draft-ietf-suit-information-model-01.txt   draft-ietf-suit-information-model-02.txt 
SUIT B. Moran SUIT B. Moran
Internet-Draft H. Tschofenig Internet-Draft H. Tschofenig
Intended status: Standards Track Arm Limited Intended status: Standards Track Arm Limited
Expires: January 3, 2019 H. Birkholz Expires: July 22, 2019 H. Birkholz
Fraunhofer SIT Fraunhofer SIT
July 02, 2018 January 18, 2019
Firmware Updates for Internet of Things Devices - An Information Model Firmware Updates for Internet of Things Devices - An Information Model
for Manifests for Manifests
draft-ietf-suit-information-model-01 draft-ietf-suit-information-model-02
Abstract Abstract
Vulnerabilities with Internet of Things (IoT) devices have raised the Vulnerabilities with Internet of Things (IoT) devices have raised the
need for a solid and secure firmware update mechanism that is also need for a solid and secure firmware update mechanism that is also
suitable for constrained devices. Incorporating such update suitable for constrained devices. Incorporating such update
mechanism to fix vulnerabilities, to update configuration settings as mechanism to fix vulnerabilities, to update configuration settings as
well as adding new functionality is recommended by security experts. well as adding new functionality is recommended by security experts.
One component of such a firmware update is the meta-data, or One component of such a firmware update is the meta-data, or
skipping to change at page 1, line 35 skipping to change at page 1, line 35
present in the manifest. present in the manifest.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2019. This Internet-Draft will expire on July 22, 2019.
Copyright Notice Copyright Notice
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document authors. All rights reserved. document authors. All rights reserved.
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modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 5 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 5
3. Motivation for Manifest Fields . . . . . . . . . . . . . . . 5 3. Manifest Information Elements . . . . . . . . . . . . . . . . 5
3.1. Threat Model . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Manifest Element: version identifier of the manifest
3.2. Threat Descriptions . . . . . . . . . . . . . . . . . . . 6 structure . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. Threat MFT1: Old Firmware . . . . . . . . . . . . . . 6 3.2. Manifest Element: Monotonic Sequence Number . . . . . . . 6
3.2.2. Threat MFT2: Mismatched Firmware . . . . . . . . . . 6 3.3. Manifest Element: Vendor ID Condition . . . . . . . . . . 6
3.2.3. Threat MFT3: Offline device + Old Firmware . . . . . 7 3.3.1. Example: Domain Name-based UUIDs . . . . . . . . . . 6
3.2.4. Threat MFT4: The target device misinterprets the type 3.4. Manifest Element: Class ID Condition . . . . . . . . . . 6
of payload . . . . . . . . . . . . . . . . . . . . . 7 3.4.1. Example 1: Different Classes . . . . . . . . . . . . 7
3.2.5. Threat MFT5: The target device installs the payload 3.4.2. Example 2: Upgrading Class ID . . . . . . . . . . . . 7
to the wrong location . . . . . . . . . . . . . . . . 7 3.4.3. Example 3: Shared Functionality . . . . . . . . . . . 8
3.2.6. Threat MFT6: Redirection . . . . . . . . . . . . . . 8 3.5. Manifest Element: Precursor Image Digest Condition . . . 8
3.2.7. Threat MFT7: Payload Verification on Boot . . . . . . 8 3.6. Manifest Element: Required Image Version List . . . . . . 8
3.2.8. Threat MFT8: Unauthenticated Updates . . . . . . . . 8 3.7. Manifest Element: Best-Before timestamp condition . . . . 9
3.2.9. Threat MFT9: Unexpected Precursor images . . . . . . 8 3.8. Manifest Element: Payload Format . . . . . . . . . . . . 9
3.2.10. Threat MFT10: Unqualified Firmware . . . . . . . . . 9 3.9. Manifest Element: Processing Steps . . . . . . . . . . . 9
3.2.11. Threat MFT11: Reverse Engineering Of Firmware Image 3.10. Manifest Element: Storage Location . . . . . . . . . . . 9
for Vulnerability Analysis . . . . . . . . . . . . . 10 3.10.1. Example 1: Two Storage Locations . . . . . . . . . . 10
3.2.12. Threat MFT12: Overriding Critical Manifest Elements . 10 3.10.2. Example 2: File System . . . . . . . . . . . . . . . 10
3.3. Security Requirements . . . . . . . . . . . . . . . . . . 11 3.10.3. Example 3: Flash Memory . . . . . . . . . . . . . . 10
3.3.1. Security Requirement MFSR1: Monotonic Sequence 3.11. Manifest Element: Component Identifier . . . . . . . . . 10
Numbers . . . . . . . . . . . . . . . . . . . . . . . 11 3.12. Manifest Element: URIs . . . . . . . . . . . . . . . . . 10
3.3.2. Security Requirement MFSR2: Vendor, Device-type 3.13. Manifest Element: Payload Digest . . . . . . . . . . . . 11
Identifiers . . . . . . . . . . . . . . . . . . . . . 11 3.14. Manifest Element: Size . . . . . . . . . . . . . . . . . 11
3.3.3. Security Requirement MFSR3: Best-Before Timestamps . 11 3.15. Manifest Element: Signature . . . . . . . . . . . . . . . 11
3.3.4. Security Requirement MFSR5: Cryptographic 3.16. Manifest Element: Directives . . . . . . . . . . . . . . 11
Authenticity . . . . . . . . . . . . . . . . . . . . 12 3.17. Manifest Element: Aliases . . . . . . . . . . . . . . . . 12
3.3.5. Security Requirement MFSR4a: Authenticated Payload 3.18. Manifest Element: Dependencies . . . . . . . . . . . . . 12
Type . . . . . . . . . . . . . . . . . . . . . . . . 12 3.19. Manifest Element: Content Key Distribution Method . . . . 12
3.3.6. Security Requirement MFSR4b: Authenticated Storage 3.20. Manifest Element: XIP Address . . . . . . . . . . . . . . 12
Location . . . . . . . . . . . . . . . . . . . . . . 12 3.21. Manifest Element: Load-time metadata . . . . . . . . . . 13
3.3.7. Security Requirement MFSR4c: Authenticated Remote 4. Motivation for Manifest Fields . . . . . . . . . . . . . . . 13
Resource Location . . . . . . . . . . . . . . . . . . 12 4.1. Threat Model . . . . . . . . . . . . . . . . . . . . . . 13
3.3.8. Security Requirement MFSR4d: Secure Boot . . . . . . 13 4.2. Threat Descriptions . . . . . . . . . . . . . . . . . . . 13
3.3.9. Security Requirement MFSR4e: Authenticated precursor 4.2.1. Threat MFT1: Old Firmware . . . . . . . . . . . . . . 13
images . . . . . . . . . . . . . . . . . . . . . . . 13 4.2.2. Threat MFT2: Mismatched Firmware . . . . . . . . . . 14
3.3.10. Security Requirement MFSR4f: Authenticated Vendor and 4.2.3. Threat MFT3: Offline device + Old Firmware . . . . . 14
Class IDs . . . . . . . . . . . . . . . . . . . . . . 13 4.2.4. Threat MFT4: The target device misinterprets the type
3.3.11. Security Requirement MFSR4f: Authenticated Vendor and of payload . . . . . . . . . . . . . . . . . . . . . 15
Class IDs . . . . . . . . . . . . . . . . . . . . . . 13 4.2.5. Threat MFT5: The target device installs the payload
3.3.12. Security Requirement MFSR6: Rights Require to the wrong location . . . . . . . . . . . . . . . . 15
Authenticity . . . . . . . . . . . . . . . . . . . . 13 4.2.6. Threat MFT6: Redirection . . . . . . . . . . . . . . 15
3.3.13. Security Requirement MFSR7: Firmware encryption . . . 14 4.2.7. Threat MFT7: Payload Verification on Boot . . . . . . 16
3.3.14. Security Requirement MFSR8: Access Control Lists . . 14 4.2.8. Threat MFT8: Unauthenticated Updates . . . . . . . . 16
3.4. User Stories . . . . . . . . . . . . . . . . . . . . . . 14 4.2.9. Threat MFT9: Unexpected Precursor images . . . . . . 16
3.4.1. Use Case MFUS1: Installation Instructions . . . . . . 15 4.2.10. Threat MFT10: Unqualified Firmware . . . . . . . . . 17
3.4.2. Use Case MFUS2: Override Non-Critical Manifest 4.2.11. Threat MFT11: Reverse Engineering Of Firmware Image
Elements . . . . . . . . . . . . . . . . . . . . . . 15 for Vulnerability Analysis . . . . . . . . . . . . . 18
3.4.3. Use Case MFUS3: Modular Update . . . . . . . . . . . 16 4.2.12. Threat MFT12: Overriding Critical Manifest Elements . 18
3.4.4. Use Case MFUS4: Multiple Authorisations . . . . . . . 16 4.2.13. Threat MFT13: Manifest Element Exposure . . . . . . . 18
3.4.5. Use Case MFUS5: Multiple Payload Formats . . . . . . 16 4.3. Security Requirements . . . . . . . . . . . . . . . . . . 19
3.4.6. Use Case MFUS6: Prevent Confidential Information 4.3.1. Security Requirement MFSR1: Monotonic Sequence
Disclosures . . . . . . . . . . . . . . . . . . . . . 16 Numbers . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.7. Use Case MFUS7: Prevent Devices from Unpacking 4.3.2. Security Requirement MFSR2: Vendor, Device-type
Unknown Formats . . . . . . . . . . . . . . . . . . . 16 Identifiers . . . . . . . . . . . . . . . . . . . . . 19
3.4.8. Use Case MFUS8: Specify Version Numbers of Target 4.3.3. Security Requirement MFSR3: Best-Before Timestamps . 19
Firmware . . . . . . . . . . . . . . . . . . . . . . 17 4.3.4. Security Requirement MFSR5: Cryptographic
3.4.9. Use Case MFUS9: Enable devices to choose between Authenticity . . . . . . . . . . . . . . . . . . . . 20
images . . . . . . . . . . . . . . . . . . . . . . . 17 4.3.5. Security Requirement MFSR4a: Authenticated Payload
3.5. Usability Requirements . . . . . . . . . . . . . . . . . 17 Type . . . . . . . . . . . . . . . . . . . . . . . . 20
3.5.1. Usability Requirement MFUR1 . . . . . . . . . . . . . 17 4.3.6. Security Requirement MFSR4b: Authenticated Storage
3.5.2. Usability Requirement MFUR2 . . . . . . . . . . . . . 17 Location . . . . . . . . . . . . . . . . . . . . . . 20
3.5.3. Usability Requirement MFUR3 . . . . . . . . . . . . . 18 4.3.7. Security Requirement MFSR4c: Authenticated Remote
3.5.4. Usability Requirement MFUR4 . . . . . . . . . . . . . 19 Resource Location . . . . . . . . . . . . . . . . . . 20
3.5.5. Usability Requirement MFUR5 . . . . . . . . . . . . . 19 4.3.8. Security Requirement MFSR4d: Secure Boot . . . . . . 21
