RATS Working Group A. Fuchs
Internet-Draft H. Birkholz
Intended status: Standards Track Fraunhofer SIT
Expires: September 10, 2020 I. McDonald
High North Inc
C. Bormann
Universitaet Bremen TZI
March 09, 2020
Time-Based Uni-Directional Attestation
draft-birkholz-rats-tuda-02
Abstract
This documents defines the method and bindings used to conduct Time-
based Uni-Directional Attestation (TUDA) between two RATS (Remote
ATtestation procedureS) Principals over the Internet. 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. Conversely, TUDA enables the creation of Secure Audit Logs
that can constitute Evidence about current and past operational
states of an Attester. As a prerequisite for TUDA, every RATS
Principal requires access to a trusted and synchronized time-source.
Per default, in TUDA this is a Time Stamp Authority (TSA) issuing
signed Time Stamp Tokens (TST).
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 4
1.2. Evidence . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Creating Evidence about Software Component Integrity . . 5
1.3.1. Data Items . . . . . . . . . . . . . . . . . . . . . 5
1.3.2. System Components . . . . . . . . . . . . . . . . . . 5
1.3.3. Operations . . . . . . . . . . . . . . . . . . . . . 6
1.4. Remote Attestation Principles . . . . . . . . . . . . . . 6
1.5. System Component Requirements . . . . . . . . . . . . . . 7
1.6. Evidence Appraisal . . . . . . . . . . . . . . . . . . . 7
1.7. Activities and Actions . . . . . . . . . . . . . . . . . 8
1.8. Attestation and Verification . . . . . . . . . . . . . . 8
1.9. Information Elements and Conveyance . . . . . . . . . . . 8
1.10. TUDA Objectives . . . . . . . . . . . . . . . . . . . . . 9
1.11. Hardware Dependencies . . . . . . . . . . . . . . . . . . 10
2. TUDA Core Concept . . . . . . . . . . . . . . . . . . . . . . 10
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Universal Terms . . . . . . . . . . . . . . . . . . . . . 11
3.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.1. General Types . . . . . . . . . . . . . . . . . . . . 13
3.2.2. RoT specific terms . . . . . . . . . . . . . . . . . 13
3.3. Certificates . . . . . . . . . . . . . . . . . . . . . . 13
4. Time-Based Uni-Directional Attestation . . . . . . . . . . . 13
4.1. TUDA Information Elements Update Cycles . . . . . . . . . 15
5. Sync Base Protocol . . . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 18
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . 19
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10.2. Informative References . . . . . . . . . . . . . . . . . 20
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 . . . . . . . . . . . . . . . . . . . 25
B.1.3. Fragment Index . . . . . . . . . . . . . . . . . . . 25
B.2. Relationship to Host Resources MIB . . . . . . . . . . . 26
B.3. Relationship to Entity MIB . . . . . . . . . . . . . . . 26
B.4. Relationship to Other MIBs . . . . . . . . . . . . . . . 26
B.5. Definition of TUDA MIB . . . . . . . . . . . . . . . . . 26
Appendix C. YANG Realization . . . . . . . . . . . . . . . . . . 43
Appendix D. Realization with TPM functions . . . . . . . . . . . 57
D.1. TPM Functions . . . . . . . . . . . . . . . . . . . . . . 57
D.1.1. Tick-Session and Tick-Stamp . . . . . . . . . . . . . 57
D.1.2. Platform Configuration Registers (PCRs) . . . . . . . 58
D.1.3. PCR restricted Keys . . . . . . . . . . . . . . . . . 59
D.1.4. CertifyInfo . . . . . . . . . . . . . . . . . . . . . 59
D.2. IE Generation Procedures for TPM 1.2 . . . . . . . . . . 59
D.2.1. AIK and AIK Certificate . . . . . . . . . . . . . . . 59
D.2.2. Synchronization Token . . . . . . . . . . . . . . . . 60
D.2.3. RestrictionInfo . . . . . . . . . . . . . . . . . . . 62
D.2.4. Measurement Log . . . . . . . . . . . . . . . . . . . 64
D.2.5. Implicit Attestation . . . . . . . . . . . . . . . . 65
D.2.6. Attestation Verification Approach . . . . . . . . . . 66
D.3. IE Generation Procedures for TPM 2.0 . . . . . . . . . . 68
D.3.1. AIK and AIK Certificate . . . . . . . . . . . . . . . 68
D.3.2. Synchronization Token . . . . . . . . . . . . . . . . 69
D.3.3. Measurement Log . . . . . . . . . . . . . . . . . . . 69
D.3.4. Explicit time-based Attestation . . . . . . . . . . . 70
D.3.5. Sync Proof . . . . . . . . . . . . . . . . . . . . . 70
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 71
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 71
1. Introduction
Remote ATtestation procedureS (RATS) describe the attempt to
determine and appraise properties, such as integrity and
trustworthiness, of a communication partner - the Attester - over the
Internet to another communication parter - the Verifier - without
direct access. TUDA uses the architectural constituents of the RATS
Architecture [I-D.ietf-rats-architecture] that defines the Roles
Attester and Verifier in detail. The RATS Architecture also defines
Role Messages. TUDA creates and conveys a specific type of Role
Message called Evidence, a composition of trustwrthiness Claims
provided by an Attester and consumed by a Verifier (potentially
relayed by another RATS Role that is a Relying Party). TUDA - in
contrast to traditional bi-directional challenge-response protocols
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[I-D.birkholz-rats-reference-interaction-model] - enables a uni-
directional conveyance of attestation Evidence that allows for
providing attestation information without solicitation (e.g. as
beacons or push data via YANG Push [RFC8641], [RFC8640], [RFC8639]).
As a result, this document introduces the term Forward Authenticity.
Forward Authenticity (FA): 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. FA is achieved by timely recording of assessments of
the authenticity from system components (via "audit logs" during
"audit sessions") that are authorized for this purpose and
trustworthy (e.g via endorsed roots of trust), 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.
1.1. Requirements Notation
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.
1.2. Evidence
Remote attestation Evidence is basically a set of trustworthiness
claims (assertions about the Attester and its system characteristics
including security posture and protection characteristics) that are
accompanied by a proof of their veracity - typically a signature
based on shielded, private and potentially restricted key material.
