[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Nits]



RATS                                                         H. Birkholz
Internet-Draft                                            Fraunhofer SIT
Intended status: Standards Track                                B. Moran
Expires: January 14, 2021                                    Arm Limited
                                                           July 13, 2020


 Trustworthiness Vectors for the Software Updates of Internet of Things
                         (SUIT) Workflow Model
                   draft-birkholz-rats-suit-claims-00

Abstract

   The IETF Remote Attestation Procedures (RATS) architecture defines
   Conceptual Messages as input and output of the appraisal process that
   assesses the trustworthiness of remote peers: Evidence and
   Attestation Results.  Based on the Trustworthiness Vectors defined in
   Trusted Path Routing, this document defines a core set of Claims to
   be used in Evidence and Attestation Results for the Software Update
   for the Internet of Things (SUIT) Workflow Model.  Consecutively,
   this document is in support of the Trusted Execution Environment
   Provisioning (TEEP) architecture, which defines the assessment of
   remote peers via RATS and uses SUIT for evidence generation as well
   as a remediation measure to improve trustworthiness of given remote
   peers.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 14, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




Birkholz & Moran        Expires January 14, 2021                [Page 1]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  SUIT Workflow Model and Procedures  . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Trustworthiness Vectors . . . . . . . . . . . . . . . . . . .   4
   3.  SUIT Claims . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  System Properties Claims  . . . . . . . . . . . . . . . .   5
       3.1.1.  vendor-identifier . . . . . . . . . . . . . . . . . .   6
       3.1.2.  class-identifier  . . . . . . . . . . . . . . . . . .   6
       3.1.3.  device-identifier . . . . . . . . . . . . . . . . . .   6
       3.1.4.  component-identifier  . . . . . . . . . . . . . . . .   6
       3.1.5.  image-digest  . . . . . . . . . . . . . . . . . . . .   6
       3.1.6.  image-size  . . . . . . . . . . . . . . . . . . . . .   6
       3.1.7.  minimum-battery . . . . . . . . . . . . . . . . . . .   7
       3.1.8.  version . . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  Interpreter Record Claims . . . . . . . . . . . . . . . .   7
       3.2.1.  record-success  . . . . . . . . . . . . . . . . . . .   7
       3.2.2.  component-index . . . . . . . . . . . . . . . . . . .   7
       3.2.3.  dependency-index  . . . . . . . . . . . . . . . . . .   7
       3.2.4.  command-index . . . . . . . . . . . . . . . . . . . .   7
       3.2.5.  nominal-parameters  . . . . . . . . . . . . . . . . .   8
       3.2.6.  nominal-parameters  . . . . . . . . . . . . . . . . .   8
     3.3.  Generic Record Conditions (TBD) . . . . . . . . . . . . .   8
   4.  List of Commands (TBD)  . . . . . . . . . . . . . . . . . . .   8
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Attestation Results are an essential output of Verifiers as defined
   in the Remote ATtestation procedureS (RATS) architecture
   [I-D.ietf-rats-architecture].  They are consumed by Relying Parties:
   the entities that intend to build future decisions on trustworthiness
   assessments of remote peers.  Attestation Results must be easily




Birkholz & Moran        Expires January 14, 2021                [Page 2]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


   digestable by Relying Parties - in contrast to the rather complex or
   domain-specific Evidence digested by Verifiers.

   In order to create Attestation Results, a Verifier must consume
   Evidence generated by a given Attester (amongst other Conceptual
   Messages, such as Endorsements and Attestation Policies).  Both
   Evidence and Attestation Results are composed of Claims.  This
   document highlights and defines a set of Claims to be used in
   Evidence and Attestation Results that are based on the SUIT Workflow
   Model [I-D.ietf-suit-manifest].  In the scope of this document, an
   Attester takes on the role of a SUIT Recipient: the system that
   receives a SUIT Manifest.

1.1.  SUIT Workflow Model and Procedures

   This document focuses on Evidence and Attestation Results that can be
   generated based on the output of SUIT Procedures.  The SUIT Workflow
   Model allows for two types of SUIT Procedures generating Reports on
   the Attester as defined in the SUIT Manifest specification:

   Update Procedures:  A procedure that updates a device by fetching
      dependencies, software images, and installing them

      An Update Procedure creates a Report on mutable software
      components that are installed or updated on hardware components.

   Boot Procedures:  A procedure that boots a device by checking
      dependencies and images, loading images, and invoking one or more
      image

      A Boot Procedure creates a Report on measured boot events (e.g.
      during Secure Boot).

   The Records contained in each type of Report can be used as Claims in
   Evidence generation on the Attester and in Attestation as described
   in this document.  Analogously, a corresponding Verifier appraising
   that Evidence can create Attestation Results using the Claims defined
   in this document.

