Use of Remote Attestation with Certification Signing Requests
draft-ietf-lamps-csr-attestation-14
| Document | Type | Active Internet-Draft (lamps WG) | |
|---|---|---|---|
| Authors | Mike Ounsworth , Hannes Tschofenig , Henk Birkholz , Monty Wiseman , Ned Smith | ||
| Last updated | 2024-10-21 | ||
| Replaces | draft-ounsworth-csr-attestation, draft-stjohns-csr-attest | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-lamps-csr-attestation-14
Network Working Group M. Ounsworth
Internet-Draft Entrust
Intended status: Standards Track H. Tschofenig
Expires: 24 April 2025 Siemens
H. Birkholz
Fraunhofer SIT
M. Wiseman
Beyond Identity
N. Smith
Intel Corporation
21 October 2024
Use of Remote Attestation with Certification Signing Requests
draft-ietf-lamps-csr-attestation-14
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 in Certificate Signing Requests (CSRs)
such as PKCS#10 or Certificate Request Message Format (CRMF) payloads
which provides an elegant and automatable mechanism for transporting
Evidence to a Certification Authority.
Including Evidence 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. These Evidence Claims can include
information about the hardware component's manufacturer, the version
of installed or running firmware, the version of software installed
or running in layers above the firmware, or the presence of hardware
components providing specific protection capabilities or shielded
locations (e.g., to protect keys).
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/.
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Source for this draft and an issue tracker can be found at
https://github.com/lamps-wg/csr-attestation.
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
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This Internet-Draft will expire on 24 April 2025.
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Copyright (c) 2024 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 5
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Information Model . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Interaction with an HSM . . . . . . . . . . . . . . . . . 7
4.2. Encoding Strategy . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Case 1 - Evidence Bundle without Certificate Chain . 9
4.2.2. Case 2 - Evidence Bundle with Certificate Chain . . . 10
4.2.3. Case 3 - Evidence Bundles with Multiple Evidence
Statements and Complete Certificate Chains . . . . . 10
5. ASN.1 Elements . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Object Identifiers . . . . . . . . . . . . . . . . . . . 10
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5.2. Evidence Attribute and Extension . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
6.1. Module Registration - SMI Security for PKIX Module
Identifier . . . . . . . . . . . . . . . . . . . . . . . 14
6.2. Object Identifier Registrations - SMI Security for S/MIME
Attributes . . . . . . . . . . . . . . . . . . . . . . . 14
6.3. "SMI Security for PKIX Evidence Statement Formats"
Registry . . . . . . . . . . . . . . . . . . . . . . . . 14
6.4. Attestation Evidence OID Registry . . . . . . . . . . . . 15
6.4.1. Registration Template . . . . . . . . . . . . . . . . 15
6.4.2. Initial Registry Contents . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
7.1. Freshness . . . . . . . . . . . . . . . . . . . . . . . . 19
7.2. Publishing evidence in an X.509 extension . . . . . . . . 20
7.3. Type OID and verifier hint . . . . . . . . . . . . . . . 21
7.4. Additional security considerations . . . . . . . . . . . 21
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Normative References . . . . . . . . . . . . . . . . . . 21
8.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 24
A.1. Extending EvidenceStatementSet . . . . . . . . . . . . . 24
A.2. TPM V2.0 Evidence in CSR . . . . . . . . . . . . . . . . 25
A.2.1. TCG Key Attestation Certify . . . . . . . . . . . . . 25
A.2.2. TCG OIDs . . . . . . . . . . . . . . . . . . . . . . 25
A.2.3. TPM2 AttestationStatement . . . . . . . . . . . . . . 26
A.2.4. Introduction to TPM2 concepts . . . . . . . . . . . . 26
A.2.5. TCG Objects and Key Attestation . . . . . . . . . . . 26
A.2.6. Sample CSR . . . . . . . . . . . . . . . . . . . . . 31
A.3. PSA Attestation Token in CSR . . . . . . . . . . . . . . 33
Appendix B. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 34
B.1. TCG DICE Example in ASN.1 . . . . . . . . . . . . . . . . 36
B.2. TCG DICE TcbInfo Example in CSR . . . . . . . . . . . . . 39
Appendix C. Acknowledgments . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction
When requesting a certificate from a Certification Authority (CA), a
PKI end entity may wish to include Evidence of the security
properties of its environments in which the private keys are stored
in that request. This Evidence can be appraised by authoritative
entities, such as a Registration Authority (RA) or a CA, or
associated trusted Verifiers as part of validating an incoming
certificate request against given certificate policies. Regulatory
bodies are beginning to require proof of hardware residency for
certain classifications of cryptographic keys. At the time of
writing, the most notable example is the Code-Signing Baseline
Requirements [CSBR] document maintained by the CA/Browser Forum,
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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".
