--- 1/draft-ietf-lake-edhoc-06.txt 2021-05-24 06:13:12.438393614 -0700 +++ 2/draft-ietf-lake-edhoc-07.txt 2021-05-24 06:13:12.602397702 -0700 @@ -1,19 +1,19 @@ Network Working Group G. Selander Internet-Draft J. Mattsson Intended status: Standards Track F. Palombini -Expires: 23 October 2021 Ericsson AB - 21 April 2021 +Expires: 25 November 2021 Ericsson AB + 24 May 2021 Ephemeral Diffie-Hellman Over COSE (EDHOC) - draft-ietf-lake-edhoc-06 + draft-ietf-lake-edhoc-07 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 @@ -27,21 +27,21 @@ 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 on 23 October 2021. + This Internet-Draft will expire on 25 November 2021. 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) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights @@ -60,99 +60,99 @@ 1.5. Terminology and Requirements Language . . . . . . . . . . 6 2. EDHOC Outline . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Protocol Elements . . . . . . . . . . . . . . . . . . . . . . 9 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Method and Correlation . . . . . . . . . . . . . . . . . 10 3.2.1. Method . . . . . . . . . . . . . . . . . . . . . . . 10 3.2.2. Connection Identifiers . . . . . . . . . . . . . . . 10 3.2.3. Transport . . . . . . . . . . . . . . . . . . . . . . 11 3.2.4. Message Correlation . . . . . . . . . . . . . . . . . 11 3.3. Authentication Parameters . . . . . . . . . . . . . . . . 11 - 3.3.1. Authentication Keys . . . . . . . . . . . . . . . . . 12 + 3.3.1. Authentication Keys . . . . . . . . . . . . . . . . . 11 3.3.2. Identities . . . . . . . . . . . . . . . . . . . . . 12 3.3.3. Authentication Credentials . . . . . . . . . . . . . 13 - 3.3.4. Identification of Credentials . . . . . . . . . . . . 14 + 3.3.4. Identification of Credentials . . . . . . . . . . . . 15 3.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 16 - 3.5. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 17 - 3.6. Auxiliary Data . . . . . . . . . . . . . . . . . . . . . 18 - 3.7. Applicability Statement . . . . . . . . . . . . . . . . . 18 + 3.5. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 18 + 3.6. External Authorization Data . . . . . . . . . . . . . . . 18 + 3.7. Applicability Statement . . . . . . . . . . . . . . . . . 19 4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . 20 - 4.1. EDHOC-Exporter Interface . . . . . . . . . . . . . . . . 22 - 5. Message Formatting and Processing . . . . . . . . . . . . . . 22 - 5.1. Encoding of bstr_identifier . . . . . . . . . . . . . . . 23 - 5.2. Message Processing Outline . . . . . . . . . . . . . . . 23 - 5.3. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 24 - 5.3.1. Formatting of Message 1 . . . . . . . . . . . . . . . 24 - 5.3.2. Initiator Processing of Message 1 . . . . . . . . . . 25 - 5.3.3. Responder Processing of Message 1 . . . . . . . . . . 26 - 5.4. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 26 - 5.4.1. Formatting of Message 2 . . . . . . . . . . . . . . . 27 - 5.4.2. Responder Processing of Message 2 . . . . . . . . . . 27 - 5.4.3. Initiator Processing of Message 2 . . . . . . . . . . 29 - 5.5. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 29 - 5.5.1. Formatting of Message 3 . . . . . . . . . . . . . . . 30 - 5.5.2. Initiator Processing of Message 3 . . . . . . . . . . 30 - 5.5.3. Responder Processing of Message 3 . . . . . . . . . . 32 - 6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 33 - 6.1. Success . . . . . . . . . . . . . . . . . . . . . . . . . 34 - 6.2. Unspecified . . . . . . . . . . . . . . . . . . . . . . . 34 - 6.3. Wrong Selected Cipher Suite . . . . . . . . . . . . . . . 35 - 6.3.1. Cipher Suite Negotiation . . . . . . . . . . . . . . 35 - 6.3.2. Examples . . . . . . . . . . . . . . . . . . . . . . 35 - 7. Transferring EDHOC and Deriving an OSCORE Context . . . . . . 37 - 7.1. EDHOC Message 4 . . . . . . . . . . . . . . . . . . . . . 37 - 7.1.1. Formatting of Message 4 . . . . . . . . . . . . . . . 37 - 7.1.2. Responder Processing of Message 4 . . . . . . . . . . 38 - 7.1.3. Initiator Processing of Message 4 . . . . . . . . . . 38 - 7.2. Transferring EDHOC in CoAP . . . . . . . . . . . . . . . 39 - 7.2.1. Deriving an OSCORE Context from EDHOC . . . . . . . . 41 - 7.2.2. Error Messages with CoAP Transport . . . . . . . . . 42 + 4.1. EDHOC-Exporter Interface . . . . . . . . . . . . . . . . 23 + 5. Message Formatting and Processing . . . . . . . . . . . . . . 23 + 5.1. Encoding of bstr_identifier . . . . . . . . . . . . . . . 24 + 5.2. Message Processing Outline . . . . . . . . . . . . . . . 24 + 5.3. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 25 + 5.3.1. Formatting of Message 1 . . . . . . . . . . . . . . . 25 + 5.3.2. Initiator Processing of Message 1 . . . . . . . . . . 26 + 5.3.3. Responder Processing of Message 1 . . . . . . . . . . 27 + 5.4. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 28 + 5.4.1. Formatting of Message 2 . . . . . . . . . . . . . . . 28 + 5.4.2. Responder Processing of Message 2 . . . . . . . . . . 28 + 5.4.3. Initiator Processing of Message 2 . . . . . . . . . . 30 + 5.5. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 31 + 5.5.1. Formatting of Message 3 . . . . . . . . . . . . . . . 31 + 5.5.2. Initiator Processing of Message 3 . . . . . . . . . . 31 + 5.5.3. Responder Processing of Message 3 . . . . . . . . . . 34 + 6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 34 + 6.1. Success . . . . . . . . . . . . . . . . . . . . . . . . . 36 + 6.2. Unspecified . . . . . . . . . . . . . . . . . . . . . . . 36 + 6.3. Wrong Selected Cipher Suite . . . . . . . . . . . . . . . 36 + 6.3.1. Cipher Suite Negotiation . . . . . . . . . . . . . . 37 + 6.3.2. Examples . . . . . . . . . . . . . . . . . . . . . . 37 + 7. Transferring EDHOC and Deriving an OSCORE Context . . . . . . 38 + 7.1. EDHOC Message 4 . . . . . . . . . . . . . . . . . . . . . 38 + 7.1.1. Formatting of Message 4 . . . . . . . . . . . . . . . 39 + 7.1.2. Responder Processing of Message 4 . . . . . . . . . . 39 + 7.1.3. Initiator Processing of Message 4 . . . . . . . . . . 40 + 7.2. Transferring EDHOC in CoAP . . . . . . . . . . . . . . . 40 8. Security Considerations . . . . . . . . . . . . . . . . . . . 42 8.1. Security Properties . . . . . . . . . . . . . . . . . . . 42 - 8.2. Cryptographic Considerations . . . . . . . . . . . . . . 44 - 8.3. Cipher Suites and Cryptographic Algorithms . . . . . . . 45 + 8.2. Cryptographic Considerations . . . . . . . . . . . . . . 45 + 8.3. Cipher Suites and Cryptographic Algorithms . . . . . . . 46 8.4. Unprotected Data . . . . . . . . . . . . . . . . . . . . 46 - 8.5. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 46 - 8.6. Implementation Considerations . . . . . . . . . . . . . . 46 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48 - 9.1. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 48 - 9.2. EDHOC Method Type Registry . . . . . . . . . . . . . . . 49 - 9.3. EDHOC Error Codes Registry . . . . . . . . . . . . . . . 50 - 9.4. The Well-Known URI Registry . . . . . . . . . . . . . . . 50 - 9.5. Media Types Registry . . . . . . . . . . . . . . . . . . 50 - 9.6. CoAP Content-Formats Registry . . . . . . . . . . . . . . 51 - 9.7. Expert Review Instructions . . . . . . . . . . . . . . . 51 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 52 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 52 - 10.2. Informative References . . . . . . . . . . . . . . . . . 54 - Appendix A. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 56 - A.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 57 - A.2. CDDL Definitions . . . . . . . . . . . . . . . . . . . . 57 - A.3. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 59 - Appendix B. Test Vectors . . . . . . . . . . . . . . . . . . . . 59 - B.1. Test Vectors for EDHOC Authenticated with Signature Keys - (x5t) . . . . . . . . . . . . . . . . . . . . . . . . . . 60 - B.1.1. Message_1 . . . . . . . . . . . . . . . . . . . . . . 60 - B.1.2. Message_2 . . . . . . . . . . . . . . . . . . . . . . 61 - B.1.3. Message_3 . . . . . . . . . . . . . . . . . . . . . . 69 - B.1.4. OSCORE Security Context Derivation . . . . . . . . . 75 - B.2. Test Vectors for EDHOC Authenticated with Static - Diffie-Hellman Keys . . . . . . . . . . . . . . . . . . . 77 - B.2.1. Message_1 . . . . . . . . . . . . . . . . . . . . . . 78 - B.2.2. Message_2 . . . . . . . . . . . . . . . . . . . . . . 79 - B.2.3. Message_3 . . . . . . . . . . . . . . . . . . . . . . 85 - B.2.4. OSCORE Security Context Derivation . . . . . . . . . 90 - Appendix C. Applicability Template . . . . . . . . . . . . . . . 92 - Appendix D. EDHOC Message Deduplication . . . . . . . . . . . . 93 - Appendix E. Change Log . . . . . . . . . . . . . . . . . . . . . 94 - Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 96 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 97 + 8.5. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 47 + 8.6. Implementation Considerations . . . . . . . . . . . . . . 47 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . 51 + 9.6. Media Types Registry . . . . . . . . . . . . . . . . . . 51 + 9.7. CoAP Content-Formats Registry . . . . . . . . . . . . . . 52 + 9.8. Expert Review Instructions . . . . . . . . . . . . . . . 52 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 53 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 53 + 10.2. Informative References . . . . . . . . . . . . . . . . . 55 + Appendix A. Compact Representation . . . . . . . . . . . . . . . 58 + Appendix B. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 58 + B.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 59 + B.2. CDDL Definitions . . . . . . . . . . . . . . . . . . . . 59 + B.3. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 61 + Appendix C. Test Vectors . . . . . . . . . . . . . . . . . . . . 