Network Working Group M. Ounsworth
Internet-Draft Entrust
Intended status: Standards Track H. Tschofenig
Expires: 3 September 2025 Siemens
H. Birkholz
Fraunhofer SIT
M. Wiseman
Beyond Identity
N. Smith
Intel Corporation
2 March 2025
Use of Remote Attestation with Certification Signing Requests
draft-ietf-lamps-csr-attestation-17
Abstract
A PKI end entity requesting a certificate from a Certification
Authority (CA) may wish to offer trustworthy claims about the
platform generating the certification request and the environment
associated with the corresponding private key, such as whether the
private key resides on a hardware security module.
This specification defines an attribute and an extension that allow
for conveyance of Evidence and Attestation Results in Certificate
Signing Requests (CSRs), such as PKCS#10 or Certificate Request
Message Format (CRMF) payloads. This provides an elegant and
automatable mechanism for transporting Evidence to a Certification
Authority.
Including Evidence and Attestation Results along with a CSR can help
to improve the assessment of the security posture for the private
key, and can help the Certification Authority to assess whether it
satisfies the requested certificate profile.
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://lamps-
wg.github.io/csr-attestation/draft-ietf-lamps-csr-attestation.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-lamps-csr-attestation/.
Source for this draft and an issue tracker can be found at
https://github.com/lamps-wg/csr-attestation.
Ounsworth, et al. Expires 3 September 2025 [Page 1]
Internet-Draft Remote Attestation with CSRs March 2025
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 3 September 2025.
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
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 6
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Information Model . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Model for Evidence in CSR . . . . . . . . . . . . . . . . 8
4.1.1. Case 1 - Evidence Bundle without Certificate Chain . 9
4.1.2. Case 2 - Evidence Bundle with Certificate Chain . . . 10
4.1.3. Case 3 - Evidence Bundles with Multiple Evidence
Statements and Complete Certificate Chains . . . . . 10
4.2. Model for Attestation Result in CSR . . . . . . . . . . . 11
5. ASN.1 Elements for Evidence in CSR . . . . . . . . . . . . . 11
5.1. Object Identifiers . . . . . . . . . . . . . . . . . . . 11
5.2. Evidence Attribute and Extension . . . . . . . . . . . . 12
6. ASN.1 Elements for Attestation Result in CSR . . . . . . . . 15
6.1. Object Identifiers . . . . . . . . . . . . . . . . . . . 15
Ounsworth, et al. Expires 3 September 2025 [Page 2]
Internet-Draft Remote Attestation with CSRs March 2025
6.2. Attestation Result Attribute and Extension . . . . . . . 16
6.3. Implementation Considerations . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7.1. Module Registration - SMI Security for PKIX Module
Identifier . . . . . . . . . . . . . . . . . . . . . . . 18
7.2. Object Identifier Registrations - SMI Security for S/MIME
Attributes . . . . . . . . . . . . . . . . . . . . . . . 18
7.3. "SMI Security for PKIX Evidence Statement Formats"
Registry . . . . . . . . . . . . . . . . . . . . . . . . 19
7.4. Attestation Evidence OID Registry . . . . . . . . . . . . 19
7.4.1. Registration Template . . . . . . . . . . . . . . . . 20
7.4.2. Initial Registry Contents . . . . . . . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
8.1. Background Check Model Security Considerations . . . . . 23
8.2. Freshness for the Background Check Model . . . . . . . . 25
8.3. Publishing Evidence in an X.509 Extension . . . . . . . . 26
8.4. Type OID and Verifier Hint . . . . . . . . . . . . . . . 26
8.5. Additional Security Considerations . . . . . . . . . . . 27
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Normative References . . . . . . . . . . . . . . . . . . 27
9.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 31
A.1. Extending EvidenceStatementSet . . . . . . . . . . . . . 31
A.2. TPM V2.0 Evidence in CSR . . . . . . . . . . . . . . . . 31
A.2.1. TCG Key Attestation Certify . . . . . . . . . . . . . 32
A.2.2. TCG OIDs . . . . . . . . . . . . . . . . . . . . . . 32
A.2.3. TPM2 AttestationStatement . . . . . . . . . . . . . . 32
A.2.4. Introduction to TPM2 concepts . . . . . . . . . . . . 33
A.2.5. TCG Objects and Key Attestation . . . . . . . . . . . 33
A.2.6. Sample CSR . . . . . . . . . . . . . . . . . . . . . 37
A.3. PSA Attestation Token in CSR . . . . . . . . . . . . . . 41
A.4. Confidential Compute Architecture (CCA) Platform Token in
CSR . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Appendix B. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 45
B.1. TCG DICE Example in ASN.1 . . . . . . . . . . . . . . . . 47
B.2. TCG DICE TcbInfo Example in CSR . . . . . . . . . . . . . 50
Appendix C. Acknowledgments . . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction
When requesting a certificate from a Certification Authority (CA), a
PKI end entity may wish to include Evidence or Attestation Results of
the security properties of its environments in which the private keys
are stored in that request.
Ounsworth, et al. Expires 3 September 2025 [Page 3]
Internet-Draft Remote Attestation with CSRs March 2025
Evidence are appraised by Verifiers, which typically produces
Attestation Results that serve as input for validating incoming
certificate requests against specified certificate policies.
Verifiers are associated with Registration Authorities (RAs) or CAs
and function as logical entities responsible for processing Evidence
and producing Attestation Results. As remote attestation technology
matures, it is natural for a Certification Authority to want proof
that the requesting entity is in a state that matches the certificate
profile. At the time of writing, the most notable example is the
Code-Signing Baseline Requirements (CSBR) document maintained by the
CA/Browser Forum [CSBR], which requires compliant CAs to "ensure that
a Subscriber’s Private Key is generated, stored, and used in a secure
environment that has controls to prevent theft or misuse", which is a
natural fit to enforce via remote attestation.
This specification defines an attribute and an extension that allow
for conveyance of Evidence and Attestation Results in Certificate
Signing Requests (CSRs), such as PKCS#10 [RFC2986] or Certificate
Request Message Format (CRMF) [RFC4211] payloads. This CSR extension
satisfies CA/B Forum's CSBR [CSBR] requirements for key protection
assurance.
As outlined in the IETF RATS architecture [RFC9334], an Attester
(typically a device) produces a signed collection of Claims that
constitute Evidence about its running environment(s). The term
"attestation" is not explicitly defined in RFC 9334 but was later
clarified in [I-D.ietf-rats-tpm-based-network-device-attest]. It
refers to the process of generating and evaluating remote attestation
Evidence.
After the Verifier appraises the Evidence, it generates a new
structure called an Attestation Result. A Relying Party utilizes
Attestation Results to inform risk or policy-based decisions that
consider trustworthiness of the attested entity. This document
relies on Section 3 as the foundation for how the various roles
within the RATS architecture correspond to a certificate requester
and a CA/RA.
The IETF RATS architecture [RFC9334] defines two communication
patterns: the _background-check model_ and the _passport model_. In
the background-check model, the Relying Party receives Evidence in
the CSR from the Attester and must interact with a Verifier service
directly to obtain Attestation Results. In contrast, the passport
model requires the Attester to first interact with the Verifier
service to obtain an Attestation Result token that is then relayed to
the Relying Party. This specification defines both communication
patterns.
Ounsworth, et al. Expires 3 September 2025 [Page 4]
Internet-Draft Remote Attestation with CSRs March 2025
Several standard and proprietary remote attestation technologies are
in use. This specification thereby is intended to be as technology-
agnostic as it is feasible with respect to implemented remote
attestation technologies. Hence, this specification focuses on (1)
the conveyance of Evidence and Attestation Results via CSRs while
making minimal assumptions about content or format of the transported
payload and (2) the conveyance of sets of certificates used for
validation of Evidence.
The certificates typically contain one or more certification paths
rooted in a device manufacturer trust anchor and the end entity
certificate being on the device in question. The end entity
certificate is associated with key material that takes on the role of
an Attestation Key and is used as Evidence originating from the
Attester.
This document specifies a CSR Attribute (or Extension for Certificate
Request Message Format (CRMF) CSRs) for carrying Evidence and
Attestation Results.
* Evidence is placed into an EvidenceStatement along with an OID to
identify its type and optionally a hint to the Relying Party about
which Verifier (software package, a microservice or some other
service) will be capable of parsing it. A set of
EvidenceStatement structures may be grouped together along with
the set of CertificateChoice structures needed to validate them to
form a EvidenceBundle.
* Attestation Results are carried in the AttestationResult along
with an OID to identify its type. A set of AttestationResult
structures may be grouped together to form an
AttestationResultBundle.
A CSR may contain one or more Evidence payloads. For example
Evidence asserting the storage properties of a private key, Evidence
asserting firmware version and other general properties of the
device, or Evidence signed using different cryptographic algorithms.
Like-wise a CSR may also contain one or more Attestation Result
payloads.
With these attributes, additional information is available to an RA
or CA, which may be used to decide whether to issue a certificate and
what certificate profile to apply. The scope of this document is,
however, limited to the conveyance of Evidence and Attestation
Results within CSR. The exact format of the Evidence and Attestation
Results being conveyed is defined in various standard and proprietary
specifications.
Ounsworth, et al. Expires 3 September 2025 [Page 5]
Internet-Draft Remote Attestation with CSRs March 2025
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.
This document re-uses the terms defined in [RFC9334] related to
remote attestation. Readers of this document are assumed to be
familiar with the following terms: Evidence, Claim, Attestation
Result (AR), Attester, Verifier, Target Environment, Attesting
Environment, Composite Device, Lead Attester, Attestation Key, and
Relying Party (RP).
The term "Certification Request" message is defined in [RFC2986].
Specifications, such as [RFC7030], later introduced the term
"Certificate Signing Request (CSR)" to refer to the Certification
Request message. While the term "Certification Request" would have
been correct, the mistake was unnoticed. In the meanwhile CSR is an
abbreviation used beyond PKCS#10. Hence, it is equally applicable to
other protocols that use a different syntax and even a different
encoding, in particular this document also considers messages in the
Certificate Request Message Format (CRMF) [RFC4211] to be "CSRs". In
this document, the terms "CSR" and Certificate Request message are
used interchangeably.
The term Hardware Security Modules (HSM) is used generically to refer
to the combination of hardware and software designed to protect keys
from unauthorized access. Other commonly used terms include Secure
Element and Trusted Execution Environment.
3. Architecture
Figure 1 shows the high-level communication pattern of the RATS
background check model where the Attester transmits the Evidence in
the CSR to the RA and the CA, which is subsequently forwarded to the
Verifier. The Verifier appraises the received Evidence and computes
an Attestation Result, which is then processed by the RA/CA prior to
the certificate issuance.
In addition to the background-check model, the RATS architecture also
defines the passport model, as described in Section 5.2 of [RFC9334].
In the passport model, the Attester transmits Evidence directly to
the Verifier to obtain an Attestation Result, which is subsequently
forwarded to the Relying Party.
Ounsworth, et al. Expires 3 September 2025 [Page 6]
Internet-Draft Remote Attestation with CSRs March 2025
The choice of model depends on various factors. For instance, the
background-check model is preferred when direct real-time interaction
between the Attester and the Verifier is not feasible.
Note that the Verifier is a logical role that may be included in the
RA/CA product. In this case, the Relying Party role and Verifier
role collapse into a single physical entity. The Verifier
functionality can, however, also be kept separate from the RA
functionality. For example, security concerns may require parsers of
Evidence formats to be logically or physically separated from the
core RA and CA functionality.
The interface by which the Relying Party passes Evidence to the
Verifier and receives back Attestation Results may be proprietary or
standardized, but in any case is out-of-scope for this document.
Like-wise, the interface between the Attester and the Verifier used
in the passport model is also out-of-scope for this document.
Figure 1 shows an example data flow where Evidence is included in a
CSR in the background-check model. The CSR is parsed by the RA
component of a CA, which extracts the Evidence and forwards it to a
trusted Verifier. The RA receives back an Attestation Result, which
it uses to decide whether this Evidence meets its policy for
certificate issuance and if it does then the certificate request is
forwarded to the CA for issuance. This diagram overlays PKI entities
with RATS roles in parentheses.
