| Internet-Draft | TUDA | July 2021 |
| Fuchs, et al. | Expires 13 January 2022 | [Page] |
This document defines the method and bindings used to convey Evidence via Time-based Uni-Directional Attestation (TUDA) in Remote ATtestation procedureS (RATS). TUDA does not require a challenge-response handshake and thereby does not rely on the conveyance of a nonce to prove freshness of remote attestation Evidence. TUDA enables the creation of Secure Audit Logs that can constitute believable Evidence about both current and past operational states of an Attester. In TUDA, RATS entities require access to a Handle Distributor to which a trustable and synchronized time-source is available. The Handle Distributor takes on the role of a Time Stamp Authority (TSA) to distribute Handles incorporating Time Stamp Tokens (TST) to the RATS entities. RATS require an Attesting Environment that generates believable Evidence. While a TPM is used as the corresponding root of trust in this specification, any other type of root of trust can be used with TUDA.¶
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This Internet-Draft will expire on 13 January 2022.¶
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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Remote ATtestation procedureS (RATS) describe the attempt to determine and appraise system properties, such as integrity and trustworthiness, of a remote peer -- the Attester -- by the use of a Verifier in support of Relying Parties that intend to interact with the Attester. The Verifier carries the burden of appraisal of detailed Evidence about an Attester's trustworthiness. Evidence is generated by the Attester and consumed by the Verifier. To support security decisions, the Verifier generates digestable Attestation Results that can be easily consumed by Relying Parties. The RATS architecture specifies the corresponding concepts and terms [I-D.ietf-rats-architecture].¶
TUDA uses the architectural constituents of the RATS Architecture, such as the roles Attester and Verifier, and defines a method to convey Conceptual Messages between them. TUDA uses the Uni-Directional Remote Attestation interaction model described in [I-D.ietf-rats-reference-interaction-models]. While the Conceptual Message focused on in this document is RATS Evidence, any type of Conceptual Message content that requires a believable indication about the message's content freshness can be conveyed with TUDA (e.g. Attestation Results).¶
The conveyance of Evidence in RATS must ensure that Evidence always remains integrity protected, tamper-evident, originates from a trustable entity (or group of entities), and is accompanied by a proof of its freshness.¶
In contrast to bi-directional interactions as described by Challenge/Response Remote Attestation in [I-D.ietf-rats-reference-interaction-models], TUDA enables uni-directional conveyance in the interactions between Attester and Verifier. TUDA allows a Verifier to receive Evidence from an Attester without solicitation. Conversely, it allows a Verifier to retrieve Evidence from an Attester without it being generated ad-hoc. Exemplary applications of TUDA are the creation of beacons in vehicular environments [IEEE1609] or authentication mechanisms based on EAP [RFC5247].¶
The generation of Evidence in RATS requires an Attesting Environment. In this specification, the root of trust acting as an Attesting Environment is a Trusted Platform Module (TPM, see [TPM12] and [TPM2]). The Protected Capabilities [TCGGLOSS] provided by a TPM support various activities in RATS, e.g., Claims collection and Evidence generation.¶
A trusted coupling of Evidence generation with a global timescale is enabled via a Handle Distributor. Handles generated by a Handle Distributor can include nonces, signed timestamps, or other structured or opaque content used as qualifying data in Evidence generation. In TUDA, all RATS entities, such as the entities taking on the roles of Attester and Verifier, can receive signed timestamps from the Handle Distributor. These trusted timestamps replace nonces in Evidence generation and Evidence appraisal [I-D.ietf-rats-reference-interaction-models].¶
Nonces enable an implicit time-keeping in which the freshness of Evidence is inferred by recentness. Recentness is estimated via the time interval between sending a nonce as part of a challenge for Evidence and the reception of Evidence based on that nonce (as outlined in the interaction model depicted in section 8.1 in [I-D.ietf-rats-reference-interaction-models]). Conversely, the omission of nonces in TUDA allows for explicit time-keeping where freshness is not inferred from recentness. Instead, a cryptographic binding of a trusted synchronization to a global timescale in the Evidence itself allows for Evidence that can prove past operational states of an Attester. To capture and support this concept, this document introduces the term Forward Authenticity.¶
A property of secure communication protocols, in which later compromise of the long-term keys of a data origin does not compromise past authentication of data from that origin. Forward Authenticity is achieved by timely recording of authenticity Claims from Target Environments (via "audit logs" during "audit sessions") that are authorized for this purpose and trustworthy (via endorsed roots of trusts, for example), in a time-frame much shorter than that expected for the compromise of the long-term keys.¶
Forward Authenticity enables new levels of assurance and can be included in basically every protocol, such as ssh, YANG Push, router advertisements, link layer neighbor discovery, or even ICMP echo requests.¶
Time-Based Uni-directional Attestation is designed to:¶
This document uses the terms defined in the RATS Architecture [I-D.ietf-rats-architecture] and by the RATS Reference Interaction Models [I-D.ietf-rats-reference-interaction-models].¶
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.¶
Based on the RATS Architecture, the processing of TPM generated Evidence can be separated in three activities.¶
The retrieval of signed digests from an RTR based on a sequence of collected Claims about software component integrity (measurements).¶
The transfer of Evidence from the Attester to the Verifier via the Internet.¶
The validation of Evidence signatures as well as the assessment of Claim values in Evidence by comparing them with Reference Values.¶
TUDA is specified in support of these RATS activities that align with the definitions presented in [PRIRA] and [TCGGLOSS].¶
Remote attestation Evidence is composed of a set of Claims (assertions about the trustworthiness of an Attester's Target Environments) that is accompanied by a proof of its veracity -- typically a signature based on shielded, private, and potentially use-restricted key material used as an Authentication Secret as specified in section 6 of [I-D.ietf-rats-reference-interaction-models] (or a secure channel as illustrated in [I-D.birkholz-rats-uccs]). As key material alone is typically not self-descriptive with respect to its intended use (its semantics), the Evidence created via TUDA MUST be accompanied by two kinds of certificates that are cryptographically associated with a trust anchor (TA) [RFC4949] via certification paths:¶
If a Verifier decides to trust the TA of both an AK-Cert and an EK-Cert presented by an Attester -- and thereby the included Claims about the trustworthiness of an Attester's Target Environments -- the Evidence generated by the Attester can be considered trustable and believable. Ultimately, all trustable and believable Evidence MUST be appraised by a Verifier in order to assess the trustworthiness of the corresponding Attester. Assertions represented via Claims MUST NOT be considered believable by themselves.¶
In this document, Evidence is generated via TPMs that come with an AK-Cert and a EK-Cert as a basis for believable Evidence generation.¶
Evidence generated by a TPM for TUDA is based on measured hash values of all software components deployed in Target Environments (see section 4.2. in [I-D.ietf-rats-architecture]) before they are executed ("measure then execute"). The underlying concept of "Attestation Logs" is elaborated on in Section 2.4.2. of [I-D.fedorkow-rats-network-device-attestation]. This concept is implemented, for example, in the Linux kernel where it is called the Linux Integrity Measurement Architecture (IMA) [Safford] and used to generates such a sequence of hash values. A representation for conveyance of corresponding event logs is described in the Canonical Event Log [CEL] specification. Open source solutions, for example, based on [RFC5209] use an IMA log to enable remote attestation [Steffens].¶
An Attester MUST generate such an event/measurement log.¶
A hash value of a software component is created before it is executed by Attesters. These hash values are typically represented as event log entries referred to as measurements, which often occur in large quantities. Capabilities such as Linux IMA can be used to generate these measurements on an Attester. Measurements are chained by Attesters using a rolling hash function. A TPM acts as a root of trust for storage (RTS) by providing an Extend ([TPM12], [TPM2]) operation to feed hash values in a rolling hash function. Each measurement added to the sequence of all measurements results in a new current digest hash value. A TPM acts as a root of trust for reporting (RTR) by providing Quote ([TPM12], [TPM2]) operations to generate a digest of all currently extended hash values as Evidence.¶
TUDA requirements on TPM primitive operations and the information elements processed by them are illustrated using pseudocode in Appendix C and D.¶
