KEM-based Authentication for EDHOC
draft-pocero-lake-authkem-edhoc-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Lidia Pocero Fraile , Christos Koulamas , Apostolos Fournaris , Evangelos Haleplidis | ||
| Last updated | 2026-05-22 | ||
| Replaces | draft-pocero-authkem-edhoc | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-pocero-lake-authkem-edhoc-00
individual L. Pocero Fraile
Internet-Draft C. Koulamas
Intended status: Standards Track A.P. Fournaris
Expires: 23 November 2026 E. Haleplidis
ISI, R.C. ATHENA
22 May 2026
KEM-based Authentication for EDHOC
draft-pocero-lake-authkem-edhoc-00
Abstract
This document specifies extensions to the Ephemeral Diffie-Hellman
Over COSE (EDHOC) protocol to provide resistance against quantum
computer adversaries by incorporating Post-Quantum Cryptography (PQC)
Key Encapsulation Mechanisms (KEMs) for both key exchange and
authentication. It defines a new signature-free KEM-based
authentication method in which both parties authenticate using KEMs,
enabling quantum-resistant authentication without relying on digital
signatures when PQC KEMs, such as the NIST-standardized ML-KEM, are
used.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 23 November 2026.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology and Requirements Language . . . . . . . . . . 5
1.2.1. Key Encapsulation Mechanisms (KEMs) . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Protocol Elements . . . . . . . . . . . . . . . . . . . . 8
2.1.1. Ephemeral KEM . . . . . . . . . . . . . . . . . . . . 9
2.1.2. Method . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.3. Authentication Parameters . . . . . . . . . . . . . . 9
2.1.3.1. Authentication Keys . . . . . . . . . . . . . . . 10
2.1.3.2. Authentication Credentials . . . . . . . . . . . 10
2.1.3.3. Identification of Credentials . . . . . . . . . . 10
2.1.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . 11
2.1.5. Transport . . . . . . . . . . . . . . . . . . . . . . 11
3. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . 12
3.1. Keys for EDHOC Message Processing . . . . . . . . . . . . 13
3.1.1. EDHOC_Extract . . . . . . . . . . . . . . . . . . . . 13
3.1.1.1. PRK_2e . . . . . . . . . . . . . . . . . . . . . 13
3.1.1.2. PRK_3e2m . . . . . . . . . . . . . . . . . . . . 14
3.1.1.3. PRK_4e3m . . . . . . . . . . . . . . . . . . . . 14
3.1.2. EDHOC_Expand and EDHOC_KDF . . . . . . . . . . . . . 15
3.1.3. PRK_out . . . . . . . . . . . . . . . . . . . . . . . 16
3.2. Keys for EDHOC Applications . . . . . . . . . . . . . . . 16
4. Message Formatting and Processing . . . . . . . . . . . . . . 16
4.1. KEM-based Authentication EDHOC Message 1 . . . . . . . . 16
4.1.1. Formating of Message 1 . . . . . . . . . . . . . . . 16
4.1.2. Initiator Composition of Message 1 . . . . . . . . . 17
4.1.3. Responder Processing of Message 1 . . . . . . . . . . 17
4.2. KEM-based authentication EDHOC Message 2 . . . . . . . . 17
4.2.1. Formating of Message 2 . . . . . . . . . . . . . . . 18
4.2.2. Responder Composition of Message 2 . . . . . . . . . 18
4.2.3. Initiator Processing of Message 2 . . . . . . . . . . 19
4.3. KEM-based authentication EDHOC Message 3 . . . . . . . . 20
4.3.1. Formating of Message 3 . . . . . . . . . . . . . . . 20
4.3.2. Initiator Composition of Message 3 . . . . . . . . . 20
4.3.3. Responder Processing of Message 3 . . . . . . . . . . 21
4.4. KEM-based authentication EDHOC Message 4 . . . . . . . . 22
4.4.1. Formating of Message 4 . . . . . . . . . . . . . . . 22
4.4.2. Responder Composition of Message 4 . . . . . . . . . 22
4.4.3. Initaitor Processing of Message 4 . . . . . . . . . . 23
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4.5. KEM-based authentication EDHOC Message 5 . . . . . . . . 24
4.5.1. Formating of Message 5 . . . . . . . . . . . . . . . 24
4.5.2. Initiator Composition of Message 5 . . . . . . . . . 24
4.5.3. Responder Processing of Message 5 . . . . . . . . . . 25
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
5.1. COSE Algorithms Registry . . . . . . . . . . . . . . . . 26
5.2. EDHOC Cipher Suites Registry . . . . . . . . . . . . . . 27
5.3. EDHOC Method Types Registry . . . . . . . . . . . . . . . 27
6. Security Considerations . . . . . . . . . . . . . . . . . . . 28
6.1. Security Properties . . . . . . . . . . . . . . . . . . . 28
6.2. KEM Security Considerations . . . . . . . . . . . . . . . 31
6.3. Four-Message Variant . . . . . . . . . . . . . . . . . . 31
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. Normative References . . . . . . . . . . . . . . . . . . 31
7.2. Informative References . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
The purpose of this document is to address the quantum-resistant
transition of the Ephemeral Diffie-Hellman Over COSE (EDHOC) protocol
by defining a new authentication method in which both parties use Key
Encapsulation Mechanism (KEM)-based authentication together with
Post-Quantum Cryptography (PQC) cipher suites supporting PQC KEM
algorithms such as the NIST-standardized ML-KEM-512.
The specified protocol is part of a broader analysis of the post-
quantum transition for EDHOC [PQ-EDHOC-Access25].
1.1. Motivation
The emerging Quantum Computing technologies bring new potential risks
to the existing cryptographic infrastructures. Security mechanisms
that rely on integer factorization or the discrete logarithm problem
will be vulnerable to attacks by a Cryptographically Relevant Quantum
Computer (CRQC). The European Commission recently issued a roadmap
for the transition to Post-Quantum Cryptography (PQC), establishing a
2030 deadline for high-risk use cases and 2035 for medium-risk use
cases, in alignment with the 2035 deadline set by the U.S. government
for completing the transition to PQC in federal systems.
The U.S. National Institute of Standards and Technology (NIST) has
concluded its PQC standardization process with the release of its
first standardized PQC algorithms in three new Federal Information
Processing Standards (FIPS): FIPS 203 (ML-KEM, based on CRYSTALS-
Kyber), FIPS 204 (ML-DSA, based on CRYSTALS-Dilithium), and FIPS 205
(SLH-DSA, based on SPHINCS+). Additionally, FALCON has been selected
for future standardization, and NIST has launched a new initiative to
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evaluate alternative PQC signature schemes with compact signatures
and efficient verification speeds. Complementing these efforts, the
Post-Quantum Use in Protocols (PQUIC) IETF Working Group (WG) is
developing operational and design guidelines to support the
transition. For example, [RFC9794] defines terminology for post-
quantum/traditional Hybrid schemes, while ongoings draft such as
[I-D.ietf-pquip-pqc-engineers] analyze the impact of CRQCs on
existing systems and the challenges involved in transitioning to
post-quantum algorithms.
The growing urgency to transition to PQC highlights the need to adapt
EDHOC, whose current security relies on traditional Elliptic-Curve
Cryptography(ECC), based on the discrete logarithm problem that is
known to be vulnerable to attacks by CRQCs. The integration of the
PQC mechanism into EDHOC raises important considerations around
performance, as the protocol is explicitly designed for constrained
environments where the number of handshake message rounds, network
overhead, processing time, and power consumption are critical
factors.
