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Versions: (draft-moran-suit-architecture) 00 01 02 03

SUIT                                                            B. Moran
Internet-Draft                                             H. Tschofenig
Intended status: Standards Track                             Arm Limited
Expires: December 5, 2018                                    H. Birkholz
                                                          Fraunhofer SIT
                                                              J. Jimenez
                                                                Ericsson
                                                           June 03, 2018


 Firmware Updates for Internet of Things Devices - An Information Model
                             for Manifests
                  draft-ietf-suit-information-model-00

Abstract

   Vulnerabilities with Internet of Things (IoT) devices have raised the
   need for a solid and secure firmware update mechanism that is also
   suitable for constrained devices.  Incorporating such update
   mechanism to fix vulnerabilities, to update configuration settings as
   well as adding new functionality is recommended by security experts.

   One component of such a firmware update is the meta-data, or
   manifest, that describes the firmware image(s) and offers appropriate
   protection.  This document describes all the information that must be
   present in the manifest.

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 http://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 December 5, 2018.








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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   This document may contain material from IETF Documents or IETF
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   Without obtaining an adequate license from the person(s) controlling
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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
   3.  Motivation for Manifest Fields  . . . . . . . . . . . . . . .   4
     3.1.  Threat Model  . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Threat Descriptions . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Threat MFT1: Old Firmware . . . . . . . . . . . . . .   5
       3.2.2.  Threat MFT2: Mismatched Firmware  . . . . . . . . . .   5
       3.2.3.  Threat MFT3: Offline device + Old Firmware  . . . . .   5
       3.2.4.  Threat MFT4: The target device misinterprets the type
               of payload  . . . . . . . . . . . . . . . . . . . . .   6
       3.2.5.  Threat MFT5: The target device installs the payload
               to the wrong location . . . . . . . . . . . . . . . .   6
       3.2.6.  Threat MFT6: Redirection  . . . . . . . . . . . . . .   6
       3.2.7.  Threat MFT7: Payload Verification on Boot . . . . . .   6
       3.2.8.  Threat MFT8: Unauthenticated Updates  . . . . . . . .   7
       3.2.9.  Threat MFT9: Unexpected Precursor images  . . . . . .   7
       3.2.10. Threat MFT10: Unqualified Firmware  . . . . . . . . .   7
       3.2.11. Threat MFT11: Reverse Engineering Of Firmware Image
               for Vulnerability Analysis  . . . . . . . . . . . . .   8



