EDHOC Authenticated with Pre-Shared Keys (PSK)
draft-ietf-lake-edhoc-psk-06
| Document | Type | Active Internet-Draft (lake WG) | |
|---|---|---|---|
| Authors | Elsa Lopez-Perez , Göran Selander , John Preuß Mattsson , Rafael Marin-Lopez , Francisco Lopez-Gomez | ||
| Last updated | 2025-10-20 | ||
| Replaces | draft-lopez-lake-edhoc-psk | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
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| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
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| Send notices to | (None) |
draft-ietf-lake-edhoc-psk-06
LAKE Working Group E. Lopez-Perez
Internet-Draft Inria
Intended status: Standards Track G. Selander
Expires: 23 April 2026 J. Preuß Mattsson
Ericsson
R. Marin-Lopez
F. Lopez-Gomez
University of Murcia
20 October 2025
EDHOC Authenticated with Pre-Shared Keys (PSK)
draft-ietf-lake-edhoc-psk-06
Abstract
This document specifies a Pre-Shared Key (PSK) authentication method
for the Ephemeral Diffie-Hellman Over COSE (EDHOC) key exchange
protocol. The PSK method enhances computational efficiency while
providing mutual authentication, ephemeral key exchange, identity
protection, and quantum resistance. It is particularly suited for
systems where nodes share a PSK provided out-of-band (external PSK)
and enables efficient session resumption with less computational
overhead when the PSK is provided from a previous EDHOC session
(resumption PSK). This document details the PSK method flow, key
derivation changes, message formatting, processing, and security
considerations.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://lake-
wg.github.io/psk/#go.draft-ietf-lake-edhoc-psk.html. Status
information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-lake-edhoc-psk/.
Discussion of this document takes place on the LAKE Working Group
mailing list (mailto:lake@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/lake/. Subscribe at
https://www.ietf.org/mailman/listinfo/lake/.
Source for this draft and an issue tracker can be found at
https://github.com/lake-wg/psk.
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Status of This Memo
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Credentials . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. ID_CRED_PSK . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. CRED_I and CRED_R . . . . . . . . . . . . . . . . . . 6
3.1.3. Encoding and processing guidelines . . . . . . . . . 7
3.2. Message Flow of EDHOC-PSK . . . . . . . . . . . . . . . . 7
4. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . 8
5. Message Formatting and Processing . . . . . . . . . . . . . . 10
5.1. Message 1 . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Message 2 . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2.1. Formatting of Message 2 . . . . . . . . . . . . . . . 10
5.2.2. Responder Composition of Message 2 . . . . . . . . . 10
5.2.3. Initiator Processing of Message 2 . . . . . . . . . . 10
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5.3. Message 3 . . . . . . . . . . . . . . . . . . . . . . . . 11
5.3.1. Formatting of Message 3 . . . . . . . . . . . . . . . 11
5.3.2. Initiator Composition of Message 3 . . . . . . . . . 11
5.3.3. Responder Processing of Message 3 . . . . . . . . . . 12
5.4. Message 4 . . . . . . . . . . . . . . . . . . . . . . . . 12
6. PSK usage for Session Resumption . . . . . . . . . . . . . . 13
6.1. Cipher Suite Requirements for Resumption . . . . . . . . 14
6.2. Privacy Considerations for Resumption . . . . . . . . . . 14
6.3. Security Considerations for Resumption . . . . . . . . . 14
7. EDHOC-PSK and Extensible Authentication Protocol (EAP) . . . 15
8. EDHOC-PSK and OSCORE . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9.1. Identity Protection . . . . . . . . . . . . . . . . . . . 16
9.2. Mutual Authentication . . . . . . . . . . . . . . . . . . 16
9.3. Protection of External Authorization Data (EAD) . . . . . 17
9.4. Cryptographic strength . . . . . . . . . . . . . . . . . 17
9.5. Downgrade Protection . . . . . . . . . . . . . . . . . . 17
9.6. Post Quantum Considerations . . . . . . . . . . . . . . . 17
9.7. Confidentiality . . . . . . . . . . . . . . . . . . . . . 18
9.8. Independence of Session Keys . . . . . . . . . . . . . . 18
9.9. Unified Approach and Recommendations . . . . . . . . . . 18
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10.1. EDHOC Method Type Registry . . . . . . . . . . . . . . . 19
10.2. EDHOC Exporter Label Registry . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. CDDL Definitions . . . . . . . . . . . . . . . . . . 22
Appendix B. Test Vectors . . . . . . . . . . . . . . . . . . . . 23
B.1. message_1 . . . . . . . . . . . . . . . . . . . . . . . . 23
B.2. message_2 . . . . . . . . . . . . . . . . . . . . . . . . 24
B.3. message_3 . . . . . . . . . . . . . . . . . . . . . . . . 26
B.4. message_4 . . . . . . . . . . . . . . . . . . . . . . . . 28
B.5. PRK_out and PRK_exporter . . . . . . . . . . . . . . . . 29
B.6. rPSK and rKID . . . . . . . . . . . . . . . . . . . . . . 29
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 29
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
This document defines a Pre-Shared Key (PSK) authentication method
for the Ephemeral Diffie-Hellman Over COSE (EDHOC) key exchange
protocol [RFC9528]. The PSK method balances the complexity of
credential distribution with computational efficiency. While
symmetric key distribution is more complex than asymmetric
approaches, PSK authentication offers greater computational
efficiency compared to the methods outlined in [RFC9528]. The PSK
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method retains mutual authentication, asymmetric ephemeral key
exchange, and identity protection established by [RFC9528].
EDHOC with PSK authentication benefits use cases where two nodes
share a Pre-Shared Key (PSK) provided out-of-band (external PSK).
Examples include the Authenticated Key Management Architecture (AKMA)
in mobile systems or the Peer and Authenticator in Extensible
Authentication Protocol (EAP) systems. The PSK method enables the
nodes to perform ephemeral key exchange, achieving Perfect Forward
Secrecy (PFS). This ensures that even if the PSK is compromised,
past communications remain secure against active attackers, while
future communications are protected against passive attackers.
Additionally, by leveraging the PSK for both authentication and key
derivation, the method provides quantum-resistant key exchange and
authentication even when used with ECDHE.
Another important use case of PSK authentication in the EDHOC
protocol is session resumption. This allows previously connected
parties to quickly reestablish secure communication using pre-shared
keys from a prior session, reducing the overhead associated with key
exchange and asymmetric authentication. By using PSK authentication,
EDHOC allows session keys to be refreshed with significantly lower
computational overhead compared to public-key authentication. In
this case, the resumption PSK is provisioned after the establishment
of a previous EDHOC session by using EDHOC_Exporter. Thus, the
external PSK serves as a long-term credential while the resumption
PSK acts as a session key.
