Remote attestation over EDHOC
draft-ietf-lake-ra-05
| Document | Type | Active Internet-Draft (lake WG) | |
|---|---|---|---|
| Authors | SONG Yuxuan , Göran Selander | ||
| Last updated | 2026-04-26 | ||
| Replaces | draft-song-lake-ra | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| 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 | Yes | ||
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draft-ietf-lake-ra-05
Lightweight Authenticated Key Exchange Y. Song
Internet-Draft Inria
Intended status: Standards Track G. Selander
Expires: 29 October 2026 Ericsson AB
27 April 2026
Remote attestation over EDHOC
draft-ietf-lake-ra-05
Abstract
This document specifies how to perform remote attestation as part of
the lightweight authenticated Diffie-Hellman key exchange protocol
EDHOC (Ephemeral Diffie-Hellman Over COSE), based on the Remote
ATtestation procedureS (RATS) architecture.
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/ra/draft-ietf-lake-ra.html. Status information for this
document may be found at https://datatracker.ietf.org/doc/draft-ietf-
lake-ra/.
Discussion of this document takes place on the Lightweight
Authenticated Key Exchange Working Group mailing list
(mailto:lake@ietf.org), which is archived at
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Source for this draft and an issue tracker can be found at
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This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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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 . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Reuse of EDHOC . . . . . . . . . . . . . . . . . . . . . 7
5. Remote Attestation in EDHOC . . . . . . . . . . . . . . . . . 7
5.1. Target: Initiator Attestation (I) . . . . . . . . . . . . 7
5.2. Target: Responder Attestation (R) . . . . . . . . . . . . 8
5.3. Model: Background-check Model (BG) . . . . . . . . . . . 8
5.3.1. Attestation_proposal . . . . . . . . . . . . . . . . 9
5.3.2. Attestation_request . . . . . . . . . . . . . . . . . 9
5.3.3. Evidence . . . . . . . . . . . . . . . . . . . . . . 10
5.3.4. Trigger Remote Attestation BG . . . . . . . . . . . . 12
5.4. Model: Passport Model (PP) . . . . . . . . . . . . . . . 13
5.4.1. Result_proposal . . . . . . . . . . . . . . . . . . . 14
5.4.2. Result_request . . . . . . . . . . . . . . . . . . . 14
5.4.3. Result . . . . . . . . . . . . . . . . . . . . . . . 15
5.4.4. Trigger Remote Attestation PP . . . . . . . . . . . . 15
6. Instantiation of Remote Attestation Protocol . . . . . . . . 16
6.1. (I, BG): EDHOC Initiator Attestation in the
Background-check Model . . . . . . . . . . . . . . . . . 16
6.2. (R, PP): EDHOC Responder Attestation in the Passport
Model . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.3. (R, BG): EDHOC Responder Attestation in the
Background-check Model . . . . . . . . . . . . . . . . . 19
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6.4. (I, PP): EDHOC Initiator Attestation in the Passport
Model . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7. Mutual Attestation in EDHOC . . . . . . . . . . . . . . . . . 23
7.1. (I, BG) - (R, PP) . . . . . . . . . . . . . . . . . . . . 23
8. Verifier . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.1. Processing in the Background-check Model . . . . . . . . 25
8.2. Processing in the Passport Model . . . . . . . . . . . . 26
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
10.1. EDHOC External Authorization Data Registry . . . . . . . 27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
11.1. Normative References . . . . . . . . . . . . . . . . . . 27
11.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Example: Device Onboarding: Firmware Version
Check . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Appendix B. Re-attestation . . . . . . . . . . . . . . . . . . . 32
B.1. Intra-handshake Re-attestation using EDHOC Resumption with
PSK . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
B.2. Post-handshake Re-attestation using OSCORE . . . . . . . 33
B.2.1. Flight 1 . . . . . . . . . . . . . . . . . . . . . . 33
B.2.2. Flight 2 . . . . . . . . . . . . . . . . . . . . . . 33
B.2.3. Flight 3 . . . . . . . . . . . . . . . . . . . . . . 34
B.3. Differences between Intra-handshake and Post-handshake
Attestation . . . . . . . . . . . . . . . . . . . . . . . 34
B.3.1. Performance properties . . . . . . . . . . . . . . . 34
B.3.2. Security properties . . . . . . . . . . . . . . . . . 34
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
Remote attestation is a security process that verifies and confirms
the integrity and trustworthiness of a remote target (e.g., device,
system, group of devices) in the network. This process helps
establish a level of trust in the remote system, e.g., before
allowing the device to join the network or get access to some
sensitive information and resources. The use cases that require
remote attestation include secure boot and firmware management, cloud
computing, network access control, etc.
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The IETF working group Remote ATtestation procedureS (RATS) has
defined an architecture [RFC9334] for remote attestation. The three
main roles in the RATS architecture are the Attester, the Verifier
and the Relying Party. The Attester generates evidence (a set of
claims) concerning its identity and integrity, which must be
appraised by the Verifier for its validity. Then, the Verifier
produces the attestation result, which is consequently used by the
Relying Party for the purposes of reliably applying application-
specific actions.
One type of interaction model defined in the RATS architecture is
called the background-check model. It resembles the procedure of how
employers perform background checks to determine the prospective
employee's trustworthiness, by contacting the respective organization
that issues a report. In this case, the employer acts as the Relying
Party, the employee acts as the Attester and the organization acts as
the Verifier. The Attester conveys evidence directly to the Relying
Party and the Relying Party forwards the evidence to the Verifier for
appraisal. Once the attestation result is computed by the Verifier,
it is sent back to the Relying Party to decide what action to take
based on the attestation result. Another model is called passport
model, where the Attester communicates directly with the Verifier.
The Attester presents the evidence to the Verifier and gets an
attestation result from the Verifier. Then the Attester conveys the
attestation result to the Relying Party. This specification employs
both the RATS background-check model and the passport model.
This document specifies the protocol between the Attester and the
Relying Party. The details of the protocol between the Relying Party
and the Verifier in the background-check model, and the protocol
between the Attester and the Verifier in the passport model are out
of the scope. The establishment of the secure association may be
provided by EDHOC, TLS, and the communication may be secured through
protocols such as OSCORE, TLS or other security protocols that
support secure message exchange with the Verifier.
One way of conveying attestation evidence or the attestation result
is the Entity Attestation Token (EAT) [RFC9711]. It provides an
attested claims set which can be used to determine a level of
trustworthiness. This specification relies on the EAT as the format
for attestation evidence and the attestation result.
Ephemeral Diffie-Hellman over COSE (EDHOC) [RFC9528] is a lightweight
authenticated key exchange protocol for highly constrained networks.
