wdiff draft-ietf-suit-architecture-12.txt draft-ietf-suit-architecture-13.txt

SUIT B. Moran
Internet-Draft H. Tschofenig
Intended status: Informational Arm Limited
Expires: March 21, April 19, 2021 D. Brown
Linaro
M. Meriac
Consultant
September 17,
October 16, 2020

A Firmware Update Architecture for Internet of Things
draft-ietf-suit-architecture-12
draft-ietf-suit-architecture-13

Abstract

Vulnerabilities with Internet of Things (IoT) devices have raised the
need for a solid reliable and secure firmware update mechanism that is also suitable for constrained devices.
devices with resource constraints. Incorporating such an update
mechanism to fix vulnerabilities, to update is a fundamental requirement for fixing vulnerabilities but
it also enables other important capabilities such as updating
configuration settings as well as adding new functionality is recommended by security experts.

This document lists requirements functionality.

In addition to the definition of terminology and describes an architecture for a
firmware update mechanism suitable for IoT devices. The architecture
is agnostic to this
document motivates the transport standardization of the firmware images a manifest format as a
transport-agnostic means for describing and associated
meta-data. protecting firmware
updates.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on March 21, April 19, 2021.

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

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Agnostic to how firmware images are distributed . . . . . 7
3.2. Friendly to broadcast delivery . . . . . . . . . . . . . 8
3.3. Use state-of-the-art security mechanisms . . . . . . . . 8
3.4. Rollback attacks must be prevented . . . . . . . . . . . 9
3.5. High reliability . . . . . . . . . . 5
2.1. Terms . . . . . . . . . . 9
3.6. Operate with a small bootloader . . . . . . . . . . . . . 9
3.7. Small Parsers . . . 5
2.2. Stakeholders . . . . . . . . . . . . . . . . . . . 10
3.8. Minimal impact on existing firmware formats . . . 6
2.3. Functions . . . . 10
3.9. Robust permissions . . . . . . . . . . . . . . . . . . . 10
3.10. Operating modes . 7
3. Architecture . . . . . . . . . . . . . . . . . . . . 11
3.11. Suitability to software and personalization data . . . . 13 8
4. Claims . Invoking the Firmware . . . . . . . . . . . . . . . . . . . . 12
4.1. The Bootloader . . . . . . 13
5. Communication Architecture . . . . . . . . . . . . . . . 14
5. Types of IoT Devices . . 14
6. Manifest . . . . . . . . . . . . . . . . . . 15
5.1. Single MCU . . . . . . . . 18
7. Device Firmware Update Examples . . . . . . . . . . . . . . . 19
7.1. 15
5.2. Single CPU SoC . . . . with Secure - Normal Mode Partitioning . . . . 16
5.3. Symmetric Multiple CPUs . . . . . . . . . . . . . 19
7.2. Single CPU with Secure - Normal Mode Partitioning . . . . 19
7.3. Symmetric Multiple CPUs 16
5.4. Dual CPU, shared memory . . . . . . . . . . . . . . . . . 19
7.4. 16
5.5. Dual CPU, shared memory other bus . . . . . . . . . . . . . . . . . 20
7.5. Dual CPU, other bus . . 17
6. Manifests . . . . . . . . . . . . . . . . . 20
8. Bootloader . . . . . . . . . 17
7. Securing Firmware Updates . . . . . . . . . . . . . . . . 20
9. . . 19
8. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10. 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
11. 25
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26
12. 25
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
13. 25
12. Informative References . . . . . . . . . . . . . . . . . . . 28 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 28

1. Introduction

When developing

Firmware updates can help to fix security vulnerabilities and are
considered to be an important building block in securing IoT devices.
Due to rising concerns about insecure IoT devices the Internet
Architecture Board (IAB) organized a 'Workshop on Internet of Things
(IoT) devices, one of Software Update (IOTSU)', which took place at Trinity College
Dublin, Ireland on the most
difficult problems 13th and 14th of June, 2016 to solve is how take a look at
the bigger picture. A report about this workshop can be found at
[RFC8240]. The workshop revealed a number of challenges for
developers and led to update firmware on the device.
Once formation of the device IETF Software Updates for
Internet of Things (SUIT) working group.

Developing secure Internet of Things (IoT) devices is not an easy
task and supporting a firmware update solution requires skillful
engineers. Once devices are deployed, firmware updates play a
critical part in
its lifetime, their lifecycle management, particularly when
devices have a long lifetime, or are deployed in remote or
inaccessible areas where manual intervention is cost prohibitive or
otherwise difficult. Updates to the firmware of
an Firmware updates
for IoT device devices are expected to work automatically, i.e. without user
involvement. Automatic updates that do not require human
intervention are key to a scalable solution for fixing software
vulnerabilities.

Firmware updates are not only done to fix bugs in software, to bugs, but they can also add
new functionality, and to re-configure the device to work in new
environments or to behave differently in an already deployed context.

The firmware update process, among other goals, process has to ensure that

- The firmware image is authenticated and integrity protected.
Attempts to flash a maliciously modified firmware image or an
image from an
unknown unknown, untrusted source are must be prevented. In
examples this document uses asymmetric cryptography because it is
the preferred approach by many IoT deployments. The use of
symmetric credentials is also supported and can be used by very
constrained IoT devices.

- The firmware image can be confidentiality protected so that
attempts by an adversary to recover the plaintext binary can be
prevented.
mitigated or at least made more difficult. Obtaining the firmware
is often one of the first steps to mount an attack since it gives
the adversary valuable insights into used the software libraries, libraries used,
configuration settings and generic
functionality (even functionality. Even though
reverse engineering the binary can be a tedious process).

This version of the document assumes asymmetric cryptography and a
public key infrastructure. Future versions may also describe process modern
reverse engineering frameworks have made this task a
symmetric key approach for very constrained devices. lot easier.

While the standardization work has been informed by and optimised optimized for
firmware update use cases of Class 1 devices (according to the device
class definitions in RFC 7228 [RFC7228]) devices, there is nothing in
the architecture that restricts its use to only these constrained IoT
devices. Moreover, this architecture is not limited to managing
software updates, but can also be applied to managing the delivery of
arbitrary data, such as configuration information and keys.

More Unlike
higher end devices, like laptops and desktop PCs, many IoT devices do
not have user interfaces and support for unattended updates is,
therefore, essential for the design of a practical solution.
Constrained IoT devices often use a software engineering model where
a developer is responsible for creating and compiling all software
running on the device into a single, monolithic firmware image. On
higher end devices application software is, on the other hand, often
downloaded separately and even obtained from developers different to
the developers of the lower level software. The details about for how to
obtain those application layer software binaries then depends heavily
on the security goals platform, programming language uses and the sandbox the
software is executed in.

While the IETF standardization work has been focused on the manifest
format, a fully interoperable solution needs more than a standardized
manifest. For example, protocols for transferring firmware images
and manifests to the device need to be available as well as the
status tracker functionality. Devices also require a mechanism to
discover the status tracker(s) and/or firmware servers. These
building blocks have been developed by various organizations under
the umbrella of an IoT device management solution. The LwM2M
protocol is one IoT device management protocol.

There are, however, several areas that (partially) fall outside the
scope of the IETF and other standards organizations but need to be
considered by firmware authors, as well as device and network
operators. Here are discussed some of them, as highlighted during the IOTSU
workshop:

- Installing firmware updates in Section 5 a robust fashion so that the update
does not break the device functionality of the environment this
device operates in. This requires proper testing and
requirements are described offering
recovery strategies when a firmware update is unsuccessful.

- Making firmware updates available in Section 3. a timely fashion considering
the complexity of the decision making process for updating
devices, potential re-certification requirements, the length of a
supply chain an update needs to go through before it reaches the
end customer, and the need for user consent to install updates.

- Ensuring an energy efficient design of a battery-powered IoT
devices because a firmware update, particularly writing the
firmware image to flash, is a heavy task for a device.

- Creating incentives for device operators to use a firmware update
mechanism and to demand the integration of it from IoT device
vendors.

