draft-ietf-lake-edhoc-13.txt   draft-ietf-lake-edhoc-14.txt 
Network Working Group G. Selander Network Working Group G. Selander
Internet-Draft J. Preuß Mattsson Internet-Draft J. Preuß Mattsson
Intended status: Standards Track F. Palombini Intended status: Standards Track F. Palombini
Expires: 20 October 2022 Ericsson Expires: 19 November 2022 Ericsson
18 April 2022 18 May 2022
Ephemeral Diffie-Hellman Over COSE (EDHOC) Ephemeral Diffie-Hellman Over COSE (EDHOC)
draft-ietf-lake-edhoc-13 draft-ietf-lake-edhoc-14
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,
forward secrecy, and identity protection. EDHOC is intended for forward secrecy, and identity protection. EDHOC is intended for
usage in constrained scenarios and a main use case is to establish an usage in constrained scenarios and a main use case is to establish an
OSCORE security context. By reusing COSE for cryptography, CBOR for OSCORE security context. By reusing COSE for cryptography, CBOR for
encoding, and CoAP for transport, the additional code size can be encoding, and CoAP for transport, the additional code size can be
skipping to change at page 1, line 38 skipping to change at page 1, line 38
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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 . . . . . . . . . . . . . . . . . . . . . . 5 1.2. Message Size Examples . . . . . . . . . . . . . . . . . . 5
1.3. Message Size Examples . . . . . . . . . . . . . . . . . . 5 1.3. Document Structure . . . . . . . . . . . . . . . . . . . 6
1.4. Document Structure . . . . . . . . . . . . . . . . . . . 6 1.4. Terminology and Requirements Language . . . . . . . . . . 6
1.5. Terminology and Requirements Language . . . . . . . . . . 6
2. EDHOC Outline . . . . . . . . . . . . . . . . . . . . . . . . 7 2. EDHOC Outline . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 8 3. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 8
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Method . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2. Method . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3. Connection Identifiers . . . . . . . . . . . . . . . . . 10 3.3. Connection Identifiers . . . . . . . . . . . . . . . . . 10
3.4. Transport . . . . . . . . . . . . . . . . . . . . . . . . 11 3.4. Transport . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Authentication Parameters . . . . . . . . . . . . . . . . 12 3.5. Authentication Parameters . . . . . . . . . . . . . . . . 13
3.6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 18 3.6. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 17
3.7. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 19 3.7. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 19
3.8. External Authorization Data (EAD) . . . . . . . . . . . . 20 3.8. External Authorization Data (EAD) . . . . . . . . . . . . 19
3.9. Applicability Statement . . . . . . . . . . . . . . . . . 21 3.9. Application Profile . . . . . . . . . . . . . . . . . . . 20
4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . 22 4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . 22
4.1. Extract . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.1. Keys for EDHOC Message Processing . . . . . . . . . . . . 22
4.2. Expand . . . . . . . . . . . . . . . . . . . . . . . . . 24 4.2. Keys for EDHOC Applications . . . . . . . . . . . . . . . 25
4.3. EDHOC-Exporter . . . . . . . . . . . . . . . . . . . . . 25 5. Message Formatting and Processing . . . . . . . . . . . . . . 27
4.4. EDHOC-KeyUpdate . . . . . . . . . . . . . . . . . . . . . 26
5. Message Formatting and Processing . . . . . . . . . . . . . . 26
5.1. Message Processing Outline . . . . . . . . . . . . . . . 27 5.1. Message Processing Outline . . . . . . . . . . . . . . . 27
5.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 28 5.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 28
5.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 29 5.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 30
5.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 32 5.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 32
5.5. EDHOC Message 4 . . . . . . . . . . . . . . . . . . . . . 35 5.5. EDHOC Message 4 . . . . . . . . . . . . . . . . . . . . . 36
6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 37 6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 37
6.1. Success . . . . . . . . . . . . . . . . . . . . . . . . . 38 6.1. Success . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.2. Unspecified . . . . . . . . . . . . . . . . . . . . . . . 38 6.2. Unspecified Error . . . . . . . . . . . . . . . . . . . . 39
6.3. Wrong Selected Cipher Suite . . . . . . . . . . . . . . . 38 6.3. Wrong Selected Cipher Suite . . . . . . . . . . . . . . . 39
7. Mandatory-to-Implement Compliance Requirements . . . . . . . 41 7. Compliance Requirements . . . . . . . . . . . . . . . . . . . 42
8. Security Considerations . . . . . . . . . . . . . . . . . . . 42 8. Security Considerations . . . . . . . . . . . . . . . . . . . 43
8.1. Security Properties . . . . . . . . . . . . . . . . . . . 42 8.1. Security Properties . . . . . . . . . . . . . . . . . . . 43
8.2. Cryptographic Considerations . . . . . . . . . . . . . . 44 8.2. Cryptographic Considerations . . . . . . . . . . . . . . 45
8.3. Cipher Suites and Cryptographic Algorithms . . . . . . . 45 8.3. Cipher Suites and Cryptographic Algorithms . . . . . . . 47
8.4. Post-Quantum Considerations . . . . . . . . . . . . . . . 46 8.4. Post-Quantum Considerations . . . . . . . . . . . . . . . 47
8.5. Unprotected Data . . . . . . . . . . . . . . . . . . . . 46 8.5. Unprotected Data and Privacy . . . . . . . . . . . . . . 48
8.6. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 47 8.6. Updated Internet Threat Model Considerations . . . . . . 48
8.7. Implementation Considerations . . . . . . . . . . . . . . 47 8.7. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 49
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49 8.8. Implementation Considerations . . . . . . . . . . . . . . 49
9.1. EDHOC Exporter Label Registry . . . . . . . . . . . . . . 49 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 51
9.2. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 49 9.1. EDHOC Exporter Label Registry . . . . . . . . . . . . . . 52
9.3. EDHOC Method Type Registry . . . . . . . . . . . . . . . 51 9.2. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 52
9.4. EDHOC Error Codes Registry . . . . . . . . . . . . . . . 51 9.3. EDHOC Method Type Registry . . . . . . . . . . . . . . . 53
9.5. EDHOC External Authorization Data Registry . . . . . . . 52 9.4. EDHOC Error Codes Registry . . . . . . . . . . . . . . . 54
9.6. COSE Header Parameters Registry . . . . . . . . . . . . . 52 9.5. EDHOC External Authorization Data Registry . . . . . . . 54
9.7. COSE Header Parameters Registry . . . . . . . . . . . . . 52 9.6. COSE Header Parameters Registry . . . . . . . . . . . . . 54
9.8. COSE Key Common Parameters Registry . . . . . . . . . . . 53 9.7. The Well-Known URI Registry . . . . . . . . . . . . . . . 54
9.9. CWT Confirmation Methods Registry . . . . . . . . . . . . 53 9.8. Media Types Registry . . . . . . . . . . . . . . . . . . 55
9.10. The Well-Known URI Registry . . . . . . . . . . . . . . . 53 9.9. CoAP Content-Formats Registry . . . . . . . . . . . . . . 57
9.11. Media Types Registry . . . . . . . . . . . . . . . . . . 54 9.10. Resource Type (rt=) Link Target Attribute Values
9.12. CoAP Content-Formats Registry . . . . . . . . . . . . . . 55 Registry . . . . . . . . . . . . . . . . . . . . . . . . 57
9.13. Resource Type (rt=) Link Target Attribute Values 9.11. Expert Review Instructions . . . . . . . . . . . . . . . 57
Registry . . . . . . . . . . . . . . . . . . . . . . . . 55 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 58
9.14. Expert Review Instructions . . . . . . . . . . . . . . . 55 10.1. Normative References . . . . . . . . . . . . . . . . . . 58
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 56 10.2. Informative References . . . . . . . . . . . . . . . . . 61
10.1. Normative References . . . . . . . . . . . . . . . . . . 56 Appendix A. Use with OSCORE and Transfer over CoAP . . . . . . . 65
10.2. Informative References . . . . . . . . . . . . . . . . . 59 A.1. Deriving the OSCORE Security Context . . . . . . . . . . 65
Appendix A. Use with OSCORE and Transfer over CoAP . . . . . . . 61 A.2. Transferring EDHOC over CoAP . . . . . . . . . . . . . . 66
A.1. Selecting EDHOC Connection Identifier . . . . . . . . . . 62 Appendix B. Compact Representation . . . . . . . . . . . . . . . 70
A.2. Deriving the OSCORE Security Context . . . . . . . . . . 62 Appendix C. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 70
A.3. Transferring EDHOC over CoAP . . . . . . . . . . . . . . 64 C.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 71
Appendix B. Compact Representation . . . . . . . . . . . . . . . 67 C.2. CDDL Definitions . . . . . . . . . . . . . . . . . . . . 72
Appendix C. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 67 C.3. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 73
C.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 68 Appendix D. Authentication Related Verifications . . . . . . . . 75
C.2. CDDL Definitions . . . . . . . . . . . . . . . . . . . . 69 D.1. Validating the Authentication Credential . . . . . . . . 76
C.3. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 70 D.2. Identities . . . . . . . . . . . . . . . . . . . . . . . 76
Appendix D. Applicability Template . . . . . . . . . . . . . . . 72 D.3. Certification Path and Trust Anchors . . . . . . . . . . 77
Appendix E. EDHOC Message Deduplication . . . . . . . . . . . . 73 D.4. Revocation Status . . . . . . . . . . . . . . . . . . . . 78
Appendix F. Transports Not Natively Providing Correlation . . . 74 D.5. Trust-on-first-use . . . . . . . . . . . . . . . . . . . 78
Appendix G. Change Log . . . . . . . . . . . . . . . . . . . . . 74 Appendix E. Use of External Authorization Data . . . . . . . . . 78
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 79 Appendix F. Application Profile Example . . . . . . . . . . . . 80
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 80 Appendix G. EDHOC Message Deduplication . . . . . . . . . . . . 80
Appendix H. Transports Not Natively Providing Correlation . . . 82
Appendix I. Change Log . . . . . . . . . . . . . . . . . . . . . 82
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 90
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 90
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 27 skipping to change at page 4, line 28
Some security solutions for such settings exist already. CBOR Object Some security solutions for such settings exist already. CBOR Object
Signing and Encryption (COSE, [I-D.ietf-cose-rfc8152bis-struct]) Signing and Encryption (COSE, [I-D.ietf-cose-rfc8152bis-struct])
specifies basic application-layer security services efficiently specifies basic application-layer security services efficiently
encoded in CBOR. Another example is Object Security for Constrained encoded in CBOR. Another example is Object Security for Constrained
RESTful Environments (OSCORE, [RFC8613]) which is a lightweight RESTful Environments (OSCORE, [RFC8613]) which is a lightweight
communication security extension to CoAP using CBOR and COSE. In communication security extension to CoAP using CBOR and COSE. In
order to establish good quality cryptographic keys for security order to establish good quality cryptographic keys for security
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 keying 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 forward secrecy, identity protection, security properties including forward secrecy, identity protection,
and cipher suite negotiation. Authentication can be based on raw and cipher suite negotiation. Authentication can be based on raw
public keys (RPK) or public key certificates and requires the public keys (RPK) or public key certificates and requires the
application to provide input on how to verify that endpoints are application to provide input on how to verify that endpoints are
trusted. This specification focuses on referencing instead of trusted. This specification emphasizes the possibility to reference
transporting credentials to reduce message overhead. EDHOC does rather than to transport credentials in order to reduce message
currently not support pre-shared key (PSK) authentication as overhead, but the latter is also supported. EDHOC does not currently
authentication with static Diffie-Hellman public keys by reference support pre-shared key (PSK) authentication as authentication with
produces equally small message sizes but with much simpler key static Diffie-Hellman public keys by reference produces equally small
distribution and identity protection. message sizes but with much simpler key distribution and identity
protection.
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]. EDHOC uses COSE for [SIGMA] and Extract-and-Expand [RFC5869]. EDHOC uses COSE for
cryptography and identification of credentials (including COSE_Key, cryptography and identification of credentials (including COSE_Key,
CWT, CCS, X.509, C509, see Section 3.5.3). COSE provides crypto CBOR Web Token (CWT), CWT Claims Set (CCS), X.509, and CBOR encoded
agility and enables the use of future algorithms and credentials X.509 (C509) certificates, see Section 3.5.2). COSE provides crypto
agility and enables the use of future algorithms and credential types
targeting IoT. targeting IoT.
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] involving 'things' with
web transfer protocol for use with constrained nodes and networks, embedded microcontrollers, sensors, and actuators. By reusing the
providing a request/response interaction model between application same lightweight primitives as OSCORE (CBOR, COSE, CoAP) the
endpoints. As such, EDHOC is targeting a large variety of use cases additional code size can be kept very low. Note that while CBOR and
involving 'things' with embedded microcontrollers, sensors, and COSE primitives are built into the protocol messages, EDHOC is not
actuators. bound to a particular transport.
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). Thing-to-thing interactions over
(such as a gateway). Thing-to-thing interactions over constrained constrained networks are also relevant since both endpoints would
networks are also relevant since both endpoints would then benefit then benefit from the lightweight properties of the protocol. EDHOC
from the lightweight properties of the protocol. EDHOC could e.g., could, e.g., be run when a device connects for the first time, or to
be run when a device connects for the first time, or to establish establish fresh keys which are not revealed by a later compromise of
fresh keys which are not revealed by a later compromise of the long- the long-term keys.
term keys. Further security properties are described in Section 8.1.
EDHOC enables the reuse of the same lightweight primitives as OSCORE:
CBOR for encoding, COSE for cryptography, and CoAP for transport. By
reusing existing libraries, the additional code size can be kept very
low. Note that, while CBOR and COSE primitives are built into the
protocol messages, EDHOC is not bound to a particular transport.
Transfer of EDHOC messages in CoAP payloads is detailed in
Appendix A.3.
1.3. Message Size Examples 1.2. Message Size Examples
Compared to the DTLS 1.3 handshake [I-D.ietf-tls-dtls13] with ECDHE Compared to the DTLS 1.3 handshake [RFC9147] with ECDHE and
and connection ID, the number of bytes in EDHOC + CoAP can be less connection ID, the EDHOC message size when transferred in CoAP can be
than 1/6 when RPK authentication is used, see less than 1/6 when RPK authentication is used, see
[I-D.ietf-lwig-security-protocol-comparison]. Figure 1 shows [I-D.ietf-lwig-security-protocol-comparison]. Figure 1 shows
examples of message sizes for EDHOC with different kinds of examples of EDHOC message sizes based on the assumptions in Section 2
authentication keys and different COSE header parameters for of [I-D.ietf-lwig-security-protocol-comparison], comparing different
kinds of authentication keys and COSE header parameters for
identification: static Diffie-Hellman keys or signature keys, either identification: static Diffie-Hellman keys or signature keys, either
in CBOR Web Token (CWT) / CWT Claims Set (CCS) [RFC8392] identified in CBOR Web Token (CWT) / CWT Claims Set (CCS) [RFC8392] identified
by a key identifier using 'kid' [I-D.ietf-cose-rfc8152bis-struct], or by a key identifier using 'kid' [I-D.ietf-cose-rfc8152bis-struct], or
in X.509 certificates identified by a hash value using 'x5t' in X.509 certificates identified by a hash value using 'x5t'
[I-D.ietf-cose-x509]. [I-D.ietf-cose-x509].
======================================================== ========================================================
Static DH Keys Signature Keys Static DH Keys Signature Keys
-------------- -------------- -------------- --------------
kid x5t kid x5t kid x5t kid x5t
-------------------------------------------------------- --------------------------------------------------------
message_1 37 37 37 37 message_1 37 37 37 37
message_2 45 58 102 115 message_2 45 58 102 115
message_3 19 33 77 90 message_3 19 33 77 90
-------------------------------------------------------- --------------------------------------------------------
Total 101 128 216 242 Total 101 128 216 242
======================================================== ========================================================
Figure 1: Example of message sizes in bytes. Figure 1: Examples of EDHOC message sizes in bytes.
1.4. Document Structure 1.3. 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 signature keys, Section 3 describes
describes the protocol elements of EDHOC, including formatting of the the protocol elements of EDHOC, including formatting of the ephemeral
ephemeral public keys, Section 4 specifies the key derivation, public keys, Section 4 specifies the key derivation, Section 5
Section 5 specifies message processing for EDHOC authenticated with specifies message processing for EDHOC authenticated with signature
signature keys or static Diffie-Hellman keys, Section 6 describes the keys or static Diffie-Hellman keys, Section 6 describes the error
error messages, and Appendix A shows how to transfer EDHOC with CoAP messages, and Appendix A shows how to transfer EDHOC with CoAP and
and establish an OSCORE security context. establish an OSCORE security context.
1.5. Terminology and Requirements Language 1.4. 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 processing [I-D.ietf-cose-rfc8152bis-struct], COSE structures and processing [I-D.ietf-cose-rfc8152bis-struct], COSE
algorithms [I-D.ietf-cose-rfc8152bis-algs], CWT and CWT Claims Set algorithms [I-D.ietf-cose-rfc8152bis-algs], CWT and CWT Claims Set
[RFC8392], and CDDL [RFC8610]. The Concise Data Definition Language [RFC8392], and the Concise Data Definition Language (CDDL,
(CDDL) is used to express CBOR data structures [RFC8949]. Examples [RFC8610]), which is used to express CBOR data structures. Examples
of CBOR and CDDL are provided in Appendix C.1. When referring to of CBOR and CDDL are provided in Appendix C.1. When referring to
CBOR, this specification always refers to Deterministically Encoded CBOR, this specification always refers to Deterministically Encoded
CBOR as specified in Sections 4.2.1 and 4.2.2 of [RFC8949]. The CBOR as specified in Sections 4.2.1 and 4.2.2 of [RFC8949]. The
single output from authenticated encryption (including the single output from authenticated encryption (including the
authentication tag) is called "ciphertext", following [RFC5116]. authentication tag) is called "ciphertext", following [RFC5116].
2. EDHOC Outline 2. EDHOC Outline
EDHOC specifies different authentication methods of the Diffie- EDHOC specifies different authentication methods of the ephemeral
Hellman key exchange: digital signatures and static Diffie-Hellman Diffie-Hellman key exchange: signature keys and static Diffie-Hellman
keys. This section outlines the digital signature-based method. keys. This section outlines the signature key based method. Further
Further details of protocol elements and other authentication methods details of protocol elements and other authentication methods are
are provided in the remainder of this document. 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][RFC9147], EDHOC authenticated with signature keys is
on a variant of the SIGMA protocol which provides identity protection built on a variant of the SIGMA protocol which provides identity
of the initiator (SIGMA-I) against active attackers, and like IKEv2 protection of the initiator (SIGMA-I) against active attackers, and
[RFC7296], EDHOC implements the MAC-then-Sign variant of the SIGMA-I like IKEv2, EDHOC implements the MAC-then-Sign variant of the SIGMA-I
protocol shown in Figure 2. protocol shown in Figure 2.
Initiator Responder Initiator Responder
| G_X | | G_X |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| | | |
| G_Y, Enc( ID_CRED_R, Sig( R; MAC( CRED_R, G_X, G_Y ) ) ) | | G_Y, Enc( ID_CRED_R, Sig( R; MAC( CRED_R, G_X, G_Y ) ) ) |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| | | |
| AEAD( ID_CRED_I, Sig( I; MAC( CRED_I, G_Y, G_X ) ) ) | | AEAD( ID_CRED_I, Sig( I; MAC( CRED_I, G_Y, G_X ) ) ) |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| | | |
Figure 2: MAC-then-Sign variant of the SIGMA-I protocol. Figure 2: MAC-then-Sign variant of the SIGMA-I protocol used by
EDHOC.
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 key PRK_out, and derive symmetric application keys used to
application data. protect application data.
* 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.
* CRED_I and CRED_R are the credentials containing the public * CRED_I and CRED_R are the authentication credentials containing
authentication keys of I and R, respectively. the public authentication keys of I and R, respectively.
* ID_CRED_I and ID_CRED_R are credential identifiers enabling the * ID_CRED_I and ID_CRED_R are used to identify and optionally
recipient party to retrieve the credential of I and R, transport the credentials of the Initiator and the Responder,
respectively. respectively.
* 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.
* Enc(), AEAD(), and MAC() denotes encryption, authenticated * Enc(), AEAD(), and MAC() denotes encryption, authenticated
encryption with additional data, and message authentication code encryption with additional data, and message authentication code
using keys derived from the shared secret. using keys 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:
* 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.
* 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.
* An optional fourth message giving explicit key confirmation to I * An optional fourth message giving key confirmation to I in
in deployments where no protected application data is sent from R deployments where no protected application data is sent from R to
to I. I.
* A key material exporter and a key update function with forward * A keying material exporter and a key update function with forward
secrecy. secrecy.
* Verification of a common preferred cipher suite. * Verification of the selected cipher suite.
* Method types and error handling. * Method types and error handling.
* 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. in EDHOC to identify protocol state.
* 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. Test vectors including CBOR diagnostic summarized in Appendix C. Test vectors including CBOR diagnostic
notation are provided in [I-D.selander-lake-traces]. notation are provided in [I-D.ietf-lake-traces].
3. Protocol Elements 3. Protocol Elements
3.1. General 3.1. General
The EDHOC protocol consists of three mandatory messages (message_1, The EDHOC protocol consists of three mandatory messages (message_1,
message_2, message_3) between Initiator and Responder, an optional message_2, message_3) between Initiator and Responder, an optional
fourth message (message_4), and an error message. All EDHOC messages fourth message (message_4), and an error message. All EDHOC messages
are CBOR Sequences [RFC8742]. Figure 3 illustrates an EDHOC message are CBOR Sequences [RFC8742], and are deterministically encoded.
flow with the optional fourth message as well as the content of each Figure 3 illustrates an EDHOC message flow with the optional fourth
message. The protocol elements in the figure are introduced in message as well as the content of each message. The protocol
Section 3 and Section 5. Message formatting and processing is elements in the figure are introduced in Section 3 and Section 5.
specified in Section 5 and Section 6. Message formatting and processing are specified in Section 5 and
Section 6.
Application data may be protected using the agreed application Application data may be protected using the agreed application
algorithms (AEAD, hash) in the selected cipher suite (see algorithms (AEAD, hash) in the selected cipher suite (see
Section 3.6) and the application can make use of the established Section 3.6) and the application can make use of the established
connection identifiers C_I and C_R (see Section 3.3). EDHOC may be connection identifiers C_I and C_R (see Section 3.3). EDHOC may be
used with the media type application/edhoc defined in Section 9. used with the media type application/edhoc+cbor-seq defined in
Section 9.8.
The Initiator can derive symmetric application keys after creating The Initiator can derive symmetric application keys after creating
EDHOC message_3, see Section 4.3. Protected application data can EDHOC message_3, see Section 4.2.1. 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.
EDHOC message_4 is typically not sent. EDHOC message_4 is typically not sent.
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, Enc( ID_CRED_R, Signature_or_MAC_2, EAD_2 ), C_R | | G_Y, Enc( ID_CRED_R, Signature_or_MAC_2, EAD_2 ), C_R |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| message_2 | | message_2 |
| | | |
| AEAD( ID_CRED_I, Signature_or_MAC_3, EAD_3 ) | | AEAD( ID_CRED_I, Signature_or_MAC_3, EAD_3 ) |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_3 | | message_3 |
| | | |
| AEAD( EAD_4 ) | | AEAD( EAD_4 ) |
|<- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + |<- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
| message_4 | | message_4 |
Figure 3: EDHOC Message Flow with the Optional Fourth Message Figure 3: EDHOC message flow including the optional fourth message.
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. When using a authentication methods: 0, 1, 2, and 3, see Figure 4. When using a
static Diffie-Hellman key the authentication is provided by a Message static 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.
The Initiator and the Responder need to have agreed on a single The Initiator and the Responder need to have agreed on a single
method to be used for EDHOC, see Section 3.9. method to be used for EDHOC, see Section 3.9.
