Internet DRAFT - draft-xia-rats-pubsub-model
draft-xia-rats-pubsub-model
Remote ATtestation ProcedureS L. Xia
Internet-Draft W. Pan
Intended status: Standards Track Huawei
Expires: August 30, 2020 February 27, 2020
Using NETCONF Pub/Sub Model for RATS Interaction Procedures
draft-xia-rats-pubsub-model-02
Abstract
This draft defines a new method of using the netconf pub/sub model in
the RATS interaction procedure, to increase its flexibility,
efficiency and scalability.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Pub/sub Model for Remote Attestation Procedure . . . . . . . 4
3.1. Solution Overview . . . . . . . . . . . . . . . . . . . . 4
3.2. Remote Attestation Event Stream Definition . . . . . . . 7
3.3. Remote Attestation Subscription Definition . . . . . . . 8
3.4. Remote Attestation Selection Filters Definition . . . . . 9
3.5. Remote Attestation Subscription Parameters Handling . . . 9
3.6. Remote Attestation Notification Distribution . . . . . . 10
3.7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. The YANG Module for Sub/pub Model Remote Attestation
Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Tree Format . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Raw Format . . . . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . 14
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Remote attestation is for acquiring the evidence about various
integrity information from remote endpoints to assess its
trustworthiness (aka, behave in the expected manner). These evidence
should be about: system component identity, composition of system
components, roots of trust, system component integrity, system
component configuration, operational state and so on.
[I-D.richardson-rats-usecases] describes possible use cases which
remote attestation are using for different industries, like: network
devices, FIDO authentication for online transaction, Cryptographic
Key Attestation for mobile devices, and so on.
[I-D.ietf-rats-architecture] lays a foundation of RATS architecture
about the key RATS roles (i.e., Relying Party, Verifier, Attester and
asserter) and the messages they exchange, as well as some key
concepts. Based on it,
[I-D.birkholz-rats-reference-interaction-model] specifies a basic
challenge-response-based interaction model for the remote attestation
procedure, which a complete remote attestation procedure is triggered
by a challenge message originated from the verifier, and finished
when the attester sends its response message back. This is a very
generic interaction model with wide adoption. This document proposes
an alternative interaction model for Remote attestation procedure, by
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customizing the NETCONF pub/sub model [RFC8639][RFC8640][RFC8641].
YANG push [RFC8641] is basically an extensive NETCONF pub/sub model
mainly for the YANG datastore. With the nature of asynchronous
communication, the pub/sub model for remote attestation procedure is
optimal for large-scale and loosely coupled distributed systems,
especially for the network devices, which has the advantages as:
loose coupling, scalability, time delivery sensitivity, supporting
filtering capability, event-driven and so on. The pub/sub model can
be used independently, or together with the challenge-response model
to complement each other as a whole. Note that in which way these
models are combined together are currently out of the scope of this
draft.
In summary, by utilizing the pub/sub model in remote attestation
procedure, the gained benefits are as below:
o Flexibility: the verifier does not need to send the challenge
message every time. The whole thing of the verifier is to
subscribe a topic to the attester and then to anticipate the
period or timely on-change notification from the attester about
its integrity evidence.
o Efficiency: once the verifier has subscribed its interested topics
related with its triggering condition to the attester, it will get
all the condition triggered notifications on time, which are the
integrity related evidence for remote attestation in fact. It
will ensure any integrity change/deviation of the remote endpoint
to be detected with the minimum latency.
o Scalability: it will save a lot of challenge messages by replacing
with single subscription message for one topic stream, and
decrease the total number of stateful connection between the
verifier and attester, especially for a very large scale network.
Thus, the scalability of the solution will increase.
This document is organized as follows. Section 2 defines conventions
and acronyms used. Section 3 discusses pub/sub model of remote
attestation procedure.
2. Conventions Used in This Document
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.
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This document uses terminology defined in
[I-D.ietf-rats-architecture] and
[I-D.birkholz-rats-reference-interaction-model] for security related
and RATS scoped terminology.
3. Pub/sub Model for Remote Attestation Procedure
3.1. Solution Overview
The following sequence diagram illustrates the reference remote
attestation procedure by utilizing the NETCONF pub/sub model defined
by this document.