3.5.6. Usability Requirement MFUR6 . . . . . . . . . . . . . 19 4.3.9. Security Requirement MFSR4e: Authenticated precursor
3.5.7. Usability Requirement MFUR7 . . . . . . . . . . . . . 19 images . . . . . . . . . . . . . . . . . . . . . . . 21
3.5.8. Usability Requirement MFUR8 . . . . . . . . . . . . . 20 4.3.10. Security Requirement MFSR4f: Authenticated Vendor and
4. Manifest Information Elements . . . . . . . . . . . . . . . . 20 Class IDs . . . . . . . . . . . . . . . . . . . . . . 21
4.1. Manifest Element: version identifier of the manifest 4.3.11. Security Requirement MFSR4f: Authenticated Vendor and
structure . . . . . . . . . . . . . . . . . . . . . . . . 20 Class IDs . . . . . . . . . . . . . . . . . . . . . . 21
4.2. Manifest Element: Monotonic Sequence Number . . . . . . . 20 4.3.12. Security Requirement MFSR6: Rights Require
4.3. Manifest Element: Vendor ID Condition . . . . . . . . . . 20 Authenticity . . . . . . . . . . . . . . . . . . . . 21
4.3.1. Example: Domain Name-based UUIDs . . . . . . . . . . 21 4.3.13. Security Requirement MFSR7: Firmware encryption . . . 22
4.4. Manifest Element: Class ID Condition . . . . . . . . . . 21 4.3.14. Security Requirement MFSR8: Access Control Lists . . 22
4.4.1. Example 1: Different Classes . . . . . . . . . . . . 21 4.3.15. Security Requirement MFSR9: Encrypted Manifests . . . 22
4.4.2. Example 2: Upgrading Class ID . . . . . . . . . . . . 22 4.4. User Stories . . . . . . . . . . . . . . . . . . . . . . 23
4.4.3. Example 3: Shared Functionality . . . . . . . . . . . 22 4.4.1. Use Case MFUS1: Installation Instructions . . . . . . 23
4.5. Manifest Element: Precursor Image Digest Condition . . . 23 4.4.2. Use Case MFUS2: Override Non-Critical Manifest
4.6. Manifest Element: Required Image Version List . . . . . . 23 Elements . . . . . . . . . . . . . . . . . . . . . . 23
4.7. Manifest Element: Best-Before timestamp condition . . . . 23 4.4.3. Use Case MFUS3: Modular Update . . . . . . . . . . . 24
4.8. Manifest Element: Payload Format . . . . . . . . . . . . 23 4.4.4. Use Case MFUS4: Multiple Authorisations . . . . . . . 24
4.9. Manifest Element: Processing Steps . . . . . . . . . . . 24 4.4.5. Use Case MFUS5: Multiple Payload Formats . . . . . . 24
4.10. Manifest Element: Storage Location . . . . . . . . . . . 24 4.4.6. Use Case MFUS6: Prevent Confidential Information
4.10.1. Example 1: Two Storage Locations . . . . . . . . . . 24 Disclosures . . . . . . . . . . . . . . . . . . . . . 24
4.10.2. Example 2: File System . . . . . . . . . . . . . . . 24 4.4.7. Use Case MFUS7: Prevent Devices from Unpacking
4.10.3. Example 3: Flash Memory . . . . . . . . . . . . . . 24 Unknown Formats . . . . . . . . . . . . . . . . . . . 24
4.11. Manifest Element: Component Identifier . . . . . . . . . 25 4.4.8. Use Case MFUS8: Specify Version Numbers of Target
4.12. Manifest Element: URIs . . . . . . . . . . . . . . . . . 25 Firmware . . . . . . . . . . . . . . . . . . . . . . 25
4.13. Manifest Element: Payload Digest . . . . . . . . . . . . 25 4.4.9. Use Case MFUS9: Enable Devices to Choose Between
4.14. Manifest Element: Size . . . . . . . . . . . . . . . . . 25 Images . . . . . . . . . . . . . . . . . . . . . . . 25
4.15. Manifest Element: Signature . . . . . . . . . . . . . . . 26 4.4.10. Use Case MFUS10: Secure Boot Using Manifests . . . . 25
4.16. Manifest Element: Directives . . . . . . . . . . . . . . 26 4.4.11. Use Case MFUS11: Decompress on Load . . . . . . . . . 25
4.17. Manifest Element: Aliases . . . . . . . . . . . . . . . . 26 4.4.12. Use Case MFUS12: Payload in Manifest . . . . . . . . 26
4.18. Manifest Element: Dependencies . . . . . . . . . . . . . 26 4.4.13. Use Case MFUS13: Simple Parsing . . . . . . . . . . . 26
4.19. Manifest Element: Content Key Distribution Method . . . . 27 4.5. Usability Requirements . . . . . . . . . . . . . . . . . 26
4.20. Manifest Element: XIP Address . . . . . . . . . . . . . . 27 4.5.1. Usability Requirement MFUR1 . . . . . . . . . . . . . 26
5. Security Considerations . . . . . . . . . . . . . . . . . . . 27 4.5.2. Usability Requirement MFUR2 . . . . . . . . . . . . . 26
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 4.5.3. Usability Requirement MFUR3 . . . . . . . . . . . . . 27
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27 4.5.4. Usability Requirement MFUR4 . . . . . . . . . . . . . 28
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 4.5.5. Usability Requirement MFUR5 . . . . . . . . . . . . . 28
8.1. Normative References . . . . . . . . . . . . . . . . . . 28 4.5.6. Usability Requirement MFUR6 . . . . . . . . . . . . . 28
8.2. Informative References . . . . . . . . . . . . . . . . . 28 4.5.7. Usability Requirement MFUR7 . . . . . . . . . . . . . 28
Appendix A. Mailing List Information . . . . . . . . . . . . . . 29 4.5.8. Usability Requirement MFUR8 . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 4.5.9. Usability Requirement MFUR9: Bootable Manifest . . . 29
4.5.10. Usability Requirement MFUR10: Load-Time Information . 29
4.5.11. Usability Requirement MFUR11: Payload in Manifest
Superstructure . . . . . . . . . . . . . . . . . . . 29
4.5.12. Usability Requirement MFUR12: Simple Parsing . . . . 30
5. Security Considerations . . . . . . . . . . . . . . . . . . . 30
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.1. Normative References . . . . . . . . . . . . . . . . . . 30
8.2. Informative References . . . . . . . . . . . . . . . . . 31
Appendix A. Mailing List Information . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction 1. Introduction
The information model describes all the information elements required The information model describes all the information elements required
to secure firmware updates of IoT devices from the threats described to secure firmware updates of IoT devices from the threats described
in Section 3.1 and enable the user stories captured in Section 3.4. in Section 4.1 and enable the user stories captured in Section 4.4.
These threats and user stories are not intended to be an exhaustive These threats and user stories are not intended to be an exhaustive
list of the threats against IoT devices, nor of the possible use list of the threats against IoT devices, nor of the possible use
cases of firmware update; instead they are intended to describe the cases of firmware update; instead they are intended to describe the
threats against firmware update in isolation and provide sufficient threats against firmware update in isolation and provide sufficient
motivation to provide information elements that cover a wide range of motivation to provide information elements that cover a wide range of
use cases. The information model does not define the encoding, use cases. The information model does not define the encoding,
ordering, or structure of information elements, only their semantics. ordering, or structure of information elements, only their semantics.
Because the information model covers a wide range of user stories and Because the information model covers a wide range of user stories and
a wide range of threats, not all information elements apply to all a wide range of threats, not all information elements apply to all
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2. Conventions and Terminology 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC "OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119]. 2119 [RFC2119].
This document uses terms defined in [I-D.ietf-suit-architecture]. This document uses terms defined in [I-D.ietf-suit-architecture].
The term 'Operator' refers to both, Device and Network Operator. The term 'Operator' refers to both, Device and Network Operator.
3. Motivation for Manifest Fields 3. Manifest Information Elements
Each manifest element is anchored in a security requirement or a
usability requirement. The manifest elements are described below and
justified by their requirements.
3.1. Manifest Element: version identifier of the manifest structure
An identifier that describes which iteration of the manifest format
is contained in the structure.
This element is MANDATORY and must be present in order to allow
devices to identify the version of the manifest data model that is in
use.
3.2. Manifest Element: 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.
This element is MANDATORY and is necessary to prevent malicious
actors from reverting a firmware update against the wishes of the
relevant authority.
Implements: Security Requirement MFSR1.
3.3. Manifest Element: 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 type 5 UUIDs with the vendor's domain name and the UUID DNS
prefix. Other options include type 1 and type 4 UUIDs.
This ID is RECOMMENDED and helps to distinguish between identically
named products from different vendors.
Implements: Security Requirement MFSR2, MFSR4f.
3.3.1. Example: Domain Name-based UUIDs
Vendor A creates a UUID based on their domain name:
vendorId = UUID5(DNS, "vendor-a.com")
Because the DNS infrastructure prevents multiple registrations of the
same domain name, this UUID is guaranteed to be unique. Because the
domain name is known, this UUID is reproducible. Type 1 and type 4
UUIDs produce similar guarantees of uniqueness, but not
reproducibility.
3.4. Manifest Element: Class ID Condition
A device "Class" is defined as any device that can accept the same
firmware update without modification. 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. 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.
Note Well: Class ID is not a human-readable element. It is intended
for match/mismatch use only.
This ID is RECOMMENDED and allows devices to determine applicability
of a firmware in an unambiguous way.
Implements: Security Requirement MFSR2, MFSR4f.