Section 3 provides an overview of the PSK method flow and
credentials. Section 4 outlines the changes to key derivation
compared to [RFC9528]. Section 5 details message formatting and
processing, and Section 6 describes the usage of PSK for resumption.
Section 7 defines the use of EDHOC-PSK with OSCORE. Security
considerations are described in Section 8, and Section 9 outlines the
IANA considerations.
2. Conventions and Definitions
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.
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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], COSE Algorithms
[RFC9053], CWT and CCS [RFC8392], and the Concise Data Definition
Language (CDDL) [RFC8610], which is used to express CBOR data
structures.
3. Protocol
This document specifies a new EDHOC authentication method (see
Section 3.2 of [RFC9528]) referred to as the Pre-Shared Key method
(EDHOC-PSK). This method shares some features with, and differs in
other respects from, the authentication methods previously defined in
EDHOC.
Authentication is based on a Pre-Shared Key (PSK) shared between the
Initiator and the Responder. As in the methods defined in [RFC9528],
CRED_I and CRED_R are authentication credentials containing
identifying information for the Initiator and Responder,
respectively. However, unlike those methods, there is a single
shared authentication credential identifier, ID_CRED_PSK, which the
Responder uses to retrieve the PSK and the associated authentication
credentials.
3.1. Credentials
The Initiator and Responder are assumed to share a PSK (either an
external PSK or a resumption PSK) with high entropy that meets the
following requirements:
* Only the Initiator and the Responder have access to the PSK.
* The Responder can retrieve the PSK, CRED_I, and CRED_R, using
ID_CRED_PSK.
3.1.1. ID_CRED_PSK
ID_CRED_PSK is a COSE header map containing header parameters that
can identify a pre-shared key. For example:
ID_CRED_PSK = {4 : h'0f' }; 4 = 'kid'
The purpose of ID_CRED_PSK is to facilitate retrieval of the correct
PSK. While ID_CRED_PSK use encoding and representation patterns from
[RFC9528], it differs fundamentally in that it identifies a symmetric
key rather than a public authentication key.
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It is RECOMMENDED that ID_CRED_PSK uniquely or stochastically
identifies the corresponding PSK. Uniqueness avoids ambiguity that
could require the recipient to try multiple keys, while stochasticity
reduces the risk of identifier collisions and supports stateless
processing. These properties align with the requirements for rKID in
session resumption.
3.1.2. CRED_I and CRED_R
CRED_I and CRED_R are authentication credentials associated with the
PSK. The notation CRED_x refers to either CRED_I or CRED_R.
Authentication is achieved implicitly through the successful use of
the PSK to derive keying material, and to encrypt and subsequently
decrypt protected messages.
When using an external PSK, a common representation of CRED_I and
CRED_R is a CBOR Web Token (CWT) or CWT Claims Set (CCS) [RFC8392],
where the 'cnf' claim includes the confirmation method COSE_Key. An
example of CRED_I and CRED_R is shown below:
{ /CCS/
2 : "42-50-31-FF-EF-37-32-39", /sub/
8 : { /cnf/
1 : { /COSE_Key/
1 : 4, /kty/
2 : h'0f', /kid/
}
}
}
{ /CCS/
2 : "23-11-58-AA-B3-7F-10", /sub/
8 : { /cnf/
1 : { /COSE_Key/
1 : 4, /kty/
2 : h'0f', /kid/
}
}
}
Alternative formats for CRED_I and CRED_R MAY be used. When a
resumption PSK is employed, CRED_I and CRED_R MUST be the same
credentials used in the initial EDHOC exchange, for example, public-
key credentials such as X.509 certificates.
Implementations MUST ensure that CRED_I and CRED_R are distinct, for
example by including different identities in their sub-claims (e.g.,
"42-50-31-FF-EF-37-32-39" and "23-11-58-AA-B3-7F-10"). Ensuring
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distinct credentials simplifies correct party identification and
prevents reflection and misbinding attacks, as described in
Appendix D.2 of [RFC9528].
3.1.3. Encoding and processing guidelines
The following guidelines apply to the encoding and handling of CRED_x
and ID_CRED_PSK. Requirements on CRED_x applies both to CRED_I and
to CRED_R.
* If CRED_x is CBOR-encoded, it SHOULD use deterministic encoding as
specified in Sections 4.2.1 and 4.2.2. of [RFC8949].
Deterministic encoding ensures consistent identification and
avoids interoperability issues caused by non-deterministic CBOR
variants.
* If CRED_x is provisioned out-of-band and transported by value, it
SHOULD be used as received without re-encoding. Re-encoding can
cause mismatches when comparing identifiers such as hash values or
'kid' references.
* ID_CRED_PSK SHOULD uniquely identify the corresponding PSK to
avoid ambiguity. When ID_CRED_PSK contains a key identifier, care
must be taken to ensure that 'kid' is unique for the PSK.
* When ID_CRED_PSK consists solely of a 'kid' parameter (i.e., { 4 :
kid }), the compact encoding optimization defined in
Section 3.5.3.2 of [RFC9528] MUST be applied in plaintext fields
(such as PLAINTEXT_3A). For example:
- { 4 : h'0f' } encoded as h'0f' (CBOR byte string)
- { 4 : 21 } encoded as 0x15 (CBOR integer)
These optimizations MUST NOT be applied in COSE header parameters or
in other contexts where the full map structure is required.
* To mitigate misbinding attacks, identity information such as a
'sub' (subject) claim MUST be included in both CRED_I and CRED_R.
3.2. Message Flow of EDHOC-PSK
The message flow of EDHOC-PSK follows the structure defined in
[RFC9528], with authentication based on symmetric keys rather than
public keys. For identity protection, credential-related message
fields appear first in message_3.
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ID_CRED_PSK is encrypted using a key derived from a shared secret
obtained through the first two messages. If Diffie-Hellman key
exchange is used, G_X and G_Y are the ephemeral public keys, and the
shared secret G_XY is the DH shared secret, as in [RFC9528]. If the
Diffie-Hellman procedure is replaced by a KEM, then G_X and G_Y are
encapsulation key and ciphertext, respectively, and the shared secret
G_XY is derived by the KEM, see [I-D.spm-lake-pqsuites].
The Responder authenticates the Initiator first. Figure 1
illustrates the message flow of the EDHOC-PSK authentication method.
