PKI-based Attestation Evidence
draft-ietf-rats-pkix-evidence-00
| Document | Type | Active Internet-Draft (rats WG) | |
|---|---|---|---|
| Authors | Mike Ounsworth , Richard Kettlewell , Jean-Pierre Fiset , Hannes Tschofenig , Tirumaleswar Reddy.K , Monty Wiseman | ||
| Last updated | 2024-11-18 (Latest revision 2024-10-11) | ||
| Replaces | draft-ounsworth-rats-pkix-evidence | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-ietf-rats-pkix-evidence-00
RATS M. Ounsworth
Internet-Draft R. Kettlewell
Intended status: Standards Track Entrust
Expires: 14 April 2025 J. P. Fiset
Crypto4A
H. Tschofenig
H-BRS
T. Reddy
Nokia
M. Wiseman
Beyond Identity
11 October 2024
PKI-based Attestation Evidence
draft-ietf-rats-pkix-evidence-00
Abstract
This document specifies ASN.1 structures produced by an Attester as
part of the remote attestation procedures and constitute Evidence.
This document follows the Remote ATtestation procedureS (RATS)
architecture where Evidence is sent by an Attester and processed by a
Verifier.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 April 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 5
3. Attestation Evidence . . . . . . . . . . . . . . . . . . . . 5
4. Signing and Verification Procedure . . . . . . . . . . . . . 7
4.1. Signing Procedure . . . . . . . . . . . . . . . . . . . . 7
4.2. Verification Procedure . . . . . . . . . . . . . . . . . 7
5. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Platform Claims . . . . . . . . . . . . . . . . . . . . . 8
5.2. Key Claims . . . . . . . . . . . . . . . . . . . . . . . 9
5.3. Device Identifier . . . . . . . . . . . . . . . . . . . . 9
5.3.1. ueid (Universal Entity ID) Claim . . . . . . . . . . 9
5.3.2. sueids (Semi-permanent UEIDs) Claim (SUEIDs) . . . . 10
5.3.3. oemid (Hardware OEM Identification) Claim . . . . . . 10
5.3.4. hwmodel (Hardware Model) Claim . . . . . . . . . . . 11
5.3.5. hwversion (Hardware Version) Claim . . . . . . . . . 11
5.4. Environment Identifier . . . . . . . . . . . . . . . . . 11
5.5. Software Identifier . . . . . . . . . . . . . . . . . . . 12
5.6. OEM Boot . . . . . . . . . . . . . . . . . . . . . . . . 12
5.7. Dbgstat (Debug Status) . . . . . . . . . . . . . . . . . 12
5.8. Location . . . . . . . . . . . . . . . . . . . . . . . . 12
5.9. Uptime . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.10. Bootcount {sect-bootcount} . . . . . . . . . . . . . . . 13
5.11. Bootseed . . . . . . . . . . . . . . . . . . . . . . . . 13
5.12. dloas (Digital Letters of Approval) . . . . . . . . . . . 13
5.13. Endorsements . . . . . . . . . . . . . . . . . . . . . . 14
5.14. Manifests . . . . . . . . . . . . . . . . . . . . . . . . 14
5.15. Measurements . . . . . . . . . . . . . . . . . . . . . . 14
5.16. Measres (Software Measurement Results) . . . . . . . . . 14
5.17. Submods (Submodules) . . . . . . . . . . . . . . . . . . 14
5.18. iat (Issuance Time) . . . . . . . . . . . . . . . . . . . 14
5.19. intuse (Intended Use) . . . . . . . . . . . . . . . . . . 15
5.20. FipsMode . . . . . . . . . . . . . . . . . . . . . . . . 15
5.21. VendorInfo . . . . . . . . . . . . . . . . . . . . . . . 15
5.22. NestedEvidences . . . . . . . . . . . . . . . . . . . . . 16
5.23. Nonce . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.24. KeyId . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.25. PubKey . . . . . . . . . . . . . . . . . . . . . . . . . 16
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5.26. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.27. NonExportable . . . . . . . . . . . . . . . . . . . . . . 17
5.28. Imported . . . . . . . . . . . . . . . . . . . . . . . . 17
5.29. KeyExpiry . . . . . . . . . . . . . . . . . . . . . . . . 17
5.30. Unrecognized claims . . . . . . . . . . . . . . . . . . . 17
6. Evidence Claims Certificate Extension . . . . . . . . . . . . 17
6.1. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . 18
7. Implementation Considerations . . . . . . . . . . . . . . . . 19
7.1. API for requesting evidence from an attesting device . . 19
7.1.1. Request by ID and claim profile . . . . . . . . . . . 20
7.1.2. Request by claim set . . . . . . . . . . . . . . . . 20
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20
8.1. Publishing Evidence in a certificate . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
10.1. OIDs for Evidence Claims Certificate Extension . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 24
Appendix B. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Trusted execution environments, like secure elements and hardware
security modules (HSMs), are now widely used, which provide a safe
environment to place cryptographic key material and security
sensitive code which uses it, such as signing and decryption
services, secure boot, secure storage, and other essential security
functions. These security functions are typically exposed through a
narrow and well-defined interface, and can be used by operating
system libraries and applications.
