Network Working Group G. Selander Internet-Draft J. Mattsson Intended status: Standards Track F. Palombini Expires:25 November 2021January 13, 2022 Ericsson AB24 MayJuly 12, 2021 Ephemeral Diffie-Hellman Over COSE (EDHOC)draft-ietf-lake-edhoc-07draft-ietf-lake-edhoc-08 Abstract This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a very compact and lightweight authenticated Diffie-Hellman key exchange with ephemeral keys. EDHOC provides mutual authentication, perfect forward secrecy, and identity protection. EDHOC is intended for usage in constrained scenarios and a main use case is to establish an OSCORE security context. By reusing COSE for cryptography, CBOR for encoding, and CoAP for transport, the additional code size can be kept very low. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on25 November 2021.January 13, 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents(https://trustee.ietf.org/ license-info)(https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . .43 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . .43 1.2. Use of EDHOC . . . . . . . . . . . . . . . . . . . . . .54 1.3. Message Size Examples . . . . . . . . . . . . . . . . . .65 1.4. Document Structure . . . . . . . . . . . . . . . . . . . 6 1.5. Terminology and Requirements Language . . . . . . . . . . 6 2. EDHOC Outline . . . . . . . . . . . . . . . . . . . . . . . .76 3. Protocol Elements . . . . . . . . . . . . . . . . . . . . . .98 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . .98 3.2. Methodand Correlation .. . . . . . . . . . . . . . . .10 3.2.1. Method. . . . . . . . . 9 3.3. Connection Identifiers . . . . . . . . . . . . . .10 3.2.2. Connection Identifiers. . . 9 3.4. Transport . . . . . . . . . . . .10 3.2.3. Transport. . . . . . . . . . . . 11 3.5. Authentication Parameters . . . . . . . . . .11 3.2.4. Message Correlation. . . . . . 11 3.6. Cipher Suites . . . . . . . . . . .11 3.3. Authentication Parameters. . . . . . . . . . . 16 3.7. Ephemeral Public Keys . . . . .11 3.3.1. Authentication Keys. . . . . . . . . . . . . 18 3.8. External Authorization Data . . . .11 3.3.2. Identities. . . . . . . . . . . 18 3.9. Applicability Statement . . . . . . . . . .12 3.3.3. Authentication Credentials. . . . . . . 19 4. Key Derivation . . . . . .13 3.3.4. Identification of Credentials. . . . . . . . . . . .15 3.4. Cipher Suites. . . . . 21 4.1. EDHOC-Exporter Interface . . . . . . . . . . . . . . . . 23 5. Message Formatting and Processing .16 3.5. Ephemeral Public Keys. . . . . . . . . . . . . 24 5.1. Message Processing Outline . . . . .18 3.6. External Authorization Data. . . . . . . . . . 24 5.2. EDHOC Message 1 . . . . .18 3.7. Applicability Statement. . . . . . . . . . . . . . . . 25 5.3. EDHOC Message 2 .19 4. Key Derivation. . . . . . . . . . . . . . . . . . . . 27 5.4. EDHOC Message 3 . . .20 4.1. EDHOC-Exporter Interface. . . . . . . . . . . . . . . .23 5. Message Formatting and Processing. . 30 5.5. EDHOC Message 4 . . . . . . . . . . . .23 5.1. Encoding of bstr_identifier. . . . . . . . . 33 6. Error Handling . . . . . .24 5.2. Message Processing Outline. . . . . . . . . . . . . . .24 5.3. EDHOC Message 1. . 35 6.1. Success . . . . . . . . . . . . . . . . . . .25 5.3.1. Formatting of Message 1. . . . . . 36 6.2. Unspecified . . . . . . . . .25 5.3.2. Initiator Processing of Message 1. . . . . . . . . .26 5.3.3. Responder Processing of Message 1. . . . 36 6.3. Wrong Selected Cipher Suite . . . . . .27 5.4. EDHOC Message 2. . . . . . . . . 36 7. Security Considerations . . . . . . . . . . . .28 5.4.1. Formatting of Message 2. . . . . . . 38 7.1. Security Properties . . . . . . . .28 5.4.2. Responder Processing of Message 2. . . . . . . . . .28 5.4.3. Initiator Processing of Message 2. 38 7.2. Cryptographic Considerations . . . . . . . . .30 5.5. EDHOC Message 3. . . . . 40 7.3. Cipher Suites and Cryptographic Algorithms . . . . . . . 41 7.4. Unprotected Data . . . . . . . . .31 5.5.1. Formatting of Message 3. . . . . . . . . . . 42 7.5. Denial-of-Service . . . .31 5.5.2. Initiator Processing of Message 3. . . . . . . . . .31 5.5.3. Responder Processing of Message 3. . . . . . 42 7.6. Implementation Considerations . . . .34 6. Error Handling. . . . . . . . . . 43 8. IANA Considerations . . . . . . . . . . . . .34 6.1. Success. . . . . . . . 44 8.1. EDHOC Exporter Label . . . . . . . . . . . . . . . . .36 6.2. Unspecified. 44 8.2. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 45 8.3. EDHOC Method Type Registry . . . . . . . .36 6.3. Wrong Selected Cipher Suite. . . . . . . 47 8.4. EDHOC Error Codes Registry . . . . . . . .36 6.3.1. Cipher Suite Negotiation. . . . . . . 47 8.5. COSE Header Parameters Registry . . . . . . .37 6.3.2. Examples. . . . . . 47 8.6. COSE Header Parameters Registry . . . . . . . . . . . . . 47 8.7. COSE Key Common Parameters Registry . . .37 7. Transferring EDHOC and Deriving an OSCORE Context. . . . . .38 7.1. EDHOC Message 4. . 48 8.8. The Well-Known URI Registry . . . . . . . . . . . . . . . 48 8.9. Media Types Registry . . . .38 7.1.1. Formatting of Message 4. . . . . . . . . . . . . . 48 8.10. CoAP Content-Formats Registry .39 7.1.2. Responder Processing of Message 4. . . . . . . . . .39 7.1.3. Initiator Processing of Message 4. . . 49 8.11. EDHOC External Authorization Data . . . . . . .40 7.2. Transferring EDHOC in CoAP. . . . . 49 8.12. Expert Review Instructions . . . . . . . . . .40 8. Security Considerations. . . . . 50 9. References . . . . . . . . . . . . . .42 8.1. Security Properties. . . . . . . . . . . 50 9.1. Normative References . . . . . . . .42 8.2. Cryptographic Considerations. . . . . . . . . . 50 9.2. Informative References . . . .45 8.3. Cipher Suites and Cryptographic Algorithms. . . . . . .46 8.4. Unprotected Data. . . . . . 53 Appendix A. Use with OSCORE and Transfer over CoAP . . . . . . . 55 A.1. Selecting EDHOC Connection Identifier . . . . . . .46 8.5. Denial-of-Service. . . 55 A.2. Deriving the OSCORE Security Context . . . . . . . . . . 56 A.3. Transferring EDHOC over CoAP . . . . . . .47 8.6. Implementation Considerations. . . . . . . 57 Appendix B. Compact Representation . . . . . . .47 9. IANA Considerations. . . . . . . . 60 Appendix C. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 60 C.1. CBOR and CDDL . . . . .49 9.1. EDHOC Exporter Label. . . . . . . . . . . . . . . . .. 49 9.2. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 49 9.3. EDHOC Method Type Registry . . . . . . . . . . . . . . . 50 9.4. EDHOC Error Codes Registry . . . . . . . . . . . . . . . 51 9.5. The Well-Known URI Registry . . . . . .60 C.2. CDDL Definitions . . . . . . . . .51 9.6. Media Types Registry . .. . . . . . . . . . . 61 C.3. COSE . . . . .51 9.7. CoAP Content-Formats Registry. . . . . . . . . . . . . .52 9.8. Expert Review Instructions. . . . . . . 62 Appendix D. Test Vectors . . . . . . . .52 10. References. . . . . . . . . . . . 63 D.1. Test Vectors for EDHOC Authenticated with Signature Keys (x5t) . . . . . . . . . . . . .53 10.1. Normative References. . . . . . . . . . . . . 63 D.2. Test Vectors for EDHOC Authenticated with Static Diffie- Hellman Keys . . . . .53 10.2. Informative References. . . . . . . . . . . . . . . . .5581 AppendixA. Compact RepresentationE. Applicability Template . . . . . . . . . . . . . . .5896 AppendixB. Use of CBOR, CDDL and COSE inF. EDHOC. . . . . . . . 58 B.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 59 B.2. CDDL Definitions . . . . . . . . . . . . . . . . . . . . 59 B.3. COSE . . . . . . . . . . . . . .Message Deduplication . . . . . . . . . . . .6196 AppendixC. Test Vectors . . . . . . . .G. Transports Not Natively Providing Correlation . . . 97 Appendix H. Change Log . . . . . . . . .61 C.1. Test Vectors for EDHOC Authenticated with Signature Keys (x5t). . . . . . . . . . . . 98 Acknowledgments . . . . . . . . . . . . . .62 C.1.1. Message_1. . . . . . . . . . . 101 Authors' Addresses . . . . . . . . . . .62 C.1.2. Message_2. . . . . . . . . . . .. . . . . . . . . . 63 C.1.3. Message_3 . . . . . . . . . . . . . . . . . . . . . . 71 C.1.4. OSCORE Security Context Derivation . . . . . . . . . 77 C.2. Test Vectors for EDHOC Authenticated with Static Diffie-Hellman Keys . . . . . . . . . . . . . . . . . . . 79 C.2.1. Message_1 . . . . . . . . . . . . . . . . . . . . . . 80 C.2.2. Message_2 . . . . . . . . . . . . . . . . . . . . . . 81 C.2.3. Message_3 . . . . . . . . . . . . . . . . . . . . . . 87 C.2.4. OSCORE Security Context Derivation . . . . . . . . . 92 Appendix D. Applicability Template . . . . . . . . . . . . . . . 94 Appendix E. EDHOC Message Deduplication . . . . . . . . . . . . 95 Appendix F. Change Log . . . . . . . . . . . . . . . . . . . . . 96 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 99101 1. Introduction 1.1. Motivation Many Internet of Things (IoT) deployments require technologies which are highly performant in constrained environments [RFC7228]. IoT devices may be constrained in various ways, including memory, storage, processing capacity, and power. The connectivity for these settings may also exhibit constraints such as unreliable and lossy channels, highly restricted bandwidth, and dynamic topology. The IETF has acknowledged this problem by standardizing a range of lightweight protocols and enablers designed for the IoT, including the Constrained Application Protocol (CoAP, [RFC7252]), Concise Binary Object Representation (CBOR, [RFC8949]), and Static Context Header Compression (SCHC, [RFC8724]). The need for special protocols targeting constrained IoT deployments extends also to the security domain [I-D.ietf-lake-reqs]. Important characteristics in constrained environments are the number of round trips and protocol message sizes, which if kept low can contribute to good performance by enabling transport over a small number of radio frames, reducing latency due to fragmentation or duty cycles, etc. Another important criteria is code size, which may be prohibitive for certain deployments due to device capabilities or network load during firmware update. Some IoT deployments also need to support a variety of underlying transport technologies, potentially even with a single connection. Some security solutions for such settings exist already. CBOR Object Signing and Encryption (COSE, [I-D.ietf-cose-rfc8152bis-struct]) specifies basic application-layer security services efficiently encoded in CBOR. Another example is Object Security for Constrained RESTful Environments (OSCORE, [RFC8613]) which is a lightweight communication security extension to CoAP using CBOR and COSE. In order to establish good quality cryptographic keys for security protocols such as COSE and OSCORE, the two endpoints may run an authenticated Diffie-Hellman key exchange protocol, from which shared secret key material can be derived. Such a key exchange protocol should also be lightweight; to prevent bad performance in case of repeated use, e.g., due to device rebooting or frequent rekeying for security reasons; or to avoid latencies in a network formation setting with many devices authenticating at the same time. This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a lightweight authenticated key exchange protocol providing good security properties including perfect forward secrecy, identity protection, and cipher suite negotiation. Authentication can be based on raw public keys (RPK) or public key certificates, and requires the application to provide input on how to verify that endpoints are trusted. This specification focuses on referencing instead of transporting credentials to reduce message overhead. EDHOC makes use of known protocol constructions, such as SIGMA [SIGMA] and Extract-and-Expand [RFC5869]. COSE also provides crypto agility and enables the use of future algorithms targeting IoT. 1.2. Use of EDHOC 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. A main objective for EDHOC is to be a lightweight authenticated key exchange for OSCORE, i.e. to provide authentication and session key establishment for IoT use cases such as those built on CoAP [RFC7252]. CoAP is a specialized web transfer protocol for use with constrained nodes and networks, providing a request/response interaction model between application endpoints. As such, EDHOC is targeting a large variety of use cases involving 'things' with embedded microcontrollers, sensors, and actuators. A typical setting is when one of the endpoints is constrained or in a constrained network, and the other endpoint is a node on the Internet (such as a mobile phone) or at the edge of the constrained network (such as a gateway). Thing-to-thing interactions over constrained networks are also relevant since both endpoints would then benefit from the lightweight properties of the protocol. EDHOC could e.g. be run when a device connects for the first time, or to establish fresh keys which are not revealed by a later compromise of the long-term keys. Further security properties are described in Section8.1.7.1. EDHOC enables the reuse of the same lightweight primitives as OSCORE: CBOR for encoding, COSE for cryptography, and CoAP for transport. By reusing existing libraries the additional code size can be kept very low. Note that, while CBOR and COSE primitives are built into the protocol messages, EDHOC is not bound to a particular transport. However, it is recommended to transfer EDHOC messages in CoAP payloads as is detailed inSection 7.2.Appendix A.3. 1.3. Message Size Examples Compared to the DTLS 1.3 handshake [I-D.ietf-tls-dtls13] with ECDHE and connection ID, the number of bytes in EDHOC + CoAP can be less than 1/6 when RPK authentication is used, see [I-D.ietf-lwig-security-protocol-comparison]. Figure 1 shows two examples of message sizes for EDHOC with different kinds of authentication keys and different COSE header parameters for identification: static Diffie-Hellman keys identified by 'kid' [I-D.ietf-cose-rfc8152bis-struct], and X.509 signature certificates identified by a hash value using 'x5t' [I-D.ietf-cose-x509]. ================================= kid x5t --------------------------------- message_1 37 37 message_246 11745 116 message_3 20 91 --------------------------------- Total 103 245 ================================= Figure 1: Example of message sizes in bytes. 1.4. Document Structure The remainder of the document is organized as follows: Section 2 outlines EDHOC authenticated with digital signatures, Section 3 describes the protocol elements of EDHOC, including message flow, and formatting of the ephemeral public keys, Section 4 describes the key derivation, Section 5 specifies EDHOC with authentication based on signature keys or static Diffie-Hellman keys, Section 6 specifies the EDHOC error message, andSection 7Appendix A describes how EDHOC can be transferred in CoAP and used to establish an OSCORE security context. 1.5. Terminology and Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Readers are expected to be familiar with the terms and concepts described in CBOR [RFC8949], CBOR Sequences [RFC8742], COSE structures and process [I-D.ietf-cose-rfc8152bis-struct], COSE algorithms [I-D.ietf-cose-rfc8152bis-algs], and CDDL [RFC8610]. The Concise Data Definition Language (CDDL) is used to express CBOR data structures [RFC8949]. Examples of CBOR and CDDL are provided in AppendixB.1.C.1. When referring to CBOR, this specification always refer to Deterministically Encoded CBOR as specified in Sections 4.2.1 and 4.2.2 of [RFC8949]. The single output from authenticated encryption (including the authentication tag) is called 'ciphertext', following [RFC5116]. 2. EDHOC Outline EDHOC specifies different authentication methods of the Diffie- Hellman key exchange: digital signatures and static Diffie-Hellman keys. This section outlines the digital signature based method. Further details of protocol elements and other authentication methods are provided in the remainder of this document. SIGMA (SIGn-and-MAc) is a family of theoretical protocols with a large number of variants [SIGMA]. Like IKEv2 [RFC7296] and (D)TLS 1.3 [RFC8446], EDHOC authenticated with digital signatures is built on a variant of the SIGMA protocol which provides identity protection of the initiator (SIGMA-I), and like IKEv2 [RFC7296], EDHOC implements the SIGMA-I variant as MAC-then-Sign. The SIGMA-I protocol using an authenticated encryption algorithm is shown in Figure 2. Initiator Responder | G_X | +-------------------------------------------------------->| | | | G_Y, AEAD( K_2; ID_CRED_R, Sig(R; CRED_R, G_X, G_Y) ) | |<--------------------------------------------------------+ | | | AEAD( K_3; ID_CRED_I, Sig(I; CRED_I, G_Y, G_X) ) | +-------------------------------------------------------->| | | Figure 2: Authenticated encryption variant of the SIGMA-I protocol. The parties exchanging messages are called Initiator (I) and Responder (R). They exchange ephemeral public keys, compute a shared secret, and derive symmetric application keys used to protect application data.*o G_X and G_Y are the ECDH ephemeral public keys of I and R, respectively.*o CRED_I and CRED_R are the credentials containing the public authentication keys of I and R, respectively.*o ID_CRED_I and ID_CRED_R are credential identifiers enabling the recipient party to retrieve the credential of I and R, respectively.*o Sig(I; . ) and Sig(R; . ) denote signatures made with the private authentication key of I and R, respectively.*o AEAD(K; . ) denotes authenticated encryption with additional data using a key K derived from the shared secret. In order to create a "full-fledged" protocol some additional protocol elements are needed. EDHOC adds:* Explicit connection identifiers C_I, C_R chosen by I and R, respectively, enabling the recipient to find the protocol state. *o Transcript hashes (hashes of message data) TH_2, TH_3, TH_4 used for key derivation and as additional authenticated data.*o Computationally independent keys derived from the ECDH shared secret and used for authenticated encryption of different messages.*o An optional fourth message giving explicit key confirmation to I in deployments where no protected application data is sent from R to I.*o A key material exporter and a key update function enabling frequent forward secrecy.*o Verification of a common preferred cipher suite:-* The Initiator lists supported cipher suites in order of preference-* The Responder verifies that the selected cipher suite is the first supported cipher suite (or else rejects and states supported cipher suites).*o Method types and error handling.*o Selection of connection identifiers C_I and C_R which may be used to identify established keys or protocol state. o Transport of external authorization data. EDHOC is designed to encrypt and integrity protect as much information as possible, and all symmetric keys are derived using as much previous information as possible. EDHOC is furthermore designed to be as compact and lightweight as possible, in terms of message sizes, processing, and the ability to reuse already existing CBOR, COSE, and CoAP libraries. To simplify for implementors, the use of CBOR and COSE in EDHOC is summarized in AppendixBC and test vectors including CBOR diagnostic notation are given in AppendixC.D. 3. Protocol Elements 3.1. General An EDHOC message flow consists of three mandatory messages (message_1, message_2, message_3) between Initiator and Responder, an optional fourth message (message_4), plus an EDHOC error message. EDHOC messages are CBOR Sequences [RFC8742], see Figure 3. The protocol elements in the figure are introduced in the following sections. Message formatting and processing is specified in Section 5 and Section 6. An implementation may support only Initiator or only Responder. Application data is protected using the agreed application algorithms (AEAD, hash) in the selected cipher suite (see Section3.4)3.6) and the application can make use of the established connection identifiersC_1, C_I,C_I and C_R (see Section3.2.4).3.3). EDHOC may be used with the media type application/edhoc defined in Section9.8. The Initiator can derive symmetric application keys after creating EDHOC message_3, see Section 4.1. Application protected data can therefore be sent in parallel or together with EDHOC message_3. Initiator Responder |C_1, METHOD_CORR,METHOD, SUITES_I, G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | | | |C_I,G_Y, C_R, Enc(ID_CRED_R, Signature_or_MAC_2, EAD_2) | |<------------------------------------------------------------------+ | message_2 | | | |C_R,AEAD(K_3ae; ID_CRED_I, Signature_or_MAC_3, EAD_3) | +------------------------------------------------------------------>| | message_3 | Figure 3: EDHOC Message Flow 3.2. Methodand CorrelationThe data itemMETHOD_CORRMETHOD in message_1 (see Section5.3.1),5.2.1), is an integer specifying themethod and the correlation properties of the transport, which are described in this section. 3.2.1. Methodauthentication method. EDHOC supports authentication with signature or static Diffie-Hellman keys, as defined in the four authentication methods: 0, 1, 2, and 3, see Figure 4. (Method 0 corresponds to the case outlined in Section 2 where both Initiator and Responder authenticate with signature keys.) An implementation may support only a single method. The Initiator and the Responder need to have agreed on a single method to be used for EDHOC, see Section3.7.3.9. +-------+-------------------+-------------------+-------------------+ | Value | Initiator | Responder | Reference | +-------+-------------------+-------------------+-------------------+ | 0 | Signature Key | Signature Key | [[this document]] | | 1 | Signature Key | Static DH Key | [[this document]] | | 2 | Static DH Key | Signature Key | [[this document]] | | 3 | Static DH Key | Static DH Key | [[this document]] | +-------+-------------------+-------------------+-------------------+ Figure 4: Method Types3.2.2.3.3. Connection Identifiers EDHOC includesoptionalthe selection of connection identifiers(C_1, C_I, C_R).(C_I, C_R) identifying a connection for which keys are agreed. Connection identifiers may be used in the ongoing EDHOC protocol (see Section 3.3.2) or in a subsequent application protocol, e.g., OSCORE (see Section 3.3.3). The connection identifiersC_1, C_I, and C_Rdo not have any cryptographic purpose in EDHOC.They contain information facilitating retrieval of the protocol state and may therefore be very short. C_1 is always set to "null", while C_I and C_RConnection identifiers in EDHOC arechosen by I and R, respectively.byte strings or integers, encoded in CBOR. One byte connection identifiers (the integers -24 to 23 and the empty bytestring h'') are realistic in many scenarios as most constrained devices only have a few connections.In cases where3.3.1. Selection of Connection Identifiers C_I and C_R are chosen by I and R, respectively. The Initiator selects C_I and sends it in message_1 for the Responder to use as anode only has one connection,reference to theidentifiers may even beconnection in communications with theempty byte string.Initiator. The Responder selects C_R and sends in message_2 for the Initiator to use as a reference to the connectionidentifier MAY be usedin communications with the Responder. If connection identifiers are used by an application protocol(e.g. OSCORE)for which EDHOC establisheskeys,keys then the selected connection identifiers SHALL adhere to the requirements for that protocol, see Section 3.3.3 for an example. 3.3.2. Use of Connection Identifiers in EDHOC Connection identifiers may be used to correlate EDHOC messages and facilitate the retrieval of protocol state during EDHOC protocol execution. EDHOC transports that do not inherently provide correlation across all messages of an exchange can send connection identifiers along with EDHOC messages to gain that required capability, see Section 3.4. For an example when CoAP is used as transport, see Appendix A.3. 3.3.3. Use of Connection Identifiers in OSCORE For OSCORE, the choice of a connection identifier results in the endpoint selecting its Recipient ID, see Section 3.1 of [RFC8613]), for whichcasecertain uniqueness requirements apply, see Section 3.3 of [RFC8613]). Therefore the Initiator and the Responder MUST NOT select connection identifiers such that it results in same OSCORE Recipient ID. Since the Recipient ID is a byte string and a EDHOC connection identifier is either a CBOR byte string or a CBOR integer, care must be taken when selecting the connection identifiersSHALL adhereand converting them tothe requirements for that protocol. Each party choses aRecipient IDs. A mapping from EDHOC connection identifierit desires the other partytouse in outgoing messages. (ForOSCOREthis results in the endpoint selecting itsRecipientID, see Section 3.1 of [RFC8613]). 3.2.3.ID is specified in Appendix A.1. 3.4. Transport Cryptographically, EDHOC does not put requirements on the lower layers. EDHOC is not bound to a particular transport layer, and can even be used in environments without IP. Theapplication using EDHOCtransport isresponsibleresponsible, where necessary, tohandlehandle: o message loss, o message reordering, o message duplication, o fragmentation, o demultiplex EDHOC messages from other types of messages, and o denial of serviceprotection, where necessary. The Initiator and the Responder needprotection. Besides these common transport oriented properties, EDHOC transport additionally needs tohave agreed onsupport the correlation between EDHOC messages, including an indication of a message being message_1. The correlation may reuse existing mechanisms in the transporttoprotocol. For example, the CoAP Token may be usedfor EDHOC, see Section 3.7. It is recommendedtotransportcorrelate EDHOC messages in a CoAPpayloads, see Section 7. 3.2.4. Message Correlation Ifresponse and an associated CoAP request. In thewhole transport path providesabsense of correlation between amechanism for correlating messagesmessage receivedwith messagesand a message previouslysent, then some ofsent inherent to the transport, the EDHOC connection identifiers may beomitted. There are four cases: * corr = 0,added, e.g. by prepending thetransport does not provide a correlation mechanism. * corr = 1,appropriate connection identifier (when available from thetransport provides a correlation mechanism that enablesEDHOC protocol) to theResponderEDHOC message. Transport of EDHOC in CoAP payloads is described in Appendix A.3, which also shows how tocorrelate message_2use connection identifiers and message_1as well as message_4 and message_3. * corr = 2, the transport provides a correlation mechanism that enables theindication with CoAP. The Initiatorto correlate message_3andmessage_2. * corr = 3, the transport providesthe Responder need to have agreed on acorrelation mechanism that enables both partiestransport tocorrelate all three messages. For example, if the key exchange is transported over CoAP, the CoAP Token canbe usedto correlate messages,for EDHOC, see Section7.2. 3.3.3.9. 