This specification defines an attribute and an extension that allow
for conveyance of Evidence in Certificate Signing Requests (CSRs)
such as PKCS#10 [RFC2986] or Certificate Request Message Format
(CRMF) [RFC4211] payloads which provides an elegant and automatable
mechanism for transporting Evidence to a Certification Authority and
meeting requirements such as those in the CA/B Forum's [CSBR].
As outlined in the RATS Architecture [RFC9334], an Attester
(typically a device) produces a signed collection of Claims that
constitute Evidence about its running environment(s). While the term
"attestation" is not defined in RFC 9334, it was later defined in
[I-D.ietf-rats-tpm-based-network-device-attest], it refers to the
activity of producing and appraising remote attestation Evidence. A
Relying Party may consult an Attestation Result produced by a
Verifier that has appraised the Evidence in making policy decisions
about the trustworthiness of the Target Environment being assessed
via appraisal of Evidence. Section 3 provides the basis to
illustrate in this document how the various roles in the RATS
architecture map to a certificate requester and a CA/RA.
At the time of writing, several standard and several 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 via CSRs
while making minimal assumptions about content or format of the
transported Evidence 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. Evidence
can be 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) 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. The id-aa-evidence CSR Attribute (or CRMF Extension)
contains one EvidenceBundle.
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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.
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 within CSR. The exact
format of the Evidence being conveyed is defined in various standard
and proprietary specifications.
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
Results (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.
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.
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In addition to the background check model, the RATS architecture also
specifies the passport model and combinations. See Section 5.2 of
[RFC9334] for a description of the passport model. The passport
model requires the Attester to transmit Evidence to the Verifier
directly in order to obtain the Attestation Result, which is then
forwarded to the Relying Party. This specification utilizes the
background check model since CSRs are often used as one-shot messages
where no direct real-time interaction between the Attester and the
Verifier is possible.
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 entity. The Verifier functionality can,
however, also be kept separate from the RA functionality, such as a
utility or library provided by the device manufacturer. 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.
The diagram below shows an example data flow where Evidence is
included in a CSR. The CSR is parsed by the Registration Authority
(RA) component of a Certification Authority 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 Certification Authority for
issuance. This diagram overlays PKI entities with RATS roles in
parentheses.
.-----------------.
| | Compare Evidence
| (Verifier) | against Appraisal
| | Policy
'------------+----'
^ |
Evidence | | Attestation
| | Result (AR)
| v
.------------. .----|-------|----. .-----.
| +----------->|----' '--->|--------------->| |
| HSM | Evidence | Reg. Authority | Attestation | CA |
| (Attester) | in CSR | (Relying Party) | Result Meets | |
| | | | Cert policy? | |
'------------' '-----------------' '-----'
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Figure 1: Example data flow demonstrating the architecture with
Background Check Model.
As discussed in RFC 9334 [RFC9334], different security and privacy
aspects need to be considered. 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 from the Attester to the Relying Party via
existing CSR messages.
4. Information Model
4.1. Interaction with an HSM
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.
Cases where the CSR is generated internally to the Attesting
Environment are straightforward: the 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 round-
trips of 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:
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+---------+ +-----+
| Crypto | | HSM |
| Library | | |
+---------+ +-----+
| |
| getEvidence() |
|----------------->|
| |
|<-----------------|
+---------------------+ | |
| CSR = assembleCSR() |-| |
+---------------------+ | |
| |
| sign(CSR) |
|----------------->|
| |
|<-----------------|
| |
Figure 2: Example interaction between CSR generator and HSM.
4.2. Encoding Strategy
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.
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], it is RECOMMENDED to include the
PKCS#10 attribute or the CRMF extension only once in a CSR.