As key material alone is typically not self-descriptive with respect
to its intended use (its semantics), the remote attestation Evidence
created via TUDA is accompanied by two kinds of certificates that are
cryptographically associated with a Trust Anchor (TA) [RFC4949] via a
certification path:
o an Attestation Key (AK) Certificate (AK-Cert) that represents the
attestation provenance of the created Evidence, and
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o an Endorsement Key (EK) Certificate (EK-Cert) that represents the
protection characteristics of the system components the AK is
stored in.
If a Verifier decides to trust both the TA of an AK-Cert and an EK-
Cert presented by an Attester - and the included assertions about the
system characteristics describing the Attester, the attestation
Evidence created via TUDA by the Attester is considered believable.
Ultimately, believable Evidence is appraised by a Verifier in order
to assess the trustworthiness of the corresponding Attester.
1.3. Creating Evidence about Software Component Integrity
The TUDA protocol mechanism uses hash values of all started software
components as a basis to provide and create Evidence about the
integrity of the software components of an Attester. This section
defines the processed data items, the required system components, and
corresponding operations to enable the creation of Evidence about
software component integrity for TUDA.
1.3.1. Data Items
The hash value of a software component created before it is executed
is referred to as a "measurement" in the remainder of this document.
Measurements are chained using a rolling hash function. Each
measurement added to the sequence of all measurements results in a
new current hash value that is referred to as a "digest" in the
remainder of this document.
1.3.2. System Components
The function to store these measurements via a rolling hash function
is provided by a root of trust for storage - a system component that
MUST be a component of the attester.
With respect to the boot sequence of an Attester, the very first
measurements of software components (e.g. the BIOS, or a sometimes a
bootloader) have to be conducted by a root of trust for measurement
that is implemented in hardware and MUST be a system component of the
Attester.
All measurements retained in the root of trust for measurements are
handed over to the root of trust for storage when it becomes
available during the boot procedure of the Attester. During that
hand-over the sequence of measurements retained in the root of trust
for measurement are processed by the rolling hash function of the
root of trust for storage.
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The function of retrieving the current output value of the rolling
hash function, including a signature to provide a proof of veracity,
is provided by a root of trust for reporting and MUST be a system
component of the Attester.
Typically, a root of trust for storage and a root of trust for
reporting are tightly coupled. Analogously, a root of trust for
measurement is typically independent from the root of trust for
storage, but has to be able to interact with root of trust for
storage at some point of the boot sequence of the Attester to hand
over the retained measurements.
1.3.3. Operations
The operation of processing a measurement and adding it to the
sequence of measurements via the rolling hash function is called
"extend" and is provided by the root of trust for storage.
The operation of retrieving the current available hash value that is
the result of the rolling hash function including a signature based
on an Attestation Key is called "quote" and is provided by the
corresponding root of trust for reporting.
1.4. Remote Attestation Principles
In essence, RATS are composed of three base activities. The
following definitions are derived from the definitions presented in
[PRIRA] and [TCGGLOSS], and are a simplified summary of the RATS
Architecture relevant for TUDA. The complete RATS Architecture and
every corresponding constituent, message and interaction is defined
in [I-D.ietf-rats-architecture].
Attestation: The creation of one ore more claims about the
trustworthiness properties of an Attester, such that the claims
can be used as Evidence.
Conveyance: The transfer of Evidence from the Attester to the
Verifier via an interconnect.
Verification: The appraisal of Evidence by evaluating it against
known-good-values (a type of declarative guidance).
With TUDA, the claims that compose the evidence are signatures over
trustworthy integrity measurements created by leveraging roots of
trust. The evidence is appraised via corresponding signatures over
reference integrity measurements (RIM, represented, for example via
[I-D.ietf-sacm-coswid]).
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Protocols that facilitate Trust-Anchor based signatures in order to
provide RATS are usually bi-directional challenge/response protocols,
such as the Platform Trust Service protocol [PTS] or CAVES [PRIRA],
where one entity sends a challenge that is included inside the
response to prove the recentness - the freshness (see fresh in
[RFC4949]) - of the attestation information. The corresponding
interaction model tightly couples the three activities of creating,
transferring and appraising evidence.
The Time-Based Uni-directional Attestation family of protocols - TUDA
- described in this document can decouple the three activities RATS
are composed of. 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 verification of past states,
o secure audit logs by combining the evidence created via TUDA with
integrity measurement logs that represent a detailed record of
corresponding past states,
o an uni-directional interaction model that can traverse "diode-
like" network security functions (NSF) or can be leveraged in
RESTful architectures (e.g. CoAP [RFC7252]), analogously.
1.5. System Component Requirements
TUDA is a family of protocols that bundles results from specific
attestation activities. The attestation activities of TUDA are based
on a hardware roots of trust that provides the following
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).
1.6. Evidence Appraisal
To appraise the evidence created by an Attester, the Verifier
requires corresponding Reference Integrity Measurements (RIM).
Typical set of RIMs are required to assess the integrity of an
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Attester. These sets are called RIM Bundles. The scope of a RIM
Bundle encompasses, e.g., a platform, a device, a computing context,
or a virtualised function. In order to be comparable, the hashing
algorithms used by the Attester to create the integrity measurements
have to match the hashing algorithms used to create the corresponding
RIM that are used by the Verifier to appraise the attestation
Evidence about software component integrity.
1.7. Activities and Actions
Depending on the platform (i.e. one or more computing contexts
including a dedicated hardware RoT), a generic RA activity results in
platform-specific actions that have to be conducted. In consequence,
there are multiple specific operations and data models (defining the
input and output of operations). Hence, specific actions are are not
covered by this document. Instead, the requirements on operations
and the information elements that are the input and output to these
operations are illustrated using pseudo code in Appendix C and D.
1.8. Attestation and Verification
Both the attestation and the verification activity of TUDA also
require a trusted Time Stamp Authority (TSA) as an additional third
party next to the Attester and the Verifier. The protocol uses a
Time Stamp Authority based on [RFC3161]. The combination of the
local source of time provided by the hardware RoT (located on the
Attester) and the Time Stamp Tokens provided by the TSA (to both the
Attester and the Verifier) enable the attestation and verification of
an appropriate freshness of the evidence conveyed by the Attester --
without requiring a challenge/response interaction model that uses a
nonce to ensure the freshness.
Typically, the verification activity requires declarative guidance
(representing desired or compliant endpoint characteristics in the
form of RIM, see above) to appraise the individual integrity
measurements the conveyed evidence is composed on. The acquisition
or representation (data models) of declarative guidance as well as
the corresponding evaluation methods are out of the scope of this
document.
