Time-Based Uni-Directional Attestation
draft-birkholz-rats-tuda-04
RATS Working Group A. Fuchs
Internet-Draft H. Birkholz
Intended status: Standards Track Fraunhofer SIT
Expires: July 17, 2021 I. McDonald
High North Inc
C. Bormann
Universitaet Bremen TZI
January 13, 2021
Time-Based Uni-Directional Attestation
draft-birkholz-rats-tuda-04
Abstract
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.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Forward Authenticity . . . . . . . . . . . . . . . . . . 4
1.2. TUDA Objectives . . . . . . . . . . . . . . . . . . . . . 5
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Remote Attestation Principles . . . . . . . . . . . . . . . . 6
2.1. Authenticity of Evidence . . . . . . . . . . . . . . . . 6
2.2. Generating Evidence about Software Component Integrity . 7
2.3. Measurements and Digests Generated by an Attester . . . . 7
2.4. Attesting Environments and Roots of Trust . . . . . . . . 8
2.5. Indeterministic Measurements . . . . . . . . . . . . . . 9
3. TUDA Principles and Requirements . . . . . . . . . . . . . . 10
3.1. Attesting Environment Requirements . . . . . . . . . . . 11
3.2. Handle Distributor Requirements: Time Stamp Authority . . 11
4. Information Elements and Conveyance . . . . . . . . . . . . . 11
5. TUDA Core Concept . . . . . . . . . . . . . . . . . . . . . . 12
5.1. TPM Specific Terms . . . . . . . . . . . . . . . . . . . 13
5.2. Certificates . . . . . . . . . . . . . . . . . . . . . . 13
6. The TUDA Protocol Family . . . . . . . . . . . . . . . . . . 14
6.1. TUDA Information Elements Update Cycles . . . . . . . . . 15
7. Sync Base Protocol . . . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. REST Realization . . . . . . . . . . . . . . . . . . 24
Appendix B. SNMP Realization . . . . . . . . . . . . . . . . . . 24
B.1. Structure of TUDA MIB . . . . . . . . . . . . . . . . . . 25
B.1.1. Cycle Index . . . . . . . . . . . . . . . . . . . . . 25
B.1.2. Instance Index . . . . . . . . . . . . . . . . . . . 26
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B.1.3. Fragment Index . . . . . . . . . . . . . . . . . . . 26
B.2. Relationship to Host Resources MIB . . . . . . . . . . . 26
B.3. Relationship to Entity MIB . . . . . . . . . . . . . . . 26
B.4. Relationship to Other MIBs . . . . . . . . . . . . . . . 27
B.5. Definition of TUDA MIB . . . . . . . . . . . . . . . . . 27
Appendix C. YANG Realization . . . . . . . . . . . . . . . . . . 43
Appendix D. Realization with TPM functions . . . . . . . . . . . 59
D.1. TPM Functions . . . . . . . . . . . . . . . . . . . . . . 59
D.1.1. Tick-Session and Tick-Stamp . . . . . . . . . . . . . 59
D.1.2. Platform Configuration Registers (PCRs) . . . . . . . 59
D.1.3. PCR restricted Keys . . . . . . . . . . . . . . . . . 60
D.1.4. CertifyInfo . . . . . . . . . . . . . . . . . . . . . 60
D.2. IE Generation Procedures for TPM 1.2 . . . . . . . . . . 60
D.2.1. AIK and AIK Certificate . . . . . . . . . . . . . . . 60
D.2.2. Synchronization Token . . . . . . . . . . . . . . . . 61
D.2.3. RestrictionInfo . . . . . . . . . . . . . . . . . . . 63
D.2.4. Measurement Log . . . . . . . . . . . . . . . . . . . 65
D.2.5. Implicit Attestation . . . . . . . . . . . . . . . . 66
D.2.6. Attestation Verification Approach . . . . . . . . . . 67
D.3. IE Generation Procedures for TPM 2.0 . . . . . . . . . . 69
D.3.1. AIK and AIK Certificate . . . . . . . . . . . . . . . 69
D.3.2. Synchronization Token . . . . . . . . . . . . . . . . 70
D.3.3. Measurement Log . . . . . . . . . . . . . . . . . . . 70
D.3.4. Explicit time-based Attestation . . . . . . . . . . . 71
D.3.5. Sync Proof . . . . . . . . . . . . . . . . . . . . . 71
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 72
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 72
1. Introduction
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 focussed on in this document is RATS Evidence, any type of
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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].