In EDHOC, the two parties involved in the key exchange are referred
to as the Initiator (I) and the Responder (R). EDHOC supports the
transport of external authorization data, through the dedicated EAD
fields. This specification delivers EAT through EDHOC.
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Specifically, EAT is transported as an EAD item. This specification
also defines new EAD items needed to perform remote attestation over
EDHOC in Section 5.3 and Section 5.4.
For the generation of evidence, the Attester incorporates an internal
attestation service, including a specific trusted element known as
the "root of trust". Root of trust serves as the starting point for
establishing and validating the trustworthiness appraisals of other
components on the system. The measurements signed by the attestation
service are referred to as the Evidence. The signing is requested
through an attestation API. How the components are separated between
the secure and non-secure worlds on a target is out of the scope of
this specification.
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.
The reader is assumed to be familiar with the terms and concepts
defined in EDHOC [RFC9528], RATS architecture [RFC9334] and CBOR
[RFC8949].
3. Overview
EDHOC provides the benefit of minimal message overhead and reduced
round trips for lightweight authentication between an Initiator and a
Responder. However, authentication ensures only identity-level
security, and additional integrity assurance may be required through
remote attestation. This specification describes how to perform
remote attestation over the EDHOC protocol, following the RATS
architecture. More importantly, by integrating remote attestation
with EDHOC, attestation can be run in parallel with authentication,
improving the efficiency and maintaining lightweight properties.
Remote attestation protocol elements are carried within EDHOC's
External Authorization Data (EAD) fields. EDHOC [RFC9528] supports
one or more EAD items in each EAD field.
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The Attester can act as either the EDHOC Initiator or the EDHOC
Responder, depending on the attesting target. In the background-
check model, the Attester exchanges evidence with the Relying Party
during the EDHOC session. In the passport model, the Attester
exchanges the attestation result with the Relying Party during the
EDHOC session. Section 5 defines two independent dimensions for
performing remote attestation over EDHOC:
1. Target (see Section 5.1, Section 5.2) defining the entity that
undergoes the attestation process (EDHOC Initiator or EDHOC
Responder), which could be a constrained device or not.
2. Model (see Section 5.3, Section 5.4) defining the attestation
model in use based on the RATS architecture (background-check
model or passport model).
This document specifies the cases that are suited for constrained IoT
environments. See this document [I-D.ietf-iotops-7228bis] as a
reference for classification of IoT devices.
The remote attestation operation defined in this document preserves
the properties of EDHOC:
1. The EDHOC protocol is not modified, the remote attestation
elements are carried within EDHOC EAD fields.
2. The attestation protocol is performed in parallel but does not
interfere with the authentication flow.
3. The privacy and security properties of EDHOC are not changed.
4. Assumptions
In the background-check model, the Verifier is assumed to support
verification of at least one evidence format provided by the
Attester. The Verifier is assumed to be provisioned with the
Attester's attestation public key and the reference values required
for evidence validation prior to the attestation procedure. It is
assumed that the Relying Party also has knowledge about the Attester,
so it can narrow down the evidence type selection and send to the
Attester only one format of the evidence type.
In the passport model, the authentication credential of the Verifier
is assumed to be stored at the Attester and the Relying Party. Also,
the Attester and the Relying Party consider the Verifier a trusted
source of the issued attestation result that they obtain. If
timestamps are used to ensure freshness in the passport model,
synchronized time between the Attester and Relying Party is assumed.
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For detailed time considerations, refer to Appendix A of [RFC9334].
If a nonce is used to ensure freshness, the device that generates the
nonce is assumed to be able to generate a random byte string that is
not predictable.
4.1. Reuse of EDHOC
This specification reuses several components of EDHOC.
* EAD is the External Authorization Data message field of EDHOC
messages, see Section 3.8 of [RFC9528]. This specification
specifies four new EAD items in background-check model, and four
new EAD items in passport model (see Section 5).
* ID_CRED_I is used to identify the authentication credential of the
Initiator in the authentication session.
* EDHOC hash algorithm of the selected cipher suite is used to
generate the attestation_binder_m3 (see Section 5.3.3.1) when
Evidence is sent in EDHOC message_3.
* EDHOC_Exporter is used to generate the attestation_binder_m4 (see
Section 5.3.3.1) when Evidence is sent in EDHOC message_4.
5. Remote Attestation in EDHOC
This section specifies two independent dimensions that characterize
the remote attestation process over EDHOC.
1. Target: Defines the entity that undergoes the attestation
process.
2. Model: Defines the attestation models based on RATS architecture.
This specification supports both the RATS background-check model
(see Section 5.3) and the passport model (see Section 5.4). The
corresponding EAD items for background-check model and the
passport model are independent of each other.
When transferred over CoAP [RFC7252], the EDHOC protocol can be
performed according to two possible message flows, namely the EDHOC
forward message flow and the EDHOC reverse message flow (see
Appendix A.2.2 of [RFC9528]). In this specification, both flows are
supported to perform remote attestation.
5.1. Target: Initiator Attestation (I)
The Initiator acts as the Attester.
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5.2. Target: Responder Attestation (R)
The Responder acts as the Attester.
5.3. Model: Background-check Model (BG)
In the background-check model, the Attester sends the evidence to the
Relying Party. Evidence contains a set of claims about the current
status of the Attester, including configurations, health or
construction that have security relevance (see Section 8.1 of
[RFC9334]). The Relying Party transfers the evidence to the Verifier
and gets back the attestation result from the Verifier.
An EDHOC session is established between the Attester and the Relying
Party. A negotiation of the evidence type is required before the
Attester sends the evidence. All three parties must agree on a
selected evidence type.
The Attester first sends a list of the proposed evidence types to the
Relying Party. The list is formatted as an Attestation proposal in
an EDHOC EAD item. The Relying Party relays the list to the Verifier
and receives at least one supported evidence type from the Verifier
in return. If the Relying Party receives more than one evidence
type, a single evidence type should be selected by the Relying Party
based on its knowledge of the Attester. The Relying Party then sends
it back within the Attestation request to the Attester.
A nonce, at least 8 bytes long [RFC9711], is required to guarantee
the freshness of the attestation procedure. The nonce is generated
by the Verifier and sent to the Relying Party. The Relying Party
includes the nonce in the same Attestation request sent to the
Attester, together with the selected evidence type.
Once the Attester receives the Attestation request, it can call its
attestation service to generate the evidence, with the nonce value as
one of the inputs.
