| Remote ATtestation ProcedureS | L. Xia |
| Internet-Draft | W. Pan |
| Intended status: Standards Track | Huawei |
| Expires: April 23, 2020 | October 21, 2019 |
Using Netconf Pub/Sub Model for RATS Interaction Procedure
draft-xia-rats-pubsub-model-00
This draft defines the a new method of using the netconf pub/sub model in the RATS interaction procedure, to increse its flexibility, efficiency and scalability.
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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 onlline transaction, Cryptographic Key Attestation for mobile devices, and so on.
[I-D.birkholz-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 customizing the IETF NETCONF pub/sub model [RFC8639][RFC8640][RFC8641]. With its nature of asynchronous communication, the new 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, 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 combinded together are currently out of the scope of this draft.
In summary, by untilizing the pub/sub model in remote attestation procedure, the gained benefits are as below:
This document is organized as follows. Section 2 defines conventions and acronyms used. Section 3 discusses pub/sub model of remote attestation procedure.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This document uses terminology defined in[I-D.birkholz-rats-architecture][I-D.birkholz-rats-reference-interaction-model] for security related and RATS scoped terminology.
The following sequence diagram illustrates the reference remote attestation procedure by utilizing the netconf pub/sub model defined by this document.
[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
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. 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 upate 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):
The following sections decribe the above key steps one by one.
The event streams here refers to various integrity evidence information related to device trustworthiness. 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 generation, operating system and application dynamic integrity information (e.g., IMA logs) recorded during device running time.
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.birkholz-rats-basic-yang-module] with YANG data format, and [I-D.ietf-rats-eat] with COSE data format.
NETCONF pub/sub model provides several suscription types in which approriate one or more types are choosed 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 key service processes). 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 data 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 NETCONF Session. The corresponding subscription RPC needs to be established dynamically. This way can reduce unnecessary NETCONF sessions.
Furthermore, certain pre-defined events 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 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.
The selection filters may be applied to the subscription, so that only the event that pass the filter will be distributed out.
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").
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 nonce is maintained. Specifically, there may be several ways to do it:
To be written.
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:
<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:
<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:
Figure 4: Configured Event-triggered Subscription Message
To be written.
To be written.
To be written
Thanks to ...
To be written, possibly.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [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. |
| [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. |
| [RFC8641] | Clemm, A. and E. Voit, "Subscription to YANG Notifications for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641, September 2019. |
| [I-D.birkholz-rats-architecture] | Birkholz, H., Wiseman, M., Tschofenig, H. and N. Smith, "Remote Attestation Procedures Architecture", Internet-Draft draft-birkholz-rats-architecture-02, September 2019. |
| [I-D.birkholz-rats-basic-yang-module] | Birkholz, H., Eckel, M., Bhandari, S., Sulzen, B., Voit, E., Xia, L., Laffey, T. and G. Fedorkow, "YANG Module for Basic Challenge-Response-based Remote Attestation Procedures", Internet-Draft draft-birkholz-rats-basic-yang-module-01, July 2019. |
| [I-D.birkholz-rats-information-model] | Birkholz, H. and M. Eckel, "An Information Model for Assertions used in RATS", Internet-Draft draft-birkholz-rats-information-model-00, July 2019. |
| [I-D.birkholz-rats-reference-interaction-model] | Birkholz, H. and M. Eckel, "Reference Interaction Model for Challenge-Response-based Remote Attestation", Internet-Draft draft-birkholz-rats-reference-interaction-model-01, July 2019. |
| [I-D.birkholz-rats-tuda] | Fuchs, A., Birkholz, H., McDonald, I. and C. Bormann, "Time-Based Uni-Directional Attestation", Internet-Draft draft-birkholz-rats-tuda-01, 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", Internet-Draft draft-bryskin-netconf-automation-yang-03, July 2019. |
| [I-D.ietf-rats-eat] | Mandyam, G., Lundblade, L., Ballesteros, M. and J. O'Donoghue, "The Entity Attestation Token (EAT)", Internet-Draft draft-ietf-rats-eat-01, July 2019. |
| [I-D.richardson-rats-usecases] | Richardson, M., Wallace, C. and W. Pan, "Use cases for Remote Attestation common encodings", Internet-Draft draft-richardson-rats-usecases-05, October 2019. |