+-------+-------------------+-------------------+-------------------+ +-------------+--------------------+--------------------+
| Value | Initiator | Responder | Reference | | Method Type | Initiator | Responder |
+-------+-------------------+-------------------+-------------------+ | Value | Authentication Key | Authentication Key |
| 0 | Signature Key | Signature Key | [[this document]] | +-------------+--------------------+--------------------+
| 1 | Signature Key | Static DH Key | [[this document]] | | 0 | Signature Key | Signature Key |
| 2 | Static DH Key | Signature Key | [[this document]] | | 1 | Signature Key | Static DH Key |
| 3 | Static DH Key | Static DH Key | [[this document]] | | 2 | Static DH Key | Signature Key |
+-------+-------------------+-------------------+-------------------+ | 3 | Static DH Key | Static DH Key |
+-------------+--------------------+--------------------+
Figure 4: Method Types Figure 4: Authentication Keys for Method Types
EDHOC does not have a dedicated message field to indicate protocol
version. Breaking changes to EDHOC can be introduced by specifying
and registering new methods.
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. identifying a connection for which keys are agreed.
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 execution
execution (see Section 3.4) or in a subsequent application protocol, (see Section 3.4) or in subsequent applications of EDHOC, e.g., in
e.g., OSCORE (see Section 3.3.2). The connection identifiers do not OSCORE (see Section 3.3.3). The connection identifiers do not have
have any cryptographic purpose in EDHOC. any cryptographic purpose in EDHOC except facilitating the retrieval
of security data associated to the protocol state.
Connection identifiers in EDHOC are byte strings or integers, encoded Connection identifiers in EDHOC are CBOR byte strings. Since most
in CBOR. One byte connection identifiers (the integers -24 to 23 and constrained devices only have a few connections, short identifiers
the empty CBOR byte string h'') are realistic in many scenarios as are desirable in many cases. However, except for the empty byte
most constrained devices only have a few connections. string h'', which encodes as one byte (0x40), all byte strings are
CBOR encoded as two or more bytes. Therefore EDHOC specifies certain
byte strings to be represented as CBOR ints on the wire, see
Section 3.3.2.
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 it in message_2 for the Initiator
use as a reference to the connection in communications with the to 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 3.3.2 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 with OSCORE 3.3.2. Representation of Byte String Identifiers
For OSCORE, the choice of a connection identifier results in the To allow identifiers with minimal overhead on the wire, certain byte
strings are defined to have integer representations.
The integers with one-byte CBOR encoding are -24, ..., 23, see
Figure 5. This correspondence between integers and byte strings is a
natural mapping between the byte strings with CBOR diagnostic
notation h'00', h'01', ..., h'37' (except h'18', h'19', ..., h'1F')
and integers which are CBOR encoded as one byte.
Integer: -24 -23 ... -2 -1 0 1 ... 23
CBOR encoding (1 byte): 37 36 ... 21 20 00 01 ... 17
Figure 5: One-Byte CBOR Encoded Integers
The byte strings which coincide with a one-byte CBOR encoding of an
integer MUST be represented by the CBOR encoding of that integer.
Other byte strings are encoded as normal CBOR byte strings.
For example:
* h'21' is represented by 0x21 (CBOR encoding of the integer -2),
not by 0x4121.
* h'0D' is represented by 0x0D (CBOR encoding of the integer 13),
not by 0x410D.
* h'18' is represented by 0x4118.
* h'38' is represented by 0x4138.
* h'ABCD' is represented by 0x42ABCD.
One way to view this representation of byte strings is as a transport
encoding: A byte string which parses as a CBOR int in the range -24,
..., 23 is just copied directly into the message, a byte string which
doesn't is encoded as a CBOR bstr during transport.
3.3.3. Use of Connection Identifiers with OSCORE
For OSCORE, the choice of 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 connection identifier is a byte string, it
connection identifier is either a CBOR byte string or a CBOR integer, is converted to an OSCORE Recipient ID equal to the byte string.
care must be taken when selecting the connection identifiers and
converting them to Recipient IDs. A mapping from EDHOC connection For example, a C_I equal to 0xFF is converted to a (typically client)
identifier to OSCORE Recipient ID is specified in Appendix A.1. Responder ID equal to 0xFF; a C_R equal to 0x21 is converted to a
(typically server) Responder ID equal to 0x21. Note that the
representation of connection identifiers as CBOR byte strings or CBOR
ints in EDHOC messages as described in Section 3.3.2 has no impact on
this mapping.
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. In addition to transport of
responsible, where necessary, to handle: messages including errors, the transport is responsible, where
necessary, to handle:
* message loss, * message loss,
* message reordering, * message reordering,
* message duplication, * message duplication,
* fragmentation, * fragmentation,
* demultiplex EDHOC messages from other types of messages, * demultiplex EDHOC messages from other types of messages,
skipping to change at page 12, line 8 skipping to change at page 13, line 8
* denial-of-service protection, * denial-of-service protection,
* message correlation. * message correlation.
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.
3.4.1. Use of Connection Identifiers for EDHOC Message Correlation 3.4.1. Use of Connection Identifiers for EDHOC Message Correlation
The transport needs to support the correlation between EDHOC messages The transport needs to support the correlation between EDHOC messages
and facilitate the retrieval of protocol state during EDHOC protocol and facilitate the retrieval of protocol state and security context
execution, including an indication of a message being message_1. The during EDHOC protocol execution, including an indication of a message
correlation may reuse existing mechanisms in the transport protocol. being message_1. The correlation may reuse existing mechanisms in
For example, the CoAP Token may be used to correlate EDHOC messages the transport protocol. For example, the CoAP Token may be used to
in a CoAP response and an associated CoAP request. correlate EDHOC messages in a CoAP response and an associated CoAP
request.
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/security context during
execution. EDHOC transports that do not inherently provide EDHOC protocol execution. Transports that do not inherently provide
correlation across all messages of an exchange can send connection correlation across all EDHOC messages of an exchange can send
identifiers along with EDHOC messages to gain that required connection identifiers along with EDHOC messages to gain that
capability, e.g., by prepending the appropriate connection identifier required capability, e.g., by prepending the appropriate connection
(when available from the EDHOC protocol) to the EDHOC message. identifier (when available from the EDHOC protocol) to the EDHOC
Transport of EDHOC in CoAP payloads is described in Appendix A.3, message. Transport of EDHOC in CoAP payloads is described in
which also shows how to use connection identifiers and message_1 Appendix A.2, which also shows how to use connection identifiers and
indication with CoAP. message_1 indication with CoAP.
3.5. Authentication Parameters 3.5. Authentication Parameters
EDHOC supports various settings for how the other endpoint's EDHOC supports various settings for how the other endpoint's
authentication (public) key is transported, identified, and trusted authentication (public) key may be transported, identified, and
as described in this section. trusted.
The authentication key (see Section 3.5.2) is used in several parts
of EDHOC:
1. as part of the authentication credential 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 authentication credential (CRED_x) contains, in addition to the
authentication key, also the authentication key algorithm and
optionally other parameters such as identity, key usage, expiry,
issuer, etc. (see Section 3.5.3). Identical authentication
credentials need to be established in both endpoints to be able to
verify integrity. For many settings it is not necessary to transport
the authentication credential within EDHOC over constrained links,
for example, it may be pre-provisioned or acquired out-of-band over
less constrained links.
EDHOC relies on COSE for identification of authentication credentials
(using ID_CRED_x, see Section 3.5.4) and supports all credential
types for which COSE header parameters are defined (see
Section 3.5.3).
The choice of authentication credential depends also on the trust
model (see Section 3.5.1). For example, a certificate or CWT may
rely on a trusted third party, whereas a CCS or a self-signed
certificate/CWT may be used when trust in the public key can be
achieved by other means, or in the case of trust-on-first-use.
The type of authentication key, authentication credential, and the
way to identify the credential have a large impact on the message
size. For example, the signature_or_MAC field is much smaller with a
static DH key than with a signature key. A CCS is much smaller than
a self-signed certificate/CWT, but if it is possible to reference the
credential with a COSE header like 'kid', then that is typically much
smaller than to transport a CCS.
3.5.1. Identities and trust anchors EDHOC performs the following authentication related operations:
Policies for what connections to allow are typically set based on the * EDHOC transports information about credentials in ID_CRED_I and
identity of the other party, and parties typically only allow ID_CRED_R (described in Section 3.5.3). Based on this
connections from a specific identity or a small restricted set of information, the authentication credentials CRED_I and CRED_R
identities. For example, in the case of a device connecting to a (described in Section 3.5.2) can be obtained. EDHOC may also
network, the network may only allow connections from devices which transport certain authentication related information as External
authenticate with certificates having a particular range of serial Authorization Data (see Section 3.8).
numbers and signed by a particular CA. On the other hand, 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.
EDHOC assumes the existence of mechanisms (certification authority, * EDHOC uses the authentication credentials in two ways (see
trusted third party, pre-provisioning, etc.) for specifying and Section 5.3.2 and Section 5.4.2):
distributing authentication credentials.
* When a Public Key Infrastructure (PKI) is used with certificates, - The authentication credential is input to the integrity
the trust anchor is a Certification Authority (CA) certificate, verification using the MAC fields.
and the identity is the subject whose unique name (e.g., a domain
name, NAI, or EUI) is included in the endpoint's certificate. In
order to run 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 - The authentication key of the authentication credential is used
a trusted third party public key as trust anchor to verify the with the Signature_or_MAC field to verify proof-of-possession
end-entity CWTs, and a specific identity or set of identities in of the private key.
the 'sub' (subject) claim of the CWT to determine if it is allowed
to communicate with. The trusted third party public key can,
e.g., be stored in a self-signed CWT or in a CCS.
* When PKI is not used (CCS, self-signed certificate/CWT), the trust Other authentication related verifications are out of scope for
anchor is the authentication key of the other party. In this EDHOC, and is the responsibility of the application. In particular,
case, the identity is typically directly associated to the the authentication credential needs to be validated in the context of
authentication key of the other party. For example, the name of the connection for which EDHOC is used, see Appendix D. EDHOC MUST
the subject may be a canonical representation of the public key. allow the application to read received information about credential
Alternatively, if identities can be expressed in the form of (ID_CRED_R, ID_CRED_I). EDHOC MUST have access to the authentication
unique subject names assigned to public keys, then a binding to key and the authentication credential.
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 CCS
containing the authentication key and the subject name, see
Section 3.5.3. In order to run 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 the proof
that the other party possesses the private authentication key
corresponding to the public authentication key.
To prevent misbinding attacks in systems where an attacker can Note that the type of authentication key, authentication credential,
register public keys without proving knowledge of the private key, and the identification of the credential have a large impact on the
SIGMA [SIGMA] enforces a MAC to be calculated over the "identity". message size. For example, the signature_or_MAC field is much
EDHOC follows SIGMA by calculating a MAC over the whole credential, smaller with a static DH key than with a signature key. A CCS is
which in case of an X.509 or C509 certificate includes the "subject" much smaller than a self-signed certificate/CWT, but if it is
and "subjectAltName" fields, and in the case of CWT or CCS includes possible to reference the credential with a COSE header like 'kid',
the "sub" claim. While the SIGMA paper only focuses on the identity, then that is in turn much smaller than a CCS.
the same principle is true for other information such as policies
associated to the public key.
3.5.2. Authentication Keys 3.5.1. Authentication Keys
The authentication key (i.e. the public key used for authentication) The authentication key (i.e. the public key used for authentication)
MUST be a signature key or static Diffie-Hellman key. The Initiator MUST be a signature key or static Diffie-Hellman key. The Initiator
and the Responder MAY use different types of authentication keys, and the Responder MAY use different types of authentication keys,
e.g., one uses a signature key and the other uses a static Diffie- e.g., one uses a signature key and the other uses a static Diffie-
Hellman key. The authentication key algorithm needs to be compatible Hellman key.
with the method and the cipher suite. The authentication key
algorithm needs to be compatible with the EDHOC key exchange The authentication key algorithm needs to be compatible with the
method and the cipher suite (see Section 3.6). The authentication
key algorithm needs to be compatible with the EDHOC key exchange
algorithm when static Diffie-Hellman authentication is used, and algorithm when static Diffie-Hellman authentication is used, and
compatible with the EDHOC signature algorithm when signature compatible with the EDHOC signature algorithm when signature
authentication is used. authentication is used.
Note that for most signature algorithms, the signature is determined Note that for most signature algorithms, the signature is determined
by the signature algorithm and the authentication key algorithm by the signature algorithm and the authentication key algorithm
together. When using static Diffie-Hellman keys the Initiator's and together. When using static Diffie-Hellman keys the Initiator's and
Responder's private authentication keys are called I and R, Responder's private authentication keys are denoted I and R,
respectively, and the public authentication keys are called G_I and respectively, and the public authentication keys are denoted G_I and
G_R, respectively. G_R, respectively.
For X.509 the authentication key is represented with a For X.509 certificates the authentication key is represented with a
SubjectPublicKeyInfo field. For CWT and CCS, the authentication key SubjectPublicKeyInfo field. For CWT and CCS (see Section 3.5.2)) the
is represented with a 'cnf' claim [RFC8747] containing a COSE_Key authentication key is represented with a 'cnf' claim [RFC8747]
[I-D.ietf-cose-rfc8152bis-struct]. containing a COSE_Key [I-D.ietf-cose-rfc8152bis-struct].
3.5.3. Authentication Credentials 3.5.2. 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.
EDHOC relies on COSE for identification of authentication credentials EDHOC relies on COSE for identification of credentials (see
(see Section 3.5.4) and supports all credential types for which COSE Section 3.5.3), for example X.509 certificates [RFC5280], C509
header parameters are defined including X.509 [RFC5280], C509 certificates [I-D.ietf-cose-cbor-encoded-cert], CWTs [RFC8392] and
[I-D.ietf-cose-cbor-encoded-cert], CWT [RFC8392] and CWT Claims Set CWT Claims Sets (CCS) [RFC8392]. When the identified credential is a
(CCS) [RFC8392]. When the identified credential is a chain or bag, chain or a bag, the authentication credential CRED_x is just the end
CRED_x is just the end-entity X.509 or C509 certificate / CWT. In entity X.509 or C509 certificate / CWT.
X.509 and C509 certificates, signature keys typically have key usage
"digitalSignature" and Diffie-Hellman public keys typically have key
usage "keyAgreement".
CRED_x needs to be defined such that it is identical when used by Since CRED_R is used in the integrity verification, see
Initiator or Responder. The Initiator and Responder are expected to Section 5.3.2, it needs to be specified such that it is identical
agree on a specific encoding of the credential, see Section 3.9. It when used by Initiator or Responder. Similarly for CRED_I, see
is RECOMMENDED that the COSE 'kid' parameter, when used, refers to a Section 5.4.2. The Initiator and Responder are expected to agree on
specific encoding. The Initiator and Responder SHOULD use an a specific encoding of the credential, see Section 3.9.
available authentication credential (transported in EDHOC or
otherwise provisioned) without re-encoding. If for some reason re- It is RECOMMENDED that the COSE 'kid' parameter, when used to
encoding of the authentication credential may occur, then a potential identify the authentication credential, refers to a specific
common encoding for CBOR based credentials is bytewise lexicographic encoding. The Initiator and Responder SHOULD use an available
order of their deterministic encodings as specified in Section 4.2.1 authentication credential (transported in EDHOC or otherwise
of [RFC8949]. provisioned) without re-encoding. If for some reason re-encoding of
the authentication credential may occur, then a potential common
encoding for CBOR based credentials is bytewise lexicographic order
of their deterministic encodings as specified in Section 4.2.1 of
[RFC8949].
* When the authentication credential is an X.509 certificate, CRED_x * When the authentication credential is an X.509 certificate, CRED_x
SHALL be the end-entity DER encoded certificate, encoded as a bstr SHALL be the DER encoded certificate, encoded as a bstr
[I-D.ietf-cose-x509]. [I-D.ietf-cose-x509].
* When the authentication credential is a C509 certificate, CRED_x * When the authentication credential is a C509 certificate, CRED_x
SHALL be the end-entity C509Certificate SHALL be the C509Certificate [I-D.ietf-cose-cbor-encoded-cert].
[I-D.ietf-cose-cbor-encoded-cert]
* When the authentication credential is a COSE_Key in a CWT, CRED_x * When the authentication credential is a COSE_Key in a CWT, CRED_x
SHALL be the untagged CWT. SHALL be the untagged CWT.
* When the authentication credential is a COSE_Key but not in a CWT, * When the authentication credential is a COSE_Key but not in a CWT,
CRED_x SHALL be an untagged CCS. CRED_x SHALL be an untagged CCS.
- Naked COSE_Keys are thus dressed as CCS when used in EDHOC, - Naked COSE_Keys are thus dressed as CCS when used in EDHOC,
which is done by prefixing the COSE_Key with 0xA108A101. which is done by prefixing the COSE_Key with 0xA108A101.
An example of a CRED_x is shown below: An example of a CRED_x is shown below:
{ /CCS/ { /CCS/
2 : "42-50-31-FF-EF-37-32-39", /sub/ 2 : "42-50-31-FF-EF-37-32-39", /sub/
8 : { /cnf/ 8 : { /cnf/
1 : { /COSE_Key/ 1 : { /COSE_Key/
1 : 1, /kty/ 1 : 1, /kty/
2 : 0, /kid/ 2 : h'00', /kid/
-1 : 4, /crv/ -1 : 4, /crv/
-2 : h'b1a3e89460e88d3a8d54211dc95f0b90 /x/ -2 : h'b1a3e89460e88d3a8d54211dc95f0b90 /x/
3ff205eb71912d6db8f4af980d2db83a' 3ff205eb71912d6db8f4af980d2db83a'
} }
} }
} }
Figure 5: A CCS Containing an X25519 Static Diffie-Hellman Key Figure 6: CWT Claims Set (CCS) containing an X25519 static
and an EUI-64 Identity. Diffie-Hellman key and an EUI-64 identity.
3.5.4. Identification of Credentials 3.5.3. Identification of Credentials
ID_CRED_R and ID_CRED_I are transported in message_2 and message_3, ID_CRED_R and ID_CRED_I are transported in message_2 and message_3,
respectively (see Section 5.3.2 and Section 5.4.2). They are used to respectively, see Section 5.3.2 and Section 5.4.2. They are used to
identify and optionally transport the authentication keys of the identify and optionally transport credentials:
Initiator and the Responder, respectively. ID_CRED_I and ID_CRED_R
do not have any cryptographic purpose in EDHOC since EDHOC integrity
protects the authentication credential. EDHOC relies on COSE for
identification of authentication credentials and supports all types
of COSE header parameters used to identify authentication credentials
including X.509, C509, CWT and CCS.
* 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 authentication key. the authentication credential CRED_R and the authentication key of
R.
* 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 authentication key. the authentication credential CRED_I and the authentication key of
I.
ID_CRED_x may contain the authentication credential CRED_x, but for
many settings it is not necessary to transport the authentication
credential within EDHOC, for example, it may be pre-provisioned or
acquired out-of-band over less constrained links. ID_CRED_I and
ID_CRED_R do not have any cryptographic purpose in EDHOC since the
authentication credentials are integrity protected.
EDHOC relies on COSE for identification of credentials and supports
all credential types for which COSE header parameters are defined
including X.509 certificates ([I-D.ietf-cose-x509]), C509
certificates ([I-D.ietf-cose-cbor-encoded-cert]), CWT (Section 9.6)
and CWT Claims Set (CCS) (Section 9.6).
ID_CRED_I and ID_CRED_R are COSE header maps and contains one or more ID_CRED_I and ID_CRED_R are COSE header maps and contains one or more
COSE header parameter. ID_CRED_I and ID_CRED_R MAY contain different COSE header parameters. ID_CRED_I and ID_CRED_R MAY contain
header parameters. The header parameters typically provide some different header parameters. The header parameters typically provide
information about the format of authentication credential. some information about the format of the credential.
Note that COSE header parameters in ID_CRED_x are used to identify Note that COSE header parameters in ID_CRED_x are used to identify
the sender's authentication credential. There is therefore no reason the sender's credential. There is therefore no reason to use the
to use the "-sender" header parameters, such as x5t-sender, defined "-sender" header parameters, such as x5t-sender, defined in Section 3
in Section 3 of [I-D.ietf-cose-x509]. Instead, the corresponding of [I-D.ietf-cose-x509]. Instead, the corresponding parameter
parameter without "-sender", such as x5t, SHOULD be used. without "-sender", such as x5t, SHOULD be used.
Example: X.509 certificates can be identified by a hash value using Example: X.509 certificates can be identified by a hash value using
the 'x5t' parameter: the 'x5t' parameter:
* ID_CRED_x = { 34 : COSE_CertHash }, for x = I or R, * ID_CRED_x = { 34 : COSE_CertHash }, for x = I or R,
Example: CWT or CCS can be identified by a key identifier using the Example: CWT or CCS can be identified by a key identifier using the
'kid' parameter: 'kid' parameter:
* ID_CRED_x = { 4 : key_id_x }, where key_id_x : kid, for x = I or * ID_CRED_x = { 4 : key_id_x }, where key_id_x : kid, for x = I or
R. R.
Note that 'kid' is extended to support int values to allow more one- The value of a COSE 'kid' parameter is a byte string. To allow one-
byte identifiers (see Section 9.7 and Section 9.8) which may be byte encodings of ID_CRED_x with key identifiers 'kid', which is
useful in many scenarios since constrained devices only have a few useful in scenarios with only a few keys, the integer representation
keys. As stated in Section 3.1 of [I-D.ietf-cose-rfc8152bis-struct], of identifiers in Section 3.3.2 MUST be applied. For details, see
Section 5.3.2 and Section 5.4.2.
As stated in Section 3.1 of [I-D.ietf-cose-rfc8152bis-struct],
applications MUST NOT assume that 'kid' values are unique and several applications MUST NOT assume that 'kid' values are unique and several
keys associated with a 'kid' may need to be checked before the keys associated with a 'kid' may need to be checked before the
correct one is found. Applications might use additional information correct one is found. Applications might use additional information
such as 'kid context' or lower layers to determine which key to try such as 'kid context' or lower layers to determine which key to try
first. Applications should strive to make ID_CRED_x as unique as first. Applications should strive to make ID_CRED_x as unique as
possible, since the recipient may otherwise have to try several keys. possible, since the recipient may otherwise have to try several keys.
See Appendix C.3 for more examples. See Appendix C.3 for more examples.
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 as well the "COSE Algorithms" and "COSE Elliptic Curves" registries as well
as the EDHOC MAC length. Algorithms need to be specified with enough as the EDHOC MAC length. All algorithm names and definitions follows
parameters to make them completely determined. EDHOC is currently from COSE [I-D.ietf-cose-rfc8152bis-algs]. Note that COSE sometimes
uses peculiar names such as ES256 for ECDSA with SHA-256, A128 for
AES-128, and Ed25519 for the curve edwards25519. Algorithms need to
be specified with enough parameters to make them completely
determined. The MAC length MUST be at least 8 bytes. Any
cryptographic algorithm used in the COSE header parameters in ID_CRED
is selected independently of the cipher suite. EDHOC is currently
only specified for use with key exchange algorithms of type ECDH only specified for use with key exchange algorithms of type ECDH
curves, but any Key Encapsulation Method (KEM), including Post- curves, but any Key Encapsulation Method (KEM), including Post-
Quantum Cryptography (PQC) KEMs, can be used in method 0, see Quantum Cryptography (PQC) KEMs, can be used in method 0, see
Section 8.4. Use of other types of key exchange algorithms to Section 8.4. Use of other types of key exchange algorithms to
replace static DH authentication (method 1,2,3) would likely require replace static DH authentication (method 1,2,3) would likely require
a specification updating EDHOC with new methods. a specification updating EDHOC with new methods.