3.4.1. Example 1: Different Classes
Vendor A creates product Z and product Y. The firmware images of
products Z and Y are not interchangeable. Vendor A creates UUIDs as
follows:
- vendorId = UUID5(DNS, "vendor-a.com")
- ZclassId = UUID5(vendorId, "Product Z")
- YclassId = UUID5(vendorId, "Product Y")
This ensures that Vendor A's Product Z cannot install firmware for
Product Y and Product Y cannot install firmware for Product Z.
3.4.2. Example 2: Upgrading Class ID
Vendor A creates product X. Later, Vendor A adds a new feature to
product X, creating product X v2. Product X requires a firmware
update to work with firmware intended for product X v2.
Vendor A creates UUIDs as follows:
- vendorId = UUID5(DNS, "vendor-a.com")
- XclassId = UUID5(vendorId, "Product X")
- Xv2classId = UUID5(vendorId, "Product X v2")
When product X receives the firmware update necessary to be
compatible with product X v2, part of the firmware update changes the
class ID to Xv2classId.
3.4.3. Example 3: Shared Functionality
Vendor A produces two products, product X and product Y. These
components share a common core (such as an operating system), but
have different applications. The common core and the applications
can be updated independently. To enable X and Y to receive the same
common core update, they require the same class ID. To ensure that
only product X receives application X and only product Y receives
application Y, product X and product Y must have different class IDs.
The vendor creates Class IDs as follows:
- vendorId = UUID5(DNS, "vendor-a.com")
- XclassId = UUID5(vendorId, "Product X")
- YclassId = UUID5(vendorId, "Product Y")
- CommonClassId = UUID5(vendorId, "common core")
Product X matches against both XclassId and CommonClassId. Product Y
matches against both YclassId and CommonClassId.
3.5. Manifest Element: 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. The
precursor image may be installed or stored as a candidate.
This element is MANDATORY for differential updates. Otherwise, it is
not needed.
Implements: Security Requirement MFSR4e
3.6. Manifest Element: Required Image Version List
When a payload applies to multiple versions of a firmware, the
required image version list specifies which versions must be present
for the update to be applied. This allows the update author to
target specific versions of firmware for an update, while excluding
those to which it should not be applied.
Where an update can only be applied over specific predecessor
versions, that version MUST be specified by the Required Image
Version List.
This element is OPTIONAL.
Implements: MFUR7
3.7. Manifest Element: Best-Before timestamp condition
This element tells a device the last application time. This is only
usable in conjunction with a secure clock.
This element is OPTIONAL and MAY enable use cases where a secure
clock is provided and firmware is intended to expire regularly.
Implements: Security Requirement MFSR3
3.8. Manifest Element: Payload Format
The format of the payload must be indicated to devices is in an
unambiguous way. This element provides a mechanism to describe the
payload format, within the signed metadata.
This element is MANDATORY and MUST be present to enable devices to
decode payloads correctly.
Implements: Security Requirement MFSR4a, Usability Requirement MFUR5
3.9. Manifest Element: Processing Steps
A list of all payload processors necessary to process a nested format
and any parameters needed by those payload processors. Each
Processing Step SHOULD indicate the expected digest of the payload
after the processing is complete. Processing steps are distinct from
Directives in that Directives apply to the manifest as a whole,
whereas Processing Steps apply to an individual payload and provide
instructions on how to unpack it.
Implements: Usability Requirement MFUR6
3.10. Manifest Element: Storage Location
This element 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.
This element is MANDATORY and MUST be present to enable devices to
store payloads to the correct location.
Implements: Security Requirement MFSR4b
3.10.1. Example 1: Two Storage Locations
A device supports two components: an OS and an application. These
components can be updated independently, expressing dependencies to
ensure compatibility between the components. The firmware authority
chooses two storage identifiers:
- OS
- APP
3.10.2. Example 2: File System
A device supports a full filesystem. The firmware authority chooses
to make the storage identifier the path at which to install the
payload. The payload may be a tarball, in which case, it unpacks the
tarball into the specified path.
3.10.3. Example 3: Flash Memory
A device supports flash memory. The firmware authority chooses to
make the storage identifier the offset where the image should be
written.
3.11. Manifest Element: Component Identifier
In a heterogeneous storage architecture, a storage identifier is
insufficient to identify where and how to store a payload. To
resolve this, a component identifier indicates which part of the
storage architecture is targeted by the payload. In a homogeneous
storage architecture, this element is unnecessary.
This element is OPTIONAL and only necessary in heterogeneous storage
architecture devices.
Implements: MFUR3
3.12. Manifest Element: URIs
This element is a list of weighted URIs that the device uses to
select where to obtain a payload.
This element is OPTIONAL and only needed when the target device does
not intrinsically know where to find the payload.
Note: Devices will typically require URIs.
Implements: Security Requirement MFSR4c
3.13. Manifest Element: Payload Digest
This element contains the digest of the payload. This allows the
target device to ensure authenticity of the payload. It MUST be
possible to specify more than one payload digest, indexed by Manifest
Element: XIP Address.
This element is MANDATORY and fundamentally necessary to ensure the
authenticity and integrity of the payload.
Implements: Security Requirement MFSR4d, Usability Requirement MFUR8
3.14. Manifest Element: Size
The size of the payload in bytes.
This element is MANDATORY and informs the target device how big of a
payload to expect. Without it, devices are exposed to some classes
of denial of service attack.
Implements: Security Requirement MFSR4d
3.15. Manifest Element: Signature
This is not strictly a manifest element. 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.
This element is MANDATORY and represents the foundation of all
security properties of the manifest.
Implements: Security Requirement MFSR5, MFSR6, MFUR4
3.16. Manifest Element: Directives
A list of instructions that the device should execute, in order, when
processing the manifest. This information is distinct from the
information necessary to process a payload (Processing Steps) and
applies to the whole manifest including all payloads that it
references. Directives include information such as update timing
(For example, install only on Sunday, at 0200), procedural
considerations (for example, shut down the equipment under control
before executing the update), pre and post-installation steps (for
example, run a script).
This element is OPTIONAL and enables some use cases.
Implements: Usability Requirement MFUR1
3.17. Manifest Element: Aliases
A list of Digest/URI pairs. A device should build an alias table
while paring a manifest tree and treat any aliases as top-ranked URIs
for the corresponding digest.
This element is OPTIONAL and enables some use cases.
Implements: Usability Requirement MFUR2
3.18. Manifest Element: Dependencies
A list of Digest/URI 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.
This element is MANDATORY to use in deployments that include both
multiple authorities and multiple payloads.
Implements: Usability Requirement MFUR3
3.19. Manifest Element: Content Key Distribution Method
Encrypting firmware images requires symmetric content encryption
keys. Since there are several methods to protect or distribute the
symmetric content encryption keys, the manifest contains a element
for the Content Key Distribution Method. One examples 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. This MAY be included in a decryption step
contained in Processing Steps.
This element is MANDATORY to use for encrypted payloads,
Implements: Security Requirement MFSR7.
3.20. Manifest Element: XIP Address
In order to support XIP systems with multiple possible base
addresses, it is necessary to specify which address the payload is
linked for.
For example a microcontroller may have a simple bootloader that
chooses one of two images to boot. That microcontroller then needs
to choose one of two firmware images to install, based on which of
its two images is older.
Implements: MFUR8
3.21. Manifest Element: Load-time metadata
## Manifest Element: Boot-time metadata ## Manifest Element: Payload
4. Motivation for Manifest Fields
The following sub-sections describe the threat model, user stories, The following sub-sections describe the threat model, user stories,
security requirements, and usability requirements. security requirements, and usability requirements.
3.1. Threat Model 4.1. Threat Model
The following sub-sections aim to provide information about the The following sub-sections aim to provide information about the
threats that were considered, the security requirements that are threats that were considered, the security requirements that are
derived from those threats and the fields that permit implementation derived from those threats and the fields that permit implementation
of the security requirements. This model uses the S.T.R.I.D.E. of the security requirements. This model uses the S.T.R.I.D.E.
[STRIDE] approach. Each threat is classified according to: [STRIDE] approach. Each threat is classified according to:
- Spoofing Identity - Spoofing Identity
- Tampering with data - Tampering with data
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- Tampering with data - Tampering with data
- Repudiation - Repudiation
- Information disclosure - Information disclosure
- Denial of service - Denial of service
- Elevation of privilege - Elevation of privilege
This threat model only covers elements related to the transport of This threat model only covers elements related to the transport of
firmware updates. It explicitly does not cover threats outside of firmware updates. It explicitly does not cover threats outside of
the transport of firmware updates. For example, threats to an IoT the transport of firmware updates. For example, threats to an IoT
device due to physical access are out of scope. device due to physical access are out of scope.
3.2. Threat Descriptions 4.2. Threat Descriptions
3.2.1. Threat MFT1: Old Firmware 4.2.1. Threat MFT1: Old Firmware
Classification: Elevation of Privilege Classification: Elevation of Privilege
An attacker sends an old, but valid manifest with an old, but valid 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 firmware image to a device. If there is a known vulnerability in the
provided firmware image, this may allow an attacker to exploit the provided firmware image, this may allow an attacker to exploit the
vulnerability and gain control of the device. vulnerability and gain control of the device.
Threat Escalation: If the attacker is able to exploit the known Threat Escalation: If the attacker is able to exploit the known
vulnerability, then this threat can be escalated to ALL TYPES. vulnerability, then this threat can be escalated to ALL TYPES.
Mitigated by: MFSR1 Mitigated by: MFSR1
3.2.2. Threat MFT2: Mismatched Firmware 4.2.2. Threat MFT2: Mismatched Firmware
Classification: Denial of Service Classification: Denial of Service
An attacker sends a valid firmware image, for the wrong type of An attacker sends a valid firmware image, for the wrong type of
device, signed by an actor with firmware installation permission on device, signed by an actor with firmware installation permission on
both types of device. The firmware is verified by the device both types of device. The firmware is verified by the device
positively because it is signed by an actor with the appropriate positively because it is signed by an actor with the appropriate
permission. This could have wide-ranging consequences. For devices permission. This could have wide-ranging consequences. For devices
that are similar, it could cause minor breakage, or expose security that are similar, it could cause minor breakage, or expose security
vulnerabilities. For devices that are very different, it is likely vulnerabilities. For devices that are very different, it is likely
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name in different geographic regions, and they both make products name in different geographic regions, and they both make products
with the same names, or product name matching is not used. This with the same names, or product name matching is not used. This
causes firmware from Vendor A to match devices from Vendor B. causes firmware from Vendor A to match devices from Vendor B.