The EAD item Remote Attestation BG with ead_label TBD1 conveys a
different ead_value, namely Attestation_proposal,
Attestation_request, or Evidence, depending on the EDHOC message
where the EAD item is included. Specifically, if the EAD item
Trigger Remote Attestation BG (see Section 5.3.4) is not included in
EDHOC message_1, these three values are carried in EDHOC message_1,
message_2, and message_3, respectively (see Section 6.1). In
contrast, if Trigger Remote Attestation BG is included in EDHOC
message_1, the exchange is shifted by one message:
Attestation_proposal is carried in message_2, Attestation_request in
message_3, and Evidence in message_4 (see Section 6.3).
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5.3.1. Attestation_proposal
The Attester indicates to the Relying Party its proposal to do remote
attestation, together with the Proposed_EvidenceType object that
specifies which types of attestation claims the Attester supports.
The Proposed_EvidenceType is encoded in CBOR in the form of a
sequence (see[RFC8742]).
The EAD item Remote Attestation BG for an attestation proposal is:
* ead_label = TBD1
* ead_value = Attestation_proposal, which is a CBOR byte string:
Attestation_proposal = bstr .cborseq Proposed_EvidenceType
;This defines an array, the elements of which are
;to be used in the CBOR Sequence Proposed_EvidenceType:
Proposed_EvidenceType = [ + content-format ]
content-format = uint
where
* Proposed_EvidenceType is a CBOR sequence of an array that carries
all the supported evidence types by the Attester.
* There MUST be at least one item in the array.
* content-format is an indicator of the format type (e.g.,
application/eat+cwt with an appropriate eat_profile parameter
set), from [IANA-CoAP-Content-Formats].
5.3.2. Attestation_request
As a response to the attestation proposal, the Relying Party signals
to the Attester the supported and requested evidence type. In case
none of the evidence types is supported, the Relying Party rejects
the previous message with an error indicating support for another
evidence type.
The EAD item Remote Attestation BG for an attestation request is:
* ead_label = TBD1
* ead_value = Attestation_request, which is a CBOR byte string:
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Attestation_request = bstr .cborseq Selected_EvidenceType
;This defines an array, the elements of which are
;to be used in the CBOR Sequence Selected_EvidenceType:
Selected_EvidenceType = [
content-format: uint,
nonce: bstr .size (8..64)
]
where
* content-format is the evidence type selected by the Relying Party
and supported by the Verifier.
* nonce is generated by the Verifier and forwarded by the Relying
Party.
5.3.3. Evidence
The Attester calls its local attestation service to generate and
return a serialized Entity Attestation Token (EAT) [RFC9711] as
Evidence.
The EAD item Remote Attestation BG is:
* ead_label = TBD1
* ead_value is the serialization of a COSE_Sign1 structure
protecting an EAT. For remote attestation over EDHOC, the EAT
MUST be formatted as a CBOR Web Token (CWT) [RFC8392] containing
attestation-oriented claims. The complete set of attestation
claims for the EAT is specified in [RFC9711]. An example is
provided in Appendix A.
A minimal claims set is defined as the payload of COSE_Sign1 when the
Attester operates under constrained message size requirements and/or
limited computational resources:
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minimal-claim-set = {
10 => bstr .size 8 ;eat_nonce
256 => bstr .size (7..33) ;ueid
273 => measurements-type ;measurements
}
measurements-type = [+ measurements-format]
measurements-format = [
content-format: uint,
content: bytes
]
where
* eat-nonce is the nonce generated by the Verifier (see
Section 5.3.2), which is included by the Attester within the
Evidence.
* The "measurements" claim could be a CoSWID [RFC9393], a CoRIM
[I-D.ietf-rats-corim] or other claim formats, and MUST be
identified by CoAP Content Format. An example as CoSWID is shown
in Appendix A.
5.3.3.1. Attestation binder
The signing of the Evidence MUST also take as input an attestation
binder. By doing so, the attestation binder cryptographically binds
the attestation to the authentication and ensures that the attester
is the authenticated peer. The attestation binder prevents relay
attacks whereby an attacker relays Evidence generated in a different
session.
The Relying Party has to provide the Verifier with the Evidence
together with the attestation binder. Otherwise, the Verifier would
lack the information for verifying the signed EAT.
When Evidence is sent in EDHOC message_3 in EAD_3, the attestation
binder is computed using HKDF-Expand defined in [RFC5869].
attestation_binder_m3 = HKDF-Expand(0, attest_info, hash_length)
attest_info = [ H_12, "attestation", ID_CRED_I ]
H_12 = H(H(message_1), message_2)
where
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* hash_length is the length in bytes of the output of the EDHOC hash
algorithm of the selected cipher suite.
* attest_info is a CBOR array containing H_12, the text string
"attestation" and ID_CRED_I.
* H() is the EDHOC hash algorithm of the selected cipher suite.
When Evidence is sent in EDHOC message_4, the attestation binder is
derived using EDHOC_Exporter defined in [RFC9528].
attestation_binder_m4 = EDHOC_Exporter (exporter_label, context, length)
where
* exporter_label = 2
* context = "attestation"
* length is the length in bytes of the output of the EDHOC hash
algorithm of the selected cipher suite.
The signature in COSE_Sign1 is computed over a Sig_structure
containing protected header, externally supplied data (external_aad)
and payload using a private attestation key. The COSE Unprotected
Header is empty. The message to be signed is:
[ "Signature1", body_protected, external_aad, payload ]
where
* body_protected is the same CBOR byte string as the protected
header in COSE_Sign1
* external_aad is set to attestation_binder_m3 when Evidence is
carried in EDHOC message_3, and to attestation_binder_m4 when
Evidence is carried in EDHOC message_4
* payload is the same CBOR byte string as the payload in COSE_Sign1
5.3.4. Trigger Remote Attestation BG
The EAD item Trigger Remote Attestation BG is used when the Relying
Party triggers the Attester to start a remote attestation in the
background-check model. This EAD item can only be carried in EDHOC
message_1. The Attester MUST reply with an EAD item Remote
Attestation BG, with the ead_value Attestation_proposal in
Section 5.3.1. The ead_value MUST not be present, as the ead_label
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serves as the trigger.
The EAD item Trigger Remote Attestation BG is:
* ead_label = TBD3
5.4. Model: Passport Model (PP)
In the passport model, the Attester sends the evidence to the
Verifier. After the Attester receives the attestation result from
the Verifier, the Attester sends the attestation result to the
Relying Party. The attestation result may carry a boolean value
indicating compliance or non-compliance with a Verifier's appraisal
policy, or may carry a set of claims to indicate the results in
different aspects (Section 8.4 of [RFC9334]).
