draft-ietf-lake-edhoc-00.txt   draft-ietf-lake-edhoc-01.txt 
Network Working Group G. Selander Network Working Group G. Selander
Internet-Draft J. Mattsson Internet-Draft J. Mattsson
Intended status: Standards Track F. Palombini Intended status: Standards Track F. Palombini
Expires: January 7, 2021 Ericsson AB Expires: February 3, 2021 Ericsson AB
July 06, 2020 August 02, 2020
Ephemeral Diffie-Hellman Over COSE (EDHOC) Ephemeral Diffie-Hellman Over COSE (EDHOC)
draft-ietf-lake-edhoc-00 draft-ietf-lake-edhoc-01
Abstract Abstract
This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a
very compact, and lightweight authenticated Diffie-Hellman key very compact, and lightweight authenticated Diffie-Hellman key
exchange with ephemeral keys. EDHOC provides mutual authentication, exchange with ephemeral keys. EDHOC provides mutual authentication,
perfect forward secrecy, and identity protection. EDHOC is intended perfect forward secrecy, and identity protection. EDHOC is intended
for usage in constrained scenarios and a main use case is to for usage in constrained scenarios and a main use case is to
establish an OSCORE security context. By reusing COSE for establish an OSCORE security context. By reusing COSE for
cryptography, CBOR for encoding, and CoAP for transport, the cryptography, CBOR for encoding, and CoAP for transport, the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 7, 2021. This Internet-Draft will expire on February 3, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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3.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 10 3.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 10
3.5. Communication/Negotiation of Protocol Features . . . . . 11 3.5. Communication/Negotiation of Protocol Features . . . . . 11
3.6. Auxiliary Data . . . . . . . . . . . . . . . . . . . . . 12 3.6. Auxiliary Data . . . . . . . . . . . . . . . . . . . . . 12
3.7. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 12 3.7. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 12
3.8. Key Derivation . . . . . . . . . . . . . . . . . . . . . 12 3.8. Key Derivation . . . . . . . . . . . . . . . . . . . . . 12
4. EDHOC Authenticated with Asymmetric Keys . . . . . . . . . . 15 4. EDHOC Authenticated with Asymmetric Keys . . . . . . . . . . 15
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 15 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 17 4.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 17
4.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 19 4.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 19
4.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 22 4.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 22
5. EDHOC Authenticated with Symmetric Keys . . . . . . . . . . . 25 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 25
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 25 5.1. EDHOC Error Message . . . . . . . . . . . . . . . . . . . 25
5.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 26 6. Transferring EDHOC and Deriving an OSCORE Context . . . . . . 27
5.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 27 6.1. Transferring EDHOC in CoAP . . . . . . . . . . . . . . . 27
5.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 28 7. Security Considerations . . . . . . . . . . . . . . . . . . . 30
6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 28 7.1. Security Properties . . . . . . . . . . . . . . . . . . . 30
6.1. EDHOC Error Message . . . . . . . . . . . . . . . . . . . 28 7.2. Cryptographic Considerations . . . . . . . . . . . . . . 31
7. Transferring EDHOC and Deriving an OSCORE Context . . . . . . 30 7.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 32
7.1. Transferring EDHOC in CoAP . . . . . . . . . . . . . . . 30 7.4. Unprotected Data . . . . . . . . . . . . . . . . . . . . 32
8. Security Considerations . . . . . . . . . . . . . . . . . . . 33 7.5. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 32
8.1. Security Properties . . . . . . . . . . . . . . . . . . . 33 7.6. Implementation Considerations . . . . . . . . . . . . . . 33
8.2. Cryptographic Considerations . . . . . . . . . . . . . . 34 7.7. Other Documents Referencing EDHOC . . . . . . . . . . . . 34
8.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 35 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
8.4. Unprotected Data . . . . . . . . . . . . . . . . . . . . 35 8.1. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 34
8.5. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 36 8.2. EDHOC Method Type Registry . . . . . . . . . . . . . . . 35
8.6. Implementation Considerations . . . . . . . . . . . . . . 36 8.3. The Well-Known URI Registry . . . . . . . . . . . . . . . 35
8.7. Other Documents Referencing EDHOC . . . . . . . . . . . . 37 8.4. Media Types Registry . . . . . . . . . . . . . . . . . . 36
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 8.5. CoAP Content-Formats Registry . . . . . . . . . . . . . . 37
9.1. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 37 8.6. Expert Review Instructions . . . . . . . . . . . . . . . 37
9.2. EDHOC Method Type Registry . . . . . . . . . . . . . . . 38 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.3. The Well-Known URI Registry . . . . . . . . . . . . . . . 39 9.1. Normative References . . . . . . . . . . . . . . . . . . 37
9.4. Media Types Registry . . . . . . . . . . . . . . . . . . 39 9.2. Informative References . . . . . . . . . . . . . . . . . 39
9.5. CoAP Content-Formats Registry . . . . . . . . . . . . . . 40 Appendix A. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 42
9.6. Expert Review Instructions . . . . . . . . . . . . . . . 40 A.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 42
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 A.2. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 43
10.1. Normative References . . . . . . . . . . . . . . . . . . 41 Appendix B. Test Vectors . . . . . . . . . . . . . . . . . . . . 43
10.2. Informative References . . . . . . . . . . . . . . . . . 42
Appendix A. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 45
A.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 45
A.2. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Appendix B. Test Vectors . . . . . . . . . . . . . . . . . . . . 46
B.1. Test Vectors for EDHOC Authenticated with Signature Keys B.1. Test Vectors for EDHOC Authenticated with Signature Keys
(x5t) . . . . . . . . . . . . . . . . . . . . . . . . . . 46 (x5t) . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 60 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 57
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 57
1. Introduction 1. Introduction
Security at the application layer provides an attractive option for Security at the application layer provides an attractive option for
protecting Internet of Things (IoT) deployments, for example where protecting Internet of Things (IoT) deployments, for example where
transport layer security is not sufficient transport layer security is not sufficient
[I-D.hartke-core-e2e-security-reqs] or where the protection needs to [I-D.hartke-core-e2e-security-reqs] or where the protection needs to
work over a variety of underlying protocols. IoT devices may be work over a variety of underlying protocols. IoT devices may be
constrained in various ways, including memory, storage, processing constrained in various ways, including memory, storage, processing
capacity, and energy [RFC7228]. A method for protecting individual capacity, and energy [RFC7228]. A method for protecting individual
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the Constrained Application Protocol (CoAP), using COSE. the Constrained Application Protocol (CoAP), using COSE.
In order for a communication session to provide forward secrecy, the In order for a communication session to provide forward secrecy, the
communicating parties can run an Elliptic Curve Diffie-Hellman (ECDH) communicating parties can run an Elliptic Curve Diffie-Hellman (ECDH)
key exchange protocol with ephemeral keys, from which shared key key exchange protocol with ephemeral keys, from which shared key
material can be derived. This document specifies Ephemeral Diffie- material can be derived. This document specifies Ephemeral Diffie-
Hellman Over COSE (EDHOC), a lightweight key exchange protocol Hellman Over COSE (EDHOC), a lightweight key exchange protocol
providing perfect forward secrecy and identity protection. providing perfect forward secrecy and identity protection.
Authentication is based on credentials established out of band, e.g. Authentication is based on credentials established out of band, e.g.
from a trusted third party, such as an Authorization Server as from a trusted third party, such as an Authorization Server as
specified by [I-D.ietf-ace-oauth-authz]. EDHOC supports specified by [I-D.ietf-ace-oauth-authz]. The construction provided
authentication using pre-shared keys (PSK), raw public keys (RPK), by EDHOC can be applied to authenticate raw public keys (RPK) and
and public key certificates. After successful completion of the public key certificates. This version of the protocol is focusing on
EDHOC protocol, application keys and other application specific data RPK and certificates by reference which is the initial focus for the
can be derived using the EDHOC-Exporter interface. A main use case LAKE WG (see Section 2.2 of [I-D.ietf-lake-reqs]).
for EDHOC is to establish an OSCORE security context. EDHOC uses
COSE for cryptography, CBOR for encoding, and CoAP for transport. By
reusing existing libraries, the additional code footprint can be kept
very low. Note that this document focuses on authentication and key
establishment: for integration with authorization of resource access,
refer to [I-D.ietf-ace-oscore-profile].
EDHOC is designed to work in highly constrained scenarios making it After successful completion of the EDHOC protocol, application keys
especially suitable for network technologies such as Cellular IoT, and other application specific data can be derived using the EDHOC-
6TiSCH [I-D.ietf-6tisch-dtsecurity-zerotouch-join], and LoRaWAN Exporter interface. A main use case for EDHOC is to establish an
[LoRa1][LoRa2]. These network technologies are characterized by OSCORE security context. EDHOC uses COSE for cryptography, CBOR for
their low throughput, low power consumption, and small frame sizes. encoding, and CoAP for transport. By reusing existing libraries, the
Compared to the DTLS 1.3 handshake [I-D.ietf-tls-dtls13] with ECDH additional code footprint can be kept very low. Note that this
and connection ID, the number of bytes in EDHOC + CoAP is less than document focuses on authentication and key establishment: for
1/4 when PSK authentication is used and less than 1/6 when RPK integration with authorization of resource access, refer to
[I-D.ietf-ace-oscore-profile].
EDHOC is designed for highly constrained settings making it
especially suitable for low-power wide area networks [RFC8376] such
as Cellular IoT, 6TiSCH, and LoRaWAN. Compared to the DTLS 1.3
handshake [I-D.ietf-tls-dtls13] with ECDH and connection ID, the
number of bytes in EDHOC + CoAP can be less than 1/6 when RPK
authentication is used, see authentication is used, see
[I-D.ietf-lwig-security-protocol-comparison]. Typical message sizes [I-D.ietf-lwig-security-protocol-comparison]. Figure 1 shows two
for EDHOC with pre-shared keys, raw public keys with static Diffie- examples of message sizes for EDHOC with different kinds of
Hellman keys, and two different ways to identify X.509 certificates authentication keys and different COSE header parameters for
with signature keys are shown in Figure 1. Further reductions of identification: static Diffie-Hellman keys identified by 'kid'
message sizes are possible by eliding redundant length indications. [RFC8152], and X.509 signature certificates identified by a hash
value using 'x5t' [I-D.ietf-cose-x509]. Further reductions of
message sizes are possible, for example by eliding redundant length
indications.
===================================================================== =================================
PSK RPK x5t x5chain kid x5t
--------------------------------------------------------------------- ---------------------------------
message_1 38 37 37 37 message_1 37 37
message_2 44 46 117 110 + Certificate message_2 46 117
message_3 10 20 91 84 + Certificate message_3 20 91
--------------------------------------------------------------------- ----------------------------------
Total 92 103 245 231 + Certificates Total 103 245
===================================================================== =================================
Figure 1: Typical message sizes in bytes Figure 1: Example of message sizes in bytes.
The ECDH exchange and the key derivation follow known protocol The ECDH exchange and the key derivation follow known protocol
constructions such as [SIGMA], NIST SP-800-56A [SP-800-56A], and HKDF constructions such as [SIGMA], NIST SP-800-56A [SP-800-56A], and HKDF
[RFC5869]. CBOR [RFC7049] and COSE [RFC8152] are used to implement [RFC5869]. CBOR [RFC7049] and COSE [RFC8152] are used to implement
these standards. The use of COSE provides crypto agility and enables these standards. The use of COSE provides crypto agility and enables
use of future algorithms and headers designed for constrained IoT. use of future algorithms and headers designed for constrained IoT.
This document is organized as follows: Section 2 describes how EDHOC This document is organized as follows: Section 2 describes how EDHOC
authenticated with digital signatures builds on SIGMA-I, Section 3 authenticated with digital signatures builds on SIGMA-I, Section 3
specifies general properties of EDHOC, including message flow, specifies general properties of EDHOC, including message flow,
formatting of the ephemeral public keys, and key derivation, formatting of the ephemeral public keys, and key derivation,
Section 4 specifies EDHOC with signature key and static Diffie- Section 4 specifies EDHOC with signature key and static Diffie-
Hellman key authentication, Section 5 specifies EDHOC with symmetric Hellman key authentication, Section 5 specifies the EDHOC error
key authentication, Section 6 specifies the EDHOC error message, and message, and Section 6 describes how EDHOC can be transferred in CoAP
Section 7 describes how EDHOC can be transferred in CoAP and used to and used to establish an OSCORE security context.
establish an OSCORE security context.