If the vendors are the firmware authorities, then devices from Vendor If the vendors are the firmware authorities, then devices from Vendor
A will reject images signed by Vendor B since they use different A will reject images signed by Vendor B since they use different
credentials. However, if both devices trust the same firmware credentials. However, if both devices trust the same firmware
authority, then, devices from Vendor A could install firmware authority, then, devices from Vendor A could install firmware
intended for devices from Vendor B. intended for devices from Vendor B.
3.2.3. Threat MFT3: Offline device + Old Firmware 4.2.3. Threat MFT3: Offline device + Old Firmware
Classification: Elevation of Privilege Classification: Elevation of Privilege
An attacker targets a device that has been offline for a long time 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 and runs an old firmware version. The attacker sends an old, but
valid manifest to a device with an old, but valid firmware image. valid manifest to a device with an old, but valid firmware image.
The attacker-provided firmware is newer than the installed one but The attacker-provided firmware is newer than the installed one but
older than the most recently available firmware. If there is a known older than the most recently available firmware. If there is a known
vulnerability in the provided firmware image then this may allow an vulnerability in the provided firmware image then this may allow an
attacker to gain control of a device. Because the device has been 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 offline for a long time, it is unaware of any new updates. As such
it will treat the old manifest as the most current. it will treat the old manifest as the most current.
Threat Escalation: If the attacker is able to exploit the known Threat Escalation: If the attacker is able to exploit the known
vulnerability, then this threat can be escalated to ALL TYPES. vulnerability, then this threat can be escalated to ALL TYPES.
Mitigated by: MFSR3 Mitigated by: MFSR3
3.2.4. Threat MFT4: The target device misinterprets the type of payload 4.2.4. Threat MFT4: The target device misinterprets the type of payload
Classification: Denial of Service Classification: Denial of Service
If a device misinterprets the type of the firmware image, it may If a device misinterprets the type of the firmware image, it may
cause a device to install a firmware image incorrectly. An cause a device to install a firmware image incorrectly. An
incorrectly installed firmware image would likely cause the device to incorrectly installed firmware image would likely cause the device to
stop functioning. stop functioning.
Threat Escalation: An attacker that can cause a device to Threat Escalation: An attacker that can cause a device to
misinterpret the received firmware image may gain elevation of misinterpret the received firmware image may gain elevation of
privilege and potentially expand this to all types of threat. privilege and potentially expand this to all types of threat.
Mitigated by: MFSR4a Mitigated by: MFSR4a
3.2.5. Threat MFT5: The target device installs the payload to the wrong 4.2.5. Threat MFT5: The target device installs the payload to the wrong
location location
Classification: Denial of Service Classification: Denial of Service
If a device installs a firmware image to the wrong location on the 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 device, then it is likely to break. For example, a firmware image
installed as an application could cause a device and/or an installed as an application could cause a device and/or an
application to stop functioning. application to stop functioning.
Threat Escalation: An attacker that can cause a device to Threat Escalation: An attacker that can cause a device to
misinterpret the received code may gain elevation of privilege and misinterpret the received code may gain elevation of privilege and
potentially expand this to all types of threat. potentially expand this to all types of threat.
Mitigated by: MFSR4b Mitigated by: MFSR4b
3.2.6. Threat MFT6: Redirection 4.2.6. Threat MFT6: Redirection
Classification: Denial of Service Classification: Denial of Service
If a device does not know where to obtain the payload for an update, 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 it may be redirected to an attacker's server. This would allow an
attacker to provide broken payloads to devices. attacker to provide broken payloads to devices.
Mitigated by: MFSR4c Mitigated by: MFSR4c
3.2.7. Threat MFT7: Payload Verification on Boot 4.2.7. Threat MFT7: Payload Verification on Boot
Classification: Elevation of Privilege Classification: Elevation of Privilege
An attacker replaces a newly downloaded firmware after a device An attacker replaces a newly downloaded firmware after a device
finishes verifying a manifest. This could cause the device to finishes verifying a manifest. This could cause the device to
execute the attacker's code. This attack likely requires physical execute the attacker's code. This attack likely requires physical
access to the device. However, it is possible that this attack is access to the device. However, it is possible that this attack is
carried out in combination with another threat that allows remote carried out in combination with another threat that allows remote
execution. execution.
Threat Escalation: If the attacker is able to exploit a known Threat Escalation: If the attacker is able to exploit a known
vulnerability, or if the attacker can supply their own firmware, then vulnerability, or if the attacker can supply their own firmware, then
this threat can be escalated to ALL TYPES. this threat can be escalated to ALL TYPES.
Mitigated by: MFSR4d Mitigated by: MFSR4d
3.2.8. Threat MFT8: Unauthenticated Updates 4.2.8. Threat MFT8: Unauthenticated Updates
Classification: Elevation of Privilege Classification: Elevation of Privilege
If an attacker can install their firmware on a device, by If an attacker can install their firmware on a device, by
manipulating either payload or metadata, then they have complete manipulating either payload or metadata, then they have complete
control of the device. control of the device.
Threat Escalation: If the attacker is able to exploit a known Threat Escalation: If the attacker is able to exploit a known
vulnerability, or if the attacker can supply their own firmware, then vulnerability, or if the attacker can supply their own firmware, then
this threat can be escalated to ALL TYPES. this threat can be escalated to ALL TYPES.
Mitigated by: MFSR5 Mitigated by: MFSR5
3.2.9. Threat MFT9: Unexpected Precursor images 4.2.9. Threat MFT9: Unexpected Precursor images
Classification: Denial of Service Classification: Denial of Service
An attacker sends a valid, current manifest to a device that has an An attacker sends a valid, current manifest to a device that has an
unexpected precursor image. If a payload format requires a precursor unexpected precursor image. If a payload format requires a precursor
image (for example, delta updates) and that precursor image is not image (for example, delta updates) and that precursor image is not
available on the target device, it could cause the update to break. available on the target device, it could cause the update to break.
Threat Escalation: An attacker that can cause a device to install a Threat Escalation: An attacker that can cause a device to install a
payload against the wrong precursor image could gain elevation of payload against the wrong precursor image could gain elevation of
privilege and potentially expand this to all types of threat. privilege and potentially expand this to all types of threat.
Mitigated by: MFSR4e Mitigated by: MFSR4e
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unexpected precursor image. If a payload format requires a precursor unexpected precursor image. If a payload format requires a precursor
image (for example, delta updates) and that precursor image is not image (for example, delta updates) and that precursor image is not
available on the target device, it could cause the update to break. available on the target device, it could cause the update to break.
Threat Escalation: An attacker that can cause a device to install a Threat Escalation: An attacker that can cause a device to install a
payload against the wrong precursor image could gain elevation of payload against the wrong precursor image could gain elevation of
privilege and potentially expand this to all types of threat. privilege and potentially expand this to all types of threat.
Mitigated by: MFSR4e Mitigated by: MFSR4e
3.2.10. Threat MFT10: Unqualified Firmware 4.2.10. Threat MFT10: Unqualified Firmware
Classification: Denial of Service, Elevation of Privilege Classification: Denial of Service, Elevation of Privilege
This threat can appear in several ways, however it is ultimately This threat can appear in several ways, however it is ultimately
about interoperability of devices with other systems. The owner or about interoperability of devices with other systems. The owner or
operator of a network needs to approve firmware for their network in operator of a network needs to approve firmware for their network in
order to ensure interoperability with other devices on the network, order to ensure interoperability with other devices on the network,
or the network itself. If the firmware is not qualified, it may not or the network itself. If the firmware is not qualified, it may not
work. Therefore, if a device installs firmware without the approval work. Therefore, if a device installs firmware without the approval
of the network owner or operator, this is a threat to devices and the of the network owner or operator, this is a threat to devices and the
network. network.
Threat Escalation: If the firmware expects configuration that is Threat Escalation: If the firmware expects configuration that is
present in devices deployed in Network A, but not in devices deployed present in devices deployed in Network A, but not in devices deployed
in Network B, then the device may experience degraded security, in Network B, then the device may experience degraded security,
leading to threats of All Types. leading to threats of All Types.
Mitigated by: MFSR6, MFSR8 Mitigated by: MFSR6, MFSR8
3.2.10.1. Example 1: Multiple Network Operators with a Single Device 4.2.10.1. Example 1: Multiple Network Operators with a Single Device
Operator Operator
In this example let us assume that Device Operators expect the rights In this example let us assume that Device Operators expect the rights
to create firmware but that Network Operators expect the rights to to create firmware but that Network Operators expect the rights to
qualify firmware as fit-for-purpose on their networks. Additionally qualify firmware as fit-for-purpose on their networks. Additionally
assume that an Device Operators manage devices that can be deployed assume that an Device Operators manage devices that can be deployed
on any network, including Network A and B in our example. on any network, including Network A and B in our example.
An attacker may obtain a manifest for a device on Network A. Then, An attacker may obtain a manifest for a device on Network A. Then,
this attacker sends that manifest to a device on Network B. Because this attacker sends that manifest to a device on Network B. Because
Network A and Network B are under control of different Operators, and Network A and Network B are under control of different Operators, and
the firmware for a device on Network A has not been qualified to be the firmware for a device on Network A has not been qualified to be
deployed on Network B, the target device on Network B is now in deployed on Network B, the target device on Network B is now in
violation of the Operator B's policy and may get disabled by this violation of the Operator B's policy and may get disabled by this
unqualified, but signed firmware. unqualified, but signed firmware.
This is a denial of service because it can render devices inoperable. This is a denial of service because it can render devices inoperable.
This is an elevation of privilege because it allows the attacker to This is an elevation of privilege because it allows the attacker to
make installation decisions that should be made by the Operator. make installation decisions that should be made by the Operator.
3.2.10.2. Example 2: Single Network Operator with Multiple Device 4.2.10.2. Example 2: Single Network Operator with Multiple Device
Operators Operators
Multiple devices that interoperate are used on the same network and Multiple devices that interoperate are used on the same network and
communicate with each other. Some devices are manufactured and communicate with each other. Some devices are manufactured and
managed by Device Operator A and other devices by Device Operator B. managed by Device Operator A and other devices by Device Operator B.