PQC algorithms generally have higher computational and memory costs
compared to the classical cryptography algorithms they aim to replace
because they often involve complex calculations and require larger
byte sizes. Notably, the PQC digital signature schemes standardized
by NIST, such as ML-DSA and SLH-DSA, use significantly large public
keys and signatures, which can be difficult to transmit over
constrained networks. It is important to note that while FALCON,
also selected for standardization by NIST, provides much shorter
signatures than the lattice-based schemes, its current
implementations have been shown to be vulnerable to side-channel
attacks. The new compact schemes under NIST evaluation should be
more suitable for constrained environments. However, the current
Cortex-M4 implementations of some of the most compact PQC signature
schemes, like SNOVA, MAYO and OV-LP, still demand substantial memory
resources, making them impractical for many constrained devices.
Additionally, others, such as SQISign, have only recently been
supported on such platforms, and performance benchmarks for their
signature operations are still unavailable.
On the other hand, the standardized ML-KEM offers significantly
higher computational efficiency compared to all other PQC KEMs (order
of magnitude faster) and is at least three times more efficient than
the fastest PQC signature schemes. Therefore, extending EDHOC with a
new authentication method that enables a signature-free KEM-based
EDHOC has the potential to reduce memory and processing requirements
when ML-KEM is used. The approach can also result in lower network
overhead compared to signature-based EDHOC implementations that rely
on standardized PQC signature-based algorithms.
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Some standardization efforts propose adopting the KEM-based
authentication mechanism to mitigate the overhead introduced by PQC
digital signatures. For example, [I-D.celi-wiggers-tls-authkem]
specifies a KEM-based authentication scheme for TLS 1.3, while
[I-D.uri-lake-pquake] aims to define a general Post-Quantum
Authentication Key exchange protocoll, which based on the same
approach.
This document describes a KEM-based authentication mechanism
specifically for the EDHOC protocol, introducing a new authentication
method intended to provide a PQC signature-free variant as the static
DH authentication method intends. The static-DH authentication of
EDHOC is based on the XX pattern of the Noise framework protocol
[Noise], where channel security guarantees are increasingly
established by encrypting transmitted messages with keys derived from
chains of shared secrets, as soon as those secrets become available.
To align with this model, the KEM-based authentication Method defined
in this document follows the approach outlined in [PQNoise-CCS22],
which provides a recipe for transforming classical Noise patterns
into PQ variants. This specification defines the necessary
modifications to the EDHOC protocol to support the PQ-Noise framework
while preserving security properties comparable to those of the
static-DH authentication method.
1.2. Terminology and Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119].
Readers are expected to be familiar with the terms and concepts
described in EDHOC [RFC9528], CBOR [RFC8949], CBOR Sequences
[RFC8742], COSE Structures and Processing [RFC9052] and COSE
Algorithms [RFC9053], When referring to CBOR, this specification
always refers to Deterministically Encoded CBOR, as specified in
Section 4.2.1 and 4.2.2 of [RFC8949]. The single output from
authenticated encryption (including the authentication tag) is called
"ciphertext", following [RFC5116].
1.2.1. Key Encapsulation Mechanisms (KEMs)
The Key Encapsulation Mechanism consists of 3 algorithms:
* *( pk, sk ) <- KEM.KeyGen( )*: The probabilistic key generation
algorithm generates a KEM key pair consisting of a public
encapsulation key ( pk ) and secret decapsulation key ( sk ).
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* *( ss , ct ) <- KEM.Encapsulate( pk )*: The probabilistic
encapsulation algorithm takes as input a public encapsulation key
( pk ) and produces a shared secret ( ss ) and ciphertext ( ct ).
* *( ss ) <- KEM.Decapsulate( ct, sk )*: The decapsulation algorithm
takes as input a secret encacpsulation key ( sk ) and produce a
shared secret ( ss ).
2. Protocol Overview
This document defines a new authentication method for EDHOC for
general scenarios in which both parties authenticate using KEMs and
may initially be mutually unknown. It aims to provide a free-
signature authentication scheme as the static DH authentication EDHOC
method 3 does, which relies on the XX pattern from the Noise
framework [Noise], supporting mutual authentication and the
transmission of encrypted public credentials. The proposed protocol
adopts the approach provided by [PQNoise-CCS22] to transform the
classical Noise XX pattern in EDHOC into a PQ Noise XX variant. This
results in a quantum-resistant, KEM-only version of EDHOC when a PQC
KEM is used.
The PQ translation of the Noise XX pattern requires introducing up to
one additional round trip. With KEMs, the owner of the static key
cannot combine their static private key with the ephemeral public key
belonging to the other party to immediately prove their identity in
the next message, as is possible with DH. Instead, the party must
first receive a ciphertext that encapsulates its static public key,
generated by the peer, before it can authenticate itself. This
necessitates an additional key-confirmation message from the key
owner, using the key derived from the encapsulated value.
The KEM-based EDHOC protocol consists of five mandatory messages
(message_1, message_2, message_3, message_4, and message_5), and an
error message, between an Initiator (I) and a Responder (R). Error
handling and cipher suit negotiation mechanisms are the same as
defined in Section 6 of [RFC9528]. All EDHOC messages are CBOR
Sequences as specified in [RFC9528]. Figure 1 illustrates a KEM-
based authentication EDHOC message flow as well as the content of
each message. The protocol elements in Figure 1 are introduced in
this Section and in Section 4. Message formatting and processing are
specified in Section 4
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Initiator Responder
| METHOD, SUITES_I, pk_eph, C_I, EAD_1 |
+------------------------------------------------------------------->
| message_1 |
| |
| ct_eph, Enc( C_R, ID_CRED_R, EAD_2 ) |
<-------------------------------------------------------------------+
| message_2 |
| |
| ct_R, Enc( ID_CRED_I, EAD_3 ) |
+------------------------------------------------------------------->
| message_3 |
| |
| ct_I, AEAD( EAD_4, MAC_2 ) |
<-------------------------------------------------------------------+
| message_4 |
| |
| AEAD( EAD_5, MAC_3 ) |
+------------------------------------------------------------------->
| message_5 |
Figure 1: EDHOC Message Flow using the KEM-based Authentication
Method
The parties exchange ephemeral and static KEM public keys, along with
ciphertexts that encapsulate these keys, compute shared secrets and
pseudorandom keys PRK, and derive symmetric session keys to encrypt
message elements contained in intermediate handshake messages. All
handshake messages include encrypted components protected with these
derived session keys, offering varying levels of confidentiality and
authenticity, except for the first message, which is sent in
plaintext. The parties compute a shared secret session key, PRK_out,
from which symmetric application keys are derived to protect
application data. The Initiator derives these keys after receiving
message_4, and the Responder after receiving message_5.
* pk_eph is the ephemeral KEM public key generated by the Initiator.
* ct_eph is the ephemeral ciphertext computed by the Responder with
the KEM.encapsulation algorithm over the received ephemeral public
key (pk_eph).
* ct_R is the responder ciphertext computed by the Initiator with
the KEM.encapsulation algorithm over the static KEM public key of
the Responder, retrieved from the received ID_CRED_R in message_2.
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* ct_I is the Iniatiator ciphertext computed by the Responder with
the KEM.encapsulation algorithm over the static KEM public key of
the Initiator, retrieved from the received ID_CRED_I in message_1.
* "CRED_I and CRED_R are the authentication credentials containing
the public authentication keys of I and R, respectively", as
defined in Section 2 of [RFC9528].
* "ID_CRED_I and ID_CRED_R are used to identify and optionally
transport the credentials of I and R, respectively", as defined in
Section 2 of [RFC9528].
* "Enc(), AEAD(), and MAC() denote encryption, Authenticated
Encryption with Associated Data, and Message Authentication Code,
crypto algorithms applied with keys derived from one or more
shared secrets calculated during the protocol", as defined in
Section 2 of [RFC9528].