1.9. Information Elements and Conveyance
TUDA defines a set of information elements (IE) that are created and
stored on the Attester and are intended to be transferred to the
Verifier in order to enable appraisal. Each TUDA IE:
o is encoded in the Concise Binary Object Representation (CBOR
[RFC7049]) to minimize the volume of data in motion. In this
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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 is only created/updated when
out-dated, which reduces the overall resources required from the
Attester, including the utilization of the hardware root of trust.
The IE that have to be created are determined by their age or by
specific state changes on the Attester (e.g. state changes due to
a reboot-cycle)
o is only 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 can be reused for multiple
remote attestation procedures in the limits of its corresponding
freshness-window, further reducing the load imposed on the
Attester and its corresponding hardware RoT.
1.10. TUDA Objectives
The Time-Based Uni-directional Attestation family of protocols 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.
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1.11. Hardware Dependencies
The binding of the attestation scheme used by TUDA to generate the
TUDA IE is specific to the methods provided by the hardware RoT used
(see above). In this document,expositional text and pseudo-code that
is provided as a reference to instantiate the TUDA IE is based on TPM
1.2 and TPM 2.0 operations. The corresponding TPM commands are
specified in [TPM12] and [TPM2]. The references to TPM commands and
corresponding pseudo-code only serve as guidance to enable a better
understanding of the attestation scheme and is intended to encourage
the use of any appropriate hardware RoT or equivalent set of
functions available to a CPU or Trusted Execution Environment [TEE].
2. TUDA Core Concept
There are significant differences between conventional bi-directional
attestation and TUDA regarding both the information elements conveyed
between Attester and Verifier and the time-frame, in which an
attestation can be considered to be fresh (and therefore
trustworthy).
In general, remote attestation using a bi-directional communication
scheme includes sending a nonce-challenge within a signed attestation
token. 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 the attestation
response, 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 platform's state by creating evidence that a certain key is
bound to that state. The latter provides proof that the platform 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 trustworthy). In consequence, each TUDA
IE that composes data in motion is based on different methods of
creation.
The freshness properties of a challenge-response based protocol
define the point-of-time of attestation between:
o the time of transmission of the nonce, and
o the reception of the corresponding response.
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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
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 TSA. The
time between the two tickstamps acquired via the hardware RoT
define the scope of the maximum drift ("left" and "right" in
respect to the timeline) to the TSA timestamp, and
o the drift of clocks included in the hardware 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 TSA and the hardware RoT. In
consequence, TUDA evidence can even serve as proof of integrity in
audit logs with precise point-in-time guarantees, in contrast to
classical attestations.
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 CoMI.
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.
3. Terminology
This document introduces roles, information elements and types
required to conduct TUDA and uses terminology (e.g. specific
certificate names) typically seen in the context of attestation or
hardware security modules.
3.1. Universal Terms
Attestation Identity Key (AIK): a special purpose signature
(therefore asymmetric) key that supports identity related
operations. The private portion of the key pair is maintained
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confidential to the entity via appropriate measures (that have an
impact on the scope of confidence). The public portion of the key
pair may be included in AIK credentials that provide a claim about
the entity.
Claim: A piece of information asserted about a subject [RFC4949]. A
claim is represented as a name/value pair consisting of a Claim
Name and a Claim Value [RFC7519].
In the context of SACM, a claim is also specialized as an
attribute/value pair that is intended to be related to a statement
[I-D.ietf-sacm-terminology].
Endpoint Attestation: the creation of evidence on the Attester that
provides proof of a set of the endpoints's integrity measurements.
This is done by digitally signing a set of PCRs using an AIK
shielded by the hardware RoT.
Endpoint Characteristics: the context, composition, configuration,
state, and behavior of an endpoint.
Evidence: a trustworthy set of claims about an endpoint's
characteristics.
Identity: a set of claims that is intended to be related to an
entity.
Integrity Measurements: Metrics of endpoint characteristics (i.e.
composition, configuration and state) that affect the confidence
in the trustworthiness of an endpoint. Digests of integrity
measurements can be stored in shielded locations (i.e. PCR of a
TPM).
Reference Integrity Measurements: Signed measurements about the
characteristics of an endpoint's characteristics that are provided
by a vendor and are intended to be used as declarative guidance
[I-D.ietf-sacm-terminology] (e.g. a signed CoSWID).
Trustworthy: the qualities of an endpoint that guarantee a specific
behavior and/or endpoint characteristics defined by declarative
guidance. Analogously, trustworthiness is the quality of being
trustworthy with respect to declarative guidance. Trustworthiness
is not an absolute property but defined with respect to an entity,
corresponding declarative guidance, and has a scope of confidence.
Trustworthy Endpoint: an endpoint that guarantees trustworthy
behavior and/or composition (with respect to certain declarative
guidance and a scope of confidence).
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Trustworthy Statement: evidence that is trustworthy conveyed by an
endpoint that is not necessarily trustworthy.
3.2. Roles
Attester: the endpoint that is the subject of the attestation to
another endpoint.
Verifier: the endpoint that consumes the attestation of another
endpoint to conduct a verification.
TSA: a Time Stamp Authority [RFC3161]
3.2.1. General Types
Byte: the now customary synonym for octet
Cert: an X.509 certificate represented as a byte-string
3.2.2. RoT specific terms
PCR: a Platform Configuration Register that is part of a hardware
root of trust 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
3.3. Certificates
TSA-CA: the Certificate Authority that provides the certificate for
the TSA represented as a Cert
AIK-CA: the Certificate Authority that provides the certificate for
the attestation identity key of the TPM. This is the client
platform credential for this protocol. It is a placeholder for a
specific CA and AIK-Cert is a placeholder for the corresponding
certificate, depending on what protocol was used. The specific
protocols are out of scope for this document, see also
[AIK-Enrollment] and [IEEE802.1AR].
4. Time-Based Uni-Directional Attestation
A Time-Based Uni-Directional Attestation (TUDA) consists of the
following seven information elements. They are used to gain
assurance of the Attester's platform configuration at a certain point
in time:
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TSA Certificate: The certificate of the Time Stamp Authority that is
used in a subsequent synchronization protocol token. This
certificate is signed by the TSA-CA.
AIK Certificate: A certificate about the Attestation Identity Key
(AIK) used. This may or may not also 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 for attestations are the
relative timestanps provided by the hardware RoT. In order to put
attestations 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, a synchronization protocol
is run with a Time Stamp Authority (TSA).