A new firmware is released by Device Operator A that breaks A new firmware is released by Device Operator A that breaks
compatibility with devices from Device Operator B. An attacker sends compatibility with devices from Device Operator B. An attacker sends
the new firmware to the devices managed by Device Operator A without the new firmware to the devices managed by Device Operator A without
approval of the Network Operator. This breaks the behaviour of the approval of the Network Operator. This breaks the behaviour of the
larger system causing denial of service and possibly other threats. larger system causing denial of service and possibly other threats.
Where the network is a distributed SCADA system, this could cause Where the network is a distributed SCADA system, this could cause
misbehaviour of the process that is under control. misbehaviour of the process that is under control.
3.2.11. Threat MFT11: Reverse Engineering Of Firmware Image for 4.2.11. Threat MFT11: Reverse Engineering Of Firmware Image for
Vulnerability Analysis Vulnerability Analysis
Classification: All Types Classification: All Types
An attacker wants to mount an attack on an IoT device. To prepare An attacker wants to mount an attack on an IoT device. To prepare
the attack he or she retrieves the provided firmware image and the attack he or she retrieves the provided firmware image and
performs reverse engineering of the firmware image to analyze it for performs reverse engineering of the firmware image to analyze it for
specific vulnerabilities. specific vulnerabilities.
Mitigated by: MFSR7 Mitigated by: MFSR7
3.2.12. Threat MFT12: Overriding Critical Manifest Elements 4.2.12. Threat MFT12: Overriding Critical Manifest Elements
Classification: Elevation of Privilege Classification: Elevation of Privilege
An authorised actor, but not the firmware authority, uses an override An authorised actor, but not the firmware authority, uses an override
mechanism (MFUS2) to change an information element in a manifest mechanism (MFUS2) to change an information element in a manifest
signed by the firmware authority. For example, if the authorised signed by the firmware authority. For example, if the authorised
actor overrides the digest and URI of the payload, the actor can actor overrides the digest and URI of the payload, the actor can
replace the entire payload with a payload of their choice. replace the entire payload with a payload of their choice.
Threat Escalation: By overriding elements such as payload Threat Escalation: By overriding elements such as payload
installation instructions or firmware digest, this threat can be installation instructions or firmware digest, this threat can be
escalated to all types. escalated to all types.
Mitigated by: MFSR8 Mitigated by: MFSR8
3.3. Security Requirements 4.2.13. Threat MFT13: Manifest Element Exposure
Classification: Information Disclosure
A third party may be able to extract sensitive information from the
manifest.
Mitigated by: MFSR9
4.3. Security Requirements
The security requirements here are a set of policies that mitigate The security requirements here are a set of policies that mitigate
the threats described in Section 3.1. the threats described in Section 4.1.
3.3.1. Security Requirement MFSR1: Monotonic Sequence Numbers 4.3.1. Security Requirement MFSR1: Monotonic Sequence Numbers
Only an actor with firmware installation authority is permitted to Only an actor with firmware installation authority is permitted to
decide when device firmware can be installed. To enforce this rule, decide when device firmware can be installed. To enforce this rule,
manifests MUST contain monotonically increasing sequence numbers. manifests MUST contain monotonically increasing sequence numbers.
Manifests MAY use UTC epoch timestamps to coordinate monotonically Manifests MAY use UTC epoch timestamps to coordinate monotonically
increasing sequence numbers across many actors in many locations. If increasing sequence numbers across many actors in many locations. If
UTC epoch timestamps are used, they MUST NOT be treated as times, UTC epoch timestamps are used, they MUST NOT be treated as times,
they MUST be treated only as sequence numbers. Devices MUST reject they MUST be treated only as sequence numbers. Devices MUST reject
manifests with sequence numbers smaller than any onboard sequence manifests with sequence numbers smaller than any onboard sequence
number. number.
Note: This is not a firmware version. It is a manifest sequence Note: This is not a firmware version. It is a manifest sequence
number. A firmware version may be rolled back by creating a new number. A firmware version may be rolled back by creating a new
manifest for the old firmware version with a later sequence number. manifest for the old firmware version with a later sequence number.
Mitigates: Threat MFT1 Mitigates: Threat MFT1
Implemented by: Manifest Element: Monotonic Sequence Number Implemented by: Manifest Element: Monotonic Sequence Number
3.3.2. Security Requirement MFSR2: Vendor, Device-type Identifiers 4.3.2. Security Requirement MFSR2: Vendor, Device-type Identifiers
Devices MUST only apply firmware that is intended for them. Devices Devices MUST only apply firmware that is intended for them. Devices
MUST know with fine granularity that a given update applies to their MUST know with fine granularity that a given update applies to their
vendor, model, hardware revision, software revision. Human-readable vendor, model, hardware revision, software revision. Human-readable
identifiers are often error-prone in this regard, so unique identifiers are often error-prone in this regard, so unique
identifiers SHOULD be used. identifiers SHOULD be used.
Mitigates: Threat MFT2 Mitigates: Threat MFT2
Implemented by: Manifest Elements: Vendor ID Condition, Class ID Implemented by: Manifest Elements: Vendor ID Condition, Class ID
Condition Condition
3.3.3. Security Requirement MFSR3: Best-Before Timestamps 4.3.3. Security Requirement MFSR3: Best-Before Timestamps
Firmware MAY expire after a given time. Devices MAY provide a secure Firmware MAY expire after a given time. Devices MAY provide a secure
clock (local or remote). If a secure clock is provided and the clock (local or remote). If a secure clock is provided and the
Firmware manifest has a best-before timestamp, the device MUST reject Firmware manifest has a best-before timestamp, the device MUST reject
the manifest if current time is larger than the best-before time. the manifest if current time is larger than the best-before time.
Mitigates: Threat MFT3 Mitigates: Threat MFT3
Implemented by: Manifest Element: Best-Before timestamp condition Implemented by: Manifest Element: Best-Before timestamp condition
3.3.4. Security Requirement MFSR5: Cryptographic Authenticity 4.3.4. Security Requirement MFSR5: Cryptographic Authenticity
The authenticity of an update must be demonstrable. Typically, this The authenticity of an update must be demonstrable. Typically, this
means that updates must be digitally authenticated. Because the means that updates must be digitally authenticated. Because the
manifest contains information about how to install the update, the manifest contains information about how to install the update, the
manifest's authenticity must also be demonstrable. To reduce the manifest's authenticity must also be demonstrable. To reduce the
overhead required for validation, the manifest contains the digest of overhead required for validation, the manifest contains the digest of
the firmware image, rather than a second digital signature. The the firmware image, rather than a second digital signature. The
authenticity of the manifest can be verified with a digital signature authenticity of the manifest can be verified with a digital signature
or Message Authentication Code, the authenticity of the firmware or Message Authentication Code, the authenticity of the firmware
image is tied to the manifest by the use of a digest of the firmware image is tied to the manifest by the use of a digest of the firmware
image. image.
Mitigates: Threat MFT8 Mitigates: Threat MFT8
Implemented by: Signature, Payload Digest Implemented by: Signature, Payload Digest
3.3.5. Security Requirement MFSR4a: Authenticated Payload Type 4.3.5. Security Requirement MFSR4a: Authenticated Payload Type
The type of payload (which may be independent of format) MUST be The type of payload (which may be independent of format) MUST be
authenticated. For example, the target must know whether the payload authenticated. For example, the target must know whether the payload
is XIP firmware, a loadable module, or serialized configuration data. is XIP firmware, a loadable module, or serialized configuration data.
Mitigates: MFT4 Mitigates: MFT4
Implemented by: Manifest Elements: Payload Format, Storage Location Implemented by: Manifest Elements: Payload Format, Storage Location
3.3.6. Security Requirement MFSR4b: Authenticated Storage Location 4.3.6. Security Requirement MFSR4b: Authenticated Storage Location
The location on the target where the payload is to be stored MUST be The location on the target where the payload is to be stored MUST be
authenticated. authenticated.
Mitigates: MFT5 Mitigates: MFT5
Implemented by: Manifest Elements: Storage Location Implemented by: Manifest Elements: Storage Location
3.3.7. Security Requirement MFSR4c: Authenticated Remote Resource 4.3.7. Security Requirement MFSR4c: Authenticated Remote Resource
Location Location
The location where a target should find a payload MUST be The location where a target should find a payload MUST be
authenticated. authenticated.
Mitigates: MFT6 Mitigates: MFT6
Implemented by: Manifest Elements: URIs Implemented by: Manifest Elements: URIs
3.3.8. Security Requirement MFSR4d: Secure Boot 4.3.8. Security Requirement MFSR4d: Secure Boot
The target SHOULD verify firmware at time of boot. This requires The target SHOULD verify firmware at time of boot. This requires
authenticated payload size, and digest. authenticated payload size, and digest.
Mitigates: MFT7 Mitigates: MFT7
Implemented by: Manifest Elements: Payload Digest, Size Implemented by: Manifest Elements: Payload Digest, Size
3.3.9. Security Requirement MFSR4e: Authenticated precursor images 4.3.9. Security Requirement MFSR4e: Authenticated precursor images
If an update uses a differential compression method, it MUST specify If an update uses a differential compression method, it MUST specify
the digest of the precursor image and that digest MUST be the digest of the precursor image and that digest MUST be
authenticated. authenticated.
Mitigates: MFT9 Mitigates: MFT9
Implemented by: Manifest Elements: Precursor Image Digest Condition Implemented by: Manifest Elements: Precursor Image Digest Condition
3.3.10. Security Requirement MFSR4f: Authenticated Vendor and Class IDs 4.3.10. Security Requirement MFSR4f: Authenticated Vendor and Class IDs
The identifiers that specify firmware compatibility MUST be The identifiers that specify firmware compatibility MUST be
authenticated to ensure that only compatible firmware is installed on authenticated to ensure that only compatible firmware is installed on
a target device. a target device.
Mitigates: MFT2 Mitigates: MFT2
Implemented By: Manifest Elements: Vendor ID Condition, Class ID Implemented By: Manifest Elements: Vendor ID Condition, Class ID
Condition Condition
3.3.11. Security Requirement MFSR4f: Authenticated Vendor and Class IDs 4.3.11. Security Requirement MFSR4f: Authenticated Vendor and Class IDs
The identifiers that specify firmware compatibility MUST be The identifiers that specify firmware compatibility MUST be
authenticated to ensure that only compatible firmware is installed on authenticated to ensure that only compatible firmware is installed on
a target device. a target device.