The primitive operations used to generate an initial set of measurements at the beginning of an Attester's boot sequence MUST be provided by a Root of Trust for Measurement (RTM) that is a system component of the Attester. An RTM MUST be trusted via trust-relationships to TAs enabled by appropriate Endorsements (e.g.,EK-Certs). If a Verifier cannot trust an RTM, measurements based on values generated by the RTM MUST be considered invalid. At least one RTM MUST be accessible to the first Attesting Environment in Attester conducting Layered Attestation (see section 4.3. in [I-D.ietf-rats-architecture]). An RTM MAY aggregate and retain measurements until the first RTS becomes available in a Layered Attestation procedure -- instead of feeding measurements into an RTS, instantly. The Protection Capabilities of an RTM to also act as a temporary RTS MUST be trusted via trust-relationships to TAs enabled by appropriate Endorsements. System components supporting the use of a TPM typically include such an appropriate RTM. In general, feeding measurements from an initial RTM into a TPM is automated and separated from Protected Capabilities that provide Claims collection from Target Environments that are regular execution environments. A TPM providing the Protection Capabilities for an isolated and shielded location to feed measurements into (integrity and confidentiality) is an appropriate RTS for TUDA.¶
The primitive operations used to store and chain measurements via a rolling hash function MUST be provided by an appropriate root of trust for storage (RTS) that is a system component of the Attester. An RTS MUST be trusted via trust-relationships to TAs enabled by appropriate Endorsements (e.g.,EK-Certs). If a Verifier cannot trust an RTS, Evidence generated based on digest values acquired from the RTS MUST be considered invalid. An RTS MUST be accessible to all Attesting Environments that are chained in a Layered Attestation procedure. A TPM providing the primitive operation for Extend is an appropriate RTM for TUDA.¶
The primitive operations used to generate Evidence based on digests MUST be provided by roots of trust for reporting (RTR) that are system components of the Attester. An RTR MUST be be trusted via trust-relationships to TAs enabled by appropriate Endorsements (e.g.,EK-Certs). If a Verifier cannot trust an RTR, Evidence generated by the RTR MUST be considered invalid. A TPM providing the primitive operations for Quote is an appropriate RTR for TUDA. In a Composite Device (see Section 3.5. in [I-D.ietf-rats-architecture] conducting a Layered Attestation procedure, Attesting Environments MAY not be TPMs. At least one Attesting Environment MUST be a TPM. At least one TPM MUST act as an RTR. Attesting Environments that are not TPMs MUST NOT act as an RTR.¶
A concise definition of the terms RTM, RTS, and RTR can be found in the Trusted Computing Group (TCG) Glossary [TCGGLOSS]. An RTS and an RTR are often tightly coupled. In TUDA, a Trusted Platform Module (TPM, see [TPM12] and [TPM2]) takes on the roles of an RTS and an RTR. The specification in this document requires the use of a TPM as a component of the Attester. The protocol part of this specification can also be used with other RTS and RTR as long as essential functional requirements are satisfied (e.g., a trusted relative source of time, such as a tick-counter). A sequence of Layered Attestation using at least an RTM, RTS, and RTR enables an authenticated boot sequence typically referred to as Secure Boot.¶
The sequence of measurements that is extended into the RTS provided by a TPM may not be deterministic due to race conditions that are side-effects of parallelization. Parallelization occurs, for example, between different isolated execution environments or separate software components started in a execution environment. In order to enable the appraisal of Evidence in cases where sequence of measurement varies, a corresponding event log that records all measurements in sequence, such as the IMA log, has to be conveyed next to the Evidence as depicted in section 8.2. in [I-D.ietf-rats-reference-interaction-models].¶
In contrast to Evidence, event logs do not necessarily have to be integrity protected or tamper-evident. Event logs are conveyed to a Verifier in order to compute the reference values required for comparison with digest values (output of TPM Quote operations). While digest values MUST constitute Evidence, measurements in event logs MAY be part of Evidence, but do not have to be MAY be conveyed separately. If the values in event logs or their sequence are tampered with before or during conveyance from an Attester to a Verifier, the corresponding Evidence Appraisal fails. While this dependency reflects the intended behavior of RATS, integrity protected or tamper-evident can be beneficial or convenient in some usage scenarios. Additionally, event logs my allow insights into the composition of an Attester and typically come with confidentiality requirements.¶
In order to compute reference values to compare digest Claims in Evidence with, a Verifier MUST be able to replay the rolling hash function of the Extend operation provided by a TPM (see Section 2.4.2. in [I-D.fedorkow-rats-network-device-attestation]).¶
A Verifier has to replay the event log using its own extend operation with an identical rolling hash function in order to generate reference values as outlined in section 2.4.1. of [I-D.fedorkow-rats-network-device-attestation]. During reply, the validity of each event log record MUST be appraised individually by the Verifier in order to infer if each started software component satisfies integrity requirements. These appraisal procedures require Reference Integrity Measurements/Manifests (RIM) as are provided via [I-D.birkholz-rats-coswid-rim] or [TCGRIM]. Each RIM includes Reference Values that are nominal reference hash values for sets of software components. The Reference Values can be compared with hash values about executed software components included in an event log. A Verifier requires an appropriate set of RIMs to compare every record in an event log successfully. RIMs or other sets Reverence Value are supplied by Reference Value Providers as defined in the RATS Architecture [I-D.ietf-rats-architecture]. Corresponding procedures that enable a Verifier to acquire Reference Values are out-of-scope of this document.¶
Traditional remote attestation protocols typically use bi-directional challenge/response interaction models. Examples include the Platform Trust Service protocol [PTS] or CAVES [PRIRA], where one entity sends a challenge that is included inside the response to prove the freshness of Evidence via recentness. The corresponding interaction model depicted in Section 8.1. of [I-D.ietf-rats-reference-interaction-models] tightly couples the three RATS activities of generating, conveying and appraising Evidence.¶
Time-Based Uni-directional Attestation can decouple these three activities. As a result, TUDA provides additional capabilities, such as:¶
An Attesting Environment that generates Evidence in TUDA MUST support three specific Protected Capabilities:¶
A TPM is capable of providing these Protected Capabilities for TUDA.¶
TUDA defines a set of information elements (IE) that represent a set of Claims, are generated and stored on the Attester, and are intended to be transferred to the Verifier in order to enable the appraisal of Evidence. Each TUDA IE:¶
Traditional Challenge/Response Remote Attestation [I-D.ietf-rats-reference-interaction-models] includes sending a nonce in the challenge to be used in ad-hoc Evidence generation. Using the TPM 1.2 as an example, a corresponding nonce-challenge would be included within the signature created by the TPM_Quote command in order to prove the freshness of a response containing evidence, see e.g. [PTS].¶
In contrast, the TUDA protocol uses the combined output of TPM_CertifyInfo and TPM_TickStampBlob. The former provides a proof about the Attester's state by creating Evidence that a certain key is bound to that state. The latter provides proof that the Attester was in the specified state by using the bound key in a time operation. This combination enables a time-based attestation scheme. The approach is based on the concepts introduced in [SCALE] and [SFKE2008].¶
Each TUDA IE has an individual time-frame, in which it is considered to be fresh (and therefore valid and trustworthy). In consequence, each TUDA IE that composes data in motion is based on different methods of creation.¶
As highlighted above, the freshness properties of a challenge-response based protocol enable implicit time-keeping via a time window between:¶
Given the time-based attestation scheme, the freshness property of TUDA is equivalent to that of bi-directional challenge response attestation, if the point-in-time of attestation lies between:¶
The accuracy of this time-frame is defined by two factors:¶
Since the conveyance of TUDA Evidence does not rely upon a Verifier provided value (i.e. the nonce), the security guarantees of the protocol only incorporate the Handle Distributor and the RoT used. In consequence, TUDA Evidence can even serve as proof of integrity in audit logs with precise point-in-time guarantees.¶
Appendix A contains guidance on how to utilize a REST architecture.¶
Appendix B contains guidance on how to create an SNMP binding and a corresponding TUDA-MIB.¶
Appendix C contains a corresponding YANG module that supports both RESTCONF and CoREDONF.¶
Appendix D.2 contains a realization of TUDA using TPM 1.2 primitives.¶
Appendix D.3 contains a realization of TUDA using TPM 2.0 primitives.¶
The Certificate Authority that provides the certificate for the TSA role of a Handle Distributor (HD)¶
The Certificate Authority that provides the certificate for the AK of the TPM. This is the client platform credential for this protocol. It is a placeholder for a specific CA and AK-Cert is a placeholder for the corresponding certificate, depending on what protocol was used. The specific protocols are out of scope for this document, see also [AIK-Enrollment] and [IEEE802.1AR].¶
Time-Based Uni-Directional Attestation consists of the following seven information elements:¶
The certificate of the Handle Distributor that takes on the role of TSA. The Handle Distributor certificate is used in a subsequent synchronization protocol tokens. This certificate is signed by the HD-CA.¶
A certificate about the Attestation Key (AIK) used. An AK-Cert may be an [IEEE802.1AR] IDevID or LDevID, depending on their setting of the corresponding identity property ([AIK-Credential], [AIK-Enrollment]; see Appendix D.2.1).¶
The reference frame for Evidence is provided by the relative timestamps generated by the TPM. In order to put Evidence into relation with a Real Time Clock (RTC), it is necessary to provide a cryptographic synchronization between these trusted relative timestamps and the regular RTC that is a hardware component of the Attester. To do so, trustable timestamps are acquired from a Handle Distributor.¶