61 + C.1. Test Vectors for EDHOC Authenticated with Signature Keys + (x5t) . . . . . . . . . . . . . . . . . . . . . . . . . . 62 + C.1.1. Message_1 . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . 99 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 @@ -277,21 +277,21 @@ "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 - Appendix A.1. When referring to CBOR, this specification always + Appendix B.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 @@ -366,32 +366,32 @@ - 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). * Method types and error handling. - * Transport of opaque auxiliary data. + * 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 Appendix A and test vectors including CBOR diagnostic - notation are given in Appendix B. + summarized in Appendix B and test vectors including CBOR diagnostic + notation are given in Appendix C. 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 @@ -403,29 +403,29 @@ (AEAD, hash) in the selected cipher suite (see Section 3.4) and the application can make use of the established connection identifiers C_1, C_I, and C_R (see Section 3.2.4). EDHOC may be used with the media type application/edhoc defined in Section 9. 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, SUITES_I, G_X, C_I, AD_1 | + | C_1, METHOD_CORR, SUITES_I, G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | | | - | C_I, G_Y, C_R, Enc(ID_CRED_R, Signature_or_MAC_2, AD_2) | + | 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, AD_3) | + | C_R, AEAD(K_3ae; ID_CRED_I, Signature_or_MAC_3, EAD_3) | +------------------------------------------------------------------>| | message_3 | Figure 3: EDHOC Message Flow 3.2. Method and Correlation The data item METHOD_CORR in message_1 (see Section 5.3.1), is an integer specifying the method and the correlation properties of the transport, which are described in this section. @@ -470,23 +470,24 @@ connection identifiers SHALL adhere to the requirements for that protocol. Each party choses a connection identifier it desires the other party to use in outgoing messages. (For OSCORE this results in the endpoint selecting its Recipient ID, see Section 3.1 of [RFC8613]). 3.2.3. Transport Cryptographically, EDHOC does not put requirements on the lower layers. EDHOC is not bound to a particular transport layer, and can - be used in environments without IP. The transport is responsible to - handle message loss, reordering, message duplication, fragmentation, - and denial of service protection, where necessary. + be used in environments without IP. The application using EDHOC is + responsible to handle message loss, reordering, message duplication, + fragmentation, demultiplex EDHOC messages from other types of + messages, and denial of service protection, where necessary. The Initiator and the Responder need to have agreed on a transport to be used for EDHOC, see Section 3.7. It is recommended to transport EDHOC in CoAP payloads, see Section 7. 3.2.4. Message Correlation If the whole transport path provides a mechanism for correlating messages received with messages previously sent, then some of the connection identifiers may be omitted. There are four cases: @@ -513,43 +515,49 @@ 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. + 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. * Only the Responder SHALL have access to the Responder's private authentication key. * Only the Initiator SHALL have access to the Initiator's private authentication key. 3.3.2. 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 Auxiliary Data, - see Section 3.6). + which may be provisioned, e.g., out of band or in the external + authorization data, see Section 3.6). 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. * 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 @@ -636,182 +644,204 @@ CRED_x = { 1: 1, -1: 4, -2: h'b1a3e89460e88d3a8d54211dc95f0b90 3ff205eb71912d6db8f4af980d2db83a', "subject name" : "42-50-31-FF-EF-37-32-39" } 3.3.4. Identification of Credentials - ID_CRED_I and ID_CRED_R are identifiers of 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. + 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. * ID_CRED_R is intended to facilitate for the Initiator to retrieve the Responder's public authentication key. * 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: * ID_CRED_x = { 4 : kid_x }, where kid_x : bstr, for x = I or R. Public key certificates can be identified in different ways. Header parameters for identifying C509 certificates and X.509 certificates - are defined in [I-D.mattsson-cose-cbor-cert-compress] and + are defined in [I-D.ietf-cose-cbor-encoded-cert] and [I-D.ietf-cose-x509], for example: * 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, * 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, * 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.mattsson-cose-cbor-cert-compress] and + 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 Section 5.5 and Section 5.4. 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. Cipher Suites - An EDHOC cipher suite consists of an ordered set of COSE code points - from the "COSE Algorithms" and "COSE Elliptic Curves" registries: + 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 Section 3.3.1. * EDHOC AEAD algorithm * EDHOC hash algorithm - * EDHOC ECDH curve + * EDHOC key exchange algorithm (ECDH curve) * EDHOC signature algorithm - * EDHOC signature algorithm curve - * Application AEAD algorithm * 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 - (Section 9.1) or use any combination of COSE algorithms to define - their own private cipher suite. Private cipher suites can be - identified with any of the four values -24, -23, -22, -21. + (Section 9.2) 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 cipher suites are for constrained IoT where message overhead is a very important factor: - 0. ( 10, -16, 4, -8, 6, 10, -16 ) - (AES-CCM-16-64-128, SHA-256, X25519, EdDSA, Ed25519, + 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, 6, 10, -16 ) - (AES-CCM-16-128-128, SHA-256, X25519, EdDSA, Ed25519, + 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, 1, 10, -16 ) - (AES-CCM-16-64-128, SHA-256, P-256, ES256, P-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, 1, 10, -16 ) - (AES-CCM-16-128-128, SHA-256, P-256, ES256, P-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 cipher suite is for general non-constrained applications. It uses very high performance algorithms that also are widely supported: - 4. ( 1, -16, 4, -7, 1, 1, -16 ) - (A128GCM, SHA-256, X25519, ES256, P-256, + 4. ( 1, -16, 4, -7, 1, -16 ) + (A128GCM, SHA-256, X25519, ES256, A128GCM, SHA-256) The following cipher suite is for high security application such as government use and financial applications. It is compatible with the CNSA suite [CNSA]. - 5. ( 3, -43, 2, -35, 2, 3, -43 ) - (A256GCM, SHA-384, P-384, ES384, P-384, + 5. ( 3, -43, 2, -35, 3, -43 ) + (A256GCM, SHA-384, P-384, ES384, A256GCM, SHA-384) The different methods use the same cipher suites, but some algorithms - are not used in some methods. The EDHOC signature algorithm and the - EDHOC signature algorithm curve are not used in methods without - signature authentication. + 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 Section 5.3.1 to secure the cipher suite negotiation. Examples of cipher suite negotiation are given in Section 6.3.2. 3.5. Ephemeral Public Keys - The ECDH ephemeral public keys are formatted as a COSE_Key of type - EC2 or OKP according to Sections 7.1 and 7.2 of - [I-D.ietf-cose-rfc8152bis-algs], but only the 'x' parameter is - included G_X and G_Y. For Elliptic Curve Keys of type EC2, compact - representation as per [RFC6090] MAY be used also in the COSE_Key. If - the COSE implementation requires an 'y' parameter, any of the - possible values of the y-coordinate can be used, see Appendix C of - [RFC6090]. COSE always use compact output for Elliptic Curve Keys of + EDHOC always uses compact representation of elliptic curve points, + see Appendix A. 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. Auxiliary Data +3.6. External Authorization Data - In order to reduce round trips and number of messages, and in some - cases also streamline processing, certain security applications may - be integrated into EDHOC by transporting auxiliary data together with - the messages. One example is the transport of third-party - authorization information protected outside of EDHOC + 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 auxiliary data (AD) to be sent in the EDHOC - messages. Unprotected Auxiliary Data (AD_1, AD_2) may be sent in - message_1 and message_2, respectively. Protected Auxiliary Data - (AD_3) may be sent in message_3. + 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 Section 8.4. External authorization data sent in message_3 + (EAD_3) or message_4 (EAD_4) is protected between Initiator and + Responder. - Since data carried in AD_1 and AD_2 may not be protected, and the - content of AD_3 is available to both the Initiator and the Responder, - special considerations need to be made such that the availability of - the data a) does not violate security and privacy requirements of the - service which uses this data, and b) does not violate the security - properties of EDHOC. + External authorization data is a CBOR sequence (see Appendix B.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. 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 Section 3.4) but other parameters may need to be known out-of-band (e.g., which authentication method is used, see Section 3.2.1). The purpose of the applicability statement is describe the intended @@ -823,42 +853,45 @@ payload of a CoAP message with a certain Uri-Path or Content- Format; see Section 7.2. 2. Method and correlation of underlying transport messages (METHOD_CORR; see Section 3.2.1 and Section 3.2.4). This gives information about the optional connection identifier fields. 