1.1. Rationale for EDHOC 1.1. Rationale for EDHOC
Many constrained IoT systems today do not use any security at all, Many constrained IoT systems today do not use any security at all,
and when they do, they often do not follow best practices. One and when they do, they often do not follow best practices. One
reason is that many current security protocols are not designed with reason is that many current security protocols are not designed with
constrained IoT in mind. Constrained IoT systems often deal with constrained IoT in mind. Constrained IoT systems often deal with
personal information, valuable business data, and actuators personal information, valuable business data, and actuators
interacting with the physical world. Not only do such systems need interacting with the physical world. Not only do such systems need
security and privacy, they often need end-to-end protection with security and privacy, they often need end-to-end protection with
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1.2. Terminology and Requirements Language 1.2. 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 [RFC7049], CBOR Sequences [RFC8742], COSE described in CBOR [RFC7049], CBOR Sequences [RFC8742], COSE
[RFC8152], and CDDL [RFC8610]. The Concise Data Definition Language [RFC8152], and CDDL [RFC8610]. The Concise Data Definition Language
(CDDL) is used to express CBOR data structures [RFC7049]. Examples (CDDL) is used to express CBOR data structures [RFC7049]. Examples
of CBOR and CDDL are provided in Appendix A.1. of CBOR and CDDL are provided in Appendix A.1.
2. Background 2. Background
EDHOC specifies different authentication methods of the Diffie- EDHOC specifies different authentication methods of the Diffie-
Hellman key exchange: digital signatures, static Diffie-Hellman keys Hellman key exchange: digital signatures and static Diffie-Hellman
and symmetric keys. This section outlines the digital signature keys. This section outlines the digital signature based method.
based method.
SIGMA (SIGn-and-MAc) is a family of theoretical protocols with a SIGMA (SIGn-and-MAc) is a family of theoretical protocols with a
large number of variants [SIGMA]. Like IKEv2 [RFC7296] and (D)TLS large number of variants [SIGMA]. Like IKEv2 [RFC7296] and (D)TLS
1.3 [RFC8446], EDHOC authenticated with digital signatures is built 1.3 [RFC8446], EDHOC authenticated with digital signatures is built
on a variant of the SIGMA protocol which provide identity protection on a variant of the SIGMA protocol which provide identity protection
of the initiator (SIGMA-I), and like IKEv2 [RFC7296], EDHOC of the initiator (SIGMA-I), and like IKEv2 [RFC7296], EDHOC
implements the SIGMA-I variant as Mac-then-Sign. The SIGMA-I implements the SIGMA-I variant as Mac-then-Sign. The SIGMA-I
protocol using an authenticated encryption algorithm is shown in protocol using an authenticated encryption algorithm is shown in
Figure 2. Figure 2.
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given in Appendix B. given in Appendix B.
3. EDHOC Overview 3. EDHOC Overview
EDHOC consists of three messages (message_1, message_2, message_3) EDHOC consists of three messages (message_1, message_2, message_3)
that maps directly to the three messages in SIGMA-I, plus an EDHOC that maps directly to the three messages in SIGMA-I, plus an EDHOC
error message. EDHOC messages are CBOR Sequences [RFC8742], where error message. EDHOC messages are CBOR Sequences [RFC8742], where
the first data item (METHOD_CORR) of message_1 is an int specifying the first data item (METHOD_CORR) of message_1 is an int specifying
the method and the correlation properties of the transport used, see the method and the correlation properties of the transport used, see
Section 3.1. The method specifies the authentication methods used Section 3.1. The method specifies the authentication methods used
(signature, static DH, symmetric), see Section 9.2. An (signature, static DH), see Section 8.2. An implementation may
implementation may support only Initiator or Responder. An support only Initiator or Responder. An implementation may support
implementation may support only a single method. The Initiator and only a single method. The Initiator and the Responder need to have
the Responder need to have agreed on a single method to be used for agreed on a single method to be used for EDHOC.
EDHOC.
While EDHOC uses the COSE_Key, COSE_Sign1, and COSE_Encrypt0 While EDHOC uses the COSE_Key, COSE_Sign1, and COSE_Encrypt0
structures, only a subset of the parameters is included in the EDHOC structures, only a subset of the parameters is included in the EDHOC
messages. The unprotected COSE header in COSE_Sign1, and messages. The unprotected COSE header in COSE_Sign1, and
COSE_Encrypt0 (not included in the EDHOC message) MAY contain COSE_Encrypt0 (not included in the EDHOC message) MAY contain
parameters (e.g. 'alg'). After creating EDHOC message_3, the parameters (e.g. 'alg'). After creating EDHOC message_3, the
Initiator can derive symmetric application keys, and application Initiator can derive symmetric application keys, and application
protected data can therefore be sent in parallel with EDHOC protected data can therefore be sent in parallel with EDHOC
message_3. The application may protect data using the algorithms message_3. The application may protect data using the algorithms
(AEAD, hash, etc.) in the selected cipher suite and the connection (AEAD, hash, etc.) in the selected cipher suite and the connection
identifiers (C_I, C_R). EDHOC may be used with the media type identifiers (C_I, C_R). EDHOC may be used with the media type
application/edhoc defined in Section 9. application/edhoc defined in Section 8.
Initiator Responder Initiator Responder
| | | |
| ------------------ EDHOC message_1 -----------------> | | ------------------ EDHOC message_1 -----------------> |
| | | |
| <----------------- EDHOC message_2 ------------------ | | <----------------- EDHOC message_2 ------------------ |
| | | |
| ------------------ EDHOC message_3 -----------------> | | ------------------ EDHOC message_3 -----------------> |
| | | |
| <----------- Application Protected Data ------------> | | <----------- Application Protected Data ------------> |
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3.1. Transport and Message Correlation 3.1. Transport and Message Correlation
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
be used in environments without IP. The transport is responsible to be used in environments without IP. The transport is responsible to
handle message loss, reordering, message duplication, fragmentation, handle message loss, reordering, message duplication, fragmentation,
and denial of service protection, where necessary. The Initiator and and denial of service protection, where necessary. The Initiator and
the Responder need to have agreed on a transport to be used for the Responder need to have agreed on a transport to be used for
EDHOC. It is recommended to transport EDHOC in CoAP payloads, see EDHOC. It is recommended to transport EDHOC in CoAP payloads, see
Section 7. Section 6.
EDHOC includes connection identifiers (C_I, C_R) to correlate EDHOC includes connection identifiers (C_I, C_R) to correlate
messages. The connection identifiers C_I and C_R do not have any messages. The connection identifiers C_I and C_R do not have any
cryptographic purpose in EDHOC. They contain information cryptographic purpose in EDHOC. They contain information
facilitating retrieval of the protocol state and may therefore be facilitating retrieval of the protocol state and may therefore be
very short. The connection identifier MAY be used with an very short. The connection identifier MAY be used with an
application protocol (e.g. OSCORE) for which EDHOC establishes keys, application protocol (e.g. OSCORE) for which EDHOC establishes keys,
in which case the connection identifiers SHALL adhere to the in which case the connection identifiers SHALL adhere to the
requirements for that protocol. Each party choses a connection requirements for that protocol. Each party choses a connection
identifier it desires the other party to use in outgoing messages. identifier it desires the other party to use in outgoing messages.
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o corr = 1, the transport provides a correlation mechanism that o corr = 1, the transport provides a correlation mechanism that
enables the Responder to correlate message_2 and message_1. enables the Responder to correlate message_2 and message_1.
o corr = 2, the transport provides a correlation mechanism that o corr = 2, the transport provides a correlation mechanism that
enables the Initiator to correlate message_3 and message_2. enables the Initiator to correlate message_3 and message_2.
o corr = 3, the transport provides a correlation mechanism that o corr = 3, the transport provides a correlation mechanism that
enables both parties to correlate all three messages. enables both parties to correlate all three messages.
For example, if the key exchange is transported over CoAP, the CoAP For example, if the key exchange is transported over CoAP, the CoAP
Token can be used to correlate messages, see Section 7.1. Token can be used to correlate messages, see Section 6.1.
3.2. Authentication Keys and Identities 3.2. Authentication Keys and Identities
The EDHOC message exchange may be authenticated using pre-shared keys The EDHOC message exchange may be authenticated using raw public keys
(PSK), raw public keys (RPK), or public key certificates. The (RPK) or public key certificates. The certificates and RPKs can
certificates and RPKs can contain signature keys or static Diffie- contain signature keys or static Diffie-Hellman keys. In X.509
Hellman keys. In X.509 certificates, signature keys typically have certificates, signature keys typically have key usage
key usage "digitalSignature" and Diffie-Hellman keys typically have "digitalSignature" and Diffie-Hellman keys typically have key usage
key usage "keyAgreement". EDHOC assumes the existence of mechanisms "keyAgreement". EDHOC assumes the existence of mechanisms
(certification authority, trusted third party, manual distribution, (certification authority, trusted third party, manual distribution,
etc.) for distributing authentication keys (public or pre-shared) and etc.) for distributing authentication keys and identities. Policies
identities. Policies are set based on the identity of the other are set based on the identity of the other party, and parties
party, and parties typically only allow connections from a small typically only allow connections from a small restricted set of
restricted set of identities. identities.
o When a Public Key Infrastructure (PKI) is used, the trust anchor o When a Public Key Infrastructure (PKI) is used, the trust anchor
is a Certification Authority (CA) certificate, and the identity is is a Certification Authority (CA) certificate, and the identity is
the subject whose unique name (e.g. a domain name, NAI, or EUI) is the subject whose unique name (e.g. a domain name, NAI, or EUI) is
included in the other party's certificate. Before running EDHOC included in the other party's certificate. Before running EDHOC
each party needs at least one CA public key certificate, or just each party needs at least one CA public key certificate, or just
the public key, and a set of identities it is allowed to the public key, and a set of identities it is allowed to
communicate with. Any validated public-key certificate with an communicate with. Any validated public-key certificate with an
allowed subject name is accepted. EDHOC provides proof that the allowed subject name is accepted. EDHOC provides proof that the
other party possesses the private authentication key corresponding other party possesses the private authentication key corresponding
skipping to change at page 10, line 25 skipping to change at page 10, line 23
including both public key and associated subject name in the including both public key and associated subject name in the
protocol message computation: CRED_I or CRED_R may be a self- protocol message computation: CRED_I or CRED_R may be a self-
signed certificate or COSE_Key containing the public signed certificate or COSE_Key containing the public
authentication key and the subject name, see Figure 2. Before authentication key and the subject name, see Figure 2. Before
running EDHOC, each party need a set of public authentication running EDHOC, each party need a set of public authentication
keys/unique associated subject names it is allowed to communicate keys/unique associated subject names it is allowed to communicate
with. EDHOC provides proof that the other party possesses the with. EDHOC provides proof that the other party possesses the
private authentication key corresponding to the public private authentication key corresponding to the public
authentication key. authentication key.
o When pre-shared keys are used the information about the other
party is carried in the PSK identifier field of the protocol,
ID_PSK. The purpose of ID_PSK is to facilitate retrieval of the
pre-shared key, which is used to authenticate and assert trust.
In this case no other identities or trust anchors are used.
3.3. Identifiers 3.3. Identifiers
One byte connection and credential identifiers are realistic in many One byte connection and credential identifiers are realistic in many
scenarios as most constrained devices only have a few keys and scenarios as most constrained devices only have a few keys and
connections. In cases where a node only has one connection or key, connections. In cases where a node only has one connection or key,
the identifiers may even be the empty byte string. the identifiers may even be the empty byte string.