Increasingly, parties that rely on these secure elements want
evidence that the security sensitive operations are in fact being
performed within a secure element. This evidence can pertain to the
secure element platform itself, or to the storage and protection
properties of the cryptographic keys, or both. This is generally
referred to as remote attestation, and is covered by the Remote
ATtestation procedureS (RATS) architecture [RFC9344]. This document
species an evidence data format specified in ASN.1 and re-using many
data structures from the PKIX ASN.1 modules [RFC5912] so to be a
convenient format for secure elements and verifiers that are designed
primarily for use within X.509 Public Key Infrastructures.
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When a Certificate Signing Request (CSR) library is requesting a
certificate from a Certification Authority (CA), a PKI end entity may
wish to provide Evidence of the security properties of the trusted
execution environment in which the private key is stored. This
Evidence is to be verified by a Relying Party, such as the
Registration Authority or the Certification Authority as part of
validating an incoming CSR against a given certificate policy.
[I-D.ietf-lamps-csr-attestation] defines how to carry Evidence in
either PKCS#10 [RFC2986] or Certificate Request Message Format (CRMF)
[RFC4211].
[I-D.ietf-lamps-csr-attestation] is agnostic to the content and the
encoding of Evidence. To offer interoperability it is necessary to
define a format that is utilized in a specific deployment
environment. Hardware security modules and other trusted execution
environments, which have been using ASN.1-based encodings for a long
time prefer the use of the same format throughout their software
ecosystem. For those use cases this specification has been
developed.
This specification re-uses the claims defined in [I-D.ietf-rats-eat].
While the encoding of the claims is different to what is defined in
[I-D.ietf-rats-eat], the semantics of the claims is retained. This
specification is not an EAP profile, as defined in Section 6 of
[I-D.ietf-rats-eat]
This specification was designed to meet the requirements published by
the CA Browser Forum to convey properties about hardware security
models, such as non-exportability, which must be enabled for storing
publicly-trusted code-signing keys. Hence, this specification is
supposed to be used with the attestation extension for Certificate
Signing Requests (CSRs), see [I-D.ietf-lamps-csr-attestation].
There are, however, other use cases where remote attestation may also
be used, such as
* A Certification Authority receives a certificate signing request
and wishes to verify that the subject public key was generated in
an HSM (for example to satisfy CA/B Forum subscriber private key
verification requirement). They may also wish to verify that the
operations the HSM will allow for the corresponding private key
are consistent with the purpose of the requested certificate.
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* A user of a Cloud Service Provider's 'Bring Your Own Key' service
wishes to transfer their locally-generated key securely to the
CSP's service by encrypting it under the CSP's public key. As
part of their due diligence on the CSP's key they wish to verify
(1) that it was generated by an HSM and (2) may only be used to
unwrap the key into an HSM (i.e. unwrap permission but not decrypt
permission).
* An auditor of an identity provision service (or a competent end
user) may wish to verify that keys representing end-user
identities are held in an HSM and have permissions that are in
line with the applicable regulations. For example, they may wish
verify that the protection arrangements for assigned keys cannot
be changed.
* A manufacturer needs to provision configuration info, software,
and credentials to a device from remote. With the help of remote
attestation the manufacturer is provided enough information to
verify that information is only sent to devices it has built.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document re-uses the terms defined in [RFC9334] related to
remote attestation. Readers of this document are assumed to be
familiar with the following terms: Evidence, Claim, Attestation
Result, Attester, Verifier, and Relying Party.
3. Attestation Evidence
This specification defines the following Evidence format, which
contains a set of claims. To protect Evidence against modification,
it is protected with a digital signature.
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PkixEvidenceStatement ::= SEQUENCE {
tbsEvidence TBSEvidenceStatement
signatureValues SEQUENCE SIZE (1..MAX) OF BIT STRING,
relatedCertificates [0] IMPLICIT SEQUENCE of Certificate OPTIONAL
-- As defined in RFC 5280
}
TBSEvidenceStatement ::= SEQUENCE {
version INTEGER,
claims SEQUENCE SIZE (1..MAX) OF EVIDENCE-CLAIM,
signatureInfos SEQUENCE SIZE (1..MAX) OF SignatureInfo
}
EVIDENCE-CLAIM ::= TYPE-IDENTIFIER
-- TYPE-IDENTIFIER definition from X.681
TYPE-IDENTIFIER ::= CLASS
{
&id OBJECT IDENTIFIER UNIQUE,
&Type
}
WITH SYNTAX {&Type IDENTIFIED BY &id}
SignatureInfo ::= SEQUENCE {
signatureAlgorithm AlgorithmIdentifier,
sid [0] SignerIdentifier OPTIONAL
}
SignerIdentifier ::= SEQUENCE {
keyId [0] EXPLICIT OCTET STRING OPTIONAL,
subjectKeyIdentifier [1] EXPLICIT SubjectPublicKeyInfo OPTIONAL,
-- As defined in RFC 5280
certificate [2] EXPLICIT Certificate OPTIONAL,
-- As defined in RFC 5280
certHash [3] EXPLICIT CertHash OPTIONAL
}
CertHash ::= SEQUENCE {
hash AlgorithmIdentifier,
value OCTET STRING
}
-- There is bound to already exist an ASN.1 structure for this somewhere.