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[Attester] [Verifier]
| |
| <--Sub(nonce,authSecID,assertionSelection, event/period) |
| |
collectAssertions(assertionSelection) |
| => assertions |
| |
signAttestationEvidence(authSecID, assertions, nonce) |
| => signedAttestationEvidence |
| |
| signedAttestationEvidence ----------------------------------> |
| |
| verifyAttestationEvidence(signedAttestationEvidence, refAssertions)
| attestationResult <= |
| |
| ............................................................. |
| |
collectAssertions(assertionSelection) |
| => assertions |
| |
signAttestationEvidence(authSecID, assertions, nonce) |
| => signedAttestationEvidence |
| |
| signedAttestationEvidence ----------------------------------> |
| |
| verifyAttestationEvidence(signedAttestationEvidence, refAssertions)
| attestationResult <= |
| |
| ............................................................. |
| |
| |
|on-change/event happens |
| | |
| \|/ |
collectAssertions(assertionSelection) |
| => assertions |
| |
signAttestationEvidence(authSecID, assertions, nonce) |
| => signedAttestationEvidence |
| |
| signedAttestationEvidence ----------------------------------> |
| |
| verifyAttestationEvidence(signedAttestationEvidence, refAssertions)
| attestationResult <= |
| |
| ............................................................. |
Figure 1: Pub/sub model of Remote Attestation
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In short, the basic idea of pub/sub model for remote attestation is
the verifier subscribes its interested event streams about the
integrity evidence to the attester. The event streams can be in the
YANG datastore, or not. After the subscription succeeds, the
attester sends the subscribed integrity evidence back to the
verifier. During subscription, the verifier may also specify how the
attester returns the subscribed information, that is, the update
trigger as periodic subscription or on-change subscription. And when
the selection filters are applied to the subscription, only the
information that pass the filter will be distributed out.
More detailed, the key steps of the remote attestation workflow with
this model can be summarized as below (using the network devices as
the example):
o The verifier subscribes its interested event streams about the
integrity evidence to the attester. More specifically:
* The event stream here refers to various integrity evidence
information related to device trustworthiness, which can be in
YANG datastore, or not. The basic event streams may include:
software integrity information (including PCR values and system
boot logs) of each layer of the trust chain recorded during
device booting time; device identity certificates & Attestation
Key certificate; operating system, application dynamic
integrity information (e.g., IMA logs) and the device
configuration information recorded during device running time.
* Periodic subscription is mainly used by the verifier for the
general and non-critical information collection, which are not
strictly time sensitive and aims for collecting the latest
integrity evidence and checking the possible deviation. In
contrary, on-change subscription is basically used to to
monitor the critical integrity evidence (e.g., integrity values
and log files during device booting time, or integrity values
of some key service processes). If these integrity values
change, notifications are sent immediately.
* The selection filters may be applied to the subscription, so
that only the event records that pass the filter will be
distributed out. Some specific examples include: event records
of a component (e.g., line card) in the composite device, the
event records in a specific time period that includes a start
time and an end time, and so on.
o Consider how to send the existing parameters (i.e., nonce, hash
signature algorithm, and specified TPM name, etc.) carried in the
challenge message of the previous challenge-response model to the
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attester through the subscription message of the new sub/pub model
in advance, and the follow-up usage of them. A very important
point is how to ensure that the nonce carried in every
notification message is different, and both the attester and the
verifier know the correct value in advance.
o Both configuration subscription and dynamic subscription are
considered. More specifically:
* Configure subscription is for the important security event
stream. For example, it enables the monitoring the important
integrity information by using the on-change mode.
* Dynamic subscription is for the normal integrity information,
that is, periodically receive those related information during
NETCONF Session. The corresponding subscription RPC needs to
be established dynamically. This way can reduce unnecessary
NETCONF sessions.
o In addition to the update trigger of on-change, the other possible
update trigger may be certain pre-defined events according to
[I-D.bryskin-netconf-automation-yang], that is: When these events
occur, the specified integrity information is triggered to be
sent, which is the relevant event stream plus optional selection
filter. The events may include: device startup completion, device
upgrade completion, specific attack event, active/standby
switchover, line card insertion/removal/switchover, certificate
life cycle event (expiration), etc.
o The attester notification delivery mechanisms thus vary as the
above subscription mechanisms of verifier vary.
