Internet DRAFT - draft-selander-ace-cose-ecdhe
draft-selander-ace-cose-ecdhe
Network Working Group G. Selander
Internet-Draft J. Mattsson
Intended status: Standards Track F. Palombini
Expires: March 14, 2020 Ericsson AB
September 11, 2019
Ephemeral Diffie-Hellman Over COSE (EDHOC)
draft-selander-ace-cose-ecdhe-14
Abstract
This document specifies Ephemeral Diffie-Hellman Over COSE (EDHOC), a
very compact, and lightweight authenticated Diffie-Hellman key
exchange with ephemeral keys. EDHOC provides mutual authentication,
perfect forward secrecy, and identity protection. EDHOC is intended
for usage in constrained scenarios and a main use case is to
establish an OSCORE security context. By reusing COSE for
cryptography, CBOR for encoding, and CoAP for transport, the
additional code footprint can be kept very low.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Rationale for EDHOC . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology and Requirements Language . . . . . . . . . . 5
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. EDHOC Overview . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Ephemeral Public Keys . . . . . . . . . . . . . . . . . . 9
3.3. Key Derivation . . . . . . . . . . . . . . . . . . . . . 9
4. EDHOC Authenticated with Asymmetric Keys . . . . . . . . . . 12
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 14
4.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 16
4.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 19
5. EDHOC Authenticated with Symmetric Keys . . . . . . . . . . . 21
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2. EDHOC Message 1 . . . . . . . . . . . . . . . . . . . . . 22
5.3. EDHOC Message 2 . . . . . . . . . . . . . . . . . . . . . 23
5.4. EDHOC Message 3 . . . . . . . . . . . . . . . . . . . . . 23
6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 24
6.1. EDHOC Error Message . . . . . . . . . . . . . . . . . . . 24
7. Transferring EDHOC and Deriving Application Keys . . . . . . 25
7.1. Transferring EDHOC in CoAP . . . . . . . . . . . . . . . 25
7.2. Transferring EDHOC over Other Protocols . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 28
8.1. Security Properties . . . . . . . . . . . . . . . . . . . 28
8.2. Cryptographic Considerations . . . . . . . . . . . . . . 29
8.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 30
8.4. Unprotected Data . . . . . . . . . . . . . . . . . . . . 30
8.5. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 30
8.6. Implementation Considerations . . . . . . . . . . . . . . 31
8.7. Other Documents Referencing EDHOC . . . . . . . . . . . . 32
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
9.1. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 32
9.2. EDHOC Method Type Registry . . . . . . . . . . . . . . . 32
9.3. The Well-Known URI Registry . . . . . . . . . . . . . . . 33
9.4. Media Types Registry . . . . . . . . . . . . . . . . . . 33
9.5. CoAP Content-Formats Registry . . . . . . . . . . . . . . 34
9.6. Expert Review Instructions . . . . . . . . . . . . . . . 34
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
10.1. Normative References . . . . . . . . . . . . . . . . . . 35
10.2. Informative References . . . . . . . . . . . . . . . . . 37
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Appendix A. Use of CBOR, CDDL and COSE in EDHOC . . . . . . . . 39
A.1. CBOR and CDDL . . . . . . . . . . . . . . . . . . . . . . 39
A.2. COSE . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Appendix B. EDHOC Authenticated withDiffie-Hellman Keys . . . . 40
Appendix C. Test Vectors . . . . . . . . . . . . . . . . . . . . 41
C.1. Test Vectors for EDHOC Authenticated with Asymmetric Keys
(RPK) . . . . . . . . . . . . . . . . . . . . . . . . . . 41
C.2. Test Vectors for EDHOC Authenticated with Symmetric Keys
(PSK) . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 70
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 70
1. Introduction
Security at the application layer provides an attractive option for
protecting Internet of Things (IoT) deployments, for example where
transport layer security is not sufficient
[I-D.hartke-core-e2e-security-reqs] or where the protection needs to
work over a variety of underlying protocols. IoT devices may be
constrained in various ways, including memory, storage, processing
capacity, and energy [RFC7228]. A method for protecting individual
messages at the application layer suitable for constrained devices,
is provided by CBOR Object Signing and Encryption (COSE) [RFC8152]),
which builds on the Concise Binary Object Representation (CBOR)
[I-D.ietf-cbor-7049bis]. Object Security for Constrained RESTful
Environments (OSCORE) [RFC8613] is a method for application-layer
protection of the Constrained Application Protocol (CoAP), using
COSE.
In order for a communication session to provide forward secrecy, the
communicating parties can run an Elliptic Curve Diffie-Hellman (ECDH)
key exchange protocol with ephemeral keys, from which shared key
material can be derived. This document specifies Ephemeral Diffie-
Hellman Over COSE (EDHOC), a lightweight key exchange protocol
providing perfect forward secrecy and identity protection.
Authentication is based on credentials established out of band, e.g.
from a trusted third party, such as an Authorization Server as
specified by [I-D.ietf-ace-oauth-authz]. EDHOC supports
authentication using pre-shared keys (PSK), raw public keys (RPK),
and public key certificates. After successful completion of the
EDHOC protocol, application keys and other application specific data
can be derived using the EDHOC-Exporter interface. A main use case
for EDHOC is to establish an OSCORE security context. EDHOC uses
COSE for cryptography, CBOR for encoding, and CoAP for transport. By
reusing existing libraries, the additional code footprint can be kept
very low. Note that this document focuses on authentication and key
establishment: for integration with authorization of resource access,
refer to [I-D.ietf-ace-oscore-profile].
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EDHOC is designed to work in highly constrained scenarios making it
especially suitable for network technologies such as Cellular IoT,
6TiSCH [I-D.ietf-6tisch-dtsecurity-zerotouch-join], and LoRaWAN
[LoRa1][LoRa2]. These network technologies are characterized by
their low throughput, low power consumption, and small frame sizes.
Compared to the DTLS 1.3 handshake [I-D.ietf-tls-dtls13] with ECDH
and connection ID, the number of bytes in EDHOC is less than 1/4 when
PSK authentication is used and less than 1/3 when RPK authentication
is used, see [I-D.ietf-lwig-security-protocol-comparison]. Typical
message sizes for EDHOC with pre-shared keys, raw public keys, and
X.509 certificates are shown in Figure 1.
=====================================================================
PSK RPK x5t x5chain
---------------------------------------------------------------------
message_1 40 38 38 38
message_2 45 114 126 116 + Certificate chain
message_3 11 80 91 81 + Certificate chain
---------------------------------------------------------------------
Total 96 232 255 235 + Certificate chains
=====================================================================
Figure 1: Typical message sizes in bytes
The ECDH exchange and the key derivation follow [SIGMA], NIST SP-
800-56A [SP-800-56A], and HKDF [RFC5869]. CBOR
[I-D.ietf-cbor-7049bis] and COSE [RFC8152] are used to implement
these standards. The use of COSE provides crypto agility and enables
use of future algorithms and headers designed for constrained IoT.
This document is organized as follows: Section 2 describes how EDHOC
builds on SIGMA-I, Section 3 specifies general properties of EDHOC,
including message flow, formatting of the ephemeral public keys, and
key derivation, Section 4 specifies EDHOC with asymmetric key
authentication, Section 5 specifies EDHOC with symmetric key
authentication, Section 6 specifies the EDHOC error message, and
Section 7 describes how EDHOC can be transferred in CoAP and used to
establish an OSCORE security context.
1.1. Rationale for EDHOC
Many constrained IoT systems today do not use any security at all,
and when they do, they often do not follow best practices. One
reason is that many current security protocols are not designed with
constrained IoT in mind. Constrained IoT systems often deal with
personal information, valuable business data, and actuators
interacting with the physical world. Not only do such systems need
security and privacy, they often need end-to-end protection with
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source authentication and perfect forward secrecy. EDHOC and OSCORE
[RFC8613] enables security following current best practices to
devices and systems where current security protocols are impractical.
EDHOC is optimized for small message sizes and can therefore be sent
over a small number of radio frames. The message size of a key
exchange protocol may have a large impact on the performance of an
IoT deployment, especially in noisy environments. For example, in a
network bootstrapping setting a large number of devices turned on in
a short period of time may result in large latencies caused by
parallel key exchanges. Requirements on network formation time in
constrained environments can be translated into key exchange
overhead. In networks technologies with transmission back-off time,
each additional frame significantly increases the latency even if no
other devices are transmitting.
Power consumption for wireless devices is highly dependent on message
transmission, listening, and reception. For devices that only send a
few bytes occasionally, the battery lifetime may be significantly
reduced by a heavy key exchange protocol. Moreover, a key exchange
may need to be executed more than once, e.g. due to a device losing
power or rebooting for other reasons.
EDHOC is adapted to primitives and protocols designed for the
Internet of Things: EDHOC is built on CBOR and COSE which enables
small message overhead and efficient parsing in constrained devices.
EDHOC is not bound to a particular transport layer, but it is
recommended to transport the EDHOC message in CoAP payloads. EDHOC
is not bound to a particular communication security protocol but
works off-the-shelf with OSCORE [RFC8613] providing the necessary
input parameters with required properties. Maximum code complexity
(ROM/Flash) is often a constraint in many devices and by reusing
already existing libraries, the additional code footprint for EDHOC +
OSCORE can be kept very low.
1.2. Terminology and Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The word "encryption" without qualification always refers to
authenticated encryption, in practice implemented with an
Authenticated Encryption with Additional Data (AEAD) algorithm, see
[RFC5116].
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Readers are expected to be familiar with the terms and concepts
described in CBOR [I-D.ietf-cbor-7049bis], COSE [RFC8152], and CDDL
[RFC8610]. The Concise Data Definition Language (CDDL) is used to
express CBOR data structures [I-D.ietf-cbor-7049bis]. Examples of
CBOR and CDDL are provided in Appendix A.1.
2. Background
SIGMA (SIGn-and-MAc) is a family of theoretical protocols with a
large number of variants [SIGMA]. Like IKEv2 and (D)TLS 1.3
[RFC8446], EDHOC is built on a variant of the SIGMA protocol which
provide identity protection of the initiator (SIGMA-I), and like
(D)TLS 1.3, EDHOC implements the SIGMA-I variant as Sign-then-MAC.
The SIGMA-I protocol using an authenticated encryption algorithm is
shown in Figure 2.
Party U Party V
| G_X |
+-------------------------------------------------------->|
| |
| G_Y, AEAD( K_2; ID_CRED_V, Sig(V; CRED_V, G_X, G_Y) ) |
|<--------------------------------------------------------+
| |
| AEAD( K_3; ID_CRED_U, Sig(U; CRED_U, G_Y, G_X) ) |
+-------------------------------------------------------->|
| |
Figure 2: Authenticated encryption variant of the SIGMA-I protocol.
The parties exchanging messages are called "U" and "V". They
exchange identities and ephemeral public keys, compute the shared
secret, and derive symmetric application keys.
o G_X and G_Y are the ECDH ephemeral public keys of U and V,
respectively.
o CRED_U and CRED_V are the credentials containing the public
authentication keys of U and V, respectively.
o ID_CRED_U and ID_CRED_V are data enabling the recipient party to
retrieve the credential of U and V, respectively.
o Sig(U; . ) and S(V; . ) denote signatures made with the private
authentication key of U and V, respectively.
o AEAD(K; . ) denotes authenticated encryption with additional data
using the key K derived from the shared secret. The authenticated
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encryption MUST NOT be replaced by plain encryption, see
Section 8.
In order to create a "full-fledged" protocol some additional protocol
elements are needed. EDHOC adds:
o Explicit connection identifiers C_U, C_V chosen by U and V,
respectively, enabling the recipient to find the protocol state.
o Transcript hashes TH_2, TH_3, TH_4 used for key derivation and as
additional authenticated data.
o Computationally independent keys derived from the ECDH shared
secret and used for encryption of different messages.
o Verification of a common preferred cipher suite (AEAD algorithm,
ECDH algorithm, ECDH curve, signature algorithm):
* U lists supported cipher suites in order of preference
* V verifies that the selected cipher suite is the first
supported cipher suite
o Method types and error handling.
o Transport of opaque application defined 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 in EDHOC is summarized
in Appendix A and test vectors including CBOR diagnostic notation are
given in Appendix C.
3. EDHOC Overview
EDHOC consists of three flights (message_1, message_2, message_3)
that maps directly to the three messages in SIGMA-I, plus an EDHOC
error message. EDHOC messages are CBOR Sequences
[I-D.ietf-cbor-sequence], where the first data item of message_1 is
an int (TYPE) specifying the method (asymmetric, symmetric) and the
correlation properties of the transport used.
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While EDHOC uses the COSE_Key, COSE_Sign1, and COSE_Encrypt0
structures, only a subset of the parameters is included in the EDHOC
messages. After creating EDHOC message_3, Party U can derive
symmetric application keys, and application protected data can
therefore be sent in parallel with EDHOC message_3. The application
may protect data using the algorithms (AEAD, HMAC, etc.) in the
selected cipher suite and the connection identifiers (C_U, C_V).
EDHOC may be used with the media type application/edhoc defined in
Section 9.
Party U Party V
| |
| ------------------ EDHOC message_1 -----------------> |
| |
| <----------------- EDHOC message_2 ------------------ |
| |
| ------------------ EDHOC message_3 -----------------> |
| |
| <----------- Application Protected Data ------------> |
| |
Figure 3: EDHOC message flow
The EDHOC message exchange may be authenticated using pre-shared keys
(PSK), raw public keys (RPK), or public key certificates. EDHOC
assumes the existence of mechanisms (certification authority, manual
distribution, etc.) for binding identities with authentication keys
(public or pre-shared). When a public key infrastructure is used,
the identity is included in the certificate and bound to the
authentication key by trust in the certification authority. When the
credential is manually distributed (PSK, RPK, self-signed
certificate), the identity and authentication key is distributed out-
of-band and bound together by trust in the distribution method.
EDHOC with symmetric key authentication is very similar to EDHOC with
asymmetric key authentication, the difference being that information
is only MACed, not signed, and that session keys are derived from the
ECDH shared secret and the PSK.
EDHOC allows opaque application data (UAD and PAD) to be sent in the
EDHOC messages. Unprotected Application Data (UAD_1, UAD_2) may be
sent in message_1 and message_2 and can be e.g. be used to transfer
access tokens that are protected outside of EDHOC. Protected
application data (PAD_3) may be used to transfer any application data
in message_3.