Restriction Info: The attestation relies on the capability of the
hardware RoT 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 corresponding signing
capabilities of the hardware RoT are used. It creates a signed
certificate using the AIK about the newly created restricted key.
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 (in the form of RIM available
to the Verifier) exists and no measurement log is required.
Implicit Attestation: The actual attestation is then based upon a
signed timestamp provided by the hardware RoT using the restricted
temporary key that was certified in the steps above. The signed
timestamp provides evidence that at this point in time (with
respect to the relative time of the hardware RoT) a certain
configuration existed (namely the PCR values associated with the
restricted key). Together with the synchronization token this
timestamp represented in relative time can then be related to the
real-time clock.
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Concise SWID tags: As an option to better assess the trustworthiness
of an Attester, a Verifier can request the reference hashes (RIM,
which are often referred to as golden measurements) of all started
software components to compare them with the entries in the
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 CBOR array (a RIM Manifest). Ideally, the reference hashes
include a signature created by the manufacturer of the software to
prove their integrity.
These information elements could 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 endpoint, 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 the whole certificate provisioning completely in order to save
bandwidth and computation time for certificate verification.
4.1. TUDA Information Elements Update Cycles
An endpoint can be in various states and have various information
associated with it during its life cycle. For TUDA, a subset of the
states (which can include associated information) that an endpoint
and its hardware root of trust can be in, is important to the
attestation process. States can be:
o persistent, even after a hard reboot. This includes certificates
that are associated with the endpoint itself or with services it
relies on.
o volatile to a degree, because they change at the beginning of each
boot cycle. This includes the capability of a hardware RoT to
provide relative time which provides the basis for the
synchronization token and implicit attestation--and which can
reset after an endpoint is powered off.
o very volatile, because they change during an uptime cycle (the
period of time an endpoint is powered on, starting with its boot).
This includes the content of PCRs of a hardware RoT and thereby
also the PCR-restricted signing keys used for attestation.
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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 a renewed attestation:
o The Attester completes a boot-cycle
o A relevant PCR changes
o Too much time has passed since the last attestation statement
The third event listed above is variable per application use case and
also depends on the precision of the clock included in the hardware
RoT. For usage scenarios, in which the device would periodically
push information to be used in an audit-log, a time-frame of
approximately one update per minute should be sufficient in most
cases. For those usage scenarios, where Verifiers request (pull) a
fresh attestation statement, an implementation could use the hardware
RoT continuously to always present the most freshly created results.
To save some utilization of the hardware RoT for other purposes,
however, a time-frame of once per ten seconds is recommended, which
would typically leave about 80% of utilization for other
applications.
Attester Verifier
| |
Boot |
| |
Create Sync-Token |
| |
Create Restricted Key |
Certify Restricted Key |
| |
| AIK-Cert ---------------------------------------------> |
| Sync-Token -------------------------------------------> |
| Certify-Info -----------------------------------------> |
| Measurement Log --------------------------------------> |
| Attestation ------------------------------------------> |
| Verify Attestation
| |
| <Time Passed> |
| |
| Attestation ------------------------------------------> |
| Verify Attestation
| |
| <Time Passed> |
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| |
PCR-Change |
| |
Create Restricted Key |
Certify Restricted Key |
| |
| Certify-Info -----------------------------------------> |
| Measurement Log --------------------------------------> |
| Attestation ------------------------------------------> |
| Verify Attestation
| |
Boot |
| |
Create Sync-Token |
| |
Create Restricted Key |
Certify Restricted Key |
| |
| Sync-Token -------------------------------------------> |
| Certify-Info -----------------------------------------> |
| Measurement Log --------------------------------------> |
| Attestation ------------------------------------------> |
| Verify Attestation
| |
| <Time Passed> |
| |
| Attestation ------------------------------------------> |
| Verify Attestation
| |
Figure 1: Example sequence of events
5. 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.
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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.
content TBD
6. IANA Considerations
This memo includes requests to IANA, including registrations for
media type definitions.
TBD
7. Security Considerations
There are Security Considerations. TBD
8. Change Log
Changes from version 04 to I2NSF related document version 00: *
Refactored main document to be more technology agnostic * Added first
draft of procedures for TPM 2.0 * Improved content consistency and
structure of all sections
Changes from version 03 to version 04:
o Refactoring of Introduction, intend, scope and audience
o Added first draft of Sync Base Prootoll section illustrated
background for interaction with TSA
o Added YANG module
o Added missing changelog entry
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Changes from version 02 to version 03:
o Moved base concept out of Introduction
o First refactoring of Introduction and Concept
o First restructuring of Appendices and improved references
Changes from version 01 to version 02:
o Restructuring of Introduction, highlighting conceptual
prerequisites
o Restructuring of Concept to better illustrate differences to hand-
shake based attestation and deciding factors regarding freshness
properties
o Subsection structure added to Terminology
o Clarification of descriptions of approach (these were the FIXMEs)
o Correction of RestrictionInfo structure: Added missing signature
member
Changes from version 00 to version 01:
Major update to the SNMP MIB and added a table for the Concise SWID
profile Reference Hashes that provides additional information to be
compared with the measurement logs.
9. Contributors
TBD
10. References
10.1. Normative References
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture",
draft-ietf-rats-architecture-02 (work in progress), March
2020.
[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>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
10.2. 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>.
[I-D.birkholz-rats-reference-interaction-model]
Birkholz, H. and M. Eckel, "Reference Interaction Models
for Remote Attestation Procedures", draft-birkholz-rats-
reference-interaction-model-02 (work in progress), January
2020.
[I-D.ietf-core-comi]
Veillette, M., Stok, P., Pelov, A., Bierman, A., and I.
Petrov, "CoAP Management Interface", draft-ietf-core-
comi-09 (work in progress), March 2020.
[I-D.ietf-sacm-coswid]
Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
Waltermire, "Concise Software Identification Tags", draft-
ietf-sacm-coswid-13 (work in progress), November 2019.
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[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.
[IEEE802.1AR]
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>.
[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>.
[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>.
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[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>.
[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>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[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>.
[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>.
[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", BCP 190,
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>.
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[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>.
[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>.
[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.
[TCGGLOSS]
TCG, "TCG Glossary", 2012,
<https://www.trustedcomputinggroup.org/wp-content/uploads/
TCG_Glossary_Board-Approved_12.13.2012.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 Platform Module Library Specification, Family
2.0, Level 00, Revision 01.16 ed., Trusted Computing
Group", 2014.