   Both types of SUIT Procedures pass several stages (e.g. dependency-
   checking is one stage).  The type and sequence of stages are defined
   by the Command Sequences included in a SUIT Manifest.  For each stage
   in which a Command from the Command Sequence is executed a Record is
   created.  All Records of a SUIT procedure contain binary results
   limited to "fail" or "pass".  The aggregated sequence of all Records
   is composed into a Report.





Birkholz & Moran        Expires January 14, 2021                [Page 3]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


   This document specifies new Claims derived from Command Sequence
   Reports and highlights existing Claims as defined in Trusted Path
   Routing [I-D.voit-rats-trusted-path-routing] that are applicable to
   the operational state of installed and updated software.

   The Claims defined in this document are in support of the Trusted
   Execution Environment Provisioning (TEEP) architecture.  During TEEP,
   the current operational state of an Attester is assessed via RATS.
   If the corresponding Attestation Results - as covered in this
   document - indicate insufficient Trustworthiness Levels with respect
   to installed software, the SUIT Workflow Model is used for
   remediation.

1.2.  Terminology

   This document uses the terms and concepts defined in
   [I-D.ietf-rats-architecture], [I-D.ietf-suit-manifest], and
   [I-D.ietf-teep-architecture].

   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.

2.  Trustworthiness Vectors

   While there are usage scenarios where Attestation Results can be
   binary decisions, more often than not the assessment of
   trustworthiness is represented by a more fine-grained spectrum or
   based on multiple factors.  These shades of Attestation Results are
   captured by the definition of Trustworthiness Vectors in Trusted Path
   Routing [I-D.voit-rats-trusted-path-routing].  Trustworthiness
   Vectors are sets of Claims representing appraisal outputs created by
   a Verifier.  Each of these Claims is called a Trustworthiness Level.
   Multiple Trustworthiness Levels are composed into a vector.

   An Attester processing SUIT Manifests can create three types of
   Claims about its Target Environments.  This includes Claims about:

   o  installed manifests including initial state (e.g. factory
      default),

   o  hardware component identifiers that represent the targets of
      updates, and

   o  SUIT Interpreter results (e.g. test-failed) created during
      updates.



Birkholz & Moran        Expires January 14, 2021                [Page 4]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


   Every SUIT Manifest maps to a certain intended state of a device.
   Every intended device composition of software components associated
   with hardware components can therefore be expressed based on a SUIT
   Manifest.  The current operational state of a device can be
   represented in the same form, including the initial state.

   As a result, the Claims defined in this document are bundled by the
   scope of the information represented in SUIT Manifests, i.e.,
   dedicated blobs of software that are the payload of a SUIT Manifest.
   All Claims associated with an identifiable SUIT Manifest must always
   be bundled together in a Claims set that is limited to the Claims
   defined in this document.

3.  SUIT Claims

   The Claim description in this document uses CDDL as the formal
   modeling language for Claims.  This approach is derived from
   [I-D.ietf-rats-eat].  All Claims are based on information elements as
   used in the SUIT Manifest specification [I-D.ietf-suit-manifest].
   For instance, a SUIT Vendor ID is represented as an UUID.
   Analogously, the corresponding vendor-identifier Claim found below is
   based on a UUID.  SUIT Claims are differentiated in:

   o  software and hardware characteristics (System Properties), and

   o  reports about updates their SUIT Commands (SUIT Records).

   Both types of Claims are always bundled in dedicated Claim Sets.
   Implementations can encode this information in various different ways
   (data models), e.g., sets, sequences, or nested structures.  The
   following subsections define the SUIT Report Claims for RATS and are
   structured according to the following CDDL expression.

   suit-report = {
     suit-system-properties => [ + system-property-claims ],
     suit-records => [ + interpreter-record-claims ],
   }

   system-property-claims => { + $$system-property-claim }
   interpreter-record-claims => { + $$interpreter-record-claim }

3.1.  System Properties Claims

   System Properties Claims are composed of:

   o  Hardware Component Claims and

   o  Software Component Claims.



Birkholz & Moran        Expires January 14, 2021                [Page 5]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


   Correspondingly, the Claim definitions below highlight if a Claim is
   generic or hw/sw-component specific.

3.1.1.  vendor-identifier

   A RFC 4122 UUID representing the vendor of the Attester or one of its
   hardware and/or software components.

   $$system-property-claim //= ( vendor-identifier => RFC4122_UUID )

3.1.2.  class-identifier

   A RFC 4122 UUID representing the class of the Attester or one of its
   hardware and/or software components.

   $$system-property-claim //= ( class-identifier => RFC4122_UUID )

3.1.3.  device-identifier

   A RFC 4122 UUID representing the Attester.

   $$system-property-claim //= ( device-identifier => RFC4122_UUID )

3.1.4.  component-identifier

   A sequence of binary identifiers that is intended to identify a
   software-component of an Attester uniquely.  A binary identifier can
   represent a CoSWID [I-D.ietf-sacm-coswid] tag-id.

   $$system-property-claim //=  ( class-identifier => [ + identifier ] )

3.1.5.  image-digest

   A fingerprint computed over a software component image on the
   Attester.  This Claim is always bundled with a component-identifier
   or component-index.