* "SUITES_I contains cipher suites supported by the Initiator and
formatted and processed as specified in Section 3.6 and 6.3.2 of
[RFC9528]".
* "METHOD is an integer specifying the authentication method",as
defined in Section 3.2 of [RFC9528]. In this case method 5; see
Section 2.1.2.
* C_I and C_R are Connection Identifiers chosen by the Initiator and
Responder, respectively, as specified in Section 3.3 of [RFC9528].
* EAD_1, EAD_2, EAD_3, EAD_4, EAD_5 are External Authorization Data
included in message_1, message_2, message_3, message_4 and
message_5 respectively.
This protocol is designed so that it follows the provisions of
[RFC9528], that is, to encrypt and integrity protect as much
information as possible and derive symmetric keys and random material
using EDHOC_KDF with as much previous information as possible
2.1. Protocol Elements
This section describes the principal protocol elements that differ
from the definitions of EDHOC and highlights the most important
similarities. For the missing elements, the definitions in Section 3
of [RFC9528] SHOULD be consulted.
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2.1.1. Ephemeral KEM
The ephemeral KEM is used to provide forward secrecy. The Initiator
generates a new ephemeral KEM key pair in every new session to ensure
that the compromise of long-term keys does not compromise past
communications. The elements of the Ephemeral KEM are:
* The ephemeral KEM key pair ( pk_eph, sk_eph ) is generated by the
Initiator using the following function:
pk_eph, sk_eph <- KEM.KeyGen()
* The ephemeral shared secret ( ss_eph ) and the ephemeral
ciphertext ( ct_eph ) are generated using the encapsulation and
decapsulation functions: in the Responder
ss_eph, ct_eph <- KEM.Encapsulate( pk_eph )
in the Initiator
ss_eph <- KEM.decapsulation( ct_eph, sk_eph )
2.1.2. Method
The protocol extends EDHOC with a new KEM-based authentication
method, where both parties use static KEM key pairs. The
authentication is provided by a Message Authentication Code (MAC)
included in message_4 and message_5 to authenticate the Responder and
Initiator, respectively. The Initiator and Responder must agree on
the authentication method to be used. The selected method is
indicated by the Initiator in message_1.
+===================+====================+====================+
| Method Type Value | Initiator | Responder |
| | Authentication Key | Authentication Key |
+===================+====================+====================+
| 5 (suggested) | Static KEM Key | Static KEM Key |
+-------------------+--------------------+--------------------+
Table 1: Authentication Keys for Method Types
2.1.3. Authentication Parameters
The protocol performs the same authentication-related operations as
described in Section 3.5 of [RFC9528]
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The protocol transports information about credentials ID_CRED_I and
ID_CRED_R in message_2 and message_3, respectively. The
authentication of these credentials is verified through MAC_2 and
MAC_3, sent by the Responder and the Initiator in message_4 and
message_5, respectively.
2.1.3.1. Authentication Keys
The authentication key MUST be a static KEM authentication key pair.
The authentication key algorithm must be compatible with the chosen
method and selected cipher suite. The same KEM algorithm selected
for the EDHOC key exchange in the cipher suite MUST be used for both
the ephemeral KEM key exchange and the authentication static KEM
keys. The Initiator’s and Responder’s private and public
authentication keys are denoted as follows:
* The Initiator static KEM authentication key pair: ( pk_I, sk_I )
* The Responder static KEM authentication key pair: ( pk_R, sk_R )
2.1.3.2. Authentication Credentials
The authentication credentials, CRED_I and CRED_R, contain the
authentication public key of the Initiator and Responder,
respectively, as described in Section 3.5.2 of [RFC9528].
* The authentication credentials can be X.509 certificates seconded
as bstr, as defined in Section 3.5.2 of [RFC9528], using
[RFC9360]. [I-D.ietf-lamps-kyber-certificates] describes the
conventions for using the ML-KEM in X.509 Public Key
Infrastructure.
* Additionally, the authentication credential may include a
COSE_key, formatted as specified in [RFC8392], to reduce the
credential size and avoid the PQC signature verification needed
when X.509 certificates are used. New IANA value registries
should be defined to extend COSE Algorithms with the corresponding
KEMs algorithm values.
2.1.3.3. Identification of Credentials
The ID_CRED fields are used to identify and optionally transport
credentials as defined in Section 3.5.3 of [RFC9528]. The
authentication method defined in this document operates within the
general EDHOC framework described in Section 3.5.3 of [RFC9528],
where ID_CRED_X can either contain the full CRED_X credentials or an
identifier of those credentials if they have already been provided
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out-of-band.
* "ID_CRED_R is intended to facilitate for the Initiator retrieving
the authentication credential CRED_R and the authentication key of
R", as defined in Section 3.5.3 of [RFC9528]. For the
authentication method defined in this document, the authentication
key is the static KEM public key.
* "ID_CRED_I is intended to facilitate for the Responder retrieving
the authentication credential CRED_I and the authentication key of
I", as defined in Section 3.5.3 of [RFC9528]. For the
authentication method defined in this document, the authentication
key is the static KEM public key.
2.1.4. Cipher Suites
The authentication method specified in this document uses the EDHOC
cipher suites element, as defined in Section 3.6 of [RFC9528]. An
EDHOC cipher suit consists of an ordered set of algorithms from the
"COSE Algorithms" IANA registry [RFC9053]. The predefined EDHOC
cipher suites are also listed in the IANA registry, as specified in
Section 10.2 of [RFC9528].
A new predefined cipher suite SHOULD be added to the IANA registry,
specifying each supported KEM in the EDHOC Key Exchange Algorithm
parameter. An example of this, when ML-KEM is used, is shown in
Section 5. The same KEM algorithm selected for key exchange SHOULD
also be used for KEM-based authentication when method 5 is selected.
Furthermore, the KEM algorithms used SHOULD also be added to the COSE
Algorithms IANA registry to identify them, as is shown in Section 5.
2.1.5. Transport
The KEM-based authentication method for EDHOC is not bound to any
specific transport layer, similar to the classical EDHOC methods
defined in Section 3.4 of [RFC9528]. However, the resulting message
sizes are expected to be larger than those of the original EDHOC
methods specified in [RFC9528]. This is because the currently
standardized NIST KEM algorithms use comparatively large public keys
and key encapsulation (ciphertext) sizes, thereby increasing the
overall size of EDHOC messages.
In highly constrained networks, larger message sizes MAY necessitate
transport support for fragmentation. For example, if the network MTU
is insufficient to carry a complete message, the messages can be
transported over CoAP [RFC7252] using the Block-Wise Transfer
mechanism to support fragmentation and reassembly, as specified in
[RFC7959] or [RFC9177]. [RFC7959] defines the Block1 and Block2
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options for request/response block-wise transfer in CoAP, while
[RFC9177] extends this mechanism with the Q-Block1 and Q-Block2
options, allowing multiple blocks to be transmitted without waiting
for per-block acknowledgments.
3. Key Derivation
This section highlights the differences and similarities in the key
derivation process of the KEM-based authentication method compared to
[RFC9528]. An overview of the EDHOC key schedule when using the KEM-
based authentication method is shown in Figure 2, and each key
derivation step is explained in the following subsections.
