| Internet-Draft | Remote Attestation with CSRs | October 2024 |
| Ounsworth, et al. | Expires 23 April 2025 | [Page] |
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).¶
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.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
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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, 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.¶
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.¶
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.¶
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 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.¶
As discussed in RFC 9334, different security and privacy aspects need to be considered. For example, Evidence may need to be protected against replay and Section 10 of RFC 9334 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 RFC 9334. 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 RFC 9334. 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.¶
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:¶
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.¶
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.¶
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.¶
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.¶
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.¶
This document references id-pkix and id-aa, both defined in [RFC5911] and [RFC5912].¶
This document defines the arc depicted in Figure 7.¶
-- Arc for Evidence types
id-ata OBJECT IDENTIFIER ::= { id-pkix (TBD1) }
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 --
}
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
}
In Figure 9, type is an OID that indicates the format of the value of stmt.¶
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".¶
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
}
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.¶
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.¶
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.¶
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 definition to which this Object Identifier shall be bound.¶
Columns:¶
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.¶
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.¶
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 23 133 5 4 1 | tcg-dice-TcbInfo | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 3 | tcg-dice-endorsement-manifest-uri | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 4 | tcg-dice-Ueid | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 5 | tcg-dice-MultiTcbInfo | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 6 | tcg-dice-UCCS-evidence | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 7 | tcg-dice-manifest-evidence | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 8 | tcg-dice-MultiTcbInfoComp | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 9 | tcg-dice-conceptual-message-wrapper | [TCGDICE1.1] | TCG |
| 2 23 133 5 4 11 | tcg-dice-TcbFreshness | [TCGDICE1.1] | TCG |
| 2 23 133 20 1 | tcg-attest-tpm-certify | Private Registry | TCG |
| 1 3 6 1 5 5 7 1 35 | id-pe-cmw | [I-D.ietf-rats-msg-wrap] | IETF |
The current registry values can be retrieved from the IANA online website.¶
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).¶
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.¶
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 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.¶
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 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.¶
