Network Working Group A. Fuchs
Internet-Draft H. Birkholz
Intended status: Informational Fraunhofer SIT
Expires: September 22, 2016 I. McDonald
High North Inc
C. Bormann
Universitaet Bremen TZI
March 21, 2016
Time-Based Uni-Directional Attestation
draft-birkholz-tuda-01
Abstract
This memo documents the method and bindings used to conduct time-
based uni-directional attestation between distinguishable endpoints
over the network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Concept . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Time-Based Uni-Directional Attestation . . . . . . . . . . . 5
2.1. TUDA Information Elements Update Cycles . . . . . . . . . 7
3. REST Realization . . . . . . . . . . . . . . . . . . . . . . 9
4. SNMP Realization . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Structure of TUDA MIB . . . . . . . . . . . . . . . . . . 10
4.1.1. Cycle Index . . . . . . . . . . . . . . . . . . . . . 10
4.1.2. Instance Index . . . . . . . . . . . . . . . . . . . 11
4.1.3. Fragment Index . . . . . . . . . . . . . . . . . . . 11
4.2. Relationship to Host Resources MIB . . . . . . . . . . . 11
4.3. Relationship to Entity MIB . . . . . . . . . . . . . . . 12
4.4. Relationship to Other MIBs . . . . . . . . . . . . . . . 12
4.5. Definition of TUDA MIB . . . . . . . . . . . . . . . . . 12
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 27
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1. Normative References . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Realization with TPM 1.2 functions . . . . . . . . . 30
A.1. TPM Functions . . . . . . . . . . . . . . . . . . . . . . 30
A.1.1. Tick-Session and Tick-Stamp . . . . . . . . . . . . . 30
A.1.2. Platform Configuration Registers (PCRs) . . . . . . . 31
A.1.3. PCR restricted Keys . . . . . . . . . . . . . . . . . 32
A.1.4. CertifyInfo . . . . . . . . . . . . . . . . . . . . . 32
A.2. Protocol and Procedure . . . . . . . . . . . . . . . . . 32
A.2.1. AIK and AIK Certificate . . . . . . . . . . . . . . . 32
A.2.2. Synchronization Token . . . . . . . . . . . . . . . . 33
A.2.3. RestrictionInfo . . . . . . . . . . . . . . . . . . . 35
A.2.4. Measurement Log . . . . . . . . . . . . . . . . . . . 37
A.2.5. Implicit Attestation . . . . . . . . . . . . . . . . 38
A.2.6. Attestation Verification Approach . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction
Remote attestation describes the attempt to determine the integrity
and trustworthiness of a computing platform or device without direct
access. One way to do so is based on measurements of software
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components, where the hash values of all started software components
are stored (extended into) a Trust Anchor implemented as Hardware
Security Module (such as TPM and similar) and reported via a
signature over these measurements. Protocols that facilitate these
Trust Anchor based signatures in order to provide remote attestations
are usually bi-directional protocols, where one entity sends a
challenge that is included inside the response to ensure the
recentness of the attestation information.
In many contexts and scenarios it is not feasible to deploy bi-
directional protocols, due to constraints in the underlying
communication schemes. Furthermore, many communication schemes do
not have a notion of connection, which disallows the usage of
connection context related state information. These constraints may
make it impossible to deploy challenge-response based schemes to
achieve freshness of messages in security protocols. Examples of
these constrained environments include broadcast and multicast
schemes such as automotive IEEE802.1p as well as communication models
that do not maintain connection state over time, such as REST [REST]
and SNMP [RFC3411].
This document describes the protocol TUDA for remote attestation that
works over uni-directional communication channels whilst still
providing up-to-date information about the integrity and thereby
trustworthiness of the attested device. The information elements
that are transported by TUDA are encoded in the Concise Binary Object
Representation, CBOR [RFC7049]. In this specification, the
composition of the CBOR data items that represent the information
elements is described using the CBOR Data Definition Language, CDDL
[I-D.greevenbosch-appsawg-cbor-cddl].