- Ensuring that firmware updates addressing critical flaws can be
obtained even after a product is discontinued or a vendor goes out
of business.

This document starts with a terminology followed by the description
of the architecture. We then explain the bootloader and how it
integrates with the firmware update mechanism. Subsequently, we
offer a categorization of IoT devices in terms of their hardware
capabilities relevant for firmware updates. Next, we talk about the
manifest structure and how to use it to secure firmware updates. We
conclude with a more detailed example.

2. Conventions and Terminology

2.1. Terms

This document uses the following terms:

- Manifest: The manifest contains meta-data about the firmware
image. The manifest is protected against modification and
provides information about the author.

- Firmware Image: The firmware image, or image, is a binary that may
contain the complete software of a device or a subset of it. The
firmware image may consist of multiple images, if the device
contains more than one microcontroller. Often it is also a
compressed archive that contains code, configuration data, and
even the entire file system. The image may consist of a
differential update for performance reasons. Firmware is the more
universal term.

The terms, firmware image, firmware, and image, are used in this
document and are interchangeable.

- Software: The terms "software" and "firmware" are used
interchangeably.

- Bootloader: A bootloader is a piece of software that is executed
once a microcontroller has been reset. It is responsible for
deciding whether We use the term application
firmware image to boot differentiate it from a firmware image that is present or
whether to obtain and verify a new
contains the bootloader. An application firmware image. Since image, as the
bootloader is a security critical component its functionality may
be split into separate stages. Such a multi-stage bootloader may
offer very basic functionality in
name indicates, contains the first stage and resides in
ROM whereas application program often including
all the second stage may implement more complex
functionality and resides in flash memory so that necessary code to run it can be
updated in the future (in case bugs have been found). (such as protocol stacks, and
embedded operating system).

- Manifest: The exact
split of components into the different stages, manifest contains meta-data about the number of firmware images stored by an IoT device,
image. The manifest is protected against modification and
provides information about the detailed
functionality varies throughout different implementations. A more
detailed discussion is provided in Section 8. author.

- Microcontroller (MCU for microcontroller unit): An MCU is a
compact integrated circuit designed for use in embedded systems.
A typical microcontroller includes a processor, memory (RAM and
flash), input/output (I/O) ports and other features connected via
some bus on a single chip. The term 'system on chip (SoC)' is
often used for these types of devices.

- System on Chip (SoC): An SoC is an integrated circuit that
integrates all components of a computer, such as CPU, memory,
input/output ports, secondary storage, etc.

- Homogeneous Storage Architecture (HoSA): A device that stores all
firmware components in the same way, for example in a file system
or in flash memory.

- Heterogeneous Storage Architecture (HeSA): A device that stores at
least one firmware component differently from the rest, for
example a device with an external, updatable radio, or a device interchangeably with internal and external flash memory.

- Trusted Execution Environments (TEEs): An execution environment
that runs alongside of, MCU, but is isolated from, an REE. MCU tends to imply more
limited peripheral functions.

- Rich Execution Environment (REE): An environment that is provided
and governed by a typical OS (e.g., Linux, Windows, Android, iOS),
potentially in conjunction with other supporting operating systems
and hypervisors; it is outside of the TEE. This environment and
applications running on it are considered un-trusted.

- System on Chip (SoC): An SoC is an integrated circuit that
contains all components of a computer, such as CPU, memory, input/
output ports, secondary storage, a bus to connect the components,
and other hardware blocks of logic.

- Trust Anchor: A trust anchor, as defined in [RFC6024], represents
an authoritative entity via a public key and associated data. The
public key is used to verify digital signatures, and the
associated data is used to constrain the types of information for
which the trust anchor is authoritative."

- Trust Anchor Store: A trust anchor store, as defined in [RFC6024],
is a set of one or more trust anchors stored in a device. A
device may have more than one trust anchor store, each of which
may be used by one or more applications. A trust anchor store
must resist modification against unauthorized insertion, deletion,
and modification.

- Trusted applications Applications (TAs): An application component that runs in
a TEE.

- Trusted Execution Environments (TEEs): An execution environment
that runs alongside of, but is isolated from, an REE. For more
information about TEEs see [I-D.ietf-teep-architecture].
TEEP requires the use of SUIT for delivering TAs.

2.2. Stakeholders

The following entities stakeholders are used: used in this document:

- Author: The author is the entity that creates the firmware image.
There may be multiple authors involved in a system either when a device
consists of multiple micro-controllers or when the the final producing firmware image consists of software components from multiple
companies.
running on an IoT device. Section 5 talks about those IoT device
deployment cases.

- Firmware Consumer: Device Operator: The firmware consumer device operator is responsible for the recipient day-
to-day operation of a fleet of IoT devices. Customers of IoT
devices, as the
firmware image and owners of IoT devices - such as enterprise
customers or end users, interact with their IoT devices indirectly
through the manifest. It device operator via web or smart phone apps.

- Network Operator: The network operator is responsible for parsing
and verifying the received manifest and for storing the obtained
firmware image. The firmware consumer plays the role
operation of the
update component on the a network to which IoT device typically running devices connect.

- Trust Provisioning Authority (TPA): The TPA distributes trust
anchors and authorization policies to various stakeholders. The
TPA may also delegate rights to stakeholders. For example, in
some cases, the
application firmware. It interacts with the firmware server Original Design Manufacturer (ODM), which is a
company that designs and
with manufactures a product, may act as a TPA
and may decide to remain in full control over the status tracker, if present. firmware update
process of their products.

2.3. Functions

- (IoT) Device: A device refers to the entire IoT product, which
consists of one or many MCUs, sensors and/or actuators. Many IoT
devices sold today contain multiple MCUs and therefore a single
device may need to obtain more than one firmware image and
manifest to succesfully successfully perform an update.

- Status Tracker: The terms device status tracker has a client and
firmware consumer are used interchangably since a server
component and performs three tasks: 1) It communicates the
availability of a new firmware
consumer is one version. This information will
flow from the server to the client.
2) It conveys information about software component running on an MCU on and hardware
characteristics of the device.

- Status Tracker: The status tracker offers device management
functionality information flow is from the
client to retrieve the server.
3) It can remotely trigger the firmware update process. The
information about flow is from the server to the client.

For example, a device operator may want to read the installed
firmware version number running on a the device and other information
about available flash memory. Once an update has been triggered,
the device characteristics (including free
memory and hardware components), operator may want to obtain information about the state
of the firmware update cycle update. If errors occurred, the device is currently in, and operator
may want to trigger troubleshoot problems by first obtaining diagnostic
information (typically using a device management protocol).

We make no assumptions about where the update process. server-side component is
deployed. The deployment of status trackers is flexible and they may
be used as found at
cloud-based servers, on-premise servers,
embedded in edge computing device (such as Internet access
gateways or protocol translation gateways), or even in smart
phones and tablets. IoT devices that self-initiate updates may
run a status tracker. Similarly, IoT devices that act as a proxy
for other IoT devices be embedded in a protocol translation or
edge computing
device node may also run a device. A status tracker. However, tracker server component may even
be deployed on an IoT device. For example, if the IoT device
contains multiple MCUs, then the main MCU may act as a limited status
tracker towards the other MCUs if MCUs. Such deployment is useful when
updates are have to be synchronized across MCUs. How much functionality a

The status tracker includes
depends on may be operated by any suitable stakeholder;
typically the selected configuration Author, Device Operator, or Network Operator.

- Firmware Consumer: The firmware consumer is the recipient of the device management
functionality
firmware image and the communication environment it manifest. It is used in. In
a generic networking environment the protocol used between responsible for parsing
and verifying the
client received manifest and for storing the server-side obtained
firmware image. The firmware consumer plays the role of the status tracker need to deal
update component on the IoT device typically running in the
application firmware. It interacts with
Internet communication challenges involving firewall and NAT
traversal. In other cases, the communication interaction may be
rather simple. This architecture document does not impose
requirements on firmware server and
with the status tracker. tracker client (locally).