.-----------------.
| | Compare Evidence
| (Verifier) | against Appraisal
| | Policy
'------------+----'
^ |
Evidence | | Attestation
| | Result
| v
.------------. .----|-------|----. .-----.
| +----------->|----' '--->|--------------->| |
| End | Evidence | Registration | Attestation | CA |
| Entity | in CSR | Authority (RA) | Result in |(RP) |
| (Attester) | | (Relying Party) | CSR | |
'------------' '-----------------' '-----'
Figure 1: Example data flow demonstrating the architecture with
Background Check Model.
Ounsworth, et al. Expires 3 September 2025 [Page 7]
Internet-Draft Remote Attestation with CSRs March 2025
Figure 2 illustrates the passport model, where the Attester first
communicates with the Verifier to obtain the Attestation Result,
which is subsequently included in the CSR.
Evidence .-----------------.
+--------------------->| | Compare Evidence
| | (Verifier) | against Appraisal
| +----------------| | Policy
| | '-----------------'
| | Attestation
| | Result
| v
.--------|---. .-----------------. .------.
| +-->+------------>| Registration |------------->| |
| End | Attestation | Authority | Attestation | CA |
| Entity | Result in | | Result in | (RP) |
| (Attester) | CSR | (Relying Party) | CSR | |
'------------' '-----------------' '------'
Figure 2: Example data flow demonstrating the architecture with
Passport Model.
RFC 9334 [RFC9334] discusses different security and privacy aspects
that need to be considered when developing and deploying a remote
attestation solution. For example, Evidence may need to be protected
against replay and Section 10 of [RFC9334] lists approach for
offering freshness. There are also concerns about the exposure of
persistent identifiers by utilizing attestation technology, which are
discussed in Section 11 of [RFC9334]. Finally, the keying material
used by the Attester needs to be protected against unauthorized
access, and against signing arbitrary content that originated from
outside the device. This aspect is described in Section 12 of
[RFC9334]. Most of these aspects are, however, outside the scope of
this specification but relevant for use with a given attestation
technology.
The focus of this specification is on the transport of Evidence and
Attesation Results from the Attester to the Relying Party via
existing CSR messages.
4. Information Model
4.1. Model for Evidence in CSR
To support a number of different use cases for the transmission of
Evidence and certificate chains in a CSR the structure shown in
Figure 3 is used.
Ounsworth, et al. Expires 3 September 2025 [Page 8]
Internet-Draft Remote Attestation with CSRs March 2025
On a high-level, the structure is composed as follows: A PKCS#10
attribute or a CRMF extension contains one EvidenceBundle structure.
The EvidenceBundle contains one or more EvidenceStatement structures
as well as one or more CertificateChoices which enable to carry
various format of certificates.
Note: Since an extension must only be included once in a certificate
see Section 4.2 of [RFC5280], this PKCS#10 attribute or the CRMF
extension MUST only be included once in a CSR.
+-------------------+
| PKCS#10 Attribute |
| or |
| CRMF Extension |
+--------+----------+
1 ^
| 1..n +-------------------------+
| +------------>| CertificateChoices |
| | +-------------------------+
| | | Certificate OR |
| | | OtherCertificateFormat |
1 | | +-------------------------+
v 1 v
+--------------------+ 1 1..n +-------------------+
| EvidenceBundle |<--------------->| EvidenceStatement |
+--------------------+ +-------------------+
| Type |
| Statement |
| Hint |
+-------------------+
Figure 3: Information Model for CSR Evidence Conveyance.
A conformant implementation of an entity processing the CSR
structures MUST be prepared to use certificates found in the
EvidenceBundle structure to build a certification path to validate
any EvidenceStatement. The following use cases are supported, as
described in the sub-sections below.
4.1.1. Case 1 - Evidence Bundle without Certificate Chain
A single Attester, which only distributes Evidence without an
attached certificate chain. In the use case, the Verifier is assumed
to be in possession of the certificate chain already or the Verifier
directly trusts the Attestation Key and therefore no certificate
chain needs to be conveyed in the CSR.
Ounsworth, et al. Expires 3 September 2025 [Page 9]
Internet-Draft Remote Attestation with CSRs March 2025
As a result, one EvidenceBundle is included in a CSR that contains a
single EvidenceStatement without the CertificateChoices structure.
Figure 4 shows this use case.
+--------------------+
| EvidenceBundle |
+....................+
| EvidenceStatement |
+--------------------+
Figure 4: Case 1: Evidence Bundle without Certificate Chain.
4.1.2. Case 2 - Evidence Bundle with Certificate Chain
A single Attester, which shares Evidence together with a certificate
chain, is shown in Figure 5. The CSR conveys an EvidenceBundle with
a single EvidenceStatement and a CertificateChoices structure.
+-------------------------+
| EvidenceBundle |
+.........................+
| EvidenceStatement |
| CertificateChoices |
+-------------------------+
Figure 5: Case 2: Single Evidence Bundle with Certificate Chain.
4.1.3. Case 3 - Evidence Bundles with Multiple Evidence Statements and
Complete Certificate Chains
In a Composite Device, which contains multiple Attesters, a
collection of Evidence statements is obtained. In this use case,
each Attester returns its Evidence together with a certificate chain.
As a result, multiple EvidenceStatement structures and the
corresponding CertificateChoices structure with the certification
chains as provided by the Attester, are included in the CSR. This
approach does not require any processing capabilities by a Lead
Attester since the information is merely forwarded. Figure 6 shows
this use case.
+-------------------------+
| EvidenceBundle |
+.........................+
| EvidenceStatement (1) | Provided by Attester 1
| EvidenceStatement (2) | Provided by Attester 2
| CertificateChoices | Certificates provided by Attester 1 and 2
+-------------------------+
Ounsworth, et al. Expires 3 September 2025 [Page 10]
Internet-Draft Remote Attestation with CSRs March 2025
Figure 6: Case 3: Multiple Evidence Structures each with Complete
Certificate Chains.
4.2. Model for Attestation Result in CSR
Figure 7 illustrates the information model for transmitting
Attestation Results as a PKCS#10 attribute or a CRMF extension. This
structure includes a single AttestationResultBundle, which in turn
comprises one or more AttestationResult structures.
+-------------------+
| PKCS#10 Attribute |
| or |
| CRMF Extension |
+-------------------+
1 ^ +-------------------+
| 1..n | AttestationResult |
| +------------->+-------------------+
| | | Type |
| | | Result |
| | | |
1 | | +-------------------+
v 1 v
+-------------------------+
| AttestationResultBundle |
+-------------------------+
Figure 7: Information Model for CSR Attestation Result Conveyance.
5. ASN.1 Elements for Evidence in CSR
5.1. Object Identifiers
This document references id-pkix and id-aa, both defined in [RFC5911]
and [RFC5912].
This document defines the arc depicted in Figure 8.
-- Arc for Evidence types
id-ata OBJECT IDENTIFIER ::= { id-aa (TBD1) }
Figure 8: New OID Arc for PKIX Evidence Statement Formats
Ounsworth, et al. Expires 3 September 2025 [Page 11]
Internet-Draft Remote Attestation with CSRs March 2025
5.2. Evidence Attribute and Extension
By definition, attributes within a PKCS#10 CSR are typed as ATTRIBUTE
and within a CRMF CSR are typed as EXTENSION. This attribute
definition contains one Evidence bundle of type EvidenceBundle
containing one or more Evidence statements of a type
EvidenceStatement along with optional certificates for certification
path building. This structure enables different Evidence statements
to share a certification path without duplicating it in the
attribute.
EVIDENCE-STATEMENT ::= TYPE-IDENTIFIER
EvidenceStatementSet EVIDENCE-STATEMENT ::= {
... -- None defined in this document --
}
Figure 9: Definition of EvidenceStatementSet
The expression illustrated in Figure 9 maps ASN.1 Types for Evidence
Statements to the OIDs that identify them. These mappings are used
to construct or parse EvidenceStatements. Evidence Statements are
typically defined in other IETF standards, other standards bodies, or
vendor proprietary formats along with corresponding OIDs that
identify them.
This list is left unconstrained in this document. However,
implementers can populate it with the formats that they wish to
support.
EvidenceStatement ::= SEQUENCE {
type EVIDENCE-STATEMENT.&id({EvidenceStatementSet}),
stmt EVIDENCE-STATEMENT.&Type({EvidenceStatementSet}{@type}),
hint IA5String OPTIONAL
}
Figure 10: Definition of EvidenceStatement
In Figure 10, type is an OID that indicates the format of the value
of stmt.
Ounsworth, et al. Expires 3 September 2025 [Page 12]
Internet-Draft Remote Attestation with CSRs March 2025
Based on the responsibilities of the different roles in the RATS
architecture, Relying Parties need to relay Evidence to Verifiers for
evaluation and obtain an Attestation Result in return. Ideally, the
Relying Party should select a Verifier based on the received Evidence
without requiring the Relying Party to inspect the Evidence itself.
This "routing" decision is simple when there is only a single
Verifier configured for use by a Relying Party but gets more complex
when there are different Verifiers available and each of them capable
of parsing only certain Evidence formats.
In some cases, the EvidenceStatement.type OID will be sufficient
information for the Relying Party to correctly route it to an
appropriate Verifier, however since the type OID only identifies the
general data format, it is possible that multiple Verifiers are
registered against the same type OID in which case the Relying Party
will either require additional parsing of the evidence statement, or
the Attester will be required to provide additional information.
To simplify the task for the Relying Party to select an appropriate
Verifier an optional field, the hint, is available in the
EvidenceStatement structure, as shown in Figure 10. An Attester MAY
include the hint to the EvidenceStatement and it MAY be processed by
the Relying Party. The Relying Party MAY decide not to trust the
information embedded in the hint or policy MAY override any
information provided by the Attester via this hint.
When the Attester populates the hint, it MUST contain a server name
which uniquely identifies a Verifier. Server names are ASCII strings
that contain a hostname and optional port, where the port is implied
to be "443" if missing. The names use the format of the authority
portion of a URI as defined in Section 3.2 of [RFC3986]. The names
MUST NOT include a "userinfo" portion of an authority. For example,
a valid server name might be "verifier.example.com" or
"verifier.example.com:8443", but not "verifier@example.com".
Relying Parties SHOULD NOT connect to a host name provided in the
hint, especially if the verifier has no previous trust relationship
with that host name, instead this SHOULD be used only as a lookup
string for determining between a list of Verifiers that the Relying
Party is pre-configured to use.
In a typical usage scenario, the Relying Party is pre-configured with
a list of trusted Verifiers and the corresponding hint values can be
used to look up appropriate Verifier. The Relying Party is also
configured with a trust anchor for each Verifier, which allows the
Verifier to validate the signature protecting the Attestation Result.
Tricking a Relying Party into interacting with an unknown and
untrusted Verifier must be avoided.
Ounsworth, et al. Expires 3 September 2025 [Page 13]
Internet-Draft Remote Attestation with CSRs March 2025
Usage of the hint field can be seen in the TPM2_attest example in
Appendix A.2 where the type OID indicates the OID id-TcgAttestCertify
and the corresponding hint identifies the Verifier as
"tpmverifier.example.com".
EvidenceBundle ::= SEQUENCE {
evidences SEQUENCE SIZE (1..MAX) OF EvidenceStatement,
certs SEQUENCE SIZE (1..MAX) OF CertificateChoices OPTIONAL
-- CertificateChoices MUST only contain certificate or other,
-- see Section 10.2.2 of [RFC5652]
}
The CertificateChoices structure defined in [RFC6268] allows for
carrying certificates in the default X.509 [RFC5280] format, or in
other non-X.509 certificate formats. CertificateChoices MUST only
contain certificate or other. CertificateChoices MUST NOT contain
extendedCertificate, v1AttrCert, or v2AttrCert. Note that for non-
ASN.1 certificate formats, the CertificateChoices MUST use other [3]
with an OtherCertificateFormat.Type of OCTET STRING, and then can
carry any binary data.
The certs field contains a set of certificates that is intended to
validate the contents of an Evidence statement contained in
evidences, if required. For each Evidnece statement the set of
certificates should contain the certificate that contains the public
key needed to directly validate the Evidence statement. Additional
certificates may be provided, for example, to chain the Evidence
signer key back to an agreed upon trust anchor. No specific order of
the certificates in certs SHOULD be expected because certificates
contained in certs may be needed to validate different Evidence
statements.