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL
}
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version MUST be set to 1.
4. Signing and Verification Procedure
EDNOTE: Can we start our versions at some number to avoid versions
that Crypto4A has already used?
4.1. Signing Procedure
1. The message to be signed is the TBSEvidenceStatement, including
the SignatureInfo for each of the signatures to be performed.
2. Each signature is computed in parallel and placed into index of
the signatureValues SEQUENCE that matches the position of the
corresponding SignatureInfo in the signatureInfos sequence.
The signer MUST produce one signature per signatureInfo, it MUST NOT
omit signatures and MUST NOT produce a subset of the signatures
listed in signatureInfos.
4.2. Verification Procedure
1. The message to be verified is the TBSEvidenceStatement.
2. For each signatureInfo, the corresponding verification public key
and signature algorithm is found according to the information
contained in the SignatureInfo for that signature and any
accompanying certificates or key material.
3. For each signature, the message is verified using the value from
the corresponding element of the signatureValue sequence.
4. The PkixEvidenceStatement SHOULD be considered valid if and only
if all signatures are valid; i.e. multiple signatures are to be
treated as an AND mode. This item is a recommendation and not a
hard requirement since verification policy is of course at the
discretion of the Verifier.
EDNOTE: the major change here from the original Crypto4A QASM
Attestation is that the original only includes the claims in the
signature, whereas this includes everything, including the version,
list of signature algorithms. This prevents possible attacks where
those values are manipulated by attackers. We should debate whether
the certificates should be protected by the signature. Pro:
generally better for security to sign everything. Con: in some
contexts, it may be difficult to have the certificates prior to
signing, but that's ok because most evidence carrier formats also
allow you to attach the signatures externally.
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5. Claims
Since no claims are marked as MANDATORY, the sequence 'claims' may be
constituted of differing claims from one instance to the next. This
is expected as each evidence statement may be providing information
to support different use cases.
Once an evidence statement is signed, the Attester is guaranteeing
that all of the claims carried by the evidence statement are true.
It is important to note that multiple claims in the sequence may have
the same 'id'. Implementers should ensure that this case is handled
by verifying logic.
For ease of reading, claims have been separated into two lists:
"platform claims" and "key claims".
5.1. Platform Claims
| Claim | OID | Value | Section | Status |
| -------- | -------- | ------------ | ----------------- | ------------ |
| Oemid | TBD | UTF8String | {{sect-deviceID}} | RECOMMENDED |
| Hwmodel | TBD | UTF8String | {{sect-deviceID}} | RECOMMENDED |
| Hwversion | TBD | UTF8String | {{sect-deviceID}} | RECOMMENDED |
| Hwserial | TBD | UTF8String | {{sect-deviceID}} | RECOMMENDED |
| Ueid | TBD | UTF8String | {{sect-ueid} } | OPTIONAL |
| Sueid | TBD | UTF8String | {{sect-sueid}} | OPTIONAL |
| EnvID | TBD | UTF8String | {{sect-envID}} | OPTIONAL |
| Swname | TBD | UTF8String | {{sect-swID}} | RECOMMENDED |
| Swversion | TBD | UTF8String | {{sect-swID}} | RECOMMENDED |
| Oemboot | TBD | BOOLEAN | {{sect-oemboot}} | RECOMMENDED |
| Location | TBD | ??? | {{sect-location}} | OPTIONAL |
| Dbgstat | TBD | CHOICE | {{sect-dbgstat}} | RECOMMENDED |
| Uptime | TBD | INTEGER | {{sect-uptime}} | OPTIONAL |
| Bootcount | TBD | INTEGER | {{sect-bootcount}}| OPTIONAL |
| Bootseed | TBD | BIT STRING | {{sect-bootseed}} | OPTIONAL |
| Dloas | TBD | SEQUENCE OF Dloa | {{sect-dloas}} | OPTIONAL |
| Endorsements | TBD | SEQUENCE of Endorsement | {{sect-endorsements}} | OPTIONAL |
| Manifests | TBD | ?? | {{sect-manifests}} | OPTIONAL |
| Measurements | TBD | ?? | {{sect-measurements}} | OPTIONAL |
| Measres | TBD | ?? | {{sect-measres}} | OPTIONAL |
| Submods | TBD | ?? | {{sect-submods}} | OPTIONAL |