An EDHOC session is established between the Attester and the Relying
Party. The Attester and the Relying Party should decide from which
Verifier the Attester obtains the attestation result before
transferring it to the Relying Party. The Attester first sends a
list of the Verifier identities that it can get the attestation
result from. The Relying Party selects one trusted Verifier identity
and sends it back within a Result request.
Regarding the freshness in passport model, the Attester could either
establish a real-time connection with the selected Verifier, or use a
pre-stored attestation result from the selected Verifier. If the
attestation result is not obtained via a real-time connection, it
MUST include a time stamp and/or expiry time to indicate its
validity. Time synchronization is out of scope of this
specification.
Once the Attester obtains the attestation result from the selected
Verifier, it sends the attestation result to the Relying Party.
The EAD item Remote Attestation PP with ead_label TBD2 conveys a
different ead_value, namely Result_proposal, Result_request, or
Result, depending on the EDHOC message where the EAD item is
included. Specifically, if the EAD item Trigger Remote Attestation
PP (see Section 5.4.4) is not included in EDHOC message_1, these
three values are carried in EDHOC message_1, message_2, and
message_3, respectively (see Section 6.4). In contrast, if Trigger
Remote Attestation PP is included in EDHOC message_1, the exchange is
shifted by one message: Result_proposal is carried in message_2,
Result_request in message_3, and Result in message_4 (see
Section 6.2).
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5.4.1. Result_proposal
An attestation result proposal contains the identification of the
credentials of the Verifiers to indicate Verifiers' identities. The
identification of credentials relies on COSE header parameters
[IANA-COSE-Header-Parameters], with a header label and credential
value.
The EAD item Remote Attestation PP for the attestation result
proposal is:
* ead_label = TBD2
* ead_value = Result_proposal, which is a CBOR byte string:
Result_proposal = bstr .cbor Proposed_VerifierIdentity
Proposed_VerifierIdentity = [ + VerifierIdentity ]
VerifierIdentity = {
label => any
}
label = int / tstr
where
* Proposed_VerifierIdentity is defined as a list of one or more
VerifierIdentity elements.
5.4.2. Result_request
As a response to the attestation result proposal, the Relying Party
signals to the Attester the trusted Verifier. In case none of the
Verifiers can be trusted by the Relying Party, the session is
aborted.
The EAD item Remote Attestation PP for an attestation result request
is:
* ead_label = TBD2
* ead_value = Result_request, which is a CBOR byte string:
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Result_request = bstr .cbor Request_structure
Request_structure = {
selected_verifier: VerifierIdentity,
? nonce: bstr .size (8..64)
}
The nonce is optional and depends on whether the Relying Party
requires an attestation result based on a real-time interaction with
the Verifier. If the Relying Party can accept and evaluate a cached
attestation result with a timestamp, the nonce does not need to be
included in the result request. Otherwise, the Relying Party
generates a random nonce and sends it to the Attester. The Attester
must forward the nonce together with the evidence to the Verifier,
which must include the nonce in the Attestation Result that it
produces and provides to the Attester.
5.4.3. Result
The attestation result is generated and signed by the Verifier as a
serialized EAT [RFC9711], and MUST be protected using a COSE_Sign1
structure. The Relying Party can decide what action to take with
regard to the Attester based on the information elements in
attestation result.
The EAD item Remote Attestation PP is:
* ead_label = TBD2
* ead_value is the serialization of a COSE_Sign1 structure
protecting an EAT.
5.4.4. Trigger Remote Attestation PP
The EAD item Trigger Remote Attestation PP is used when the Relying
Party triggers the Attester to start a remote attestation in the
passport model. This EAD item can only be carried in the EDHOC
message_1. The Attester MUST reply with an EAD item Remote
Attestation PP, with the ead_value Result_proposal in Section 5.4.1.
The ead_value MUST not be present, as the ead_label serves as the
trigger.
The EAD item Trigger Remote Attestation PP is:
* ead_label = TBD4
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6. Instantiation of Remote Attestation Protocol
We use the format (Target, Model) to denote instantiations. In
particular:
* I means that the EDHOC Initiator is the Attester.
* R means that the EDHOC Responder is the Attester.
* BG denotes the background-check model.
* PP denotes the passport model.
For example, (I, BG) represents the Initiator as an Attester
performing attestation using the background-check model. The four
possible instantiations are therefore: (I, BG), (R, PP), (R, BG), and
(I, PP). In the remainder of this section we provide examples of
these instantiations, starting with two instances of constrained
Initiator followed by two instances of constrained Responder.
6.1. (I, BG): EDHOC Initiator Attestation in the Background-check Model
In this instantiation, the constrained EDHOC Initiator acts as the
RATS Attester and the EDHOC Responder acts as the RATS Relying Party.
An overview of EDHOC Initiator attestation in the background-check
model is illustrated in Figure 1. The Attester and the Relying Party
communicate by transporting messages within EDHOC External
Authorization Data (EAD) fields. An external entity plays the role
of the RATS Verifier (V). The EAD items specific to the background-
check model are defined in Section 5.3.
The Attester starts the attestation by sending an Attestation
proposal in EDHOC message_1. The Relying Party generates EAD_2 with
the received evidence type(s) and nonce from the Verifier, and sends
an Attestation request to the Attester. The Attester generates the
Evidence with the nonce embedded and signs the EAT with the
attestation binder as an input, then sends the Evidence to the
Relying Party in EAD_3. The Relying Party verifies the attestation
binder and then sends the Evidence together with the attestation
binder to the Verifier. The Verifier evaluates the Evidence and
sends the Attestation result to the Relying Party.
A common use case for (I, BG) is to attest an IoT device (EDHOC
Initiator) to a network server (EDHOC Responder). For example, a
simple illustrative example is the performance of remote attestation
to verify that the latest version of firmware is running on the IoT
device before the network server allows it to join the network (see
Appendix A).
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+--------------------------------+ +-------------------+
| Constrained EDHOC Initiator | | EDHOC Responder |
+--------------------------------+ +-------------------+ +----------+
| Attestation Service | Attester | | Relying Party | | Verifier |
+--+------------------------+----+ +---------+---------+ +-----+----+
| | | |
| | | |
| | EDHOC message_1 | |
| +----------------------------->| |
| | EAD_1 = Attestation_proposal | |
| | { types(a,b,c) } | |
| | | Body: { types(a,b,c) } |
| | +---------------------------->|
| | | |
| | | Body:{ types(a,b), nonce } |
| | |<----------------------------+
| | EDHOC message_2 | |
| |<-----------------------------+ |
| | EAD_2 = Attestation_request | |
| | { types(a), nonce } | |
| | | |
| type(a), nonce, | | |
| attestation binder | | |
|<-------------------+ | |
| | | |
| Evidence (EAT) | | |
+------------------->| | |
| | EDHOC message_3 | |
| +----------------------------->| |
| | EAD_3 = Evidence | |
| | { EAT } | |
| | | |
| | | Body:{ EAT, |
| | | attestation binder } |
| | +---------------------------->|
| | | Body:{ att-result: AR{} } |
| | |<----------------------------+
| | +---. |
| | | | verify AR{} |
| | |<--' |
| | application data | |
| |<============================>| |
| | | |
Figure 1: Overview of EDHOC Initiator attestation in background-
check model. EDHOC is used between A and RP.