3. How message_1 is identified, in particular if the optional initial C_1 = "null" of message_1 is present; see Section 5.3.1 - 4. Authentication credentials (CRED_I, CRED_R; see Section 3.3.3). + 4. Profile for authentication credentials (CRED_I, CRED_R; see + Section 3.3.3), e.g., profile for certificate or COSE_key, + including supported authentication key algorithms (subject public + key algorithm in X.509 certificate). 5. Type used to identify authentication credentials (ID_CRED_I, ID_CRED_R; see Section 3.3.4). - 6. Use and type of Auxiliary Data (AD_1, AD_2, AD_3; see - Section 3.6). + 6. Use and type of external authorization data (EAD_1, EAD_2, EAD_3, + EAD_4; see Section 3.6). 7. Identifier used as identity of endpoint; see Section 3.3.2. 8. 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 Section 7.1. 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 Appendix C. + An example of an applicability statement is shown in Appendix D. - For some parameters, like METHOD_CORR, ID_CRED_x, type of AD_x, the + For some parameters, like METHOD_CORR, 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 @@ -874,22 +907,22 @@ 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 protocol instance, - for example based on URI or Auxiliary Data type. + 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. @@ -936,21 +969,21 @@ 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 PRK using Expand + 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, @@ -989,37 +1022,52 @@ 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, length) - = EDHOC-KDF(PRK_4x3m, TH_4, label, length) + EDHOC-Exporter(label, context, length) + = EDHOC-KDF(PRK_4x3m, TH_4, label_context, length) - where label is a tstr defined by the application and length is a uint - defined by the application. The label SHALL be different for each - different exporter value. The transcript hash TH_4 is a CBOR encoded - bstr and the input to the hash function is a CBOR Sequence. + 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 9.1), context is a bstr defined by the application, + and length is a uint defined by the application. The (label, + context) pair must be unique, i.e. a (label, context) MUST NOT be + used for two different purposes. However an application can re- + derive the same key several times as long as it is done in a secure + way. For example, in most encryption algorithms the same (key, + nonce) pair must not be reused. + + The transcript hash TH_4 is a CBOR encoded bstr and the input to the + hash function is a CBOR Sequence. TH_4 = H( TH_3, CIPHERTEXT_3 ) - where H() is the hash function in the selected cipher suite. Example - use of the EDHOC-Exporter is given in Sections 7.2.1. + where H() is the hash function in the selected cipher suite. + Examples of use of the EDHOC-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 provides the function EDHOC-KeyUpdate. When EDHOC-KeyUpdate is called the old PRK_4x3m is deleted and the new - PRk_4x3m is calculated as a "hash" of the old key using the Extract + PRK_4x3m is calculated as a "hash" of the old key using the Extract function as illustrated by the following pseudocode: EDHOC-KeyUpdate( nonce ): PRK_4x3m = Extract( nonce, PRK_4x3m ) 5. Message Formatting and Processing This section specifies formatting of the messages and processing steps. Error messages are specified in Section 6. @@ -1055,26 +1103,26 @@ bstr_identifier = bstr / int Note that, despite what could be interpreted by the CDDL definition only, bstr_identifier once decoded are always byte strings. 5.2. Message Processing Outline This section outlines the message processing of EDHOC. - For each protocol instance, the endpoints 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 to an applicability - statement (Section 3.7) which provides the context for how messages - are transported, identified and processed. + For each session, the endpoints 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 to an applicability statement + (Section 3.7) which provides the context for how messages are + transported, identified and processed. EDHOC messages SHALL be processed according to the current protocol state. The following 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 3.7). 2. Retrieve the protocol state, e.g. using the received connection identifier (Section 3.2.2) or with the help of message @@ -1087,41 +1135,40 @@ 3. If the message received is an error message then process according to Section 6, else process as the expected next message according to the protocol state. If the processing fails, then the protocol is discontinued, an error message sent, and the protocol state erased. Further details are provided in the following subsections. Different instances of the same message MUST NOT be processed in one - protocol instance. Note that processing will fail if the same - message appears a second time for EDHOC processing because the state - of the protocol has moved on and now expects something else. This - assumes that message duplication due to re-transmissions is handled - by the transport protocol, see Section 3.2.3. The case when the - transport does not support message deduplication is addressed in - Appendix D. + session. Note that processing will fail if the same message appears + a second time for EDHOC processing because the state of the protocol + has moved on and now expects something else. This assumes that + message duplication due to re-transmissions is handled by the + transport protocol, see Section 3.2.3. The case when the transport + does not support message deduplication is addressed in Appendix E. 5.3. EDHOC Message 1 5.3.1. Formatting of Message 1 - message_1 SHALL be a CBOR Sequence (see Appendix A.1) as defined + message_1 SHALL be a CBOR Sequence (see Appendix B.1) as defined below message_1 = ( ? C_1 : null, METHOD_CORR : int, SUITES_I : [ selected : suite, supported : 2* suite ] / suite, G_X : bstr, C_I : bstr_identifier, - ? AD_1 : bstr, + ? EAD ; EAD_1 ) suite = int where: * C_1 - an initial 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 @@ -1136,74 +1183,76 @@ selected. The selected suite is the first suite in the SUITES_I CBOR array. If a single supported cipher suite is conveyed then that cipher suite is selected and SUITES_I is encoded as an int instead of an array. * G_X - the ephemeral public key of the Initiator * C_I - variable length connection identifier, encoded as a bstr_identifier (see Section 5.1). - * AD_1 - bstr containing unprotected opaque auxiliary data + * EAD_1 - unprotected external authorization data, see Section 3.6. 5.3.2. Initiator Processing of Message 1 The Initiator SHALL compose message_1 as follows: * The supported cipher suites and the order of preference MUST NOT be changed based on previous error messages. However, the list SUITES_I sent to the Responder 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. * The Initiator MUST select its most preferred cipher suite, conditioned on what it can assume to be supported by the Responder. If the Initiator previously received from the - Responder an error message with error code 1 (see Section 6.3) + Responder an error message with error code 2 (see Section 6.3) indicating cipher suites supported by the Responder which also are supported by the Initiator, then the Initiator SHOULD select the most preferred cipher suite of those (note that error messages are not authenticated and may be forged). - * Generate an ephemeral ECDH key pair as specified in Section 5 of - [SP-800-56A] using the curve in the selected cipher suite and - format it as a COSE_Key. Let G_X be the 'x' parameter of the - COSE_Key. + * Generate an ephemeral ECDH key pair using the curve in the + selected cipher suite and format it as a COSE_Key. Let G_X be the + 'x' parameter of the COSE_Key. * Choose a connection identifier C_I and store it for the length of the protocol. * Encode message_1 as a sequence of CBOR encoded data items as specified in Section 5.3.1 5.3.3. Responder Processing of Message 1 The Responder SHALL process message_1 as follows: - * Decode message_1 (see Appendix A.1). + * Decode message_1 (see Appendix B.1). * Verify that the selected cipher suite is supported and that no prior cipher suite in SUITES_I is supported. - * Pass AD_1 to the security application. + * Pass EAD_1 to the security application. - If any verification step fails, the Responder MUST send an EDHOC + If any processing step fails, the Responder SHOULD send an EDHOC error message back, formatted as defined in Section 6, and the - protocol MUST be discontinued. + session MUST be discontinued. Sending error messages is essential + for debugging but MAY e.g. be skipped due to denial of service + reasons, see Section 8. 