| Iat | TBD | Time | {{sect-iat}} | RECOMMENDED |
| FipsMode | TBD | Boolean | {{sect-fipsmode}} | RECOMMENDED |
| VendorInfo | TBD | TYPE-IDENTIFIER | {{sect-vendorinfo}}| OPTIONAL |
| NestedEvidences| TBD | SEQUENCE OF PkixEvidenceStatement | {{sect-nestedevidences}} | OPTIONAL |
| Nonce | TBD | OCTET STRING | {{sect-nonce}} | OPTIONAL |
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5.2. Key Claims
| Claim | OID | Value | Section | Status |
| -------- | -------- | ------------ | ----------------- | ------------ |
| KeyId | TBD | IA5String | {{sect-keyid}} | OPTIONAL |
| PubKey | TBD | OCTET STRING | {{sect-pubkey}} | RECOMMENDED |
| Purpose | TBD | CHOICE | {{sect-purpose}} | RECOMMENDED |
| NonExportable | TBD | BOOLEAN | {{sect-nonexportable}} | RECOMMENDED |
| Imported | TBD | BOOLEAN | {{sect-imported}} | RECOMMENDED |
| KeyExpiry | TBD | Time | {{sect-keyexpiry}}| OPTIONAL |
Even though no specific claims are required, a Verifier or Relying
Party MAY reject an Evidence claim if it is missing information
required by the appraisal policy. For example, a Relying Party which
requires a FIPS-certified device SHOULD reject Evidence if it does
not contain sufficient information to determine the FIPS
certification status of the device.
5.3. Device Identifier
Devices assigned a Universal Entity ID compliant with RATS EAT SHOULD
provide this in the Ueid or Sueid claim. Devices with a traditional
human-readable serial number SHOULD provide this in the Hwserial
claim. Both MAY be provided.
The set {OemID, Hwmodel, Hwversion, Hwserial}, when provided, SHOULD
represent a universally unique identification of the device. Where
applicable, {OemID, Hwmodel, Hwversion} SHOULD match the way the
device is identified in relevant endorsements, such as published FIPS
or Common Criteria certificates.
5.3.1. ueid (Universal Entity ID) Claim
The "ueid" claim conveys a UEID, which identifies an individual
manufactured entity. This identifier is a globally unique and
permanent identifier. See Section 4.2.1 of [I-D.ietf-rats-eat] for a
description of this claim. Three types of UEIDs are defined, which
are distinguished via a type field.
The ueid claim is defined as follows:
id-ce-evidence-ueid OBJECT IDENTIFIER ::=
{ id-ce TBD_evidence TBD_ueid }
claim_ueid ::= SEQUENCE {
type INTEGER ( RAND(1), EUI(2), IMEI(3),...),
value OCTET STRING
}
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5.3.2. sueids (Semi-permanent UEIDs) Claim (SUEIDs)
The "sueids" claim conveys one or more semi-permanent UEIDs (SUEIDs).
An SUEID has the same format, characteristics and requirements as a
UEID, but MAY change to a different value on entity life-cycle events
while the ueid claim is permanent. An entity MAY have both a UEID
and SUEIDs, neither, one or the other.
There MAY be multiple SUEIDs and each has a text string label the
purpose of which is to distinguish it from others.
See Section 4.2.2 of [I-D.ietf-rats-eat] for a description of this
claim.
The sueids claim is defined as follows:
id-ce-evidence-sueids OBJECT IDENTIFIER ::=
{ id-ce TBD_evidence TBD_sueids }
claim_sueids ::= SEQUENCE {
label OCTET STRING,
type INTEGER ( RAND(1), EUI(2), IMEI(3),...),
value OCTET STRING
}
5.3.3. oemid (Hardware OEM Identification) Claim
The "oemid" claim identifies the Original Equipment Manufacturer
(OEM) of the hardware.
See Section 4.2.3 of [I-D.ietf-rats-eat] for a description of this
claim.
The value of this claim depends on the type of OEMID and three types
of IDs are defined:
* OEMIDs using a 128-bit random number. Section 4.2.3.1 of
[I-D.ietf-rats-eat] defines this type.
* an IEEE based OEMID using a global registry for MAC addresses and
company IDs. Section 4.2.3.1 of [I-D.ietf-rats-eat] defines this
type.
* OEMIDs using Private Enterprise Numbers maintained by IANA.
Section 4.2.3.3 of [I-D.ietf-rats-eat] defines this type.
The oemid claim is defined as follows:
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id-ce-evidence-oemid OBJECT IDENTIFIER ::=
{ id-ce TBD_evidence TBD_oemid }
claim_oemid ::= SEQUENCE {
type INTEGER ( PEN(1), IEEE(2), RANDOM(3),...),
value OCTET STRING
}
Editor's Note: The value for the PEN is numeric. For the other two
types it is a binary string.