Initiator Responder
| METHOD, SUITES_I, G_X, C_I, EAD_1 |
+------------------------------------------------------------------>|
| message_1 |
| |
| G_Y, Enc( C_R, EAD_2 ) |
|<------------------------------------------------------------------+
| message_2 |
| |
| Enc( ID_CRED_PSK, AEAD( EAD_3 ) ) |
+------------------------------------------------------------------>|
| message_3 |
| |
| AEAD( EAD_4 ) |
|<------------------------------------------------------------------+
| message_4 |
Figure 1: Overview of Message Flow of EDHOC-PSK.
This approach provides identity protection against passive attackers
for both Initiator and Responder. EDHOC message_4 remains OPTIONAL,
but is needed to authenticate the Responder and achieve mutual
authentication in EDHOC when external applications (e.g., OSCORE) are
not relied upon. In either case, the inclusion of a fourth message
provides mutual authentication and explicit key confirmation (see
Section 5.4).
4. Key Derivation
The pseudorandom keys (PRKs) used in the EDHOC-PSK authentication
method are derived with EDHOC_Extract, as in [RFC9528].
PRK = EDHOC_Extract( salt, IKM )
where salt and input keying material (IKM) are defined for each key.
The definition of EDHOC_Extract depends on the EDHOC hash algorithm
selected in the cipher suite, see Section 4.1.1 of [RFC9528].
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To maintain a uniform key schedule across all EDHOC authentication
methods, the same pseudorandom key notation (PRK_2e, PRK_3e2m, and
PRK_4e3m) is retained. The index notation is preserved for
consistency with other EDHOC authentication variants, even though it
does not fully reflect the functional role of the keys in this
method; for example, no MACs are used in EDHOC-PSK.
PRK_2e is extracted as in [RFC9528] with
* salt = TH_2, and
* IKM = G_XY,
where the transcript hash TH_2 = H( G_Y, H(message_1) ) is defined in
Section 5.3.2 of [RFC9528].
SALT_4e3m is derived from PRK_3e2m and TH_3, as shown in Figure 6 of
[RFC9528].
The other PRKs and transcript hashes are modified as specified below.
Figure 2 lists the key derivations that differ from Section 4.1.2 of
[RFC9528].
PRK_3e2m = PRK_2e
KEYSTREAM_2A = EDHOC_KDF( PRK_2e, 0, TH_2, plaintext_length_2a )
PRK_4e3m = EDHOC_Extract( SALT_4e3m, PSK )
KEYSTREAM_3A = EDHOC_KDF( PRK_3e2m, 12, TH_3, plaintext_length_3a )
K_3 = EDHOC_KDF( PRK_4e3m, 3, TH_3, key_length )
IV_3 = EDHOC_KDF( PRK_4e3m, 4, TH_3, iv_length )
Figure 2: Key Derivation of EDHOC-PSK.
where:
* KEYSTREAM_2A is used to encrypt PLAINTEXT_2A in message_2.
- plaintext_length_2a is the length of PLAINTEXT_2A in message_2.
* KEYSTREAM_3A is used to encrypt PLAINTEXT_3A (the concatenation of
ID_CRED_PSK and CIPHERTEXT_3B) in message_3.
- plaintext_length_3a is the length of PLAINTEXT_3A in message_3.
* TH_3 = H( TH_2, PLAINTEXT_2A ).
The definition of the transcript hash TH_4 is modified as follows:
* TH_4 = H( TH_3, ID_CRED_PSK, PLAINTEXT_3B, CRED_I, CRED_R )
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5. Message Formatting and Processing
This section specifies the differences in message formatting and
processing compared to Section 5 of [RFC9528]. Note that if any
processing step fails, then the Responder MUST send an EDHOC error
message back as defined in Section 6 of [RFC9528], and the EDHOC
session MUST be aborted.
5.1. Message 1
Message 1 is formatted and processed as specified in Section 5.2 of
[RFC9528].
5.2. Message 2
5.2.1. Formatting of Message 2
Message 2 is formatted as specified in Section 5.3.1 of [RFC9528].
5.2.2. Responder Composition of Message 2
CIPHERTEXT_2A is calculated with a binary additive stream cipher,
using a keystream generated with EDHOC_Expand, and the following
plaintext:
* PLAINTEXT_2A = ( C_R, ? EAD_2 )
* CIPHERTEXT_2A = PLAINTEXT_2A XOR KEYSTREAM_2A
C_R, EAD_2 are defined in Section 5.3.2 of [RFC9528]. In contrast to
[RFC9528], ID_CRED_R, MAC_2, and Signature_or_MAC_2 are not included
in message_2. This omission is the primary difference from the
signature and MAC-based authentication methods defined in [RFC9528],
as authentication in EDHOC-PSK relies solely on the shared PSK and
the successful decryption of protected messages. KEYSTREAM_2A is
defined in Section 4.
5.2.3. Initiator Processing of Message 2
Upon receiving message_2, the Initiator processes it as follows:
* Compute KEYSTREAM_2A as defined in Section 4.
* Decrypt CIPHERTEXT_2A using binary XOR, i.e., PLAINTEXT_2A =
CIPHERTEXT_2A XOR KEYSTREAM_2A
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In contrast to Section 5.3.3 of [RFC9528], ID_CRED_R is not made
available to the application in step 4, and steps 5 and 6 are
skipped.
5.3. Message 3
5.3.1. Formatting of Message 3
Message 3 is formatted as specified in Section 5.4.1 of [RFC9528].
5.3.2. Initiator Composition of Message 3
* CIPHERTEXT_3A is computed using a binary additive stream cipher
with a keystream generated by EDHOC_Expand, applied to the
following plaintext:
- PLAINTEXT_3A = ( ID_CRED_PSK / bstr / -24..23, CIPHERTEXT_3B )
o If ID_CRED_PSK contains a single 'kid' parameter, i.e.,
ID_CRED_PSK = { 4 : kid_PSK }, then the compact encoding is
applied, see Section 3.5.3.2 of [RFC9528].
o For the case of plaintext_length exceeding the EDHOC_KDF
output size, see Appendix G of [RFC9528].
- Compute KEYSTREAM_3A as in Section 4.
- CIPHERTEXT_3A = PLAINTEXT_3A XOR KEYSTREAM_3A
* CIPHERTEXT_3B is the 'ciphertext' of COSE_Encrypt0 object as
defined in Section 5.2 and Section 5.3 of [RFC9528], 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 parameters described in Section 5.2 of
[RFC9528], plaintext PLAINTEXT_3B and the following parameters as
input:
- protected = h''
- external_aad = << ID_CRED_PSK, TH_3, CRED_I, CRED_R >>
- K_3 and IV_3 as defined in Section 4
- PLAINTEXT_3B = ( ? EAD_3 )
The Initiator computes TH_4 as defined in Section 4.