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6.2. (R, PP): EDHOC Responder Attestation in the Passport Model
In this instantiation, the constrained EDHOC Initiator acts as the
RATS Relying Party and the EDHOC Responder acts as the RATS Attester.
An overview of the message flow is illustrated in Figure 2. The EAD
items specific to the passport model are defined in Section 5.4.
The Relying Party asks the Attester to do a remote attestation by
sending a trigger_pp (see Section 5.4.4) in EDHOC message_1. The
Attester replies to the Relying Party with a Result proposal in
EAD_2. Then the Relying Party selects a trusted Verifier identity
and sends it as a Result request. How the Attester negotiates with
the selected Verifier to get the attestation result is out of scope
of this specification. A fourth EDHOC message is required to send
the Result from the Attester to the Relying Party.
One use case for (R, PP) is when a network server (EDHOC Responder)
needs to attest itself to a client (e.g., an IoT device (EDHOC
Initiator)). For example, the client needs to send some sensitive
data to the network server, which requires the network server to be
attested first.
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+-----------------------------+ +-----------------+
| Constrained EDHOC Initiator | | EDHOC Responder |
+-----------------------------+ +-----------------+ +--------------+
| Relying Party | | Attester | | Verifier (2) |
+--------------+--------------+ +--------+--------+ +-------+------+
| | |
| EDHOC message_1 | |
+------------------------------->| |
| EAD_1 = trigger_pp | |
| | |
| EDHOC message_2 | |
|<-------------------------------+ |
| EAD_2 = Result_proposal | |
| { Verifier(1,2,3) } | |
| | |
| EDHOC message_3 | |
+------------------------------->| |
| EAD_3 = Result_request | |
| { Verifier(2), nonce } | |
| | Evidence + nonce |
| +--- --- --- --- --- -->|
| | Result |
| |<--- --- --- --- --- --+
| EDHOC message_4 | |
|<-------------------------------+ |
| EAD_4 = Result | |
| { EAT } | |
| | |
Figure 2: Overview of EDHOC Responder attestation in passport
model. EDHOC is used between RP and A. The dashed line
illustrates a logical connection that does not need to occur in
real time.
6.3. (R, BG): EDHOC Responder Attestation in the Background-check Model
In this instantiation, the constrained EDHOC Responder acts as the
RATS Attester and the EDHOC Initiator acts as the RATS Relying Party.
An overview of the message flow is illustrated in Figure 3. The EAD
items specific to the background-check model are defined in
Section 5.3.
The Relying Party initiates the procedure by sending trigger_bg in
EAD_1 of message_1. The Attester responds with an Attestation
proposal in EAD_2 of message_2, indicating the evidence types it can
provide. The Relying Party forwards this proposal to the Verifier,
which selects its supported evidence types and provides a nonce. The
Relying Party then sends an Attestation request in EAD_3 of
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message_3, which contains the nonce generated from the Verifier.
Upon receipt of the Attestation request, the Attester generates the
Evidence with the nonce embedded and signs the EAT with the
attestation binder as an input. Evidence is carried in EAD_4 of
message_4. The Relying Party forwards the Evidence to the Verifier
together with the attestation binder and receives an Attestation
result.
Note that this is a post-handshake attestation since EDHOC completes
the authenticated key exchange after message_3. Therefore, the
attestation binder in this instantiation is derived using
EDHOC_Exporter (see Section 5.3.3.1).
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+-------------------+ +--------------------------------+
| EDHOC Initiator | | Constrained EDHOC Responder |
+----------+ +-------------------+ +--------------------------------+
| Verifier | | Relying Party | | Attester | Attestation Service |
+----------+ +---------+---------+ +----+-------------------+-------+
| | | |
| | EDHOC message_1 | |
| +----------------------------->| |
| | EAD_1 = trigger_bg | |
| | | |
| | | |
| | EDHOC message_2 | |
| |<-----------------------------+ |
| | EAD_2 = Attestation_proposal | |
| | { types(a,b,c) } | |
| Body: { types(a,b,c) } | | |
|<---------------------------+ | |
| | | |
| Body: { types(a,b), nonce }| | |
+--------------------------->| | |
| | EDHOC message_3 | |
| +----------------------------->| |
| | EAD_3 = Attestation_request | |
| | { types(a), nonce } | |
| | | types(a), nonce, |
| | | attestation binder|
| | |------------------>+
| | | |
| | | Evidence (EAT) |
| | |<------------------+
| | EDHOC message_4 | |
| |<-----------------------------+ |
| | EAD_4 = Evidence | |
| | { EAT } | |
| Body: { EAT, | | |
| attestation binder }| | |
|<---------------------------+ | |
| | | |
| Body: { att-result: AR{} } | | |
+--------------------------->| | |
| +---. | |
| | | verify AR {} | |
| |<--' | |
| | | |
| | application data | |
| |<============================>| |
| | | |
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Figure 3: Overview of EDHOC Responder attestation in background-
check model. EDHOC is used between A and RP.
6.4. (I, PP): EDHOC Initiator Attestation in the Passport Model
In this instantiation, the EDHOC Initiator acts as the RATS Attester
and the constrained EDHOC Responder acts as the RATS Relying Party.
An overview of the message flow is illustrated in Figure 4. The EAD
items specific to the passport model are defined in Section 5.4.
The Attester initiates the procedure by sending a Result proposal in
EAD_1 of message_1, indicating the Verifier identities it can
communicate with. The Relying Party selects a Verifier and sends a
Result request in EAD_2 of message_2, together with a nonce. The
Attester interacts with the selected Verifier to obtain an
Attestation Result. How the Attester negotiates with the selected
Verifier to get the attestation result is out of scope of this
specification. The Attester then returns the Result in EAD_3 of
message_3, after which the Relying Party can decide whether to
continue with EDHOC message_4 or application data exchange.
