| Internet-Draft | CoSWID RIM | January 2021 |
| Birkholz, et al. | Expires 17 July 2021 | [Page] |
This document specifies the CDDL and usage description for Reference Integrity Measurements (RIM) in Remote Attestation Procedures (RATS). The specification is based on Concise Software Identification (CoSWID) and TCG Reference Integrity Manifest Information Model - based on Host Integrity at Runtime and Start-up (HIRS). Extension points defined in CoSWID used to augment CoSWID tags with new attributes that can express the TCG Reference Integrity Manifest extensions.¶
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Reference Integrity Measurements describe the intended state of (composite) software components installed on a (composite) device. A measurement of all installed software components of a devices allows for assertions about the trustworthiness of the given device. In combination with a root of trust (RoT) for reporting (RTR), these measurements can be refined into evidence and enable Remote ATtestation procedureS (RATS). RATS support the decision process of whether to put trust in the trustworthiness of a device - or not.¶
The RATS architecture [I-D.ietf-rats-architecture] defines the following roles: Verifier, Attester, Endorse, and Relying Party, and Reference Value Provider. The RATS architecture also specifies that attestation Evidence is created by Attesters and consumed by Verifiers. Ultimately, the goal is to enable a Relying Party to put trust in the trustworthiness of a remote peer (the Attester). Attestation Evidence is composed of believable assertions about an Attester's trustworthiness characteristics. In RATS, these assertions are called Claims. The Verifier conducts a set of appraisal procedures in order to assess the compliance of an Attester's trustworthiness characteristics.¶
A prominent appraisal procedure in RATS is the comparison of Claim values included in attestation Evidence with reference Claim values provided by Reference Value Providers (RVP, e.g. a supply chain entity). The comparison of Claim values via Reference Claim Values (RCV) is vital for the assessment of compliance metrics with respect to software components installed on an Attester. A typical objective here is the remediation of vulnerabilities discovered in certain versions of installed software components.¶
The Integrity Measurement Architecture (IMA) of the Linux Security Modules (LSM) provides a detailed Event Log (sometimes also referred to as a Measurement Log) that retains a sequence of hash measurements of every software sub-component (e.g. a firmware, an ELF executable, or a configuration file) that is created and appended to the sequence of measurements that composes the event log before the software component in question is started or read - "first measure, than start".¶
In essence, to enable this appraisal procedure conducted by Verfiers an Attester's IMA provides Event Logs that include the hash values of every started software component and therefore are part of the attestation Evidence an Attester creates. The complementary well-known-values that Verifiers require are included in the Reference Integrity Measurements (RIM). RIMs for software components can be provided via Concise Software Identification (CoSWID) tags created or maintained by RVPs, such as the software creators, manufacturers, vendors, or other trusted third parties (e.g. a certification entity).¶
This document provides an extension to the CoSWID specification defined in [I-D.ietf-sacm-coswid]. The extension adds attributes to CoSWID tags that enable them to express RIMs. One prominent subset of these attributes are illustrated in the TCG Reference Integrity Manifest Information Model [ref] specification. These attributes are added to the existing CoSWID specification via the most general extension point the CoSWID specification provides: $$coswid-extensions. An new map type-definition named "reference-values" is added and is defined in section [ref] of this document.¶
Furthermore, a usage profile for signed CoSWID tags is defined in this specification in support of the software-component structure of systems managed by package managers. Signed CoSWID tags that are aligned with that software model can be used to describe the contents of one or multiple of the packages that make up the contents of a system. In order to minimize the impact on the sizes of packages, it is likely that any CoSWID tags delivered as part of packages as part of a package manager managed system will not contain actual reference values, but instead a link-entry to a CoSWID tag published by the vendor in a repository.¶
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 specification defines two types of attribute sets that can be added to the CoSWID specification via the specified defined extension points:¶
As defined by NIST IR 8060 [ref], there are required "Meta Attributes" for XML SWID tags that have to be included in a SWID tag in order to compose a valid SWID RIM. In this section, these attributes are mapped to CoSWID attributes and corresponding requirements on attributes defined in the CoSWID specification to compose valid NIST IR 8060 signed Payload content in the Concise Software Identity Reference Integrity Measurement (CoSWID RIM) representation.¶