3.5. Authentication Parameters3.3.1.3.5.1. Authentication Keys The authentication key MUST be a signature key or static Diffie- Hellman key. The Initiator and the Responder MAY use different types 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 authentication is provided by a signature. When using a static Diffie-Hellman key the authentication is provided by a Message Authentication Code (MAC) computed from an ephemeral-static ECDH shared secret which enables significant reductions in message sizes. The MAC is implemented with an AEAD algorithm. When using static Diffie-Hellman keys the Initiator's and Responder's private authentication keys are called I and R, respectively, and the public authentication keys are called G_I and G_R, respectively. The authentication key algorithm needs to specified with enough parameters to make it completely determined. Note that for most signature algorithms, the signature is determined by the signature algorithm and the authentication key algorithm together. For example, the curve used in the signature is typically determined by the authentication key parameters.*o Only the Responder SHALL have access to the Responder's private authentication key.*o Only the Initiator SHALL have access to the Initiator's private authentication key.3.3.2.3.5.2. Identities EDHOC assumes the existence of mechanisms (certification authority, trusted third party, manual distribution, etc.) for specifying and distributing authentication keys and identities. Policies are set based on the identity of the other party, and parties typically only allow connections from a specific identity or a small restricted set of identities. For example, in the case of a device connecting to a network, the network may only allow connections from devices which authenticate with certificates having a particular range of serial numbers in the subject field and signed by a particular CA. On the other side, the device may only be allowed to connect to a network which authenticates with a particular public key (information of which may be provisioned, e.g., out of band or in the external authorization data, see Section3.6).3.8). The EDHOC implementation must be able to receive and enforce information from the application about what is the intended endpoint, and in particular whether it is a specific identity or a set of identities.*o When a Public Key Infrastructure (PKI) is used, the trust anchor is a Certification Authority (CA) certificate, and the identity is the subject whose unique name (e.g. a domain name, NAI, or EUI) is included in the endpoint's certificate. Before running EDHOC each party needs at least one CA public key certificate, or just the public key, and a specific identity or set of identities it is allowed to communicate with. Only validated public-key certificates with an allowed subject name, as specified by the application, are to be accepted. EDHOC provides proof that the other party possesses the private authentication key corresponding to the public authentication key in its certificate. The certification path provides proof that the subject of the certificate owns the public key in the certificate.*o When public keys are used but not with a PKI (RPK, self-signed certificate), the trust anchor is the public authentication key of the other party. In this case, the identity is typically directly associated to the public authentication key of the other party. For example, the name of the subject may be a canonical representation of the public key. Alternatively, if identities can be expressed in the form of unique subject names assigned to public keys, then a binding to identity can be achieved by including both public key and associated subject name in the protocol message computation: CRED_I or CRED_R may be a self- signed certificate or COSE_Key containing the public authentication key and the subject name, see Section3.3.3.3.5.3. Before running EDHOC, each endpoint needs a specific public authentication key/unique associated subject name, or a set of public authentication keys/unique associated subject names, which it is allowed to communicate with. EDHOC provides proof that the other party possesses the private authentication key corresponding to the public authentication key.3.3.3.3.5.3. Authentication Credentials The authentication credentials, CRED_I and CRED_R, contain the public authentication key of the Initiator and the Responder, respectively. The Initiator and the Responder MAY use different types of credentials, e.g. one uses an RPK and the other uses a public key certificate. The credentials CRED_I and CRED_R are signed or MAC:ed (depending on method) by the Initiator and the Responder, respectively, see Section5.55.4 and Section5.4.5.3. When the credential is a certificate, CRED_x is an end-entity certificate (i.e. not the certificate chain) encoded as a CBOR bstr. In X.509 certificates, signature keys typically have key usage "digitalSignature" and Diffie-Hellman keys typically have key usage "keyAgreement". To prevent misbinding attacks in systems where an attacker can register public keys without proving knowledge of the private key, SIGMA [SIGMA] enforces a MAC to be calculated over the "Identity", which in case of a X.509 certificate would be the 'subject' and 'subjectAltName' fields. EDHOC follows SIGMA by calculating a MAC over the whole certificate. While the SIGMA paper only focuses on the identity, the same principle is true for any information such as policies connected to the public key. When the credential is a COSE_Key, CRED_x is a CBOR map only containing specific fields from the COSE_Key identifying the public key, and optionally the "Identity". CRED_x needs to be defined such that it is identical when generated by Initiator or Responder. The parameters SHALL be encoded in bytewise lexicographic order of their deterministic encodings as specified in Section 4.2.1 of [RFC8949]. If the parties have agreed on an identity besides the public key, the identity is included in the CBOR map with the label "subject name", otherwise the subject name is the empty text string. The public key parameters depend on key type.*o For COSE_Keys of type OKP the CBOR map SHALL, except for subject name, only include the parameters 1 (kty), -1 (crv), and -2 (x-coordinate).*o For COSE_Keys of type EC2 the CBOR map SHALL, except for subject name, only include the parameters 1 (kty), -1 (crv), -2 (x-coordinate), and -3 (y-coordinate). An example of CRED_x when the RPK contains an X25519 static Diffie- Hellman key and the parties have agreed on an EUI-64 identity is shown below: CRED_x = { 1: 1, -1: 4, -2: h'b1a3e89460e88d3a8d54211dc95f0b90 3ff205eb71912d6db8f4af980d2db83a', "subject name" : "42-50-31-FF-EF-37-32-39" }3.3.4.3.5.4. Identification of Credentials ID_CRED_I and ID_CRED_R are used to identify and optionally transport the public authentication keys of the Initiator and the Responder, respectively. ID_CRED_I and ID_CRED_R do not have any cryptographic purpose in EDHOC.*o ID_CRED_R is intended to facilitate for the Initiator to retrieve the Responder's public authentication key.*o ID_CRED_I is intended to facilitate for the Responder to retrieve the Initiator's public authentication key. The identifiers ID_CRED_I and ID_CRED_R are COSE header_maps, i.e. CBOR maps containing Common COSE Header Parameters, see Section 3.1 of [I-D.ietf-cose-rfc8152bis-struct]). In the following we give some examples of COSE header_maps. Raw public keys are most optimally stored as COSE_Key objects and identified with a'kid' parameter: *'kid2' parameter (see Section 8.6 and Section 8.7): o ID_CRED_x = { 4 : kid_x }, where kid_x :bstr,bstr / int, for x = I or R. Note that the integers -24 to 23 and the empty bytestring h'' are encoded as one byte. Public key certificates can be identified in different ways. Header parameters for identifying C509 certificates and X.509 certificates are defined in [I-D.ietf-cose-cbor-encoded-cert] and [I-D.ietf-cose-x509], for example:*o by a hash value with the 'c5t' or 'x5t' parameters;-* ID_CRED_x = { 34 : COSE_CertHash }, for x = I or R,-* ID_CRED_x = { TDB3 : COSE_CertHash }, for x = I or R,*o by a URI with the 'c5u' or 'x5u' parameters;-* ID_CRED_x = { 35 : uri }, for x = I or R,-* ID_CRED_x = { TBD4 : uri }, for x = I or R,*o ID_CRED_x MAY contain the actual credential used for authentication, CRED_x. For example, a certificate chain can be transported in ID_CRED_x with COSE header parameter c5c or x5chain, defined in [I-D.ietf-cose-cbor-encoded-cert] and [I-D.ietf-cose-x509]. It is RECOMMENDED that ID_CRED_x uniquely identify the public authentication key as the recipient may otherwise have to try several keys. ID_CRED_I and ID_CRED_R are transported in the 'ciphertext', see Section5.55.4 and Section5.4.5.3. When ID_CRED_x does not contain the actual credential it may be very short. One byte credential identifiers are realistic in many scenarios as most constrained devices only have a few keys. In cases where a node only has one key, the identifier may even be the empty byte string.3.4.3.6. Cipher Suites An EDHOC cipher suite consists of an ordered set of algorithms from the "COSE Algorithms" and "COSE Elliptic Curves" registries. Algorithms need to be specified with enough parameters to make them completely determined. Currently, none of the algorithms require parameters. EDHOC is only specified for use with key exchange algorithms of type ECDH curves. Use with other types of key exchange algorithms would likely require a specification updating EDHOC. Note that for most signature algorithms, the signature is determined by the signature algorithm and the authentication key algorithm together, see Section3.3.1. *3.5.1. o EDHOC AEAD algorithm*o EDHOC hash algorithm*o EDHOC key exchange algorithm (ECDH curve)*o EDHOC signature algorithm*o Application AEAD algorithm*o Application hash algorithm Each cipher suite is identified with a pre-defined int label. EDHOC can be used with all algorithms and curves defined for COSE. Implementation can either use one of the pre-defined cipher suites (Section9.2)8.2) or use any combination of COSE algorithms and parameters to define their own private cipher suite. Private cipher suites can be identified with any of the four values -24, -23, -22, -21. The following CCM cipher suites are for constrained IoT where message overhead is a very importantfactor:factor. Cipher suites 1 and 3 use a larger tag length (128-bit) in the EDHOC AEAD algorithm than the Application AEAD algorithm (64-bit): 0. ( 10, -16, 4, -8, 10, -16 ) (AES-CCM-16-64-128, SHA-256, X25519, EdDSA, AES-CCM-16-64-128, SHA-256) 1. ( 30, -16, 4, -8, 10, -16 ) (AES-CCM-16-128-128, SHA-256, X25519, EdDSA, AES-CCM-16-64-128, SHA-256) 2. ( 10, -16, 1, -7, 10, -16 ) (AES-CCM-16-64-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256) 3. ( 30, -16, 1, -7, 10, -16 ) (AES-CCM-16-128-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256) The following ChaCha20 cipher suites are for less constrained applications and only use 128-bit tag lengths. 4. ( 24, -16, 4, -8, 24, -16 ) (ChaCha20/Poly1305, SHA-256, X25519, EdDSA, ChaCha20/Poly1305, SHA-256) 5. ( 24, -16, 1, -7, 24, -16 ) (ChaCha20/Poly1305, SHA-256, P-256, ES256, ChaCha20/Poly1305, SHA-256) The following GCM cipher suite is for general non-constrained applications. It usesveryhigh performance algorithms thatalsoare widely supported:4.6. ( 1, -16, 4, -7, 1, -16 ) (A128GCM, SHA-256, X25519, ES256, A128GCM, SHA-256) The following two ciphersuite issuites are for high security application such as government use and financial applications.ItThe two cipher suites do not share any algorithms. The first of the two cipher suites is compatible with the CNSA suite [CNSA].5.24. ( 3, -43, 2, -35, 3, -43 ) (A256GCM, SHA-384, P-384, ES384, A256GCM, SHA-384) 25. ( 24, -45, 5, -8, 24, -45 ) (ChaCha20/Poly1305, SHAKE256, X448, EdDSA, ChaCha20/Poly1305, SHAKE256) The different methods use the same cipher suites, but some algorithms are not used in some methods. The EDHOC signature algorithm is not used in methods without signature authentication. The Initiator needs to have a list of cipher suites it supports in order of preference. The Responder needs to have a list of cipher suites it supports. SUITES_I is a CBOR array containing cipher suites that the Initiator supports. SUITES_I is formatted and processed as detailed in Section5.3.15.2.1 to secure the cipher suite negotiation. Examples of cipher suite negotiation are given in Section 6.3.2.3.5.3.7. Ephemeral Public Keys EDHOC always uses compact representation of elliptic curve points, see AppendixA.B. In COSE compact representation is achieved by formatting the ECDH ephemeral public keys as COSE_Keys of type EC2 or OKP according to Sections 7.1 and 7.2 of [I-D.ietf-cose-rfc8152bis-algs], but only including the 'x' parameter in G_X and G_Y. For Elliptic Curve Keys of type EC2, compact representation MAY be used also in the COSE_Key. If the COSE implementation requires an 'y' parameter, the value y = false SHALL be used. COSE always use compact output for Elliptic Curve Keys of type EC2.3.6.3.8. External Authorization Data In order to reduce round trips and number of messages or to simplify processing, external security applications may be integrated into EDHOC by transporting authorization related data together with the messages. One example is the transport third-party identity and authorization information protected out of scope of EDHOC [I-D.selander-ace-ake-authz]. Another example is the embedding of a certificate enrolment request or a newly issued certificate. EDHOC allows opaque external authorization data (EAD) to be sent in the EDHOC messages. External authorization data sent in message_1 (EAD_1) or message_2 (EAD_2) must be considered unprotected by EDHOC, see Section8.4.7.4. External authorization data sent in message_3 (EAD_3) or message_4 (EAD_4) is protected between Initiator and Responder. External authorization data is a CBOR sequence (see AppendixB.1)C.1) as defined below: EAD = ( type : int, 1* ext_authz_data : any, ) where type is an int and is followed by one or more ext_authz_data depending on type as defined in a separate specification. The EAD fields of EDHOC are not intended for generic application data. Since data carried in EAD_1 and EAD_2 fields may not be protected, special considerations need to be made such that a) it does not violate security, privacy etc. requirements of the service which uses this data, and b) it does not violate the security properties of EDHOC. Security applications making use of the EAD fields must perform the necessary security analysis.3.7.3.9. Applicability Statement EDHOC requires certain parameters to be agreed upon between Initiator and Responder. Some parameters can be agreed through the protocol execution (specifically cipher suite negotiation, see Section3.4)3.6) but other parameters may need to be known out-of-band (e.g., which authentication method is used, see Section3.2.1).3.2). The purpose of the applicability statement is describe the intended use of EDHOC to allow for the relevant processing and verifications to be made, including things like: 1. How the endpoint detects that an EDHOC message is received. This includes how EDHOC messages are transported, for example in the payload of a CoAP message with a certain Uri-Path or Content- Format; seeSection 7.2. 2. Method and correlationAppendix A.3. * The method ofunderlying transporttransporting EDHOC messages(METHOD_CORR; see Section 3.2.1 and Section 3.2.4). This gives information aboutmay also describe data carried along with the messages that are needed for theoptional connection identifier fields. 3. How message_1 is identified, in particular iftransport to satisfy theoptional initial C_1 = "null"requirements ofmessage_1 is present;Section 3.4, e.g., connection identifiers used with certain messages, see Appendix A.3. 2. Authentication method (METHOD; see Section5.3.1 4.3.2). 3. Profile for authentication credentials (CRED_I, CRED_R; see Section3.3.3),3.5.3), e.g., profile for certificate or COSE_key, including supported authentication key algorithms (subject public key algorithm in X.509 certificate).5.4. Type used to identify authentication credentials (ID_CRED_I, ID_CRED_R; see Section3.3.4). 6.3.5.4). 5. Use and type of external authorization data (EAD_1, EAD_2, EAD_3, EAD_4; see Section3.6). 7.3.8). 6. Identifier used as identity of endpoint; see Section3.3.2. 8.3.5.2. 7. If message_4 shall be sent/expected, and if not, how to ensure a protected application message is sent from the Responder to the Initiator; see Section7.1.5.5. The applicability statement may also contain information about supported cipher suites. The procedure for selecting and verifying cipher suite is still performed as specified by the protocol, but it may become simplified by this knowledge. An example of an applicability statement is shown in AppendixD.E. For some parameters, likeMETHOD_CORR,METHOD, ID_CRED_x, type of EAD, the receiver is able to verify compliance with applicability statement, and if it needs to fail because of incompliance, to infer the reason why the protocol failed. For other parameters, like CRED_x in the case that it is not transported, it may not be possible to verify that incompliance with applicability statement was the reason for failure: Integrity verification in message_2 or message_3 may fail not only because of wrong authentication credential. For example, in case the Initiator uses public key certificate by reference (i.e. not transported within the protocol) then both endpoints need to use an identical data structure as CRED_I or else the integrity verification will fail. Note that it is not necessary for the endpoints to specify a single transport for the EDHOC messages. For example, a mix of CoAP and HTTP may be used along the path, and this may still allow correlation between messages. The applicability statement may be dependent on the identity of the other endpoint, but this applies only to the later phases of the protocol when identities are known. (Initiator does not know identity of Responder before having verified message_2, and Responder does not know identity of Initiator before having verified message_3.) Other conditions may be part of the applicability statement, such as target application or use (if there is more than one application/use) to the extent that EDHOC can distinguish between them. In case multiple applicability statements are used, the receiver needs to be able to determine which is applicable for a given session, for example based on URI or external authorization data type. 4. Key Derivation EDHOC uses Extract-and-Expand [RFC5869] with the EDHOC hash algorithm in the selected cipher suite to derive keys used in EDHOC and in the application. Extract is used to derive fixed-length uniformly pseudorandom keys (PRK) from ECDH shared secrets. Expand is used to derive additional output keying material (OKM) from the PRKs. The PRKs are derived using Extract. PRK = Extract( salt, IKM ) If the EDHOC hash algorithm is SHA-2, then Extract( salt, IKM ) = HKDF-Extract( salt, IKM ) [RFC5869]. If the EDHOC hash algorithm is SHAKE128, then Extract( salt, IKM ) = KMAC128( salt, IKM, 256, "" ). If the EDHOC hash algorithm is SHAKE256, then Extract( salt, IKM ) = KMAC256( salt, IKM, 512, "" ). PRK_2e is used to derive a keystream to encrypt message_2. PRK_3e2m is used to derive keys and IVs to produce a MAC in message_2 and to encrypt message_3. PRK_4x3m is used to derive keys and IVs to produce a MAC in message_3 and to derive application specific data. PRK_2e is derived with the following input:*o The salt SHALL be the empty byte string. Note that [RFC5869] specifies that if the salt is not provided, it is set to a string 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 G_XY (calculated from G_X and Y or G_Y and X) as defined in Section 6.3.1 of [I-D.ietf-cose-rfc8152bis-algs]. Example: Assuming the use of SHA-256 the extract phase of HKDF produces PRK_2e as follows: PRK_2e = HMAC-SHA-256( salt, G_XY ) where salt = 0x (the empty byte string). The pseudorandom keys PRK_3e2m and PRK_4x3m are defined as follow:*o If the Responder authenticates with a static Diffie-Hellman key, then PRK_3e2m = Extract( PRK_2e, G_RX ), where G_RX is the ECDH shared secret calculated from G_R and X, or G_X and R, else PRK_3e2m = PRK_2e.*o If the Initiator authenticates with a static Diffie-Hellman key, then PRK_4x3m = Extract( PRK_3e2m, G_IY ), where G_IY is the ECDH shared secret calculated from G_I and Y, or G_Y and I, else PRK_4x3m = PRK_3e2m. Example: Assuming the use of curve25519, the ECDH shared secrets G_XY, G_RX, and G_IY are the outputs of the X25519 function [RFC7748]: G_XY = X25519( Y, G_X ) = X25519( X, G_Y ) The keys and IVs used in EDHOC are derived from PRKs using Expand [RFC5869] where the EDHOC-KDF is instantiated with the EDHOC AEAD algorithm in the selected cipher suite. OKM = EDHOC-KDF( PRK, transcript_hash, label, length ) = Expand( PRK, info, length ) where info is the CBOR encoding of info = [ edhoc_aead_id : int / tstr, transcript_hash : bstr, label : tstr, length : uint ] where*o edhoc_aead_id is an int or tstr containing the algorithm identifier of the EDHOC AEAD algorithm in the selected cipher suite encoded as defined in [I-D.ietf-cose-rfc8152bis-algs]. Note that a single fixed edhoc_aead_id is used in all invocations of EDHOC-KDF, including the derivation of KEYSTREAM_2 and invocations of the EDHOC-Exporter.*o transcript_hash is a bstr set to one of the transcript hashes TH_2, TH_3, or TH_4 as defined in Sections 5.3.1, 5.4.1,5.5.1,and 4.1.*o label is a tstr set to the name of the derived key or IV, i.e. "K_2m", "IV_2m", "KEYSTREAM_2", "K_3m", "IV_3m", "K_3ae", or "IV_3ae".*o length is the length of output keying material (OKM) in bytes If the EDHOC hash algorithm is SHA-2, then Expand( PRK, info, length ) = HKDF-Expand( PRK, info, length ) [RFC5869]. If the EDHOC hash algorithm is SHAKE128, then Expand( PRK, info, length ) = KMAC128( PRK, info, L, "" ). If the EDHOC hash algorithm is SHAKE256, then Expand( PRK, info, length ) = KMAC256( PRK, info, L, "" ). KEYSTREAM_2 are derived using the transcript hashTH_2TH_2 and the pseudorandom key PRK_2e. K_2m and IV_2m are derived using the transcript hash TH_2 and the pseudorandom key PRK_3e2m. K_3ae and IV_3ae are derived using the transcript hash TH_3 and the pseudorandom key PRK_3e2m. K_3m and IV_3m are derived using the transcript hash TH_3 and the pseudorandom key PRK_4x3m. IVs are only used if the EDHOC AEAD algorithm uses IVs. 4.1. EDHOC-Exporter Interface Application keys and other application specific data can be derived using the EDHOC-Exporter interface defined as: EDHOC-Exporter(label, context, length) = EDHOC-KDF(PRK_4x3m, TH_4, label_context, length) label_context is a CBOR sequence: label_context = ( label : tstr, context : bstr, ) where label is a registered tstr from the EDHOC Exporter Label registry (Section 8.1), context is a bstr defined by the application, and length is a uint defined by the application. The (label, context) pair must be unique, i.e. a (label, context) MUST NOT be used for two different purposes. However an application can re- derive the same key several times as long as it is done in a secure way. For example, in most encryption algorithms the same (key, nonce) pair must not be reused. The transcript hash TH_4 is a CBOR encoded bstr and thepseudorandom key PRK_2e. K_2m and IV_2m are derived usinginput to thetranscripthashTH_2 andfunction is a CBOR Sequence. TH_4 = H( TH_3, CIPHERTEXT_3 ) where H() is thepseudorandom key PRK_3e2m. K_3ae and IV_3aehash function in the selected cipher suite. Examples of use of the EDHOC-Exporter arederived usinggiven in Section 5.5.2 and Appendix A. To provide forward secrecy in an even more efficient way than re- running EDHOC, EDHOC provides thetranscript hash TH_3function EDHOC-KeyUpdate. When EDHOC-KeyUpdate is called the old PRK_4x3m is deleted and thepseudorandomnew PRK_4x3m is calculated as a "hash" of the old keyPRK_3e2m. K_3m and IV_3m are derivedusing thetranscript hash TH_3Extract function as illustrated by the following pseudocode: EDHOC-KeyUpdate( nonce ): PRK_4x3m = Extract( nonce, PRK_4x3m ) 5. Message Formatting and Processing This section specifies formatting of thepseudorandom key PRK_4x3m. IVsmessages and processing steps. Error messages areonly used if thespecified in Section 6. An EDHOCAEAD algorithm uses IVs. 4.1. EDHOC-Exporter Interface Application keys and other application specific data can be derived using the EDHOC-Exporter interface defined as: EDHOC-Exporter(label, context, length) = EDHOC-KDF(PRK_4x3m, TH_4, label_context, length) label_contextmessage is encoded as a sequence of CBORsequence: label_context = ( label : tstr, context : bstr, ) where label isdata (CBOR Sequence, [RFC8742]). Additional optimizations are made to reduce message overhead. While EDHOC uses the COSE_Key, COSE_Sign1, and COSE_Encrypt0 structures, only aregistered tstr fromsubset of the parameters is included in the EDHOC messages. The unprotected COSE header in COSE_Sign1, and COSE_Encrypt0 (not included in the EDHOCExporter Label registry (Section 9.1), context is a bstr defined bymessage) MAY contain parameters (e.g. 'alg'). 5.1. Message Processing Outline This section outlines theapplication, and length is a uint defined bymessage processing of EDHOC. For each session, theapplication. The (label, context) pair must be unique, i.e. a (label, context) MUST NOT beendpoints are assumed to keep an associated protocol state containing identifiers, keys, etc. used fortwo different purposes. However an application can re- derive the same key several times as long as itsubsequent processing of protocol related data. The protocol state isdone in a secure way. For example, in most encryption algorithmsassumed to be associated to an applicability statement (Section 3.9) which provides thesame (key, nonce) pair must notcontext for how messages are transported, identified and processed. EDHOC messages SHALL bereused.processed according to the current protocol state. Thetranscript hash TH_4 is a CBOR encoded bstr andfollowing steps are expected to be performed at reception of an EDHOC message: 1. Detect that an EDHOC message has been received, for example by means of port number, URI, or media type (Section 3.9). 2. Retrieve theinputprotocol state according to thehash functionmessage correlation provided by the transport, see Section 3.4. If there is no protocol state, in the case of message_1, aCBOR Sequence. TH_4 = H( TH_3, CIPHERTEXT_3 ) where H()new protocol state is created. The Responder endpoint needs to make use of available Denial-of-Service mitigation (Section 7.5). 3. If thehash function inmessage received is an error message then process according to Section 6, else process as theselected cipher suite. Examples of use ofexpected next message according to theEDHOC-Exporter are given in Section 7.1.2 and [I-D.ietf-core-oscore-edhoc]. To provide forward secrecy in an even more efficient way than re- running EDHOC, EDHOC providesprotocol state. If thefunction EDHOC-KeyUpdate. When EDHOC-KeyUpdate is calledprocessing fails, then theold PRK_4x3mprotocol isdeleteddiscontinued, an error message sent, and thenew PRK_4x3m is calculated as a "hash"protocol state erased. Further details are provided in the following subsections. Different instances of theold key usingsame message MUST NOT be processed in one session. Note that processing will fail if theExtract function as illustrated bysame message appears a second time for EDHOC processing because thefollowing pseudocode: EDHOC-KeyUpdate( nonce ): PRK_4x3m = Extract( nonce, PRK_4x3m ) 5. Message Formatting and Processing This section specifies formattingstate of themessagesprotocol has moved on andprocessing steps. Error messages are specified innow expects something else. This assumes that message duplication due to re-transmissions is handled by the transport protocol, see Section6. An EDHOC3.4. The case when the transport does not support message deduplication isencoded as a sequenceaddressed in Appendix F. 5.2. EDHOC Message 1 5.2.1. Formatting of Message 1 message_1 SHALL be a CBORdata (CBOR Sequence, [RFC8742]). Additional optimizations are made to reduce message overhead. While EDHOC usesSequence (see Appendix C.1) as defined below message_1 = ( METHOD : int, SUITES_I : [ selected : suite, supported : 2* suite ] / suite, G_X : bstr, C_I : bstr / int, ? EAD ; EAD_1 ) suite = int where: o METHOD = 0, 1, 2, or 3 (see Figure 4). o SUITES_I - cipher suites which theCOSE_Key, COSE_Sign1, and COSE_Encrypt0 structures, only a subsetInitiator supports in order of (decreasing) preference. The list of supported cipher suites can be truncated at theparametersend, as isincludeddetailed in theEDHOC messages. The unprotected COSE header in COSE_Sign1,processing steps below andCOSE_Encrypt0 (not included in the EDHOC message) MAY contain parameters (e.g. 