5.4. EDHOC Message 2 + 5.4.1. Formatting of Message 2 - message_2 and data_2 SHALL be CBOR Sequences (see Appendix A.1) as + 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, @@ -1217,378 +1266,394 @@ * 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: * If corr (METHOD_CORR mod 4) equals 1 or 3, C_I is omitted, otherwise C_I is not omitted. - * Generate an ephemeral ECDH key pair as specified in Section 5 of - [SP-800-56A] using the curve in the selected cipher suite and - format it as a COSE_Key. Let G_Y be the 'x' parameter of the - COSE_Key. + * Generate an ephemeral ECDH key pair using the curve in the + selected cipher suite and format it as a COSE_Key. Let G_Y be the + 'x' parameter of the COSE_Key. * Choose a connection identifier C_R and store it for the length of the protocol. - * Compute the transcript hash TH_2 = H(message_1, data_2) where H() - is the hash function in the selected cipher suite. The transcript - hash TH_2 is a CBOR encoded bstr and the input to the hash - function is a CBOR Sequence. + * Compute the transcript hash TH_2 = H( H(message_1), data_2 ) where + H() is the hash function in the selected cipher suite. The + transcript hash TH_2 is a CBOR encoded bstr and the input to the + hash function is a CBOR Sequence. Note that H(message_1) can be + computed and cached already in the processing of message_1. * 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, and the following parameters: - protected = << ID_CRED_R >> o ID_CRED_R - identifier to facilitate retrieval of CRED_R, see Section 3.3.4 - - external_aad = << TH_2, CRED_R, ? AD_2 >> + - external_aad = << TH_2, CRED_R, ? EAD_2 >> o CRED_R - bstr containing the credential of the Responder, - see Section 3.3.4. + see Section 3.3.4 - o AD_2 = bstr containing opaque unprotected auxiliary data + o EAD_2 = unprotected external authorization data, see + Section 3.6 - plaintext = h'' COSE constructs the input to the AEAD [RFC5116] as follows: - Key K = EDHOC-KDF( PRK_3e2m, TH_2, "K_2m", length ) - Nonce N = EDHOC-KDF( PRK_3e2m, TH_2, "IV_2m", length ) - Plaintext P = 0x (the empty string) - Associated data A = - [ "Encrypt0", << ID_CRED_R >>, << TH_2, CRED_R, ? AD_2 >> ] + [ "Encrypt0", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >> ] MAC_2 is the 'ciphertext' of the inner COSE_Encrypt0. * If the Responder authenticates with a static Diffie-Hellman key (method equals 1 or 3), then Signature_or_MAC_2 is MAC_2. If the Responder authenticates with a signature key (method equals 0 or 2), then Signature_or_MAC_2 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 the Responder, and the following parameters: - protected = << ID_CRED_R >> - - external_aad = << TH_2, CRED_R, ? AD_2 >> + - 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 the Responder. - The message M to be signed = - [ "Signature1", << ID_CRED_R >>, << TH_2, CRED_R, ? AD_2 >>, + [ "Signature1", << ID_CRED_R >>, << TH_2, CRED_R, ? EAD_2 >>, MAC_2 ] * CIPHERTEXT_2 is encrypted by using the Expand function as a binary additive stream cipher. - plaintext = ( ID_CRED_R / bstr_identifier, Signature_or_MAC_2, - ? AD_2 ) + ? EAD_2 ) o Note that if 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, see Section 3.3.4 and Section 5.1. - CIPHERTEXT_2 = plaintext XOR KEYSTREAM_2 * Encode message_2 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 A.1). + * Decode message_2 (see Appendix B.1). * Retrieve the protocol state using the connection identifier C_I and/or other external information such as the CoAP Token and the 5-tuple. * Decrypt CIPHERTEXT_2, see Section 5.4.2. + * Pass EAD_2 to the security application. + * Verify that the identity of the Responder is an allowed identity for this connection, see Section 3.3. * Verify Signature_or_MAC_2 using the algorithm in the selected cipher suite. The verification process depends on the method, see Section 5.4.2. - * Pass AD_2 to the security application. - - If any verification step fails, the Initiator MUST send an EDHOC - error message back, formatted as defined in Section 6, and the - protocol MUST be discontinued. + If any processing step fails, the Initiator SHOULD send an EDHOC + error message back, formatted as defined in Section 6. 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, the session 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 A.1) as + 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 Processing of Message 3 The Initiator SHALL compose message_3 as follows: * If corr (METHOD_CORR mod 4) equals 2 or 3, C_R is omitted, otherwise C_R is not omitted. - * Compute the transcript hash TH_3 = H(TH_2 , CIPHERTEXT_2, data_3) - where H() is the hash function in the selected cipher suite. The - transcript hash TH_3 is a CBOR encoded bstr and the input to the - hash function is a CBOR Sequence. + * Compute the transcript hash TH_3 = H( H(TH_2, CIPHERTEXT_2), + data_3 ) where H() is the hash function in the selected cipher + suite. The transcript hash TH_3 is a CBOR encoded bstr and the + input to the hash function is a CBOR Sequence. Note that H(TH_2, + CIPHERTEXT_2) can be computed and cached already in the processing + of message_2. * 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_3m, IV_3m, and the following parameters: - protected = << ID_CRED_I >> o ID_CRED_I - identifier to facilitate retrieval of CRED_I, see Section 3.3.4 - - external_aad = << TH_3, CRED_I, ? AD_3 >> - + - external_aad = << TH_3, CRED_I, ? EAD_3 >> o CRED_I - bstr containing the credential of the Initiator, see Section 3.3.4. - o AD_3 = bstr containing opaque protected auxiliary data + o EAD_3 = protected external authorization data, see + Section 3.6 - plaintext = h'' COSE constructs the input to the AEAD [RFC5116] as follows: - Key K = EDHOC-KDF( PRK_4x3m, TH_3, "K_3m", length ) + - Nonce N = EDHOC-KDF( PRK_4x3m, TH_3, "IV_3m", length ) - Plaintext P = 0x (the empty string) - Associated data A = - [ "Encrypt0", << ID_CRED_I >>, << TH_3, CRED_I, ? AD_3 >> ] + [ "Encrypt0", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >> ] MAC_3 is the 'ciphertext' of the inner COSE_Encrypt0. * If the Initiator authenticates with a static Diffie-Hellman key (method equals 2 or 3), then Signature_or_MAC_3 is MAC_3. If the Initiator authenticates with a signature key (method equals 0 or 1), then Signature_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 the Initiator, and the following parameters: - protected = << ID_CRED_I >> - - external_aad = << TH_3, CRED_I, ? AD_3 >> + - external_aad = << TH_3, CRED_I, ? EAD_3 >> - payload = MAC_3 COSE constructs the input to the Signature Algorithm as: - The key is the private authentication key of the Initiator. - The message M to be signed = - [ "Signature1", << ID_CRED_I >>, << TH_3, CRED_I, ? AD_3 >>, + [ "Signature1", << ID_CRED_I >>, << TH_3, CRED_I, ? EAD_3 >>, MAC_3 ] * Compute an 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, 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, - ? AD_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 in the plaintext encoded as a bstr_identifier, see Section 3.3.4 and Section 5.1. COSE constructs the input to the AEAD [RFC5116] as follows: - Key K = EDHOC-KDF( PRK_3e2m, TH_3, "K_3ae", length ) - Nonce N = EDHOC-KDF( PRK_3e2m, TH_3, "IV_3ae", length ) - Plaintext P = ( ID_CRED_I / bstr_identifier, - Signature_or_MAC_3, ? AD_3 ) + Signature_or_MAC_3, ? EAD_3 ) - Associated data A = [ "Encrypt0", h'', TH_3 ] CIPHERTEXT_3 is the 'ciphertext' of the outer COSE_Encrypt0. * Encode message_3 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 does however not know that the - Responder has actually computed the key PRK_4x3m. While the - Initiator can securely send protected application data, the Initiator - SHOULD NOT permanently store the keying material PRK_4x3m and TH_4 - until the Initiator is assured that the Responder has actually - computed the key PRK_4x3m (explicit key confirmation). Explicit 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. Responder Processing of Message 3 The Responder SHALL process message_3 as follows: - * Decode message_3 (see Appendix A.1). + * Decode message_3 (see Appendix B.1). * Retrieve the protocol state using the connection identifier C_R and/or other external information such as the CoAP Token and the 5-tuple. * 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, and IV_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 using the algorithm in the selected cipher suite. The verification process depends on the method, see Section 5.5.2. - * Pass AD_3, the connection identifiers (C_I, C_R), and the - application algorithms in the selected cipher suite to the - security application. The application can now derive application - keys using the EDHOC-Exporter interface. + * Pass the connection identifiers (C_I, C_R), and the application + algorithms in the selected cipher suite to the security + application. The application can now derive application keys + using the EDHOC-Exporter interface. - If any verification step fails, the Responder MUST send an EDHOC - error message back, formatted as defined in Section 6, and the - protocol MUST be discontinued. + If any processing step fails, the Responder SHOULD send an EDHOC + error message back, formatted as defined in Section 6. 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, 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. - All error messages 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 messages might also have been - sent by an attacker and the receiver MAY therefore try to continue - the protocol. + Errors in EDHOC are fatal. After sending an error message, the + sender MUST discontinue the protocol. The receiver SHOULD treat an + error message as an indication that the other party likely has + discontinued the protocol. But as the error message is not + authenticated, a received error message might also have been sent by + an attacker and the receiver MAY therefore try to continue the + protocol. - error SHALL be a CBOR Sequence (see Appendix A.1) as defined below + 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 set to C_R, else C_x is omitted. - * ERR_CODE - error code encoded as an integer. + * ERR_CODE - error code encoded as an integer. The value 0 is used + for success, all other values (negative or positive) indicate + errors. * 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, 0 and -1 MUST be supported. + 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 | +==========+===============+========================================+ - | -1 | TBD | Success | + | 0 | any | Success | +----------+---------------+----------------------------------------+ - | 0 | tstr | Unspecified | + | 1 | tstr | Unspecified | +----------+---------------+----------------------------------------+ - | 1 | SUITES_R | Wrong selected cipher suite | + | 2 | SUITES_R | Wrong selected cipher suite | +----------+---------------+----------------------------------------+ Figure 6: Error Codes and Error Information 