+-----------------+ +-----------------------------+
| EDHOC Initiator | | Constrained EDHOC Responder |
+--------------+ +-----------------+ +-----------------------------+
| Verifier (2) | | Attester | | Relying Party |
+-------+------+ +--------+--------+ +--------------+--------------+
| | |
| | EDHOC message_1 |
| +-------------------------------->|
| | EAD_1 = Result_proposal |
| | { Verifier(1,2,3) } |
| | |
| | EDHOC message_2 |
| |<--------------------------------+
| | EAD_2 = Result_request |
| | { Verifier(2), nonce } |
| Evidence + nonce | |
|<-- --- --- --- --- ---+ |
| Result | |
+--- --- --- --- --- -->| EDHOC message_3 |
| +-------------------------------->|
| | EAD_3 = Result |
| | { EAT } |
| | |
Figure 4: Overview of EDHOC Initiator attestation in passport
model. EDHOC is used between A and RP.
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7. Mutual Attestation in EDHOC
In this section we demonstrate mutual attestation over EDHOC
combining the cases (I, BG), see Section 6.1, and (R, PP), see
Section 6.2, which is potentially the most relevant mutual
attestation example for constrained IoT environments. This
demonstrates combined mutual authentication with mutual attestation
at a reduced message overhead and number of round trips.
7.1. (I, BG) - (R, PP)
In this example, the mutual attestation is performed in EDHOC forward
message flow, by one IoT device attestation in background-check model
and another network service attestation in passport model. The
process is illustrated in Figure 5. How the Network service connects
with the Verifier_1 and potential Verifier_2 is out of scope in this
specification.
The first remote attestation is initiated by the IoT device (A_1) in
background-check model. In parallel, the IoT device (A_1) requests
the network service (A_2) to perform a remote attestation in passport
model. EAD_2 carries the EAD items Attestation request and Result
proposal. EAD_3 carries the EAD items Evidence and Result request.
EAD_4 carries the EAD item Result for the passport model.
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+-----------------------------+ +-----------------+
| Constrained EDHOC Initiator | | EDHOC Responder |
+-----------------------------+ +-----------------+ +------------+ +------------+
| A_1/RP_2 | | RP_1/A_2 | | Verifier_1 | | Verifier_2 |
+--------------+--------------+ +--------+--------+ +------+-----+ +------+-----+
| | | |
| EAD_1 = Attestation proposal, | | |
| trigger_PP | | |
+------------------------------------>| | |
| | | |
| | | |
| | Attestation proposal | |
| +---------------------------->| |
| |<----------------------------+ |
| | EvidenceType(s), NonceI | |
| EAD_2 = Attestation request, | | |
| Result proposal | | |
|<------------------------------------+ | |
| | | |
| | | |
| EAD_3 = EvidenceI | | |
| Result request (nonceR) | | |
+------------------------------------>| | |
| | | |
| |EvidenceI, attestation binder| |
| +---------------------------->| EvidenceR + nonceR |
| +--- --- --- --- --- --- ----+ --- --- --- --- --- --->|
| | | |
| | Attestation result | |
| |<----------------------------+ |
| | | |
| |<--- --- --- --- --- ---+ --- --- --- --- --- ---+
| | | Result (nonceR) |
| EAD_4 = Result | | |
|<------------------------------------+ | |
| | | |
Figure 5: Overview of mutual attestation of (I, BG) - (R, PP).
EDHOC is used between A and RP. The dashed line illustrates a
logical connection that does not need to occur in real time.
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8. Verifier
The Verifier maintains an explicit trust relationship with the
Attester, whereby the Verifier is provisioned with the Attester's
attestation public key prior to the remote attestation process. This
explicit relationship may be established through various means, such
as manufacturer provisioning, trusted certification authorities, or
direct configuration. Reference values used for comparison against
received evidence should also be provided to the Verifier before the
attestation. The evaluation policy employed by the Verifier varies
according to specific use cases and should be determined prior to the
attestation; such policy definition is out of scope in this
specification.
The Verifier maintains an implicit trust relationship with the
Relying Party, established through mechanisms such as web PKI with
trusted Certificate Authority (CA) certificates, enabling the Relying
Party to trust the attestation result that is generated by the
Verifier.
8.1. Processing in the Background-check Model
The Verifier is connected with the Relying Party and is responsible
for evaluating evidence forwarded by the Relying Party. After the
Relying Party receives EDHOC message_1 from the Attester, it extracts
and transmits the Attestation proposal to the Verifier. If the
Verifier does not support any evidence type for evaluation, it
returns an empty list. Otherwise, alongside the selected evidence
type, the Verifier generates a random nonce and sends both elements
to the Relying Party.
When the Relying Party receives EDHOC message_3, it forwards the
evidence and the attestation binder (see Section 5.3.3.1) to the
Verifier for evaluation.
The evidence evaluation process MUST include the signature
verification, nonce validation, and comparison of measurement values
against trusted reference values. An example evaluation procedure
for evidence formatted as an Entity Attestation Token (EAT) protected
by a COSE_Sign1 structure is as follows:
1. Decode the COSE_Sign1 structure and extract constituent
components: headers, payload, signature.
2. Verify the signature using the Attester's attestation public key.
The Verifier reconstructs the Sig_Structure, with the attestation
binder as the external_aad.
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3. Verify that the nonce exists in the Verifier's local nonce list.
If the nonce is found, validation passes and the nonce is removed
from the list to prevent replay attacks.
4. Compare the received evidence measurement values against the
reference value. The attestation result is returned to the
Relying Party, with result generation conforming to the
attestation token format defined in [RFC9711].
8.2. Processing in the Passport Model
When the Attester utilizes a cached attestation result previously
generated by the Verifier, real-time re-evaluation by the Verifier is
not required but the attestation result is supposed to be still fresh
and valid. If the Attester receives result_request from the Relying
Party and performs real-time attestation with the Verifier, the
Verifier then generates the attestation result formatted as an Entity
Attestation Token (EAT). The token uses the "Software Measurement
Results (measres)" claim as defined in [RFC9711], and incorporates
the nonce generated by the Relying Party as an input parameter.
9. Security Considerations
This specification builds on EDHOC [RFC9528] and uses EDHOC EAD
fields. The general security and privacy considerations about EAD
fields apply to this specification too.
EAD_1 is not resistant to either active attackers or passive
attackers, because neither the Initiator nor the Responder has been
authenticated.
Although EAD_2 is encrypted, the Initiator has not been
authenticated, rendering EAD_2 vulnerable against active attackers.
When included in EAD_1 or EAD_2, the EAD items defined in this
document could reveal sensitive information about the Attester, due
to their very specific purpose and conveyed information. The leaking
of the data in EAD_1 and/or EAD_2 MAY risk to be used by attackers
for malicious purposes. Data in EAD_3 and EAD_4 are protected
between the Initiator and the Responder in EDHOC.
