IETF                                                         K. Moriarty
Internet-Draft                        Center for Internet Security (CIS)
Intended status: Standards Track                             May 4, 2021
Expires: November 5, 2021

 Scalable Remote Attestation for Systems, Containers, and Applications


   This document establishes an architectural pattern whereby a remote
   attestation could be issued for a complete set of benchmarks or
   controls that are defined and grouped by an external entity,
   preventing the need to send over individual attestations for each
   item within a benchmark or control framework.  This document
   establishes a pattern to list sets of benchmarks and controls within
   CWT and JWT formats for use as an Entity Attestation Token (EAT).

Status of This Memo

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   This Internet-Draft will expire on November 5, 2021.

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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
   2.  Policy and Measurement Set Definitions  . . . . . . . . . . .   4
   3.  Supportability and Re-Attestation . . . . . . . . . . . . . .   4
   4.  Configuration Sets  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Remediation . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .   7
   Appendix B.  Open Issues  . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Posture assessment has long been desired, but has been difficult to
   achieve due to complexities of customization requirements at each
   organization.  By using policy and measurement sets that may be
   offered at various assurance levels, automating posture assessment
   through attestation becomes achievable for organizations of all
   sizes.  The measurement and policy groupings may be provided by the
   vendor or by a neutral third party to enable ease of use and
   consistent implementations.  This provides simpler options to enable
   posture assessment at selected levels by organizations without the
   need to have in-house expertise.  The measurement and policy sets may
   also be customized, but not necessary to achieve posture assessment
   to predefined options.  This document describes a method to use
   existing attestation formats and protocols while allowing for
   profiles of policies, benchmarks, and measurements at defined
   assurance levels that scale to provide transparency to posture
   assessment results with remote attestation.

   By way of example, the Center for Internet Security (CIS) hosts
   recommended configuration settings to secure operating systems,
   applications, and devices in CIS Benchmarks developed with industry
   experts.  Attestations aligned to the CIS Benchmarks or other
   configuration guide such as a DISA STIG could be used to assert the
   configuration meets expectations.  This has already been done for
   multiple platforms to demonstrate assurance for firmware according to
   NIST SP 800-193, Firmware Resiliency Guidelines.  In order to scale
   remote attestation, a single attestation for a set of Benchmarks or

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   policies being met may be sent to the remote atteststaion management

   On traditional servers, assurance to NIST SP 800-193 is provable
   through attestation from a root of trust (RoT), using the Trusted
   Computing Group (TCG) Trusted Platform Module (TPM) chip and
   attestation formats.  At boot, policy and measurement expectations
   are verified against a set of "golden policies" from collected and
   attested evidence.  Device identity and measurements can also be
   attestated at runtime.  The attestations on evidence (e.g. hash of
   boot element) and verification of attestations are typically
   contained within a system and are limited to the control plane for
   management.  The policy and measurement sets for comparison are
   protected to assure the result in the attestation verification
   process for boot element.  Event logs and PCR values may be exposed
   to provide transparency into the verified attestations.  Remote
   attestation on systems is intended to provide an assessment of
   posture for all managed systems and across various layers in each of
   these systems in an environment.

   There is a balance of exposure and evidence needed to assess posture
   when providing assurance of controls and system state.  Currently,
   logs and TPM PCR values may be passed to provide assurance of
   verification of attestation evidence meeting set requirements.
   Providing the assurance can be accomplished with a remote attestation
   format such as the Entity Attestation Token (EAT) [I-D.ietf-rats-eat]
   and a RESTful interface such as ROLIE or RedFish.  Policy definition
   blocks may be scoped to control measurement sets, where the EAT
   asserts compliance to the policy or measurement block specified and
   may include claims with the log and PCR value evidence.  Measurement
   and Policy sets may be published and maintained by separate entities
   (e.g.  CIS Benchmarks, DISA STIGs).  The policy and measurement sets
   should be maintained separately even if associated with the same
   benchmark or control set.  This avoids the need to transition the
   verifying entity to a remote system for individual policy and
   measurements which are performed locally for more immediate
   remediation as well as other functions.

   Examples of measurement and policy sets include, but are not limited

   o  Hardware attribute certificates

   o  Hardware Attribute Certificate Comparison Results

   o  Reference Integrity Measurements for firmware

   o  Operating system benchmarks at Specified Assurance Levels

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   o  Application hardening Benchmarks at Specified Assurance Levels

   o  Container security benchmarks at Specified Assurance Levels

   Scale, ease of use, full automation, and consistency for customer
   consumption of a remote attestation function or service are essential
   toward the goal of consistently securing systems against known
   threats and vulnerabilities.  Mitigations may be baked into policy.
   Measurement verification sets and the attestation that the sets meet
   expected policies and measurements are conveyed in an Entity
   Attestation Token made available to a RESTful interface in aggregate
   for the systems managed.