5.3.4. hwmodel (Hardware Model) Claim
The "hwmodel" claim differentiates hardware models, products and
variants manufactured by a particular OEM, the one identified by OEM
ID. It MUST be unique within a given OEM ID. The concatenation of
the OEM ID and "hwmodel" give a global identifier of a particular
product. The "hwmodel" claim MUST only be present if an "oemid"
claim is present.
See Section 4.2.4 of [I-D.ietf-rats-eat] for a description of this
claim.
The hwmodel claim is defined as follows:
id-ce-evidence-hwmodel OBJECT IDENTIFIER ::=
{ id-ce TBD_evidence TBD_hwmodel }
claim_hwmodel ::= OCTET STRING
5.3.5. hwversion (Hardware Version) Claim
The "hwversion" claim is a text string the format of which is set by
each manufacturer. A "hwversion" claim MUST only be present if a
"hwmodel" claim is present.
See Section 4.2.5 of [I-D.ietf-rats-eat] for a description of this
claim.
The hwversion claim is defined as follows:
id-ce-evidence-hwversion OBJECT IDENTIFIER ::=
{ id-ce TBD_evidence TBD_hwwversion }
hwversion ::= OCTET STRING
5.4. Environment Identifier
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EnvID EVIDENCE-CLAIM ::= UTF8String IDENTIFIED BY TBD
This claim MAY be used to identify a partition within a cryptographic
device, or a logical environment that spans multiple cryptographic
devices such as a Security World or a cloud tenant. The format of
these identifiers will be vendor or environment specific.
5.5. Software Identifier
Swname EVIDENCE-CLAIM ::= UTF8String IDENTIFIED BY TBD
-- semantics defined in rats-eat-4.2.6
Swversion EVIDENCE-CLAIM ::= UTF8String IDENTIFIED BY TBD
-- semantics defined in rats-eat-4.2.7
SwName and Swversion together identify the device firmware and SHOULD
match the way the firmware is identified in relevant endorsements,
such as published FIPS or Common Criteria certificates.
5.6. OEM Boot
Oemboot EVIDENCE-CLAIM ::= BOOLEAN IDENTIFIED BY TBD
-- semantics defined in rats-eat-4.2.8
5.7. Dbgstat (Debug Status)
The "dbgstat" claim applies to entity-wide or submodule-wide debug
facilities and diagnostic hardware built into chips. It applies to
any software debug facilities related to privileged software that
allows system-wide memory inspection, tracing or modification of non-
system software like user mode applications.
See Section 4.2.9 of [I-D.ietf-rats-eat] for a description of this
claim and the semantic of the values in the enumerated list.
The dbgstat claim is defined as follows:
Dbgstat EVIDENCE-CLAIM ::= CHOICE {
enabled [0] IMPLICIT NULL,
disabled [1] IMPLICIT NULL,
disabled-Since-Boot [2] IMPLICIT NULL,
disabled-Permanently [3] IMPLICIT NULL,
disabled-Fully-and-Permanently [4] IMPLICIT NULL
}
-- semantics defined in rats-eat-4.2.9
5.8. Location
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Location EVIDENCE-CLAIM ::= ???? IDENTIFIED BY TBD
-- semantics defined in rats-eat-4.2.10
Most HSMs will likely not know their own physical location, but
cryptographic modules on mobile devices may.
5.9. Uptime
The "uptime" claim contains the number of seconds that have elapsed
since the entity or submodule was last booted.
Uptime EVIDENCE-CLAIM ::= INTEGER IDENTIFIED BY TBD
-- semantics defined in rats-eat-4.2.11
5.10. Bootcount {sect-bootcount}
The "bootcount" claim contains a count of the number times the entity
or submodule has been booted. Support for this claim requires a
persistent storage on the device.
Bootcount EVIDENCE-CLAIM ::= INTEGER IDENTIFIER BY TBD
-- semantics defined in rats-eat-4.2.12
5.11. Bootseed
The "bootseed" claim contains a value created at system boot time
that allows differentiation of attestation reports from different
boot sessions of a particular entity (e.g., a certain UEID).
This value is usually public. It is not a secret and MUST NOT be
used for any purpose that a secret seed is needed, such as seeding a
random number generator.
Bootseed EVIDENCE-CLAIM ::= BIT STRING IDENTIFIED BY TBD
-- semantics defined in rats-eat-4.2.13
5.12. dloas (Digital Letters of Approval)
The "dloas" claim conveys one or more Digital Letters of Approval
(DLOAs). A DLOA is a document that describes a certification that an
entity has received. Examples of certifications represented by a
DLOA include those issued by Global Platform and those based on
Common Criteria. The DLOA is unspecific to any particular
certification type or those issued by any particular organization.