+-------+
| TH_2 |
+-------+
|
+----+ +--v+ +------+ +---+ +-----+ +-+ +---+
|ss_e|->|Ext|->|PRK_2e|--|Exp|->|KEY_2|->| |->|C_2|
+----+ +---+ +--+---+ +--++ +-----+ |X| +---+
| | PLAIN_2-->| |
+------+ | +-+
| +--+----------------------+
| |TH_2=H(H(Message1),ct_eph|
| +-------------------------+
|
+----+ +--++ +--v-----+ +------+ +---+ +----+ +---+
|ss_R|->|Ext|->|PRK_3e2m|+-|Expand|->|K_3|->|AEAD|->|C_3|
+----+ +---+ +----+---+ |+--+---+ +---+ +----+ +---+
| | | |
| | | PLAINTEXT_3
+--------+ | +--+--------------------+
| | |TH_3= |
| | H(TH_2,PLAINTEXT_2, |
| | CRED_R,ct_R| |
| | +-----------------------+
| |
| | +------+ +-----+
| +--|Expand|->|MAC_2|
| +-+----+ +-----+
| |
| +---------------+--------------------+
| |TH_4=H(TH_3,PLAINTEXT_3,CRED_I,ct_I)|
| +------------------+-----------------+
| |
+----+ +--+-+ +--------+ +---+ +---+ +----+ +---+
|ss_I|->|Ext|->|PRK_4e3m|+-|Exp|->|K_4|->|AEAD|->|C_4|
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+----+ +----+ +--------+|+---+ |+---+ |+-^--+ +---+
| | | |
| | | PLAINTEXT_4
| | |+----+ +---+
| | -|AEAD|->|C_5|
+------------------------+| | +-^--+ +---+
|TH_5=H(TH_4,PLAINTEXT_4)|| | |
+--+---------------------+| | PLAINTEXT_5
| | |
+-----+ +-+----+ | |
|MAC_3|<--|Expand|--| |
+-----+ +------+ | +-------+
|-->|PRK_out|
+--+----+
|
+--v---+
|Expand|
+------+
|
v
+------------+
|PRK_exporter|
+---+--------+
|
+--v---+
|Expand|
+--+---+
|
v
Aplication Key
Figure 2: EDHOC Message Key Derivation using the KEM-based
Authentication Method
3.1. Keys for EDHOC Message Processing
3.1.1. EDHOC_Extract
The pseudorandom keys (PRKs) used for KEM-based authentication method
are derived using the same EDHOC_Extract function defined in
[RFC9528], where the input keying material (IKM) and Salt are
specified for each PRK below.
3.1.1.1. PRK_2e
The pseudorandom key PRK_2e is derived with the following input:
* The salt SHALL be TH_2.
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* The IKM SHALL be the ephemeral KEM shared secret (ss_eph)
When SHA-256 is used PRK_2e is produced as follows:
PRK_2e = HMAC-SHA-256( TH_2, ss_eph )
Where the ephemeral shared secret ss_eph is the output of the
following functions in the Initiator and Responder respectively
Initiator:
ss_eph <- KEM.Decapsulate( ct_eph, sk_eph )
Responder:
ss_eph, ct_eph <- KEM.Encapsulate( pk_eph )
3.1.1.2. PRK_3e2m
The pseudorandom key PRK_3e2m is derived with the following input:
* The salt SHALL be the SALT_3e2m derived from PRK_2e
* The IKM SHALL be the KEM shared secret ss_R, used to authenticate
the Responder
PRk_3e2m is derived as follows:
PRK_3e2m = EDHOC_Extract( SALT_3e2m, ss_R )
Where the KEM shared secret ss_R used to authenticate the Responder
is the output of the following functions in the Initiator and
Responder, respectively
Initiator:
ss_R, ct_R <- KEM.Encapsulate( pk_R )
Responder:
ss_R <- KEM.Decapsulate( ct_R, sk_R )
3.1.1.3. PRK_4e3m
The pseudorandom key PRK_4e3m is derived with the following input:
* The salt SHALL be the SALT_4e3m, derived from PRK_3e2m
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* The IKM SHALL be the KEM shared secret ss_I, used to authenticate
the Initiator
PRk_4e3m is derived as follows:
PRK_4e3m = EDHOC_Extract( SALT_4e3m, ss_I )
Where the KEM shared secret ss_I used to authenticate the Initiator
is the output of the following functions in the Initiator and
Responder, respectively
Initiator:
ss_I <- KEM.Decapsulate( ct_I, sk_I )
Responder:
ss_I, ct_I <- KEM.Encapsulate( pk_I )
3.1.2. EDHOC_Expand and EDHOC_KDF
The output key materials (OKMs) are derived from the PRKs in the same
way as described in Section 4.1.2 of [RFC9528], with modifications in
the transcript hashes THs input contraction as specified in
Section 4.
The same OKMs, including keys, initialization vectors (IV), and salts
as those shows in Section 4.1.2 of [RFC9528] Figure 6 are derived,
just notice that:
* K_3 and IV_3 are computed to provide integrity protection and
confidentiality for message_3 ensuring that the Initiator’s
identity is protected against active attacks. However, this does
not provide authentication of the Initiator’s identity.
The final key derivations using EDHOC_KDF is shwon in Figure 3.
Further details of the key derivation and how the output keying
material is used are specified in Section 4
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KEYSTREAM_2 = EDHOC_KDF( PRK_2e, 0, TH_2, plaintext_length )
SALT_3e2m = EDHOC_KDF( PRK_2e, 1, TH_2, hash_length )
MAC_2 = EDHOC_KDF( PRK_3e2m, 2, context_2, mac_length_2 )
K_3 = EDHOC_KDF( PRK_3e2m, 3, TH_3, key_length )
IV_3 = EDHOC_KDF( PRK_3e2m, 4, TH_3, iv_length )
SALT_4e3m = EDHOC_KDF( PRK_3e2m, 5, TH_4, hash_length )
MAC_3 = EDHOC_KDF( PRK_4e3m, 6, context_3, mac_length_3 )
PRK_out = EDHOC_KDF( PRK_4e3m, 7, TH_4, hash_length )
K_4 = EDHOC_KDF( PRK_4e3m, 8, TH_4, key_length )
IV_4 = EDHOC_KDF( PRK_4e3m, 9, TH_4, iv_length )
PRK_exporter = EDHOC_KDF( PRK_out, 10, h'', hash_length )
Figure 3: Key Derivations Using EDHOC_KDF for the KEM-based
Authentication Methods
Notice that a new key session (K_5/IV_5) can be derived from the same
PRK_4e3m, using TH_5 as the info parameter, to encrypt message_5, if
separate keys are shown to enhance security in any way. The initial
version of this protocol adopts a simpler approach by deriving a
single session key to protect both messages, which are different from
the MAC keys.
3.1.3. PRK_out
The pseudorandom key PRK_out is the output session key of a completed
EDHOC session and is derived as follows:
PRK_out = EDHOC_KDF( PRK_4e3m, TH_4, hash_length )
3.2. Keys for EDHOC Applications
Keying material for the application can be derived using the same
EDHOC_Exporter interface defined in Section 4.2.1 of [RFC9528]
4. Message Formatting and Processing
This section outlines the message format and the procedures for
composing and processing each message.
4.1. KEM-based Authentication EDHOC Message 1
4.1.1. Formating of Message 1
message_1 retains the same format as defined in Section 5.2.1 of
[RFC9528]. The same fields are used, except that GX is replaced by
the KEM ephemeral public key ( pk_eph ) computed by the Initiator.
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message_1 = (
METHOD : int,
SUITES_I : suites,
pk_eph : bstr,
C_I : bstr / -24..23,
? EAD_1,
)
suites = [ 2* int ] / int
EAD_1 = 1* ead
The KEM-based authentication method (proposed method 5) should be
seletect in the METHOD field.
4.1.2. Initiator Composition of Message 1
The Initiator SHALL compose message_1 as follows:
* Construct SUITES_I following the Section 5.2.2 of [RFC9528]
specifications
* Generate an ephemeral KEM Key pair (pk_eph) using the KEM
algorithm from the selected cipher suit. The ephemeral key pair
is computed by the Initiator using the following function:
pk_eph, sk_eph <- KEM.KeyGen()
* Choose a conection identifier as in Section 5.2.2 of [RFC9528].