1.1. Concept
The protocols usually employed for Remote Attestations using the
Trusted Platform Module (TPM) - such as the Platform Trust Service
(PTS) Protocol [PTS] - as specified by the Trusted Computing Group
(TCG) are based upon the TPM_Quote() function. It consists of the
sending of a nonce-challenge that is then used within TPM_Quote()'s
signature to prove the freshness of the Attestation response. This
scheme requires bi-directional communication.
The TUDA protocol specification describes a new scheme for remote
attestations based upon a combination of TPM_CertifyInfo() and
TPM_TickStampBlob() to implement a time-based attestation scheme.The
approach is based upon the work described in [MTAF] and [SFKE2008].
The freshness properties of a challenge-response based protocol
define the time-frame between the transmission of the nonce and the
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reception of the response as the point in time of attestation. Given
the time-based attestation scheme, the point in time of attestation
lies within the time-frame given by the accuracy of the time-
synchronization and the drift of clocks. If the point in time is
within the range of the typical round-trip of a challenge response
attestation, the freshness property of TUDA is equivalent to that of
classic challenge response attestation. Even if the typical round-
trip time is exceeded slightly, the TUDA attestation statements
provide sufficiently fresh proofs for most scenarios.
In contrast to classical attestations, TUDA attestations can serve as
proof of integrity in audit logs with point in time guarantees.
Also, it can be used via uni-directional and connection-less
communication channels.
Appendix A contains a realization of TUDA using TPM 1.2 primitives.
A realization of TUDA using TPM 2.0 primitives will be added with the
next iteration of this document.
1.2. Terminology
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 RFC
2119, BCP 14 [RFC2119].
This specification makes use of the terminology defined in [RFC4949]
and uses CDDL as defined in [I-D.greevenbosch-appsawg-cbor-cddl] to
define the composition of the TUDA information elements.
The data structures defined by this protocol specification (for use
by other specifications) introduce TUDA-specific terminology:
tuda = [TUDA-Synctoken, TUDA-Verifytoken, TUDA-RestrictionInfo,
TUDA-Cert, TUDA-Measurement-Log]
Common types used in these are:
Cert = bytes ; an X.509 certificate
PCR-Hash = Hash
Hash = bytes
The roles used in the TUDA protocol are:
Attestee: the endpoint that is the subject of the attestation to
another endpoint.
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Verifier: the endpoint that consumes the attestation of another
endpoint.
TSA: Time Stamp Authority [RFC3161].
Types of certificates that are essential to the TUDA protocol:
TSA-CA: a Certificate Authority, that provides the certificate for
the TSA.
AIK-CA: The Attestation Identity Key (AIK) is a special key type
used within TPMs for identity-related operations (such as
TPM_Certify or TPM_Quote). Such an AIK can be established in many
ways, using either a combination of TPM_MakeIdentity and
TPM_ActivateIdentity with a so-called PrivacyCA [AIK-Enrollment]
or by means of TPM_CreateWrapKey, readout in a secure environment
and regular certification by a custom CA similar to IDevIDs or
LDevIDs in [IEEE802.1AR]. AIK-CA is a placeholder for any 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.
Terms that are commonly used in this document and not necessarily
self-explaining:
PCR: a Platform Configuration Register that is part of a Trusted
Platform Module and is used to securely store and report
measurements about security posture.
In this specification, the term "byte" is used in its now customary
sense as a synonym for "octet".
2. 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 Attestee's platform configuration at a certain point
in time:
o 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.
o AIK Certificate ([AIK-Credential], [AIK-Enrollment]; see
Appendix A.2.1).
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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.
o 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).
o Restriction Info
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.
o 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.
o Implicit Attestation
The actual attestation is then based upon a TPM_TickStampBlob
operation using the restricted temporary key that was certified in
the steps above. The TPM_TickStampBlob 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.
o Concise SWID tags
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As an option to better assess the trustworthiness of an Attestee,
a Verifier can request the reference hashes (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 Attestee using the Concise SWID representation
[I-D-birkholz-sacm-coswid] and bundled into a CBOR array.