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There is no need for MAC_3 or signature, since AEAD's built-in
integrity and the use of PSK-based key derivation provides implicit
authentication of the Initiator.
5.3.3. Responder Processing of Message 3
Upon receiving message_3, the Responder proceeds as follows:
* Derive K_3 and IV_3 as defined in Section 4.
* Parse the structure of message_3, which consists of a stream-
cipher encrypted structure, CIPHERTEXT_3A = PLAINTEXT_3A XOR
KEYSTREAM_3A, where PLAINTEXT_3A = ( ID_CRED_PSK, CIPHERTEXT_3B )
and CIPHERTEXT_3B is the inner AEAD-encrypted object.
* Generate KEYSTREAM_3A with the same method the Initiator used.
* Decrypt CIPHERTEXT_3A using binary XOR with KEYSTREAM_3A to
recover PLAINTEXT_3A.
* Use ID_CRED_PSK to identify the authentication credentials and
retrieve PSK.
* AEAD-decrypt CIPHERTEXT_3B using:
- K_3, IV_3
- external_aad = << ID_CRED_PSK, TH_3, CRED_I, CRED_R >>
- protected = h''
- AEAD algorithm from cipher suite
If AEAD verification fails, this indicates a processing problem or
that the message was tampered with. If it succeeds, the Responder
concludes that the Initiator possesses the PSK, correctly derived
TH_3, and is actively participating in the protocol.
Finally, the Responder computes TH_4 as defined in Section 4.
No MAC_3 or signature is needed, as the AEAD tag guarantees both
integrity and authenticity in this symmetric setting.
5.4. Message 4
Message 4 is formatted and processed as specified in Section 5.5 of
[RFC9528].
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After successfully verifying message_4, or another fourth message
from the Responder protected with an exported application key such as
an OSCORE message, the Initiator is assured that the Responder has
derived PRK_out (key confirmation) and that no other party can derive
this key.
The Initiator MUST NOT persistently store PRK_out or application keys
until it has successfully verified such a fourth message and the
application has authenticated the Responder.
Compared to [RFC9528], the fourth message not only provides key
confirmation but also authenticates the Responder. For mutual
authentication a fourth message is therefore mandatory.
6. PSK usage for Session Resumption
This section specifies how EDHOC-PSK is used for session resumption
in EDHOC. The EDHOC_Exporter, as defined in Section 4.2 of
[RFC9528], is used to derive the resumption parameters rPSK and rKID:
rPSK = EDHOC_Exporter( TBD2, h'', resumption_psk_length )
rKID = EDHOC_Exporter( TBD3, h'', id_cred_psk_length )
rID_CRED_PSK = { 4 : rKID }
Figure 3: Resumption Parameters.
where:
* resumption_psk_length defaults to the key_length, i.e., the length
of the encryption key of the EDHOC AEAD algorithm in the selected
cipher suite of the session where the EDHOC_Exporter is invoked.
* id_cred_psk_length defaults to 2 bytes.
A peer that has successfully completed an EDHOC session, regardless
of the authentication method used or whether the session was a PSK
resumption, MUST generate a resumption key for the next resumption
within the current "session series", provided that PSK resumption is
supported.
To ensure both peers share the same resumption key, when a resumption
session is run using rPSK_i as the resumption key:
* The Responder MAY delete the previous resumption key rPSK_(i-1),
if present, after successfully verifying message_3. At that point
the Responder can be certain that the Initiator has access to the
current resumption key rPSK_i.
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* The Initiator MAY delete rPSK_i after successfully verifying the
fourth message. At that point, the Initiator can be certain that
the Responder already has derived the next resumption key,
rPSK_(i+1).
* The Responder MAY delete rPSK_i after successfully verifying a
fifth message from the Initiator protected with an exported
application key such as an OSCORE message, if present. At that
point, the Initiator can be certain that the Responder already has
derived the next resumption key, rPSK_(i+1).
6.1. Cipher Suite Requirements for Resumption
When using a resumption PSK derived from a previous EDHOC exchange:
1. The resumption PSK MUST only be used with the same cipher suite
from which it was derived, or with a cipher suite that provides
stronger security guarantees.
2. Implementations MUST maintain a mapping between each resumption
PSK and its originating cipher suite to enforce this requirement.
3. If a resumption PSK is offered with a cipher suite that provides
weaker security, the Responder MUST reject the ongoing EDHOC
session.
6.2. Privacy Considerations for Resumption
When using resumption PSKs:
* ID_CRED_PSK is not exposed to passive attackers, and under normal
operation it is not reused. Reuse of the same ID_CRED_PSK can
occur due to transmission errors or when a peer loses its stored
resumption key. An active attacker can obtain the value of
ID_CRED_PSK and force its reuse. This aligns with the security
goals of EDHOC-PSK, which are to provide identity protection
against passive attackers, but not against active attackers.
6.3. Security Considerations for Resumption
* Resumption PSKs MUST NOT be used for purposes other than EDHOC
session resumption.
* Resumption PSKs MUST be securely stored with the same level of
protection as the session keys.
* Parties SHOULD prevent excessive reuse of the same resumption PSK.
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7. EDHOC-PSK and Extensible Authentication Protocol (EAP)
EDHOC with PSK authentication has several important use cases within
the Extensible Authentication Protocol (EAP).
One use case is the resumption of a session established with the EAP
method EAP-EDHOC [I-D.ietf-emu-eap-edhoc], regardless of the EDHOC-
based authentication method originally used in that session. This is
similar to the resumption mechanism in EAP-TLS 1.3 [RFC9190].
Resumption reduces the number of round trips and allows the EAP-EDHOC
server to avoid database lookups that might be required during an
initial handshake. If the server accepts resumption, the resumed
session is considered authenticated and securely bound to the prior
authentication or resumption.
The use of resumption with EAP-EDHOC is optional for the peer, but it
is RECOMMENDED whenever a valid rPSK is available. On the server
side, resumption acceptance is also optional, but it is RECOMMENDED
if the rPSK remains valid. The server may, however, require a new
initial handshake by refusing resumption. It is further RECOMMENDED
to use Network Access Identifiers (NAIs) with the same realm in the
identity response during both the full handshake and resumption. For
example, the NAI @realm can safely be reused since it does not expose
information that links a user’s resumption attempt with the original
full handshake.