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     3.3.  Security Requirements . . . . . . . . . . . . . . . . . .   9
       3.3.1.  Security Requirement MFSR1: Monotonic Sequence
               Numbers . . . . . . . . . . . . . . . . . . . . . . .   9
       3.3.2.  Security Requirement MFSR2: Vendor, Device-type
               Identifiers . . . . . . . . . . . . . . . . . . . . .   9
       3.3.3.  Security Requirement MFSR3: Best-Before Timestamps  .   9
       3.3.4.  Security Requirement MFSR4: Signed Payload Descriptor   9
       3.3.5.  Security Requirement MFSR5: Cryptographic
               Authenticity  . . . . . . . . . . . . . . . . . . . .  10
       3.3.6.  Security Requirement MFSR6: Rights Require
               Authenticity  . . . . . . . . . . . . . . . . . . . .  10
       3.3.7.  Security Requirement MFSR7: Firmware encryption . . .  11
     3.4.  User Stories  . . . . . . . . . . . . . . . . . . . . . .  11
       3.4.1.  Use Case MFUC1: Installation Instructions . . . . . .  11
       3.4.2.  Use Case MFUC2: Reuse Local Infrastructure  . . . . .  12
       3.4.3.  Use Case MFUC3: Modular Update  . . . . . . . . . . .  12
       3.4.4.  Use Case MFUC4: Multiple Authorisations . . . . . . .  12
       3.4.5.  Use Case MFUC5: Multiple Payload Formats  . . . . . .  12
       3.4.6.  Use Case MFUC6: IP Protection . . . . . . . . . . . .  12
     3.5.  Usability Requirements  . . . . . . . . . . . . . . . . .  13
       3.5.1.  Usability Requirement MFUR1 . . . . . . . . . . . . .  13
       3.5.2.  Usability Requirement MFUR2 . . . . . . . . . . . . .  13
       3.5.3.  Usability Requirement MFUR3 . . . . . . . . . . . . .  13
       3.5.4.  Usability Requirement MFUR4 . . . . . . . . . . . . .  13
       3.5.5.  Usability Requirement MFUR5 . . . . . . . . . . . . .  13
   4.  Manifest Fields . . . . . . . . . . . . . . . . . . . . . . .  14
     4.1.  Manifest Version Field: version identifier of the
           manifest structure  . . . . . . . . . . . . . . . . . . .  14
     4.2.  Manifest Field: Monotonic Sequence Number . . . . . . . .  14
     4.3.  Manifest Field: Vendor ID Condition . . . . . . . . . . .  14
     4.4.  Manifest Field: Class ID Condition  . . . . . . . . . . .  15
     4.5.  Manifest Field: Precursor Image Digest Condition  . . . .  15
     4.6.  Manifest Field: Best-Before timestamp condition . . . . .  15
     4.7.  Manifest Field: Payload Format  . . . . . . . . . . . . .  15
     4.8.  Manifest Field: Storage Location  . . . . . . . . . . . .  15
     4.9.  Manifest Field: URIs  . . . . . . . . . . . . . . . . . .  16
     4.10. Manifest Field: Digests . . . . . . . . . . . . . . . . .  16
     4.11. Manifest Field: Size  . . . . . . . . . . . . . . . . . .  16
     4.12. Manifest Field: Signature . . . . . . . . . . . . . . . .  16
     4.13. Manifest Field: Directives  . . . . . . . . . . . . . . .  16
     4.14. Manifest Field: Aliases . . . . . . . . . . . . . . . . .  16
     4.15. Manifest Field: Dependencies  . . . . . . . . . . . . . .  17
     4.16. Manifest Field: Content Key Distribution Method . . . . .  17
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  17



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     8.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Appendix A.  Mailing List Information . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   The information model aims to describe all the information that must
   be present in the manifest that is consumed by an IoT device.
   Additional information is possible.  The fields that are described
   here are the minimum required to meet the usability and security
   requirements outlined in Section 3.3.

2.  Conventions and 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 RFC
   2119 [RFC2119].

3.  Motivation for Manifest Fields

   The following sub-sections describe the threat model, user stories,
   security requirements, and usability requirements.

3.1.  Threat Model

   The following sub-sections aim to provide information about the
   threats that were considered, the security requirements that are
   derived from those threats and the fields that permit implementation
   of the security requirements.  This model uses the S.T.R.I.D.E.
   [STRIDE] approach.  Each threat is classified according to:

   -  Spoofing Identity

   -  Tampering with data

   -  Repudiation

   -  Information disclosure

   -  Denial of service

   -  Elevation of privilege

   This threat model only covers elements related to the transport of
   firmware updates.  It explicitly does not cover threats outside of
   the transport of firmware updates.  For example, threats to an IoT
   device due to physical access are out of scope.



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3.2.  Threat Descriptions

3.2.1.  Threat MFT1: Old Firmware

   Classification: Elevation of Privilege

   An attacker sends an old, but valid manifest with an old, but valid
   firmware image to a device.  If there is a known vulnerability in the
   provided firmware image, this may allow an attacker to exploit the
   vulnerability and gain control of the device.

   Threat Escalation: If the attacker is able to exploit the known
   vulnerability, then this threat can be escalated to ALL TYPES.