Mitigates: MFT2 Mitigates: MFT2
Implemented By: Manifest Elements: Vendor ID Condition, Class ID Implemented By: Manifest Elements: Vendor ID Condition, Class ID
Condition Condition
3.3.12. Security Requirement MFSR6: Rights Require Authenticity 4.3.12. Security Requirement MFSR6: Rights Require Authenticity
If a device grants different rights to different actors, exercising If a device grants different rights to different actors, exercising
those rights MUST be accompanied by proof of those rights, in the those rights MUST be accompanied by proof of those rights, in the
form of proof of authenticity. Authenticity mechanisms such as those form of proof of authenticity. Authenticity mechanisms such as those
required in MFSR5 are acceptable but need to follow the end-to-end required in MFSR5 are acceptable but need to follow the end-to-end
security model. security model.
For example, if a device has a policy that requires that firmware For example, if a device has a policy that requires that firmware
have both an Authorship right and a Qualification right and if that have both an Authorship right and a Qualification right and if that
device grants Authorship and Qualification rights to different device grants Authorship and Qualification rights to different
parties, such as a Device Operator and a Network Operator, parties, such as a Device Operator and a Network Operator,
respectively, then the firmware cannot be installed without proof of respectively, then the firmware cannot be installed without proof of
rights from both the Device and the Network Operator. rights from both the Device and the Network Operator.
Mitigates: MFT10 Mitigates: MFT10
Implemented by: Signature Implemented by: Signature
3.3.13. Security Requirement MFSR7: Firmware encryption 4.3.13. Security Requirement MFSR7: Firmware encryption
The manifest information model must enable encrypted payloads. The manifest information model must enable encrypted payloads.
Encryption helps to prevent third parties, including attackers, from Encryption helps to prevent third parties, including attackers, from
reading the content of the firmware image. This can protect against reading the content of the firmware image. This can protect against
confidential information disclosures and discovery of vulnerabilities confidential information disclosures and discovery of vulnerabilities
through reverse engineering. Therefore the manifest must convey the through reverse engineering. Therefore the manifest must convey the
information required to allow an intended recipient to decrypt an information required to allow an intended recipient to decrypt an
encrypted payload. encrypted payload.
Mitigates: MFT11 Mitigates: MFT11
Implemented by: Manifest Element: Content Key Distribution Method Implemented by: Manifest Element: Content Key Distribution Method
3.3.14. Security Requirement MFSR8: Access Control Lists 4.3.14. Security Requirement MFSR8: Access Control Lists
If a device grants different rights to different actors, then an If a device grants different rights to different actors, then an
exercise of those rights must be validated against a list of rights exercise of those rights must be validated against a list of rights
for the actor. This typically takes the form of an Access Control for the actor. This typically takes the form of an Access Control
List (ACL). ACLs are applied to two scenarios: List (ACL). ACLs are applied to two scenarios:
1. An ACL decides which elements of the manifest may be overridden 1. An ACL decides which elements of the manifest may be overridden
and by which actors. and by which actors.
2. An ACL decides which component identifier/storage identifier 2. An ACL decides which component identifier/storage identifier
pairs can be written by which actors. pairs can be written by which actors.
Mitigates: MFT12, MFT10 Mitigates: MFT12, MFT10
Implemented by: Client-side code, not specified in manifest. Implemented by: Client-side code, not specified in manifest.
3.4. User Stories 4.3.15. Security Requirement MFSR9: Encrypted Manifests
It must be possible to encrypt part or all of the manifest. This may
be accomplished with either transport encryption or with at-rest
encryption, for example COSE_Encrypt.
Mitigates: MFT13
Implemented by: TLS/COSE
4.4. User Stories
User stories provide expected use cases. These are used to feed into User stories provide expected use cases. These are used to feed into
usability requirements. usability requirements.
3.4.1. Use Case MFUS1: Installation Instructions 4.4.1. Use Case MFUS1: Installation Instructions
As an Device Operator, I want to provide my devices with additional As an Device Operator, I want to provide my devices with additional
installation instructions so that I can keep process details out of installation instructions so that I can keep process details out of
my payload data. my payload data.
Some installation instructions might be: Some installation instructions might be:
- Use a table of hashes to ensure that each block of the payload is - Use a table of hashes to ensure that each block of the payload is
validate before writing. validate before writing.
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- Pre-cache the update, but do not install. - Pre-cache the update, but do not install.
- Install the pre-cached update matching this manifest. - Install the pre-cached update matching this manifest.
- Install this update immediately, overriding any long-running - Install this update immediately, overriding any long-running
tasks. tasks.
Satisfied by: MFUR1 Satisfied by: MFUR1
3.4.2. Use Case MFUS2: Override Non-Critical Manifest Elements 4.4.2. Use Case MFUS2: Override Non-Critical Manifest Elements
As a Network Operator, I would like to be able to override the non- As a Network Operator, I would like to be able to override the non-
critical information in the manifest so that I can control my devices critical information in the manifest so that I can control my devices
more precisely. This assumes that the Device Operator delegated more precisely. This assumes that the Device Operator delegated
rights about the device to the Network Operator. rights about the device to the Network Operator.
Some examples of potentially overridable information: Some examples of potentially overridable information:
- URIs: this allows the Network Operator to direct devices to their - URIs: this allows the Network Operator to direct devices to their
own infrastructure in order to reduce network load. own infrastructure in order to reduce network load.
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instructions such as time of installation. instructions such as time of installation.
- Processing Steps: If an intermediary performs an action on behalf - Processing Steps: If an intermediary performs an action on behalf
of a device, it may need to override the processing steps. It is of a device, it may need to override the processing steps. It is
still possible for a device to verify the final content and the still possible for a device to verify the final content and the
result of any processing step that specifies a digest. Some result of any processing step that specifies a digest. Some
processing steps should be non-overridable. processing steps should be non-overridable.
Satisfied by: MFUR2, MFUR3 Satisfied by: MFUR2, MFUR3
3.4.3. Use Case MFUS3: Modular Update 4.4.3. Use Case MFUS3: Modular Update
As an Operator, I want to divide my firmware into frequently updated As an Operator, I want to divide my firmware into frequently updated
and infrequently updated components, so that I can reduce the size of and infrequently updated components, so that I can reduce the size of
updates and make different parties responsible for different updates and make different parties responsible for different
components. components.
Satisfied by: MFUR3 Satisfied by: MFUR3
3.4.4. Use Case MFUS4: Multiple Authorisations 4.4.4. Use Case MFUS4: Multiple Authorisations
As a Device Operator, I want to ensure the quality of a firmware As a Device Operator, I want to ensure the quality of a firmware
update before installing it, so that I can ensure interoperability of update before installing it, so that I can ensure interoperability of
all devices in my product family. I want to restrict the ability to all devices in my product family. I want to restrict the ability to
make changes to my devices to require my express approval. make changes to my devices to require my express approval.
Satisfied by: MFUR4, MFSR8 Satisfied by: MFUR4, MFSR8
3.4.5. Use Case MFUS5: Multiple Payload Formats 4.4.5. Use Case MFUS5: Multiple Payload Formats
As an Operator, I want to be able to send multiple payload formats to As an Operator, I want to be able to send multiple payload formats to
suit the needs of my update, so that I can optimise the bandwidth suit the needs of my update, so that I can optimise the bandwidth
used by my devices. used by my devices.
Satisfied by: MFUR5 Satisfied by: MFUR5
3.4.6. Use Case MFUS6: Prevent Confidential Information Disclosures 4.4.6. Use Case MFUS6: Prevent Confidential Information Disclosures
As an firmware author, I want to prevent confidential information As an firmware author, I want to prevent confidential information
from being disclosed during firmware updates. It is assumed that from being disclosed during firmware updates. It is assumed that
channel security is adequate to protect the manifest itself against channel security is adequate to protect the manifest itself against
information disclosure. information disclosure.
Satisfied by: MFSR7 Satisfied by: MFSR7
3.4.7. Use Case MFUS7: Prevent Devices from Unpacking Unknown Formats 4.4.7. Use Case MFUS7: Prevent Devices from Unpacking Unknown Formats
As a Device Operator, I want devices to determine whether they can As a Device Operator, I want devices to determine whether they can
process a payload prior to downloading it. process a payload prior to downloading it.
In some cases, it may be desirable for a third party to perform some In some cases, it may be desirable for a third party to perform some
processing on behalf of a target. For this to occur, the third party processing on behalf of a target. For this to occur, the third party
MUST indicate what processing occurred and how to verify it against MUST indicate what processing occurred and how to verify it against
the Trust Provisioning Authority's intent. the Trust Provisioning Authority's intent.
This amounts to overriding Processing Steps and URIs. This amounts to overriding Processing Steps and URIs.
Satisfied by: MFUR6, MFUR2 Satisfied by: MFUR6, MFUR2
3.4.8. Use Case MFUS8: Specify Version Numbers of Target Firmware 4.4.8. Use Case MFUS8: Specify Version Numbers of Target Firmware
As a Device Operator, I want to be able to target devices for updates As a Device Operator, I want to be able to target devices for updates
based on their current firmware version, so that I can control which based on their current firmware version, so that I can control which
versions are replaced with a single manifest. versions are replaced with a single manifest.
Satisfied by: MFUR7 Satisfied by: MFUR7
3.4.9. Use Case MFUS9: Enable devices to choose between images 4.4.9. Use Case MFUS9: Enable Devices to Choose Between Images
As a developer, I want to be able to sign two or more versions of my As a developer, I want to be able to sign two or more versions of my
firmware in a single manifest so that I can use a very simple firmware in a single manifest so that I can use a very simple
bootloader that chooses between two or more images that are executed bootloader that chooses between two or more images that are executed
in-place. in-place.
Satisfied by: MFUR8 Satisfied by: MFUR8
3.5. Usability Requirements 4.4.10. Use Case MFUS10: Secure Boot Using Manifests
As a signer for both secure boot and firmware deployment, I would
like to use the same signed document for both tasks so that my data
size is smaller, I can share common code, and I can reduce signature
verifications.
Satisfied by: MFUR9
4.4.11. Use Case MFUS11: Decompress on Load
As a developer of firmware for a run-from-RAM device, I would like to
use compressed images and to indicate to the bootloader that I am
using a compressed image in the manifest so that it can be used with
secure boot.
Satisfied by: MFUR10
4.4.12. Use Case MFUS12: Payload in Manifest
As an operator of a constrained network, I would like to be able to
send a small payload in the same packet as the manifest so that I can
reduce network traffic.