EAP-EDHOC-PSK also provides a significant improvement over EAP-PSK
[RFC4764], which lacks support for identity protection, cryptographic
agility, and ephemeral key exchange, now considered essential for
meeting current security requirements. Without perfect forward
secrecy, compromise of the PSK enables a passive attacker to decrypt
both past and future sessions. Note that PSK authentication is not
allowed in EAP-TLS [RFC9190].
8. EDHOC-PSK and OSCORE
Before sending message_3 the Initiator can derive PRK_out and create
an OSCORE-protected request. The request payload MAY convey both an
EDHOC message_3 and OSCORE-protected data combined together, as
described in Section 3 of [RFC9668].
9. Security Considerations
The EDHOC-PSK authentication method introduces deviations from the
initial specification of EDHOC [RFC9528]. This section analyzes the
security implications of these changes and discusses the security
properties of EDHOC authenticated with PSK.
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9.1. Identity Protection
In EDHOC-PSK, the ID_CRED_PSK in message_3 is encrypted with a
keystream derived from the ephemeral shared secret G_XY. As a
result, EDHOC-PSK protects both the Initiator and the Responder
identities against passive attackers. This contrasts with the
asymmetric authentication methods in Section 9.1 of [RFC9528], which
protect the Initiator’s identity against active attackers and the
Responder’s identity against passive ones.
However, EDHOC-PSK does not satisfy the stronger identity protection
notion defined by Cottier and Pointcheval [Cottier-Pointcheval],
which requires security against an active Man-in-the-Middle (MitM)
attacker. Under this stronger notion, an active attacker must not
only be prevented from learning the identity but also from forcing a
specific identity to be used in a way that allows them to later
distinguish between the legitimate owner of a secret (the PSK) and
any other user. Because message_3 is sent before the key material
used for the keystream is cryptographically bound to the
authenticated identities, the MitM retains full control over the
communication channel and can conduct a distinguisher attack.
Specifically, the attacker can intercept message_3 and perform a
chosen-plaintext attack by manipulating the ciphertext. By observing
the protocol's subsequent behavior, such as the Responder's failure
to retrieve a valid PSK and aborting the session, the attacker can
link the Initiator's identity to the specific (coerced) ID_CRED_PSK
value, thereby breaking the strong guarantee of anonymity that would
otherwise be expected under an active threat model.
9.2. Mutual Authentication
EDHOC-PSK provides mutual authentication and explicit key
confirmation through an additional message that demonstrates
possession of the PSK. This may be message_4 or an application
message (e.g., an OSCORE message) protected with a key derived from
EDHOC.
To mitigate reflection or Selfie attacks, the identities in CRED_I
and CRED_R MUST be distinct.
EDHOC-PSK does not provide Key Compromise Impersonation (KCI)
protection. Compromise of the long-term PSK enables an attacker to
impersonate either the Initiator or the Responder to the other party.
While compromise of the ephemeral Diffie-Hellman secret only affects
the specific session in which it is used, compromise of the PSK
allows full active impersonation in all future sessions that rely on
the compromised key.
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9.3. Protection of External Authorization Data (EAD)
As in [RFC9528], EDHOC-PSK ensures the confidentiality and integrity
of External Authorization Data (EAD). The security guarantees for
EAD fields remain unchanged from the original EDHOC specification.
9.4. Cryptographic strength
EDHOC-PSK provides a minimum of 64-bit security against online brute
force attacks and, provided the PSK has sufficient entropy, a minimum
of 128-bit security against offline brute force attacks. If the PSK
entropy is lower, the effective offline security is limited by the
entropy of the PSK. To break 64-bit security against online brute
force, an attacker would on average have to send 4.3 billion messages
per second for 68 years, which is infeasible in constrained IoT radio
technologies. A successful forgery of the AEAD authentication tag in
EDHOC-PSK breaks the security of all future application data derived
from the session, while a forgery in the subsequent application
protocol (e.g., OSCORE [RFC8613]) typically only breaks the security
of the forged packet.
9.5. Downgrade Protection
Following [RFC9528], EDHOC-PSK must support cryptographic agility,
including modularity and negotiation of preferred cryptographic
primitives. In message 1, the Initiator sends an ordered list of
supported cipher suites (SUITES_I). The Responder verifies that the
suite selected by the Initiator is the most preferred option in
SUITES_I that is mutually supported. If this condition is not met,
the Responder MUST abort the session.
9.6. Post Quantum Considerations
Advances in quantum computing suggest that a Cryptographically
Relevant Quantum Computer (CRQC) may eventually be realized. Such a
machine would render many asymmetric algorithms, including Elliptic
Curve Diffie-Hellman (ECDH), insecure.
EDHOC-PSK derives authentication and session keys primarily from a
symmetric PSK, which provides quantum resistance even when combined
with ECDHE. However, if a CRQC is realized, the ECDHE contribution
degenerates to providing only randomness. In that case, EDHOC-PSK
with ECDHE offers neither identity protection nor Perfect Forward
Secrecy (PFS) against quantum adversaries. Moreover, if the PSK is
compromised, a passive quantum attacker could decrypt both past and
future sessions.
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By contrast, combining EDHOC-PSK with a quantum-resistant Key
Encapsulation Mechanism (KEM), such as ML-KEM, ensures both identity
protection and PFS even against quantum-capable attackers. Future
EDHOC cipher suites incorporating ML-KEM are expected to be
registered; see [I-D.spm-lake-pqsuites].
9.7. Confidentiality
The primary security goal of EDHOC-PSK is to establish a shared
secret known only to the authenticated Initiator and Responder. The
protocol ensures key indistinguishability by relying on the security
of the PSK and the ephemeral key shares, making it computationally
infeasible for an adversary to distinguish the true session secret
from a random value.
9.8. Independence of Session Keys
NIST requires that an ephemeral private key be used in only one key-
establishment transaction ([SP-800-56A], Section 5.6.3.3). This
requirement preserves session key independence and forward secrecy,
and EDHOC-PSK complies with it. By deriving the final shared secret
from a fresh, session-specific ephemeral secret (G_XY), the protocol
ensures that even if the PSK is compromised, an attacker is unable to
decrypt the past sessions. Similarly, if a session secret were to be
compromised, future session secrets remain protected by fresh
ephemeral keys.
In other protocols, reuse of ephemeral keys, especially when combined
with missing public key validation, has led to severe
vulnerabilities, enabling attackers to recover “ephemeral” private
keys and compromise both past and future sessions between two
legitimate parties. Assuming breach and minimizing the impact of
compromise are fundamental principles of zero-trust security.