   $$system-property-claim //= ( image-digest => digest )

3.1.6.  image-size

   The size of a firmware image on the Attester.

   $$system-property-claim //= ( image-size => size )







Birkholz & Moran        Expires January 14, 2021                [Page 6]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


3.1.7.  minimum-battery

   The configured minimum battery level of the Attester in mWh.

   $$system-property-claim //= ( minimum-battery => charge )

3.1.8.  version

   The Version of a hardware or software component of the Attester.

   $$system-property-claim //= ( version => version-value )

3.2.  Interpreter Record Claims

   This class of Claims represents the content of SUIT Records generated
   by Interpreters running on Recipients.  They are always bundled into
   Claim Sets representing SUIT Reports and are intended to be included
   in Evidence generated by an Attester.  The Interpreter Record Claims
   appraised by a Verifier can steer a corresponding a Firmware
   Appraisal procedures that consumes this Evidence.  Analogously, these
   Claims can be re-used in generated Attestation Results as
   Trustworthiness Vectors [I-D.voit-rats-trusted-path-routing].

3.2.1.  record-success

   The result of a Command that was executed by the Interpreter on an
   Attester.

   $$interpreter-record-claim //= ( record-success => bool )

3.2.2.  component-index

   A positive integer representing an entry in a flat list of indices
   mapped to software component identifiers to be updated.

   $$system-property-claim //= ( component-index => uint )

3.2.3.  dependency-index

   A thumbprint of a software component that an update depends on.

   $$interpreter-record-claim //= ( dependency-index => digest )

3.2.4.  command-index

   A positive integer representing an entry in a SUIT_Command_Sequence
   identifying a Command encoded as a SUIT Manifest Directive or SUIT
   Manifest Condition.



Birkholz & Moran        Expires January 14, 2021                [Page 7]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


   $$interpreter-record-claim //= ( command-index => uint )

3.2.5.  nominal-parameters

   A list of SUIT_Parameters associated with a specific Command encoded
   as a SUIT Manifest Directive.

 $$interpreter-record-claim //= ( nominal-parameters => parameter-list )

3.2.6.  nominal-parameters

   A list of SUIT_Parameters associated with a specific Command that was
   executed by the Interpreter on an Attester.

  $$interpreter-record-claim //= ( actual-parameters => parameter-list )

3.3.  Generic Record Conditions (TBD)

   o  test-failed

   o  unsupported-command

   o  unsupported-parameter

   o  unsupported-component-id

   o  payload-unavailable

   o  dependency-unavailable

   o  critical-application-failure

   o  watchdog-timeout

4.  List of Commands (TBD)

   o  Check Vendor Identifier

   o  Check Class Identifier

   o  Verify Image

   o  Set Component Index

   o  Override Parameters

   o  Set Dependency Index




Birkholz & Moran        Expires January 14, 2021                [Page 8]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


   o  Set Parameters

   o  Process Dependency

   o  Run

   o  Fetch

   o  Use Before

   o  Check Component Offset

   o  Check Device Identifier

   o  Check Image Not Match

   o  Check Minimum Battery

   o  Check Update Authorized

   o  Check Version

   o  Abort

   o  Try Each

   o  Copy

   o  Swap

   o  Wait For Event

   o  Run Sequence

   o  Run with Arguments

5.  References

5.1.  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>.



Birkholz & Moran        Expires January 14, 2021                [Page 9]


Internet-Draft         SUIT Trustworthiness Vectos             July 2020


5.2.  Informative References

   [I-D.ietf-rats-architecture]
              Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
              W. Pan, "Remote Attestation Procedures Architecture",
              draft-ietf-rats-architecture-05 (work in progress), July
              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.

   [I-D.ietf-sacm-coswid]
              Birkholz, H., Fitzgerald-McKay, J., Schmidt, C., and D.
              Waltermire, "Concise Software Identification Tags", draft-
              ietf-sacm-coswid-15 (work in progress), May 2020.

   [I-D.ietf-suit-manifest]
              Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
              "A Concise Binary Object Representation (CBOR)-based
              Serialization Format for the Software Updates for Internet
              of Things (SUIT) Manifest", draft-ietf-suit-manifest-08
              (work in progress), July 2020.

   [I-D.ietf-teep-architecture]
              Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
              "Trusted Execution Environment Provisioning (TEEP)
              Architecture", draft-ietf-teep-architecture-11 (work in
              progress), July 2020.

   [I-D.voit-rats-trusted-path-routing]
              Voit, E., "Trusted Path Routing", draft-voit-rats-trusted-
              path-routing-02 (work in progress), June 2020.

Authors' Addresses

   Henk Birkholz
   Fraunhofer SIT

   EMail: henk.birkholz@sit.fraunhofer.de


   Brendan Moran
   Arm Limited

   EMail: Brendan.Moran@arm.com




Birkholz & Moran        Expires January 14, 2021               [Page 10]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/