Evidence Generation relies on the capability of the Rot to operate on restricted keys. Whenever the PCR values of an Attesting Environment change, a new restricted key is created that can only be operated as long as the PCRs remain in their current state.¶
In order to prove to the Verifier that this restricted temporary key actually has these properties and also to provide the PCR value that it is restricted, the corresponding signing capabilities of the RoT are used. The TPM creates a signed certificate using the AK about the newly created restricted key.¶
A Verifier requires the means to derive the PCRs' values in order to appraise the trustworthiness of an Attester. As such, a list of those elements that were extended into the PCRs is reported. For certain environments, this step may be optional if a list of valid PCR configurations (in the form of RIM available to the Verifier) exists and no measurement log is required.¶
The actual Evidence is then based on a signed timestamp provided by the RoT using the restricted temporary key that was certified in the steps above. The signed timestamp generated provides the trustable assertion that at this point in time (with respect to the relative time of the TPM s tick counter) a certain configuration existed (namely the PCR values associated with the restricted key). In combination with the synchronization token this timestamp represented in relative time can then be related to the real-time clock.¶
As an option to better assess the trustworthiness of an Attester, a Verifier can request the reference hashes (RIM, sometimes called golden measurements, known-good-values, or nominal values) of all started software components to compare them with the entries in a measurement log. References hashes regarding installed (and therefore running) software can be provided by the manufacturer via SWID tags. SWID tags are provided by the Attester using the Concise SWID representation [I-D.ietf-sacm-coswid] and bundled into a collection (a RIM Manifest [I-D.birkholz-rats-coswid-rim]).¶
These information elements can be sent en bloc, but it is recommended to retrieve them separately to save bandwidth, since these elements have different update cycles. In most cases, retransmitting all seven information elements would result in unnecessary redundancy.¶
Furthermore, in some scenarios it might be feasible not to store all elements on the Attester, but instead they could be retrieved from another location or be pre-deployed to the Verifier. It is also feasible to only store public keys on the Verifier and skip certificate provisioning completely in order to save bandwidth and computation time for certificate verification.¶
An Attester can be in various states during its uptime cycles. For TUDA, a subset of these states (which imply associated information) are important to the Evidence Generation. The specific states defined are:¶
Depending on this "lifetime of state", data has to be transported over the wire, or not. E.g. information that does not change due to a reboot typically has to be transported only once between the Attester and the Verifier.¶
There are three kinds of events that require fresh Evidence to be generated:¶
The third event listed above is variable per application use case and also depends on the precision of the clock included in the RoT. For usage scenarios, in which the Attester would periodically push information to be used in an audit-log, a time-frame of approximately one update per minute should be sufficient. For those usage scenarios, where Verifiers request (pull) fresh Evidence, an implementation could potentially use a TPM continuously to always present the most freshly created Evidence. This kind of utilization can result in a bottle-neck with respect to other purposes: if unavoidable, a periodic interval of once per ten seconds is recommended, which typically leaves about 80% of available TPM resource for other applications.¶
The following diagram is based on the reference interaction model found in section 8.1. of [I-D.ietf-rats-reference-interaction-models] and is enriched with the IE update cycles defined in this section.¶
.----------. .----------.
| Attester | | Verifier |
'----------' '----------'
| |
boot |
| |
valueGeneration(targetEnvironment) |
| => claims |
| .--------------------. |
| <----------handle | | |
| | Handle Distributor | |
| | | handle----------> |
| '--------------------' |
syncTokenGeneration |
| => syncToken |
| |
restrictedKeyGeneration |
restrictedKeyCertify |
| |
evidenceGeneration(handle, authSecIDs, collectedClaims) |
| => evidence |
| |
| pushAKCert ----------------------------------------------> |
| pushSyncToken -------------------------------------------> |
| pushCertifyInfo -----------------------------------------> |
| pushEventLog --------------------------------------------> |
| pushEvidenceon ------------------------------------------> |
| |
| evidenceAppraisal(evidence, eventLog, refClaims)
| attestationResult <= |
~ ~
pcr-change |
| |
restrictedKeyGeneration |
restrictedKeyCertify |
| |
evidenceGeneration(handle, authSecIDs, collectedClaims) |
| => evidence |
| |
| pushCertifyInfo -----------------------------------------> |
| pushEventLog --------------------------------------------> |
| pushEvidenceon ------------------------------------------> |
| |
| evidenceAppraisal(evidence, eventLog, refClaims)
| attestationResult <= |
| |
The uni-directional approach of TUDA requires evidence on how the TPM time represented in ticks (relative time since boot of the TPM) relates to the standard time provided by the TSA. The Sync Base Protocol (SBP) creates evidence that binds the TPM tick time to the TSA timestamp. The binding information is used by and conveyed via the Sync Token (TUDA IE). There are three actions required to create the content of a Sync Token:¶
The three time-related values --- the relative timestamps provided by the hardware RoT ("left" and "right") and the TSA timestamp --- and their corresponding signatures are aggregated in order to create a corresponding Sync Token to be used as a TUDA Information Element that can be conveyed as evidence to a Verifier.¶
The drift of a clock incorporated in the hardware RoT that drives the increments of the tick counter constitutes one of the triggers that can initiate a TUDA Information Element Update Cycle in respect to the freshness of the available Sync Token.¶
This memo includes requests to IANA, including registrations for media type definitions.¶
TBD¶
There are Security Considerations. TBD¶
TBD¶
Each of the seven data items is defined as a media type (Section 8). Representations of resources for each of these media types can be retrieved from URIs that are defined by the respective servers [RFC8820]. As can be derived from the URI, the actual retrieval is via one of the HTTPs ([RFC7230], [RFC7540]) or CoAP [RFC7252]. How a client obtains these URIs is dependent on the application; e.g., CoRE Web links [RFC6690] can be used to obtain the relevant URIs from the self-description of a server, or they could be prescribed by a RESTCONF data model [RFC8040].¶
SNMPv3 (RFC 3411, [STD62]) is widely available on computers and also constrained devices. To transport the TUDA information elements, an SNMP MIB is defined below which encodes each of the seven TUDA information elements into a table. Each row in a table contains a single read-only columnar SNMP object of datatype OCTET-STRING. The values of a set of rows in each table can be concatenated to reconstitute a CBOR-encoded TUDA information element. The Verifier can retrieve the values for each CBOR fragment by using SNMP GetNext requests to "walk" each table and can decode each of the CBOR-encoded data items based on the corresponding CDDL [RFC8610] definition.¶
Design Principles:¶
The following table summarizes the object groups, tables and their indexes, and conformance requirements for the TUDA MIB:¶
| Group/Table | Cycle | Instance | Fragment | Required |
|---|---|---|---|---|
| General | x | |||
| AIKCert | x | x | x | |
| TSACert | x | x | x | |
| SyncToken | x | x | x | |
| Restrict | x | x | ||
| Measure | x | x | ||
| VerifyToken | x | x | ||
| SWIDTag | x | x | x |
A tudaV1<Group>CycleIndex is the:¶
A tudaV1<Group>InstanceIndex is the:¶
A tudaV1<Group>FragmentIndex is the:¶
The General group in the TUDA MIB is analogous to the System group in the Host Resources MIB [RFC2790] and provides context information for the TUDA attestation process.¶
The Verify Token group in the TUDA MIB is analogous to the Device group in the Host MIB and represents the verifiable state of a TPM device and its associated system.¶
The SWID Tag group (containing a Concise SWID reference hash profile [I-D.ietf-sacm-coswid]) in the TUDA MIB is analogous to the Software Installed and Software Running groups in the Host Resources MIB [RFC2790].¶
The General group in the TUDA MIB is analogous to the Entity General group in the Entity MIB v4 [RFC6933] and provides context information for the TUDA attestation process.¶
The SWID Tag group in the TUDA MIB is analogous to the Entity Logical group in the Entity MIB v4 [RFC6933].¶
The General group in the TUDA MIB is analogous to the System group in MIB-II [RFC1213] and the System group in the SNMPv2 MIB (RFC 3418, [STD62]) and provides context information for the TUDA attestation process.¶
<CODE BEGINS>
TUDA-V1-ATTESTATION-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, Integer32, Counter32,
enterprises, NOTIFICATION-TYPE
FROM SNMPv2-SMI -- RFC 2578
MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
FROM SNMPv2-CONF -- RFC 2580
SnmpAdminString
FROM SNMP-FRAMEWORK-MIB; -- RFC 3411
tudaV1MIB MODULE-IDENTITY
LAST-UPDATED "202101130000Z" -- 13 January 2021
ORGANIZATION
"Fraunhofer SIT"
CONTACT-INFO
"Andreas Fuchs
Fraunhofer Institute for Secure Information Technology
Email: andreas.fuchs@sit.fraunhofer.de
Henk Birkholz
Fraunhofer Institute for Secure Information Technology
Email: henk.birkholz@sit.fraunhofer.de
Ira E McDonald
High North Inc
Email: blueroofmusic@gmail.com
Carsten Bormann
Universitaet Bremen TZI
Email: cabo@tzi.org"
DESCRIPTION
"The MIB module for monitoring of time-based unidirectional
attestation information from a network endpoint system,
based on the Trusted Computing Group TPM 1.2 definition.
Copyright (C) High North Inc (2021)."