1.1. Forward Authenticity
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
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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.
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.
1.2. TUDA Objectives
Time-Based Uni-directional Attestation is designed to:
o increase the confidence in authentication and authorization
procedures,
o address the requirements of constrained-node networks,
o support interaction models that do not maintain connection-state
over time, such as REST architectures [REST],
o be able to leverage existing management interfaces, such as SNMP
[RFC3411]. RESTCONF [RFC8040] or CoMI [I-D.ietf-core-comi] -- and
corresponding bindings,
o support broadcast and multicast schemes (e.g. [IEEE1609]),
o be able to cope with temporary loss of connectivity, and to
o provide trustworthy audit logs of past endpoint states.
1.3. Terminology
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].
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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.
2. Remote Attestation Principles
Based on the RATS Architecture, the processing of TPM generated
Evidence can be separated in three activities.
Evidence Generation: The retrieval of signed digests from an RTR
based on a sequence of collected Claims about software component
integrity (measurements).
Evidence Conveyance: The transfer of Evidence from the Attester to
the Verifier via the Internet.
Evidence Appraisal: 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].
2.1. Authenticity of Evidence
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:
o an Attestation Key (AK) Certificate (AK-Cert) that represents the
attestation provenance of the Attesting Environment (see section
4.2. in [I-D.ietf-rats-architecture]) that generates Evidence, and
o an Endorsement Key (EK) Certificate (EK-Cert) that represents the
Protection Capabilities of an Attesting Environment the AK is
stored in.
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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.
2.2. Generating Evidence about Software Component Integrity
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.
2.3. Measurements and Digests Generated by an Attester
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 pseudo code in
Appendix C and D.
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2.4. Attesting Environments and Roots of Trust
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.
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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.
2.5. Indeterministic Measurements
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
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[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.
3. TUDA Principles and Requirements
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:
o remote attestation for Attesters that might not always be able to
reach the Internet by enabling the appraisal of past states,
o secure audit logs by combining the Evidence generated with
integrity measurement logs (e.g. IMA logs) that represent a
detailed record of corresponding past states,
o the use of the uni-directional interaction model
[I-D.ietf-rats-reference-interaction-models] that can traverse
"diode-like" network security functions (NSF) or can be leveraged
RESTful telemetry as enabled by the CoAP Observe option
[RFC7252]).
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3.1. Attesting Environment Requirements
An Attesting Environment that generates Evidence in TUDA MUST support
three specific Protected Capabilities:
o Platform Configuration Registers (PCR) that can extend
measurements consecutively and represent the sequence of
measurements as a single digest,
o Restricted Signing Keys (RSK) that can only be accessed, if a
specific signature about a set of measurements can be provided as
authentication, and
o a dedicated source of (relative) time, e.g. a tick counter (a tick
being a specific time interval, for example 10 ms).
A TPM is capable of providing these Protected Capabilities for TUDA.
3.2. Handle Distributor Requirements: Time Stamp Authority
Both Evidence generation and Evidence appraisal require a Handle
Distributor that can take on the role of a trusted Time Stamp
Authority (TSA) as an additional third party. Time Stamp Tokens
(TST) included in Handles MUST be generated by Time Stamp Authority
based on [RFC3161] that acts as the Handle Distributor. The
combination of a local source of time provided by a TPM (on the
Attester) and the TST provided by the Handle Distributor (to both the
Attester and the Verifier) enable an appropriate proof of freshness.
4. Information Elements and Conveyance
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:
o MUST be encoded in the Concise Binary Object Representation (CBOR
[RFC7049]) to minimize the volume of data in motion. In this
document, the composition of the CBOR data items that represent IE
is described using the Concise Data Definition Language, CDDL
[RFC8610]
o that requires a certain freshness SHOULD only be re-generated when
out-dated (not fresh, but stale), which reduces the overall
resources required from the Attester, including the usage of a
TPM's resources (re-generation of IE is determined by their age or
by specific state changes on the Attester, e.g., due to a reboot-
cycle)
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o SHOULD only be transferred when required, which reduces the amount
of data in motion necessary to conduct remote attestation
significantly (only IE that have changed since their last
conveyance have to be transferred)
o that requires a certain freshness SHOULD be reused for multiple
remote attestation procedures in the limits of its corresponding
freshness-window, further reducing the load imposed on the
Attester and corresponding TPMs.
5. TUDA Core Concept
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:
o the time of transmission of the nonce, and
o the reception of the corresponding response.