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. It is recommended to transport
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the EDHOC message in CoAP payloads, see Section 7. An implementation
may support only Party U or only Party V.
3.1. Cipher Suites
EDHOC cipher suites consist of an ordered set of COSE algorithms: an
AEAD algorithm, an HMAC algorithm, an ECDH curve, a signature
algorithm, and signature algorithm parameters. The signature
algorithm is not used when EDHOC is authenticated with symmetric
keys. Each cipher suite is either identified with a pre-defined int
label or with an array of labels and values from the COSE Algorithms
and Elliptic Curves registries.
suite = int / [ 4*4 algs: int / tstr, ? para: any ]
This document specifies two pre-defined cipher suites.
0. [ 10, 5, 4, -8, 6 ]
(AES-CCM-16-64-128, HMAC 256/256, X25519, EdDSA, Ed25519)
1. [ 10, 5, 1, -7, 1 ]
(AES-CCM-16-64-128, HMAC 256/256, P-256, ES256, P-256)
3.2. Ephemeral Public Keys
The ECDH ephemeral public keys are formatted as a COSE_Key of type
EC2 or OKP according to Sections 13.1 and 13.2 of [RFC8152], but only
the x-coordinate is included in the EDHOC messages. 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-coordinate, any of the possible values of the y-coordinate can be
used, see Appendix C of [RFC6090]. COSE [RFC8152] always use compact
output for Elliptic Curve Keys of type EC2.
3.3. Key Derivation
Key and IV derivation SHALL be performed with HKDF [RFC5869]
following the specification in Section 11 of [RFC8152] using the HMAC
algorithm in the selected cipher suite. The pseudorandom key (PRK)
is derived using HKDF-Extract [RFC5869]
PRK = HKDF-Extract( salt, IKM )
with the following input:
o The salt SHALL be the PSK when EDHOC is authenticated with
symmetric keys, and the empty byte string when EDHOC is
authenticated with asymmetric keys. The PSK is used as 'salt' to
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simplify implementation. Note that [RFC5869] specifies that if
the salt is not provided, it is set to a string of zeros (see
Section 2.2 of [RFC5869]). For implementation purposes, not
providing the salt is the same as setting the salt to the empty
byte string.
o The input keying material (IKM) SHALL be the ECDH shared secret
G_XY as defined in Section 12.4.1 of [RFC8152]. When using the
curve25519, the ECDH shared secret is the output of the X25519
function [RFC7748].
Example: Assuming use of HMAC 256/256 the extract phase of HKDF
produces a PRK as follows:
PRK = HMAC-SHA-256( salt, G_XY )
where salt = 0x (the empty byte string) in the asymmetric case and
salt = PSK in the symmetric case.
The keys and IVs used in EDHOC are derived from PRK using HKDF-Expand
[RFC5869]
OKM = HKDF-Expand( PRK, info, L )
where L is the length of output keying material (OKM) in bytes and
info is the CBOR encoding of a COSE_KDF_Context
info = [
AlgorithmID,
[ null, null, null ],
[ null, null, null ],
[ keyDataLength, h'', other ]
]
where
o AlgorithmID is an int or tstr, see below
o keyDataLength is a uint set to the length of output keying
material in bits, see below
o other is a bstr set to one of the transcript hashes TH_2, TH_3, or
TH_4 as defined in Sections 4.3.1, 4.4.1, and 3.3.1.
For message_2 and message_3, the keys K_2 and K_3 SHALL be derived
using transcript hashes TH_2 and TH_3 respectively. The key SHALL be
derived using AlgorithmID set to the integer value of the AEAD in the
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selected cipher suite, and keyDataLength equal to the key length of
the AEAD.
If the AEAD algorithm uses an IV, then IV_2 and IV_3 for message_2
and message_3 SHALL be derived using the transcript hashes TH_2 and
TH_3 respectively. The IV SHALL be derived using AlgorithmID = "IV-
GENERATION" as specified in Section 12.1.2. of [RFC8152], and
keyDataLength equal to the IV length of the AEAD.
Assuming the output OKM length L is smaller than the hash function
output size, the expand phase of HKDF consists of a single HMAC
invocation
OKM = first L bytes of HMAC( PRK, info || 0x01 )
where || means byte string concatenation.
Example: Assuming use of the algorithm AES-CCM-16-64-128 and HMAC
256/256, K_i and IV_i are therefore the first 16 and 13 bytes,
respectively, of
HMAC-SHA-256( PRK, info || 0x01 )
calculated with (AlgorithmID, keyDataLength) = (10, 128) and
(AlgorithmID, keyDataLength) = ("IV-GENERATION", 104), respectively.
3.3.1. EDHOC-Exporter Interface
Application keys and other application specific data can be derived
using the EDHOC-Exporter interface defined as:
EDHOC-Exporter( label, length ) = HKDF-Expand( PRK, info, length )
The output of the EDHOC-Exporter function SHALL be derived using
AlgorithmID = label, keyDataLength = 8 * length, and other = TH_4
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.
TH_4 = H( TH_3, CIPHERTEXT_3 )
where H() is the hash function in the HMAC algorithm. Example use of
the EDHOC-Exporter is given in Sections 3.3.2 and 7.1.1.
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3.3.2. EDHOC PSK Chaining
An application using EDHOC may want to derive new PSKs to use for
authentication in future EDHOC exchanges. In this case, the new PSK
and the ID_PSK 'kid_value' parameter SHOULD be derived as follows
where length is the key length (in bytes) of the AEAD Algorithm.
PSK = EDHOC-Exporter( "EDHOC Chaining PSK", length )
ID_PSK = EDHOC-Exporter( "EDHOC Chaining ID_PSK", 4 )
4. EDHOC Authenticated with Asymmetric Keys
4.1. Overview
EDHOC supports authentication with raw public keys (RPK) and public
key certificates with the requirements that:
o Only Party V SHALL have access to the private authentication key
of Party V,
o Only Party U SHALL have access to the private authentication key
of Party U,
o Party U is able to retrieve Party V's public authentication key
using ID_CRED_V,
o Party V is able to retrieve Party U's public authentication key
using ID_CRED_U,
where the identifiers ID_CRED_U and ID_CRED_V are COSE header_maps,
i.e. a CBOR map containing COSE Common Header Parameters, see
[RFC8152]). ID_CRED_U and ID_CRED_V need to contain parameters that
can identify a public authentication key, see Appendix A.2. In the
following we give some examples of possible COSE header parameters.
Raw public keys are most optimally stored as COSE_Key objects and
identified with a 'kid' parameter (see [RFC8152]):
o ID_CRED_x = { 4 : kid_value }, where kid_value : bstr, for x = U
or V.
Public key certificates can be identified in different ways. Several
header parameters for identifying X.509 certificates are defined in
[I-D.ietf-cose-x509] (the exact labels are TBD):
o by a hash value with the 'x5t' parameter;
* ID_CRED_x = { TBD1 : COSE_CertHash }, for x = U or V,
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o by a URL with the 'x5u' parameter;
* ID_CRED_x = { TBD2 : uri }, for x = U or V,
o or by a bag of certificates with the 'x5bag' parameter;
* ID_CRED_x = { TBD3 : COSE_X509 }, for x = U or V.
o by a certificate chain with the 'x5chain' parameter;
* ID_CRED_x = { TBD4 : COSE_X509 }, for x = U or V,
In the latter two examples, ID_CRED_U and ID_CRED_V contain the
actual credential used for authentication. The purpose of ID_CRED_U
and ID_CRED_V is to facilitate retrieval of a public authentication
key and when they do not contain the actual credential, they may be
very short. It is RECOMMENDED that they uniquely identify the public
authentication key as the recipient may otherwise have to try several
keys. ID_CRED_U and ID_CRED_V are transported in the ciphertext, see
Section 4.3.2 and Section 4.4.2.
The actual credentials CRED_U and CRED_V (e.g. a COSE_Key or a single
X.509 certificate) are signed by party U and V, respectively to
prevent duplicate-signature key selection (DSKS) attacks, see
Section 4.4.1 and Section 4.3.1. Party U and Party V MAY use
different types of credentials, e.g. one uses RPK and the other uses
certificate. When included in the signature payload, COSE_Keys of
type OKP SHALL only include the parameters 1 (kty), -1 (crv), and -2
(x-coordinate). COSE_Keys of type EC2 SHALL only include the
parameters 1 (kty), -1 (crv), -2 (x-coordinate), and -3
(y-coordinate). The parameters SHALL be encoded in decreasing order.
The connection identifiers C_U and C_V do not have any cryptographic
purpose in EDHOC. They contain information facilitating retrieval of
the protocol state and may therefore be very short. The connection
identifier MAY be used with an application protocol (e.g. OSCORE)
for which EDHOC establishes keys, in which case the 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.
The first data item of message_1 is an int TYPE = 4 * method + corr
specifying the method and the correlation properties of the transport
used. corr = 0 is used when there is no external correlation
mechanism. corr = 1 is used when there is an external correlation
mechanism (e.g. the Token in CoAP) that enables Party U to correlate
message_1 and message_2. corr = 2 is used when there is an external
correlation mechanism that enables Party V to correlate message_2 and
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message_3. corr = 3 is used when there is an external correlation
mechanism that enables the parties to correlate all the messages.
The use of the correlation parameter is exemplified in Section 7.1.
1 byte connection and credential identifiers are realistic in many
scenarios as most constrained devices only have a few keys and
connections. In cases where a node only has one connection or key,
the identifiers may even be the empty byte string.
EDHOC with asymmetric key authentication is illustrated in Figure 4.
Party U Party V
| TYPE, SUITES_U, G_X, C_U, UAD_1 |
+------------------------------------------------------------------>|
| message_1 |
| |
| C_U, G_Y, C_V, AEAD(K_2; ID_CRED_V, Sig(V; CRED_V, TH_2), UAD_2) |
|<------------------------------------------------------------------+
| message_2 |
| |
| C_V, AEAD(K_3; ID_CRED_U, Sig(U; CRED_U, TH_3), PAD_3) |
+------------------------------------------------------------------>|
| message_3 |
Figure 4: Overview of EDHOC with asymmetric key authentication.
4.2. EDHOC Message 1
4.2.1. Formatting of Message 1
message_1 SHALL be a CBOR Sequence (see Appendix A.1) as defined
below
message_1 = (
TYPE : int,
SUITES_U : suite / [ index : uint, 2* suite ],
G_X : bstr,
C_U : bstr,
? UAD_1 : bstr,
)
where:
o TYPE = 4 * method + corr, where the method = 0 and the correlation
parameter corr is chosen based on the transport and determines
which connection identifiers that are omitted (see Section 4.1).
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o SUITES_U - cipher suites which Party U supports in order of
decreasing preference. One cipher suite is selected. If a single
cipher suite is conveyed then that cipher suite is selected. If
multiple cipher suites are conveyed then zero-based index (i.e. 0
for the first suite, 1 for the second suite, etc.) identifies the
selected cipher suite out of the array elements listing the cipher
suites (see Section 6).
o G_X - the x-coordinate of the ephemeral public key of Party U
o C_U - variable length connection identifier
o UAD_1 - bstr containing unprotected opaque application data
4.2.2. Party U Processing of Message 1
Party U SHALL compose message_1 as follows:
o The supported cipher suites and the order of preference MUST NOT
be changed based on previous error messages. However, the list
SUITES_U sent to Party V 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.
o Determine the cipher suite to use with Party V in message_1. If
Party U previously received from Party V an error message to
message_1 with diagnostic payload identifying a cipher suite that
U supports, then U SHALL use that cipher suite. Otherwise the
first cipher suite in SUITES_U MUST be used.
o Generate an ephemeral ECDH key pair as specified in Section 5 of
[SP-800-56A] using the curve in the selected cipher suite. Let
G_X be the x-coordinate of the ephemeral public key.
o Choose a connection identifier C_U and store it for the length of
the protocol.
o Encode message_1 as a sequence of CBOR encoded data items as
specified in Section 4.2.1
4.2.3. Party V Processing of Message 1
Party V SHALL process message_1 as follows:
o Decode message_1 (see Appendix A.1).
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o Verify that the selected cipher suite is supported and that no
prior cipher suites in SUITES_U are supported.
o Validate that there is a solution to the curve definition for the
given x-coordinate G_X.
o Pass UAD_1 to the application.
If any verification step fails, Party V MUST send an EDHOC error
message back, formatted as defined in Section 6, and the protocol
MUST be discontinued. If V does not support the selected cipher
suite, then SUITES_V MUST include one or more supported cipher
suites. If V does not support the selected cipher suite, but
supports another cipher suite in SUITES_U, then SUITES_V MUST include
the first supported cipher suite in SUITES_U.
4.3. EDHOC Message 2
4.3.1. Formatting of Message 2
message_2 and data_2 SHALL be CBOR Sequences (see Appendix A.1) as
defined below
message_2 = (
data_2,
CIPHERTEXT_2 : bstr,
)
data_2 = (
? C_U : bstr,
G_Y : bstr,
C_V : bstr,
)
where:
o G_Y - the x-coordinate of the ephemeral public key of Party V
o C_V - variable length connection identifier
4.3.2. Party V Processing of Message 2
Party V SHALL compose message_2 as follows:
o If TYPE mod 4 equals 1 or 3, C_U is omitted, otherwise C_U is not
omitted.
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o Generate an ephemeral ECDH key pair as specified in Section 5 of
[SP-800-56A] using the curve in the selected cipher suite. Let
G_Y be the x-coordinate of the ephemeral public key.
o Choose a connection identifier C_V and store it for the length of
the protocol.
o Compute the transcript hash TH_2 = H( message_1, data_2 ) where
H() is the hash function in the HMAC algorithm. The transcript
hash TH_2 is a CBOR encoded bstr and the input to the hash
function is a CBOR Sequence.
o Compute COSE_Sign1 as defined in Section 4.4 of [RFC8152], using
the signature algorithm in the selected cipher suite, the private
authentication key of Party V, and the parameters below. Note
that only 'signature' of the COSE_Sign1 object is used to create
message_2, see next bullet. The unprotected header (not included
in the EDHOC message) MAY contain parameters (e.g. 'alg').