REVISION "202101130000Z" -- 13 January 2021
DESCRIPTION
"Twelfth version, published as draft-birkholz-rats-tuda-04."
REVISION "202007130000Z" -- 13 July 2020
DESCRIPTION
"Eleventh version, published as draft-birkholz-rats-tuda-03."
REVISION "202003090000Z" -- 09 March 2020
DESCRIPTION
"Tenth version, published as draft-birkholz-rats-tuda-02."
REVISION "201909110000Z" -- 11 September 2019
DESCRIPTION
"Ninth version, published as draft-birkholz-rats-tuda-01."
REVISION "201903120000Z" -- 12 March 2019
DESCRIPTION
"Eighth version, published as draft-birkholz-rats-tuda-00."
REVISION "201805030000Z" -- 03 May 2018
DESCRIPTION
"Seventh version, published as draft-birkholz-i2nsf-tuda-03."
REVISION "201805020000Z" -- 02 May 2018
DESCRIPTION
"Sixth version, published as draft-birkholz-i2nsf-tuda-02."
REVISION "201710300000Z" -- 30 October 2017
DESCRIPTION
"Fifth version, published as draft-birkholz-i2nsf-tuda-01."
REVISION "201701090000Z" -- 09 January 2017
DESCRIPTION
"Fourth version, published as draft-birkholz-i2nsf-tuda-00."
REVISION "201607080000Z" -- 08 July 2016
DESCRIPTION
"Third version, published as draft-birkholz-tuda-02."
REVISION "201603210000Z" -- 21 March 2016
DESCRIPTION
"Second version, published as draft-birkholz-tuda-01."
REVISION "201510180000Z" -- 18 October 2015
DESCRIPTION
"Initial version, published as draft-birkholz-tuda-00."
::= { enterprises fraunhofersit(21616) mibs(1) tudaV1MIB(1) }
tudaV1MIBNotifications OBJECT IDENTIFIER ::= { tudaV1MIB 0 }
tudaV1MIBObjects OBJECT IDENTIFIER ::= { tudaV1MIB 1 }
tudaV1MIBConformance OBJECT IDENTIFIER ::= { tudaV1MIB 2 }
--
-- General
--
tudaV1General OBJECT IDENTIFIER ::= { tudaV1MIBObjects 1 }
tudaV1GeneralCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of TUDA update cycles that have occurred, i.e.,
sum of all the individual group cycle counters.
DEFVAL intentionally omitted - counter object."
::= { tudaV1General 1 }
tudaV1GeneralVersionInfo OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..255))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Version information for TUDA MIB, e.g., specific release
version of TPM 1.2 base specification and release version
of TPM 1.2 errata specification and manufacturer and model
TPM module itself."
DEFVAL { "" }
::= { tudaV1General 2 }
--
-- AIK Cert
--
tudaV1AIKCert OBJECT IDENTIFIER ::= { tudaV1MIBObjects 2 }
tudaV1AIKCertCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of AIK Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1AIKCert 1 }
tudaV1AIKCertTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1AIKCertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of AIK Certificate data."
::= { tudaV1AIKCert 2 }
tudaV1AIKCertEntry OBJECT-TYPE
SYNTAX TudaV1AIKCertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of AIK Certificate data."
INDEX { tudaV1AIKCertCycleIndex,
tudaV1AIKCertInstanceIndex,
tudaV1AIKCertFragmentIndex }
::= { tudaV1AIKCertTable 1 }
TudaV1AIKCertEntry ::=
SEQUENCE {
tudaV1AIKCertCycleIndex Integer32,
tudaV1AIKCertInstanceIndex Integer32,
tudaV1AIKCertFragmentIndex Integer32,
tudaV1AIKCertData OCTET STRING
}
tudaV1AIKCertCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this AIK Certificate fragment.
Index of an AIK Certificate chain update cycle that has
occurred (bounded by the value of tudaV1AIKCertCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 1 }
tudaV1AIKCertInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this AIK Certificate fragment.
Ordinal of this AIK Certificate in this chain, where the AIK
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 2 }
tudaV1AIKCertFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this AIK Certificate fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 3 }
tudaV1AIKCertData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded AIK Certificate data."
DEFVAL { "" }
::= { tudaV1AIKCertEntry 4 }
--
-- TSA Cert
--
tudaV1TSACert OBJECT IDENTIFIER ::= { tudaV1MIBObjects 3 }
tudaV1TSACertCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of TSA Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1TSACert 1 }
tudaV1TSACertTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1TSACertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of TSA Certificate data."
::= { tudaV1TSACert 2 }
tudaV1TSACertEntry OBJECT-TYPE
SYNTAX TudaV1TSACertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of TSA Certificate data."
INDEX { tudaV1TSACertCycleIndex,
tudaV1TSACertInstanceIndex,
tudaV1TSACertFragmentIndex }
::= { tudaV1TSACertTable 1 }
TudaV1TSACertEntry ::=
SEQUENCE {
tudaV1TSACertCycleIndex Integer32,
tudaV1TSACertInstanceIndex Integer32,
tudaV1TSACertFragmentIndex Integer32,
tudaV1TSACertData OCTET STRING
}
tudaV1TSACertCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this TSA Certificate fragment.
Index of a TSA Certificate chain update cycle that has
occurred (bounded by the value of tudaV1TSACertCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 1 }
tudaV1TSACertInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this TSA Certificate fragment.
Ordinal of this TSA Certificate in this chain, where the TSA
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 2 }
tudaV1TSACertFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this TSA Certificate fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 3 }
tudaV1TSACertData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded TSA Certificate data."
DEFVAL { "" }
::= { tudaV1TSACertEntry 4 }
--
-- Sync Token
--
tudaV1SyncToken OBJECT IDENTIFIER ::= { tudaV1MIBObjects 4 }
tudaV1SyncTokenCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Sync Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1SyncToken 1 }
tudaV1SyncTokenInstances OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Sync Token instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object."
::= { tudaV1SyncToken 2 }
tudaV1SyncTokenTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1SyncTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of Sync Token data."
::= { tudaV1SyncToken 3 }
tudaV1SyncTokenEntry OBJECT-TYPE
SYNTAX TudaV1SyncTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of Sync Token data."
INDEX { tudaV1SyncTokenCycleIndex,
tudaV1SyncTokenInstanceIndex,
tudaV1SyncTokenFragmentIndex }
::= { tudaV1SyncTokenTable 1 }
TudaV1SyncTokenEntry ::=
SEQUENCE {
tudaV1SyncTokenCycleIndex Integer32,
tudaV1SyncTokenInstanceIndex Integer32,
tudaV1SyncTokenFragmentIndex Integer32,
tudaV1SyncTokenData OCTET STRING
}
tudaV1SyncTokenCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this Sync Token fragment.
Index of a Sync Token update cycle that has
occurred (bounded by the value of tudaV1SyncTokenCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1SyncTokenEntry 1 }
tudaV1SyncTokenInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this Sync Token fragment.
Ordinal of this instance of Sync Token data
(NOT bounded by the value of tudaV1SyncTokenInstances).
DEFVAL intentionally omitted - index object."
::= { tudaV1SyncTokenEntry 2 }
tudaV1SyncTokenFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this Sync Token fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1SyncTokenEntry 3 }
tudaV1SyncTokenData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded Sync Token data."
DEFVAL { "" }
::= { tudaV1SyncTokenEntry 4 }
--
-- Restriction Info
--
tudaV1Restrict OBJECT IDENTIFIER ::= { tudaV1MIBObjects 5 }
tudaV1RestrictCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Restriction Info update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1Restrict 1 }
tudaV1RestrictTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1RestrictEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Restriction Info data."
::= { tudaV1Restrict 2 }
tudaV1RestrictEntry OBJECT-TYPE
SYNTAX TudaV1RestrictEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Restriction Info data."
INDEX { tudaV1RestrictCycleIndex }
::= { tudaV1RestrictTable 1 }
TudaV1RestrictEntry ::=
SEQUENCE {
tudaV1RestrictCycleIndex Integer32,
tudaV1RestrictData OCTET STRING
}
tudaV1RestrictCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of this Restriction Info entry.
Index of a Restriction Info update cycle that has
occurred (bounded by the value of tudaV1RestrictCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1RestrictEntry 1 }
tudaV1RestrictData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"An instance of CBOR encoded Restriction Info data."
DEFVAL { "" }
::= { tudaV1RestrictEntry 2 }
--
-- Measurement Log
--
tudaV1Measure OBJECT IDENTIFIER ::= { tudaV1MIBObjects 6 }
tudaV1MeasureCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Measurement Log update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1Measure 1 }
tudaV1MeasureInstances OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Measurement Log instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object."
::= { tudaV1Measure 2 }
tudaV1MeasureTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1MeasureEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Measurement Log data."
::= { tudaV1Measure 3 }
tudaV1MeasureEntry OBJECT-TYPE
SYNTAX TudaV1MeasureEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Measurement Log data."