3.4. Cipher Suites 3.4. Cipher Suites
EDHOC cipher suites consist of an ordered set of COSE algorithms: an EDHOC cipher suites consist of an ordered set of COSE algorithms: an
skipping to change at page 11, line 44 skipping to change at page 11, line 44
o The Initiator proposes a cipher suite (see Section 3.4), and the o The Initiator proposes a cipher suite (see Section 3.4), and the
Responder either accepts or rejects, and may make a counter Responder either accepts or rejects, and may make a counter
proposal. proposal.
o The Initiator decides on the correlation parameter corr (see o The Initiator decides on the correlation parameter corr (see
Section 3.1). This is typically given by the transport which the Section 3.1). This is typically given by the transport which the
Initiator and the Responder have agreed on beforehand. The Initiator and the Responder have agreed on beforehand. The
Responder either accepts or rejects. Responder either accepts or rejects.
o The Initiator decides on the method parameter, see Section 9.2. o The Initiator decides on the method parameter, see Section 8.2.
The Responder either accepts or rejects. The Responder either accepts or rejects.
o The Initiator and the Responder decide on the representation of o The Initiator and the Responder decide on the representation of
the identifier of their respective credentials, ID_CRED_I and the identifier of their respective credentials, ID_CRED_I and
ID_CRED_R. The decision is reflected by the label used in the ID_CRED_R. The decision is reflected by the label used in the
CBOR map, see for example Section 4.1. CBOR map, see for example Section 4.1.
3.6. Auxiliary Data 3.6. Auxiliary Data
In order to reduce round trips and number of messages, and in some In order to reduce round trips and number of messages, and in some
skipping to change at page 13, line 7 skipping to change at page 13, line 7
PRK = HKDF-Extract( salt, IKM ) PRK = HKDF-Extract( salt, IKM )
PRK_2e is used to derive key and IV to encrypt message_2. PRK_3e2m PRK_2e is used to derive key and IV to encrypt message_2. PRK_3e2m
is used to derive keys and IVs produce a MAC in message_2 and to is used to derive keys and IVs produce a MAC in message_2 and to
encrypt message_3. PRK_4x3m is used to derive keys and IVs produce a encrypt message_3. PRK_4x3m is used to derive keys and IVs produce a
MAC in message_3 and to derive application specific data. MAC in message_3 and to derive application specific data.
PRK_2e is derived with the following input: PRK_2e is derived with the following input:
o The salt SHALL be the PSK when EDHOC is authenticated with o The salt SHALL be the empty byte string. Note that [RFC5869]
symmetric keys, and the empty byte string when EDHOC is specifies that if the salt is not provided, it is set to a string
authenticated with asymmetric keys (signature or static DH). The of zeros (see Section 2.2 of [RFC5869]). For implementation
PSK is used as 'salt' to simplify implementation. Note that purposes, not providing the salt is the same as setting the salt
[RFC5869] specifies that if the salt is not provided, it is set to to the empty byte string.
a string of zeros (see Section 2.2 of [RFC5869]). For
implementation purposes, not providing the salt is the same as
setting the salt to the empty byte string.
o The input keying material (IKM) SHALL be the ECDH shared secret o The input keying material (IKM) SHALL be the ECDH shared secret
G_XY (calculated from G_X and Y or G_Y and X) as defined in G_XY (calculated from G_X and Y or G_Y and X) as defined in
Section 12.4.1 of [RFC8152]. Section 12.4.1 of [RFC8152].
Example: Assuming the use of SHA-256 the extract phase of HKDF Example: Assuming the use of SHA-256 the extract phase of HKDF
produces PRK_2e as follows: produces PRK_2e as follows:
PRK_2e = HMAC-SHA-256( salt, G_XY ) PRK_2e = HMAC-SHA-256( salt, G_XY )
where salt = 0x (the empty byte string) in the asymmetric case and where salt = 0x (the empty byte string).
salt = PSK in the symmetric case.
The pseudorandom keys PRK_3e2m and PRK_4x3m are defined as follow: The pseudorandom keys PRK_3e2m and PRK_4x3m are defined as follow:
o If the Reponder authenticates with a static Diffie-Hellman key, o If the Reponder authenticates with a static Diffie-Hellman key,
then PRK_3e2m = HKDF-Extract( PRK_2e, G_RX ), where G_RX is the then PRK_3e2m = HKDF-Extract( PRK_2e, G_RX ), where G_RX is the
ECDH shared secret calculated from G_R and X, or G_X and R, else ECDH shared secret calculated from G_R and X, or G_X and R, else
PRK_3e2m = PRK_2e. PRK_3e2m = PRK_2e.
o If the Initiator authenticates with a static Diffie-Hellman key, o If the Initiator authenticates with a static Diffie-Hellman key,
then PRK_4x3m = HKDF-Extract( PRK_3e2m, G_IY ), where G_IY is the then PRK_4x3m = HKDF-Extract( PRK_3e2m, G_IY ), where G_IY is the
skipping to change at page 14, line 27 skipping to change at page 14, line 24
identifier of the EDHOC AEAD algorithm in the selected cipher identifier of the EDHOC AEAD algorithm in the selected cipher
suite encoded as defined in [RFC8152]. Note that a single fixed suite encoded as defined in [RFC8152]. Note that a single fixed
edhoc_aead_id is used in all invocations of EDHOC-KDF, including edhoc_aead_id is used in all invocations of EDHOC-KDF, including
the derivation of K_2e and invocations of the EDHOC-Exporter. the derivation of K_2e and invocations of the EDHOC-Exporter.
o transcript_hash is a bstr set to one of the transcript hashes o transcript_hash is a bstr set to one of the transcript hashes
TH_2, TH_3, or TH_4 as defined in Sections 4.3.1, 4.4.1, and TH_2, TH_3, or TH_4 as defined in Sections 4.3.1, 4.4.1, and
3.8.1. 3.8.1.
o label is a tstr set to the name of the derived key or IV, i.e. o label is a tstr set to the name of the derived key or IV, i.e.
"K_2m", "IV_2m", "K_2e", "K_2ae", "IV_2ae", "K_3m", "IV_3m", "K_2m", "IV_2m", "K_2e", "K_3m", "IV_3m", "K_3ae", or "IV_3ae".
"K_3ae", or "IV_2ae".
o length is the length of output keying material (OKM) in bytes o length is the length of output keying material (OKM) in bytes
K_2ae and IV_2ae are derived using the transcript hash TH_2 and the K_2m and IV_2m are derived using the transcript hash TH_2 and the
pseudorandom key PRK_2e. K_2m and IV_2m are derived using the pseudorandom key PRK_3e2m. K_3ae and IV_3ae are derived using the
transcript hash TH_2 and the pseudorandom key PRK_3e2m. K_3ae and transcript hash TH_3 and the pseudorandom key PRK_3e2m. K_3m and
IV_3ae are derived using the transcript hash TH_3 and the IV_3m are derived using the transcript hash TH_3 and the pseudorandom
pseudorandom key PRK_3e2m. K_3m and IV_3m are derived using the key PRK_4x3m. IVs are only used if the EDHOC AEAD algorithm uses
transcript hash TH_3 and the pseudorandom key PRK_4x3m. IVs are only IVs.
used if the EDHOC AEAD algorithm uses IVs.
3.8.1. EDHOC-Exporter Interface 3.8.1. EDHOC-Exporter Interface
Application keys and other application specific data can be derived Application keys and other application specific data can be derived
using the EDHOC-Exporter interface defined as: using the EDHOC-Exporter interface defined as:
EDHOC-Exporter(label, length) EDHOC-Exporter(label, length)
= EDHOC-KDF(PRK_4x3m, TH_4, label, length) = EDHOC-KDF(PRK_4x3m, TH_4, label, length)
where label is a tstr defined by the application and length is an where label is a tstr defined by the application and length is a uint
uint defined by the application. The label SHALL be different for defined by the application. The label SHALL be different for each
each different exporter value. The transcript hash TH_4 is a CBOR different exporter value. The transcript hash TH_4 is a CBOR encoded
encoded bstr and the input to the hash function is a CBOR Sequence. bstr and the input to the hash function is a CBOR Sequence.
TH_4 = H( TH_3, CIPHERTEXT_3 ) TH_4 = H( TH_3, CIPHERTEXT_3 )
where H() is the hash function in the selected cipher suite. Example where H() is the hash function in the selected cipher suite. Example
use of the EDHOC-Exporter is given in Sections 3.8.2 and 7.1.1. use of the EDHOC-Exporter is given in Sections 6.1.1.
3.8.2. EDHOC PSK Chaining
An application using EDHOC may want to derive new PSKs to use for
authentication in future EDHOC exchanges. In this case, the new PSK
and the ID_PSK 'kid_value' parameter SHOULD be derived as follows
where length is the key length (in bytes) of the EDHOC AEAD
Algorithm.
PSK = EDHOC-Exporter( "EDHOC Chaining PSK", length )
kid_psk = EDHOC-Exporter( "EDHOC Chaining kid_psk", 4 )
4. EDHOC Authenticated with Asymmetric Keys 4. EDHOC Authenticated with Asymmetric Keys
4.1. Overview 4.1. Overview
This section specifies authentication method = 0, 1, 2, and 3, see This section specifies authentication method = 0, 1, 2, and 3, see
Section 9.2. EDHOC supports authentication with signature or static Section 8.2. EDHOC supports authentication with signature or static
Diffie-Hellman keys in the form of raw public keys (RPK) and public Diffie-Hellman keys in the form of raw public keys (RPK) and public
key certificates with the requirements that: key certificates with the requirements that:
o Only the Responder SHALL have access to the Responder's private o Only the Responder SHALL have access to the Responder's private
authentication key, authentication key,
o Only the Initiator SHALL have access to the Initiator's private o Only the Initiator SHALL have access to the Initiator's private
authentication key, authentication key,
o The Initiator is able to retrieve the Responder's public o The Initiator is able to retrieve the Responder's public
skipping to change at page 16, line 5 skipping to change at page 15, line 38
Section 3.1 of [RFC8152]). ID_CRED_I and ID_CRED_R need to contain Section 3.1 of [RFC8152]). ID_CRED_I and ID_CRED_R need to contain
parameters that can identify a public authentication key. In the parameters that can identify a public authentication key. In the
following paragraph we give some examples of possible COSE header following paragraph we give some examples of possible COSE header
parameters used. parameters used.
Raw public keys are most optimally stored as COSE_Key objects and Raw public keys are most optimally stored as COSE_Key objects and
identified with a 'kid' parameter: identified with a 'kid' parameter:
o ID_CRED_x = { 4 : kid_x }, where kid_x : bstr, for x = I or R. o ID_CRED_x = { 4 : kid_x }, where kid_x : bstr, for x = I or R.
Public key certificates can be identified in different ways. Several Public key certificates can be identified in different ways. Header
header parameters for identifying X.509 certificates are defined in parameters for identifying X.509 certificates are defined in
[I-D.ietf-cose-x509]: [I-D.ietf-cose-x509], for example:
o by a bag of certificates with the 'x5bag' parameter; or
* ID_CRED_x = { 32 : COSE_X509 }, for x = I or R,
o by a certificate chain with the 'x5chain' parameter;
* ID_CRED_x = { 33 : COSE_X509 }, for x = I or R,
o by a hash value with the 'x5t' parameter; o by a hash value with 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,
o by a URL with the 'x5u' parameter; o by a URL with the 'x5u' parameter;
* ID_CRED_x = { 35 : uri }, for x = I or R, * ID_CRED_x = { 35 : uri }, for x = I or R,
In the first two examples, ID_CRED_I and ID_CRED_R contain the actual The purpose of ID_CRED_I and ID_CRED_R is to facilitate retrieval of
credential used for authentication. The purpose of ID_CRED_I and a public authentication key and when they do not contain the actual
ID_CRED_R is to facilitate retrieval of a public authentication key credential, they may be very short. ID_CRED_I and ID_CRED_R MAY
and when they do not contain the actual credential, they may be very contain the actual credential used for authentication. It is
short. It is RECOMMENDED that they uniquely identify the public RECOMMENDED that they uniquely identify the public authentication key
authentication key as the recipient may otherwise have to try several as the recipient may otherwise have to try several keys. ID_CRED_I
keys. ID_CRED_I and ID_CRED_R are transported in the ciphertext, see and ID_CRED_R are transported in the ciphertext, see Section 4.3.2
Section 4.3.2 and Section 4.4.2. and Section 4.4.2.