9.9. Unified Approach and Recommendations
For use cases where application data is transmitted, it can be sent
together with message_3, maintaining efficiency. In applications
such as EAP-EDHOC [I-D.ietf-emu-eap-edhoc], where no application data
is exchanged between Initiator and Responder, message_4 is mandatory.
In such cases, EDHOC-PSK does not increase the total number of
messages. Other implementations may replace message_4 with an
OSCORE-protected message. In this case, the following requirement
applies: The Initiator SHALL NOT persistently store PRK_out or
derived application keys until successfully verifying message_4 or a
message protected with an exported application key (e.g., an OSCORE
message). This ensures that key material is stored only after its
authenticity is confirmed, thereby strengthening privacy by
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preventing premature storage of potentially compromised keys.
Finally, the order of authentication (i.e., whether the Initiator or
the Responder authenticates first) is not relevant in EDHOC-PSK.
While this ordering affects privacy properties in the asymmetric
methods of [RFC9528], it has no significant impact in EDHOC-PSK.
10. IANA Considerations
This document requires the following IANA actions.
10.1. EDHOC Method Type Registry
IANA is requested to register the following entry in the "EDHOC
Method Type" registry under the group name "Ephemeral Diffie-Hellman
Over COSE (EDHOC)".
+=======+==============================+====================+
| Value | Initiator Authentication Key | Responder |
| | | Authentication Key |
+=======+==============================+====================+
| TBD4 | PSK | PSK |
+-------+------------------------------+--------------------+
Table 1: Addition to the EDHOC Method Type Registry.
NOTE: Suggested value: TBD4 = 4. RFC Editor: Remove this note.
10.2. EDHOC Exporter Label Registry
IANA is requested to register the following entry in the "EDHOC
Exporter Label" registry under the group name "Ephemeral Diffie-
Hellman Over COSE (EDHOC)".
+=======+================+===================+===========+
| Label | Description | Change Controller | Reference |
+=======+================+===================+===========+
| TBD2 | Resumption PSK | IETF | Section 7 |
+-------+----------------+-------------------+-----------+
| TBD3 | Resumption kid | IETF | Section 7 |
+-------+----------------+-------------------+-----------+
Table 2: Additions to the EDHOC Exporter Label Registry.
NOTE: Suggested values: TBD2 = 2, TBD3 = 3. RFC Editor: Remove this
note.
11. References
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11.1. Normative References
[Cottier-Pointcheval]
Cottier, B. and D. Pointcheval, "Security Analysis of
Improved EDHOC Protocol", FPS International Symposium on
Foundations and Practice of Security, December 2022,
<https://doi.org/10.1007/978-3-031-30122-3_1>.
[I-D.ietf-emu-eap-edhoc]
Garcia-Carrillo, D., Marin-Lopez, R., Selander, G.,
Mattsson, J. P., and F. Lopez-Gomez, "Using the Extensible
Authentication Protocol (EAP) with Ephemeral Diffie-
Hellman over COSE (EDHOC)", Work in Progress, Internet-
Draft, draft-ietf-emu-eap-edhoc-06, 15 October 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-emu-eap-
edhoc-06>.
[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-00, 6 July 2025,
<https://datatracker.ietf.org/doc/html/draft-spm-lake-
pqsuites-00>.
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[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/rfc/rfc8392>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/rfc/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/rfc/rfc8613>.
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[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/rfc/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/rfc/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/rfc/rfc9052>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.
[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/rfc/rfc9528>.
[RFC9668] Palombini, F., Tiloca, M., Höglund, R., Hristozov, S., and
G. Selander, "Using Ephemeral Diffie-Hellman Over COSE
(EDHOC) with the Constrained Application Protocol (CoAP)
and Object Security for Constrained RESTful Environments
(OSCORE)", RFC 9668, DOI 10.17487/RFC9668, November 2024,
<https://www.rfc-editor.org/rfc/rfc9668>.
[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>.
11.2. Informative References
[RFC4764] Bersani, F. and H. Tschofenig, "The EAP-PSK Protocol: A
Pre-Shared Key Extensible Authentication Protocol (EAP)
Method", RFC 4764, DOI 10.17487/RFC4764, January 2007,
<https://www.rfc-editor.org/rfc/rfc4764>.
[RFC9190] Preuß Mattsson, J. and M. Sethi, "EAP-TLS 1.3: Using the
Extensible Authentication Protocol with TLS 1.3",
RFC 9190, DOI 10.17487/RFC9190, February 2022,
<https://www.rfc-editor.org/rfc/rfc9190>.
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Appendix A. CDDL Definitions
This section compiles the CDDL definitions for convenience,
incorporating errata filed against [RFC9528].
suites = [ 2* int ] / int
ead = (
ead_label : int,
? ead_value : bstr,
)
EAD_1 = (1* ead)
EAD_2 = (1* ead)
EAD_3 = (1* ead)
EAD_4 = (1* ead)
message_1 = (
METHOD : int,
SUITES_I : suites,
G_X : bstr,
C_I : bstr / -24..23,
? EAD_1,
)
message_2 = (
G_Y_CIPHERTEXT_2 : bstr,
)
PLAINTEXT_2A = (
C_R : bstr / -24..23,
? EAD_2,
)
message_3 = (
CIPHERTEXT_3 : bstr,
)
PLAINTEXT_3A = (
ID_CRED_PSK : header_map / bstr / -24..23,
CIPHERTEXT_3B : bstr,
)
PLAINTEXT_3B = (
? EAD_3
)
message_4 = (
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CIPHERTEXT_4 : bstr,
)
PLAINTEXT_4 = (
? EAD_4,
)
error = (
ERR_CODE : int,
ERR_INFO : any,
)
info = (
info_label : int,
context : bstr,
length : uint,
)
Appendix B. Test Vectors
B.1. message_1
Both endpoints are authenticated with Pre-Shared Keys (METHOD = 4)
NOTE: Assuming TBD4 = 4, to be confirmed by IANA. RFC Editor: Remove
this note.