EDHOC supports all signature algorithms defined by COSE, including EDHOC supports all signature algorithms defined by COSE. Just like
PQC signature algorithms such as HSS-LMS. Just like in TLS 1.3 in (D)TLS 1.3 [RFC8446][RFC9147] and IKEv2 [RFC7296], a signature in
[RFC8446] and IKEv2 [RFC7296], a signature in COSE is determined by COSE is determined by the signature algorithm and the authentication
the signature algorithm and the authentication key algorithm key algorithm together, see Section 3.5.1. The exact details of the
together, see Section 3.5.2. The exact details of the authentication authentication key algorithm depend on the type of authentication
key algorithm depend on the type of authentication credential. COSE credential. COSE supports different formats for storing the public
supports different formats for storing the public authentication keys authentication keys including COSE_Key and X.509, which use different
including COSE_Key and X.509, which have different names and ways to names and ways to represent the authentication key and the
represent the authentication key and the authentication key authentication key algorithm.
algorithm.
An EDHOC cipher suite consists of the following parameters: An EDHOC cipher suite consists of the following parameters:
* EDHOC AEAD algorithm * EDHOC AEAD algorithm
* EDHOC hash algorithm * EDHOC hash algorithm
* EDHOC MAC length in bytes (Static DH) * EDHOC MAC length in bytes (Static DH)
* EDHOC key exchange algorithm (ECDH curve) * EDHOC key exchange algorithm (ECDH curve)
* EDHOC signature algorithm * EDHOC signature algorithm
* Application AEAD algorithm * Application AEAD algorithm
* Application hash algorithm * Application hash algorithm
Each cipher suite is identified with a pre-defined int label. Each cipher suite is identified with a pre-defined integer 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 any combination of COSE algorithms and Implementations can either use any combination of COSE algorithms and
parameters to define their own private cipher suite, or use one of parameters to define their own private cipher suite, or use one of
the pre-defined cipher suites. Private cipher suites can be the pre-defined cipher suites. Private cipher suites can be
identified with any of the four values -24, -23, -22, -21. The pre- identified with any of the four values -24, -23, -22, -21. The pre-
defined cipher suites are listed in the IANA registry (Section 9.2) defined cipher suites are listed in the IANA registry (Section 9.2)
with initial content outlined here: with initial content outlined here:
* Cipher suites 0-3, based on AES-CCM, are intended for constrained * Cipher suites 0-3, based on AES-CCM, are intended for constrained
IoT where message overhead is a very important factor. Note that IoT where message overhead is a very important factor. Note that
AES-CCM-16-64-128 and AES-CCM-16-64-128 are compatible with the AES-CCM-16-64-128 and AES-CCM-16-64-128 are compatible with the
IEEE CCM* mode. IEEE CCM* mode.
- Cipher suites 1 and 3 use a larger tag length (128-bit) in - Cipher suites 1 and 3 use a larger tag length (128-bit) in
EDHOC than in the Application AEAD algorithm (64-bit). EDHOC than in the Application AEAD algorithm (64-bit).
* Cipher suites 4 and 5, based on ChaCha20, are intended for less * Cipher suites 4 and 5, based on ChaCha20, are intended for less
constrained applications and only use 128-bit tag lengths. constrained applications and only use 128-bit tag lengths.
* Cipher suite 6, based on AES-GCM, is for general non-constrained * Cipher suite 6, based on AES-GCM, is for general non-constrained
applications. It uses high performance algorithms that are widely applications. It consists of high performance algorithms that are
supported. widely used in non-constrained applications.
* Cipher suites 24 and 25 are intended for high security * Cipher suites 24 and 25 are intended for high security
applications such as government use and financial applications. applications such as government use and financial applications.
These cipher suites do not share any algorithms. Cipher suite 24 These cipher suites do not share any algorithms. Cipher suite 24
is compatible with the CNSA suite [CNSA]. consists of algorithms from the CNSA suite [CNSA].
The different methods (Section 3.2) use the same cipher suites, but The different methods (Section 3.2) use the same cipher suites, but
some algorithms are not used in some methods. The EDHOC signature some algorithms are not used in some methods. The EDHOC signature
algorithm is not used in methods without signature authentication. algorithm is not 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 contains cipher suites supported by the suites it supports. SUITES_I contains cipher suites supported by the
Initiator, formatted and processed as detailed in Section 5.2.1 to Initiator, formatted and processed as detailed in Section 5.2.1 to
secure the cipher suite negotiation. Examples of cipher suite secure the cipher suite negotiation. Examples of cipher suite
negotiation are given in Section 6.3.2. negotiation are given in Section 6.3.2.
3.7. Ephemeral Public Keys 3.7. Ephemeral Public Keys
EDHOC always uses compact representation of elliptic curve points, The ephemeral public keys in EDHOC (G_X and G_Y) use compact
see Appendix B. In COSE compact representation is achieved by representation of elliptic curve points, see Appendix B. In COSE
formatting the ECDH ephemeral public keys as COSE_Keys of type EC2 or compact representation is achieved by formatting the ECDH ephemeral
OKP according to Sections 7.1 and 7.2 of public keys as COSE_Keys of type EC2 or OKP according to Sections 7.1
[I-D.ietf-cose-rfc8152bis-algs], but only including the 'x' parameter and 7.2 of [I-D.ietf-cose-rfc8152bis-algs], but only including the
in G_X and G_Y. For Elliptic Curve Keys of type EC2, compact 'x' parameter in G_X and G_Y. For Elliptic Curve Keys of type EC2,
representation MAY be used also in the COSE_Key. If the COSE compact representation MAY be used also in the COSE_Key. If the COSE
implementation requires an 'y' parameter, the value y = false SHALL implementation requires a 'y' parameter, the value y = false SHALL be
be used. COSE always use compact output for Elliptic Curve Keys of used. COSE always use compact output for Elliptic Curve Keys of type
type EC2. EC2.
3.8. External Authorization Data (EAD) 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 the number of messages or to
processing, external security applications may be integrated into simplify processing, external security applications may be integrated
EDHOC by transporting authorization related data in the messages. into EDHOC by transporting authorization related data in the
One example is third-party identity and authorization information messages.
protected out of scope of EDHOC [I-D.selander-ace-ake-authz].
Another example is a certificate enrolment request or the resulting
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 each of the four EDHOC messages (EAD_1, EAD_2, EAD_3, EAD_4).
(EAD_1) or message_2 (EAD_2) should be considered unprotected by
EDHOC, see Section 8.5. External authorization data sent in
message_3 (EAD_3) or message_4 (EAD_4) is protected between Initiator
and Responder.
External authorization data is a CBOR sequence (see Appendix C.1) External authorization data is a CBOR sequence (see Appendix C.1)
consisting of one or more (ead_label, ead_value) pairs as defined consisting of one or more (ead_label, ead_value) pairs as defined
below: below:
ead = 1* ( ead = 1* (
ead_label : int, ead_label : int,
ead_value : any, ead_value : bstr,
) )
Applications using external authorization data need to specify A security application using external authorization data need to
format, processing, and security considerations and register the register an ead_label, specify the ead_value format for each message
(ead_label, ead_value) pair, see Section 9.5. The CDDL type of (see Section 9.5), and describe processing and security
ead_value is determined by the int ead_label and MUST be specified. considerations.
The EAD fields of EDHOC are not intended for generic application The EAD fields of EDHOC must not be used for generic application
data. Since data carried in EAD_1 and EAD_2 fields may not be data. Examples of the use of EAD is provided in Appendix E.
protected, special considerations need to be made such that it does
not violate security and privacy requirements of the service which
uses this data. Moreover, the content in an EAD field may impact the
security properties provided by EDHOC. Security applications making
use of the EAD fields must perform the necessary security analysis.
3.9. Applicability Statement 3.9. Application Profile
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 negotiated through the
execution (specifically cipher suite negotiation, see Section 3.6) protocol execution (specifically, cipher suite, see Section 3.6) but
but other parameters may need to be known out-of-band (e.g., which other parameters are only communicated and may not be negotiated
authentication method is used, see Section 3.2). (e.g., which authentication method is used, see Section 3.2). Yet
other parameters need to be known out-of-band.
The purpose of the applicability statement is to describe the The purpose of an application profile is to describe the intended use
intended use of EDHOC to allow for the relevant processing and of EDHOC to allow for the relevant processing and verifications to be
verifications to be made, including things like: 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. Format; see Appendix A.2.
* The method of transporting EDHOC messages may also describe * The method of transporting EDHOC messages may also describe
data carried along with the messages that are needed for the data carried along with the messages that are needed for the
transport to satisfy the requirements of Section 3.4, e.g., transport to satisfy the requirements of Section 3.4, e.g.,
connection identifiers used with certain messages, see connection identifiers used with certain messages, see
Appendix A.3. Appendix A.2.
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 CCS, including Section 3.5.2), e.g., profile for certificate or CCS, including
supported authentication key algorithms (subject public key supported authentication key algorithms (subject public key
algorithm in X.509 or C509 certificate). algorithm in X.509 or C509 certificate).
4. Type used to identify authentication credentials (ID_CRED_I, 4. Type used to identify credentials (ID_CRED_I, ID_CRED_R; see
ID_CRED_R; see Section 3.5.4). Section 3.5.3).
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 3.5.1. 6. Identifier used as the identity of the endpoint; see
Appendix D.2.
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 application profile may also contain information about supported
supported cipher suites. The procedure for selecting and verifying cipher suites. The procedure for selecting and verifying a cipher
cipher suite is still performed as described in Section 5.2.1 and suite is still performed as described in Section 5.2.1 and
Section 6.3, but it may become simplified by this knowledge. Section 6.3, but it may become simplified by this knowledge.
An example of an applicability statement is shown in Appendix D. An example of an application profile is shown in Appendix F.
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 the application profile,
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 the profile of CRED_x in the case that it
transported, it may not be possible to verify that incompliance with is not transported, it may not be possible to verify that
applicability statement was the reason for failure: Integrity incompliance with the application profile was the reason for failure:
verification in message_2 or message_3 may fail not only because of Integrity verification in message_2 or message_3 may fail not only
wrong authentication credential. For example, in case the Initiator because of wrong credential. For example, in case the Initiator uses
uses public key certificate by reference (i.e., not transported public key certificate by reference (i.e., not transported within the
within the protocol) then both endpoints need to use an identical protocol) then both endpoints need to use an identical data structure
data structure as CRED_I or else the integrity verification will as CRED_I or else the integrity verification will fail.
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 application profile may be dependent on the identity of the other
other endpoint, or other information carried in an EDHOC message, but endpoint, or other information carried in an EDHOC message, but it
it then applies only to the later phases of the protocol when such then applies only to the later phases of the protocol when such
information is known. (The Initiator does not know identity of information is known. (The Initiator does not know the identity of
Responder before having verified message_2, and the Responder does the Responder before having verified message_2, and the Responder
not know identity of the Initiator before having verified message_3.) does not know the 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 application profile, 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 application profiles are used, the receiver needs to be able
able to determine which is applicable for a given session, for to determine which is applicable for a given session, for example
example based on URI or external authorization data type. based on URI or external authorization data type.
4. Key Derivation 4. Key Derivation
4.1. Keys for EDHOC Message Processing
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 message
application. Extract is used to derive fixed-length uniformly processing. This section defines Extract (Section 4.1.1) and Expand
pseudorandom keys (PRK) from ECDH shared secrets. Expand is used to (Section 4.1.2), and how to use them to derive PRK_out
derive additional output keying material (OKM) from the PRKs. (Section 4.1.3) which is the shared secret key resulting from a
successful EDHOC exchange.
This section defines Extract, Expand and other key derivation Extract is used to derive fixed-length uniformly pseudorandom keys
functions based on these: Expand is used to define EDHOC-KDF and in (PRK) from ECDH shared secrets. Expand is used to define EDHOC-KDF
turn EDHOC-Exporter, whereas Extract is used to define EDHOC- for generating MACs and for deriving output keying material (OKM)
KeyUpdate. from PRKs.
4.1. Extract In EDHOC a specific message is protected with a certain pseudorandom
key, but how the key is derived depends on the method as detailed in
Section 5.
The pseudorandom keys (PRKs) are derived using Extract. 4.1.1. Extract
The pseudorandom keys (PRKs) used for EDHOC message processing are
derived using Extract:
PRK = Extract( salt, IKM ) PRK = Extract( salt, IKM )
where the input keying material (IKM) and salt are defined for each where the input keying material (IKM) and salt are defined for each
PRK below. PRK below.
The definition of Extract depends on the EDHOC hash algorithm of the The definition of Extract depends on the EDHOC hash algorithm of the
selected cipher suite: selected cipher suite:
* if the EDHOC hash algorithm is SHA-2, then Extract( salt, IKM ) = * if the EDHOC hash algorithm is SHA-2, then Extract( salt, IKM ) =
HKDF-Extract( salt, IKM ) [RFC5869] HKDF-Extract( salt, IKM ) [RFC5869]
* if the EDHOC hash algorithm is SHAKE128, then Extract( salt, IKM ) * if the EDHOC hash algorithm is SHAKE128, then Extract( salt, IKM )
= KMAC128( salt, IKM, 256, "" ) = KMAC128( salt, IKM, 256, "" )
* if the EDHOC hash algorithm is SHAKE256, then Extract( salt, IKM ) * if the EDHOC hash algorithm is SHAKE256, then Extract( salt, IKM )
= KMAC256( salt, IKM, 512, "" ) = KMAC256( salt, IKM, 512, "" )
4.1.1. PRK_2e The rest of the section defines the pseudo-random keys PRK_2e,
PRK_3e2m and PRK_4e3m; their use is shown in Figure 7.
PRK_2e is used to derive a keystream to encrypt message_2. PRK_2e is 4.1.1.1. PRK_2e
derived with the following input:
The pseudo-random key PRK_2e is derived with the following input:
* The salt SHALL be a zero-length byte string. Note that [RFC5869] * The salt SHALL be a zero-length 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 zero-length byte string (0x). to the zero-length byte string (0x).
* The IKM SHALL be the ephemeral-ephemeral ECDH shared secret G_XY * The IKM SHALL be the ephemeral-ephemeral ECDH shared secret G_XY
(calculated from G_X and Y or G_Y and X) as defined in (calculated from G_X and Y or G_Y and X) as defined in
Section 6.3.1 of [I-D.ietf-cose-rfc8152bis-algs]. The use of G_XY Section 6.3.1 of [I-D.ietf-cose-rfc8152bis-algs]. The use of G_XY
skipping to change at page 24, line 7 skipping to change at page 23, line 36
G_XY = X25519( Y, G_X ) = X25519( X, G_Y ) 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 (zero-length byte string). where salt = 0x (zero-length byte string).
4.1.2. PRK_3e2m 4.1.1.2. PRK_3e2m
PRK_3e2m is used to produce a MAC in message_2 and to encrypt The pseudo-random key PRK_3e2m is derived as follows:
message_3. PRK_3e2m is derived as follows:
If the Responder authenticates with a static Diffie-Hellman key, then If the Responder authenticates with a static Diffie-Hellman key, then
PRK_3e2m = Extract( PRK_2e, G_RX ), where G_RX is the ECDH shared PRK_3e2m = Extract( SALT_3e2m, G_RX ), where
secret calculated from G_R and X, or G_X and R, else PRK_3e2m =
PRK_2e.
4.1.3. PRK_4x3m * SALT_3e2m is derived from PRK_2e, see Section 4.1.2, and
PRK_4x3m is used to produce a MAC in message_3, to encrypt message_4, * G_RX is the ECDH shared secret calculated from G_R and X, or G_X
and to derive application specific data. PRK_4x3m is derived as and R (the Responder's private authentication key, see
follows: Section 3.5.1),
else PRK_3e2m = PRK_2e.
4.1.1.3. PRK_4e3m
The pseudo-random key PRK_4e3m is derived as follows:
If the Initiator authenticates with a static Diffie-Hellman key, then If the Initiator authenticates with a static Diffie-Hellman key, then
PRK_4x3m = Extract( PRK_3e2m, G_IY ), where G_IY is the ECDH shared PRK_4e3m = Extract( SALT_4e3m, G_IY ), where
secret calculated from G_I and Y, or G_Y and I, else PRK_4x3m =
PRK_3e2m.
4.2. Expand * SALT_4e3m is derived from PRK_3e2m, see Section 4.1.2, and
The keys, IVs and MACs used in EDHOC are derived from the PRKs using * G_IY is the ECDH shared secret calculated from G_I and Y, or G_Y
Expand, and instantiated with the EDHOC AEAD algorithm in the and I (the Initiator's private authentication key, see
selected cipher suite. Section 3.5.1),
OKM = EDHOC-KDF( PRK, transcript_hash, label, context, length ) else PRK_4e3m = PRK_3e2m.
4.1.2. Expand and EDHOC-KDF
The output keying material (OKM) - including keys, IVs, and salts -
are derived from the PRKs using the EDHOC-KDF, which is defined
through Expand:
OKM = EDHOC-KDF( PRK, label, context, length )
= Expand( PRK, info, length ) = Expand( PRK, info, length )
where info is encoded as the CBOR sequence where info is encoded as the CBOR sequence
info = ( info = (
transcript_hash : bstr, label : uint,
label : tstr,
context : bstr, context : bstr,
length : uint, length : uint,
) )
where where
* transcript_hash is a bstr set to one of the transcript hashes * label is a uint
TH_2, TH_3, or TH_4 as defined in Sections 5.3.1, 5.4.1, and 4.3.
* label is a tstr set to the name of the derived key, IV or MAC;
i.e., "KEYSTREAM_2", "MAC_2", "K_3", "IV_3", or "MAC_3".
* context is a bstr * context is a bstr
* length is the length of output keying material (OKM) in bytes * length is the length of OKM in bytes
When EDHOC-KDF is used to derive OKM for EDHOC message processing,
then context includes one of the transcript hashes TH_2, TH_3, or
TH_4 defined in Sections 5.3.2 and 5.4.2.
The definition of Expand depends on the EDHOC hash algorithm of the The definition of Expand depends on the EDHOC hash algorithm of the
selected cipher suite: selected cipher suite:
* if the EDHOC hash algorithm is SHA-2, then Expand( PRK, info, * if the EDHOC hash algorithm is SHA-2, then Expand( PRK, info,
length ) = HKDF-Expand( PRK, info, length ) [RFC5869] length ) = HKDF-Expand( PRK, info, length ) [RFC5869]
* if the EDHOC hash algorithm is SHAKE128, then Expand( PRK, info, * if the EDHOC hash algorithm is SHAKE128, then Expand( PRK, info,
length ) = KMAC128( PRK, info, L, "" ) length ) = KMAC128( PRK, info, L, "" )
* if the EDHOC hash algorithm is SHAKE256, then Expand( PRK, info, * if the EDHOC hash algorithm is SHAKE256, then Expand( PRK, info,
length ) = KMAC256( PRK, info, L, "" ) length ) = KMAC256( PRK, info, L, "" )
where L = 8*length, the output length in bits. where L = 8*length, the output length in bits.
The keys, IVs and MACs are derived as follows: Figure 7 lists derivations made with EDHOC-KDF during message
processing. How the output keying material is used is specified in
Section 5.
* KEYSTREAM_2 is derived using the transcript hash TH_2 and the KEYSTREAM_2 = EDHOC-KDF( PRK_2e, 0, TH_2, plaintext_length )
pseudorandom key PRK_2e. SALT_3e2m = EDHOC-KDF( PRK_2e, 1, TH_2, hash_length )
MAC_2 = EDHOC-KDF( PRK_3e2m, 2, context_2, mac_length_2 )
K_3 = EDHOC-KDF( PRK_3e2m, 3, TH_3, key_length )
IV_3 = EDHOC-KDF( PRK_3e2m, 4, TH_3, iv_length )
SALT_4e3m = EDHOC-KDF( PRK_3e2m, 5, TH_3, hash_length )
MAC_3 = EDHOC-KDF( PRK_4e3m, 6, context_3, mac_length_3 )
PRK_out = EDHOC-KDF( PRK_4e3m, 7, TH_4, hash_length )
K_4 = EDHOC-KDF( PRK_4e3m, 8, TH_4, key_length )
IV_4 = EDHOC-KDF( PRK_4e3m, 9, TH_4, iv_length )
* MAC_2 is derived using the transcript hash TH_2 and the Figure 7: Key derivations using EDHOC-KDF.
pseudorandom key PRK_3e2m.
* K_3 and IV_3 are derived using the transcript hash TH_3 and the 4.1.3. PRK_out
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 The pseudo-random key PRK_out, derived as shown in Figure 7, is the
pseudorandom key PRK_4x3m. only secret key shared between Initiator and Responder that needs to
be stored after a successful EDHOC exchange, see Section 5.4. Keys
for applications are derived from PRK_out, see Section 4.2.1.
KEYSTREAM_2, K_3, and IV_3 use an empty CBOR byte string h'' as 4.2. Keys for EDHOC Applications
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 This section defines EDHOC-Exporter and EDHOC-KeyUpdate in terms of
EDHOC-KDF and PRK_out.
Application keys and other application specific data can be derived 4.2.1. EDHOC-Exporter
using the EDHOC-Exporter interface defined as:
Keying material for the application can be derived 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_exporter, label, context, length)
where label is a registered tstr from the EDHOC Exporter Label where
registry (Section 9.1), context is a bstr defined by the application,
and length is a uint defined by the application. The (label,
context) pair must be unique, i.e., a (label, context) MUST NOT be
used for two different purposes. However an application can re-
derive the same key several times as long as it is done in a secure
way. For example, in most encryption algorithms the same key kan be
reused with different nonces. 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 * label is a registered uint from the EDHOC Exporter Label registry
hash function is a CBOR Sequence. (Section 9.1)
TH_4 = H( TH_3, CIPHERTEXT_3 ) * context is a bstr defined by the application
where H() is the hash function in the selected cipher suite. * length is a uint defined by the application
Examples of use of the EDHOC-Exporter are given in Section 5.5.2 and
Appendix A.
* K_4 and IV_4 are derived with the EDHOC-Exporter using the empty * PRK_exporter is derived from PRK_out:
CBOR byte string h'' as context, and labels "EDHOC_K_4" and
"EDHOC_IV_4", respectively. IVs are only used if the EDHOC AEAD
algorithm uses IVs.
4.4. EDHOC-KeyUpdate PRK_exporter = EDHOC-KDF( PRK_out, 10, h'', hash_length )
where hash_length denotes the length of the hash function output in
bytes, as specified by the COSE hash algorithm definition.
PRK_exporter MUST be derived anew if PRK_out is updated, in
particular if EDHOC-KeyUpdate is used, see Section 4.2.2.
The (label, context) pair must be unique, i.e., a (label, context)
MUST NOT be used for two different purposes. However an application
can re-derive the same key several times as long as it is done in a
secure way. For example, in most encryption algorithms the same key
can be reused with different nonces. The context can for example be
the empty CBOR byte string.
Examples of use of the EDHOC-Exporter are given in Appendix A.
4.2.2. 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_out is deleted and the new
PRK_4x3m is calculated as a "hash" of the old key using the Extract PRK_out is calculated as a "hash" of the old key using the Expand
function as illustrated by the following pseudocode: function as illustrated by the following pseudocode:
EDHOC-KeyUpdate( nonce ): EDHOC-KeyUpdate( context ):
PRK_4x3m = Extract( nonce, PRK_4x3m ) PRK_out = EDHOC-KDF( PRK_out, 11, context, hash_length )
The EDHOC-KeyUpdate takes a nonce as input to guarantee that there where hash_length denotes the length of the hash function output in
are no short cycles. The Initiator and the Responder need to agree bytes, as specified by the COSE hash algorithm definition.
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 The EDHOC-KeyUpdate takes a context as input to enable binding of the
strong security properties as re-running EDHOC, see Section 8. updated PRK_out to some event that triggered the keyUpdate. The
Initiator and the Responder need to agree on the context, which can,
e.g., be a counter or a pseudo-random number such as a hash. The
Initiator and the Responder also need to cache the old PRK_out until
it has verfied that the other endpoint has the correct new PRK_out.