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:
o the transmission of a TUDA time-synchronization token, and
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o the typical round-trip time between the Verifier and the Attester.
The accuracy of this time-frame is defined by two factors:
o the time-synchronization between the Attester and the Handle
Distributor. The time between the two tickstamps acquired via the
RoT define the scope of the maximum drift (time "left" and time
"right" in respect to the timeline) to the handle including the
signed timestamp, and
o the drift of clocks included in the RoT.
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.
5.1. TPM Specific Terms
PCR: A Platform Configuration Register that is part of the TPM and
is used to securely store and report measurements about security
posture
PCR-Hash: A hash value of the security posture measurements stored
in a TPM PCR (e.g. regarding running software instances)
represented as a byte-string
5.2. Certificates
HD-CA: The Certificate Authority that provides the certificate for
the TSA role of a Handle Distributor (HD)
AIK-CA: 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
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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].
6. The TUDA Protocol Family
Time-Based Uni-Directional Attestation consists of the following
seven information elements:
Handle Distributor Certificate: 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.
AK Certificate: 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).
Synchronization Token: The reference frame for Evidence is provided
by the relative timestanps 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 timesamps are
acquired from a Handle Distributor.
Restriction Info: 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.
Measurement Log: 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.
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Implicit Evidence: 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.
Concise SWID tags: 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.
6.1. TUDA Information Elements Update Cycles
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:
o persistent, even after a hard reboot: includes certificates that
are associated with the endpoint itself or with services it relies
on.
o volatile to a degree: may change at the beginning of each boot
cycle. This includes the capability of a TPM to provide relative
time which provides the basis for the synchronization token and
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implicit attestation - and which can reset after an Attester is
powered off.
o very volatile: can change during any time of an uptime cycle
(periods of time an Attester is powered on, starting with its boot
sequence). This includes the content of PCRs of a hardware RoT
and thereby also the PCR-restricted signing keys used for
attestation.
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:
o The Attester completes a boot-cycle
o A relevant PCR changes
o Too much time has passed since the Evidence Generation
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.
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.----------. .----------.
| 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 <= |
| |
Figure 1: Example sequence of events
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7. Sync Base Protocol
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:
o At a given point in time (called "left"), a signed tickstamp
counter value is acquired from the hardware RoT. The hash of
counter and signature is used as a nonce in the request directed
at the TSA.
o The corresponding response includes a data-structure incorporating
the trusted timestamp token and its signature created by the TSA.
o At the point-in-time the response arrives (called "right"), a
signed tickstamp counter value is acquired from the hardware RoT
again, using a hash of the signed TSA timestamp as a nonce.
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.
8. IANA Considerations
This memo includes requests to IANA, including registrations for
media type definitions.
TBD
9. Security Considerations
There are Security Considerations. TBD
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10. Contributors
TBD
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3161] Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,
"Internet X.509 Public Key Infrastructure Time-Stamp
Protocol (TSP)", RFC 3161, DOI 10.17487/RFC3161, August
2001, <https://www.rfc-editor.org/info/rfc3161>.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<https://www.rfc-editor.org/info/rfc3411>.
[RFC5209] Sangster, P., Khosravi, H., Mani, M., Narayan, K., and J.
Tardo, "Network Endpoint Assessment (NEA): Overview and
Requirements", RFC 5209, DOI 10.17487/RFC5209, June 2008,
<https://www.rfc-editor.org/info/rfc5209>.
[RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible
Authentication Protocol (EAP) Key Management Framework",
RFC 5247, DOI 10.17487/RFC5247, August 2008,
<https://www.rfc-editor.org/info/rfc5247>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7320] Nottingham, M., "URI Design and Ownership", RFC 7320,
DOI 10.17487/RFC7320, July 2014,
<https://www.rfc-editor.org/info/rfc7320>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8639] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Subscription to YANG Notifications",
RFC 8639, DOI 10.17487/RFC8639, September 2019,
<https://www.rfc-editor.org/info/rfc8639>.
[RFC8640] Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
E., and A. Tripathy, "Dynamic Subscription to YANG Events
and Datastores over NETCONF", RFC 8640,
DOI 10.17487/RFC8640, September 2019,
<https://www.rfc-editor.org/info/rfc8640>.
[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
September 2019, <https://www.rfc-editor.org/info/rfc8641>.
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11.2. Informative References
[AIK-Credential]
TCG Infrastructure Working Group, "TCG Credential
Profile", 2007, <https://www.trustedcomputinggroup.org/wp-
content/uploads/IWG-Credential_Profiles_V1_R1_14.pdf>.