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Appendix A. REST Realization
Each of the seven data items is defined as a media type (Section 6).
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.
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).
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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
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
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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].
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
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LAST-UPDATED "202003090000Z" -- 09 March 2020
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 (2020)."
REVISION "202003090000Z" -- 09 March 2020
DESCRIPTION
"Eighth 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
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DESCRIPTION
"Fifth version, published as draft-birkholz-i2nsf-tuda-01."
REVISION "201701090000Z" -- 09 January 2017
DESCRIPTION
"Fourth version, published as draft-birkholz-i2nsf-tuda-00."
REVISION "201607080000Z" -- 08 July 2016
DESCRIPTION
"Third version, published as draft-birkholz-tuda-02."
REVISION "201603210000Z" -- 21 March 2016
DESCRIPTION
"Second version, published as draft-birkholz-tuda-01."
REVISION "201510180000Z" -- 18 October 2015
DESCRIPTION
"Initial version, published as draft-birkholz-tuda-00."
::= { enterprises fraunhofersit(21616) mibs(1) tudaV1MIB(1) }
tudaV1MIBNotifications OBJECT IDENTIFIER ::= { tudaV1MIB 0 }
tudaV1MIBObjects OBJECT IDENTIFIER ::= { tudaV1MIB 1 }
tudaV1MIBConformance OBJECT IDENTIFIER ::= { tudaV1MIB 2 }
--
-- General
--
tudaV1General OBJECT IDENTIFIER ::= { tudaV1MIBObjects 1 }
tudaV1GeneralCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of TUDA update cycles that have occurred, i.e.,
sum of all the individual group cycle counters.
DEFVAL intentionally omitted - counter object."
::= { tudaV1General 1 }
tudaV1GeneralVersionInfo OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..255))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Version information for TUDA MIB, e.g., specific release
version of TPM 1.2 base specification and release version
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of TPM 1.2 errata specification and manufacturer and model
TPM module itself."
DEFVAL { "" }
::= { tudaV1General 2 }
--
-- AIK Cert
--
tudaV1AIKCert OBJECT IDENTIFIER ::= { tudaV1MIBObjects 2 }
tudaV1AIKCertCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of AIK Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1AIKCert 1 }
tudaV1AIKCertTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1AIKCertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of AIK Certificate data."
::= { tudaV1AIKCert 2 }
tudaV1AIKCertEntry OBJECT-TYPE
SYNTAX TudaV1AIKCertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of AIK Certificate data."
INDEX { tudaV1AIKCertCycleIndex,
tudaV1AIKCertInstanceIndex,
tudaV1AIKCertFragmentIndex }
::= { tudaV1AIKCertTable 1 }
TudaV1AIKCertEntry ::=
SEQUENCE {
tudaV1AIKCertCycleIndex Integer32,
tudaV1AIKCertInstanceIndex Integer32,
tudaV1AIKCertFragmentIndex Integer32,
tudaV1AIKCertData OCTET STRING
}
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tudaV1AIKCertCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this AIK Certificate fragment.
Index of an AIK Certificate chain update cycle that has
occurred (bounded by the value of tudaV1AIKCertCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 1 }
tudaV1AIKCertInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this AIK Certificate fragment.
Ordinal of this AIK Certificate in this chain, where the AIK
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 2 }
tudaV1AIKCertFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this AIK Certificate fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 3 }
tudaV1AIKCertData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded AIK Certificate data."
DEFVAL { "" }
::= { tudaV1AIKCertEntry 4 }
--
-- TSA Cert
--
tudaV1TSACert OBJECT IDENTIFIER ::= { tudaV1MIBObjects 3 }
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tudaV1TSACertCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of TSA Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1TSACert 1 }
tudaV1TSACertTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1TSACertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of TSA Certificate data."
::= { tudaV1TSACert 2 }
tudaV1TSACertEntry OBJECT-TYPE
SYNTAX TudaV1TSACertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of TSA Certificate data."
INDEX { tudaV1TSACertCycleIndex,
tudaV1TSACertInstanceIndex,
tudaV1TSACertFragmentIndex }
::= { tudaV1TSACertTable 1 }
TudaV1TSACertEntry ::=
SEQUENCE {
tudaV1TSACertCycleIndex Integer32,
tudaV1TSACertInstanceIndex Integer32,
tudaV1TSACertFragmentIndex Integer32,
tudaV1TSACertData OCTET STRING
}
tudaV1TSACertCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this TSA Certificate fragment.
Index of a TSA Certificate chain update cycle that has
occurred (bounded by the value of tudaV1TSACertCycles).
DEFVAL intentionally omitted - index object."
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::= { tudaV1TSACertEntry 1 }
tudaV1TSACertInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this TSA Certificate fragment.
Ordinal of this TSA Certificate in this chain, where the TSA
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 2 }
tudaV1TSACertFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this TSA Certificate fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 3 }
tudaV1TSACertData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded TSA Certificate data."
DEFVAL { "" }
::= { tudaV1TSACertEntry 4 }
--
-- Sync Token
--
tudaV1SyncToken OBJECT IDENTIFIER ::= { tudaV1MIBObjects 4 }
tudaV1SyncTokenCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Sync Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
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::= { tudaV1SyncToken 1 }
tudaV1SyncTokenInstances OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Sync Token instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object."
::= { tudaV1SyncToken 2 }
tudaV1SyncTokenTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1SyncTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of Sync Token data."
::= { tudaV1SyncToken 3 }
tudaV1SyncTokenEntry OBJECT-TYPE
SYNTAX TudaV1SyncTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of Sync Token data."
INDEX { tudaV1SyncTokenCycleIndex,
tudaV1SyncTokenInstanceIndex,
tudaV1SyncTokenFragmentIndex }
::= { tudaV1SyncTokenTable 1 }
TudaV1SyncTokenEntry ::=
SEQUENCE {
tudaV1SyncTokenCycleIndex Integer32,
tudaV1SyncTokenInstanceIndex Integer32,
tudaV1SyncTokenFragmentIndex Integer32,
tudaV1SyncTokenData OCTET STRING
}
tudaV1SyncTokenCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this Sync Token fragment.
Index of a Sync Token update cycle that has
occurred (bounded by the value of tudaV1SyncTokenCycles).