INDEX { tudaV1MeasureCycleIndex,
tudaV1MeasureInstanceIndex }
::= { tudaV1MeasureTable 1 }
TudaV1MeasureEntry ::=
SEQUENCE {
tudaV1MeasureCycleIndex Integer32,
tudaV1MeasureInstanceIndex Integer32,
tudaV1MeasureData OCTET STRING
}
tudaV1MeasureCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this Measurement Log entry.
Index of a Measurement Log update cycle that has
occurred (bounded by the value of tudaV1MeasureCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1MeasureEntry 1 }
tudaV1MeasureInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this Measurement Log entry.
Ordinal of this instance of Measurement Log data
(NOT bounded by the value of tudaV1MeasureInstances).
DEFVAL intentionally omitted - index object."
::= { tudaV1MeasureEntry 2 }
tudaV1MeasureData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A instance of CBOR encoded Measurement Log data."
DEFVAL { "" }
::= { tudaV1MeasureEntry 3 }
--
-- Verify Token
--
tudaV1VerifyToken OBJECT IDENTIFIER ::= { tudaV1MIBObjects 7 }
tudaV1VerifyTokenCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Verify Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1VerifyToken 1 }
tudaV1VerifyTokenTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1VerifyTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Verify Token data."
::= { tudaV1VerifyToken 2 }
tudaV1VerifyTokenEntry OBJECT-TYPE
SYNTAX TudaV1VerifyTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Verify Token data."
INDEX { tudaV1VerifyTokenCycleIndex }
::= { tudaV1VerifyTokenTable 1 }
TudaV1VerifyTokenEntry ::=
SEQUENCE {
tudaV1VerifyTokenCycleIndex Integer32,
tudaV1VerifyTokenData OCTET STRING
}
tudaV1VerifyTokenCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of this instance of Verify Token data.
Index of a Verify Token update cycle that has
occurred (bounded by the value of tudaV1VerifyTokenCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1VerifyTokenEntry 1 }
tudaV1VerifyTokenData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A instance of CBOR encoded Verify Token data."
DEFVAL { "" }
::= { tudaV1VerifyTokenEntry 2 }
--
-- SWID Tag
--
tudaV1SWIDTag OBJECT IDENTIFIER ::= { tudaV1MIBObjects 8 }
tudaV1SWIDTagCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of SWID Tag update cycles that have occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1SWIDTag 1 }
tudaV1SWIDTagTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1SWIDTagEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of SWID Tag data."
::= { tudaV1SWIDTag 2 }
tudaV1SWIDTagEntry OBJECT-TYPE
SYNTAX TudaV1SWIDTagEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of SWID Tag data."
INDEX { tudaV1SWIDTagCycleIndex,
tudaV1SWIDTagInstanceIndex,
tudaV1SWIDTagFragmentIndex }
::= { tudaV1SWIDTagTable 1 }
TudaV1SWIDTagEntry ::=
SEQUENCE {
tudaV1SWIDTagCycleIndex Integer32,
tudaV1SWIDTagInstanceIndex Integer32,
tudaV1SWIDTagFragmentIndex Integer32,
tudaV1SWIDTagData OCTET STRING
}
tudaV1SWIDTagCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this SWID Tag fragment.
Index of an SWID Tag update cycle that has
occurred (bounded by the value of tudaV1SWIDTagCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 1 }
tudaV1SWIDTagInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this SWID Tag fragment.
Ordinal of this SWID Tag instance in this update cycle.
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 2 }
tudaV1SWIDTagFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this SWID Tag fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 3 }
tudaV1SWIDTagData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded SWID Tag data."
DEFVAL { "" }
::= { tudaV1SWIDTagEntry 4 }
--
-- Trap Cycles
--
tudaV1TrapV2Cycles NOTIFICATION-TYPE
OBJECTS {
tudaV1GeneralCycles,
tudaV1AIKCertCycles,
tudaV1TSACertCycles,
tudaV1SyncTokenCycles,
tudaV1SyncTokenInstances,
tudaV1RestrictCycles,
tudaV1MeasureCycles,
tudaV1MeasureInstances,
tudaV1VerifyTokenCycles,
tudaV1SWIDTagCycles
}
STATUS current
DESCRIPTION
"This trap is sent when the value of any cycle or instance
counter changes (i.e., one or more tables are updated).
Note: The value of sysUpTime in IETF MIB-II (RFC 1213) is
always included in SNMPv2 traps, per RFC 3416."
::= { tudaV1MIBNotifications 1 }
--
-- Conformance Information
--
tudaV1Compliances OBJECT IDENTIFIER
::= { tudaV1MIBConformance 1 }
tudaV1ObjectGroups OBJECT IDENTIFIER
::= { tudaV1MIBConformance 2 }
tudaV1NotificationGroups OBJECT IDENTIFIER
::= { tudaV1MIBConformance 3 }
--
-- Compliance Statements
--
tudaV1BasicCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"An implementation that complies with this module MUST
implement all of the objects defined in the mandatory
group tudaV1BasicGroup."
MODULE -- this module
MANDATORY-GROUPS { tudaV1BasicGroup }
GROUP tudaV1OptionalGroup
DESCRIPTION
"The optional TUDA MIB objects.
An implementation MAY implement this group."
GROUP tudaV1TrapGroup
DESCRIPTION
"The TUDA MIB traps.
An implementation SHOULD implement this group."
::= { tudaV1Compliances 1 }
--
-- Compliance Groups
--
tudaV1BasicGroup OBJECT-GROUP
OBJECTS {
tudaV1GeneralCycles,
tudaV1GeneralVersionInfo,
tudaV1SyncTokenCycles,
tudaV1SyncTokenInstances,
tudaV1SyncTokenData,
tudaV1RestrictCycles,
tudaV1RestrictData,
tudaV1VerifyTokenCycles,
tudaV1VerifyTokenData
}
STATUS current
DESCRIPTION
"The basic mandatory TUDA MIB objects."
::= { tudaV1ObjectGroups 1 }
tudaV1OptionalGroup OBJECT-GROUP
OBJECTS {
tudaV1AIKCertCycles,
tudaV1AIKCertData,
tudaV1TSACertCycles,
tudaV1TSACertData,
tudaV1MeasureCycles,
tudaV1MeasureInstances,
tudaV1MeasureData,
tudaV1SWIDTagCycles,
tudaV1SWIDTagData
}
STATUS current
DESCRIPTION
"The optional TUDA MIB objects."
::= { tudaV1ObjectGroups 2 }
tudaV1TrapGroup NOTIFICATION-GROUP
NOTIFICATIONS { tudaV1TrapV2Cycles }
STATUS current
DESCRIPTION
"The recommended TUDA MIB traps - notifications."
::= { tudaV1NotificationGroups 1 }
END
<CODE ENDS>¶
<CODE BEGINS>
module TUDA-V1-ATTESTATION-MIB {
namespace "urn:ietf:params:xml:ns:yang:smiv2:TUDA-V1-ATTESTATION-MIB";
prefix "tuda-v1";
import SNMP-FRAMEWORK-MIB { prefix "snmp-framework"; }
import yang-types { prefix "yang"; }
organization
"Fraunhofer SIT";
contact
"Andreas Fuchs
Fraunhofer Institute for Secure Information Technology
Email: andreas.fuchs@sit.fraunhofer.de
Henk Birkholz
Fraunhofer Institute for Secure Information Technology
Email: henk.birkholz@sit.fraunhofer.de
Ira E McDonald
High North Inc
Email: blueroofmusic@gmail.com
Carsten Bormann
Universitaet Bremen TZI
Email: cabo@tzi.org";
description
"The MIB module for monitoring of time-based unidirectional
attestation information from a network endpoint system,
based on the Trusted Computing Group TPM 1.2 definition.
Copyright (C) High North Inc (2021).";
revision "2021-01-13" {
description
"Twelfth version, published as draft-birkholz-rats-tuda-04.";
reference
"draft-birkholz-rats-tuda-04";
}
revision "2020-07-13" {
description
"Eleventh version, published as draft-birkholz-rats-tuda-03.";
reference
"draft-birkholz-rats-tuda-03";
}
revision "2020-03-09" {
description
"Tenth version, published as draft-birkholz-rats-tuda-02.";
reference
"draft-birkholz-rats-tuda-02";
}
revision "2019-09-11" {
description
"Ninth version, published as draft-birkholz-rats-tuda-01.";
reference
"draft-birkholz-rats-tuda-01";
}
revision "2019-03-12" {
description
"Eighth version, published as draft-birkholz-rats-tuda-00.";
reference
"draft-birkholz-rats-tuda-00";
}
revision "2018-05-03" {
description
"Seventh version, published as draft-birkholz-i2nsf-tuda-03.";
reference
"draft-birkholz-i2nsf-tuda-03";
}
revision "2018-05-02" {
description
"Sixth version, published as draft-birkholz-i2nsf-tuda-02.";
reference
"draft-birkholz-i2nsf-tuda-02";
}
revision "2017-10-30" {
description
"Fifth version, published as draft-birkholz-i2nsf-tuda-01.";
reference
"draft-birkholz-i2nsf-tuda-01";
}
revision "2017-01-09" {
description
"Fourth version, published as draft-birkholz-i2nsf-tuda-00.";
reference
"draft-birkholz-i2nsf-tuda-00";
}
revision "2016-07-08" {
description
"Third version, published as draft-birkholz-tuda-02.";
reference
"draft-birkholz-tuda-02";
}
revision "2016-03-21" {
description
"Second version, published as draft-birkholz-tuda-01.";
reference
"draft-birkholz-tuda-01";
}
revision "2015-10-18" {
description
"Initial version, published as draft-birkholz-tuda-00.";
reference
"draft-birkholz-tuda-00";
}
container tudaV1General {
description
"TBD";
leaf tudaV1GeneralCycles {
type yang:counter32;
config false;
description
"Count of TUDA update cycles that have occurred, i.e.,
sum of all the individual group cycle counters.