   Mitigated by: MFSR1

3.2.2.  Threat MFT2: Mismatched Firmware

   Classification: Denial of Service

   An attacker sends a valid firmware image, for the wrong type of
   device, signed by an actor with firmware installation permission on
   both types of device.  The firmware is verified by the device
   positively because it is signed by an actor with the appropriate
   permission.  This could have wide-ranging consequences.  For devices
   that are similar, it could cause minor breakage, or expose security
   vulnerabilities.  For devices that are very different, it is likely
   to render devices inoperable.

   Mitigated by: MFSR2

3.2.3.  Threat MFT3: Offline device + Old Firmware

   Classification: Elevation of Privilege

   An attacker targets a device that has been offline for a long time
   and runs an old firmware version.  The attacker sends an old, but
   valid manifest to a device with an old, but valid firmware image.
   The attacker-provided firmware is newer than the installed one but
   older than the most recently available firmware.  If there is a known
   vulnerability in the provided firmware image then this may allow an
   attacker to gain control of a device.  Because the device has been
   offline for a long time, it is unaware of any new updates.  As such
   it will treat the old manifest as the most current.

   Threat Escalation: If the attacker is able to exploit the known
   vulnerability, then this threat can be escalated to ALL TYPES.




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   Mitigated by: MFSR3

3.2.4.  Threat MFT4: The target device misinterprets the type of payload

   Classification: Denial of Service

   If a device misinterprets the type of the firmware image, it may
   cause a device to install a firmware image incorrectly.  An
   incorrectly installed firmware image would likely cause the device to
   stop functioning.

   Threat Escalation: An attacker that can cause a device to
   misinterpret the received firmware image may gain elevation of
   privilege and potentially expand this to all types of threat.

   Mitigated by: MFSR4

3.2.5.  Threat MFT5: The target device installs the payload to the wrong
        location

   Classification: Denial of Service

   If a device installs a firmware image to the wrong location on the
   device, then it is likely to break.  For example, a firmware image
   installed as an application could cause a device and/or an
   application to stop functioning.

   Threat Escalation: An attacker that can cause a device to
   misinterpret the received code may gain elevation of privilege and
   potentially expand this to all types of threat.

   Mitigated by: MFSR4

3.2.6.  Threat MFT6: Redirection

   Classification: Denial of Service

   If a device does not know where to obtain the payload for an update,
   it may be redirected to an attacker's server.  This would allow an
   attacker to provide broken payloads to devices.

   Mitigated by: MFSR4

3.2.7.  Threat MFT7: Payload Verification on Boot

   Classification: Elevation of Privilege





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   An attacker replaces a newly downloaded firmware after a device
   finishes verifying a manifest.  This could cause the device to
   execute the attacker's code.  This attack likely requires physical
   access to the device.  However, it is possible that this attack is
   carried out in combination with another threat that allows remote
   execution.

   Threat Escalation: If the attacker is able to exploit the known
   vulnerability, then this threat can be escalated to ALL TYPES.

   Mitigated by: MFSR4

3.2.8.  Threat MFT8: Unauthenticated Updates

   Classification: Elevation of Privilege

   If an attacker can install their firmware on a device, by
   manipulating either payload or metadata, then they have complete
   control of the device.

   Threat Escalation: If the attacker is able to exploit the known
   vulnerability, then this threat can be escalated to ALL TYPES.

   Mitigated by: MFSR5

3.2.9.  Threat MFT9: Unexpected Precursor images

   Classification: Denial of Service

   An attacker sends a valid, current manifest to a device that has an
   unexpected precursor image.  If a payload format requires a precursor
   image (for example, delta updates) and that precursor image is not
   available on the target device, it could cause the update to break.

   Threat Escalation: An attacker that can cause a device to install a
   payload against the wrong precursor image could gain elevation of
   privilege and potentially expand this to all types of threat.

   Mitigated by: MFSR4

3.2.10.  Threat MFT10: Unqualified Firmware

   Classification: Denial of Service, Elevation of Privilege

   This threat can appear in several ways, however it is ultimately
   about interoperability of devices with other systems.  The owner or
   operator of a network needs to approve firmware for their network in
   order to ensure interoperability with other devices on the network,



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   or the network itself.  If the firmware is not qualified, it may not
   work.  Therefore, if a device installs firmware without the approval
   of the network owner or operator, this is a threat to devices and the
   network.

