ERR_CODE,
ERR_INFO Type and Description, where ERR_CODE is an integer, ERR_INFO ERR_INFO Type and Description, where ERR_CODE is an integer, ERR_INFO
is a CDDL defined type, and Description is a text string. The is a CDDL defined type, and Description is a text string. The
initial contents of the registry is shown in Figure 6. initial contents of the registry are shown in Figure 6.
8.5. COSE Header Parameters Registry 8.5. COSE Header Parameters Registry
This document registers the following entries in the "COSE Header This document registers the following entries in the "COSE Header
Parameters" registry under the "CBOR Object Signing and Encryption Parameters" registry under the "CBOR Object Signing and Encryption
(COSE)" heading. The value of the 'cwt' header parameter is a CWT (COSE)" heading. The value of the 'cwt' header parameter is a CWT
[RFC8392] or an unprotected CWT Claims Set [I-D.ietf-rats-uccs]. [RFC8392] or an Unprotected CWT Claims Set, see Section 1.5.
+-----------+-------+----------------+------------------------------+ +-----------+-------+----------------+------------------------------+
| Name | Label | Value Type | Description | | Name | Label | Value Type | Description |
+===========+=======+================+==============================+ +===========+=======+================+==============================+
| cwt | TBD1 | COSE_Messages | A CBOR Web Token (CWT) or an | | cwt | TBD1 | COSE_Messages | A CBOR Web Token (CWT) or an |
| | | / map | unprotected CWT Claims Set | | | | / map | Unprotected CWT Claims Set |
+-----------+-------+----------------+------------------------------+ +-----------+-------+----------------+------------------------------+
8.6. COSE Header Parameters Registry 8.6. COSE Header Parameters Registry
IANA has added the COSE header parameter 'kid2' to the COSE Header IANA has extended the Value Type of the COSE Header Parameter 'kid'
Parameters registry. The kid2 parameter may point to a COSE key to also allow the Value Type int. The resulting Value Type is bstr /
common parameter 'kid' or 'kid2'. The kid2 parameter can be used to int. The 'kid' parameter can be used to identify a key stored in a
identify a key stored in a "raw" COSE_Key, in a CWT, or in a UCCS, in a CWT, or in a public key certificate. (The Value Registry
certificate. The Value Reference for this item is empty and omitted for this item is empty and omitted from the table below.)
from the table below.
+------+-------+------------+----------------+-------------------+ +------+-------+------------+----------------+-------------------+
| Name | Label | Value Type | Description | Reference | | Name | Label | Value Type | Description | Reference |
+------+-------+------------+----------------+-------------------+ +------+-------+------------+----------------+-------------------+
| kid2 | TBD | bstr / int | Key identifier | [[This document]] | | kid | 4 | bstr / int | Key identifier | [RFC9052] |
| | | | | [[This document]] |
+------+-------+------------+----------------+-------------------+ +------+-------+------------+----------------+-------------------+
8.7. COSE Key Common Parameters Registry 8.7. COSE Key Common Parameters Registry
IANA has added the COSE key common parameter 'kid2' to the COSE Key IANA has extended the Value Type of the COSE Key Common Parameter
Common Parameters registry. The Value Reference for this item is 'kid' to the COSE Key Value Type int. The resulting Value Type is
empty and omitted from the table below. bstr / int. (The Value Registry for this item is empty and omitted
from the table below.)
+------+-------+------------+----------------+-------------------+ +------+-------+------------+----------------+-------------------+
| Name | Label | Value Type | Description | Reference | | Name | Label | Value Type | Description | Reference |
+------+-------+------------+----------------+-------------------+ +------+-------+------------+----------------+-------------------+
| kid2 | TBD | bstr / int | Key identifi- | [[This document]] | | kid | 2 | bstr / int | Key identifi- | [RFC9052] |
| | | | cation value - | | | | | | cation value - | [[This document]] |
| | | | match to kid2 | | | | | | match to kid | |
| | | | in message | | | | | | in message | |
+------+-------+------------+----------------+-------------------+ +------+-------+------------+----------------+-------------------+
8.8. The Well-Known URI Registry 8.8. The Well-Known URI Registry
IANA has added the well-known URI 'edhoc' to the Well-Known URIs IANA has added the well-known URI "edhoc" to the Well-Known URIs
registry. registry.
o URI suffix: edhoc * URI suffix: edhoc
o Change controller: IETF
o Specification document(s): [[this document]] * Change controller: IETF
o Related information: None * Specification document(s): [[this document]]
* Related information: None
8.9. Media Types Registry 8.9. Media Types Registry
IANA has added the media type 'application/edhoc' to the Media Types IANA has added the media type "application/edhoc" to the Media Types
registry. registry.
o Type name: application * Type name: application
o Subtype name: edhoc * Subtype name: edhoc
o Required parameters: N/A * Required parameters: N/A
o Optional parameters: N/A * Optional parameters: N/A
o Encoding considerations: binary * Encoding considerations: binary
o Security considerations: See Section 7 of this document.
o Interoperability considerations: N/A * Security considerations: See Section 7 of this document.
o Published specification: [[this document]] (this document) * Interoperability considerations: N/A
o Applications that use this media type: To be identified * Published specification: [[this document]] (this document)
o Fragment identifier considerations: N/A * Applications that use this media type: To be identified
o Additional information: * Fragment identifier considerations: N/A
* Magic number(s): N/A * Additional information:
* File extension(s): N/A - Magic number(s): N/A
* Macintosh file type code(s): N/A - File extension(s): N/A
o Person & email address to contact for further information: See - Macintosh file type code(s): N/A
* Person & email address to contact for further information: See
"Authors' Addresses" section. "Authors' Addresses" section.
o Intended usage: COMMON * Intended usage: COMMON
o Restrictions on usage: N/A * Restrictions on usage: N/A
o Author: See "Authors' Addresses" section. * Author: See "Authors' Addresses" section.
o Change Controller: IESG * Change Controller: IESG
8.10. CoAP Content-Formats Registry 8.10. CoAP Content-Formats Registry
IANA has added the media type 'application/edhoc' to the CoAP IANA has added the media type "application/edhoc" to the CoAP
Content-Formats registry. Content-Formats registry.
o Media Type: application/edhoc * Media Type: application/edhoc
o Encoding: * Encoding:
o ID: TBD42 * ID: TBD42
o Reference: [[this document]] * Reference: [[this document]]
8.11. EDHOC External Authorization Data 8.11. EDHOC External Authorization Data
IANA has created a new registry entitled "EDHOC External IANA has created a new registry entitled "EDHOC External
Authorization Data" under the new heading "EDHOC". The registration Authorization Data" under the new heading "EDHOC". The registration
procedure is "Expert Review". The columns of the registry are Value, procedure is "Expert Review". The columns of the registry are Value,
Description, and Reference, where Value is an integer and the other Description, and Reference, where Value is an integer and the other
columns are text strings. columns are text strings.
8.12. Expert Review Instructions 8.12. Expert Review Instructions
The IANA Registries established in this document is defined as The IANA Registries established in this document is defined as
"Expert Review". This section gives some general guidelines for what "Expert Review". This section gives some general guidelines for what
the experts should be looking for, but they are being designated as the experts should be looking for, but they are being designated as
experts for a reason so they should be given substantial latitude. experts for a reason so they should be given substantial latitude.
Expert reviewers should take into consideration the following points: Expert reviewers should take into consideration the following points:
o Clarity and correctness of registrations. Experts are expected to * Clarity and correctness of registrations. Experts are expected to
check the clarity of purpose and use of the requested entries. check the clarity of purpose and use of the requested entries.
Expert needs to make sure the values of algorithms are taken from Expert needs to make sure the values of algorithms are taken from
the right registry, when that's required. Expert should consider the right registry, when that is required. Expert should consider
requesting an opinion on the correctness of registered parameters requesting an opinion on the correctness of registered parameters
from relevant IETF working groups. Encodings that do not meet from relevant IETF working groups. Encodings that do not meet
these objective of clarity and completeness should not be these objective of clarity and completeness should not be
registered. registered.
o Experts should take into account the expected usage of fields when * Experts should take into account the expected usage of fields when
approving point assignment. The length of the encoded value approving point assignment. The length of the encoded value
should be weighed against how many code points of that length are should be weighed against how many code points of that length are
left, the size of device it will be used on, and the number of left, the size of device it will be used on, and the number of
code points left that encode to that size. code points left that encode to that size.
o Specifications are recommended. When specifications are not * Specifications are recommended. When specifications are not
provided, the description provided needs to have sufficient provided, the description provided needs to have sufficient
information to verify the points above. information to verify the points above.
9. References 9. References
9.1. Normative References 9.1. Normative References
[I-D.ietf-core-echo-request-tag] [I-D.ietf-core-echo-request-tag]
Amsuess, C., Mattsson, J. P., and G. Selander, "CoAP: Amsüss, C., Mattsson, J. P., and G. Selander, "CoAP: Echo,
Echo, Request-Tag, and Token Processing", draft-ietf-core- Request-Tag, and Token Processing", Work in Progress,
echo-request-tag-12 (work in progress), February 2021. Internet-Draft, draft-ietf-core-echo-request-tag-13, 12
July 2021, <https://www.ietf.org/archive/id/draft-ietf-
core-echo-request-tag-13.txt>.
[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", Work in Progress, Internet-Draft,
(work in progress), September 2020. draft-ietf-cose-rfc8152bis-algs-12, 24 September 2020,
<https://www.ietf.org/archive/id/draft-ietf-cose-
rfc8152bis-algs-12.txt>.
[I-D.ietf-cose-rfc8152bis-struct] [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", Work in Progress, Internet-Draft,
struct-15 (work in progress), February 2021. draft-ietf-cose-rfc8152bis-struct-15, 1 February 2021,
<https://www.ietf.org/archive/id/draft-ietf-cose-
rfc8152bis-struct-15.txt>.
[I-D.ietf-cose-x509] [I-D.ietf-cose-x509]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header parameters for carrying and referencing X.509 Header parameters for carrying and referencing X.509
certificates", draft-ietf-cose-x509-08 (work in progress), certificates", Work in Progress, Internet-Draft, draft-
December 2020. ietf-cose-x509-08, 14 December 2020,
<https://www.ietf.org/internet-drafts/draft-ietf-cose-
[I-D.ietf-lake-reqs] x509-08.txt>.
Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia-
Carrillo, "Requirements for a Lightweight AKE for OSCORE",
draft-ietf-lake-reqs-04 (work in progress), June 2020.
[I-D.ietf-rats-uccs]
Birkholz, H., O'Donoghue, J., Cam-Winget, N., and C.
Bormann, "A CBOR Tag for Unprotected CWT Claims Sets",
draft-ietf-rats-uccs-00 (work in progress), May 2021.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>. <https://www.rfc-editor.org/info/rfc5116>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869, Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010, DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>. <https://www.rfc-editor.org/info/rfc5869>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic [RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090, Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011, DOI 10.17487/RFC6090, February 2011,
<https://www.rfc-editor.org/info/rfc6090>. <https://www.rfc-editor.org/info/rfc6090>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature [RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
2013, <https://www.rfc-editor.org/info/rfc6979>. 2013, <https://www.rfc-editor.org/info/rfc6979>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>. <https://www.rfc-editor.org/info/rfc7252>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015,
<https://www.rfc-editor.org/info/rfc7624>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>. 2016, <https://www.rfc-editor.org/info/rfc7748>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959, the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016, DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>. <https://www.rfc-editor.org/info/rfc7959>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
skipping to change at page 52, line 43 skipping to change at page 56, line 17
Express Concise Binary Object Representation (CBOR) and Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>. June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[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>.
[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header Zúñiga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724, Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020, DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>. <https://www.rfc-editor.org/info/rfc8724>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR) [RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020, Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>. <https://www.rfc-editor.org/info/rfc8742>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/info/rfc8747>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949, Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020, DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>. <https://www.rfc-editor.org/info/rfc8949>.
9.2. Informative References 9.2. Informative References
[Bruni18] Bruni, A., Sahl Joergensen, T., Groenbech Petersen, T., [Bruni18] Bruni, A., Sahl Jørgensen, T., Grønbech Petersen, T., and
and C. Schuermann, "Formal Verification of Ephemeral C. Schürmann, "Formal Verification of Ephemeral Diffie-
Diffie-Hellman Over COSE (EDHOC)", November 2018, Hellman Over COSE (EDHOC)", November 2018,
<https://www.springerprofessional.de/en/formal- <https://www.springerprofessional.de/en/formal-
verification-of-ephemeral-diffie-hellman-over-cose- verification-of-ephemeral-diffie-hellman-over-cose-
edhoc/16284348>. edhoc/16284348>.
[CborMe] Bormann, C., "CBOR Playground", May 2018, [CborMe] Bormann, C., "CBOR Playground", May 2018,
<http://cbor.me/>. <http://cbor.me/>.
[CNSA] (Placeholder), ., "Commercial National Security Algorithm [CNSA] (Placeholder), ., "Commercial National Security Algorithm
Suite", August 2015, Suite", August 2015,
<https://apps.nsa.gov/iaarchive/programs/iad-initiatives/ <https://apps.nsa.gov/iaarchive/programs/iad-initiatives/
cnsa-suite.cfm>. cnsa-suite.cfm>.
[I-D.ietf-core-oscore-edhoc] [I-D.ietf-core-oscore-edhoc]
Palombini, F., Tiloca, M., Hoeglund, R., Hristozov, S., Palombini, F., Tiloca, M., Hoeglund, R., Hristozov, S.,
and G. Selander, "Combining EDHOC and OSCORE", draft-ietf- and G. Selander, "Combining EDHOC and OSCORE", Work in
core-oscore-edhoc-00 (work in progress), April 2021. Progress, Internet-Draft, draft-ietf-core-oscore-edhoc-01,
12 July 2021, <https://www.ietf.org/archive/id/draft-ietf-
core-oscore-edhoc-01.txt>.
[I-D.ietf-core-resource-directory] [I-D.ietf-core-resource-directory]
Amsuess, C., Shelby, Z., Koster, M., Bormann, C., and P. Amsüss, C., Shelby, Z., Koster, M., Bormann, C., and P. V.
V. D. Stok, "CoRE Resource Directory", draft-ietf-core- D. Stok, "CoRE Resource Directory", Work in Progress,
resource-directory-28 (work in progress), March 2021. Internet-Draft, draft-ietf-core-resource-directory-28, 7
March 2021, <https://www.ietf.org/archive/id/draft-ietf-
core-resource-directory-28.txt>.