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DEFVAL intentionally omitted - index object."
::= { tudaV1SyncTokenEntry 1 }
tudaV1SyncTokenInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this Sync Token fragment.
Ordinal of this instance of Sync Token data
(NOT bounded by the value of tudaV1SyncTokenInstances).
DEFVAL intentionally omitted - index object."
::= { tudaV1SyncTokenEntry 2 }
tudaV1SyncTokenFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this Sync Token fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1SyncTokenEntry 3 }
tudaV1SyncTokenData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded Sync Token data."
DEFVAL { "" }
::= { tudaV1SyncTokenEntry 4 }
--
-- Restriction Info
--
tudaV1Restrict OBJECT IDENTIFIER ::= { tudaV1MIBObjects 5 }
tudaV1RestrictCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Restriction Info update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
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::= { tudaV1Restrict 1 }
tudaV1RestrictTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1RestrictEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Restriction Info data."
::= { tudaV1Restrict 2 }
tudaV1RestrictEntry OBJECT-TYPE
SYNTAX TudaV1RestrictEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Restriction Info data."
INDEX { tudaV1RestrictCycleIndex }
::= { tudaV1RestrictTable 1 }
TudaV1RestrictEntry ::=
SEQUENCE {
tudaV1RestrictCycleIndex Integer32,
tudaV1RestrictData OCTET STRING
}
tudaV1RestrictCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of this Restriction Info entry.
Index of a Restriction Info update cycle that has
occurred (bounded by the value of tudaV1RestrictCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1RestrictEntry 1 }
tudaV1RestrictData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"An instance of CBOR encoded Restriction Info data."
DEFVAL { "" }
::= { tudaV1RestrictEntry 2 }
--
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-- Measurement Log
--
tudaV1Measure OBJECT IDENTIFIER ::= { tudaV1MIBObjects 6 }
tudaV1MeasureCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Measurement Log update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1Measure 1 }
tudaV1MeasureInstances OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Measurement Log instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object."
::= { tudaV1Measure 2 }
tudaV1MeasureTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1MeasureEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Measurement Log data."
::= { tudaV1Measure 3 }
tudaV1MeasureEntry OBJECT-TYPE
SYNTAX TudaV1MeasureEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Measurement Log data."
INDEX { tudaV1MeasureCycleIndex,
tudaV1MeasureInstanceIndex }
::= { tudaV1MeasureTable 1 }
TudaV1MeasureEntry ::=
SEQUENCE {
tudaV1MeasureCycleIndex Integer32,
tudaV1MeasureInstanceIndex Integer32,
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tudaV1MeasureData OCTET STRING
}
tudaV1MeasureCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this Measurement Log entry.
Index of a Measurement Log update cycle that has
occurred (bounded by the value of tudaV1MeasureCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1MeasureEntry 1 }
tudaV1MeasureInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this Measurement Log entry.
Ordinal of this instance of Measurement Log data
(NOT bounded by the value of tudaV1MeasureInstances).
DEFVAL intentionally omitted - index object."
::= { tudaV1MeasureEntry 2 }
tudaV1MeasureData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A instance of CBOR encoded Measurement Log data."
DEFVAL { "" }
::= { tudaV1MeasureEntry 3 }
--
-- Verify Token
--
tudaV1VerifyToken OBJECT IDENTIFIER ::= { tudaV1MIBObjects 7 }
tudaV1VerifyTokenCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Verify Token update cycles that have
occurred.
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DEFVAL intentionally omitted - counter object."
::= { tudaV1VerifyToken 1 }
tudaV1VerifyTokenTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1VerifyTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Verify Token data."
::= { tudaV1VerifyToken 2 }
tudaV1VerifyTokenEntry OBJECT-TYPE
SYNTAX TudaV1VerifyTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Verify Token data."
INDEX { tudaV1VerifyTokenCycleIndex }
::= { tudaV1VerifyTokenTable 1 }
TudaV1VerifyTokenEntry ::=
SEQUENCE {
tudaV1VerifyTokenCycleIndex Integer32,
tudaV1VerifyTokenData OCTET STRING
}
tudaV1VerifyTokenCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of this instance of Verify Token data.
Index of a Verify Token update cycle that has
occurred (bounded by the value of tudaV1VerifyTokenCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1VerifyTokenEntry 1 }
tudaV1VerifyTokenData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A instance of CBOR encoded Verify Token data."
DEFVAL { "" }
::= { tudaV1VerifyTokenEntry 2 }
--
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-- SWID Tag
--
tudaV1SWIDTag OBJECT IDENTIFIER ::= { tudaV1MIBObjects 8 }
tudaV1SWIDTagCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of SWID Tag update cycles that have occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1SWIDTag 1 }
tudaV1SWIDTagTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1SWIDTagEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of SWID Tag data."
::= { tudaV1SWIDTag 2 }
tudaV1SWIDTagEntry OBJECT-TYPE
SYNTAX TudaV1SWIDTagEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of SWID Tag data."
INDEX { tudaV1SWIDTagCycleIndex,
tudaV1SWIDTagInstanceIndex,
tudaV1SWIDTagFragmentIndex }
::= { tudaV1SWIDTagTable 1 }
TudaV1SWIDTagEntry ::=
SEQUENCE {
tudaV1SWIDTagCycleIndex Integer32,
tudaV1SWIDTagInstanceIndex Integer32,
tudaV1SWIDTagFragmentIndex Integer32,
tudaV1SWIDTagData OCTET STRING
}
tudaV1SWIDTagCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this SWID Tag fragment.
Index of an SWID Tag update cycle that has
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occurred (bounded by the value of tudaV1SWIDTagCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 1 }
tudaV1SWIDTagInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this SWID Tag fragment.
Ordinal of this SWID Tag instance in this update cycle.
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 2 }
tudaV1SWIDTagFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this SWID Tag fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 3 }
tudaV1SWIDTagData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded SWID Tag data."
DEFVAL { "" }
::= { tudaV1SWIDTagEntry 4 }
--
-- Trap Cycles
--
tudaV1TrapV2Cycles NOTIFICATION-TYPE
OBJECTS {
tudaV1GeneralCycles,
tudaV1AIKCertCycles,
tudaV1TSACertCycles,
tudaV1SyncTokenCycles,
tudaV1SyncTokenInstances,
tudaV1RestrictCycles,
tudaV1MeasureCycles,
tudaV1MeasureInstances,
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tudaV1VerifyTokenCycles,
tudaV1SWIDTagCycles
}
STATUS current
DESCRIPTION
"This trap is sent when the value of any cycle or instance
counter changes (i.e., one or more tables are updated).