'alg'). 5.1. EncodingSection 6.3. One ofbstr_identifier Byte strings are encoded in CBOR as two or more bytes, whereas integers intheinterval -24 to 23 are encodedsupported cipher suites is selected. The selected suite is the first suite in the SUITES_I CBORas one byte. bstr_identifier isarray. If aspecial encodingsingle supported cipher suite is conveyed then that cipher suite is selected and SUITES_I is encoded as an int instead ofbyte strings, used throughout the protocol to enablean array. o G_X - theencodingephemeral public key of theshortest byte strings as integers that only require one byteInitiator o C_I - variable length connection identifier o EAD_1 - unprotected external authorization data, see Section 3.8. 5.2.2. Initiator Processing ofCBOR encoding.Message 1 Thebstr_identifier encoding is definedInitiator SHALL compose message_1 as follows:Byte strings ino The supported cipher suites and theinterval h'00'order of preference MUST NOT be changed based on previous error messages. However, the list SUITES_I sent toh'2f' are encoded asthecorresponding integer minus 24,Responder MAY be truncated such that cipher suites which areall represented by one byte CBOR ints. Other byte stringsthe least preferred are omitted. The amount of truncation MAY be changed between sessions, e.g. based on previous error messages (see next bullet), but all cipher suites which areencoded as CBOR byte strings. For example,more preferred than thebyte string h'59e9' encoded as a bstr_identifier is equal to h'59e9', whileleast preferred cipher suite in thebyte string h'2a' is encoded aslist MUST be included in theinteger 18.list. o TheCDDL definition of the bstr_identifier is given below: bstr_identifier = bstr / int Note that, despiteInitiator MUST select its most preferred cipher suite, conditioned on whatcouldit can assume to beinterpretedsupported by theCDDL definition only, bstr_identifier once decoded are always byte strings. 5.2. Message Processing Outline This section outlinesResponder. If themessage processing of EDHOC. For each session,Initiator previously received from theendpoints are assumed to keep an associated protocol state containing connection identifiers, keys, etc. used for subsequent processing of protocol related data. The protocol state is assumed to be associated toResponder anapplicability statement (Section 3.7)error message with error code 2 (see Section 6.3) indicating cipher suites supported by the Responder whichprovidesalso are supported by thecontext for howInitiator, then the Initiator SHOULD select the most preferred cipher suite of those (note that error messages aretransported, identifiednot authenticated andprocessed. EDHOC messages SHALL be processed according to the current protocol state. The following steps are expected tomay beperformed at reception of an EDHOC message: 1. Detect thatforged). o Generate anEDHOC message has been received, for example by means of port number, URI, or media type (Section 3.7). 2. Retrieve the protocol state, e.g.ephemeral ECDH key pair using thereceivedcurve in the selected cipher suite and format it as a COSE_Key. Let G_X be the 'x' parameter of the COSE_Key. o Choose a connection identifier(Section 3.2.2) or withC_I and store it for thehelplength ofmessage correlation provided by the transport protocol (Section 3.2.4). If there is no protocol state, inthecase of message_1,protocol. o Encode message_1 as anew protocol state is created. An initial C_1 = "null" bytesequence of CBOR encoded data items as specified inmessage_1 (Section 5.3.1) can be used to distinguish message_1 from other messages. TheSection 5.2.1 5.2.3. Responderendpoint needs to make useProcessing ofavailable Denial-of-Service mitigation (Section 8.5). 3. If the message received is an error message then process according to Section 6, elseMessage 1 The Responder SHALL process message_1 as follows: o Decode message_1 (see Appendix C.1). o Verify that theexpected next message accordingselected cipher suite is supported and that no prior cipher suite in SUITES_I is supported. o Pass EAD_1 to theprotocol state.security application. Iftheany processing step fails,thentheprotocol is discontinued,Responder SHOULD send an EDHOC error messagesent, and the protocol state erased. Further details are providedback, formatted as defined in Section 6, and thefollowing subsections. Different instances of the same messagesession MUSTNOTbeprocessed in one session. Note that processing will fail if the same message appears a second timediscontinued. Sending error messages is essential forEDHOC processing because the state of the protocol has moved on and now expects something else. This assumes that message duplicationdebugging but MAY e.g. be skipped due tore-transmissions is handled by the transport protocol,denial of service reasons, see Section3.2.3. The case when the transport does not support message deduplication is addressed in Appendix E.7. 5.3. EDHOC Message12 5.3.1. Formatting of Message1 message_12 message_2 and data_2 SHALL beaCBORSequenceSequences (see AppendixB.1)C.1) as defined belowmessage_1message_2 = (? C_1 : null, METHOD_CORR : int, SUITES_I : [ selected : suite, supporteddata_2, CIPHERTEXT_2 :2* suite ] / suite, G_Xbstr, ) data_2 = ( G_Y : bstr,C_IC_R :bstr_identifier, ? EAD ; EAD_1bstr / int, )suite = intwhere:* C_1o G_Y - the ephemeral public key of the Responder o C_R - variable length connection identifier 5.3.2. Responder Processing of Message 2 The Responder SHALL compose message_2 as follows: o Generate aninitial CBOR simple value "null" (= 0xf6) MAY be used to distinguish message_1 from other messages. * METHOD_CORR = 4 * method + corr, where method = 0, 1, 2, or 3 (see Figure 4)ephemeral ECDH key pair using the curve in the selected cipher suite and format it as a COSE_Key. Let G_Y be thecorrelation'x' parametercorr is chosen based onof thetransport and determines whichCOSE_Key. o Choose a connectionidentifiers that are omitted (see Section 3.2.4). * SUITES_I - cipher suites whichidentifier C_R and store it for theInitiator supports in order of (decreasing) preference. The listlength ofsupportedthe protocol. o Compute the transcript hash TH_2 = H( H(message_1), data_2 ) where H() is the hash function in the selected ciphersuites can be truncated atsuite. The transcript hash TH_2 is a CBOR encoded bstr and theend, asinput to the hash function isdetaileda CBOR Sequence. Note that H(message_1) can be computed and cached already in the processingsteps below and Section 6.3. Oneof message_1. o Compute an inner COSE_Encrypt0 as defined in Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with thesupported cipher suites is selected. The selected suite is the first suiteEDHOC AEAD algorithm in theSUITES_I CBOR array. If a single supported cipher suite is conveyed then that cipher suite isselected cipher suite, K_2m, IV_2m, andSUITES_I is encoded as an int insteadthe following parameters: * protected = << ID_CRED_R >> + ID_CRED_R - identifier to facilitate retrieval ofan array.CRED_R, see Section 3.5.4 *G_Xexternal_aad = << TH_2, CRED_R, ? EAD_2 >> + CRED_R - bstr containing theephemeral public keycredential of theInitiator * C_I - variable length connection identifier, encoded as a bstr_identifier (seeResponder, see Section5.1). * EAD_1 -3.5.4 + EAD_2 = unprotected external authorization data, see Section3.6. 5.3.2. Initiator Processing of Message 1 The Initiator SHALL compose message_1 as follows:3.8 *The supported cipher suites and the order of preference MUST NOT be changed based on previous error messages. However,plaintext = h'' COSE constructs thelist SUITES_I sentinput to theResponder MAY be truncated such that cipher suites which are the least preferred are omitted. The amount of truncation MAY be changed between sessions, e.g. based on previous error messages (see next bullet), but all cipher suites which are more preferred than the least preferred cipher suite in the list MUST be included in the list.AEAD [RFC5116] as follows: *The Initiator MUST select its most preferred cipher suite, conditioned on what it can assume to be supported byKey K = EDHOC-KDF( PRK_3e2m, TH_2, "K_2m", length ) * Nonce N = EDHOC-KDF( PRK_3e2m, TH_2, "IV_2m", length ) * Plaintext P = 0x (the empty string) * Associated data A = [ "Encrypt0", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >> ] MAC_2 is theResponder. If'ciphertext' of theInitiator previously received frominner COSE_Encrypt0. o If the Responderan error messageauthenticates witherror code 2 (see Section 6.3) indicating cipher suites supported bya static Diffie-Hellman key (method equals 1 or 3), then Signature_or_MAC_2 is MAC_2. If the Responderwhich also are supported by the Initiator,authenticates with a signature key (method equals 0 or 2), then Signature_or_MAC_2 is theInitiator SHOULD select the most preferred cipher suite'signature' ofthose (note that error messages are not authenticated and may be forged). * Generate an ephemeral ECDH key paira COSE_Sign1 object as defined in Section 4.4 of [I-D.ietf-cose-rfc8152bis-struct] using thecurvesignature algorithm in the selected ciphersuitesuite, the private authentication key of the Responder, andformat it as a COSE_Key. Let G_X bethe'x' parameterfollowing parameters: * protected = << ID_CRED_R >> * external_aad = << TH_2, CRED_R, ? EAD_2 >> * payload = MAC_2 COSE constructs the input to the Signature Algorithm as: * The key is the private authentication key of theCOSE_Key.Responder. *ChooseThe message M to be signed = [ "Signature1", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >>, MAC_2 ] o CIPHERTEXT_2 is encrypted by using the Expand function as aconnection identifier C_I and store it forbinary additive stream cipher. * plaintext = ( ID_CRED_R / bstr / int, Signature_or_MAC_2, ? EAD_2 ) + Note that if ID_CRED_R contains a single 'kid2' parameter, i.e., ID_CRED_R = { 4 : kid_R }, only thelength ofbyte string or integer kid_R is conveyed in theprotocol.plaintext encoded as a bstr / int. * CIPHERTEXT_2 = plaintext XOR KEYSTREAM_2 o Encodemessage_1message_2 as a sequence of CBOR encoded data items as specified in Section5.3.15.3.1. 5.3.3.ResponderInitiator Processing of Message12 TheResponderInitiator SHALL processmessage_1message_2 as follows:*o Decodemessage_1message_2 (see AppendixB.1). * Verify thatC.1). o Retrieve theselected cipher suite is supportedprotocol state using the message correlation provided by the transport (e.g., the CoAP Token andthat no prior cipher suite in SUITES_I is supported. *the 5-tuple as a client, or the prepended C_I as a server). o Decrypt CIPHERTEXT_2, see Section 5.3.2. o PassEAD_1EAD_2 to the security application. o Verify that the identity of the Responder is an allowed identity for this connection, see Section 3.5. o Verify Signature_or_MAC_2 using the algorithm in the selected cipher suite. The verification process depends on the method, see Section 5.3.2. If any processing step fails, theResponderInitiator SHOULD send an EDHOC error message back, formatted as defined in Section6, and the session MUST be discontinued.6. Sending error messages is essential for debugging but MAYe.g. bee.g.be skipped if a session cannot be found or due to denial of service reasons, see Section8. 5.4. EDHOC Message 2 5.4.1. Formatting of Message 2 message_2 and data_2 SHALL be CBOR Sequences (see Appendix B.1) as defined below message_2 = ( data_2, CIPHERTEXT_2 : bstr, ) data_2 = ( ? C_I : bstr_identifier, G_Y : bstr, C_R : bstr_identifier, ) where: * G_Y - the ephemeral public key of the Responder * C_R - variable length connection identifier, encoded as a bstr_identifier (see Section 5.1). 5.4.2. Responder Processing of Message 2 The Responder SHALL compose message_2 as follows: *7. Ifcorr (METHOD_CORR mod 4) equals 1 or 3, C_I is omitted, otherwise C_I is not omitted. * Generateanephemeral ECDH key pair using the curve in the selected cipher suite and format it as a COSE_Key. Let G_Y beerror message is sent, the'x' parametersession MUST be discontinued. 5.4. EDHOC Message 3 5.4.1. Formatting ofthe COSE_Key. * ChooseMessage 3 message_3 SHALL be aconnection identifier C_R and store it for the lengthCBOR Sequence (see Appendix C.1) as defined below message_3 = ( CIPHERTEXT_3 : bstr, ) 5.4.2. Initiator Processing ofthe protocol. *Message 3 The Initiator SHALL compose message_3 as follows: o Compute the transcript hashTH_2TH_3 =H( H(message_1), data_2 )H(TH_2, CIPHERTEXT_2) where H() is the hash function in the selected cipher suite. The transcript hashTH_2TH_3 is a CBOR encoded bstr and the input to the hash function is a CBOR Sequence. Note thatH(message_1)H(TH_2, CIPHERTEXT_2) can be computed and cached already in the processing ofmessage_1. *message_2. o Compute an inner COSE_Encrypt0 as defined in Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm in the selected cipher suite,K_2m, IV_2m,K_3m, IV_3m, and the following parameters:-* protected = <<ID_CRED_RID_CRED_I >>o ID_CRED_R+ ID_CRED_I - identifier to facilitate retrieval ofCRED_R,CRED_I, see Section3.3.4 -3.5.4 * external_aad = <<TH_2, CRED_R,TH_3, CRED_I, ?EAD_2EAD_3 >>o CRED_R+ CRED_I - bstr containing the credential of theResponder,Initiator, see Section3.3.4 o EAD_23.5.4. + EAD_3 =unprotectedprotected external authorization data, see Section3.6 -3.8 * plaintext = h'' COSE constructs the input to the AEAD [RFC5116] as follows:-* Key K = EDHOC-KDF(PRK_3e2m, TH_2, "K_2m",PRK_4x3m, TH_3, "K_3m", length )-* Nonce N = EDHOC-KDF(PRK_3e2m, TH_2, "IV_2m",PRK_4x3m, TH_3, "IV_3m", length )-* Plaintext P = 0x (the empty string)-* Associated data A = [ "Encrypt0", <<ID_CRED_RID_CRED_I >>, <<TH_2, CRED_R,TH_3, CRED_I, ?EAD_2EAD_3 >> ]MAC_2MAC_3 is the 'ciphertext' of the inner COSE_Encrypt0.*o If theResponderInitiator authenticates with a static Diffie-Hellman key (method equals12 or 3), thenSignature_or_MAC_2Signature_or_MAC_3 isMAC_2.MAC_3. If theResponderInitiator authenticates with a signature key (method equals 0 or2),1), thenSignature_or_MAC_2Signature_or_MAC_3 is the 'signature' of a COSE_Sign1 object as defined in Section 4.4 of [I-D.ietf-cose-rfc8152bis-struct] using the signature algorithm in the selected cipher suite, the private authentication key of theResponder,Initiator, and the following parameters:-* protected = <<ID_CRED_RID_CRED_I >>-* external_aad = <<TH_2, CRED_R,TH_3, CRED_I, ?EAD_2EAD_3 >>-* payload =MAC_2MAC_3 COSE constructs the input to the Signature Algorithm as:-* The key is the private authentication key of theResponder. -Initiator. * The message M to be signed = [ "Signature1", <<ID_CRED_RID_CRED_I >>, <<TH_2, CRED_R,TH_3, CRED_I, ?EAD_2EAD_3 >>,MAC_2MAC_3 ]* CIPHERTEXT_2 is encrypted by using the Expand functiono Compute an outer COSE_Encrypt0 asa binary additive stream cipher. -defined in Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm in the selected cipher suite, K_3ae, IV_3ae, and the following parameters. The protected header SHALL be empty. * external_aad = TH_3 * plaintext = (ID_CRED_RID_CRED_I /bstr_identifier, Signature_or_MAC_2,bstr / int, Signature_or_MAC_3, ?EAD_2EAD_3 )o+ Note that ifID_CRED_RID_CRED_I contains a single'kid''kid2' parameter, i.e.,ID_CRED_RID_CRED_I = { 4 :kid_Rkid_I }, only the byte stringkid_Ror integer kid_I is conveyed in the plaintext encoded as abstr_identifier, see Section 3.3.4 and Section 5.1. - CIPHERTEXT_2bstr or int. COSE constructs the input to the AEAD [RFC5116] as follows: * Key K =plaintext XOR KEYSTREAM_2EDHOC-KDF( PRK_3e2m, TH_3, "K_3ae", length ) * Nonce N = EDHOC-KDF( PRK_3e2m, TH_3, "IV_3ae", length ) * Plaintext P = ( ID_CRED_I / bstr / int, Signature_or_MAC_3, ? EAD_3 ) * Associated data A = [ "Encrypt0", h'', TH_3 ] CIPHERTEXT_3 is the 'ciphertext' of the outer COSE_Encrypt0. o Encodemessage_2message_3 as a sequence of CBOR encoded data items as specified in Section 5.4.1.5.4.3. Initiator Processing of Message 2 The Initiator SHALL process message_2 as follows: * Decode message_2 (see Appendix B.1). * Retrieve the protocol state usingPass the connectionidentifier C_I and/or other external information such as the CoAP Tokenidentifiers (C_I, C_R) and the5-tuple. * Decrypt CIPHERTEXT_2, see Section 5.4.2. * Pass EAD_2application algorithms in the selected cipher suite to thesecurityapplication.* Verify thatThe application can now derive application keys using theidentity ofEDHOC-Exporter interface. After sending message_3, theResponderInitiator isan allowed identity for this connection, see Section 3.3. * Verify Signature_or_MAC_2 usingassured that no other party than thealgorithm inResponder can compute theselected cipher suite.key PRK_4x3m (implicit key authentication). Theverification process depends onInitiator can securely derive application keys and send protected application data. However, themethod, see Section 5.4.2. If any processing step fails,Initiator does not know that the Responder has actually computed the key PRK_4x3m and therefore the Initiator SHOULD NOT permanently store the keying material PRK_4x3m and TH_4, or derived application keys, until the InitiatorSHOULD send an EDHOC error message back, formatted as defined in Section 6. Sending error messagesisessentialassured that the Responder has actually computed the key PRK_4x3m (explicit key confirmation). This is similar to waiting fordebugging but MAY e.g.be skipped ifacknowledgement (ACK) in asession cannot be found or due to denial of service reasons, see Section 8. If an error messagetransport protocol. Explicit key confirmation issent,e.g. assured when thesession MUST be discontinued. 5.5. EDHOC Message 3 5.5.1. Formatting of Message 3 message_3 and data_3 SHALL be CBOR Sequences (see Appendix B.1) as defined below message_3 = ( data_3, CIPHERTEXT_3 : bstr, ) data_3 = ( ? C_R : bstr_identifier, ) 5.5.2.Initiator has verified an OSCORE message or message_4 from the Responder. 5.4.3. Responder Processing of Message 3 TheInitiatorResponder SHALLcomposeprocess message_3 as follows:* If corr (METHOD_CORR mod 4) equals 2 or 3, C_R is omitted, otherwise C_R is not omitted. * Computeo Decode message_3 (see Appendix C.1). o Retrieve thetranscript hash TH_3 = H( H(TH_2, CIPHERTEXT_2), data_3 ) where H() isprotocol state using thehash function inmessage correlation provided by theselected cipher suite. The transcript hash TH_3 is a CBOR encoded bstrtransport (e.g., the CoAP Token and theinput to5-tuple as a client, or thehash function isprepended C_R as aCBOR Sequence. Note that H(TH_2, CIPHERTEXT_2) can be computedserver). o Decrypt andcached already inverify theprocessing of message_2. * Compute an innerouter COSE_Encrypt0 as defined in Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm in the selected cipher suite,K_3m, IV_3m,K_3ae, andthe following parameters: - protected = << ID_CRED_I >>IV_3ae. oID_CRED_I - identifier to facilitate retrieval of CRED_I, see Section 3.3.4 - external_aad = << TH_3, CRED_I, ?Pass EAD_3>>to the security application. oCRED_I - bstr containingVerify that thecredentialidentity of theInitiator,Initiator is an allowed identity for this connection, see Section3.3.4.3.5. oEAD_3 = protected external authorization data,Verify Signature_or_MAC_3 using the algorithm in the selected cipher suite. The verification process depends on the method, see Section3.6 - plaintext = h'' COSE constructs5.4.2. o Pass theinputconnection identifiers (C_I, C_R), and the application algorithms in the selected cipher suite to theAEAD [RFC5116]security application. The application can now derive application keys using the EDHOC-Exporter interface. If any processing step fails, the Responder SHOULD send an EDHOC error message back, formatted asfollows: - Key K = EDHOC-KDF( PRK_4x3m, TH_3, "K_3m", length ) - Nonce N = EDHOC-KDF( PRK_4x3m, TH_3, "IV_3m", length ) - Plaintext P = 0x (the empty string) - Associated data A = [ "Encrypt0", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >> ] MAC_3defined in Section 6. Sending error messages isthe 'ciphertext'essential for debugging but MAY e.g.be skipped if a session cannot be found or due to denial ofthe inner COSE_Encrypt0. *service reasons, see Section 7. If an error message is sent, the session MUST be discontinued. After verifying message_3, the Responder is assured that the Initiatorauthenticates with a static Diffie-Hellmanhas calculated the key(method equals 2 or 3), then Signature_or_MAC_3PRK_4x3m (explicit key confirmation) and that no other party than the Responder can compute the key. The Responder can securely send protected application data and store the keying material PRK_4x3m and TH_4. 5.5. EDHOC Message 4 This section specifies message_4 which is OPTIONAL to support. Key confirmation isMAC_3. Ifnormally provided by sending an application message from the Responder to the Initiatorauthenticatesprotected with asignaturekey(method equals 0 or 1), then Signature_or_MAC_3 isderived with the'signature' of a COSE_Sign1 object as defined in Section 4.4 of [I-D.ietf-cose-rfc8152bis-struct]EDHOC-Exporter, e.g., using OSCORE (see Appendix A). In deployments where no protected application message is sent from thesignature algorithm inResponder to theselected cipher suite,Initiator, theprivate authentication keyResponder MUST send message_4. Two examples ofthe Initiator,such deployments: 1. When EDHOC is only used for authentication and no application data is sent. 2. When application data is only sent from thefollowing parameters: - protected = << ID_CRED_I >> - external_aad = << TH_3, CRED_I, ? EAD_3 >> - payload = MAC_3 COSE constructs the inputInitiator to theSignature Algorithm as: - The key is the private authentication keyResponder. Further considerations are provided in Section 3.9. 5.5.1. Formatting ofthe Initiator. - The message M toMessage 4 message_4 SHALL besigneda CBOR Sequence (see Appendix C.1) as defined below message_4 =[ "Signature1", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >>, MAC_3 ] *( CIPHERTEXT_4 : bstr, ) 5.5.2. Responder Processing of Message 4 The Responder SHALL compose message_4 as follows: o Computean outera COSE_Encrypt0 as defined in Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm in the selected ciphersuite, K_3ae, IV_3ae, and the following parameters. The protected header SHALL be empty. - external_aad = TH_3 - plaintext = ( ID_CRED_I / bstr_identifier, Signature_or_MAC_3, ? EAD_3 ) o Note that if ID_CRED_I contains a single 'kid' parameter, i.e., ID_CRED_I = { 4 : kid_I }, only the byte string kid_I is conveyed insuite, and the following parameters. The protected header SHALL be empty. * protected = h'' * external_aad = TH_4 * plaintextencoded as a bstr_identifier,= ( ? EAD_4 ) where EAD_4 is protected external authorization data, see Section3.3.4 and Section 5.1.3.8. COSE constructs the input to the AEAD [RFC5116] as follows:-* Key K =EDHOC-KDF( PRK_3e2m, TH_3, "K_3ae",EDHOC-Exporter( "EDHOC_message_4_Key", h'', length )-* Nonce N =EDHOC-KDF( PRK_3e2m, TH_3, "IV_3ae",EDHOC-Exporter( "EDHOC_message_4_Nonce", h'', length )-* Plaintext P = (ID_CRED_I / bstr_identifier, Signature_or_MAC_3,?EAD_3EAD_4 )-* Associated data A = [ "Encrypt0", h'',TH_3TH_4 ]CIPHERTEXT_3CIPHERTEXT_4 is the 'ciphertext' of theouterCOSE_Encrypt0.*o Encodemessage_3message_4 as a sequence of CBOR encoded data items as specified in Section 5.5.1.Pass the connection identifiers (C_I, C_R) and the application algorithms in the selected cipher suite to the application. The application can now derive application keys using the EDHOC-Exporter interface. After sending message_3, the Initiator is assured that no other party than the Responder can compute the key PRK_4x3m (implicit key authentication). The Initiator can securely derive application keys and send protected application data. However, the Initiator does not know that the Responder has actually computed the key PRK_4x3m and therefore the Initiator SHOULD NOT permanently store the keying material PRK_4x3m and TH_4, or derived application keys, until the Initiator is assured that the Responder has actually computed the key PRK_4x3m (explicit key confirmation). This is similar to waiting for acknowledgement (ACK) in a transport protocol. Explicit key confirmation is e.g. assured when the Initiator has verified an OSCORE message or message_4 from the Responder.5.5.3.ResponderInitiator Processing of Message34 TheResponderInitiator SHALL processmessage_3message_4 as follows:*o Decodemessage_3message_4 (see AppendixB.1). *C.1). o Retrieve the protocol state using theconnection identifier C_R and/or other external information such asmessage correlation provided by the transport (e.g., the CoAP Token and the5-tuple. *5-tuple as a client, or the prepended C_I as a server). o Decrypt and verify the outer COSE_Encrypt0 as defined in Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm in the selected cipher suite,K_3ae,andIV_3ae. * Pass EAD_3 to the security application. * Verify that the identity of the Initiator is an allowed identity for this connection, see Section 3.3. * Verify Signature_or_MAC_3 usingthealgorithmparameters defined inthe selected cipher suite. The verification process depends on the method, seeSection 5.5.2.*o Passthe connection identifiers (C_I, C_R), and the application algorithms in the selected cipher suiteEAD_4 to the security application.The application can now derive application keys using the EDHOC-Exporter interface.If anyprocessingverification stepfails,fails theResponder SHOULDInitiator MUST send an EDHOC error message back, formatted as defined in Section6. Sending error messages is essential for debugging but MAY e.g.be skipped if a session cannot be found or due to denial of service reasons, see Section 8. If an error message is sent,6, and the session MUST be discontinued.After verifying message_3, the Responder is assured that the Initiator has calculated the key PRK_4x3m (explicit key confirmation) and that no other party than the Responder can compute the key. The Responder can securely send protected application data and store the keying material PRK_4x3m and TH_4.6. Error Handling This section defines the format for error messages. An EDHOC error message can be sent by either endpoint as a reply to any non-error EDHOC message. How errors at the EDHOC layer are transported depends on lower layers, which need to enable error messages to be sent and processed as intended. Errors in EDHOC are fatal. After sending an error message, the sender MUST discontinue the protocol. The receiver SHOULD treat an error message as an indication that the other party likely has discontinued the protocol. But as the error message is not authenticated, a received error message might also have been sent by anattacker and the receiver MAY therefore try to continue the protocol. error SHALL be a CBOR Sequence (see Appendix B.1) as defined below error = ( ? C_x : bstr_identifier, ERR_CODE : int, ERR_INFO : any ) Figure 5: EDHOC Error Message where: * C_x - (optional) variable length connection identifier, encoded as a bstr_identifier (see Section 5.1). If error is sent by the Responder and corr (METHOD_CORR mod 4) equals 0 or 2 then C_x is set to C_I, else if error is sent by the Initiator and corr (METHOD_CORR mod 4) equals 0 or 1 then C_x is setattacker and the receiver MAY therefore try toC_R, else C_x is omitted. *continue the protocol. error SHALL be a CBOR Sequence (see Appendix C.1) as defined below error = ( ERR_CODE : int, ERR_INFO : any ) Figure 5: EDHOC Error Message where: o ERR_CODE - error code encoded as an integer. The value 0 is used for success, all other values (negative or positive) indicate errors.