[AIK-Enrollment]
TCG Infrastructure Working Group, "A CMC Profile for AIK
Certificate Enrollment", 2011,
<https://www.trustedcomputinggroup.org/wp-content/uploads/
IWG_CMC_Profile_Cert_Enrollment_v1_r7.pdf>.
[CEL] TCG TNC Working Group, "DRAFT Canonical Event Log Format
Version: 1.0, Revision: .12", 2018.
[I-D.birkholz-rats-coswid-rim]
Birkholz, H., Uiterwijk, P., Smith, N., Fitzgerald-McKay,
J., Waltermire, D., and S. Bhandari, "Reference Integrity
Measurement Extension for Concise Software Identities",
draft-birkholz-rats-coswid-rim-01 (work in progress), July
2020.
[I-D.birkholz-rats-uccs]
Birkholz, H., O'Donoghue, J., Cam-Winget, N., and C.
Bormann, "A CBOR Tag for Unprotected CWT Claims Sets",
draft-birkholz-rats-uccs-02 (work in progress), December
2020.
[I-D.fedorkow-rats-network-device-attestation]
Fedorkow, G., Voit, E., and J. Fitzgerald-McKay, "TPM-
based Network Device Remote Integrity Verification",
draft-fedorkow-rats-network-device-attestation-05 (work in
progress), April 2020.
[I-D.ietf-core-comi]
Veillette, M., Stok, P., Pelov, A., Bierman, A., and I.
Petrov, "CoAP Management Interface (CORECONF)", draft-
ietf-core-comi-10 (work in progress), July 2020.
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture",
draft-ietf-rats-architecture-08 (work in progress),
December 2020.
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[I-D.ietf-rats-reference-interaction-models]
Birkholz, H., Eckel, M., Newton, C., and L. Chen,
"Reference Interaction Models for Remote Attestation
Procedures", draft-ietf-rats-reference-interaction-
models-01 (work in progress), October 2020.
[I-D.ietf-sacm-coswid]
Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
Waltermire, "Concise Software Identification Tags", draft-
ietf-sacm-coswid-16 (work in progress), November 2020.
[I-D.ietf-sacm-terminology]
Birkholz, H., Lu, J., Strassner, J., Cam-Winget, N., and
A. Montville, "Security Automation and Continuous
Monitoring (SACM) Terminology", draft-ietf-sacm-
terminology-16 (work in progress), December 2018.
[IEEE1609]
IEEE Computer Society, "1609.4-2016 - IEEE Standard for
Wireless Access in Vehicular Environments (WAVE) -- Multi-
Channel Operation", IEEE Std 1609.4, 2016.
[IEEE802.11P]
IEEE Computer Society, "802.11P-2010 - IEEE Standard for
Information technology-- Local and metropolitan area
networks-- Specific requirements-- Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY)
Specifications Amendment 6: Wireless Access in Vehicular
Environments", IEEE Std 802.11P, 2010.
[IEEE802.1AR]
IEEE Computer Society, "802.1AR-2009 - IEEE Standard for
Local and metropolitan area networks - Secure Device
Identity", IEEE Std 802.1AR, 2009.
[PRIRA] Coker, G., Guttman, J., Loscocco, P., Herzog, A., Millen,
J., O'Hanlon, B., Ramsdell, J., Segall, A., Sheehy, J.,
and B. Sniffen, "Principles of Remote Attestation",
Springer International Journal of Information Security,
Vol. 10, pp. 63-81, DOI 10.1007/s10207-011-0124-7, April
2011.
[PTS] TCG TNC Working Group, "TCG Attestation PTS Protocol
Binding to TNC IF-M", 2011,
<https://www.trustedcomputinggroup.org/wp-content/uploads/
IFM_PTS_v1_0_r28.pdf>.
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[REST] Fielding, R., "Architectural Styles and the Design of
Network-based Software Architectures", Ph.D. Dissertation,
University of California, Irvine, 2000,
<http://www.ics.uci.edu/~fielding/pubs/dissertation/
fielding_dissertation.pdf>.
[RFC1213] McCloghrie, K. and M. Rose, "Management Information Base
for Network Management of TCP/IP-based internets: MIB-II",
STD 17, RFC 1213, DOI 10.17487/RFC1213, March 1991,
<https://www.rfc-editor.org/info/rfc1213>.