   Example 1: We assume that OEMs expect the rights to create firmware,
   but that Operators expect the rights to qualify firmware as fit-for-
   purpose on their networks.

   An attacker obtains a manifest for a device on Network A.  They send
   that manifest to a device on Network B.  Because Network A and
   Network B are different, and the firmware has not been qualified for
   Network B, the target device is disabled by this unqualified, but
   signed firmware.

   This is a denial of service because it can render devices inoperable.
   This is an elevation of privilege because it allows the attacker to
   make installation decisions that should be made by the Operator.

   Example 2: Multiple devices that interoperate are used on the same
   network.  Some devices are manufactured by OEM A and other devices by
   OEM B.  These devices communicate with each other.  A new firmware is
   released by OEM A that breaks compatibility with OEM B devices.  An
   attacker sends the new firmware to the OEM A devices without approval
   of the network operator.  This breaks the behaviour of the larger
   system causing denial of service and possibly other threats.  Where
   the network is a distributed SCADA system, this could cause
   misbehaviour of the process that is under control.

   Threat Escalation: If the firmware expects configuration that is
   present in Network A devices, but not Network B devices, then the
   device may experience degraded security, leading to threats of All
   Types.

   Mitigated by: MFSR6

3.2.11.  Threat MFT11: Reverse Engineering Of Firmware Image for
         Vulnerability Analysis

   Classification: All Types

   An attacker wants to mount an attack on an IoT device.  To prepare
   the attack he or she retrieves the provided firmware image and
   performs reverse engineering of the firmware image to analyze it for
   specific vulnerabilities.

   Mitigated by: MFSR7




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3.3.  Security Requirements

   The security requirements here are a set of policies that mitigate
   the threats described in Section 3.1.

3.3.1.  Security Requirement MFSR1: Monotonic Sequence Numbers

   Only an actor with firmware installation authority is permitted to
   decide when device firmware can be installed.  To enforce this rule,
   Manifests MUST contain monotonically increasing sequence numbers.
   Manifests MAY use UTC epoch timestamps to coordinate monotonically
   increasing sequence numbers across many actors in many locations.
   Devices MUST reject manifests with sequence numbers smaller than any
   onboard sequence number.

   N.B.  This is not a firmware version.  It is a manifest sequence
   number.  A firmware version may be rolled back by creating a new
   manifest for the old firmware version with a later sequence number.

   Mitigates: Threat MFT1 Implemented by: Manifest Field: Timestamp

3.3.2.  Security Requirement MFSR2: Vendor, Device-type Identifiers

   Devices MUST only apply firmware that is intended for them.  Devices
   MUST know with fine granularity that a given update applies to their
   vendor, model, hardware revision, software revision.  Human-readable
   identifiers are often error-prone in this regard, so unique
   identifiers SHOULD be used.

   Mitigates: Threat MFT2 Implemented by: Manifest Fields: Vendor ID
   Condition, Class ID Condition

3.3.3.  Security Requirement MFSR3: Best-Before Timestamps

   Firmware MAY expire after a given time.  Devices MAY provide a secure
   clock (local or remote).  If a secure clock is provided and the
   Firmware manifest has a best-before timestamp, the device MUST reject
   the manifest if current time is larger than the best-before time.

   Mitigates: Threat MFT3 Implemented by: Manifest Field: Best-Before
   timestamp condition

3.3.4.  Security Requirement MFSR4: Signed Payload Descriptor

   All descriptive information about the payload MUST be signed.  This
   MUST include:

   -  The type of payload (which may be independent of format)



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   -  The location to store the payload

   -  The payload digest, in each state of installation (encrypted,
      plaintext, installed, etc.)