[I-D.ietf-core-oscore-key-update] describes key update for OSCORE
using EDHOC-KeyUpdate.
While this key update method provides forward secrecy it does not
give as strong security properties as re-running EDHOC, see
Section 8.
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. Annotated traces steps. Error messages are specified in Section 6. Annotated traces
of EDHOC protocol runs are provided in [I-D.selander-lake-traces]. of EDHOC protocol runs are provided in [I-D.ietf-lake-traces].
An EDHOC message is encoded as a sequence of CBOR data items (CBOR An EDHOC message is encoded as a sequence of CBOR data items (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, see Appendix C.3. The unprotected COSE header in messages, see Appendix C.3. The unprotected COSE header in
COSE_Sign1, and COSE_Encrypt0 (not included in the EDHOC message) MAY COSE_Sign1, and COSE_Encrypt0 (not included in the EDHOC message) MAY
contain 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 new/ongoing session, the endpoints are assumed to keep an For each new/ongoing session, the endpoints are assumed to keep an
associated protocol state containing identifiers, keying material, associated protocol state containing identifiers, keying material,
etc. used for subsequent processing of protocol related data. The etc. used for subsequent processing of protocol related data. The
protocol state is assumed to be associated to an applicability protocol state is assumed to be associated to an application profile
statement (Section 3.9) which provides the context for how messages (Section 3.9) which provides the context for how messages are
are transported, identified, and processed. transported, identified, 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 8.6). Denial-of-Service mitigation (Section 8.7).
3. If the message received is an error message, then process 3. If the message received is an error message, then process it
according to Section 6, else process as the expected next message according to Section 6, else process it as the expected next
according to the protocol state. message according to the protocol state.
If the processing fails for some reason then, typically, an error If the processing fails for some reason then, typically, an error
message is sent, the protocol is discontinued, and the protocol state message is sent, the protocol is discontinued, and the protocol state
erased. Further details are provided in the following subsections erased. Further details are provided in the following subsections
and in Section 6. 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 in the same session because the
has moved on and now expects something else. This assumes that state of the protocol has moved on and now expects something else.
message duplication due to re-transmissions is handled by the This assumes that message duplication due to re-transmissions is
transport protocol, see Section 3.4. The case when the transport handled by the transport protocol, see Section 3.4. The case when
does not support message deduplication is addressed in Appendix E. the transport does not support message deduplication is addressed in
Appendix G.
5.2. EDHOC Message 1 5.2. EDHOC Message 1
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 : suites, SUITES_I : suites,
G_X : bstr, G_X : bstr,
C_I : bstr / int, C_I : bstr / -24..23,
? EAD_1 : ead, ? EAD_1 : ead,
) )
suites = [ 2* int ] / int suites = [ 2* int ] / int
where: where:
* METHOD - authentication method, see Section 3.2. * METHOD - authentication method, see Section 3.2.
* SUITES_I - array of cipher suites which the Initiator supports in * SUITES_I - array of cipher suites which the Initiator supports in
order of preference, starting with the most preferred and ending order of preference, the first cipher suite in network byte order
with the cipher suite selected for this session. If the most is the most preferred by I, the last is the one selected by I for
preferred cipher suite is selected then SUITES_I is encoded as this session. If the most preferred cipher suite is selected then
that cipher suite, i.e., as an int. The processing steps are SUITES_I contains only that cipher suite and is encoded as an int.
detailed below and in Section 6.3. The processing steps are detailed below and in Section 6.3.
* G_X - the ephemeral public key of the Initiator * G_X - the ephemeral public key of the Initiator
* C_I - variable length connection identifier * C_I - variable length connection identifier. Note that connection
identifiers are byte strings but certain values are represented as
integers in the message, see Section 3.3.2.
* EAD_1 - unprotected external authorization data, see Section 3.8. * EAD_1 - 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:
* SUITES_I contains a list of supported cipher suites, in order of * Construct SUITES_I complying with the definition in
preference, truncated after the cipher suite selected for this Section 5.2.1}, and furthermore:
session.
- 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. Responder.
- The selected cipher suite MAY be changed between sessions, - The selected cipher suite (i.e. the last cipher suite in
e.g., based on previous error messages (see next bullet), but SUITES_I) MAY be different between sessions, e.g., based on
all cipher suites which are more preferred than the selected previous error messages (see next bullet), but all cipher
cipher suite in the list MUST be included in SUITES_I. suites which are more preferred by I than the selected cipher
suite MUST be included in SUITES_I.
- If the Initiator previously received from the Responder an - If the Initiator previously received from the Responder an
error message with error code 2 (see Section 6.3) indicating error message with error code 2 containing SUITES_R (see
cipher suites supported by the Responder, then the Initiator Section 6.3) which indicates cipher suites supported by the
SHOULD select the most preferred supported cipher suite among Responder, then the Initiator SHOULD select its most preferred
those (note that error messages are not authenticated and may supported cipher suite among those (bearing in mind that error
be forged). messages are not authenticated and may be forged).
- The supported cipher suites and the order of preference MUST - The Initiator MUST NOT change the supported cipher suites and
NOT be changed based on previous error messages. the order of preference in SUITES_I based on previous error
messages.
* 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.
* 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.
* 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:
* Decode message_1 (see Appendix C.1). * Decode message_1 (see Appendix C.1).
* 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.
* Pass EAD_1 to the security application. * If EAD_1 is present then make it available to the application for
EAD processing.
If any processing step fails, the Responder SHOULD send an EDHOC If any processing step fails, the Responder MUST send an EDHOC error
error message back, formatted as defined in Section 6, and the message back, formatted as defined in Section 6, and the session MUST
session MUST be discontinued. Sending error messages is essential be discontinued.
for debugging but MAY e.g., be skipped due to denial-of-service
reasons, see Section 8.6. If an error message is sent, the session
MUST be discontinued.
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 SHALL be a CBOR Sequence (see Appendix C.1) as defined message_2 SHALL be a CBOR Sequence (see Appendix C.1) as defined
below below
message_2 = ( message_2 = (
G_Y_CIPHERTEXT_2 : bstr, G_Y_CIPHERTEXT_2 : bstr,
C_R : bstr / int, C_R : bstr / -24..23,
) )
where: where:
* G_Y_CIPHERTEXT_2 - the concatenation of G_Y, the ephemeral public * G_Y_CIPHERTEXT_2 - the concatenation of G_Y (i.e., the ephemeral
key of the Responder, and CIPHERTEXT_2 public key of the Responder) and CIPHERTEXT_2.
* C_R - variable length connection identifier * C_R - variable length connection identifier. Note that connection
identifiers are byte strings but certain values are represented as
integers in the message, see Section 3.3.2.
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:
* 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.
* 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.
* Compute the transcript hash TH_2 = H( H(message_1), G_Y, C_R ) * Compute the transcript hash TH_2 = H( G_Y, C_R, H(message_1) )
where H() is the hash function in the selected cipher suite. The where H() is the EDHOC hash algorithm of the selected cipher
transcript hash TH_2 is a CBOR encoded bstr and the input to the suite. The transcript hash TH_2 is a CBOR encoded bstr and the
hash function is a CBOR Sequence. Note that H(message_1) can be input to the hash function is a CBOR Sequence. Note that
computed and cached already in the processing of message_1. H(message_1) can be computed and cached already in the processing
of message_1.
* Compute MAC_2 = EDHOC-KDF( PRK_3e2m, TH_2, "MAC_2", << ID_CRED_R, * Compute MAC_2 as in Section 4.1.2 with context_2 = << ID_CRED_R,
CRED_R, ? EAD_2 >>, mac_length_2 ). If the Responder TH_2, CRED_R, ? EAD_2 >>
authenticates with a static Diffie-Hellman key (method equals 1 or
3), then mac_length_2 is the EDHOC MAC length given by the
selected cipher suite. If the Responder authenticates with a
signature key (method equals 0 or 2), then mac_length_2 is equal
to the output size of the EDHOC hash algorithm given by the
selected cipher suite.
- ID_CRED_R - identifier to facilitate retrieval of CRED_R, see - If the Responder authenticates with a static Diffie-Hellman key
Section 3.5.4 (method equals 1 or 3), then mac_length_2 is the EDHOC MAC
length given by the selected cipher suite. If the Responder
authenticates with a signature key (method equals 0 or 2), then
mac_length_2 is equal to the output size of the EDHOC hash
algorithm given by the selected cipher suite.
- CRED_R - CBOR item containing the credential of the Responder, - ID_CRED_R - identifier to facilitate the retrieval of CRED_R,
see Section 3.5.3 see Section 3.5.3
- EAD_2 - unprotected external authorization data, see - CRED_R - CBOR item containing the authentication credential of
Section 3.8 the Responder, see Section 3.5.2
- EAD_2 - external authorization data, see Section 3.8
* 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' field of a 2), then Signature_or_MAC_2 is the 'signature' field of a
COSE_Sign1 object as defined in Section 4.4 of COSE_Sign1 object, computed as specified in Section 4.4 of
[I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm of [I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm of
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 as input (see Responder, and the following parameters as input (see Appendix C.3
Appendix C.3): for an overview of COSE and Appendix C.1 for notation):
- 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
* CIPHERTEXT_2 is calculated by using the Expand function as a * CIPHERTEXT_2 is calculated by using the Expand function as a
binary additive stream cipher. binary additive stream cipher over the following plaintext:
- plaintext = ( ID_CRED_R / bstr / int, Signature_or_MAC_2, ? - PLAINTEXT_2 = ( ? PAD, ID_CRED_R / bstr / -24..23,
EAD_2 ) Signature_or_MAC_2, ? EAD_2 )
o If ID_CRED_R contains a single 'kid' parameter, i.e., o If ID_CRED_R contains a single 'kid' parameter, i.e.,
ID_CRED_R = { 4 : kid_R }, then only the byte string or ID_CRED_R = { 4 : kid_R }, then only the byte string kid_R
integer kid_R is conveyed in the plaintext encoded is conveyed in the plaintext, represented as described in
accordingly as bstr or int. Section 3.3.2.
- Compute KEYSTREAM_2 = EDHOC-KDF( PRK_2e, TH_2, "KEYSTREAM_2", o PAD = 1*true is padding that may be used to hide the length
h'', plaintext_length ), where plaintext_length is the length of the unpadded plaintext
of the plaintext.
- CIPHERTEXT_2 = plaintext XOR KEYSTREAM_2 - Compute KEYSTREAM_2 as in Section 4.1.2, where plaintext_length
is the length of PLAINTEXT_2.
- CIPHERTEXT_2 = PLAINTEXT_2 XOR KEYSTREAM_2
* 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:
* Decode message_2 (see Appendix C.1). * Decode message_2 (see Appendix C.1).
* 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, the 5-tuple, or the by the transport (e.g., the CoAP Token, the 5-tuple, or the
prepended C_I, see Appendix A.3). prepended C_I, see Appendix A.2).
* Decrypt CIPHERTEXT_2, see Section 5.3.2. * Decrypt CIPHERTEXT_2, see Section 5.3.2, and discard padding, if
present.
* Pass EAD_2 to the security application. * Make ID_CRED_R and EAD_2 (if present) available to the application
for authentication- and EAD processing.
* Verify that the identity of the Responder is an allowed identity * Obtain the authentication credential (CRED_R) and the
for this connection, see Section 3.5.1. authentication key of R from the application (or by other means).
* 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 Responder MUST send an EDHOC error
error message back, formatted as defined in Section 6. Sending error message back, formatted as defined in Section 6, and the session MUST
messages is essential for debugging but MAY e.g., be skipped if a be discontinued.
session cannot be found or due to denial-of-service reasons, see
Section 8.6. If an error message is sent, the session MUST be
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 32, line 38 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:
* Compute the transcript hash TH_3 = H(TH_2, CIPHERTEXT_2) where H() * Compute the transcript hash TH_3 = H(TH_2, PLAINTEXT_2) where H()
is the hash function in the selected cipher suite. The transcript is the EDHOC hash algorithm of the selected cipher suite. The
hash TH_3 is a CBOR encoded bstr and the input to the hash transcript hash TH_3 is a CBOR encoded bstr and the input to the
function is a CBOR Sequence. Note that H(TH_2, CIPHERTEXT_2) can hash function is a CBOR Sequence. Note that H(TH_2, PLAINTEXT_2)
be computed and cached already in the processing of message_2. can be computed and cached already in the processing of message_2.
* Compute MAC_3 = EDHOC-KDF( PRK_4x3m, TH_3, "MAC_3", << ID_CRED_I, * Compute MAC_3 as in Section 4.1.2, with context_3 = << ID_CRED_I,
CRED_I, ? EAD_3 >>, mac_length_3 ). If the Initiator TH_3, CRED_I, ? EAD_3 >>
authenticates with a static Diffie-Hellman key (method equals 2 or
3), then mac_length_3 is the EDHOC MAC length given by the
selected cipher suite. If the Initiator authenticates with a
signature key (method equals 0 or 1), then mac_length_3 is equal
to the output size of the EDHOC hash algorithm given by the
selected cipher suite.
- ID_CRED_I - identifier to facilitate retrieval of CRED_I, see - If the Initiator authenticates with a static Diffie-Hellman key
Section 3.5.4 (method equals 2 or 3), then mac_length_3 is the EDHOC MAC
length given by the selected cipher suite. If the Initiator
authenticates with a signature key (method equals 0 or 1), then
mac_length_3 is equal to the output size of the EDHOC hash
algorithm given by the selected cipher suite.
- CRED_I - CBOR item containing the credential of the Initiator, - ID_CRED_I - identifier to facilitate the retrieval of CRED_I,
see Section 3.5.3 see Section 3.5.3
- EAD_3 - protected external authorization data, see Section 3.8 - CRED_I - CBOR item containing the authentication credential of
the Initiator, see Section 3.5.2
- EAD_3 - external authorization data, see Section 3.8
* 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' field of a 1), then Signature_or_MAC_3 is the 'signature' field of a
COSE_Sign1 object as defined in Section 4.4 of COSE_Sign1 object, computed as specified in Section 4.4 of
[I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm of [I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm of
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 as input (see Initiator, and the following parameters as input (see
Appendix C.3): Appendix C.3):
- protected = << ID_CRED_I >> - protected = << ID_CRED_I >>
- external_aad = << TH_3, CRED_I, ? EAD_3 >> - external_aad = << TH_3, CRED_I, ? EAD_3 >>
- payload = MAC_3 - payload = MAC_3
* Compute a COSE_Encrypt0 object as defined in Section 5.3 of * Compute a COSE_Encrypt0 object as defined in Sections 5.2 and 5.3
[I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD
of the selected cipher suite, using the encryption key K_3, the algorithm of the selected cipher suite, using the encryption key
initialization vector IV_3, the plaintext P, and the following K_3, the initialization vector IV_3 (if used by the AEAD
algorithm), the plaintext PLAINTEXT_3, and the following
parameters as input (see Appendix C.3): parameters as input (see Appendix C.3):
- protected = h'' - protected = h''
- external_aad = TH_3 - external_aad = TH_3
where - K_3 and IV_3 are defined in Section 4.1.2, with
- K_3 = EDHOC-KDF( PRK_3e2m, TH_3, "K_3", h'', key_length )
o key_length - length of the encryption key of the EDHOC AEAD o key_length - length of the encryption key of the EDHOC AEAD
algorithm algorithm
- IV_3 = EDHOC-KDF( PRK_3e2m, TH_3, "IV_3", h'', iv_length ) o iv_length - length of the initialization vector of the EDHOC
o iv_length - length of the intialization vector of the EDHOC
AEAD algorithm AEAD algorithm
- P = ( ID_CRED_I / bstr / int, Signature_or_MAC_3, ? EAD_3 ) - PLAINTEXT_3 = ( ? PAD, ID_CRED_I / bstr / -24..23,
Signature_or_MAC_3, ? EAD_3 )
o If ID_CRED_I contains a single 'kid' parameter, i.e., o If ID_CRED_I contains a single 'kid' parameter, i.e.,
ID_CRED_I = { 4 : kid_I }, only the byte string or integer ID_CRED_I = { 4 : kid_I }, then only the byte string kid_I
kid_I is conveyed in the plaintext encoded accordingly as is conveyed in the plaintext, represented as described in
bstr or int. Section 3.3.2.
o PAD = 1*true is padding that may be used to hide the length
of the unpadded plaintext
CIPHERTEXT_3 is the 'ciphertext' of COSE_Encrypt0. CIPHERTEXT_3 is the 'ciphertext' of COSE_Encrypt0.
* Compute the transcript hash TH_4 = H(TH_3, PLAINTEXT_3) where H()
is the EDHOC hash algorithm of the selected cipher suite. The
transcript hash TH_4 is a CBOR encoded bstr and the input to the
hash function is a CBOR Sequence.
* Calculate PRK_out as defined in Figure 7. The Initiator can now
derive application keys using the EDHOC-Exporter interface, see
Section 4.2.1.
* Encode message_3 as a CBOR data item as specified in * Encode message_3 as a CBOR data item as specified in
Section 5.4.1. Section 5.4.1.
Pass the connection identifiers (C_I, C_R) and the application * Make 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 available to the
application can now derive application keys using the EDHOC-Exporter application.
interface, see Section 4.3.
After sending message_3, the Initiator is assured that no other party The Initiator SHOULD NOT persistently store PRK_out or application
than the Responder can compute the key PRK_4x3m (implicit key keys until the Initiator has verified message_4 or a message
authentication). The Initiator can securely derive application keys protected with a derived application key, such as an OSCORE message,
and send protected application data. However, the Initiator does not from the Responder. This is similar to waiting for acknowledgement
know that the Responder has actually computed the key PRK_4x3m and (ACK) in a transport protocol.
therefore the Initiator SHOULD NOT permanently store the keying
material PRK_4x3m and TH_4, or derived application keys, until the
Initiator is assured that the Responder has actually computed the key
PRK_4x3m (explicit key confirmation). This is similar to waiting for
acknowledgement (ACK) in a transport protocol. Explicit key
confirmation is e.g., assured when the Initiator has verified an
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:
* Decode message_3 (see Appendix C.1). * Decode message_3 (see Appendix C.1).
* 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, the 5-tuple, or the by the transport (e.g., the CoAP Token, the 5-tuple, or the
prepended C_I, see Appendix A.3). prepended C_R, see Appendix A.2).
* Decrypt and verify the COSE_Encrypt0 as defined in Section 5.3 of * Decrypt and verify the COSE_Encrypt0 as defined in Sections 5.2
[I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm and 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD
in the selected cipher suite, and the parameters defined in algorithm in the selected cipher suite, and the parameters defined
Section 5.4.2. in Section 5.4.2. Discard padding, if present.
* Pass EAD_3 to the security application. * Make ID_CRED_I and EAD_3 (if present) available to the application
for authentication- and EAD processing.
* Verify that the identity of the Initiator is an allowed identity * Obtain the authentication credential (CRED_I) and the
for this connection, see Section 3.5.1. authentication key of I from the application (or by other means).
* 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.
* Pass the connection identifiers (C_I, C_R), and the application * Make 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 available to the
application. The application can now derive application keys application.
using the EDHOC-Exporter interface.
If any processing step fails, the Responder SHOULD send an EDHOC After verifying message_3, the Responder can compute PRK_out, see
error message back, formatted as defined in Section 6. Sending error Section 4.1.3, derive application keys using the EDHOC-Exporter
messages is essential for debugging but MAY e.g., be skipped if a interface, see Section 4.2.1, persistently store the keying material,
session cannot be found or due to denial-of-service reasons, see and send protected application data.
Section 8.6. If an error message is sent, the session MUST be
discontinued.
After verifying message_3, the Responder is assured that the If any processing step fails, the Responder MUST send an EDHOC error
Initiator has calculated the key PRK_4x3m (explicit key confirmation) message back, formatted as defined in Section 6, and the session MUST
and that no other party than the Responder can compute the key. The be discontinued.
Responder can securely send protected application data and store the
keying material PRK_4x3m and TH_4.
5.5. EDHOC Message 4 5.5. EDHOC Message 4
This section specifies message_4 which is OPTIONAL to support. Key This section specifies message_4 which is OPTIONAL to support. Key
confirmation is normally provided by sending an application message confirmation is normally provided by sending an application message
from the Responder to the Initiator protected with a key derived with from the Responder to the Initiator protected with a key derived with
the EDHOC-Exporter, e.g., using OSCORE (see Appendix A). In the EDHOC-Exporter, e.g., using OSCORE (see Appendix A). In
deployments where no protected application message is sent from the deployments where no protected application message is sent from the
Responder to the Initiator, the Responder MUST send message_4. Two Responder to the Initiator, message_4 MUST be supported and MUST be
examples of such deployments: used. Two examples of such deployments:
1. When EDHOC is only used for authentication and no application 1. When EDHOC is only used for authentication and no application
data is sent. data is sent.
2. When application data is only sent from the Initiator to the 2. When application data is only sent from the Initiator to the
Responder. Responder.
Further considerations about when to use message_4 are provided in Further considerations about when to use message_4 are provided in
Section 3.9 and Section 8.1. Section 3.9 and Section 8.1.
skipping to change at page 36, line 4 skipping to change at page 36, line 28
2. When application data is only sent from the Initiator to the 2. When application data is only sent from the Initiator to the
Responder. Responder.
Further considerations about when to use message_4 are provided in Further considerations about when to use message_4 are provided in
Section 3.9 and Section 8.1. Section 3.9 and Section 8.1.
5.5.1. Formatting of Message 4 5.5.1. Formatting of Message 4
message_4 SHALL be a CBOR Sequence (see Appendix C.1) as defined message_4 SHALL be a CBOR Sequence (see Appendix C.1) as defined
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:
* Compute a COSE_Encrypt0 as defined in Section 5.3 of * Compute a COSE_Encrypt0 as defined in Sections 5.2 and 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
of the selected cipher suite, using the encryption key K_4, the of the selected cipher suite, using the encryption key K_4, the
initialization vector IV_4, the plaintext P, and the following initialization vector IV_4 (if used by the AEAD algorithm), the
parameters as input (see Appendix C.3): plaintext PLAINTEXT_4, and the following parameters as input (see
Appendix C.3):
- protected = h'' - protected = h''
- external_aad = TH_4 - external_aad = TH_4
where - K_4 and IV_4 are defined in Section 4.1.2, with
- K_4 = EDHOC-Exporter( "EDHOC_K_4", h'', key_length )
o key_length - length of the encryption key of the EDHOC AEAD o key_length - length of the encryption key of the EDHOC AEAD
algorithm algorithm
- IV_4 = EDHOC-Exporter( "EDHOC_IV_4", h'', iv_length ) o iv_length - length of the initialization vector of the EDHOC
o iv_length - length of the intialization vector of the EDHOC
AEAD algorithm AEAD algorithm
- P = ( ? EAD_4 ) - PLAINTEXT_4 = ( ? PAD, ? EAD_4 )
o EAD_4 - protected external authorization data, see o PAD = 1*true is padding that may be used to hide the length
Section 3.8. of the unpadded plaintext.
o EAD_4 - external authorization data, see Section 3.8.
CIPHERTEXT_4 is the 'ciphertext' of COSE_Encrypt0. CIPHERTEXT_4 is the 'ciphertext' of COSE_Encrypt0.
* Encode message_4 as a CBOR data item as specified in * Encode message_4 as a CBOR data item as specified in
Section 5.5.1. 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:
* Decode message_4 (see Appendix C.1). * Decode message_4 (see Appendix C.1).
* 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, the 5-tuple, or the by the transport (e.g., the CoAP Token, the 5-tuple, or the
prepended C_I, see Appendix A.3). prepended C_I, see Appendix A.2).