Note: The value of sysUpTime in IETF MIB-II (RFC 1213) is
always included in SNMPv2 traps, per RFC 3416."
::= { tudaV1MIBNotifications 1 }
--
-- Conformance Information
--
tudaV1Compliances OBJECT IDENTIFIER
::= { tudaV1MIBConformance 1 }
tudaV1ObjectGroups OBJECT IDENTIFIER
::= { tudaV1MIBConformance 2 }
tudaV1NotificationGroups OBJECT IDENTIFIER
::= { tudaV1MIBConformance 3 }
--
-- Compliance Statements
--
tudaV1BasicCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"An implementation that complies with this module MUST
implement all of the objects defined in the mandatory
group tudaV1BasicGroup."
MODULE -- this module
MANDATORY-GROUPS { tudaV1BasicGroup }
GROUP tudaV1OptionalGroup
DESCRIPTION
"The optional TUDA MIB objects.
An implementation MAY implement this group."
GROUP tudaV1TrapGroup
DESCRIPTION
"The TUDA MIB traps.
An implementation SHOULD implement this group."
::= { tudaV1Compliances 1 }
--
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-- Compliance Groups
--
tudaV1BasicGroup OBJECT-GROUP
OBJECTS {
tudaV1GeneralCycles,
tudaV1GeneralVersionInfo,
tudaV1SyncTokenCycles,
tudaV1SyncTokenInstances,
tudaV1SyncTokenData,
tudaV1RestrictCycles,
tudaV1RestrictData,
tudaV1VerifyTokenCycles,
tudaV1VerifyTokenData
}
STATUS current
DESCRIPTION
"The basic mandatory TUDA MIB objects."
::= { tudaV1ObjectGroups 1 }
tudaV1OptionalGroup OBJECT-GROUP
OBJECTS {
tudaV1AIKCertCycles,
tudaV1AIKCertData,
tudaV1TSACertCycles,
tudaV1TSACertData,
tudaV1MeasureCycles,
tudaV1MeasureInstances,
tudaV1MeasureData,
tudaV1SWIDTagCycles,
tudaV1SWIDTagData
}
STATUS current
DESCRIPTION
"The optional TUDA MIB objects."
::= { tudaV1ObjectGroups 2 }
tudaV1TrapGroup NOTIFICATION-GROUP
NOTIFICATIONS { tudaV1TrapV2Cycles }
STATUS current
DESCRIPTION
"The recommended TUDA MIB traps - notifications."
::= { tudaV1NotificationGroups 1 }
END
<CODE ENDS>
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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
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 (2017).";
revision "2017-10-30" {
description
"Fifth version, published as draft-birkholz-tuda-04.";
reference
"draft-birkholz-tuda-04";
}
revision "2017-01-09" {
description
"Fourth version, published as draft-birkholz-tuda-03.";
reference
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"draft-birkholz-tuda-03";
}
revision "2016-07-08" {
description
"Third version, published as draft-birkholz-tuda-02.";
reference
"draft-birkholz-tuda-02";
}
revision "2016-03-21" {
description
"Second version, published as draft-birkholz-tuda-01.";
reference
"draft-birkholz-tuda-01";
}
revision "2015-10-18" {
description
"Initial version, published as draft-birkholz-tuda-00.";
reference
"draft-birkholz-tuda-00";
}
container tudaV1General {
description
"TBD";
leaf tudaV1GeneralCycles {
type yang:counter32;
config false;
description
"Count of TUDA update cycles that have occurred, i.e.,
sum of all the individual group cycle counters.
DEFVAL intentionally omitted - counter object.";
}
leaf tudaV1GeneralVersionInfo {
type snmp-framework:SnmpAdminString {
length "0..255";
}
config false;
description
"Version information for TUDA MIB, e.g., specific release
version of TPM 1.2 base specification and release version
of TPM 1.2 errata specification and manufacturer and model
TPM module itself.";
}
}
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container tudaV1AIKCert {
description
"TBD";
leaf tudaV1AIKCertCycles {
type yang:counter32;
config false;
description
"Count of AIK Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1AIKCertEntry {
key "tudaV1AIKCertCycleIndex tudaV1AIKCertInstanceIndex
tudaV1AIKCertFragmentIndex";
config false;
description
"An entry for one fragment of AIK Certificate data.";
leaf tudaV1AIKCertCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this AIK Certificate fragment.
Index of an AIK Certificate chain update cycle that has
occurred (bounded by the value of tudaV1AIKCertCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1AIKCertInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this AIK Certificate fragment.
Ordinal of this AIK Certificate in this chain, where the AIK
Certificate itself has an ordinal of '1' and higher ordinals
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go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1AIKCertFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this AIK Certificate fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1AIKCertData {
type binary {
length "0..1024";
}
config false;
description
"A fragment of CBOR encoded AIK Certificate data.";
}
}
}
container tudaV1TSACert {
description
"TBD";
leaf tudaV1TSACertCycles {
type yang:counter32;
config false;
description
"Count of TSA Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1TSACertEntry {
key "tudaV1TSACertCycleIndex tudaV1TSACertInstanceIndex
tudaV1TSACertFragmentIndex";
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config false;
description
"An entry for one fragment of TSA Certificate data.";
leaf tudaV1TSACertCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this TSA Certificate fragment.
Index of a TSA Certificate chain update cycle that has
occurred (bounded by the value of tudaV1TSACertCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1TSACertInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this TSA Certificate fragment.
Ordinal of this TSA Certificate in this chain, where the TSA
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1TSACertFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this TSA Certificate fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1TSACertData {
type binary {
length "0..1024";
}
config false;
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description
"A fragment of CBOR encoded TSA Certificate data.";
}
}
}
container tudaV1SyncToken {
description
"TBD";
leaf tudaV1SyncTokenCycles {
type yang:counter32;
config false;
description
"Count of Sync Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
leaf tudaV1SyncTokenInstances {
type yang:counter32;
config false;
description
"Count of Sync Token instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
list tudaV1SyncTokenEntry {
key "tudaV1SyncTokenCycleIndex
tudaV1SyncTokenInstanceIndex
tudaV1SyncTokenFragmentIndex";
config false;
description
"An entry for one fragment of Sync Token data.";
leaf tudaV1SyncTokenCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this Sync Token fragment.