[I-D.ietf-cose-cbor-encoded-cert] [I-D.ietf-cose-cbor-encoded-cert]
Raza, S., Hoeglund, J., Selander, G., Mattsson, J. P., and Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
M. Furuhed, "CBOR Encoded X.509 Certificates (C509 M. Furuhed, "CBOR Encoded X.509 Certificates (C509
Certificates)", draft-ietf-cose-cbor-encoded-cert-00 (work Certificates)", Work in Progress, Internet-Draft, draft-
in progress), April 2021. ietf-cose-cbor-encoded-cert-02, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-cose-cbor-
encoded-cert-02.txt>.
[I-D.ietf-lake-reqs]
Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia-
Carrillo, "Requirements for a Lightweight AKE for OSCORE",
Work in Progress, Internet-Draft, draft-ietf-lake-reqs-04,
8 June 2020, <https://www.ietf.org/archive/id/draft-ietf-
lake-reqs-04.txt>.
[I-D.ietf-lwig-security-protocol-comparison] [I-D.ietf-lwig-security-protocol-comparison]
Mattsson, J. P., Palombini, F., and M. Vucinic, Mattsson, J. P., Palombini, F., and M. Vucinic,
"Comparison of CoAP Security Protocols", draft-ietf-lwig- "Comparison of CoAP Security Protocols", Work in Progress,
security-protocol-comparison-05 (work in progress), Internet-Draft, draft-ietf-lwig-security-protocol-
November 2020. comparison-05, 2 November 2020,
<https://www.ietf.org/archive/id/draft-ietf-lwig-security-
protocol-comparison-05.txt>.
[I-D.ietf-rats-uccs]
Birkholz, H., O'Donoghue, J., Cam-Winget, N., and C.
Bormann, "A CBOR Tag for Unprotected CWT Claims Sets",
Work in Progress, Internet-Draft, draft-ietf-rats-uccs-01,
12 July 2021, <https://www.ietf.org/archive/id/draft-ietf-
rats-uccs-01.txt>.
[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-dtls13-43 (work in progress), April 1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
2021. dtls13-43, 30 April 2021, <https://www.ietf.org/internet-
drafts/draft-ietf-tls-dtls13-43.txt>.
[I-D.mattsson-cfrg-det-sigs-with-noise] [I-D.mattsson-cfrg-det-sigs-with-noise]
Mattsson, J. P., Thormarker, E., and S. Ruohomaa, Mattsson, J. P., 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", Work in Progress, Internet-Draft, draft-
(work in progress), March 2020. mattsson-cfrg-det-sigs-with-noise-02, 11 March 2020,
<https://www.ietf.org/archive/id/draft-mattsson-cfrg-det-
sigs-with-noise-02.txt>.
[I-D.selander-ace-ake-authz] [I-D.selander-ace-ake-authz]
Selander, G., Mattsson, J. P., Vucinic, M., Richardson, Selander, G., Mattsson, J. P., Vucinic, M., Richardson,
M., and A. Schellenbaum, "Lightweight Authorization for M., and A. Schellenbaum, "Lightweight Authorization for
Authenticated Key Exchange.", draft-selander-ace-ake- Authenticated Key Exchange.", Work in Progress, Internet-
authz-02 (work in progress), November 2020. Draft, draft-selander-ace-ake-authz-03, 4 May 2021,
<https://www.ietf.org/archive/id/draft-selander-ace-ake-
authz-03.txt>.
[Norrman20] [Norrman20]
Norrman, K., Sundararajan, V., and A. Bruni, "Formal Norrman, K., Sundararajan, V., and A. Bruni, "Formal
Analysis of EDHOC Key Establishment for Constrained IoT Analysis of EDHOC Key Establishment for Constrained IoT
Devices", September 2020, Devices", September 2020,
<https://arxiv.org/abs/2007.11427>. <https://arxiv.org/abs/2007.11427>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014, DOI 10.17487/RFC7228, May 2014,
skipping to change at page 55, line 22 skipping to change at page 59, line 27
[SP-800-56A] [SP-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", Schemes Using Discrete Logarithm Cryptography",
NIST Special Publication 800-56A Revision 3, April 2018, NIST Special Publication 800-56A Revision 3, April 2018,
<https://doi.org/10.6028/NIST.SP.800-56Ar3>. <https://doi.org/10.6028/NIST.SP.800-56Ar3>.
Appendix A. Use with OSCORE and Transfer over CoAP Appendix A. Use with OSCORE and Transfer over CoAP
This sppendix describes how to select EDHOC connection identifiers This appendix describes how to select EDHOC connection identifiers
and derive an OSCORE security context when OSCORE is used with EDHOC, and derive an OSCORE security context when OSCORE is used with EDHOC,
and how to transfer EDHOC messages over CoAP. and how to transfer EDHOC messages over CoAP.
A.1. Selecting EDHOC Connection Identifier A.1. Selecting EDHOC Connection Identifier
This section specifies a rule for converting from EDHOC connection This section specifies a rule for converting from EDHOC connection
identifier to OSCORE Sender/Recipient ID. (An identifier is Sender identifier to OSCORE Sender/Recipient ID. (An identifier is Sender
ID or Recipient ID depending on from which endpoint is the point of ID or Recipient ID depending on from which endpoint is the point of
view, see Section 3.1 of [RFC8613].) view, see Section 3.1 of [RFC8613].)
o If the EDHOC connection identifier is numeric, i.e. encoded as a * If the EDHOC connection identifier is numeric, i.e., encoded as a
CBOR integer on the wire, it is converted to a (naturally byte- CBOR integer on the wire, it is converted to a (naturally byte-
string shaped) OSCORE Sender/Recipient ID equal to its CBOR string shaped) OSCORE Sender/Recipient ID equal to its CBOR
encoded form. encoded form.
For example, a numeric C_R equal to 10 (0x0A in CBOR encoding) is For example, a numeric C_R equal to 10 (0x0A in CBOR encoding) is
converted to a (typically client) Sender ID equal to 0x0A, while a converted to a (typically client) Sender ID equal to 0x0A, while a
numeric C_I equal to -12 (0x2B in CBOR encoding) is converted to a numeric C_I equal to -12 (0x2B in CBOR encoding) is converted to a
(typically client) Sender ID equal to 0x2B. (typically client) Sender ID equal to 0x2B.
o If the EDHOC connection identifier is byte-valued, hence encoded * If the EDHOC connection identifier is byte-valued, hence encoded
as a CBOR byte string on the wire, it is converted to an OSCORE as a CBOR byte string on the wire, it is converted to an OSCORE
Sender/Recipient ID equal to the byte string. Sender/Recipient ID equal to the byte string.
For example, a byte-string valued C_R equal to 0xFF (0x41FF in CBOR For example, a byte-string valued C_R equal to 0xFF (0x41FF in CBOR
encoding) is converted to a (typically client) Sender ID equal to encoding) is converted to a (typically client) Sender ID equal to
0xFF. 0xFF.
Two EDHOC connection identifiers are called "equivalent" if and only Two EDHOC connection identifiers are called "equivalent" if and only
if, by applying the conversion above, they both result in the same if, by applying the conversion above, they both result in the same
OSCORE Sender/Recipient ID. For example, the two EDHOC connection OSCORE Sender/Recipient ID. For example, the two EDHOC connection
skipping to change at page 56, line 26 skipping to change at page 60, line 33
A.2. Deriving the OSCORE Security Context A.2. Deriving the OSCORE Security Context
This section specifies how to use EDHOC output to derive the OSCORE This section specifies how to use EDHOC output to derive the OSCORE
security context. security context.
After successful processing of EDHOC message_3, Client and Server After successful processing of EDHOC message_3, Client and Server
derive Security Context parameters for OSCORE as follows (see derive Security Context parameters for OSCORE as follows (see
Section 3.2 of [RFC8613]): Section 3.2 of [RFC8613]):
o The Master Secret and Master Salt are derived by using the EDHOC- * The Master Secret and Master Salt are derived by using the EDHOC-
Exporter interface, see Section 4.1. Exporter interface, see Section 4.3.
The EDHOC Exporter Labels for deriving the OSCORE Master Secret and The EDHOC Exporter Labels for deriving the OSCORE Master Secret and
the OSCORE Master Salt, are "OSCORE Master Secret" and "OSCORE Master the OSCORE Master Salt, are "OSCORE Master Secret" and "OSCORE Master
Salt", respectively. Salt", respectively.
The context parameter is h'' (0x40), the empty CBOR byte string. The context parameter is h'' (0x40), the empty CBOR byte string.
By default, key_length is the key length (in bytes) of the By default, key_length is the key length (in bytes) of the
application AEAD Algorithm of the selected cipher suite for the EDHOC application AEAD Algorithm of the selected cipher suite for the EDHOC
session. Also by default, salt_length has value 8. The Initiator session. Also by default, salt_length has value 8. The Initiator
and Responder MAY agree out-of-band on a longer key_length than the and Responder MAY agree out-of-band on a longer key_length than the
default and on a different salt_length. default and on a different salt_length.
Master Secret = EDHOC-Exporter( "OSCORE Master Secret", h'', key_length ) Master Secret = EDHOC-Exporter( "OSCORE Master Secret", , key_length )
Master Salt = EDHOC-Exporter( "OSCORE Master Salt", h'', salt_length ) Master Salt = EDHOC-Exporter( "OSCORE Master Salt", , salt_length )
o The AEAD Algorithm is the application AEAD algorithm of the * The AEAD Algorithm is the application AEAD algorithm of the
selected cipher suite for the EDHOC session. selected cipher suite for the EDHOC session.
o The HKDF Algorithm is the one based on the application hash * The HKDF Algorithm is the one based on the application hash
algorithm of the selected cipher suite for the EDHOC session. For algorithm of the selected cipher suite for the EDHOC session. For
example, if SHA-256 is the application hash algorithm of the example, if SHA-256 is the application hash algorithm of the
selected ciphersuite, HKDF SHA-256 is used as HKDF Algorithm in selected ciphersuite, HKDF SHA-256 is used as HKDF Algorithm in
the OSCORE Security Context. the OSCORE Security Context.
o In case the Client is Initiator and the Server is Responder, the * In case the Client is Initiator and the Server is Responder, the
Client's OSCORE Sender ID and the Server's OSCORE Sender ID are Client's OSCORE Sender ID and the Server's OSCORE Sender ID are
determined from the EDHOC connection identifiers C_R and C_I for determined from the EDHOC connection identifiers C_R and C_I for
the EDHOC session, respectively, by applying the conversion in the EDHOC session, respectively, by applying the conversion in
Appendix A.1. The reverse applies in case the Client is the Appendix A.1. The reverse applies in case the Client is the
Responder and the Server is the Initiator. Responder and the Server is the Initiator.
Client and Server use the parameters above to establish an OSCORE Client and Server use the parameters above to establish an OSCORE
Security Context, as per Section 3.2.1 of [RFC8613]. Security Context, as per Section 3.2.1 of [RFC8613].
From then on, Client and Server retrieve the OSCORE protocol state From then on, Client and Server retrieve the OSCORE protocol state
using the Recipient ID, and optionally other transport information using the Recipient ID, and optionally other transport information
such as the 5-tuple. such as the 5-tuple.
A.3. Transferring EDHOC over CoAP A.3. Transferring EDHOC over CoAP
This section specifies one instance for how EDHOC can be transferred This section specifies one instance for how EDHOC can be transferred
as an exchange of CoAP [RFC7252] messages. CoAP is a reliable as an exchange of CoAP [RFC7252] messages. CoAP is a reliable
transport that can preserve packet ordering and handle message transport that can preserve packet ordering and handle message
duplication. CoAP can also perform fragmentation and protect against duplication. CoAP can also perform fragmentation and protect against
denial of service attacks. According to this specification, EDHOC denial-of-service attacks. According to this specification, EDHOC
messages are carried in Confirmable messages, which is beneficial messages are carried in Confirmable messages, which is beneficial
especially if fragmentation is used. especially if fragmentation is used.
By default, the CoAP client is the Initiator and the CoAP server is By default, the CoAP client is the Initiator and the CoAP server is
the Responder, but the roles SHOULD be chosen to protect the most the Responder, but the roles SHOULD be chosen to protect the most
sensitive identity, see Section 7. According to this specification, sensitive identity, see Section 7. According to this specification,
EDHOC is transferred in POST requests and 2.04 (Changed) responses to EDHOC is transferred in POST requests and 2.04 (Changed) responses to
the Uri-Path: "/.well-known/edhoc". An application may define its the Uri-Path: "/.well-known/edhoc". An application may define its
own path that can be discovered, e.g., using resource directory own path that can be discovered, e.g., using resource directory
[I-D.ietf-core-resource-directory]. [I-D.ietf-core-resource-directory].
skipping to change at page 58, line 6 skipping to change at page 62, line 12
if EDHOC message_4 is used, it is sent from the server to the client if EDHOC message_4 is used, it is sent from the server to the client
in the payload of a 2.04 (Changed) response analogously to message_2. in the payload of a 2.04 (Changed) response analogously to message_2.
In order to correlate a message received from a client to a message In order to correlate a message received from a client to a message
previously sent by the server, messages sent by the client are previously sent by the server, messages sent by the client are
prepended with the CBOR serialization of the connection identifier prepended with the CBOR serialization of the connection identifier
which the server has chosen. This applies independently of if the which the server has chosen. This applies independently of if the
CoAP server is Responder or Initiator. For the default case when the CoAP server is Responder or Initiator. For the default case when the
server is Responder, the prepended connection identifier is C_R, and server is Responder, the prepended connection identifier is C_R, and
C_I if the server is Initiator. If message_1 is sent to the server, C_I if the server is Initiator. If message_1 is sent to the server,
the CBOR simple value "null" (0xf6) is sent in its place (given that the CBOR simple value "true" (0xf5) is sent in its place (given that
the server has not selected C_R yet). the server has not selected C_R yet).
These identifiers are encoded in CBOR and thus self-delimiting. They These identifiers are encoded in CBOR and thus self-delimiting. They
are sent in front of the actual EDHOC message, and only the part of are sent in front of the actual EDHOC message, and only the part of
the body following the identifier is used for EDHOC processing. the body following the identifier is used for EDHOC processing.
Consequently, the application/edhoc media type does not apply to Consequently, the application/edhoc media type does not apply to
these messages; their media type is unnamed. these messages; their media type is unnamed.
An example of a successful EDHOC exchange using CoAP is shown in An example of a successful EDHOC exchange using CoAP is shown in
Figure 9. In this case the CoAP Token enables correlation on the Figure 9. In this case the CoAP Token enables correlation on the
Initiator side, and the prepended C_R enables correlation on the Initiator side, and the prepended C_R enables correlation on the
Responder (server) side. Responder (server) side.