* Encode message_1 as sequence of CBOR-encoded elements, as
specified in Section 4.1.1
4.1.3. Responder Processing of Message 1
The Responder SHALL process message_1 in the following order:
1. "Decode message_1", as specified in Section 5.2.3 of [RFC9528]
2. "Process message_1", as specify in Section 5.2.3 of [RFC9528]
3. "If all processing is completed successfully, and if EAD_1 is
present, then make it available to the application", as specified
in Section 5.2.3 of [RFC9528]
4.2. KEM-based authentication EDHOC Message 2
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4.2.1. Formating of Message 2
message_2 keeps the same formatting as Section 5.3.1 of [RFC9528].
The same fields are used instead GY is replaced with the ephemeral
KEM ciphertext ( ct_eph ) computed on the Responder.
message_2 = (
ct_eph_CIPHERTEXT_2 : bstr,
)
where cc_eph_CIPHERTEXT_2 is the concatenation of ct_eph and
CIPHERTEXT_2.
4.2.2. Responder Composition of Message 2
The Responder SHALL compose message_2 as follows:
* Encapsulate the ephemeral KEM key received within message_1 using
the KEM algorithm in the selected cipher suit. The ephemeral KEM
ciphertext and the KEM ephemeral shared secret are computed by the
Responder using the following function:
ss_eph, ct_eph <- KEM.Encapsulate(pk_eph)
* Compute the transcript hash TH_2 = H(pk_eph,H(message_1)) as
specified in Section 5.3.2 of [RFC9528]
* Compute the PRK_2e pseudorandom key from the ephemeral KEM shared
secret ( ss_eph )
* "Choose a connection identifier C_R", as specified in
Section 5.3.2 of [RFC9528]
* At this point, the Responder is not jet able to authenticate
itself, so MAC_2 is not computed
* CIPHERTEXT_2 is calculated, with a binary additive stream cipher
as in Section 5.3.2 of [RFC9528], using a keystream (KEYSTREAM_2)
generated with EDHOC_Expand and the following plaintext:
- Compute PLAINTEXT_2 as:
PLAINTEXT_2 = (C_R,ID_CRED_R,?EAD_2)
where C_R, ID_CRED_R and EAD_2 elements corresponds with the
ones in Section 5.3.2 of [RFC9528].
- Compute KEYSTREAM_2 as in Section 3.1.2
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- Compute CIPHERTEXT_2 as in Section 5.3.2 of [RFC9528]
CIPHERTEXT_2 = PLAINTEXT_2 XOR KEYSTREAM_2
* Encode message_2 as a sequence of CBOR-encoded data items as
specified in Section 4.2.1
4.2.3. Initiator Processing of Message 2
The Initiator SHALL process message_2 in the following order:
1. Decode message_2
2. "Retrieve the protocol state" as proposed in Section 5.3.3 of
[RFC9528]
3. Compute the ephemeral KEM shared_secret ( ss_eph ) by
decapsulating the KEM ciphertext ( ct_eph ) received in
message_2 using the ephemeral secret key ( sk_eph ). The
ephemeral KEM shared secret is computed by the Initiator using
the following function:
ss_eph <- KEM.Decapsulate( ct_eph, sk_eph )
4. Compute the transcript hash TH_2 = H(pk_eph,H(message_1))
5. Compute the PRK_2e pseudorandom key from the ephemeral KEM
shared secret ( ss_eph )
6. Derive KEYSTREAM_2 as in Section 3.1.2
7. Decrypt CIPHERTEXT_2; see Section 4.2.2
8. If all processing is completed successfully, ID_CRED_R and (if
present) EAD_2 SHALL be made available to the application, as
specified in Section 5.3.3 of [RFC9528]. In this specification,
the application MUST authenticate and validate the credentials
associated with ID_CRED_R at this point before proceeding. The
Initiator’s credentials are transmitted in the subsequent
message and are encrypted under a key that can only be derived
by a party possessing the private key corresponding to
ID_CRED_R. Prior to sending its credentials, the Initiator MUST
ensure that the credentials associated with ID_CRED_R have been
successfully validated and accepted according to local policy.
This prevents disclosure of the Initiator’s credentials to a
party presenting credentials that are cryptographically valid
but untrusted or unintended.
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9. Obtain the authentication credential (CRED_R) from the
(ID_CRED_R) as in Section 5.3.3 of [RFC9528], and the static
authentication key of the Responder
10. Encapsulate the retrieved static KEM authentication key of the
Responder ( pk_R ) calculating the corresponding ciphertext (
ct_R ) and shared secret ( ss_R ) with the following function:
ss_R, ct_R <- KEM.Encapsulate(pk_R)
11. Compute the new PRK_3e2m from a chain that includes both the
ephemeral KEM shared secret ( ss_eph ) and the latest KEM shared
secret for the Authentication of the Responder ( ss_R ), as
defined in Section 3.1.1.2
4.3. KEM-based authentication EDHOC Message 3
4.3.1. Formating of Message 3
message_3 SHALL be a CBOR Sequence as defined below:
message_3 = (
ct_R : bstr,
CIPHERTEXT_3 : bstr,
)
4.3.2. Initiator Composition of Message 3
The Initiator SHALL process the composition of message_3 as follows:
* Compute the transcript hash TH_3=H(ct_R,TH_2,PLAINTEXT_2,CRED_R)
as specified in Section 5.4.2 of [RFC9528].
* Derive the new session key K_3/IV_3 as defined in Section 3.1.2.
The Initiator can use this key to compute CIPHERTEXT_3, but it
cannot be used to authenticate itself.
* At this point, the Responder is not jet able to authenticate
itself, so MAC_3 is not computed.
* Compute a COSE_Encrypt0 object as defined in Section 5.2 and 5.3
of [RFC9052], with the EDHOC AEAD algorithm of the selected cipher
suite, using the encryption key K_3, the initialization vector
IV_3 (if used by the AEAD algorithm), the plaintext PLAINTEXT_3,
and the following parameters as input:
- protected = h''
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- external_aad = TH_3
- K_3 and IV_3 are defined in Section 3.1.2
- PLAINTEXT_3 = (C_I,ID_CRED_I,?EAD_3) where C_I, ID_CRED_I and
EAD_3 elements corresponds with the ones in Section 5.3.3 of
[RFC9528]
CIPHERTEXT_3 is the 'ciphertext' of COSE_Encrypt0.
* Encode message_3 as a CBOR data item as specified in
Section 4.3.1.
4.3.3. Responder Processing of Message 3
The Responder SHALL process message_3 in the following order:
1. Decode message_3
2. "Retrieve the protocol state", as defined in Section 5.4.3 of
[RFC9528]
3. Compute the KEM shared_secret ( ss_R ) for the authentication of
the Responder by decapsulating the KEM ciphertext ( ct_R )
received in message_3 using the Responder static KEM secret key (
sk_R ). The KEM shared secret is computed by the Responder using
the following function:
ss_R <- KEM.Decapsulate( ct_R, sk_R )
4. Compute the new PRK_3e2m from a chain that includes both the
ephemeral KEM shared secret ( ss_eph ) and the latest KEM shared
secret for the Authentication of the Responder ( ss_R ), as
defined in Section 3.1.1.2
5. Compute the transcript hash TH_3=H(ct_R,TH_2,PLAINTEXT_2,CRED_R)
6. Compute K_3/IV_3 as in Section 3.1.2, where plaintext_length is
the length of PLAINTEXT_3
7. Decrypt CIPHERTEXT_3; see Section 4.3.2
8. "If all processing is completed successfully, then make ID_CRED_I
and (if present) EAD_2 available to the application", as in
Section 5.3.4 of [RFC9528]
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9. "Obtain the authentication credential (CRED_I) from the
(ID_CRED_I)" as in Section 5.3.4 of [RFC9528] and the static
authentication key of the Initiator.