Index of a Sync Token update cycle that has
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occurred (bounded by the value of tudaV1SyncTokenCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SyncTokenInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this Sync Token fragment.
Ordinal of this instance of Sync Token data
(NOT bounded by the value of tudaV1SyncTokenInstances).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SyncTokenFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this Sync Token fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SyncTokenData {
type binary {
length "0..1024";
}
config false;
description
"A fragment of CBOR encoded Sync Token data.";
}
}
}
container tudaV1Restrict {
description
"TBD";
leaf tudaV1RestrictCycles {
type yang:counter32;
config false;
description
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"Count of Restriction Info update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1RestrictEntry {
key "tudaV1RestrictCycleIndex";
config false;
description
"An entry for one instance of Restriction Info data.";
leaf tudaV1RestrictCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Index of this Restriction Info entry.
Index of a Restriction Info update cycle that has
occurred (bounded by the value of tudaV1RestrictCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1RestrictData {
type binary {
length "0..1024";
}
config false;
description
"An instance of CBOR encoded Restriction Info data.";
}
}
}
container tudaV1Measure {
description
"TBD";
leaf tudaV1MeasureCycles {
type yang:counter32;
config false;
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description
"Count of Measurement Log update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
leaf tudaV1MeasureInstances {
type yang:counter32;
config false;
description
"Count of Measurement Log instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
list tudaV1MeasureEntry {
key "tudaV1MeasureCycleIndex tudaV1MeasureInstanceIndex";
config false;
description
"An entry for one instance of Measurement Log data.";
leaf tudaV1MeasureCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this Measurement Log entry.
Index of a Measurement Log update cycle that has
occurred (bounded by the value of tudaV1MeasureCycles).
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1MeasureInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this Measurement Log entry.
Ordinal of this instance of Measurement Log data
(NOT bounded by the value of tudaV1MeasureInstances).
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DEFVAL intentionally omitted - index object.";
}
leaf tudaV1MeasureData {
type binary {
length "0..1024";
}
config false;
description
"A instance of CBOR encoded Measurement Log data.";
}
}
}
container tudaV1VerifyToken {
description
"TBD";
leaf tudaV1VerifyTokenCycles {
type yang:counter32;
config false;
description
"Count of Verify Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
/* XXX table comments here XXX */
list tudaV1VerifyTokenEntry {
key "tudaV1VerifyTokenCycleIndex";
config false;
description
"An entry for one instance of Verify Token data.";
leaf tudaV1VerifyTokenCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Index of this instance of Verify Token data.
Index of a Verify Token update cycle that has
occurred (bounded by the value of tudaV1VerifyTokenCycles).
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DEFVAL intentionally omitted - index object.";
}
leaf tudaV1VerifyTokenData {
type binary {
length "0..1024";
}
config false;
description
"A instanc-V1-ATTESTATION-MIB.yang
}
}
}
container tudaV1SWIDTag {
description
"see CoSWID and YANG SIWD module for now"
leaf tudaV1SWIDTagCycles {
type yang:counter32;
config false;
description
"Count of SWID Tag update cycles that have occurred.
DEFVAL intentionally omitted - counter object.";
}
list tudaV1SWIDTagEntry {
key "tudaV1SWIDTagCycleIndex tudaV1SWIDTagInstanceIndex
tudaV1SWIDTagFragmentIndex";
config false;
description
"An entry for one fragment of SWID Tag data.";
leaf tudaV1SWIDTagCycleIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"High-order index of this SWID Tag fragment.
Index of an SWID Tag update cycle that has
occurred (bounded by the value of tudaV1SWIDTagCycles).
DEFVAL intentionally omitted - index object.";
}
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leaf tudaV1SWIDTagInstanceIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Middle index of this SWID Tag fragment.
Ordinal of this SWID Tag instance in this update cycle.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SWIDTagFragmentIndex {
type int32 {
range "1..2147483647";
}
config false;
description
"Low-order index of this SWID Tag fragment.
DEFVAL intentionally omitted - index object.";
}
leaf tudaV1SWIDTagData {
type binary {
length "0..1024";
}
config false;
description
"A fragment of CBOR encoded SWID Tag data.";
}
}
}
notification tudaV1TrapV2Cycles {
description
"This trap is sent when the value of any cycle or instance
counter changes (i.e., one or more tables are updated).
Note: The value of sysUpTime in IETF MIB-II (RFC 1213) is
always included in SNMPv2 traps, per RFC 3416.";
container tudaV1TrapV2Cycles-tudaV1GeneralCycles {
description
"TPD"
leaf tudaV1GeneralCycles {
type yang:counter32;
description
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"Count of TUDA update cycles that have occurred, i.e.,
sum of all the individual group cycle counters.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1AIKCertCycles {
description
"TPD"
leaf tudaV1AIKCertCycles {
type yang:counter32;
description
"Count of AIK Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1TSACertCycles {
description
"TPD"
leaf tudaV1TSACertCycles {
type yang:counter32;
description
"Count of TSA Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1SyncTokenCycles {
description
"TPD"
leaf tudaV1SyncTokenCycles {
type yang:counter32;
description
"Count of Sync Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1SyncTokenInstances {
description
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"TPD"
leaf tudaV1SyncTokenInstances {
type yang:counter32;
description
"Count of Sync Token instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1RestrictCycles {
description
"TPD"
leaf tudaV1RestrictCycles {
type yang:counter32;
description
"Count of Restriction Info update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1MeasureCycles {
description
"TPD"
leaf tudaV1MeasureCycles {
type yang:counter32;
description
"Count of Measurement Log update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1MeasureInstances {
description
"TPD"
leaf tudaV1MeasureInstances {
type yang:counter32;
description
"Count of Measurement Log instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object.";
}
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}
container tudaV1TrapV2Cycles-tudaV1VerifyTokenCycles {
description
"TPD"
leaf tudaV1VerifyTokenCycles {
type yang:counter32;
description
"Count of Verify Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object.";
}
}
container tudaV1TrapV2Cycles-tudaV1SWIDTagCycles {
description
"TPD"
leaf tudaV1SWIDTagCycles {
type yang:counter32;
description
"Count of SWID Tag update cycles that have occurred.
DEFVAL intentionally omitted - counter object.";
}
}
}
}
<CODE ENDS>
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.
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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
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).
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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].
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.
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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
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
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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 4.1), 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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