6.1. Success - TBD + 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 0 is used for unspecified errors and contain a diagnostic - message. - - For error messages with ERR_CODE == 0, 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. + 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 1 MUST only be used in a response to message_1 in case the + 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 Section 5.3.3. - 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. @@ -1611,163 +1676,165 @@ 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, SUITES_I = 5, G_X, C_I, AD_1 | + | METHOD_CORR, SUITES_I = 5, G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | | | | C_I, DIAG_MSG, SUITES_R = 6 | |<------------------------------------------------------------------+ | error | | | - | METHOD_CORR, SUITES_I = [6, 5, 6], G_X, C_I, AD_1 | + | METHOD_CORR, SUITES_I = [6, 5, 6], G_X, C_I, 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, SUITES_I = [6, 5, 6], G_X, C_I, AD_1 | + | METHOD_CORR, SUITES_I = [6, 5, 6], G_X, C_I, EAD_1 | +------------------------------------------------------------------>| | message_1 | | | | C_I, DIAG_MSG, SUITES_R = [9, 8] | |<------------------------------------------------------------------+ | error | | | - | METHOD_CORR, SUITES_I = [8, 5, 6, 7, 8], G_X, C_I, AD_1 | + | METHOD_CORR, 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 Section 5.3.1 and Section 5.3.2). Furthermore, the Responder shall only accept message_1 if the selected cipher suite is the first cipher suite in SUITES_I that the Responder supports (see Section 5.3.3). Following this procedure ensures that the selected cipher suite is the most preferred (by the Initiator) cipher suite supported by both parties. If the selected cipher suite is not the first cipher suite which the Responder supports in SUITES_I received in message_1, then Responder MUST discontinue the protocol, see Section 5.3.3. If SUITES_I in message_1 is manipulated then the integrity verification of message_2 - containing the transcript hash TH_2 = H( message_1, data_2 ) will - fail and the Initiator will discontinue the protocol. + containing the transcript hash TH_2 will fail and the Initiator will + discontinue the protocol. 7. Transferring EDHOC and Deriving an OSCORE Context 7.1. EDHOC Message 4 This section specifies message_4 which is OPTIONAL to support. Key confirmation is normally provided by sending an application message from the Responder to the Initiator protected with a key derived with - the EDHOC-Exporter, e.g., using OSCORE (see Section 7.2.1). In - deployments where no protected application message is sent from the - Responder to the Initiator, the Responder MUST send message_4. Two - examples of such deployments: + the EDHOC-Exporter, e.g., using OSCORE (see + [I-D.ietf-core-oscore-edhoc]). In deployments where no protected + application message is sent from the Responder to the Initiator, the + Responder MUST send message_4. Two examples of such deployments: 1. When EDHOC is only used for authentication and no application data is sent. 2. When application data is only sent from the Initiator to the Responder. Further considerations are provided in Section 3.7. 7.1.1. Formatting of Message 4 - message_4 and data_4 SHALL be CBOR Sequences (see Appendix A.1) as + message_4 and data_4 SHALL be CBOR Sequences (see Appendix B.1) as defined below message_4 = ( data_4, - MAC_4 : bstr, + CIPHERTEXT_4 : bstr, ) data_4 = ( ? C_I : bstr_identifier, ) 7.1.2. Responder Processing of Message 4 The Responder SHALL compose message_4 as follows: * If corr (METHOD_CORR mod 4) equals 1 or 3, C_I is omitted, otherwise C_I is not omitted. - * Compute an inner COSE_Encrypt0 as defined in Section 5.3 of + * Compute a COSE_Encrypt0 as defined in Section 5.3 of [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm - in the selected cipher suite, and the following parameters: + in the selected cipher suite, and the following parameters. The + protected header SHALL be empty. - protected = h'' - - external_aad = << TH_4 >> + - external_aad = TH_4 - - plaintext = h'' + - plaintext = ( ? EAD_4 ) - COSE constructs the input to the AEAD [RFC5116] as follows: + where EAD_4 is protected external authorization data, see + Section 3.6. COSE constructs the input to the AEAD [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 ) - - Plaintext P = 0x (the empty string) - - - Associated data A = - - [ "Encrypt0", h'', << TH_4 >> ] + - Associated data A = [ "Encrypt0", h'', TH_4 ] - MAC_4 is the 'ciphertext' of the COSE_Encrypt0. + CIPHERTEXT_4 is the 'ciphertext' of the COSE_Encrypt0. * Encode message_4 as a sequence of CBOR encoded data items as specified in Section 7.1.1. 7.1.3. Initiator Processing of Message 4 The Initiator SHALL process message_4 as follows: - * Decode message_4 (see Appendix A.1). + * Decode message_4 (see Appendix B.1). * Retrieve the protocol state using the connection identifier C_I and/or other external information such as the CoAP Token and the 5-tuple. - * Verify MAC_4 as defined in Section 5.3 of - [I-D.ietf-cose-rfc8152bis-struct], with the EDHOC AEAD algorithm - in the selected cipher suite, and the parameters defined in - Section 7.1.2. + * 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, and the parameters + defined in Section 7.1.2. + + * Pass EAD_4 to the security application. If any verification step fails the Initiator MUST send an EDHOC error - message back, formatted as defined in Section 6, and the protocol - MUST be discontinued. + message back, formatted as defined in Section 6, and the session MUST + be discontinued. 7.2. Transferring EDHOC in CoAP It is recommended to transport EDHOC as an exchange of CoAP [RFC7252] messages. CoAP is a reliable transport that can preserve packet ordering and handle message duplication. CoAP can also perform fragmentation and protect against denial of service attacks. It is recommended to carry the EDHOC messages in Confirmable messages, especially if fragmentation is used. @@ -1848,78 +1915,47 @@ Figure 10: Transferring EDHOC in CoAP when the Initiator is CoAP 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 fragmentation is needed, the EDHOC messages may be fragmented using the CoAP Block-Wise Transfer - mechanism [RFC7959]. - -7.2.1. Deriving an OSCORE Context from EDHOC - - When EDHOC is used to derive parameters for OSCORE [RFC8613], the - parties make sure that the EDHOC connection identifiers are unique, - i.e. C_R MUST NOT be equal to C_I. The CoAP client and server MUST - be able to retrieve the OSCORE protocol state using its chosen - connection identifier and optionally other information such as the - 5-tuple. In case that the CoAP client is the Initiator and the CoAP - server is the Responder: - - * The client's OSCORE Sender ID is C_R and the server's OSCORE - Sender ID is C_I, as defined in this document - - * The AEAD Algorithm and the hash algorithm are the application AEAD - and hash algorithms in the selected cipher suite. - - * The Master Secret and Master Salt are derived as follows. By - default key_length is the key length (in bytes) of the application - AEAD Algorithm and salt_length is 8 bytes. The Initiator and - Responder MAY agree out-of-band on a longer key_length than the - default and a different salt_length. - - Master Secret = EDHOC-Exporter( "OSCORE Master Secret", key_length ) - Master Salt = EDHOC-Exporter( "OSCORE Master Salt", salt_length ) - -7.2.2. Error Messages with CoAP Transport - - EDHOC does not restrict how error messages are transported with CoAP, - as long as the appropriate error message can to be transported in - response to a message that failed (see Section 6). In case of - combining EDHOC and OSCORE as specified in - [I-D.ietf-core-oscore-edhoc], an error message following a combined - EDHOC message_3/OSCORE request MUST be sent with a CoAP error code - and SHALL contain the ERR_INFO as payload (see Section 6). + mechanism [RFC7959]. EDHOC does not restrict how error messages are + transported with CoAP, as long as the appropriate error message can + to be transported in response to a message that failed (see + Section 6). The use of EDHOC with OSCORE is specified in + [I-D.ietf-core-oscore-edhoc]. 8. Security Considerations 8.1. Security Properties EDHOC inherits its security properties from the theoretical SIGMA-I protocol [SIGMA]. Using the terminology from [SIGMA], EDHOC provides perfect forward secrecy, mutual authentication with aliveness, consistency, and peer awareness. As described in [SIGMA], peer awareness is provided to the Responder, but not to the Initiator. EDHOC protects the credential identifier of the Initiator against active attacks and the credential identifier of the Responder against passive attacks. The roles should be assigned to protect the most sensitive identity/identifier, typically that which is not possible to infer from routing information in the lower layers. Compared to [SIGMA], EDHOC adds an explicit method type and expands the message authentication coverage to additional elements such as - algorithms, auxiliary data, and previous messages. This protects - against an attacker replaying messages or injecting messages from - another session. + algorithms, external authorization data, and previous messages. This + protects against an attacker replaying messages or injecting messages + from another session. EDHOC also adds negotiation of connection identifiers and downgrade protected negotiation of cryptographic parameters, i.e. an attacker cannot affect the negotiated parameters. A single session of EDHOC does not include negotiation of cipher suites, but it enables the Responder to verify that the selected cipher suite is the most preferred cipher suite by the Initiator which is supported by both the Initiator and the Responder. As required by [RFC7258], IETF protocols need to