Ideally, the reference hashes include a signature created by the
manufacturer of the software.
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 Attestee endpoint, but instead they could be
retrieved from another location or pre-deployed to the Verifier. It
is also feasible to only store public keys at the Verifier and skip
the whole certificate provisioning completely in order to save
bandwidth and computation time for certificate verification.
2.1. 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 TPM can be in, is important to the attestation process.
o Some states are persistent, even after reboot. This includes
certificates that are associated with the endpoint itself or with
services it relies on.
o Some states are more volatile and change at the beginning of each
boot cycle. This includes the TPM-internal Tick-Session which
provides the basis for the synchronization token and implicit
attestation.
o Some states are even more volatile and 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 TPM and thereby
also the PCR-restricted keys used during attestation.
Depending on this "lifetime of state", data has to be transported
over the wire, or not. E.g. information that does not change due to
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a reboot typically has to be transported only once between the
Attestee and the Verifier.
There are three kinds of events that require a renewed attestation:
o The Attestee 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
can therefore be set appropriately. 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 TPM continuously to always present the
most freshly created results. To save some utilization of the TPM
for other purposes, however, a time-frame of once per ten seconds is
recommended, which would leave 80% of utilization for applications.
Attestee 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> |
| |
PCR-Change |
| |
Create Restricted Key |
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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
3. REST Realization
Each of the seven data items is defined as a media type (Section 5).
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 [I-D.ietf-netconf-restconf].
4. 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
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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
[I-D.greevenbosch-appsawg-cbor-cddl] 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).
4.1. 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 | |
|-------------|-------|----------|----------|----------|
4.1.1. Cycle Index
A tudaV1<Group>CycleIndex is the:
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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.
4.1.2. 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).
4.1.3. Fragment Index
A tudaV1<Group>FragmentIndex is the:
1. last index of a row (always an element fragment) in the
tudaV1<Group>Table; and
2. accomodation for SNMP transport mapping restrictions for large
string elements that require fragmentation.
4.2. 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-birkholz-sacm-coswid]) in the TUDA MIB is analogous to the
Software Installed and Software Running groups in the Host Resources
MIB [RFC2790].
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4.3. 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].
4.4. 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.
4.5. Definition of TUDA MIB
<CODE BEGINS>
TUDA-V1-ATTESTATION-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, Integer32, Counter32,
enterprises, NOTIFICATION-TYPE
FROM SNMPv2-SMI -- RFC 2578
MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
FROM SNMPv2-CONF -- RFC 2580
SnmpAdminString
FROM SNMP-FRAMEWORK-MIB; -- RFC 3411
tudaV1MIB MODULE-IDENTITY
LAST-UPDATED "201603210000Z" -- 21 March 2016
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
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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 (2016)."
REVISION "201603210000Z" -- 21 March 2016
DESCRIPTION
"Second version, published as draft-birkholz-tuda-01."
REVISION "201510180000Z" -- 18 October 2015
DESCRIPTION
"Initial version, published as draft-birkholz-tuda-00."
::= { enterprises fraunhofersit(21616) mibs(1) tudaV1MIB(1) }
tudaV1MIBNotifications OBJECT IDENTIFIER ::= { tudaV1MIB 0 }
tudaV1MIBObjects OBJECT IDENTIFIER ::= { tudaV1MIB 1 }
tudaV1MIBConformance OBJECT IDENTIFIER ::= { tudaV1MIB 2 }
--
-- General
--
tudaV1General OBJECT IDENTIFIER ::= { tudaV1MIBObjects 1 }
tudaV1GeneralCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of TUDA update cycles that have occurred, i.e.,
sum of all the individual group cycle counters.
DEFVAL intentionally omitted - counter object."