Satisfied by: MFUR11
4.4.13. Use Case MFUS13: Simple Parsing
As a developer for constrained devices, I want a low complexity
library for processing updates so that I can fit more application
code on my device.
Satisfied by: MFUR12
4.5. Usability Requirements
The following usability requirements satisfy the user stories listed The following usability requirements satisfy the user stories listed
above. above.
3.5.1. Usability Requirement MFUR1 4.5.1. Usability Requirement MFUR1
It must be possible to provide all information necessary for the It must be possible to provide all information necessary for the
processing of a manifest into the manifest. processing of a manifest into the manifest.
Satisfies: User story MFUS1 Satisfies: User story MFUS1
Implemented by: Manifest Element: Directives Implemented by: Manifest Element: Directives
3.5.2. Usability Requirement MFUR2 4.5.2. Usability Requirement MFUR2
It must be possible to redirect payload fetches. This applies where It must be possible to redirect payload fetches. This applies where
two manifests are used in conjunction. For example, a Device two manifests are used in conjunction. For example, a Device
Operator creates a manifest specifying a payload and signs it, and Operator creates a manifest specifying a payload and signs it, and
provides a URI for that payload. A Network Operator creates a second provides a URI for that payload. A Network Operator creates a second
manifest, with a dependency on the first. They use this second manifest, with a dependency on the first. They use this second
manifest to override the URIs provided by the Device Operator, manifest to override the URIs provided by the Device Operator,
directing them into their own infrastructure instead. Some devices directing them into their own infrastructure instead. Some devices
may provide this capability, while others may only look at canonical may provide this capability, while others may only look at canonical
sources of firmware. For this to be possible, the device must fetch sources of firmware. For this to be possible, the device must fetch
the payload, whereas a device that accpets payload pushes will ignore the payload, whereas a device that accpets payload pushes will ignore
this feature. this feature.
Satisfies: User story MFUS2 Satisfies: User story MFUS2
Implemented by: Manifest Element: Aliases Implemented by: Manifest Element: Aliases
3.5.3. Usability Requirement MFUR3 4.5.3. Usability Requirement MFUR3
It must be possible express the requirement to install one or more It must be possible express the requirement to install one or more
payloads from one or more authorities so that a multi-payload update payloads from one or more authorities so that a multi-payload update
can be described. This allows multiple parties with different can be described. This allows multiple parties with different
permissions to collaborate in creating a single update for the IoT permissions to collaborate in creating a single update for the IoT
device, across multiple components. device, across multiple components.
This requirement effectively means that it must be possible to This requirement effectively means that it must be possible to
construct a tree of manifests on a multi-image target. construct a tree of manifests on a multi-image target.
Because devices can be either HeSA or HoSA both the storage system Because devices can be either HeSA or HoSA both the storage system
and the storage location within that storage system must be possible and the storage location within that storage system must be possible
to specify. In a HoSA device, the payload location may be as simple to specify. In a HoSA device, the payload location may be as simple
as an address, or a file path. In a HeSA device, the payload as an address, or a file path. In a HeSA device, the payload
location may be scoped by a component identifier. It is expedient to location may be scoped by a component identifier. It is expedient to
consider that all HoSA devices are HeSA devices with a single consider that all HoSA devices are HeSA devices with a single
component. component.
3.5.3.1. Example 1: Multiple Microcontrollers 4.5.3.1. Example 1: Multiple Microcontrollers
An IoT device with multiple microcontrollers in the same physical An IoT device with multiple microcontrollers in the same physical
device (HeSA) will likely require multiple payloads with different device (HeSA) will likely require multiple payloads with different
component identifiers. component identifiers.
3.5.3.2. Example 2: Code and Configuration 4.5.3.2. Example 2: Code and Configuration
A firmware image can be divided into two payloads: code and A firmware image can be divided into two payloads: code and
configuration. These payloads may require authorizations from configuration. These payloads may require authorizations from
different actors in order to install (see MFSR6 and MFSR8). This different actors in order to install (see MFSR6 and MFSR8). This
structure means that multiple manifests may be required, with a structure means that multiple manifests may be required, with a
dependency structure between them. dependency structure between them.
3.5.3.3. Example 3: Multiple Chunks 4.5.3.3. Example 3: Multiple Chunks
A firmware image can be divided into multiple functional blocks for A firmware image can be divided into multiple functional blocks for
separate testing and distribution. This means that code would need separate testing and distribution. This means that code would need
to be distributed in multiple payloads. For example, this might be to be distributed in multiple payloads. For example, this might be
desirable in order to ensure that common code between devices is desirable in order to ensure that common code between devices is
identical in order to reduce distribution bandwidth. identical in order to reduce distribution bandwidth.
Satisfies: User story MFUS2, MFUS3 Satisfies: User story MFUS2, MFUS3
Implemented by Manifest Element: Dependencies, StorageIdentifier, Implemented by Manifest Element: Dependencies, StorageIdentifier,
ComponentIdentifier ComponentIdentifier
3.5.4. Usability Requirement MFUR4 4.5.4. Usability Requirement MFUR4
It MUST be possible to sign a manifest multiple times so that It MUST be possible to sign a manifest multiple times so that
signatures from multiple parties with different permissions can be signatures from multiple parties with different permissions can be
required in order to authorise installation of a manifest. required in order to authorise installation of a manifest.
Satisfies: User story MFUS4 Satisfies: User story MFUS4
Implemented by: COSE Signature (or similar) Implemented by: COSE Signature (or similar)
3.5.5. Usability Requirement MFUR5 4.5.5. Usability Requirement MFUR5
The manifest format MUST accommodate any payload format that an The manifest format MUST accommodate any payload format that an
Operator wishes to use. Some examples of payload format would be: Operator wishes to use. Some examples of payload format would be:
- Binary - Binary
- Elf - Elf
- Differential - Differential
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- Packed configuration - Packed configuration
- Intel HEX - Intel HEX
- S-Record - S-Record
Satisfies: User story MFUS5 Satisfies: User story MFUS5
Implemented by: Manifest Element: Payload Format Implemented by: Manifest Element: Payload Format
3.5.6. Usability Requirement MFUR6 4.5.6. Usability Requirement MFUR6
The manifest format must accommodate nested formats, announcing to The manifest format must accommodate nested formats, announcing to
the target device all the nesting steps and any parameters used by the target device all the nesting steps and any parameters used by
those steps. those steps.
Satisfies: User story MFUS6 Satisfies: User story MFUS6
Implemented by: Manifest Element: Processing Steps Implemented by: Manifest Element: Processing Steps
3.5.7. Usability Requirement MFUR7 4.5.7. Usability Requirement MFUR7
The manifest format must provide a method to specify multiple version The manifest format must provide a method to specify multiple version
numbers of firmware to which the manifest applies, either with a list numbers of firmware to which the manifest applies, either with a list
or with range matching. or with range matching.
Satisfies: User story MFUS8 Satisfies: User story MFUS8
Implemented by: Manifest Element: Required Image Version List Implemented by: Manifest Element: Required Image Version List
3.5.8. Usability Requirement MFUR8 4.5.8. Usability Requirement MFUR8
The manifest format must provide a mechanism to list multiple The manifest format must provide a mechanism to list multiple
equivalent payloads by Execute-In-Place Installation Address, equivalent payloads by Execute-In-Place Installation Address,
including the payload digest and, optionally, payload URIs. including the payload digest and, optionally, payload URIs.
Satisfies: User story MFUS9 Satisfies: User story MFUS9
Implemented by: Manifest Element: XIP Address Implemented by: Manifest Element: XIP Address
4. Manifest Information Elements 4.5.9. Usability Requirement MFUR9: Bootable Manifest
Each manifest element is anchored in a security requirement or a
usability requirement. The manifest elements are described below and
justified by their requirements.
4.1. Manifest Element: version identifier of the manifest structure
An identifier that describes which iteration of the manifest format
is contained in the structure.
This element is MANDATORY and must be present in order to allow
devices to identify the version of the manifest data model that is in
use.
4.2. Manifest Element: 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.
This element is MANDATORY and is necessary to prevent malicious
actors from reverting a firmware update against the wishes of the
relevant authority.
Implements: Security Requirement MFSR1.
4.3. Manifest Element: 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 type 5 UUIDs with the vendor's domain name and the UUID DNS
prefix. Other options include type 1 and type 4 UUIDs.
This ID is OPTIONAL but RECOMMENDED and helps to distinguish between
identically named products from different vendors.
Implements: Security Requirement MFSR2, MFSR4f.
4.3.1. Example: Domain Name-based UUIDs
Vendor A creates a UUID based on their domain name:
vendorId = UUID5(DNS, "vendor-a.com")
Because the DNS infrastructure prevents multiple registrations of the
same domain name, this UUID is guaranteed to be unique. Because the
domain name is known, this UUID is reproducible. Type 1 and type 4
UUIDs produce similar guarantees of uniqueness, but not
reproducibility.
4.4. Manifest Element: Class ID Condition
A device "Class" is defined as any device that can accept the same
firmware update without modification. 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. 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.
Note Well: Class ID is not a human-readable element. It is intended
for match/mismatch use only.
This ID is OPTIONAL but RECOMMENDED and allows devices to determine
applicability of a firmware in an unambiguous way.
Implements: Security Requirement MFSR2, MFSR4f.
4.4.1. Example 1: Different Classes
Vendor A creates product Z and product Y. The firmware images of
products Z and Y are not interchangeable. Vendor A creates UUIDs as
follows:
- vendorId = UUID5(DNS, "vendor-a.com")
- ZclassId = UUID5(vendorId, "Product Z")
- YclassId = UUID5(vendorId, "Product Y")
This ensures that Vendor A's Product Z cannot install firmware for
Product Y and Product Y cannot install firmware for Product Z.
4.4.2. Example 2: Upgrading Class ID
Vendor A creates product X. Later, Vendor A adds a new feature to
product X, creating product X v2. Product X requires a firmware
update to work with firmware intended for product X v2.
Vendor A creates UUIDs as follows:
- vendorId = UUID5(DNS, "vendor-a.com")
- XclassId = UUID5(vendorId, "Product X")
- Xv2classId = UUID5(vendorId, "Product X v2")
When product X receives the firmware update necessary to be
compatible with product X v2, part of the firmware update changes the
class ID to Xv2classId.