- Firmware Server: The firmware server stores firmware images and
manifests and distributes them to IoT devices. Some deployments
may require a store-and-forward concept, which requires storing
the firmware images/manifests on more than one entity before
they reach the device. There is typically some interaction
between the firmware server and the status tracker but those and these two
entities are often physically separated on different devices for
scalability reasons.

- Device Operator: The actor responsible for the day-to-day
operation of Bootloader: A bootloader is a fleet piece of IoT devices.

- Network Operator: The actor software that is executed
once a microcontroller has been reset. It is responsible for the operation of a
network
deciding what code to execute.

3. Architecture

More devices today than ever before are connected to the Internet,
which drives the need for firmware updates to be provided over the
Internet rather than through traditional interfaces, such as USB or
RS-232. Updating updates over the Internet requires the device to
fetch the new firmware image as well as the manifest.

Hence, the following components are necessary on a device for a
firmware update solution:

- the Internet protocol stack for firmware downloads. Because
firmware images are often multiple kilobytes, sometimes exceeding
one hundred kilobytes, in size for low end IoT devices connect. and even
several megabytes large for IoT devices running full-fledged
operating systems like Linux, the protocol mechanism for
retrieving these images needs to offer features like congestion
control, flow control, fragmentation and reassembly, and
mechanisms to resume interrupted or corrupted transfers.

- the capability to write the received firmware image to persistent
storage (most likely flash memory).

- Claim: A piece of information asserted about a recipient manifest parser with code to verify a digital signature or
payload.

In addition a
message authentication code.

- the ability to unpack, to decompress and/or to decrypt the entities
received firmware image.

- (optionally) a status tracker.

The features listed above are most likely offered by code in the list above there is an orthogonal
infrastructure
application firmware image running on the device rather than by the
bootloader itself. Note that cryptographic algorithms will likely
run in a trusted execution environment, on a separate MCU, in a
hardware security module, or in a secure element rather than in the
same context with the application code.

Figure 1 shows the architecture where a Trust Provisioning Authority (TPA) distributing
trust anchors firmware image is created by
an author, and authorization made available to a firmware server. For security
reasons, the author will not have the permissions to various entities in upload firmware
images to the system. The TPA may also delegate rights firmware server and to install, update,
enhance, initiate an update him- or delete trust anchors and authorization permissions
herself. Instead, authors will make firmware images available to
other parties in the system. This infrastructure overlaps the
communication architecture and different deployments may empower
certain entities while other deployments
device operators. Note that there may not. For example, in
some cases, the Original Design Manufacturer (ODM), which is be a
company longer supply chain
involved to pass software updates from the author all the way to the
party that designs and manufactures a product, may act as can then finally make a TPA and
may decide decision to remain deploy it with IoT
devices.

As a first step in full control over the firmware update process
of their products.

The terms 'trust anchor' and 'trust anchor store' are defined in
[RFC6024]:

- "A trust anchor represents an authoritative entity via a public
key and associated data. The public key is used to verify digital
signatures, and process, the associated data is used status tracker
client need to constrain the types be made aware of information for which the trust anchor is authoritative."

- "A trust anchor store is a set availability of one or more trust anchors stored
in a device. A device may have more than one trust anchor store,
each of which may be used new firmware
update by one the status tracker server. This can be accomplished via
polling (client-initiated), push notifications (server-initiated), or
more applications." A trust
anchor store must resist modification against unauthorized
insertion, deletion, complex mechanisms (such as a hybrid approach):

- Client-initiated updates take the form of a status tracker client
proactively checking (polling) for updates.

- With Server-initiated updates the server-side component of the
status tracker learns about a new firmware version and modification.

3. Requirements

The determines
what devices qualify for a firmware update mechanism described in this specification was
designed with update. Once the relevant
devices have been selected, the status tracker informs these
devices and the following requirements in mind:

- Agnostic to how firmware consumers obtain those images and
manifests. Server-initiated updates are distributed

- Friendly important because they
allow a quick response time. Note that the client-side status
tracker needs to broadcast delivery

- Use state-of-the-art security mechanisms

- Rollback attacks must be prevented

- High reliability

- Operate with a small bootloader

- Small Parsers

- Minimal impact reachable by the server-side component. This
may require devices to keep reachability information on existing firmware formats

- Robust permissions the
server-side up-to-date and state at NATs and stateful packet
filtering firewalls alive.

- Diverse modes Using a hybrid approach the server-side of operation

- Suitability the status tracker
pushes notifications of availability of an update to software the client
side and personalization data

3.1. Agnostic requests the firmware consumer to how pull the manifest and
the firmware images image from the firmware server.

Once the device operator triggers update via the status tracker, it
will keep track of the update process on the device. This allows the
device operator to know what devices have received an update and
which of them are distributed still pending an update.

Firmware images can be conveyed to devices in a variety of ways,
including USB, UART, WiFi, BLE, low-power WAN technologies, etc. mesh
networks and
use different many more. At the application layer a variety of
protocols (e.g., are also available: MQTT, CoAP, HTTP). The specified mechanism
needs to be agnostic to and HTTP are the distribution of most
popular application layer protocols used by IoT devices. This
architecture does not make assumptions about how the firmware images
are distributed to the devices and
manifests.

3.2. Friendly therefore aims to support all
these technologies.

In some cases it may be desirable to distribute firmware images using
a multicast or broadcast delivery protocol. This architecture does not specify make
recommendations for any specific broadcast such protocol. However, given that broadcast
may be desirable for some networks, updates must cause the least
disruption possible both in metadata and firmware transmission. For
an update to be broadcast friendly, it cannot rely on link layer,
network layer, or transport layer security. A solution has to rely
on security protection applied to the manifest and firmware image
instead. In addition, the same manifest must be deliverable to many
devices, both those to which it applies and those to which it does
not, without a chance that the wrong device will accept the update.
Considerations that apply to network broadcasts apply equally to the
use of third-party content distribution networks for payload
distribution.

3.3. Use state-of-the-art security mechanisms

End-to-end security between the author and the device is shown in
Section 5.

Authentication ensures that the device can cryptographically identify
the author(s) creating firmware

+----------+
| |
| Author |
| |
+----------+
Firmware + Manifest |
+----------------------------------+ | Firmware +
| | | Manifest
| ---+------- |
| ---- | --|-
| //+----------+ | \\
-+-- // | | | \
----/ | ---- |/ | Firmware |<-+ | \
// | \\ | | Server | | | \
/ | \ / | | + + \
/ | \ / +----------+ \ / |
/ +--------+--------+ \ / | |
/ | v | \ / v |
| | +------------+ | | | +----------------+ |
| | | Firmware | | | Device | |
| | | Consumer | | | | | Management | |
| | +------------+ | | | | | |
| | +------------+ | | | | +--------+ | |
| | | Status |<-+--------------------+-> | | | |
| | | Tracker | | | | | | Status | | |
| | | Client | | | | | | Tracker| | |
| | +------------+ | | | | | Server | | |
| | Device | | | | +--------+ | |
| +-----------------+ | \ | | /
\ / \ +----------------+ /
\ Network / \ /
\ Operator / \ Device Operator /
\\ // \ \ //
---- ---- ---- ----
----- -----------

Figure 1: Architecture.

Firmware images and manifests. Authenticated
identities manifests may be used conveyed as input to the authorization process.

Integrity protection ensures that no third party can modify the
manifest or the firmware image.

For confidentiality protection of the firmware image, it must be done
in such a way that every intended recipient can decrypt it. bundle or
detached. The
information that is encrypted individually for each device must
maintain friendliness to Content Distribution Networks, bulk storage,
and broadcast protocols.

A manifest specification must support different cryptographic
algorithms and algorithm extensibility. Due of the nature of
unchangeable code in ROM for use with bootloaders the use of post-
quantum secure signature mechanisms, such both approaches.

For distribution as hash-based signatures
[RFC8778], are attractive. These algorithms maintain security in
presence of quantum computers.

A mandatory-to-implement set of algorithms will be specified in the
manifest specification [I-D.ietf-suit-manifest]}.