The 'software-meta-entry' type defined in the CoSWID specification includes the optional members 'product', 'colloquial-version', 'revision', and 'edition'. These four members MUST be included in a CoSWID RIM in order to compose a valid Reference Integrity Measurement in alignment with NIST IR 8060. Furthermore, the semantics of the text (tstr) typed values MUST convey content that allows for semantic interoperability in a given scope (e.g., an administrative domain). The software-meta-entries provide vital support for steering decisions made by the RATS verifier role in order to enable discovery and matching of related or additional CoSWID RIM available to or discoverable by the verifier.¶
The following attributes are derived from the TCG Reference Integrity Manifest Information Model [ref] specification. These attributes support the creation of very small CoSWID RIM tags that enable the Remote Integrity Verification (RIV [I-D.fedorkow-rats-network-device-attestation]) of small things, i.e., constrained devices in constrained network environments. In consequence, the majority of the attributes listed in this section represent metadata about firmware and supply chain entities that provide firmware for a device (platform). Analogously to the mandated software-meta-entries illustrated above, the attributes defined in the table below provide more context and enable steering decisions for the appraisal procedures of a Verifier. Consecutively, RIM have to be managed and curated in a consistent manner so that there is no significant threshold for a Verifier to make use of them during an appraisal procedure.¶
The design of the additional RIM attributes in this section is motivated by the vast variety of identifier types used in production today, e.g. endorsement documents [I-D.ietf-rats-architecture] that are enrolled or on-boarded on the Attester itself. It is vital to highlight that this variety can render semantic self-descriptiveness more difficult. Most importantly though: interoperability beats self-descriptiveness. A convergence towards a common identification scheme with respect to software components and its subset that is firmware is highly encouraged - alas not achieved at the time of creating this proposed standard. The following table defines the semantics of the set of new members that are added via the reference-measurement-entry map. The reference-measurement-entry map is added using the $$coswid-extension CDDL extension point.¶
| Attribute Name | Quantity | Description |
|---|---|---|
| payload-type | 0-1 | The value of this attribute MUST be one equivalent of the following three choices. 'direct': the representation used in this RIM (and referred RIMs) is using the CoSWID encoding as its representation. 'indirect': the representation used in referred RIMs ('Support RIMs) is using a different representation than CoSWID as it's encoding. Analogously, a reference to the corresponding specification MUST be provided if the value is set to an equivalent of 'indirect' (see binding-spec-name and binding-spec-version). 'hybrid': the representation used in the referred RIMs ('Support RIMs') is a mix of CoSWID representations and other representations. In this case, a reference to the representation used MUST be included - even if it is the CoSWID representation - for every Support RIM (see 'binding-spec-name' and 'binding-spec-version' definition in this table). |
| platform-configuration-uri-global | 0-1 | A byte-comparable reference to a Platform Configuration URI as defined by the TCG Platform Certificate Profile [ref TCG Platform Certificate Profile, Version 1.1] for X.509v3 certificates that MUST be identical to the URI included in a TCG Platform Certificate pointing to a resource providing a copy of the CoSWID RIM this attribute is included in. |
| platform-configuration-uri-local | 0-1 | A byte-comparable reference to a Platform Configuration URI defined by the TCG Platform Certificate Profile [ref TCG Platform Certificate Profile, Version 1.1] that MUST represent the resource at which a copy of this CoSWID RIM can be found within the (composite) device/platform itself. |
| binding-spec-name | 1 | If the value of 'payload-type' is an equivalent to the enumeration 'indirect', the value of this attribute MUST contain a global unique text (tstr) identifier referring to the specification that defines the representation of the referred RIM in order to enable its decoding. |
| binding-spec-version | 1 | If the value of 'payload-type' is an equivalent to the enumeration 'indirect', the value of this attribute MUST contain a unique version number with respect to the specification represented in the value of 'binding-spec-name'. |
| platform-manufacturer-id | 0-1 | An identifier based on the IANA Private Enterprise Number registry that is assigned to firmware manufacturer. This identifier MUST be included unless the firmware manufacturer and the platform manufacturer are represented by the same text (tstr) value. Analogously, if the firmware manufacturer and the platform manufacturer are represented via the same text (tstr) value, this attribute MAY be omitted. |
| platform-manufacturer-name | 0-1 | An identifier number (uint) value that uniquely represents the firmware manufacturer. This identifier MUST be included unless the firmware manufacturer and the platform manufacturer are represented via the same number (unit) value, this attribute MAY be omitted. |