*o ERR_INFO - error information. Content and encoding depend on error code. The remainder of this section specifies the currently defined error codes, see Figure 6. Error codes 1 and 2 MUST be supported. Additional error codes and corresponding error information may be specified. +----------+---------------+----------------------------------------+ | ERR_CODE | ERR_INFO Type | Description | +==========+===============+========================================+ | 0 | any | Success | +----------+---------------+----------------------------------------+ | 1 | tstr | Unspecified | +----------+---------------+----------------------------------------+ | 2 | SUITES_R | Wrong selected cipher suite | +----------+---------------+----------------------------------------+ Figure 6: Error Codes and Error Information 6.1. Success Error code 0 MAY be used internally in an application to indicate success, e.g. in log files. ERR_INFO can contain any type of CBOR item. Error code 0 MUST NOT be used as part of the EDHOC message exchange flow. 6.2. Unspecified Error code 1 is used for errors that do not have a specific error code defined. ERR_INFO MUST be a text string containing a human- readable diagnostic message written in English. The diagnostic text message is mainly intended for software engineers that during debugging need to interpret it in the context of the EDHOC specification. The diagnostic message SHOULD be provided to the calling application where it SHOULD be logged. 6.3. Wrong Selected Cipher Suite Error code 2 MUST only be used in a response to message_1 in case the cipher suite selected by the Initiator is not supported by the Responder, or if the Responder supports a cipher suite more preferred by the Initiator than the selected cipher suite, see Section5.3.3.5.2.3. ERR_INFO is of type SUITES_R: SUITES_R : [ supported : 2* suite ] / suite If the Responder does not support the selected cipher suite, then SUITES_R MUST include one or more supported cipher suites. If the Responder does not support the selected cipher suite, but supports another cipher suite in SUITES_I, then SUITES_R MUST include the first supported cipher suite in SUITES_I. 6.3.1. Cipher Suite Negotiation After receiving SUITES_R, the Initiator can determine which cipher suite to select for the next EDHOC run with the Responder. If the Initiator intends to contact the Responder in the future, the Initiator SHOULD remember which selected cipher suite to use until the next message_1 has been sent, otherwise the Initiator and Responder will likely run into an infinite loop. After a successful run of EDHOC, the Initiator MAY remember the selected cipher suite to use in future EDHOC runs. Note that if the Initiator or Responder is updated with new cipher suite policies, any cached information may be outdated. 6.3.2. Examples Assume that the Initiator supports the five cipher suites 5, 6, 7, 8, and 9 in decreasing order of preference. Figures 7 and 8 show examples of how the Initiator can truncate SUITES_I and how SUITES_R is used by Responders to give the Initiator information about the cipher suites that the Responder supports. In the first example (Figure 7), the Responder supports cipher suite 6 but not the initially selected cipher suite 5. Initiator Responder |METHOD_CORR,METHOD, SUITES_I = 5, G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | | | |C_I,DIAG_MSG, SUITES_R = 6 | |<------------------------------------------------------------------+ | error | | | |METHOD_CORR,METHOD, SUITES_I = [6, 5, 6], G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | Figure 7: Example of Responder supporting suite 6 but not suite 5. In the second example (Figure 8), the Responder supports cipher suites 8 and 9 but not the more preferred (by the Initiator) cipher suites 5, 6 or 7. To illustrate the negotiation mechanics we let the Initiator first make a guess that the Responder supports suite 6 but not suite 5. Since the Responder supports neither 5 nor 6, it responds with an error and SUITES_R, after which the Initiator selects its most preferred supported suite. The order of cipher suites in SUITES_R does not matter. (If the Responder had supported suite 5, it would include it in SUITES_R of the response, and it would in that case have become the selected suite in the second message_1.) Initiator Responder |METHOD_CORR,METHOD, SUITES_I = [6, 5, 6], G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | | | |C_I,DIAG_MSG, SUITES_R = [9, 8] | |<------------------------------------------------------------------+ | error | | | |METHOD_CORR,METHOD, SUITES_I = [8, 5, 6, 7, 8], G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | Figure 8: Example of Responder supporting suites 8 and 9 but not 5, 6 or 7. Note that the Initiator's list of supported cipher suites and order of preference is fixed (see Section5.3.15.2.1 and Section5.3.2).5.2.2). Furthermore, the Responder shall only accept message_1 if the selected cipher suite is the first cipher suite in SUITES_I that the Responder supports (see Section5.3.3).5.2.3). Following this procedure ensures that the selected cipher suite is the most preferred (by the Initiator) cipher suite supported by both parties. If the selected cipher suite is not the first cipher suite which the Responder supports in SUITES_I received in message_1, then Responder MUST discontinue the protocol, see Section5.3.3.5.2.3. If SUITES_I in message_1 is manipulated then the integrity verification of message_2 containing the transcript hash TH_2 will fail and the Initiator will discontinue the protocol. 7.Transferring EDHOC and Deriving an OSCORE ContextSecurity Considerations 7.1. Security Properties EDHOCMessage 4 This section specifies message_4 which is OPTIONAL to support. Key confirmation is normally provided by sending an application messageinherits its security properties from theResponder totheoretical SIGMA-I protocol [SIGMA]. Using theInitiator protected with a key derivedterminology from [SIGMA], EDHOC provides perfect forward secrecy, mutual authentication withthe EDHOC-Exporter, e.g., using OSCORE (see [I-D.ietf-core-oscore-edhoc]). In deployments where no protected application messagealiveness, consistency, and peer awareness. As described in [SIGMA], peer awareness issent fromprovided to theResponderResponder, but not to theInitiator,Initiator. EDHOC protects theResponder MUST send message_4. Two examplescredential identifier ofsuch deployments: 1. When EDHOC is only used for authentication and no application data is sent. 2. When application data is only sent fromthe Initiatortoagainst active attacks and theResponder. Further considerations are provided in Section 3.7. 7.1.1. Formattingcredential identifier ofMessage 4 message_4 and data_4 SHALL be CBOR Sequences (see Appendix B.1) as defined below message_4 = ( data_4, CIPHERTEXT_4 : bstr, ) data_4 = ( ? C_I : bstr_identifier, ) 7.1.2.the ResponderProcessing of Message 4against passive attacks. TheResponder SHALL compose message_4 as follows: * If corr (METHOD_CORR mod 4) equals 1 or 3, C_I is omitted, otherwise C_Iroles should be assigned to protect the most sensitive identity/identifier, typically that which is notomitted. * Compute a COSE_Encrypt0 as definedpossible to infer from routing information inSection 5.3the lower layers. Compared to [SIGMA], EDHOC adds an explicit method type and expands the message authentication coverage to additional elements such as algorithms, external authorization data, and previous messages. This protects against an attacker replaying messages or injecting messages from another session. EDHOC also adds selection of[I-D.ietf-cose-rfc8152bis-struct], withconnection identifiers and downgrade protected negotiation of cryptographic parameters, i.e. an attacker cannot affect the negotiated parameters. A single session of EDHOCAEAD algorithm indoes not include negotiation of cipher suites, but it enables the Responder to verify that the selected ciphersuite, andsuite is thefollowing parameters. The protected header SHALL be empty. - protected = h'' - external_aad = TH_4 - plaintext = ( ? EAD_4 ) where EAD_4most preferred cipher suite by the Initiator which isprotected external authorization data, see Section 3.6. COSE constructssupported by both theinputInitiator and the Responder. As required by [RFC7258], IETF protocols need to mitigate pervasive monitoring when possible. One way to mitigate pervasive monitoring is to use a key exchange that provides perfect forward secrecy. EDHOC therefore only supports methods with perfect forward secrecy. To limit theAEAD [RFC5116] as follows: - Key K = EDHOC-Exporter( "EDHOC_message_4_Key", length ) - Nonce N = EDHOC-Exporter( "EDHOC_message_4_Nonce", length ) - Plaintext P = ( ? EAD_4 ) - Associated data A = [ "Encrypt0", h'', TH_4 ] CIPHERTEXT_4effect of breaches, it is important to limit the use of symmetrical group keys for bootstrapping. EDHOC therefore strives to make the'ciphertext'additional cost ofthe COSE_Encrypt0. * Encode message_4using raw public keys and self-signed certificates as small as possible. Raw public keys and self-signed certificates are not asequencereplacement for a public key infrastructure, but SHOULD be used instead ofCBOR encoded data items as specified in Section 7.1.1. 7.1.3. Initiator Processingsymmetrical group keys for bootstrapping. Compromise ofMessage 4 The Initiator SHALL process message_4 as follows: * Decode message_4 (see Appendix B.1). * Retrieve the protocol state using the connection identifier C_I and/or other external information such astheCoAP Token andlong-term keys (private signature or static DH keys) does not compromise the5-tuple. * Decrypt and verifysecurity of completed EDHOC exchanges. Compromising theouter COSE_Encrypt0 as defined in Section 5.3private authentication keys of[I-D.ietf-cose-rfc8152bis-struct],one party lets an active attacker impersonate that compromised party in EDHOC exchanges with other parties, but does not let theEDHOC AEAD algorithmattacker impersonate other parties in EDHOC exchanges with theselected cipher suite, andcompromised party. Compromise of theparameters defined in Section 7.1.2. * Pass EAD_4long-term keys does not enable a passive attacker to compromise future session keys. Compromise of thesecurity application. If any verification step fails the Initiator MUST send an EDHOC error message back, formatted as defined in Section 6, and theHDKF input parameters (ECDH shared secret) leads to compromise of all sessionMUST be discontinued. 7.2. Transferring EDHOC in CoAP It is recommendedkeys derived from that compromised shared secret. Compromise of one session key does not compromise other session keys. Compromise of PRK_4x3m leads totransport EDHOC as an exchangecompromise of all exported keying material derived after the last invocation ofCoAP [RFC7252] messages. CoAP isthe EDHOC-KeyUpdate function. EDHOC provides areliable transport that can preserve packet ordering and handle message duplication. CoAP can also perform fragmentation and protectminimum of 64-bit security againstdenialonline brute force attacks and a minimum ofservice128-bit security against offline brute force attacks.ItThis isrecommendedin line with IPsec, TLS, and COSE. To break 64-bit security against online brute force an attacker would on average have tocarry the EDHOCsend 4.3 billion messagesin Confirmable messages, especially if fragmentationper second for 68 years, which isused. By default,infeasible in constrained IoT radio technologies. After sending message_3, theCoAP clientInitiator is assured that no other party than the Responder can compute the key PRK_4x3m (implicit key authentication). The Initiatoranddoes however not know that theCoAP server isResponder has actually computed theResponder, butkey PRK_4x3m. While therolesInitiator can securely send protected application data, the Initiator SHOULDbe chosen to protectNOT permanently store themost sensitive identity, see Section 8. By default, EDHOC is transferred in POST requestskeying material PRK_4x3m and2.04 (Changed) responses toTH_4 until theUri-Path: "/.well-known/edhoc", but an application may define its own pathInitiator is assured thatcan be discoveredthe Responder has actually computed the key PRK_4x3m (explicit key confirmation). Explicit key confirmation is e.g.using resource directory [I-D.ietf-core-resource-directory]. By default,assured when the Initiator has verified an OSCORE messageflow is as follows: EDHOC message_1or message_4 from the Responder. After verifying message_3, the Responder issent inassured that the Initiator has calculated the key PRK_4x3m (explicit key confirmation) and that no other party than thepayload of a POST request fromResponder can compute theclient tokey. The Responder can securely send protected application data and store theserver's resource for EDHOC.keying material PRK_4x3m and TH_4. Key compromise impersonation (KCI): In EDHOCmessage_2 or theauthenticated with signature keys, EDHOCerror message is sent from the serverprovides KCI protection against an attacker having access to theclient in the payload of a 2.04 (Changed) response. EDHOC message_3long term key or theEDHOC error message is sent fromephemeral secret key. With static Diffie-Hellman key authentication, KCI protection would be provided against an attacker having access to theclientlong-term Diffie- Hellman key, but not to an attacker having access to theserver's resource inephemeral secret key. Note that thepayloadterm KCI has typically been used for compromise ofa POST request. If needed,long-term keys, and that an attacker with access to the ephemeral secret key can only attack that specific protocol run. Repudiation: In EDHOCerror message is sent fromauthenticated with signature keys, theserver toInitiator could theoretically prove that theclientResponder performed a run of the protocol by presenting the private ephemeral key, and vice versa. Note that storing the private ephemeral keys violates the protocol requirements. With static Diffie-Hellman key authentication, both parties can always deny having participated in thepayloadprotocol. Two earlier versions ofa 2.04 (Changed) response. Alternatively, ifEDHOCmessage_4 is used, it is sent from the server tohave been formally analyzed [Norrman20] [Bruni18] and theclient inspecification has been updated based on thepayloadanalysis. 7.2. Cryptographic Considerations The security ofa 2.04 (Changed) response analogouslythe SIGMA protocol requires the MAC tomessage_2. An examplebe bound to the identity ofa successful EDHOC exchange using CoAP is shown in Figure 9. In this casetheCoAP Token enablessigner. Hence theInitiator to correlate message_1 and message_2 somessage authenticating functionality of thecorrelation parameter corr = 1. Client Server | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | Content-Format: application/edhoc | | Payload: EDHOC message_1 | | |<---------+ Header: 2.04 Changed | 2.04 | Content-Format: application/edhoc | | Payload:authenticated encryption in EDHOCmessage_2 | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | Content-Format: application/edhoc | | Payload:is critical: authenticated encryption MUST NOT be replaced by plain encryption only, even if authentication is provided at another level or through a different mechanism. EDHOCmessage_3 | | |<---------+ Header: 2.04 Changed | 2.04 | | | Figure 9: Transferringimplements SIGMA-I using a MAC-then- Sign approach. To reduce message overhead EDHOCin CoAP whendoes not use explicit nonces and instead rely on theInitiatorephemeral public keys to provide randomness to each session. A good amount of randomness isCoAP Client The exchange in Figure 9 protectsimportant for theclient identitykey generation, to provide liveness, and to protect againstactive attackersinterleaving attacks. For this reason, the ephemeral keys MUST NOT be reused, and both parties SHALL generate fresh random ephemeral key pairs. As discussed theserver identity against passive attackers. An alternative exchange that protects[SIGMA], theserver identityencryption of message_2 does only need to protect against passive attacker as active attackersandcan always get theclientResponders identityagainst passive attackers is shown in Figure 10. In this case the CoAP Token enables the Responder to correlate message_2 and message_3 so the correlation parameter corr = 2. Ifby sending their own message_1. EDHOCmessage_4uses the Expand function (typically HKDF-Expand) as a binary additive stream cipher. HKDF-Expand provides better confidentiality than AES- CTR but isused,not often used as it istransported with CoAP inslow on long messages, and most applications require both IND-CCA confidentiality as well as integrity protection. For thepayloadencryption ofa POST request with a 2.04 (Changed) response. Client Server | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | |<---------+ Header: 2.04 Changed | 2.04 | Content-Format: application/edhoc | | Payload: EDHOC message_1 | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | Content-Format: application/edhoc | | Payload: EDHOC message_2 | | |<---------+ Header: 2.04 Changed | 2.04 | Content-Format: application/edhoc | | Payload: EDHOC message_3 | | Figure 10: Transferring EDHOC in CoAP when the Initiatormessage_2, any speed difference isCoAP Server To protect against denial-of-service attacks, the CoAP server MAY respond to the first POST request with a 4.01 (Unauthorized) containing an Echo option [I-D.ietf-core-echo-request-tag]. This forces the initiator to demonstrate its reachability at its apparent network address. If message fragmentationnegligible, IND-CCA does not increase security, and integrity isneeded,provided by theEDHOC messages may be fragmented usinginner MAC (and signature depending on method). The data rates in many IoT deployments are very limited. Given that theCoAP Block-Wise Transfer mechanism [RFC7959]. EDHOC does not restrict how error messagesapplication keys aretransported with CoAP,protected aslongwell as theappropriate error messagelong-term authentication keys they cantooften betransported in response to a message that failed (see Section 6). The use ofused for years or even decades before the cryptographic limits are reached. If the application keys established through EDHOC need to be renewed, the communicating parties can derive application keys withOSCORE is specified in [I-D.ietf-core-oscore-edhoc]. 8. Security Considerations 8.1. Security Propertiesother labels or run EDHOCinherits its security properties fromagain. Requirement for how to securely generate, validate, and process thetheoretical SIGMA-I protocol [SIGMA]. Usingephermeral public keys depend on theterminology from [SIGMA], EDHOC provides perfect forward secrecy, mutual authentication with aliveness, consistency,elliptic curve. For X25519 andpeer awareness. As describedX448, the requirements are defined in[SIGMA], peer awareness[RFC7748]. For secp256r1, secp384r1, and secp521r1, the requirements are defined in Section 5 of [SP-800-56A]. For secp256r1, secp384r1, and secp521r1, at least partial public-key validation MUST be done. 7.3. Cipher Suites and Cryptographic Algorithms For many constrained IoT devices it isprovidedproblematic tothe Responder, but notsupport more than one cipher suite. Existing devices can be expected to support either ECDSA or EdDSA. To enable as much interoperability as we can reasonably achieve, less constrained devices SHOULD implement both cipher suite 0 (AES-CCM-16-64-128, SHA-256, X25519, EdDSA, AES-CCM- 16-64-128, SHA-256) and cipher suite 2 (AES-CCM-16-64-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256). Constrained endpoints SHOULD implement cipher suite 0 or cipher suite 2. Implementations only need to implement theInitiator. EDHOC protectsalgorithms needed for their supported methods. When using private cipher suite or registering new cipher suites, thecredential identifierchoice of key length used in theInitiator against active attacksdifferent algorithms needs to be harmonized, so that a sufficient security level is maintained for certificates, EDHOC, and thecredential identifierprotection of application data. The Initiator and the Responderagainst passive attacks. The rolesshouldbe assignedenforce a minimum security level. The hash algorithms SHA-1 and SHA-256/64 (256-bit Hash truncated toprotect the most sensitive identity/identifier, typically64-bits) SHALL NOT be supported for use in EDHOC except for certificate identification with x5u and c5u. Note thatwhichsecp256k1 is only defined for use with ECDSA and notpossible to infer from routing information infor ECDH. 7.4. Unprotected Data The Initiator and thelower layers. ComparedResponder must make sure that unprotected data and metadata do not reveal any sensitive information. This also applies for encrypted data sent to[SIGMA], EDHOC addsanexplicit method type and expands the message authentication coverageunauthenticated party. In particular, it applies toadditional elements such as algorithms, external authorization data,EAD_1, ID_CRED_R, EAD_2, andpreviouserror messages.This protects against an attacker replaying messages or injecting messages from another session.Using the same EAD_1 in several EDHOCalso adds negotiationsessions allows passive eavesdroppers to correlate the different sessions. Another consideration is that the list ofconnection identifierssupported cipher suites may potentially be used to identify the application. The Initiator anddowngrade protected negotiation of cryptographic parameters, i.e. an attacker cannot affectthenegotiated parameters. A single session ofResponder must also make sure that unauthenticated data does not trigger any harmful actions. In particular, this applies to EAD_1 and error messages. 7.5. Denial-of-Service EDHOC itself does notinclude negotiationprovide countermeasures against Denial-of- Service attacks. By sending a number ofcipher suites, but it enablesnew or replayed message_1 an attacker may cause the Responder toverify that the selected cipher suite is the most preferred cipher suite by the Initiator which is supported by both the Initiatorallocate state, perform cryptographic operations, and amplify messages. To mitigate such attacks, an implementation SHOULD rely on lower layer mechanisms such as theResponder. As required by [RFC7258], IETF protocols needEcho option in CoAP [I-D.ietf-core-echo-request-tag] that forces the initiator tomitigate pervasive monitoring when possible. One waydemonstrate reachability at its apparent network address. An attacker can also send faked message_2, message_3, message_4, or error in an attempt tomitigate pervasive monitoring istrick the receiving party touse a key exchange that provides perfect forward secrecy. EDHOC therefore only supports methods with perfect forward secrecy. To limitsend an error message and discontinue theeffect of breaches, itsession. EDHOC implementations MAY evaluate if a received message isimportantlikely tolimithave be forged by and attacker and ignore it without sending an error message or discontinuing theusesession. 