* protected = bstr .cbor ID_CRED_V
* payload = CRED_V
* external_aad = TH_2
* ID_CRED_V - identifier to facilitate retrieval of CRED_V, see
Section 4.1
* CRED_V - bstr credential containing the credential of Party V,
e.g. its public authentication key or X.509 certificate see
Section 4.1. The public key must be a signature key. Note
that if objects that are not bstr are used, such as COSE_Key
for public authentication keys, these objects must be wrapped
in a CBOR bstr.
COSE constructs the input to the Signature Algorithm as follows:
* The key is the private authentication key of V.
* The message M to be signed is the CBOR encoding of:
[ "Signature1", << ID_CRED_V >>, TH_2, CRED_V ]
o Compute COSE_Encrypt0 as defined in Section 5.3 of [RFC8152], with
the AEAD algorithm in the selected cipher suite, K_2, IV_2, and
the parameters below. Note that only 'ciphertext' of the
COSE_Encrypt0 object is used to create message_2, see next bullet.
The protected header SHALL be empty. The unprotected header (not
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included in the EDHOC message) MAY contain parameters (e.g.
'alg').
* plaintext = ( ID_CRED_V / kid_value, signature, ? UAD_2 )
* external_aad = TH_2
* UAD_2 = bstr containing opaque unprotected application data
where signature is taken from the COSE_Sign1 object, ID_CRED_V is
a COSE header_map (i.e. a CBOR map containing COSE Common Header
Parameters, see [RFC8152]), and kid_value is a bstr. If ID_CRED_V
contains a single 'kid' parameter, i.e., ID_CRED_V = { 4 :
kid_value }, only kid_value is conveyed in the plaintext.
COSE constructs the input to the AEAD [RFC5116] as follows:
* Key K = K_2
* Nonce N = IV_2
* Plaintext P = ( ID_CRED_V / kid_value, signature, ? UAD_2 )
* Associated data A = [ "Encrypt0", h'', TH_2 ]
o Encode message_2 as a sequence of CBOR encoded data items as
specified in Section 4.3.1. CIPHERTEXT_2 is the COSE_Encrypt0
ciphertext.
4.3.3. Party U Processing of Message 2
Party U SHALL process message_2 as follows:
o Decode message_2 (see Appendix A.1).
o Retrieve the protocol state using the connection identifier C_U
and/or other external information such as the CoAP Token and the
5-tuple.
o Validate that there is a solution to the curve definition for the
given x-coordinate G_Y.
o Decrypt and verify COSE_Encrypt0 as defined in Section 5.3 of
[RFC8152], with the AEAD algorithm in the selected cipher suite,
K_2, and IV_2.
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o Verify COSE_Sign1 as defined in Section 4.4 of [RFC8152], using
the signature algorithm in the selected cipher suite and the
public authentication key of Party V.
If any verification step fails, Party U MUST send an EDHOC error
message back, formatted as defined in Section 6, and the protocol
MUST be discontinued.
4.4. EDHOC Message 3
4.4.1. Formatting of Message 3
message_3 and data_3 SHALL be CBOR Sequences (see Appendix A.1) as
defined below
message_3 = (
data_3,
CIPHERTEXT_3 : bstr,
)
data_3 = (
? C_V : bstr,
)
4.4.2. Party U Processing of Message 3
Party U SHALL compose message_3 as follows:
o If TYPE mod 4 equals 2 or 3, C_V is omitted, otherwise C_V is not
omitted.
o Compute the transcript hash TH_3 = H( TH_2 , CIPHERTEXT_2, data_3
) where H() is the hash function in the HMAC algorithm. The
transcript hash TH_3 is a CBOR encoded bstr and the input to the
hash function is a CBOR Sequence.
o Compute COSE_Sign1 as defined in Section 4.4 of [RFC8152], using
the signature algorithm in the selected cipher suite, the private
authentication key of Party U, and the parameters below. Note
that only 'signature' of the COSE_Sign1 object is used to create
message_3, see next bullet. The unprotected header (not included
in the EDHOC message) MAY contain parameters (e.g. 'alg').
* protected = bstr .cbor ID_CRED_U
* payload = CRED_U
* external_aad = TH_3
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* ID_CRED_U - identifier to facilitate retrieval of CRED_U, see
Section 4.1
* CRED_U - bstr credential containing the credential of Party U,
e.g. its public authentication key or X.509 certificate see
Section 4.1. The public key must be a signature key. Note
that if objects that are not bstr are used, such as COSE_Key
for public authentication keys, these objects must be wrapped
in a CBOR bstr.
COSE constructs the input to the Signature Algorithm as follows:
* The key is the private authentication key of U.
* The message M to be signed is the CBOR encoding of:
[ "Signature1", << ID_CRED_U >>, TH_3, CRED_U ]
o Compute COSE_Encrypt0 as defined in Section 5.3 of [RFC8152], with
the AEAD algorithm in the selected cipher suite, K_3, and IV_3 and
the parameters below. Note that only 'ciphertext' of the
COSE_Encrypt0 object is used to create message_3, see next bullet.
The protected header SHALL be empty. The unprotected header (not
included in the EDHOC message) MAY contain parameters (e.g.
'alg').
* plaintext = ( ID_CRED_U / kid_value, signature, ? PAD_3 )
* external_aad = TH_3
* PAD_3 = bstr containing opaque protected application data
where signature is taken from the COSE_Sign1 object, ID_CRED_U is
a COSE header_map (i.e. a CBOR map containing COSE Common Header
Parameters, see [RFC8152]), and kid_value is a bstr. If ID_CRED_U
contains a single 'kid' parameter, i.e., ID_CRED_U = { 4 :
kid_value }, only kid_value is conveyed in the plaintext.
COSE constructs the input to the AEAD [RFC5116] as follows:
* Key K = K_3
* Nonce N = IV_2
* Plaintext P = ( ID_CRED_U / kid_value, signature, ? PAD_3 )
* Associated data A = [ "Encrypt0", h'', TH_3 ]
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o Encode message_3 as a sequence of CBOR encoded data items as
specified in Section 4.4.1. CIPHERTEXT_3 is the COSE_Encrypt0
ciphertext.
o Pass the connection identifiers (C_U, C_V) and the selected cipher
suite to the application. The application can now derive
application keys using the EDHOC-Exporter interface.
4.4.3. Party V Processing of Message 3
Party V SHALL process message_3 as follows:
o Decode message_3 (see Appendix A.1).
o Retrieve the protocol state using the connection identifier C_V
and/or other external information such as the CoAP Token and the
5-tuple.
o Decrypt and verify COSE_Encrypt0 as defined in Section 5.3 of
[RFC8152], with the AEAD algorithm in the selected cipher suite,
K_3, and IV_3.
o Verify COSE_Sign1 as defined in Section 4.4 of [RFC8152], using
the signature algorithm in the selected cipher suite and the
public authentication key of Party U.
If any verification step fails, Party V MUST send an EDHOC error
message back, formatted as defined in Section 6, and the protocol
MUST be discontinued.
o Pass PAD_3, the connection identifiers (C_U, C_V), and the
selected cipher suite to the application. The application can now
derive application keys using the EDHOC-Exporter interface.
5. EDHOC Authenticated with Symmetric Keys
5.1. Overview
EDHOC supports authentication with pre-shared keys. Party U and V
are assumed to have a pre-shared key (PSK) with a good amount of
randomness and the requirement that:
o Only Party U and Party V SHALL have access to the PSK,
o Party V is able to retrieve the PSK using ID_PSK.
where the identifier ID_PSK is a COSE header_map (i.e. a CBOR map
containing COSE Common Header Parameters, see [RFC8152]) containing
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COSE header parameter that can identify a pre-shared key. Pre-shared
keys are typically stored as COSE_Key objects and identified with a
'kid' parameter (see [RFC8152]):
o ID_PSK = { 4 : kid_value } , where kid_value : bstr
The purpose of ID_PSK is to facilitate retrieval of the PSK and in
the case a 'kid' parameter is used it may be very short. It is
RECOMMENDED that it uniquely identify the PSK as the recipient may
otherwise have to try several keys.
EDHOC with symmetric key authentication is illustrated in Figure 5.
Party U Party V
| TYPE, SUITES_U, G_X, C_U, ID_PSK, UAD_1 |
+------------------------------------------------------------------>|
| message_1 |
| |
| C_U, G_Y, C_V, AEAD(K_2; TH_2, UAD_2) |
|<------------------------------------------------------------------+
| message_2 |
| |
| C_V, AEAD(K_3; TH_3, PAD_3) |
+------------------------------------------------------------------>|
| message_3 |
Figure 5: Overview of EDHOC with symmetric key authentication.
EDHOC with symmetric key authentication is very similar to EDHOC with
asymmetric key authentication. In the following subsections the
differences compared to EDHOC with asymmetric key authentication are
described.
5.2. EDHOC Message 1
5.2.1. Formatting of Message 1
message_1 SHALL be a CBOR Sequence (see Appendix A.1) as defined
below
message_1 = (
TYPE : int,
SUITES_U : suite / [ index : uint, 2* suite ],
G_X : bstr,
C_U : bstr,
ID_PSK : header_map // kid_value : bstr,
? UAD_1 : bstr,
)
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where:
o TYPE = 4 * method + corr, where the method = 1 and the connection
parameter corr is chosen based on the transport and determines
which connection identifiers that are omitted (see Section 4.1).
o ID_PSK - identifier to facilitate retrieval of the pre-shared key.
If ID_PSK contains a single 'kid' parameter, i.e., ID_PSK = { 4 :
kid_value }, with kid_value: bstr, only kid_value is conveyed.
5.3. EDHOC Message 2
5.3.1. Processing of Message 2
o COSE_Sign1 is not used.
o COSE_Encrypt0 is computed as defined in Section 5.3 of [RFC8152],
with the AEAD algorithm in the selected cipher suite, K_2, IV_2,
and the following parameters. The protected header SHALL be
empty. The unprotected header MAY contain parameters (e.g.
'alg').
* external_aad = TH_2
* plaintext = ? UAD_2
* UAD_2 = bstr containing opaque unprotected application data
5.4. EDHOC Message 3
5.4.1. Processing of Message 3
o COSE_Sign1 is not used.
o COSE_Encrypt0 is computed as defined in Section 5.3 of [RFC8152],
with the AEAD algorithm in the selected cipher suite, K_3, IV_3,
and the following parameters. The protected header SHALL be
empty. The unprotected header MAY contain parameters (e.g.
'alg').
* external_aad = TH_3
* plaintext = ? PAD_3
* PAD_3 = bstr containing opaque protected application data
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6. Error Handling
6.1. EDHOC Error Message
This section defines a message format for the EDHOC error message,
used during the protocol. An EDHOC error message can be sent by both
parties as a reply to any non-error EDHOC message. After sending an
error message, the protocol MUST be discontinued. Errors at the
EDHOC layer are sent as normal successful messages in the lower
layers (e.g. CoAP POST and 2.04 Changed). An advantage of using
such a construction is to avoid issues created by usage of cross
protocol proxies (e.g. UDP to TCP).
error SHALL be a CBOR Sequence (see Appendix A.1) as defined below
error = (
? C_x : bstr,
ERR_MSG : tstr,
? SUITES_V : suite / [ 2* suite ],
)
where:
o C_x - if error is sent by Party V and TYPE mod 4 equals 0 or 2
then C_x is set to C_U, else if error is sent by Party U and TYPE
mod 4 equals 0 or 1 then C_x is set to C_V, else C_x is omitted.
o ERR_MSG - text string containing the diagnostic payload, defined
in the same way as in Section 5.5.2 of [RFC7252]. ERR_MSG MAY be
a 0-length text string.
o SUITES_V - cipher suites from SUITES_U or the EDHOC cipher suites
registry that V supports. Note that SUITES_V only contains the
values from the EDHOC cipher suites registry and no index.
SUITES_V MUST only be included in replies to message_1.
6.1.1. Example Use of EDHOC Error Message with SUITES_V
Assuming that Party U supports the five cipher suites {5, 6, 7, 8, 9}
in decreasing order of preference, Figures 6 and 7 show examples of
how Party U can truncate SUITES_U and how SUITES_V is used by Party V
to give Party U information about the cipher suites that Party V
supports. In Figure 6, Party V supports cipher suite 6 but not the
selected cipher suite 5.
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Party U Party V
| TYPE, SUITES_U {0, 5, 6, 7}, G_X, C_U, UAD_1 |
+------------------------------------------------------------------>|
| message_1 |
| |
| C_U, ERR_MSG, SUITES_V {6} |
|<------------------------------------------------------------------+
| error |
| |
| TYPE, SUITES_U {1, 5, 6}, G_X, C_U, UAD_1 |
+------------------------------------------------------------------>|
| message_1 |
Figure 6: Example use of error message with SUITES_V.
In Figure 7, Party V supports cipher suite 7 but not cipher suites 5
and 6.
Party U Party V
| TYPE, SUITES_U {0, 5, 6}, G_X, C_U, UAD_1 |
+------------------------------------------------------------------>|
| message_1 |
| |
| C_U, ERR_MSG, SUITES_V {7, 9} |
|<------------------------------------------------------------------+
| error |
| |
| TYPE, SUITES_U {2, 5, 6, 7}, G_X, C_U, UAD_1 |
+------------------------------------------------------------------>|
| message_1 |
Figure 7: Example use of error message with SUITES_V.
As Party U's list of supported cipher suites and order of preference
is fixed, and Party V only accepts message_1 if the selected cipher
suite is the first cipher suite in SUITES_U that Party V supports,
the parties can verify that the selected cipher suite is the most
preferred (by Party U) cipher suite supported by both parties. If
the selected cipher suite is not the first cipher suite in SUITES_U
that Party V supports, Party V will discontinue the protocol.
7. Transferring EDHOC and Deriving Application Keys
7.1. 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
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fragmentation and protect against denial of service attacks. It is
recommended to carry the EDHOC flights in Confirmable messages,
especially if fragmentation is used.
By default, the CoAP client is Party U and the CoAP server is Party
V, but the roles SHOULD be chosen to protect the most sensitive
identity, see Section 8. By default, EDHOC is transferred in POST
requests and 2.04 (Changed) responses to the Uri-Path: "/.well-known/
edhoc", but an application may define its own path that can be
discovered e.g. using resource directory
[I-D.ietf-core-resource-directory].