4.4.3. Example 3: Shared Functionality
Vendor A produces two products, product X and product Y. These
components share a common core (such as an operating system), but
have different applications. The common core and the applications
can be updated independently. To enable X and Y to receive the same
common core update, they require the same class ID. To ensure that
only product X receives application X and only product Y receives
application Y, product X and product Y must have different class IDs.
The vendor creates Class IDs as follows:
- vendorId = UUID5(DNS, "vendor-a.com")
- XclassId = UUID5(vendorId, "Product X")
- YclassId = UUID5(vendorId, "Product Y")
- CommonClassId = UUID5(vendorId, "common core")
Product X matches against both XclassId and CommonClassId. Product Y
matches against both YclassId and CommonClassId.
4.5. Manifest Element: 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. The
precursor image may be installed or stored as a candidate.
This element is MANDATORY for differential updates. Otherwise, it is
not needed.
Implements: Security Requirement MFSR4e
4.6. Manifest Element: Required Image Version List
When a payload applies to multiple versions of a firmware, the
required image version list specifies which versions must be present
for the update to be applied. This allows the update author to
target specific versions of firmware for an update, while excluding
those to which it should not be applied.
Where an update can only be applied over specific predecessor
versions, that version MUST be specified by the Required Image
Version List.
This element is OPTIONAL.
Implements: MFUR7
4.7. Manifest Element: Best-Before timestamp condition
This element tells a device the last application time. This is only
usable in conjunction with a secure clock.
This element is OPTIONAL and MAY enable use cases where a secure
clock is provided and firmware is intended to expire regularly.
Implements: Security Requirement MFSR3
4.8. Manifest Element: Payload Format
The format of the payload must be indicated to devices is in an
unambiguous way. This element provides a mechanism to describe the
payload format, within the signed metadata.
This element is MANDATORY and MUST be present to enable devices to
decode payloads correctly.
Implements: Security Requirement MFSR4a, Usability Requirement MFUR5
4.9. Manifest Element: Processing Steps
A list of all payload processors necessary to process a nested format
and any parameters needed by those payload processors. Each
Processing Step SHOULD indicate the expected digest of the payload
after the processing is complete. Processing steps are distinct from
Directives in that Directives apply to the manifest as a whole,
whereas Processing Steps apply to an individual payload and provide
instructions on how to unpack it.
Implements: Usability Requirement MFUR6
4.10. Manifest Element: Storage Location
This element 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.
This element is MANDATORY and MUST be present to enable devices to
store payloads to the correct location.
Implements: Security Requirement MFSR4b
4.10.1. Example 1: Two Storage Locations
A device supports two components: an OS and an application. These
components can be updated independently, expressing dependencies to
ensure compatibility between the components. The firmware authority
chooses two storage identifiers:
- OS
- APP
4.10.2. Example 2: File System
A device supports a full filesystem. The firmware authority chooses
to make the storage identifier the path at which to install the
payload. The payload may be a tarball, in which case, it unpacks the
tarball into the specified path.
4.10.3. Example 3: Flash Memory
A device supports flash memory. The firmware authority chooses to
make the storage identifier the offset where the image should be
written.
4.11. Manifest Element: Component Identifier
In a heterogeneous storage architecture, a storage identifier is
insufficient to identify where and how to store a payload. To
resolve this, a component identifier indicates which part of the
storage architecture is targeted by the payload. In a homogeneous
storage architecture, this element is unnecessary.
This element is OPTIONAL and only necessary in heterogeneous storage
architecture devices.
Implements: MFUR3
4.12. Manifest Element: URIs
This element is a list of weighted URIs that the device uses to
select where to obtain a payload.
This element is OPTIONAL and only needed when the target device does
not intrinsically know where to find the payload.
Note: Devices will typically require URIs.
Implements: Security Requirement MFSR4c
4.13. Manifest Element: Payload Digest
This element contains the digest of the payload. This allows the
target device to ensure authenticity of the payload. It MUST be
possible to specify more than one payload digest, indexed by Manifest
Element: XIP Address.
This element is MANDATORY and fundamentally necessary to ensure the
authenticity and integrity of the payload.
Implements: Security Requirement MFSR4d, Usability Requirement MFUR8
4.14. Manifest Element: Size
The size of the payload in bytes.
This element is MANDATORY and informs the target device how big of a
payload to expect. Without it, devices are exposed to some classes
of denial of service attack.
Implements: Security Requirement MFSR4d
4.15. Manifest Element: Signature
This is not strictly a manifest element. 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.
This element is MANDATORY and represents the foundation of all
security properties of the manifest.
Implements: Security Requirement MFSR5, MFSR6, MFUR4
4.16. Manifest Element: Directives
A list of instructions that the device should execute, in order, when
processing the manifest. This information is distinct from the
information necessary to process a payload (Processing Steps) and
applies to the whole manifest including all payloads that it
references. Directives include information such as update timing
(For example, install only on Sunday, at 0200), procedural
considerations (for example, shut down the equipment under control
before executing the update), pre and post-installation steps (for
example, run a script).
This element is OPTIONAL and enables some use cases.
Implements: Usability Requirement MFUR1
4.17. Manifest Element: Aliases
A list of Digest/URI pairs. A device should build an alias table It must be possible to describe a bootable system with a manifest on
while paring a manifest tree and treat any aliases as top-ranked URIs both Execute-In-Place microcontrollers and on complex operating
for the corresponding digest. systems. This requires the manifest to specify the digest of each
statically linked storage location. In addition, the manifest must
be able to express metadata used by the bootloader, such as a kernel
command-line.
This element is OPTIONAL and enables some use cases. Satisfies: User story MFUS10
Implements: Usability Requirement MFUR2 Implemented by: Manifest Element: Boot-time Metadata
4.18. Manifest Element: Dependencies 4.5.10. Usability Requirement MFUR10: Load-Time Information
A list of Digest/URI pairs that refer to other manifests by digest. It must be possible to specify additional metadata for load time
The manifests that are linked in this way must be acquired and processing of a payload, such as load-address, and compression
installed simultaneously in order to form a complete update. algorithm.
This element is MANDATORY to use in deployments that include both N.B. load comes before boot.
multiple authorities and multiple payloads.
Implements: Usability Requirement MFUR3 Satisfies: User Story MFUS11
4.19. Manifest Element: Content Key Distribution Method Implemented by: Manifest Element: Load-time Metadata
Encrypting firmware images requires symmetric content encryption 4.5.11. Usability Requirement MFUR11: Payload in Manifest
keys. Since there are several methods to protect or distribute the Superstructure
symmetric content encryption keys, the manifest contains a element
for the Content Key Distribution Method. One examples 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. This MAY be included in a decryption step
contained in Processing Steps.
This element is MANDATORY to use for encrypted payloads, It must be possible to place a payload in the same structure as the
manifest. This typically places the payload in the same packet as
the manifest.
Implements: Security Requirement MFSR7. Satisfies: User Story MFUS12
Implemented by: Manifest Element: Payload
4.20. Manifest Element: XIP Address 4.5.12. Usability Requirement MFUR12: Simple Parsing
In order to support XIP systems with multiple possible base The structure of the manifest must be simple to parse, without need
addresses, it is necessary to specify which address the payload is for a general-purpose parser.
linked for.
For example a microcontroller may have a simple bootloader that Satisfies: User Story MFUS13
chooses one of two images to boot. That microcontroller then needs
to choose one of two firmware images to install, based on which of
its two images is older.
Implements: MFUR8 Implemented by: N/A
5. Security Considerations 5. Security Considerations
Security considerations for this document are covered in Section 3. Security considerations for this document are covered in Section 4.
6. IANA Considerations 6. IANA Considerations
This document does not require any actions by IANA. This document does not require any actions by IANA.
7. Acknowledgements 7. Acknowledgements
We would like to thank our working group chairs, Dave Thaler, Russ We would like to thank our working group chairs, Dave Thaler, Russ
Housley and David Waltermire, for their review comments and their Housley and David Waltermire, for their review comments and their
support. support.
skipping to change at page 28, line 15 skipping to change at page 30, line 46
Steve Patrick, Fabio Utzig, Paul Lambert, Benjamin Kaduk, Said Steve Patrick, Fabio Utzig, Paul Lambert, Benjamin Kaduk, Said
Gharout, and Milen Stoychev. Gharout, and Milen Stoychev.
8. References 8. References
8.1. Normative References 8.1. Normative References
[I-D.ietf-suit-architecture] [I-D.ietf-suit-architecture]
Moran, B., Meriac, M., Tschofenig, H., and D. Brown, "A Moran, B., Meriac, M., Tschofenig, H., and D. Brown, "A
Firmware Update Architecture for Internet of Things Firmware Update Architecture for Internet of Things
Devices", draft-ietf-suit-architecture-01 (work in Devices", draft-ietf-suit-architecture-02 (work in
progress), July 2018. progress), January 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References 8.2. Informative References
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122, Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005, <https://www.rfc- DOI 10.17487/RFC4122, July 2005,
editor.org/info/rfc4122>. <https://www.rfc-editor.org/info/rfc4122>.
[STRIDE] Microsoft, "The STRIDE Threat Model", May 2018, [STRIDE] Microsoft, "The STRIDE Threat Model", May 2018,
<https://msdn.microsoft.com/en-us/library/ <https://msdn.microsoft.com/en-us/library/
ee823878(v=cs.20).aspx>. ee823878(v=cs.20).aspx>.
8.3. URIs 8.3. URIs
[1] mailto:suit@ietf.org [1] mailto:suit@ietf.org
[2] https://www1.ietf.org/mailman/listinfo/suit
[3] https://www.ietf.org/mail-archive/web/suit/current/index.html
Appendix A. Mailing List Information Appendix A. Mailing List Information
The discussion list for this document is located at the e-mail The discussion list for this document is located at the e-mail
address suit@ietf.org [1]. Information on the group and information address suit@ietf.org [1]. Information on the group and information
on how to subscribe to the list is at on how to subscribe to the list is at
https://www1.ietf.org/mailman/listinfo/suit https://www1.ietf.org/mailman/listinfo/suit [2]
Archives of the list can be found at: https://www.ietf.org/mail- Archives of the list can be found at: https://www.ietf.org/mail-
archive/web/suit/current/index.html archive/web/suit/current/index.html [3]
Authors' Addresses Authors' Addresses
Brendan Moran Brendan Moran
Arm Limited Arm Limited
EMail: Brendan.Moran@arm.com EMail: Brendan.Moran@arm.com
Hannes Tschofenig Hannes Tschofenig
Arm Limited Arm Limited
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