The authentication key MUST be a signature key or static Diffie- The authentication key MUST be a signature key or static Diffie-
Hellman key. The Initiator and the Responder MAY use different types Hellman key. The Initiator and the Responder MAY use different types
of authentication keys, e.g. one uses a signature key and the other of authentication keys, e.g. one uses a signature key and the other
uses a static Diffie-Hellman key. When using a signature key, the uses a static Diffie-Hellman key. When using a signature key, the
authentication is provided by a signature. When using a static authentication is provided by a signature. When using a static
Diffie-Hellman key the authentication is provided by a Message Diffie-Hellman key the authentication is provided by a Message
Authentication Code (MAC) computed from an ephemeral-static ECDH Authentication Code (MAC) computed from an ephemeral-static ECDH
shared secret which enables significant reductions in message sizes. shared secret which enables significant reductions in message sizes.
The MAC is implemented with an AEAD algorithm. When using a static The MAC is implemented with an AEAD algorithm. When using a static
Diffie-Hellman keys the Initiator's and Responder's private Diffie-Hellman keys the Initiator's and Responder's private
authentication keys are called I and R, respectively, and the public authentication keys are called I and R, respectively, and the public
authentication keys are called G_I and G_R, respectively. authentication keys are called G_I and G_R, respectively.
The actual credentials CRED_I and CRED_R are signed or MAC:ed by the The actual credentials CRED_I and CRED_R are signed or MAC:ed by the
Initiator and the Responder respectively, see Section 4.4.1 and Initiator and the Responder respectively, see Section 4.4.1 and
Section 4.3.1. The Initiator and the Responder MAY use different Section 4.3.1. The Initiator and the Responder MAY use different
types of credentials, e.g. one uses RPK and the other uses types of credentials, e.g. one uses RPK and the other uses
certificate. When the credential is a certificate, CRED_x is end- certificate. When the credential is a certificate, CRED_x is end-
entity certificate (i.e. not the certificate chain) encoded as a CBOR entity certificate (i.e. not the certificate chain) encoded as a CBOR
bstr. When the credential is a COSE_Key, CREX_x is a CBOR map only bstr. When the credential is a COSE_Key, CRED_x is a CBOR map only
contains specific fields from the COSE_Key. For COSE_Keys of type contains specific fields from the COSE_Key. For COSE_Keys of type
OKP the CBOR map SHALL only include the parameters 1 (kty), -1 (crv), OKP the CBOR map SHALL only include the parameters 1 (kty), -1 (crv),
and -2 (x-coordinate). For COSE_Keys of type EC2 the CBOR map SHALL and -2 (x-coordinate). For COSE_Keys of type EC2 the CBOR map SHALL
only include the parameters 1 (kty), -1 (crv), -2 (x-coordinate), and only include the parameters 1 (kty), -1 (crv), -2 (x-coordinate), and
-3 (y-coordinate). If the parties have agreed on an identity besides -3 (y-coordinate). If the parties have agreed on an identity besides
the public key, the indentity is included in the CBOR map with the the public key, the indentity is included in the CBOR map with the
label "subject name", otherwise the subject name is the empty text label "subject name", otherwise the subject name is the empty text
string. The parameters SHALL be encoded in decreasing order with int string. The parameters SHALL be encoded in decreasing order with int
labels first and text string labels last. An example of CRED_x when labels first and text string labels last. An example of CRED_x when
the RPK contains a X25519 static Diffie-Hellman key and the parties the RPK contains an X25519 static Diffie-Hellman key and the parties
have agreed on an EUI-64 identity is shown below: have agreed on an EUI-64 identity is shown below:
CRED_x = { CRED_x = {
1: 1, 1: 1,
-1: 4, -1: 4,
-2: h'b1a3e89460e88d3a8d54211dc95f0b90 -2: h'b1a3e89460e88d3a8d54211dc95f0b90
3ff205eb71912d6db8f4af980d2db83a', 3ff205eb71912d6db8f4af980d2db83a',
"subject name" : "42-50-31-FF-EF-37-32-39" "subject name" : "42-50-31-FF-EF-37-32-39"
} }
Initiator Responder Initiator Responder
| METHOD_CORR, SUITES_I, G_X, C_I, AD_1 | | METHOD_CORR, SUITES_I, G_X, C_I, AD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
| | | |
| C_I, G_Y, C_R, Enc(K_2e; ID_CRED_R, Signature_or_MAC_2, AD_2) | | C_I, G_Y, C_R, Enc(K_2e; ID_CRED_R, Signature_or_MAC_2, AD_2) |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| message_2 | | message_2 |
| | | |
| C_R, AEAD(K_3ae; ID_CRED_I, Signature_or_MAC_3, AD_3) | | C_R, AEAD(K_3ae; ID_CRED_I, Signature_or_MAC_3, AD_3) |
skipping to change at page 18, line 4 skipping to change at page 17, line 25
| message_3 | | message_3 |
Figure 4: Overview of EDHOC with asymmetric key authentication. Figure 4: Overview of EDHOC with asymmetric key authentication.
4.2. EDHOC Message 1 4.2. EDHOC Message 1
4.2.1. Formatting of Message 1 4.2.1. Formatting of Message 1
message_1 SHALL be a CBOR Sequence (see Appendix A.1) as defined message_1 SHALL be a CBOR Sequence (see Appendix A.1) as defined
below below
message_1 = ( message_1 = (
METHOD_CORR : int, METHOD_CORR : int,
SUITES_I : [ selected : suite, supported : 2* suite ] / suite, SUITES_I : [ selected : suite, supported : 2* suite ] / suite,
G_X : bstr, G_X : bstr,
C_I : bstr_identifier, C_I : bstr_identifier,
? AD_1 : bstr, ? AD_1 : bstr,
) )
suite = int suite = int
bstr_identifier = bsrt / int bstr_identifier = bstr / int
where: where:
o METHOD_CORR = 4 * method + corr, where method = 0, 1, 2, or 3 (see o METHOD_CORR = 4 * method + corr, where method = 0, 1, 2, or 3 (see
Section 9.2) and the correlation parameter corr is chosen based on Section 8.2) and the correlation parameter corr is chosen based on
the transport and determines which connection identifiers that are the transport and determines which connection identifiers that are
omitted (see Section 3.1). omitted (see Section 3.1).
o SUITES_I - cipher suites which the Initiator supports in order of o SUITES_I - cipher suites which the Initiator supports in order of
(decreasing) preference. The list of supported cipher suites can (decreasing) preference. The list of supported cipher suites can
be truncated at the end, as is detailed in the processing steps be truncated at the end, as is detailed in the processing steps
below. One of the supported cipher suites is selected. If a below. One of the supported cipher suites is selected. If a
single supported cipher suite is conveyed then that cipher suite single supported cipher suite is conveyed then that cipher suite
is selected and the selected cipher suite is encoded as an int is selected and the selected cipher suite is encoded as an int
instead of an array. instead of an array.
skipping to change at page 19, line 35 skipping to change at page 19, line 8
The Responder SHALL process message_1 as follows: The Responder SHALL process message_1 as follows:
o Decode message_1 (see Appendix A.1). o Decode message_1 (see Appendix A.1).
o Verify that the selected cipher suite is supported and that no o Verify that the selected cipher suite is supported and that no
prior cipher suites in SUITES_I are supported. prior cipher suites in SUITES_I are supported.
o Pass AD_1 to the security application. o Pass AD_1 to the security application.
If any verification step fails, the Initiator MUST send an EDHOC If any verification step fails, the Initiator MUST send an EDHOC
error message back, formatted as defined in Section 6, and the error message back, formatted as defined in Section 5, and the
protocol MUST be discontinued. If V does not support the selected protocol MUST be discontinued. If V does not support the selected
cipher suite, then SUITES_R MUST include one or more supported cipher cipher suite, then SUITES_R MUST include one or more supported cipher
suites. If the Responder does not support the selected cipher suite, suites. If the Responder does not support the selected cipher suite,
but supports another cipher suite in SUITES_I, then SUITES_R MUST but supports another cipher suite in SUITES_I, then SUITES_R MUST
include the first supported cipher suite in SUITES_I. include the first supported cipher suite in SUITES_I.
4.3. EDHOC Message 2 4.3. EDHOC Message 2
4.3.1. Formatting of Message 2 4.3.1. Formatting of Message 2
skipping to change at page 22, line 38 skipping to change at page 22, line 12
o Verify that the identity of the Responder is among the allowed o Verify that the identity of the Responder is among the allowed
identities for this connection. identities for this connection.
o Verify Signature_or_MAC_2 using the algorithm in the selected o 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 4.3.2. Section 4.3.2.
o Pass AD_2 to the security application. o Pass AD_2 to the security application.
If any verification step fails, the Responder MUST send an EDHOC If any verification step fails, the Responder MUST send an EDHOC
error message back, formatted as defined in Section 6, and the error message back, formatted as defined in Section 5, and the
protocol MUST be discontinued. protocol MUST be discontinued.
4.4. EDHOC Message 3 4.4. EDHOC Message 3
4.4.1. Formatting of Message 3 4.4.1. Formatting of Message 3
message_3 and data_3 SHALL be CBOR Sequences (see Appendix A.1) as message_3 and data_3 SHALL be CBOR Sequences (see Appendix A.1) as
defined below defined below
message_3 = ( message_3 = (
skipping to change at page 25, line 41 skipping to change at page 25, line 15
o Verify Signature_or_MAC_3 using the algorithm in the selected o 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 4.4.2. Section 4.4.2.
o Pass AD_3, the connection identifiers (C_I, C_R), and the o Pass AD_3, the connection identifiers (C_I, C_R), and the
application algorithms in the selected cipher suite to the application algorithms in the selected cipher suite to the
security application. The application can now derive application security application. The application can now derive application
keys using the EDHOC-Exporter interface. keys using the EDHOC-Exporter interface.
If any verification step fails, the Responder MUST send an EDHOC If any verification step fails, the Responder MUST send an EDHOC
error message back, formatted as defined in Section 6, and the error message back, formatted as defined in Section 5, and the
protocol MUST be discontinued. protocol MUST be discontinued.
5. EDHOC Authenticated with Symmetric Keys 5. Error Handling
5.1. Overview
EDHOC supports authentication with pre-shared keys (authentication
method = 4, see Section 9.2). The Initiator and the Responder are
assumed to have a pre-shared key (PSK) with a good amount of
randomness and the requirement that:
o Only the Initiator and the Responder SHALL have access to the PSK,
o The Responder is able to retrieve the PSK using ID_PSK.
where the identifier ID_PSK is a COSE header_map (i.e. a CBOR map
containing COSE Common Header Parameters, see [RFC8152]) containing
COSE header parameter that can identify a pre-shared key. Pre-shared
keys are typically stored as COSE_Key objects and identified with a
'kid' parameter (see [RFC8152]):
o ID_PSK = { 4 : kid_psk } , where kid_psk : bstr
The purpose of ID_PSK is to facilitate retrieval of the PSK and in
the case a 'kid' parameter is used it may be very short. It is
RECOMMENDED that it uniquely identify the PSK as the recipient may
otherwise have to try several keys.
EDHOC with symmetric key authentication is illustrated in Figure 5.
Initiator Responder
| METHOD_CORR, SUITES_I, G_X, C_I, ID_PSK, AD_1 |
+------------------------------------------------------------------>|
| message_1 |
| |
| C_I, G_Y, C_R, AEAD(K_2ae; TH_2, AD_2) |
|<------------------------------------------------------------------+
| message_2 |
| |
| C_R, AEAD(K_3ae; TH_3, AD_3) |
+------------------------------------------------------------------>|
| message_3 |
Figure 5: Overview of EDHOC with symmetric key authentication.
EDHOC with symmetric key authentication is very similar to EDHOC with
asymmetric authentication. In the following subsections the
differences compared to EDHOC with asymmetric authentication are
described.
5.2. EDHOC Message 1
5.2.1. Formatting of Message 1
message_1 SHALL be a CBOR Sequence (see Appendix A.1) as defined
below
message_1 = (
METHOD_CORR : int,
SUITES_I : [ selected : suite, supported : 2* suite ] / suite,
G_X : bstr,
C_I : bstr_identifier,
ID_PSK : header_map / bstr_identifier,
? AD_1 : bstr,
)
where:
o METHOD_CORR = 4 * method + corr, where method = 4 and the
connection parameter corr is chosen based on the transport and
determines which connection identifiers that are omitted (see
Section 3.1).
o ID_PSK - identifier to facilitate retrieval of the pre-shared key.