mitigate pervasive @@ -2023,70 +2059,84 @@ method). The data rates in many IoT deployments are very limited. Given that the application keys are protected as well as the long-term authentication keys they can often be used for years or even decades before the cryptographic limits are reached. If the application keys established through EDHOC need to be renewed, the communicating parties can derive application keys with other labels or run EDHOC again. + Requirement for how to securely generate, validate, and process the + ephermeral public keys depend on the elliptic curve. For X25519 and + X448, the requirements are defined in [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. + 8.3. Cipher Suites and Cryptographic Algorithms For many constrained IoT devices it is problematic 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 suite 0 (AES-CCM-16-64-128, SHA-256, X25519, EdDSA, Ed25519, - AES-CCM-16-64-128, SHA-256) and cipher suite 2 (AES-CCM-16-64-128, - SHA-256, P-256, ES256, P-256, 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. + 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 the algorithms needed for their supported + methods. When using private cipher suite or registering new cipher suites, the choice of key length used in the different algorithms needs to be harmonized, so that a sufficient security level is maintained for certificates, EDHOC, and the protection of application data. The Initiator and the Responder 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 use in EDHOC except for certificate identification with x5u and c5u. Note that secp256k1 is only defined for use with ECDSA and not for ECDH. 8.4. Unprotected Data The Initiator and the Responder must make sure that unprotected data and metadata do not reveal any sensitive information. This also applies for encrypted data sent to an unauthenticated party. In - particular, it applies to AD_1, ID_CRED_R, AD_2, and ERR_MSG. Using - the same AD_1 in several EDHOC sessions allows passive eavesdroppers - to correlate the different sessions. Another consideration is that - the list of supported cipher suites may potentially be used to - identify the application. + particular, it applies to EAD_1, ID_CRED_R, EAD_2, and error + messages. Using the same EAD_1 in several EDHOC sessions allows + passive eavesdroppers to correlate the different sessions. Another + consideration is that the list of supported cipher suites may + potentially be used to identify the application. The Initiator and the Responder must also make sure that unauthenticated data does not trigger any harmful actions. In - particular, this applies to AD_1 and ERR_MSG. + 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 sending a number of new or replayed message_1 an attacker may cause the Responder to allocate state, perform cryptographic operations, and amplify messages. To mitigate such attacks, an implementation SHOULD rely on lower layer mechanisms such as the Echo option in CoAP [I-D.ietf-core-echo-request-tag] that forces the initiator to demonstrate reachability at its apparent network address. + An attacker can also send faked message_2, message_3, message_4, or + error in an attempt to trick the receiving party to send an error + message and discontinue the session. EDHOC implementations MAY + evaluate if a received message is likely to have be forged by and + attacker and ignore it without sending an error message or + discontinuing the session. + 8.6. Implementation Considerations The availability of a secure random number generator is essential for the security of EDHOC. 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 only be used 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 writing to @@ -2103,79 +2153,96 @@ unaugmented random numbers on the wire. If ECDSA is supported, "deterministic ECDSA" as specified in [RFC6979] MAY be used. Pure deterministic elliptic-curve signatures such as deterministic ECDSA and EdDSA have gained popularity over randomized ECDSA as their security do not depend on a source of high- quality randomness. Recent research has however found that implementations of these signature algorithms may be vulnerable to certain side-channel and fault injection attacks due to their determinism. See e.g. Section 1 of + [I-D.mattsson-cfrg-det-sigs-with-noise] for a list of attack papers. As suggested in Section 6.1.2 of [I-D.ietf-cose-rfc8152bis-algs] this can be addressed by combining randomness and determinism. - The referenced processing instructions in [SP-800-56A] must be - complied with, including deleting the intermediate computed values - along with any ephemeral ECDH secrets after the key derivation is - completed. The ECDH shared secrets, keys, and IVs MUST be secret. + All private keys, symmetric keys, and IVs MUST be secret. Implementations should provide countermeasures to side-channel - attacks such as timing attacks. Depending on the selected curve, the - parties should perform various validations of each other's public - keys, see e.g. Section 5 of [SP-800-56A]. + attacks such as timing attacks. Intermediate computed values such as + ephemeral ECDH keys and ECDH shared secrets MUST be deleted after key + derivation is completed. The Initiator and the Responder are responsible for verifying the integrity of certificates. The selection of trusted CAs should be done very carefully and certificate revocation should be supported. The private authentication keys MUST be kept secret. The Initiator and the Responder are allowed to select the connection identifiers C_I and C_R, respectively, for the other party to use in the ongoing EDHOC protocol as well as in a subsequent application protocol (e.g. OSCORE [RFC8613]). The choice of connection identifier is not security critical in EDHOC but intended to simplify the retrieval of the right security context in combination with using short identifiers. If the wrong connection identifier of the other party is used in a protocol message it will result in the 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). - The Responder MUST finish the verification step of message_3 before - passing AD_3 to the application. - 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 be discarded to mitigate reflection attacks. Note that in the case of two simultaneous EDHOC exchanges where the nodes only complete one and where the nodes have different preferred cipher suites, an attacker can affect which of the two nodes' preferred cipher suites will be used by blocking the other exchange. If supported by the device, it is RECOMMENDED that at least the long- - term private keys is stored in a Trusted Execution Environment (TEE) + term private keys are stored in a Trusted Execution Environment (TEE) and that sensitive operations using these keys are performed inside - the TEE. To achieve even higher security it is RECOMMENDED that + the TEE. To achieve even higher security it is RECOMMENDED that in additional operations such as ephemeral key generation, all - computations of shared secrets, and storage of the PRK keys can be - done inside the TEE. The TEE can also be used to protect the EDHOC - and application protocol (e.g. OSCORE) implementation using some - form of "secure boot", memory protection etc. The use of a TEE - enforces that code within that environment cannot be tampered with, - and that any data used by such code cannot be read or tampered with - by code outside that environment. + computations of shared secrets, and storage of the pseudorandom keys + (PRK) can be done inside the TEE. The use of a TEE enforces that + code within that environment cannot be tampered with, and that any + 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 read EDHOC data and tamper with EDHOC code, to + protect against such attacks EDHOC needs to be in its own zone. To + provide better protection against some forms of physical attacks, + sensitive EDHOC data should be stored inside the SoC or encrypted and + integrity protected when sent on a data bus (e.g. between the CPU and + RAM or Flash). Secure boot can be used to increase the security of + code and data in the Rich Execution Environment (REE) by validating + the REE image. 9. IANA Considerations -9.1. EDHOC Cipher Suites Registry +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, and + Reference. All columns are text strings. The initial contents of + 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]] + +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 columns of the registry are Value, Array, Description, and Reference, where Value is an 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 @@ -2189,86 +2256,86 @@ 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 - Array: 10, 5, 4, -8, 6, 10, 5 - Desc: AES-CCM-16-64-128, SHA-256, X25519, EdDSA, Ed25519, + 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, 5, 4, -8, 6, 10, 5 - Desc: AES-CCM-16-128-128, SHA-256, X25519, EdDSA, Ed25519, + 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, 5, 1, -7, 1, 10, 5 - Desc: AES-CCM-16-64-128, SHA-256, P-256, ES256, P-256, + 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, 5, 1, -7, 1, 10, 5 - Desc: AES-CCM-16-128-128, SHA-256, P-256, ES256, P-256, + 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, 1, -16 - Desc: A128GCM, SHA-256, X25519, ES256, P-256, + 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, 2, 3, -43 - Desc: A256GCM, SHA-384, P-384, ES384, P-384, + Array: 3, -43, 2, -35, 3, -43 + Desc: A256GCM, SHA-384, P-384, ES384, A256GCM, SHA-384 Reference: [[this document]] -9.2. EDHOC Method Type Registry +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". The columns of the registry are Value, Description, and Reference, where Value is an integer and the other columns are text strings. The initial contents of the registry is shown in Figure 4. -9.3. EDHOC Error Codes Registry +9.4. EDHOC Error 