* Decrypt and verify the COSE_Encrypt0 as defined in Section 5.3 of * Decrypt and verify the COSE_Encrypt0 as defined in Sections 5.2
[I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm and 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD
in the selected cipher suite, and the parameters defined in algorithm in the selected cipher suite, and the parameters defined
Section 5.5.2. in Section 5.5.2. Discard padding, if present.
* Pass EAD_4 to the security application. * Make EAD_4 (if present) available to the application for EAD
processing.
If any processing step fails, the Responder SHOULD send an EDHOC If any processing step fails, the Responder MUST send an EDHOC error
error message back, formatted as defined in Section 6. Sending error message back, formatted as defined in Section 6, and the session MUST
messages is essential for debugging but MAY e.g., be skipped if a be discontinued.
session cannot be found or due to denial-of-service reasons, see
Section 8.6. If an error message is sent, the session MUST be After verifying message_4, the Initiator is assured that the
discontinued. Responder has calculated the key PRK_out (key confirmation) and that
no other party can derive the key.
6. Error Handling 6. Error Handling
This section defines the format for error messages. This section defines the format for error messages, and the
processing associated to the currently defined error codes.
Additional error codes may be registered, see Section 9.4.
There are many kinds of errors that can occur during EDHOC
processing. As in CoAP, an error can be triggered by errors in the
received message or internal errors in the recieving endpoint.
Except for processing and formatting errors, it is up to the
implementation when to send an error message. Sending error messages
is essential for debugging but MAY be skipped if, for example, a
session cannot be found or due to denial-of-service reasons, see
Section 8.7. Errors messages in EDHOC are always fatal. After
sending an error message, the sender MUST discontinue the protocol.
The receiver SHOULD treat an error message as an indication that the
other party likely has discontinued the protocol. But as the error
message is not authenticated, a received error message might also
have been sent by an attacker and the receiver MAY therefore try to
continue the protocol.
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.
Errors in EDHOC are fatal. After sending an error message, the
sender MUST discontinue the protocol. The receiver SHOULD treat an
error message as an indication that the other party likely has
discontinued the protocol. But as the error message is not
authenticated, a received error message might also have been sent by
an attacker and the receiver MAY therefore try to continue the
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 6: EDHOC Error Message Figure 8: EDHOC error message.
where: where:
* 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.
* 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 7. Additional error codes and corresponding error codes, see Figure 9. Additional error codes and corresponding error
information may be specified. information may be specified.
+----------+---------------+----------------------------------------+ +----------+---------------+----------------------------------------+
| ERR_CODE | ERR_INFO Type | Description | | ERR_CODE | ERR_INFO Type | Description |
+==========+===============+========================================+ +==========+===============+========================================+
| 0 | any | Success | | 0 | any | Success |
+----------+---------------+----------------------------------------+ +----------+---------------+----------------------------------------+
| 1 | tstr | Unspecified | | 1 | tstr | Unspecified error |
+----------+---------------+----------------------------------------+ +----------+---------------+----------------------------------------+
| 2 | suites | Wrong selected cipher suite | | 2 | suites | Wrong selected cipher suite |
+----------+---------------+----------------------------------------+ +----------+---------------+----------------------------------------+
Figure 7: Error Codes and Error Information Figure 9: Error codes and error information included in the EDHOC
error message.
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, i.e., as a standard value in case of no error, e.g., in
item. Error code 0 MUST NOT be used as part of the EDHOC message status reporting or log files. ERR_INFO can contain any type of CBOR
exchange flow. item, the content is out of scope for this specification. Error code
0 MUST NOT be used as part of the EDHOC message exchange flow. If an
endpoint receives an error message with error code 0, then it MUST
discontinue the protocol and MUST NOT send an error message.
6.2. Unspecified 6.2. Unspecified Error
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, for example "Method
message is mainly intended for software engineers that during not supported". The diagnostic text message is mainly intended for
debugging need to interpret it in the context of the EDHOC software engineers that during debugging need to interpret it in the
specification. The diagnostic message SHOULD be provided to the context of the EDHOC specification. The diagnostic message SHOULD be
calling application where it SHOULD be logged. provided to the calling application where it SHOULD be logged.
6.3. Wrong Selected Cipher Suite 6.3. Wrong Selected Cipher Suite
Error code 2 MUST only be used in a response to message_1 in case the Error code 2 MUST only be used when replying to message_1 in case the
cipher suite selected by the Initiator is not supported by the cipher suite selected by the Initiator is not supported by the
Responder, or if the Responder supports a cipher suite more preferred Responder, or if the Responder supports a cipher suite more preferred
by the Initiator than the selected cipher suite, see Section 5.2.3. by the Initiator than the selected cipher suite, see Section 5.2.3.
ERR_INFO is in this case denoted SUITES_R and is of type suites, see ERR_INFO is in this case denoted SUITES_R and is of type suites, see
Section 5.2.1. If the Responder does not support the selected cipher Section 5.2.1. If the Responder does not support the selected cipher
suite, then SUITES_R MUST include one or more supported cipher suite, then SUITES_R MUST include one or more supported cipher
suites. If the Responder supports a cipher suite in SUITES_I other suites. If the Responder supports a cipher suite in SUITES_I other
than the selected cipher suite (independently of if the selected than the selected cipher suite (independently of if the selected
cipher suite is supported or not) then SUITES_R MUST include the cipher suite is supported or not) then SUITES_R MUST include the
supported cipher suite in SUITES_I which is most preferred by the supported cipher suite in SUITES_I which is most preferred by the
Initiator. SUITES_R MAY include a single cipher suite, i.e., be Initiator. SUITES_R MAY include a single cipher suite, i.e., be
encoded as an int. If the Responder does not support any cipher encoded as an int. If the Responder does not support any cipher
suite in SUITES_I, then it SHOULD include all its supported cipher suite in SUITES_I, then it SHOULD include all its supported cipher
suites in SUITES_R in any order. suites in SUITES_R.
In contrast to SUITES_I, the order of the cipher suites in SUITES_R
has no significance.
6.3.1. Cipher Suite Negotiation 6.3.1. Cipher Suite Negotiation
After receiving SUITES_R, the Initiator can determine which cipher After receiving SUITES_R, the Initiator can determine which cipher
suite to select (if any) for the next EDHOC run with the Responder. suite to select (if any) for the next EDHOC run with the Responder.
If the Initiator intends to contact the Responder in the future, the If the Initiator intends to contact the Responder in the future, the
Initiator SHOULD remember which selected cipher suite to use until Initiator SHOULD remember which selected cipher suite to use until
the next message_1 has been sent, otherwise the Initiator and the next message_1 has been sent, otherwise the Initiator and
Responder will likely run into an infinite loop where the Initiator Responder will likely run into an infinite loop where the Initiator
selects its most preferred and the Responder sends an error with selects its most preferred and the Responder sends an error with
supported cipher suites. After a successful run of EDHOC, the supported cipher suites. After a successful run of EDHOC, the
Initiator MAY remember the selected cipher suite to use in future Initiator MAY remember the selected cipher suite to use in future
EDHOC sessions. Note that if the Initiator or Responder is updated EDHOC sessions. Note that if the Initiator or Responder is updated
with new cipher suite policies, any cached information may be with new cipher suite policies, any cached information may be
outdated. outdated.
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).
Furthermore, the Responder SHALL only accept message_1 if the
selected cipher suite is the first cipher suite in SUITES_I that the
Responder supports (see Section 5.2.3). Following this procedure
ensures that the selected cipher suite is the most preferred (by the
Initiator) cipher suite supported by both parties.
If the selected cipher suite is not the first cipher suite which the
Responder supports in SUITES_I received in message_1, then the
Responder MUST discontinue the protocol, see Section 5.2.3. If
SUITES_I in message_1 is manipulated, then the integrity verification
of message_2 containing the transcript hash TH_2 will fail and the
Initiator will discontinue the protocol.
6.3.2. Examples 6.3.2. Examples
Assume that the Initiator supports the five cipher suites 5, 6, 7, 8, Assume that the Initiator supports the five cipher suites 5, 6, 7, 8,
and 9 in decreasing order of preference. Figures 8 and 9 show and 9 in decreasing order of preference. Figures 10 and 11 show
examples of how the Initiator can format SUITES_I and how SUITES_R is examples of how the Initiator can format SUITES_I and how SUITES_R is
used by Responders to give the Initiator information about the cipher used by Responders to give the Initiator information about the cipher
suites that the Responder supports. suites that the Responder supports.
In the first example (Figure 8), the Responder supports cipher suite In the first example (Figure 10), the Responder supports cipher suite
6 but not the initially selected cipher suite 5. 6 but not the initially selected cipher suite 5.
Initiator Responder Initiator Responder
| METHOD, SUITES_I = 5, G_X, C_I, EAD_1 | | METHOD, SUITES_I = 5, G_X, C_I, EAD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
| | | |
| ERR_CODE = 2, SUITES_R = 6 | | ERR_CODE = 2, SUITES_R = 6 |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| error | | error |
| | | |
| METHOD, SUITES_I = [5, 6], G_X, C_I, EAD_1 | | METHOD, SUITES_I = [5, 6], G_X, C_I, EAD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
Figure 8: Example of Responder supporting suite 6 but not suite 5. Figure 10: Example of an Initiator supporting suites 5, 6, 7, 8,
and 9 in decreasing order of preference, and a Responder
supporting suite 6 but not suite 5. The Responder rejects the
first message_1 with an error indicating support for suite 6.
The Initiator also supports suite 6, and therefore selects suite
6 in the second message_1. The initiator prepends in SUITES_I
the selected suite 6 with the more preferred suites, in this case
suite 5, to mitigate a potential attack on the cipher suite
negotiation.
In the second example (Figure 9), the Responder supports cipher In the second example (Figure 11), 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 SUITES_R containing the supported suites, after which responds with SUITES_R containing the supported suites, after which
the Initiator selects its most preferred supported suite. The order the Initiator selects its most preferred supported suite. (If the
of cipher suites in SUITES_R does not matter. (If the Responder had Responder had supported suite 5, it would have included it in
supported suite 5, it would have included it in SUITES_R of the SUITES_R of the response, and it would in that case have become the
response, and it would in that case have become the selected suite in selected suite in the second message_1.)
the second message_1.)
Initiator Responder Initiator Responder
| METHOD, SUITES_I = [5, 6], G_X, C_I, EAD_1 | | METHOD, SUITES_I = [5, 6], G_X, C_I, EAD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
| | | |
| ERR_CODE = 2, SUITES_R = [9, 8] | | ERR_CODE = 2, SUITES_R = [9, 8] |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| error | | error |
| | | |
| METHOD, SUITES_I = [5, 6, 7, 8], G_X, C_I, EAD_1 | | METHOD, SUITES_I = [5, 6, 7, 8], G_X, C_I, EAD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
Figure 11: Example of an Initiator supporting suites 5, 6, 7, 8,
and 9 in decreasing order of preference, and a Responder
supporting suites 8 and 9 but not 5, 6 or 7. The Responder
rejects the first message_1 with an error indicating support for
suites 8 and 9 (in any order). The Initiator also supports
suites 8 and 9, and prefers suite 8, so therefore selects suite 8
in the second message_1. The initiator prepends in SUITES_I the
selected suite 8 with the more preferred suites in order of
preference, in this case suites 5, 6 and 7, to mitigate a
potential attack on the cipher suite negotiation.
Figure 9: Example of Responder supporting suites 8 and 9 but not 7. Compliance Requirements
5, 6 or 7.
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).
Furthermore, the Responder shall only accept message_1 if the
selected cipher suite is the first cipher suite in SUITES_I that the
Responder supports (see Section 5.2.3). Following this procedure
ensures that the selected cipher suite is the most preferred (by the
Initiator) cipher suite supported by both parties.
If the selected cipher suite is not the first cipher suite which the
Responder supports in SUITES_I received in message_1, then Responder
MUST discontinue the protocol, see Section 5.2.3. If SUITES_I in
message_1 is manipulated, then the integrity verification of
message_2 containing the transcript hash TH_2 will fail and the
Initiator will discontinue the protocol.
7. Mandatory-to-Implement Compliance Requirements In the absence of an application profile specifying otherwise:
An implementation may support only Initiator or only Responder. An implementation MAY support only Initiator or only Responder.
An implementation may support only a single method. None of the An implementation MAY support only a single method. None of the
methods are mandatory-to-implement. methods are mandatory-to-implement.
Implementations MUST support 'kid' parameters of type int. None of Implementations MUST support 'kid' parameters. None of the other
the other COSE header parameters are mandatory-to-implement. COSE header parameters are mandatory-to-implement.
An implementation may support only a single credential type (CCS, An implementation MAY support only a single credential type (CCS,
CWT, X.509, C509). None of the credential types are mandatory-to- CWT, X.509, C509). None of the credential types are mandatory-to-
implement. implement.
Implementations MUST support the EDHOC-Exporter. Implementations Implementations MUST support the EDHOC-Exporter. Implementations
SHOULD support EDHOC-KeyUpdate. SHOULD support EDHOC-KeyUpdate.
Implementations MAY support message_4. Error codes 1 and 2 MUST be Implementations MAY support message_4. Error codes (ERR_CODE) 1 and
supported. 2 MUST be supported.
Implementations MAY support EAD. Implementations MAY support EAD.
For many constrained IoT devices it is problematic to support more Implementations MAY support padding of plaintext when sending
than one cipher suite. Existing devices can be expected to support messages. Implementations MUST support padding of plaintext when
either ECDSA or EdDSA. To enable as much interoperability as we can receiving messages, i.e. MUST be able to parse padded messages.
reasonably achieve, less constrained devices SHOULD implement both
cipher suite 0 (AES-CCM-16-64-128, SHA-256, 8, X25519, EdDSA, AES- Implementations MUST support cipher suite 2 and 3. Cipher suites 2
CCM-16-64-128, SHA-256) and cipher suite 2 (AES-CCM-16-64-128, SHA- (AES-CCM-16-64-128, SHA-256, 8, P-256, ES256, AES-CCM-16-64-128, SHA-
256, 8, P-256, ES256, AES-CCM-16-64-128, SHA-256). Constrained 256) and 3 (AES-CCM-16-128-128, SHA-256, 16, P-256, ES256, AES-CCM-
endpoints SHOULD implement cipher suite 0 or cipher suite 2. 16-64-128, SHA-256) only differ in size of the MAC length, so
supporting one or both of these is no essential difference.
Implementations only need to implement the algorithms needed for Implementations only need to implement the algorithms needed for
their supported methods. their supported methods.
8. Security Considerations 8. Security Considerations
8.1. Security Properties 8.1. 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
forward secrecy, mutual authentication with aliveness, consistency, forward secrecy, mutual authentication with aliveness, consistency,
and peer awareness. As described in [SIGMA], peer awareness is and peer awareness. As described in [SIGMA], peer awareness is
provided to the Responder, but not to the Initiator. provided to the Responder, but not to the Initiator.
As described in [SIGMA], different levels of identity protection is As described in [SIGMA], different levels of identity protection are
provided to the Initiator and the Responder. EDHOC protects the provided to the Initiator and the Responder. EDHOC protects the
credential identifier of the Initiator against active attacks and the credential identifier of the Initiator against active attacks and the
credential identifier of the Responder against passive attacks. The credential identifier of the Responder against passive attacks. An
roles should be assigned to protect the most sensitive identity/ active attacker can get the credential identifier of the Responder by
identifier, typically that which is not possible to infer from eavesdropping on the destination address used for transporting
routing information in the lower layers. message_1 and send its own message_1 to the same address. The roles
should be assigned to protect the most sensitive identity/identifier,
typically that which is not possible 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
skipping to change at page 43, line 27 skipping to change at page 44, line 30
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_out leads to
compromise of all exported keying material derived after the last compromise of all keying material derived with the EDHOC-Exporter
invocation of the EDHOC-KeyUpdate function. since the last invocation (if any) of the EDHOC-KeyUpdate function.
EDHOC provides a minimum of 64-bit security against online brute Based on the cryptographic algorithms requirements Section 8.3, EDHOC
force attacks and a minimum of 128-bit security against offline brute provides a minimum of 64-bit security against online brute force
force attacks. This is in line with IPsec, TLS, and COSE. To break attacks and a minimum of 128-bit security against offline brute force
64-bit security against online brute force an attacker would on attacks. To break 64-bit security against online brute force an
average have to send 4.3 billion messages per second for 68 years, attacker would on average have to send 4.3 billion messages per
which is infeasible in constrained IoT radio technologies. second for 68 years, which is infeasible in constrained IoT radio
technologies. A forgery against a 64-bit MAC in EDHOC breaks the
security of all future application data, while a forgery against a
64-bit MAC in the subsequent application protocol (e.g., OSCORE
[RFC8613]) typically only breaks the security of the data in the
forged packet.
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_out. While the Initiator
authentication). The Initiator does however not know that the can securely send protected application data, the Initiator SHOULD
Responder has actually computed the key PRK_4x3m. While the NOT persistently store the keying material PRK_out until the
Initiator can securely send protected application data, the Initiator Initiator has verified an OSCORE message or message_4 from the
SHOULD NOT permanently store the keying material PRK_4x3m and TH_4 Responder. After verifying message_3, the Responder is assured that
until the Initiator is assured that the Responder has actually an honest Initiator has computed the key PRK_out. The Responder can
computed the key PRK_4x3m (explicit key confirmation). Explicit key securely derive and store the keying material PRK_out, and send
confirmation is e.g., assured when the Initiator has verified an protected application data.
OSCORE message or message_4 from the Responder. After verifying
message_3, the Responder is assured that the Initiator has calculated External authorization data sent in message_1 (EAD_1) or message_2
the key PRK_4x3m (explicit key confirmation) and that no other party (EAD_2) should be considered unprotected by EDHOC, see Section 8.5.
than the Responder can compute the key. The Responder can securely EAD_2 is encrypted but the Responder has not yet authenticated the
send protected application data and store the keying material Initiator. External authorization data sent in message_3 (EAD_3) or
PRK_4x3m and TH_4. message_4 (EAD_4) is protected between Initiator and Responder by the
protocol, but note that EAD fields may be used by the application
before the message verification is completed, see Section 3.8.
Designing a secure mechanism that uses EAD is not necessarily
straightforward. This document only provides the EAD transport
mechanism, but the problem of agreeing on the surrounding context and
the meaning of the information passed to and from the application
remains. Any new uses of EAD should be subject to careful review.
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 session. ephemeral secret key can only attack that specific session.
Repudiation: In EDHOC authenticated with signature keys, the Repudiation: If an endpoint authenticates with a signature, the other
Initiator could theoretically prove that the Responder performed a endpoint can prove that the endpoint performed a run of the protocol
run of the protocol by presenting the private ephemeral key, and vice by presenting the data being signed as well as the signature itself.
versa. Note that storing the private ephemeral keys violates the With static Diffie-Hellman key authentication, the authenticating
protocol requirements. With static Diffie-Hellman key endpoint can deny having participated in the protocol.
authentication, both parties can always deny having participated in
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.
8.2. Cryptographic Considerations 8.2. Cryptographic Considerations
The SIGMA protocol requires that the encryption of message_3 provides The SIGMA protocol requires that the encryption of message_3 provides
confidentiality against active attackers and EDHOC message_4 relies confidentiality against active attackers and EDHOC message_4 relies
on the use of authenticated encryption. Hence the message on the use of authenticated encryption. Hence the message
authenticating functionality of the authenticated encryption in EDHOC authenticating functionality of the authenticated encryption in EDHOC
is critical: authenticated encryption MUST NOT be replaced by plain is critical: authenticated encryption MUST NOT be replaced by plain
encryption only, even if authentication is provided at another level encryption only, even if authentication is provided at another level
or through a different mechanism. 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 relies 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 used in attacks. For this reason, the ephemeral keys MUST NOT be used in
more than one EDHOC message, and both parties SHALL generate fresh more than one EDHOC message, and both parties SHALL generate fresh
random ephemeral key pairs. Note that an ephemeral key may be used random ephemeral key pairs. Note that an ephemeral key may be used
to calculate several ECDH shared secrets. When static Diffie-Hellman to calculate several ECDH shared secrets. When static Diffie-Hellman
authentication is used the same ephemeral key is used in both authentication is used the same ephemeral key is used in both
ephemeral-ephemeral and ephemeral-static ECDH. ephemeral-ephemeral and ephemeral-static ECDH.
As discussed in [SIGMA], the encryption of message_2 does only need As discussed in [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 Responder's 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 which is proven secure as long as the expand function
CTR but is not often used as it is slow on long messages, and most is a PRF. HKDF-Expand is not often used as a stream cipher as it is
applications require both IND-CCA confidentiality as well as slow on long messages, and most applications require both IND-CCA
integrity protection. For the encryption of message_2, any speed confidentiality as well as integrity protection. For the encryption
difference is negligible, IND-CCA does not increase security, and of message_2, any speed difference is negligible, IND-CCA does not
integrity is provided by the inner MAC (and signature depending on increase security, and integrity is provided by the inner MAC (and
method). signature depending on method).
Requirement for how to securely generate, validate, and process the Requirements for how to securely generate, validate, and process the
ephemeral 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.
As noted in Section 12 of [I-D.ietf-cose-rfc8152bis-struct] the use
of a single key for multiple algorithms is strongly disencouraged
unless proven secure by a dedicated cryptographic analysis. In
particular this recommendation applies to using the same private key
for static Diffie-Hellman authentication and digital signature
authentication. A preliminary conjecture is that a minor change to
EDHOC may be sufficient to fit the analysis of secure shared
signature and ECDH key usage in [Degabriele11] and [Thormarker21].
So-called selfie attacks are mitigated as long as the Initiator does
not have its own identity in the set of Responder identities it is
allowed to communicate with. In trust on first use (TOFU) use cases
the Initiator should verify that the the Responder's identity is not
equal to its own. Any future EHDOC methods using e.g., pre-shared
keys might need to mitigate this in other ways.
8.3. Cipher Suites and Cryptographic Algorithms 8.3. Cipher Suites and Cryptographic Algorithms
When using private cipher suite or registering new cipher suites, the When using private cipher suite or registering new cipher suites, the
choice of key length used in the different algorithms needs to be choice of key length used in the different algorithms needs to be
harmonized, so that a sufficient security level is maintained for harmonized, so that a sufficient security level is maintained for
certificates, EDHOC, and the protection of application data. The certificates, EDHOC, and the protection of application data. The
Initiator and the Responder should enforce a minimum security level. Initiator and the Responder should enforce a minimum security level.
The hash algorithms SHA-1 and SHA-256/64 (SHA-256 truncated to The output size of the EDHOC hash algorithm MUST be at least
64-bits) SHALL NOT be supported for use in EDHOC except for 256-bits, i.e., the hash algorithms SHA-1 and SHA-256/64 (SHA-256
certificate identification with x5t and c5t. Note that secp256k1 is truncated to 64-bits) SHALL NOT be supported for use in EDHOC except
only defined for use with ECDSA and not for ECDH. Note that some for certificate identification with x5t and c5t. For security
COSE algorithms are marked as not recommended in the COSE IANA considerations of SHA-1, see [RFC6194]. As EDHOC integrity protects
registry. the whole authentication credential, the choice of hash algorithm in
x5t and c5t does not affect security and it is RECOMMENDED to use the
same hash algorithm as in the cipher suite but with as much
truncation as possible, i.e, when the EDHOC hash algorithm is SHA-256
it is RECOMMENDED to use SHA-256/64 in x5t and c5t. The EDHOC MAC
length MUST be at least 8 bytes and the tag length of the EDHOC AEAD
algorithm MUST be at least 64-bits. Note that secp256k1 is only
defined for use with ECDSA and not for ECDH. Note that some COSE
algorithms are marked as not recommended in the COSE IANA registry.