3.4. Rollback attacks must be prevented

A device presented with an old, but valid manifest and firmware must
not be tricked into installing such firmware since a vulnerability in bundle, the old firmware image may allow an attacker to gain control of the
device.

3.5. High reliability

A power failure at any time must not cause a failure of the device.
Equally, adverse network conditions during an update must not cause
the failure of the device. A failure to validate any part of an
update must not cause a failure of the device. One way to achieve
this functionality is to provide a minimum of two storage locations
for firmware and one bootable location for firmware. An alternative
approach is to use a 2nd stage bootloader with build-in full featured
firmware update functionality such that it is possible to return to
the update process after power down.

Note: This is an implementation requirement rather than a requirement
on the manifest format.

3.6. Operate with a small bootloader

Throughout this document we assume that the bootloader itself is
distinct from the role of the firmware consumer and therefore does
not manage embedded into the firmware update process.
manifest. This may give the impression
that the bootloader itself is a completely separate component, which
is mainly responsible useful approach for selecting a firmware image deployments where devices
are not connected to boot.

The overlap between the firmware update process Internet and the bootloader
functionality comes in two forms, namely

- First, cannot contact a bootloader must verify the firmware image it boots as
part of the secure boot process. Doing so requires meta-data to
be stored alongside the firmware image so that the bootloader can
cryptographically verify the dedicated
firmware image before booting it to
ensure it has not been tampered with or replaced. This meta-data
used by the bootloader may well be the same manifest obtained with server for the firmware image during the update process (with the severable
fields stripped off).

- Second, an IoT device needs a recovery strategy in case download. It is also applicable
when the firmware update / boot process fails. The recovery strategy may
include storing two or more firmware images on the device or
offering the ability to have happens via a second stage bootloader perform the
firmware update process again using firmware updates over serial, USB sticks or even wireless connectivity like a limited version of short range
radio technologies (such as Bluetooth Smart. In the latter case the firmware consumer
functionality is contained in the second stage bootloader and
requires the necessary functionality for executing the firmware
update process, including manifest parsing.

In general, it is assumed that the bootloader itself, or a minimal
part of it, will not be updated since a failed update of the
bootloader poses a risk in reliability.

All information necessary for a device to make a decision about the
installation of a firmware update must fit into the available RAM of
a constrained IoT device. This prevents flash write exhaustion.
This is typically not a difficult requirement to accomplish because
there are not other task/processing running while the bootloader is
active (unlike it may be the case when running the application
firmware).

Note: This is an implementation requirement.

3.7. Small Parsers

Since parsers are known sources of bugs, any parsers used to process Smart).

Alternatively, the manifest must be minimal. Additionally, it must be easy to parse
only those fields that are required to validate at least one
signature or MAC with minimal exposure.

3.8. Minimal impact on existing firmware formats

The design of the firmware update mechanism must not require changes
to existing firmware formats.

3.9. Robust permissions

When a device obtains a monolithic firmware image from a single
author without any additional approval steps then the authorization
flow is relatively simple. There are, however, other cases where
more complex policy decisions need to be made before updating a
device.

In this architecture the authorization policy is separated from the
underlying communication architecture. This is accomplished by
separating the entities distributed detached from their permissions. For example, an
author may not have the authority to install a firmware image on a
device in critical infrastructure without the authorization of a
device operator. In
image. Using this case, the device may be programmed to
reject firmware updates unless they are signed both by approach, the firmware
author and by the device operator.

Alternatively, a device may trust precisely one entity, which does
all permission management and coordination. This entity allows the
device to offload complex permissions calculations for the device.

3.10. Operating modes

There are three broad classifications of update operating modes.

- Client-initiated Update

- Server-initiated Update

- Hybrid Update

Client-initiated updates take the form of a firmware consumer on a
device proactively checking (polling) for new firmware images.

Server-initiated updates are important to consider because timing of
updates may need to be tightly controlled in some high- reliability
environments. In this case the status tracker determines what
devices qualify for a firmware update. Once those devices have been
selected the firmware server distributes updates to the firmware
consumers.

Note: This assumes that the status tracker is able to reach the
device, which may require devices to keep reachability information at
the status tracker up-to-date. This may also require keeping state
at NATs and stateful packet filtering firewalls alive.

Hybrid updates are those that require an interaction between the
firmware consumer and the status tracker. The status tracker pushes
notifications of availability of an update to presented with
the firmware consumer, manifest first and it then downloads the image from a needs to obtain one or more firmware server as soon as
possible.

While these broad classifications encompass the majority of operating
modes, some may not be covered in these classifications. By
reinterpreting these modes as a set of operations performed by the
system
images as a whole, all operating modes can be represented.

The steps performed dictated in the course of an update by the system
containing an updatable device are:

- Notification

- Pre-authorisation

- Dependency resolution
- Download

- Installation

This is a coarse-grained high level view of steps required to install
a new firmware. By considering where in the system each of these
steps is performed, each operating mode can be represented. Each of
these steps is broken down into smaller constituent parts. Section 5
defines the steps taken from the perspective of the communication
between actors in the system. Section 8 describes some additional
steps that a bootloader takes in addition to those described here.
Section 9 shows an example of the steps undertaken by each party in
the course of an update.

The notification step consists of the status tracker informing the
firmware consumer that an update is available. This can be
accomplished via polling (client-initiated), push notifications
(server-initiated), or more complex mechanisms. manifest.

The pre-authorisation step involves verifying whether the entity
signing the manifest is indeed authorized to perform an update. The
firmware consumer must also determine whether it should fetch and
process a firmware image, which is referenced in a manifest.

A dependency resolution phase is needed when more than one component
can be updated or when a differential update is used. The necessary
dependencies must be available prior to installation.

The download step is the process of acquiring a local copy of the
firmware image. When the download is client-initiated, this means
that the firmware consumer chooses when a download occurs and
initiates the download process. When a download is server-initiated,
this means that the status tracker tells the device when to download
or that it initiates the transfer directly to the firmware consumer.
For example, a download from an HTTP-based HTTP/1.1-based firmware server is client-
initiated.
client-initiated. Pushing a manifest and firmware image to the transfer to
the
Package resource of the LwM2M Firmware Update object [LwM2M] is
server-initiated.
server-initiated update.

If the firmware consumer has downloaded a new firmware image and is
ready to install it, to initiate the installation, it may - either
need to wait for a trigger from the status tracker to initiate the installation, may tracker, - or trigger the
update automatically, - or may go through a more complex decision making
process to determine the appropriate timing for an update (such as
delaying update. Sometimes
the update process to a later time when end users are less
impacted by final decision may require confirmation of the update process). user of the device
for safety reasons.

Installation is the act of processing the payload into a format that
the IoT device can recognise recognize and the bootloader is responsible for
then booting from the newly installed firmware image.

Each of these steps may require This process
is different permissions.

3.11. Suitability to software and personalization data

The work on a standardized manifest format initially focused on the
most constrained IoT devices and those devices contain code put
together by when a single author (although that author may obtain code
from other developers, some of it only bootloader is not involved. For example, when an
application is updated in binary form).

Later it turns out that other use cases may benefit from a
standardized manifest format also for conveying software full-featured operating system, the
updater may halt and even
personalization data alongside software. Trusted Execution
Environments (TEEs), for example, greatly benefit from restart the application in isolation. Devices
must not fail when a protocol for
managing disruption occurs during the lifecycle of trusted applications (TAs) running inside update process.
For example, a
TEE. TEEs may obtain TAs from different authors and those TAs may
require personalization data, such as payment information, to be
securely conveyed to power failure or network disruption during the TEE.

To support this wider range of use cases update
process must not cause the manifest format should
therefore be extensible device to convey other forms of payloads as well. fail.