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Dloas EVIDENCE-CLAIM ::= SEQUENCE SIZE (1..MAX) OF Dloa
Dloa ::= SEQUENCE IDENTIFIED BY TBD {
dloaRegistrar IA5STRING,
dloaPlatformLabel UTF8STRING,
dloaApplicationLabal [0] IMPLICIT UTF8String OPTIONAL
}
-- semantics defined in rats-eat-4.2.14
5.13. Endorsements
This claim allows referencing third party endorsements; for example
from the device vendor or a certification such as FIPS or Common
Criteria. The content MAY be referenced by URI, or placed directly
inline, but either way, the endorsement content or its URI MUST be
known by the attester at the time that the evidence is generated.
Endorsements EVIDENCE-CLAIM ::= SEQUENCE SIZE (1..MAX) OF Endorsement
Endorsement ::= CHOICE IDENTIFIED BY TBD {
uri [0] IMPLICIT IA5String,
content [1] IMPLICIT OCTET STRING
}
EDNOTE: this needs a bit of thought about what types of endorsements
we will likely see, and whether OCTET STRING is the right format.
5.14. Manifests
TODO -- rats-eat-4.2.15
5.15. Measurements
TODO -- rats-eat-4.2.16
5.16. Measres (Software Measurement Results)
TODO -- rats-eat-4.2.17
5.17. Submods (Submodules)
TODO -- rats-eat-4.2.18
5.18. iat (Issuance Time)
The time at which the evidence was created. Here we differ from the
iat claim in rats-eat-4.3.1 in that we use the PKIX time format Time
instead of the 64-bit CBOR time structure.
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Iat EVIDENCE-CLAIM ::= Time
It is recognized that many HSMs, especially if air-gapped, will not
have an accurate system clock. If the system is not anticipated to
have a reliable clock, then this claim SHOULD be omitted and the
Nonce claim used instead.
5.19. intuse (Intended Use)
Intuse EVIDENCE-CLAIM ::= CHOICE IDENTIFIED BY TBD {
generic [1] IMPLICIT NULL,
registration [2] IMPLICIT NULL,
provisioning [3] IMPLICIT NULL,
certificateIssuance [4] IMPLICIT NULL,
proofOfPossession [5] IMPLICIT NULL
}
-- semantics defined in rats-eat-4.3.3
Note: tags intentionally started at 1 to align with EAT. If the IANA
registry of intended use claims is extended, then the this CHOICE MAY
be extended using the same tag values as indicated in the EAT
registry.
5.20. FipsMode
The cryptographic module was booted in FIPS mode, including the
required self-tests and any other requiremnts of its FIPS
certificate.
Note to verifiers and relying parties: "FIPS Mode" does not imply
"FIPS Certified". For example, a device may have a FIPS Mode even if
the device was never submitted for FIPS certification. This claim
SHOULD only be taken in conjunction with a valid FIPS certification
for this hardware and software version, and appraising any other
claims as required by the FIPS certification.
FipsMode EVIDENCE-CLAIM ::= BOOLEAN IDENTIFIED BY TBD
5.21. VendorInfo
This claim provides a place for vendor to place propriatary data;
i.e. any proprietary data that does not fit in any other claim.
VendorInfo ::= TYPE-IDENTIFIER IDENTIFIED BY TBD
Vendors must specify an OID and data type for their VendorInfo, and
communicate this to verifiers who wish to parse this data.
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5.22. NestedEvidences
NestedEvidences EVIDENCE-CLAIM ::= SEQUENCE OF PkixEvidenceStatement IDENTIFIED BY TBD
Composite devices may produce multiple signed evidence statements
that need to be signed in a hiearchical manner.
PkixEvidenceStatements MAY be nested.
5.23. Nonce
The "nonce" claim is used to provide freshness.
The Nonce claim is used to carry the challenge provided by the caller
to demonstrate freshness of the generated token. The following
constraints apply to the nonce-type:
* The length must be reasonable as it may be processed by end
entities with limited resources. Therefore, it is RECOMMENDED
that the length does not exceed 64 bytes.
* Only a single nonce value is conveyed.
The nonce claim is defined as follows:
Nonce EVIDENCE-CLAIM ::= OCTET STRING IDENTIFIED BY TBD
See Section 4.1 of [I-D.ietf-rats-eat] for a description of this
claim.
5.24. KeyId
An identifier for the subject key. The format MAY be vendor-
specific, but MUST be an ASCII value (IA5String).
KeyId EVIDENCE-CLAIM ::= IA5String IDENTIFIED BY TBD
5.25. PubKey
The subject public key being attested by this evidence.
PubKey EVIDENCE-CLAIM ::= OCTET STRING IDENTIFIED BY TBD
5.26. Purpose
TODO: align with PKCS#11 Purposes
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Purpose EVIDENCE-CLAIM ::= CHOICE IDENTIFIED BY TBD {
... Sign, Decrypt, Unwrap, etc..
}
5.27. NonExportable
TODO align with PKCS#11
NonExportable EVIDENCE-CLAIM ::= BOOLEAN IDENTIFIED BY TBD
5.28. Imported
TODO align with PKCS#11
Imported EVIDENCE-CLAIM ::= BOOLIAN IDENTIFIED BY TBD
5.29. KeyExpiry
If the key has a known expiry time or "not after" date.