   -  The payload size

   -  The payload format

   -  Where to obtain the payload

   -  All instructions or parameters for applying the payload

   -  Any rules that identify whether or not the payload can be used on
      this device

   Mitigates: Threats MFT4, MFT5, MFT6, MFT7, MFT9 Implemented by:
   Manifest Fields: Vendor ID Condition, Class ID Condition, Precursor
   Image Digest Condition, Payload Format, Storage Location, URIs,
   Digests, Size

3.3.5.  Security Requirement MFSR5: Cryptographic Authenticity

   The authenticity of an update must be demonstrable.  Typically, this
   means that updates must be digitally signed.  Because the manifest
   contains information about how to install the update, the manifest's
   authenticity must also be demonstrable.  To reduce the overhead
   required for validation, the manifest contains the digest of the
   firmware image, rather than a second digital signature.  The
   authenticity of the manifest can be verified with a digital
   signature, the authenticity of the firmware image is tied to the
   manifest by the use of a fingerprint of the firmware image.

   Mitigates: Threat MFT8 Implemented by: Signature

3.3.6.  Security Requirement MFSR6: Rights Require Authenticity

   If a device grants different rights to different actors, exercising
   those rights MUST be accompanied by proof of those rights, in the
   form of proof of authenticity.  Authenticity mechanisms such as those
   required in MFSR5 are acceptable but need to follow the end-to-end
   security model.

   For example, if a device has a policy that requires that firmware
   have both an Authorship right and a Qualification right and if that
   device grants Authorship and Qualification rights to different
   parties, such as an OEM and an Operator, respectively, then the




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   firmware cannot be installed without proof of rights from both the
   OEM and the Operator.

   Mitigates: MFT10 Implemented by: Signature

3.3.7.  Security Requirement MFSR7: Firmware encryption

   Firmware images must support encryption.  Encryption helps to prevent
   third parties, including attackers, from reading the content of the
   firmware image and to reverse engineer the code.

   Mitigates: MFT11 Implemented by: Manifest Field: Content Key
   Distribution Method

3.4.  User Stories

   User stories provide expected use cases.  These are used to feed into
   usability requirements.

3.4.1.  Use Case MFUC1: Installation Instructions

   As an OEM for IoT devices, I want to provide my devices with
   additional installation instructions so that I can keep process
   details out of my payload data.

   Some installation instructions might be:

   -  Specify a package handler

   -  Use a table of hashes to ensure that each block of the payload is
      validated before writing.

   -  Run post-processing script after the update is installed

   -  Do not report progress

   -  Pre-cache the update, but do not install

   -  Install the pre-cached update matching this manifest

   -  Install this update immediately, overriding any long-running
      tasks.

   Satisfied by: MFUR1







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3.4.2.  Use Case MFUC2: Reuse Local Infrastructure

   As an Operator of IoT devices, I would like to tell my devices to
   look at my own infrastructure for payloads so that I can manage the
   traffic generated by firmware updates on my network and my peers'
   networks.

   Satisfied by: MFUR2, MFUR3

3.4.3.  Use Case MFUC3: Modular Update

   As an OEM of IoT devices, I want to divide my firmware into
   frequently updated and infrequently updated components, so that I can
   reduce the size of updates and make different parties responsible for
   different components.

   Satisfied by: MFUR3

3.4.4.  Use Case MFUC4: Multiple Authorisations

   As an Operator, I want to ensure the quality of a firmware update
   before installing it, so that I can ensure a high standard of
   reliability on my network.  The OEM may restrict my ability to create
   firmware, so I cannot be the only authority on the device.

   Satisfied by: MFUR4

3.4.5.  Use Case MFUC5: Multiple Payload Formats

   As an OEM or Operator of devices, I want to be able to send multiple
   payload formats to suit the needs of my update, so that I can
   optimise the bandwidth used by my devices.

   Satisfied by: MFUR5

3.4.6.  Use Case MFUC6: IP Protection

   As an OEM or developer for IoT devices, I want to protect the IP
   contained in the firmware image, such as the utilized algorithms.
   The need for protecting IP may have also been imposed on me due to
   the use of some third party code libraries.