7.6. Implementation Considerations The availability ofsymmetrical group keysa secure random number generator is essential forbootstrapping. EDHOC therefore strives to maketheadditional costsecurity ofusing raw public keys and self-signed certificates as small as possible. Raw public keysEDHOC. If no true random number generator is available, a truly random seed MUST be provided from an external source andself-signed certificates are not a replacement forused with apublic key infrastructure, but SHOULDcryptographically secure pseudorandom number generator. As each pseudorandom number must only be usedinstead of symmetrical group keysonce, an implementation need to get a new truly random seed after reboot, or continuously store state in nonvolatile memory, see ([RFC8613], Appendix B.1.1) forbootstrapping. Compromise of the long-term keys (private signatureissues and solution approaches for writing to nonvolatile memory. Intentionally orstatic DH keys) does not compromise theunintentionally weak or predictable pseudorandom number generators can be abused or exploited for malicious purposes. [RFC8937] describes a way for securityof completed EDHOC exchanges. Compromising the private authentication keys of one party lets an active attacker impersonate that compromised party in EDHOC exchanges with other parties, but does not let the attacker impersonate other parties in EDHOC exchanges with the compromised party. Compromise of theprotocol implementations to augment their (pseudo)random number generators using a long-term private keysdoes not enableand apassive attacker to compromise future session keys. Compromise of the HDKF input parameters (ECDH shared secret) leads to compromise of all session keys deriveddeterministic signature function. This improves randomness fromthat compromised shared secret. Compromise of one session key does not compromisebroken or otherwise subverted random number generators. The same idea can be used with othersession keys. Compromise of PRK_4x3m leads to compromise of all exported keying material derived after the last invocation of the EDHOC-KeyUpdate function. EDHOC providessecrets and functions such as aminimum of 64-bit security against online brute force attacksDiffie-Hellman function or a symmetric secret and aminimumPRF like HMAC or KMAC. It is RECOMMENDED to not trust a single source of128-bit security against offline brute force attacks. Thisrandomness and to not put unaugmented random numbers on the wire. If ECDSA is supported, "deterministic ECDSA" as specified inline with IPsec, TLS,[RFC6979] MAY be used. Pure deterministic elliptic-curve signatures such as deterministic ECDSA andCOSE. To break 64-bitEdDSA have gained popularity over randomized ECDSA as their securityagainst online brute force an attacker woulddo not depend onaverage havea source of high- quality randomness. Recent research has however found that implementations of these signature algorithms may be vulnerable tosend 4.3 billion messages per secondcertain side-channel and fault injection attacks due to their determinism. See e.g. Section 1 of [I-D.mattsson-cfrg-det-sigs-with-noise] for68 years, which is infeasiblea list of attack papers. As suggested inconstrained IoT radio technologies. After sending message_3, the Initiator is assured that no other party than the Responder can compute the key PRK_4x3m (implicit key authentication). The Initiator does however not know that the Responder has actually computed the key PRK_4x3m. While the InitiatorSection 6.1.2 of [I-D.ietf-cose-rfc8152bis-algs] this cansecurely send protected application data, the Initiator SHOULD NOT permanently store the keying material PRK_4x3mbe addressed by combining randomness andTH_4 until the Initiator is assured that the Responder has actuallydeterminism. All private keys, symmetric keys, and IVs MUST be secret. Implementations should provide countermeasures to side-channel attacks such as timing attacks. Intermediate computedthe key PRK_4x3m (explicit key confirmation). Explicitvalues such as ephemeral ECDH keys and ECDH shared secrets MUST be deleted after keyconfirmation is e.g. assured when the Initiator has verified an OSCORE message or message_4 from the Responder. After verifying message_3, the Responderderivation isassured that thecompleted. The Initiatorhas calculated the key PRK_4x3m (explicit key confirmation)andthat no other party thanthe Respondercan computeare responsible for verifying thekey.integrity of certificates. TheResponder can securely send protected application data and store the keying material PRK_4x3mselection of trusted CAs should be done very carefully andTH_4. Key compromise impersonation (KCI): In EDHOC authenticated with signature keys, EDHOC provides KCI protection against an attacker having access to the long term key or the ephemeral secret key. With static Diffie-Hellman key authentication, KCI protection wouldcertificate revocation should beprovided against an attacker having access tosupported. The private authentication keys MUST be kept secret. The Initiator and thelong-term Diffie- Hellman key, but not to an attacker having accessResponder are allowed to select theephemeral secret key. Note that the term KCI has typically been used for compromise of long-term keys,connection identifiers C_I andthat an attacker with accessC_R, respectively, for the other party to use in theephemeral secret key can only attack that specific protocol run. Repudiation: Inongoing EDHOCauthenticated with signature keys, the Initiator could theoretically prove that the Responder performedprotocol as well as in arunsubsequent application protocol (e.g. OSCORE [RFC8613]). The choice of connection identifier is not security critical in EDHOC but intended to simplify theprotocol by presentingretrieval of theprivate ephemeral key, and vice versa. Note that storingright security context in combination with using short identifiers. If theprivate ephemeral keys violateswrong connection identifier of the other party is used in a protocolrequirements. With static Diffie-Hellman key authentication, both parties can always deny having participatedmessage it will result in theprotocol. Two earlier versions of EDHOC have been formally analyzed [Norrman20] [Bruni18] andreceiving party not being able to retrieve a security context (which will terminate thespecification has been updated based onprotocol) or retrieve theanalysis. 8.2. Cryptographic Considerations Thewrong securityofcontext (which also terminates theSIGMAprotocolrequiresas theMACmessage cannot be verified). If two nodes unintentionally initiate two simultaneous EDHOC message exchanges with each other even if they only want to complete a single EDHOC message exchange, they MAY terminate the exchange with the lexicographically smallest G_X. If the two G_X values are equal, the received message_1 MUST bebounddiscarded to mitigate reflection attacks. Note that in theidentitycase of two simultaneous EDHOC exchanges where thesigner. Hencenodes only complete one and where themessage authenticating functionalitynodes have different preferred cipher suites, an attacker can affect which of theauthenticated encryption in EDHOC is critical: authenticated encryption MUST NOTtwo nodes' preferred cipher suites will bereplacedused byplain encryption only, even if authenticationblocking the other exchange. If supported by the device, it isprovidedRECOMMENDED that atanother level or through a different mechanism. EDHOC implements SIGMA-I usingleast the long- term private keys are stored in aMAC-then- Sign approach. To reduce message overhead EDHOC does not use explicit noncesTrusted Execution Environment (TEE) andinstead rely on the ephemeral publicthat sensitive operations using these keysto provide randomness to each session. A good amount of randomness is important forare performed inside the TEE. To achieve even higher security it is RECOMMENDED that in additional operations such as ephemeral key generation,to provide liveness,all computations of shared secrets, andto protect against interleaving attacks. For this reason,storage of theephemeralpseudorandom keysMUST NOT(PRK) can bereused, and both parties SHALL generate fresh random ephemeral key pairs. As discussed the [SIGMA],done inside theencryptionTEE. The use ofmessage_2 does only need to protect against passive attacker as active attackers can always get the Responders identity by sending their own message_1. EDHOC uses the Expand function (typically HKDF-Expand) asabinary additive stream cipher. HKDF-Expand provides better confidentiality than AES- CTR but is not often used as it is slow on long messages,TEE enforces that code within that environment cannot be tampered with, andmost applications require both IND-CCA confidentiality as well as integrity protection. For the encryption of message_2,that anyspeed difference is negligible, IND-CCA does not increase security, and integrity is provideddata used by such code cannot be read or tampered with by code outside that environment. Note that non-EDHOC code inside theinner MAC (and signature depending on method). TheTEE might still be able to read EDHOC dataratesand tamper with EDHOC code, to protect against such attacks EDHOC needs to be inmany IoT deployments are very limited. Given thatits own zone. To provide better protection against some forms of physical attacks, sensitive EDHOC data should be stored inside theapplication keys areSoC or encrypted and integrity protectedas well aswhen sent on a data bus (e.g. between thelong-term authentication keys theyCPU and RAM or Flash). Secure boot canoftenbe usedfor years or even decades before the cryptographic limits are reached. If the application keys established through EDHOC needtobe renewed,increase thecommunicating parties can derive application keys with other labels or run EDHOC again. Requirement for how to securely generate, validate,security of code andprocessdata in theephermeral public keys depend onRich Execution Environment (REE) by validating theelliptic curve. For X25519 and X448,REE image. 8. IANA Considerations 8.1. EDHOC Exporter Label IANA has created a new registry titled "EDHOC Exporter Label" under therequirementsnew heading "EDHOC". The registration procedure is "Expert Review". The columns of the registry aredefined in [RFC7748]. For secp256r1, secp384r1,Label, Description, andsecp521r1, the requirementsReference. All columns aredefined in Section 5text strings. The initial contents of[SP-800-56A]. For secp256r1, secp384r1, and secp521r1, at least partial public-key validation MUST be done. 8.3.the registry are: Label: EDHOC_message_4_Key Description: Key used to protect EDHOC message_4 Reference: [[this document]] Label: EDHOC_message_4_Nonce Description: Nonce used to protect EDHOC message_4 Reference: [[this document]] Label: OSCORE Master Secret Description: Derived OSCORE Master Secret Reference: [[this document]] Label: OSCORE Master Salt Description: Derived OSCORE Master Salt Reference: [[this document]] 8.2. EDHOC Cipher Suitesand Cryptographic Algorithms For many constrained IoT devices itRegistry IANA has created a new registry titled "EDHOC Cipher Suites" under the new heading "EDHOC". The registration procedure is "Expert Review". The columns of the registry are Value, Array, Description, and Reference, where Value isproblematic to support more than one cipher suite. Existing devices can be expected to support either ECDSA or EdDSA. To enable as much interoperability as we can reasonably achieve, less constrained devices SHOULD implement both cipher suitean integer and the other columns are text strings. The initial contents of the registry are: Value: -24 Algorithms: N/A Desc: Reserved for Private Use Reference: [[this document]] Value: -23 Algorithms: N/A Desc: Reserved for Private Use Reference: [[this document]] Value: -22 Algorithms: N/A Desc: Reserved for Private Use Reference: [[this document]] Value: -21 Algorithms: N/A Desc: Reserved for Private Use Reference: [[this document]] Value: 0(AES-CCM-16-64-128,Array: 10, -16, 4, -8, 10, -16 Desc: AES-CCM-16-64-128, SHA-256, X25519, EdDSA, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value: 1 Array: 30, -16, 4, -8, 10, -16 Desc: AES-CCM-16-128-128, SHA-256, X25519, EdDSA, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value: 2 Array: 10, -16, 1, -7, 10, -16 Desc: AES-CCM-16-64-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value: 3 Array: 30, -16, 1, -7, 10, -16 Desc: AES-CCM-16-128-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value: 4 Array: 24, -16, 4, -8, 24, -16 Desc: ChaCha20/Poly1305, SHA-256, X25519, EdDSA, ChaCha20/Poly1305, SHA-256 Reference: [[this document]] Value: 5 Array: 24, -16, 1, -7, 24, -16 Desc: ChaCha20/Poly1305, SHA-256, P-256, ES256, ChaCha20/Poly1305, SHA-256 Reference: [[this document]] Value: 6 Array: 1, -16, 4, -7, 1, -16 Desc: A128GCM, SHA-256, X25519, ES256, A128GCM, SHA-256 Reference: [[this document]] Value: 24 Array: 3, -43, 2, -35, 3, -43 Desc: A256GCM, SHA-384, P-384, ES384, A256GCM, SHA-384 Reference: [[this document]] Value: 25 Array: 24, -45, 5, -8, 24, -45 Desc: ChaCha20/Poly1305, SHAKE256, X448, EdDSA,AES-CCM- 16-64-128, SHA-256) and cipher suite 2 (AES-CCM-16-64-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256). Constrained endpoints SHOULD implement cipher suite 0 or cipher suite 2. Implementations only need to implement the algorithms needed for their supported methods. When using private cipher suite or registeringChaCha20/Poly1305, SHAKE256 Reference: [[this document]] 8.3. EDHOC Method Type Registry IANA has created a newcipher suites,registry entitled "EDHOC Method Type" under thechoicenew heading "EDHOC". The registration procedure is "Expert Review". The columns ofkey length used inthedifferent algorithms needs to be harmonized, so that a sufficient security levelregistry are Value, Description, and Reference, where Value ismaintained for certificates, EDHOC,an integer and theprotection of application data.other columns are text strings. TheInitiator andinitial contents of theResponder should enforce a minimum security level. The hash algorithms SHA-1 and SHA-256/64 (256-bit Hash truncated to 64-bits) SHALL NOT be supported for useregistry is shown in Figure 4. 8.4. EDHOCexcept for certificate identification with x5uError Codes Registry IANA has created a new registry entitled "EDHOC Error Codes" under the new heading "EDHOC". The registration procedure is "Specification Required". The columns of the registry are ERR_CODE, ERR_INFO Type andc5u. Note that secp256k1Description, where ERR_CODE isonlyan integer, ERR_INFO is a CDDL definedfor use with ECDSAtype, andnot for ECDH. 8.4. Unprotected DataDescription is a text string. TheInitiatorinitial contents of the registry is shown in Figure 6. 8.5. COSE Header Parameters Registry This document registers the following entries in the "COSE Header Parameters" registry under the "CBOR Object Signing and Encryption (COSE)" heading. The value of theResponder must make sure that'cwt' header parameter is a CWT [RFC8392] or an unprotecteddata and metadata do not reveal any sensitive information. This also applies for encrypted data sent toCWT Claims Set [I-D.ietf-rats-uccs]. +-----------+-------+----------------+------------------------------+ | Name | Label | Value Type | Description | +===========+=======+================+==============================+ | cwt | TBD1 | COSE_Messages | A CBOR Web Token (CWT) or anunauthenticated party. In particular, it applies to EAD_1, ID_CRED_R, EAD_2, and error messages. Using| | | | / map | unprotected CWT Claims Set | +-----------+-------+----------------+------------------------------+ 8.6. COSE Header Parameters Registry IANA has added thesame EAD_1 in several EDHOC sessions allows passive eavesdroppersCOSE header parameter 'kid2' tocorrelate the different sessions. Another consideration is thatthelist of supported cipher suitesCOSE Header Parameters registry. The kid2 parameter maypotentiallypoint to a COSE key common parameter 'kid' or 'kid2'. The kid2 parameter can be used to identifythe application. The Initiator and the Responder must also make sure that unauthenticated data does not trigger any harmful actions. In particular, this applies to EAD_1 and error messages. 8.5. Denial-of-Service EDHOC itself does not provide countermeasures against Denial-of- Service attacks. By sendinganumber of newkey stored in a "raw" COSE_Key, in a CWT, orreplayed message_1 an attacker may cause the Responder to allocate state, perform cryptographic operations,in a certificate. The Value Reference for this item is empty andamplify messages. To mitigate such attacks, an implementation SHOULD rely on lower layer mechanisms such asomitted from theEcho option in CoAP [I-D.ietf-core-echo-request-tag] that forcestable below. +------+-------+------------+----------------+-------------------+ | Name | Label | Value Type | Description | Reference | +------+-------+------------+----------------+-------------------+ | kid2 | TBD | bstr / int | Key identifier | [[This document]] | +------+-------+------------+----------------+-------------------+ 8.7. COSE Key Common Parameters Registry IANA has added theinitiator to demonstrate reachability at its apparent network address. An attacker can also send faked message_2, message_3, message_4, or error in an attemptCOSE key common parameter 'kid2' totrickthereceiving party to send an error messageCOSE Key Common Parameters registry. The Value Reference for this item is empty anddiscontinueomitted from thesession. EDHOC implementations MAY evaluate if a received message is likelytable below. +------+-------+------------+----------------+-------------------+ | Name | Label | Value Type | Description | Reference | +------+-------+------------+----------------+-------------------+ | kid2 | TBD | bstr / int | Key identifi- | [[This document]] | | | | | cation value - | | | | | | match tohave be forged by and attacker and ignore it without sending an errorkid2 | | | | | | in messageor discontinuing the session. 8.6. Implementation Considerations| | +------+-------+------------+----------------+-------------------+ 8.8. Theavailability of a secure random number generator is essential forWell-Known URI Registry IANA has added thesecuritywell-known URI 'edhoc' to the Well-Known URIs registry. o URI suffix: edhoc o Change controller: IETF o Specification document(s): [[this document]] o Related information: None 8.9. Media Types Registry IANA has added the media type 'application/edhoc' to the Media Types registry. o Type name: application o Subtype name: edhoc o Required parameters: N/A o Optional parameters: N/A o Encoding considerations: binary o Security considerations: See Section 7 ofEDHOC. If no true random number generator is available, a truly random seed MUST be provided from an external source and used with a cryptographically secure pseudorandom number generator. As each pseudorandom number must onlythis document. o Interoperability considerations: N/A o Published specification: [[this document]] (this document) o Applications that use this media type: To beused once, an implementation need to get a new truly random seed after reboot, or continuously store state in nonvolatile memory, see ([RFC8613], Appendix B.1.1) for issues and solution approaches for writingidentified o Fragment identifier considerations: N/A o Additional information: * Magic number(s): N/A * File extension(s): N/A * Macintosh file type code(s): N/A o Person & email address tononvolatile memory. Intentionally or unintentionally weak or predictable pseudorandom number generators can be abused or exploited for malicious purposes. [RFC8937] describes a waycontact forsecurity protocol implementationsfurther information: See "Authors' Addresses" section. o Intended usage: COMMON o Restrictions on usage: N/A o Author: See "Authors' Addresses" section. o Change Controller: IESG 8.10. CoAP Content-Formats Registry IANA has added the media type 'application/edhoc' toaugment their (pseudo)random number generators using a long-term private keys andthe CoAP Content-Formats registry. o Media Type: application/edhoc o Encoding: o ID: TBD42 o Reference: [[this document]] 8.11. EDHOC External Authorization Data IANA has created adeterministic signature function. This improves randomness from broken or otherwise subverted random number generators.new registry entitled "EDHOC External Authorization Data" under the new heading "EDHOC". Thesame idea can be used with other secrets and functions such as a Diffie-Hellman function or a symmetric secret and a PRF like HMAC or KMAC. Itregistration procedure isRECOMMENDED to not trust a single source"Expert Review". The columns ofrandomnessthe registry are Value, Description, and Reference, where Value is an integer andto not put unaugmented random numbers onthewire. If ECDSAother columns are text strings. 8.12. Expert Review Instructions The IANA Registries established in this document issupported, "deterministic ECDSA"defined asspecified in [RFC6979] MAY"Expert Review". This section gives some general guidelines for what the experts should beused. Pure deterministic elliptic-curve signatures such as deterministic ECDSA and EdDSA have gained popularity over randomized ECDSAlooking for, but they are being designated astheir security do not depend onexperts for asource of high- quality randomness. Recent research has however found that implementations of these signature algorithms mayreason so they should bevulnerablegiven substantial latitude. Expert reviewers should take into consideration the following points: o Clarity and correctness of registrations. Experts are expected tocertain side-channelcheck the clarity of purpose andfault injection attacks dueuse of the requested entries. Expert needs totheir determinism. See e.g. Section 1make sure the values of[I-D.mattsson-cfrg-det-sigs-with-noise] for a listalgorithms are taken from the right registry, when that's required. Expert should consider requesting an opinion on the correctness ofattack papers. As suggested in Section 6.1.2registered parameters from relevant IETF working groups. Encodings that do not meet these objective of[I-D.ietf-cose-rfc8152bis-algs] this can be addressed by combining randomness and determinism. All private keys, symmetric keys,clarity andIVs MUST be secret. Implementationscompleteness shouldprovide countermeasures to side-channel attacks such as timing attacks. Intermediate computed values such as ephemeral ECDH keys and ECDH shared secrets MUSTnot bedeleted after key derivation is completed. The Initiator and the Responder are responsible for verifyingregistered. o Experts should take into account theintegrityexpected usage ofcertificates.fields when approving point assignment. Theselectionlength oftrusted CAs should be done very carefully and certificate revocationthe encoded value should besupported. The private authentication keys MUST be kept secret. The Initiator and the Responderweighed against how many code points of that length areallowed to selectleft, theconnection identifiers C_Isize of device it will be used on, andC_R, respectively, fortheother party to use in the ongoing EDHOC protocol as well as in a subsequent application protocol (e.g. OSCORE [RFC8613]). The choicenumber ofconnection identifier is not security critical in EDHOC but intendedcode points left that encode tosimplifythat size. o Specifications are recommended. When specifications are not provided, theretrieval ofdescription provided needs to have sufficient information to verify theright security contextpoints above. 9. References 9.1. Normative References [I-D.ietf-core-echo-request-tag] Amsuess, C., Mattsson, J. P., and G. Selander, "CoAP: Echo, Request-Tag, and Token Processing", draft-ietf-core- echo-request-tag-12 (work incombination with using short identifiers. If the wrong connection identifier of the other party is usedprogress), February 2021. [I-D.ietf-cose-rfc8152bis-algs] Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", draft-ietf-cose-rfc8152bis-algs-12 (work ina protocol message it will resultprogress), September 2020. [I-D.ietf-cose-rfc8152bis-struct] Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", draft-ietf-cose-rfc8152bis- struct-15 (work inthe receiving party not being able to retrieve a security context (which will terminate the protocol) or retrieve the wrong security context (which also terminates the protocol as the message cannot be verified). If two nodes unintentionally initiate two simultaneous EDHOC message exchanges with each other even if they only want to completeprogress), February 2021. [I-D.ietf-cose-x509] Schaad, J., "CBOR Object Signing and Encryption (COSE): Header parameters for carrying and referencing X.509 certificates", draft-ietf-cose-x509-08 (work in progress), December 2020. [I-D.ietf-lake-reqs] Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia- Carrillo, "Requirements for asingle EDHOC message exchange, they MAY terminate the exchange with the lexicographically smallest G_X. If the two G_X values are equal, the received message_1 MUST be discarded to mitigate reflection attacks. Note thatLightweight AKE for OSCORE", draft-ietf-lake-reqs-04 (work inthe case of two simultaneous EDHOC exchanges where the nodes only complete oneprogress), June 2020. [I-D.ietf-rats-uccs] Birkholz, H., O'Donoghue, J., Cam-Winget, N., andwhere the nodes have different preferred cipher suites, an attacker can affect whichC. Bormann, "A CBOR Tag for Unprotected CWT Claims Sets", draft-ietf-rats-uccs-00 (work in progress), May 2021. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, <https://www.rfc-editor.org/info/rfc5116>. [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)", RFC 5869, DOI 10.17487/RFC5869, May 2010, <https://www.rfc-editor.org/info/rfc5869>. [RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic Curve Cryptography Algorithms", RFC 6090, DOI 10.17487/RFC6090, February 2011, <https://www.rfc-editor.org/info/rfc6090>. [RFC6979] Pornin, T., "Deterministic Usage of thetwo nodes' preferred cipher suites will be used by blocking the other exchange. If supported by the device, it is RECOMMENDED that at least the long- term private keys are stored in a Trusted Execution Environment (TEE)Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August 2013, <https://www.rfc-editor.org/info/rfc6979>. [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, <https://www.rfc-editor.org/info/rfc7252>. [RFC7748] Langley, A., Hamburg, M., andthat sensitive operations using these keys are performed inside the TEE. To achieve even higher security it is RECOMMENDED thatS. Turner, "Elliptic Curves for Security", RFC 7748, DOI 10.17487/RFC7748, January 2016, <https://www.rfc-editor.org/info/rfc7748>. [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers inadditional operations such as ephemeral key generation, all computationsthe Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016, <https://www.rfc-editor.org/info/rfc7959>. [RFC8174] Leiba, B., "Ambiguity ofshared secrets,Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. [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>. [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, May 2018, <https://www.rfc-editor.org/info/rfc8392>. [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019, <https://www.rfc-editor.org/info/rfc8610>. [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, <https://www.rfc-editor.org/info/rfc8613>. [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. Zuniga, "SCHC: Generic Framework for Static Context Header Compression and Fragmentation", RFC 8724, DOI 10.17487/RFC8724, April 2020, <https://www.rfc-editor.org/info/rfc8724>. [RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR) Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020, <https://www.rfc-editor.org/info/rfc8742>. [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020, <https://www.rfc-editor.org/info/rfc8949>. 9.2. Informative References [Bruni18] Bruni, A., Sahl Joergensen, T., Groenbech Petersen, T., andstorage of the pseudorandom keys (PRK) can be done inside the TEE. The useC. Schuermann, "Formal Verification ofa TEE enforces that code within that environment cannot be tampered with,Ephemeral Diffie-Hellman Over COSE (EDHOC)", November 2018, <https://www.springerprofessional.de/en/formal- verification-of-ephemeral-diffie-hellman-over-cose- edhoc/16284348>. [CborMe] Bormann, C., "CBOR Playground", May 2018, <http://cbor.me/>. [CNSA] (Placeholder), ., "Commercial National Security Algorithm Suite", August 2015, <https://apps.nsa.gov/iaarchive/programs/iad-initiatives/ cnsa-suite.cfm>. [I-D.ietf-core-oscore-edhoc] Palombini, F., Tiloca, M., Hoeglund, R., Hristozov, S., andthat any data used by such code cannot be read or tampered with by code outside that environment. Note that non-EDHOC code inside the TEE might still be able to readG. Selander, "Combining EDHOCdataandtamper with EDHOC code, to protect against such attacks EDHOC needs to beOSCORE", draft-ietf- core-oscore-edhoc-00 (work inits own zone. To provide better protection against some forms of physical attacks, sensitive EDHOC data should be stored inside the SoC or encryptedprogress), April 2021. [I-D.ietf-core-resource-directory] Amsuess, C., Shelby, Z., Koster, M., Bormann, C., andintegrity protected when sent on a data bus (e.g. between the CPUP. V. D. Stok, "CoRE Resource Directory", draft-ietf-core- resource-directory-28 (work in progress), March 2021. [I-D.ietf-cose-cbor-encoded-cert] Raza, S., Hoeglund, J., Selander, G., Mattsson, J. P., andRAM or Flash). Secure boot can be used to increase the securityM. Furuhed, "CBOR Encoded X.509 Certificates (C509 Certificates)", draft-ietf-cose-cbor-encoded-cert-00 (work in progress), April 2021. [I-D.ietf-lwig-security-protocol-comparison] Mattsson, J. P., Palombini, F., and M. Vucinic, "Comparison ofcodeCoAP Security Protocols", draft-ietf-lwig- security-protocol-comparison-05 (work in progress), November 2020. [I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", draft-ietf-tls-dtls13-43 (work in progress), April 2021. [I-D.mattsson-cfrg-det-sigs-with-noise] Mattsson, J. P., Thormarker, E., and S. Ruohomaa, "Deterministic ECDSA anddataEdDSA Signatures with Additional Randomness", draft-mattsson-cfrg-det-sigs-with-noise-02 (work inthe Rich Execution Environment (REE) by validating the REE image. 