METHOD (CBOR Data Item) (1 byte)
04
The initiator selects cipher suite 02. A single cipher suite is
encoded as an int:
SUITES_I (CBOR Data Item) (1 byte)
02
The Initiator creates an ephemeral key pair for use with the EDHOC
key exchange algorithm:
Initiator's ephemeral private key
X (Raw Value) (32 bytes)
09 97 2D FE F1 EA AB 92 6E C9 6E 80 05 FE D2 9F
70 FF BF 4E 36 1C 3A 06 1A 7A CD B5 17 0C 10 E5
Initiator's ephemeral public key
G_X (Raw Value) (32 bytes)
7E C6 81 02 94 06 02 AA B5 48 53 9B F4 2A 35 99
2D 95 72 49 EB 7F 18 88 40 6D 17 8A 04 C9 12 DB
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The Initiator selects its connection identifier C_I to be the byte
string 0xA, which is encoded as 0xA since it is represented by the
1-byte CBOR int 10:
Connection identifier chosen by the Initiator
C_I (CBOR Data Item) (1 byte)
0A
No external authorization data
EAD_1 (CBOR Sequence) (0 bytes)
The Initiator constructs message_1:
message_1 (CBOR Sequence) (37 bytes)
04 02 58 20 7E C6 81 02 94 06 02 AA B5 48 53 9B
F4 2A 35 99 2D 95 72 49 EB 7F 18 88 40 6D 17 8A
04 C9 12 DB 0A
B.2. message_2
The Responder supports the most preferred and selected cipher suite
02, so SUITES_I is acceptable.
The Responder creates an ephemeral key pair for use with the EDHOC
key exchange algorithm:
Responder's ephemeral private key
Y (Raw Value) (32 bytes)
1E 1C 8F 2D F1 AA 71 10 B3 9F 33 BA 5E A8 DC CF
31 41 1E B3 3D 4F 9A 09 4C F6 51 92 D3 35 A7 A3
Responder's ephemeral public key
G_Y (Raw Value) (32 bytes)
ED 15 6A 62 43 E0 AF EC 9E FB AA BC E8 42 9D 5A
D5 E4 E1 C4 32 F7 6A 6E DE 8F 79 24 7B B9 7D 83
The Responder selects its connection identifier C_R to be the byte
string 0x05, which is encoded as 0x05 since it is represented by the
1-byte CBOR int 05:
Connection identifier chosen by the Responder
C_R (CBOR Data Item) (1 byte)
05
The transcript hash TH_2 is calculated using the EDHOC hash
algorithm: TH_2 = H( G_Y, H(message_1) ), where H(message_1) is:
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H(message_1) (Raw Value) (32 bytes)
19 CC 2D 2A 95 7E DD 80 10 90 42 FD E6 CC 20 C2
4B 6A 34 BC 21 C6 D4 9F EA 89 5D 4C 75 92 34 0E
H(message_1) (CBOR Data Item) (34 bytes)
58 20 19 CC 2D 2A 95 7E DD 80 10 90 42 FD E6 CC 20
C2 4B 6A 34 BC 21 C6 D4 9F EA 89 5D 4C 75 92 34 0E
TH_2 (Raw Value) (32 bytes)
5B 48 34 AE 63 0A 8A 0E D0 B0 C6 F3 66 42 60 4D
01 64 78 C4 BC 81 87 BB 76 4D D4 0F 2B EE 3D DE
TH_2 (CBOR Data Item) (34 bytes)
58 20 5B 48 34 AE 63 0A 8A 0E D0 B0 C6 F3 66 42 60
4D 01 64 78 C4 BC 81 87 BB 76 4D D4 0F 2B EE 3D DE
PRK_2e is specified in Section 4.1.2 of [RFC9528]. To compute it,
the Elliptic Curve Diffie-Hellman (ECDH) shared secret G_XY is
needed. It is computed from G_X and Y or G_Y and X:
G_XY (Raw Value) (ECDH shared secret) (32 bytes)
2F 4A 79 9A 5A B0 C5 67 22 0C B6 72 08 E6 CF 8F
4C A5 FE 38 5D 1B 11 FD 9A 57 3D 41 60 F3 B0 B2
Then, PRK_2e is calculated as defined in Section 4.1.2 of [RFC9528]
PRK_2e (Raw Value) (32 bytes)
D0 39 D6 C3 CF 35 EC A0 CD F8 19 E3 25 79 C7 7E
1F 30 3E FC C4 36 20 50 99 48 A9 FD 47 FB D9 29
Since the Responder authenticates using PSK, PRK_3e2m = PRK_2e.
PRK_3e2m (Raw Value) (32 bytes)
D0 39 D6 C3 CF 35 EC A0 CD F8 19 E3 25 79 C7 7E
1F 30 3E FC C4 36 20 50 99 48 A9 FD 47 FB D9 29
No external authorization data:
EAD_2 (CBOR Sequence) (0 bytes)
The Responder constructs PLAINTEXT_2A:
PLAINTEXT_2A (CBOR Sequence) (1 byte)
05
The Responder computes KEYSTREAM_2 as defined in Section 4.1.2 of
[RFC9528]
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KEYSTREAM_2A (Raw Value) (1 byte)
EC
The Responder calculates CIPHERTEXT_2B as XOR between PLAINTEXT_2A
and KEYSTREAM_2:
CIPHERTEXT_2B (CBOR Sequence) (1 byte)
E9
The Responder constructs message_2 as defined in Section 5.3.1 of
[RFC9528]:
message_2 (CBOR Sequence) (35 bytes)
58 21 ED 15 6A 62 43 E0 AF EC 9E FB AA BC E8 42
9D 5A D5 E4 E1 C4 32 F7 6A 6E DE 8F 79 24 7B B9
7D 83 E9
B.3. message_3
The Initiator computes PRK_4e3m, as described in Section 4, using
SALT_4e3m and PSK:
SALT_4e3m (Raw Value) (32 bytes)
ED E0 76 12 14 83 19 EB 72 59 52 71 2A 54 2C 20
97 61 0A 13 9C 4A 14 1C 8E C5 7A 5F 62 E5 E9 DD
PSK (Raw Value) (16 bytes)
50 93 0F F4 62 A7 7A 35 40 CF 54 63 25 DE A2 14
PRK_4e3m (Raw Value) (32 bytes)
C6 2C C0 4F 55 D0 08 CF EB 8A 68 1E 84 63 FD DD
A2 FF 6C A8 4B 9E D6 11 6C 86 5C D8 1E 06 24 60
The transcript hash TH_3 is calculated using the EDHOC hash
algorithm:
TH_3 = H( TH_2, PLAINTEXT_2A )
TH_3 (Raw Value) (32 bytes)
38 6A 9D 05 2B 25 59 92 EE E5 FF B5 94 34 7D 32
74 18 A2 EA 51 83 48 6C 0C 9E 20 42 6E 0B CA 2F
TH_3 (CBOR Data Item) (34 bytes)
58 20 38 6A 9D 05 2B 25 59 92 EE E5 FF B5 94 34 7D
32 74 18 A2 EA 51 83 48 6C 0C 9E 20 42 6E 0B CA 2F
No external authorization data:
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EAD_3 (CBOR Sequence) (0 bytes)