DEFVAL intentionally omitted - counter object.";
}
leaf tudaV1GeneralVersionInfo {
type snmp-framework:SnmpAdminString {
length "0..255";
}
config false;
description
"Version information for TUDA MIB, e.g., specific release
version of TPM 1.2 base specification and release version
of TPM 1.2 errata specification and manufacturer and model
TPM module itself.";
}
}
container tudaV1AIKCert {
description
"TBD";
leaf tudaV1AIKCertCycles {
type yang:counter32;
config false;
description
"Count of AIK Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1AIKCertEntry {
key "tudaV1AIKCertCycleIndex tudaV1AIKCertInstanceIndex
tudaV1AIKCertFragmentIndex";
config false;
description
"An entry for one fragment of AIK Certificate data.";
leaf tudaV1AIKCertCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this AIK Certificate fragment.
Index of an AIK Certificate chain update cycle that has
occurred (bounded by the value of tudaV1AIKCertCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1AIKCertInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this AIK Certificate fragment.
Ordinal of this AIK Certificate in this chain, where the AIK
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1AIKCertFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this AIK Certificate fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1AIKCertData {
type binary {
length "0..1024";
}
config false;
description
"A fragment of CBOR encoded AIK Certificate data.";
}
}
}
container tudaV1TSACert {
description
"TBD";
leaf tudaV1TSACertCycles {
type yang:counter32;
config false;
description
"Count of TSA Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1TSACertEntry {
key "tudaV1TSACertCycleIndex tudaV1TSACertInstanceIndex
tudaV1TSACertFragmentIndex";
config false;
description
"An entry for one fragment of TSA Certificate data.";
leaf tudaV1TSACertCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this TSA Certificate fragment.
Index of a TSA Certificate chain update cycle that has
occurred (bounded by the value of tudaV1TSACertCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1TSACertInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this TSA Certificate fragment.
Ordinal of this TSA Certificate in this chain, where the TSA
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1TSACertFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this TSA Certificate fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1TSACertData {
type binary {
length "0..1024";
}
config false;
description
"A fragment of CBOR encoded TSA Certificate data.";
}
}
}
container tudaV1SyncToken {
description
"TBD";
leaf tudaV1SyncTokenCycles {
type yang:counter32;
config false;
description
"Count of Sync Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
leaf tudaV1SyncTokenInstances {
type yang:counter32;
config false;
description
"Count of Sync Token instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
list tudaV1SyncTokenEntry {
key "tudaV1SyncTokenCycleIndex
tudaV1SyncTokenInstanceIndex
tudaV1SyncTokenFragmentIndex";
config false;
description
"An entry for one fragment of Sync Token data.";
leaf tudaV1SyncTokenCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this Sync Token fragment.
Index of a Sync Token update cycle that has
occurred (bounded by the value of tudaV1SyncTokenCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SyncTokenInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this Sync Token fragment.
Ordinal of this instance of Sync Token data
(NOT bounded by the value of tudaV1SyncTokenInstances).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SyncTokenFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this Sync Token fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SyncTokenData {
type binary {
length "0..1024";
}
config false;
description
"A fragment of CBOR encoded Sync Token data.";
}
}
}
container tudaV1Restrict {
description
"TBD";
leaf tudaV1RestrictCycles {
type yang:counter32;
config false;
description
"Count of Restriction Info update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1RestrictEntry {
key "tudaV1RestrictCycleIndex";
config false;
description
"An entry for one instance of Restriction Info data.";
leaf tudaV1RestrictCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Index of this Restriction Info entry.
Index of a Restriction Info update cycle that has
occurred (bounded by the value of tudaV1RestrictCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1RestrictData {
type binary {
length "0..1024";
}
config false;
description
"An instance of CBOR encoded Restriction Info data.";
}
}
}
container tudaV1Measure {
description
"TBD";
leaf tudaV1MeasureCycles {
type yang:counter32;
config false;
description
"Count of Measurement Log update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
leaf tudaV1MeasureInstances {
type yang:counter32;
config false;
description
"Count of Measurement Log instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
list tudaV1MeasureEntry {
key "tudaV1MeasureCycleIndex tudaV1MeasureInstanceIndex";
config false;
description
"An entry for one instance of Measurement Log data.";
leaf tudaV1MeasureCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this Measurement Log entry.
Index of a Measurement Log update cycle that has
occurred (bounded by the value of tudaV1MeasureCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1MeasureInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this Measurement Log entry.
Ordinal of this instance of Measurement Log data
(NOT bounded by the value of tudaV1MeasureInstances).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1MeasureData {
type binary {
length "0..1024";
}
config false;
description
"A instance of CBOR encoded Measurement Log data.";
}
}
}
container tudaV1VerifyToken {
description
"TBD";
leaf tudaV1VerifyTokenCycles {
type yang:counter32;
config false;
description
"Count of Verify Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1VerifyTokenEntry {
key "tudaV1VerifyTokenCycleIndex";
config false;
description
"An entry for one instance of Verify Token data.";
leaf tudaV1VerifyTokenCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Index of this instance of Verify Token data.
Index of a Verify Token update cycle that has
occurred (bounded by the value of tudaV1VerifyTokenCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1VerifyTokenData {
type binary {
length "0..1024";
}
config false;
description
"A instanc-V1-ATTESTATION-MIB.yang
}
}
}
container tudaV1SWIDTag {
description
"see CoSWID and YANG SIWD module for now"
leaf tudaV1SWIDTagCycles {
type yang:counter32;
config false;
description
"Count of SWID Tag update cycles that have occurred.
DEFVAL intentionally omitted - counter object.";
}
list tudaV1SWIDTagEntry {
key "tudaV1SWIDTagCycleIndex tudaV1SWIDTagInstanceIndex
tudaV1SWIDTagFragmentIndex";
config false;
description
"An entry for one fragment of SWID Tag data.";
leaf tudaV1SWIDTagCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this SWID Tag fragment.
Index of an SWID Tag update cycle that has
occurred (bounded by the value of tudaV1SWIDTagCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SWIDTagInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this SWID Tag fragment.
Ordinal of this SWID Tag instance in this update cycle.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SWIDTagFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this SWID Tag fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SWIDTagData {
type binary {
length "0..1024";
}
config false;
description
"A fragment of CBOR encoded SWID Tag data.";
}
}
}
notification tudaV1TrapV2Cycles {
description
"This trap is sent when the value of any cycle or instance
counter changes (i.e., one or more tables are updated).
Note: The value of sysUpTime in IETF MIB-II (RFC 1213) is
always included in SNMPv2 traps, per RFC 3416.";
container tudaV1TrapV2Cycles-tudaV1GeneralCycles {
description
"TPD"
leaf tudaV1GeneralCycles {
type yang:counter32;
description
"Count of TUDA update cycles that have occurred, i.e.,
sum of all the individual group cycle counters.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1AIKCertCycles {
description
"TPD"
leaf tudaV1AIKCertCycles {
type yang:counter32;
description
"Count of AIK Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1TSACertCycles {
description
"TPD"
leaf tudaV1TSACertCycles {
type yang:counter32;
description
"Count of TSA Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1SyncTokenCycles {
description
"TPD"
leaf tudaV1SyncTokenCycles {
type yang:counter32;
description
"Count of Sync Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1SyncTokenInstances {
description
"TPD"
leaf tudaV1SyncTokenInstances {
type yang:counter32;
description
"Count of Sync Token instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1RestrictCycles {
description
"TPD"
leaf tudaV1RestrictCycles {
type yang:counter32;
description
"Count of Restriction Info update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1MeasureCycles {
description
"TPD"
leaf tudaV1MeasureCycles {
type yang:counter32;
description
"Count of Measurement Log update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1MeasureInstances {
description
"TPD"
leaf tudaV1MeasureInstances {
type yang:counter32;
description
"Count of Measurement Log instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1VerifyTokenCycles {
description
"TPD"
leaf tudaV1VerifyTokenCycles {
type yang:counter32;
description
"Count of Verify Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1SWIDTagCycles {
description
"TPD"
leaf tudaV1SWIDTagCycles {
type yang:counter32;
description
"Count of SWID Tag update cycles that have occurred.