[RFC2790] Waldbusser, S. and P. Grillo, "Host Resources MIB",
RFC 2790, DOI 10.17487/RFC2790, March 2000,
<https://www.rfc-editor.org/info/rfc2790>.
[RFC3418] Presuhn, R., Ed., "Management Information Base (MIB) for
the Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, DOI 10.17487/RFC3418, December 2002,
<https://www.rfc-editor.org/info/rfc3418>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC6933] Bierman, A., Romascanu, D., Quittek, J., and M.
Chandramouli, "Entity MIB (Version 4)", RFC 6933,
DOI 10.17487/RFC6933, May 2013,
<https://www.rfc-editor.org/info/rfc6933>.
[Safford] Safford, D., Zohar, M., and R. Sailer, "Using IMA for
Integrity Measurement and Attestation", Linux Plumbers
Conference 2009 , 2009.
[SCALE] Fuchs, A., "Improving Scalability for Remote Attestation",
Master Thesis (Diplomarbeit), Technische Universitaet
Darmstadt, Germany, 2008.
[SFKE2008]
Stumpf, F., Fuchs, A., Katzenbeisser, S., and C. Eckert,
"Improving the scalability of platform attestation",
ACM Proceedings of the 3rd ACM workshop on Scalable
trusted computing - STC '08 , page 1-10,
DOI 10.1145/1456455.1456457, 2008.
[STD62] "Internet Standard 62", STD 62, RFCs 3411 to 3418,
December 2002.
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[Steffens]
Steffen, A., "The linux Integrity Measurement Architecture
and TPM-based Network Endpoint Assessment", Linux Security
Summit , 2012.
[TCGGLOSS]
TCG, "TCG Glossary", 2012,
<https://www.trustedcomputinggroup.org/wp-content/uploads/
TCG_Glossary_Board-Approved_12.13.2012.pdf>.
[TCGRIM] TCG, "TCG Reference Integrity Manifest (RIM) Information
Model", 2019, <https://trustedcomputinggroup.org/wp-
content/uploads/TCG_RIM_Model_v1-r13_2feb20.pdf>.
[TEE] Global Platform, "TEE System Architecture v1.1,
GPD_SPE_009", 2017.
[TPM12] "Information technology -- Trusted Platform Module -- Part
1: Overview", ISO/IEC 11889-1, 2009.
[TPM2] Trusted Computing Group, "Trusted Platform Module Library
Specification, Family 2.0, Level 00, Revision 01.16 ed.",
2014.
Appendix A. REST Realization
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
[RFC7320]. 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].
Appendix B. SNMP Realization
SNMPv3 [STD62] [RFC3411] 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.
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Design Principles:
1. Over time, TUDA attestation values age and should no longer be
used. Every table in the TUDA MIB has a primary index with the
value of a separate scalar cycle counter object that
disambiguates the transition from one attestation cycle to the
next.
2. Over time, the measurement log information (for example) may grow
large. Therefore, read-only cycle counter scalar objects in all
TUDA MIB object groups facilitate more efficient access with SNMP
GetNext requests.
3. Notifications are supported by an SNMP trap definition with all
of the cycle counters as bindings, to alert a Verifier that a new
attestation cycle has occurred (e.g., synchronization data,
measurement log, etc. have been updated by adding new rows and
possibly deleting old rows).
B.1. Structure of TUDA MIB
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 | |
|-------------|-------|----------|----------|----------|
B.1.1. Cycle Index
A tudaV1<Group>CycleIndex is the:
1. first index of a row (element instance or element fragment) in
the tudaV1<Group>Table;
2. identifier of an update cycle on the table, when rows were added
and/or deleted from the table (bounded by tudaV1<Group>Cycles);
and
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3. binding in the tudaV1TrapV2Cycles notification for directed
polling.
B.1.2. Instance Index
A tudaV1<Group>InstanceIndex is the:
1. second index of a row (element instance or element fragment) in
the tudaV1<Group>Table; except for
2. a row in the tudaV1SyncTokenTable (that has only one instance per
cycle).
B.1.3. Fragment Index
A tudaV1<Group>FragmentIndex is the:
1. last index of a row (always an element fragment) in the
tudaV1<Group>Table; and
2. accomodation for SNMP transport mapping restrictions for large
string elements that require fragmentation.
B.2. Relationship to Host Resources MIB
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].
B.3. Relationship to Entity MIB
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].
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B.4. Relationship to Other MIBs
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 [RFC3418] and
provides context information for the TUDA attestation process.
B.5. Definition of TUDA MIB
<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)."