The risks discussed above are lower in the case of mutual attestation
where the Responder is the Attester. For the mutual attestation at
the EDHOC Responder, only the Attestation_proposal/Result_proposal in
EAD_2 is not protected against active attackers. Both the
Attestation_request/Result_request in EAD_3 and the Evidence/Result
in EAD_4 are protected.
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The privacy considerations of remote attestation refer to Section 11
of [RFC9334].
10. IANA Considerations
10.1. EDHOC External Authorization Data Registry
IANA is requested to register the following entry in the "EDHOC
External Authorization Data" registry under the group name "Ephemeral
Diffie-Hellman Over Cose (EDHOC)".
+-------------------------------+-------+------------------------+-----------------------------+
| Name | Label | Description | Reference |
+===============================+=======+========================+=============================+
| Remote Attestation BG | TBD1 | BG model | |
| | | related information | Section 5.3.1, 5.3.2, 5.3.3 |
+-------------------------------+-------+------------------------+-----------------------------+
| Remote Attestation PP | TBD2 | PP model | |
| | | related information | Section 5.4.1, 5.4.2, 5.4.3 |
+-------------------------------+-------+------------------------+-----------------------------+
| Trigger Remote Attestation BG | TBD3 | trigger to start | |
| | | attestation in BG | Section 5.3.4 |
+-------------------------------+-------+------------------------+-----------------------------+
| Trigger Remote Attestation PP | TBD4 | trigger to start | |
| | | attestation in PP | Section 5.4.4 |
+-------------------------------+-------+------------------------+-----------------------------+
Figure 6: EAD labels.
11. References
11.1. Normative References
[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>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/rfc/rfc5869>.
[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>.
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[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>.
[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>.
[RFC9334] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", RFC 9334, DOI 10.17487/RFC9334, January
2023, <https://www.rfc-editor.org/rfc/rfc9334>.
[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>.
[RFC9711] Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
Wallace, "The Entity Attestation Token (EAT)", RFC 9711,
DOI 10.17487/RFC9711, April 2025,
<https://www.rfc-editor.org/rfc/rfc9711>.
11.2. Informative References
[I-D.ietf-iotops-7228bis]
Bormann, C., Ersue, M., Keränen, A., and C. Gomez,
"Terminology for Constrained-Node Networks", Work in
Progress, Internet-Draft, draft-ietf-iotops-7228bis-07, 23
April 2026, <https://datatracker.ietf.org/doc/html/draft-
ietf-iotops-7228bis-07>.
[I-D.ietf-lake-authz]
Selander, G., Mattsson, J. P., Vučinić, M., Fedrecheski,
G., and M. Richardson, "Lightweight Authorization using
Ephemeral Diffie-Hellman Over COSE (ELA)", Work in
Progress, Internet-Draft, draft-ietf-lake-authz-07, 2
March 2026, <https://datatracker.ietf.org/doc/html/draft-
ietf-lake-authz-07>.
[I-D.ietf-lake-edhoc-psk]
Lopez-Perez, Selander, G., Mattsson, J. P., Marin-Lopez,
R., and F. Lopez-Gomez, "EDHOC Authenticated with Pre-
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Shared Keys (PSK)", Work in Progress, Internet-Draft,
draft-ietf-lake-edhoc-psk-07, 2 March 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-lake-
edhoc-psk-07>.
[I-D.ietf-rats-corim]
Birkholz, H., Fossati, T., Deshpande, Y., Smith, N., and
W. Pan, "Concise Reference Integrity Manifest", Work in
Progress, Internet-Draft, draft-ietf-rats-corim-10, 2
March 2026, <https://datatracker.ietf.org/doc/html/draft-
ietf-rats-corim-10>.
[IANA-CoAP-Content-Formats]
"CoAP Content-Formats", n.d.,
<https://www.iana.org/assignments/core-parameters>.
[IANA-COSE-Header-Parameters]
"COSE Header Parameters", n.d.,
<https://www.iana.org/cose/header-parameters>.
[IANA.CWT.Claims]
IANA, "CBOR Web Token (CWT) Claims",
<https://www.iana.org/assignments/cwt>.
[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/rfc/rfc7252>.
[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>.
[RFC9393] Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
Waltermire, "Concise Software Identification Tags",
RFC 9393, DOI 10.17487/RFC9393, June 2023,
<https://www.rfc-editor.org/rfc/rfc9393>.
[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>.
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Appendix A. Example: Device Onboarding: Firmware Version Check
The goal in this device onboarding example is to verify that the
firmware running on the device is the latest version, and is neither
tampered with or compromised. The objective of onboarding is both
authentication and integrity verification. If either one is
compromised, the objective fails. In particular, if the attestation
private key is leaked, the device firmware can no longer be trusted,
so the value of valid authentication is significantly reduced.
In this example, a device acts as the Attester, currently in an
untrusted state. The Attester needs to generate the evidence to
attest itself. A gateway that can communicate with the Attester and
can control its access to the network acts as the Relying Party. The
gateway will finally decide whether the device can join the network
or not depending on the attestation result. The attestation result
is produced by the Verifier, which is a web server that can be seen
as the manufacturer of the device. Therefore it can appraise the
evidence that is sent by the Attester. The remote attestation
session starts with the Attester sending EAD_1 in EDHOC message 1.
An example of the EAD_1 in EDHOC message_1 could be:
[60,61,258]
If the Verifier and the Relying Party can support at least one
evidence type that is proposed by the Attester, the Relying Party
will include in the EAD_2 field the same evidence type, alongside a
nonce for message freshness.
(258, h'a29f62a4c6cdaae5')
The Evidence in EAD_3 field is an Entity Attestation Token (EAT)
[RFC9711], with the measurements claim formatted in CoSWID[RFC9393].