Client Server Client Server
| | | |
+--------->| Header: POST (Code=0.02) +--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc" | POST | Uri-Path: "/.well-known/edhoc"
| | Payload: null, EDHOC message_1 | | Payload: true, EDHOC message_1
| | | |
|<---------+ Header: 2.04 Changed |<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc | 2.04 | Content-Format: application/edhoc
| | Payload: EDHOC message_2 | | Payload: EDHOC message_2
| | | |
+--------->| Header: POST (Code=0.02) +--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc" | POST | Uri-Path: "/.well-known/edhoc"
| | Payload: C_R, EDHOC message_3 | | Payload: C_R, EDHOC message_3
| | | |
|<---------+ Header: 2.04 Changed |<---------+ Header: 2.04 Changed
| 2.04 | | 2.04 |
| | | |
Figure 9: Transferring EDHOC in CoAP when the Initiator is CoAP Figure 9: Transferring EDHOC in CoAP when the Initiator is CoAP
Client Client
The exchange in Figure 9 protects the client identity against active The exchange in Figure 9 protects the client identity against active
attackers and the server identity against passive attackers. attackers and the server identity against passive attackers.
An alternative exchange that protects the server identity against An alternative exchange that protects the server identity against
active attackers and the client identity against passive attackers is active attackers and the client identity against passive attackers is
shown in Figure 10. In this case the CoAP Token enables the shown in Figure 10. In this case the CoAP Token enables the
Responder to correlate message_2 and message_3, and the prepended C_I Responder to correlate message_2 and message_3, and the prepended C_I
enables correlation on the Initiator (server) side. If EDHOC enables correlation on the Initiator (server) side. If EDHOC
message_4 is used, C_I is prepended, and it is transported with CoAP message_4 is used, C_I is prepended, and it is transported with CoAP
skipping to change at page 59, line 23 skipping to change at page 63, line 31
| | | |
+--------->| Header: POST (Code=0.02) +--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc" | POST | Uri-Path: "/.well-known/edhoc"
| | Payload: C_I, EDHOC message_2 | | Payload: C_I, EDHOC message_2
| | | |
|<---------+ Header: 2.04 Changed |<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc | 2.04 | Content-Format: application/edhoc
| | Payload: EDHOC message_3 | | Payload: EDHOC message_3
| | | |
Figure 10: Transferring EDHOC in CoAP when the Initiator is CoAP Figure 10: Transferring EDHOC in CoAP when the Initiator is CoAP
Server Server
To protect against denial-of-service attacks, the CoAP server MAY To protect against denial-of-service attacks, the CoAP server MAY
respond to the first POST request with a 4.01 (Unauthorized) respond to the first POST request with a 4.01 (Unauthorized)
containing an Echo option [I-D.ietf-core-echo-request-tag]. This containing an Echo option [I-D.ietf-core-echo-request-tag]. This
forces the initiator to demonstrate its reachability at its apparent forces the initiator to demonstrate its reachability at its apparent
network address. If message fragmentation is needed, the EDHOC network address. If message fragmentation is needed, the EDHOC
messages may be fragmented using the CoAP Block-Wise Transfer messages may be fragmented using the CoAP Block-Wise Transfer
mechanism [RFC7959]. EDHOC does not restrict how error messages are mechanism [RFC7959].
transported with CoAP, as long as the appropriate error message can
to be transported in response to a message that failed (see EDHOC does not restrict how error messages are transported with CoAP,
Section 6). as long as the appropriate error message can to be transported in
response to a message that failed (see Section 6). EDHOC error
messages transported with CoAP are carried in the payload.
A.3.1. Transferring EDHOC and OSCORE over CoAP A.3.1. Transferring EDHOC and OSCORE over CoAP
When using EDHOC over CoAP for establishing an OSCORE Security
Context, EDHOC error messages sent as CoAP responses MUST be sent in
the payload of error responses, i.e., they MUST specify a CoAP error
response code. In particular, it is RECOMMENDED that such error
responses have response code either 4.00 (Bad Request) in case of
client error (e.g., due to a malformed EDHOC message), or 5.00
(Internal Server Error) in case of server error (e.g., due to failure
in deriving EDHOC key material). The Content-Format of the error
response MUST be set to application/edhoc.
A method for combining EDHOC and OSCORE protocols in two round-trips A method for combining EDHOC and OSCORE protocols in two round-trips
is specified in [I-D.ietf-core-oscore-edhoc]. is specified in [I-D.ietf-core-oscore-edhoc].
When using EDHOC over CoAP for establishing an OSCORE Security
Context, EDHOC error messages sent as CoAP responses MUST be error
responses, i.e., they MUST specify a CoAP error response code. In
particular, it is RECOMMENDED that such error responses have response
code either 4.00 (Bad Request) in case of client error (e.g., due to
a malformed EDHOC message), or 5.00 (Internal Server Error) in case
of server error (e.g., due to failure in deriving EDHOC key
material).
Appendix B. Compact Representation Appendix B. Compact Representation
As described in Section 4.2 of [RFC6090] the x-coordinate of an As described in Section 4.2 of [RFC6090] the x-coordinate of an
elliptic curve public key is a suitable representative for the entire elliptic curve public key is a suitable representative for the entire
point whenever scalar multiplication is used as a one-way function. point whenever scalar multiplication is used as a one-way function.
One example is ECDH with compact output, where only the x-coordinate One example is ECDH with compact output, where only the x-coordinate
of the computed value is used as the shared secret. of the computed value is used as the shared secret.
This section defines a format for compact representation based on the This section defines a format for compact representation based on the
Elliptic-Curve-Point-to-Octet-String Conversion defined in Elliptic-Curve-Point-to-Octet-String Conversion defined in
skipping to change at page 60, line 31 skipping to change at page 64, line 46
(log2 q) / 8 ) octets using the conversion routine specified in (log2 q) / 8 ) octets using the conversion routine specified in
Section 2.3.5 of [SECG]. Section 2.3.5 of [SECG].
2. Output M = X 2. Output M = X
The encoding of the point at infinity is not supported. Compact The encoding of the point at infinity is not supported. Compact
representation does not change any requirements on validation. If a representation does not change any requirements on validation. If a
y-coordinate is required for validation or compatibily with APIs the y-coordinate is required for validation or compatibily with APIs the
value ~yp SHALL be set to zero. For such use, the compact value ~yp SHALL be set to zero. For such use, the compact
representation can be transformed into the SECG point compressed representation can be transformed into the SECG point compressed
format by prepending it with the single byte 0x02 (i.e. M = 0x02 || format by prepending it with the single byte 0x02 (i.e., M = 0x02 ||
X). X).
Using compact representation have some security benefits. An Using compact representation have some security benefits. An
implementation does not need to check that the point is not the point implementation does not need to check that the point is not the point
at infinity (the identity element). Similarly, as not even the sign at infinity (the identity element). Similarly, as not even the sign
of the y-coordinate is encoded, compact representation trivially of the y-coordinate is encoded, compact representation trivially
avoids so called "benign malleability" attacks where an attacker avoids so called "benign malleability" attacks where an attacker
changes the sign, see [SECG]. changes the sign, see [SECG].
Appendix C. Use of CBOR, CDDL and COSE in EDHOC Appendix C. Use of CBOR, CDDL and COSE in EDHOC
This Appendix is intended to simplify for implementors not familiar This Appendix is intended to simplify for implementors not familiar
with CBOR [RFC8949], CDDL [RFC8610], COSE with CBOR [RFC8949], CDDL [RFC8610], COSE
[I-D.ietf-cose-rfc8152bis-struct], and HKDF [RFC5869]. [I-D.ietf-cose-rfc8152bis-struct], and HKDF [RFC5869].
C.1. CBOR and CDDL C.1. CBOR and CDDL
The Concise Binary Object Representation (CBOR) [RFC8949] is a data The Concise Binary Object Representation (CBOR) [RFC8949] is a data
format designed for small code size and small message size. CBOR format designed for small code size and small message size. CBOR
builds on the JSON data model but extends it by e.g. encoding binary builds on the JSON data model but extends it by e.g., encoding binary
data directly without base64 conversion. In addition to the binary data directly without base64 conversion. In addition to the binary
CBOR encoding, CBOR also has a diagnostic notation that is readable CBOR encoding, CBOR also has a diagnostic notation that is readable
and editable by humans. The Concise Data Definition Language (CDDL) and editable by humans. The Concise Data Definition Language (CDDL)
[RFC8610] provides a way to express structures for protocol messages [RFC8610] provides a way to express structures for protocol messages
and APIs that use CBOR. [RFC8610] also extends the diagnostic and APIs that use CBOR. [RFC8610] also extends the diagnostic
notation. notation.
CBOR data items are encoded to or decoded from byte strings using a CBOR data items are encoded to or decoded from byte strings using a
type-length-value encoding scheme, where the three highest order bits type-length-value encoding scheme, where the three highest order bits
of the initial byte contain information about the major type. CBOR of the initial byte contain information about the major type. CBOR
supports several different types of data items, in addition to supports several different types of data items, in addition to
integers (int, uint), simple values (e.g. null), byte strings (bstr), integers (int, uint), simple values, byte strings (bstr), and text
and text strings (tstr), CBOR also supports arrays [] of data items, strings (tstr), CBOR also supports arrays [] of data items, maps {}
maps {} of pairs of data items, and sequences [RFC8742] of data of pairs of data items, and sequences [RFC8742] of data items. Some
items. Some examples are given below. For a complete specification examples are given below.
and more examples, see [RFC8949] and [RFC8610]. We recommend
implementors to get used to CBOR by using the CBOR playground For a complete specification and more examples, see [RFC8949] and
[CborMe]. [RFC8610]. We recommend implementors to get used to CBOR by using
the CBOR playground [CborMe].
Diagnostic Encoded Type Diagnostic Encoded Type
------------------------------------------------------------------ ------------------------------------------------------------------
1 0x01 unsigned integer 1 0x01 unsigned integer
24 0x1818 unsigned integer 24 0x1818 unsigned integer
-24 0x37 negative integer -24 0x37 negative integer
-25 0x3818 negative integer -25 0x3818 negative integer
null 0xf6 simple value true 0xf5 simple value
h'12cd' 0x4212cd byte string h'12cd' 0x4212cd byte string
'12cd' 0x4431326364 byte string '12cd' 0x4431326364 byte string
"12cd" 0x6431326364 text string "12cd" 0x6431326364 text string
{ 4 : h'cd' } 0xa10441cd map { 4 : h'cd' } 0xa10441cd map
<< 1, 2, null >> 0x430102f6 byte string << 1, 2, true >> 0x430102f5 byte string
[ 1, 2, null ] 0x830102f6 array [ 1, 2, true ] 0x830102f5 array
( 1, 2, null ) 0x0102f6 sequence ( 1, 2, true ) 0x0102f5 sequence
1, 2, null 0x0102f6 sequence 1, 2, true 0x0102f5 sequence
------------------------------------------------------------------ ------------------------------------------------------------------
C.2. CDDL Definitions C.2. CDDL Definitions
This sections compiles the CDDL definitions for ease of reference. This sections compiles the CDDL definitions for ease of reference.
suite = int suite = int
SUITES_R : [ supported : 2* suite ] / suite ead = 1* (
type : int,
ext_authz_data : any,
)
message_1 = ( message_1 = (
METHOD : int, METHOD : int,
SUITES_I : [ selected : suite, supported : 2* suite ] / suite, SUITES_I : [ selected : suite, supported : 2* suite ] / suite,
G_X : bstr, G_X : bstr,
C_I : bstr / int, C_I : bstr / int,
? EAD ; EAD_1 ? EAD_1 : ead,
) )
message_2 = ( message_2 = (
data_2, G_Y_CIPHERTEXT_2 : bstr,
CIPHERTEXT_2 : bstr,
)
data_2 = (
G_Y : bstr,
C_R : bstr / int, C_R : bstr / int,
) )
message_3 = ( message_3 = (
CIPHERTEXT_3 : bstr, CIPHERTEXT_3 : bstr,
) )
message_4 = ( message_4 = (
CIPHERTEXT_4 : bstr, CIPHERTEXT_4 : bstr,
) )
SUITES_R : [ supported : 2* suite ] / suite
error = ( error = (
ERR_CODE : int, ERR_CODE : int,
ERR_INFO : any ERR_INFO : any,
) )
info = [ info = [
edhoc_aead_id : int / tstr, edhoc_aead_id : int / tstr,
transcript_hash : bstr, transcript_hash : bstr,
label : tstr, label : tstr,
length : uint * context : any,
length : uint,
] ]
C.3. COSE C.3. COSE
CBOR Object Signing and Encryption (COSE) CBOR Object Signing and Encryption (COSE)
[I-D.ietf-cose-rfc8152bis-struct] describes how to create and process [I-D.ietf-cose-rfc8152bis-struct] describes how to create and process
signatures, message authentication codes, and encryption using CBOR. signatures, message authentication codes, and encryption using CBOR.
COSE builds on JOSE, but is adapted to allow more efficient COSE builds on JOSE, but is adapted to allow more efficient
processing in constrained devices. EDHOC makes use of COSE_Key, processing in constrained devices. EDHOC makes use of COSE_Key,
COSE_Encrypt0, and COSE_Sign1 objects. COSE_Encrypt0, and COSE_Sign1 objects in the message processing:
Appendix D. Test Vectors
NOTE 0. These test vectors are compatible with versions -05 and -06
of the specification.
This appendix provides detailed test vectors to ease implementation
and ensure interoperability. In addition to hexadecimal, all CBOR
data items and sequences are given in CBOR diagnostic notation. The
test vectors use the default mapping to CoAP where the Initiator acts
as CoAP client (this means that corr = 1).
A more extensive test vector suite covering more combinations of
authentication method used between Initiator and Responder and
related code to generate them can be found at https://github.com/
lake-wg/edhoc/tree/master/test-vectors-05.
NOTE 1. In the previous and current test vectors the same name is
used for certain byte strings and their CBOR bstr encodings. For
example the transcript hash TH_2 is used to denote both the output of
the hash function and the input into the key derivation function,
whereas the latter is a CBOR bstr encoding of the former. Some
attempts are made to clarify that in this Appendix (e.g. using "CBOR
encoded"/"CBOR unencoded").
NOTE 2. If not clear from the context, remember that CBOR sequences
and CBOR arrays assume CBOR encoded data items as elements.
D.1. Test Vectors for EDHOC Authenticated with Signature Keys (x5t)
EDHOC with signature authentication and X.509 certificates is used.
In this test vector, the hash value 'x5t' is used to identify the
certificate. The optional C_1 in message_1 is omitted. No external
authorization data is sent in the message exchange.
method (Signature Authentication)
0
CoAP is used as transport and the Initiator acts as CoAP client:
corr (the Initiator can correlate message_1 and message_2)
1
From there, METHOD_CORR has the following value:
METHOD_CORR (4 * method + corr) (int)
1
The Initiator indicates only one cipher suite in the (potentially
truncated) list of cipher suites.