This specification places no restriction on mixing certificate types
within the certs field. For example a non-X.509 Evidence signer
certificate MAY chain to a trust anchor via a chain of X.509
certificates. It is up to the Attester and its Verifier to agree on
supported certificate formats.
Ounsworth, et al. Expires 3 September 2025 [Page 14]
Internet-Draft Remote Attestation with CSRs March 2025
id-aa-evidence OBJECT IDENTIFIER ::= { id-aa 59 }
-- For PKCS#10
attr-evidence ATTRIBUTE ::= {
TYPE EvidenceBundle
COUNTS MAX 1
IDENTIFIED BY id-aa-evidence
}
-- For CRMF
ext-evidence EXTENSION ::= {
SYNTAX EvidenceBundle
IDENTIFIED BY id-aa-evidence
}
Figure 11: Definitions of CSR attribute and extension
The Extension variant illustrated in Figure 11 is intended only for
use within CRMF CSRs and is NOT RECOMMENDED to be used within X.509
certificates due to the privacy implications of publishing Evidence
about the end entity's hardware environment. See Section 8.3 for
more discussion.
By the nature of the PKIX ASN.1 classes [RFC5912], there are multiple
ways to convey multiple Evidence statements: by including multiple
copies of attr-evidence or ext-evidence, multiple values within the
attribute or extension, and finally, by including multiple
EvidenceStatement structures within an EvidenceBundle. The latter is
the preferred way to carry multiple Evidence statements.
Implementations MUST NOT place multiple copies of attr-evidence into
a PKCS#10 CSR due to the COUNTS MAX 1 declaration. In a CRMF CSR,
implementers SHOULD NOT place multiple copies of ext-evidence.
6. ASN.1 Elements for Attestation Result in CSR
6.1. Object Identifiers
This document defines the OID depicted in Figure 12 as an additional
CSR Attribute (PKCS#10) or Extension (CRMF) to carry Attestation
Results in a CSR.
-- Arc for Attestation Result types
id-aa-ar OBJECT IDENTIFIER ::= { id-aa (TBD2) }
Figure 12: New OID Arc for PKIX Attestation Result Formats
Ounsworth, et al. Expires 3 September 2025 [Page 15]
Internet-Draft Remote Attestation with CSRs March 2025
6.2. Attestation Result Attribute and Extension
By definition, attributes within a PKCS#10 CSR are typed as ATTRIBUTE
and within a CRMF CSR are typed as EXTENSION. This attribute
definition contains one AttestationResultBundle structure.
ATTESTATION-RESULT ::= TYPE-IDENTIFIER
AttestationResultSet ATTESTATION-RESULT ::= {
... -- None defined in this document --
}
Figure 13: Definition of AttestationResultSet
The expression illustrated in Figure 13 maps ASN.1 Types for
Attestation Result to the OIDs that identify them. These mappings
are used to construct or parse AttestationResults. Attestation
Results are defined in other IETF standards (see
[I-D.ietf-rats-ar4si]), other standards bodies, or vendor proprietary
formats along with corresponding OIDs that identify them.
This list is left unconstrained in this document. However,
implementers can populate it with the formats that they wish to
support.
AttestationResult ::= SEQUENCE {
type ATTESTATION-RESULT.&id({AttestationResultSet}),
stmt ATTESTATION-RESULT.&Type({AttestationResultSet}{@type}),
}
Figure 14: Definition of AttestationResult
In Figure 14, type is an OID that indicates the format of the value
of stmt.
AttestationResultBundle ::= SEQUENCE SIZE (1..MAX) OF AttestationResult
Ounsworth, et al. Expires 3 September 2025 [Page 16]
Internet-Draft Remote Attestation with CSRs March 2025
-- For PKCS#10
attr-ar ATTRIBUTE ::= {
TYPE AttestationResultBundle
COUNTS MAX 1
IDENTIFIED BY id-aa-ar
}
-- For CRMF
ext-ar EXTENSION ::= {
SYNTAX AttestationResultBundle
IDENTIFIED BY id-aa-ar
}
Figure 15: Definitions of CSR attribute and extension
6.3. Implementation Considerations
This specification is applicable both in cases where a CSR is
constructed internally or externally to the Attesting Environment,
from the point of view of the calling application. This section is
particularly applicable to the background check model.
Cases where the CSR is generated internally to the Attesting
Environment are straightforward: the Hardware Security Model (HSM)
generates and embeds the Evidence and the corresponding certification
paths when constructing the CSR.
Cases where the CSR is generated externally may require extra
communication between the CSR generator and the Attesting
Environment, first to obtain the necessary Evidence about the subject
key, and then to use the subject key to sign the CSR; for example, a
CSR generated by a popular crypto library about a subject key stored
on a PKCS#11 [PKCS11] device.
As an example, assuming that the HSM is, or contains, the Attesting
Environment and some cryptographic library is assembling a CSR by
interacting with the HSM over some network protocol, then the
interaction would conceptually be:
Ounsworth, et al. Expires 3 September 2025 [Page 17]
Internet-Draft Remote Attestation with CSRs March 2025
+---------+ +-----+
| Crypto | | HSM |
| Library | | |
+---------+ +-----+
| |
| getEvidence() |
|----------------->|
| |
|<-----------------|
+---------------------+ | |
| CSR = assembleCSR() |-| |
+---------------------+ | |
| |
| sign(CSR) |
|----------------->|
| |
|<-----------------|
| |
Figure 16: Example interaction between CSR generator and HSM.
7. IANA Considerations
IANA is requested to open two new registries, allocate a value from
the "SMI Security for PKIX Module Identifier" registry for the
included ASN.1 module, and allocate values from "SMI Security for S/
MIME Attributes" to identify two attributes defined within.
7.1. Module Registration - SMI Security for PKIX Module Identifier
IANA is asked to register the following within the registry id-mod
SMI Security for PKIX Module Identifier (1.3.6.1.5.5.7.0).
* Decimal: IANA Assigned - *Replace TBDMOD*
* Description: CSR-ATTESTATION-2023 - id-mod-pkix-attest-01
* References: This Document
7.2. Object Identifier Registrations - SMI Security for S/MIME
Attributes
IANA is asked to register the following within the registry id-aa SMI
Security for S/MIME Attributes (1.2.840.113549.1.9.16.2).
* Evidence Statement
Ounsworth, et al. Expires 3 September 2025 [Page 18]
Internet-Draft Remote Attestation with CSRs March 2025
* Decimal: IANA Assigned - This was early-allocated as 59 so that we
could generate the sample data.
* Description: id-aa-evidence
* References: This Document
* Attestation Result
* Decimal: IANA Assigned - - *Replace TBD2*
* Description: id-aa-ar
* References: This Document
7.3. "SMI Security for PKIX Evidence Statement Formats" Registry
IANA is asked to create a registry for Evidence Statement Formats
within the SMI-numbers registry, allocating an assignment from id-
pkix ("SMI Security for PKIX" Registry) for the purpose.
* Decimal: IANA Assigned - *replace TBD1*
* Description: id-ata
* References: This document
* Initial contents: None
* Registration Regime: Specification Required. Document must
specify an EVIDENCE-STATEMENT or ATTESTATION-RESULT definition to
which this Object Identifier shall be bound.
Columns:
* Decimal: The subcomponent under id-ata
* Description: Begins with id-ata
* References: RFC or other document
7.4. Attestation Evidence OID Registry
IANA is asked to create a registry that helps developers to find OID/
Evidence mappings.
Ounsworth, et al. Expires 3 September 2025 [Page 19]
Internet-Draft Remote Attestation with CSRs March 2025
Registration requests are evaluated using the criteria described in
the registration template below after a three-week review period on
the [[TBD]] mailing list, with the advice of one or more Designated
Experts [RFC8126]. However, to allow for the allocation of values
prior to publication, the Designated Experts may approve registration
once they are satisfied that such a specification will be published.
Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register attestation
evidence: example").
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.
7.4.1. Registration Template
The registry has the following columns:
* OID: The OID number, which has already been allocated. IANA does
not allocate OID numbers for use with this registry.
* Description: Brief description of the use of the Evidence and the
registration of the OID.
* Reference(s): Reference to the document or documents that register
the OID for use with a specific attestation technology, preferably
including URIs that can be used to retrieve copies of the
documents. An indication of the relevant sections may also be
included but is not required.
* Change Controller: For Standards Track RFCs, list the "IESG". For
others, give the name of the responsible party. In most cases the
third party requesting registration in this registry will also be
the party that registered the OID.
7.4.2. Initial Registry Contents
The initial registry contents is shown in the table below. It lists
entries for several evidence encoding OIDs including an entry for the
Conceptual Message Wrapper (CMW) [I-D.ietf-rats-msg-wrap].
+========+==================+==========================+============+
| OID | Description | Reference(s) | Change |
| | | | Controller |
+========+==================+==========================+============+
| 2 23 | tcg-dice-TcbInfo | [TCGRegistry] | TCG |
| 133 5 | | | |
Ounsworth, et al. Expires 3 September 2025 [Page 20]
Internet-Draft Remote Attestation with CSRs March 2025
| 4 1 | | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice- | [TCGRegistry] | TCG |
| 133 5 | endorsement- | | |
| 4 3 | manifest-uri | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice-Ueid | [TCGRegistry] | TCG |
| 133 5 | | | |
| 4 4 | | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice- | [TCGRegistry] | TCG |
| 133 5 | MultiTcbInfo | | |
| 4 5 | | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice-UCCS- | [TCGRegistry] | TCG |
| 133 5 | evidence | | |
| 4 6 | | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice- | [TCGRegistry] | TCG |
| 133 5 | manifest- | | |
| 4 7 | evidence | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice- | [TCGRegistry] | TCG |
| 133 5 | MultiTcbInfoComp | | |
| 4 8 | | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice- | [TCGRegistry] | TCG |
| 133 5 | conceptual- | | |
| 4 9 | message-wrapper | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-dice- | [TCGRegistry] | TCG |
| 133 5 | TcbFreshness | | |
| 4 11 | | | |
+--------+------------------+--------------------------+------------+
| 2 23 | tcg-attest-tpm- | [TCGRegistry] | TCG |
| 133 | certify | | |
| 20 1 | | | |
+--------+------------------+--------------------------+------------+
| 1 3 6 | id-pe-cmw | [I-D.ietf-rats-msg-wrap] | IETF |
| 1 5 5 | | | |
| 7 1 | | | |
| 35 | | | |
+--------+------------------+--------------------------+------------+
Table 1: Initial Contents of the Attestation Evidence OID Registry
The current registry values can be retrieved from the IANA online
website.
Ounsworth, et al. Expires 3 September 2025 [Page 21]
Internet-Draft Remote Attestation with CSRs March 2025
8. Security Considerations
In the RATS architecture, when Evidence or an Attestation Result is
presented to a Relying Party (RP), the RP may learn detailed
information about the Attester unless that information has been
redacted or encrypted. Consequently, a certain amount of trust must
be placed in the RP, which raises potential privacy concerns because
an RP could be used to track devices. This observation is noted in
Section 11 of [RFC9334].
Typically, the RPs considered in the RATS architecture are
application services that use remote attestation, rather than RAs or
CAs. Devices inherently place significant trust in RA/CA
infrastructure elements, and therefore any additional information
revealed through remote attestation to such entities is generally
less concerning than disclosure to application services. The problem
of copying Evidence by CAs into an X.509 certificate is discussed in
Section 8.3.
These privacy risks can be mitigated using several approaches,
including:
* Shared Attestation Keys: A manufacturer of devices may provision
all devices with the same attestation key(s), or share a common
attestation key across devices of the same product family. This
approach anonymizes individual devices by making them
indistinguishable from others using the same key(s). However, it
also means losing the ability to revoke a single attestation key
if a specific device is compromised. Care must be taken to avoid
embedding uniquely identifying information in the Evidence, as
that would reduce the privacy benefits of using remote
attestation.
* Per-Use Attestation Keys: Devices may be designed to dynamically
generate distinct attestation keys (and request the corresponding
certificates) for each use case, device, or session. This is
analogous to the Privacy CA model, in which a device is initially
provisioned with an attestation key and certificate; then, in
conjunction with a privacy-preserving CA, it can obtain unique
keys and certificates as needed. This strategy reduces the
potential for tracking while maintaining strong security
assurances. This is the model described in this document.