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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."
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::= { 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."
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::= { 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
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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 }
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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
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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."
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::= { 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
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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 }
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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
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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
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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 }
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::= { 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
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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)
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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 }
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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 }
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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>
Appendix C. YANG Realization
<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
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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" {
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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;
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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 {
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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 {
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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.
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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.";
}
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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 {
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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.";
}
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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;
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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 */
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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
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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
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"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.
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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;
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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.";
}
}
}
}
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<CODE ENDS>
Appendix D. Realization with TPM functions
D.1. TPM Functions
The following TPM structures, resources and functions are used within
this approach. They are based upon the TPM specifications [TPM12]
and [TPM2].
D.1.1. Tick-Session and Tick-Stamp
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.
D.1.2. Platform Configuration Registers (PCRs)
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
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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).
D.1.3. PCR restricted Keys
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.
D.1.4. CertifyInfo
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.
D.2. IE Generation Procedures for TPM 1.2
D.2.1. AIK and AIK Certificate
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].
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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
Figure 2: TUDA-Cert element in CDDL
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)
| }
Figure 3: Creating the TUDA-Cert element
D.2.2. Synchronization Token
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:
o The TPM creates a TickStampBlob using the AIK
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o This TickstampBlob is used as nonce to the Timestamp of the TSA
o Another TickStampBlob with the AIK is created using the TSA's
Timestamp a nonce
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
Figure 4: TUDA-Sync element in CDDL
Required TPM functions:
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| 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 */
| }
Figure 5: Creating the Sync-Token element
D.2.3. RestrictionInfo
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:
o PCR list,
o the newly created restricted public key, and
o the certificate.
TUDA-RestrictionInfo = [Composite,
restrictedKey_Pub: Pubkey,
CertifyInfo]
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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
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; "If the key is using the default exponent then the exponentSize
; MUST be 0" -> we represent this case as null
]
Figure 6: TUDA-Key element in CDDL
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 */
| }
Figure 7: Creating the pubkey
D.2.4. Measurement Log
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.
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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]
D.2.5. Implicit Attestation
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
Figure 8: TUDA-Verify element in CDDL
Required TPM functions:
| imp_att = TPM_TickStampBlob(
| keyHandle = restrictedKey_Handle, /*TPM_KEY_HANDLE*/
| antiReplay = dummyNonce, /*TPM_NONCE*/
| digestToStamp = dummyDigest) /*TPM_DIGEST*/
|
| VerifyToken = imp_att
Figure 9: Creating the Verify Token
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D.2.6. Attestation Verification Approach
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)
Figure 10: Verification of Certificates
| 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
Figure 11: Verification of Synchronization Token
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| 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)
Figure 12: Verification of Restriction Info
| 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++]
Figure 13: Verification of Measurement Log
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| 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]
Figure 14: Verification of Attestation Token
D.3. IE Generation Procedures for TPM 2.0
The pseudo code below includes general operations that are conducted
as specific TPM commands:
o hash() : description TBD
o sig() : description TBD
o X.509-Certificate() : description TBD
These represent the output structure of that command in the form of a
byte string value.
D.3.1. AIK and AIK Certificate
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.
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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)
Figure 15: TUDA-Cert element for TPM 2.0
D.3.2. Synchronization Token
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
]
)
]
Figure 16: TUDA-Sync element for TPM 2.0
D.3.3. Measurement Log
The creation procedure is identical to Appendix D.2.4.
Measurement-Log = [
* [ EventName,
PCR-Num,
Event-Hash ]
]
Figure 17: TUDA-Log element for TPM 2.0
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D.3.4. Explicit time-based Attestation
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
)
Figure 18: TUDA-Attest element for TPM 2.0
D.3.5. Sync Proof
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
]
),
Figure 19: TUDA-Proof element for TPM 2.0
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Acknowledgements
Authors' Addresses
Andreas Fuchs
Fraunhofer Institute for Secure Information Technology
Rheinstrasse 75
Darmstadt 64295
Germany
Email: andreas.fuchs@sit.fraunhofer.de
Henk Birkholz
Fraunhofer Institute for Secure Information Technology
Rheinstrasse 75
Darmstadt 64295
Germany
Email: henk.birkholz@sit.fraunhofer.de
Ira E McDonald
High North Inc
PO Box 221
Grand Marais 49839
US
Email: blueroofmusic@gmail.com
Carsten Bormann
Universitaet Bremen TZI
Bibliothekstr. 1
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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