If ID_PSK contains a single 'kid' parameter, i.e., ID_PSK = { 4 :
kid_psk }, only the byte string kid_psk is conveyed encoded as an
bstr_identifier.
5.3. EDHOC Message 2
5.3.1. Processing of Message 2
o Signature_or_MAC_2 is not used.
o The outer COSE_Encrypt0 is computed as defined in Section 5.3 of
[RFC8152], with the EDHOC AEAD algorithm in the selected cipher
suite, K_2ae, IV_2ae, and the following parameters. The protected
header SHALL be empty.
* plaintext = ? AD_2
+ AD_2 = bstr containing opaque unprotected auxiliary data
* external_aad = TH_2
COSE constructs the input to the AEAD [RFC5116] as follows:
* Key K = EDHOC-KDF( PRK_2e, TH_2, "K_2ae", length )
* Nonce N = EDHOC-KDF( PRK_2e, TH_2, "IV_2ae", length )
* Plaintext P = ? AD_2
* Associated data A = [ "Encrypt0", h'', TH_2 ]
5.4. EDHOC Message 3
5.4.1. Processing of Message 3
o Signature_or_MAC_3 is not used.
o COSE_Encrypt0 is computed as defined in Section 5.3 of [RFC8152],
with the EDHOC AEAD algorithm in the selected cipher suite, K_3ae,
IV_3ae, and the following parameters. The protected header SHALL
be empty.
* plaintext = ? AD_3
+ AD_3 = bstr containing opaque protected auxiliary data
* external_aad = TH_3
COSE constructs the input to the AEAD [RFC5116] as follows:
* Key K = EDHOC-KDF( PRK_3e2m, TH_3, "K_3ae", length )
* Nonce N = EDHOC-KDF( PRK_3e2m, TH_3, "IV_3ae", length )
* Plaintext P = ? AD_3
* Associated data A = [ "Encrypt0", h'', TH_3 ]
6. Error Handling
6.1. EDHOC Error Message 5.1. EDHOC Error Message
This section defines a message format for the EDHOC error message, This section defines a message format for the EDHOC error message,
used during the protocol. An EDHOC error message can be sent by both used during the protocol. An EDHOC error message can be sent by both
parties as a reply to any non-error EDHOC message. After sending an parties as a reply to any non-error EDHOC message. After sending an
error message, the protocol MUST be discontinued. Errors at the error message, the protocol MUST be discontinued. Errors at the
EDHOC layer are sent as normal successful messages in the lower EDHOC layer are sent as normal successful messages in the lower
layers (e.g. CoAP POST and 2.04 Changed). An advantage of using layers (e.g. CoAP POST and 2.04 Changed). An advantage of using
such a construction is to avoid issues created by usage of cross such a construction is to avoid issues created by usage of cross
protocol proxies (e.g. UDP to TCP). protocol proxies (e.g. UDP to TCP).
skipping to change at page 29, line 21 skipping to change at page 26, line 7
o ERR_MSG - text string containing the diagnostic payload, defined o ERR_MSG - text string containing the diagnostic payload, defined
in the same way as in Section 5.5.2 of [RFC7252]. ERR_MSG MAY be in the same way as in Section 5.5.2 of [RFC7252]. ERR_MSG MAY be
a 0-length text string. a 0-length text string.
o SUITES_R - cipher suites from SUITES_I or the EDHOC cipher suites o SUITES_R - cipher suites from SUITES_I or the EDHOC cipher suites
registry that the Responder supports. SUITES_R MUST only be registry that the Responder supports. SUITES_R MUST only be
included in replies to message_1. If a single supported cipher included in replies to message_1. If a single supported cipher
suite is conveyed then the supported cipher suite is encoded as an suite is conveyed then the supported cipher suite is encoded as an
int instead of an array. int instead of an array.
6.1.1. Example Use of EDHOC Error Message with SUITES_R 5.1.1. Example Use of EDHOC Error Message with SUITES_R
Assuming that the Initiator supports the five cipher suites 5, 6, 7, Assuming that the Initiator supports the five cipher suites 5, 6, 7,
8, and 9 in decreasing order of preference, Figures 6 and 7 show 8, and 9 in decreasing order of preference, Figures 5 and 6 show
examples of how the Responder can truncate SUITES_I and how SUITES_R examples of how the Responder can truncate SUITES_I and how SUITES_R
is used by the Responder to give the Initiator information about the is used by the Responder to give the Initiator information about the
cipher suites that the Responder supports. In Figure 6, the cipher suites that the Responder supports. In Figure 5, the
Responder supports cipher suite 6 but not the selected cipher suite Responder supports cipher suite 6 but not the selected cipher suite
5. 5.
Initiator Responder Initiator Responder
| METHOD_CORR, SUITES_I = [5, 5, 6, 7], G_X, C_I, AD_1 | | METHOD_CORR, SUITES_I = [5, 5, 6, 7], G_X, C_I, AD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
| | | |
| C_I, ERR_MSG, SUITES_R = 6 | | C_I, ERR_MSG, SUITES_R = 6 |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| error | | error |
| | | |
| METHOD_CORR, SUITES_I = [6, 5, 6], G_X, C_I, AD_1 | | METHOD_CORR, SUITES_I = [6, 5, 6], G_X, C_I, AD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
Figure 6: Example use of error message with SUITES_R. Figure 5: Example use of error message with SUITES_R.
In Figure 7, the Responder supports cipher suite 7 but not cipher In Figure 6, the Responder supports cipher suite 7 but not cipher
suites 5 and 6. suites 5 and 6.
Initiator Responder Initiator Responder
| METHOD_CORR, SUITES_I = [5, 5, 6], G_X, C_I, AD_1 | | METHOD_CORR, SUITES_I = [5, 5, 6], G_X, C_I, AD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
| | | |
| C_I, ERR_MSG, SUITES_R = [7, 9] | | C_I, ERR_MSG, SUITES_R = [7, 9] |
|<------------------------------------------------------------------+ |<------------------------------------------------------------------+
| error | | error |
| | | |
| METHOD_CORR, SUITES_I = [7, 5, 6, 7], G_X, C_I, AD_1 | | METHOD_CORR, SUITES_I = [7, 5, 6, 7], G_X, C_I, AD_1 |
+------------------------------------------------------------------>| +------------------------------------------------------------------>|
| message_1 | | message_1 |
Figure 7: Example use of error message with SUITES_R. Figure 6: Example use of error message with SUITES_R.
As the Initiator's list of supported cipher suites and order of As the Initiator's list of supported cipher suites and order of
preference is fixed, and the Responder only accepts message_1 if the preference is fixed, and the Responder only accepts message_1 if the
selected cipher suite is the first cipher suite in SUITES_I that the selected cipher suite is the first cipher suite in SUITES_I that the
Responder supports, the parties can verify that the selected cipher Responder supports, the parties can verify that the selected cipher
suite is the most preferred (by the Initiator) cipher suite supported suite is the most preferred (by the Initiator) cipher suite supported
by both parties. If the selected cipher suite is not the first by both parties. If the selected cipher suite is not the first
cipher suite in SUITES_I that the Responder supports, the Responder cipher suite in SUITES_I that the Responder supports, the Responder
will discontinue the protocol. will discontinue the protocol.
7. Transferring EDHOC and Deriving an OSCORE Context 6. Transferring EDHOC and Deriving an OSCORE Context
7.1. Transferring EDHOC in CoAP 6.1. Transferring EDHOC in CoAP
It is recommended to transport EDHOC as an exchange of CoAP [RFC7252] It is recommended to transport EDHOC as an exchange of CoAP [RFC7252]
messages. CoAP is a reliable transport that can preserve packet messages. CoAP is a reliable transport that can preserve packet
ordering and handle message duplication. CoAP can also perform ordering and handle message duplication. CoAP can also perform
fragmentation and protect against denial of service attacks. It is fragmentation and protect against denial of service attacks. It is
recommended to carry the EDHOC messages in Confirmable messages, recommended to carry the EDHOC messages in Confirmable messages,
especially if fragmentation is used. especially if fragmentation is used.
By default, the CoAP client is the Initiator and the CoAP server is By default, the CoAP client is the Initiator and the CoAP server is
the Responder, but the roles SHOULD be chosen to protect the most the Responder, but the roles SHOULD be chosen to protect the most
sensitive identity, see Section 8. By default, EDHOC is transferred sensitive identity, see Section 7. By default, EDHOC is transferred
in POST requests and 2.04 (Changed) responses to the Uri-Path: in POST requests and 2.04 (Changed) responses to the Uri-Path:
"/.well-known/edhoc", but an application may define its own path that "/.well-known/edhoc", but an application may define its own path that
can be discovered e.g. using resource directory can be discovered e.g. using resource directory
[I-D.ietf-core-resource-directory]. [I-D.ietf-core-resource-directory].
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 a 2.04 (Changed)
response. EDHOC message_3 or the EDHOC error message is sent from response. EDHOC message_3 or the EDHOC error message is sent from
the client to the server's resource in the payload of a POST request. the client to the server's resource in the payload of a POST request.
If needed, an EDHOC error message is sent from the server to the If needed, an EDHOC error message is sent from the server to the
client in the payload of a 2.04 (Changed) response. client in the payload of a 2.04 (Changed) response.
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 8. In this case the CoAP Token enables the Initiator to Figure 7. In this case the CoAP Token enables the Initiator to
correlate message_1 and message_2 so the correlation parameter corr = correlate message_1 and message_2 so the correlation parameter corr =
1. 1.
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"
| | Content-Format: application/edhoc | | Content-Format: application/edhoc
| | Payload: EDHOC message_1 | | Payload: EDHOC message_1
| | | |
skipping to change at page 31, line 33 skipping to change at page 28, line 25
| | | |
+--------->| Header: POST (Code=0.02) +--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc" | POST | Uri-Path: "/.well-known/edhoc"
| | Content-Format: application/edhoc | | Content-Format: application/edhoc
| | Payload: EDHOC message_3 | | Payload: EDHOC message_3
| | | |
|<---------+ Header: 2.04 Changed |<---------+ Header: 2.04 Changed
| 2.04 | | 2.04 |
| | | |
Figure 8: Transferring EDHOC in CoAP Figure 7: Transferring EDHOC in CoAP
The exchange in Figure 8 protects the client identity against active The exchange in Figure 7 protects the client identity against active
attackers and the server identity against passive attackers. An attackers and the server identity against passive attackers. An
alternative exchange that protects the server identity against active alternative exchange that protects the server identity against active
attackers and the client identity against passive attackers is shown attackers and the client identity against passive attackers is shown
in Figure 9. In this case the CoAP Token enables the Responder to in Figure 8. In this case the CoAP Token enables the Responder to
correlate message_2 and message_3 so the correlation parameter corr = correlate message_2 and message_3 so the correlation parameter corr =
2. 2.
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
skipping to change at page 32, line 24 skipping to change at page 29, line 24
+--------->| Header: POST (Code=0.02) +--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc" | POST | Uri-Path: "/.well-known/edhoc"
| | Content-Format: application/edhoc | | Content-Format: application/edhoc
| | Payload: EDHOC message_2 | | Payload: EDHOC message_2
| | | |
|<---------+ Header: 2.04 Changed |<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc | 2.04 | Content-Format: application/edhoc
| | Payload: EDHOC message_3 | | Payload: EDHOC message_3
| | | |
Figure 9: Transferring EDHOC in CoAP Figure 8: Transferring EDHOC in CoAP
To protect against denial-of-service attacks, the CoAP server MAY To protect against denial-of-service attacks, the CoAP server MAY
respond to the first POST request with a 4.01 (Unauthorized) respond to the first POST request with a 4.01 (Unauthorized)
containing an Echo option [I-D.ietf-core-echo-request-tag]. This containing an Echo option [I-D.ietf-core-echo-request-tag]. This
forces the initiator to demonstrate its reachability at its apparent forces the initiator to demonstrate its reachability at its apparent
network address. If message fragmentation is needed, the EDHOC network address. If message fragmentation is needed, the EDHOC
messages may be fragmented using the CoAP Block-Wise Transfer messages may be fragmented using the CoAP Block-Wise Transfer
mechanism [RFC7959]. mechanism [RFC7959].