By default, the message flow is as follows: EDHOC message_1 is sent
in the payload of a POST request from the client to the server's
resource for EDHOC. EDHOC message_2 or the EDHOC error message is
sent from the server to the client in the payload of a 2.04 (Changed)
response. EDHOC message_3 or the EDHOC error message is sent from
the client to the server's resource in the payload of a POST request.
If needed, an EDHOC error message is sent from the server to the
client in the payload of a 2.04 (Changed) response.
An example of a successful EDHOC exchange using CoAP is shown in
Figure 8. In this case the CoAP Token enables Party U to correlate
message_1 and message_2 so the correlation parameter corr = 1.
Client Server
| |
+--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc"
| | Content-Format: application/edhoc
| | Payload: EDHOC message_1
| |
|<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc
| | Payload: EDHOC message_2
| |
+--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc"
| | Content-Format: application/edhoc
| | Payload: EDHOC message_3
| |
|<---------+ Header: 2.04 Changed
| 2.04 |
| |
Figure 8: Transferring EDHOC in CoAP
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The exchange in Figure 8 protects the client identity against active
attackers and the server identity against passive attackers. An
alternative exchange that protects the server identity against active
attackers and the client identity against passive attackers is shown
in Figure 9. In this case the CoAP Token enables Party V to
correlate message_2 and message_3 so the correlation parameter corr =
2.
Client Server
| |
+--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc"
| |
|<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc
| | Payload: EDHOC message_1
| |
+--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/.well-known/edhoc"
| | Content-Format: application/edhoc
| | Payload: EDHOC message_2
| |
|<---------+ Header: 2.04 Changed
| 2.04 | Content-Format: application/edhoc
| | Payload: EDHOC message_3
| |
Figure 9: Transferring EDHOC in CoAP
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].
7.1.1. Deriving an OSCORE Context from EDHOC
When EDHOC is used to derive parameters for OSCORE [RFC8613], the
parties must make sure that the EDHOC connection identifiers are
unique, i.e. C_V MUST NOT be equal to C_U. 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 party U and the CoAP
server is party V:
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o The client's OSCORE Sender ID is C_V and the server's OSCORE
Sender ID is C_U, as defined in this document
o The AEAD Algorithm and the HMAC algorithms are the AEAD and HMAC
algorithms in the selected cipher suite.
o The Master Secret and Master Salt are derived as follows where
length is the key length (in bytes) of the AEAD Algorithm.
Master Secret = EDHOC-Exporter( "OSCORE Master Secret", length )
Master Salt = EDHOC-Exporter( "OSCORE Master Salt", 8 )
7.2. Transferring EDHOC over Other Protocols
EDHOC may be transported over a different transport than CoAP. In
this case the lower layers need to handle message loss, reordering,
message duplication, fragmentation, and denial of service protection.
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, peer awareness, and identity protection. As described
in [SIGMA], peer awareness is provided to Party V, but not to Party
U. EDHOC also inherits Key Compromise Impersonation (KCI) resistance
from SIGMA-I.
EDHOC with asymmetric authentication offers identity protection of
Party U against active attacks and identity protection of Party V
against passive attacks. The roles should be assigned to protect the
most sensitive identity, 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, application 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 Party V
to verify that the selected cipher suite is the most preferred cipher
suite by U which is supported by both U and V.
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As required by [RFC7258], IETF protocols need to mitigate pervasive
monitoring when possible. One way to mitigate pervasive monitoring
is to use a key exchange that provides perfect forward secrecy.
EDHOC therefore only supports methods with perfect forward secrecy.
To limit the effect of breaches, it is important to limit the use of
symmetrical group keys for bootstrapping. EDHOC therefore strives to
make the additional cost of using raw public keys and self-signed
certificates as small as possible. Raw public keys and self-signed
certificates are not a replacement for a public key infrastructure,
but SHOULD be used instead of symmetrical group keys for
bootstrapping.
Compromise of the long-term keys (PSK or private authentication keys)
does not compromise the security of completed EDHOC exchanges.
Compromising the private authentication keys of one party lets the
attacker impersonate that compromised party in EDHOC exchanges with
other parties, but does not let the attacker impersonate other
parties in EDHOC exchanges with the compromised party. Compromising
the PSK lets the attacker impersonate Party U in EDHOC exchanges with
Party V and impersonate Party V in EDHOC exchanges with Party U.
Compromise of the HDKF input parameters (ECDH shared secret and/or
PSK) leads to compromise of all session keys derived from that
compromised shared secret. Compromise of one session key does not
compromise other session keys.
8.2. Cryptographic Considerations
The security of the SIGMA protocol requires the MAC to be bound to
the identity of the signer. Hence the message authenticating
functionality of the authenticated encryption in EDHOC is critical:
authenticated encryption MUST NOT be replaced by plain encryption
only, even if authentication is provided at another level or through
a different mechanism. EDHOC implements SIGMA-I using the same Sign-
then-MAC approach as TLS 1.3.
To reduce message overhead EDHOC does not use explicit nonces and
instead rely on the ephemeral public keys to provide randomness to
each session. A good amount of randomness is important for the key
generation, to provide liveness, and to protect against interleaving
attacks. For this reason, the ephemeral keys MUST NOT be reused, and
both parties SHALL generate fresh random ephemeral key pairs.
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. Party U
and V should enforce a minimum security level.
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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.
8.3. Cipher Suites
Cipher suite number 0 (AES-CCM-64-64-128, ECDH-SS + HKDF-256, X25519,
Ed25519) is mandatory to implement. For many constrained IoT devices
it is problematic to support more than one cipher suites, so some
deployments with P-256 may not support the mandatory cipher suite.
This is not a problem for local deployments.
The HMAC algorithm HMAC 256/64 (HMAC w/ SHA-256 truncated to 64 bits)
SHALL NOT be supported for use in EDHOC.
8.4. Unprotected Data
Party U and V 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 UAD_1, ID_CRED_V, UAD_2, and ERR_MSG in the asymmetric
case, and ID_PSK, UAD_1, and ERR_MSG in the symmetric case. Using
the same ID_PSK or UAD_1 in several EDHOC sessions allows passive
eavesdroppers to correlate the different sessions. The communicating
parties may therefore anonymize ID_PSK. Another consideration is
that the list of supported cipher suites may be used to identify the
application.
Party U and V must also make sure that unauthenticated data does not
trigger any harmful actions. In particular, this applies to UAD_1
and ERR_MSG in the asymmetric case, and ID_PSK, UAD_1, and ERR_MSG in
the symmetric case.
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 Party V 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.
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8.6. Implementation Considerations
The availability of a secure pseudorandom number generator and truly
random seeds are 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. As each pseudoranom number must
only be used once, an implementation need to get a new truly random
seed after reboot, or continously store state in nonvolatile memory,
see ([RFC8613], Appendix B.1.1) for issues and solution approaches
for writing to nonvolatile memory. If ECDSA is supported,
"deterministic ECDSA" as specified in [RFC6979] is RECOMMENDED.
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 secret, keys (K_2, K_3), and IVs (IV_2,
IV_3) MUST be secret. Implementations should provide countermeasures
to side-channel attacks such as timing attacks.
Party U and V 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 and the PSK (even though it is used as
salt) MUST be kept secret.
Party U and V are allowed to select the connection identifiers C_U
and C_V, 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).
Party V MUST finish the verification step of message_3 before passing
PAD_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
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cipher suites, an attacker can affect which of the two nodes'
preferred cipher suites will be used by blocking the other exchange.
8.7. Other Documents Referencing EDHOC
EDHOC has been analyzed in several other documents. A formal
verification of EDHOC was done in [SSR18], an analysis of EDHOC for
certificate enrollment was done in [Kron18], the use of EDHOC in
LoRaWAN is analyzed in [LoRa1] and [LoRa2], the use of EDHOC in IoT
bootstrapping is analyzed in [Perez18], and the use of EDHOC in
6TiSCH is described in [I-D.ietf-6tisch-dtsecurity-zerotouch-join].
9. IANA Considerations
9.1. 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: 1
Array: [ 10, 5, 1, -7, 1 ]
Desc: AES-CCM-16-64-128, HMAC 256/256, P-256, ES256, P-256
Reference: [[this document]]
Value: 0
Array: [ 10, 5, 4, -8, 6 ]
Desc: AES-CCM-16-64-128, HMAC 256/256, X25519, EdDSA, Ed25519
Reference: [[this document]]
Value: -5
Array:
Desc: Reserved for Private Use
Reference: [[this document]]
Value: -6
Array:
Desc: Reserved for Private Use
Reference: [[this document]]
9.2. EDHOC Method Type Registry
IANA has created a new registry titled "EDHOC Method Type" under the
new heading "EDHOC". The registration procedure is "Expert Review".
The columns of the registry are Value, Description, and Reference,
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where Value is an integer and the other columns are text strings.
The initial contents of the registry are:
+-------+------------------------------------------+-------------------+
| Value | Specification | Reference |
+-------+------------------------------------------+-------------------+
| 0 | EDHOC Authenticated with Asymmetric Keys | [[this document]] |
| 1 | EDHOC Authenticated with Symmetric Keys | [[this document]] |
+-------+------------------------------------------+-------------------+
9.3. The Well-Known URI Registry
IANA has added the well-known URI 'edhoc' to the Well-Known URIs
registry.
o URI suffix: edhoc
o Change controller: IETF
o Specification document(s): [[this document]]
o Related information: None
9.4. Media Types Registry
IANA has added the media type 'application/edhoc' to the Media Types
registry.
o Type name: application
o Subtype name: edhoc
o Required parameters: N/A
o Optional parameters: N/A
o Encoding considerations: binary
o Security considerations: See Section 7 of this document.
o Interoperability considerations: N/A
o Published specification: [[this document]] (this document)
o Applications that use this media type: To be identified
o Fragment identifier considerations: N/A
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o Additional information:
* Magic number(s): N/A
* File extension(s): N/A
* Macintosh file type code(s): N/A
o Person & email address to contact for further information: See
"Authors' Addresses" section.
o Intended usage: COMMON
o Restrictions on usage: N/A
o Author: See "Authors' Addresses" section.
o Change Controller: IESG
9.5. CoAP Content-Formats Registry
IANA has added the media type 'application/edhoc' to the CoAP
Content-Formats registry.
o Media Type: application/edhoc
o Encoding:
o ID: TBD42
o Reference: [[this document]]
9.6. 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:
o Clarity and correctness of registrations. Experts are expected to
check the clarity of purpose and use of the requested entries.
Expert needs to make sure the values of algorithms are taken from
the right registry, when that's required. Expert should consider
requesting an opinion on the correctness of registered parameters
from relevant IETF working groups. Encodings that do not meet
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these objective of clarity and completeness should not be
registered.
o Experts should take into account the expected usage of fields when
approving point assignment. The length of the encoded value
should be weighed against how many code points of that length are
left, the size of device it will be used on, and the number of
code points left that encode to that size.
o Specifications are recommended. When specifications are not
provided, the description provided needs to have sufficient
information to verify the points above.
10. References
10.1. Normative References
[I-D.ietf-cbor-7049bis]
Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", draft-ietf-cbor-7049bis-07 (work
in progress), August 2019.
[I-D.ietf-cbor-sequence]
Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", draft-ietf-cbor-sequence-01 (work in
progress), August 2019.
[I-D.ietf-core-echo-request-tag]
Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo,
Request-Tag, and Token Processing", draft-ietf-core-echo-
request-tag-05 (work in progress), May 2019.
[I-D.ietf-cose-x509]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Headers for carrying and referencing X.509 certificates",
draft-ietf-cose-x509-03 (work in progress), August 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
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[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011,
<https://www.rfc-editor.org/info/rfc6090>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
2013, <https://www.rfc-editor.org/info/rfc6979>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
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[SIGMA] Krawczyk, H., "SIGMA - The 'SIGn-and-MAc' Approach to
Authenticated Diffie-Hellman and Its Use in the IKE-
Protocols (Long version)", June 2003,
<http://webee.technion.ac.il/~hugo/sigma-pdf.pdf>.
[SP-800-56A]
Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
Davis, "Recommendation for Pair-Wise Key-Establishment
Schemes Using Discrete Logarithm Cryptography",
NIST Special Publication 800-56A Revision 3, April 2018,
<https://doi.org/10.6028/NIST.SP.800-56Ar3>.
10.2. Informative References
[CborMe] Bormann, C., "CBOR Playground", May 2018,
<http://cbor.me/>.
[I-D.hartke-core-e2e-security-reqs]
Selander, G., Palombini, F., and K. Hartke, "Requirements
for CoAP End-To-End Security", draft-hartke-core-e2e-
security-reqs-03 (work in progress), July 2017.
[I-D.ietf-6tisch-dtsecurity-zerotouch-join]
Richardson, M., "6tisch Zero-Touch Secure Join protocol",
draft-ietf-6tisch-dtsecurity-zerotouch-join-04 (work in
progress), July 2019.
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-24
(work in progress), March 2019.
[I-D.ietf-ace-oscore-profile]
Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"OSCORE profile of the Authentication and Authorization
for Constrained Environments Framework", draft-ietf-ace-
oscore-profile-08 (work in progress), July 2019.
[I-D.ietf-core-resource-directory]
Shelby, Z., Koster, M., Bormann, C., Stok, P., and C.
Amsuess, "CoRE Resource Directory", draft-ietf-core-
resource-directory-23 (work in progress), July 2019.
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[I-D.ietf-lwig-security-protocol-comparison]
Mattsson, J. and F. Palombini, "Comparison of CoAP
Security Protocols", draft-ietf-lwig-security-protocol-
comparison-03 (work in progress), March 2019.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-32 (work in progress), July
2019.
[Kron18] Krontiris, A., "Evaluation of Certificate Enrollment over
Application Layer Security", May 2018,
<https://www.nada.kth.se/~ann/exjobb/
alexandros_krontiris.pdf>.
[LoRa1] Sanchez-Iborra, R., Sanchez-Gomez, J., Perez, S.,
Fernandez, P., Santa, J., Hernandez-Ramos, J., and A.
Skarmeta, "Enhancing LoRaWAN Security through a
Lightweight and Authenticated Key Management Approach",
June 2018,
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6021899/pdf/
sensors-18-01833.pdf>.
