Strong Assertions of IoT Network Access Requirements
draft-ietf-suit-mud-04

SUIT                                                            B. Moran
Internet-Draft                                               Arm Limited
Intended status: Standards Track                           H. Tschofenig
Expires: 5 January 2024                                      4 July 2023

          Strong Assertions of IoT Network Access Requirements
                         draft-ietf-suit-mud-04

Abstract

   The Manufacturer Usage Description (MUD) specification describes the
   access and network functionality required for a device to properly
   function.  The MUD description has to reflect the software running on
   the device and its configuration.  Because of this, the most
   appropriate entity for describing device network access requirements
   is the same as the entity developing the software and its
   configuration.

   A network presented with a MUD file by a device allows detection of
   misbehavior by the device software and configuration of access
   control.

   This document defines a way to link a SUIT manifest to a MUD file
   offering a stronger binding between the two.

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 5 January 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Moran & Tschofenig       Expires 5 January 2024                 [Page 1]
Internet-Draft              SUIT MUD Linkage                   July 2023

   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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Workflow  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Advantages over previous MUD URL reporting mechanisms . . . .   4
   5.  Extensions to SUIT  . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Under [RFC8520], devices report a URL to a MUD manager in the
   network.  RFC 8520 envisions different approaches for conveying the
   information from the device to the network such as:

   *  DHCP,

   *  IEEE802.1AB Link Layer Discovery Protocol (LLDP), and

   *  IEEE 802.1X whereby the URL to the MUD file would be contained in
      the certificate used in an EAP method.

   The MUD manager then uses the URL to fetch the MUD file, which
   contains access and network functionality required for a device to
   properly function.

Moran & Tschofenig       Expires 5 January 2024                 [Page 2]
Internet-Draft              SUIT MUD Linkage                   July 2023

   The MUD manager must trust the service from which the MUD file is
   fetched to return an authentic copy of the MUD file.  This concern
   may be mitigated using the optional signature reference in the MUD
   file.  The MUD manager must also trust the device to report a correct
   URL.  In case of DHCP and LLDP the URL is unprotected.  When the URL
   to the MUD file is included in a certificate then it is authenticated
   and integrity protected.  A certificate created for use with network
   access authentication is typically not signed by the entity that
   wrote the software and configured the device, which leads to
   conflation of local network access rights with rights to assert all
   network access requirements.

   There is a need to bind the entity that creates the software and
   configuration to the MUD file because only that entity can attest the
   network access requirements of the device.  This specification
   defines an extension to the Software Updates for Internet of Things
   (SUIT) manifest format [I-D.ietf-suit-manifest] to include a MUD file
   (by reference or by value).  When combining a MUD file with a
   manifest used for software/firmware updates (potentially augmented
   with attestation) then a network operator can get more confidence in
   the description of the access and network functionality required for
   a device to properly function.

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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Workflow

   The intended workflow is as follows:

   *  At the time of onboarding, devices report their manifest in use to
      the MUD manager via attestation evidence.

   *  If the SUIT_MUD_container, see Section 5, has been severed, the
      MUD manager can use the suit-reference-uri to retrieve the
      complete SUIT manifest.

   *  The manifest authenticity is verified by the MUD manager, which
      enforces that the MUD file presented is also authentic and as
      intended by the device software vendor.

   *  Each time a device is updated, rebooted, or otherwise
      substantially changed, it will execute an attestation.

Moran & Tschofenig       Expires 5 January 2024                 [Page 3]
Internet-Draft              SUIT MUD Linkage                   July 2023

      -  Among other claims in the Entity Attestation Token (EAT)
         [I-D.ietf-rats-eat], the device will report its software
         digest(s), configuration digest(s), manifest URI, and manifest
         digest to the MUD manager.

      -  The MUD manager can then validate these attestation reports in
         order to check that the device is operating with the expected
         version of software and configuration.

      -  Since the manifest digest is reported, the MUD manager can look
         up the corresponding manifest.

   *  If the MUD manager does not already have a full copy of the
      manifest, it can be acquired using the reference URI.

   *  Once a full copy of the manifest is provided, the MUD manager can
      verify the device attestation report

   *  The MUD manager acquires the MUD file from the MUD URL.

   *  The MUD manager verifies the MUD file signature using the provided
      Subject Key Identifier.

   *  Then, the MUD manager can apply any appropriate policy as
      described by the MUD file.

4.  Advantages over previous MUD URL reporting mechanisms

   Binding within the manifest has several advantages over other MUD URL
   reporting mechanisms:

   *  The MUD URL is tightly coupled to device software/firmware
      version.

   *  The device does not report the URL, so the device cannot tamper
      with the URL.

   *  The onus is placed on the software/firmware author to provide a
      MUD file that describes the behavior of the software running on a
      device.