* Anonymous Attestation Mechanisms: Direct anonymous attestation
(DAA) or similar cryptographic methods can be employed to generate
blinded attestation signatures. In these schemes, the verifier
can validate the attestation using a root key but does not gain a
global correlation handle. Thus, repeated use of the same
Ounsworth, et al. Expires 3 September 2025 [Page 22]
Internet-Draft Remote Attestation with CSRs March 2025
attestation key cannot be exploited to track devices.
[I-D.ietf-rats-daa] extends the RATS architecture with such a DAA
scheme, significantly enhancing privacy.
8.1. Background Check Model Security Considerations
A PKCS#10 or CRMF Certification Request message typically consists of
a distinguished name, a public key, and optionally a set of
attributes, collectively signed by the entity requesting
certification. In general usage, the private key used to sign the
CSR MUST be different from the Attesting Key utilized to sign
Evidence about the Target Environment, though exceptions MAY be made
where CSRs and Evidence are involved in bootstrapping the Attesting
Key.
To demonstrate that the private key applied to sign the CSR is
generated, and stored in a secure environment that has controls to
prevent theft or misuse (including being non-exportable / non-
recoverable), the Attesting Environment has to collect claims about
this secure environment (or Target Environment, as shown in
Figure 17).
Figure 17 shows the interaction inside an Attester. The Attesting
Environment, which is provisioned with an Attestation Key, retrieves
claims about the Target Environment. The Target Environment offers
key generation, storage and usage, which it makes available to
services. The Attesting Environment collects these claims about the
Target Environment and signs them and exports Evidence for use in
remote attestation via a CSR.
Ounsworth, et al. Expires 3 September 2025 [Page 23]
Internet-Draft Remote Attestation with CSRs March 2025
^
|CSR with
|Evidence
.-------------+-------------.
| |
| CSR Library |<-----+
| | |
'---------------------------' |
| ^ ^ |
Private | | Public | Signature |
Key | | Key | Operation |
Generation | | Export | |
| | | |
.----------|--|---------|------------. |
| | | | Attester| |
| v | v (HSM) | |
| .-----------------------. | |
| | Target Environment | | |
| | (with key generation, | | |
| | storage and usage) | | |
| '--------------+--------' | |
| | | |
| Collect | | |
| Claims | | |
| | | |
| v | |
| .-------------. | |
|Attestation | Attesting | | |
| Key ----->| Environment +----------+
| | (Firmware) |Evidence|
| '-------------' |
| |
'------------------------------------'
Figure 17: Interaction between Attesting and Target Environment
Figure 17 places the CSR library outside the Attester, which is a
valid architecture for certificate enrollment. The CSR library may
also be located inside the trusted computing base. Regardless of the
placement of the CSR library, an Attesting Environment MUST be able
to collect claims about the Target Environment such that statements
about the storage of the keying material can be made. For the
Verifier, the provided Evidence must allow an assessment to be made
whether the key used to sign the CSR is stored in a secure location
and cannot be exported.
Ounsworth, et al. Expires 3 September 2025 [Page 24]
Internet-Draft Remote Attestation with CSRs March 2025
Evidence communicated in the attributes and structures defined in
this document are meant to be used in a CSR. It is up to the
Verifier and to the Relying Party (RA/CA) to place as much or as
little trust in this information as dictated by policies.
This document defines the transport of Evidence of different formats
in a CSR. Some of these encoding formats are based on standards
while others are proprietary formats. A Verifier will need to
understand these formats for matching the received claim values
against policies.
Policies drive the processing of Evidence at the Verifier: the
Verifier's Appraisal Policy for Evidence will often be based on
specifications by the manufacturer of a hardware security module, a
regulatory agency, or specified by an oversight body, such as the CA
Browser Forum. The Code-Signing Baseline Requirements [CSBR]
document is an example of such a policy that has been published by
the CA Browser Forum and specifies certain properties, such as non-
exportability, which must be enabled for storing publicly-trusted
code-signing keys. Other policies influence the decision making at
the Relying Party when evaluating the Attestation Result. The
Relying Party is ultimately responsible for making a decision of what
information in the Attestation Result it will accept. The presence
of the attributes defined in this specification provide the Relying
Party with additional assurance about an Attester. Policies used at
the Verifier and the Relying Party are implementation dependent and
out of scope for this document. Whether to require the use of
Evidence in a CSR is out-of-scope for this document.
8.2. Freshness for the Background Check Model
Evidence generated by an Attester generally needs to be fresh to
provide value to the Verifier since the configuration on the device
may change over time. Section 10 of [RFC9334] discusses different
approaches for providing freshness, including a nonce-based approach,
the use of timestamps and an epoch-based technique. The use of
nonces requires that nonce to be provided by the Relying Party in
some protocol step prior to Evidence and CSR generation, and the use
of timestamps requires synchronized clocks which cannot be guaranteed
in all operating environments. Epochs also require an out-of-band
communication channel. This document leaves the exchange of nonces
and other freshness data to certificate management protocols, see
[I-D.ietf-lamps-attestation-freshness]. Developers, operators, and
designers of protocols, which embed Evidence-carrying-CSRs, MUST
consider what notion of freshness is appropriate and available in-
context; thus the issue of freshness is left up to the discretion of
protocol designers and implementers.
Ounsworth, et al. Expires 3 September 2025 [Page 25]
Internet-Draft Remote Attestation with CSRs March 2025
In the case of Hardware Security Modules (HSM), the definition of
"fresh" is somewhat ambiguous in the context of CSRs, especially
considering that non-automated certificate enrollments are often
asynchronous, and considering the common practice of re-using the
same CSR for multiple certificate renewals across the lifetime of a
key. "Freshness" typically implies both asserting that the data was
generated at a certain point-in-time, as well as providing non-
replayability. Certain use cases may have special properties
impacting the freshness requirements. For example, HSMs are
typically designed to not allow downgrade of private key storage
properties; for example if a given key was asserted at time T to have
been generated inside the hardware boundary and to be non-exportable,
then it can be assumed that those properties of that key will
continue to hold into the future.
Note: Freshness is also a concern for remote attestation in the
passport model; however, the protocol between the Attester and the
Verifier lies outside the scope of this specification.
8.3. Publishing Evidence in an X.509 Extension
This document specifies an Extension for carrying Evidence in a CRMF
Certificate Signing Request (CSR), but it is intentionally NOT
RECOMMENDED for a CA to copy the ext-evidence extension into the
published certificate. The reason for this is that certificates are
considered public information and the Evidence might contain detailed
information about hardware and patch levels of the device on which
the private key resides. The certificate requester has consented to
sharing this detailed device information with the CA but might not
consent to having these details published. These privacy
considerations are beyond the scope of this document and may require
additional signaling mechanisms in the CSR to prevent unintended
publication of sensitive information, so we leave it as "NOT
RECOMMENDED". Often, the correct layer at which to address this is
either in certificate profiles, a Certificate Practice Statement
(CPS), or in the protocol or application that carries the CSR to the
RA/CA where a flag can be added indicating whether the RA/CA should
consider the evidence to be public or private.
8.4. Type OID and Verifier Hint
The EvidenceStatement includes both a type OID and a hint field with
which the Attester can provide information to the Relying Party about
which Verifier to invoke to parse a given piece of Evidence. Care
should be taken when processing these data since at the time they are
used, they are not yet verified. In fact, they are protected by the
CSR signature but not by the signature from the Attester and so could
be maliciously replaced in some cases. The authors' intent is that
Ounsworth, et al. Expires 3 September 2025 [Page 26]
Internet-Draft Remote Attestation with CSRs March 2025
the type OID and hint will allow an RP to select between Verifier
with which it has pre-established trust relationships. The RP MUST
NOT blindly make network calls to unknown domain names and trust the
results. Implementers should also be cautious around type OID or
hint values that cause a short-circuit in the verification logic,
such as None, Null, or similar values that could cause the Evidence
to appear to be valid when in fact it was not properly checked.
8.5. Additional Security Considerations
In addition to the security considerations listed here, implementers
should be familiar with the security considerations of the
specifications on this this depends: PKCS#10 [RFC2986], CRMF
[RFC4211], as well as general security concepts relating to remote
attestation; many of these concepts are discussed in Section 6 of
[RFC9334], Section 7 of [RFC9334], Section 9 of [RFC9334], Section 11
of [RFC9334], and Section 12 of [RFC9334]. Implementers should also
be aware of any security considerations relating to the specific
Evidence and Attestation Result formats being carried within the CSR.
9. References
9.1. 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>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/rfc/rfc2986>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure
Certificate Request Message Format (CRMF)", RFC 4211,
DOI 10.17487/RFC4211, September 2005,
<https://www.rfc-editor.org/rfc/rfc4211>.
Ounsworth, et al. Expires 3 September 2025 [Page 27]
Internet-Draft Remote Attestation with CSRs March 2025
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>.
[RFC5911] Hoffman, P. and J. Schaad, "New ASN.1 Modules for
Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
DOI 10.17487/RFC5911, June 2010,
<https://www.rfc-editor.org/rfc/rfc5911>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<https://www.rfc-editor.org/rfc/rfc5912>.
[RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules
for the Cryptographic Message Syntax (CMS) and the Public
Key Infrastructure Using X.509 (PKIX)", RFC 6268,
DOI 10.17487/RFC6268, July 2011,
<https://www.rfc-editor.org/rfc/rfc6268>.
[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>.
[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>.
9.2. Informative References
[CSBR] CA/Browser Forum, "Baseline Requirements for Code-Signing
Certificates, v.3.7", February 2024,
<https://cabforum.org/uploads/Baseline-Requirements-for-
the-Issuance-and-Management-of-Code-Signing.v3.7.pdf>.
[I-D.bft-rats-kat]
Brossard, M., Fossati, T., Tschofenig, H., and H.
Birkholz, "An EAT-based Key Attestation Token", Work in
Progress, Internet-Draft, draft-bft-rats-kat-05, 21
November 2024, <https://datatracker.ietf.org/doc/html/
draft-bft-rats-kat-05>.
[I-D.ffm-rats-cca-token]
Frost, S., Fossati, T., and G. Mandyam, "Arm's
Confidential Compute Architecture Reference Attestation
Ounsworth, et al. Expires 3 September 2025 [Page 28]
Internet-Draft Remote Attestation with CSRs March 2025
Token", Work in Progress, Internet-Draft, draft-ffm-rats-
cca-token-00, 4 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ffm-rats-cca-
token-00>.
[I-D.ietf-lamps-attestation-freshness]
Tschofenig, H. and H. Brockhaus, "Nonce-based Freshness
for Remote Attestation in Certificate Signing Requests
(CSRs) for the Certification Management Protocol (CMP) and
for Enrollment over Secure Transport (EST)", Work in
Progress, Internet-Draft, draft-ietf-lamps-attestation-
freshness-03, 5 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
attestation-freshness-03>.
[I-D.ietf-rats-ar4si]
Voit, E., Birkholz, H., Hardjono, T., Fossati, T., and V.
Scarlata, "Attestation Results for Secure Interactions",
Work in Progress, Internet-Draft, draft-ietf-rats-ar4si-
08, 6 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-rats-
ar4si-08>.
[I-D.ietf-rats-daa]
Birkholz, H., Newton, C., Chen, L., and D. Thaler, "Direct
Anonymous Attestation for the Remote Attestation
Procedures Architecture", Work in Progress, Internet-
Draft, draft-ietf-rats-daa-06, 5 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-rats-
daa-06>.
[I-D.ietf-rats-msg-wrap]
Birkholz, H., Smith, N., Fossati, T., Tschofenig, H., and
D. Glaze, "RATS Conceptual Messages Wrapper (CMW)", Work
in Progress, Internet-Draft, draft-ietf-rats-msg-wrap-12,
28 February 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-msg-wrap-12>.
[I-D.ietf-rats-tpm-based-network-device-attest]
Fedorkow, G., Voit, E., and J. Fitzgerald-McKay, "TPM-
based Network Device Remote Integrity Verification", Work
in Progress, Internet-Draft, draft-ietf-rats-tpm-based-
network-device-attest-14, 22 March 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-rats-
tpm-based-network-device-attest-14>.