2.  Policy and Measurement Set Definitions

   This document defines EAT claims in the JWT [RFC7519] and CWT
   [RFC8392] registries to provide attestation to a set of verified
   claims within a defined grouping.  The trustworthiness will be
   conveyed on original verified evidence as well as the attestation on
   the grouping.

      | Claim | Long Name                  | Description                     | Format        |
      | MPS   | Measurement or Policy Set  | Name for the MPS                |               |
      | LEM   | Log Evidence of MPS        | Log File or URI                 |               |
      | PCR   | TPM PCR Values             |                                 |               |
      | FMA   | Format of MPS Attestations | Format of included attestations |               |
      | HSH   | Hash Value/Message Digest  | Hash va,ue of configuration set |               |

3.  Supportability and Re-Attestation

   The remote attestation framework shall include provisions within the
   system and attestation authority to allow for Product modification.

   Over its lifecycle, the Product may experience modification due to:
   maintenance, failures, upgrades, expansion, moves, etc..

   The customer can chose to:

   o  Run remote attestation after product modification, or

   o  Not take action and remain un-protected

   In the case of Re-Attestation:

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   o  framework needs to invalidate previous TPM PCR values and tokens,

   o  framework needs to collect new measurements,

   o  framework needs to maintain history or allow for history to be
      logged to enable change traceability attestation, and

   o  framework needs to notify that the previous attestation has been

4.  Configuration Sets

   In some cases, it may be difficult to attest to configuration
   settings for the initial or subsequent attestation and verification
   processes.  The use of an expected hash value for configuration
   settings can be used to compare the attested configuration set.  In
   this case, the creator of the attestation verification measurements
   would define a set of values for which a message digest would be
   created and then signed by the attestor.  The expected measurements
   would include the expected hash value for comparison.  The
   configuration set could be the full attestation set to a Benchmark or
   a defined subset.

5.  Remediation

   If policy and configration settings or measurements attestated do not
   meet expected values, remediation is desireable.  Automated
   remediation performed with alignment to zero trust architecture
   principles would require that the remeidation be performed prior to
   any relying component executing.  The relying component would verifiy
   before continuing in a zero trust architecture.

   Ideally, remediation would occur on system as part of the process to
   attest to a set of attestations, similar to how attestation is
   performed for firmware in the boot process.  If automated remediation
   is not possible, an alert should be generated to allow for
   notification of the variance from expected values.

6.  Security Considerations

   This document establishes a pattern to list sets of benchmarks and
   controls within CWT and JWT formats.  The contents of the benchmarks
   and controls are out of scope for this document.  This establishes an
   architectural pattern whereby a remote attestation could be issued
   for a complete set of benchmarks or controls as defined and grouped
   by external entities, preventing the need to send over individual
   attestations for each item within a benchmark or control framework.

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   This document does not add security consideration over what has been
   described in the EAT, JWT, or CWT specifications.

7.  IANA Considerations

   This memo includes no request to IANA, yet.  This will list the
   initial registration sets to the JWT and CWT registries if adopted.

8.  Contributors

   Thank you to reviewers and contributors who helped to improve this
   document.  Thank you to Nick Grobelney, Dell Technologies, for your
   review and contribution to separate out the policy and measurement
   sets.  Thank you, Samant Kakarla and Huijun Xie from Dell
   Technologies, for your detailed review and corrections on boot
   process details.  Section 3 has been contributed by Rudy Bauer from
   Dell as well and an author will be added on the next reveision.

9.  References

9.1.  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,

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,

   [RFC8392]  Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <>.

9.2.  Informative References

              Mandyam, G., Lundblade, L., Ballesteros, M., and J.
              O'Donoghue, "The Entity Attestation Token (EAT)", draft-
              ietf-rats-eat-09 (work in progress), March 2021.

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Appendix A.  Change Log

   Note to RFC Editor: if this document does not obsolete an existing
   RFC, please remove this appendix before publication as an RFC.

Appendix B.  Open Issues

   Note to RFC Editor: please remove this appendix before publication as
   an RFC.

Author's Address

   Kathleen M. Moriarty
   Center for Internet Security (CIS)
   31 Tech Valley Drive
   East Greenbush, NY


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