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+-------------------+
| PKCS#10 Attribute |
| or |
| CRMF Extension |
+--------+----------+
|
| (1 or more) +-------------------------+
| +-------------+ CertificateChoices |
| | +-------------------------+
| | | Certificate OR |
| | | OtherCertificateFormat |
(1 or | | +-------------------------+
more) | | (1 or
+--------+---------+-+ more) +-------------------+
| 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.
4.2.1. 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. As a result, an
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.
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4.2.2. Case 2 - Evidence Bundle with Certificate Chain
A single Attester, which shares Evidence together with a certificate
chain. The CSR conveys an EvidenceBundle with a single
EvidenceStatement and a CertificateChoices structure. Figure 5 shows
this use case.
+-------------------------+
| EvidenceBundle |
+.........................+
| EvidenceStatement |
| CertificateChoices |
+-------------------------+
Figure 5: Case 2: Single Evidence Bundle with Certificate Chain.
4.2.3. 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
+-------------------------+
Figure 6: Case 3: Multiple Evidence Structures each with Complete
Certificate Chains.
5. ASN.1 Elements
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 7.
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-- Arc for Evidence types
id-ata OBJECT IDENTIFIER ::= { id-pkix (TBD1) }
Figure 7: New OID Arc for PKIX Evidence Statement Formats
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 8: Definition of EvidenceStatementSet
The expression illustrated in Figure 8 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 UTF8String OPTIONAL
}
Figure 9: Definition of EvidenceStatement
In Figure 9, type is an OID that indicates the format of the value of
stmt.
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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 an optional field, the
hint, is available in the EvidenceStatement structure, as shown in
Figure 9. 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 fully
qualified domain name (FQDN) which uniquely identifies a Verifier.
The problem of mapping hint FQDNs to Verifiers, and the problem of
FQDN collision is out of scope for this specification; it is assumed
that Attester and Verifier makers can manage this appropriately on
their own FQDN trees, however if this becomes problematic then a
public registry may be needed.
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. Tricking an Relying Party into
interacting with an unknown and untrusted Verifier must be avoided.
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".
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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.
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 10: Definitions of CSR attribute and extension
The Extension variant illustrated in Figure 10 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 7.2 for
more discussion.
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 the certificates
needed for different Evidence statements may be contained in certs.
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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.
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. 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.
6.1. Module Registration - SMI Security for PKIX Module Identifier
* Decimal: IANA Assigned - *Replace TBDMOD*
* Description: CSR-ATTESTATION-2023 - id-mod-pkix-attest-01
* References: This Document
6.2. Object Identifier Registrations - SMI Security for S/MIME
Attributes
* Evidence Statement
- Decimal: IANA Assigned - This was early-allocated as 59 so that
we could generate the sample data.
- Description: id-aa-evidence
- References: This Document
6.3. "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.
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* Decimal: IANA Assigned - *replace TBD1*
* Description: id-ata
* References: This document
* Initial contents: None
* Registration Regime: Specification Required. Document must
specify an EVIDENCE-STATEMENT 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
6.4. Attestation Evidence OID Registry
IANA is asked to create a registry that helps developers to find OID/
Evidence mappings.
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.
6.4.1. 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.
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* 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.
6.4.2. 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 | | | |
| 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 | | |
+--------+------------------+--------------------------+------------+
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| 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.
7. 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 11).
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Figure 11 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.
^
|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 11: Interaction between Attesting and Target Environment
Figure 11 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
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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.
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.
7.1. Freshness
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 only specifies how to carry
existing Evidence formats inside a CSR, and so issues of
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synchronizing freshness data is left to be handled, for example, via
certificate management protocols. 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.
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.
7.2. 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.
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7.3. Type OID and verifier hint
The EvidenceStatement includes both a type OID and a free form 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 the type OID and hint will allow an RP to
select between Verifier with which it has pre-established trust
relationships, such as Verifier libraries that have been compiled in
to the RP application. As an example, the hint may take the form of
an FQDN to uniquely identify a Verifier implementation, but 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, Debug, empty CMW contents, or similar values that
could cause the Evidence to appear to be valid when in fact it was
not properly checked.
7.4. 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 evidence
and 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 format being carried within the
CSR.
8. References
8.1. 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>.
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[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>.
[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>.
8.2. 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>.
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[I-D.bft-rats-kat]
Brossard, M., Fossati, T., and H. Tschofenig, "An EAT-
based Key Attestation Token", Work in Progress, Internet-
Draft, draft-bft-rats-kat-04, 3 September 2024,
<https://datatracker.ietf.org/doc/html/draft-bft-rats-kat-
04>.