9. IANA Considerations 9.1. EDHOC Exporter Label IANA has created a new registry titled "EDHOC Exporter Label" under the new heading "EDHOC". The registration procedure is "Expert Review". The columns of the registry are Label, Description,progress), March 2020. [I-D.selander-ace-ake-authz] Selander, G., Mattsson, J. P., Vucinic, M., Richardson, M., andReference. All columns are text strings. The initial contents of the registry are: Label: EDHOC_message_4_Key Description:A. Schellenbaum, "Lightweight Authorization for Authenticated Keyused to protect EDHOC message_4 Reference: [[this document]] Label: EDHOC_message_4_Nonce Description: Nonce used to protect EDHOC message_4 Reference: [[this document]] 9.2. EDHOC Cipher Suites Registry IANA has created a new registry titled "EDHOC Cipher Suites" under the new heading "EDHOC". The registration procedure is "Expert Review". The columnsExchange.", draft-selander-ace-ake- authz-02 (work in progress), November 2020. [Norrman20] Norrman, K., Sundararajan, V., and A. Bruni, "Formal Analysis ofthe registry are Value, Array, Description,EDHOC Key Establishment for Constrained IoT Devices", September 2020, <https://arxiv.org/abs/2007.11427>. [RFC7228] Bormann, C., Ersue, M., andReference, where Value isA. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, <https://www.rfc-editor.org/info/rfc7228>. [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is anintegerAttack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014, <https://www.rfc-editor.org/info/rfc7258>. [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, <https://www.rfc-editor.org/info/rfc7296>. [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>. [RFC8937] Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N., andthe other columns are text strings. The initial contents of the registry are: Value: -24 Algorithms: N/A Desc: Reserved for Private Use Reference: [[this document]] Value: -23 Algorithms: N/A Desc: Reserved for Private Use Reference: [[this document]] Value: -22 Algorithms: N/A Desc: ReservedC. Wood, "Randomness Improvements forPrivate Use Reference: [[this document]] Value: -21 Algorithms: N/A Desc: ReservedSecurity Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020, <https://www.rfc-editor.org/info/rfc8937>. [SECG] "Standards forPrivate Use Reference: [[this document]] Value: 0 Array: 10, -16, 4, -8, 10, -16 Desc: AES-CCM-16-64-128, SHA-256, X25519, EdDSA, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value:Efficient Cryptography 1Array: 30, -16, 4, -8, 10, -16 Desc: AES-CCM-16-128-128, SHA-256, X25519, EdDSA, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value: 2 Array: 10, -16, 1, -7, 10, -16 Desc: AES-CCM-16-64-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value: 3 Array: 30, -16, 1, -7, 10, -16 Desc: AES-CCM-16-128-128, SHA-256, P-256, ES256, AES-CCM-16-64-128, SHA-256 Reference: [[this document]] Value: 4 Array: 1, -16, 4, -7, 1, -16 Desc: A128GCM, SHA-256, X25519, ES256, A128GCM, SHA-256 Reference: [[this document]] Value: 5 Array: 3, -43, 2, -35, 3, -43 Desc: A256GCM, SHA-384, P-384, ES384, A256GCM, SHA-384 Reference: [[this document]] 9.3. EDHOC Method Type Registry IANA has created a new registry entitled "EDHOC Method Type" under the new heading "EDHOC". The registration procedure is "Expert Review".(SEC 1)", May 2009, <https://www.secg.org/sec1-v2.pdf>. [SIGMA] Krawczyk, H., "SIGMA - Thecolumns of'SIGn-and-MAc' Approach to Authenticated Diffie-Hellman and Its Use in theregistry are Value, Description,IKE- Protocols (Long version)", June 2003, <http://webee.technion.ac.il/~hugo/sigma-pdf.pdf>. [SP-800-56A] Barker, E., Chen, L., Roginsky, A., Vassilev, A., andReference, where Value is an integerR. Davis, "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography", NIST Special Publication 800-56A Revision 3, April 2018, <https://doi.org/10.6028/NIST.SP.800-56Ar3>. Appendix A. Use with OSCORE andthe other columns are text strings. The initial contents of the registry is shown in Figure 4. 9.4.Transfer over CoAP This sppendix describes how to select EDHOCError Codes Registry IANA has created a new registry entitled "EDHOC Error Codes" under the new heading "EDHOC". The registration procedure is "Specification Required". The columns of the registry are ERR_CODE, ERR_INFO Typeconnection identifiers andDescription, where ERR_CODE isderive aninteger, ERR_INFOOSCORE security context when OSCORE isa CDDL defined type,used with EDHOC, andDescription is a text string. The initial contents of the registry is shown in Figure 6. 9.5. The Well-Known URI Registry IANA has added the well-known URI 'edhoc' to the Well-Known URIs registry. * URI suffix: edhoc * Change controller: IETF * Specification document(s): [[this document]] * Related information: None 9.6. Media Types Registry IANA has added the media type 'application/edhoc' to the Media Types registry. * Type name: application * Subtype name: edhoc * Required parameters: N/A * Optional parameters: N/A * Encoding considerations: binary * Security considerations: See Section 7 of this document. * Interoperability considerations: N/A * Published specification: [[this document]] (this document) * Applications that use this media type: To be identified * Fragment identifier considerations: N/A * Additional information: - Magic number(s): N/A - File extension(s): N/A - Macintosh file type code(s): N/A * Person & email addresshow tocontacttransfer EDHOC messages over CoAP. A.1. Selecting EDHOC Connection Identifier This section specifies a rule forfurther information: See "Authors' Addresses" section. * Intended usage: COMMON * Restrictionsconverting from EDHOC connection identifier to OSCORE Sender/Recipient ID. (An identifier is Sender ID or Recipient ID depending onusage: N/A * Author: See "Authors' Addresses" section. * Change Controller: IESG 9.7. CoAP Content-Formats Registry IANA has addedfrom which endpoint is themedia type 'application/edhoc' topoint of view, see Section 3.1 of [RFC8613].) o If theCoAP Content-Formats registry. * Media Type: application/edhoc * Encoding: * ID: TBD42 * Reference: [[this document]] 9.8. Expert Review Instructions The IANA Registries established in this documentEDHOC connection identifier isdefinednumeric, i.e. encoded as"Expert Review". This section gives some general guidelines for whata CBOR integer on theexperts should be looking for, but they are being designatedwire, it is converted to a (naturally byte- string shaped) OSCORE Sender/Recipient ID equal to its CBOR encoded form. For example, a numeric C_R equal to 10 (0x0A in CBOR encoding) is converted to a (typically client) Sender ID equal to 0x0A, while a numeric C_I equal to -12 (0x2B in CBOR encoding) is converted to a (typically client) Sender ID equal to 0x2B. o If the EDHOC connection identifier is byte-valued, hence encoded asexperts forareason so they should be given substantial latitude. Expert reviewers should take into considerationCBOR byte string on thefollowing points: * Clarity and correctness of registrations. Experts are expectedwire, it is converted to an OSCORE Sender/Recipient ID equal tochecktheclarity of purposebyte string. For example, a byte-string valued C_R equal to 0xFF (0x41FF in CBOR encoding) is converted to a (typically client) Sender ID equal to 0xFF. Two EDHOC connection identifiers are called "equivalent" if anduse ofonly if, by applying the conversion above, they both result in therequested entries. Expert needs to make suresame OSCORE Sender/Recipient ID. For example, thevalues of algorithmstwo EDHOC connection identifiers with CBOR encoding 0x0A (numeric) and 0x410A (byte- valued) aretaken fromequivalent since they both result in theright registry, when that's required. Expert should consider requestingsame OSCORE Sender/Recipient ID 0x0A. When EDHOC is used to establish anopinion onOSCORE security context, thecorrectness of registered parameters from relevant IETF working groups. Encodings that do not meet these objective of clarityconnection identifiers C_I andcompleteness should not be registered. * Experts should take into account the expected usage of fields when approving point assignment. The length of the encoded value shouldC_R MUST NOT beweighed against how many code pointsequivalent. Furthermore, in case ofthat length are left, the sizemultiple OSCORE security contexts with potentially different endpoints, to facilitate retrieval ofdevice it will be used on, andthenumber of code points leftcorrect OSCORE security context, an endpoint SHOULD select an EDHOC connection identifier thatencodewhen converted tothat size. * Specifications are recommended. When specifications areOSCORE Recipient ID does notprovided,coincide with its other Recipient IDs. A.2. Deriving thedescription provided needsOSCORE Security Context This section specifies how tohave sufficient informationuse EDHOC output toverifyderive thepoints above. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key wordsOSCORE security context. After successful processing of EDHOC message_3, Client and Server derive Security Context parameters foruse in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC5116] McGrew, D., "An InterfaceOSCORE as follows (see Section 3.2 of [RFC8613]): o The Master Secret andAlgorithmsMaster Salt are derived by using the EDHOC- Exporter interface, see Section 4.1. The EDHOC Exporter Labels forAuthenticated Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, <https://www.rfc-editor.org/info/rfc5116>. [RFC5869] Krawczyk, H.deriving the OSCORE Master Secret andP. Eronen, "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)", RFC 5869, DOI 10.17487/RFC5869, May 2010, <https://www.rfc-editor.org/info/rfc5869>. [RFC6090] McGrew, D., Igoe, K.,the OSCORE Master Salt, are "OSCORE Master Secret" andM. Salter, "Fundamental Elliptic Curve Cryptography Algorithms", RFC 6090, DOI 10.17487/RFC6090, February 2011, <https://www.rfc-editor.org/info/rfc6090>. [RFC6979] Pornin, T., "Deterministic Usage"OSCORE Master Salt", respectively. The context parameter is h'' (0x40), the empty CBOR byte string. By default, key_length is the key length (in bytes) of theDigital Signature Algorithm (DSA) and Elliptic Curve Digital Signatureapplication AEAD Algorithm(ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August 2013, <https://www.rfc-editor.org/info/rfc6979>. [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, <https://www.rfc-editor.org/info/rfc7252>. [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curvesof the selected cipher suite forSecurity", RFC 7748, DOI 10.17487/RFC7748, January 2016, <https://www.rfc-editor.org/info/rfc7748>. [RFC8949] Bormann, C.the EDHOC session. Also by default, salt_length has value 8. The Initiator andP. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020, <https://www.rfc-editor.org/info/rfc8949>. [RFC7959] Bormann, C.Responder MAY agree out-of-band on a longer key_length than the default andZ. Shelby, Ed., "Block-Wise Transfers inon a different salt_length. Master Secret = EDHOC-Exporter( "OSCORE Master Secret", h'', key_length ) Master Salt = EDHOC-Exporter( "OSCORE Master Salt", h'', salt_length ) o The AEAD Algorithm is the application AEAD algorithm of the selected cipher suite for the EDHOC session. o The HKDF Algorithm is the one based on the application hash algorithm of the selected cipher suite for theConstrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016, <https://www.rfc-editor.org/info/rfc7959>. [RFC8174] Leiba, B., "AmbiguityEDHOC session. For example, if SHA-256 is the application hash algorithm ofUppercase vs Lowercasethe selected ciphersuite, HKDF SHA-256 is used as HKDF Algorithm inRFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/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.,the OSCORE Security Context. o In case the Client is Initiator andC. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR)the Server is Responder, the Client's OSCORE Sender ID andJSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019, <https://www.rfc-editor.org/info/rfc8610>. [RFC8613] Selander, G., Mattsson, J., Palombini, F.,the Server's OSCORE Sender ID are determined from the EDHOC connection identifiers C_R andL. Seitz, "Object SecurityC_I forConstrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, <https://www.rfc-editor.org/info/rfc8613>. [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D.,the EDHOC session, respectively, by applying the conversion in Appendix A.1. The reverse applies in case the Client is the Responder andJC. Zúñiga, "SCHC: Generic Framework for Static Context Header Compressionthe Server is the Initiator. Client andFragmentation", RFC 8724, DOI 10.17487/RFC8724, April 2020, <https://www.rfc-editor.org/info/rfc8724>. [RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR) Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020, <https://www.rfc-editor.org/info/rfc8742>. [I-D.ietf-cose-rfc8152bis-struct] Schaad, J., "CBOR Object SigningServer use the parameters above to establish an OSCORE Security Context, as per Section 3.2.1 of [RFC8613]. From then on, Client and Server retrieve the OSCORE protocol state using the Recipient ID, andEncryption (COSE): Structuresoptionally other transport information such as the 5-tuple. A.3. Transferring EDHOC over CoAP This section specifies one instance for how EDHOC can be transferred as an exchange of CoAP [RFC7252] messages. CoAP is a reliable transport that can preserve packet ordering andProcess", Workhandle message duplication. CoAP can also perform fragmentation and protect against denial of service attacks. According to this specification, EDHOC messages are carried inProgress, Internet-Draft, draft-ietf-cose-rfc8152bis-struct-15, 1 February 2021, <https://www.ietf.org/archive/id/draft-ietf-cose- rfc8152bis-struct-15.txt>. [I-D.ietf-cose-rfc8152bis-algs] Schaad, J., "CBOR Object SigningConfirmable messages, which is beneficial especially if fragmentation is used. By default, the CoAP client is the Initiator andEncryption (COSE): Initial Algorithms", Workthe CoAP server is the Responder, but the roles SHOULD be chosen to protect the most sensitive identity, see Section 7. According to this specification, EDHOC is transferred inProgress, Internet-Draft, draft-ietf-cose-rfc8152bis-algs-12, 24 September 2020, <https://www.ietf.org/archive/id/draft-ietf-cose- rfc8152bis-algs-12.txt>. [I-D.ietf-cose-x509] Schaad, J., "CBOR Object SigningPOST requests andEncryption (COSE): Header parameters2.04 (Changed) responses to the Uri-Path: "/.well-known/edhoc". An application may define its own path that can be discovered, e.g., using resource directory [I-D.ietf-core-resource-directory]. 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 resource forcarrying and referencing X.509 certificates", WorkEDHOC. EDHOC message_2 or the EDHOC error message is sent from the server to the client inProgress, Internet-Draft, draft- ietf-cose-x509-08, 14 December 2020, <https://www.ietf.org/internet-drafts/draft-ietf-cose- x509-08.txt>. [I-D.ietf-core-echo-request-tag] Amsüss, C., Mattsson, J. P., and G. Selander, "CoAP: Echo, Request-Tag, and Token Processing", Workthe payload of a 2.04 (Changed) 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. If needed, an EDHOC error message is sent from the server to the client inProgress, Internet-Draft, draft-ietf-core-echo-request-tag-12, 1 February 2021, <https://www.ietf.org/archive/id/draft- ietf-core-echo-request-tag-12.txt>. [I-D.ietf-lake-reqs] Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia- Carrillo, "Requirements forthe payload of aLightweight AKE for OSCORE", Work2.04 (Changed) response. Alternatively, if EDHOC message_4 is used, it is sent from the server to the client inProgress, Internet-Draft, draft-ietf-lake-reqs-04, 8 June 2020, <https://www.ietf.org/archive/id/draft-ietf- lake-reqs-04.txt>. 10.2. Informative References [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, <https://www.rfc-editor.org/info/rfc7228>. [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014, <https://www.rfc-editor.org/info/rfc7258>. [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. Kivinen, "Internet Key Exchange Protocol Version 2 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 2014, <https://www.rfc-editor.org/info/rfc7296>. [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>. [RFC8937] Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N.,the payload of a 2.04 (Changed) response analogously to message_2. In order to correlate a message received from a client to a message previously sent by the server, messages sent by the client are prepended with the CBOR serialization of the connection identifier which the server has chosen. This applies independently of if the CoAP server is Responder or Initiator. For the default case when the server is Responder, the prepended connection identifier is C_R, andC. Wood, "Randomness Improvements for Security Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020, <https://www.rfc-editor.org/info/rfc8937>. [I-D.ietf-core-resource-directory] Amsüss, C., Shelby, Z., Koster, M., Bormann, C.,C_I if the server is Initiator. If message_1 is sent to the server, the CBOR simple value "null" (0xf6) is sent in its place (given that the server has not selected C_R yet). These identifiers are encoded in CBOR andP. V. D. Stok, "CoRE Resource Directory", Workthus self-delimiting. They are sent inProgress, Internet-Draft, draft-ietf-core-resource-directory-28, 7 March 2021, <https://www.ietf.org/archive/id/draft-ietf- core-resource-directory-28.txt>. [I-D.ietf-lwig-security-protocol-comparison] Mattsson, J. P., Palombini, F.,front of the actual EDHOC message, andM. Vucinic, "Comparisononly the part of the body following the identifier is used for EDHOC processing. Consequently, the application/edhoc media type does not apply to these messages; their media type is unnamed. An example of a successful EDHOC exchange using CoAPSecurity Protocols", Workis shown inProgress, Internet-Draft, draft-ietf-lwig-security-protocol- comparison-05, 2 November 2020, <https://www.ietf.org/archive/id/draft-ietf-lwig-security- protocol-comparison-05.txt>. [I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H.,Figure 9. In this case the CoAP Token enables correlation on the Initiator side, andN. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", Workthe prepended C_R enables correlation on the Responder (server) side. Client Server | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | Payload: null, EDHOC message_1 | | |<---------+ Header: 2.04 Changed | 2.04 | Content-Format: application/edhoc | | Payload: EDHOC message_2 | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | Payload: C_R, EDHOC message_3 | | |<---------+ Header: 2.04 Changed | 2.04 | | | Figure 9: Transferring EDHOC inProgress, Internet-Draft, draft-ietf-tls- dtls13-43, 30 April 2021, <https://www.ietf.org/internet- drafts/draft-ietf-tls-dtls13-43.txt>. [I-D.selander-ace-ake-authz] Selander, G., Mattsson, J. P., Vucinic, M., Richardson, M.,CoAP when the Initiator is CoAP Client The exchange in Figure 9 protects the client identity against active attackers andA. Schellenbaum, "Lightweight Authorization for Authenticated Key Exchange.", Workthe server identity against passive attackers. An alternative exchange that protects the server identity against active attackers and the client identity against passive attackers is shown inProgress, Internet- Draft, draft-selander-ace-ake-authz-02, 2 November 2020, <https://www.ietf.org/archive/id/draft-selander-ace-ake- authz-02.txt>. [I-D.ietf-core-oscore-edhoc] Palombini, F., Tiloca, M., Hoeglund, R., Hristozov, S.,Figure 10. In this case the CoAP Token enables the Responder to correlate message_2 andG. Selander, "Combiningmessage_3, and the prepended C_I enables correlation on the Initiator (server) side. If EDHOC message_4 is used, C_I is prepended, andOSCORE", Workit is transported with CoAP inProgress, Internet-Draft, draft-ietf-core-oscore-edhoc-00, 1 April 2021, <https://www.ietf.org/internet-drafts/draft- ietf-core-oscore-edhoc-00.txt>. [I-D.ietf-cose-cbor-encoded-cert] Raza, S., Höglund, J., Selander, G., Mattsson, J. P., and M. Furuhed, "CBOR Encoded X.509 Certificates (C509 Certificates)", Workthe payload of a POST request with a 2.04 (Changed) response. Client Server | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | |<---------+ Header: 2.04 Changed | 2.04 | Content-Format: application/edhoc | | Payload: EDHOC message_1 | | +--------->| Header: POST (Code=0.02) | POST | Uri-Path: "/.well-known/edhoc" | | Payload: C_I, EDHOC message_2 | | |<---------+ Header: 2.04 Changed | 2.04 | Content-Format: application/edhoc | | Payload: EDHOC message_3 | | Figure 10: Transferring EDHOC inProgress, Internet-Draft, draft- ietf-cose-cbor-encoded-cert-00, 28 April 2021, <https://www.ietf.org/archive/id/draft-ietf-cose-cbor- encoded-cert-00.txt>. [I-D.mattsson-cfrg-det-sigs-with-noise] Mattsson, J. P., Thormarker, E., and S. Ruohomaa, "Deterministic ECDSA and EdDSA SignaturesCoAP when the Initiator is CoAP Server To protect against denial-of-service attacks, the CoAP server MAY respond to the first POST request withAdditional Randomness", Worka 4.01 (Unauthorized) containing an Echo option [I-D.ietf-core-echo-request-tag]. This forces the initiator to demonstrate its reachability at its apparent network address. If message fragmentation is needed, the EDHOC messages may be fragmented using the CoAP Block-Wise Transfer mechanism [RFC7959]. EDHOC does not restrict how error messages are transported with CoAP, as long as the appropriate error message can to be transported inProgress, Internet-Draft, draft- mattsson-cfrg-det-sigs-with-noise-02, 11 March 2020, <https://www.ietf.org/archive/id/draft-mattsson-cfrg-det- sigs-with-noise-02.txt>. [SP-800-56A] Barker, E., Chen, L., Roginsky, A., Vassilev, A.,response to a message that failed (see Section 6). A.3.1. Transferring EDHOC andR. Davis, "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography", NIST Special Publication 800-56A Revision 3, April 2018, <https://doi.org/10.6028/NIST.SP.800-56Ar3>. [SECG] "StandardsOSCORE over CoAP A method forEfficient Cryptography 1 (SEC 1)", May 2009, <https://www.secg.org/sec1-v2.pdf>. [SIGMA] Krawczyk, H., "SIGMA - The 'SIGn-and-MAc' Approach to Authenticated Diffie-Hellmancombining EDHOC andIts UseOSCORE protocols inthe IKE- Protocols (Long version)", June 2003, <http://webee.technion.ac.il/~hugo/sigma-pdf.pdf>. [CNSA] (Placeholder), ., "Commercial Nationaltwo round-trips is specified in [I-D.ietf-core-oscore-edhoc]. When using EDHOC over CoAP for establishing an OSCORE SecurityAlgorithm Suite", August 2015, <https://apps.nsa.gov/iaarchive/programs/iad-initiatives/ cnsa-suite.cfm>. [Norrman20] Norrman, K., Sundararajan, V., and A. Bruni, "Formal AnalysisContext, EDHOC error messages sent as CoAP responses MUST be error responses, i.e., they MUST specify a CoAP error response code. In particular, it is RECOMMENDED that such error responses have response code either 4.00 (Bad Request) in case of client error (e.g., due to a malformed EDHOCKey Establishment for Constrained IoT Devices", September 2020, <https://arxiv.org/abs/2007.11427>. [Bruni18] Bruni, A., Sahl Jørgensen, T., Grønbech Petersen, T., and C. Schürmann, "Formal Verificationmessage), or 5.00 (Internal Server Error) in case ofEphemeral Diffie- Hellman Over COSE (EDHOC)", November 2018, <https://www.springerprofessional.de/en/formal- verification-of-ephemeral-diffie-hellman-over-cose- edhoc/16284348>. [CborMe] Bormann, C., "CBOR Playground", May 2018, <http://cbor.me/>.server error (e.g., due to failure in deriving EDHOC key material). AppendixA.B. Compact Representation As described in Section 4.2 of [RFC6090] the x-coordinate of an elliptic curve public key is a suitable representative for the entire point whenever scalar multiplication is used as a one-way function. One example is ECDH with compact output, where only the x-coordinate of the computed value is used as the shared secret. This section defines a format for compact representation based on the Elliptic-Curve-Point-to-Octet-String Conversion defined in Section 2.3.3 of [SECG]. Using the notation from [SECG], the output is an octet string of length ceil( (log2 q) / 8 ). See [SECG] for a definition of q, M, X, xp, and ~yp. The steps in Section 2.3.3 of [SECG] are replaced by: 1. Convert the field element xp to an octet string X of length ceil( (log2 q) / 8 ) octets using the conversion routine specified in Section 2.3.5 of [SECG]. 