Supported Cipher Suites (1 byte)
00
The Initiator selected the indicated cipher suite.
Selected Cipher Suite (int)
0
Cipher suite 0 is supported by both the Initiator and the Responder,
see Section 3.6.
D.1.1. Message_1
The Initiator generates its ephemeral key pair.
X (Initiator's ephemeral private key) (32 bytes)
8f 78 1a 09 53 72 f8 5b 6d 9f 61 09 ae 42 26 11 73 4d 7d bf a0 06 9a 2d
f2 93 5b b2 e0 53 bf 35
G_X (Initiator's ephemeral public key, CBOR unencoded) (32 bytes)
89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6 ec 07 6b ba
02 59 d9 04 b7 ec 8b 0c
The Initiator chooses a connection identifier C_I:
Connection identifier chosen by Initiator (1 byte)
09
Note that since C_I is a byte string in the interval h'00' to h'2f',
it is encoded as the corresponding integer subtracted by 24. Thus
0x09 = 09, 9 - 24 = -15, and -15 in CBOR encoding is equal to 0x2e.
C_I (1 byte)
2e
Since no external authorization data is sent:
EAD_1 (0 bytes)
The list of supported cipher suites needs to contain the selected
cipher suite. The initiator truncates the list of supported cipher
suites to one cipher suite only. In this case there is only one
supported cipher suite indicated, 00.
Because one single selected cipher suite is conveyed, it is encoded
as an int instead of an array:
SUITES_I (int)
0
message_1 is constructed as the CBOR Sequence of the data items above
encoded as CBOR. In CBOR diagnostic notation:
message_1 =
(
1,
0,
h'898FF79A02067A16EA1ECCB90FA52246F5AA4DD6EC076BBA0259D904B7EC8B0C',
-15
)
Which as a CBOR encoded data item is:
message_1 (CBOR Sequence) (37 bytes)
01 00 58 20 89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6
ec 07 6b ba 02 59 d9 04 b7 ec 8b 0c 2e
D.1.2. Message_2
Since METHOD_CORR mod 4 equals 1, C_I is omitted from data_2.
The Responder generates the following ephemeral key pair.
Y (Responder's ephemeral private key) (32 bytes)
fd 8c d8 77 c9 ea 38 6e 6a f3 4f f7 e6 06 c4 b6 4c a8 31 c8 ba 33 13 4f
d4 cd 71 67 ca ba ec da
G_Y (Responder's ephemeral public key, CBOR unencoded) (32 bytes)
71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0 19 52
81 75 4c 5e bc af 30 1e
From G_X and Y or from G_Y and X the ECDH shared secret is computed:
G_XY (ECDH shared secret) (32 bytes)
2b b7 fa 6e 13 5b c3 35 d0 22 d6 34 cb fb 14 b3 f5 82 f3 e2 e3 af b2 b3
15 04 91 49 5c 61 78 2b
The key and nonce for calculating the 'ciphertext' are calculated as
follows, as specified in Section 4.
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK_2e = HMAC-SHA-256(salt, G_XY)
Salt is the empty byte string.
salt (0 bytes)
From there, PRK_2e is computed:
PRK_2e (32 bytes)
ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f
d8 2f be b7 99 71 39 4a
The Responder's sign/verify key pair is the following:
SK_R (Responder's private authentication key) (32 bytes)
df 69 27 4d 71 32 96 e2 46 30 63 65 37 2b 46 83 ce d5 38 1b fc ad cd 44
0a 24 c3 91 d2 fe db 94
PK_R (Responder's public authentication key) (32 bytes)
db d9 dc 8c d0 3f b7 c3 91 35 11 46 2b b2 38 16 47 7c 6b d8 d6 6e f5 a1
a0 70 ac 85 4e d7 3f d2
Since neither the Initiator nor the Responder authenticates with a
static Diffie-Hellman key, PRK_3e2m = PRK_2e
PRK_3e2m (32 bytes)
ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f
d8 2f be b7 99 71 39 4a
The Responder chooses a connection identifier C_R.
Connection identifier chosen by Responder (1 byte)
00
Note that since C_R is a byte string in the interval h'00' to h'2f',
it is encoded as the corresponding integer subtracted by 24. Thus
0x00 = 0, 0 - 24 = -24, and -24 in CBOR encoding is equal to 0x37.
C_R (1 byte)
37
Data_2 is constructed as the CBOR Sequence of G_Y and C_R, encoded as
CBOR byte strings. The CBOR diagnostic notation is:
data_2 =
(
h'71a3d599c21da18902a1aea810b2b6382ccd8d5f9bf0195281754c5ebcaf301e',
-24
)
Which as a CBOR encoded data item is:
data_2 (CBOR Sequence) (35 bytes)
58 20 71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0
19 52 81 75 4c 5e bc af 30 1e 37
From data_2 and message_1, compute the input to the transcript hash
TH_2 = H( H(message_1), data_2 ), as a CBOR Sequence of these 2 data
items.
Input to calculate TH_2 (CBOR Sequence) (72 bytes)
01 00 58 20 89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6
ec 07 6b ba 02 59 d9 04 b7 ec 8b 0c 2e 58 20 71 a3 d5 99 c2 1d a1 89 02
a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0 19 52 81 75 4c 5e bc af 30 1e 37
And from there, compute the transcript hash TH_2 = SHA-256(
H(message_1), data_2 )
TH_2 (CBOR unencoded) (32 bytes)
86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2
c1 53 c1 7f 8e 96 29 ff
The Responder's subject name is the empty string:
Responder's subject name (text string)
""
In this version of the test vectors CRED_R is not a DER encoded X.509
certificate, but a string of random bytes.
CRED_R (CBOR unencoded) (100 bytes)
c7 88 37 00 16 b8 96 5b db 20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40 6e 86
44 2b 87 ec 3f f2 45 b7 0a 47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e c9 d6
b0 53 4b 71 c2 b4 9e 4b f9 03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b 38 1e
98 db 71 41 08 41 5e 5c 50 db 78 97 4c 27 15 79 b0 16 33 a3 ef 62 71 be
5c 22 5e b2
CRED_R is defined to be the CBOR bstr containing the credential of
the Responder.
CRED_R (102 bytes)
58 64 c7 88 37 00 16 b8 96 5b db 20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40
6e 86 44 2b 87 ec 3f f2 45 b7 0a 47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e
c9 d6 b0 53 4b 71 c2 b4 9e 4b f9 03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b
38 1e 98 db 71 41 08 41 5e 5c 50 db 78 97 4c 27 15 79 b0 16 33 a3 ef 62
71 be 5c 22 5e b2
And because certificates are identified by a hash value with the
'x5t' parameter, ID_CRED_R is the following:
ID_CRED_R = { 34 : COSE_CertHash }. In this example, the hash
algorithm used is SHA-2 256-bit with hash truncated to 64-bits (value
-15). The hash value is calculated over the CBOR unencoded CRED_R.
The CBOR diagnostic notation is:
ID_CRED_R =
{
34: [-15, h'6844078A53F312F5']
}
which when encoded as a CBOR map becomes:
ID_CRED_R (14 bytes)
a1 18 22 82 2e 48 68 44 07 8a 53 f3 12 f5
Since no external authorization data is sent:
EAD_2 (0 bytes)
The plaintext is defined as the empty string:
P_2m (0 bytes)
The Enc_structure is defined as follows: [ "Encrypt0",
<< ID_CRED_R >>, << TH_2, CRED_R >> ], indicating that ID_CRED_R is
encoded as a CBOR byte string, and that the concatenation of the CBOR
byte strings TH_2 and CRED_R is wrapped as a CBOR bstr. The CBOR
diagnostic notation is the following:
A_2m =
[
"Encrypt0",
h'A11822822E486844078A53F312F5',
h'5820864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF
5864C788370016B8965BDB2074BFF82E5A20E09BEC21F8406E86442B87EC3FF245B70A
47624DC9CDC6824B2A4C52E95EC9D6B0534B71C2B49E4BF9031500CEE6869979C297BB
5A8B381E98DB714108415E5C50DB78974C271579B01633A3EF6271BE5C225EB2'
]
Which encodes to the following byte string to be used as Additional
Authenticated Data:
A_2m (CBOR-encoded) (163 bytes)
83 68 45 6e 63 72 79 70 74 30 4e a1 18 22 82 2e 48 68 44 07 8a 53 f3 12
f5 58 88 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99
72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 58 64 c7 88 37 00 16 b8 96 5b db
20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40 6e 86 44 2b 87 ec 3f f2 45 b7 0a
47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e c9 d6 b0 53 4b 71 c2 b4 9e 4b f9
03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b 38 1e 98 db 71 41 08 41 5e 5c 50
db 78 97 4c 27 15 79 b0 16 33 a3 ef 62 71 be 5c 22 5e b2
info for K_2m is defined as follows in CBOR diagnostic notation:
info for K_2m =
[
10,
h'864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF',
"K_2m",
16
]
Which as a CBOR encoded data item is:
info for K_2m (CBOR-encoded) (42 bytes)
84 0a 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72
d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 64 4b 5f 32 6d 10
From these parameters, K_2m is computed. Key K_2m is the output of
HKDF-Expand(PRK_3e2m, info, L), where L is the length of K_2m, so 16
bytes.
K_2m (16 bytes)
80 cc a7 49 ab 58 f5 69 ca 35 da ee 05 be d1 94
info for IV_2m is defined as follows, in CBOR diagnostic notation (10
is the COSE algorithm no. of the AEAD algorithm in the selected
cipher suite 0):
info for IV_2m =
[
10,
h'864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF',
"IV_2m",
13
]
Which as a CBOR encoded data item is:
info for IV_2m (CBOR-encoded) (43 bytes)
84 0a 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72
d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 65 49 56 5f 32 6d 0d
From these parameters, IV_2m is computed. IV_2m is the output of
HKDF-Expand(PRK_3e2m, info, L), where L is the length of IV_2m, so 13
bytes.
IV_2m (13 bytes)
c8 1e 1a 95 cc 93 b3 36 69 6e d5 02 55
Finally, COSE_Encrypt0 is computed from the parameters above.
o protected header = CBOR-encoded ID_CRED_R
o external_aad = A_2m
o empty plaintext = P_2m
MAC_2 (CBOR unencoded) (8 bytes)
fa bb a4 7e 56 71 a1 82
To compute the Signature_or_MAC_2, the key is the private
authentication key of the Responder and the message M_2 to be signed
= [ "Signature1", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >>, MAC_2
]. ID_CRED_R is encoded as a CBOR byte string, the concatenation of
the CBOR byte strings TH_2 and CRED_R is wrapped as a CBOR bstr, and
MAC_2 is encoded as a CBOR bstr.
M_2 =
[
"Signature1",
h'A11822822E486844078A53F312F5',
h'5820864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629F
F5864C788370016B8965BDB2074BFF82E5A20E09BEC21F8406E86442B87EC3FF245B7
0A47624DC9CDC6824B2A4C52E95EC9D6B0534B71C2B49E4BF9031500CEE6869979C29
7BB5A8B381E98DB714108415E5C50DB78974C271579B01633A3EF6271BE5C225EB2',
h'FABBA47E5671A182'
]
Which as a CBOR encoded data item is:
M_2 (174 bytes)
84 6a 53 69 67 6e 61 74 75 72 65 31 4e a1 18 22 82 2e 48 68 44 07 8a 53
f3 12 f5 58 88 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a
ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 58 64 c7 88 37 00 16 b8 96
5b db 20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40 6e 86 44 2b 87 ec 3f f2 45
b7 0a 47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e c9 d6 b0 53 4b 71 c2 b4 9e
4b f9 03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b 38 1e 98 db 71 41 08 41 5e
5c 50 db 78 97 4c 27 15 79 b0 16 33 a3 ef 62 71 be 5c 22 5e b2 48 fa bb
a4 7e 56 71 a1 82
Since the method = 0, Signature_or_MAC_2 is a signature. The
algorithm with selected cipher suite 0 is Ed25519 and the output is
64 bytes.
Signature_or_MAC_2 (CBOR unencoded) (64 bytes)
1f 17 00 6a 98 48 c9 77 cb bd ca a7 57 b6 fd 46 82 c8 17 39 e1 5c 99 37
c2 1c f5 e9 a0 e6 03 9f 54 fd 2a 6c 3a 11 18 f2 b9 d8 eb cd 48 23 48 b9
9c 3e d7 ed 1b d9 80 6c 93 c8 90 68 e8 36 b4 0f
CIPHERTEXT_2 is the ciphertext resulting from XOR between plaintext
and KEYSTREAM_2 which is derived from TH_2 and the pseudorandom key
PRK_2e.
o plaintext = CBOR Sequence of the items ID_CRED_R and
Signature_or_MAC_2 encoded as CBOR byte strings, in this order
(EAD_2 is empty).
The plaintext is the following:
P_2e (CBOR Sequence) (80 bytes)
a1 18 22 82 2e 48 68 44 07 8a 53 f3 12 f5 58 40 1f 17 00 6a 98 48 c9 77
cb bd ca a7 57 b6 fd 46 82 c8 17 39 e1 5c 99 37 c2 1c f5 e9 a0 e6 03 9f
54 fd 2a 6c 3a 11 18 f2 b9 d8 eb cd 48 23 48 b9 9c 3e d7 ed 1b d9 80 6c
93 c8 90 68 e8 36 b4 0f
KEYSTREAM_2 = HKDF-Expand( PRK_2e, info, length ), where length is
the length of the plaintext, so 80.
info for KEYSTREAM_2 =
[
10,
h'864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF',
"KEYSTREAM_2",
80
]
Which as a CBOR encoded data item is:
info for KEYSTREAM_2 (CBOR-encoded) (50 bytes)
84 0a 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72
d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 6b 4b 45 59 53 54 52 45 41 4d 5f 32
18 50
From there, KEYSTREAM_2 is computed:
KEYSTREAM_2 (80 bytes)
ae ea 8e af 50 cf c6 70 09 da e8 2d 8d 85 b0 e7 60 91 bf 0f 07 0b 79 53
6c 83 23 dc 3d 9d 61 13 10 35 94 63 f4 4b 12 4b ea b3 a1 9d 09 93 82 d7
30 80 17 f4 92 62 06 e4 f5 44 9b 9f c9 24 bc b6 bd 78 ec 45 0a 66 83 fb
8a 2f 5f 92 4f c4 40 4f
Using the parameters above, the ciphertext CIPHERTEXT_2 can be
computed:
CIPHERTEXT_2 (CBOR unencoded) (80 bytes)
0f f2 ac 2d 7e 87 ae 34 0e 50 bb de 9f 70 e8 a7 7f 86 bf 65 9f 43 b0 24
a7 3e e9 7b 6a 2b 9c 55 92 fd 83 5a 15 17 8b 7c 28 af 54 74 a9 75 81 48
64 7d 3d 98 a8 73 1e 16 4c 9c 70 52 81 07 f4 0f 21 46 3b a8 11 bf 03 97
19 e7 cf fa a7 f2 f4 40
message_2 is the CBOR Sequence of data_2 and CIPHERTEXT_2, in this
order:
message_2 =
(
data_2,
h'0FF2AC2D7E87AE340E50BBDE9F70E8A77F86BF659F43B024A73EE97B6A2B9C5592FD
835A15178B7C28AF5474A9758148647D3D98A8731E164C9C70528107F40F21463BA811
BF039719E7CFFAA7F2F440'
)
Which as a CBOR encoded data item is:
message_2 (CBOR Sequence) (117 bytes)
58 20 71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0
19 52 81 75 4c 5e bc af 30 1e 37 58 50 0f f2 ac 2d 7e 87 ae 34 0e 50 bb
de 9f 70 e8 a7 7f 86 bf 65 9f 43 b0 24 a7 3e e9 7b 6a 2b 9c 55 92 fd 83
5a 15 17 8b 7c 28 af 54 74 a9 75 81 48 64 7d 3d 98 a8 73 1e 16 4c 9c 70
52 81 07 f4 0f 21 46 3b a8 11 bf 03 97 19 e7 cf fa a7 f2 f4 40
D.1.3. Message_3
Since corr equals 1, C_R is not omitted from data_3.