4.4. KEM-based authentication EDHOC Message 4
4.4.1. Formating of Message 4
message_4 SHALL be a CBOR Sequence as defined below:
message_3 = (
ct_I : bstr,
CIPHERTEXT_4 : bstr,
)
4.4.2. Responder Composition of Message 4
The Responder SHALL process the composition of message_4 as follows:
* Encapsulate the retrieved static KEM authentication key of the
Initiator ( pk_I ) calculating the corresponding ciphertext ( ct_I
) and shared secret ( ss_I ) with the following function:
ss_I, ct_I <- KEM.Encapsulate(pk_I)
* Compute the transcript hash TH_4 = H(ct_I,TH_3, PLAINTEXT_3,
CRED_I)
* Compute MAC_2 as defined in Section 3.1.2, with context_2 =<< C_R,
ID_CRED_R, TH_4, CRED_R, ? EAD_4 >>
- The Responder authenticates with a PRK_3e2m derived from the
KEM ephemeral shared secret and with the shared secret computed
over its static KEM key.
- The mac_lenght_2 is equal to the EDHOC MAC length of the
selected cipher suit.
- The C_R, ID_CRED_R and CRED_R elements corresponds with the
ones in Section 5.3.2 of [RFC9528]
- The latest transcript hash TH_4 and the External Application
Data included in Message 4 (EAD_4) are used.
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* Compute the new PRK_4e3m from a chain that includes the ephemeral
KEM shared secret ( ss_eph ), the KEM shared secret for the
Authentication of the Responder ( ss_R ) , and the latest KEM
shared secret for the Authentication of the Initiator ( ss_I ) as
defined in Section 3.1.1.3
* Derive the session key K_4/IV4 as in Section 3.1.2.
* Compute a COSE_Encrypt0 object as defined in Section 5.2 and 5.3
of [RFC9052], with the EDHOC AEAD algorithm of the selected cipher
suite, using the encryption key K_4, the initialization vector
IV_4 (if used by the AEAD algorithm), the plaintext PLAINTEXT_4,
and the following parameters as input:
- protected = h''
- external_aad = TH_4
- K_4 and IV_4 are defined in Section 3.1.2
- PLAINTEXT_4 = ( MAC_2, ?EAD_4 )
CIPHERTEXT_4 is the 'ciphertext' of COSE_Encrypt0.
* Compute the transcript hash TH_5 = H(TH_4, PLAINTEXT_4)
* Encode message_4 as a CBOR data item as specified in
Section 4.4.1.
4.4.3. Initaitor Processing of Message 4
The Initiator SHALL process message_4 in the following order:
1. Decode message_4
2. "Retrieve the protocol state using available message
correlation", as in Section 3.4.2 of [RFC9528].
3. Compute the KEM shared secret ( ss_I ) for the authentication of
the Initiator by decapsulating the KEM ciphertext ( ct_I )
received in message_4 using the Responder static KEM secret key (
sk_I ). The KEM shared secret is computed by the Initiator using
the following function:
ss_I <- KEM.Decapsulate( ct_I, sk_I )
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4. Compute the new PRK_4e3m from a chain that includes the ephemeral
KEM shared secret ( ss_eph ), the KEM shared secret for the
Authentication of the Responder ( ss_R ), and the latest KEM
shared secret for the Authentication of the Initiator ( ss_I ) as
defined in Section 3.1.1.3
5. Derive the session key K_4/IV4 as in Section 3.1.2.
6. Decrypt and verify the COSE_Encrypt0 (CIPHERTEXT_4) as defined
Section 5.2 and 5.3 of [RFC9052]], with the EDHOC AEAD algorithm
in the selected cipher suite and the parameters defined in
Section 4.4.2.
7. Verify MAC_2 as defined in Section 4.4.2, and make the result of
the verification available to the application.
4.5. KEM-based authentication EDHOC Message 5
4.5.1. Formating of Message 5
message_5 SHALL be a CBOR Sequence as defined below:
message_3 = (
CIPHERTEXT_5 : bstr,
)
4.5.2. Initiator Composition of Message 5
The Initiator SHALL process the composition of message_5 as follows:
* Compute the transcript hash TH_5 = H(TH_4, PLAINTEXT_4)
* Compute MAC_3 as defined in Section 3.1.2, with context_3 =<< C_I,
ID_CRED_I, TH_5, CRED_I, ? EAD_5 >>
- The Initiator authenticates with a PRK_4e3m derived from the
three shared secrets, including the shared secret computed over
its static KEM key ( ss_I ).
- The mac_lenght_3 is equal to the EDHOC MAC length of the
selected cipher suit.
- The C_I, ID_CRED_I and CRED_I elements corresponds with the
ones in Section 5.4.2 of [RFC9528]
- The latest transcript hash TH_5 and the External Application
Data included on Message 5 (EAD_5) are used.
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* Compute a COSE_Encrypt0 object as defined inSection 5.2 and 5.3 of
[RFC9052], with the EDHOC AEAD algorithm of the selected cipher
suite, using the encryption key K_4, the initialization vector
IV_4 (if used by the AEAD algorithm), the plaintext PLAINTEXT_5,
and the following parameters as input:
- protected = h''
- external_aad = TH_5
- K_5 and IV_5 are defined in Section 3.1.2
- PLAINTEXT_5 = ( MAC_3, ? EAD_5 )
CIPHERTEXT_5 is the 'ciphertext' of COSE_Encrypt0.
* Calculate PRK_out as defined in Section 3.1.3. The Initiator can
now derive application keys using the EDHOC_Exporter interface;
see Section 3.2
* Encode message_5 as a CBOR data item as specified in Section 4.5.1
* "Make the connection identifiers (C_I and C_R) and the application
algorithms in the selected cipher suite available to the
application" as in Section 5.4.2 of [RFC9528]
After creating message_5, the Initiator can compute PRK_out and
derive application keys using the EDHOC_Exporter interface. The
Initiator SHOULD now persistently store PRK_out or application keys
and send protected application data, since it has already verified
message_4, which is protected with a derived application key by the
Responder, and the application has authenticated the Responder.
4.5.3. Responder Processing of Message 5
The Responder SHALL process message_5 in the following order:
1. Decode message_5
2. "Retrieve the protocol state using available message correlation"
as in Section 3.4.2 of [RFC9528].
3. Decrypt and verify the COSE_Encrypt0 (CIPHERTEXT_5) as defined in
Section 5.2 and 5.3 of [RFC9052], with the EDHOC AEAD algorithm
in the selected cipher suite and the parameters defined in
Section 4.5.2.
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4. Verify MAC_3 as defined in Section 4.5.2, and make the result of
the verification available to the application.
5. Calculate PRK_out as defined in Section 3.1.3. The Initiator can
now derive application keys using the EDHOC_Exporter interface;
see Section 3.2
After verifying message_5, the Responder can compute PRK_out and
derive application keys using the EDHOC_Exporter interface. The
Responder SHOULD now persistently store PRK_out or application keys
and send protected application data, since it has already verified
message_5, which is protected with a derived application key by the
Initiator, and the application has authenticated the Initiator.