[LoRa2] Sanchez-Iborra, R., Sanchez-Gomez, J., Perez, S.,
Fernandez, P., Santa, J., Hernandez-Ramos, J., and A.
Skarmeta, "Internet Access for LoRaWAN Devices Considering
Security Issues", June 2018,
<https://ants.inf.um.es/~josesanta/doc/GIoTS1.pdf>.
[OPTLS] Krawczyk, H. and H. Wee, "The OPTLS Protocol and TLS 1.3",
October 2015, <https://eprint.iacr.org/2015/978.pdf>.
[Perez18] Perez, S., Garcia-Carrillo, D., Marin-Lopez, R.,
Hernandez-Ramos, J., Marin-Perez, R., and A. Skarmeta,
"Architecture of security association establishment based
on bootstrapping technologies for enabling critical IoT
infrastructures", October 2018, <http://www.anastacia-
h2020.eu/publications/Architecture_of_security_association
_establishment_based_on_bootstrapping_technologies_for_ena
bling_critical_IoT_infrastructures.pdf>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
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[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[SSR18] Bruni, A., Sahl Joergensen, T., Groenbech Petersen, T.,
and C. Schuermann, "Formal Verification of Ephemeral
Diffie-Hellman Over COSE (EDHOC)", November 2018,
<https://www.springerprofessional.de/en/formal-
verification-of-ephemeral-diffie-hellman-over-cose-
edhoc/16284348>.
Appendix A. Use of CBOR, CDDL and COSE in EDHOC
This Appendix is intended to simplify for implementors not familiar
with CBOR [I-D.ietf-cbor-7049bis], CDDL [RFC8610], COSE [RFC8152],
and HKDF [RFC5869].
A.1. CBOR and CDDL
The Concise Binary Object Representation (CBOR)
[I-D.ietf-cbor-7049bis] is a data format designed for small code size
and small message size. CBOR builds on the JSON data model but
extends it by e.g. encoding binary data directly without base64
conversion. In addition to the binary CBOR encoding, CBOR also has a
diagnostic notation that is readable and editable by humans. The
Concise Data Definition Language (CDDL) [RFC8610] provides a way to
express structures for protocol messages and APIs that use CBOR.
[RFC8610] also extends the diagnostic notation.
CBOR data items are encoded to or decoded from byte strings using a
type-length-value encoding scheme, where the three highest order bits
of the initial byte contain information about the major type. CBOR
supports several different types of data items, in addition to
integers (int, uint), simple values (e.g. null), byte strings (bstr),
and text strings (tstr), CBOR also supports arrays [] of data items,
maps {} of pairs of data items, and sequences
[I-D.ietf-cbor-sequence] of data items. Some examples are given
below. For a complete specification and more examples, see
[I-D.ietf-cbor-7049bis] and [RFC8610]. We recommend implementors to
get used to CBOR by using the CBOR playground [CborMe].
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Diagnostic Encoded Type
------------------------------------------------------------------
1 0x01 unsigned integer
24 0x1818 unsigned integer
-24 0x37 negative integer
-25 0x3818 negative integer
null 0xf6 simple value
h'12cd' 0x4212cd byte string
'12cd' 0x4431326364 byte string
"12cd" 0x6431326364 text string
{ 4 : h'cd' } 0xa10441cd map
<< 1, 2, null >> 0x430102f6 byte string
[ 1, 2, null ] 0x830102f6 array
( 1, 2, null ) 0x0102f6 sequence
1, 2, null 0x0102f6 sequence
------------------------------------------------------------------
EDHOC messages are CBOR Sequences [I-D.ietf-cbor-sequence]. The
message format specification uses the construct '.cbor' enabling
conversion between different CDDL types matching different CBOR items
with different encodings. Some examples are given below.
A type (e.g. an uint) may be wrapped in a byte string (bstr):
CDDL Type Diagnostic Encoded
------------------------------------------------------------------
uint 24 0x1818
bstr .cbor uint << 24 >> 0x421818
------------------------------------------------------------------
A.2. COSE
CBOR Object Signing and Encryption (COSE) [RFC8152] 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, COSE_Sign1, and COSE_KDF_Context objects.
Appendix B. EDHOC Authenticated withDiffie-Hellman Keys
The SIGMA protocol is mainly optimized for PKI and certificates. The
OPTLS protocol [OPTLS] shows how authentication can be provided by a
MAC computed from an ephemeral-static ECDH shared secret. Instead of
signature authentication keys, U and V would have Diffie-Hellman
authentication keys G_U and G_V, respectively. This type of
authentication keys could easily be used with RPK and would provide
significant reductions in message sizes as the 64 bytes signature
would be replaced by an 8 bytes MAC.
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EDHOC authenticated with asymmetric Diffie-Hellman keys should have
similar security properties as EDHOC authenticated with asymmetric
signature keys with a few differences:
o Repudiation: In EDHOC authenticated with asymmetric signature
keys, Party U could theoretically prove that Party V performed a
run of the protocol by presenting the private ephemeral key, and
vice versa. Note that storing the private ephemeral keys violates
the protocol requirements. With asymmetric Diffie-Hellman key
authentication, both parties can always deny having participated
in the protocol, this is similar to EDHOC with symmetric key
authentication.
o Key compromise impersonation (KCI): In EDHOC authenticated with
asymmetric signature keys, EDHOC provides KCI protection against
an attacker having access to the long term key or the ephemeral
secret key. In EDHOC authenticated with symmetric keys, EDHOC
provides KCI protection against an attacker having access to the
ephemeral secret key, but not against an attacker having access to
the long-term PSK. With asymmetric Diffie-Hellman key
authentication, KCI protection would be provided against an
attacker having access to the long-term Diffie-Hellman key, but
not to an attacker having access to the ephemeral secret key.
Note that the term KCI has typically been used for compromise of
long-term keys, and that an attacker with access to the ephemeral
secret key can only attack that specific protocol run.
TODO: Initial suggestion for key derivation, message formats, and
processing
Appendix C. Test Vectors
This appendix provides detailed test vectors to ease implementation
and ensure interoperability. In addition to hexadecimal, all CBOR
data items and sequences are given in CBOR diagnostic notation. The
test vectors use 1 byte key identifiers, 1 byte connection IDs, and
the default mapping to CoAP where Party U is CoAP client (this means
that corr = 1).
C.1. Test Vectors for EDHOC Authenticated with Asymmetric Keys (RPK)
Asymmetric EDHOC is used:
method (Asymmetric Authentication)
0
CoAP is used as transport:
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corr (Party U is CoAP client)
1
No unprotected opaque application data is sent in the message
exchanges.
The pre-defined Cipher Suite 0 is in place both on Party U and Party
V, see Section 3.1.
C.1.1. Input for Party U
The following are the parameters that are set in Party U before the
first message exchange.
Party U's private authentication key (32 bytes)
53 21 fc 01 c2 98 20 06 3a 72 50 8f c6 39 25 1d c8 30 e2 f7 68 3e b8 e3 8a
f1 64 a5 b9 af 9b e3
Party U's public authentication key (32 bytes)
42 4c 75 6a b7 7c c6 fd ec f0 b3 ec fc ff b7 53 10 c0 15 bf 5c ba 2e c0 a2
36 e6 65 0c 8a b9 c7
kid value to identify U's public authentication key (1 bytes)
a2
This test vector uses COSE_Key objects to store the raw public keys.
Moreover, EC2 keys with curve Ed25519 are used. That is in agreement
with the Cipher Suite 0.
CRED_U =
<< {
1: 1,
-1: 6,
-2: h'424c756ab77cc6fdecf0b3ecfcffb75310c015bf5cba2ec0a236e6650c8ab9c7'
} >>
CRED_U (COSE_Key) (CBOR-encoded) (42 bytes)
58 28 a3 01 01 20 06 21 58 20 42 4c 75 6a b7 7c c6 fd ec f0 b3 ec fc ff b7
53 10 c0 15 bf 5c ba 2e c0 a2 36 e6 65 0c 8a b9 c7
Because COSE_Keys are used, and because kid = h'a2':
ID_CRED_U =
{
4: h'a2'
}
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Note that since the map for ID_CRED_U contains a single 'kid'
parameter, ID_CRED_U is used when transported in the protected header
of the COSE Object, but only the kid_value is used when added to the
plaintext (see Section 4.4.2):
ID_CRED_U (in protected header) (CBOR-encoded) (4 bytes)
a1 04 41 a2
kid_value (in plaintext) (CBOR-encoded) (2 bytes)
41 a2
C.1.2. Input for Party V
The following are the parameters that are set in Party V before the
first message exchange.
Party V's private authentication key (32 bytes)
74 56 b3 a3 e5 8d 8d 26 dd 36 bc 75 d5 5b 88 63 a8 5d 34 72 f4 a0 1f 02 24
62 1b 1c b8 16 6d a9
Party V's public authentication key (32 bytes)
1b 66 1e e5 d5 ef 16 72 a2 d8 77 cd 5b c2 0f 46 30 dc 78 a1 14 de 65 9c 7e
50 4d 0f 52 9a 6b d3
kid value to identify U's public authentication key (1 bytes)
a3
This test vector uses COSE_Key objects to store the raw public keys.
Moreover, EC2 keys with curve Ed25519 are used. That is in agreement
with the Cipher Suite 0.
CRED_V =
<< {
1: 1,
-1: 6,
-2: h'1b661ee5d5ef1672a2d877cd5bc20f4630dc78a114de659c7e504d0f529a6bd3'
} >>
CRED_V (COSE_Key) (CBOR-encoded) (42 bytes)
58 28 a3 01 01 20 06 21 58 20 1b 66 1e e5 d5 ef 16 72 a2 d8 77 cd 5b c2 0f
46 30 dc 78 a1 14 de 65 9c 7e 50 4d 0f 52 9a 6b d3
Because COSE_Keys are used, and because kid = h'a3':
ID_CRED_V =
{
4: h'a3'
}
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Note that since the map for ID_CRED_U contains a single 'kid'
parameter, ID_CRED_U is used when transported in the protected header
of the COSE Object, but only the kid_value is used when added to the
plaintext (see Section 4.4.2):
ID_CRED_V (in protected header) (CBOR-encoded) (4 bytes)
a1 04 41 a3
kid_value (in plaintext) (CBOR-encoded) (2 bytes)
41 a3
C.1.3. Message 1
From the input parameters (in Appendix C.1.1):
TYPE (4 * method + corr)
1
suite
0
SUITES_U : suite
0
G_X (X-coordinate of the ephemeral public key of Party U) (32 bytes)
b1 a3 e8 94 60 e8 8d 3a 8d 54 21 1d c9 5f 0b 90 3f f2 05 eb 71 91 2d 6d b8
f4 af 98 0d 2d b8 3a
C_U (Connection identifier chosen by U) (1 bytes)
c3
No UAD_1 is provided, so UAD_1 is absent from message_1.
Message_1 is constructed, as the CBOR Sequence of the CBOR data items
above.
message_1 =
(
1,
0,
h'b1a3e89460e88d3a8d54211dc95f0b903ff205eb71912d6db8f4af980d2db83a',
h'c3'
)
message_1 (CBOR Sequence) (38 bytes)
01 00 58 20 b1 a3 e8 94 60 e8 8d 3a 8d 54 21 1d c9 5f 0b 90 3f f2 05 eb 71
91 2d 6d b8 f4 af 98 0d 2d b8 3a 41 c3
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C.1.4. Message 2
Since TYPE mod 4 equals 1, C_U is omitted from data_2.
G_Y (X-coordinate of the ephemeral public key of Party V) (32 bytes)
8d b5 77 f9 b9 c2 74 47 98 98 7d b5 57 bf 31 ca 48 ac d2 05 a9 db 8c 32 0e
5d 49 f3 02 a9 64 74
C_V (Connection identifier chosen by V) (1 bytes)
c4
Data_2 is constructed, as the CBOR Sequence of the CBOR data items
above.
data_2 =
(
h'8db577f9b9c2744798987db557bf31ca48acd205a9db8c320e5d49f302a96474',
h'c4'
)
data_2 (CBOR Sequence) (36 bytes)
58 20 8d b5 77 f9 b9 c2 74 47 98 98 7d b5 57 bf 31 ca 48 ac d2 05 a9 db 8c
32 0e 5d 49 f3 02 a9 64 74 41 c4
From data_2 and message_1 (from Appendix C.1.3), compute the input to
the transcript hash TH_2 = H( message_1, data_2 ), as a CBOR Sequence
of these 2 data items.
( message_1, data_2 ) (CBOR Sequence)
(74 bytes)
01 00 58 20 b1 a3 e8 94 60 e8 8d 3a 8d 54 21 1d c9 5f 0b 90 3f f2 05 eb 71
91 2d 6d b8 f4 af 98 0d 2d b8 3a 41 c3 58 20 8d b5 77 f9 b9 c2 74 47 98 98
7d b5 57 bf 31 ca 48 ac d2 05 a9 db 8c 32 0e 5d 49 f3 02 a9 64 74 41 c4
And from there, compute the transcript hash TH_2 = SHA-256(
message_1, data_2 )
TH_2 value (32 bytes)
55 50 b3 dc 59 84 b0 20 9a e7 4e a2 6a 18 91 89 57 50 8e 30 33 2b 11 da 68
1d c2 af dd 87 03 55
When encoded as a CBOR bstr, that gives:
TH_2 (CBOR-encoded) (34 bytes)
58 20 55 50 b3 dc 59 84 b0 20 9a e7 4e a2 6a 18 91 89 57 50 8e 30 33 2b 11
da 68 1d c2 af dd 87 03 55
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C.1.4.1. Signature Computation
COSE_Sign1 is computed with the following parameters. From
Appendix C.1.2:
o protected = bstr .cbor ID_CRED_V
o payload = CRED_V
And from Appendix C.1.4:
o external_aad = TH_2
The Sig_structure M_V to be signed is: [ "Signature1",
<< ID_CRED_V >>, TH_2, CRED_V ] , as defined in Section 4.3.2:
M_V =
[
"Signature1",
<< { 4: h'a3' } >>,
h'5550b3dc5984b0209ae74ea26a18918957508e30332b11da681dc2afdd870355',
<< {
1: 1,
-1: 6,
-2: h'1b661ee5d5ef1672a2d877cd5bc20f4630dc78a114de659c7e504d0f529a6b
d3'
} >>
]
Which encodes to the following byte string ToBeSigned:
M_V (message to be signed with Ed25519) (CBOR-encoded) (93 bytes)
84 6a 53 69 67 6e 61 74 75 72 65 31 44 a1 04 41 a3 58 20 55 50 b3 dc 59 84
b0 20 9a e7 4e a2 6a 18 91 89 57 50 8e 30 33 2b 11 da 68 1d c2 af dd 87 03
55 58 28 a3 01 01 20 06 21 58 20 1b 66 1e e5 d5 ef 16 72 a2 d8 77 cd 5b c2
0f 46 30 dc 78 a1 14 de 65 9c 7e 50 4d 0f 52 9a 6b d3
The message is signed using the private authentication key of V, and
produces the following signature:
V's signature (64 bytes)
52 3d 99 6d fd 9e 2f 77 c7 68 71 8a 30 c3 48 77 8c 5e b8 64 dd 53 7e 55 5e
4a 00 05 e2 09 53 07 13 ca 14 62 0d e8 18 7e 81 99 6e e8 04 d1 53 b8 a1 f6
08 49 6f dc d9 3d 30 fc 1c 8b 45 be cc 06
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C.1.4.2. Key and Nonce Computation
The key and nonce for calculating the ciphertext are calculated as
follows, as specified in Section 3.3.