The Initiator's sign/verify key pair is the following:
SK_I (Initiator's private authentication key) (32 bytes)
2f fc e7 a0 b2 b8 25 d3 97 d0 cb 54 f7 46 e3 da 3f 27 59 6e e0 6b 53 71
48 1d c0 e0 12 bc 34 d7
PK_I (Responder's public authentication key) (32 bytes)
38 e5 d5 45 63 c2 b6 a4 ba 26 f3 01 5f 61 bb 70 6e 5c 2e fd b5 56 d2 e1
69 0b 97 fc 3c 6d e1 49
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK_4x3m = HMAC-SHA-256 (PRK_3e2m, G_IY)
PRK_4x3m (32 bytes)
ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f
d8 2f be b7 99 71 39 4a
data 3 is equal to C_R.
data_3 (CBOR Sequence) (1 byte)
37
From data_3, CIPHERTEXT_2, and TH_2, compute the input to the
transcript hash TH_3 = H( H(TH_2 , CIPHERTEXT_2), data_3), as a CBOR
Sequence of 2 data items.
Input to calculate TH_3 (CBOR Sequence) (117 bytes)
58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76
d2 c2 c1 53 c1 7f 8e 96 29 ff 58 50 0f f2 ac 2d 7e 87 ae 34 0e 50 bb de
9f 70 e8 a7 7f 86 bf 65 9f 43 b0 24 a7 3e e9 7b 6a 2b 9c 55 92 fd 83 5a
15 17 8b 7c 28 af 54 74 a9 75 81 48 64 7d 3d 98 a8 73 1e 16 4c 9c 70 52
81 07 f4 0f 21 46 3b a8 11 bf 03 97 19 e7 cf fa a7 f2 f4 40 37
And from there, compute the transcript hash TH_3 = SHA-256( H(TH_2 ,
CIPHERTEXT_2), data_3)
TH_3 (CBOR unencoded) (32 bytes)
f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70
b6 f5 1e 68 e2 ae bb 60
The Initiator's subject name is the empty string:
Initiator's subject name (text string)
""
In this version of the test vectors CRED_I is not a DER encoded X.509
certificate, but a string of random bytes.
CRED_I (CBOR unencoded) (101 bytes)
54 13 20 4c 3e bc 34 28 a6 cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce 7e c6
56 1e 52 43 3a a5 5e 71 f1 fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1 76 60
88 09 84 49 cb 84 8f fc 79 5f 88 af c4 9c be 8a fd d1 ba 00 9f 21 67 5e
8f 6c 77 a4 a2 c3 01 95 60 1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44 48 65
02 ff 7b dd a6
CRED_I is defined to be the CBOR bstr containing the credential of
the Initiator.
CRED_I (103 bytes)
58 65 54 13 20 4c 3e bc 34 28 a6 cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce
7e c6 56 1e 52 43 3a a5 5e 71 f1 fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1
76 60 88 09 84 49 cb 84 8f fc 79 5f 88 af c4 9c be 8a fd d1 ba 00 9f 21
67 5e 8f 6c 77 a4 a2 c3 01 95 60 1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44
48 65 02 ff 7b dd a6
And because certificates are identified by a hash value with the
'x5t' parameter, ID_CRED_I is the following:
ID_CRED_I = { 34 : COSE_CertHash }. In this example, the hash
algorithm used is SHA-2 256-bit with hash truncated to 64-bits (value
-15). The hash value is calculated over the CBOR unencoded CRED_I.
ID_CRED_I =
{
34: [-15, h'705D5845F36FC6A6']
}
which when encoded as a CBOR map becomes:
ID_CRED_I (14 bytes)
a1 18 22 82 2e 48 70 5d 58 45 f3 6f c6 a6
Since no external authorization data is exchanged:
EAD_3 (0 bytes)
The plaintext of the COSE_Encrypt is the empty string:
P_3m (0 bytes)
The associated data is the following: [ "Encrypt0", << ID_CRED_I >>,
<< TH_3, CRED_I, ? EAD_3 >> ].
A_3m (CBOR-encoded) (164 bytes)
83 68 45 6e 63 72 79 70 74 30 4e a1 18 22 82 2e 48 70 5d 58 45 f3 6f c6
a6 58 89 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c
0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 58 65 54 13 20 4c 3e bc 34 28 a6
cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce 7e c6 56 1e 52 43 3a a5 5e 71 f1
fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1 76 60 88 09 84 49 cb 84 8f fc 79
5f 88 af c4 9c be 8a fd d1 ba 00 9f 21 67 5e 8f 6c 77 a4 a2 c3 01 95 60
1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44 48 65 02 ff 7b dd a6
Info for K_3m is computed as follows:
info for K_3m =
[
10,
h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60',
"K_3m",
16
]
Which as a CBOR encoded data item is:
info for K_3m (CBOR-encoded) (42 bytes)
84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f
65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 64 4b 5f 33 6d 10
From these parameters, K_3m is computed. Key K_3m is the output of
HKDF-Expand(PRK_4x3m, info, L), where L is the length of K_2m, so 16
bytes.
K_3m (16 bytes)
83 a9 c3 88 02 91 2e 7f 8f 0d 2b 84 14 d1 e5 2c
Nonce IV_3m is the output of HKDF-Expand(PRK_4x3m, info, L), where L
= 13 bytes.
Info for IV_3m is defined as follows:
info for IV_3m =
[
10,
h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60',
"IV_3m",
13
]
Which as a CBOR encoded data item is:
info for IV_3m (CBOR-encoded) (43 bytes)
84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f
65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 65 49 56 5f 33 6d 0d
From these parameters, IV_3m is computed:
IV_3m (13 bytes)
9c 83 9c 0e e8 36 42 50 5a 8e 1c 9f b2
MAC_3 is the 'ciphertext' of the COSE_Encrypt0:
MAC_3 (CBOR unencoded) (8 bytes)
2f a1 e3 9e ae 7d 5f 8d
Since the method = 0, Signature_or_MAC_3 is a signature. The
algorithm with selected cipher suite 0 is Ed25519.
o The message M_3 to be signed = [ "Signature1", << ID_CRED_I >>,
<< TH_3, CRED_I >>, MAC_3 ], i.e. ID_CRED_I encoded as CBOR bstr,
the concatenation of the CBOR byte strings TH_3 and CRED_I wrapped
as a CBOR bstr, and MAC_3 encoded as a CBOR bstr.
o The signing key is the private authentication key of the
Initiator.
M_3 =
[
"Signature1",
h'A11822822E48705D5845F36FC6A6',
h'5820F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB6
058655413204C3EBC3428A6CF57E24C9DEF59651770449BCE7EC6561E52433AA55E71
F1FA34B22A9CA4A1E12924EAE1D1766088098449CB848FFC795F88AFC49CBE8AFDD1B
A009F21675E8F6C77A4A2C30195601F6F0A0852978BD43D28207D44486502FF7BDD
A6',
h'2FA1E39EAE7D5F8D']
Which as a CBOR encoded data item is:
M_3 (175 bytes)
84 6a 53 69 67 6e 61 74 75 72 65 31 4e a1 18 22 82 2e 48 70 5d 58 45 f3
6f c6 a6 58 89 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea
9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 58 65 54 13 20 4c 3e bc 34
28 a6 cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce 7e c6 56 1e 52 43 3a a5 5e
71 f1 fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1 76 60 88 09 84 49 cb 84 8f
fc 79 5f 88 af c4 9c be 8a fd d1 ba 00 9f 21 67 5e 8f 6c 77 a4 a2 c3 01
95 60 1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44 48 65 02 ff 7b dd a6 48 2f
a1 e3 9e ae 7d 5f 8d
From there, the 64 byte signature can be computed:
Signature_or_MAC_3 (CBOR unencoded) (64 bytes)
ab 9f 7b bd eb c4 eb f8 a3 d3 04 17 9b cc a3 9d 9c 8a 76 73 65 76 fb 3c
32 d2 fa c7 e2 59 34 e5 33 dc c7 02 2e 4d 68 61 c8 f5 fe cb e9 2d 17 4e
b2 be af 0a 59 a4 15 84 37 2f 43 2e 6b f4 7b 04
Finally, the outer COSE_Encrypt0 is computed.
The plaintext is the CBOR Sequence of the items ID_CRED_I and the
CBOR encoded Signature_or_MAC_3, in this order (EAD_3 is empty).
P_3ae (CBOR Sequence) (80 bytes)
a1 18 22 82 2e 48 70 5d 58 45 f3 6f c6 a6 58 40 ab 9f 7b bd eb c4 eb f8
a3 d3 04 17 9b cc a3 9d 9c 8a 76 73 65 76 fb 3c 32 d2 fa c7 e2 59 34 e5
33 dc c7 02 2e 4d 68 61 c8 f5 fe cb e9 2d 17 4e b2 be af 0a 59 a4 15 84
37 2f 43 2e 6b f4 7b 04
The Associated data A is the following: Associated data A = [
"Encrypt0", h'', TH_3 ]
A_3ae (CBOR-encoded) (45 bytes)
83 68 45 6e 63 72 79 70 74 30 40 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63
29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60
Key K_3ae is the output of HKDF-Expand(PRK_3e2m, info, L).
info is defined as follows:
info for K_3ae =
[
10,
h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60',
"K_3ae",
16
]
Which as a CBOR encoded data item is:
info for K_3ae (CBOR-encoded) (43 bytes)
84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f
65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 65 4b 5f 33 61 65 10
L is the length of K_3ae, so 16 bytes.
From these parameters, K_3ae is computed:
K_3ae (16 bytes)
b8 79 9f e3 d1 50 4f d8 eb 22 c4 72 62 cd bb 05
Nonce IV_3ae is the output of HKDF-Expand(PRK_3e2m, info, L).
info is defined as follows:
info for IV_3ae =
[
10,
h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60',
"IV_3ae",
13
]
Which as a CBOR encoded data item is:
info for IV_3ae (CBOR-encoded) (44 bytes)
84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f
65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 66 49 56 5f 33 61 65 0d
L is the length of IV_3ae, so 13 bytes.
From these parameters, IV_3ae is computed:
IV_3ae (13 bytes)
74 c7 de 41 b8 4a 5b b7 19 0a 85 98 dc
Using the parameters above, the 'ciphertext' CIPHERTEXT_3 can be
computed:
CIPHERTEXT_3 (CBOR unencoded) (88 bytes)
f5 f6 de bd 82 14 05 1c d5 83 c8 40 96 c4 80 1d eb f3 5b 15 36 3d d1 6e
bd 85 30 df dc fb 34 fc d2 eb 6c ad 1d ac 66 a4 79 fb 38 de aa f1 d3 0a
7e 68 17 a2 2a b0 4f 3d 5b 1e 97 2a 0d 13 ea 86 c6 6b 60 51 4c 96 57 ea
89 c5 7b 04 01 ed c5 aa 8b bc ab 81 3c c5 d6 e7
From the parameter above, message_3 is computed, as the CBOR Sequence
of the following CBOR encoded data items: (C_R, CIPHERTEXT_3).
message_3 =
(
-24,
h'F5F6DEBD8214051CD583C84096C4801DEBF35B15363DD16EBD8530DFDCFB34FCD2EB
6CAD1DAC66A479FB38DEAAF1D30A7E6817A22AB04F3D5B1E972A0D13EA86C66B60514C
9657EA89C57B0401EDC5AA8BBCAB813CC5D6E7'
)
Which encodes to the following byte string:
message_3 (CBOR Sequence) (91 bytes)
37 58 58 f5 f6 de bd 82 14 05 1c d5 83 c8 40 96 c4 80 1d eb f3 5b 15 36
3d d1 6e bd 85 30 df dc fb 34 fc d2 eb 6c ad 1d ac 66 a4 79 fb 38 de aa
f1 d3 0a 7e 68 17 a2 2a b0 4f 3d 5b 1e 97 2a 0d 13 ea 86 c6 6b 60 51 4c
96 57 ea 89 c5 7b 04 01 ed c5 aa 8b bc ab 81 3c c5 d6 e7
D.1.4. OSCORE Security Context Derivation
From here, the Initiator and the Responder can derive an OSCORE
Security Context, using the EDHOC-Exporter interface.
From TH_3 and CIPHERTEXT_3, compute the input to the transcript hash
TH_4 = H( TH_3, CIPHERTEXT_3 ), as a CBOR Sequence of these 2 data
items.