   Satisfied by: MFSR7








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3.5.  Usability Requirements

   The following usability requirements satisfy the user stories listed
   above.

3.5.1.  Usability Requirement MFUR1

   It must be possible to write additional installation instructions
   into the manifest.

   Satisfies: Use-Case MFUC1 Implemented by: Manifest Field: Directives

3.5.2.  Usability Requirement MFUR2

   It must be possible to redirect payload fetches.  This applies where
   two manifests are used in conjunction.  For example, an OEM manifest
   specifies a payload and signs it, and provides a URI for that
   payload.  An Operator creates a second manifest, with a dependency on
   the first.  They use this second manifest to override the URIs
   provided by the OEM, directing them into their own infrastructure
   instead.

   Satisfies: Use-Case MFUC2 Implemented by: Manifest Field: Aliases

3.5.3.  Usability Requirement MFUR3

   It MUST be possible to link multiple manifests together so that a
   multi-component update can be described.  This allows multiple
   parties with different permissions to collaborate in creating a
   single update for the IoT device, across multiple components.

   Satisfies: Use-Case MFUC2, MFUC3 Implemented by: Manifest Field:
   Dependencies

3.5.4.  Usability Requirement MFUR4

   It MUST be possible to sign a manifest multiple times so that
   signatures from multiple parties with different permissions can be
   required in order to authorise installation of a manifest.

   Satisfies: Use-Case MFUC4 Implemented by: COSE Signature (or similar)

3.5.5.  Usability Requirement MFUR5

   The manifest format MUST accommodate any payload format that an
   operator or OEM wishes to use.  Some examples of payload format would
   be:




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   -  Binary

   -  Elf

   -  Differential

   -  Compressed

   -  Packed configuration

   Satisfies: Use-Case MFUC5 Implemented by: Manifest Field: Payload
   Format

4.  Manifest Fields

   Each manifest field is anchored in a security requirement or a
   usability requirement.  The manifest fields are described below and
   justified by their requirements.

4.1.  Manifest Version Field: version identifier of the manifest
      structure

   An identifier that describes which iteration of the manifest format
   is contained in the structure.

4.2.  Manifest Field: Monotonic Sequence Number

   A monotonically increasing sequence number.  For convenience, the
   monotonic sequence number MAY be a UTC timestamp.  This allows global
   synchronisation of sequence numbers without any additional
   management.

   Implements: Security Requirement MFSR1.

4.3.  Manifest Field: Vendor ID Condition

   Vendor IDs MUST be unique.  This is to prevent similarly, or
   identically named entities from different geographic regions from
   colliding in their customer's infrastructure.  Recommended practice
   is to use version 5 UUIDs with the vendor's domain name and the UUID
   DNS prefix [RFC4122].  Other options include version 1 and type 4
   UUIDs.

   Implements: Security Requirement MFSR2, MFSR4.







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4.4.  Manifest Field: Class ID Condition

   Class Identifiers MUST be unique within a Vendor ID.  This is to
   prevent similarly, or identically named devices colliding in their
   customer's infrastructure.  Recommended practice is to use type 5
   UUIDs with the model, hardware revision, etc. and use the Vendor ID
   as the UUID prefix.  Other options include type 1 and type 4 UUIDs.
   A device "Class" is defined as any device that can run the same
   firmware without modification.  Classes MAY be implemented in a more
   granular way.  Classes MUST NOT be implemented in a less granular
   way.  Class ID can encompass model name, hardware revision, software
   revision.  Devices MAY have multiple Class IDs.

   Implements: Security Requirement MFSR2, MFSR4.

4.5.  Manifest Field: Precursor Image Digest Condition

   When a precursor image is required by the payload format, a precursor
   image digest condition MUST be present in the conditions list.

   Implements: Security Requirement MFSR4

4.6.  Manifest Field: Best-Before timestamp condition

   This field tells a device the last application time.  This is only
   usable in conjunction with a secure clock.