Ounsworth, et al. Expires 3 September 2025 [Page 29]
Internet-Draft Remote Attestation with CSRs March 2025
[I-D.tschofenig-rats-psa-token]
Tschofenig, H., Frost, S., Brossard, M., Shaw, A. L., and
T. Fossati, "Arm's Platform Security Architecture (PSA)
Attestation Token", Work in Progress, Internet-Draft,
draft-tschofenig-rats-psa-token-24, 23 September 2024,
<https://datatracker.ietf.org/doc/html/draft-tschofenig-
rats-psa-token-24>.
[PKCS11] OASIS, "PKCS #11 Cryptographic Token Interface Base
Specification Version 2.40", April 2015,
<http://docs.oasis-open.org/pkcs11/pkcs11-base/v2.40/os/
pkcs11-base-v2.40-os.html>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/rfc/rfc7030>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[SampleData]
"CSR Attestation Sample Data", n.d.,
<https://github.com/lamps-wg/csr-attestation-examples>.
[TCGDICE1.1]
Trusted Computing Group, "DICE Attestation Architecture",
January 2024, <https://trustedcomputinggroup.org/wp-
content/uploads/DICE-Attestation-Architecture-Version-1.1-
Revision-18_pub.pdf>.
[TCGRegistry]
Trusted Computing Group, "TCG OID Registry", October 2024,
<https://trustedcomputinggroup.org/resource/tcg-oid-
registry/>.
[TPM20] Trusted Computing Group, "Trusted Platform Module Library
Specification, Family 2.0", n.d.,
<https://trustedcomputinggroup.org/resource/tpm-library-
specification/>.
Ounsworth, et al. Expires 3 September 2025 [Page 30]
Internet-Draft Remote Attestation with CSRs March 2025
Appendix A. Examples
This section provides several examples and sample data for embedding
Evidence in CSRs. The first example embeds Evidence produced by a
TPM in the CSR. The second example conveys an Arm Platform Security
Architecture token, which provides claims about the used hardware and
software platform, into the CSR.
After publication of this document, additional examples and sample
data will be collected at the following GitHub repository
[SampleData]:
https://github.com/lamps-wg/csr-attestation-examples
A.1. Extending EvidenceStatementSet
As defined in Section 5.2, EvidenceStatementSet acts as a way to
provide an ASN.1 compiler or runtime parser with a list of OBJECT
IDENTIFIERs that are known to represent EvidenceStatements -- and are
expected to appear in an EvidenceStatement.type field, along with the
ASN.1 type that should be used to parse the data in the associated
EvidenceStatement.stmt field. Essentially this is a mapping of OIDs
to data structures. Implementers are expected to populate it with
mappings for the Evidence types that their application will be
handling.
This specification aims to be agnostic about the type of data being
carried, and therefore does not specify any mandatory-to-implement
Evidence types.
As an example of how to populate EvidenceStatementSet, implementing
the TPM 2.0 and PSA Evidence types given below would result in the
following EvidenceStatementSet definition:
EvidenceStatementSet EVIDENCE-STATEMENT ::= {
--- TPM 2.0
{ Tcg-attest-tpm-certify IDENTIFIED BY tcg-attest-tpm-certify },
...,
--- PSA
{ OCTET STRING IDENTIFIED BY { 1 3 6 1 5 5 7 1 99 } }
}
A.2. TPM V2.0 Evidence in CSR
This section describes TPM2 key attestation for use in a CSR.
Ounsworth, et al. Expires 3 September 2025 [Page 31]
Internet-Draft Remote Attestation with CSRs March 2025
This is a complete and canonical example that can be used to test
parsers implemented against this specification. Readers who wish the
sample data may skip to Appendix A.2.6; the following sections
explain the TPM-specific data structures needed to fully parse the
contents of the evidence statement.
A.2.1. TCG Key Attestation Certify
There are several ways in TPM2 to provide proof of a key's
properties. (i.e., key attestation). This description uses the
simplest and most generally expected to be used, which is the
TPM2_Certify and the TPM2_ReadPublic commands.
This example does not describe how platform attestation augments key
attestation. The properties of the key (such as the name of the key,
the key usage) in this example do not change during the lifetime of
the key.
A.2.2. TCG OIDs
The OIDs in this section are defined by TCG TCG has a registered arc
of 2.23.133
tcg OBJECT IDENTIFIER ::= { 2 23 133 }
tcg-kp-AIKCertificate OBJECT IDENTIFIER ::= { id-tcg 8 3 }
tcg-attest OBJECT IDENTIFIER ::= { tcg 20 }
tcg-attest-tpm-certify OBJECT IDENTIFIER ::= { tcg-attest 1 }
The tcg-kp-AIKCertificate OID in extendedKeyUsage identifies an AK
Certificate in RFC 5280 format defined by TCG. This certificate
would be a certificate in the EvidenceBundle defined in Section 5.2.
(Note: The abbreviation AIK was used in TPM 1.2 specification. TPM
2.0 specifications use the abbreviation AK. The abbreviations are
interchangeable.)
A.2.3. TPM2 AttestationStatement
The EvidenceStatement structure contains a sequence of two fields: a
type and a stmt. The 'type' field contains the OID of the Evidence
format and it is set to tcg-attest-tpm-certify. The content of the
structure shown below is placed into the stmt, which is a
concatenation of existing TPM2 structures. These structures will be
explained in the rest of this section.
Ounsworth, et al. Expires 3 September 2025 [Page 32]
Internet-Draft Remote Attestation with CSRs March 2025
Tcg-csr-tpm-certify ::= SEQUENCE {
tpmSAttest OCTET STRING,
signature OCTET STRING,
tpmTPublic OCTET STRING OPTIONAL
}
A.2.4. Introduction to TPM2 concepts
The definitions in the following sections are specified by the
Trusted Computing Group (TCG). TCG specification including the TPM2
set of specifications [TPM20], specifically Part 2 defines the TPM
2.0 structures. Those familiar with TPM2 concepts may skip to
Appendix A.2.3 which defines an ASN.1 structure specific for bundling
a TPM attestation into an EvidenceStatement, and Appendix A.2.6 which
provides the example. For those unfamiliar with TPM2 concepts this
section provides only the minimum information to understand TPM2
Attestation in CSR and is not a complete description of the
technology in general.
A.2.5. TCG Objects and Key Attestation
This provides a brief explanation of the relevant TPM2 commands and
data structures needed to understand TPM2 Attestation used in this
RFC. NOTE: The TPM2 specification used in this explanation is
version 1.59, section number cited are based on that version. Note
also that the TPM2 specification comprises four documents: Part 1:
Architecture; Part 2: Structures; Part 3: Commands; Part 4:
Supporting Routines.
Note about convention: All structures starting with TPM2B_ are:
* a structure that is a sized buffer where the size of the buffer is
contained in a 16-bit, unsigned value.
* The first parameter is the size in octets of the second parameter.
The second parameter may be any type.
A full explanation of the TPM structures is outside the scope of this
document. As a simplification references to TPM2B_ structures will
simply use the enclosed TPMT_ structure by the same name following
the '_'.
A.2.5.1. TPM2 Object Names
All TPM2 Objects (e.g., keys are key objects which is the focus of
this specification). A TPM2 object name is persistent across the
object's life cycle whether the TPM2 object is transient or
persistent.
Ounsworth, et al. Expires 3 September 2025 [Page 33]
Internet-Draft Remote Attestation with CSRs March 2025
A TPM2 Object name is a concatenation of a hash algorithm identifier
and a hash of the TPM2 Object's TPMT_PUBLIC.
Name ≔ nameAlg || HnameAlg (handle→publicArea)
nameAlg is a TCG defined 16 bit algorithm identifier
publicArea is the TPMT_PUBLIC structure for that TPM2 Object.
The size of the Name field can be derived by examining the nameAlg
value, which defines the hashing algorithm and the resulting size.
The Name field is returned in the TPM2B_ATTEST data field.
typedef struct {
TPM_GENERATED magic;
TPMI_ST_ATTEST type;
TPM2B_NAME qualifiedSigner;
TPM2B_DATA extraData;
TPMS_CLOCK_INFO clockInfo;
UINT64 firmwareVersion;
TPMU_ATTEST attested;
} TPMS_ATTEST;
where for a key object the attested field is
typedef struct {
TPM2B_NAME name;
TPM2B_NAME qualifiedName;
} TPMS_CERTIFY_INFO;
A.2.5.2. TPM2 Public Structure
Any TPM2 Object has an associated TPM2 Public structure defined as
TPMT_PUBLIC. This is defined below as a 'C' structure. While there
are many types of TPM2 Objects each with its own specific TPMT_PUBLIC
structure (handled by the use of 'unions') this document will
specifically define TPMT_PUBLIC for a TPM2 key object.
typedef struct {
TPMI_ALG_PUBLIC type;
TPMI_ALG_HASH nameAlg;
TPMA_OBJECT objectAttributes;
TPM2B_DIGEST authPolicy;
TPMU_PUBLIC_PARMS parameters;
TPMU_PUBLIC_ID unique;
} TPMT_PUBLIC;
Ounsworth, et al. Expires 3 September 2025 [Page 34]
Internet-Draft Remote Attestation with CSRs March 2025
Where: * type and nameAlg are 16 bit TCG defined algorithms. *
objectAttributes is a 32 bit field defining properties of the object,
as shown below
typedef struct TPMA_OBJECT {
unsigned Reserved_bit_at_0 : 1;
unsigned fixedTPM : 1;
unsigned stClear : 1;
unsigned Reserved_bit_at_3 : 1;
unsigned fixedParent : 1;
unsigned sensitiveDataOrigin : 1;
unsigned userWithAuth : 1;
unsigned adminWithPolicy : 1;
unsigned Reserved_bits_at_8 : 2;
unsigned noDA : 1;
unsigned encryptedDuplication : 1;
unsigned Reserved_bits_at_12 : 4;
unsigned restricted : 1;
unsigned decrypt : 1;
unsigned sign : 1;
unsigned x509sign : 1;
unsigned Reserved_bits_at_20 : 12;
} TPMA_OBJECT;
* authPolicy is the Policy Digest needed to authorize use of the
object.
* Parameters are the object type specific public information about
the key.
- For key objects, this would be the key's public parameters.
* unique is the identifier for parameters
The size of the TPMT_PUBLIC is provided by the following structure:
typedef struct {
UINT16 size;
TPMT_PUBLIC publicArea;
} TPM2B_PUBLIC;
A.2.5.3. TPM2 Signatures
TPM2 signatures use a union where the first field (16 bits)
identifies the signature scheme. The example below shows an RSA
signature where TPMT_SIGNATURE->sigAlg will indicate to use
TPMS_SIGNATURE_RSA as the signature.
Ounsworth, et al. Expires 3 September 2025 [Page 35]
Internet-Draft Remote Attestation with CSRs March 2025
typedef struct {
TPMI_ALG_SIG_SCHEME sigAlg;
TPMU_SIGNATURE signature;
} TPMT_SIGNATURE;
typedef struct {
TPMI_ALG_HASH hash;
TPM2B_PUBLIC_KEY_RSA sig;
} TPMS_SIGNATURE_RSA;
A.2.5.4. Attestation Key
The uniquely identifying TPM2 key is the Endorsement Key (the EK).
As this is a privacy sensitive key, the EK is not directly used to
attest to any TPM2 asset. Instead, the EK is used by an Attestation
CA to create an Attestation Key (the AK). The AK is assumed trusted
by the Verifier and is assume to be loaded in the TPM during the
execution of the process described in the subsequent sections. The
description of how to create the AK is outside the scope of this
document.
A.2.5.5. Attester Processing
The only signed component is the TPM2B_ATTEST structure, which
returns only the (key's) Name and the signature computed over the
Name but no detailed information about the key. As the Name is
comprised of public information, the Name can be calculated by the
Verifier but only if the Verify knows all the public information
about the Key.
The Attester's processing steps are as follows:
Using the TPM2 command TPM2_Certify obtain the TPM2B_ATTEST and
TPMT_SIGNATURE structures from the TPM2. The signing key for
TPMT_SIGNATURE is an Attention Key (or AK), which is assumed to be
available to the TPM2 upfront. More details are provided in
Appendix A.2.5.4
The TPM2 command TPM2_Certify takes the following input:
* TPM2 handle for Key (the key to be attested to)
* TPM2 handle for the AK (see Appendix A.2.5.4)
It produces the following output:
* TPM2B_ATTEST in binary format
Ounsworth, et al. Expires 3 September 2025 [Page 36]
Internet-Draft Remote Attestation with CSRs March 2025
* TPMT_SIGNATURE in binary format
Then, using the TPM2 command TPM2_ReadPublic obtain the Keys
TPM2B_PUBLIC structure. While the Key's public information can be
obtained by the Verifier in a number ways, such as storing it from
when the Key was created, this may be impractical in many situations.