DEFVAL intentionally omitted - counter object.";
}
}
}
}
<CODE ENDS>¶
The following TPM structures, resources and functions are used within this approach. They are based upon the TPM specifications [TPM12] and [TPM2].¶
On every boot, the TPM initializes a new Tick-Session. Such a tick-session consists of a nonce that is randomly created upon each boot to identify the current boot-cycle -- the phase between boot-time of the device and shutdown or power-off -- and prevent replaying of old tick-session values. The TPM uses its internal entropy source that guarantees virtually no collisions of the nonce values between two of such boot cycles.¶
It further includes an internal timer that is being initialize to Zero on each reboot. From this point on, the TPM increments this timer continuously based upon its internal secure clocking information until the device is powered down or set to sleep. By its hardware design, the TPM will detect attacks on any of those properties.¶
The TPM offers the function TPM_TickStampBlob, which allows the TPM to create a signature over the current tick-session and two externally provided input values. These input values are designed to serve as a nonce and as payload data to be included in a TickStampBlob: TickstampBlob := sig(TPM-key, currentTicks || nonce || externalData).¶
As a result, one is able to proof that at a certain point in time (relative to the tick-session) after the provisioning of a certain nonce, some certain externalData was known and provided to the TPM. If an approach however requires no input values or only one input value (such as the use in this document) the input values can be set to well-known value. The convention used within TCG specifications and within this document is to use twenty bytes of zero h'0000000000000000000000000000000000000000' as well-known value.¶
The TPM is a secure cryptoprocessor that provides the ability to store measurements and metrics about an endpoint's configuration and state in a secure, tamper-proof environment. Each of these security relevant metrics can be stored in a volatile Platform Configuration Register (PCR) inside the TPM. These measurements can be conducted at any point in time, ranging from an initial BIOS boot-up sequence to measurements taken after hundreds of hours of uptime.¶
The initial measurement is triggered by the Platforms so-called pre-BIOS or ROM-code. It will conduct a measurement of the first loadable pieces of code; i.e.\ the BIOS. The BIOS will in turn measure its Option ROMs and the BootLoader, which measures the OS-Kernel, which in turn measures its applications. This describes a so-called measurement chain. This typically gets recorded in a so-called measurement log, such that the values of the PCRs can be reconstructed from the individual measurements for validation.¶
Via its PCRs, a TPM provides a Root of Trust that can, for example, support secure boot or remote attestation. The attestation of an endpoint's identity or security posture is based on the content of an TPM's PCRs (platform integrity measurements).¶
Every key inside the TPM can be restricted in such a way that it can only be used if a certain set of PCRs are in a predetermined state. For key creation the desired state for PCRs are defined via the PCRInfo field inside the keyInfo parameter. Whenever an operation using this key is performed, the TPM first checks whether the PCRs are in the correct state. Otherwise the operation is denied by the TPM.¶
The TPM offers a command to certify the properties of a key by means of a signature using another key. This includes especially the keyInfo which in turn includes the PCRInfo information used during key creation. This way, a third party can be assured about the fact that a key is only usable if the PCRs are in a certain state.¶
Attestations are based upon a cryptographic signature performed by the TPM using a so-called Attestation Identity Key (AIK). An AIK has the properties that it cannot be exported from a TPM and is used for attestations. Trust in the AIK is established by an X.509 Certificate emitted by a Certificate Authority. The AIK certificate is either provided directly or via a so-called PrivacyCA [AIK-Enrollment].¶
This element consists of the AIK certificate that includes the AIK's public key used during verification as well as the certificate chain up to the Root CA for validation of the AIK certificate itself.¶
TUDA-Cert = [AIK-Cert, TSA-Cert]; maybe split into two for SNMP AIK-Cert = Cert TSA-Cert = Cert
The TSA-Cert is a standard certificate of the TSA.¶
The AIK-Cert may be provisioned in a secure environment using standard means or it may follow the PrivacyCA protocols. Figure 3 gives a rough sketch of this protocol. See [AIK-Enrollment] for more information.¶
The X.509 Certificate is built from the AIK public key and the corresponding PKCS #7 certificate chain, as shown in Figure 3.¶
Required TPM functions:¶
| create_AIK_Cert(...) = {
| AIK = TPM_MakeIdentity()
| IdReq = CollateIdentityRequest(AIK,EK)
| IdRes = Call(AIK-CA, IdReq)
| AIK-Cert = TPM_ActivateIdentity(AIK, IdRes)
| }
|
| /* Alternative */
|
| create_AIK_Cert(...) = {
| AIK = TPM_CreateWrapKey(Identity)
| AIK-Cert = Call(AIK-CA, AIK.pubkey)
| }
The reference for Attestations are the Tick-Sessions of the TPM. In order to put Attestations into relation with a Real Time Clock (RTC), it is necessary to provide a cryptographic synchronization between the tick session and the RTC. To do so, a synchronization protocol is run with a Time Stamp Authority (TSA) that consists of three steps:¶
The first TickStampBlob is called "left" and the second "right" in a reference to their position on a time-axis.¶
These three elements, with the TSA's certificate factored out, form the synchronization token¶
TUDA-Synctoken = [
left: TickStampBlob-Output,
timestamp: TimeStampToken,
right: TickStampBlob-Output,
]
TimeStampToken = bytes ; RFC 3161
TickStampBlob-Output = [
currentTicks: TPM-CURRENT-TICKS,
sig: bytes,
]
TPM-CURRENT-TICKS = [
currentTicks: uint
? (
tickRate: uint
tickNonce: TPM-NONCE
)
]
; Note that TickStampBlob-Output "right" can omit the values for
; tickRate and tickNonce since they are the same as in "left"
TPM-NONCE = bytes .size 20
Required TPM functions:¶
| dummyDigest = h'0000000000000000000000000000000000000000'
| dummyNonce = dummyDigest
|
| create_sync_token(AIKHandle, TSA) = {
| ts_left = TPM_TickStampBlob(
| keyHandle = AIK_Handle, /*TPM_KEY_HANDLE*/
| antiReplay = dummyNonce, /*TPM_NONCE*/
| digestToStamp = dummyDigest /*TPM_DIGEST*/)
|
| ts = TSA_Timestamp(TSA, nonce = hash(ts_left))
|
| ts_right = TPM_TickStampBlob(
| keyHandle = AIK_Handle, /*TPM_KEY_HANDLE*/
| antiReplay = dummyNonce, /*TPM_NONCE*/
| digestToStamp = hash(ts)) /*TPM_DIGEST*/
|
| TUDA-SyncToken = [[ts_left.ticks, ts_left.sig], ts,
| [ts_right.ticks.currentTicks, ts_right.sig]]
| /* Note: skip the nonce and tickRate field for ts_right.ticks */
| }
The attestation relies on the capability of the TPM to operate on restricted keys. Whenever the PCR values for the machine to be attested change, a new restricted key is created that can only be operated as long as the PCRs remain in their current state.¶
In order to prove to the Verifier that this restricted temporary key actually has these properties and also to provide the PCR value that it is restricted, the TPM command TPM_CertifyInfo is used. It creates a signed certificate using the AIK about the newly created restricted key.¶
This token is formed from the list of:¶
TUDA-RestrictionInfo = [Composite,
restrictedKey_Pub: Pubkey,
CertifyInfo]
PCRSelection = bytes .size (2..4) ; used as bit string
Composite = [
bitmask: PCRSelection,
values: [*PCR-Hash],
]
Pubkey = bytes ; may be extended to COSE pubkeys
CertifyInfo = [
TPM-CERTIFY-INFO,
sig: bytes,
]
TPM-CERTIFY-INFO = [
; we don't encode TPM-STRUCT-VER:
; these are 4 bytes always equal to h'01010000'
keyUsage: uint, ; 4byte? 2byte?