8.4. Post-Quantum Considerations 8.4. Post-Quantum Considerations
As of the publication of this specification, it is unclear when or As of the publication of this specification, it is unclear when or
even if a quantum computer of sufficient size and power to exploit even if a quantum computer of sufficient size and power to exploit
public key cryptography will exist. Deployments that need to public key cryptography will exist. Deployments that need to
consider risks decades into the future should transition to Post- consider risks decades into the future should transition to Post-
Quantum Cryptography (PQC) in the not-too-distant future. Many other Quantum Cryptography (PQC) in the not-too-distant future. Many other
systems should take a slower wait-and-see approach where PQC is systems should take a slower wait-and-see approach where PQC is
phased in when the quantum threat is more imminent. Current PQC phased in when the quantum threat is more imminent. Current PQC
skipping to change at page 46, line 31 skipping to change at page 48, line 5
including PQC signature algorithms such as HSS-LMS. EDHOC is including PQC signature algorithms such as HSS-LMS. EDHOC is
currently only specified for use with key exchange algorithms of type currently only specified for use with key exchange algorithms of type
ECDH curves, but any Key Encapsulation Method (KEM), including PQC ECDH curves, but any Key Encapsulation Method (KEM), including PQC
KEMs, can be used in method 0. While the key exchange in method 0 is KEMs, can be used in method 0. While the key exchange in method 0 is
specified with terms of the Diffie-Hellman protocol, the key exchange specified with terms of the Diffie-Hellman protocol, the key exchange
adheres to a KEM interface: G_X is then the public key of the adheres to a KEM interface: G_X is then the public key of the
Initiator, G_Y is the encapsulation, and G_XY is the shared secret. Initiator, G_Y is the encapsulation, and G_XY is the shared secret.
Use of PQC KEMs to replace static DH authentication would likely Use of PQC KEMs to replace static DH authentication would likely
require a specification updating EDHOC with new methods. require a specification updating EDHOC with new methods.
8.5. Unprotected Data 8.5. Unprotected Data and Privacy
The Initiator and the Responder must make sure that unprotected data The Initiator and the Responder must make sure that unprotected data
and metadata do not reveal any sensitive information. This also and metadata do not reveal any sensitive information. This also
applies for encrypted data sent to an unauthenticated party. In applies for encrypted data sent to an unauthenticated party. In
particular, it applies to EAD_1, ID_CRED_R, EAD_2, and error particular, it applies to EAD_1, ID_CRED_R, EAD_2, and error
messages. Using the same EAD_1 in several EDHOC sessions allows messages. Using the same EAD_1 in several EDHOC sessions allows
passive eavesdroppers to correlate the different sessions. Another passive eavesdroppers to correlate the different sessions. Another
consideration is that the list of supported cipher suites may consideration is that the list of supported cipher suites may
potentially be used to identify the application. potentially be used to identify the application. The Initiator and
the Responder must also make sure that unauthenticated data does not
trigger any harmful actions. In particular, this applies to EAD_1
and error messages.
The Initiator and the Responder must also make sure that An attacker observing network traffic may use connection identifiers
unauthenticated data does not trigger any harmful actions. In sent in clear in EDHOC or the subsequent application protocol to
particular, this applies to EAD_1 and error messages. correlate packets sent on different paths or at different times. The
attacker may use this information for traffic flow analysis or to
track an endpoint. Application protocols using connection
identifiers from EDHOC SHOULD provide mechanisms to update the
connection identifier and MAY provide mechanisms to issue several
simultaneously active connection identifiers. See [RFC9000] for a
non-constrained example of such mechanisms.
8.6. Denial-of-Service 8.6. Updated Internet Threat Model Considerations
As CoAP provides Denial-of-Service protection in the form of the Echo Since the publication of [RFC3552] there has been an increased
option [RFC9175], EDHOC itself does not provide countermeasures awareness of the need to protect against endpoints that are
against Denial-of-Service attacks. By sending a number of new or compromised, malicious, or whose interests simply do not align with
the interests of users
[I-D.arkko-arch-internet-threat-model-guidance]. [RFC7624] describes
an updated threat model for Internet confidentiality, see
Section 8.1. [I-D.arkko-arch-internet-threat-model-guidance] further
expands the threat model. Implementations and users SHOULD consider
these threat models. In particular, even data sent protected to the
other endpoint such as ID_CRED and EAD can be used for tracking, see
Section 2.7 of [I-D.arkko-arch-internet-threat-model-guidance].
The fields ID_CRED_I, ID_CRED_R, EAD_2, EAD_3, and EAD_4 have
variable length and information regarding the length may leak to an
attacker. An passive attacker may e.g., be able to differentiating
endpoints using identifiers of different length. To mitigate this
information leakage an inmplementation may ensure that the fields
have fixed length or use padding. An implementation may e.g., only
use fix length identifiers like 'kid' of length 1. Alternatively
padding may be used to hide the true length of e.g., certificates by
value in 'x5chain' or 'c5c'.
8.7. Denial-of-Service
EDHOC itself does not provide countermeasures against Denial-of-
Service attacks. In particular, by sending a number of new or
replayed message_1 an attacker may cause the Responder to allocate replayed message_1 an attacker may cause the Responder to allocate
state, perform cryptographic operations, and amplify messages. To state, perform cryptographic operations, and amplify messages. To
mitigate such attacks, an implementation SHOULD rely on lower layer mitigate such attacks, an implementation SHOULD rely on lower layer
mechanisms such as the Echo option in CoAP that forces the initiator mechanisms. For instance, when EDHOC is transferred as an exchange
to demonstrate reachability at its apparent network address. of CoAP messages, the CoAP server can use the Echo option defined in
[RFC9175] which forces the CoAP client to demonstrate reachability at
its apparent 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 been forged by an evaluate if a received message is likely to have been forged by an
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.
8.7. Implementation Considerations 8.8. 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 random seed must be provided from an external source and
source and used with a cryptographically secure pseudorandom number used with a cryptographically secure pseudorandom number generator.
generator. As each pseudorandom number must only be used once, an As each pseudorandom number must only be used once, an implementation
implementation needs to get a new truly random seed after reboot, or needs to get a unique input to the pseudorandom number generator
continuously store state in nonvolatile memory, see ([RFC8613], after reboot, or continuously store state in nonvolatile memory.
Appendix B.1.1) for issues and solution approaches for writing to Appendix B.1.1 in [RFC8613] describes issues and solution approaches
nonvolatile memory. Intentionally or unintentionally weak or for writing to nonvolatile memory. Intentionally or unintentionally
predictable pseudorandom number generators can be abused or exploited weak or predictable pseudorandom number generators can be abused or
for malicious purposes. [RFC8937] describes a way for security exploited for malicious purposes. [RFC8937] describes a way for
protocol implementations to augment their (pseudo)random number security protocol implementations to augment their (pseudo)random
generators using a long-term private key and a deterministic number 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 Implementations might consider deriving secret and non-secret
[RFC6979] MAY be used. Pure deterministic elliptic-curve signatures randomness from different PNRG/PRF/KDF instances to limit the damage
such as deterministic ECDSA and EdDSA have gained popularity over if the PNRG/PRF/KDF turns out to be fundamentally broken. NIST
randomized ECDSA as their security do not depend on a source of high- generally forbids deriving secret and non-secret randomness from the
quality randomness. Recent research has however found that same KDF instance, but this decision has been criticized by Krawczyk
implementations of these signature algorithms may be vulnerable to [HKDFpaper] and doing so is common practice. In addition to IVs,
certain side-channel and fault injection attacks due to their other examples are the challenge in EAP-TTLS, the RAND in 3GPP AKAs,
determinism. See e.g., Section 1 of and the Session-Id in EAP-TLS 1.3. Note that part of KEYSTREAM_2 is
also non-secret randomness as it is known or predictable to an
attacker. As explained by Krawczyk, if any attack is mitigated by
the NIST requirement it would mean that the KDF is fully broken and
would have to be replaced anyway.
For many constrained IoT devices it is problematic to support several
crypto primitives. Existing devices can be expected to support
either ECDSA or EdDSA. If ECDSA is supported, "deterministic ECDSA"
as specified in [RFC6979] MAY be used. Pure deterministic elliptic-
curve signatures such as deterministic ECDSA and EdDSA have gained
popularity over randomized ECDSA as their security do not depend on a
source of high-quality randomness. Recent research has however found
that implementations of these signature algorithms may be vulnerable
to certain side-channel and fault injection attacks due to their
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 2.1.1 of [I-D.ietf-cose-rfc8152bis-algs] this
can be addressed by combining randomness and determinism. can be addressed by combining randomness and determinism.
Appendix D of [I-D.ietf-lwig-curve-representations] describes how
Montgomery curves such as X25519 and X448 and (twisted) Edwards
curves as curves such as Ed25519 and Ed448 can mapped to and from
short-Weierstrass form for implementation on platforms that
accelerate elliptic curve group operations in short-Weierstrass form.
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 and validity of certificates. The selection of trusted CAs
done very carefully and certificate revocation should be supported. should be done very carefully and certificate revocation should be
The private authentication keys MUST be kept secret, only the supported. The choice of revocation mechanism is left to the
application. For example, in case of X.509 certificates, Certificate
Revocation Lists [RFC5280] or OCSP [RFC6960] may be used.
Verification of validity may require the use of a Real-Time Clock
(RTC). The private authentication keys MUST be kept secret, only the
Responder SHALL have access to the Responder's private authentication Responder SHALL have access to the Responder's private authentication
key and only the Initiator SHALL have access to the Initiator's key and only the Initiator SHALL have access to the Initiator's
private authentication key. private authentication key.
The Initiator and the Responder are allowed to select the connection The Initiator and the Responder are allowed to select its 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
EDHOC message exchange, they MAY terminate the exchange with the EDHOC message exchange, they MAY terminate the exchange with the
lexicographically smallest G_X. If the two G_X values are equal, the lexicographically smallest G_X. Note that in cases where several
received message_1 MUST be discarded to mitigate reflection attacks. EDHOC exchanges with different parameter sets (method, COSE headers,
Note that in the case of two simultaneous EDHOC exchanges where the etc.) are used, an attacker can affect which of the parameter sets
nodes only complete one and where the nodes have different preferred that will be used by blocking some of the parameter sets.
cipher suites, an attacker can affect which of the two nodes'
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 the TEE. To achieve even higher security it is RECOMMENDED that
additional operations such as ephemeral key generation, all additional operations such as ephemeral key generation, all
computations of shared secrets, and storage of the PRK keys can be computations of shared secrets, and storage of the PRK keys can be
done inside the TEE. The use of a TEE enforces that code within that done inside the TEE. The use of a TEE aims at preventing code within
environment cannot be tampered with, and that any data used by such that environment to be tampered with, and preventing data used by
code cannot be read or tampered with by code outside that such code to be read or tampered with by code outside that
environment. environment.
9. IANA Considerations Note that HKDF-Expand has a relativly small maximum output length of
255 * hash_length. This means that when when SHA-256 is used as hash
algorithm, message_2 cannot be longer than 8160 bytes.
The sequence of transcript hashes in EHDOC (TH_2, TH_3, TH_4) do not
make use of a so called running hash, this is a design choice as
running hashes are often not supported on constrained platforms.
When parsing a received EDHOC message, implementations MUST terminate
the protocol if the message does not comply with the CDDL for that
message. It is RECOMMENDED to terminate the protocol if the received
EDHOC message is not deterministic CBOR.
9. IANA Considerations
9.1. EDHOC Exporter Label Registry 9.1. EDHOC Exporter Label Registry
IANA has created a new registry titled "EDHOC Exporter Label" under IANA has created a new registry titled "EDHOC Exporter Label" under
the new group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The the new group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The
registration procedure is "Expert Review". The columns of the registration procedure is "Expert Review". The columns of the
registry are Label, Description, and Reference. All columns are text registry are Label and Description. Label is a uint. Description is
strings where Label consists only of the printable ASCII characters a text string. The initial contents of the registry are:
0x21 - 0x7e. Labels beginning with "PRIVATE" MAY be used for private
use without registration. All other label values MUST be registered.
The initial contents of the registry are:
Label: EDHOC_K_4
Description: Key used to protect EDHOC message_4
Reference: [[this document]]
Label: EDHOC_IV_4
Description: IV used to protect EDHOC message_4
Reference: [[this document]]
Label: OSCORE_Master_Secret Label: 0
Description: Derived OSCORE Master Secret Description: Derived OSCORE Master Secret
Reference: [[this document]]
Label: OSCORE_Master_Salt Label: 1
Description: Derived OSCORE Master Salt Description: Derived OSCORE Master Salt
Reference: [[this document]]
9.2. EDHOC Cipher Suites Registry 9.2. EDHOC Cipher Suites Registry
IANA has created a new registry titled "EDHOC Cipher Suites" under IANA has created a new registry titled "EDHOC Cipher Suites" under
the new group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The the new group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The
registration procedure is "Expert Review". The columns of the registration procedure is "Expert Review". The columns of the
registry are Value, Array, Description, and Reference, where Value is registry are Value, Array and Description, where Value is an integer
an integer and the other columns are text strings. The initial and the other columns are text strings. The initial contents of the
contents of the registry are: registry are:
Value: -24 Value: -24
Algorithms: N/A Algorithms: N/A
Desc: Reserved for Private Use Desc: Reserved for Private Use
Reference: [[this document]]
Value: -23 Value: -23
Algorithms: N/A Algorithms: N/A
Desc: Reserved for Private Use Desc: Reserved for Private Use
Reference: [[this document]]
Value: -22 Value: -22
Algorithms: N/A Algorithms: N/A
Desc: Reserved for Private Use Desc: Reserved for Private Use
Reference: [[this document]]
Value: -21 Value: -21
Algorithms: N/A Algorithms: N/A
Desc: Reserved for Private Use Desc: Reserved for Private Use
Reference: [[this document]]
Value: 0 Value: 0
Array: 10, -16, 8, 4, -8, 10, -16 Array: 10, -16, 8, 4, -8, 10, -16
Desc: AES-CCM-16-64-128, SHA-256, 8, X25519, EdDSA, Desc: AES-CCM-16-64-128, SHA-256, 8, X25519, EdDSA,
AES-CCM-16-64-128, SHA-256 AES-CCM-16-64-128, SHA-256
Reference: [[this document]]
Value: 1 Value: 1
Array: 30, -16, 16, 4, -8, 10, -16 Array: 30, -16, 16, 4, -8, 10, -16
Desc: AES-CCM-16-128-128, SHA-256, 16, X25519, EdDSA, Desc: AES-CCM-16-128-128, SHA-256, 16, X25519, EdDSA,
AES-CCM-16-64-128, SHA-256 AES-CCM-16-64-128, SHA-256
Reference: [[this document]]
Value: 2 Value: 2
Array: 10, -16, 8, 1, -7, 10, -16 Array: 10, -16, 8, 1, -7, 10, -16
Desc: AES-CCM-16-64-128, SHA-256, 8, P-256, ES256, Desc: 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
Reference: [[this document]]
Value: 3 Value: 3
Array: 30, -16, 16, 1, -7, 10, -16 Array: 30, -16, 16, 1, -7, 10, -16
Desc: AES-CCM-16-128-128, SHA-256, 16, P-256, ES256, Desc: 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
Reference: [[this document]]
Value: 4 Value: 4
Array: 24, -16, 16, 4, -8, 24, -16 Array: 24, -16, 16, 4, -8, 24, -16
Desc: ChaCha20/Poly1305, SHA-256, 16, X25519, EdDSA, Desc: ChaCha20/Poly1305, SHA-256, 16, X25519, EdDSA,
ChaCha20/Poly1305, SHA-256 ChaCha20/Poly1305, SHA-256
Reference: [[this document]]
Value: 5 Value: 5
Array: 24, -16, 16, 1, -7, 24, -16 Array: 24, -16, 16, 1, -7, 24, -16
Desc: ChaCha20/Poly1305, SHA-256, 16, P-256, ES256, Desc: ChaCha20/Poly1305, SHA-256, 16, P-256, ES256,
ChaCha20/Poly1305, SHA-256 ChaCha20/Poly1305, SHA-256
Reference: [[this document]]
Value: 6 Value: 6
Array: 1, -16, 16, 4, -7, 1, -16 Array: 1, -16, 16, 4, -7, 1, -16
Desc: A128GCM, SHA-256, 16, X25519, ES256, Desc: A128GCM, SHA-256, 16, X25519, ES256,
A128GCM, SHA-256 A128GCM, SHA-256
Reference: [[this document]]
Value: 24 Value: 24
Array: 3, -43, 16, 2, -35, 3, -43 Array: 3, -43, 16, 2, -35, 3, -43
Desc: A256GCM, SHA-384, 16, P-384, ES384, Desc: A256GCM, SHA-384, 16, P-384, ES384,
A256GCM, SHA-384 A256GCM, SHA-384
Reference: [[this document]]
Value: 25 Value: 25
Array: 24, -45, 16, 5, -8, 24, -45 Array: 24, -45, 16, 5, -8, 24, -45
Desc: ChaCha20/Poly1305, SHAKE256, 16, X448, EdDSA, Desc: ChaCha20/Poly1305, SHAKE256, 16, X448, EdDSA,
ChaCha20/Poly1305, SHAKE256 ChaCha20/Poly1305, SHAKE256
Reference: [[this document]]
9.3. EDHOC Method Type Registry 9.3. 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 group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The the new group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The
registration procedure is "Expert Review". The columns of the registration procedure is "Specification Required". The columns of
registry are Value, Description, and Reference, where Value is an the registry are Value, Initiator Authentication Key, and Responder
integer and the other columns are text strings. The initial contents Authentication Key, where Value is an integer and the other columns
of the registry are shown in Figure 4. are text strings describing the authentication keys. The initial
contents of the registry are shown in Figure 4.
9.4. EDHOC Error Codes Registry 9.4. 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 group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The the new group name "Ephemeral Diffie-Hellman Over COSE (EDHOC)". The
registration procedure is "Expert Review". The columns of the registration procedure is "Expert Review". The columns of the
registry are ERR_CODE, ERR_INFO Type and Description, where ERR_CODE registry are ERR_CODE, ERR_INFO Type and Description, where ERR_CODE
is an integer, ERR_INFO is a CDDL defined type, and Description is a is an integer, ERR_INFO is a CDDL defined type, and Description is a
text string. The initial contents of the registry are shown in text string. The initial contents of the registry are shown in
Figure 7. Figure 9.
9.5. EDHOC External Authorization Data Registry 9.5. EDHOC External Authorization Data Registry
IANA has created a new registry entitled "EDHOC External IANA has created a new registry entitled "EDHOC External
Authorization Data" under the new group name "Ephemeral Diffie- Authorization Data" under the new group name "Ephemeral Diffie-
Hellman Over COSE (EDHOC)". The registration procedure is "Expert Hellman Over COSE (EDHOC)". The registration procedure is
Review". The columns of the registry are Label, Description, Value "Specification Required". The columns of the registry are Label,
Type, and Reference, where Label is an integer and the other columns Message, Description, and Reference, where Label is an integer and
are text strings. the other columns are text strings.
9.6. COSE Header Parameters Registry 9.6. COSE Header Parameters Registry
IANA has registered the following entries in the "COSE Header IANA has registered the following entries in the "COSE Header
Parameters" registry under the group name "CBOR Object Signing and Parameters" registry under the group name "CBOR Object Signing and
Encryption (COSE)". The value of the 'kcwt' header parameter is a Encryption (COSE)". The value of the 'kcwt' header parameter is a
COSE Web Token (CWT) [RFC8392], and the value of the 'kccs' header COSE Web Token (CWT) [RFC8392], and the value of the 'kccs' header
parameter is an CWT Claims Set (CCS), see Section 1.5. The CWT/CCS parameter is a CWT Claims Set (CCS), see Section 1.4. The CWT/CCS
must contain a COSE_Key in a 'cnf' claim [RFC8747]. The Value must contain a COSE_Key in a 'cnf' claim [RFC8747]. The Value
Registry for this item is empty and omitted from the table below. Registry for this item is empty and omitted from the table below.
+-----------+-------+----------------+---------------------------+ +-----------+-------+----------------+---------------------------+
| Name | Label | Value Type | Description | | Name | Label | Value Type | Description |
+===========+=======+================+===========================+ +===========+=======+================+===========================+
| kcwt | TBD1 | COSE_Messages | A CBOR Web Token (CWT) | | kcwt | TBD1 | COSE_Messages | A CBOR Web Token (CWT) |
| | | | containing a COSE_Key in | | | | | containing a COSE_Key in |
| | | | a 'cnf' claim | | | | | a 'cnf' claim |
+-----------+-------+----------------+---------------------------+ +-----------+-------+----------------+---------------------------+
| kccs | TBD2 | map / #6(map) | A CWT Claims Set (CCS) | | kccs | TBD2 | map / #6(map) | A CWT Claims Set (CCS) |
| | | | containing a COSE_Key in | | | | | containing a COSE_Key in |
| | | | a 'cnf' claim | | | | | a 'cnf' claim |
+-----------+-------+----------------+---------------------------+ +-----------+-------+----------------+---------------------------+
9.7. COSE Header Parameters Registry 9.7. The Well-Known URI Registry
IANA has extended the Value Type of 'kid' in the "COSE Header IANA has added the well-known URI "edhoc" to the "Well-Known URIs"
Parameters" registry under the group name "CBOR Object Signing and registry under the group name "Well-Known URIs".
Encryption (COSE)" to also allow the Value Type int. The resulting
Value Type is bstr / int. The Value Registry for this item is empty
and omitted from the table below.
+------+-------+------------+----------------+-------------------+ * URI suffix: edhoc
| Name | Label | Value Type | Description | Reference | * Change controller: IETF
+------+-------+------------+----------------+-------------------+
| kid | 4 | bstr / int | Key identifier | [[This document]] |
+------+-------+------------+----------------+-------------------+
9.8. COSE Key Common Parameters Registry * Specification document(s): [[this document]]
IANA has extended the Value Type of 'kid' in the "COSE Key Common * Related information: None
Parameters" registry under the group name "CBOR Object Signing and
Encryption (COSE)" to also allow the Value Type int. The resulting
Value Type is bstr / int. The Value Registry for this item is empty
and omitted from the table below.
+------+-------+------------+----------------+-------------------+ 9.8. Media Types Registry
| Name | Label | Value Type | Description | Reference |
+------+-------+------------+----------------+-------------------+
| kid | 2 | bstr / int | Key identifi- | [[This document]] |
| | | | cation value - | |
| | | | match to kid | |
| | | | in message | |
+------+-------+------------+----------------+-------------------+
9.9. CWT Confirmation Methods Registry IANA has added the media types "application/edhoc+cbor-seq" and
"application/cid-edhoc+cbor-seq" to the "Media Types" registry.
IANA has extended the Value Type of 'kid' in the "CWT Confirmation 9.8.1. application/edhoc+cbor-seq Media Type Registration
Methods" registry under the group name "CBOR Web Token (CWT) Claims"
to also allow the Value Type int. The incorrect term binary string
has been corrected to bstr. The resulting Value Type is bstr / int.
The new updated content for the 'kid' method is shown in the list
below.
* Confirmation Method Name: kid * Type name: application
* Confirmation Method Description: Key Identifier * Subtype name: edhoc+cbor-seq
* JWT Confirmation Method Name: kid * Required parameters: N/A
* Confirmation Key: 3 * Optional parameters: N/A
* Confirmation Value Type(s): bstr / int * Encoding considerations: binary
* Change Controller: IESG * Security considerations: See Section 7 of this document.
* Specification Document(s): Section 3.4 of RFC 8747 [[This * Interoperability considerations: N/A
document]]
9.10. The Well-Known URI Registry * Published specification: [[this document]] (this document)
IANA has added the well-known URI "edhoc" to the "Well-Known URIs" * Applications that use this media type: To be identified
registry under the group name "Well-Known URIs".
* URI suffix: edhoc * Fragment identifier considerations: N/A
* Change controller: IETF
* Specification document(s): [[this document]] * Additional information:
* Related information: None - Magic number(s): N/A
9.11. Media Types Registry - File extension(s): N/A
IANA has added the media type "application/edhoc" to the "Media - Macintosh file type code(s): N/A
Types" registry.