Input to calculate TH_4 (CBOR Sequence) (124 bytes)
58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c
30 70 b6 f5 1e 68 e2 ae bb 60 58 58 f5 f6 de bd 82 14 05 1c d5 83 c8 40
96 c4 80 1d eb f3 5b 15 36 3d d1 6e bd 85 30 df dc fb 34 fc d2 eb 6c ad
1d ac 66 a4 79 fb 38 de aa f1 d3 0a 7e 68 17 a2 2a b0 4f 3d 5b 1e 97 2a
0d 13 ea 86 c6 6b 60 51 4c 96 57 ea 89 c5 7b 04 01 ed c5 aa 8b bc ab 81
3c c5 d6 e7
And from there, compute the transcript hash TH_4 = SHA-256(TH_3 ,
CIPHERTEXT_4)
TH_4 (CBOR unencoded) (32 bytes)
3b 69 a6 7f ec 7e 73 6c c1 a9 52 6c da 00 02 d4 09 f5 b9 ea 0a 2b e9 60
51 a6 e3 0d 93 05 fd 51
The Master Secret and Master Salt are derived as follows:
Master Secret = EDHOC-Exporter( "OSCORE Master Secret", 16 ) = EDHOC-
KDF(PRK_4x3m, TH_4, "OSCORE Master Secret", 16) = HKDF-Expand(
PRK_4x3m, info_ms, 16 )
Master Salt = EDHOC-Exporter( "OSCORE Master Salt", 8 ) = EDHOC-
KDF(PRK_4x3m, TH_4, "OSCORE Master Salt", 8) = HKDF-Expand( PRK_4x3m,
info_salt, 8 )
info_ms for OSCORE Master Secret is defined as follows:
info_ms = [
10,
h'3B69A67FEC7E736CC1A9526CDA0002D409F5B9EA0A2BE96051A6E30D9305FD51',
"OSCORE Master Secret",
16
]
Which as a CBOR encoded data item is:
info_ms for OSCORE Master Secret (CBOR-encoded) (58 bytes)
84 0a 58 20 3b 69 a6 7f ec 7e 73 6c c1 a9 52 6c da 00 02 d4 09 f5 b9 ea
0a 2b e9 60 51 a6 e3 0d 93 05 fd 51 74 4f 53 43 4f 52 45 20 4d 61 73 74
65 72 20 53 65 63 72 65 74 10
info_salt for OSCORE Master Salt is defined as follows:
info_salt = [
10,
h'3B69A67FEC7E736CC1A9526CDA0002D409F5B9EA0A2BE96051A6E30D9305FD51',
"OSCORE Master Salt",
8
]
Which as a CBOR encoded data item is:
info for OSCORE Master Salt (CBOR-encoded) (56 Bytes)
84 0a 58 20 3b 69 a6 7f ec 7e 73 6c c1 a9 52 6c da 00 02 d4 09 f5 b9 ea
0a 2b e9 60 51 a6 e3 0d 93 05 fd 51 72 4f 53 43 4f 52 45 20 4d 61 73 74
65 72 20 53 61 6c 74 08
From these parameters, OSCORE Master Secret and OSCORE Master Salt
are computed:
OSCORE Master Secret (16 bytes)
96 aa 88 ce 86 5e ba 1f fa f3 89 64 13 2c c4 42
OSCORE Master Salt (8 bytes)
5e c3 ee 41 7c fb ba e9
The client's OSCORE Sender ID is C_R and the server's OSCORE Sender
ID is C_I.
Client's OSCORE Sender ID (1 byte)
00
Server's OSCORE Sender ID (1 byte)
09
The AEAD Algorithm and the hash algorithm are the application AEAD
and hash algorithms in the selected cipher suite.
OSCORE AEAD Algorithm (int)
10
OSCORE Hash Algorithm (int)
-16
D.2. Test Vectors for EDHOC Authenticated with Static Diffie-Hellman
Keys
EDHOC with static Diffie-Hellman keys and raw public keys is used.
In this test vector, a key identifier is used to identify the raw
public key. The optional C_1 in message_1 is omitted. No external
authorization data is sent in the message exchange.
method (Static DH Based Authentication)
3
CoAP is used as transport and the Initiator acts as CoAP client:
corr (the Initiator can correlate message_1 and message_2)
1
From there, METHOD_CORR has the following value:
METHOD_CORR (4 * method + corr) (int)
13
The Initiator indicates only one cipher suite in the (potentially
truncated) list of cipher suites.
Supported Cipher Suites (1 byte)
00
The Initiator selected the indicated cipher suite.
Selected Cipher Suite (int)
0
Cipher suite 0 is supported by both the Initiator and the Responder,
see Section 3.6.
D.2.1. Message_1
The Initiator generates its ephemeral key pair.
X (Initiator's ephemeral private key) (32 bytes)
ae 11 a0 db 86 3c 02 27 e5 39 92 fe b8 f5 92 4c 50 d0 a7 ba 6e ea b4 ad
1f f2 45 72 f4 f5 7c fa
G_X (Initiator's ephemeral public key, CBOR unencoded) (32 bytes)
8d 3e f5 6d 1b 75 0a 43 51 d6 8a c2 50 a0 e8 83 79 0e fc 80 a5 38 a4 44
ee 9e 2b 57 e2 44 1a 7c
The Initiator chooses a connection identifier C_I:
Connection identifier chosen by Initiator (1 byte)
16
Note that since C_I is a byte string in the interval h'00' to h'2f',
it is encoded as the corresponding integer - 24, i.e. 0x16 = 22, 22 -
24 = -2, and -2 in CBOR encoding is equal to 0x21.
C_I (1 byte)
21
Since no external authorization data is sent:
EAD_1 (0 bytes)
Since the list of supported cipher suites needs to contain the
selected cipher suite, the initiator truncates the list of supported
cipher suites to one cipher suite only, 00.
Because one single selected cipher suite is conveyed, it is encoded
as an int instead of an array:
SUITES_I (int)
0
message_1 is constructed as the CBOR Sequence of the data items above
encoded as CBOR. In CBOR diagnostic notation:
message_1 =
(
13,
0,
h'8D3EF56D1B750A4351D68AC250A0E883790EFC80A538A444EE9E2B57E2441A7C',
-2
)
Which as a CBOR encoded data item is:
message_1 (CBOR Sequence) (37 bytes)
0d 00 58 20 8d 3e f5 6d 1b 75 0a 43 51 d6 8a c2 50 a0 e8 83 79 0e fc 80
a5 38 a4 44 ee 9e 2b 57 e2 44 1a 7c 21
D.2.2. Message_2
Since METHOD_CORR mod 4 equals 1, C_I is omitted from data_2.
The Responder generates the following ephemeral key pair.
Y (Responder's ephemeral private key) (32 bytes)
c6 46 cd dc 58 12 6e 18 10 5f 01 ce 35 05 6e 5e bc 35 f4 d4 cc 51 07 49
a3 a5 e0 69 c1 16 16 9a
G_Y (Responder's ephemeral public key, CBOR unencoded) (32 bytes)
52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db fc 33
01 04 70 69 45 1b af 35
From G_X and Y or from G_Y and X the ECDH shared secret is computed:
G_XY (ECDH shared secret) (32 bytes)
de fc 2f 35 69 10 9b 3d 1f a4 a7 3d c5 e2 fe b9 e1 15 0d 90 c2 5e e2 f0
66 c2 d8 85 f4 f8 ac 4e
The key and nonce for calculating the 'ciphertext' are calculated as
follows, as specified in Section 4.
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK_2e = HMAC-SHA-256(salt, G_XY)
Salt is the empty byte string.
salt (0 bytes)
From there, PRK_2e is computed:
PRK_2e (32 bytes)
93 9f cb 05 6d 2e 41 4f 1b ec 61 04 61 99 c2 c7 63 d2 7f 0c 3d 15 fa 16
71 fa 13 4e 0d c5 a0 4d
The Responder's static Diffie-Hellman key pair is the following:
R (Responder's private authentication key) (32 bytes)
bb 50 1a ac 67 b9 a9 5f 97 e0 ed ed 6b 82 a6 62 93 4f bb fc 7a d1 b7 4c
1f ca d6 6a 07 94 22 d0
G_R (Responder's public authentication key) (32 bytes)
a3 ff 26 35 95 be b3 77 d1 a0 ce 1d 04 da d2 d4 09 66 ac 6b cb 62 20 51
b8 46 59 18 4d 5d 9a 32
Since the Responder authenticates with a static Diffie-Hellman key,
PRK_3e2m = HKDF-Extract( PRK_2e, G_RX ), where G_RX is the ECDH
shared secret calculated from G_R and X, or G_X and R.
From the Responder's authentication key and the Initiator's ephemeral
key (see Appendix D.2.1), the ECDH shared secret G_RX is calculated.
G_RX (ECDH shared secret) (32 bytes)
21 c7 ef f4 fb 69 fa 4b 67 97 d0 58 84 31 5d 84 11 a3 fd a5 4f 6d ad a6
1d 4f cd 85 e7 90 66 68
PRK_3e2m (32 bytes)
75 07 7c 69 1e 35 01 2d 48 bc 24 c8 4f 2b ab 89 f5 2f ac 03 fe dd 81 3e
43 8c 93 b1 0b 39 93 07
The Responder chooses a connection identifier C_R.
Connection identifier chosen by Responder (1 byte)
00
Note that since C_R is a byte string in the interval h'00' to h'2f',
it is encoded as the corresponding integer - 24, i.e. 0x00 = 0, 0 -
24 = -24, and -24 in CBOR encoding is equal to 0x37.
C_R (1 byte)
37
Data_2 is constructed as the CBOR Sequence of G_Y and C_R.
data_2 =
(
h'52FBA0BDC8D953DD86CE1AB2FD7C05A4658C7C30AFDBFC3301047069451BAF35',
-24
)
Which as a CBOR encoded data item is:
data_2 (CBOR Sequence) (35 bytes)
58 20 52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db
fc 33 01 04 70 69 45 1b af 35 37
From data_2 and message_1, compute the input to the transcript hash
TH_2 = H( H(message_1), data_2 ), as a CBOR Sequence of these 2 data
items.
Input to calculate TH_2 (CBOR Sequence) (72 bytes)
0d 00 58 20 8d 3e f5 6d 1b 75 0a 43 51 d6 8a c2 50 a0 e8 83 79 0e fc 80
a5 38 a4 44 ee 9e 2b 57 e2 44 1a 7c 21 58 20 52 fb a0 bd c8 d9 53 dd 86
ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db fc 33 01 04 70 69 45 1b af 35 37
And from there, compute the transcript hash TH_2 = SHA-256(
H(message_1), data_2 )
TH_2 (CBOR unencoded) (32 bytes)
de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c
73 a6 e8 a7 c3 62 1e 26
The Responder's subject name is the empty string:
Responder's subject name (text string)
""
ID_CRED_R is the following:
ID_CRED_R =
{
4: h'05'
}
ID_CRED_R (4 bytes)
a1 04 41 05
CRED_R is the following COSE_Key:
{
1: 1,
-1: 4,
-2: h'A3FF263595BEB377D1A0CE1D04DAD2D40966AC6BCB622051B84659184D5D9A32,
"subject name": ""
}
Which encodes to the following byte string:
CRED_R (54 bytes)
a4 01 01 20 04 21 58 20 a3 ff 26 35 95 be b3 77 d1 a0 ce 1d 04 da d2 d4
09 66 ac 6b cb 62 20 51 b8 46 59 18 4d 5d 9a 32 6c 73 75 62 6a 65 63 74
20 6e 61 6d 65 60
Since no external authorization data is sent:
EAD_2 (0 bytes)
The plaintext is defined as the empty string:
P_2m (0 bytes)
The Enc_structure is defined as follows: [ "Encrypt0",
<< ID_CRED_R >>, << TH_2, CRED_R >> ], so ID_CRED_R is encoded as a
CBOR bstr, and the concatenation of the CBOR byte strings TH_2 and
CRED_R is wrapped in a CBOR bstr.
A_2m =
[
"Encrypt0",
h'A1044105',
h'5820DECFD64A3667640A0233B04AA8AA91F68956B8A536D0CF8C73A6E8A7C3621E2
6A401012004215820A3FF263595BEB377D1A0CE1D04DAD2D40966AC6BCB622051B846
59184D5D9A326C7375626A656374206E616D6560'
]
Which encodes to the following byte string to be used as Additional
Authenticated Data:
A_2m (CBOR-encoded) (105 bytes)
83 68 45 6e 63 72 79 70 74 30 44 a1 04 41 05 58 58 58 20 de cf d6 4a 36
67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c 73 a6 e8 a7 c3
62 1e 26 a4 01 01 20 04 21 58 20 a3 ff 26 35 95 be b3 77 d1 a0 ce 1d 04
da d2 d4 09 66 ac 6b cb 62 20 51 b8 46 59 18 4d 5d 9a 32 6c 73 75 62 6a
65 63 74 20 6e 61 6d 65 60
info for K_2m is defined as follows:
info for K_2m =
[
10,
h'DECFD64A3667640A0233B04AA8AA91F68956B8A536D0CF8C73A6E8A7C3621E26',
"K_2m",
16
]
Which as a CBOR encoded data item is:
info for K_2m (CBOR-encoded) (42 bytes)
84 0a 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5
36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 64 4b 5f 32 6d 10
From these parameters, K_2m is computed. Key K_2m is the output of
HKDF-Expand(PRK_3e2m, info, L), where L is the length of K_2m, so 16
bytes.
K_2m (16 bytes)
4e cd ef ba d8 06 81 8b 62 51 b9 d7 86 78 bc 76
info for IV_2m is defined as follows:
info for IV_2m =
[
10,
h'A51C76463E8AE58FD3B8DC5EDE1E27143CC92D223EACD9E5FF6E3FAC876658A5',
"IV_2m",
13
]
Which as a CBOR encoded data item is:
info for IV_2m (CBOR-encoded) (43 bytes)
84 0a 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5
36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 65 49 56 5f 32 6d 0d
From these parameters, IV_2m is computed. IV_2m is the output of
HKDF-Expand(PRK_3e2m, info, L), where L is the length of IV_2m, so 13
bytes.
IV_2m (13 bytes)
e9 b8 e4 b1 bd 02 f4 9a 82 0d d3 53 4f
Finally, COSE_Encrypt0 is computed from the parameters above.
o protected header = CBOR-encoded ID_CRED_R
o external_aad = A_2m
o empty plaintext = P_2m
MAC_2 is the 'ciphertext' of the COSE_Encrypt0 with empty plaintext.
In case of cipher suite 0 the AEAD is AES-CCM truncated to 8 bytes:
MAC_2 (CBOR unencoded) (8 bytes)
42 e7 99 78 43 1e 6b 8f
Since method = 2, Signature_or_MAC_2 is MAC_2:
Signature_or_MAC_2 (CBOR unencoded) (8 bytes)
42 e7 99 78 43 1e 6b 8f
CIPHERTEXT_2 is the ciphertext resulting from XOR between plaintext
and KEYSTREAM_2 which is derived from TH_2 and the pseudorandom key
PRK_2e.
The plaintext is the CBOR Sequence of the items ID_CRED_R and the
CBOR encoded Signature_or_MAC_2, in this order (EAD_2 is empty).
Note that since ID_CRED_R contains a single 'kid' parameter, i.e.,
ID_CRED_R = { 4 : kid_R }, only the byte string kid_R is conveyed in
the plaintext encoded as a bstr_identifier. kid_R is encoded as the
corresponding integer - 24, i.e. 0x05 = 5, 5 - 24 = -19, and -19 in
CBOR encoding is equal to 0x32.