::= { tudaV1General 1 }
tudaV1GeneralVersionInfo OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..255))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Version information for TUDA MIB, e.g., specific release
version of TPM 1.2 base specification and release version
of TPM 1.2 errata specification and manufacturer and model
TPM module itself."
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DEFVAL { "" }
::= { tudaV1General 2 }
--
-- AIK Cert
--
tudaV1AIKCert OBJECT IDENTIFIER ::= { tudaV1MIBObjects 2 }
tudaV1AIKCertCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of AIK Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1AIKCert 1 }
tudaV1AIKCertTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1AIKCertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of AIK Certificate data."
::= { tudaV1AIKCert 2 }
tudaV1AIKCertEntry OBJECT-TYPE
SYNTAX TudaV1AIKCertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of AIK Certificate data."
INDEX { tudaV1AIKCertCycleIndex,
tudaV1AIKCertInstanceIndex,
tudaV1AIKCertFragmentIndex }
::= { tudaV1AIKCertTable 1 }
TudaV1AIKCertEntry ::=
SEQUENCE {
tudaV1AIKCertCycleIndex Integer32,
tudaV1AIKCertInstanceIndex Integer32,
tudaV1AIKCertFragmentIndex Integer32,
tudaV1AIKCertData OCTET STRING
}
tudaV1AIKCertCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
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MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this AIK Certificate fragment.
Index of an AIK Certificate chain update cycle that has
occurred (bounded by the value of tudaV1AIKCertCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 1 }
tudaV1AIKCertInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this AIK Certificate fragment.
Ordinal of this AIK Certificate in this chain, where the AIK
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 2 }
tudaV1AIKCertFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this AIK Certificate fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1AIKCertEntry 3 }
tudaV1AIKCertData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded AIK Certificate data."
DEFVAL { "" }
::= { tudaV1AIKCertEntry 4 }
--
-- TSA Cert
--
tudaV1TSACert OBJECT IDENTIFIER ::= { tudaV1MIBObjects 3 }
tudaV1TSACertCycles OBJECT-TYPE
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SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of TSA Certificate chain update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1TSACert 1 }
tudaV1TSACertTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1TSACertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of TSA Certificate data."
::= { tudaV1TSACert 2 }
tudaV1TSACertEntry OBJECT-TYPE
SYNTAX TudaV1TSACertEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of TSA Certificate data."
INDEX { tudaV1TSACertCycleIndex,
tudaV1TSACertInstanceIndex,
tudaV1TSACertFragmentIndex }
::= { tudaV1TSACertTable 1 }
TudaV1TSACertEntry ::=
SEQUENCE {
tudaV1TSACertCycleIndex Integer32,
tudaV1TSACertInstanceIndex Integer32,
tudaV1TSACertFragmentIndex Integer32,
tudaV1TSACertData OCTET STRING
}
tudaV1TSACertCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this TSA Certificate fragment.
Index of a TSA Certificate chain update cycle that has
occurred (bounded by the value of tudaV1TSACertCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 1 }
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tudaV1TSACertInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this TSA Certificate fragment.
Ordinal of this TSA Certificate in this chain, where the TSA
Certificate itself has an ordinal of '1' and higher ordinals
go *up* the certificate chain to the Root CA.
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 2 }
tudaV1TSACertFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this TSA Certificate fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1TSACertEntry 3 }
tudaV1TSACertData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded TSA Certificate data."
DEFVAL { "" }
::= { tudaV1TSACertEntry 4 }
--
-- Sync Token
--
tudaV1SyncToken OBJECT IDENTIFIER ::= { tudaV1MIBObjects 4 }
tudaV1SyncTokenCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Sync Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1SyncToken 1 }
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tudaV1SyncTokenTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1SyncTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of Sync Token data."
::= { tudaV1SyncToken 2 }
tudaV1SyncTokenEntry OBJECT-TYPE
SYNTAX TudaV1SyncTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one fragment of Sync Token data."