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.¶
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.¶
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 the Remote ATtestation prodedureS (RATS) Architecture [RFC9334] sections 6 Roles and Entities, 7 Trust Model, 9 Freshness, 11 Privacy Considerations, and 12 Security Considerations. Implementers should also be aware of any security considerations relating to the specific evidence format being carried within the CSR.¶
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¶
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 } }
}
¶
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.¶
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.¶
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.)¶
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
}
¶
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.¶
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 '_'.¶
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;
¶
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.¶
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;
¶
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;
¶
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.¶
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:¶
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¶
The Verifier has to perform the following steps once it receives the Evidence:¶
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.¶
This example does not demonstrate an EvidenceBundle that contains multiple EvidenceStatements sharing a certificate chain.¶
-----BEGIN CERTIFICATE REQUEST----- MIINnjCCDIgCAQAwcjELMAkGA1UEBhMCQVUxDDAKBgNVBAgMA1FMRDERMA8GA1UE BwwIQnJpc2JhbmUxGzAZBgNVBAoMEmlldGYtMTE5LWhhY2thdGhvbjEWMBQGA1UE CwwNaWV0Zi1jc3ItdGVzdDENMAsGA1UEAwwEa2V5MTCCASIwDQYJKoZIhvcNAQEB BQADggEPADCCAQoCggEBALHs46qywIKk3JpICeppzL7laofTNESwwzov2RNKHp3J CmpnpvK9pn1RycQGxEnCK+hyFUjgezMo656zjPsMlNs2Cb2KLj7W2oP75x8cb/k8 aLbok+4qnnUd+6wvZKOvNuprj/AWeXuebsq6U5R0wFN0yHU1dEzzMpK3DhpDoq61 fRWDy2KSxlt3Vs9YtKYr54+u9DSLEYMmwx/gOEThXy1hQ3hMaJsgBZlCI2vI8NG2 rEGZdyuHyQJhjKVKwsY6MgUoslKpKhkEZIolPKbSDeRHtvrJOtjwSFo3zfuFm03Q /m3xEPn//i0icKwPNm5hVsyS02ZU7FCQuytgJpVW2s8CAwEAAaCCCucwDwYJKoZI hvcNAQkOMQIwADCCCtIGCyqGSIb3DQEJEAI7MYIKwTCCCr0wggq5MIIC2jCCAtYG BWeBBRQBMIICsgSBkf9UQ0eAFwAiAAt4r6q4eL+MRkZVMf4zVfg3vCBxjkAv7lB8 ZnNxaHQNbgAEAP9VqgAAAAAAACLaAAAAAAAAAAABIBUBEwAVSCIAIgALGGteNQ9z gSzgw5UUDHgJOG0UpLZVbstlorgYM1dGRI4AIgALqYkehoHN34Yg7HNO/HOG7/UN bNOVPKp1fg4MTz0DbKAEggEAOFmcmbvoqJL3CRKvCdyEGuIL44kJKPrfLevba85c OTf5m2G+4W57HR8w5gYHozrTVhbx6oUla9rAb3fxC6ViqwMdPqdkFeNtzIc/TB2U hh0yW5gp6GRK5No+JDJ6OKVoqvy2mBZLnUbvTOoGyeYZnuVqK62wL2cKDv0ARRjs QwRBWClo7n3UYs8/0ycXFnYtBzPpSjRMMW79bzG3JsFQLtj/pFzTpBu9fzu88Ylo wm6HmvwdMyTw3Hq4ou2+hcjl1/NVu5EThfiwTsllDpRuGgzp42L1nJHNlLW9KGYQ eyGesvtoX9JTTYG0r72rXA9VMw7OSsmHhRWXL0TJmdUccwSCARYAAQALAAYAcgAA ABAAEAgAAAAAAAEAsezjqrLAgqTcmkgJ6mnMvuVqh9M0RLDDOi/ZE0oenckKamem 8r2mfVHJxAbEScIr6HIVSOB7MyjrnrOM+wyU2zYJvYouPtbag/vnHxxv+TxotuiT 7iqedR37rC9ko6826muP8BZ5e55uyrpTlHTAU3TIdTV0TPMykrcOGkOirrV9FYPL YpLGW3dWz1i0pivnj670NIsRgybDH+A4ROFfLWFDeExomyAFmUIja8jw0basQZl3 K4fJAmGMpUrCxjoyBSiyUqkqGQRkiiU8ptIN5Ee2+sk62PBIWjfN+4WbTdD+bfEQ +f/+LSJwrA82bmFWzJLTZlTsUJC7K2AmlVbazwwXdHBtdmVyaWZpZXIuZXhhbXBs ZS5jb20wggfXMIIEYDCCA0igAwIBAgIUJ65JvgeACRrqSqGBIEY5mH7SiHUwDQYJ KoZIhvcNAQELBQAwdDELMAkGA1UEBhMCQVUxDDAKBgNVBAgMA1FMRDERMA8GA1UE BwwIQnJpc2JhbmUxGzAZBgNVBAoMEmlldGYtMTE5LWhhY2thdGhvbjEWMBQGA1UE CwwNaWV0Zi1jc3ItdGVzdDEPMA0GA1UEAwwGcm9vdENBMB4XDTI0MDcwNzAxMDMx OVoXDTI0MDgwNjAxMDMxOVowcDELMAkGA1UEBhMCQVUxDDAKBgNVBAgMA1FMRDER