The plaintext is the following:
P_2e (CBOR Sequence) (10 bytes)
32 48 42 e7 99 78 43 1e 6b 8f
KEYSTREAM_2 = HKDF-Expand( PRK_2e, info, length ), where length is
the length of the plaintext, so 10.
info for KEYSTREAM_2 =
[
10,
h'DECFD64A3667640A0233B04AA8AA91F68956B8A536D0CF8C73A6E8A7C3621E26',
"KEYSTREAM_2",
10
]
Which as a CBOR encoded data item is:
info for KEYSTREAM_2 (CBOR-encoded) (49 bytes)
84 0a 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5
36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 6b 4b 45 59 53 54 52 45 41 4d 5f 32
0a
From there, KEYSTREAM_2 is computed:
KEYSTREAM_2 (10 bytes)
91 b9 ff ba 9b f5 5a d1 57 16
Using the parameters above, the ciphertext CIPHERTEXT_2 can be
computed:
CIPHERTEXT_2 (CBOR unencoded) (10 bytes)
a3 f1 bd 5d 02 8d 19 cf 3c 99
message_2 is the CBOR Sequence of data_2 and CIPHERTEXT_2, in this
order:
message_2 =
(
data_2,
h'A3F1BD5D028D19CF3C99'
)
Which as a CBOR encoded data item is:
message_2 (CBOR Sequence) (46 bytes)
58 20 52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db
fc 33 01 04 70 69 45 1b af 35 37 4a a3 f1 bd 5d 02 8d 19 cf 3c 99
D.2.3. Message_3
Since corr equals 1, C_R is not omitted from data_3.
The Initiator's static Diffie-Hellman key pair is the following:
I (Initiator's private authentication key) (32 bytes)
2b be a6 55 c2 33 71 c3 29 cf bd 3b 1f 02 c6 c0 62 03 38 37 b8 b5 90 99
a4 43 6f 66 60 81 b0 8e
G_I (Initiator's public authentication key, CBOR unencoded) (32 bytes)
2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae da fe 9c aa 4f 4e 7a bb 83 5e c3
0f 1d e8 8a db 96 ff 71
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
From the Initiator's authentication key and the Responder's ephemeral
key (see Appendix D.2.2), the ECDH shared secret G_IY is calculated.
G_IY (ECDH shared secret) (32 bytes)
cb ff 8c d3 4a 81 df ec 4c b6 5d 9a 57 2e bd 09 64 45 0c 78 56 3d a4 98
1d 80 d3 6c 8b 1a 75 2a
PRK_4x3m = HMAC-SHA-256 (PRK_3e2m, G_IY).
PRK_4x3m (32 bytes)
02 56 2f 1f 01 78 5c 0a a5 f5 94 64 0c 49 cb f6 9f 72 2e 9e 6c 57 83 7d
8e 15 79 ec 45 fe 64 7a
data 3 is equal to C_R.
data_3 (CBOR Sequence) (1 byte)
37
From data_3, CIPHERTEXT_2, and TH_2, compute the input to the
transcript hash TH_3 = H( H(TH_2 , CIPHERTEXT_2), data_3), as a CBOR
Sequence of these 2 data items.
Input to calculate TH_3 (CBOR Sequence) (46 bytes)
58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0
cf 8c 73 a6 e8 a7 c3 62 1e 26 4a a3 f1 bd 5d 02 8d 19 cf 3c 99 37
And from there, compute the transcript hash TH_3 = SHA-256( H(TH_2 ,
CIPHERTEXT_2), data_3)
TH_3 (CBOR unencoded) (32 bytes)
b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84
db 03 ff a5 83 a3 5f cb
The initiator's subject name is the empty string:
Initiator's subject name (text string)
""
And its credential is:
ID_CRED_I =
{
4: h'23'
}
ID_CRED_I (4 bytes)
a1 04 41 23
CRED_I is the following COSE_Key:
{
1:1,
-1:4,
-2:h'2C440CC121F8D7F24C3B0E41AEDAFE9CAA4F4E7ABB835EC30F1DE88ADB96FF71',
"subject name":""
}
Which encodes to the following byte string:
CRED_I (54 bytes)
a4 01 01 20 04 21 58 20 2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae da fe 9c
aa 4f 4e 7a bb 83 5e c3 0f 1d e8 8a db 96 ff 71 6c 73 75 62 6a 65 63 74
20 6e 61 6d 65 60
Since no external authorization data is exchanged:
EAD_3 (0 bytes)
The plaintext of the COSE_Encrypt is the empty string:
P_3m (0 bytes)
The associated data is the following: [ "Encrypt0", << ID_CRED_I >>,
<< TH_3, CRED_I, ? EAD_3 >> ].
A_3m (CBOR-encoded) (105 bytes)
83 68 45 6e 63 72 79 70 74 30 44 a1 04 41 23 58 58 58 20 b6 cd 80 4f c4
b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83
a3 5f cb a4 01 01 20 04 21 58 20 2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae
da fe 9c aa 4f 4e 7a bb 83 5e c3 0f 1d e8 8a db 96 ff 71 6c 73 75 62 6a
65 63 74 20 6e 61 6d 65 60
Info for K_3m is computed as follows:
info for K_3m =
[
10,
h'B6CD804FC4B9D7CAC502ABD77CDA74E41CB01182D7CB8B84DB03FFA583A35FCB',
"K_3m",
16
]
Which as a CBOR encoded data item is:
info for K_3m (CBOR-encoded) (42 bytes)
84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82
d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 64 4b 5f 33 6d 10
From these parameters, K_3m is computed. Key K_3m is the output of
HKDF-Expand(PRK_4x3m, info, L), where L is the length of K_2m, so 16
bytes.
K_3m (16 bytes)
02 c7 e7 93 89 9d 90 d1 28 28 10 26 96 94 c9 58
Nonce IV_3m is the output of HKDF-Expand(PRK_4x3m, info, L), where L
= 13 bytes.
Info for IV_3m is defined as follows:
info for IV_3m =
[
10,
h'B6CD804FC4B9D7CAC502ABD77CDA74E41CB01182D7CB8B84DB03FFA583A35FCB',
"IV_3m",
13
]
Which as a CBOR encoded data item is:
info for IV_3m (CBOR-encoded) (43 bytes)
84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82
d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 65 49 56 5f 33 6d 0d
From these parameters, IV_3m is computed:
IV_3m (13 bytes)
0d a7 cc 3a 6f 9a b2 48 52 ce 8b 37 a6
MAC_3 is the 'ciphertext' of the COSE_Encrypt0 with empty plaintext.
In case of cipher suite 0 the AEAD is AES-CCM truncated to 8 bytes:
MAC_3 (CBOR unencoded) (8 bytes)
ee 59 8e a6 61 17 dc c3
Since method = 3, Signature_or_MAC_3 is MAC_3:
Signature_or_MAC_3 (CBOR unencoded) (8 bytes)
ee 59 8e a6 61 17 dc c3
Finally, the outer COSE_Encrypt0 is computed.
The plaintext is the CBOR Sequence of the items ID_CRED_I and the
CBOR encoded Signature_or_MAC_3, in this order (EAD_3 is empty).
Note that since ID_CRED_I contains a single 'kid' parameter, i.e.,
ID_CRED_I = { 4 : kid_I }, only the byte string kid_I is conveyed in
the plaintext encoded as a bstr_identifier. kid_I is encoded as the
corresponding integer - 24, i.e. 0x23 = 35, 35 - 24 = 11, and 11 in
CBOR encoding is equal to 0x0b.
P_3ae (CBOR Sequence) (10 bytes)
0b 48 ee 59 8e a6 61 17 dc c3
The Associated data A is the following: Associated data A = [
"Encrypt0", h'', TH_3 ]
A_3ae (CBOR-encoded) (45 bytes)
83 68 45 6e 63 72 79 70 74 30 40 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab
d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb
Key K_3ae is the output of HKDF-Expand(PRK_3e2m, info, L).
info is defined as follows:
info for K_3ae =
[
10,
h'B6CD804FC4B9D7CAC502ABD77CDA74E41CB01182D7CB8B84DB03FFA583A35FCB',
"K_3ae",
16
]
Which as a CBOR encoded data item is:
info for K_3ae (CBOR-encoded) (43 bytes)
84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82
d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 65 4b 5f 33 61 65 10
L is the length of K_3ae, so 16 bytes.
From these parameters, K_3ae is computed:
K_3ae (16 bytes)
6b a4 c8 83 1d e3 ae 23 e9 8e f7 35 08 d0 95 86
Nonce IV_3ae is the output of HKDF-Expand(PRK_3e2m, info, L).
info is defined as follows:
info for IV_3ae =
[
10,
h'97D8AD42334833EB25B960A5EB0704505F89671A0168AA1115FAF92D9E67EF04',
"IV_3ae",
13
]
Which as a CBOR encoded data item is:
info for IV_3ae (CBOR-encoded) (44 bytes)
84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82
d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 66 49 56 5f 33 61 65 0d
L is the length of IV_3ae, so 13 bytes.
From these parameters, IV_3ae is computed:
IV_3ae (13 bytes)
6c 6d 0f e1 1e 9a 1a f3 7b 87 84 55 10
Using the parameters above, the 'ciphertext' CIPHERTEXT_3 can be
computed:
CIPHERTEXT_3 (CBOR unencoded) (18 bytes)
d5 53 5f 31 47 e8 5f 1c fa cd 9e 78 ab f9 e0 a8 1b bf
From the parameter above, message_3 is computed, as the CBOR Sequence
of the following items: (C_R, CIPHERTEXT_3).
message_3 =
(
-24,
h'D5535F3147E85F1CFACD9E78ABF9E0A81BBF'
)
Which encodes to the following byte string:
message_3 (CBOR Sequence) (20 bytes)
37 52 d5 53 5f 31 47 e8 5f 1c fa cd 9e 78 ab f9 e0 a8 1b bf
D.2.4. OSCORE Security Context Derivation
From here, the Initiator and the Responder can derive an OSCORE
Security Context, using the EDHOC-Exporter interface.
From TH_3 and CIPHERTEXT_3, compute the input to the transcript hash
TH_4 = H( TH_3, CIPHERTEXT_3 ), as a CBOR Sequence of these 2 data
items.
Input to calculate TH_4 (CBOR Sequence) (53 bytes)
58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb
8b 84 db 03 ff a5 83 a3 5f cb 52 d5 53 5f 31 47 e8 5f 1c fa cd 9e 78 ab
f9 e0 a8 1b bf
And from there, compute the transcript hash TH_4 = SHA-256(TH_3 ,
CIPHERTEXT_4)
TH_4 (CBOR unencoded) (32 bytes)
7c cf de dc 2c 10 ca 03 56 e9 57 b9 f6 a5 92 e0 fa 74 db 2a b5 4f 59 24
40 96 f9 a2 ac 56 d2 07
The Master Secret and Master Salt are derived as follows:
Master Secret = EDHOC-Exporter( "OSCORE Master Secret", 16 ) = EDHOC-
KDF(PRK_4x3m, TH_4, "OSCORE Master Secret", 16) = HKDF-Expand(
PRK_4x3m, info_ms, 16 )
Master Salt = EDHOC-Exporter( "OSCORE Master Salt", 8 ) = EDHOC-
KDF(PRK_4x3m, TH_4, "OSCORE Master Salt", 8) = HKDF-Expand( PRK_4x3m,
info_salt, 8 )
info_ms for OSCORE Master Secret is defined as follows:
info_ms = [
10,
h'7CCFDEDC2C10CA0356E957B9F6A592E0FA74DB2AB54F59244096F9A2AC56D207',
"OSCORE Master Secret",
16
]
Which as a CBOR encoded data item is:
info_ms for OSCORE Master Secret (CBOR-encoded) (58 bytes)
84 0a 58 20 7c cf de dc 2c 10 ca 03 56 e9 57 b9 f6 a5 92 e0 fa 74 db 2a
b5 4f 59 24 40 96 f9 a2 ac 56 d2 07 74 4f 53 43 4f 52 45 20 4d 61 73 74
65 72 20 53 65 63 72 65 74 10
info_salt for OSCORE Master Salt is defined as follows:
info_salt = [
10,
h'7CCFDEDC2C10CA0356E957B9F6A592E0FA74DB2AB54F59244096F9A2AC56D207',
"OSCORE Master Salt",
8
]
Which as a CBOR encoded data item is:
info for OSCORE Master Salt (CBOR-encoded) (56 Bytes)
84 0a 58 20 7c cf de dc 2c 10 ca 03 56 e9 57 b9 f6 a5 92 e0 fa 74 db 2a
b5 4f 59 24 40 96 f9 a2 ac 56 d2 07 72 4f 53 43 4f 52 45 20 4d 61 73 74
65 72 20 53 61 6c 74 08
From these parameters, OSCORE Master Secret and OSCORE Master Salt
are computed:
OSCORE Master Secret (16 bytes)
c3 4a 50 6d 0e bf bd 17 03 04 86 13 5f 9c b3 50
OSCORE Master Salt (8 bytes)
c2 24 34 9d 9b 34 ca 8c
The client's OSCORE Sender ID is C_R and the server's OSCORE Sender * ECDH ephemeral public keys of type EC2 or OKP in message_1 and
ID is C_I. message_2 consist of the COSE_Key parameter named 'x', see
Section 7.1 and 7.2 of [I-D.ietf-cose-rfc8152bis-algs]
Client's OSCORE Sender ID (1 byte) * Certain ciphertexts in message_2 and message_3 consist of a subset
00 of the single recipient encrypted data object COSE_Encrypt0, which
is described in Sections 5.2-5.3 of
[I-D.ietf-cose-rfc8152bis-struct]. The ciphertext is computed
over the plaintext and associated data, using an encryption key
and a nonce. The associated data is an Enc_structure consisting
of protected headers and externally supplied data (external_aad).
Server's OSCORE Sender ID (1 byte) * Signatures in message_2 of method 0 and 2, and in message_3 of
16 method 0 and 1, consist of a subset of the single signer data
The AEAD Algorithm and the hash algorithm are the application AEAD object COSE_Sign1, which is described in Sections 4.2-4.4 of
and hash algorithms in the selected cipher suite. [I-D.ietf-cose-rfc8152bis-struct]. The signature is computed over
a Sig_structure containing payload, protected headers and
externally supplied data (external_aad) using a private signature
key and verified using the corresponding public signature key.
OSCORE AEAD Algorithm (int) Appendix D. Test Vectors
10
OSCORE Hash Algorithm (int) TBD
-16
Appendix E. Applicability Template Appendix E. Applicability Template
This appendix contains an example of an applicability statement, see This appendix contains a rudimentary example of an applicability
Section 3.9. statement, see Section 3.9.