keyFlags: bytes .size 4, ; 4byte
authDataUsage: uint, ; 1byte (enum)
algorithmParms: TPM-KEY-PARMS,
pubkeyDigest: Hash,
; we don't encode TPM-NONCE data, which is 20 bytes, all zero
parentPCRStatus: bool,
; no need to encode pcrinfosize
pcrinfo: TPM-PCR-INFO, ; we have exactly one
]
TPM-PCR-INFO = [
pcrSelection: PCRSelection; /* TPM_PCR_SELECTION */
digestAtRelease: PCR-Hash; /* TPM_COMPOSITE_HASH */
digestAtCreation: PCR-Hash; /* TPM_COMPOSITE_HASH */
]
TPM-KEY-PARMS = [
; algorithmID: uint, ; <= 4 bytes -- not encoded, constant for TPM1.2
encScheme: uint, ; <= 2 bytes
sigScheme: uint, ; <= 2 bytes
parms: TPM-RSA-KEY-PARMS,
]
TPM-RSA-KEY-PARMS = [
; "size of the RSA key in bits":
keyLength: uint
; "number of prime factors used by this RSA key":
numPrimes: uint
; "This SHALL be the size of the exponent":
exponentSize: null / uint / biguint
; "If the key is using the default exponent then the exponentSize
; MUST be 0" -> we represent this case as null
]
Required TPM functions:¶
| dummyDigest = h'0000000000000000000000000000000000000000'
| dummyNonce = dummyDigest
|
| create_Composite
|
| create_restrictedKey_Pub(pcrsel) = {
| PCRInfo = {pcrSelection = pcrsel,
| digestAtRelease = hash(currentValues(pcrSelection))
| digestAtCreation = dummyDigest}
| / * PCRInfo is a TPM_PCR_INFO and thus also a TPM_KEY */
|
| wk = TPM_CreateWrapKey(keyInfo = PCRInfo)
| wk.keyInfo.pubKey
| }
|
| create_TPM-Certify-Info = {
| CertifyInfo = TPM_CertifyKey(
| certHandle = AIK, /* TPM_KEY_HANDLE */
| keyHandle = wk, /* TPM_KEY_HANDLE */
| antiReply = dummyNonce) /* TPM_NONCE */
|
| CertifyInfo.strip()
| /* Remove those values that are not needed */
| }
Similarly to regular attestations, the Verifier needs a way to reconstruct the PCRs' values in order to estimate the trustworthiness of the device. As such, a list of those elements that were extended into the PCRs is reported. Note though that for certain environments, this step may be optional if a list of valid PCR configurations exists and no measurement log is required.¶
TUDA-Measurement-Log = [*PCR-Event] PCR-Event = [ type: PCR-Event-Type, pcr: uint, template-hash: PCR-Hash, filedata-hash: tagged-hash, pathname: text; called filename-hint in ima (non-ng) ] PCR-Event-Type = &( bios: 0 ima: 1 ima-ng: 2 ) ; might want to make use of COSE registry here ; however, that might never define a value for sha1 tagged-hash /= [sha1: 0, bytes .size 20] tagged-hash /= [sha256: 1, bytes .size 32]¶
The actual attestation is then based upon a TickStampBlob using the restricted temporary key that was certified in the steps above. The TPM-Tickstamp is executed and thereby provides evidence that at this point in time (with respect to the TPM internal tick-session) a certain configuration existed (namely the PCR values associated with the restricted key). Together with the synchronization token this tick-related timing can then be related to the real-time clock.¶
This element consists only of the TPM_TickStampBlock with no nonce.¶
TUDA-Verifytoken = TickStampBlob-Output
Required TPM functions:¶
| imp_att = TPM_TickStampBlob( | keyHandle = restrictedKey_Handle, /*TPM_KEY_HANDLE*/ | antiReplay = dummyNonce, /*TPM_NONCE*/ | digestToStamp = dummyDigest) /*TPM_DIGEST*/ | | VerifyToken = imp_att
The seven TUDA information elements transport the essential content that is required to enable verification of the attestation statement at the Verifier. The following listings illustrate the verification algorithm to be used at the Verifier in pseudocode. The pseudocode provided covers the entire verification task. If only a subset of TUDA elements changed (see Section 6.1), only the corresponding code listings need to be re-executed.¶
| TSA_pub = verifyCert(TSA-CA, Cert.TSA-Cert) | AIK_pub = verifyCert(AIK-CA, Cert.AIK-Cert)
| ts_left = Synctoken.left | ts_right = Synctoken.right | | /* Reconstruct ts_right's omitted values; Alternatively assert == */ | ts_right.currentTicks.tickRate = ts_left.currentTicks.tickRate | ts_right.currentTicks.tickNonce = ts_left.currentTicks.tickNonce | | ticks_left = ts_left.currentTicks | ticks_right = ts_right.currentTicks | | /* Verify Signatures */ | verifySig(AIK_pub, dummyNonce || dummyDigest || ticks_left) | verifySig(TSA_pub, hash(ts_left) || timestamp.time) | verifySig(AIK_pub, dummyNonce || hash(timestamp) || ticks_right) | | delta_left = timestamp.time - | ticks_left.currentTicks * ticks_left.tickRate / 1000 | | delta_right = timestamp.time - | ticks_right.currentTicks * ticks_right.tickRate / 1000
| compositeHash = hash_init() | for value in Composite.values: | hash_update(compositeHash, value) | compositeHash = hash_finish(compositeHash) | | certInfo = reconstruct_static(TPM-CERTIFY-INFO) | | assert(Composite.bitmask == ExpectedPCRBitmask) | assert(certInfo.pcrinfo.PCRSelection == Composite.bitmask) | assert(certInfo.pcrinfo.digestAtRelease == compositeHash) | assert(certInfo.pubkeyDigest == hash(restrictedKey_Pub)) | | verifySig(AIK_pub, dummyNonce || certInfo)
| for event in Measurement-Log: | if event.pcr not in ExpectedPCRBitmask: | continue | if event.type == BIOS: | assert_whitelist-bios(event.pcr, event.template-hash) | if event.type == ima: | assert(event.pcr == 10) | assert_whitelist(event.pathname, event.filedata-hash) | assert(event.template-hash == | hash(event.pathname || event.filedata-hash)) | if event.type == ima-ng: | assert(event.pcr == 10) | assert_whitelist-ng(event.pathname, event.filedata-hash) | assert(event.template-hash == | hash(event.pathname || event.filedata-hash)) | | virtPCR[event.pcr] = hash_extend(virtPCR[event.pcr], | event.template-hash) | | for pcr in ExpectedPCRBitmask: | assert(virtPCR[pcr] == Composite.values[i++]
| ts = Verifytoken | | /* Reconstruct ts's omitted values; Alternatively assert == */ | ts.currentTicks.tickRate = ts_left.currentTicks.tickRate | ts.currentTicks.tickNonce = ts_left.currentTicks.tickNonce | | verifySig(restrictedKey_pub, dummyNonce || dummyDigest || ts) | | ticks = ts.currentTicks | | time_left = delta_right + ticks.currentTicks * ticks.tickRate / 1000 | time_right = delta_left + ticks.currentTicks * ticks.tickRate / 1000 | | [time_left, time_right]
The pseudocode below includes general operations that are conducted as specific TPM commands:¶
These represent the output structure of that command in the form of a byte string value.¶
Attestations are based upon a cryptographic signature performed by the TPM using a so-called Attestation Identity Key (AIK). An AIK has the properties that it cannot be exported from a TPM and is used for attestations. Trust in the AIK is established by an X.509 Certificate emitted by a Certificate Authority. The AIK certificate is either provided directly or via a so-called PrivacyCA [AIK-Enrollment].¶
This element consists of the AIK certificate that includes the AIK's public key used during verification as well as the certificate chain up to the Root CA for validation of the AIK certificate itself.¶
TUDA-Cert = [AIK-Cert, TSA-Cert]; maybe split into two for SNMP AIK-Certificate = X.509-Certificate(AIK-Key,Restricted-Flag) TSA-Certificate = X.509-Certificate(TSA-Key, TSA-Flag)
The synchronization token uses a different TPM command, TPM2 GetTime() instead of TPM TickStampBlob(). The TPM2 GetTime() command contains the clock and time information of the TPM. The clock information is the equivalent of TUDA v1's tickSession information.¶
TUDA-SyncToken = [
left_GetTime = sig(AIK-Key,
TimeInfo = [
time,
resetCount,
restartCount
]
),
middle_TimeStamp = sig(TSA-Key,
hash(left_TickStampBlob),
UTC-localtime
),
right_TickStampBlob = sig(AIK-Key,
hash(middle_TimeStamp),
TimeInfo = [
time,
resetCount,
restartCount
]
)
]
The creation procedure is identical to Appendix D.2.4.¶
Measurement-Log = [
* [ EventName,
PCR-Num,
Event-Hash ]
]
The TUDA attestation token consists of the result of TPM2_Quote() or a set of TPM2_PCR_READ followed by a TPM2_GetSessionAuditDigest. It proves that --- at a certain point-in-time with respect to the TPM's internal clock --- a certain configuration of PCRs was present, as denoted in the keys restriction information.¶
TUDA-AttestationToken = TUDA-AttestationToken_quote / TUDA-AttestationToken_audit
TUDA-AttestationToken_quote = sig(AIK-Key,
TimeInfo = [
time,
resetCount,
restartCount
],
PCR-Selection = [ * PCR],
PCR-Digest := PCRDigest
)
TUDA-AttestationToken_audit = sig(AIK-key,
TimeInfo = [
time,
resetCount,
restartCount
],
Session-Digest := PCRDigest
)
In order to proof to the Verifier that the TPM's clock was not 'fast-forwarded' the result of a TPM2_GetTime() is sent after the TUDA-AttestationToken.¶
TUDA-SyncProof = sig(AIK-Key,
TimeInfo = [
time,
resetCount,
restartCount
]
),