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK = HMAC-SHA-256(salt, G_XY)
Since this is the asymmetric case, salt is the empty byte string.
G_XY is the shared secret, and since the curve25519 is used, the ECDH
shared secret is the output of the X25519 function.
G_XY (32 bytes)
c6 1e 09 09 a1 9d 64 24 01 63 ec 26 2e 9c c4 f8 8c e7 7b e1 23 c5 ab 53 8d
26 b0 69 22 a5 20 67
From there, PRK is computed:
PRK (32 bytes)
ba 9c 2c a1 c5 62 14 a6 e0 f6 13 ed a8 91 86 8a 4c a3 e3 fa bc c7 79 8f dc
01 60 80 07 59 16 71
Key K_2 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
info for K_2
[
10,
[ null, null, null ],
[ null, null, null ],
[ 128, h'', h'5550b3dc5984b0209ae74ea26a18918957508e30332b11da681dc2afdd
870355' ]
]
Which as a CBOR encoded data item is:
info (K_2) (CBOR-encoded) (48 bytes)
84 0a 83 f6 f6 f6 83 f6 f6 f6 83 18 80 40 58 20 55 50 b3 dc 59 84 b0 20 9a
e7 4e a2 6a 18 91 89 57 50 8e 30 33 2b 11 da 68 1d c2 af dd 87 03 55
L is the length of K_2, so 16 bytes.
From these parameters, K_2 is computed:
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K_2 (16 bytes)
da d7 44 af 07 c4 da 27 d1 f0 a3 8a 0c 4b 87 38
Nonce IV_2 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
info for IV_2
[
"IV-GENERATION",
[ null, null, null ],
[ null, null, null ],
[ 104, h'', h'5550b3dc5984b0209ae74ea26a18918957508e30332b11da681dc2afdd
870355' ]
]
Which as a CBOR encoded data item is:
info (IV_2) (CBOR-encoded) (61 bytes)
84 6d 49 56 2d 47 45 4e 45 52 41 54 49 4f 4e 83 f6 f6 f6 83 f6 f6 f6 83 18
68 40 58 20 55 50 b3 dc 59 84 b0 20 9a e7 4e a2 6a 18 91 89 57 50 8e 30 33
2b 11 da 68 1d c2 af dd 87 03 55
L is the length of IV_2, so 13 bytes.
From these parameters, IV_2 is computed:
IV_2 (13 bytes)
fb a1 65 d9 08 da a7 8e 4f 84 41 42 d0
C.1.4.3. Ciphertext Computation
COSE_Encrypt0 is computed with the following parameters. Note that
UAD_2 is omitted.
o empty protected header
o external_aad = TH_2
o plaintext = CBOR Sequence of the items kid_value, signature, in
this order.
with kid_value taken from Appendix C.1.2, and signature as calculated
in Appendix C.1.4.1.
The plaintext is the following:
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P_2 (68 bytes)
41 a3 58 40 52 3d 99 6d fd 9e 2f 77 c7 68 71 8a 30 c3 48 77 8c 5e b8 64 dd
53 7e 55 5e 4a 00 05 e2 09 53 07 13 ca 14 62 0d e8 18 7e 81 99 6e e8 04 d1
53 b8 a1 f6 08 49 6f dc d9 3d 30 fc 1c 8b 45 be cc 06
From the parameters above, the Enc_structure A_2 is computed.
A_2 =
[
"Encrypt0",
h'',
h'5550b3dc5984b0209ae74ea26a18918957508e30332b11da681dc2afdd870355'
]
Which encodes to the following byte string to be used as Additional
Authenticated Data:
A_2 (CBOR-encoded) (45 bytes)
83 68 45 6e 63 72 79 70 74 30 40 58 20 55 50 b3 dc 59 84 b0 20 9a e7 4e a2
6a 18 91 89 57 50 8e 30 33 2b 11 da 68 1d c2 af dd 87 03 55
The key and nonce used are defined in Appendix C.1.4.2:
o key = K_2
o nonce = IV_2
Using the parameters above, the ciphertext CIPHERTEXT_2 can be
computed:
CIPHERTEXT_2 (76 bytes)
1e 6b fe 0e 77 99 ce f0 66 a3 4f 08 ef aa 90 00 6d b4 4c 90 1c f7 9b 23 85
3a b9 7f d8 db c8 53 39 d5 ed 80 87 78 3c f7 a4 a7 e0 ea 38 c2 21 78 9f a3
71 be 64 e9 3c 43 a7 db 47 d1 e3 fb 14 78 8e 96 7f dd 78 d8 80 78 e4 9b 78
bf
C.1.4.4. message_2
From the parameter computed in Appendix C.1.4 and Appendix C.1.4.3,
message_2 is computed, as the CBOR Sequence of the following items:
(G_Y, C_V, CIPHERTEXT_2).
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message_2 =
(
h'8db577f9b9c2744798987db557bf31ca48acd205a9db8c320e5d49f302a96474',
h'c4',
h'1e6bfe0e7799cef066a34f08efaa90006db44c901cf79b23853ab97fd8dbc85339d5ed
8087783cf7a4a7e0ea38c221789fa371be64e93c43a7db47d1e3fb14788e967fdd78d880
78e49b78bf'
)
Which encodes to the following byte string:
message_2 (CBOR Sequence) (114 bytes)
58 20 8d b5 77 f9 b9 c2 74 47 98 98 7d b5 57 bf 31 ca 48 ac d2 05 a9 db 8c
32 0e 5d 49 f3 02 a9 64 74 41 c4 58 4c 1e 6b fe 0e 77 99 ce f0 66 a3 4f 08
ef aa 90 00 6d b4 4c 90 1c f7 9b 23 85 3a b9 7f d8 db c8 53 39 d5 ed 80 87
78 3c f7 a4 a7 e0 ea 38 c2 21 78 9f a3 71 be 64 e9 3c 43 a7 db 47 d1 e3 fb
14 78 8e 96 7f dd 78 d8 80 78 e4 9b 78 bf
C.1.5. Message 3
Since TYPE mod 4 equals 1, C_V is not omitted from data_3.
C_V (1 bytes)
c4
Data_3 is constructed, as the CBOR Sequence of the CBOR data item
above.
data_3 =
(
h'c4'
)
data_3 (CBOR Sequence) (2 bytes)
41 c4
From data_3, CIPHERTEXT_2 (Appendix C.1.4.3), and TH_2
(Appendix C.1.4), compute the input to the transcript hash TH_2 =
H(TH_2 , CIPHERTEXT_2, data_3), as a CBOR Sequence of these 3 data
items.
( TH_2, CIPHERTEXT_2, data_3 )
(CBOR Sequence) (114 bytes)
58 20 55 50 b3 dc 59 84 b0 20 9a e7 4e a2 6a 18 91 89 57 50 8e 30 33 2b 11
da 68 1d c2 af dd 87 03 55 58 4c 1e 6b fe 0e 77 99 ce f0 66 a3 4f 08 ef aa
90 00 6d b4 4c 90 1c f7 9b 23 85 3a b9 7f d8 db c8 53 39 d5 ed 80 87 78 3c
f7 a4 a7 e0 ea 38 c2 21 78 9f a3 71 be 64 e9 3c 43 a7 db 47 d1 e3 fb 14 78
8e 96 7f dd 78 d8 80 78 e4 9b 78 bf 41 c4
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And from there, compute the transcript hash TH_3 = SHA-256(TH_2 ,
CIPHERTEXT_2, data_3)
TH_3 value (32 bytes)
21 cc b6 78 b7 91 14 96 09 55 88 5b 90 a2 b8 2e 3b 2c a2 7e 8e 37 4a 79 07
f3 e7 85 43 67 fc 22
When encoded as a CBOR bstr, that gives:
TH_3 (CBOR-encoded) (34 bytes)
58 20 21 cc b6 78 b7 91 14 96 09 55 88 5b 90 a2 b8 2e 3b 2c a2 7e 8e 37 4a
79 07 f3 e7 85 43 67 fc 22
C.1.5.1. Signature Computation
COSE_Sign1 is computed with the following parameters. From
Appendix C.1.2:
o protected = bstr .cbor ID_CRED_U
o payload = CRED_U
And from Appendix C.1.4:
o external_aad = TH_3
The Sig_structure M_V to be signed is: [ "Signature1",
<< ID_CRED_U >>, TH_3, CRED_U ] , as defined in Section 4.4.2:
M_U =
[
"Signature1",
<< { 4: h'a2' } >>,
h'734bef323d867a12956127c2e62ade42c0f119e5487750c0c31fd093376dceed',
<< {
1: 1,
-1: 6,
-2: h'424c756ab77cc6fdecf0b3ecfcffb75310c015bf5cba2ec0a236e6650c8ab9
c7'
} >>
]
Which encodes to the following byte string ToBeSigned:
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M_U (message to be signed with Ed25519) (CBOR-encoded) (93 bytes)
84 6a 53 69 67 6e 61 74 75 72 65 31 44 a1 04 41 a2 58 20 73 4b ef 32 3d 86
7a 12 95 61 27 c2 e6 2a de 42 c0 f1 19 e5 48 77 50 c0 c3 1f d0 93 37 6d ce
ed 58 28 a3 01 01 20 06 21 58 20 42 4c 75 6a b7 7c c6 fd ec f0 b3 ec fc ff
b7 53 10 c0 15 bf 5c ba 2e c0 a2 36 e6 65 0c 8a b9 c7
The message is signed using the private authentication key of U, and
produces the following signature:
U's signature (64 bytes)
5c 7d 7d 64 c9 61 c5 f5 2d cf 33 91 25 92 a1 af f0 2c 33 62 b0 e7 55 0e 4b
c5 66 b7 0c 20 61 f3 c5 f6 49 e5 ed 32 3d 30 a2 6c 61 2f bb 5c bd 25 f3 1c
27 22 8c ea ec 64 29 31 95 41 fe 07 8e 0e
C.1.5.2. Key and Nonce Computation
The key and nonce for calculating the ciphertext are calculated as
follows, as specified in Section 3.3.
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK = HMAC-SHA-256(salt, G_XY)
Since this is the asymmetric case, salt is the empty byte string.
G_XY is the shared secret, and since the curve25519 is used, the ECDH
shared secret is the output of the X25519 function.
G_XY (32 bytes)
c6 1e 09 09 a1 9d 64 24 01 63 ec 26 2e 9c c4 f8 8c e7 7b e1 23 c5 ab 53 8d
26 b0 69 22 a5 20 67
From there, PRK is computed:
PRK (32 bytes)
ba 9c 2c a1 c5 62 14 a6 e0 f6 13 ed a8 91 86 8a 4c a3 e3 fa bc c7 79 8f dc
01 60 80 07 59 16 71
Key K_3 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
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info for K_3
[
10,
[ null, null, null ],
[ null, null, null ],
[ 128, h'', h'21ccb678b79114960955885b90a2b82e3b2ca27e8e374a7907f3e78543
67fc22' ]
]
Which as a CBOR encoded data item is:
info (K_3) (CBOR-encoded) (48 bytes)
84 0a 83 f6 f6 f6 83 f6 f6 f6 83 18 80 40 58 20 21 cc b6 78 b7 91 14 96 09
55 88 5b 90 a2 b8 2e 3b 2c a2 7e 8e 37 4a 79 07 f3 e7 85 43 67 fc 22
L is the length of K_3, so 16 bytes.
From these parameters, K_3 is computed:
K_3 (16 bytes)
e1 ac d4 76 f5 96 a4 60 72 44 a8 da 8c ff 49 df
Nonce IV_3 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
info for IV_3
[
"IV-GENERATION",
[ null, null, null ],
[ null, null, null ],
[ 104, h'', h'21ccb678b79114960955885b90a2b82e3b2ca27e8e374a7907f3e78543
67fc22' ]
]
Which as a CBOR encoded data item is:
info (IV_3) (CBOR-encoded) (61 bytes)
84 6d 49 56 2d 47 45 4e 45 52 41 54 49 4f 4e 83 f6 f6 f6 83 f6 f6 f6 83 18
68 40 58 20 21 cc b6 78 b7 91 14 96 09 55 88 5b 90 a2 b8 2e 3b 2c a2 7e 8e
37 4a 79 07 f3 e7 85 43 67 fc 22
L is the length of IV_3, so 13 bytes.
From these parameters, IV_3 is computed:
IV_3 (13 bytes)
de 53 02 13 ab a2 6a 47 1a 51 f3 d6 fb
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C.1.5.3. Ciphertext Computation
COSE_Encrypt0 is computed with the following parameters. Note that
PAD_3 is omitted.
o empty protected header
o external_aad = TH_3
o plaintext = CBOR Sequence of the items kid_value, signature, in
this order.
with kid_value taken from Appendix C.1.1, and signature as calculated
in Appendix C.1.5.1.