7.1.1. Deriving an OSCORE Context from EDHOC 6.1.1. Deriving an OSCORE Context from EDHOC
When EDHOC is used to derive parameters for OSCORE [RFC8613], the When EDHOC is used to derive parameters for OSCORE [RFC8613], the
parties make sure that the EDHOC connection identifiers are unique, parties make sure that the EDHOC connection identifiers are unique,
i.e. C_R MUST NOT be equal to C_I. The CoAP client and server MUST i.e. C_R MUST NOT be equal to C_I. The CoAP client and server MUST
be able to retrieve the OSCORE protocol state using its chosen be able to retrieve the OSCORE protocol state using its chosen
connection identifier and optionally other information such as the connection identifier and optionally other information such as the
5-tuple. In case that the CoAP client is the Initiator and the CoAP 5-tuple. In case that the CoAP client is the Initiator and the CoAP
server is the Responder: server is the Responder:
o The client's OSCORE Sender ID is C_R and the server's OSCORE o The client's OSCORE Sender ID is C_R and the server's OSCORE
skipping to change at page 33, line 8 skipping to change at page 30, line 8
o The AEAD Algorithm and the hash algorithm are the application AEAD o The AEAD Algorithm and the hash algorithm are the application AEAD
and hash algorithms in the selected cipher suite. and hash algorithms in the selected cipher suite.
o The Master Secret and Master Salt are derived as follows where o The Master Secret and Master Salt are derived as follows where
length is the key length (in bytes) of the application AEAD length is the key length (in bytes) of the application AEAD
Algorithm. Algorithm.
Master Secret = EDHOC-Exporter( "OSCORE Master Secret", length ) Master Secret = EDHOC-Exporter( "OSCORE Master Secret", length )
Master Salt = EDHOC-Exporter( "OSCORE Master Salt", 8 ) Master Salt = EDHOC-Exporter( "OSCORE Master Salt", 8 )
8. Security Considerations 7. Security Considerations
8.1. Security Properties 7.1. Security Properties
EDHOC inherits its security properties from the theoretical SIGMA-I EDHOC inherits its security properties from the theoretical SIGMA-I
protocol [SIGMA]. Using the terminology from [SIGMA], EDHOC provides protocol [SIGMA]. Using the terminology from [SIGMA], EDHOC provides
perfect forward secrecy, mutual authentication with aliveness, perfect forward secrecy, mutual authentication with aliveness,
consistency, peer awareness. As described in [SIGMA], peer awareness consistency, peer awareness. As described in [SIGMA], peer awareness
is provided to the Responder, but not to the Initiator. is provided to the Responder, but not to the Initiator.
When a Public Key Infrastructure (PKI) is used, EDHOC provides EDHOC protects the credential identifier of the Initiator against
identity protection of the Initiator against active attacks and active attacks and the credential identifier of the Responder against
identity protection of the Responder against passive attacks. When passive attacks. The roles should be assigned to protect the most
PKI is not used (kid, x5t) the identity is not sent on the wire and sensitive identity/identifier, typically that which is not possible
EDHOC with asymmetric authentication protects the credential to infer from routing information in the lower layers.
identifier of the Initiator against active attacks and the credential
identifier of the Responder against passive attacks. 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. EDHOC with symmetric authentication
does not offer protection of the PSK identifier ID_PSK.
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, auxiliary data, and previous messages. This protects algorithms, auxiliary data, and previous messages. This protects
against an attacker replaying messages or injecting messages from against an attacker replaying messages or injecting messages from
another session. another session.
EDHOC also adds negotiation of connection identifiers and downgrade EDHOC also adds negotiation 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 34, line 7 skipping to change at page 30, line 50
is to use a key exchange that provides perfect forward secrecy. is to use a key exchange that provides perfect forward secrecy.
EDHOC therefore only supports methods with perfect forward secrecy. EDHOC therefore only supports methods with perfect forward secrecy.
To limit the effect of breaches, it is important to limit the use of To limit the effect of breaches, it is important to limit the use of
symmetrical group keys for bootstrapping. EDHOC therefore strives to symmetrical group keys for bootstrapping. EDHOC therefore strives to
make the additional cost of using raw public keys and self-signed make the additional cost of using raw public keys and self-signed
certificates as small as possible. Raw public keys and self-signed certificates as small as possible. Raw public keys and self-signed
certificates are not a replacement for a public key infrastructure, certificates are not a replacement for a public key infrastructure,
but SHOULD be used instead of symmetrical group keys for but SHOULD be used instead of symmetrical group keys for
bootstrapping. bootstrapping.
Compromise of the long-term keys (PSK or private authentication keys) Compromise of the long-term keys (private signature or static DH
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. Compromising parties in EDHOC exchanges with the compromised party. Compromise of
the PSK lets an active attacker impersonate the Initiator in EDHOC the long-term keys does not enable a passive attacker to compromise
exchanges with the Responder and impersonate the Responder in EDHOC future session keys. Compromise of the HDKF input parameters (ECDH
exchanges with the Initiator. Compromise of the long-term keys does shared secret) leads to compromise of all session keys derived from
not enable a passive attacker to compromise future session keys. that compromised shared secret. Compromise of one session key does
Compromise of the HDKF input parameters (ECDH shared secret and/or not compromise other session keys.
PSK) leads to compromise of all session keys derived from that
compromised shared secret. Compromise of one session key does not
compromise other session keys.
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. In having access to the long term key or the ephemeral secret key. With
EDHOC authenticated with symmetric keys, EDHOC provides KCI static Diffie-Hellman key authentication, KCI protection would be
protection against an attacker having access to the ephemeral secret provided against an attacker having access to the long-term Diffie-
key, but not against an attacker having access to the long-term PSK. Hellman key, but not to an attacker having access to the ephemeral
With static Diffie-Hellman key authentication, KCI protection would secret key. Note that the term KCI has typically been used for
be provided against an attacker having access to the long-term compromise of long-term keys, and that an attacker with access to the
Diffie-Hellman key, but not to an attacker having access to the ephemeral secret key can only attack that specific protocol run.
ephemeral 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 ephemeral secret key can only attack that specific protocol run.
Repudiation: In EDHOC authenticated with signature keys, Party U Repudiation: In EDHOC authenticated with signature keys, Party U
could theoretically prove that Party V performed a run of the could theoretically prove that Party V performed a run of the
protocol by presenting the private ephemeral key, and vice versa. protocol by presenting the private ephemeral key, and vice versa.
Note that storing the private ephemeral keys violates the protocol Note that storing the private ephemeral keys violates the protocol
requirements. With static Diffie-Hellman key authentication or PSK requirements. With static Diffie-Hellman key authentication, both
authentication, both parties can always deny having participated in parties can always deny having participated in the protocol.
the protocol.
8.2. Cryptographic Considerations 7.2. Cryptographic Considerations
The security of the SIGMA protocol requires the MAC to be bound to The security of the SIGMA protocol requires the MAC to be bound to
the identity of the signer. Hence the message authenticating the identity of the signer. Hence the message authenticating
functionality of the authenticated encryption in EDHOC is critical: functionality of the authenticated encryption in EDHOC is critical:
authenticated encryption MUST NOT be replaced by plain encryption authenticated encryption MUST NOT be replaced by plain encryption
only, even if authentication is provided at another level or through only, even if authentication is provided at another level or through
a different mechanism. EDHOC implements SIGMA-I using the same Sign- a different mechanism. EDHOC implements SIGMA-I using the same Sign-
then-MAC approach as TLS 1.3. then-MAC approach as TLS 1.3.
To reduce message overhead EDHOC does not use explicit nonces and To reduce message overhead EDHOC does not use explicit nonces and
skipping to change at page 35, line 25 skipping to change at page 32, line 13
Initiator and the Responder should enforce a minimum security level. Initiator and the Responder should enforce a minimum security level.
The data rates in many IoT deployments are very limited. Given that The data rates in many IoT deployments are very limited. Given that
the application keys are protected as well as the long-term the application keys are protected as well as the long-term
authentication keys they can often be used for years or even decades authentication keys they can often be used for years or even decades
before the cryptographic limits are reached. If the application keys before the cryptographic limits are reached. If the application keys
established through EDHOC need to be renewed, the communicating established through EDHOC need to be renewed, the communicating
parties can derive application keys with other labels or run EDHOC parties can derive application keys with other labels or run EDHOC
again. again.
8.3. Cipher Suites 7.3. Cipher Suites
Cipher suite number 0 (AES-CCM-16-64-128, SHA-256, X25519, EdDSA, Cipher suite number 0 (AES-CCM-16-64-128, SHA-256, X25519, EdDSA,
Ed25519, AES-CCM-16-64-128, SHA-256) is mandatory to implement. Ed25519, AES-CCM-16-64-128, SHA-256) is mandatory to implement.
Implementations only need to implement the algorithms needed for Implementations only need to implement the algorithms needed for
their supported methods. For many constrained IoT devices it is their supported methods. For many constrained IoT devices it is
problematic to support more than one cipher suites, so some problematic to support more than one cipher suites, so some
deployments with P-256 may not support the mandatory cipher suite. deployments with P-256 may not support the mandatory cipher suite.
This is not a problem for local deployments. This is not a problem for local deployments.
The HMAC algorithm HMAC 256/64 (HMAC w/ SHA-256 truncated to 64 bits) The HMAC algorithm HMAC 256/64 (HMAC w/ SHA-256 truncated to 64 bits)
SHALL NOT be supported for use in EDHOC. SHALL NOT be supported for use in EDHOC.
8.4. Unprotected Data 7.4. Unprotected Data
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 AD_1, ID_CRED_R, AD_2, and ERR_MSG in the particular, it applies to AD_1, ID_CRED_R, AD_2, and ERR_MSG. Using
asymmetric case, and ID_PSK, AD_1, and ERR_MSG in the symmetric case. the same AD_1 in several EDHOC sessions allows passive eavesdroppers
Using the same ID_PSK or AD_1 in several EDHOC sessions allows to correlate the different sessions. Another consideration is that
passive eavesdroppers to correlate the different sessions. The the list of supported cipher suites may potentially be used to
communicating parties may therefore anonymize ID_PSK. Another identify the application.
consideration is that the list of supported cipher suites may be used
to identify the application.
The Initiator and the Responder must also make sure that The Initiator and the Responder must also make sure that
unauthenticated data does not trigger any harmful actions. In unauthenticated data does not trigger any harmful actions. In
particular, this applies to AD_1 and ERR_MSG in the asymmetric case, particular, this applies to AD_1 and ERR_MSG.
and ID_PSK, AD_1, and ERR_MSG in the symmetric case.
8.5. Denial-of-Service 7.5. Denial-of-Service
EDHOC itself does not provide countermeasures against Denial-of- EDHOC itself does not provide countermeasures against Denial-of-
Service attacks. By sending a number of new or replayed message_1 an Service attacks. By sending a number of new or replayed message_1 an
attacker may cause the Responder to allocate state, perform attacker may cause the Responder to allocate state, perform
cryptographic operations, and amplify messages. To mitigate such cryptographic operations, and amplify messages. To mitigate such
attacks, an implementation SHOULD rely on lower layer mechanisms such attacks, an implementation SHOULD rely on lower layer mechanisms such
as the Echo option in CoAP [I-D.ietf-core-echo-request-tag] that as the Echo option in CoAP [I-D.ietf-core-echo-request-tag] that
forces the initiator to demonstrate reachability at its apparent forces the initiator to demonstrate reachability at its apparent
network address. network address.