   Implements: Security Requirement MFSR3

4.7.  Manifest Field: Payload Format

   The format of the payload must be indicated to devices in an
   unambiguous way.  This field provides a mechanism to describe the
   payload format, within the signed metadata.

   Implements: Security Requirement MFSR4, Usability Requirement MFUR5

4.8.  Manifest Field: Storage Location

   This field tells the device which component is being updated.  The
   device can use this to establish which permissions are necessary and
   the physical location to use.

   Implements: Security Requirement MFSR4







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4.9.  Manifest Field: URIs

   This field is a list of weighted URIs, which are used to select where
   to obtain a payload.

   Implements: Security Requirement MFSR4

4.10.  Manifest Field: Digests

   This field is a map of digests, each for a separate stage of
   installation.  This allows the target device to ensure authenticity
   of the payload at every step of installation.

   Implements: Security Requirement MFSR4

4.11.  Manifest Field: Size

   The size of the payload in bytes.

   Implements: Security Requirement MFSR4

4.12.  Manifest Field: Signature

   This is not strictly a manifest field.  Instead, the manifest is
   wrapped by a standardised authentication container, such as a COSE or
   CMS signature object.  The authentication container MUST support
   multiple actors and multiple authentications.

   Implements: Security Requirement MFSR5, MFSR6, MFUR4

4.13.  Manifest Field: Directives

   A list of instructions that the device should execute, in order, when
   installing the payload.

   Implements: Usability Requirement MFUR1

4.14.  Manifest Field: Aliases

   A list of URI/Digest pairs.  A device is expected to build an alias
   table while paring a manifest tree and treat any aliases as top-
   ranked URIs for the corresponding digest.

   Implements: Usability Requirement MFUR2







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4.15.  Manifest Field: Dependencies

   A list of URI/Digest pairs that refer to other manifests by digest.
   The manifests that are linked in this way must be acquired and
   installed simultaneously in order to form a complete update.

   Implements: Usability Requirement MFUR3

4.16.  Manifest Field: Content Key Distribution Method

   Efficiently encrypting firmware images requires the use of symmetric
   key cryptography.  Since there are several methods to protect or
   distribute the symmetric content encryption keys, the manifest
   contains a field for the Content Key Distribution Method.  One
   example for such a Content Key Distribution Method is the usage of
   Key Tables, pointing to content encryption keys, which themselves are
   encrypted using the public keys of devices.

   Implements: Security Requirement MFSR7.

5.  Security Considerations

   Security considerations for this document are covered in Section 3.

6.  IANA Considerations

   This document does not require any actions by IANA.

7.  Acknowledgements

   We would like to thank our working group chairs, Dave Thaler, Russ
   Housley and David Waltermire, for their review comments and their
   support.

8.  References

8.1.  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>.

8.2.  Informative References







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   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005, <https://www.rfc-
              editor.org/info/rfc4122>.

   [STRIDE]   Microsoft, "The STRIDE Threat Model", May 2018,
              <https://msdn.microsoft.com/en-us/library/
              ee823878(v=cs.20).aspx>.

8.3.  URIs

   [1] mailto:suit@ietf.org







































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Appendix A.  Mailing List Information

   The discussion list for this document is located at the e-mail
   address suit@ietf.org [1].  Information on the group and information
   on how to subscribe to the list is at
   https://www1.ietf.org/mailman/listinfo/suit

   Archives of the list can be found at: https://www.ietf.org/mail-
   archive/web/suit/current/index.html

Authors' Addresses

   Brendan Moran
   Arm Limited

   EMail: Brendan.Moran@arm.com


   Hannes Tschofenig
   Arm Limited

   EMail: hannes.tschofenig@gmx.net


   Henk Birkholz
   Fraunhofer SIT

   EMail: henk.birkholz@sit.fraunhofer.de


   Jaime Jimenez
   Ericsson

   EMail: jaime.jimenez@ericsson.com

















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