4. Claims

The information conveyed from an Author to a Invoking the Firmware Consumer can be
considered to be Claims as described in [RFC7519] and [RFC8392]. The
same security considerations apply to

Section 3 describes the Claims expressed in steps for getting the
manifest. The chief difference between manifest Claims firmware image and CWT or
JWT claims is that a manifest has multiple subjects. The manifest
contains:

1. Claims about the Firmware, including its dependencies

2. Claims about the Firmware Consumer's physical or software
properties

3. Claims about the Author, or
manifest from the Author's delegate

The credential used to authenticate these Claims must be directly or
indirectly related author to the trust anchor installed at firmware consumer on the device by IoT device.
Once the
Trust Provisioning Authority.

The baseline claims for all manifests are described in
[I-D.ietf-suit-information-model].

5. Communication Architecture

Figure 1 shows firmware consumer has retrieved and successfully processed
the manifest and the communication architecture where a firmware image it needs to invoke the new
firmware image. This is created by an author, and uploaded managed in many different ways, depending on
the type of device, but it typically involves halting the current
version of the firmware, handing control over to a firmware server. The with a
higher privilege/trust level (the firmware image/manifest verifier) verifying the
new firmware's authenticity & integrity, and then invoking it.

In an execute-in-place microcontroller, this is distributed often done by
rebooting into a bootloader (simultaneously halting the application &
handing over to the device either in higher privilege level) then executing a push secure
boot process (verifying and invoking the new image).

In a rich OS, this may be done by halting one or pull manner using more processes, then
invoking new applications. In some OSs, this implicitly involves the firmware consumer residing
kernel verifying the code signatures on the device. new applications.

The device operator keeps track of the invocation process using the status
tracker. This allows is security sensitive. An attacker will
typically try to retrieve a firmware image from the device operator for
reverse engineering or will try to know and control what
devices have received an update and which of them are still pending get the firmware verifier to
execute an update.

Firmware + +----------+ Firmware + +-----------+
Manifest | |-+ Manifest | |-+
+--------->| Firmware | |<---------------| | |
| | Server | | | Author | |
| | | | | | |
| +----------+ | +-----------+ |
| +----------+ +-----------+
|
|
|
-+-- ------
---- | ---- ---- ----
// | \\ // \\
/ | \ / \
/ | \ / \
/ | \ / \
/ | \ / \
| v | | |
| +------------+ |
| | Firmware | | | |
| | Consumer | | Device | +--------+ |
| +------------+ | Management| | | |
| | |<------------------------->| Status | |
| | Device | | | | Tracker| |
| +------------+ | || | | |
| | || +--------+ |
| | | |
| | \ /
\ / \ /
\ / \ Device /
\ Network / \ Operator /
\ Operator / \\ //
\\ // ---- ----
---- ---- ------
-----

Figure 1: Architecture.

End-to-end security mechanisms are used attacker-modified firmware image. The firmware verifier
will therefore have to protect perform security checks on the firmware image
and the manifest although Figure 2 does not show the manifest itself
since
before it may can be distributed independently.

+-----------+
+--------+ | | +--------+
| | Firmware Image | Firmware | Firmware Image | |
| Device |<-----------------| Server |<------------------| Author |
| | | | | |
+--------+ +-----------+ +--------+
^ *
* *
************************************************************
End-to-End Security

Figure 2: End-to-End Security.

Whether invoked. These security checks by the firmware
verifier happen in addition to the security checks that took place
when the firmware image and the manifest is pushed to the device
or fetched were downloaded by the device is a deployment specific decision.
firmware consumer.

The following assumptions are made to allow overlap between the firmware consumer to
verify and the received firmware image and manifest before updating
software: verifier
functionality comes in two forms, namely

- To accept an update, a device needs to A firmware verifier must verify the signature
covering firmware image it boots as
part of the manifest. There may be one or multiple manifests
that need to be validated, potentially signed by different
parties. The device needs secure boot process. Doing so requires meta-data to
be in possession of stored alongside the trust
anchors to firmware image so that the firmware
verifier can cryptographically verify those signatures. Installing trust anchors to
devices via the Trust Provisioning Authority happens in an out-of-
band fashion prior firmware image before
booting it to ensure it has not been tampered with or replaced.
This meta-data used by the firmware verifier may well be the same
manifest obtained with the firmware image during the update
process.

- Not all entities creating and signing manifests have the same
permissions. A An IoT device needs a recovery strategy in case the firmware
update / invocation process fails. The recovery strategy may
include storing two or more application firmware images on the
device or offering the ability to determine whether invoke a recovery image to
perform the requested
action firmware update process again using firmware updates
over serial, USB or even wireless connectivity like Bluetooth
Smart. In the latter case the firmware consumer functionality is indeed covered by
contained in the permission of recovery image and requires the party that
signed necessary
functionality for executing the manifest. Informing firmware update process, including
manifest parsing.

While this document assumes that the device about firmware verifier itself is
distinct from the permissions role of the different parties also happens in an out-of-band fashion firmware consumer and therefore does
not manage the firmware update process, this is also not a duty of requirement and
these roles may be combined in practice.

Using a bootloader as the Trust Provisioning Authority.

- For confidentiality protection of firmware images verifier requires some special
considerations, particularly when the author needs
to be bootloader implements the
robustness requirements identified by the IOTSU workshop [RFC8240].

4.1. The Bootloader

In most cases the MCU must restart in possession of order to hand over control to
the certificate/public key or bootloader. Once the MCU has initiated a pre-shared
key of restart, the bootloader
determines whether a device. The use of confidentiality protection of newly available firmware images image should be
executed. If the bootloader concludes that the newly available
firmware image is deployment specific. invalid, a recovery strategy is necessary. There
are different types only two approaches recovering from an invalid firmware: either
the bootloader must be able to select a different, valid firmware, or
it must be able to obtain a new, valid firmware. Both of delivery modes, which these
approaches have implications for the architecture of the update
system.

Assuming the first approach, there are illustrated
based (at least) three firmware
images available on examples below.

There the device:

- First, the bootloader is an option for embedding also firmware. If a bootloader is
updatable then its firmware image into a manifest.
This is a useful approach for deployments where devices are not
connected to the Internet and cannot contact a dedicated treated like any other
application firmware
server for image.

- Second, the firmware download. It image that has to be replaced is also applicable when the
firmware update happens via a USB stick or via Bluetooth Smart.
Figure 3 shows this delivery mode graphically.

Figure 3: Manifest with attached firmware.

Figure 4 shows an option for remotely updating a device where still
available on the device fetches as a backup in case the freshly downloaded
firmware image from some file server. The
manifest itself does not boot or operate correctly.

- Third, there is delivered independently and provides information
about the newly downloaded firmware image(s) image.

Therefore, the firmware consumer must know where to download.

/--------\ /--------\
/ \ / \
| Manifest | | Manifest |
\ / \ /
\--------/ \--------/
+-----------+
+--------+ | | +--------+
| |<.................| Status |................>| |
| Device | | Tracker | -- | Author |
| |<- | | --- | |
+--------+ -- +-----------+ --- +--------+
-- ---
--- ---
-- +-----------+ --
-- | | --
/------------\ -- | Firmware |<- /------------\
/ \ -- | Server | / \
| Firmware | | | | Firmware |
\ / +-----------+ \ /
\------------/ \------------/

Figure 4: Independent retrieval of store the new
firmware. In some cases, this may be implicit, for example replacing
the least-recently-used firmware image.

This architecture does not mandate a specific delivery mode but a
solution must support both types.

6. Manifest In order other cases, the storage
location of the new firmware must be explicit, for example when a
device has one or more application firmware images and a recovery
image with limited functionality, sufficient only to apply perform an update, it has
update.

Since many low end IoT devices use non-relocatable code, either the
bootloader needs to make several
decisions about copy the update:

- Does it trust newly downloaded application firmware
image into the author location of the update?

- Has the old application firmware been corrupted?

- Does image and
vice versa or multiple versions of the firmware update apply need to this device?

- Is be prepared
for different locations.

In general, it is assumed that the bootloader itself, or a minimal
part of it, will not be updated since a failed update older than the active firmware?

- When should of the device apply
bootloader poses a reliability risk.