MA8GA1UEBwwIQnJpc2JhbmUxGzAZBgNVBAoMEmlldGYtMTE5LWhhY2thdGhvbjEW MBQGA1UECwwNaWV0Zi1jc3ItdGVzdDELMAkGA1UEAwwCYWswggEiMA0GCSqGSIb3 DQEBAQUAA4IBDwAwggEKAoIBAQCSMnAsx2LBunwXqcOL0zHHWKctsL2EovzKAZev 9452fqmDpJqcud3m3JLTHBsgBElIniaCuwUutixde1aPRrBHRyqmkrX2j/+SDEX3 iG5nu5Qy6Rp7fZ1DEUPjZhYV2/9TJx/zyEg5BWGj18RhI0zd5Ol60GG6PuS3i2Ob mVk5vP5fbUgLSAfbkDbERaHeCMW3UK4jU7C3rlT4uvbUREBWQCms6z5CllRGEfA1 VboppYeYIitwC0kRM3mZeMDlNDwCd07wQGoDXFpvDJREKBgkdMucYfdIc5dZIp7H 4bdtZrhyIO9wNq2F5YLyCTYbuWGCvnReJa7FKHcUvr4/4BVpAgMBAAGjge0wgeow gZsGA1UdIwSBkzCBkKF4pHYwdDELMAkGA1UEBhMCQVUxDDAKBgNVBAgMA1FMRDER MA8GA1UEBwwIQnJpc2JhbmUxGzAZBgNVBAoMEmlldGYtMTE5LWhhY2thdGhvbjEW MBQGA1UECwwNaWV0Zi1jc3ItdGVzdDEPMA0GA1UEAwwGcm9vdENBghRQ7rf2DEoY njMJYOpzRC+T1bCtgjAMBgNVHRMBAf8EAjAAMAsGA1UdDwQEAwIHgDAQBgNVHSUE CTAHBgVngQUIAzAdBgNVHQ4EFgQUESCd2wrVJVr9vLFDz5gqgrzq2zYwDQYJKoZI hvcNAQELBQADggEBAAG1vzkQMMCbpHKy0ZNu59VOzUO86sP1x/8MuyTSKxNf3r8E dSYHvsrhMlC/mvi3LpyHaQEg67sSC/jYP6xwrqq0uEOJoGr3iiDDtooakM+ozCag PbkQw3kjYvPujzUX2iHej7LHPb8QGVSE4ZhKKthfQCt+8t9+ZRC5U6wqDLAcOFST VwOgnrjFqeCFtjGKWezRovRIGmKmEesoiGA3VZPjf8B+gu9ddLfpNwf/f8GE18Rw eAG37yZhrNB+7sDHofPkRXf40z13EykgobEE5mU/iXJekW0kop6ldSmakIXZ8QZr KZbDzJhJBgfRmOPIDKebRN1+OcsqUCUaDfGFBowwggNvMIICVwIUUO639gxKGJ4z CWDqc0Qvk9WwrYIwDQYJKoZIhvcNAQELBQAwdDELMAkGA1UEBhMCQVUxDDAKBgNV BAgMA1FMRDERMA8GA1UEBwwIQnJpc2JhbmUxGzAZBgNVBAoMEmlldGYtMTE5LWhh Y2thdGhvbjEWMBQGA1UECwwNaWV0Zi1jc3ItdGVzdDEPMA0GA1UEAwwGcm9vdENB MB4XDTI0MDcwNzAxMDMxNloXDTI0MDgwNjAxMDMxNlowdDELMAkGA1UEBhMCQVUx DDAKBgNVBAgMA1FMRDERMA8GA1UEBwwIQnJpc2JhbmUxGzAZBgNVBAoMEmlldGYt MTE5LWhhY2thdGhvbjEWMBQGA1UECwwNaWV0Zi1jc3ItdGVzdDEPMA0GA1UEAwwG cm9vdENBMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAs2+3Q20cUvVf BrZosxB9htUE6hGa44l2dOaXBqLroXu4/i/3jNt7W1TWenrtOSVhxyrefyzqWlGn pBKZ/MtA8iP2vBzUEHpMDP5mcpZgh6kmiNypbg1BTujshUtDZwDdsisfxozQp3z1 0KYTL3m0VUZZSHkbHzY8LJgfPRh93euGVkdwKlwrZuiH19Z3rAOTOET0IjG0ybkb oM/VMBf6R8wOpMJrdsdy3vmO1aQSB/NPjDG5zmjFeg2IpUeIXYnNbIpR4wYMmT4w SIExS392DZdZcjPhCBmo4Bg+TuNJoduNF3vI76AF9MS6Raim8gUU5xRO+C1eOedT z4QcfNc+NwIDAQABMA0GCSqGSIb3DQEBCwUAA4IBAQBW69bpm7cy/qVyZtEwHVzt UcQk6KixM/gmMJMMfaix5n4E0iVtKnEFnAixWSmD+nOws+uieg6kMm10pCVqU6bi VlRQNEyJxVm+Hz2XSycI68W/8nJRg76rtOwSaLIjgCLDNz2ZfEfy9/xLWKtfdRGt ttFtVi/W18cy0EBhxDiQWMKx+WPXqnkC2P1L+lYf6It4ycam6C2XTwcguxpxlivm AcDZeU0Cbc2Ro5Mb6FtqhjDUWBZ6P5j0IN7OYqIF5rYVfvovHrDcoK4xLKD/FS2P IL6geH1tc6allU/BzbthJ3JKYAWpuF2Icoocj5OeL0kDl+rY/aBk6T2s8qwAW8Vb MAsGCSqGSIb3DQEBCwOCAQEAcLTWODv93R8sjE3Ngjyuiy9HfucYNoxrQLzwuKtI FPRqBdyPXYgFh/kNBKSZmye/sPSZN0CJNcO9V2Apz8kjpAlnmff1sEF7Zxxxh3ON sA/F2qwzMfDuKOH2+u12odbznVZHie+QxZhA+rvCWfrrbfOGN7uy05/B4tijshhH wVS4NF274Uraw2og8tG6YTAPaGGxyVckf3gn3yLPnfi/3LhZGTvMcFoM84icmo2V aWDwGZY94LhTse1jLUeiBimQ/I+8qA1zQSXKDRYodY6DRmd04nP7QGdrCmk7am/w w4jj5p8WFydZ4tFAQfwAKY54BUmLvBN/0Fk3B+wjzJuoLQ== -----END CERTIFICATE REQUEST-----¶
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.¶
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'
}
¶
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
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
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
¶
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-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,
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 {
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
¶
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].¶
// 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
// 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
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
¶
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.¶