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 and Description, where ERR_CODE is an integer, ERR_INFO is a CDDL defined type, and Description is a text string. The initial contents of the registry is shown in Figure 6. -9.4. The Well-Known URI Registry +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 -9.5. Media Types Registry +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 @@ -2298,34 +2365,34 @@ "Authors' Addresses" section. * Intended usage: COMMON * Restrictions on usage: N/A * Author: See "Authors' Addresses" section. * Change Controller: IESG -9.6. CoAP Content-Formats Registry +9.7. CoAP Content-Formats Registry IANA has added the media type 'application/edhoc' to the CoAP Content-Formats registry. * Media Type: application/edhoc * Encoding: * ID: TBD42 * Reference: [[this document]] -9.7. Expert Review Instructions +9.8. Expert Review Instructions The IANA Registries established in this document is defined as "Expert Review". This section gives some general guidelines for what the experts should be looking for, but they are being designated as experts for a reason so they should be given substantial latitude. Expert reviewers should take into consideration the following points: * Clarity and correctness of registrations. Experts are expected to check the clarity of purpose and use of the requested entries. @@ -2418,51 +2485,52 @@ DOI 10.17487/RFC8724, April 2020, . [RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR) Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020, . [I-D.ietf-cose-rfc8152bis-struct] Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", Work in Progress, Internet-Draft, - draft-ietf-cose-rfc8152bis-struct-14, 24 September 2020, - . + draft-ietf-cose-rfc8152bis-struct-15, 1 February 2021, + . [I-D.ietf-cose-rfc8152bis-algs] Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", Work in Progress, Internet-Draft, draft-ietf-cose-rfc8152bis-algs-12, 24 September 2020, - . [I-D.ietf-cose-x509] Schaad, J., "CBOR Object Signing and Encryption (COSE): Header parameters for carrying and referencing X.509 certificates", Work in Progress, Internet-Draft, draft- - ietf-cose-x509-08, 14 December 2020, . + ietf-cose-x509-08, 14 December 2020, + . [I-D.ietf-core-echo-request-tag] - Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo, + Amsüss, C., Mattsson, J. P., and G. Selander, "CoAP: Echo, Request-Tag, and Token Processing", Work in Progress, - Internet-Draft, draft-ietf-core-echo-request-tag-11, 2 - November 2020, . + Internet-Draft, draft-ietf-core-echo-request-tag-12, 1 + February 2021, . [I-D.ietf-lake-reqs] - Vucinic, M., Selander, G., Mattsson, J., and D. Garcia- - Carillo, "Requirements for a Lightweight AKE for OSCORE", + Vucinic, M., Selander, G., Mattsson, J. P., and D. Garcia- + Carrillo, "Requirements for a Lightweight AKE for OSCORE", Work in Progress, Internet-Draft, draft-ietf-lake-reqs-04, - 8 June 2020, . + 8 June 2020, . 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, . [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May @@ -2476,78 +2544,82 @@ [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [RFC8937] Cremers, C., Garratt, L., Smyshlyaev, S., Sullivan, N., and C. Wood, "Randomness Improvements for Security Protocols", RFC 8937, DOI 10.17487/RFC8937, October 2020, . [I-D.ietf-core-resource-directory] - Amsuess, C., Shelby, Z., Koster, M., Bormann, C., and P. - Stok, "CoRE Resource Directory", Work in Progress, - Internet-Draft, draft-ietf-core-resource-directory-26, 2 - November 2020, . + Amsüss, C., Shelby, Z., Koster, M., Bormann, C., and P. V. + D. Stok, "CoRE Resource Directory", Work in Progress, + Internet-Draft, draft-ietf-core-resource-directory-28, 7 + March 2021, . [I-D.ietf-lwig-security-protocol-comparison] - Mattsson, J., Palombini, F., and M. Vucinic, "Comparison - of CoAP Security Protocols", Work in Progress, Internet- - Draft, draft-ietf-lwig-security-protocol-comparison-05, 2 - November 2020, . + Mattsson, J. P., Palombini, F., and M. Vucinic, + "Comparison of CoAP Security Protocols", Work in Progress, + Internet-Draft, draft-ietf-lwig-security-protocol- + comparison-05, 2 November 2020, + . [I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", Work in Progress, Internet-Draft, draft-ietf-tls- - dtls13-40, 20 January 2021, . + dtls13-43, 30 April 2021, . [I-D.selander-ace-ake-authz] - Selander, G., Mattsson, J., Vucinic, M., Richardson, M., - and A. Schellenbaum, "Lightweight Authorization for + Selander, G., Mattsson, J. P., Vucinic, M., Richardson, + M., and A. Schellenbaum, "Lightweight Authorization for Authenticated Key Exchange.", Work in Progress, Internet- Draft, draft-selander-ace-ake-authz-02, 2 November 2020, - . + . [I-D.ietf-core-oscore-edhoc] Palombini, F., Tiloca, M., Hoeglund, R., Hristozov, S., and G. Selander, "Combining EDHOC and OSCORE", Work in Progress, Internet-Draft, draft-ietf-core-oscore-edhoc-00, 1 April 2021, . - [I-D.mattsson-cose-cbor-cert-compress] - Raza, S., Hoglund, J., Selander, G., Mattsson, J., and M. - Furuhed, "CBOR Encoding of X.509 Certificates (CBOR + [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)", Work in Progress, Internet-Draft, draft- - mattsson-cose-cbor-cert-compress-06, 19 January 2021, - . + ietf-cose-cbor-encoded-cert-00, 28 April 2021, + . [I-D.mattsson-cfrg-det-sigs-with-noise] - Mattsson, J., Thormarker, E., and S. Ruohomaa, + Mattsson, J. P., Thormarker, E., and S. Ruohomaa, "Deterministic ECDSA and EdDSA Signatures with Additional Randomness", Work in Progress, Internet-Draft, draft- mattsson-cfrg-det-sigs-with-noise-02, 11 March 2020, - . + . [SP-800-56A] Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R. Davis, "Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography", NIST Special Publication 800-56A Revision 3, April 2018, . + [SECG] "Standards for Efficient Cryptography 1 (SEC 1)", May + 2009, . + [SIGMA] Krawczyk, H., "SIGMA - The 'SIGn-and-MAc' Approach to Authenticated Diffie-Hellman and Its Use in the IKE- Protocols (Long version)", June 2003, . [CNSA] (Placeholder), ., "Commercial National Security Algorithm Suite", August 2015, . @@ -2560,27 +2632,63 @@ [Bruni18] Bruni, A., Sahl Jørgensen, T., Grønbech Petersen, T., and C. Schürmann, "Formal Verification of Ephemeral Diffie- Hellman Over COSE (EDHOC)", November 2018, . [CborMe] Bormann, C., "CBOR Playground", May 2018, . -Appendix A. Use of CBOR, CDDL and COSE in EDHOC +Appendix A. 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]. + +Appendix B. 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]. -A.1. CBOR and CDDL +B.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. @@ -2607,37 +2715,37 @@ 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 ------------------------------------------------------------------ -A.2. CDDL Definitions +B.2. CDDL Definitions This sections compiles the CDDL definitions for ease of reference. bstr_identifier = bstr / int suite = int SUITES_R : [ supported : 2* suite ] / suite message_1 = ( ? C_1 : null, METHOD_CORR : int, SUITES_I : [ selected : suite, supported : 2* suite ] / suite, G_X : bstr, C_I : bstr_identifier, - ? AD_1 : bstr, + ? EAD ; EAD_1 ) message_2 = ( data_2, CIPHERTEXT_2 : bstr, ) data_2 = ( ? C_I : bstr_identifier, G_Y : bstr, @@ -2648,81 +2756,85 @@ data_3, CIPHERTEXT_3 : bstr, ) data_3 = ( ? C_R : bstr_identifier, ) message_4 = ( data_4, - MAC_4 : bstr, + CIPHERTEXT_4 : bstr, ) data_4 = ( ? C_I : bstr_identifier, ) error = ( ? C_x : bstr_identifier, ERR_CODE : int, ERR_INFO : any ) info = [ edhoc_aead_id : int / tstr, transcript_hash : bstr, label : tstr, length : uint ] -A.3. COSE +B.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. -Appendix B. Test Vectors +Appendix C. Test Vectors - This appendix provides detailed test vectors compatible with versions - -05 and -06 of this specification, to ease implementation and ensure - interoperability. In addition to hexadecimal, all CBOR data items - and sequences are given in CBOR diagnostic notation. The test - vectors use the default mapping to CoAP where the Initiator acts as - CoAP client (this means that corr = 1). + Note: The test vectors are not updated to version -07 of the draft. + More changes affecting the test vectors are anticipated for -08. + + 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. -B.1. Test Vectors for EDHOC Authenticated with Signature Keys (x5t) +C.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 auxiliary - data is sent in the message exchange. + 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: @@ -2737,21 +2849,21 @@ 00 The Initiator selected the indicated cipher suite. Selected Cipher Suite (int) 0 Cipher suite 0 is supported by both the Initiator and the Responder, see Section 3.4. -B.1.1. Message_1 +C.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 @@ -2762,23 +2874,23 @@ 09 Note that since C_I is a byte string in the interval h'00' to h'2f', it is encoded as the corresponding integer subtracted by 24 (see bstr_identifier in Section 5.1). Thus 0x09 = 09, 9 - 24 = -15, and -15 in CBOR encoding is equal to 0x2e. C_I (1 byte) 2e - Since no auxiliary data is sent: + Since no external authorization data is sent: - AD_1 (0 bytes) + 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) @@ -2794,21 +2906,21 @@ h'898FF79A02067A16EA1ECCB90FA52246F5AA4DD6EC076BBA0259D904B7EC8B0C', -15 ) Which as a CBOR encoded data item is: message_1 (CBOR Sequence) (37 bytes) 01 00 58 20 89 8f f7 9a 02 06 7a 16 ea 1e cc b9 0f a5 22 46 f5 aa 4d d6 ec 07 6b ba 02 59 d9 04 b7 ec 8b 0c 2e -B.1.2. Message_2 +C.