As TPM2 provided a command to obtain this information, this
specification will include it in the TPM2 Attestation CSR extension.
The TPM2 command TPM2_ReadPublic takes the following input:
* TPM2 handle for Key (the key to be attested to)
It produces the following output:
* TPM2B_PUBLIC in binary format
A.2.5.6. Verifier Processing
The Verifier has to perform the following steps once it receives the
Evidence:
* Verify the TPM2B_ATTEST using the TPMT_SIGNATURE.
* Use the Key's "expected" Name from the provided TPM2B_PUBLIC
structure. If Key's "expected" Name equals
TPM2B_ATTEST->attestationData then returned TPM2B_PUBLIC is the
verified.
A.2.6. Sample CSR
This CSR demonstrates a certification request for a key stored in a
TPM using the following structure:
Ounsworth, et al. Expires 3 September 2025 [Page 37]
Internet-Draft Remote Attestation with CSRs March 2025
CSR {
attributes {
id-aa-evidence {
EvidenceBundle {
Evidences {
EvidenceStatement {
type: tcg-attest-tpm-certify,
stmt: <TcgAttestTpmCertify_data>
hint: "tpmverifier.example.com"
}
},
certs {
akCertificate,
caCertificate
}
}
}
}
}
Note that this example demonstrates most of the features of this
specification:
* The data type is identified by the OID id-TcgCsrCertify contained
in the EvidenceStatement.type field.
* The signed evidence is carried in the EvidenceStatement.stmt
field.
* The EvidenceStatement.hint provides information to the Relying
Party about which Verifier (software) will be able to correctly
parse this data. Note that the type OID indicates the format of
the data, but that may itself be a wrapper format that contains
further data in a proprietary format. In this example, the hint
says that software from the package "tpmverifier.example.com" will
be able to parse this data.
* The evidence statement is accompanied by a certificate chain in
the EvidenceBundle.certs field which can be used to verify the
signature on the evidence statement. How the Verifier establishes
trust in the provided certificates is outside the scope of this
specification.
This example does not demonstrate an EvidenceBundle that contains
multiple EvidenceStatements sharing a certificate chain.
Ounsworth, et al. Expires 3 September 2025 [Page 38]
Internet-Draft Remote Attestation with CSRs March 2025
=============== NOTE: '\' line wrapping per RFC 8792 ================
-----BEGIN CERTIFICATE REQUEST-----
MIINmzCCDIUCAQAwdTELMAkGA1UEBhMCWloxETAPBgNVBAgMCFByb3ZpbmNlMREwDwYD\
VQQ
HDAhMb2NhbGl0eTETMBEGA1UECgwKaWV0Zi1sYW1wczEXMBUGA1UECwwOaWV0Zi1sYW1\
wcy
1jc3IxEjAQBgNVBAMMCXRlc3Qta2V5MTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQ\
oCg
gEBAN/RvsGNf32W6tIAU4QZgFPs98rPv4ed7QnB9aK/+x8u+\
1qhiTNpNC2me0FsQEDvToRO
Ghkxtiift2RKPaVR2hyF05tthjNDnfDaMqvkNN24rmzTuVZE3Oz86zSWE+\
Lk3ZfWHROVb5Z
TME/VOZdYMAvwyi2fRHa/1cK9F/61WwIpY4qMlLsabSsSmyd8RJ+/\
g3exfCeCYJ73Cu90F0
wNtYOTxVN5o4ELvJdElT99QaC38TFvJ+yW94wQua2/4Lt6cx0I+\
NVDFHLMELwFydVdZspqF
dEGp4X+i59hjD4AFDPOyJJJiF84Zo7+Qf1tIbUCbFV+\
Rmvob7uCiOs8O3ZEL4kCAwEAAaCC
CuEwggrdBgsqhkiG9w0BCRACOzGCCswwggrIMIIC2jCCAtYGBWeBBRQBMIICsgSBkf9U\
Q0e
AFwAiAAs7ZAoM+pOXvuDS3cZXWSGXpKzEfn3C/\
aWh2zIlNmdIvQAEAP9VqgAAAAB96ovmAA
AANwAAAAABIBUBEwAVSCIAIgALRsPuEbWtPA+\
cXiHVz6zdm6DfOYX8urrRWvLWAoEkW8MAI
gALVNyWWGbUmLvXnu/\
dEowodTbdqKJlrhaYITil2pXo7ooEggEAhnwVHoLE43BfVyozOqnx
9VfsdS7U4ZOP4pS04vrfGCLegjXEHjxcMyU3DcJtd7svjw5/IxnLXLD/\
WXAe1H5XbOreOgY
VejzMO16DPWBV2m7LOUvvwSsIRhHJaL5wUxfuLZoWY6Up7Q+\
gFtDvoHfRrKsbeMRoOWwQul
Uok0PhZw0R4ZQyFrc4/rBr9kS9VpmtA+3IMuZ/qujraPqbC/zn1OE20+\
AtiKU6L9kJUtlej
f8RchWn4ffi4ugK4u7RvMQS/lGn+5G1IfVQY55iMKdlHa9nyzknQQBYopF2JP+\
sntC2Zf65
IasWyE7NWOsQSbyr6/\
OSLggeNf5gU8SrRfzaAgSCARYAAQALAAYAcgAAABAAEAgAAAAAAAE
A39G+wY1/fZbq0gBThBmAU+z3ys+/h53tCcH1or/\
7Hy77WqGJM2k0LaZ7QWxAQO9OhE4aGT
G2KJ+3ZEo9pVHaHIXTm22GM0Od8Noyq+\
Q03biubNO5VkTc7PzrNJYT4uTdl9YdE5VvllMwT
9U5l1gwC/DKLZ9Edr/Vwr0X/rVbAiljioyUuxptKxKbJ3xEn7+\
Dd7F8J4JgnvcK73QXTA21
g5PFU3mjgQu8l0SVP31BoLfxMW8n7Jb3jBC5rb/\
gu3pzHQj41UMUcswQvAXJ1V1mymoV0Qa
nhf6Ln2GMPgAUM87IkkmIXzhmjv5B/W0htQJsVX5Ga+\
hvu4KI6zw7dkQviRYXdHBtdmVyaW
ZpZXIuZXhhbXBsZS5jb20wggfmMIIEaTCCA1GgAwIBAgIUfX4oc7u4KUbyz61VtQN5g2\
Ounsworth, et al. Expires 3 September 2025 [Page 39]
Internet-Draft Remote Attestation with CSRs March 2025
A2Q
MQwDQYJKoZIhvcNAQELBQAwdzELMAkGA1UEBhMCWloxETAPBgNVBAgMCFByb3ZpbmNlM\
REw
DwYDVQQHDAhMb2NhbGl0eTETMBEGA1UECgwKaWV0Zi1sYW1wczEXMBUGA1UECwwOaWV0\
Zi1
sYW1wcy1jc3IxFDASBgNVBAMMC3Rlc3Qtcm9vdENBMB4XDTI0MTAyMTIwMTcxMloXDTI\
0MT
EyMDIwMTcxMlowczELMAkGA1UEBhMCWloxETAPBgNVBAgMCFByb3ZpbmNlMREwDwYDVQ\
QHD
AhMb2NhbGl0eTETMBEGA1UECgwKaWV0Zi1sYW1wczEXMBUGA1UECwwOaWV0Zi1sYW1wc\
y1j
c3IxEDAOBgNVBAMMB3Rlc3QtYWswggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIB\
AQD
XjF+XF1wsywJx5e5MT1Q1TD8deZqxkQYGZM9TpW+rvFjnRdSDP88MiLOPYcRIJQ+\
efHvo81
o6IL7n0U0TSmaP63gaMCkOLr2BgNpBHGkfSbN2b16usBrQcYQF+o9NU5Itt/\
s7knvlhNiOb
OeWRBgtNPXeikyHycYjcZgoGd/\
UDvPRiRJ0pSruSBDeS1x0uoTsvep0JSRBUiKh8d7D0H3U
CmZZzVPzVBS1Z/Vl3a3HOjUgoAvXIBzukh/\
5BKdQSh5hfRnXi5v6lJGroWFWvsHVF2PLoOC
2oaIrLZ3UVa05K4wVT/wKbi0OcReufE9rK6CvmHEAUXi1cs+\
jynZfYaFDAgMBAAGjgfAwge
0wgZ4GA1UdIwSBljCBk6F7pHkwdzELMAkGA1UEBhMCWloxETAPBgNVBAgMCFByb3Zpbm\
NlM
REwDwYDVQQHDAhMb2NhbGl0eTETMBEGA1UECgwKaWV0Zi1sYW1wczEXMBUGA1UECwwOa\
WV0
Zi1sYW1wcy1jc3IxFDASBgNVBAMMC3Rlc3Qtcm9vdENBghR5pP+\
xxKsc67pLOqPiIZSU4fg
pzDAMBgNVHRMBAf8EAjAAMAsGA1UdDwQEAwIHgDAQBgNVHSUECTAHBgVngQUIAzAdBgN\
VHQ
4EFgQUH4QfxvcmPg9x21uQW5cfGyfxbMcwDQYJKoZIhvcNAQELBQADggEBAC3Zz6B+\
u1H+7
2CG0j/s6lRPX/YP/DPjh5IIt9HdOJaWc5lsbCvgHSED7N/+voCfCRf7IU2Oh5+2q9+\
9N5AR
inXPmrsPZNyLR8vWkb27/\
hl9OTi0Ly7DtJMtUJTRzq53dZc7kdTDNYpPnbIbanSOW3lSL5E
173C8wyTsp/\
vQKteYTfmsDKw9hXHIU2eSeUpZmKcHShXlbDEEbTuYLJMDASKmMCmPjIgJrS
X/\
18wEoAgo2BVjjzwfhoc2SLnQdikvN6oa6Ee0zYRiImXpM7cuErC88jOr0quURA1U8fsQd
8hYGRUk/6oPMXzIfZKsz/yzAUQ570+mkdd2iFVlqTCQ9eUwggN1MIICXQIUeaT/\
scSrHOu6
Szqj4iGUlOH4KcwwDQYJKoZIhvcNAQELBQAwdzELMAkGA1UEBhMCWloxETAPBgNVBAgM\
CFB
yb3ZpbmNlMREwDwYDVQQHDAhMb2NhbGl0eTETMBEGA1UECgwKaWV0Zi1sYW1wczEXMBU\
GA1
UECwwOaWV0Zi1sYW1wcy1jc3IxFDASBgNVBAMMC3Rlc3Qtcm9vdENBMB4XDTI0MTAyMT\
Ounsworth, et al. Expires 3 September 2025 [Page 40]
Internet-Draft Remote Attestation with CSRs March 2025
IwM
TcwOFoXDTI0MTEyMDIwMTcwOFowdzELMAkGA1UEBhMCWloxETAPBgNVBAgMCFByb3Zpb\
mNl
MREwDwYDVQQHDAhMb2NhbGl0eTETMBEGA1UECgwKaWV0Zi1sYW1wczEXMBUGA1UECwwO\
aWV
0Zi1sYW1wcy1jc3IxFDASBgNVBAMMC3Rlc3Qtcm9vdENBMIIBIjANBgkqhkiG9w0BAQE\
FAA
OCAQ8AMIIBCgKCAQEAxPODF6ujxbdDWuXnzlqzYIO4rpQKolKfKbOFUCB6SjdA5XzArL\
TSY
KD3ZXhqm7unFkmHC2HtqArq5jgvcQ2fzJeNGbcuyJYSwa9WJjJ5qY6gXEY+\
G7sFgZ5ZeEWG
Q+zjrnuJh/PtlhJ2/\
R7wtdC82DAULaxnFjOS6Xm6pUB8RaZEtZ6HwfPUXYgeK9IRG2CbEs8
jkoBQTrSKpdpC0myJrrS0PoTFClDpq61je7uQgU6b9IAOfXi1oX5NdYcfqxcPch4wqbk\
ldK
sjC/i7xMcem8hnb3WUvAmbsLP1I0Fx8nb0ug/T2ED5U9tPBXbKgeD72aU2L9GNs+\
ypE9Azb
TB6cwIDAQABMA0GCSqGSIb3DQEBCwUAA4IBAQBFBMAGsP1xKq4R4bzbWnQ4K2H+\
rYNi8UEQ
zxN6BiANi9+8hbLHfx6gFZlz+QxwVyH6oQnNrsVVDVjEYH4/\
yvy7NdOxVitFfqOYwyaNeK5
oXx1l5otOaObtwzB7RVQNSlipzEVW4RPsJmx/\
8F7yNLtdgooPU0QzUSqDcoKK36E4O3s85x
fyNlEdJ2vJcJ/ZZx5QQlnhNTf5bWlr3U9x6DebeAqs+wvvepdaNzulHBXaKIqAgSx9N+\
Y22
vj+vw8GO4L8HndDPMhdE/Ct1h1yygm65j6haCmQRUTKzj49q6W4NHG7iPea+\
7bgMq7G4LRo
9DSFEfMWOkQeVUSPPiTsaAahMAsGCSqGSIb3DQEBCwOCAQEA1aPYnm8suCRwMTC7kOdO\
jvV
P2+\
2pHxsI5vnLfffFgsaNyoOz97t6bAmQXPQCEcjCQZqAynuJQITBbf5OowrNCOL8YRLaFu
2zUS8H+XJUIU0IYSs3H8UyfeYo5VDKJClU/\
OcSzGgGm6J9JDQiHUuEFrqbpE19aSztpXrEH
9YYP87ANyW9vxpLse2rpE4akcp+V+\
C958KJEoYQc9EfjvM3LqLmzp7pvyUalv21BbOweK8V
IYVK7djq+LCmYwJwdKrOYWmrDyH8P+me8nPtk9BdcvW+sj2qu/\
opZmYEL4KAqAviBW5TzPF
UgQhmMalis/J4WY3Q0tvOMXRQQZCmO2N4Pg==
-----END CERTIFICATE REQUEST-----
A.3. PSA Attestation Token in CSR
The Platform Security Architecture (PSA) Attestation Token is defined
in [I-D.tschofenig-rats-psa-token] and specifies claims to be
included in an Entity Attestation Token (EAT). [I-D.bft-rats-kat]
defines key attestation based on the EAT format. In this section the
platform attestation offered by [I-D.tschofenig-rats-psa-token] is
combined with key attestation by binding the key attestation token
Ounsworth, et al. Expires 3 September 2025 [Page 41]
Internet-Draft Remote Attestation with CSRs March 2025
(KAT) to the platform attestation token (PAT) with the help of the
nonce. For details see [I-D.bft-rats-kat]. The resulting KAT-PAT
bundle is, according to Section 5.1 of [I-D.bft-rats-kat], combined
in a CMW collection [I-D.ietf-rats-msg-wrap].