2. Output M = X The encoding of the point at infinity is not supported. Compact representation does not change any requirements on validation. If a y-coordinate is required for validation or compatibily with APIs the value ~yp SHALL be set to zero. For such use, the compact representation can be transformed into the SECG point compressed format by prepending it with the single byte 0x02 (i.e. M = 0x02 || X). Using compact representation have some security benefits. An implementation does not need to check that the point is not the point at infinity (the identity element). Similarly, as not even the sign of the y-coordinate is encoded, compact representation trivially avoids so called "benign malleability" attacks where an attacker changes the sign, see [SECG]. AppendixB.C. Use of CBOR, CDDL and COSE in EDHOC This Appendix is intended to simplify for implementors not familiar with CBOR [RFC8949], CDDL [RFC8610], COSE [I-D.ietf-cose-rfc8152bis-struct], and HKDF [RFC5869].B.1.C.1. CBOR and CDDL The Concise Binary Object Representation (CBOR) [RFC8949] is a data format designed for small code size and small message size. CBOR builds on the JSON data model but extends it by e.g. encoding binary data directly without base64 conversion. In addition to the binary CBOR encoding, CBOR also has a diagnostic notation that is readable and editable by humans. The Concise Data Definition Language (CDDL) [RFC8610] provides a way to express structures for protocol messages and APIs that use CBOR. [RFC8610] also extends the diagnostic notation. CBOR data items are encoded to or decoded from byte strings using a type-length-value encoding scheme, where the three highest order bits of the initial byte contain information about the major type. CBOR supports several different types of data items, in addition to integers (int, uint), simple values (e.g. null), byte strings (bstr), and text strings (tstr), CBOR also supports arrays [] of data items, maps {} of pairs of data items, and sequences [RFC8742] of data items. Some examples are given below. For a complete specification and more examples, see [RFC8949] and [RFC8610]. We recommend implementors to get used to CBOR by using the CBOR playground [CborMe]. Diagnostic Encoded Type ------------------------------------------------------------------ 1 0x01 unsigned integer 24 0x1818 unsigned integer -24 0x37 negative integer -25 0x3818 negative integer null 0xf6 simple value h'12cd' 0x4212cd byte string '12cd' 0x4431326364 byte string "12cd" 0x6431326364 text string { 4 : h'cd' } 0xa10441cd map << 1, 2, null >> 0x430102f6 byte string [ 1, 2, null ] 0x830102f6 array ( 1, 2, null ) 0x0102f6 sequence 1, 2, null 0x0102f6 sequence ------------------------------------------------------------------B.2.C.2. CDDL Definitions This sections compiles the CDDL definitions for ease of reference.bstr_identifier = bstr / intsuite = int SUITES_R : [ supported : 2* suite ] / suite message_1 = (? C_1 : null, METHOD_CORRMETHOD : int, SUITES_I : [ selected : suite, supported : 2* suite ] / suite, G_X : bstr, C_I :bstr_identifier,bstr / int, ? EAD ; EAD_1 ) message_2 = ( data_2, CIPHERTEXT_2 : bstr, ) data_2 = (? C_I : bstr_identifier,G_Y : bstr, C_R :bstr_identifier,bstr / int, ) message_3 = (data_3,CIPHERTEXT_3 : bstr, )data_3 = ( ? C_R : bstr_identifier, )message_4 = (data_4, CIPHERTEXT_4 : bstr, ) data_4 = ( ? C_ICIPHERTEXT_4 :bstr_identifier,bstr, ) error = (? C_x : bstr_identifier,ERR_CODE : int, ERR_INFO : any ) info = [ edhoc_aead_id : int / tstr, transcript_hash : bstr, label : tstr, length : uint ]B.3.C.3. COSE CBOR Object Signing and Encryption (COSE) [I-D.ietf-cose-rfc8152bis-struct] describes how to create and process signatures, message authentication codes, and encryption using CBOR. COSE builds on JOSE, but is adapted to allow more efficient processing in constrained devices. EDHOC makes use of COSE_Key, COSE_Encrypt0, and COSE_Sign1 objects. AppendixC.D. Test VectorsNote: TheNOTE 0. These test vectors arenot updated to version -07compatible with versions -05 and -06 of thedraft. More changes affecting the test vectors are anticipated for -08.specification. This appendix provides detailed test vectors to ease implementation and ensure interoperability.The test vectors in this version are compatible with versions -05 and -06 of the specification.In addition to hexadecimal, all CBOR data items and sequences are given in CBOR diagnostic notation. The test vectors use the default mapping to CoAP where the Initiator acts as CoAP client (this means that corr = 1). A more extensive test vector suite covering more combinations of authentication method used between Initiator and Responder and related code to generate them can be found at https://github.com/ lake-wg/edhoc/tree/master/test-vectors-05. NOTE 1. In the previous and current test vectors the same name is used for certain byte strings and their CBOR bstr encodings. For example the transcript hash TH_2 is used to denote both the output of the hash function and the input into the key derivation function, whereas the latter is a CBOR bstr encoding of the former. Some attempts are made to clarify that in this Appendix (e.g. using "CBOR encoded"/"CBOR unencoded"). NOTE 2. If not clear from the context, remember that CBOR sequences and CBOR arrays assume CBOR encoded data items as elements.C.1.D.1. Test Vectors for EDHOC Authenticated with Signature Keys (x5t) EDHOC with signature authentication and X.509 certificates is used. In this test vector, the hash value 'x5t' is used to identify the certificate. The optional C_1 in message_1 is omitted. No external authorization data is sent in the message exchange. method (Signature Authentication) 0 CoAP is used as transport and the Initiator acts as CoAP client: corr (the Initiator can correlate message_1 and message_2) 1 From there, METHOD_CORR has the following value: METHOD_CORR (4 * method + corr) (int) 1 The Initiator indicates only one cipher suite in the (potentially truncated) list of cipher suites. Supported Cipher Suites (1 byte) 00 The Initiator selected the indicated cipher suite. Selected Cipher Suite (int) 0 Cipher suite 0 is supported by both the Initiator and the Responder, see Section3.4. C.1.1.3.6. D.1.1. Message_1 The Initiator generates its ephemeral key pair. X (Initiator's ephemeral private key) (32 bytes) 8f 78 1a 09 53 72 f8 5b 6d 9f 61 09 ae 42 26 11 73 4d 7d bf a0 06 9a 2d f2 93 5b b2 e0 53 bf 35 G_X (Initiator's ephemeral public key, CBOR unencoded) (32 bytes) 89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6 ec 07 6b ba 02 59 d9 04 b7 ec 8b 0c The Initiator chooses a connection identifier C_I: Connection identifier chosen by Initiator (1 byte) 09 Note that since C_I is a byte string in the interval h'00' to h'2f', it is encoded as the corresponding integer subtracted by24 (see bstr_identifier in Section 5.1).24. Thus 0x09 = 09, 9 - 24 = -15, and -15 in CBOR encoding is equal to 0x2e. C_I (1 byte) 2e Since no external authorization data is sent: EAD_1 (0 bytes) The list of supported cipher suites needs to contain the selected cipher suite. The initiator truncates the list of supported cipher suites to one cipher suite only. In this case there is only one supported cipher suite indicated, 00. Because one single selected cipher suite is conveyed, it is encoded as an int instead of an array: SUITES_I (int) 0 message_1 is constructed as the CBOR Sequence of the data items above encoded as CBOR. In CBOR diagnostic notation: message_1 = ( 1, 0, h'898FF79A02067A16EA1ECCB90FA52246F5AA4DD6EC076BBA0259D904B7EC8B0C', -15 ) Which as a CBOR encoded data item is: message_1 (CBOR Sequence) (37 bytes) 01 00 58 20 89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6 ec 07 6b ba 02 59 d9 04 b7 ec 8b 0c 2eC.1.2.D.1.2. Message_2 Since METHOD_CORR mod 4 equals 1, C_I is omitted from data_2. The Responder generates the following ephemeral key pair. Y (Responder's ephemeral private key) (32 bytes) fd 8c d8 77 c9 ea 38 6e 6a f3 4f f7 e6 06 c4 b6 4c a8 31 c8 ba 33 13 4f d4 cd 71 67 ca ba ec da G_Y (Responder's ephemeral public key, CBOR unencoded) (32 bytes) 71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0 19 52 81 75 4c 5e bc af 30 1e From G_X and Y or from G_Y and X the ECDH shared secret is computed: G_XY (ECDH shared secret) (32 bytes) 2b b7 fa 6e 13 5b c3 35 d0 22 d6 34 cb fb 14 b3 f5 82 f3 e2 e3 af b2 b3 15 04 91 49 5c 61 78 2b The key and nonce for calculating the 'ciphertext' are calculated as follows, as specified in Section 4. HKDF SHA-256 is the HKDF used (as defined by cipher suite 0). PRK_2e = HMAC-SHA-256(salt, G_XY) Salt is the empty byte string. salt (0 bytes) From there, PRK_2e is computed: PRK_2e (32 bytes) ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f d8 2f be b7 99 71 39 4a The Responder's sign/verify key pair is the following: SK_R (Responder's private authentication key) (32 bytes) df 69 27 4d 71 32 96 e2 46 30 63 65 37 2b 46 83 ce d5 38 1b fc ad cd 44 0a 24 c3 91 d2 fe db 94 PK_R (Responder's public authentication key) (32 bytes) db d9 dc 8c d0 3f b7 c3 91 35 11 46 2b b2 38 16 47 7c 6b d8 d6 6e f5 a1 a0 70 ac 85 4e d7 3f d2 Since neither the Initiator nor the Responder authenticates with a static Diffie-Hellman key, PRK_3e2m = PRK_2e PRK_3e2m (32 bytes) ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f d8 2f be b7 99 71 39 4a The Responder chooses a connection identifier C_R. Connection identifier chosen by Responder (1 byte) 00 Note that since C_R is a byte string in the interval h'00' to h'2f', it is encoded as the corresponding integer subtracted by24 (see bstr_identifier in Section 5.1).24. Thus 0x00 = 0, 0 - 24 = -24, and -24 in CBOR encoding is equal to 0x37. C_R (1 byte) 37 Data_2 is constructed as the CBOR Sequence of G_Y and C_R, encoded as CBOR byte strings. The CBOR diagnostic notation is: data_2 = ( h'71a3d599c21da18902a1aea810b2b6382ccd8d5f9bf0195281754c5ebcaf301e', -24 ) Which as a CBOR encoded data item is: data_2 (CBOR Sequence) (35 bytes) 58 20 71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0 19 52 81 75 4c 5e bc af 30 1e 37 From data_2 and message_1, compute the input to the transcript hash TH_2 = H( H(message_1), data_2 ), as a CBOR Sequence of these 2 data items. Input to calculate TH_2 (CBOR Sequence) (72 bytes) 01 00 58 20 89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6 ec 07 6b ba 02 59 d9 04 b7 ec 8b 0c 2e 58 20 71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0 19 52 81 75 4c 5e bc af 30 1e 37 And from there, compute the transcript hash TH_2 = SHA-256( H(message_1), data_2 ) TH_2 (CBOR unencoded) (32 bytes) 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff The Responder's subject name is the empty string: Responder's subject name (text string) "" In this version of the test vectors CRED_R is not a DER encoded X.509 certificate, but a string of random bytes. CRED_R (CBOR unencoded) (100 bytes) c7 88 37 00 16 b8 96 5b db 20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40 6e 86 44 2b 87 ec 3f f2 45 b7 0a 47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e c9 d6 b0 53 4b 71 c2 b4 9e 4b f9 03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b 38 1e 98 db 71 41 08 41 5e 5c 50 db 78 97 4c 27 15 79 b0 16 33 a3 ef 62 71 be 5c 22 5e b2 CRED_R is defined to be the CBOR bstr containing the credential of the Responder. CRED_R (102 bytes) 58 64 c7 88 37 00 16 b8 96 5b db 20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40 6e 86 44 2b 87 ec 3f f2 45 b7 0a 47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e c9 d6 b0 53 4b 71 c2 b4 9e 4b f9 03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b 38 1e 98 db 71 41 08 41 5e 5c 50 db 78 97 4c 27 15 79 b0 16 33 a3 ef 62 71 be 5c 22 5e b2 And because certificates are identified by a hash value with the 'x5t' parameter, ID_CRED_R is the following: ID_CRED_R = { 34 : COSE_CertHash }. In this example, the hash algorithm used is SHA-2 256-bit with hash truncated to 64-bits (value -15). The hash value is calculated over the CBOR unencoded CRED_R. The CBOR diagnostic notation is: ID_CRED_R = { 34: [-15, h'6844078A53F312F5'] } which when encoded as a CBOR map becomes: ID_CRED_R (14 bytes) a1 18 22 82 2e 48 68 44 07 8a 53 f3 12 f5 Since no external authorization data is sent: EAD_2 (0 bytes) The plaintext is defined as the empty string: P_2m (0 bytes) The Enc_structure is defined as follows: [ "Encrypt0", << ID_CRED_R >>, << TH_2, CRED_R >> ], indicating that ID_CRED_R is encoded as a CBOR byte string, and that the concatenation of the CBOR byte strings TH_2 and CRED_R is wrapped as a CBOR bstr. The CBOR diagnostic notation is the following: A_2m = [ "Encrypt0", h'A11822822E486844078A53F312F5', h'5820864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF 5864C788370016B8965BDB2074BFF82E5A20E09BEC21F8406E86442B87EC3FF245B70A 47624DC9CDC6824B2A4C52E95EC9D6B0534B71C2B49E4BF9031500CEE6869979C297BB 5A8B381E98DB714108415E5C50DB78974C271579B01633A3EF6271BE5C225EB2' ] Which encodes to the following byte string to be used as Additional Authenticated Data: A_2m (CBOR-encoded) (163 bytes) 83 68 45 6e 63 72 79 70 74 30 4e a1 18 22 82 2e 48 68 44 07 8a 53 f3 12 f5 58 88 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 58 64 c7 88 37 00 16 b8 96 5b db 20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40 6e 86 44 2b 87 ec 3f f2 45 b7 0a 47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e c9 d6 b0 53 4b 71 c2 b4 9e 4b f9 03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b 38 1e 98 db 71 41 08 41 5e 5c 50 db 78 97 4c 27 15 79 b0 16 33 a3 ef 62 71 be 5c 22 5e b2 info for K_2m is defined as follows in CBOR diagnostic notation: info for K_2m = [ 10, h'864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF', "K_2m", 16 ] Which as a CBOR encoded data item is: info for K_2m (CBOR-encoded) (42 bytes) 84 0a 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 64 4b 5f 32 6d 10 From these parameters, K_2m is computed. Key K_2m is the output of HKDF-Expand(PRK_3e2m, info, L), where L is the length of K_2m, so 16 bytes. K_2m (16 bytes) 80 cc a7 49 ab 58 f5 69 ca 35 da ee 05 be d1 94 info for IV_2m is defined as follows, in CBOR diagnostic notation (10 is the COSE algorithm no. of the AEAD algorithm in the selected cipher suite 0): info for IV_2m = [ 10, h'864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF', "IV_2m", 13 ] Which as a CBOR encoded data item is: info for IV_2m (CBOR-encoded) (43 bytes) 84 0a 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 65 49 56 5f 32 6d 0d From these parameters, IV_2m is computed. IV_2m is the output of HKDF-Expand(PRK_3e2m, info, L), where L is the length of IV_2m, so 13 bytes. IV_2m (13 bytes) c8 1e 1a 95 cc 93 b3 36 69 6e d5 02 55 Finally, COSE_Encrypt0 is computed from the parameters above.*o protected header = CBOR-encoded ID_CRED_R*o external_aad = A_2m*o empty plaintext = P_2m MAC_2 (CBOR unencoded) (8 bytes) fa bb a4 7e 56 71 a1 82 To compute the Signature_or_MAC_2, the key is the private authentication key of the Responder and the message M_2 to be signed = [ "Signature1", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >>, MAC_2 ]. ID_CRED_R is encoded as a CBOR byte string, the concatenation of the CBOR byte strings TH_2 and CRED_R is wrapped as a CBOR bstr, and MAC_2 is encoded as a CBOR bstr. M_2 = [ "Signature1", h'A11822822E486844078A53F312F5', h'5820864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629F F5864C788370016B8965BDB2074BFF82E5A20E09BEC21F8406E86442B87EC3FF245B7 0A47624DC9CDC6824B2A4C52E95EC9D6B0534B71C2B49E4BF9031500CEE6869979C29 7BB5A8B381E98DB714108415E5C50DB78974C271579B01633A3EF6271BE5C225EB2', h'FABBA47E5671A182' ] Which as a CBOR encoded data item is: M_2 (174 bytes) 84 6a 53 69 67 6e 61 74 75 72 65 31 4e a1 18 22 82 2e 48 68 44 07 8a 53 f3 12 f5 58 88 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 58 64 c7 88 37 00 16 b8 96 5b db 20 74 bf f8 2e 5a 20 e0 9b ec 21 f8 40 6e 86 44 2b 87 ec 3f f2 45 b7 0a 47 62 4d c9 cd c6 82 4b 2a 4c 52 e9 5e c9 d6 b0 53 4b 71 c2 b4 9e 4b f9 03 15 00 ce e6 86 99 79 c2 97 bb 5a 8b 38 1e 98 db 71 41 08 41 5e 5c 50 db 78 97 4c 27 15 79 b0 16 33 a3 ef 62 71 be 5c 22 5e b2 48 fa bb a4 7e 56 71 a1 82 Since the method = 0, Signature_or_MAC_2 is a signature. The algorithm with selected cipher suite 0 is Ed25519 and the output is 64 bytes. Signature_or_MAC_2 (CBOR unencoded) (64 bytes) 1f 17 00 6a 98 48 c9 77 cb bd ca a7 57 b6 fd 46 82 c8 17 39 e1 5c 99 37 c2 1c f5 e9 a0 e6 03 9f 54 fd 2a 6c 3a 11 18 f2 b9 d8 eb cd 48 23 48 b9 9c 3e d7 ed 1b d9 80 6c 93 c8 90 68 e8 36 b4 0f CIPHERTEXT_2 is the ciphertext resulting from XOR between plaintext and KEYSTREAM_2 which is derived from TH_2 and the pseudorandom key PRK_2e.*o plaintext = CBOR Sequence of the items ID_CRED_R and Signature_or_MAC_2 encoded as CBOR byte strings, in this order (EAD_2 is empty). The plaintext is the following: P_2e (CBOR Sequence) (80 bytes) a1 18 22 82 2e 48 68 44 07 8a 53 f3 12 f5 58 40 1f 17 00 6a 98 48 c9 77 cb bd ca a7 57 b6 fd 46 82 c8 17 39 e1 5c 99 37 c2 1c f5 e9 a0 e6 03 9f 54 fd 2a 6c 3a 11 18 f2 b9 d8 eb cd 48 23 48 b9 9c 3e d7 ed 1b d9 80 6c 93 c8 90 68 e8 36 b4 0f KEYSTREAM_2 = HKDF-Expand( PRK_2e, info, length ), where length is the length of the plaintext, so 80. info for KEYSTREAM_2 = [ 10, h'864E32B36A7B5F21F19E99F0C66D911E0ACE9972D376D2C2C153C17F8E9629FF', "KEYSTREAM_2", 80 ] Which as a CBOR encoded data item is: info for KEYSTREAM_2 (CBOR-encoded) (50 bytes) 84 0a 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 6b 4b 45 59 53 54 52 45 41 4d 5f 32 18 50 From there, KEYSTREAM_2 is computed: KEYSTREAM_2 (80 bytes) ae ea 8e af 50 cf c6 70 09 da e8 2d 8d 85 b0 e7 60 91 bf 0f 07 0b 79 53 6c 83 23 dc 3d 9d 61 13 10 35 94 63 f4 4b 12 4b ea b3 a1 9d 09 93 82 d7 30 80 17 f4 92 62 06 e4 f5 44 9b 9f c9 24 bc b6 bd 78 ec 45 0a 66 83 fb 8a 2f 5f 92 4f c4 40 4f Using the parameters above, the ciphertext CIPHERTEXT_2 can be computed: CIPHERTEXT_2 (CBOR unencoded) (80 bytes) 0f f2 ac 2d 7e 87 ae 34 0e 50 bb de 9f 70 e8 a7 7f 86 bf 65 9f 43 b0 24 a7 3e e9 7b 6a 2b 9c 55 92 fd 83 5a 15 17 8b 7c 28 af 54 74 a9 75 81 48 64 7d 3d 98 a8 73 1e 16 4c 9c 70 52 81 07 f4 0f 21 46 3b a8 11 bf 03 97 19 e7 cf fa a7 f2 f4 40 message_2 is the CBOR Sequence of data_2 and CIPHERTEXT_2, in this order: message_2 = ( data_2, h'0FF2AC2D7E87AE340E50BBDE9F70E8A77F86BF659F43B024A73EE97B6A2B9C5592FD 835A15178B7C28AF5474A9758148647D3D98A8731E164C9C70528107F40F21463BA811 BF039719E7CFFAA7F2F440' ) Which as a CBOR encoded data item is: message_2 (CBOR Sequence) (117 bytes) 58 20 71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0 19 52 81 75 4c 5e bc af 30 1e 37 58 50 0f f2 ac 2d 7e 87 ae 34 0e 50 bb de 9f 70 e8 a7 7f 86 bf 65 9f 43 b0 24 a7 3e e9 7b 6a 2b 9c 55 92 fd 83 5a 15 17 8b 7c 28 af 54 74 a9 75 81 48 64 7d 3d 98 a8 73 1e 16 4c 9c 70 52 81 07 f4 0f 21 46 3b a8 11 bf 03 97 19 e7 cf fa a7 f2 f4 40C.1.3.D.1.3. Message_3 Since corr equals 1, C_R is not omitted from data_3. The Initiator's sign/verify key pair is the following: SK_I (Initiator's private authentication key) (32 bytes) 2f fc e7 a0 b2 b8 25 d3 97 d0 cb 54 f7 46 e3 da 3f 27 59 6e e0 6b 53 71 48 1d c0 e0 12 bc 34 d7 PK_I (Responder's public authentication key) (32 bytes) 38 e5 d5 45 63 c2 b6 a4 ba 26 f3 01 5f 61 bb 70 6e 5c 2e fd b5 56 d2 e1 69 0b 97 fc 3c 6d e1 49 HKDF SHA-256 is the HKDF used (as defined by cipher suite 0). PRK_4x3m = HMAC-SHA-256 (PRK_3e2m, G_IY) PRK_4x3m (32 bytes) ec 62 92 a0 67 f1 37 fc 7f 59 62 9d 22 6f bf c4 e0 68 89 49 f6 62 a9 7f d8 2f be b7 99 71 39 4a data 3 is equal to C_R. data_3 (CBOR Sequence) (1 byte) 37 From data_3, CIPHERTEXT_2, and TH_2, compute the input to the transcript hash TH_3 = H( H(TH_2 , CIPHERTEXT_2), data_3), as a CBOR Sequence of 2 data items. Input to calculate TH_3 (CBOR Sequence) (117 bytes) 58 20 86 4e 32 b3 6a 7b 5f 21 f1 9e 99 f0 c6 6d 91 1e 0a ce 99 72 d3 76 d2 c2 c1 53 c1 7f 8e 96 29 ff 58 50 0f f2 ac 2d 7e 87 ae 34 0e 50 bb de 9f 70 e8 a7 7f 86 bf 65 9f 43 b0 24 a7 3e e9 7b 6a 2b 9c 55 92 fd 83 5a 15 17 8b 7c 28 af 54 74 a9 75 81 48 64 7d 3d 98 a8 73 1e 16 4c 9c 70 52 81 07 f4 0f 21 46 3b a8 11 bf 03 97 19 e7 cf fa a7 f2 f4 40 37 And from there, compute the transcript hash TH_3 = SHA-256( H(TH_2 , CIPHERTEXT_2), data_3) TH_3 (CBOR unencoded) (32 bytes) f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 The Initiator's subject name is the empty string: Initiator's subject name (text string) "" In this version of the test vectors CRED_I is not a DER encoded X.509 certificate, but a string of random bytes. CRED_I (CBOR unencoded) (101 bytes) 54 13 20 4c 3e bc 34 28 a6 cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce 7e c6 56 1e 52 43 3a a5 5e 71 f1 fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1 76 60 88 09 84 49 cb 84 8f fc 79 5f 88 af c4 9c be 8a fd d1 ba 00 9f 21 67 5e 8f 6c 77 a4 a2 c3 01 95 60 1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44 48 65 02 ff 7b dd a6 CRED_I is defined to be the CBOR bstr containing the credential of the Initiator. CRED_I (103 bytes) 58 65 54 13 20 4c 3e bc 34 28 a6 cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce 7e c6 56 1e 52 43 3a a5 5e 71 f1 fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1 76 60 88 09 84 49 cb 84 8f fc 79 5f 88 af c4 9c be 8a fd d1 ba 00 9f 21 67 5e 8f 6c 77 a4 a2 c3 01 95 60 1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44 48 65 02 ff 7b dd a6 And because certificates are identified by a hash value with the 'x5t' parameter, ID_CRED_I is the following: ID_CRED_I = { 34 : COSE_CertHash }. In this example, the hash algorithm used is SHA-2 256-bit with hash truncated to 64-bits (value -15). The hash value is calculated over the CBOR unencoded CRED_I. ID_CRED_I = { 34: [-15, h'705D5845F36FC6A6'] } which when encoded as a CBOR map becomes: ID_CRED_I (14 bytes) a1 18 22 82 2e 48 70 5d 58 45 f3 6f c6 a6 Since no external authorization data is exchanged: EAD_3 (0 bytes) The plaintext of the COSE_Encrypt is the empty string: P_3m (0 bytes) The associated data is the following: [ "Encrypt0", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >> ]. A_3m (CBOR-encoded) (164 bytes) 83 68 45 6e 63 72 79 70 74 30 4e a1 18 22 82 2e 48 70 5d 58 45 f3 6f c6 a6 58 89 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 58 65 54 13 20 4c 3e bc 34 28 a6 cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce 7e c6 56 1e 52 43 3a a5 5e 71 f1 fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1 76 60 88 09 84 49 cb 84 8f fc 79 5f 88 af c4 9c be 8a fd d1 ba 00 9f 21 67 5e 8f 6c 77 a4 a2 c3 01 95 60 1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44 48 65 02 ff 7b dd a6 Info for K_3m is computed as follows: info for K_3m = [ 10, h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60', "K_3m", 16 ] Which as a CBOR encoded data item is: info for K_3m (CBOR-encoded) (42 bytes) 84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 64 4b 5f 33 6d 10 From these parameters, K_3m is computed. Key K_3m is the output of HKDF-Expand(PRK_4x3m, info, L), where L is the length of K_2m, so 16 bytes. K_3m (16 bytes) 83 a9 c3 88 02 91 2e 7f 8f 0d 2b 84 14 d1 e5 2c Nonce IV_3m is the output of HKDF-Expand(PRK_4x3m, info, L), where L = 13 bytes. Info for IV_3m is defined as follows: info for IV_3m = [ 10, h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60', "IV_3m", 13 ] Which as a CBOR encoded data item is: info for IV_3m (CBOR-encoded) (43 bytes) 84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 65 49 56 5f 33 6d 0d From these parameters, IV_3m is computed: IV_3m (13 bytes) 9c 83 9c 0e e8 36 42 50 5a 8e 1c 9f b2 MAC_3 is the 'ciphertext' of the COSE_Encrypt0: MAC_3 (CBOR unencoded) (8 bytes) 2f a1 e3 9e ae 7d 5f 8d Since the method = 0, Signature_or_MAC_3 is a signature. The algorithm with selected cipher suite 0 is Ed25519.*o The message M_3 to be signed = [ "Signature1", << ID_CRED_I >>, << TH_3, CRED_I >>, MAC_3 ], i.e. ID_CRED_I encoded as CBOR bstr, the concatenation of the CBOR byte strings TH_3 and CRED_I wrapped as a CBOR bstr, and MAC_3 encoded as a CBOR bstr.*o The signing key is the private authentication key of the Initiator. M_3 = [ "Signature1", h'A11822822E48705D5845F36FC6A6', h'5820F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB6 058655413204C3EBC3428A6CF57E24C9DEF59651770449BCE7EC6561E52433AA55E71 F1FA34B22A9CA4A1E12924EAE1D1766088098449CB848FFC795F88AFC49CBE8AFDD1B A009F21675E8F6C77A4A2C30195601F6F0A0852978BD43D28207D44486502FF7BDD A6', h'2FA1E39EAE7D5F8D'] Which as a CBOR encoded data item is: M_3 (175 bytes) 84 6a 53 69 67 6e 61 74 75 72 65 31 4e a1 18 22 82 2e 48 70 5d 58 45 f3 6f c6 a6 58 89 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 58 65 54 13 20 4c 3e bc 34 28 a6 cf 57 e2 4c 9d ef 59 65 17 70 44 9b ce 7e c6 56 1e 52 43 3a a5 5e 71 f1 fa 34 b2 2a 9c a4 a1 e1 29 24 ea e1 d1 76 60 88 09 84 49 cb 84 8f fc 79 5f 88 af c4 9c be 8a fd d1 ba 00 9f 21 67 5e 8f 6c 77 a4 a2 c3 01 95 60 1f 6f 0a 08 52 97 8b d4 3d 28 20 7d 44 48 65 02 ff 7b dd a6 48 2f a1 e3 9e ae 7d 5f 8d From there, the 64 byte signature can be computed: Signature_or_MAC_3 (CBOR unencoded) (64 bytes) ab 9f 7b bd eb c4 eb f8 a3 d3 04 17 9b cc a3 9d 9c 8a 76 73 65 76 fb 3c 32 d2 fa c7 e2 59 34 e5 33 dc c7 02 2e 4d 68 61 c8 f5 fe cb e9 2d 17 4e b2 be af 0a 59 a4 15 84 37 2f 43 2e 6b f4 7b 04 Finally, the outer COSE_Encrypt0 is computed. The plaintext is the CBOR Sequence of the items ID_CRED_I and the CBOR encoded Signature_or_MAC_3, in this order (EAD_3 is empty). P_3ae (CBOR Sequence) (80 bytes) a1 18 22 82 2e 48 70 5d 58 45 f3 6f c6 a6 58 40 ab 9f 7b bd eb c4 eb f8 a3 d3 04 17 9b cc a3 9d 9c 8a 76 73 65 76 fb 3c 32 d2 fa c7 e2 59 34 e5 33 dc c7 02 2e 4d 68 61 c8 f5 fe cb e9 2d 17 4e b2 be af 0a 59 a4 15 84 37 2f 43 2e 6b f4 7b 04 The Associated data A is the following: Associated data A = [ "Encrypt0", h'', TH_3 ] A_3ae (CBOR-encoded) (45 bytes) 83 68 45 6e 63 72 79 70 74 30 40 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 Key K_3ae is the output of HKDF-Expand(PRK_3e2m, info, L). info is defined as follows: info for K_3ae = [ 10, h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60', "K_3ae", 16 ] Which as a CBOR encoded data item is: info for K_3ae (CBOR-encoded) (43 bytes) 84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 65 4b 5f 33 61 65 10 L is the length of K_3ae, so 16 bytes. From these parameters, K_3ae is computed: K_3ae (16 bytes) b8 79 9f e3 d1 50 4f d8 eb 22 c4 72 62 cd bb 05 Nonce IV_3ae is the output of HKDF-Expand(PRK_3e2m, info, L). info is defined as follows: info for IV_3ae = [ 10, h'F24D18CAFCE374D4E3736329C152AB3AEA9C7C0F650C3070B6F51E68E2AEBB60', "IV_3ae", 13 ] Which as a CBOR encoded data item is: info for IV_3ae (CBOR-encoded) (44 bytes) 84 0a 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 66 49 56 5f 33 61 65 0d L is the length of IV_3ae, so 13 bytes. From these parameters, IV_3ae is computed: IV_3ae (13 bytes) 74 c7 de 41 b8 4a 5b b7 19 0a 85 98 dc Using the parameters above, the 'ciphertext' CIPHERTEXT_3 can be computed: CIPHERTEXT_3 (CBOR unencoded) (88 bytes) f5 f6 de bd 82 14 05 1c d5 83 c8 40 96 c4 80 1d eb f3 5b 15 36 3d d1 6e bd 85 30 df dc fb 34 fc d2 eb 6c ad 1d ac 66 a4 79 fb 38 de aa f1 d3 0a 7e 68 17 a2 2a b0 4f 3d 5b 1e 97 2a 0d 13 ea 86 c6 6b 60 51 4c 96 57 ea 89 c5 7b 04 01 ed c5 aa 8b bc ab 81 3c c5 d6 e7 From the parameter above, message_3 is computed, as the CBOR Sequence of the following CBOR encoded data items: (C_R, CIPHERTEXT_3). message_3 = ( -24, h'F5F6DEBD8214051CD583C84096C4801DEBF35B15363DD16EBD8530DFDCFB34FCD2EB 6CAD1DAC66A479FB38DEAAF1D30A7E6817A22AB04F3D5B1E972A0D13EA86C66B60514C 9657EA89C57B0401EDC5AA8BBCAB813CC5D6E7' ) Which encodes to the following byte string: message_3 (CBOR Sequence) (91 bytes) 37 58 58 f5 f6 de bd 82 14 05 1c d5 83 c8 40 96 c4 80 1d eb f3 5b 15 36 3d d1 6e bd 85 30 df dc fb 34 fc d2 eb 6c ad 1d ac 66 a4 79 fb 38 de aa f1 d3 0a 7e 68 17 a2 2a b0 4f 3d 5b 1e 97 2a 0d 13 ea 86 c6 6b 60 51 4c 96 57 ea 89 c5 7b 04 01 ed c5 aa 8b bc ab 81 3c c5 d6 e7C.1.4.D.1.4. OSCORE Security Context Derivation From here, the Initiator and the Responder can derive an OSCORE Security Context, using the EDHOC-Exporter interface. From TH_3 and CIPHERTEXT_3, compute the input to the transcript hash TH_4 = H( TH_3, CIPHERTEXT_3 ), as a CBOR Sequence of these 2 data items. Input to calculate TH_4 (CBOR Sequence) (124 bytes) 58 20 f2 4d 18 ca fc e3 74 d4 e3 73 63 29 c1 52 ab 3a ea 9c 7c 0f 65 0c 30 70 b6 f5 1e 68 e2 ae bb 60 58 58 f5 f6 de bd 82 14 05 1c d5 83 c8 40 96 c4 80 1d eb f3 5b 15 36 3d d1 6e bd 85 30 df dc fb 34 fc d2 eb 6c ad 1d ac 66 a4 79 fb 38 de aa f1 d3 0a 7e 68 17 a2 2a b0 4f 3d 5b 1e 97 2a 0d 13 ea 86 c6 6b 60 51 4c 96 57 ea 89 c5 7b 04 01 ed c5 aa 8b bc ab 81 3c c5 d6 e7 And from there, compute the transcript hash TH_4 = SHA-256(TH_3 , CIPHERTEXT_4) TH_4 (CBOR unencoded) (32 bytes) 3b 69 a6 7f ec 7e 73 6c c1 a9 52 6c da 00 02 d4 09 f5 b9 ea 0a 2b e9 60 51 a6 e3 0d 93 05 fd 51 The Master Secret and Master Salt are derived as follows: Master Secret = EDHOC-Exporter( "OSCORE Master Secret", 16 ) = EDHOC- KDF(PRK_4x3m, TH_4, "OSCORE Master Secret", 16) = HKDF-Expand( PRK_4x3m, info_ms, 16 ) Master Salt = EDHOC-Exporter( "OSCORE Master Salt", 8 ) = EDHOC- KDF(PRK_4x3m, TH_4, "OSCORE Master Salt", 8) = HKDF-Expand( PRK_4x3m, info_salt, 8 ) info_ms for OSCORE Master Secret is defined as follows: info_ms = [ 10, h'3B69A67FEC7E736CC1A9526CDA0002D409F5B9EA0A2BE96051A6E30D9305FD51', "OSCORE Master Secret", 16 ] Which as a CBOR encoded data item is: info_ms for OSCORE Master Secret (CBOR-encoded) (58 bytes) 84 0a 58 20 3b 69 a6 7f ec 7e 73 6c c1 a9 52 6c da 00 02 d4 09 f5 b9 ea 0a 2b e9 60 51 a6 e3 0d 93 05 fd 51 74 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 65 63 72 65 74 10 info_salt for OSCORE Master Salt is defined as follows: info_salt = [ 10, h'3B69A67FEC7E736CC1A9526CDA0002D409F5B9EA0A2BE96051A6E30D9305FD51', "OSCORE Master Salt", 8 ] Which as a CBOR encoded data item is: info for OSCORE Master Salt (CBOR-encoded) (56 Bytes) 84 0a 58 20 3b 69 a6 7f ec 7e 73 6c c1 a9 52 6c da 00 02 d4 09 f5 b9 ea 0a 2b e9 60 51 a6 e3 0d 93 05 fd 51 72 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 61 6c 74 08 From these parameters, OSCORE Master Secret and OSCORE Master Salt are computed: OSCORE Master Secret (16 bytes) 96 aa 88 ce 86 5e ba 1f fa f3 89 64 13 2c c4 42 OSCORE Master Salt (8 bytes) 5e c3 ee 41 7c fb ba e9 The client's OSCORE Sender ID is C_R and the server's OSCORE Sender ID is C_I. Client's OSCORE Sender ID (1 byte) 00 Server's OSCORE Sender ID (1 byte) 09 The AEAD Algorithm and the hash algorithm are the application AEAD and hash algorithms in the selected cipher suite. OSCORE AEAD Algorithm (int) 10 OSCORE Hash Algorithm (int) -16C.2.D.2. Test Vectors for EDHOC Authenticated with Static Diffie-Hellman Keys EDHOC with static Diffie-Hellman keys and raw public keys is used. In this test vector, a key identifier is used to identify the raw public key. The optional C_1 in message_1 is omitted. No external authorization data is sent in the message exchange. method (Static DH Based Authentication) 3 CoAP is used as transport and the Initiator acts as CoAP client: corr (the Initiator can correlate message_1 and message_2) 1 From there, METHOD_CORR has the following value: METHOD_CORR (4 * method + corr) (int) 13 The Initiator indicates only one cipher suite in the (potentially truncated) list of cipher suites. Supported Cipher Suites (1 byte) 00 The Initiator selected the indicated cipher suite. Selected Cipher Suite (int) 0 Cipher suite 0 is supported by both the Initiator and the Responder, see Section3.4. C.2.1.3.6. D.2.1. Message_1 The Initiator generates its ephemeral key pair. X (Initiator's ephemeral private key) (32 bytes) ae 11 a0 db 86 3c 02 27 e5 39 92 fe b8 f5 92 4c 50 d0 a7 ba 6e ea b4 ad 1f f2 45 72 f4 f5 7c fa G_X (Initiator's ephemeral public key, CBOR unencoded) (32 bytes) 8d 3e f5 6d 1b 75 0a 43 51 d6 8a c2 50 a0 e8 83 79 0e fc 80 a5 38 a4 44 ee 9e 2b 57 e2 44 1a 7c The Initiator chooses a connection identifier C_I: Connection identifier chosen by Initiator (1 byte) 16 Note that since C_I is a byte string in the interval h'00' to h'2f', it is encoded as the corresponding integer -24 (see bstr_identifier in Section 5.1),24, i.e. 0x16 = 22, 22 - 24 = -2, and -2 in CBOR encoding is equal to 0x21. C_I (1 byte) 21 Since no external authorization data is sent: EAD_1 (0 bytes) Since the list of supported cipher suites needs to contain the selected cipher suite, the initiator truncates the list of supported cipher suites to one cipher suite only, 00. Because one single selected cipher suite is conveyed, it is encoded as an int instead of an array: SUITES_I (int) 0 message_1 is constructed as the CBOR Sequence of the data items above encoded as CBOR. In CBOR diagnostic notation: message_1 = ( 13, 0, h'8D3EF56D1B750A4351D68AC250A0E883790EFC80A538A444EE9E2B57E2441A7C', -2 ) Which as a CBOR encoded data item is: message_1 (CBOR Sequence) (37 bytes) 0d 00 58 20 8d 3e f5 6d 1b 75 0a 43 51 d6 8a c2 50 a0 e8 83 79 0e fc 80 a5 38 a4 44 ee 9e 2b 57 e2 44 1a 7c 21C.2.2.D.2.2. Message_2 Since METHOD_CORR mod 4 equals 1, C_I is omitted from data_2. The Responder generates the following ephemeral key pair. Y (Responder's ephemeral private key) (32 bytes) c6 46 cd dc 58 12 6e 18 10 5f 01 ce 35 05 6e 5e bc 35 f4 d4 cc 51 07 49 a3 a5 e0 69 c1 16 16 9a G_Y (Responder's ephemeral public key, CBOR unencoded) (32 bytes) 52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db fc 33 01 04 70 69 45 1b af 35 From G_X and Y or from G_Y and X the ECDH shared secret is computed: G_XY (ECDH shared secret) (32 bytes) de fc 2f 35 69 10 9b 3d 1f a4 a7 3d c5 e2 fe b9 e1 15 0d 90 c2 5e e2 f0 66 c2 d8 85 f4 f8 ac 4e The key and nonce for calculating the 'ciphertext' are calculated as follows, as specified in Section 4. HKDF SHA-256 is the HKDF used (as defined by cipher suite 0). PRK_2e = HMAC-SHA-256(salt, G_XY) Salt is the empty byte string. salt (0 bytes) From there, PRK_2e is computed: PRK_2e (32 bytes) 93 9f cb 05 6d 2e 41 4f 1b ec 61 04 61 99 c2 c7 63 d2 7f 0c 3d 15 fa 16 71 fa 13 4e 0d c5 a0 4d The Responder's static Diffie-Hellman key pair is the following: R (Responder's private authentication key) (32 bytes) bb 50 1a ac 67 b9 a9 5f 97 e0 ed ed 6b 82 a6 62 93 4f bb fc 7a d1 b7 4c 1f ca d6 6a 07 94 22 d0 G_R (Responder's public authentication key) (32 bytes) a3 ff 26 35 95 be b3 77 d1 a0 ce 1d 04 da d2 d4 09 66 ac 6b cb 62 20 51 b8 46 59 18 4d 5d 9a 32 Since the Responder authenticates with a static Diffie-Hellman key, PRK_3e2m = HKDF-Extract( PRK_2e, G_RX ), where G_RX is the ECDH shared secret calculated from G_R and X, or G_X and R. From the Responder's authentication key and the Initiator's ephemeral key (see AppendixC.2.1),D.2.1), the ECDH shared secret G_RX is calculated. G_RX (ECDH shared secret) (32 bytes) 21 c7 ef f4 fb 69 fa 4b 67 97 d0 58 84 31 5d 84 11 a3 fd a5 4f 6d ad a6 1d 4f cd 85 e7 90 66 68 PRK_3e2m (32 bytes) 75 07 7c 69 1e 35 01 2d 48 bc 24 c8 4f 2b ab 89 f5 2f ac 03 fe dd 81 3e 43 8c 93 b1 0b 39 93 07 The Responder chooses a connection identifier C_R. Connection identifier chosen by Responder (1 byte) 00 Note that since C_R is a byte string in the interval h'00' to h'2f', it is encoded as the corresponding integer -24 (see bstr_identifier in Section 5.1),24, i.e. 0x00 = 0, 0 - 24 = -24, and -24 in CBOR encoding is equal to 0x37. C_R (1 byte) 37 Data_2 is constructed as the CBOR Sequence of G_Y and C_R. data_2 = ( h'52FBA0BDC8D953DD86CE1AB2FD7C05A4658C7C30AFDBFC3301047069451BAF35', -24 ) Which as a CBOR encoded data item is: data_2 (CBOR Sequence) (35 bytes) 58 20 52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db fc 33 01 04 70 69 45 1b af 35 37 From data_2 and message_1, compute the input to the transcript hash TH_2 = H( H(message_1), data_2 ), as a CBOR Sequence of these 2 data items. Input to calculate TH_2 (CBOR Sequence) (72 bytes) 0d 00 58 20 8d 3e f5 6d 1b 75 0a 43 51 d6 8a c2 50 a0 e8 83 79 0e fc 80 a5 38 a4 44 ee 9e 2b 57 e2 44 1a 7c 21 58 20 52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db fc 33 01 04 70 69 45 1b af 35 37 And from there, compute the transcript hash TH_2 = SHA-256( H(message_1), data_2 ) TH_2 (CBOR unencoded) (32 bytes) de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 The Responder's subject name is the empty string: Responder's subject name (text string) "" ID_CRED_R is the following: ID_CRED_R = { 4: h'05' } ID_CRED_R (4 bytes) a1 04 41 05 CRED_R is the following COSE_Key: { 1: 1, -1: 4, -2: h'A3FF263595BEB377D1A0CE1D04DAD2D40966AC6BCB622051B84659184D5D9A32, "subject name": "" } Which encodes to the following byte string: CRED_R (54 bytes) a4 01 01 20 04 21 58 20 a3 ff 26 35 95 be b3 77 d1 a0 ce 1d 04 da d2 d4 09 66 ac 6b cb 62 20 51 b8 46 59 18 4d 5d 9a 32 6c 73 75 62 6a 65 63 74 20 6e 61 6d 65 60 Since no external authorization data is sent: EAD_2 (0 bytes) The plaintext is defined as the empty string: P_2m (0 bytes) The Enc_structure is defined as follows: [ "Encrypt0", << ID_CRED_R >>, << TH_2, CRED_R >> ], so ID_CRED_R is encoded as a CBOR bstr, and the concatenation of the CBOR byte strings TH_2 and CRED_R is wrapped in a CBOR bstr. A_2m = [ "Encrypt0", h'A1044105', h'5820DECFD64A3667640A0233B04AA8AA91F68956B8A536D0CF8C73A6E8A7C3621E2 6A401012004215820A3FF263595BEB377D1A0CE1D04DAD2D40966AC6BCB622051B846 59184D5D9A326C7375626A656374206E616D6560' ] Which encodes to the following byte string to be used as Additional Authenticated Data: A_2m (CBOR-encoded) (105 bytes) 83 68 45 6e 63 72 79 70 74 30 44 a1 04 41 05 58 58 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 a4 01 01 20 04 21 58 20 a3 ff 26 35 95 be b3 77 d1 a0 ce 1d 04 da d2 d4 09 66 ac 6b cb 62 20 51 b8 46 59 18 4d 5d 9a 32 6c 73 75 62 6a 65 63 74 20 6e 61 6d 65 60 info for K_2m is defined as follows: info for K_2m = [ 10, h'DECFD64A3667640A0233B04AA8AA91F68956B8A536D0CF8C73A6E8A7C3621E26', "K_2m", 16 ] Which as a CBOR encoded data item is: info for K_2m (CBOR-encoded) (42 bytes) 84 0a 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 64 4b 5f 32 6d 10 From these parameters, K_2m is computed. Key K_2m is the output of HKDF-Expand(PRK_3e2m, info, L), where L is the length of K_2m, so 16 bytes. K_2m (16 bytes) 4e cd ef ba d8 06 81 8b 62 51 b9 d7 86 78 bc 76 info for IV_2m is defined as follows: info for IV_2m = [ 10, h'A51C76463E8AE58FD3B8DC5EDE1E27143CC92D223EACD9E5FF6E3FAC876658A5', "IV_2m", 13 ] Which as a CBOR encoded data item is: info for IV_2m (CBOR-encoded) (43 bytes) 84 0a 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 65 49 56 5f 32 6d 0d From these parameters, IV_2m is computed. IV_2m is the output of HKDF-Expand(PRK_3e2m, info, L), where L is the length of IV_2m, so 13 bytes. IV_2m (13 bytes) e9 b8 e4 b1 bd 02 f4 9a 82 0d d3 53 4f Finally, COSE_Encrypt0 is computed from the parameters above.*o protected header = CBOR-encoded ID_CRED_R*o external_aad = A_2m*o empty plaintext = P_2m MAC_2 is the 'ciphertext' of the COSE_Encrypt0 with empty plaintext. In case of cipher suite 0 the AEAD is AES-CCM truncated to 8 bytes: MAC_2 (CBOR unencoded) (8 bytes) 42 e7 99 78 43 1e 6b 8f Since method = 2, Signature_or_MAC_2 is MAC_2: Signature_or_MAC_2 (CBOR unencoded) (8 bytes) 42 e7 99 78 43 1e 6b 8f CIPHERTEXT_2 is the ciphertext resulting from XOR between plaintext and KEYSTREAM_2 which is derived from TH_2 and the pseudorandom key PRK_2e. The plaintext is the CBOR Sequence of the items ID_CRED_R and the CBOR encoded Signature_or_MAC_2, in this order (EAD_2 is empty). Note that since ID_CRED_R contains a single 'kid' parameter, i.e., ID_CRED_R = { 4 : kid_R }, only the byte string kid_R is conveyed in the plaintext encoded as a bstr_identifier. kid_R is encoded as the corresponding integer -24 (see bstr_identifier in Section 5.1),24, i.e. 0x05 = 5, 5 - 24 = -19, and -19 in CBOR encoding is equal to 0x32. The plaintext is the following: P_2e (CBOR Sequence) (10 bytes) 32 48 42 e7 99 78 43 1e 6b 8f KEYSTREAM_2 = HKDF-Expand( PRK_2e, info, length ), where length is the length of the plaintext, so 10. info for KEYSTREAM_2 = [ 10, h'DECFD64A3667640A0233B04AA8AA91F68956B8A536D0CF8C73A6E8A7C3621E26', "KEYSTREAM_2", 10 ] Which as a CBOR encoded data item is: info for KEYSTREAM_2 (CBOR-encoded) (49 bytes) 84 0a 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 6b 4b 45 59 53 54 52 45 41 4d 5f 32 0a From there, KEYSTREAM_2 is computed: KEYSTREAM_2 (10 bytes) 91 b9 ff ba 9b f5 5a d1 57 16 Using the parameters above, the ciphertext CIPHERTEXT_2 can be computed: CIPHERTEXT_2 (CBOR unencoded) (10 bytes) a3 f1 bd 5d 02 8d 19 cf 3c 99 message_2 is the CBOR Sequence of data_2 and CIPHERTEXT_2, in this order: message_2 = ( data_2, h'A3F1BD5D028D19CF3C99' ) Which as a CBOR encoded data item is: message_2 (CBOR Sequence) (46 bytes) 58 20 52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db fc 33 01 04 70 69 45 1b af 35 37 4a a3 f1 bd 5d 02 8d 19 cf 3c 99C.2.3.D.2.3. Message_3 Since corr equals 1, C_R is not omitted from data_3. The Initiator's static Diffie-Hellman key pair is the following: I (Initiator's private authentication key) (32 bytes) 2b be a6 55 c2 33 71 c3 29 cf bd 3b 1f 02 c6 c0 62 03 38 37 b8 b5 90 99 a4 43 6f 66 60 81 b0 8e G_I (Initiator's public authentication key, CBOR unencoded) (32 bytes) 2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae da fe 9c aa 4f 4e 7a bb 83 5e c3 0f 1d e8 8a db 96 ff 71 HKDF SHA-256 is the HKDF used (as defined by cipher suite 0). From the Initiator's authentication key and the Responder's ephemeral key (see AppendixC.2.2),D.2.2), the ECDH shared secret G_IY is calculated. G_IY (ECDH shared secret) (32 bytes) cb ff 8c d3 4a 81 df ec 4c b6 5d 9a 57 2e bd 09 64 45 0c 78 56 3d a4 98 1d 80 d3 6c 8b 1a 75 2a PRK_4x3m = HMAC-SHA-256 (PRK_3e2m, G_IY). PRK_4x3m (32 bytes) 02 56 2f 1f 01 78 5c 0a a5 f5 94 64 0c 49 cb f6 9f 72 2e 9e 6c 57 83 7d 8e 15 79 ec 45 fe 64 7a data 3 is equal to C_R. data_3 (CBOR Sequence) (1 byte) 37 From data_3, CIPHERTEXT_2, and TH_2, compute the input to the transcript hash TH_3 = H( H(TH_2 , CIPHERTEXT_2), data_3), as a CBOR Sequence of these 2 data items. Input to calculate TH_3 (CBOR Sequence) (46 bytes) 58 20 de cf d6 4a 36 67 64 0a 02 33 b0 4a a8 aa 91 f6 89 56 b8 a5 36 d0 cf 8c 73 a6 e8 a7 c3 62 1e 26 4a a3 f1 bd 5d 02 8d 19 cf 3c 99 37 And from there, compute the transcript hash TH_3 = SHA-256( H(TH_2 , CIPHERTEXT_2), data_3) TH_3 (CBOR unencoded) (32 bytes) b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb The initiator's subject name is the empty string: Initiator's subject name (text string) "" And its credential is: ID_CRED_I = { 4: h'23' } ID_CRED_I (4 bytes) a1 04 41 23 CRED_I is the following COSE_Key: {1: 1, -1: 4, -2: h'2C440CC121F8D7F24C3B0E41AEDAFE9CAA4F4E7ABB835EC30F1DE88ADB96FF71',1:1, -1:4, -2:h'2C440CC121F8D7F24C3B0E41AEDAFE9CAA4F4E7ABB835EC30F1DE88ADB96FF71', "subjectname": ""name":"" } Which encodes to the following byte string: CRED_I (54 bytes) a4 01 01 20 04 21 58 20 2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae da fe 9c aa 4f 4e 7a bb 83 5e c3 0f 1d e8 8a db 96 ff 71 6c 73 75 62 6a 65 63 74 20 6e 61 6d 65 60 Since no external authorization data is exchanged: EAD_3 (0 bytes) The plaintext of the COSE_Encrypt is the empty string: P_3m (0 bytes) The associated data is the following: [ "Encrypt0", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >> ]. A_3m (CBOR-encoded) (105 bytes) 83 68 45 6e 63 72 79 70 74 30 44 a1 04 41 23 58 58 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb a4 01 01 20 04 21 58 20 2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae da fe 9c aa 4f 4e 7a bb 83 5e c3 0f 1d e8 8a db 96 ff 71 6c 73 75 62 6a 65 63 74 20 6e 61 6d 65 60 Info for K_3m is computed as follows: info for K_3m = [ 10, h'B6CD804FC4B9D7CAC502ABD77CDA74E41CB01182D7CB8B84DB03FFA583A35FCB', "K_3m", 16 ] Which as a CBOR encoded data item is: info for K_3m (CBOR-encoded) (42 bytes) 84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 64 4b 5f 33 6d 10 From these parameters, K_3m is computed. Key K_3m is the output of HKDF-Expand(PRK_4x3m, info, L), where L is the length of K_2m, so 16 bytes. K_3m (16 bytes) 02 c7 e7 93 89 9d 90 d1 28 28 10 26 96 94 c9 58 Nonce IV_3m is the output of HKDF-Expand(PRK_4x3m, info, L), where L = 13 bytes. Info for IV_3m is defined as follows: info for IV_3m = [ 10, h'B6CD804FC4B9D7CAC502ABD77CDA74E41CB01182D7CB8B84DB03FFA583A35FCB', "IV_3m", 13 ] Which as a CBOR encoded data item is: info for IV_3m (CBOR-encoded) (43 bytes) 84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 65 49 56 5f 33 6d 0d From these parameters, IV_3m is computed: IV_3m (13 bytes) 0d a7 cc 3a 6f 9a b2 48 52 ce 8b 37 a6 MAC_3 is the 'ciphertext' of the COSE_Encrypt0 with empty plaintext. In case of cipher suite 0 the AEAD is AES-CCM truncated to 8 bytes: MAC_3 (CBOR unencoded) (8 bytes) ee 59 8e a6 61 17 dc c3 Since method = 3, Signature_or_MAC_3 is MAC_3: Signature_or_MAC_3 (CBOR unencoded) (8 bytes) ee 59 8e a6 61 17 dc c3 Finally, the outer COSE_Encrypt0 is computed. The plaintext is the CBOR Sequence of the items ID_CRED_I and the CBOR encoded Signature_or_MAC_3, in this order (EAD_3 is empty). Note that since ID_CRED_I contains a single 'kid' parameter, i.e., ID_CRED_I = { 4 : kid_I }, only the byte string kid_I is conveyed in the plaintext encoded as a bstr_identifier. kid_I is encoded as the corresponding integer -24 (see bstr_identifier in Section 5.1),24, i.e. 0x23 = 35, 35 - 24 = 11, and 11 in CBOR encoding is equal to 0x0b. P_3ae (CBOR Sequence) (10 bytes) 0b 48 ee 59 8e a6 61 17 dc c3 The Associated data A is the following: Associated data A = [ "Encrypt0", h'', TH_3 ] A_3ae (CBOR-encoded) (45 bytes) 83 68 45 6e 63 72 79 70 74 30 40 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb Key K_3ae is the output of HKDF-Expand(PRK_3e2m, info, L). info is defined as follows: info for K_3ae = [ 10, h'B6CD804FC4B9D7CAC502ABD77CDA74E41CB01182D7CB8B84DB03FFA583A35FCB', "K_3ae", 16 ] Which as a CBOR encoded data item is: info for K_3ae (CBOR-encoded) (43 bytes) 84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 65 4b 5f 33 61 65 10 L is the length of K_3ae, so 16 bytes. From these parameters, K_3ae is computed: K_3ae (16 bytes) 6b a4 c8 83 1d e3 ae 23 e9 8e f7 35 08 d0 95 86 Nonce IV_3ae is the output of HKDF-Expand(PRK_3e2m, info, L). info is defined as follows: info for IV_3ae = [ 10, h'97D8AD42334833EB25B960A5EB0704505F89671A0168AA1115FAF92D9E67EF04', "IV_3ae", 13 ] Which as a CBOR encoded data item is: info for IV_3ae (CBOR-encoded) (44 bytes) 84 0a 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 66 49 56 5f 33 61 65 0d L is the length of IV_3ae, so 13 bytes. From these parameters, IV_3ae is computed: IV_3ae (13 bytes) 6c 6d 0f e1 1e 9a 1a f3 7b 87 84 55 10 Using the parameters above, the 'ciphertext' CIPHERTEXT_3 can be computed: CIPHERTEXT_3 (CBOR unencoded) (18 bytes) d5 53 5f 31 47 e8 5f 1c fa cd 9e 78 ab f9 e0 a8 1b bf From the parameter above, message_3 is computed, as the CBOR Sequence of the following items: (C_R, CIPHERTEXT_3). message_3 = ( -24, h'D5535F3147E85F1CFACD9E78ABF9E0A81BBF' ) Which encodes to the following byte string: message_3 (CBOR Sequence) (20 bytes) 37 52 d5 53 5f 31 47 e8 5f 1c fa cd 9e 78 ab f9 e0 a8 1b bfC.2.4.D.2.4. OSCORE Security Context Derivation From here, the Initiator and the Responder can derive an OSCORE Security Context, using the EDHOC-Exporter interface. From TH_3 and CIPHERTEXT_3, compute the input to the transcript hash TH_4 = H( TH_3, CIPHERTEXT_3 ), as a CBOR Sequence of these 2 data items. Input to calculate TH_4 (CBOR Sequence) (53 bytes) 58 20 b6 cd 80 4f c4 b9 d7 ca c5 02 ab d7 7c da 74 e4 1c b0 11 82 d7 cb 8b 84 db 03 ff a5 83 a3 5f cb 52 d5 53 5f 31 47 e8 5f 1c fa cd 9e 78 ab f9 e0 a8 1b bf And from there, compute the transcript hash TH_4 = SHA-256(TH_3 , CIPHERTEXT_4) TH_4 (CBOR unencoded) (32 bytes) 7c cf de dc 2c 10 ca 03 56 e9 57 b9 f6 a5 92 e0 fa 74 db 2a b5 4f 59 24 40 96 f9 a2 ac 56 d2 07 The Master Secret and Master Salt are derived as follows: Master Secret = EDHOC-Exporter( "OSCORE Master Secret", 16 ) = EDHOC- KDF(PRK_4x3m, TH_4, "OSCORE Master Secret", 16) = HKDF-Expand( PRK_4x3m, info_ms, 16 ) Master Salt = EDHOC-Exporter( "OSCORE Master Salt", 8 ) = EDHOC- KDF(PRK_4x3m, TH_4, "OSCORE Master Salt", 8) = HKDF-Expand( PRK_4x3m, info_salt, 8 ) info_ms for OSCORE Master Secret is defined as follows: info_ms = [ 10, h'7CCFDEDC2C10CA0356E957B9F6A592E0FA74DB2AB54F59244096F9A2AC56D207', "OSCORE Master Secret", 16 ] Which as a CBOR encoded data item is: info_ms for OSCORE Master Secret (CBOR-encoded) (58 bytes) 84 0a 58 20 7c cf de dc 2c 10 ca 03 56 e9 57 b9 f6 a5 92 e0 fa 74 db 2a b5 4f 59 24 40 96 f9 a2 ac 56 d2 07 74 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 65 63 72 65 74 10 info_salt for OSCORE Master Salt is defined as follows: info_salt = [ 10, h'7CCFDEDC2C10CA0356E957B9F6A592E0FA74DB2AB54F59244096F9A2AC56D207', "OSCORE Master Salt", 8 ] Which as a CBOR encoded data item is: info for OSCORE Master Salt (CBOR-encoded) (56 Bytes) 84 0a 58 20 7c cf de dc 2c 10 ca 03 56 e9 57 b9 f6 a5 92 e0 fa 74 db 2a b5 4f 59 24 40 96 f9 a2 ac 56 d2 07 72 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 61 6c 74 08 From these parameters, OSCORE Master Secret and OSCORE Master Salt are computed: OSCORE Master Secret (16 bytes) c3 4a 50 6d 0e bf bd 17 03 04 86 13 5f 9c b3 50 OSCORE Master Salt (8 bytes) c2 24 34 9d 9b 34 ca 8c The client's OSCORE Sender ID is C_R and the server's OSCORE Sender ID is C_I. Client's OSCORE Sender ID (1 byte) 00 Server's OSCORE Sender ID (1 byte) 16 The AEAD Algorithm and the hash algorithm are the application AEAD and hash algorithms in the selected cipher suite. OSCORE AEAD Algorithm (int) 10 OSCORE Hash Algorithm (int) -16 AppendixD.E. Applicability Template This appendix contains an example of an applicability statement, see Section3.7.3.9. For use of EDHOC in the XX protocol, the following assumptions are made on the parameters:* METHOD_CORR = 5 - methodo METHOD = 1 (I uses signature key, R uses static DH key.)- corr = 1 (CoAP Token or other transport data enables correlation between message_1 and message_2.) *o EDHOC requests are expected by the server at /app1-edh, no Content-Format needed.* C_1 = "null" is present to identify message_1 *o CRED_I is an 802.1AR IDevID encoded as a C509 Certificate of type 0 [I-D.ietf-cose-cbor-encoded-cert].-* R acquires CRED_I out-of-band, indicated in EAD_1-* ID_CRED_I = {4: h''} is a kid with value empty byte string*o CRED_R is a COSE_Key of type OKP as specified in Section3.3.4. -3.5.4. * The CBOR map has parameters 1 (kty), -1 (crv), and -2 (x-coordinate).*o ID_CRED_R = CRED_R*o No use of message_4: the application sends protected messages from R to I.*o External authorization data is defined and processed as specified in [I-D.selander-ace-ake-authz]. AppendixE.F. EDHOC Message Deduplication EDHOC by default assumes that message duplication is handled by the transport, in this section exemplified with CoAP. Deduplication of CoAP messages is described in Section 4.5 of [RFC7252]. This handles the case when the same Confirmable (CON) message is received multiple times due to missing acknowledgement on CoAP messaging layer. The recommended processing in [RFC7252] is that the duplicate message is acknowledged (ACK), but the received message is only processed once by the CoAP stack. Message deduplication is resource demanding and therefore not supported in all CoAP implementations. Since EDHOC is targeting constrained environments, it is desirable that EDHOC can optionally support transport layers which does not handle message duplication. Special care is needed to avoid issues with duplicate messages, see Section5.2.5.1. The guiding principle here is similar to the deduplication processing on CoAP messaging layer: a received duplicate EDHOC message SHALL NOT result in a response consisting of another instance of the next EDHOC message. The result MAY be that a duplicate EDHOC response is sent, provided it is still relevant with respect the current protocol state. In any case, the received message MUST NOT be processed more than once in the same EDHOC session. This is called "EDHOC message deduplication". An EDHOC implementation MAY store the previously sent EDHOC message to be able to resend it. An EDHOC implementation MAY keep the protocol state to be able to recreate the previously sent EDHOC message and resend it. The previous message or protocol state MUST NOT be kept longer than what is required for retransmission, for example, in the case of CoAP transport, no longer than the EXCHANGE_LIFETIME (see Section 4.8.2 of [RFC7252]). Note that the requirements in Section5.25.1 still apply because duplicate messages are not processed by the EDHOC state machine:*o EDHOC messages SHALL be processed according to thecurrentcurrent protocol state. o Different instances of the same message MUST NOT be processed in one session. Appendix G. Transports Not Natively Providing Correlation Protocols that do not natively provide full correlation between a series of messages can send the C_I and C_R identifiers along as needed. The transport over CoAP (Appendix A.3) can serve as a blueprint for other server-client protocols: The client prepends the C_x which the server selected (or, for message 1, a sentinel null value which is not a valid C_x) to any request message it sends. The server does not send any such indicator, as responses are matched to request by the client-server protocolstate. * Different instancesdesign. Protocols that do not provide any correlation at all can prescribe prepending of thesame message MUST NOT be processed in one session.peer's chosen C_x to all messages. AppendixF.H. Change Log Main changes: o From -07 to -08: * Prepended C_x moved from the EDHOC protocol itself to the transport mapping * METHOD_CORR renamed to METHOD, corr removed * Removed bstr_identifier and use bstr / int instead; C_x can now be int without any implied bstr semantics * Defined COSE header parameter 'kid2' with value type bstr / int for use with ID_CRED_x * Updated message sizes * New cipher suites with AES-GCM and ChaCha20 / Poly1305 * Changed from one- to two-byte identifier of CNSA compliant suite * Separate sections on transport and connection id with further sub-structure * Moved back key derivation for OSCORE from draft-ietf-core- oscore-edhoc * OSCORE and CoAP specific processing moved to new appendix * Message 4 section moved to message processing section o From -06 to -07:-* Changed transcript hash definition for TH_2 and TH_3-* Removed "EDHOC signature algorithm curve" from cipher suite-* New IANA registry "EDHOC Exporter Label"-* New application defined parameter "context" in EDHOC-Exporter-* Changed normative language for failure from MUST to SHOULD send error-* Made error codes non-negative and 0 for success-* Added detail on success error code-* Aligned terminology "protocol instance" -> "session"-* New appendix on compact EC point representation-* Added detail on use of ephemeral public keys-* Moved key derivation for OSCORE to draft-ietf-core-oscore-edhoc-* Additional security considerations-* Renamed "Auxililary Data" as "External Authorization Data"-* Added encrypted EAD_4 to message_4*o From -05 to -06:-* New section 5.2 "Message Processing Outline"-* Optional inital byte C_1 = null in message_1-* New format of error messages, table of error codes, IANA registry-* Change of recommendation transport of error in CoAP-* Merge of content in 3.7 and appendix C into new section 3.7 "Applicability Statement"-* Requiring use of deterministic CBOR-* New section on message deduplication-* New appendix containin all CDDL definitions-* New appendix with change log-* Removed section "Other Documents Referencing EDHOC"-* Clarifications based on review comments*o From -04 to -05:-* EDHOC-Rekey-FS -> EDHOC-KeyUpdate-* Clarification of cipher suite negotiation-* Updated security considerations-* Updated test vectors-* Updated applicability statement template*o From -03 to -04:-* Restructure of section 1-* Added references to C509 Certificates-* Change in CIPHERTEXT_2 -> plaintext XOR KEYSTREAM_2 (test vector not updated)-* "K_2e", "IV_2e" -> KEYSTREAM_2-* Specified optional message 4-* EDHOC-Exporter-FS -> EDHOC-Rekey-FS-* Less constrained devices SHOULD implement both suite 0 and 2-* Clarification of error message-* Added exporter interface test vector*o From -02 to -03:-* Rearrangements of section 3 and beginning of section 4-* Key derivation new section 4-* Cipher suites 4 and 5 added-* EDHOC-EXPORTER-FS - generate a new PRK_4x3m from an old one-* Change in CIPHERTEXT_2 -> COSE_Encrypt0 without tag (no change to test vector)-* Clarification of error message-* New appendix C applicability statement*o From -01 to -02:-* New section 1.2 Use of EDHOC-* Clarification of identities-* New section 4.3 clarifying bstr_identifier-* Updated security considerations-* Updated text on cipher suite negotiation and key confirmation-* Test vector for static DH*o From -00 to -01:-* Removed PSK method-* Removed references to certificate by value Acknowledgments The authors want to thank Christian Amsuess, Alessandro Bruni, Karthikeyan Bhargavan, Timothy Claeys, Martin Disch, Theis Groenbech Petersen, Dan Harkins, Klaus Hartke, Russ Housley, Stefan Hristozov, Alexandros Krontiris, Ilari Liusvaara, Karl Norrman, Salvador Perez, Eric Rescorla, Michael Richardson, Thorvald Sahl Joergensen, Jim Schaad, Carsten Schuermann, Ludwig Seitz, Stanislav Smyshlyaev, Valery Smyslov, Peter van der Stok, Rene Struik, Vaishnavi Sundararajan, Erik Thormarker, Marco Tiloca, Michel Veillette, and Malisa Vucinic for reviewing and commenting on intermediate versions of the draft. We are especially indebted to Jim Schaad for his continuous reviewing and implementation of different versions of the draft. Work on this document has in part been supported by the H2020 project SIFIS-Home (grant agreement 952652). Authors' AddressesGöranGoeran Selander Ericsson AB Email: goran.selander@ericsson.com JohnPreußPreuss Mattsson Ericsson AB Email: john.mattsson@ericsson.com Francesca Palombini Ericsson AB Email: francesca.palombini@ericsson.com