The plaintext is the following:
P_3 (68 bytes)
41 a2 58 40 5c 7d 7d 64 c9 61 c5 f5 2d cf 33 91 25 92 a1 af f0 2c 33 62 b0
e7 55 0e 4b c5 66 b7 0c 20 61 f3 c5 f6 49 e5 ed 32 3d 30 a2 6c 61 2f bb 5c
bd 25 f3 1c 27 22 8c ea ec 64 29 31 95 41 fe 07 8e 0e
From the parameters above, the Enc_structure A_3 is computed.
A_3 =
[
"Encrypt0",
h'',
h'21ccb678b79114960955885b90a2b82e3b2ca27e8e374a7907f3e7854367fc22'
]
Which encodes to the following byte string to be used as Additional
Authenticated Data:
A_2 (CBOR-encoded) (45 bytes)
83 68 45 6e 63 72 79 70 74 30 40 58 20 21 cc b6 78 b7 91 14 96 09 55 88 5b
90 a2 b8 2e 3b 2c a2 7e 8e 37 4a 79 07 f3 e7 85 43 67 fc 22
The key and nonce used are defined in Appendix C.1.4.2:
o key = K_3
o nonce = IV_3
Using the parameters above, the ciphertext CIPHERTEXT_3 can be
computed:
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CIPHERTEXT_3 (76 bytes)
de 4a 83 3d 48 b6 64 74 14 2c c9 bd ce 87 d9 3a f8 35 57 9c 2d bf 1b 9e 2f
b4 dc 66 60 0d ba c6 bb 3c c0 5c 29 0e f3 5d 51 5b 4d 7d 64 83 f5 09 61 43
b5 56 44 cf af d1 ff aa 7f 2b a3 86 36 57 83 1d d2 e5 bd 04 04 38 60 14 0d
c8
C.1.5.4. message_3
From the parameter computed in Appendix C.1.5 and Appendix C.1.5.3,
message_3 is computed, as the CBOR Sequence of the following items:
(C_V, CIPHERTEXT_3).
message_3 =
(
h'c4',
h'de4a833d48b66474142cc9bdce87d93af835579c2dbf1b9e2fb4dc66600dbac6bb3cc0
5c290ef35d515b4d7d6483f5096143b55644cfafd1ffaa7f2ba3863657831dd2e5bd0404
3860140dc8'
)
Which encodes to the following byte string:
message_3 (CBOR Sequence) (80 bytes)
41 c4 58 4c de 4a 83 3d 48 b6 64 74 14 2c c9 bd ce 87 d9 3a f8 35 57 9c 2d bf 1b 9e 2f b4 dc 66 60 0d ba c6 bb 3c c0 5c 29 0e f3 5d 51 5b 4d 7d 64 83 f5 09 61 43 b5 56 44 cf af d1 ff aa 7f 2b a3 86 36 57 83 1d d2 e5 bd 04 04 38 60 14 0d c8
C.1.5.5. OSCORE Security Context Derivation
From the previous message exchange, the Common Security Context for
OSCORE [RFC8613] can be derived, as specified in Section 3.3.1.
First af all, TH_4 is computed: TH_4 = H( TH_3, CIPHERTEXT_3 ), where
the input to the hash function is the CBOR Sequence of TH_3 and
CIPHERTEXT_3
( TH_3, CIPHERTEXT_3 )
(CBOR Sequence) (112 bytes)
58 20 21 cc b6 78 b7 91 14 96 09 55 88 5b 90 a2 b8 2e 3b 2c a2 7e 8e 37 4a
79 07 f3 e7 85 43 67 fc 22 58 4c de 4a 83 3d 48 b6 64 74 14 2c c9 bd ce 87
d9 3a f8 35 57 9c 2d bf 1b 9e 2f b4 dc 66 60 0d ba c6 bb 3c c0 5c 29 0e f3
5d 51 5b 4d 7d 64 83 f5 09 61 43 b5 56 44 cf af d1 ff aa 7f 2b a3 86 36 57
83 1d d2 e5 bd 04 04 38 60 14 0d c8
And from there, compute the transcript hash TH_4 = SHA-256( TH_3,
CIPHERTEXT_3 )
TH_4 value (32 bytes)
51 ed 39 32 bc ba e8 90 1c 1d 4d eb 94 bd 67 3a b4 d3 8c 34 81 96 09 ee 0d
5c 9d a6 e9 80 7f e5
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When encoded as a CBOR bstr, that gives:
TH_4 (CBOR-encoded) (34 bytes)
58 20 51 ed 39 32 bc ba e8 90 1c 1d 4d eb 94 bd 67 3a b4 d3 8c 34 81 96 09
ee 0d 5c 9d a6 e9 80 7f e5
To derive the Master Secret and Master Salt the same HKDF-Expand
(PRK, info, L) is used, with different info and L.
For Master Secret:
L for Master Secret = 16
Info for Master Secret =
[
"OSCORE Master Secret",
[ null, null, null ],
[ null, null, null ],
[ 128, h'', h'51ed3932bcbae8901c1d4deb94bd673ab4d38c34819609ee0d5c9da6e9
807fe5' ]
]
When encoded as a CBOR bstr, that gives:
info (OSCORE Master Secret) (CBOR-encoded) (68 bytes)
84 74 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 65 63 72 65 74 83 f6 f6
f6 83 f6 f6 f6 83 18 80 40 58 20 51 ed 39 32 bc ba e8 90 1c 1d 4d eb 94 bd
67 3a b4 d3 8c 34 81 96 09 ee 0d 5c 9d a6 e9 80 7f e5
Finally, the Master Secret value computed is:
OSCORE Master Secret (16 bytes)
09 02 9d b0 0c 3e 01 27 42 c3 a8 69 04 07 4c 0e
For Master Salt:
L for Master Secret = 8
Info for Master Salt =
[
"OSCORE Master Salt",
[ null, null, null ],
[ null, null, null ],
[ 64, h'', h'51ed3932bcbae8901c1d4deb94bd673ab4d38c34819609ee0d5c9da6e98
07fe5' ]
]
When encoded as a CBOR bstr, that gives:
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info (OSCORE Master Salt) (CBOR-encoded) (66 bytes)
84 72 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 61 6c 74 83 f6 f6 f6 83
f6 f6 f6 83 18 40 40 58 20 51 ed 39 32 bc ba e8 90 1c 1d 4d eb 94 bd 67 3a
b4 d3 8c 34 81 96 09 ee 0d 5c 9d a6 e9 80 7f e5
Finally, the Master Secret value computed is:
OSCORE Master Salt (8 bytes)
81 02 97 22 a2 30 4a 06
The Client's Sender ID takes the value of C_V:
Client's OSCORE Sender ID (1 bytes)
c4
The Server's Sender ID takes the value of C_U:
Server's OSCORE Sender ID (1 bytes)
c3
The algorithms are those negociated in the cipher suite:
AEAD Algorithm
10
HMAC Algorithm
5
C.2. Test Vectors for EDHOC Authenticated with Symmetric Keys (PSK)
Symmetric EDHOC is used:
method (Symmetric Authentication)
1
CoAP is used as transport:
corr (Party U is CoAP client)
1
No unprotected opaque application data is sent in the message
exchanges.
The pre-defined Cipher Suite 0 is in place both on Party U and Party
V, see Section 3.1.
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C.2.1. Input for Party U
The following are the parameters that are set in Party U before the
first message exchange.
Party U's ephemeral private key (32 bytes)
f4 0c ea f8 6e 57 76 92 33 32 b8 d8 fd 3b ef 84 9c ad b1 9c 69 96 bc 27 2a
f1 f6 48 d9 56 6a 4c
Party U's ephemeral public key (value of X_U) (32 bytes)
ab 2f ca 32 89 83 22 c2 08 fb 2d ab 50 48 bd 43 c3 55 c6 43 0f 58 88 97 cb
57 49 61 cf a9 80 6f
Connection identifier chosen by U (value of C_U) (1 bytes)
c1
Pre-shared Key (PSK) (16 bytes)
a1 1f 8f 12 d0 87 6f 73 6d 2d 8f d2 6e 14 c2 de
kid value to identify PSK (1 bytes)
a1
So ID_PSK is defined as the following:
ID_PSK =
{
4: h'a1'
}
This test vector uses COSE_Key objects to store the pre-shared key.
Note that since the map for ID_PSK contains a single 'kid' parameter,
ID_PSK is used when transported in the protected header of the COSE
Object, but only the kid_value is used when added to the plaintext
(see Section 5.1):
ID_PSK (in protected header) (CBOR-encoded) (4 bytes)
a1 04 41 a1
kid_value (in plaintext) (CBOR-encoded) (2 bytes)
41 a1
C.2.2. Input for Party V
The following are the parameters that are set in Party U before the
first message exchange.
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Party V's ephemeral private key (32 bytes)
d9 81 80 87 de 72 44 ab c1 b5 fc f2 8e 55 e4 2c 7f f9 c6 78 c0 60 51 81 f3
7a c5 d7 41 4a 7b 95
Party V's ephemeral public key (value of X_V) (32 bytes)
fc 3b 33 93 67 a5 22 5d 53 a9 2d 38 03 23 af d0 35 d7 81 7b 6d 1b e4 7d 94
6f 6b 09 a9 cb dc 06
Connection identifier chosen by V (value of C_V) (1 bytes)
c2
Pre-shared Key (PSK) (16 bytes)
a1 1f 8f 12 d0 87 6f 73 6d 2d 8f d2 6e 14 c2 de
kid value to identify PSK (1 bytes)
a1
So ID_PSK is defined as the following:
ID_PSK =
{
4: h'a1'
}
This test vector uses COSE_Key objects to store the pre-shared key.
Note that since the map for ID_PSK contains a single 'kid' parameter,
ID_PSK is used when transported in the protected header of the COSE
Object, but only the kid_value is used when added to the plaintext
(see Section 5.1):
ID_PSK (in protected header) (CBOR-encoded) (4 bytes)
a1 04 41 a1
kid_value (in plaintext) (CBOR-encoded) (2 bytes)
41 a1
C.2.3. Message 1
From the input parameters (in Appendix C.2.1):
TYPE (4 * method + corr)
5
suite
0
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SUITES_U : suite
0
G_X (X-coordinate of the ephemeral public key of Party U) (32 bytes)
ab 2f ca 32 89 83 22 c2 08 fb 2d ab 50 48 bd 43 c3 55 c6 43 0f 58 88 97 cb
57 49 61 cf a9 80 6f
C_U (Connection identifier chosen by U) (CBOR encoded) (2 bytes)
41 c1
kid_value of ID_PSK (CBOR encoded) (2 bytes)
41 a1
No UAD_1 is provided, so UAD_1 is absent from message_1.
Message_1 is constructed, as the CBOR Sequence of the CBOR data items
above.
message_1 =
(
5,
0,
h'ab2fca32898322c208fb2dab5048bd43c355c6430f588897cb574961cfa9806f',
h'c1',
h'a1'
)
message_1 (CBOR Sequence) (40 bytes)
05 00 58 20 ab 2f ca 32 89 83 22 c2 08 fb 2d ab 50 48 bd 43 c3 55 c6 43 0f
58 88 97 cb 57 49 61 cf a9 80 6f 41 c1 41 a1
C.2.4. Message 2
Since TYPE mod 4 equals 1, C_U is omitted from data_2.
G_Y (X-coordinate of the ephemeral public key of Party V) (32 bytes)
fc 3b 33 93 67 a5 22 5d 53 a9 2d 38 03 23 af d0 35 d7 81 7b 6d 1b e4 7d 94
6f 6b 09 a9 cb dc 06
C_V (Connection identifier chosen by V) (1 bytes)
c2
Data_2 is constructed, as the CBOR Sequence of the CBOR data items
above.
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data_2 =
(
h'fc3b339367a5225d53a92d380323afd035d7817b6d1be47d946f6b09a9cbdc06',
h'c2'
)
data_2 (CBOR Sequence) (36 bytes)
58 20 fc 3b 33 93 67 a5 22 5d 53 a9 2d 38 03 23 af d0 35 d7 81 7b 6d 1b e4
7d 94 6f 6b 09 a9 cb dc 06 41 c2
From data_2 and message_1 (from Appendix C.2.3), compute the input to
the transcript hash TH_2 = H( message_1, data_2 ), as a CBOR Sequence
of these 2 data items.
( message_1, data_2 ) (CBOR Sequence)
(76 bytes)
05 00 58 20 ab 2f ca 32 89 83 22 c2 08 fb 2d ab 50 48 bd 43 c3 55 c6 43 0f
58 88 97 cb 57 49 61 cf a9 80 6f 41 c1 41 a1 58 20 fc 3b 33 93 67 a5 22 5d
53 a9 2d 38 03 23 af d0 35 d7 81 7b 6d 1b e4 7d 94 6f 6b 09 a9 cb dc 06 41
c2
And from there, compute the transcript hash TH_2 = SHA-256(
message_1, data_2 )
TH_2 value (32 bytes)
16 4f 44 d8 56 dd 15 22 2f a4 63 f2 02 d9 c6 0b e3 c6 9b 40 f7 35 8d 34 1c
db 7b 07 de e1 70 ca
When encoded as a CBOR bstr, that gives:
TH_2 (CBOR-encoded) (34 bytes)
58 20 16 4f 44 d8 56 dd 15 22 2f a4 63 f2 02 d9 c6 0b e3 c6 9b 40 f7 35 8d
34 1c db 7b 07 de e1 70 ca
C.2.4.1. Key and Nonce Computation
The key and nonce for calculating the ciphertext are calculated as
follows, as specified in Section 3.3.
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK = HMAC-SHA-256(salt, G_XY)
Since this is the symmetric case, salt is the PSK:
salt (16 bytes)
a1 1f 8f 12 d0 87 6f 73 6d 2d 8f d2 6e 14 c2 de
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G_XY is the shared secret, and since the curve25519 is used, the ECDH
shared secret is the output of the X25519 function.