INDEX { tudaV1SyncTokenCycleIndex,
tudaV1SyncTokenFragmentIndex }
::= { tudaV1SyncTokenTable 1 }
TudaV1SyncTokenEntry ::=
SEQUENCE {
tudaV1SyncTokenCycleIndex Integer32,
tudaV1SyncTokenFragmentIndex Integer32,
tudaV1SyncTokenData OCTET STRING
}
tudaV1SyncTokenCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this Sync Token fragment.
Index of a Sync Token update cycle that has
occurred (bounded by the value of tudaV1SyncTokenCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1SyncTokenEntry 1 }
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 2 }
tudaV1SyncTokenData OBJECT-TYPE
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SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A fragment of CBOR encoded Sync Token data."
DEFVAL { "" }
::= { tudaV1SyncTokenEntry 3 }
--
-- Restriction Info
--
tudaV1Restrict OBJECT IDENTIFIER ::= { tudaV1MIBObjects 5 }
tudaV1RestrictCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Restriction Info update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1Restrict 1 }
tudaV1RestrictTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1RestrictEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Restriction Info data."
::= { tudaV1Restrict 2 }
tudaV1RestrictEntry OBJECT-TYPE
SYNTAX TudaV1RestrictEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Restriction Info data."
INDEX { tudaV1RestrictCycleIndex }
::= { tudaV1RestrictTable 1 }
TudaV1RestrictEntry ::=
SEQUENCE {
tudaV1RestrictCycleIndex Integer32,
tudaV1RestrictData OCTET STRING
}
tudaV1RestrictCycleIndex OBJECT-TYPE
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SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of this Restriction Info entry.
Index of a Restriction Info update cycle that has
occurred (bounded by the value of tudaV1RestrictCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1RestrictEntry 1 }
tudaV1RestrictData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"An instance of CBOR encoded Restriction Info data."
DEFVAL { "" }
::= { tudaV1RestrictEntry 2 }
--
-- Measurement Log
--
tudaV1Measure OBJECT IDENTIFIER ::= { tudaV1MIBObjects 6 }
tudaV1MeasureCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Measurement Log update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1Measure 1 }
tudaV1MeasureInstances OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Measurement Log instance entries that have
been recorded (some entries MAY have been pruned).
DEFVAL intentionally omitted - counter object."
::= { tudaV1Measure 2 }
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tudaV1MeasureTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1MeasureEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Measurement Log data."
::= { tudaV1Measure 3 }
tudaV1MeasureEntry OBJECT-TYPE
SYNTAX TudaV1MeasureEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Measurement Log data."
INDEX { tudaV1MeasureCycleIndex,
tudaV1MeasureInstanceIndex }
::= { tudaV1MeasureTable 1 }
TudaV1MeasureEntry ::=
SEQUENCE {
tudaV1MeasureCycleIndex Integer32,
tudaV1MeasureInstanceIndex Integer32,
tudaV1MeasureData OCTET STRING
}
tudaV1MeasureCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this Measurement Log entry.
Index of a Measurement Log update cycle that has
occurred (bounded by the value of tudaV1MeasureCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1MeasureEntry 1 }
tudaV1MeasureInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this Measurement Log entry.
Ordinal of this instance of Measurement Log data
(NOT bounded by the value of tudaV1MeasureInstances).
DEFVAL intentionally omitted - index object."
::= { tudaV1MeasureEntry 2 }
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tudaV1MeasureData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A instance of CBOR encoded Measurement Log data."
DEFVAL { "" }
::= { tudaV1MeasureEntry 3 }
--
-- Verify Token
--
tudaV1VerifyToken OBJECT IDENTIFIER ::= { tudaV1MIBObjects 7 }
tudaV1VerifyTokenCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of Verify Token update cycles that have
occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1VerifyToken 1 }
tudaV1VerifyTokenTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1VerifyTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of instances of Verify Token data."