For a bootloader to offer a secure boot functionality it needs to
implement the update? following functionality:

- How should the device apply The bootloader needs to fetch the update?

- What kind of firmware binary is it? manifest (or manifest-alike
headers) from nonvolatile storage and parse its contents for
subsequent cryptographic verification.

- Where should the update Cryptographic libraries with hash functions, digital signatures
(for asymmetric crypto), keyed message digests (for symmetric
crypto) need to be obtained? accessible.

- Where should the firmware be stored? The manifest encodes device needs to have a trust anchor store to verify the information that devices need in order
digital signature. (Alternatively, access to
make these decisions. It is a data structure that contains key store for use
with the
following information: keyed message digest.)

- information about the device(s) Ability to expose boot process-related data to the application
firmware image is intended (such as to
be applied to,

- information about when the firmware update has status tracker). This allows to be applied,

- share
information about when the manifest was created,

- dependencies on other manifests,

- pointers to the current firmware image version, and information about the format,

- information about where to store status of
the firmware image, update process and whether errors have occurred.

- cryptographic information, such Produce boot measurements as digital signatures or message
authentication codes (MACs).

The manifest information model is described in
[I-D.ietf-suit-information-model].

7. Device Firmware Update Examples

Although these documents attempt part of an attestation solution. See
[I-D.ietf-rats-architecture] for more information. (optional)

- Ability to define decrypt firmware images, in case confidentiality
protection was applied). This requires a solution for key
management. (optional)

5. Types of IoT Devices

There are billions of MCUs used in devices today produced by a large
number of silicon manufacturers. While MCUs can vary significantly
in their characteristics, there are a number of similiaries allowing
us to categorize in groups.

The firmware update
architecture that is applicable architecture, and the manifest format in
particular, needs to both existing systems, as well as
yet-to-be-conceived systems; it is still helpful offer enough flexibility to consider existing
architectures.

7.1. cover these common
deployment cases.

5.1. Single CPU SoC MCU

The simplest, and currently most common, architecture consists of a
single MCU along with its own peripherals. These SoCs generally
contain some amount of flash memory for code and fixed data, as well
as RAM for working storage. These systems either have a single
firmware image, or an immutable bootloader that runs a single image. A notable characteristic of these SoCs
is that the primary code is generally execute in place (XIP). Combined with Due to
the non-relocatable nature of the code, the firmware updates need image needs to
be done placed in a specific location in place.

7.2. flash since the code cannot be
executed from an arbitrary location in flash. Hence, then the
firmware image is updated it is necessary to swap the old and the new
image.

5.2. Single CPU with Secure - Normal Mode Partitioning

Another configuration consists of a similar architecture to the
previous, with a single CPU. However, this CPU supports a security
partitioning scheme that allows memory (in addition to other things)
to be divided into secure and normal mode. There will generally be
two images, one for secure mode, and one for normal mode. In this
configuration, firmware upgrades will generally be done by the CPU in
secure mode, which is able to write to both areas of the flash
device. In addition, there are requirements to be able to update
either image independently, as well as to update them together
atomically, as specified in the associated manifests.

7.3.

5.3. Symmetric Multiple CPUs

In more complex SoCs with symmetric multi-processing support,
advanced operating systems, such as Linux, are often used. These
SoCs frequently use an external storage medium medium, such as raw NAND
flash or eMMC. Due to the higher quantity of resources, these
devices are often capable of storing multiple copies of their
firmware images and selecting the most appropriate one to boot. Many
SoCs also support bootloaders that are capable of updating the
firmware image, however this is typically a last resort because it
requires the device to be held in the bootloader while the new
firmware is downloaded and installed, which results in down-time for
the device. Firmware updates in this class of device are typically
not done in-place.

7.4.

5.4. Dual CPU, shared memory

This configuration has two or more heterogeneous CPUs in a single SoC
that share memory (flash and RAM). Generally, they there will be a
protection
mechanism to prevent one CPU from unintentionally accessing memory
currently allocated to the other's
memory. other. Upgrades in this case will
typically be done by one of the CPUs, and is similar to the single
CPU with secure mode.

7.5.

5.5. Dual CPU, other bus

This configuration has two or more heterogeneous CPUs, each having
their own memory. There will be a communication channel between
them, but it will be used as a peripheral, not via shared memory. In
this case, each CPU will have to be responsible for its own firmware
upgrade. It is likely that one of the CPUs will be considered the
primary CPU, and will direct the other CPU to do the upgrade. This
configuration is commonly used to offload specific work to other
CPUs. Firmware dependencies are similar to the other solutions
above, sometimes allowing only one image to be upgraded, other times
requiring several to be upgraded atomically. Because the updates are
happening on multiple CPUs, upgrading the two images atomically is
challenging.

8. Bootloader

More devices today than ever before are being connected

6. Manifests

In order for a firmware consumer to apply an update, it has to make
several decisions using manifest-provided information and data
available on the
Internet, device itself. For more detailed information and a
longer list of information elements in the manifest consult the
information model specification [I-D.ietf-suit-information-model],
which drives offers justifications for each element, and the need manifest, see
[I-D.ietf-suit-manifest], for firmware updates details about how this information is
included in the manifest.

Table 1 provides examples of decisions to be provided
over made.

+----------------------------+--------------------------------------+
| Decision | Information Elements |
+----------------------------+--------------------------------------+
| Should I trust the Internet rather than through traditional interfaces, such as
USB or RS232. Updating a device over author | Trust anchors and authorization |
| of the Internet requires firmware? | policies on the device to fetch not only |
| | |
| Has the firmware image but also been | Digital signature and MAC covering |
| corrupted? | the manifest.
Hence, firmware image |
| | |
| Does the following building blocks are necessary for a firmware update solution:

- update older than | Sequence number in the capability to write manifest (1) |
| the received firmware image to persistent
storage (most likely flash memory) prior to performing active firmware? | |
| | |
| When should the update,

- device | Manifest commands |
| apply the features update? | |
| | |
| What kind of firmware | Unpack algorithms to verify an image and interpret a manifest, including digital
signature verification or checking a message authentication code,

Table 1: Firmware Update Decisions.

(1): A device presented with an old, but valid manifest and firmware
must not be tricked into installing such firmware since a device management server to
perform automatic
vulnerability in the old firmware updates and image may allow an attacker to track their progress.

(*) Because firmware images are often multiple kilobytes, sometimes
exceeding one hundred kilobytes, in gain
control of the device.

Keeping the code size for low end IoT devices and
even several megabytes large complexity of a manifest parsers small is
important for constrained IoT devices running full-fledged
operating systems like Linux, devices. Since the protocol mechanism for retrieving
these images needs to offer features like congestion control, flow
control, fragmentation and reassembly, and mechanisms to resume
interrupted or corrupted transfers.

All these features are most likely offered manifest parsing
code may also be used by the application, i.e. bootloader it is part of the trusted
computing base.

A manifest may not only be used to protect firmware consumer, running on images but also
configuration data such as network credentials or personalization
data related to firmware or software. Personalization data
demonstrates the device (except need for basic security
algorithms that may run either on a trusted execution environment mutually-distrustful delivery of two or
on
more images into a separate hardware security MCU/module) rather than by device. Personalization data is used with Trusted
Execution Environments (TEEs), which benefit from a protocol for
managing the
bootloader itself.

Once manifests have been processed and firmware images successfully
downloaded lifecycle of trusted applications (TAs) running inside a
TEE. TEEs may obtain TAs from different authors and verified the device needs those TAs may
require personalization data, such as payment information, to hand control over be
securely conveyed to the
bootloader. In most cases this requires the MCU TEE. The TA's author does not want to restart. Once
expose the MCU has initiated a restart, TA to the bootloader takes over control user, and determines whether the newly downloaded firmware image should be
executed.

The boot process is security sensitive because the firmware images
may, for example, be stored in off-chip flash memory giving attackers
easy access user does not want to expose the image for reverse engineering and potentially also
for modifying the binary. The bootloader will therefore have
payment information to
perform security checks on the TA's author.