   *  The author explicitly authorizes a key to sign MUD files,
      providing a tight coupling between the party that knows device
      behavior best (the author of the software/firmware) and the party
      that declares device behavior (MUD file signer).

Moran & Tschofenig       Expires 5 January 2024                 [Page 4]
Internet-Draft              SUIT MUD Linkage                   July 2023

   *  Network operators do not need to know, a priori, which MUD URL to
      use for each device; this can be harvested from the device's
      manifest and only replaced if necessary.

   *  A network operator can still replace a MUD URL:

      -  By providing a manifest that overrides the MUD URL.

      -  By replacing the MUD URL in their network infrastructure.

   *  Devices can be quarantined if they do not attest a known software/
      firmware version.

   *  Devices cannot lie about which MUD URL to use.

5.  Extensions to SUIT

   To enable strong assertions about the network access requirements
   that a device should have for a particular software/configuration
   pair a MUD URL is added to the SUIT manifest along with a subject key
   identifier (ski).  The subject key identifier MUST be generated
   according to the process defined in [I-D.isobe-cose-key-thumbprint].

   The following CDDL describes the extension to the SUIT_Manifest
   structure:

   $$severable-manifest-members-choice-extensions //= (
     suit-manifest-mud => SUIT_Digest / SUIT_MUD_container
   )

   The SUIT_Envelope is also amended:

   $$SUIT_severable-members-extensions //= (
     suit-manifest-mud => bstr .cbor SUIT_MUD_container
   )

   The SUIT_MUD_container structure is defined as follows:

   SUIT_MUD_container = {
       suit-mud-url => #6.32(tstr),
       suit-mud-ski => SUIT_Digest,
   }

Moran & Tschofenig       Expires 5 January 2024                 [Page 5]
Internet-Draft              SUIT MUD Linkage                   July 2023

6.  Security Considerations

   This specification links MUD files to other IETF technologies,
   particularly to SUIT manifests, for improving security protection and
   ease of use.  By including MUD files (by reference or by value) in
   SUIT manifests an extra layer of protection has been created and
   synchronization risks can be minimized.  If the MUD file and the
   software/firmware loaded onto the device gets out-of-sync a device
   may be firewalled and, with firewalling by networks in place, the
   device may stop functioning.

7.  IANA Considerations

   IANA is requested to add a new value to the SUIT manifest elements
   registry created with [I-D.ietf-suit-manifest]:

   *  Label: TBD1 [[Value allocated from the standards action address
      range]]

   *  Name: Manufacturer Usage Description (MUD)

   *  Reference: [[TBD: This document]]

   IANA is requested to add a new value to the SUIT envelope elements
   registry created with [I-D.ietf-suit-manifest]:

   *  Label: TBD2 [[Value allocated from the standards action address
      range]]

   *  Name: Manufacturer Usage Description (MUD)

   *  Reference: [[TBD: This document]]

8.  Normative References

   [I-D.ietf-rats-eat]
              Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
              Wallace, "The Entity Attestation Token (EAT)", Work in
              Progress, Internet-Draft, draft-ietf-rats-eat-21, 30 June
              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
              rats-eat-21>.

Moran & Tschofenig       Expires 5 January 2024                 [Page 6]
Internet-Draft              SUIT MUD Linkage                   July 2023

   [I-D.ietf-suit-manifest]
              Moran, B., Tschofenig, H., Birkholz, H., Zandberg, K., and
              O. Rønningstad, "A Concise Binary Object Representation
              (CBOR)-based Serialization Format for the Software Updates
              for Internet of Things (SUIT) Manifest", Work in Progress,
              Internet-Draft, draft-ietf-suit-manifest-22, 27 February
              2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
              suit-manifest-22>.

   [I-D.isobe-cose-key-thumbprint]
              Isobe, K. and H. Tschofenig, "COSE Key Thumbprint", Work
              in Progress, Internet-Draft, draft-isobe-cose-key-
              thumbprint-02, 16 June 2023,
              <https://datatracker.ietf.org/doc/html/draft-isobe-cose-
              key-thumbprint-02>.

   [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/rfc/rfc2119>.

   [RFC7093]  Turner, S., Kent, S., and J. Manger, "Additional Methods
              for Generating Key Identifiers Values", RFC 7093,
              DOI 10.17487/RFC7093, December 2013,
              <https://www.rfc-editor.org/rfc/rfc7093>.

   [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/rfc/rfc8174>.

   [RFC8520]  Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
              Description Specification", RFC 8520,
              DOI 10.17487/RFC8520, March 2019,
              <https://www.rfc-editor.org/rfc/rfc8520>.

Authors' Addresses

   Brendan Moran
   Arm Limited
   Email: brendan.moran.ietf@gmail.com

   Hannes Tschofenig
   Email: hannes.tschofenig@gmx.net

Moran & Tschofenig       Expires 5 January 2024                 [Page 7]