The encoding of this KAT-PAT bundle is shown in the example below.
EvidenceBundle
+
|
+ Evidences
|
+----> EvidenceStatement
+
|
+-> type: OID for CMW Collection
| 1 3 6 1 5 5 7 1 TBD
|
+-> stmt: KAT/PAT CMW Collection
The value in EvidenceStatement->stmt is based on the KAT/PAT example
from Section 6 of [I-D.bft-rats-kat] and the result of CBOR encoding
the CMW collection shown below (with line-breaks added for
readability purposes):
{
"kat":
h'd28443A10126A058C0A30A5820B91B03129222973C214E42BF31D68
72A3EF2DBDDA401FBD1F725D48D6BF9C8171909C4A40102200121
5820F0FFFA7BA35E76E44CA1F5446D327C8382A5A40E5F29745DF
948346C7C88A5D32258207CB4C4873CBB6F097562F61D5280768C
D2CFE35FBA97E997280DBAAAE3AF92FE08A101A40102200121582
0D7CC072DE2205BDC1537A543D53C60A6ACB62ECCD890C7FA27C9
E354089BBE13225820F95E1D4B851A2CC80FFF87D8E23F22AFB72
5D535E515D020731E79A3B4E47120584056F50D131FA83979AE06
4E76E70DC75C070B6D991AEC08ADF9F41CAB7F1B7E2C47F67DACA
8BB49E3119B7BAE77AEC6C89162713E0CC6D0E7327831E67F3284
1A',
"pat":
h'd28443A10126A05824A10A58205CA3750DAF829C30C20797EDDB794
9B1FD028C5408F2DD8650AD732327E3FB645840F9F41CAB7F1B7E
2C47F67DACA8BB49E3119B7BAE77AEC6C89162713E0CC6D0E7327
831E67F32841A56F50D131FA83979AE064E76E70DC75C070B6D99
1AEC08AD'
}
Ounsworth, et al. Expires 3 September 2025 [Page 42]
Internet-Draft Remote Attestation with CSRs March 2025
A.4. Confidential Compute Architecture (CCA) Platform Token in CSR
The Confidential Compute Architecture (CCA) Platform Token is
described in [I-D.ffm-rats-cca-token] and is also based on the EAT
format. Although the full CCA attestation is composed of Realm and
Platform Evidence, for the purposes of this example only the Platform
token is provided.
EvidenceBundle
+
|
+ Evidences
|
+----> EvidenceStatement
+
|
+-> type: OID for CCA Platform Attestation Toekn
| 1 3 6 1 5 5 7 1 TBD
|
+-> stmt: CCA Platform Token
Although the CCA Platform Token follows the EAT/CMW format, it is
untagged. This is because the encoding can be discerned in the CSR
based on the OID alone. The untagged token based on a sample claim
set is provided below:
(long lines wrapped for readability)
/ Sample Platform Claims Set in CDDL /
{
/ cca-platform-profile / 265:"tag:arm.com,2023:cca_platform#1.0.0"
/ arm-platform-challenge, SHA-256 calculation of ‘RAK’ / 10:
h'c9cdc457ebe981d563b19b5a8e0e3cbef5b944d58e278c9c6779f
77beb65bbd5’
/ arm-platform-lifecycle / 2395: h'3000' /secured/
/ arm-platform-sw-components / 2399: [ {1:"ROTFMC", 2:h'903a36d3a
0a511ecac4548fee8601af54247c110ce220f680a0b274441729105’,
5:h'd4cf61e472d18c8e926ce0d44496674792587c88706e8a123b294
c000895d9ea’},
{1:"ROTFW", 2:h'59d4116525e974b5b62ffd7c4ffcbaa0b98e08263403aeb
6638797132d2af959’, 5:h'd4cf61e472d18c8e926ce0d4449667479
2587c88706e8a123b294c000895d9ea’} ]
/arm-platform-id/ 256: h’ 946338159d767f9f37098a00a60f133b6d57886f
c656f5f9eed13760b4893fa1’
/arm-platform-implementation-id/ 2396: h’0000000000000000000000000
000000000000000000000000000000000000001’
}
Ounsworth, et al. Expires 3 September 2025 [Page 43]
Internet-Draft Remote Attestation with CSRs March 2025
/ This is a full CWT-formatted token. The payload is a sample
/ Platform Claim Set. The main structure /
/ visible is that of the COSE_Sign1. /
61( 18( [
h'a10126', / protected headers /
{}, / empty unprotected headers /
h’a419010978237461673a61726d2e636f6d2c323032333a6363615f706c746
66f726d23312e392e300a580020c9cdc457ebe981d563b19b5a8e0e3cbef5b9
44d58e278c9c6779f77beb65bbd519095b42300019095f82a30166524f54464
d4302580020903a36d3a0a511ecac4548fee8601af54247c110ce220f680a0b
27444172910505580020d4cf61e472d18c8e926ce0d44496674792587c88706
e8a123b294c000895d9eaae0165524f5446575800200259d4116525e974b5b6
2ffd7c4ffcbaa0b98e08263403aeb6638797132d2af95905580020d4cf61e47
2d18c8e926ce0d44496674792587c88706e8a123b294c000895d9ea19010078
20946338159d767f9f37098a00a60f133b6d57886fc656f5f9eed13760b4893
fa11a095c582000000000000000000000000000000000000000000000000000
00000000000001' /payload/
h'cbbfa929cb9b846cb5527d7ef9b7657256412a5f22a6e1a8d3a0c71145022
100db4b1b97913b1cd9d6e11c1fadbc0869882ba6644b9db09d221f198e3286
654b' /signature/
] ) )
/Untagged serialized token/
h'8443a10126a0590141a419010978237461673a61726d2e636f6d2c323032333a
6363615f706c74666f726d23312e392e300a580020c9cdc457ebe981d563b19b5a
8e0e3cbef5b944d58e278c9c6779f77beb65bbd519095b42300019095f82a30166
524f54464d4302580020903a36d3a0a511ecac4548fee8601af54247c110ce220f
680a0b27444172910505580020d4cf61e472d18c8e926ce0d44496674792587c88
706e8a123b294c000895d9eaae0165524f5446575800200259d4116525e974b5b6
2ffd7c4ffcbaa0b98e08263403aeb6638797132d2af95905580020d4cf61e472d1
8c8e926ce0d44496674792587c88706e8a123b294c000895d9ea19010078209463
38159d767f9f37098a00a60f133b6d57886fc656f5f9eed13760b4893fa11a095c
582000000000000000000000000000000000000000000000000000000000000000
015840cbbfa929cb9b846cb5527d7ef9b7657256412a5f22a6e1a8d3a0c7114502
2100db4b1b97913b1cd9d6e11c1fadbc0869882ba6644b9db09d221f198e3286654b'
Realm evidence can be included in a CMW bundle, similar to the PSA
token. In this case, the CSR is constructed as follows:
Ounsworth, et al. Expires 3 September 2025 [Page 44]
Internet-Draft Remote Attestation with CSRs March 2025
EvidenceBundle
+
|
+ Evidences
|
+----> EvidenceStatement
+
|
+-> type: OID for CMW Collection
| 1 3 6 1 5 5 7 1 TBD
|
+-> stmt: Realm Token/Platform Token CMW Collection or
Realm Claim Set/Platform Token CMW Collection
Appendix B. ASN.1 Module
CSR-ATTESTATION-2025
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkix-attest-01(TBDMOD) }
CsrAttestation DEFINITIONS IMPLICIT TAGS ::= BEGIN
EXPORTS ALL;
IMPORTS
Certificate, id-pkix
FROM PKIX1Explicit-2009 -- from [RFC5912]
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-explicit-02(51) }
CertificateChoices
FROM CryptographicMessageSyntax-2010
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) id-mod-cms-2009(58) }
EXTENSION, ATTRIBUTE, AttributeSet{}, SingleAttribute{}
FROM PKIX-CommonTypes-2009 -- from [RFC5912]
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
id-aa
FROM SecureMimeMessageV3dot1
{ iso(1) member-body(2) us(840) rsadsi(113549)
pkcs(1) pkcs-9(9) smime(16) modules(0) msg-v3dot1(21) }
;
Ounsworth, et al. Expires 3 September 2025 [Page 45]
Internet-Draft Remote Attestation with CSRs March 2025
-- Branch for attestation statement types
id-ata OBJECT IDENTIFIER ::= { id-aa (TBD1) }
EVIDENCE-STATEMENT ::= TYPE-IDENTIFIER
EvidenceStatementSet EVIDENCE-STATEMENT ::= {
... -- None defined in this document --
}
ATTESTATION-RESULT ::= TYPE-IDENTIFIER
AttestationResultSet ATTESTATION-RESULT ::= {
... -- None defined in this document --
}
EvidenceStatement ::= SEQUENCE {
type EVIDENCE-STATEMENT.&id({EvidenceStatementSet}),
stmt EVIDENCE-STATEMENT.&Type({EvidenceStatementSet}{@type}),
hint IA5String OPTIONAL
}
AttestationResult ::= SEQUENCE {
type ATTESTATION-RESULT.&id({AttestationResultSet}),
stmt ATTESTATION-RESULT.&Type({AttestationResultSet}{@type}),
}
-- Arc for Evidence types
id-aa-evidence OBJECT IDENTIFIER ::= { id-aa 59 }
-- Arc for Attestation Result types
id-aa-ar OBJECT IDENTIFIER ::= { id-aa (TBD2) }
-- For PKCS#10 (Evidence)
attr-evidence ATTRIBUTE ::= {
TYPE EvidenceBundle
COUNTS MAX 1
IDENTIFIED BY id-aa-evidence
}
-- For CRMF (Evidence)
ext-evidence EXTENSION ::= {
SYNTAX EvidenceBundle
IDENTIFIED BY id-aa-evidence
}
-- For PKCS#10 (Attestation Result)
attr-ar ATTRIBUTE ::= {
TYPE AttestationResultBundle
Ounsworth, et al. Expires 3 September 2025 [Page 46]
Internet-Draft Remote Attestation with CSRs March 2025
COUNTS MAX 1
IDENTIFIED BY id-aa-ar
}
-- For CRMF (Attestation Result)
ext-ar EXTENSION ::= {
SYNTAX AttestationResultBundle
IDENTIFIED BY id-aa-ar
}
EvidenceBundle ::= SEQUENCE {
evidences SEQUENCE SIZE (1..MAX) OF EvidenceStatement,
certs SEQUENCE SIZE (1..MAX) OF CertificateChoices OPTIONAL
-- CertificateChoices MUST NOT contain the depreciated
-- certificate structures or attribute certificates,
-- see Section 10.2.2 of [RFC5652]
}
AttestationResultBundle ::= SEQUENCE SIZE (1..MAX)
OF AttestationResult
END
B.1. TCG DICE Example in ASN.1
This section gives an example of extending the ASN.1 module above to
carry an existing ASN.1-based Evidence Statement. The example used
is the Trusted Computing Group DICE Attestation Conceptual Message
Wrapper, as defined in [TCGDICE1.1].