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) @@ -2876,30 +2988,30 @@ -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( message_1, data_2 ), as a CBOR Sequence of these 2 data + 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( - message_1, data_2 ) + 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 @@ -2933,23 +3045,23 @@ 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 auxiliary data is sent: + Since no external authorization data is sent: - AD_2 (0 bytes) + 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: @@ -3029,21 +3141,21 @@ * external_aad = A_2m * 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, ? AD_2 >>, MAC_2 + = [ "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 @@ -3072,21 +3184,21 @@ 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. * plaintext = CBOR Sequence of the items ID_CRED_R and Signature_or_MAC_2 encoded as CBOR byte strings, in this order - (AD_2 is empty). + (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. @@ -3136,21 +3248,21 @@ Which as a CBOR encoded data item is: message_2 (CBOR Sequence) (117 bytes) 58 20 71 a3 d5 99 c2 1d a1 89 02 a1 ae a8 10 b2 b6 38 2c cd 8d 5f 9b f0 19 52 81 75 4c 5e bc af 30 1e 37 58 50 0f f2 ac 2d 7e 87 ae 34 0e 50 bb de 9f 70 e8 a7 7f 86 bf 65 9f 43 b0 24 a7 3e e9 7b 6a 2b 9c 55 92 fd 83 5a 15 17 8b 7c 28 af 54 74 a9 75 81 48 64 7d 3d 98 a8 73 1e 16 4c 9c 70 52 81 07 f4 0f 21 46 3b a8 11 bf 03 97 19 e7 cf fa a7 f2 f4 40 -B.1.3. Message_3 +C.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) @@ -3164,32 +3276,32 @@ 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(TH_2 , CIPHERTEXT_2, data_3), as a CBOR - Sequence of these 3 data items. + 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(TH_2 , - CIPHERTEXT_2, data_3) + 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) "" @@ -3223,30 +3335,30 @@ 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 auxiliary data is exchanged: + Since no external authorization data is exchanged: - AD_3 (0 bytes) + 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, ? AD_3 >> ]. + << 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 @@ -3339,21 +3451,21 @@ 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 (AD_3 is empty). + 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 ] @@ -3432,21 +3544,21 @@ ) Which encodes to the following byte string: message_3 (CBOR Sequence) (91 bytes) 37 58 58 f5 f6 de bd 82 14 05 1c d5 83 c8 40 96 c4 80 1d eb f3 5b 15 36 3d d1 6e bd 85 30 df dc fb 34 fc d2 eb 6c ad 1d ac 66 a4 79 fb 38 de aa f1 d3 0a 7e 68 17 a2 2a b0 4f 3d 5b 1e 97 2a 0d 13 ea 86 c6 6b 60 51 4c 96 57 ea 89 c5 7b 04 01 ed c5 aa 8b bc ab 81 3c c5 d6 e7 -B.1.4. OSCORE Security Context Derivation +C.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 @@ -3524,27 +3636,27 @@ 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 -B.2. Test Vectors for EDHOC Authenticated with Static Diffie-Hellman +C.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 auxiliary - data is sent in the message exchange. + 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: @@ -3558,21 +3670,21 @@ Supported Cipher Suites (1 byte) 00 The Initiator selected the indicated cipher suite. Selected Cipher Suite (int) 0 Cipher suite 0 is supported by both the Initiator and the Responder, see Section 3.4. -B.2.1. Message_1 +C.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 @@ -3583,23 +3695,23 @@ 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), i.e. 0x16 = 22, 22 - 24 = -2, and -2 in CBOR encoding is equal to 0x21. C_I (1 byte) 21 - Since no auxiliary data is sent: + Since no external authorization data is sent: - AD_1 (0 bytes) + 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 @@ -3614,21 +3726,21 @@ h'8D3EF56D1B750A4351D68AC250A0E883790EFC80A538A444EE9E2B57E2441A7C', -2 ) Which as a CBOR encoded data item is: message_1 (CBOR Sequence) (37 bytes) 0d 00 58 20 8d 3e f5 6d 1b 75 0a 43 51 d6 8a c2 50 a0 e8 83 79 0e fc 80 a5 38 a4 44 ee 9e 2b 57 e2 44 1a 7c 21 -B.2.2. Message_2 +C.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) @@ -3666,21 +3778,21 @@ G_R (Responder's public authentication key) (32 bytes) a3 ff 26 35 95 be b3 77 d1 a0 ce 1d 04 da d2 d4 09 66 ac 6b cb 62 20 51 b8 46 59 18 4d 5d 9a 32 Since the Responder authenticates with a static Diffie-Hellman key, PRK_3e2m = HKDF-Extract( PRK_2e, G_RX ), where G_RX is the ECDH shared secret calculated from G_R and X, or G_X and R. From the Responder's authentication key and the Initiator's ephemeral - key (see Appendix B.2.1), the ECDH shared secret G_RX is calculated. + key (see Appendix C.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. @@ -3704,30 +3816,30 @@ -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( message_1, data_2 ), as a CBOR Sequence of these 2 data + 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( - message_1, data_2 ) + 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) "" @@ -3750,23 +3862,23 @@ "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 auxiliary data is sent: + Since no external authorization data is sent: - AD_2 (0 bytes) + 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. @@ -3851,21 +3963,21 @@ 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 (AD_2 is empty). + 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), 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) @@ -3908,64 +4020,64 @@ data_2, h'A3F1BD5D028D19CF3C99' ) Which as a CBOR encoded data item is: message_2 (CBOR Sequence) (46 bytes) 58 20 52 fb a0 bd c8 d9 53 dd 86 ce 1a b2 fd 7c 05 a4 65 8c 7c 30 af db fc 33 01 04 70 69 45 1b af 35 37 4a a3 f1 bd 5d 02 8d 19 cf 3c 99 -B.2.3. Message_3 +C.2.3. Message_3 Since corr equals 1, C_R is not omitted from data_3. The Initiator's static Diffie-Hellman key pair is the following: I (Initiator's private authentication key) (32 bytes) 2b be a6 55 c2 33 71 c3 29 cf bd 3b 1f 02 c6 c0 62 03 38 37 b8 b5 90 99 a4 43 6f 66 60 81 b0 8e G_I (Initiator's public authentication key, CBOR unencoded) (32 bytes) 2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae da fe 9c aa 4f 4e 7a bb 83 5e c3 0f 1d e8 8a db 96 ff 71 HKDF SHA-256 is the HKDF used (as defined by cipher suite 0). From the Initiator's authentication key and the Responder's ephemeral - key (see Appendix B.2.2), the ECDH shared secret G_IY is calculated. + key (see Appendix C.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(TH_2 , CIPHERTEXT_2, data_3), as a CBOR - Sequence of these 3 data items. + 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(TH_2 , - CIPHERTEXT_2, data_3) + 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) "" @@ -3987,30 +4099,30 @@ "subject name": "" } Which encodes to the following byte string: CRED_I (54 bytes) a4 01 01 20 04 21 58 20 2c 44 0c c1 21 f8 d7 f2 4c 3b 0e 41 ae da fe 9c aa 4f 4e 7a bb 83 5e c3 0f 1d e8 8a db 96 ff 71 6c 73 75 62 6a 65 63 74 20 6e 61 6d 65 60 - Since no auxiliary data is exchanged: + Since no external authorization data is exchanged: - AD_3 (0 bytes) + 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, ? AD_3 >> ]. + << 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: @@ -4066,21 +4178,21 @@ 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 (AD_3 is empty). + 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), 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 @@ -4154,21 +4266,21 @@ ( -24, h'D5535F3147E85F1CFACD9E78ABF9E0A81BBF' ) Which encodes to the following byte string: message_3 (CBOR Sequence) (20 bytes) 37 52 d5 53 5f 31 47 e8 5f 1c fa cd 9e 78 ab f9 e0 a8 1b bf -B.2.4. OSCORE Security Context Derivation +C.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 @@ -4244,65 +4356,61 @@ 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 -Appendix C. Applicability Template +Appendix D. Applicability Template This appendix contains an example of an applicability statement, see Section 3.7. For use of EDHOC in the XX protocol, the following assumptions are made on the parameters: * METHOD_CORR = 5 - 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.) * EDHOC requests are expected by the server at /app1-edh, no Content-Format needed. * C_1 = "null" is present to identify message_1 * CRED_I is an 802.1AR IDevID encoded as a C509 Certificate of type - 0 [I-D.mattsson-cose-cbor-cert-compress]. + 0 [I-D.ietf-cose-cbor-encoded-cert]. - - R acquires CRED_I out-of-band, indicated in AD_1 + - R acquires CRED_I out-of-band, indicated in EAD_1 - ID_CRED_I = {4: h''} is a kid with value empty byte string * CRED_R is a COSE_Key of type OKP as specified in Section 3.3.4. - The CBOR map has parameters 1 (kty), -1 (crv), and -2 (x-coordinate). * ID_CRED_R = CRED_R - * AD_1 contains Auxiliary Data of type A (TBD) - - * AD_2 contains Auxiliary Data of type B (TBD) - * No use of message_4: the application sends protected messages from R to I. - * Auxiliary Data is processed as specified in - [I-D.selander-ace-ake-authz]. + * External authorization data is defined and processed as specified + in [I-D.selander-ace-ake-authz]. -Appendix D. EDHOC Message Deduplication +Appendix E. 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. @@ -4313,44 +4421,74 @@ support transport layers which does not handle message duplication. Special care is needed to avoid issues with duplicate messages, see Section 5.2. 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 by the same EDHOC instance. This is called "EDHOC message + 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 Section 5.2 still apply because duplicate messages are not processed by the EDHOC state machine: * EDHOC messages SHALL be processed according to the current protocol state. * Different instances of the same message MUST NOT be processed in - one protocol instance. + one session. -Appendix E. Change Log +Appendix F. Change Log Main changes: + * 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 + * 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 @@ -4358,21 +4497,21 @@ "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 Referncing EDHOC" + - Removed section "Other Documents Referencing EDHOC" - Clarifications based on review comments * From -04 to -05: - EDHOC-Rekey-FS -> EDHOC-KeyUpdate - Clarification of cipher suite negotiation - Updated security considerations