KeyExpiry EVIDENCE-CLAIM ::= Time
5.30. Unrecognized claims
This document does not define an exhaustive list of claims. New
claims may be added in the future, including proprietary ones. As
such, parsers SHOULD expect to encounter unrecognized claims, and to
handle them gracefully.
In general, the correct behaviour for a verifier will be to start
with an appraisal policy of claims to look for, and where appropriate
the expected values (for example, FipsMode: true), and any additional
claims that may be in the evidence SHOULD be ignored.
6. Evidence Claims Certificate Extension
This section specifies the syntax and semantics of the Evidence
Claims certificate extension which provides a list of claims
associated with the certificate subject appraised by the CA.
The Evidence Claims certificate extension MAY be included in public
key certificates [RFC5280]. The Evidence Claims certificate
extension MUST be identified by the following object identifier:
id-pe-evidenceclaims OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-pe(1) 34 }
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This extension MUST NOT be marked critical.
The Evidence Claims extension MUST have the following syntax:
EvidenceClaims ::= SET SIZE (1..MAX) OF EVIDENCE-CLAIM
The EvidenceClaims represents an unsigned version of the evidence
claims appraised by the CA. It MUST contain at least one claim. For
privacy reasons, the CA MAY include only a subset of the
EvidenceClaims that were presented to it, for example in an
EvidenceBundle in a CSR. The CA may include in their certificate
profile a list of verified evidence claims (identified by OID) that
MAY be copied from the CSR to the certificate, while any other claims
MUST NOT be copied. By removing the signature from the evidence, the
CA is asserting that it has has verified the Evidence to chain to a
root that the CA trusts, but it is not required to disclose in the
final certificate what that root is.
See Section 8 for a discussion of privacy concerns related to re-
publishing Evidence into a certificate.
6.1. ASN.1 Module
This section provides an ASN.1 Module [X.680] for the Evidence Claims
certificate extension, and it follows the conventions established in
[RFC5912] and [RFC6268].
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<CODE BEGINS>
EvidenceClaimsCertExtn
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-evidenceclaims(TBD) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
EXTENSION
FROM PKIX-CommonTypes-2009 -- RFC 5912
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) } ;
-- Evidence Claims Certificate Extension
ext-EvidenceClaims EXTENSION ::= {
SYNTAX EvidenceClaims
IDENTIFIED BY id-pe-evidenceclaims }
-- EvidenceClaims Certificate Extension OID
id-pe-evidenceclaims OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-pe(1) 34 }
-- Evidence Claims Certificate Extension Syntax
EvidenceClaims ::= SET SIZE (1..MAX) OF EVIDENCE-CLAIM
END
<CODE ENDS>
7. Implementation Considerations
7.1. API for requesting evidence from an attesting device
While it is strictly outside the scope of this document to specify
how a calling application can request evidence from a cryptographic
device, two modes are suggested.
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7.1.1. Request by ID and claim profile
In this mode, the calling application request evidence about a given
entity -- for example, a given EnvID or a given KeyID -- and the
cryptographic device assembles a PkixEvidenceStatement containing as
many claims as it is able to populate. Implementers may have named
evidence profiles if it is desirable for the cryptographic device to
respond with multiple different sets of claims.
7.1.2. Request by claim set
In this mode, the calling application pre-constructs a sequence of
EVIDENCE-CLAIM which is passed in to the attesting device. As a
response, the attesting device returns a structure of type
PkixEvidenceStatement which includes all the expected signatures.
This mode is useful for attesting devices with more resources and
used in situations where the supported evidence profiles may not be
known during implementation.
It is left to the implementer to choose the way that the desired
claims are submitted to the attesting device, including which types
of claims are recognized and how much information is provided by the
caller.
However, when using this mode: - an attesting device MUST reject the
production of a PkixEvidenceStatement if any requested claim is not
recognized; and, - an attesting device MUST reject the production of
a PkixEvidenceStatement if any requested claim is not supported by
the observed state (claim is deemed false).
The use of this mode implies that the attesting device contains the
logic necessary to interpret and verify the submitted claims.
8. Privacy Considerations
8.1. Publishing Evidence in a certificate
The extension MUST NOT publish in the certificate any privacy-
sensitive information that could compromise the end device. What
counts as privacy-sensitive will vary by use case. For example,
consider a few scenarios:
First, consider a Hardware Security Module (HSM) backing a public
code-signing service. The model and firmware patch level could be
considered sensitive as it could give an attacker an advantage in
exploiting known vulnerabilities against un-patched systems.
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Second, consider a certificate issued to a end-user mobile computing
device, any sort of unique identifier could be used as a super-cookie
for tracking purposes.
Third, consider small IoT devices such as un-patchable wireless
sensors. Here there may be no privacy concerns and in fact knowing
exact hardware and firmware version information could help edge
gateways to deny network access to devices with known
vulnerabilities.