7. Securing Firmware Updates

Using firmware image before it can be
booted. These updates to fix vulnerabilities in devices is important
but securing this update mechanism is equally important since
security checks problems are exacerbated by the bootloader happen update mechanism: update is
essentially authorized remote code execution, so any security
problems in addition the update process expose that remote code execution
system. Failure to secure the firmware update process will help
attackers to take control over devices.

End-to-end security checks that happened when mechanisms are used to protect the firmware image
and the
manifest were downloaded. manifest. The manifest may have been stored alongside following assumptions are made to allow the
firmware image consumer to
allow re-verification of verify the received firmware image during every boot
attempt. Alternatively, secure boot-specific meta-data may have been
created by and manifest
before updating software:

- Authentication ensures that the application after a successful device can cryptographically
identify the author(s) creating firmware download images and
verification process. Whether manifests.
Authenticated identities may be used as input to re-use the standardized manifest
format that was used during authorization
process. Not all entities creating and signing manifests have the initial firmware retrieval process or
same permissions. A device needs to determine whether it the
requested action is better to use a different format for indeed covered by the secure boot-
specific meta-data depends on permission of the system design. The manifest format
does, however, have party
that signed the capability to serve manifest. Informing the device about the
permissions of the different parties also happens in an out-of-
band fashion and is also as a building block
for secure boot with its severable elements that allow shrinking the
size duty of the manifest by stripping elements Trust Provisioning
Authority.

- Integrity protection ensures that are no longer needed.

In order third party can modify the
manifest or the firmware image. To accept an update, a device
needs to satisfy verify the reliability requirements defined in
Section 3.5, devices must always signature covering the manifest. There may be able
one or multiple manifests that need to return be validated, potentially
signed by different parties. The device needs to a working
firmware image. This has implications for the design be in possession
of the
bootloader: If trust anchors to verify those signatures. Installing trust
anchors to devices via the firmware image contains Trust Provisioning Authority happens in
an out-of-band fashion prior to the firmware consumer
functionality, as described above, then update process.

- For confidentiality protection of the bootloader firmware image, it must be able
to roll back to
done in such a working way that the intended firmware image. Alternatively, consumer(s), other
authorized parties, and no one else can decrypt it. The
information that is encrypted individually for each device/
recipient must maintain friendliness to Content Distribution
Networks, bulk storage, and broadcast protocols. For
confidentiality protection of firmware images the
bootloader may have enough functionality author needs to fetch
be in possession of the certificate/public key or a firmware image
plus manifest from pre-shared key
of a device. The use of confidentiality protection of firmware server over the Internet.
images is optional.

A multi-
stage bootloader manifest specification must support different cryptographic
algorithms and algorithm extensibility. Moreover, since RSA- and
ECC-based signature schemes may soften this requirement at become vulnerable to quantum-
accelerated key extraction in the expense of a more
sophisticated boot process.

For a future, unchangeable bootloader
code in ROM is recommended to offer a use post-quantum secure boot mechanism it needs to provide
the following features:

- ability to access security algorithms, signature
schemes such as SHA-256 hash-based signatures [RFC8778]. A bootloader author
must carefully consider the service lifetime of their product and the
time horizon for quantum-accelerated key extraction. The worst-case
estimate, at time of writing, for the time horizon to compute key extraction
with quantum acceleration is approximately 2030, based on current
research [quantum-factorization].

When a fingerprint over the device obtains a monolithic firmware image and from a digital signature
algorithm.

- access keying material directly or indirectly to utilize single
author without any additional approval steps then the
digital signature. The device needs authorization
flow is relatively simple. There are, however, other cases where
more complex policy decisions need to have be made before updating a trust anchor store.

- ability to expose boot process-related data to
device.

In this architecture the application
firmware (such as to authorization policy is separated from the device management software).
underlying communication architecture. This allows
a device management server to determine whether is accomplished by
separating the firmware
update has been successful and, if not, what errors occurred.

- entities from their permissions. For example, an
author may not have the authority to (optionally) offer attestation information (such as
measurements).

While install a firmware image on a
device in critical infrastructure without the software architecture authorization of a
device operator. In this case, the bootloader and its security
mechanisms are implementation-specific, the manifest can device may be used programmed to
control
reject firmware updates unless they are signed both by the firmware download from
author and by the Internet in addition device operator.

Alternatively, a device may trust precisely one entity, which does
all permission management and coordination. This entity allows the
device to
augmenting secure boot process. These building blocks are highly
relevant offload complex permissions calculations for the design of the manifest.

9. device.

8. Example

Figure 5 2 illustrates an example message flow for distributing a
firmware image to a device starting with an author uploading the new
firmware to firmware server and creating a manifest. device. The firmware and manifest are stored on
the same firmware server. This setup does
not use a status tracker server and the firmware consumer component is
therefore responsible for periodically checking whether distributed in a new
firmware image is available for download. detached manner.

+--------+ +-----------------+ +------------+ +----------+
| | +-----------------------------+
| | | Firmware Server | | IoT Device |
| Author | | Firmware Status Tracker | | +------------+ +----------+ |
+--------+ | Server | | Consumer | Firmware | |Bootloader|
+--------+ |
| +-----------------+ | | Consumer | | | |
| | | +------------+ +----------+ |
| | + | | | |
| | | +-----------------------+ |
| Create Firmware | | |
|--------------+ Status Tracker Client | |
|--------------+ | | +-----------------------+ |
| | | `''''''''''''''''''''''''''''
|<-------------+ | | | |
| | | | |
| Upload Firmware | | | |
|------------------>| | | |
| | | | |
| Create Manifest | | | |
|---------------+ | | | |
| | | | | |
|<--------------+ | | | |
| | | | |
| Sign Manifest | | | |
|-------------+ | | | |
| | | | | |
|<------------+ | | | |
| | | | |
| Upload Manifest | | | |
|------------------>| Notification of | | |
| | new firmware image | | |
| |----------------------------->| |
| | | | |
| | |Initiate| |
| | | Update | |
| | |<-------| |
| | | | |
| | Query Manifest | | |
| |<--------------------| . |
| | | . |
| | Send Manifest | . |
| |-------------------->| . |
| | | Validate |
| | | Manifest |
| | |---------+ |--------+ |
| | | | |
| | |<--------+ |<-------+ |
| | | . |
| | Request Firmware | . |
| |<--------------------| . |
| | | . |
| | Send Firmware | . |
| |-------------------->| . |
| | | Verify . |
| | | Firmware |
| | |--------------+ |--------+ |
| | | | |
| | |<-------------+ |<-------+ |
| | | . |
| | | Store . |
| | | Firmware |
| | |-------------+ |--------+ |
| | | | |
| | |<------------+ |<-------+ |
| | | . |
| | | . |
| | | . |
| | | | |
| | | Update | |
| | |Complete| |
| | |------->| |
| | | |
| | Firmware Update Completed | |
| |<-----------------------------| |
| | | |
| | Trigger Reboot | |
| |--------------->| |----------------------------->| |
| | | | |
| | | | |
| | |Reboot |
| | | |------>|
| | | | |
| | | . |
| | +---+----------------+--+
| | S| | | |
| | E| | Verify | |
| | C| | Firmware | |
| | U| | +--------------| |
| | R| | | | |
| | E| | +------------->| |
| | | | | |
| | B| | Activate new | |
| | O| | Firmware | |
| | O| | +--------------| |
| | T| | | | |
| | | | +------------->| |
| | P| | | |
| | R| | Boot new | |
| | O| | Firmware | |
| | C| | +--------------| |
| | E| | | | |
| | S| | +------------->| |
| | S| | | |
| | +---+----------------+--+
| | | . |
| | | | |
| | . | |
| | Device running new firmware | |
| |<-----------------------------| |
| | . | |
| | | |

Figure 5: 2: First Example Flow for a Firmware Upate. Update.

Figure 6 3 shows an example follow with the device using a status
tracker. For editorial reasons the author publishing the manifest at
the status tracker and the firmware image at the firmware server is
not shown. Also omitted is the secure boot process following the
successful firmware update process.