[I-D.ietf-rats-msg-wrap]
Birkholz, H., Smith, N., Fossati, T., and H. Tschofenig,
"RATS Conceptual Messages Wrapper (CMW)", Work in
Progress, Internet-Draft, draft-ietf-rats-msg-wrap-09, 20
October 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-msg-wrap-09>.
[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>.
[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>.
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[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/>.
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.
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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.
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 used which is the
TPM2_Certify and the TPM2_ReadPublic commands.
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 }
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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.
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:
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* 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.
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;
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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;
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.
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* 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.
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:
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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
* 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.
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A.2.6. Sample CSR
This CSR demonstrates a certification request for a key stored in a
TPM using the following structure:
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.
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This example does not demonstrate an EvidenceBundle that contains
multiple EvidenceStatements sharing a certificate chain.
-----BEGIN CERTIFICATE REQUEST-----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voCfCRf7IU2Oh5+2q9+9N5ARinXPmrsPZNyLR8vWkb27/hl9OTi0Ly7DtJMtUJTR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-----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
(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.
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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'
}
Appendix B. ASN.1 Module
=============== NOTE: '\' line wrapping per RFC 8792 ================
CSR-ATTESTATION-2023
{ 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
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EXPORTS ALL;
IMPORTS
Certificate, id-pkix
FROM PKIX1Explicit-2009
{ 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) }
;
-- Branch for attestation statement types
id-ata OBJECT IDENTIFIER ::= { id-pkix (TBD1) }
EVIDENCE-STATEMENT ::= TYPE-IDENTIFIER
EvidenceStatementSet EVIDENCE-STATEMENT ::= {
... -- None defined in this document --
}
EvidenceStatement ::= SEQUENCE {
type EVIDENCE-STATEMENT.&id({EvidenceStatementSet}),
stmt EVIDENCE-STATEMENT.&Type({EvidenceStatementSet}{@type}),
hint UTF8String OPTIONAL
}
id-aa-evidence OBJECT IDENTIFIER ::= { id-aa 59 }
-- For PKCS#10
attr-evidence ATTRIBUTE ::= {
TYPE EvidenceBundle
COUNTS MAX 1
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IDENTIFIED BY id-aa-evidence
}
-- For CRMF
ext-evidence EXTENSION ::= {
SYNTAX EvidenceBundle
IDENTIFIED BY id-aa-evidence
}
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]
}
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].
=============== NOTE: '\' line wrapping per RFC 8792 ================
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-\
wrapper, DiceTcbInfo, and tcg-dice-TcbInfo
-- are defined in DICE-Attestation-Architecture-Version-1.1-Revision\
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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,
vendorInfo [8] IMPLICIT OCTET STRING OPTIONAL,
type [9] IMPLICIT OCTET STRING OPTIONAL,
flagsMask [10]IMPLICIT OperationalFlagsMask OPTIONAL,
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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 {
emUri UTF8String
}
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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].
=============== NOTE: '\' line wrapping per RFC 8792 ================
// 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)
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06 0B 2A 86 48 86 F7 0D 01 09 10 02 3B
// SET -- This attribute
31 79
// EvidenceBundles ::= SEQUENCE SIZE (1..MAX) OF \
EvidenceBundle
30 77
// 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: UTF8STRING "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
// BER only
A0 82 00 8E 30 82 00 8A 06 0B 2A 86 48 86 F7 0D
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01 09 10 02 3B 30 7B 31 79 30 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 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
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: 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, Michael StJohns, Carl
Wallace, Michael Richardson, Tomofumi Okubo, Olivier Couillard, John
Gray, Eric Amador, Johnson Darren, Herman Slatman, Tiru Reddy, Corey
Bonnell, Argenius Kushner, James Hagborg, A.J. Stein, John Kemp, Ned
Smith.
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 Monty Wiseman for providing
the appendix showing how to carry a TPM 2.0 Attestation, 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, and Daniel Migault and Russ
Housley for their review comments.
Authors' Addresses
Mike Ounsworth
Entrust Limited
2500 Solandt Road – Suite 100
Ottawa, Ontario K2K 3G5
Canada
Email: mike.ounsworth@entrust.com
Hannes Tschofenig
Siemens
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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
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