The Initiator constructs firstly PLAINTEXT_3B as defined in
Section 5.3.1.:
PLAINTEXT_3B (CBOR Sequence) (0 bytes)
It then computes CIPHERTEXT_3B as defined in Section 5.3.2. It uses
ID_CRED_PSK, CRED_I, CRED_R and TH_3 as external_aad:
ID_CRED_PSK (CBOR Data Item) (1 byte)
10
CRED_I (Raw Value) (38 bytes)
A2 02 69 69 6E 69 74 69 61 74 6F 72 08 A1 01 A3
01 04 02 41 10 20 50 50 93 0F F4 62 A7 7A 35 40
CF 54 63 25 DE A2 14
CRED_R (Raw Value) (38 bytes)
A2 02 69 72 65 73 70 6F 6E 64 65 72 08 A1 01 A3
01 04 02 41 10 20 50 50 93 0F F4 62 A7 7A 35 40
CF 54 63 25 DE A2 14
TH_3 (Raw Value) (32 bytes)
38 6A 9D 05 2B 25 59 92 EE E5 FF B5 94 34 7D 32
74 18 A2 EA 51 83 48 6C 0C 9E 20 42 6E 0B CA 2F
The Initiator computes K_3 and IV_3
K_3 (Raw Value) (16 bytes)
96 6A 57 9C EA 26 CA 3C EB 44 2A C7 27 EA B2 32
IV_3 (Raw Value) (13 bytes)
5B F1 AD 0E 4F FB 96 76 D7 8D F2 3F 6E
It then computes CIPHERTEXT_3B:
CIPHERTEXT_3B (CBOR Sequence) (9 bytes)
48 04 88 B7 F2 A6 66 B6 29
The Initiator computes KEYSTREAM_3A as defined in Section 4:
KEYSTREAM_3A (Raw Value) (10 bytes)
03 E5 D1 57 1B BC 93 32 47 1B
It then calculates PLAINTEXT_3A as stated in Section 5.3.2.:
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PLAINTEXT_3A (CBOR Sequence) (10 bytes)
10 48 04 88 B7 F2 A6 66 B6 29
It then uses KEYSTREAM_3A to derive CIPHERTEXT_3A:
CIPHERTEXT_3A (CBOR Sequence) (10 bytes)
13 AD D5 DF AC 4E 35 54 F1 32
The Initiator computes message_3 as defined in Section 5.3.2.:
message_3 (CBOR Sequence) (11 bytes)
4A 13 AD D5 DF AC 4E 35 54 F1 32
The transcript hash TH_4 is calculated using the EDHOC hash
algorithm: TH_4 = H( TH_3, ID_CRED_PSK, ? EAD_3, CRED_I, CRED_R )
TH_4 (Raw Value) (32 bytes)
11 48 1B 9A FE F9 5C 67 9A 52 03 82 17 EE DD 0E
0C E0 8F AA 86 5B DC 82 55 11 CA 6D C3 91 94 13
TH_4 (CBOR Data Item) (34 bytes)
58 20 11 48 1B 9A FE F9 5C 67 9A 52 03 82 17 EE DD
0E 0C E0 8F AA 86 5B DC 82 55 11 CA 6D C3 91 94 13
B.4. message_4
No external authorization data:
EAD_4 (CBOR Sequence) (0 bytes)
The Responder constructs PLAINTEXT_4:
PLAINTEXT_4 (CBOR Sequence) (0 bytes)
The Responder computes K_4 and IV_4:
K_4 (Raw Value) (16 bytes)
BC AB 1D F0 13 8D C0 5C 88 5F D3 71 E9 50 C6 7F
IV_4 (Raw Value) (13 bytes)
41 11 34 D0 E0 C5 08 D9 5D A7 C3 AC DC
The Responder computes message_4:
message_4 (CBOR Sequence) (9 bytes)
48 8A DD 93 DB 40 48 59 F9
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B.5. PRK_out and PRK_exporter
After the exchange, the following PRK_out and PRK_exporter are
derived by both entities:
PRK_out (Raw Value) (32 bytes)
BB A6 DE D3 B0 38 D2 32 37 74 D8 92 14 A5 13 A2
49 16 F0 42 29 6C 7C 72 9C D1 A6 7B 43 6F B4 14
PRK_exporter (Raw Value) (32 bytes)
2F CD 08 C0 C0 10 77 C6 D6 48 6B 9F 9B 67 70 20
E8 D6 8F 04 BC DC CE 71 5D D2 77 ED 25 93 1B EF
B.6. rPSK and rKID
Both peers generate a resumption key for use in the next resumption
attempt, as explained in Section 6:
rPSK (Raw Value) (16 bytes)
5B 0B C7 63 F6 EA D1 7E 0E EA ED FD D3 36 A5 EE
rKID (Raw Value) (1 byte)
55
Appendix C. Change Log
RFC Editor: Please remove this appendix.
* From -04 to -05
- Fixed misbinding attacks and resumption
- Updated privacy considerations
- Added EDHOC-PSK and EAP section
- Editorial changes
- Fixed test vectors
* From -03 to -04
- Test Vectors
- Editorial changes
* From -02 to -03
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- Updated abstract and Introduction
- Changed message_3 to hide the identity length from passive
attackers
- CDDL Definitions
- Security considerations of independence of Session Keys
- Editorial changes
* From -01 to -02
- Changes to message_3 formatting and processing
* From -00 to -01
- Editorial changes and corrections
Acknowledgments
The authors want to thank Christian Amsüss, Scott Fluhrer, Charlie
Jacomme, and Marco Tiloca for reviewing and commenting on
intermediate versions of the draft.
This work has been partly funded by PID2023-148104OB-C43 funded by
MICIU/AEI/10.13039/501100011033 (ONOFRE4), FEDER/UE EU HE CASTOR
under Grant Agreement No 101167904 and EU CERTIFY under Grant
Agreement No 101069471.
This work was supported partially by Vinnova - the Swedish Agency for
Innovation Systems - through the EUREKA CELTIC-NEXT project CYPRESS.
This work has been partially supported by the French National
Research Agency under the France 2030 label (NF-HiSec ANR-22-PEFT-
0009)
Authors' Addresses
Elsa Lopez-Perez
Inria
Email: elsa.lopez-perez@inria.fr
Göran Selander
Ericsson
Email: goran.selander@ericsson.com
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John Preuß Mattsson
Ericsson
Email: john.mattsson@ericsson.com
Rafael Marin-Lopez
University of Murcia
Email: rafa@um.es
Francisco Lopez-Gomez
University of Murcia
Email: francisco.lopezg@um.es
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