The following sections describes the above key steps one by one.
3.2. Remote Attestation Event Stream Definition
The event streams here refers to various integrity evidence
information related to device trustworthiness. By definition,
evidence is typically a set of claims about device's software and
hardware platform. So, the remote attestation event stream is
composed by the claims. For remote attestation, the basic event
streams may generally include: system integrity information
(including PCR values and system boot logs) of each layer of the
trust chain recorded during device booting time, device credentials
and their change, operating system and files integrity information
(e.g., IMA logs) recorded during device running time, and so on.
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The event streams are created and managed by the attester. And their
formal definition should be conformed to the information model
definition like Attestation Evidence or others in
[I-D.birkholz-rats-information-model], and the claim data model
definition in [I-D.ietf-rats-yang-tpm-charra] with YANG data format,
and [I-D.ietf-rats-eat] with COSE data format.
More specific, for current RATS claims YANG data model in
[I-D.ietf-rats-yang-tpm-charra] , the following event streams may be
defined if necessary:
o the rats-support-structures datastore node, or its subtree nodes
like: tpms, compute-nodes. All these nodes can be subscribed for
pushing their values periodically or on-change;
o For all the YANG RPCs, whether their output are the YANG datastore
nodes or information stored in the device with other way, the
event streams can be defined for all of them, such as: tpm12-
attestation-response, tpm20-attestation-response, attestation-
certificates and system-event-logs. If needed, the more fine-
grained event stream can be defined for the substructure of the
above, like: endorsement-cert or attestation-cer of the
attestation-certificates, bios-event-logs or ima-event-logs of the
system-event-logs.
3.3. Remote Attestation Subscription Definition
NETCONF pub/sub model provides several subscription types in which
approriate one or more types are chosen and possibly used together to
meet the service requirements.
Particularly, periodic subscription is mainly used by the verifier
for the general and non-critical information collection, which are
not strictly time sensitive and aims for collecting the latest
integrity information and checking the possible deviation. In
contrary, on-change subscription is basically used to monitor the
critical integrity evidence (e.g., integrity values and log files
during device booting time, or integrity values of some important
files). If these integrity values change, notifications are sent
immediately.
Besides, both configuration subscription and dynamic subscription are
considered. In which, configure subscription is for the important
security event stream as it lasts even the NETCONF session is closed.
For example, it enables the monitoring of the status of important
security event stream by using the on-change mode. On the other
hand, dynamic subscription is for the general security event stream,
that is, periodically receive those related information during
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NETCONF Session. The corresponding subscription RPC needs to be
established dynamically. This way can reduce unnecessary NETCONF
sessions.
For the remote attestation event streams described in the previous
section, some relatively critical and not frequently changed ones can
be subscribed as the configuration and on-change subscription, so
that the verifier can always receive them very timely. Some examples
are: tpms, compute-nodes and attestation-certificates event streams.
In contrary, some normal and frequently changed event streams can be
the dynamic and/or periodic subscription, the verifier just want to
receive and monitor them occasionally and reduce the processing. One
example is ima-event-logs event stream.
Furthermore, certain pre-defined events according to
[I-D.bryskin-netconf-automation-yang], can be the update trigger too,
that is: When these events occur, the specified integrity information
is triggered to be sent, which is the relevant event stream with
optional selection filter. The events may include: device startup
completion, device upgrade completion, specific attack event, active/
standby switchover, line card insertion/removal/switchover,
certificate life cycle event (expiration), etc.
3.4. Remote Attestation Selection Filters Definition
The selection filters may be applied to the subscription, so that
only the event that pass the filter will be distributed out. Both
the pub/sub and the YANG push selection filters can be considered.
A concrete example of selection filter is limiting the delivered
event stream to those originated from a specific component with id
("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").
The other example is filtering the event records in a specific time
period that has a start time and an end time.