8.6. Implementation Considerations 7.6. Implementation Considerations
The availability of a secure pseudorandom number generator and truly The availability of a secure pseudorandom number generator and truly
random seeds are essential for the security of EDHOC. If no true random seeds are essential for the security of EDHOC. If no true
random number generator is available, a truly random seed must be random number generator is available, a truly random seed must be
provided from an external source. As each pseudorandom number must provided from an external source. As each pseudorandom number must
only be used once, an implementation need to get a new truly random only be used once, an implementation need to get a new truly random
seed after reboot, or continuously store state in nonvolatile memory, seed after reboot, or continuously store state in nonvolatile memory,
see ([RFC8613], Appendix B.1.1) for issues and solution approaches see ([RFC8613], Appendix B.1.1) for issues and solution approaches
for writing to nonvolatile memory. If ECDSA is supported, for writing to nonvolatile memory. If ECDSA is supported,
"deterministic ECDSA" as specified in [RFC6979] is RECOMMENDED. "deterministic ECDSA" as specified in [RFC6979] is RECOMMENDED.
skipping to change at page 36, line 42 skipping to change at page 33, line 29
along with any ephemeral ECDH secrets after the key derivation is along with any ephemeral ECDH secrets after the key derivation is
completed. The ECDH shared secret, keys, and IVs MUST be secret. completed. The ECDH shared secret, 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. Depending on the selected curve, the attacks such as timing attacks. Depending on the selected curve, the
parties should perform various validations of each other's public parties should perform various validations of each other's public
keys, see e.g. Section 5 of [SP-800-56A]. keys, see e.g. Section 5 of [SP-800-56A].
The Initiator and the Responder are responsible for verifying the The Initiator and the Responder are responsible for verifying the
integrity of certificates. The selection of trusted CAs should be integrity of certificates. The selection of trusted CAs should be
done very carefully and certificate revocation should be supported. done very carefully and certificate revocation should be supported.
The private authentication keys and the PSK (even though it is used The private authentication keys MUST be kept secret.
as salt) MUST be kept secret.
The Initiator and the Responder are allowed to select the connection The Initiator and the Responder are allowed to select the connection
identifiers C_I and C_R, respectively, for the other party to use in identifiers C_I and C_R, respectively, for the other party to use in
the ongoing EDHOC protocol as well as in a subsequent application the ongoing EDHOC protocol as well as in a subsequent application
protocol (e.g. OSCORE [RFC8613]). The choice of connection protocol (e.g. OSCORE [RFC8613]). The choice of connection
identifier is not security critical in EDHOC but intended to simplify identifier is not security critical in EDHOC but intended to simplify
the retrieval of the right security context in combination with using the retrieval of the right security context in combination with using
short identifiers. If the wrong connection identifier of the other short identifiers. If the wrong connection identifier of the other
party is used in a protocol message it will result in the receiving party is used in a protocol message it will result in the receiving
party not being able to retrieve a security context (which will party not being able to retrieve a security context (which will
skipping to change at page 37, line 22 skipping to change at page 34, line 7
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. If the two G_X values are equal, the
received message_1 MUST be discarded to mitigate reflection attacks. received message_1 MUST be discarded to mitigate reflection attacks.
Note that in the case of two simultaneous EDHOC exchanges where the Note that in the case of two simultaneous EDHOC exchanges where the
nodes only complete one and where the nodes have different preferred nodes only complete one and where the nodes have different preferred
cipher suites, an attacker can affect which of the two nodes' cipher suites, an attacker can affect which of the two nodes'
preferred cipher suites will be used by blocking the other exchange. preferred cipher suites will be used by blocking the other exchange.
8.7. Other Documents Referencing EDHOC 7.7. Other Documents Referencing EDHOC
EDHOC has been analyzed in several other documents. A formal EDHOC has been analyzed in several other documents. A formal
verification of EDHOC was done in [SSR18], an analysis of EDHOC for verification of EDHOC was done in [SSR18], an analysis of EDHOC for
certificate enrollment was done in [Kron18], the use of EDHOC in certificate enrollment was done in [Kron18], the use of EDHOC in
LoRaWAN is analyzed in [LoRa1] and [LoRa2], the use of EDHOC in IoT LoRaWAN is analyzed in [LoRa1] and [LoRa2], the use of EDHOC in IoT
bootstrapping is analyzed in [Perez18], and the use of EDHOC in bootstrapping is analyzed in [Perez18], and the use of EDHOC in
6TiSCH is described in [I-D.ietf-6tisch-dtsecurity-zerotouch-join]. 6TiSCH is described in [I-D.ietf-6tisch-dtsecurity-zerotouch-join].
9. IANA Considerations 8. IANA Considerations
9.1. EDHOC Cipher Suites Registry 8.1. 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 heading "EDHOC". The registration procedure is "Expert the new heading "EDHOC". The registration procedure is "Expert
Review". The columns of the registry are Value, Array, Description, Review". The columns of the registry are Value, Array, Description,
and Reference, where Value is an integer and the other columns are and Reference, where Value is an integer and the other columns are
text strings. The initial contents of the registry are: text strings. The initial contents of the registry are:
Value: -24 Value: -24
Algorithms: N/A Algorithms: N/A
Desc: Reserved for Private Use Desc: Reserved for Private Use
skipping to change at page 38, line 28 skipping to change at page 35, line 16
Desc: AES-CCM-16-64-128, SHA-256, P-256, ES256, P-256, Desc: AES-CCM-16-64-128, SHA-256, P-256, ES256, P-256,
AES-CCM-16-64-128, SHA-256 AES-CCM-16-64-128, SHA-256
Reference: [[this document]] Reference: [[this document]]
Value: 3 Value: 3
Array: 30, 5, 1, -7, 1, 10, 5 Array: 30, 5, 1, -7, 1, 10, 5
Desc: AES-CCM-16-128-128, SHA-256, P-256, ES256, P-256, Desc: AES-CCM-16-128-128, SHA-256, P-256, ES256, P-256,
AES-CCM-16-64-128, SHA-256 AES-CCM-16-64-128, SHA-256
Reference: [[this document]] Reference: [[this document]]
9.2. EDHOC Method Type Registry 8.2. EDHOC Method Type Registry
IANA has created a new registry titled "EDHOC Method Type" under the IANA has created a new registry titled "EDHOC Method Type" under the
new heading "EDHOC". The registration procedure is "Expert Review". new heading "EDHOC". The registration procedure is "Expert Review".
The columns of the registry are Value, Description, and Reference, The columns of the registry are Value, Description, and Reference,
where Value is an integer and the other columns are text strings. where Value is an integer and the other columns are text strings.
The initial contents of the registry are: The initial contents of the registry are:
+-------+-------------------+-------------------+-------------------+ +-------+-------------------+-------------------+-------------------+
| Value | Initiator | Responder | Reference | | Value | Initiator | Responder | Reference |
+-------+-------------------+-------------------+-------------------+ +-------+-------------------+-------------------+-------------------+
| 0 | Signature Key | Signature Key | [[this document]] | | 0 | Signature Key | Signature Key | [[this document]] |
| 1 | Signature Key | Static DH Key | [[this document]] | | 1 | Signature Key | Static DH Key | [[this document]] |
| 2 | Static DH Key | Signature Key | [[this document]] | | 2 | Static DH Key | Signature Key | [[this document]] |
| 3 | Static DH Key | Static DH Key | [[this document]] | | 3 | Static DH Key | Static DH Key | [[this document]] |
| 4 | PSK | PSK | [[this document]] |
+-------+-------------------+-------------------+-------------------+ +-------+-------------------+-------------------+-------------------+
Figure 10: Method Types Figure 9: Method Types
9.3. The Well-Known URI Registry 8.3. The Well-Known URI Registry
IANA has added the well-known URI 'edhoc' to the Well-Known URIs IANA has added the well-known URI 'edhoc' to the Well-Known URIs
registry. registry.
o URI suffix: edhoc o URI suffix: edhoc
o Change controller: IETF o Change controller: IETF
o Specification document(s): [[this document]] o Specification document(s): [[this document]]
o Related information: None o Related information: None
9.4. Media Types Registry 8.4. Media Types Registry
IANA has added the media type 'application/edhoc' to the Media Types IANA has added the media type 'application/edhoc' to the Media Types
registry. registry.
o Type name: application o Type name: application
o Subtype name: edhoc o Subtype name: edhoc
o Required parameters: N/A o Required parameters: N/A
skipping to change at page 40, line 13 skipping to change at page 37, line 5
"Authors' Addresses" section. "Authors' Addresses" section.
o Intended usage: COMMON o Intended usage: COMMON
o Restrictions on usage: N/A o Restrictions on usage: N/A
o Author: See "Authors' Addresses" section. o Author: See "Authors' Addresses" section.
o Change Controller: IESG o Change Controller: IESG
9.5. CoAP Content-Formats Registry 8.5. CoAP Content-Formats Registry
IANA has added the media type 'application/edhoc' to the CoAP IANA has added the media type 'application/edhoc' to the CoAP
Content-Formats registry. Content-Formats registry.
o Media Type: application/edhoc o Media Type: application/edhoc
o Encoding: o Encoding:
o ID: TBD42 o ID: TBD42
o Reference: [[this document]] o Reference: [[this document]]
9.6. Expert Review Instructions 8.6. Expert Review Instructions
The IANA Registries established in this document is defined as The IANA Registries established in this document is defined as
"Expert Review". This section gives some general guidelines for what "Expert Review". This section gives some general guidelines for what
the experts should be looking for, but they are being designated as the experts should be looking for, but they are being designated as
experts for a reason so they should be given substantial latitude. experts for a reason so they should be given substantial latitude.
Expert reviewers should take into consideration the following points: Expert reviewers should take into consideration the following points:
o Clarity and correctness of registrations. Experts are expected to o 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.
skipping to change at page 41, line 5 skipping to change at page 37, line 46
o Experts should take into account the expected usage of fields when o Experts should take into account the expected usage of fields when
approving point assignment. The length of the encoded value approving point assignment. The length of the encoded value
should be weighed against how many code points of that length are should be weighed against how many code points of that length are
left, the size of device it will be used on, and the number of left, the size of device it will be used on, and the number of
code points left that encode to that size. code points left that encode to that size.
o Specifications are recommended. When specifications are not o Specifications are recommended. When specifications are not
provided, the description provided needs to have sufficient provided, the description provided needs to have sufficient
information to verify the points above. information to verify the points above.
10. References 9. References
10.1. Normative References 9.1. Normative References
[I-D.ietf-core-echo-request-tag] [I-D.ietf-core-echo-request-tag]
Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo, Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo,
Request-Tag, and Token Processing", draft-ietf-core-echo- Request-Tag, and Token Processing", draft-ietf-core-echo-
request-tag-09 (work in progress), March 2020. request-tag-10 (work in progress), July 2020.
[I-D.ietf-cose-x509] [I-D.ietf-cose-x509]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header parameters for carrying and referencing X.509 Header parameters for carrying and referencing X.509
certificates", draft-ietf-cose-x509-06 (work in progress), certificates", draft-ietf-cose-x509-06 (work in progress),
March 2020. March 2020.
[I-D.ietf-lake-reqs]
Vucinic, M., Selander, G., Mattsson, J., and D. Garcia-
Carillo, "Requirements for a Lightweight AKE for OSCORE",
draft-ietf-lake-reqs-04 (work in progress), June 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>. <https://www.rfc-editor.org/info/rfc5116>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
skipping to change at page 42, line 22 skipping to change at page 39, line 22
<https://www.rfc-editor.org/info/rfc7959>. <https://www.rfc-editor.org/info/rfc7959>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017, RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>. <https://www.rfc-editor.org/info/rfc8152>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8376] Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
<https://www.rfc-editor.org/info/rfc8376>.
[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>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR) [RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020, Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>. <https://www.rfc-editor.org/info/rfc8742>.
10.2. Informative References 9.2. Informative References
[CborMe] Bormann, C., "CBOR Playground", May 2018, [CborMe] Bormann, C., "CBOR Playground", May 2018,
<http://cbor.me/>. <http://cbor.me/>.
[I-D.hartke-core-e2e-security-reqs] [I-D.hartke-core-e2e-security-reqs]
Selander, G., Palombini, F., and K. Hartke, "Requirements Selander, G., Palombini, F., and K. Hartke, "Requirements
for CoAP End-To-End Security", draft-hartke-core-e2e- for CoAP End-To-End Security", draft-hartke-core-e2e-
security-reqs-03 (work in progress), July 2017. security-reqs-03 (work in progress), July 2017.