| platform-model-name | 1 | An identifier text (tstr) value enabling the identification of a certain device model/type composite. The reliability of this identifier is not absolute. In consequence this identifier MUST NOT be omitted. In an case, the use of this identifier requires foresight and preparation as it's purpose supports semantic interoperability. Arbitrary, conflicting, or unresolvable values SHOULD be avoided. |
| platform-version | 0-1 | A byte-comparable reference to a Platform Certificate's 'Manufacturer-Specific Identifier' extension value [ref TCG Platform Certificate Profile, Version 1.1]. |
| firmware-manufacturer-id | 0-1 | An IANA defined unique value that is a Private Enterprise Number (Platform manufacturer unique identifier) that SHOULD be included in a CoSWID RIM that covers firmware. |
| firmware-manufacturer-name | 0-1 | An identifier that is represented as the name of a platform manufacturer via a text (tstr) value that SHOULD be included in a CoSWID RIM that covers firmware. |
| firmware-model-name | 0-1 | An identifier that represents the target platform model via a text (tstr) value that SHOULD be included in a CoSWID RIM. |
| firmware-version | 0-1 | An identifier that is represented as the version number of a specific firmware version corresponding to a given set of platform identifiers and SHOULD be included in a CoSWID RIM. |
| boot-events | 0-1 | A reference to the platform measured boot event logs that can be compared to individual events from the platform measured boot events collected at platform runtime. |
To enable very small CoSWID tags that basically are signed references to full Base RIMs for each software package that ultimately include all the hash values required by the appraisal procedure of a Verifier, the member rim-reference is added using the $$payload-extension CDDL extension point.¶
| Attribute Name | Quantity | Description |
|---|---|---|
| rim-reference | 0-1 | A URI pointing to the CoSWID Base RIM that will list the payload reference measurements (hashes) in case of a minimal CoSWID tag. |
To enable encoding version information into a CoSWID tag for RPM packages, the SWID version scheme value index TBD1 has been registered. RPM versions are defined as epoch:version-release-architecture, where the "epoch:" component is optional. Epoch is a numerical value, which should be considered zero if the epoch component is missing. Version and Release can be any string as long as they do not contain a hyphen (-). Architecture is an alphanumerical string.¶
Sorting of RPM versions is a multi-step process: - The epoch, version and release components are compared in that order, as soon as a difference is found, that is the overall difference. - The epoch component is compared as integers. A higher number means a higher version. - The version and release components are compared alphabetically, until a digit is encountered in both strings, at which point as many digits are consumed from both to form an integer, which is then compared. If the integers are identical, the comparison continues alphabetically. - The architecture component is never sorted. If they are different between two versions, the versions are inequal, not higher or lower.¶
The following CDDL specification uses the existing CDDL extension points as defined in [I-D.ietf-sacm-coswid]:¶
<CODE BEGINS>
$$coswid-extension //= (reference-values => reference-values-entry)
reference-value-entry = {
? payload-type => direct / indirect / hybrid,
? platform-configuration-uri-global => any-uri,
? platform-configuration-uri-local => any-uri,
binding-spec-name => text,
binding-spec-version => text,
platform-manufacturer-id => uint,
platform-manufacturer-name => text,
platform-model-name => text,
? platform-version => uint,
? firmware-manufacturer-id => uint,
? firmware-manufacturer-name => text,
? firmware-model-name => text,
? firmware-version => uint,
? boot-events => [ * boot-event-entry ],
rim-link-hash => bytes,
}
boot-event-entry = {
boot-event-number => uint,
boot-event-type => uint,
boot-digest-list => [ 1* hash-entry ],
boot-event-data => bytes
}
$$payload-extension //= ( ? support-rim-type-kramdown => direct / indirect )
$$payload-extension //= ( ? support-rim-format => text )
$$payload-extension //= ( ? support-rim-uri-global => any-uri )
$$payload-extension //= ( ? rim-reference => any-uri )
reference-measurement = 58
payload-type = 59
payload-rim = 60
platform-configuration-uri-global = 61
platform-configuration-uri-local = 62
binding-spec-name = 63
binding-spec-version = 64
platform-manufacturer-id = 65
platform-manufacturer-name = 66
platform-model-name = 67
platform-version = 68
firmware-manufacturer-id = 69
firmware-manufacturer-name = 70
firmware-model-name = 71
firmware-version = 72
rim-link-hash = 73
support-rim-type-kramdown = 74
support-rim-format = 75
support-rim-uri-global = 76
rim-reference = 77
boot-events = 78
boot-event-number = 79
boot-event-type = 80
boot-digest-list = 81
boot-event-data = 82
direct = 0
indirect = 1
hybrid = 2
<CODE ENDS>¶
To be elaborated on¶
This document has added the following entries to the SWID/CoSWID Version Scheme Values registry at https://www.iana.org/assignments/swid:¶
Index: TBD1
Version Scheme Name: rpm
Specification: See {{rpm-version-scheme}}
¶