3.5. Remote Attestation Subscription Parameters Handling
Most of the parameters carried in the subscription message are not
changed during the remote attestation procedure, like: hash signature
algorithm, specified TPM name and so on. Their main goal is to
enable the dynamic negotiation with the attester about what
information the verifier needs and how to construct them together. A
very important point is how to ensure that the nonce carried in every
notification message is different, and both the attester and the
verifier know the correct value in advance. For this purpose, the
basic idea is to ensure that the nonce in two sides of the
communication is synchronously changed, and the randomness of the
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nonce is maintained. Specifically, there may be several ways to do
it:
o Verifier sends a seed with hash algorithm to the attester in the
subscription message, and then perform the synchronization
operation on both sides.
o In fact, the nonce does not need to be random every time. As long
as the receive endpoint (here for verifier) can identify
duplicated packets, other means may be used. For example: The
timestamp and increasing count.
o The RATS TUDA mechanism [I-D.birkholz-rats-tuda] can also be used
here to ensure the freshness of information.
3.6. Remote Attestation Notification Distribution
Basically, the remote attestation notification is the event stream in
the YANG notification structure, and the event stream is defined
above with the same YANG structure as the corresponding the YANG
datastore node or RPC's output.
More details are to be added.
3.7. Summary
Based on the above discussion, this section gives some examples to
illustrate the overall application of sub/pub model to remote
attestation procedure.
Below is a configured subscription example with on-change update
trigger, with specific contents as:
o There are 3 integrity evidence related event streams as follows:
pcr-trust-evidence, bios-log-trust-evidence and ima-log-trust-
evidence. The subscribed one is pcr-trust-evidence.
o The other parameters of the subscription include: pcr-list: {{1,
3, 7}}, tcg-hash-algo-id: TPM_ALG_SHA256, nonce-value: 0x564ac291,
TPM_ALG_ID-value: TPM_ALG_ECDSA, pub-key-id: 0x784a22bf, tpms:
{"tpm1"}.
o The selection filter is set as follows: a specific component with
id ("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").
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<edit-config>
<subscriptions
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
<subscription>
<id>100</id>
<stream>pcr-trust-evidence</stream>
<stream-subtree-filter>
<xxx-vendor-device
xmlns="urn:xxx:params:xml:ns:yang:xxx-vendor-device ">
<device-id>xxxxxxxxxx</device-id>
</xxx-vendor-device>
</stream-subtree-filter>
<pcr-list>
<pcr>
<pcr-indices>1</pcr-indices>
<pcr-indices>3</pcr-indices>
<pcr-indices>7</pcr-indices>
<hash-algo>
<tcg-hash-algo-id>TPM_ALG_SHA256</tcg-hash-algo-id>
</hash-algo>
</pcr>
</pcr-list>
<nonce-value>0x564ac291</nonce-value>
<TPM_ALG_ID-value>TPM_ALG_ECDSA</TPM_ALG_ID-value>
<pub-key-id>0x784a22bf</pub-key-id>
<tpms>
<tpm-name>tpm1</tpm-name>
</tpms>
<yp:on-change>
<yp:dampening-period>100</yp:dampening-period>
</yp:on-change>
</subscription>
</subscriptions>
</edit-config>
Figure 2: Configured On-change Subscription Message
Below is a dynamic subscription RPC example with periodic update
trigger, with specific contents as:
o There are 3 integrity evidence related event streams as follows:
pcr-trust-evidence, bios-log-trust-evidence and ima-log-trust-
evidence. The subscribed one is bios-log-trust-evidence.
o The other parameters of the dynamic subscription include: tpms:
{"tpm1"}, last-entry-value: 0xa34568baac79, log-type: bios, pcr-
list: {{2, 4, 8}}, tcg-hash-algo-id: TPM_ALG_SHA256.
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o The selection filter is set as follows: a specific component with
id ("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").
o Subscription period: 500 centiseconds.