Beyond that, a CA MUST have a configurable mechanism to control which
information is to be copied from the provided Evidence into the
certificate, for example this could be configured within a
certificate profile or Certificate Practice Statement (CPS) and this
must be considered on a case-by-base basis. To protect end-user
privacy, CA operators should err on the side of caution and exclude
information that is not clearly essential for security verification
by relying parties. Avoiding unnecessary claims also mitigates the
risk of targeted attacks, where an attacker could exploit knowledge
of hardware versions, models, etc.
9. Security Considerations
This specification re-uses the claims from the EAT specification and
relies on the security protection offered by digital signatures.
This digital signature is computed with the Attestation Key available
on the device, see Section 12.1 of [RFC9334] for considerations
regarding the generation, the use and the protection of these
Attestation Keys. Since the Attester located at the end entity
creates the Evidence with claims defined in this document. This
document inherits the remote attestation architecture described in
[RFC9334]. With the re-use of the claims from [I-D.ietf-rats-eat]
the security and privacy considerations apply also to this document
even though the encoding in this specification is different from the
encoding of claims discussed by [I-D.ietf-rats-eat].
Evidence contains information that may be unique to a device and may
therefore allow to single out an individual device for tracking
purposes. Deployments that have privacy requirements must take
appropriate measures to ensure that claim values can only identify a
group of devices and that the Attestation Keys are used across a
number of devices as well.
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To verify the Evidence, the primary need is to check the signature
and the correct encoding of the claims. To produce the Attestation
Result, the Verifier will use Endorsements, Reference Values, and
Appraisal Policies. The policies may require that certain claims
must be present and that their values match registered reference
values. All claims may be worthy of additional appraisal.
10. IANA Considerations
TBD: OIDs for all the claims listed in this document.
10.1. OIDs for Evidence Claims Certificate Extension
For the EvidenceClaims certificate extension in Section 6, IANA is
requested to assign an object identifier (OID) for the certificate
extension. The OID for the certificate extension should be allocated
in the "SMI Security for PKIX Certificate Extension" registry
(1.3.6.1.5.5.7.1).
For the ASN.1 Module in Section 6.1, IANA is requested to assign an
object identifier (OID) for the module identifier. The OID for the
module should be allocated in the "SMI Security for PKIX Module
Identifier" registry (1.3.6.1.5.5.7.0).
11. References
11.1. Normative References
[I-D.ietf-rats-eat]
Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
Wallace, "The Entity Attestation Token (EAT)", Work in
Progress, Internet-Draft, draft-ietf-rats-eat-31, 6
September 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-eat-31>.
[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>.
[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>.
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[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>.
11.2. Informative References
[I-D.ietf-lamps-csr-attestation]
Ounsworth, M., Tschofenig, H., Birkholz, H., Wiseman, M.,
and N. Smith, "Use of Remote Attestation with
Certification Signing Requests", Work in Progress,
Internet-Draft, draft-ietf-lamps-csr-attestation-11, 18
September 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-lamps-csr-attestation-11>.
[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>.
[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>.
[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>.
[RFC9344] Asaeda, H., Ooka, A., and X. Shao, "CCNinfo: Discovering
Content and Network Information in Content-Centric
Networks", RFC 9344, DOI 10.17487/RFC9344, February 2023,
<https://www.rfc-editor.org/rfc/rfc9344>.
[X.680] ITU-T, "Information technology -- Abstract Syntax Notation
One (ASN.1): Specification of basic notation", n.d.,
<https://www.itu.int/rec/T-REC-X.680>.
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Appendix A. Acknowledgements
This specification is the work of a design team created by the chairs
of the LAMPS working group. This specification has been developed
based on discussions in that design team.
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 Ricardson, Tomofumi Okubo,
Olivier Couillard, John Gray, Eric Amador, Johnson Darren, Herman
Slatman, Tiru Reddy, Thomas Fossati, Corey Bonnell, Argenius Kushner,
James Hagborg.
Appendix B. ASN.1 Module
TBD: Full ASN.1 goes in here.
Authors' Addresses
Mike Ounsworth
Entrust Limited
2500 Solandt Road – Suite 100
Ottawa, Ontario K2K 3G5
Canada
Email: mike.ounsworth@entrust.com
Richard Kettlewell
Entrust Limited
United Kingdom
Email: Richard.Kettlewell@entrust.com
Jean-Pierre Fiset
Crypto4A Technologies Inc.
1550A Laperriere Ave
Ottawa, Ontario K1Z 7T2
Canada
Email: jp@crypto4a.com
Hannes Tschofenig
University of Applied Sciences Bonn-Rhein-Siegx
Email: Hannes.Tschofenig@gmx.net
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Tirumaleswar Reddy
Nokia
Bangalore
Karnataka
India
Email: kondtir@gmail.com
Monty Wiseman
Beyond Identity
United States of America
Email: monty.wiseman@beyondidentity.com
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