The Evidence is protected by a COSE_Sign1 structure, where the
payload of COSE_Sign1 contains the following claims:
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{
/eat-nonce/ 10: h'a29f62a4c6cdaae5',
/ueid/ 256: 'aaabbcc',
/measurements/ 273: [
/CoAP Content-Format ID/ [ 258,
/evidence in CoSWID/ {
0: 'tagID' /tag-id/
12: 0 /tag-version/
1: "DotBot firmware" /software-name/
2: { /entity/
31: "Attester" /entity-name/
33: 1 /role, must be "tag-creator" which is 1/
},
3: { /evidence/
17: [ /file/
{
24: "partition0-nrf52840dk.bin", /fs-name/
7: [ /hash of file/
1, /alg SHA-256/
h'06294f6806b9c685eea795048579cfd02a0c025bc8b5abca42a19ea0ec23e81a'
] /hash value/
}
]
}
}
]
]
}
The Sig_structure to compute the signature of COSE_Sign1 is:
Sig_structure = [
"Signature1",
h'a10127', /ED25519 algorithm, same as the protected header in COSE_Sign1/
h'7b4c94f32a0e6db86d915a444f76525fc32912b2e07dd481a96f627ee98a110c', /hash of the first two EDHOC messages/
h'A30A48A29F62A4C6CDAAE519010047616161626263631901118182190102A50045746
16749440C00016F446F74426F74206669726D7761726502A2181F684174746573746572
18210103A11181A218187819706172746974696F6E302D6E72663532383430646B2E626
96E078201582006294F6806B9C685EEA795048579CFD02A0C025BC8B5ABCA42A19EA0EC
23E81A', /same as the payload in COSE_Sign1/
]
The complete resulting COSE object is:
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18([
/*protected header*/
h'a10127',
/*unprotected header*/
{},
/*payload*/
h'A30A48A29F62A4C6CDAAE519010047616161626263631901118182190102A50045746
16749440C00016F446F74426F74206669726D7761726502A2181F684174746573746572
18210103A11181A218187819706172746974696F6E302D6E72663532383430646B2E626
96E078201582006294F6806B9C685EEA795048579CFD02A0C025BC8B5ABCA42A19EA0EC
23E81A',
/*signature*/
h'd4100901f4c3e51312c3110c6ddc8dcf7f68d8f5d3791c19133f2f0ac158c1f5ee6ed
afe9d7c3d6eb3d2d197f82e733d375fdda9fb258b304961dfc38558950d'
])
which has the following base16 encoding:
D28443A10127A05890A30A48A29F62A4C6CDAAE51901004761616162626363190111818
2190102A5004574616749440C00016F446F74426F74206669726D7761726502A2181F68
417474657374657218210103A11181A218187819706172746974696F6E302D6E7266353
2383430646B2E62696E078201582006294F6806B9C685EEA795048579CFD02A0C025BC8
B5ABCA42A19EA0EC23E81A5840D4100901F4C3E51312C3110C6DDC8DCF7F68D8F5D3791
C19133F2F0AC158C1F5EE6EDAFE9D7C3D6EB3D2D197F82E733D375FDDA9FB258B304961
DFC38558950D
The Relying Party (co-located with the gateway) then treats the
Evidence as opaque and sends it together with the hash value of the
first two EDHOC messages to the Verifier. Once the Verifier sends
back the Attestation Result, the Relying Party can be assured of the
version of the firmware that the device is running.
Appendix B. Re-attestation
The trust relationship established during the initial EDHOC exchange
may become outdated over time due to changes in Attester state. To
maintain a valid trust relationship, a peer may require updated
assurance periodically. This section presents two re-attestation
approaches: re-attestation during EDHOC resumption and re-attestation
using OSCORE.
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B.1. Intra-handshake Re-attestation using EDHOC Resumption with PSK
Remote attestation can be applied during EDHOC session resumption
using EDHOC-PSK, as defined in Section 6 of
[I-D.ietf-lake-edhoc-psk]. This enables re-attestation without
public key based authentication.
B.2. Post-handshake Re-attestation using OSCORE
Post-handshake attestation can be performed after an EDHOC session
using Object Security for Constrained RESTful Environments (OSCORE)
[RFC8613]. In such a case, EDHOC is specifically used to establish
an OSCORE Security Context (see Appendix A.1 of [RFC9668]). OSCORE
provides application-layer protection for RESTful message exchanges,
for example the Constrained Application Protocol (CoAP), which can be
used to carry attestation information.
Post-handshake attestation decouples the attestation process from the
initial handshake, enabling re-attestation throughout the session
lifetime and guaranteeing the runtime integrity.
B.2.1. Flight 1
The CoAP client (Attester) initiates attestation with a CoAP request
where:
* The request method is POST.
* The Uri-path is "./well-known/attest".
* The payload is the Attestation_proposal CBOR sequence, where
Attestation_proposal is constructed as defined in Section 5.3.1.
B.2.2. Flight 2
The CoAP server (Relying Party) receives the request, processes it as
described in Section 5.3, and then prepares Attestation_request as
defined in Section 5.3.2. The CoAP server replies with a CoAP
response where:
* The response code is 2.04 Changed.
* The payload is the Attestation_request CBOR sequence, as defined
in Section 5.3.2.
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B.2.3. Flight 3
The CoAP client (Attester) receives the response, processes it as
described in Section 5.3, and then generates the evidence. The CoAP
client sends a CoAP request where:
* The request method is POST.
* The Uri-path is "./well-known/attest".
* The payload is the Evidence CBOR sequence, as defined in
Section 5.3.3.
B.3. Differences between Intra-handshake and Post-handshake Attestation
Intra-handshake attestation embeds evidence exchange into the
authentication handshake, cryptographically tying identity to device
state and blocking unauthenticated and untrusted devices from
completing the handshake. Post-handshake attestation separates
attestation from the authentication handshake, providing modularity
that allows attestation mechanisms to be integrated independently of
the handshake protocol. This section compares the two different
types of remote attestation methods in terms of performance and
security properties.
B.3.1. Performance properties
Intra-handshake attestation provides round-trip efficiency as
attestation occurs within the handshake, requiring no additional
round trips. The intra-handshake attestation defined in this
document does not modify the EDHOC protocol itself, though other
intra-handshake designs may require changes. Post-handshake has
higher modularity which allows the attestation process to be
integrated independently, but it requires additional round trips.
B.3.2. Security properties
Remote attestation provides security properties including evidence
integrity, freshness guarantees, and replay protection. Besides,
intra-handshake attestation is cryptographically bound to the
authentication process, and trust is established before the session
begins. Post-handshake attestation guarantees the runtime integrity
which can obtain dynamic measurements during device execution, and
can be repeatedly performed throughout the session which has the
continuous assurance.
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Acknowledgments
The author would like to thank Thomas Fossati, Malisa Vucinic, Ionut
Mihalcea, Muhammad Usama Sardar, Michael Richardson, Geovane
Fedrecheski, John Mattsson and Marco Tiloca for the provided ideas
and feedback.
Work on this document has in part been supported by the Horizon
Europe Framework Programme project OpenSwarm (grant agreement No.
101093046).
Authors' Addresses
Yuxuan Song
Inria
Email: yuxuan.song@inria.fr
Göran Selander
Ericsson AB
Email: goran.selander@ericsson.com
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