* Person & email address to contact for further information: See
"Authors' Addresses" section.
* Intended usage: COMMON
* Restrictions on usage: N/A
* Author: See "Authors' Addresses" section.
* Change Controller: IESG
9.8.2. application/cid-edhoc+cbor-seq Media Type Registration
* Type name: application * Type name: application
* Subtype name: edhoc * Subtype name: cid-edhoc+cbor-seq
* Required parameters: N/A * Required parameters: N/A
* Optional parameters: N/A * Optional parameters: N/A
* Encoding considerations: binary * Encoding considerations: binary
* Security considerations: See Section 7 of this document. * Security considerations: See Section 7 of this document.
* Interoperability considerations: N/A * Interoperability considerations: N/A
skipping to change at page 55, line 7 skipping to change at page 57, line 5
"Authors' Addresses" section. "Authors' Addresses" section.
* Intended usage: COMMON * Intended usage: COMMON
* Restrictions on usage: N/A * Restrictions on usage: N/A
* Author: See "Authors' Addresses" section. * Author: See "Authors' Addresses" section.
* Change Controller: IESG * Change Controller: IESG
9.12. CoAP Content-Formats Registry 9.9. CoAP Content-Formats Registry
IANA has added the media type "application/edhoc" to the "CoAP
Content-Formats" registry under the group name "Constrained RESTful
Environments (CoRE) Parameters".
* Media Type: application/edhoc
* Encoding: IANA has added the media types "application/edhoc+cbor-seq" and
"application/cid-edhoc+cbor-seq" to the "CoAP Content-Formats"
registry under the group name "Constrained RESTful Environments
(CoRE) Parameters".
* ID: TBD42 +--------------------------------+----------+------+-------------------+
| Media Type | Encoding | ID | Reference |
+--------------------------------+----------+------+-------------------+
| application/edhoc+cbor-seq | - | TBD5 | [[this document]] |
| application/cid-edhoc+cbor-seq | - | TBD6 | [[this document]] |
+--------------------------------+----------+------+-------------------+
* Reference: [[this document]] Figure 12: CoAP Content-Format IDs
9.13. Resource Type (rt=) Link Target Attribute Values Registry 9.10. Resource Type (rt=) Link Target Attribute Values Registry
IANA has added the resource type "core.edhoc" to the "Resource Type IANA has added the resource type "core.edhoc" to the "Resource Type
(rt=) Link Target Attribute Values" registry under the group name (rt=) Link Target Attribute Values" registry under the group name
"Constrained RESTful Environments (CoRE) Parameters". "Constrained RESTful Environments (CoRE) Parameters".
* Value: "core.edhoc" * Value: "core.edhoc"
* Description: EDHOC resource. * Description: EDHOC resource.
* Reference: [[this document]] * Reference: [[this document]]
Client applications can use this resource type to discover a server's 9.11. Expert Review Instructions
resource for EDHOC, where to send a request for executing the EDHOC
protocol.
9.14. Expert Review Instructions
The IANA Registries established in this document is defined as The IANA Registries established in this document are 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:
* 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 is required. Expert should consider the right registry, when that is required. Expert should consider
skipping to change at page 57, line 10 skipping to change at page 58, line 46
certificates", Work in Progress, Internet-Draft, draft- certificates", Work in Progress, Internet-Draft, draft-
ietf-cose-x509-08, 14 December 2020, ietf-cose-x509-08, 14 December 2020,
<https://www.ietf.org/internet-drafts/draft-ietf-cose- <https://www.ietf.org/internet-drafts/draft-ietf-cose-
x509-08.txt>. x509-08.txt>.
[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>.
[RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April
2002, <https://www.rfc-editor.org/info/rfc3279>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
[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., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>. <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>.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, DOI 10.17487/RFC6960, June 2013,
<https://www.rfc-editor.org/info/rfc6960>.
[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>.
skipping to change at page 58, line 22 skipping to change at page 60, line 26
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8376] Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN) [RFC8376] Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018, Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
<https://www.rfc-editor.org/info/rfc8376>. <https://www.rfc-editor.org/info/rfc8376>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>. May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8410] Josefsson, S. and J. Schaad, "Algorithm Identifiers for
Ed25519, Ed448, X25519, and X448 for Use in the Internet
X.509 Public Key Infrastructure", RFC 8410,
DOI 10.17487/RFC8410, August 2018,
<https://www.rfc-editor.org/info/rfc8410>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to Definition Language (CDDL): A Notational Convention to
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>.
skipping to change at page 59, line 28 skipping to change at page 61, line 38
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>.
[Degabriele11]
Degabriele, J.P., Lehmann, A., Paterson, K.G., Smart,
N.P., and M. Strefler, "On the Joint Security of
Encryption and Signature in EMV", December 2011,
<https://eprint.iacr.org/2011/615>.
[HKDFpaper]
Krawczyk, H., "Cryptographic Extraction and Key
Derivation: The HKDF Scheme", May 2010,
<https://eprint.iacr.org/2010/264.pdf>.
[I-D.arkko-arch-internet-threat-model-guidance]
Arkko, J. and S. Farrell, "Internet Threat Model
Guidance", Work in Progress, Internet-Draft, draft-arkko-
arch-internet-threat-model-guidance-00, 12 July 2021,
<https://www.ietf.org/archive/id/draft-arkko-arch-
internet-threat-model-guidance-00.txt>.
[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, "Profiling EDHOC for CoAP and OSCORE", and G. Selander, "Profiling EDHOC for CoAP and OSCORE",
Work in Progress, Internet-Draft, draft-ietf-core-oscore- Work in Progress, Internet-Draft, draft-ietf-core-oscore-
edhoc-03, 7 March 2022, <https://www.ietf.org/archive/id/ edhoc-03, 7 March 2022, <https://www.ietf.org/archive/id/
draft-ietf-core-oscore-edhoc-03.txt>. draft-ietf-core-oscore-edhoc-03.txt>.
[I-D.ietf-core-resource-directory] [I-D.ietf-core-oscore-key-update]
Amsüss, C., Shelby, Z., Koster, M., Bormann, C., and P. V. Höglund, R. and M. Tiloca, "Key Update for OSCORE
D. Stok, "CoRE Resource Directory", Work in Progress, (KUDOS)", Work in Progress, Internet-Draft, draft-ietf-
Internet-Draft, draft-ietf-core-resource-directory-28, 7 core-oscore-key-update-01, 7 March 2022,
March 2021, <https://www.ietf.org/archive/id/draft-ietf- <https://www.ietf.org/archive/id/draft-ietf-core-oscore-
core-resource-directory-28.txt>. key-update-01.txt>.
[I-D.ietf-cose-cbor-encoded-cert] [I-D.ietf-cose-cbor-encoded-cert]
Mattsson, J. P., Selander, G., Raza, S., Höglund, J., 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)", Work in Progress, Internet-Draft, draft- Certificates)", Work in Progress, Internet-Draft, draft-
ietf-cose-cbor-encoded-cert-03, 10 January 2022, ietf-cose-cbor-encoded-cert-03, 10 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-cose-cbor- <https://www.ietf.org/archive/id/draft-ietf-cose-cbor-
encoded-cert-03.txt>. encoded-cert-03.txt>.
[I-D.ietf-lake-reqs] [I-D.ietf-lake-reqs]
Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia- Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia-
Carrillo, "Requirements for a Lightweight AKE for OSCORE", Carrillo, "Requirements for a Lightweight AKE for OSCORE",
Work in Progress, Internet-Draft, draft-ietf-lake-reqs-04, Work in Progress, Internet-Draft, draft-ietf-lake-reqs-04,
8 June 2020, <https://www.ietf.org/archive/id/draft-ietf- 8 June 2020, <https://www.ietf.org/archive/id/draft-ietf-
lake-reqs-04.txt>. lake-reqs-04.txt>.
[I-D.ietf-lake-traces]
Selander, G. and J. P. Mattsson, "Traces of EDHOC", Work
in Progress, Internet-Draft, draft-ietf-lake-traces-00, 25
November 2021, <https://www.ietf.org/archive/id/draft-
ietf-lake-traces-00.txt>.
[I-D.ietf-lwig-curve-representations]
Struik, R., "Alternative Elliptic Curve Representations",
Work in Progress, Internet-Draft, draft-ietf-lwig-curve-
representations-23, 21 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-lwig-curve-
representations-23.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", Work in Progress, "Comparison of CoAP Security Protocols", Work in Progress,
Internet-Draft, draft-ietf-lwig-security-protocol- Internet-Draft, draft-ietf-lwig-security-protocol-
comparison-05, 2 November 2020, comparison-05, 2 November 2020,
<https://www.ietf.org/archive/id/draft-ietf-lwig-security- <https://www.ietf.org/archive/id/draft-ietf-lwig-security-
protocol-comparison-05.txt>. protocol-comparison-05.txt>.
[I-D.ietf-tls-dtls13] [I-D.ietf-rats-eat]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Lundblade, L., Mandyam, G., and J. O'Donoghue, "The Entity
Datagram Transport Layer Security (DTLS) Protocol Version Attestation Token (EAT)", Work in Progress, Internet-
1.3", Work in Progress, Internet-Draft, draft-ietf-tls- Draft, draft-ietf-rats-eat-12, 24 February 2022,
dtls13-43, 30 April 2021, <https://www.ietf.org/internet- <https://www.ietf.org/archive/id/draft-ietf-rats-eat-
drafts/draft-ietf-tls-dtls13-43.txt>. 12.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", Work in Progress, Internet-Draft, draft- Randomness", Work in Progress, Internet-Draft, draft-
mattsson-cfrg-det-sigs-with-noise-04, 15 February 2022, mattsson-cfrg-det-sigs-with-noise-04, 15 February 2022,
<https://www.ietf.org/archive/id/draft-mattsson-cfrg-det- <https://www.ietf.org/archive/id/draft-mattsson-cfrg-det-
sigs-with-noise-04.txt>. sigs-with-noise-04.txt>.
[I-D.selander-ace-ake-authz] [I-D.selander-ace-ake-authz]
Selander, G., Mattsson, J. P., Vučinić, M., Richardson, Selander, G., Mattsson, J. P., Vučinić, M., Richardson,
M., and A. Schellenbaum, "Lightweight Authorization for M., and A. Schellenbaum, "Lightweight Authorization for
Authenticated Key Exchange.", Work in Progress, Internet- Authenticated Key Exchange.", Work in Progress, Internet-
Draft, draft-selander-ace-ake-authz-04, 22 October 2021, Draft, draft-selander-ace-ake-authz-05, 18 April 2022,
<https://www.ietf.org/archive/id/draft-selander-ace-ake- <https://www.ietf.org/archive/id/draft-selander-ace-ake-
authz-04.txt>. authz-05.txt>.
[I-D.selander-lake-traces]
Selander, G. and J. P. Mattsson, "Traces of EDHOC", Work
in Progress, Internet-Draft, draft-selander-lake-traces-
02, 20 October 2021, <https://www.ietf.org/archive/id/
draft-selander-lake-traces-02.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>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<https://www.rfc-editor.org/info/rfc6194>.
[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,
<https://www.rfc-editor.org/info/rfc7228>. <https://www.rfc-editor.org/info/rfc7228>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>. 2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2 Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>. 2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC8366] Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"A Voucher Artifact for Bootstrapping Protocols",
RFC 8366, DOI 10.17487/RFC8366, May 2018,
<https://www.rfc-editor.org/info/rfc8366>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8937] Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N., [RFC8937] Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N.,
and C. Wood, "Randomness Improvements for Security and C. Wood, "Randomness Improvements for Security
Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020, Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020,
<https://www.rfc-editor.org/info/rfc8937>. <https://www.rfc-editor.org/info/rfc8937>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[RFC9176] Amsüss, C., Ed., Shelby, Z., Koster, M., Bormann, C., and
P. van der Stok, "Constrained RESTful Environments (CoRE)
Resource Directory", RFC 9176, DOI 10.17487/RFC9176, April
2022, <https://www.rfc-editor.org/info/rfc9176>.
[SECG] "Standards for Efficient Cryptography 1 (SEC 1)", May [SECG] "Standards for Efficient Cryptography 1 (SEC 1)", May
2009, <https://www.secg.org/sec1-v2.pdf>. 2009, <https://www.secg.org/sec1-v2.pdf>.
[SIGMA] Krawczyk, H., "SIGMA - The 'SIGn-and-MAc' Approach to [SIGMA] Krawczyk, H., "SIGMA - The 'SIGn-and-MAc' Approach to
Authenticated Diffie-Hellman and Its Use in the IKE- Authenticated Diffie-Hellman and Its Use in the IKE-
Protocols (Long version)", June 2003, Protocols (Long version)", June 2003,
<http://webee.technion.ac.il/~hugo/sigma-pdf.pdf>. <https://webee.technion.ac.il/~hugo/sigma-pdf.pdf>.
[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 [Thormarker21]
Thormarker, E., "On using the same key pair for Ed25519
This appendix describes how to select EDHOC connection identifiers and an X25519 based KEM", April 2021,
and derive an OSCORE security context when OSCORE is used with EDHOC, <https://eprint.iacr.org/2021/509.pdf>.
and how to transfer EDHOC messages over CoAP.
A.1. Selecting EDHOC Connection Identifier
This section specifies a rule for converting from EDHOC connection
identifier to OSCORE Sender/Recipient ID. (An identifier is Sender
ID or Recipient ID depending on from which endpoint is the point of
view, see Section 3.1 of [RFC8613].)
* If the EDHOC connection identifier is numeric, i.e., encoded as a
CBOR integer on the wire, it is converted to a (naturally byte-
string shaped) OSCORE Sender/Recipient ID equal to its CBOR
encoded form.
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
numeric C_I equal to -12 (0x2B in CBOR encoding) is converted to a
(typically client) Sender ID equal to 0x2B.
* If the EDHOC connection identifier is byte-valued, hence encoded
as a CBOR byte string on the wire, it is converted to an OSCORE
Sender/Recipient ID equal to the byte string.
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
0xFF.
Two EDHOC connection identifiers are called "equivalent" if and only Appendix A. Use with OSCORE and Transfer over CoAP
if, by applying the conversion above, they both result in the same
OSCORE Sender/Recipient ID. For example, the two EDHOC connection
identifiers with CBOR encoding 0x0A (numeric) and 0x410A (byte-
valued) are equivalent since they both result in the same OSCORE
Sender/Recipient ID 0x0A.
When EDHOC is used to establish an OSCORE security context, the This appendix describes how to derive an OSCORE security context when
connection identifiers C_I and C_R MUST NOT be equivalent. OSCORE is used with EDHOC, and how to transfer EDHOC messages over
Furthermore, in case of multiple OSCORE security contexts with CoAP.
potentially different endpoints, to facilitate retrieval of the
correct OSCORE security context, an endpoint SHOULD select an EDHOC
connection identifier that when converted to OSCORE Recipient ID does
not coincide with its other Recipient IDs.
A.2. Deriving the OSCORE Security Context A.1. 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]):
* 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 4.3. Exporter interface, see Section 4.2.1.
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 the OSCORE Master Salt, are the uints 0 and 1, respectively.
"OSCORE_Master_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, oscore_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, oscore_salt_length has value 8. The
and Responder MAY agree out-of-band on a longer key_length than the Initiator and Responder MAY agree out-of-band on a longer
default and on a different salt_length. oscore_key_length than the default and on a different
oscore_salt_length.
Master Secret = EDHOC-Exporter("OSCORE_Master_Secret", h'', key_length) Master Secret = EDHOC-Exporter( 0, h'', oscore_key_length )
Master Salt = EDHOC-Exporter("OSCORE_Master_Salt", h'', salt_length) Master Salt = EDHOC-Exporter( 1, h'', oscore_salt_length )
* 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.
* 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 cipher suite, HKDF SHA-256 is used as HKDF Algorithm in selected cipher suite, HKDF SHA-256 is used as HKDF Algorithm in
the OSCORE Security Context. the OSCORE Security Context.
* 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 Section 3.3.3. 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.2. 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 provides a reliable as an exchange of CoAP [RFC7252] messages. CoAP provides 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. The underlying CoAP transport should be denial-of-service attacks. The underlying CoAP transport should be
used in reliable mode, in particular when fragmentation is used, to used in reliable mode, in particular when fragmentation is used, to
avoid, e.g., situations with hanging endpoints waiting for each avoid, e.g., situations with hanging endpoints waiting for each
other. other.
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 8. According to this specification, sensitive identity, see Section 8. Client applications can use the
EDHOC is transferred in POST requests and 2.04 (Changed) responses to resource type "core.edhoc" to discover a server's EDHOC resource,
the Uri-Path: "/.well-known/edhoc". An application may define its i.e., where to send a request for executing the EDHOC protocol, see
own path that can be discovered, e.g., using resource directory Section 9.10. According to this specification, EDHOC is transferred
[I-D.ietf-core-resource-directory]. in POST requests and 2.04 (Changed) responses to the Uri-Path:
"/.well-known/edhoc", see Section 9.7. An application may define its
own path that can be discovered, e.g., using a resource directory
[RFC9176].
By default, the message flow is as follows: EDHOC message_1 is sent By default, the message flow is as follows: EDHOC message_1 is sent
in the payload of a POST request from the client to the server's in the payload of a POST request from the client to the server's
resource for EDHOC. EDHOC message_2 or the EDHOC error message is resource for EDHOC. EDHOC message_2 or the EDHOC error message is
sent from the server to the client in the payload of a 2.04 (Changed) sent from the server to the client in the payload of the response, in
response. EDHOC message_3 or the EDHOC error message is sent from the former case with response code 2.04 (Changed), in the latter with
the client to the server's resource in the payload of a POST request. response code as specified in Appendix A.2.1. EDHOC message_3 or the
If needed, an EDHOC error message is sent from the server to the EDHOC error message is sent from the client to the server's resource
client in the payload of a 2.04 (Changed) response. Alternatively, in the payload of a POST request. If EDHOC message_4 is used, or in
if EDHOC message_4 is used, it is sent from the server to the client case of an error message, it is sent from the server to the client in
in the payload of a 2.04 (Changed) response analogously to message_2. the payload of the response, with response codes analogously to
message_2. In case of an error message in response to message_4, it
is sent analogously to errors in response to message_2.
In order to correlate a message received from a client to a message In order for the server to correlate a message received from a client
previously sent by the server, messages sent by the client are to a message previously sent in the same EDHOC session over CoAP,
prepended with the CBOR serialization of the connection identifier messages sent by the client are prepended with the CBOR serialization
which the server has chosen. This applies independently of if the of the connection identifier which the server has chosen. This
CoAP server is Responder or Initiator. For the default case when the applies independently of if the CoAP server is Responder or
server is Responder, the prepended connection identifier is C_R, and Initiator.
C_I if the server is Initiator. If message_1 is sent to the server,
the CBOR simple value "true" (0xf5) is sent in its place (given that
the server has not selected C_R yet).
These identifiers are encoded in CBOR and thus self-delimiting. They * For the default case when the server is Responder, message_3 is
are sent in front of the actual EDHOC message, and only the part of sent from the client prepended with the identifier C_R. In this
the body following the identifier is used for EDHOC processing. case message_1 is also sent by the client, and to indicate that
this is a new EDHOC session it is prepended with a dummy
identifier, the CBOR simple value "true" (0xf5), since the server
has not selected C_R yet. See Figure 13.
Consequently, the application/edhoc media type does not apply to * In the case when the server is Initiator, message_2 (and
these messages; their media type is unnamed. message_4, if present) is sent from the client prepended with the
identifier C_I. See Figure 14.
The prepended identifiers are encoded in CBOR and thus self-
delimiting. The integer representation of identifiers described in
Section 3.3.2 is used, when applicable. They are sent in front of
the actual EDHOC message to keep track of messages in an EDHOC
session, and only the part of the body following the identifier is
used for EDHOC processing. In particular, the connection identifiers
within the EDHOC messages are not impacted by the prepended
identifiers.
The application/edhoc+cbor-seq media type does not apply to these
messages; their media type is application/cid-edhoc+cbor-seq.
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 10. In this case the CoAP Token enables correlation on the Figure 13. 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: true, EDHOC message_1 | | Content-Format: application/cid-edhoc+cbor-seq
| | | | Payload: true, EDHOC message_1
|<---------+ Header: 2.04 Changed | |
| 2.04 | Content-Format: application/edhoc |<---------+ Header: 2.04 Changed
| | Payload: EDHOC message_2 | 2.04 | Content-Format: application/edhoc+cbor-seq
| | | | Payload: EDHOC message_2
+--------->| Header: POST (Code=0.02) | |
| POST | Uri-Path: "/.well-known/edhoc" +--------->| Header: POST (Code=0.02)
| | Payload: C_R, EDHOC message_3 | POST | Uri-Path: "/.well-known/edhoc"
| | | | Content-Format: application/cid-edhoc+cbor-seq
|<---------+ Header: 2.04 Changed | | Payload: C_R, EDHOC message_3
| 2.04 | | |
| | |<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc+cbor-seq
| | Payload: EDHOC message_4
| |
Figure 10: Transferring EDHOC in CoAP when the Initiator is CoAP Figure 13: Example of transferring EDHOC in CoAP when the
Client Initiator is CoAP client. The optional message_4 is included in
this example, without which that message needs no payload.
The exchange in Figure 10 protects the client identity against active The exchange in Figure 13 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 11. In this case the CoAP Token enables the shown in Figure 14. 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
in the payload of a POST request with a 2.04 (Changed) response. in the payload of a POST request with a 2.04 (Changed) response.
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"
| | | |
|<---------+ Header: 2.04 Changed |<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc | 2.04 | Content-Format: application/edhoc+cbor-seq
| | Payload: EDHOC message_1 | | Payload: EDHOC message_1
| | | |
+--------->| 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 | | Content-Format: application/cid-edhoc+cbor-seq
| | | | Payload: C_I, EDHOC message_2
|<---------+ Header: 2.04 Changed | |
| 2.04 | Content-Format: application/edhoc |<---------+ Header: 2.04 Changed
| | Payload: EDHOC message_3 | 2.04 | Content-Format: application/edhoc+cbor-seq
| | | | Payload: EDHOC message_3
| |
Figure 11: Transferring EDHOC in CoAP when the Initiator is CoAP Figure 14: Example of transferring EDHOC in CoAP when the
Server Initiator is CoAP 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 [RFC9175]. This forces the initiator to containing an Echo option [RFC9175]. This forces the Initiator to
demonstrate its reachability at its apparent network address. If demonstrate its reachability at its apparent network address. If
message fragmentation is needed, the EDHOC messages may be fragmented message fragmentation is needed, the EDHOC messages may be fragmented
using the CoAP Block-Wise Transfer mechanism [RFC7959]. using the CoAP Block-Wise Transfer mechanism [RFC7959].
EDHOC does not restrict how error messages are transported with CoAP, EDHOC does not restrict how error messages are transported with CoAP,
as long as the appropriate error message can to be transported in as long as the appropriate error message can to be transported in
response to a message that failed (see Section 6). EDHOC error response to a message that failed (see Section 6). EDHOC error
messages transported with CoAP are carried in the payload. messages transported with CoAP are carried in the payload.
A.3.1. Transferring EDHOC and OSCORE over CoAP A.2.1. Transferring EDHOC and OSCORE over CoAP
When using EDHOC over CoAP for establishing an OSCORE Security When using EDHOC over CoAP for establishing an OSCORE Security
Context, EDHOC error messages sent as CoAP responses MUST be sent in 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 the payload of error responses, i.e., they MUST specify a CoAP error
response code. In particular, it is RECOMMENDED that such error response code. In particular, it is RECOMMENDED that such error
responses have response code either 4.00 (Bad Request) in case of 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 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 (Internal Server Error) in case of server error (e.g., due to failure
in deriving EDHOC key material). The Content-Format of the error in deriving EDHOC keying material). The Content-Format of the error
response MUST be set to application/edhoc. response MUST be set to application/edhoc+cbor-seq, see Section 9.9.