G_XY (32 bytes)
d5 75 05 50 6d 8f 30 a8 60 a0 63 d0 1b 5b 7a d7 6a 09 4f 70 61 3b 4a e6 6c
5a 90 e5 c2 1f 23 11
From there, PRK is computed:
PRK (32 bytes)
aa b2 f1 3c cb 1a 4f f7 96 a9 7a 32 a4 d2 fb 62 47 ef 0b 6b 06 da 04 d3 d1
06 39 4b 28 76 e2 8c
Key K_2 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
info for K_2
[
10,
[ null, null, null ],
[ null, null, null ],
[ 128, h'', h'164f44d856dd15222fa463f202d9c60be3c69b40f7358d341cdb7b07de
e170ca' ]
]
Which as a CBOR encoded data item is:
info (K_2) (CBOR-encoded) (48 bytes)
84 0a 83 f6 f6 f6 83 f6 f6 f6 83 18 80 40 58 20 16 4f 44 d8 56 dd 15 22 2f
a4 63 f2 02 d9 c6 0b e3 c6 9b 40 f7 35 8d 34 1c db 7b 07 de e1 70 ca
L is the length of K_2, so 16 bytes.
From these parameters, K_2 is computed:
K_2 (16 bytes)
ac 42 6e 5e 7d 7a d6 ae 3b 19 aa bd e0 f6 25 57
Nonce IV_2 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
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info for IV_2
[
"IV-GENERATION",
[ null, null, null ],
[ null, null, null ],
[ 104, h'', h'164f44d856dd15222fa463f202d9c60be3c69b40f7358d341cdb7b07de
e170ca' ]
]
Which as a CBOR encoded data item is:
info (IV_2) (CBOR-encoded) (61 bytes)
84 6d 49 56 2d 47 45 4e 45 52 41 54 49 4f 4e 83 f6 f6 f6 83 f6 f6 f6 83 18
68 40 58 20 16 4f 44 d8 56 dd 15 22 2f a4 63 f2 02 d9 c6 0b e3 c6 9b 40 f7
35 8d 34 1c db 7b 07 de e1 70 ca
L is the length of IV_2, so 13 bytes.
From these parameters, IV_2 is computed:
IV_2 (13 bytes)
ff 11 2e 1c 26 8a a2 a7 7c c3 ee 6c 4d
C.2.4.2. Ciphertext Computation
COSE_Encrypt0 is computed with the following parameters. Note that
UAD_2 is omitted.
o empty protected header
o external_aad = TH_2
o empty plaintext, since UAD_2 is omitted
From the parameters above, the Enc_structure A_2 is computed.
A_2 =
[
"Encrypt0",
h'',
h'164f44d856dd15222fa463f202d9c60be3c69b40f7358d341cdb7b07dee170ca'
]
Which encodes to the following byte string to be used as Additional
Authenticated Data:
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A_2 (CBOR-encoded) (45 bytes)
83 68 45 6e 63 72 79 70 74 30 40 58 20 16 4f 44 d8 56 dd 15 22 2f a4 63 f2
02 d9 c6 0b e3 c6 9b 40 f7 35 8d 34 1c db 7b 07 de e1 70 ca
The key and nonce used are defined in Appendix C.2.4.1:
o key = K_2
o nonce = IV_2
Using the parameters above, the ciphertext CIPHERTEXT_2 can be
computed:
CIPHERTEXT_2 (8 bytes)
ba 38 b9 a3 fc 1a 58 e9
C.2.4.3. message_2
From the parameter computed in Appendix C.2.4 and Appendix C.2.4.2,
message_2 is computed, as the CBOR Sequence of the following items:
(G_Y, C_V, CIPHERTEXT_2).
message_2 =
(
h'fc3b339367a5225d53a92d380323afd035d7817b6d1be47d946f6b09a9cbdc06',
h'c2',
h'ba38b9a3fc1a58e9'
)
Which encodes to the following byte string:
message_2 (CBOR Sequence) (45 bytes)
58 20 fc 3b 33 93 67 a5 22 5d 53 a9 2d 38 03 23 af d0 35 d7 81 7b 6d 1b e4
7d 94 6f 6b 09 a9 cb dc 06 41 c2 48 ba 38 b9 a3 fc 1a 58 e9
C.2.5. Message 3
Since TYPE mod 4 equals 1, C_V is not omitted from data_3.
C_V (1 bytes)
c2
Data_3 is constructed, as the CBOR Sequence of the CBOR data item
above.
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data_3 =
(
h'c2'
)
data_3 (CBOR Sequence) (2 bytes)
41 c2
From data_3, CIPHERTEXT_2 (Appendix C.2.4.2), and TH_2
(Appendix C.2.4), compute the input to the transcript hash TH_2 =
H(TH_2 , CIPHERTEXT_2, data_3), as a CBOR Sequence of these 3 data
items.
( TH_2, CIPHERTEXT_2, data_3 ) (CBOR Sequence) (45 bytes)
58 20 16 4f 44 d8 56 dd 15 22 2f a4 63 f2 02 d9 c6 0b e3 c6 9b 40 f7 35 8d
34 1c db 7b 07 de e1 70 ca 48 ba 38 b9 a3 fc 1a 58 e9 41 c2
And from there, compute the transcript hash TH_3 = SHA-256(TH_2 ,
CIPHERTEXT_2, data_3)
TH_3 value (32 bytes)
11 98 aa b3 ed db 61 b8 a1 b1 93 a9 e5 60 2b 5d 5f ea 76 bc 28 52 89 54 81
b5 2b 8a f5 66 d7 fe
When encoded as a CBOR bstr, that gives:
TH_3 (CBOR-encoded) (34 bytes)
58 20 11 98 aa b3 ed db 61 b8 a1 b1 93 a9 e5 60 2b 5d 5f ea 76 bc 28 52 89
54 81 b5 2b 8a f5 66 d7 fe
C.2.5.1. Key and Nonce Computation
The key and nonce for calculating the ciphertext are calculated as
follows, as specified in Section 3.3.
HKDF SHA-256 is the HKDF used (as defined by cipher suite 0).
PRK = HMAC-SHA-256(salt, G_XY)
Since this is the symmetric case, salt is the PSK:
salt (16 bytes)
a1 1f 8f 12 d0 87 6f 73 6d 2d 8f d2 6e 14 c2 de
G_XY is the shared secret, and since the curve25519 is used, the ECDH
shared secret is the output of the X25519 function.
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G_XY (32 bytes)
d5 75 05 50 6d 8f 30 a8 60 a0 63 d0 1b 5b 7a d7 6a 09 4f 70 61 3b 4a e6 6c
5a 90 e5 c2 1f 23 11
From there, PRK is computed:
PRK (32 bytes)
aa b2 f1 3c cb 1a 4f f7 96 a9 7a 32 a4 d2 fb 62 47 ef 0b 6b 06 da 04 d3 d1
06 39 4b 28 76 e2 8c
Key K_3 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
info for K_3
[
10,
[ null, null, null ],
[ null, null, null ],
[ 128, h'', h'1198aab3eddb61b8a1b193a9e5602b5d5fea76bc2852895481b52b8af5
66d7fe' ]
]
Which as a CBOR encoded data item is:
info (K_3) (CBOR-encoded) (48 bytes)
84 0a 83 f6 f6 f6 83 f6 f6 f6 83 18 80 40 58 20 11 98 aa b3 ed db 61 b8 a1
b1 93 a9 e5 60 2b 5d 5f ea 76 bc 28 52 89 54 81 b5 2b 8a f5 66 d7 fe
L is the length of K_3, so 16 bytes.
From these parameters, K_3 is computed:
K_3 (16 bytes)
fe 75 e3 44 27 f8 3a ad 84 16 83 c6 6f a3 8a 62
Nonce IV_3 is the output of HKDF-Expand(PRK, info, L).
info is defined as follows:
info for IV_3
[
"IV-GENERATION",
[ null, null, null ],
[ null, null, null ],
[ 104, h'', h'1198aab3eddb61b8a1b193a9e5602b5d5fea76bc2852895481b52b8af5
66d7fe' ]
]
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Which as a CBOR encoded data item is:
info (IV_3) (CBOR-encoded) (61 bytes)
84 6d 49 56 2d 47 45 4e 45 52 41 54 49 4f 4e 83 f6 f6 f6 83 f6 f6 f6 83 18
68 40 58 20 11 98 aa b3 ed db 61 b8 a1 b1 93 a9 e5 60 2b 5d 5f ea 76 bc 28
52 89 54 81 b5 2b 8a f5 66 d7 fe
L is the length of IV_3, so 13 bytes.
From these parameters, IV_3 is computed:
IV_3 (13 bytes)
60 0a 33 b4 16 de 08 23 52 67 71 ec 8a
C.2.5.2. Ciphertext Computation
COSE_Encrypt0 is computed with the following parameters. Note that
PAD_2 is omitted.
o empty protected header
o external_aad = TH_3
o empty plaintext, since PAD_2 is omitted
From the parameters above, the Enc_structure A_3 is computed.
A_3 =
[
"Encrypt0",
h'',
h'1198aab3eddb61b8a1b193a9e5602b5d5fea76bc2852895481b52b8af566d7fe'
]
Which encodes to the following byte string to be used as Additional
Authenticated Data:
A_3 (CBOR-encoded) (45 bytes)
83 68 45 6e 63 72 79 70 74 30 40 58 20 11 98 aa b3 ed db 61 b8 a1 b1 93 a9
e5 60 2b 5d 5f ea 76 bc 28 52 89 54 81 b5 2b 8a f5 66 d7 fe
The key and nonce used are defined in Appendix C.2.5.1:
o key = K_3
o nonce = IV_3
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Using the parameters above, the ciphertext CIPHERTEXT_3 can be
computed:
CIPHERTEXT_3 (8 bytes)
51 29 07 92 61 45 40 04
C.2.5.3. message_3
From the parameter computed in Appendix C.2.5 and Appendix C.2.5.2,
message_3 is computed, as the CBOR Sequence of the following items:
(C_V, CIPHERTEXT_3).
message_3 =
(
h'c2',
h'5129079261454004'
)
Which encodes to the following byte string:
message_3 (CBOR Sequence) (11 bytes)
41 c2 48 51 29 07 92 61 45 40 04
C.2.5.4. OSCORE Security Context Derivation
From the previous message exchange, the Common Security Context for
OSCORE [RFC8613] can be derived, as specified in Section 3.3.1.
First af all, TH_4 is computed: TH_4 = H( TH_3, CIPHERTEXT_3 ), where
the input to the hash function is the CBOR Sequence of TH_3 and
CIPHERTEXT_3
( TH_3, CIPHERTEXT_3 )
(CBOR Sequence) (43 bytes)
58 20 11 98 aa b3 ed db 61 b8 a1 b1 93 a9 e5 60 2b 5d 5f ea 76 bc 28 52 89
54 81 b5 2b 8a f5 66 d7 fe 48 51 29 07 92 61 45 40 04
And from there, compute the transcript hash TH_4 = SHA-256( TH_3,
CIPHERTEXT_3 )
TH_4 value (32 bytes)
df 7c 9b 06 f5 dc 0e e8 86 0b 39 6c 78 c5 be b7 57 41 3f a7 b6 a9 cf 28 3d
db 4c d4 c1 fd e4 3c
When encoded as a CBOR bstr, that gives:
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TH_4 (CBOR-encoded) (34 bytes)
58 20 df 7c 9b 06 f5 dc 0e e8 86 0b 39 6c 78 c5 be b7 57 41 3f a7 b6 a9 cf
28 3d db 4c d4 c1 fd e4 3c
To derive the Master Secret and Master Salt the same HKDF-Expand
(PRK, info, L) is used, with different info and L.
For Master Secret:
L for Master Secret = 16
Info for Master Secret =
[
"OSCORE Master Secret",
[ null, null, null ],
[ null, null, null ],
[ 128, h'', h'df7c9b06f5dc0ee8860b396c78c5beb757413fa7b6a9cf283ddb4cd4c1
fde43c' ]
]
When encoded as a CBOR bstr, that gives:
info (OSCORE Master Secret) (CBOR-encoded) (68 bytes)
84 74 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 65 63 72 65 74 83 f6 f6
f6 83 f6 f6 f6 83 18 80 40 58 20 df 7c 9b 06 f5 dc 0e e8 86 0b 39 6c 78 c5
be b7 57 41 3f a7 b6 a9 cf 28 3d db 4c d4 c1 fd e4 3c
Finally, the Master Secret value computed is:
OSCORE Master Secret (16 bytes)
8d 36 8f 09 26 2d c5 52 7f e7 19 e6 6c 91 63 75
For Master Salt:
L for Master Secret = 8
Info for Master Salt =
[
"OSCORE Master Salt",
[ null, null, null ],
[ null, null, null ],
[ 64, h'', h'df7c9b06f5dc0ee8860b396c78c5beb757413fa7b6a9cf283ddb4cd4c1f
de43c' ]
]
When encoded as a CBOR bstr, that gives:
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info (OSCORE Master Salt) (CBOR-encoded) (66 bytes)
84 72 4f 53 43 4f 52 45 20 4d 61 73 74 65 72 20 53 61 6c 74 83 f6 f6 f6 83
f6 f6 f6 83 18 40 40 58 20 df 7c 9b 06 f5 dc 0e e8 86 0b 39 6c 78 c5 be b7
57 41 3f a7 b6 a9 cf 28 3d db 4c d4 c1 fd e4 3c
Finally, the Master Secret value computed is:
OSCORE Master Salt (8 bytes)
4d b7 06 58 c5 e9 9f b6
The Client's Sender ID takes the value of C_V:
Client's OSCORE Sender ID (1 bytes)
c2
The Server's Sender ID takes the value of C_U:
Server's OSCORE Sender ID (1 bytes)
c1
The algorithms are those negociated in the cipher suite:
AEAD Algorithm
10
HMAC Algorithm
5
Acknowledgments
The authors want to thank Alessandro Bruni, Martin Disch, Theis
Groenbech Petersen, Dan Harkins, Klaus Hartke, Russ Housley,
Alexandros Krontiris, Ilari Liusvaara, Karl Norrman, Salvador Perez,
Eric Rescorla, Michael Richardson, Thorvald Sahl Joergensen, Jim
Schaad, Carsten Schuermann, Ludwig Seitz, Stanislav Smyshlyaev,
Valery Smyslov, Rene Struik, and Erik Thormarker for reviewing and
commenting on intermediate versions of the draft. We are especially
indebted to Jim Schaad for his continuous reviewing and
implementation of different versions of the draft.
Authors' Addresses
Goeran Selander
Ericsson AB
Email: goran.selander@ericsson.com
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John Mattsson
Ericsson AB
Email: john.mattsson@ericsson.com
Francesca Palombini
Ericsson AB
Email: francesca.palombini@ericsson.com
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