5. IANA Considerations
5.1. COSE Algorithms Registry
The "COSE Algorithms" Registry from "CBOR Object Signing and
Encryption (COSE)" group SHOULD be extended with new values to
include PQC KEM algorithms. The extension of values from the
"Standards Action with Expert Review" range for ML-KEM algorithms at
NIST security levels 1 and 3, is proposed in Table 2
Registry Name: COSE Algorithms
Reference: draft-pocero-lake-authkem-edhoc-00
The columns of the registry are Name, Value and Description, where
Value is an integer and the other columns are text strings. For both
new registrations, the change controller is the IETF, and the
reference field should point to this document. The new values
proposed are:
+=============+=================+===========================+
| Name | Value | Description |
+=============+=================+===========================+
| ML-KEM-512 | -54 (suggested) | CBOR object KEM Algorithm |
| | | for ML-KEM-512 |
+-------------+-----------------+---------------------------+
| ML-KEM-1024 | -55 (suggested) | CBOR object KEM Algorithm |
| | | for ML-KEM-1024 |
+-------------+-----------------+---------------------------+
Table 2: COSE Algorithms
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5.2. EDHOC Cipher Suites Registry
The "EDHOC Cipher Suites" Registry from group "Ephemeral Diffie-
Hellman Over COSE (EDHOC)" SHOULD be extended with new values to
include the cipher suits with the KEM algorithm used. While the KEM-
based authentication protocol specified in this document can support
different KEM algorithms, the NIST-standardized ML-KEM is
RECOMMENDED. The extension of values from the "Standards Action with
Expert Review" range, when the ML-KEM algorithm is used at NIST
security levels 1 and 3, is proposed in Table 3
Registry Name: EDHOC Cipher Suites
Reference: draft-pocero-lake-authkem-edhoc-00
The columns of the registry are Value, Array, Description, and
Reference, where Value is an integer and the other columns are text
strings. The new values proposed are:
+=============+==========+========================+==============+
| Value | Array | Description | Reference |
+=============+==========+========================+==============+
| 7 | 30, -16, | AES-CCM-16-128-128, | draft- |
| (suggested) | 16, -54, | SHA-256, 16, ML-KEM- | pocero-lake- |
| | -48 , | 512, ML-DSA-44, AES- | authkem- |
| | 10, -16 | CCM-16-64-128, SHA-256 | edhoc-00 |
+-------------+----------+------------------------+--------------+
| 8 | 10, -16, | A256GCM, SHA-384, 16, | draft- |
| (suggested) | 8, 1, | ML-KEM-1024, ML-DSA- | pocero-lake- |
| | -55, -49 | 65, A256GCM, SHA-384 | authkem- |
| | , -16 | | edhoc-00 |
+-------------+----------+------------------------+--------------+
Table 3: EDHOC Cipher Suites
The PQC ML-DSA signature algorithms are selected as the EDHOC
signature algorithm parameter to verify X.509 certificate signatures
when the X.509 credential type is used.
5.3. EDHOC Method Types Registry
The "EDHOC Method Types" Registry from group "Ephemeral Diffie-
Hellman Over COSE (EDHOC)" SHOULD be extended with a new value that
identifies the KEM-based authentication method. The extension value
from the "Standards Action with Expert Review" range, is proposed in
Table 4
Registry Name: EDHOC Method Types
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Reference: draft-pocero-lake-authkem-edhoc-00
The columns of the registry are Value, Initiator Authentication Key,
Responder Authentication Key and Reference, where Value is an integer
and the other columns are text strings. The new value proposed is:
+=============+================+================+================+
| Value | Initiator | Responder | Reference |
| | Authentication | Authentication | |
| | Key | Key | |
+=============+================+================+================+
| 5 | Static KEM Key | Static KEM Key | [draft-pocero- |
| (suggested) | | | lake-authkem- |
| | | | edhoc-00] |
+-------------+----------------+----------------+----------------+
Table 4: EDHOC Method Types
6. Security Considerations
6.1. Security Properties
EDHOC protocol with static DH keys enables the Initiator and
Responder to generate an ephemeral-static shared secret using the
other party's ephemeral public keys and their own credentials. This
shared secret is then used to derive a session key for
authentication. Messages 2 and 3 provide explicit authentication
through MACs, which also bind the exchanged credentials to prevent
misbinding attacks, as is described in Section 9.1 of [RFC9528]
In contrast, the KEM-based authentication mechanism requires an
initial action from the other party. The Responder must first
receive the encapsulation of its static public key generated by the
Initiator to authenticate itself. To perform this encapsulation, the
Initiator must retrieve the static KEM public key of the Responder
from the ID_CRED_R sent in Message 2. As a result, the Responder
cannot authenticate itself until Message 3 is processed, which
contains the ct_R ciphertext necessary to derive the ss_R shared
secret. Then it cannot generate MAC_2 or authenticate itself until
then. Similarly, the Initiator cannot generate MAC_3 or authenticate
itself before sending Message 3. This highlights the main challenge
in integrating KEM-based authentication method within the EDHOC
handshake.
To address this issue and maintain the same level of identity
protection than EDHOC, against active attacks on the Initiator and
passive attacks on the Responder, the credentials continue to be
encrypted in Messages 2 and 3. In message_2, the Responder’s
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credentials are included in a plaintext that is XORed with a key
derived from the ephemeral shared secrets, as defined in Section 5.3
of [RFC9528]. By employing the same construction, this specification
provides equivalent identity protection for the Responder against
passive attackers. The credentials of the Initiator ( ID_CRED_I )
are encrypted using an AEAD algorithm to provide integrity protection
and confidentiality, but not authentication, because the Initator’s
shared secret is not yet available to prove its identity. The
encryption key is derived from a combination of both ephemeral KEM
shared secret (ss_eph) and the Responder static KEM shared secret (
ss_R ), used to authenticate the Responder. At this stage in the
protocol, the specific encryption provided a form of weak forward
secrecy, as the Initiator has not yet verify the static KEM public
key of the Responder. However, the Initiator’s credentials are still
protected against active attacks, as only the legitimate Responder,
who possesses the corresponding private key ( sk_R ) is capable of
deriving the session key and decrypting message_3.
Furthermore, the protocol is extended with two additional messages
(Messages 4 and 5) to enable both parties to:
* Prove possession of the final session key, ensuring key
confirmation to the other party
* Ensure mutual authentication by explicitly authenticating
themselves using the final session key, which incorporates all
three shared secrets: the ephemeral KEM shared secret ( ss_eph )
and the KEM shared secrets ss_I and ss_R used to authenticate the
Initiator and Responder, respectively.
* Provide credential binding by including MAC_2 and MAC_3, ensuring
the integrity and authenticity of the credentials exchanged in
messages 2 and 3.
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In [RFC9528], the transcript hashes (THs) are constructed as an
accumulative hash, combining previous TH values with the current
plain-text message. Each new plain-text message in the handshake is
concatenated with the previous TH value, and the resulting hash forms
the new TH. This process links each message in the sequence to all
prior messages, creating a verifiable and continuous chain. As a
result, any changes to the message content are detected during
subsequent integrity verification using the transcript hashes. The
KEM-based authentication method described in this document extends
this approach. Both parties only need to verify the integrity and
authenticity of the latest TH_4 and TH_5, which encompass all
previous messages in the handshake. To facilitate this, the MAC-
protected data in Messages 4 and 5 is modified to include TH_4 and
TH_5 respectively. At the end of the handshake, both the Initiator
and Responder can verify the integrity and authenticity of the entire
handshake by checking the received MACs.
The payload security properties for the static DH authentication
method and the KEM-based authentication method differ during the
handshake. Unlike the static DH authentication method, the KEM-based
method exhibits no authentication until the final two messages. It
provides the same level of destination confidentiality for the first
two and the last two messages, while message_3 offers weaker forward
secrecy. The Initiator’s credentials are encrypted within message_3
using a key derived from the Responder’s static public key and the
ephemeral key, ensuring that only the intended Responder can decrypt
the credential, and protect them against active attacks.