::= { tudaV1VerifyToken 2 }
tudaV1VerifyTokenEntry OBJECT-TYPE
SYNTAX TudaV1VerifyTokenEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry for one instance of Verify Token data."
INDEX { tudaV1VerifyTokenCycleIndex }
::= { tudaV1VerifyTokenTable 1 }
TudaV1VerifyTokenEntry ::=
SEQUENCE {
tudaV1VerifyTokenCycleIndex Integer32,
tudaV1VerifyTokenData OCTET STRING
}
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tudaV1VerifyTokenCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of this instance of Verify Token data.
Index of a Verify Token update cycle that has
occurred (bounded by the value of tudaV1VerifyTokenCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1VerifyTokenEntry 1 }
tudaV1VerifyTokenData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A instance of CBOR encoded Verify Token data."
DEFVAL { "" }
::= { tudaV1VerifyTokenEntry 2 }
--
-- SWID Tag
--
tudaV1SWIDTag OBJECT IDENTIFIER ::= { tudaV1MIBObjects 8 }
tudaV1SWIDTagCycles OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Count of SWID Tag update cycles that have occurred.
DEFVAL intentionally omitted - counter object."
::= { tudaV1SWIDTag 1 }
tudaV1SWIDTagTable OBJECT-TYPE
SYNTAX SEQUENCE OF TudaV1SWIDTagEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table of fragments of SWID Tag data."
::= { tudaV1SWIDTag 2 }
tudaV1SWIDTagEntry OBJECT-TYPE
SYNTAX TudaV1SWIDTagEntry
MAX-ACCESS not-accessible
STATUS current
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DESCRIPTION
"An entry for one fragment of SWID Tag data."
INDEX { tudaV1SWIDTagCycleIndex,
tudaV1SWIDTagInstanceIndex,
tudaV1SWIDTagFragmentIndex }
::= { tudaV1SWIDTagTable 1 }
TudaV1SWIDTagEntry ::=
SEQUENCE {
tudaV1SWIDTagCycleIndex Integer32,
tudaV1SWIDTagInstanceIndex Integer32,
tudaV1SWIDTagFragmentIndex Integer32,
tudaV1SWIDTagData OCTET STRING
}
tudaV1SWIDTagCycleIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"High-order index of this SWID Tag fragment.
Index of an SWID Tag update cycle that has
occurred (bounded by the value of tudaV1SWIDTagCycles).
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 1 }
tudaV1SWIDTagInstanceIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Middle index of this SWID Tag fragment.
Ordinal of this SWID Tag instance in this update cycle.
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 2 }
tudaV1SWIDTagFragmentIndex OBJECT-TYPE
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Low-order index of this SWID Tag fragment.
DEFVAL intentionally omitted - index object."
::= { tudaV1SWIDTagEntry 3 }
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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,
tudaV1RestrictCycles,
tudaV1MeasureCycles,
tudaV1MeasureInstances,
tudaV1VerifyTokenCycles,
tudaV1SWIDTagCycles
}
STATUS current
DESCRIPTION
"This trap is sent when the value of any cycle or instance
counter changes (i.e., one or more tables are updated).
Note: The value of sysUpTime in IETF MIB-II (RFC 1213) is
always included in SNMPv2 traps, per RFC 3416."
::= { tudaV1MIBNotifications 1 }
--
-- Conformance Information
--
tudaV1Compliances OBJECT IDENTIFIER
::= { tudaV1MIBConformance 1 }
tudaV1ObjectGroups OBJECT IDENTIFIER
::= { tudaV1MIBConformance 2 }
tudaV1NotificationGroups OBJECT IDENTIFIER
::= { tudaV1MIBConformance 3 }
--
-- Compliance Statements
--
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tudaV1BasicCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"An implementation that complies with this module MUST
implement all of the objects defined in the mandatory
group tudaV1BasicGroup."
MODULE -- this module
MANDATORY-GROUPS { tudaV1BasicGroup }
GROUP tudaV1OptionalGroup
DESCRIPTION
"The optional TUDA MIB objects.