The exchange that starts with the device interacting with the status
tracker; the details of such exchange will vary with the different
device management systems being used. In any case, the status tracker learns about the firmware version of the devices it manages.
In our example,
querying the device under management is using for its current firmware version
A.B.C. At a later point in time the author uploads version. Later, a new
firmware
along with the manifest to the firmware server version becomes available and since this device is running
an older version the status
tracker, respectively. While there is no need to store tracker server interacts with the device
to initiate an update.

The manifest and the firmware are stored on different servers this example shows a common
pattern used in the industry. The status tracker may then
automatically, based on human intervention or based on a more complex
policy decide to inform this
example. When the device about the newly available firmware
image. In our example, it does so by pushing processes the manifest it learns where to
download the new firmware consumer. version. The firmware consumer downloads
the firmware image with the newer version X.Y.Z after successful
validation of the manifest. Subsequently, a reboot is initiated and
the secure boot process starts. Finally, the device reports the
successful boot of the new firmware version.

+---------+ +-----------------+ +-----------------------------+
| Status | | Firmware Server | | +------------+ +----------+ |
| Tracker | | Firmware Server Status Tracker | | | Firmware | |Bootloader| |
| Server | | Server | | | Consumer | | | |
+---------+ +-----------------+ | +------------+ | +Status | +----------+ |
| | | | Tracker | | |
| | | | Client | | |
| | | +------------+ | |
| | | | IoT Device | |
| | `''''''''''''''''''''''''''''
| | | |
| Query Firmware Version | |
|------------------------------------->| |
| Firmware Version A.B.C | |
|<-------------------------------------| |
| | | |
| <<some time later>> | |
| | | |
_,...._ _,...._ | |
,' `. ,' `. | |
| New | | New | | |
\ Manifest / \ Firmware / | |
`.._ _,,' `.._ _,,' | |
`'' `'' | |
| Push manifest | |
|----------------+-------------------->| |
| | | |
| ' | '
| | | Validate |
| | | Manifest |
| | |---------+ |
| | | | |
| | |<--------+ |
| | Request firmware | |
| | X.Y.Z | |
| |<--------------------| |
| | | |
| | Firmware X.Y.Z | |
| |-------------------->| |
| | | |
| | | Verify |
| | | Firmware |
| | |--------------+ |
| | | | |
| | |<-------------+ |
| | | |
| | | Store |
| | | Firmware |
| | |-------------+ |
| | | | |
| | |<------------+ |
| | | |
| | | |
| | | Trigger Reboot |
| | |--------------->|
| | | |
| | | |
| | | __..-------..._'
| | ,-' `-.
| | | Secure Boot |
| | `-. _/
| | |`--..._____,,.,-'
| | | |
| Device running firmware X.Y.Z | |
|<-------------------------------------| |
| | | |
| | | |

Figure 6: 3: Second Example Flow for a Firmware Upate.

10. Update.

9. IANA Considerations

This document does not require any actions by IANA.

11.

10. Security Considerations

Firmware updates fix security vulnerabilities

This document describes terminology, requirements and are considered to
be an important building block in securing IoT devices. Due to the
importance of architecture
for firmware updates for IoT devices the Internet
Architecture Board (IAB) organized a 'Workshop on Internet of Things
(IoT) Software Update (IOTSU)', which took place at Trinity College
Dublin, Ireland on the 13th and 14th IoT devices. The content of June, 2016 to take a look at the big picture. A report about this workshop can be found at
[RFC8240]. A standardized firmware manifest format providing end-to-
end document is
thereby focused on improving security from the author to the device will be specified in a
separate document.

There are, however, many other considerations raised during the
workshop. Many of them are outside the scope of standardization
organizations since they fall into the realm of product engineering,
regulatory frameworks, and business models. The following
considerations are outside the scope of this document, namely

- installing IoT devices via firmware updates in a robust fashion so that the
update
does not break mechanisms and informs the device functionality standardization of the environment this
device operates in.

- installing firmware updates in a timely fashion considering the
complexity manifest
format.

An in-depth examination of the decision making process of updating devices,
potential re-certification requirements, and the need for user
consent to install updates.

- the distribution security considerations of the actual firmware update, potentially
architecture is presented in an
efficient manner to a large number of devices without human
involvement.

- energy efficiency and battery lifetime considerations.

- key management required for verifying the digital signature
protecting the manifest.

- incentives for manufacturers to offer a firmware update mechanism
as part of their IoT products.

12. [I-D.ietf-suit-information-model].

11. Acknowledgements

We would like to thank the following persons for their feedback:

- Geraint Luff

- Amyas Phillips

- Dan Ros

- Thomas Eichinger

- Michael Richardson

- Emmanuel Baccelli

- Ned Smith

- Jim Schaad

- Carsten Bormann

- Cullen Jennings

- Olaf Bergmann

- Suhas Nandakumar

- Phillip Hallam-Baker

- Marti Bolivar

- Andrzej Puzdrowski
- Markus Gueller

- Henk Birkholz

- Jintao Zhu

- Takeshi Takahashi

- Jacob Beningo

- Kathleen Moriarty

- Bob Briscoe

- Roman Danyliw

- Brian Carpenter

- Theresa Enghardt

- Rich Salz

We would also like to thank the WG chairs, Russ Housley, David
Waltermire, Dave Thaler for their support and their reviews.

13.

12. Informative References

[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture",
draft-ietf-rats-architecture-06 (work in progress),
September 2020.

[I-D.ietf-suit-information-model]
Moran, B., Tschofenig, H., and H. Birkholz, "An
Information Model for Firmware Updates in IoT Devices",
draft-ietf-suit-information-model-07 (work in progress),
June 2020.

[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
"A Concise Binary Object Representation (CBOR)-based
Serialization Format for the Software Updates for Internet
of Things (SUIT) Manifest", draft-ietf-suit-manifest-09
(work in progress), July 2020.

[I-D.ietf-teep-architecture]
Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
"Trusted Execution Environment Provisioning (TEEP)
Architecture", draft-ietf-teep-architecture-12 (work in
progress), July 2020.

[LwM2M] OMA, ., "Lightweight Machine to Machine Technical
Specification, Version 1.0.2", February 2018,
<http://www.openmobilealliance.org/release/LightweightM2M/
V1_0_2-20180209-A/OMA-TS-LightweightM2M-
V1_0_2-20180209-A.pdf>.

[quantum-factorization]
Department of Computer Science, Purdue University, .,
Quantum Computing Institute, Oak Ridge National
Laboratory, ., Quantum Computing Institute, Oak Ridge
National Laboratory, ., Quantum Computing Institute, Oak
Ridge National Laboratory, ., and . Department of
Chemistry, Physics and Birck Nanotechnology Center, Purdue
University, "Quantum Annealing for Prime Factorization",
n.d.,
<https://www.nature.com/articles/s41598-018-36058-z>.

[RFC6024] Reddy, R. and C. Wallace, "Trust Anchor Management
Requirements", RFC 6024, DOI 10.17487/RFC6024, October
2010, <https://www.rfc-editor.org/info/rfc6024>.

[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.

[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.

[RFC8240] Tschofenig, H. and S. Farrell, "Report from the Internet
of Things Software Update (IoTSU) Workshop 2016",
RFC 8240, DOI 10.17487/RFC8240, September 2017,
<https://www.rfc-editor.org/info/rfc8240>.

[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.

[RFC8778] Housley, R., "Use of the HSS/LMS Hash-Based Signature
Algorithm with CBOR Object Signing and Encryption (COSE)",
RFC 8778, DOI 10.17487/RFC8778, April 2020,
<https://www.rfc-editor.org/info/rfc8778>.

Authors' Addresses

Brendan Moran
Arm Limited

EMail: Brendan.Moran@arm.com

Hannes Tschofenig
Arm Limited

EMail: hannes.tschofenig@arm.com

David Brown
Linaro

EMail: david.brown@linaro.org

Milosch Meriac
Consultant

EMail: milosch@meriac.com