CsrAttestationDiceExample DEFINITIONS IMPLICIT TAGS ::= BEGIN
IMPORTS
tcg-dice-conceptual-message-wrapper FROM TcgDiceAttestation
DiceConceptualMessageWrapper FROM TcgDiceAttestation
tcg-dice-TcbInfo FROM TcgDiceAttestation
DiceTcbInfo FROM TcgDiceAttestation
EvidenceStatementSet FROM CsrAttestation
;
tcgDiceCmwEvidenceStatementES EVIDENCE-STATEMENT ::= {
DiceConceptualMessageWrapper IDENTIFIED BY tcg-dice-conceptual-
message-wrapper }
tcgDiceTcbInfoEvidenceStatementES EVIDENCE-STATEMENT ::= {
DiceTcbInfo IDENTIFIED BY tcg-dice-TcbInfo }
-- where ConceptualMessageWrapper, tcg-dice-conceptual-message-
Ounsworth, et al. Expires 3 September 2025 [Page 47]
Internet-Draft Remote Attestation with CSRs March 2025
wrapper,
-- DiceTcbInfo, and tcg-dice-TcbInfo
-- are defined in DICE-Attestation-Architecture-Version-1.1-
-- Revision-18_6Jan2024.pdf
EvidenceStatementSet EVIDENCE-STATEMENT ::= {
tcgDiceEvidenceStatementES,
tcgDiceTcbInfoEvidenceStatementES
...
}
END
TcgDiceAttestation DEFINITIONS AUTOMATIC TAGS ::= BEGIN
EXPORTS ALL;
tcg OBJECT IDENTIFIER ::= { 2 23 133 }
tcg-dice OBJECT IDENTIFIER ::= { tcg platformClass(5) dice(4) }
tcg-dice-TcbInfo OBJECT IDENTIFIER ::= { tcg-dice tcbinfo(1) }
tcg-dice-endorsement-manifest-uri OBJECT IDENTIFIER ::= {
tcg-dice manifest-uri(3) }
tcg-dice-Ueid OBJECT IDENTIFIER ::= { tcg-dice ueid(4) }
tcg-dice-MultiTcbInfo OBJECT IDENTIFIER ::= {tcg-dice
multitcbinfo(5) }
tcg-dice-UCCS-evidence OBJECT IDENTIFIER ::= {tcg-dice
uccs-evidence(6) }
tcg-dice-manifest-evidence OBJECT IDENTIFIER ::= {tcg-dice
manifest-evidience(7) }
tcg-dice-MultiTcbInfoComp OBJECT IDENTIFIER ::= {tcg-dice
multitcbinfocomp(8) }
tcg-dice-conceptual-message-wrapper OBJECT IDENTIFIER ::= {
tcg-dice cmw(9) }
tcg-dice-TcbFreshness OBJECT IDENTIFIER ::= { tcg-dice
tcb-freshness(11) }
DiceConceptualMessageWrapper ::= SEQUENCE {
cmw OCTET STRING
}
DiceTcbInfo ::= SEQUENCE {
vendor [0] IMPLICIT UTF8String OPTIONAL,
model [1] IMPLICIT UTF8String OPTIONAL,
version [2] IMPLICIT UTF8String OPTIONAL,
svn [3] IMPLICIT INTEGER OPTIONAL,
layer [4] IMPLICIT INTEGER OPTIONAL,
index [5] IMPLICIT INTEGER OPTIONAL,
fwids [6] IMPLICIT FWIDLIST OPTIONAL,
flags [7] IMPLICIT OperationalFlags OPTIONAL,
Ounsworth, et al. Expires 3 September 2025 [Page 48]
Internet-Draft Remote Attestation with CSRs March 2025
vendorInfo [8] IMPLICIT OCTET STRING OPTIONAL,
type [9] IMPLICIT OCTET STRING OPTIONAL,
flagsMask [10]IMPLICIT OperationalFlagsMask OPTIONAL,
integrityRegisters [11] IMPLICIT IrList OPTIONAL
}
FWIDLIST ::= SEQUENCE SIZE (1..MAX) OF FWID
FWID ::= SEQUENCE {
hashAlg OBJECT IDENTIFIER,
digest OCTET STRING
}
OperationalFlags ::= BIT STRING {
notConfigured (0),
notSecure (1),
recovery (2),
debug (3),
notReplayProtected (4),
notIntegrityProtected (5),
notRuntimeMeasured (6),
notImmutable (7),
notTcb (8),
fixedWidth (31)
}
OperationalFlagsMask ::= BIT STRING {
notConfigured (0),
notSecure (1),
recovery (2),
debug (3),
notReplayProtected (4),
notIntegrityProtected (5),
notRuntimeMeasured (6),
notImmutable (7),
notTcb (8),
fixedWidth (31)
}
IrList ::= SEQUENCE SIZE (1..MAX) OF IntegrityRegister
IntegrityRegister ::= SEQUENCE {
registerName IA5String OPTIONAL,
registerNum INTEGER OPTIONAL,
hashAlg OBJECT IDENTIFIER,
digest OCTET STRING
}
EndorsementManifestURI ::= SEQUENCE {
Ounsworth, et al. Expires 3 September 2025 [Page 49]
Internet-Draft Remote Attestation with CSRs March 2025
emUri UTF8String
}
TcgUeid ::= SEQUENCE {
ueid OCTET STRING
}
DiceTcbInfoSeq ::= SEQUENCE SIZE (1..MAX) OF DiceTcbInfo
DiceTcbInfoComp ::= SEQUENCE SIZE (1..MAX) OF TcbInfoComp
TcbInfoComp ::= SEQUENCE {
commonFields [0] IMPLICIT DiceTcbInfo,
evidenceValues [1] IMPLICIT DiceTcbInfoSeq
}
UccsEvidence ::= SEQUENCE {
uccs OCTET STRING
}
Manifest ::= SEQUENCE {
format ManifestFormat,
manifest OCTET STRING
}
ManifestFormat ::= ENUMERATED {
swid-xml (0),
coswid-cbor (1),
coswid-json (2),
tagged-cbor (3)
}
DiceTcbFreshness ::= SEQUENCE {
nonce OCTET STRING
}
END
B.2. TCG DICE TcbInfo Example in CSR
This section gives an example of extending the ASN.1 module above to
carry an existing ASN.1-based evidence statement. The example used
is the Trusted Computing Group DiceTcbInfo, as defined in
[TCGDICE1.1].
Ounsworth, et al. Expires 3 September 2025 [Page 50]
Internet-Draft Remote Attestation with CSRs March 2025
// SET of CSR Attributes
A0 82 00 8E
// CSR attributes
30 82 00 8A
// OBJECT IDENTIFIER id-aa-evidence (1 2 840 113549 1 9 16 2 59)
06 0B 2A 86 48 86 F7 0D 01 09 10 02 3B
// SET -- This attribute
31 79
// EvidenceBundle ::= SEQUENCE
30 75
// EvidenceStatements ::= SEQUENCE SIZE (1..MAX)
OF EvidenceStatement
30 73
// EvidenceStatement ::= SEQUENCE
30 71
// type: OBJECT IDENTIFIER tcg-dice-TcbInfo
// (2.23.133.5.4.1)
06 06 67 81 05 05 04 01
// stmt: SEQUENCE
30 4E
// CONTEXT_SPECIFIC | version (02)
// version = ABCDEF123456
82 0C 41 42 43 44 45 46 31 32 33 34 35 36
// CONTEXT_SPECIFIC | svn (03)
// svn = 4
83 01 04
// CONTEXT_SPECIFIC | CONSTRUCTED | fwids (06)
A6 2F
// SEQUENCE
30 2D
// OBJECT IDENTIFIER SHA256
06 09 60 86 48 01 65 03 04 02 01
// OCTET STRING
// fwid = 0x0000....00
04 20 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
// CONTEXT_SPECIFIC | vendorInfo (08)
// vendor info = 0x00000000
88 04 00 00 00 00
// CONTEXT_SPECIFIC | type (09)
// type = 0x00000000
89 04 00 00 00 00
// hint: IA5String "DiceTcbInfo.example.com"
0C 17 44 69 63 65 54 63 62 49 6e 66 6f
2e 65 78 61 6d 70 6c 65 2e 63 6f 6d
Ounsworth, et al. Expires 3 September 2025 [Page 51]
Internet-Draft Remote Attestation with CSRs March 2025
// BER only
a0 82 00 8c 30 82 00 88 06 0b 2a 86 48 86 f7 0d
01 09 10 02 3b 30 79 31 77 30 75 30 73 30 71 06
06 67 81 05 05 04 01 30 4e 82 0c 41 42 43 44 45
46 31 32 33 34 35 36 83 01 04 a6 2f 30 2d 06 09
60 86 48 01 65 03 04 02 01 04 20 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 88 04 00 00 00
00 89 04 00 00 00 00 16 17 44 69 63 65 54 63 62
49 6e 66 6f 2e 65 78 61 6d 70 6c 65 2e 63 6f 6d
Appendix C. Acknowledgments
This specification is the work of a design team created by the chairs
of the LAMPS working group. The following persons, in no specific
order, contributed to the work directly, participated in design team
meetings, or provided review of the document.
Richard Kettlewell, Chris Trufan, Bruno Couillard, Jean-Pierre Fiset,
Sander Temme, Jethro Beekman, Zsolt Rózsahegyi, Ferenc Pető, Mike
Agrenius Kushner, Tomas Gustavsson, Dieter Bong, Christopher Meyer,
Carl Wallace, Michael Richardson, Tomofumi Okubo, Olivier Couillard,
John Gray, Eric Amador, Darren Johnson, Herman Slatman, Tiru Reddy,
James Hagborg, A.J. Stein, John Kemp, Daniel Migault and Russ
Housley.
We would like to specifically thank Mike StJohns for his work on an
earlier version of this draft.
We would also like to specifically thank Giri Mandyam for providing
the appendix illustrating the confidential computing scenario, and to
Corey Bonnell for helping with the hackathon scripts to bundle it
into a CSR.
Finally, we would like to thank Andreas Kretschmer, Hendrik
Brockhaus, David von Oheimb, and Thomas Fossati for their feedback
based on implementation experience.
Authors' Addresses
Mike Ounsworth
Entrust Limited
2500 Solandt Road – Suite 100
Ottawa, Ontario K2K 3G5
Canada
Email: mike.ounsworth@entrust.com
Ounsworth, et al. Expires 3 September 2025 [Page 52]
Internet-Draft Remote Attestation with CSRs March 2025
Hannes Tschofenig
Siemens
Email: Hannes.Tschofenig@gmx.net
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@sit.fraunhofer.de
Monty Wiseman
Beyond Identity
United States of America
Email: monty.wiseman@beyondidentity.com
Ned Smith
Intel Corporation
United States
Email: ned.smith@intel.com
Ounsworth, et al. Expires 3 September 2025 [Page 53]