<rpc netconf:message-id="101"
xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
<establish-subscription
xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications">
<stream>bios-log-trust-evidence</stream>
<stream-subtree-filter>
<xxx-vendor-device
xmlns="urn:xxx:params:xml:ns:yang:xxx-vendor-device ">
<device-id>xxxxxxxxxx</device-id>
</xxx-vendor-device>
</stream-subtree-filter>
<tpms>
<tpm-name>tpm1</tpm-name>
</tpms>
<last-entry-value>0xa34568baac79</last-entry-value>
<log-type>bios</log-type>
<pcr-list>
<pcr>
<pcr-indices>2</pcr-indices>
<pcr-indices>4</pcr-indices>
<pcr-indices>8</pcr-indices>
<hash-algo>
<tcg-hash-algo-id>TPM_ALG_SHA256</tcg-hash-algo-id>
</hash-algo>
</pcr>
</pcr-list>
<yp:periodic>
<yp:period>500</yp:period>
</yp:periodic>
</establish-subscription>
</rpc>
Figure 3: Dynamic Periodic Subscription Message
Below is a configured subscription RPC example with pre-defined
events as the update trigger, with specific contents as:
o There are 3 integrity evidence related event streams as follows:
pcr-trust-evidence, bios-log-trust-evidence and ima-log-trust-
evidence. The subscribed one is pcr-trust-evidence.
o The other parameters of the subscription include: pcr-list: {{1,
3, 7}}, tcg-hash-algo-id: TPM_ALG_SHA256, nonce-value: 0x564ac291,
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TPM_ALG_ID-value: TPM_ALG_ECDSA, pub-key-id: 0x784a22bf, tpms:
{"tpm1"}.
o The selection filter is set as follows: a specific component with
id ("xxxxxxxxxx") of a designated vendor ("xxx-vendor-device").
o The event which triggers the intergrity evidence delivery is
defined as: id: 1001, type: master-slave-swithover
NO FIGURE YET
Figure 4: Configured Event-triggered Subscription Message
4. The YANG Module for Sub/pub Model Remote Attestation Procedures
4.1. Tree Format
To be written.
4.2. Raw Format
To be written.
5. Security Considerations
To be written.
6. IANA Considerations
To be written, possibly.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
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[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>.
7.2. Informative References
[I-D.birkholz-rats-information-model]
Birkholz, H. and M. Eckel, "An Information Model for
Claims used in RATS", draft-birkholz-rats-information-
model-01 (work in progress), January 2020.
[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.birkholz-rats-tuda]
Fuchs, A., Birkholz, H., McDonald, I., and C. Bormann,
"Time-Based Uni-Directional Attestation", draft-birkholz-
rats-tuda-01 (work in progress), September 2019.
[I-D.bryskin-netconf-automation-yang]
Bryskin, I., Liu, X., Clemm, A., Birkholz, H., and T.
Zhou, "Generalized Network Control Automation YANG Model",
draft-bryskin-netconf-automation-yang-03 (work in
progress), July 2019.
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., and N. Smith,
"Remote Attestation Procedures Architecture", draft-ietf-
rats-architecture-01 (work in progress), February 2020.
[I-D.ietf-rats-eat]
Mandyam, G., Lundblade, L., Ballesteros, M., and J.
O'Donoghue, "The Entity Attestation Token (EAT)", draft-
ietf-rats-eat-03 (work in progress), February 2020.
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[I-D.ietf-rats-yang-tpm-charra]
Birkholz, H., Eckel, M., Bhandari, S., Sulzen, B., Voit,
E., Xia, L., Laffey, T., and G. Fedorkow, "A YANG Data
Model for Challenge-Response-based Remote Attestation
Procedures using TPMs", draft-ietf-rats-yang-tpm-charra-00
(work in progress), January 2020.
[I-D.richardson-rats-usecases]
Richardson, M., Wallace, C., and W. Pan, "Use cases for
Remote Attestation common encodings", draft-richardson-
rats-usecases-06 (work in progress), November 2019.
Acknowledgements
Thanks to ...
Authors' Addresses
Liang Xia (Frank)
Huawei
101 Software Avenue, Yuhuatai District,
Nanjing, Jiangsu 210012
China
Email: frank.xialiang@huawei.com
Wei Pan
Huawei
101 Software Avenue, Yuhuatai District
Nanjing, Jiangsu 210012
China
Email: william.panwei@huawei.com
Xia & Pan Expires August 30, 2020 [Page 15]