For use of EDHOC in the XX protocol, the following assumptions are For use of EDHOC in the XX protocol, the following assumptions are
made on the parameters: made:
o METHOD = 1 (I uses signature key, R uses static DH key.) 1. Transfer in CoAP as specified in Appendix A.3 with requests
expected by the CoAP server (= Responder) at /app1-edh, no
Content-Format needed.
o EDHOC requests are expected by the server at /app1-edh, no 2. METHOD = 1 (I uses signature key, R uses static DH key.)
Content-Format needed. 3. CRED_I is an IEEE 802.1AR IDevID encoded as a C509 certificate of
type 0 [I-D.ietf-cose-cbor-encoded-cert].
o CRED_I is an 802.1AR IDevID encoded as a C509 Certificate of type * R acquires CRED_I out-of-band, indicated in EAD_1.
0 [I-D.ietf-cose-cbor-encoded-cert].
* R acquires CRED_I out-of-band, indicated in EAD_1 * ID_CRED_I = {4: h''} is a 'kid' with value empty byte string.
* ID_CRED_I = {4: h''} is a kid with value empty byte string 4. CRED_R is a UCCS of type OKP as specified in Section 3.5.2.
o CRED_R is a COSE_Key of type OKP as specified in Section 3.5.4. * The CBOR map has parameters 1 (kty), -1 (crv), and -2
(x-coordinate).
* The CBOR map has parameters 1 (kty), -1 (crv), and -2 * ID_CRED_R = CRED_R
(x-coordinate).
o ID_CRED_R = CRED_R 5. External authorization data is defined and processed as specified
in [I-D.selander-ace-ake-authz].
o No use of message_4: the application sends protected messages from 6. EUI-64 used as identity of endpoint.
R to I.
o External authorization data is defined and processed as specified 7. No use of message_4: the application sends protected messages
in [I-D.selander-ace-ake-authz]. from R to I.
Appendix F. EDHOC Message Deduplication Appendix F. EDHOC Message Deduplication
EDHOC by default assumes that message duplication is handled by the EDHOC by default assumes that message duplication is handled by the
transport, in this section exemplified with CoAP. transport, in this section exemplified with CoAP.
Deduplication of CoAP messages is described in Section 4.5 of Deduplication of CoAP messages is described in Section 4.5 of
[RFC7252]. This handles the case when the same Confirmable (CON) [RFC7252]. This handles the case when the same Confirmable (CON)
message is received multiple times due to missing acknowledgement on message is received multiple times due to missing acknowledgement on
CoAP messaging layer. The recommended processing in [RFC7252] is CoAP messaging layer. The recommended processing in [RFC7252] is
skipping to change at page 97, line 39 skipping to change at page 70, line 25
to be able to resend it. An EDHOC implementation MAY keep the to be able to resend it. An EDHOC implementation MAY keep the
protocol state to be able to recreate the previously sent EDHOC protocol state to be able to recreate the previously sent EDHOC
message and resend it. The previous message or protocol state MUST message and resend it. The previous message or protocol state MUST
NOT be kept longer than what is required for retransmission, for NOT be kept longer than what is required for retransmission, for
example, in the case of CoAP transport, no longer than the example, in the case of CoAP transport, no longer than the
EXCHANGE_LIFETIME (see Section 4.8.2 of [RFC7252]). EXCHANGE_LIFETIME (see Section 4.8.2 of [RFC7252]).
Note that the requirements in Section 5.1 still apply because Note that the requirements in Section 5.1 still apply because
duplicate messages are not processed by the EDHOC state machine: duplicate messages are not processed by the EDHOC state machine:
o EDHOC messages SHALL be processed according to the current * EDHOC messages SHALL be processed according to the current
protocol state. protocol state.
o Different instances of the same message MUST NOT be processed in * Different instances of the same message MUST NOT be processed in
one session. one session.
Appendix G. Transports Not Natively Providing Correlation Appendix G. Transports Not Natively Providing Correlation
Protocols that do not natively provide full correlation between a Protocols that do not natively provide full correlation between a
series of messages can send the C_I and C_R identifiers along as series of messages can send the C_I and C_R identifiers along as
needed. needed.
The transport over CoAP (Appendix A.3) can serve as a blueprint for The transport over CoAP (Appendix A.3) can serve as a blueprint for
other server-client protocols: The client prepends the C_x which the other server-client protocols: The client prepends the C_x which the
server selected (or, for message 1, a sentinel null value which is server selected (or, for message 1, the CBOR simple value 'true'
not a valid C_x) to any request message it sends. The server does which is not a valid C_x) to any request message it sends. The
not send any such indicator, as responses are matched to request by server does not send any such indicator, as responses are matched to
the client-server protocol design. request by the client-server protocol design.
Protocols that do not provide any correlation at all can prescribe Protocols that do not provide any correlation at all can prescribe
prepending of the peer's chosen C_x to all messages. prepending of the peer's chosen C_x to all messages.
Appendix H. Change Log Appendix H. Change Log
RFC Editor: Please remove this appendix.
Main changes: Main changes:
o From -07 to -08: * From -08 to -09:
* Prepended C_x moved from the EDHOC protocol itself to the - G_Y and CIPHERTEXT_2 are now included in one CBOR bstr
- MAC_2 and MAC_3 are now generated with EDHOC-KDF
- Info field "context" is now general and explicit in EDHOC-KDF
- Restructured Section 4, Key Derivation
- Added EDHOC MAC length to cipher suite for use with static DH
- More details on the use of CWT and UCCS
- Restructured and clarified Section 3.5, Authentication
Parameters
- Replaced 'kid2' with extension of 'kid'
- EAD encoding now supports multiple ead types in one message
- Clarified EAD type
- Updated message sizes
- Replaced "perfect forward secrecy" with "forward secrecy"
- Updated security considerations
- Replaced prepended 'null' with 'true' in the CoAP transport of
message_1
- Updated CDDL definitions
- Expanded on the use of COSE
* From -07 to -08:
- Prepended C_x moved from the EDHOC protocol itself to the
transport mapping transport mapping
* METHOD_CORR renamed to METHOD, corr removed - METHOD_CORR renamed to METHOD, corr removed
* Removed bstr_identifier and use bstr / int instead; C_x can now - Removed bstr_identifier and use bstr / int instead; C_x can now
be int without any implied bstr semantics be int without any implied bstr semantics
* Defined COSE header parameter 'kid2' with value type bstr / int - Defined COSE header parameter 'kid2' with value type bstr / int
for use with ID_CRED_x for use with ID_CRED_x
* Updated message sizes - Updated message sizes
* New cipher suites with AES-GCM and ChaCha20 / Poly1305 - New cipher suites with AES-GCM and ChaCha20 / Poly1305
* Changed from one- to two-byte identifier of CNSA compliant - Changed from one- to two-byte identifier of CNSA compliant
suite suite
* Separate sections on transport and connection id with further - Separate sections on transport and connection id with further
sub-structure sub-structure
* Moved back key derivation for OSCORE from draft-ietf-core- - Moved back key derivation for OSCORE from draft-ietf-core-
oscore-edhoc oscore-edhoc
* OSCORE and CoAP specific processing moved to new appendix - OSCORE and CoAP specific processing moved to new appendix
* Message 4 section moved to message processing section - Message 4 section moved to message processing section
o From -06 to -07: * From -06 to -07:
* Changed transcript hash definition for TH_2 and TH_3 - Changed transcript hash definition for TH_2 and TH_3
* Removed "EDHOC signature algorithm curve" from cipher suite - Removed "EDHOC signature algorithm curve" from cipher suite
* New IANA registry "EDHOC Exporter Label"
* New application defined parameter "context" in EDHOC-Exporter - New IANA registry "EDHOC Exporter Label"
* Changed normative language for failure from MUST to SHOULD send - New application defined parameter "context" in EDHOC-Exporter
- Changed normative language for failure from MUST to SHOULD send
error error
* Made error codes non-negative and 0 for success - Made error codes non-negative and 0 for success
* Added detail on success error code - Added detail on success error code
* Aligned terminology "protocol instance" -> "session" - Aligned terminology "protocol instance" -> "session"
* New appendix on compact EC point representation - New appendix on compact EC point representation
* Added detail on use of ephemeral public keys - Added detail on use of ephemeral public keys
* Moved key derivation for OSCORE to draft-ietf-core-oscore-edhoc - Moved key derivation for OSCORE to draft-ietf-core-oscore-edhoc
* Additional security considerations - Additional security considerations
* Renamed "Auxililary Data" as "External Authorization Data" - Renamed "Auxililary Data" as "External Authorization Data"
* Added encrypted EAD_4 to message_4 - Added encrypted EAD_4 to message_4
o From -05 to -06: * From -05 to -06:
* New section 5.2 "Message Processing Outline" - New section 5.2 "Message Processing Outline"
* Optional inital byte C_1 = null in message_1 - Optional inital byte C_1 = null in message_1
* New format of error messages, table of error codes, IANA - New format of error messages, table of error codes, IANA
registry registry
* Change of recommendation transport of error in CoAP - Change of recommendation transport of error in CoAP
* Merge of content in 3.7 and appendix C into new section 3.7 - Merge of content in 3.7 and appendix C into new section 3.7
"Applicability Statement" "Applicability Statement"
* Requiring use of deterministic CBOR - Requiring use of deterministic CBOR
* New section on message deduplication - New section on message deduplication
* New appendix containin all CDDL definitions - New appendix containin all CDDL definitions
* New appendix with change log - New appendix with change log
* Removed section "Other Documents Referencing EDHOC" - Removed section "Other Documents Referencing EDHOC"
* Clarifications based on review comments
o From -04 to -05: - Clarifications based on review comments
* EDHOC-Rekey-FS -> EDHOC-KeyUpdate * From -04 to -05:
* Clarification of cipher suite negotiation - EDHOC-Rekey-FS -> EDHOC-KeyUpdate
* Updated security considerations - Clarification of cipher suite negotiation
* Updated test vectors - Updated security considerations
* Updated applicability statement template - Updated test vectors
o From -03 to -04: - Updated applicability statement template
* Restructure of section 1 * From -03 to -04:
* Added references to C509 Certificates - Restructure of section 1
* Change in CIPHERTEXT_2 -> plaintext XOR KEYSTREAM_2 (test - Added references to C509 Certificates
vector not updated)
* "K_2e", "IV_2e" -> KEYSTREAM_2 - Change in CIPHERTEXT_2 -> plaintext XOR KEYSTREAM_2 (test
vector not updated)
* Specified optional message 4 - "K_2e", "IV_2e" -> KEYSTREAM_2
- Specified optional message 4
* EDHOC-Exporter-FS -> EDHOC-Rekey-FS - EDHOC-Exporter-FS -> EDHOC-Rekey-FS
* Less constrained devices SHOULD implement both suite 0 and 2 - Less constrained devices SHOULD implement both suite 0 and 2
* Clarification of error message - Clarification of error message
* Added exporter interface test vector - Added exporter interface test vector
o From -02 to -03: * From -02 to -03:
* Rearrangements of section 3 and beginning of section 4 - Rearrangements of section 3 and beginning of section 4
* Key derivation new section 4 - Key derivation new section 4
* Cipher suites 4 and 5 added - Cipher suites 4 and 5 added
* EDHOC-EXPORTER-FS - generate a new PRK_4x3m from an old one - EDHOC-EXPORTER-FS - generate a new PRK_4x3m from an old one
* Change in CIPHERTEXT_2 -> COSE_Encrypt0 without tag (no change - Change in CIPHERTEXT_2 -> COSE_Encrypt0 without tag (no change
to test vector) to test vector)
* Clarification of error message - Clarification of error message
* New appendix C applicability statement - New appendix C applicability statement
o From -01 to -02: * From -01 to -02:
* New section 1.2 Use of EDHOC - New section 1.2 Use of EDHOC
* Clarification of identities - Clarification of identities
* New section 4.3 clarifying bstr_identifier - New section 4.3 clarifying bstr_identifier
* Updated security considerations - Updated security considerations
* Updated text on cipher suite negotiation and key confirmation - Updated text on cipher suite negotiation and key confirmation
* Test vector for static DH - Test vector for static DH
o From -00 to -01: * From -00 to -01:
* Removed PSK method - Removed PSK method
* Removed references to certificate by value - Removed references to certificate by value
Acknowledgments Acknowledgments
The authors want to thank Christian Amsuess, Alessandro Bruni, The authors want to thank Christian Amsuess, Alessandro Bruni,
Karthikeyan Bhargavan, Timothy Claeys, Martin Disch, Theis Groenbech Karthikeyan Bhargavan, Timothy Claeys, Martin Disch, Theis Groenbech
Petersen, Dan Harkins, Klaus Hartke, Russ Housley, Stefan Hristozov, Petersen, Dan Harkins, Klaus Hartke, Russ Housley, Stefan Hristozov,
Alexandros Krontiris, Ilari Liusvaara, Karl Norrman, Salvador Perez, Alexandros Krontiris, Ilari Liusvaara, Karl Norrman, Salvador Perez,
Eric Rescorla, Michael Richardson, Thorvald Sahl Joergensen, Jim Eric Rescorla, Michael Richardson, Thorvald Sahl Joergensen, Jim
Schaad, Carsten Schuermann, Ludwig Seitz, Stanislav Smyshlyaev, Schaad, Carsten Schuermann, Ludwig Seitz, Stanislav Smyshlyaev,
Valery Smyslov, Peter van der Stok, Rene Struik, Vaishnavi Valery Smyslov, Peter van der Stok, Rene Struik, Vaishnavi
skipping to change at page 101, line 49 skipping to change at page 75, line 25
Malisa Vucinic for reviewing and commenting on intermediate versions Malisa Vucinic for reviewing and commenting on intermediate versions
of the draft. We are especially indebted to Jim Schaad for his of the draft. We are especially indebted to Jim Schaad for his
continuous reviewing and implementation of different versions of the continuous reviewing and implementation of different versions of the
draft. draft.
Work on this document has in part been supported by the H2020 project Work on this document has in part been supported by the H2020 project
SIFIS-Home (grant agreement 952652). SIFIS-Home (grant agreement 952652).
Authors' Addresses Authors' Addresses
Goeran Selander Göran Selander
Ericsson AB Ericsson AB
SE-164 80 Stockholm
Sweden
Email: goran.selander@ericsson.com Email: goran.selander@ericsson.com
John Preuss Mattsson
John Preuß Mattsson
Ericsson AB Ericsson AB
SE-164 80 Stockholm
Sweden
Email: john.mattsson@ericsson.com Email: john.mattsson@ericsson.com
Francesca Palombini Francesca Palombini
Ericsson AB Ericsson AB
SE-164 80 Stockholm
Sweden
Email: francesca.palombini@ericsson.com Email: francesca.palombini@ericsson.com
 End of changes. 451 change blocks. 
2460 lines changed or deleted 1131 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/