Full forward secrecy and explicit mutual authentication are achieved
once the KEM-based method handshake is completed, similar to the
static-DH method handshake (described in Section 9.1 of [RFC9528]).
Additionally, a potential misbinding attack will not be detected
until the handshake concludes, specifically when the Initiator
verifies Message 4 and the Responder verifies Message 5. Therefore,
EAD data should be treated as unprotected, and keying materials
should not be persistently stored until the protocol is complete, as
with the static-DH method (described in Section 9.1 of [RFC9528]).
The final Application Session Key should only be derived at the end
of the handshake, after ensuring mutual authentication, message
handshake integrity, credentials authenticity, and proof of key
possession.
The KEM-based authentication method does not provide non-repudiation,
but only implicit proof of participation, similar to EDHOC with
static DH keys. It also maintains an equivalent level of downgrade
protection, as the negotiation base of the protocol is unchanged.
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6.2. KEM Security Considerations
[KEMBinding-CCS24] demonstrates that IND-CCA2 security alone does not
preclude re-encapsulation attacks in KEM-based key exchange
protocols. Such attacks can lead to unknown key-share conditions, in
which two honest parties derive the same shared secret while
associating it with different peer identities. Therefore, any KEM
used in this specification MUST achieve IND-CCA2 security and MUST
ensure that the derived shared secret is cryptographically bound to
the recipient’s public key. This requirement prevents re-
encapsulation and related key-substitution attacks.
6.3. Four-Message Variant
The proposed KEM-based authentication method with a 5-message
handshake is designed to meet the same security requirements as
static-DH method. However, it can be adapted to reduce the number of
round trips while remaining suitable for scenarios where neither
party knows the other beforehand. This is achieved by transmitting
the ID_CRED_I credentials of the Initiator in plain-text within the
message_1, similar to the Noise IX pattern, where the Initiator's
static key is immediately transmitted to the Responder, despite or
absent identity protection. This modification allows the Initiator
to authenticate itself in Message 2, eliminating the need for Message
5. Since the Responder includes its credentials in the first
message, Message 4 remains necessary to ensure explicit
authentication of the Responder. This adaptation reduces the message
exchange to four but sacrifices identity protection for the
Initiator's credentials.
7. References
7.1. Normative References
[I-D.ietf-lamps-kyber-certificates]
Turner, S., Kampanakis, P., Massimo, J., and B.
Westerbaan, "Internet X.509 Public Key Infrastructure -
Algorithm Identifiers for the Module-Lattice-Based Key-
Encapsulation Mechanism (ML-KEM)", Work in Progress,
Internet-Draft, draft-ietf-lamps-kyber-certificates-11, 22
July 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-lamps-kyber-certificates-11>.
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[I-D.spm-lake-pqsuites]
Selander, G. and J. P. Mattsson, "Quantum-Resistant Cipher
Suites for EDHOC", Work in Progress, Internet-Draft,
draft-spm-lake-pqsuites-02, 19 April 2026,
<https://datatracker.ietf.org/doc/html/draft-spm-lake-
pqsuites-02>.
[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>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/info/rfc8742>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/info/rfc9052>.
[RFC9360] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Header Parameters for Carrying and Referencing X.509
Certificates", RFC 9360, DOI 10.17487/RFC9360, February
2023, <https://www.rfc-editor.org/info/rfc9360>.
[RFC9528] Selander, G., Preuß Mattsson, J., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528,
DOI 10.17487/RFC9528, March 2024,
<https://www.rfc-editor.org/info/rfc9528>.
7.2. Informative References
[I-D.celi-wiggers-tls-authkem]
Wiggers, T., Celi, S., Schwabe, P., Stebila, D., and N.
Sullivan, "KEM-based Authentication for TLS 1.3", Work in
Progress, Internet-Draft, draft-celi-wiggers-tls-authkem-
07, 4 May 2026, <https://datatracker.ietf.org/doc/html/
draft-celi-wiggers-tls-authkem-07>.
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[I-D.ietf-pquip-pqc-engineers]
Banerjee, A., Reddy.K, T., Schoinianakis, D., Hollebeek,
T., and M. Ounsworth, "Post-Quantum Cryptography for
Engineers", Work in Progress, Internet-Draft, draft-ietf-
pquip-pqc-engineers-14, 25 August 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-pquip-
pqc-engineers-14>.
[I-D.uri-lake-pquake]
Blumenthal, U., Luo, B., O'Melia, S., Torres, G., and D.
A. Wilson, "PQuAKE - Post-Quantum Authenticated Key
Exchange", Work in Progress, Internet-Draft, draft-uri-
lake-pquake-00, 22 April 2025,
<https://datatracker.ietf.org/doc/html/draft-uri-lake-
pquake-00>.
[KEMBinding-CCS24]
Cremers, C., Kohlweiss, K., Dowling, B., and D. Jackson,
"Keeping Up with the KEMs: Stronger Security Notions for
KEMs and Automated Analysis of KEM-based Protocols",
Proceedings of the 2024 ACM SIGSAC Conference on Computer
and Communications Security (CCS '24). Association for
Computing Machinery, New York, NY, USA. DOI:
https://doi.org/10.1145/3658644.3670283, 2024,
<https://doi.org/10.1145/3658644.3670283>.
[Noise] Perrin, T., "The Noise Protocol Framework", Revision 34,
July 2018, <https://noiseprotocol.org/noise.html>.
[PQ-EDHOC-Access25]
Pocero Fraile, L., Koulamas, C., and A. P. Fournaris,
"Reinventing EDHOC for the Post-Quantum Era", IEEE Access,
Volume 13, pages 196622–196640, 2025. DOI:
https://doi.org/10.1109/ACCESS.2025.3633843, 2025,
<https://doi.org/10.1109/ACCESS.2025.3633843>.
[PQNoise-CCS22]
Angel, Y., Dowling, B., Hulsing, A., Schwabe, P., and F.
Weber, "Post Quantum Noise", Proceedings of the 2022 ACM
SIGSAC Conference on Computer and Communications Security
(CCS '22), pages 97–109. Association for Computing
Machinery, New York, NY, USA. DOI:
https://doi.org/10.1145/3548606.3560577, 2022,
<https://doi.org/10.1145/3548606.3560577>.
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[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>.
[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>.
[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>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/info/rfc9053>.
[RFC9177] Boucadair, M. and J. Shallow, "Constrained Application
Protocol (CoAP) Block-Wise Transfer Options Supporting
Robust Transmission", RFC 9177, DOI 10.17487/RFC9177,
March 2022, <https://www.rfc-editor.org/info/rfc9177>.
[RFC9794] Driscoll, F., Parsons, M., and B. Hale, "Terminology for
Post-Quantum Traditional Hybrid Schemes", RFC 9794,
DOI 10.17487/RFC9794, June 2025,
<https://www.rfc-editor.org/info/rfc9794>.
Authors' Addresses
Lidia Pocero Fraile
ISI, R.C. ATHENA
Patras Science Park building
26504 Platani, Patras
Greece
Email: pocero@athenarc.gr
Christos Koulamas
ISI, R.C. ATHENA
Patras Science Park building
26504 Platani, Patras
Greece
Email: koulamas@athenarc.gr
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Apostolos P. Fournaris
ISI, R.C. ATHENA
Patras Science Park building
26504 Patras
Greece
Email: fournaris@athenarc.gr
Evangelos Haleplidis
ISI, R.C. ATHENA
Patras Science Park building
26504 Platani, Patras
Greece
Email: haleplidis@athenarc.gr
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