[I-D.ietf-6tisch-dtsecurity-zerotouch-join] [I-D.ietf-6tisch-dtsecurity-zerotouch-join]
skipping to change at page 43, line 21 skipping to change at page 40, line 26
[I-D.ietf-ace-oscore-profile] [I-D.ietf-ace-oscore-profile]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson, Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"OSCORE profile of the Authentication and Authorization "OSCORE profile of the Authentication and Authorization
for Constrained Environments Framework", draft-ietf-ace- for Constrained Environments Framework", draft-ietf-ace-
oscore-profile-11 (work in progress), June 2020. oscore-profile-11 (work in progress), June 2020.
[I-D.ietf-core-resource-directory] [I-D.ietf-core-resource-directory]
Shelby, Z., Koster, M., Bormann, C., Stok, P., and C. Shelby, Z., Koster, M., Bormann, C., Stok, P., and C.
Amsuess, "CoRE Resource Directory", draft-ietf-core- Amsuess, "CoRE Resource Directory", draft-ietf-core-
resource-directory-24 (work in progress), March 2020. resource-directory-25 (work in progress), July 2020.
[I-D.ietf-lwig-security-protocol-comparison] [I-D.ietf-lwig-security-protocol-comparison]
Mattsson, J., Palombini, F., and M. Vucinic, "Comparison Mattsson, J., Palombini, F., and M. Vucinic, "Comparison
of CoAP Security Protocols", draft-ietf-lwig-security- of CoAP Security Protocols", draft-ietf-lwig-security-
protocol-comparison-04 (work in progress), March 2020. protocol-comparison-04 (work in progress), March 2020.
[I-D.ietf-tls-dtls13] [I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-38 (work in progress), May 1.3", draft-ietf-tls-dtls13-38 (work in progress), May
skipping to change at page 46, line 28 skipping to change at page 43, line 28
( 1, 2, null ) 0x0102f6 sequence ( 1, 2, null ) 0x0102f6 sequence
1, 2, null 0x0102f6 sequence 1, 2, null 0x0102f6 sequence
------------------------------------------------------------------ ------------------------------------------------------------------
A.2. COSE A.2. COSE
CBOR Object Signing and Encryption (COSE) [RFC8152] describes how to CBOR Object Signing and Encryption (COSE) [RFC8152] describes how to
create and process signatures, message authentication codes, and create and process signatures, message authentication codes, and
encryption using CBOR. COSE builds on JOSE, but is adapted to allow encryption using CBOR. COSE builds on JOSE, but is adapted to allow
more efficient processing in constrained devices. EDHOC makes use of more efficient processing in constrained devices. EDHOC makes use of
COSE_Key, COSE_Encrypt0, COSE_Sign1, and COSE_KDF_Context objects. COSE_Key, COSE_Encrypt0, and COSE_Sign1 objects.
Appendix B. Test Vectors Appendix B. Test Vectors
This appendix provides detailed test vectors to ease implementation This appendix provides detailed test vectors to ease implementation
and ensure interoperability. In addition to hexadecimal, all CBOR and ensure interoperability. In addition to hexadecimal, all CBOR
data items and sequences are given in CBOR diagnostic notation. The data items and sequences are given in CBOR diagnostic notation. The
test vectors use the default mapping to CoAP where the Initiator acts test vectors use the default mapping to CoAP where the Initiator acts
as CoAP client (this means that corr = 1). as CoAP client (this means that corr = 1).
A more extensive test vector suite covering more combinations of A more extensive test vector suite covering more combinations of
skipping to change at page 47, line 4 skipping to change at page 44, line 4
. .
B.1. Test Vectors for EDHOC Authenticated with Signature Keys (x5t) B.1. Test Vectors for EDHOC Authenticated with Signature Keys (x5t)
EDHOC with signature authentication and X.509 certificates is used. EDHOC with signature authentication and X.509 certificates is used.
In this test vector, the hash value 'x5t' is used to identify the In this test vector, the hash value 'x5t' is used to identify the
certificate. certificate.
method (Signature Authentication) method (Signature Authentication)
0 0
CoaP is used as transport and the Initiator acts as CoAP client: CoAP is used as transport and the Initiator acts as CoAP client:
corr (the Initiator can correlate message_1 and message_2) corr (the Initiator can correlate message_1 and message_2)
1 1
From there, METHOD_CORR has the following value: From there, METHOD_CORR has the following value:
METHOD_CORR (4 * method + corr) (int) METHOD_CORR (4 * method + corr) (int)
1 1
No unprotected opaque auxiliary data is sent in the message No unprotected opaque auxiliary data is sent in the message
skipping to change at page 47, line 29 skipping to change at page 44, line 29
Supported Cipher Suites (4 bytes) Supported Cipher Suites (4 bytes)
00 01 02 03 00 01 02 03
The cipher suite selected by the Initiator is the most preferred: The cipher suite selected by the Initiator is the most preferred:
Selected Cipher Suite (int) Selected Cipher Suite (int)
0 0
The mandatory-to-implement cipher suite 0 is supported by both the The mandatory-to-implement cipher suite 0 is supported by both the
Initiator and the Responder, see Section 8.3. Initiator and the Responder, see Section 7.3.
B.1.1. Message_1 B.1.1. Message_1
X (Initiator's ephemeral private key) (32 bytes) X (Initiator's ephemeral private key) (32 bytes)
8f 78 1a 09 53 72 f8 5b 6d 9f 61 09 ae 42 26 11 73 4d 7d bf a0 06 9a 2d 8f 78 1a 09 53 72 f8 5b 6d 9f 61 09 ae 42 26 11 73 4d 7d bf a0 06 9a 2d
f2 93 5b b2 e0 53 bf 35 f2 93 5b b2 e0 53 bf 35
G_X (Initiator's ephemeral public key) (32 bytes) G_X (Initiator's ephemeral public key) (32 bytes)
89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6 ec 07 6b ba 89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6 ec 07 6b ba
02 59 d9 04 b7 ec 8b 0c 02 59 d9 04 b7 ec 8b 0c
skipping to change at page 49, line 7 skipping to change at page 46, line 7
2b b7 fa 6e 13 5b c3 35 d0 22 d6 34 cb fb 14 b3 f5 82 f3 e2 e3 af b2 b3 2b b7 fa 6e 13 5b c3 35 d0 22 d6 34 cb fb 14 b3 f5 82 f3 e2 e3 af b2 b3
15 04 91 49 5c 61 78 2b 15 04 91 49 5c 61 78 2b
The key and nonce for calculating the ciphertext are calculated as The key and nonce for calculating the ciphertext are calculated as
follows, as specified in Section 3.8. follows, as specified in Section 3.8.
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0). HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK_2e = HMAC-SHA-256(salt, G_XY) PRK_2e = HMAC-SHA-256(salt, G_XY)
Since this is the asymmetric case, salt is the empty byte string. Salt is the empty byte string.
salt (0 bytes) salt (0 bytes)
From there, PRK_2e is computed: From there, PRK_2e is computed:
PRK_2e (32 bytes) PRK_2e (32 bytes)
ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f
d8 2f be b7 99 71 39 4a d8 2f be b7 99 71 39 4a
SK_R (Responders's private authentication key) (32 bytes) SK_R (Responders's private authentication key) (32 bytes)
df 69 27 4d 71 32 96 e2 46 30 63 65 37 2b 46 83 ce d5 38 1b fc ad cd 44 df 69 27 4d 71 32 96 e2 46 30 63 65 37 2b 46 83 ce d5 38 1b fc ad cd 44
0a 24 c3 91 d2 fe db 94 0a 24 c3 91 d2 fe db 94
Since neither the Initiator nor the Responder authanticates with a Since neither the Initiator nor the Responder authenticates with a
static Diffie-Hellman key, PRK_3e2m = PRK_2e static Diffie-Hellman key, PRK_3e2m = PRK_2e
PRK_3e2m (32 bytes) PRK_3e2m (32 bytes)
ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f
d8 2f be b7 99 71 39 4a d8 2f be b7 99 71 39 4a
The Responder chooses a connection identifier C_R. The Responder chooses a connection identifier C_R.
Connection identifier chosen by Responder (1 bytes) Connection identifier chosen by Responder (1 bytes)
13 13
skipping to change at page 52, line 9 skipping to change at page 49, line 9
K_2m (16 bytes) K_2m (16 bytes)
b7 48 6a 94 a3 6c f6 9e 67 3f c4 57 55 ee 6b 95 b7 48 6a 94 a3 6c f6 9e 67 3f c4 57 55 ee 6b 95
info for IV_2m is defined as follows: info for IV_2m is defined as follows:
info for K_2m = info for K_2m =
[ [
10, 10,
h'B0DC6C1BA0BAE6E2888610FA0B27BFC52E311A47B9CAFB609DE4F6A1760D6CF7', h'B0DC6C1BA0BAE6E2888610FA0B27BFC52E311A47B9CAFB609DE4F6A1760D6CF7',
" "IV_2m", "IV_2m",
13 13
] ]
Which as a CBOR encoded data item is: Which as a CBOR encoded data item is:
info for IV_2m (CBOR-encoded) (43 bytes) info for IV_2m (CBOR-encoded) (43 bytes)
84 0a 58 20 b0 dc 6c 1b a0 ba e6 e2 88 86 10 fa 0b 27 bf c5 2e 31 1a 47 84 0a 58 20 b0 dc 6c 1b a0 ba e6 e2 88 86 10 fa 0b 27 bf c5 2e 31 1a 47
b9 ca fb 60 9d e4 f6 a1 76 0d 6c f7 65 49 56 5f 32 6d 0d b9 ca fb 60 9d e4 f6 a1 76 0d 6c f7 65 49 56 5f 32 6d 0d
From these parameters, IV_2m is computed. IV_2m is the output of From these parameters, IV_2m is computed. IV_2m is the output of
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PRK_4x3m (32 bytes) PRK_4x3m (32 bytes)
ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f
d8 2f be b7 99 71 39 4a d8 2f be b7 99 71 39 4a
data 3 is equal to C_R. data 3 is equal to C_R.
data_3 (CBOR Sequence) (1 bytes) data_3 (CBOR Sequence) (1 bytes)
13 13
From data_3, CIPHERTEXT_2, and TH_2, compute the input to the From data_3, CIPHERTEXT_2, and TH_2, compute the input to the
transcript hash TH_2 = H(TH_2 , CIPHERTEXT_2, data_3), as a CBOR transcript hash TH_3 = H(TH_2 , CIPHERTEXT_2, data_3), as a CBOR
Sequence of these 3 data items. Sequence of these 3 data items.
Input to calculate TH_3 (CBOR Sequence) (117 bytes) Input to calculate TH_3 (CBOR Sequence) (117 bytes)
58 20 b0 dc 6c 1b a0 ba e6 e2 88 86 10 fa 0b 27 bf c5 2e 31 1a 47 b9 ca 58 20 b0 dc 6c 1b a0 ba e6 e2 88 86 10 fa 0b 27 bf c5 2e 31 1a 47 b9 ca
fb 60 9d e4 f6 a1 76 0d 6c f7 58 50 99 d5 38 01 a7 25 bf d6 a4 e7 1d 04 fb 60 9d e4 f6 a1 76 0d 6c f7 58 50 99 d5 38 01 a7 25 bf d6 a4 e7 1d 04
84 b7 55 ec 38 3d f7 7a 91 6e c0 db c0 2b ba 7c 21 a2 00 80 7b 4f 58 5f 84 b7 55 ec 38 3d f7 7a 91 6e c0 db c0 2b ba 7c 21 a2 00 80 7b 4f 58 5f
72 8b 67 1a d6 78 a4 3a ac d3 3b 78 eb d5 66 cd 00 4f c6 f1 d4 06 f0 1d 72 8b 67 1a d6 78 a4 3a ac d3 3b 78 eb d5 66 cd 00 4f c6 f1 d4 06 f0 1d
97 04 e7 05 b2 15 52 a9 eb 28 ea 31 6a b6 50 37 d7 17 86 2e 13 97 04 e7 05 b2 15 52 a9 eb 28 ea 31 6a b6 50 37 d7 17 86 2e 13
And from there, compute the transcript hash TH_3 = SHA-256(TH_2 , And from there, compute the transcript hash TH_3 = SHA-256(TH_2 ,
 End of changes. 95 change blocks. 
388 lines changed or deleted 216 lines changed or added

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