An implementation MAY implement this group."
GROUP tudaV1TrapGroup
DESCRIPTION
"The TUDA MIB traps.
An implementation SHOULD implement this group."
::= { tudaV1Compliances 1 }
--
-- Compliance Groups
--
tudaV1BasicGroup OBJECT-GROUP
OBJECTS {
tudaV1GeneralCycles,
tudaV1GeneralVersionInfo,
tudaV1SyncTokenCycles,
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,
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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>
5. IANA Considerations
This memo includes requests to IANA, including registrations for
media type definitions.
TBD
6. Security Considerations
There are Security Considerations. TBD
7. Acknowledgements
8. Change Log
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
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10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
10.2. Informative References
[AIK-Credential]
"TCG Credential Profile", 2007,
<http://www.trustedcomputinggroup.org/files/
temp/642686EC-1D09-3519-AD58BB4C50BD5028/
IWG%20Credential_Profiles_V1_R1_14.pdf>.
[AIK-Enrollment]
TCG Infrastructure Working Group, "A CMC Profile for AIK
Certificate Enrollment", 2011,
<https://www.trustedcomputinggroup.org/files/
resource_files/738DF0BB-1A4B-B294-D0AF6AF9CC023163/
IWG_CMC_Profile_Cert_Enrollment_v1_r7.pdf>.
[I-D-birkholz-sacm-coswid]
Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
Waltermire, "Concise Software Identifiers", draft-
birkholz-sacm-coswid-00 (work in progress), March 2016.
[I-D.greevenbosch-appsawg-cbor-cddl]
Vigano, C. and H. Birkholz, "CBOR data definition language
(CDDL): a notational convention to express CBOR data
structures", draft-greevenbosch-appsawg-cbor-cddl-08 (work
in progress), March 2016.
[I-D.ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ietf-netconf-restconf-10 (work in
progress), March 2016.
[IEEE802.1AR]
IEEE Computer Society, "IEEE Standard for Local and
metropolitan area networks -- Secure Device Identity",
IEEE Std 802.1AR, 2009.
[MTAF] Fuchs, A., "Improving Scalability for Remote Attestation",
Master Thesis (Diplomarbeit), Technische Universitaet
Darmstadt, Germany, 2008.
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[PTS] "TCG Attestation PTS Protocol Binding to TNC IF-M", 2011,
<http://www.trustedcomputinggroup.org/files/
resource_files/508E7E89-1A4B-B294-D06395D5FD7EC4E7/
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,
<http://www.rfc-editor.org/info/rfc1213>.
[RFC2790] Waldbusser, S. and P. Grillo, "Host Resources MIB",
RFC 2790, DOI 10.17487/RFC2790, March 2000,
<http://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, <http://www.rfc-editor.org/info/rfc3161>.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<http://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,
<http://www.rfc-editor.org/info/rfc3418>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<http://www.rfc-editor.org/info/rfc4949>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<http://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,
<http://www.rfc-editor.org/info/rfc6933>.
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[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <http://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,
<http://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,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7320] Nottingham, M., "URI Design and Ownership", BCP 190,
RFC 7320, DOI 10.17487/RFC7320, July 2014,
<http://www.rfc-editor.org/info/rfc7320>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
[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, page 1-10, 2008.
[STD62] "Internet Standard 62", STD 62, RFCs 3411 to 3418,
December 2002.
[TPM12] "Information technology -- Trusted Platform Module -- Part
1: Overview", ISO/IEC 11889-1, 2009.
Appendix A. Realization with TPM 1.2 functions
A.1. TPM Functions
The following TPM structures, resources and functions are used within
this approach. They are based upon the TPM 1.2 specification
[TPM12].
A.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
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the device and shutdown or power-off - and prevent replaying of old
tick-session values. The TPM uses its internal entropy source that
guarantees virtually no collisions of the nonce values between two of
such boot cycles.