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]. That specification
also contains conversion from OSCORE Sender/Recipient IDs to EDHOC
connection identifiers, web-linking and target attributes for
discovering of EDHOC resources.
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
Section 2.3.3 of [SECG]. Using the notation from [SECG], the output Section 2.3.3 of [SECG]. In EDHOC, compact representation is used
is an octet string of length ceil( (log2 q) / 8 ). See [SECG] for a for the ephemeral public keys (G_X and G_Y), see Section 3.7. Using
definition of q, M, X, xp, and ~yp. The steps in Section 2.3.3 of the notation from [SECG], the output is an octet string of length
[SECG] are replaced by: ceil( (log2 q) / 8 ). See [SECG] for a definition of q, M, X, xp,
and ~yp. The steps in Section 2.3.3 of [SECG] are replaced by:
1. Convert the field element xp to an octet string X of length ceil( 1. Convert the field element xp to an octet string X of length ceil(
(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 compatibility with APIs
value ~yp SHALL be set to zero. For such use, the compact the 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].
skipping to change at page 68, line 26 skipping to change at page 71, line 26
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, byte strings (bstr), and text integers (int, uint), simple values, byte strings (bstr), and text
strings (tstr), CBOR also supports arrays [] of data items, maps {} strings (tstr), CBOR also supports arrays [] of data items, maps {}
of pairs of data items, and sequences [RFC8742] of data items. Some of pairs of data items, and sequences [RFC8742] of data items. Some
examples are given below. examples are given below.
The EDHOC specification sometimes use CDDL names in CBOR dignostic The EDHOC specification sometimes use CDDL names in CBOR diagnostic
notation as in e.g., << ID_CRED_R, ? EAD_2 >>. This means that EAD_2 notation as in e.g., << ID_CRED_R, ? EAD_2 >>. This means that EAD_2
is optional and that ID_CRED_R and EAD_2 should be substituted with is optional and that ID_CRED_R and EAD_2 should be substituted with
their values before evaluation. I.e., if ID_CRED_R = { 4 : h'' } and their values before evaluation. I.e., if ID_CRED_R = { 4 : h'' } and
EAD_2 is omitted then << ID_CRED_R, ? EAD_2 >> = << { 4 : h'' } >>, EAD_2 is omitted then << ID_CRED_R, ? EAD_2 >> = << { 4 : h'' } >>,
which encodes to 0x43a10440. which encodes to 0x43a10440.
For a complete specification and more examples, see [RFC8949] and For a complete specification and more examples, see [RFC8949] and
[RFC8610]. We recommend implementors to get used to CBOR by using [RFC8610]. We recommend implementors to get used to CBOR by using
the CBOR playground [CborMe]. the CBOR playground [CborMe].
skipping to change at page 70, line 9 skipping to change at page 73, line 9
------------------------------------------------------------------ ------------------------------------------------------------------
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.
suites = [ 2* int ] / int suites = [ 2* int ] / int
ead = 1* ( ead = 1* (
ead_label : int, ead_label : int,
ead_value : any, ead_value : bstr,
) )
message_1 = ( message_1 = (
METHOD : int, METHOD : int,
SUITES_I : suites, SUITES_I : suites,
G_X : bstr, G_X : bstr,
C_I : bstr / int, C_I : bstr / -24..23,
? EAD_1 : ead, ? EAD_1 : ead,
) )
message_2 = ( message_2 = (
G_Y_CIPHERTEXT_2 : bstr, G_Y_CIPHERTEXT_2 : bstr,
C_R : bstr / int, C_R : bstr / -24..23,
) )
message_3 = ( message_3 = (
CIPHERTEXT_3 : bstr, CIPHERTEXT_3 : bstr,
) )
message_4 = ( message_4 = (
CIPHERTEXT_4 : bstr, CIPHERTEXT_4 : bstr,
) )
error = ( error = (
ERR_CODE : int, ERR_CODE : int,
ERR_INFO : any, ERR_INFO : any,
) )
info = ( info = (
transcript_hash : bstr,
label : tstr, label : tstr,
context : bstr, context : bstr,
length : uint, 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.
skipping to change at page 72, line 19 skipping to change at page 75, line 19
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, e.g., if the endpoints have agreed to use a key identifier short, e.g., if the endpoints have agreed to use a key identifier
parameter 'kid': parameter 'kid':
* ID_CRED_x = { 4 : key_id_x }, where key_id_x : kid, for x = I or * ID_CRED_x = { 4 : key_id_x }, where key_id_x : kid, for x = I or
R. R.
Note that a COSE header map can contain several header parameters, Note that a COSE header map can contain several header parameters,
for example { x5u, x5t } or { kid, kid_context }. for example { x5u, x5t } or { kid, kid_context }.
ID_CRED_x MAY also identify the authentication credential by value. ID_CRED_x MAY also identify the credential by value. For example, a
For example, a certificate chain can be transported in ID_CRED_x with certificate chain can be transported in ID_CRED_x with COSE header
COSE header parameter c5c or x5chain, defined in parameter c5c or x5chain, defined in
[I-D.ietf-cose-cbor-encoded-cert] and [I-D.ietf-cose-x509] and [I-D.ietf-cose-cbor-encoded-cert] and [I-D.ietf-cose-x509] and
credentials of type CWT and CCS can be transported with the COSE credentials of type CWT and CCS can be transported with the COSE
header parameters registered in Section 9.6. header parameters registered in Section 9.6.
Appendix D. Applicability Template Appendix D. Authentication Related Verifications
This appendix contains a rudimentary example of an applicability EDHOC performs certain authentication related operations, see
statement, see Section 3.9. Section 3.5, but in general it is necessary to make additional
verifications beyond EDHOC message processing. What verifications
are needed depend on the deployment, in particular the trust model
and the security policies, but most commonly it can be expressed in
terms of verifications of credential content.
For use of EDHOC in the XX protocol, the following assumptions are EDHOC assumes the existence of mechanisms (certification authority or
other trusted third party, pre-provisioning, etc.) for generating and
distributing authentication credentials and other credentials, as
well as the existence of trust anchors (CA certificates, trusted
public keys, etc.). For example, a public key certificate or CWT may
rely on a trusted third party whose public key is pre-provisioned,
whereas a CCS or a self-signed certificate/CWT may be used when trust
in the public key can be achieved by other means, or in the case of
trust-on-first-use, see Appendix D.5.
In this section we provide some examples of such verifications.
These verifications are the responsibility of the application but may
be implemented as part of an EDHOC library.
D.1. Validating the Authentication Credential
The authentication credential may contain, in addition to the
authentication key, other parameters that needs to be verified. For
example:
* In X.509 and C509 certificates, signature keys typically have key
usage "digitalSignature" and Diffie-Hellman public keys typically
have key usage "keyAgreement" [RFC3279][RFC8410].
* In X.509 and C509 certificates validity is expressed using Not
After and Not Before. In CWT and CCS, the "exp" and "nbf" claims
have similar meanings.
D.2. Identities
The application must decide on allowing a connection or not depending
on the intended endpoint, and in particular whether it is a specific
identity or a set of identities. To prevent misbinding attacks, the
identity of the endpoint is included in a MAC verified through the
protocol. More details and examples are provided in this section.
Policies for what connections to allow are typically set based on the
identity of the other endpoint, and endpoints 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 and signed by a particular CA. Conversely, a device may only
be allowed to connect to a network which authenticates with a
particular public key.
* When a Public Key Infrastructure (PKI) is used with certificates,
the identity is the subject whose unique name, e.g., a domain
name, a Network Access Identifier (NAI), or an Extended Unique
Identifier (EUI), is included in the endpoint's certificate.
* Similarly, when a PKI is used with CWTs, the identity is the
subject identified by the relevant claim(s), such as 'sub'
(subject).
* When PKI is not used (e.g., CCS, self-signed certificate/CWT) the
identity is typically directly associated to the authentication
key of the other party. For example, if identities can be
expressed in the form of unique subject names assigned to public
keys, then a binding to identity is achieved by including both
public key and associated subject name in the authentication
credential: CRED_I or CRED_R may be a self-signed certificate/CWT
or CCS containing the authentication key and the subject name, see
Section 3.5.2. Each endpoint thus needs to know the specific
authentication key/unique associated subject name, or set of
public authentication keys/unique associated subject names, which
it is allowed to communicate with.
To prevent misbinding attacks in systems where an attacker can
register public keys without proving knowledge of the private key,
SIGMA [SIGMA] enforces a MAC to be calculated over the "identity".
EDHOC follows SIGMA by calculating a MAC over the whole
authentication credential, which in case of an X.509 or C509
certificate includes the "subject" and "subjectAltName" fields, and
in the case of CWT or CCS includes the "sub" claim.
(While the SIGMA paper only focuses on the identity, the same
principle is true for other information such as policies associated
to the public key.)
D.3. Certification Path and Trust Anchors
When a Public Key Infrastructure (PKI) is used with certificates, the
trust anchor is a Certification Authority (CA) certificate. Each
party needs at least one CA public key certificate, or just the CA
public key. The certification path contains proof that the subject
of the certificate owns the public key in the certificate. Only
validated public-key certificates are to be accepted.
Similarly, when a PKI is used with CWTs, each party needs to have at
least one trusted third party public key as trust anchor to verify
the end entity CWTs. The trusted third party public key can, e.g.,
be stored in a self-signed CWT or in a CCS.
The signature of the authentication credential needs to be verified
with the public key of the issuer. X.509 and C509 certificates
includes the "Issuer" field. In CWT and CCS, the "iss" claim has a
similar meaning. The public key is either a trust anchor or the
public key in another valid and trusted credential in a certification
path from trust anchor to authentication credential.
Similar verifications as made with the authentication credential (see
Appendix D.1) are also needed for the other credentials in the
certification path.
When PKI is not used (CCS, self-signed certificate/CWT), the trust
anchor is the authentication key of the other party, in which case
there is no certification path.
D.4. Revocation Status
The application may need to verify that the credentials are not
revoked, see Section 8.8. Some use cases may be served by short-
lived credentials, for example, where the validity of the credential
is on par with with the interval between revocation checks. But, in
general, credential life time and revokation checking are
complementary measures to control credential status. Revocation
information may be transported as External Authentication Data (EAD),
see Appendix E.
D.5. Trust-on-first-use
TBD
Appendix E. Use of External Authorization Data
In order to reduce the number of messages and round trips, or to
simplify processing, external security applications may be integrated
into EDHOC by transporting external authorization related data (EAD)
in the messages.
The EAD format is specified in Section 3.8, this section contains
examples and further details of how EAD may be used with an
appropriate accompanying specification.
* One example is third-party assisted authorization, requested with
EAD_1, and an authorization artifact ("voucher", cf. [RFC8366])
returned in EAD_2, see [I-D.selander-ace-ake-authz].
* Another example is remote attestation, requested in EAD_2, and an
Entity Attestation Token (EAT, [I-D.ietf-rats-eat]) returned in
EAD_3.
* A third example is certificate enrolment, where a Certificate
Signing Request (CSR, [RFC2986]) is included EAD_3, and the issued
public key certificate (X.509 [RFC5280], C509
[I-D.ietf-cose-cbor-encoded-cert]) or a reference thereof is
returned in EAD_4.
External authorization data should be considered unprotected by
EDHOC, and the protection of EAD is the responsibility of the
security application (third party authorization, remote attestation,
certificate enrolment, etc.). The security properties of the EAD
fields (after EDHOC processing) are discussed in Section 8.1.
The content of the EAD field may be used in the EDHOC processing of
the message in which they are contained. For example, authentication
related information like assertions and revocation information,
transported in EAD fields may provide input about trust anchors or
validity of credentials relevant to the authentication processing.
The EAD fields (like ID_CRED fields) are therefore made available to
the application before the message is verified, see details of
message processing in Section 5. In the first example above, a
voucher in EAD_2 made available to the application can enable the
Initiator to verify the identity or public key of the Responder
before verifying the signature. An application allowing EAD fields
containing authentication information thus may need to handle
authentication related verifications associated with EAD processing.
Conversely, the security application may need to wait for EDHOC
message verification to complete. In the third example above, the
validation of a CSR carried in EAD_3 is not started by the Responder
before EDHOC has successfully verified message_3 and proven the
possession of the private key of the Initiator.
The security application may reuse EDHOC protocol fields which
therefore need to be available to the application. For example, the
security application may use the same crypto algorithms as in the
EDHOC session and therefore needs access to the selected cipher suite
(or the whole SUITES_I). The application may use the ephemeral
public keys G_X and G_Y, as ephemeral keys or as nonces, see
[I-D.selander-ace-ake-authz].
The processing of (ead_label, ead_value) by the security application
needs to be described in the specification where the ead_label is
registered, see Section 9.5, including the ead_value for each message
and actions in case of errors. An application may support multiple
security applications that make use of EAD, which may result in
multiple (ead_label, ead_value) pairs in one EAD field, see
Section 3.8. Any dependencies on security applications with
previously registered EAD fields needs to be documented, and the
processing needs to consider their simultaneous use.
Since data carried in EAD may not be protected, or be processed by
the application before the EDHOC message is verified, special
considerations need to be made such that it does not violate security
and privacy requirements of the service which uses this data, see
Section 8.5. The content in an EAD field may impact the security
properties provided by EDHOC. Security applications making use of
the EAD fields must perform the necessary security analysis.
Appendix F. Application Profile Example
This appendix contains a rudimentary example of an application
profile, see Section 3.9.
For use of EDHOC with application X the following assumptions are
made: made:
1. Transfer in CoAP as specified in Appendix A.3 with requests 1. Transfer in CoAP as specified in Appendix A.2 with requests
expected by the CoAP server (= Responder) at /app1-edh, no expected by the CoAP server (= Responder) at /app1-edh, no
Content-Format needed. Content-Format needed.
2. METHOD = 1 (I uses signature key, R uses static DH key.) 2. METHOD = 1 (I uses signature key, R uses static DH key.)
3. CRED_I is an IEEE 802.1AR IDevID encoded as a C509 certificate of 3. CRED_I is an IEEE 802.1AR IDevID encoded as a C509 certificate of
type 0 [I-D.ietf-cose-cbor-encoded-cert]. type 0 [I-D.ietf-cose-cbor-encoded-cert].
* R acquires CRED_I out-of-band, indicated in EAD_1. * R acquires CRED_I out-of-band, indicated in EAD_1.
* ID_CRED_I = {4: h''} is a 'kid' with value empty CBOR byte * ID_CRED_I = {4: h''} is a 'kid' with value empty CBOR byte
string. string.
4. CRED_R is a CCS of type OKP as specified in Section 3.5.3. 4. CRED_R is a CCS of type OKP as specified in Section 3.5.2.
* The CBOR map has parameters 1 (kty), -1 (crv), and -2 * The CBOR map has parameters 1 (kty), -1 (crv), and -2
(x-coordinate). (x-coordinate).
* ID_CRED_R is {TBD2 : CCS}. Editor's note: TBD2 is the COSE * ID_CRED_R is {TBD2 : CCS}. Editor's note: TBD2 is the COSE
header parameter value of 'kccs', see Section 9.6 header parameter value of 'kccs', see Section 9.6
5. External authorization data is defined and processed as specified 5. External authorization data is defined and processed as specified
in [I-D.selander-ace-ake-authz]. in [I-D.selander-ace-ake-authz].
6. EUI-64 used as identity of endpoint. 6. EUI-64 is used as the identity of the endpoint (see example in
Section 3.5.2).
7. No use of message_4: the application sends protected messages 7. No use of message_4: the application sends protected messages
from R to I. from R to I.
Appendix E. EDHOC Message Deduplication Appendix G. 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
that the duplicate message is acknowledged (ACK), but the received that the duplicate message is acknowledged (ACK), but the received
message is only processed once by the CoAP stack. message is only processed once by the CoAP stack.
Message deduplication is resource demanding and therefore not Message deduplication is resource demanding and therefore not
supported in all CoAP implementations. Since EDHOC is targeting supported in all CoAP implementations. Since EDHOC is targeting
constrained environments, it is desirable that EDHOC can optionally constrained environments, it is desirable that EDHOC can optionally
support transport layers which does not handle message duplication. support transport layers which do not handle message duplication.
Special care is needed to avoid issues with duplicate messages, see Special care is needed to avoid issues with duplicate messages, see
Section 5.1. Section 5.1.
The guiding principle here is similar to the deduplication processing The guiding principle here is similar to the deduplication processing
on CoAP messaging layer: a received duplicate EDHOC message SHALL NOT on CoAP messaging layer: a received duplicate EDHOC message SHALL NOT
result in a response consisting of another instance of the next EDHOC result in another instance of the next EDHOC message. The result MAY
message. The result MAY be that a duplicate EDHOC response is sent, be that a duplicate next EDHOC message is sent, provided it is still
provided it is still relevant with respect the current protocol relevant with respect to the current protocol state. In any case,
state. In any case, the received message MUST NOT be processed more the received message MUST NOT be processed more than once in the same
than once in the same EDHOC session. This is called "EDHOC message EDHOC session. This is called "EDHOC message deduplication".
deduplication".
An EDHOC implementation MAY store the previously sent EDHOC message An EDHOC implementation MAY store the previously sent EDHOC message
to be able to resend it. An EDHOC implementation MAY keep the to be able to resend it.
protocol state to be able to recreate the previously sent EDHOC
message and resend it. The previous message or protocol state MUST
NOT be kept longer than what is required for retransmission, for
example, in the case of CoAP transport, no longer than the
EXCHANGE_LIFETIME (see Section 4.8.2 of [RFC7252]).
Note that the requirements in Section 5.1 still apply because In principle, if the EDHOC implementation would deterministically
duplicate messages are not processed by the EDHOC state machine: regenerate the identical EDHOC message previously sent, it would be
possible to instead store the protocol state to be able to recreate
and resend the previously sent EDHOC message. However, even if the
protocol state is fixed, the message generation may introduce
differences which compromises security. For example, in the
generation of message_3, if I is performing a (non-deterministic)
ECDSA signature (say, method 0 or 1, cipher suite 2 or 3) then
PLAINTEXT_3 is randomized, but K_3 and IV_3 are the same, leading to
a key and nonce reuse.
* EDHOC messages SHALL be processed according to the current The EDHOC implementation MUST NOT store previous protocol state and
protocol state. regenerate an EDHOC message if there is a risk that the same key and
IV are used for two (or more) distinct messages.
* Different instances of the same message MUST NOT be processed in The previous message or protocol state MUST NOT be kept longer than
one session. what is required for retransmission, for example, in the case of CoAP
transport, no longer than the EXCHANGE_LIFETIME (see Section 4.8.2 of
[RFC7252]).
Appendix F. Transports Not Natively Providing Correlation Appendix H. 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.2) 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, the CBOR simple value 'true' server selected (or, for message_1, the CBOR simple value 'true'
which is not a valid C_x) to any request message it sends. The which is not a valid C_x) to any request message it sends. The
server does not send any such indicator, as responses are matched to server does not send any such indicator, as responses are matched to
request by 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 G. Change Log Appendix I. Change Log
RFC Editor: Please remove this appendix. RFC Editor: Please remove this appendix.
* From -13 to -14
- Merge of section 1.1 and 1.2
- Connection and key identifiers restricted to be byte strings
- Representation of byte strings as one-byte CBOR ints (-24..23)
- Simplified mapping between EDHOC and OSCORE identifiers
- Rewrite of 3.5
o Clarification of authentication related operations performed
by EDHOC
o Authentication related verifications, including old section
3.5.1, moved to new appendix D
- Rewrite of 3.8
o Move content about use of EAD to new appendix E
o ead_value changed to bstr
- EDHOC-KDF updated
o transcript_hash argument removed
o TH included in context argument
o label argument is now type uint, all labels replaced
- Key schedule updated
o New salts derived to avoid reuse of same key with expand and
extract
o PRK_4x3m renamed PRK_4e3m
o K_4 and IV_4 derived from PRK_4e3m
o New PRK: PRK_out derived from PRK_4e3m and TH_4
o Clarified main output of EDHOC is the shared secret PRK_out
o Exporter defined by EDHOC-KDF and new PRK PRK_exporter
derived from PRK_out
o Key update defined by Expand instead of Extract
- All applications of EDHOC-KDF in one place
- Update of processing
o EAD and ID_CRED passed to application when available
o identity verification and credential retrieval omitted in
protocol description
o Transcript hash defined by plaintext messages instead of
ciphertext
o Changed order of input to TH_2
o Removed general G_X checking against selfie-attacks
- Support for padding of plaintext
- Updated compliance requirements
- Updated security considerations
o Updated and more clear requirements on MAC length
o Clarification of key confirmation
o Forbid use of same key for signature and static DH
- Updated appendix on message deduplication
- Clarifications of
o connection identifiers
o cipher suites, including negotiation
o EAD
o Error messages
- Updated media types
- Applicability template renamed application profile
- Editorials
* From -12 to -13
- no changes
* From -12:
- Shortened labels to derive OSCORE key and salt
- ead_value changed to bstr
- Removed general G_X checking against selfie-attacks
- Updated and more clear requirements on MAC length
- Clarifications from Kathleen, Stephen, Marco, Sean, Stefan,
- Authentication Related Verifications moved to appendix
- Updated MTI section and cipher suite
- Updated security considerations
* From -11 to -12: * From -11 to -12:
- Clarified applicability to KEMs - Clarified applicability to KEMs
- Clarified use of COSE header parameters - Clarified use of COSE header parameters
- Updates on MTI - Updates on MTI
- Updated security considerations - Updated security considerations
- New section on PQC - New section on PQC
- Removed duplicate definition of cipher suites - Removed duplicate definition of cipher suites
- Explanations of use of COSE moved to Appendix C.3 - Explanations of use of COSE moved to Appendix C.3
skipping to change at page 79, line 40 skipping to change at page 90, line 8
* 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, Loic Ferreira, Karthikeyan Bhargavan, Carsten Bormann, Timothy Claeys, Martin Disch,
Theis Groenbech Petersen, Dan Harkins, Klaus Hartke, Russ Housley, Stephen Farrell, Loic Ferreira, Theis Groenbech Petersen, Felix
Stefan Hristozov, Alexandros Krontiris, Ilari Liusvaara, Karl Guenther, Dan Harkins, Klaus Hartke, Russ Housley, Stefan Hristozov,
Norrman, Salvador Perez, Eric Rescorla, Michael Richardson, Thorvald Marc Ilunga, Charlie Jacomme, Elise Klein, Steve Kremer, Alexandros
Sahl Joergensen, Jim Schaad, Carsten Schuermann, Ludwig Seitz, Krontiris, Ilari Liusvaara, Kathleen Moriarty, David Navarro, Karl
Stanislav Smyshlyaev, Valery Smyslov, Peter van der Stok, Rene Norrman, Salvador Perez, Maiwenn Racouchot, Eric Rescorla, Michael
Struik, Vaishnavi Sundararajan, Erik Thormarker, Marco Tiloca, Michel Richardson, Thorvald Sahl Joergensen, Jim Schaad, Carsten Schuermann,
Veillette, and Malisa Vucinic for reviewing and commenting on Ludwig Seitz, Stanislav Smyshlyaev, Valery Smyslov, Peter van der
intermediate versions of the draft. We are especially indebted to Stok, Rene Struik, Vaishnavi Sundararajan, Erik Thormarker, Marco
Jim Schaad for his continuous reviewing and implementation of Tiloca, Sean Turner, Michel Veillette, and Malisa Vu&#269;ini&#263;
different versions of the draft. for reviewing and commenting on intermediate versions of the draft.
We are especially indebted to Jim Schaad for his continuous reviewing
and implementation of different versions of the 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
Göran Selander Göran Selander
Ericsson AB Ericsson AB
SE-164 80 Stockholm SE-164 80 Stockholm
Sweden Sweden
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