It further includes an internal timer that is being initialize to
Zero on each reboot. From this point on, the TPM increments this
timer continuously based upon its internal secure clocking
information until the device is powered down or set to sleep. By its
hardware design, the TPM will detect attacks on any of those
properties.
The TPM offers the function TPM_TickStampBlob, which allows the TPM
to create a signature over the current tick-session and two
externally provided input values. These input values are designed to
serve as a nonce and as payload data to be included in a
TickStampBlob: TickstampBlob := sig(TPM-key, currentTicks || nonce ||
externalData).
As a result, one is able to proof that at a certain point in time
(relative to the tick-session) after the provisioning of a certain
nonce, some certain externalData was known and provided to the TPM.
If an approach however requires no input values or only one input
value (such as the use in this document) the input values can be set
to well-known value. The convention used within TCG specifications
and within this document is to use twenty bytes of zero
h'0000000000000000000000000000000000000000' as well-known value.
A.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.
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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).
A.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.
A.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.
A.2. Protocol and Procedure
A.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.
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The AIK-Cert may be provisioned in a secure environment using
standard means or it may follow the PrivacyCA protocols. Figure 3
gives a rough sketch of this protocol. See [AIK-Enrollment] for more
information.
The X.509 Certificate is built from the AIK public key and the
corresponding PKCS #7 certificate chain, as shown in Figure 3.
Required TPM functions:
| create_AIK_Cert(...) = {
| AIK = TPM_MakeIdentity()
| IdReq = CollateIdentityRequest(AIK,EK)
| IdRes = Call(AIK-CA, IdReq)
| AIK-Cert = TPM_ActivateIdentity(AIK, IdRes)
| }
|
| /* Alternative */
|
| create_AIK_Cert(...) = {
| AIK = TPM_CreateWrapKey(Identity)
| AIK-Cert = Call(AIK-CA, AIK.pubkey)
| }
Figure 3: Creating the TUDA-Cert element
A.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
A.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,
TPM-CERTIFY-INFO]
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PCRSelection = bytes .size (2..4) ; used as bit string
Composite = [
bitmask: PCRSelection,
values: [*PCR-Hash],
]
Pubkey = bytes ; do we need to expose structure here?
TPM-CERTIFY-INFO = [
; we don't encode TPM-STRUCT-VER:
; these are 4 bytes always equal to h'01010000'
keyUsage: uint, ; 4byte? 2byte?
keyFlags: bytes .size 4, ; 4byte
authDataUsage: uint, ; 1byte (enum)
algorithmParms: TPM-KEY-PARMS,
pubkeyDigest: Hash,
; we don't encode TPM-NONCE data, which is 20 bytes, all zero
parentPCRStatus: bool,
; no need to encode pcrinfosize
pcrinfo: TPM-PCR-INFO, ; we have exactly one
]
TPM-PCR-INFO = [
pcrSelection: PCRSelection; /* TPM_PCR_SELECTION */
digestAtRelease: PCR-Hash; /* TPM_COMPOSITE_HASH */
digestAtCreation: PCR-Hash; /* TPM_COMPOSITE_HASH */
]
TPM-KEY-PARMS = [
; algorithmID: uint, ; <= 4 bytes -- not encoded, constant for TPM1.2
encScheme: uint, ; <= 2 bytes
sigScheme: uint, ; <= 2 bytes
parms: TPM-RSA-KEY-PARMS,
]
TPM-RSA-KEY-PARMS = [
; "size of the RSA key in bits":
keyLength: uint
; "number of prime factors used by this RSA key":
numPrimes: uint
; "This SHALL be the size of the exponent":
exponentSize: null / uint / biguint
; "If the key is using the default exponent then the exponentSize
; MUST be 0" -> we represent this case as null
]
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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
A.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]
A.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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A.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 2.1), 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
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
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Carsten Bormann
Universitaet Bremen TZI
Bibliothekstr. 1
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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