wdiff draft-ietf-suit-architecture-14.txt draft-ietf-suit-architecture-15.txt

SUIT B. Moran
Internet-Draft H. Tschofenig
Intended status: Informational Arm Limited
Expires: April 24, July 22, 2021 D. Brown
Linaro
M. Meriac
Consultant
October 21, 2020
January 18, 2021

A Firmware Update Architecture for Internet of Things
draft-ietf-suit-architecture-14
draft-ietf-suit-architecture-15

Abstract

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

In addition to the definition of terminology functionality is recommended by security experts.

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

Status of This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on April 24, July 22, 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
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described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 5
2.1. Terms 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Agnostic to how firmware images are distributed . . 5
2.2. Stakeholders . . . 7
3.2. Friendly to broadcast delivery . . . . . . . . . . . . . 7
3.3. Use state-of-the-art security mechanisms . . . . . . 6
2.3. Functions . . 8
3.4. Rollback attacks must be prevented . . . . . . . . . . . 8
3.5. High reliability . . . . . . . . . . . 7
3. Architecture . . . . . . . . . 8
3.6. Operate with a small bootloader . . . . . . . . . . . . . 9
3.7. Small Parsers . . . . . . . . . . . . . . 8
4. Invoking the Firmware . . . . . . . . 10
3.8. Minimal impact on existing firmware formats . . . . . . . 10
3.9. Robust permissions . . . . . . . . . . . . . . . . . . . 10
3.10. Operating modes . . . . . . . . . . . . . . . . . . . . . 10
3.11. Suitability to software and personalization data . . . . 12
4.1. The Bootloader
4. Claims . . . . . . . . . . . . . . . . . . . . . . . . . . 14 . 13
5. Types of IoT Devices Communication Architecture . . . . . . . . . . . . . . . . . 13
6. Manifest . . . 15
5.1. Single MCU . . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Single CPU with Secure - Normal Mode Partitioning 17
7. Device Firmware Update Examples . . . . 16
5.3. Symmetric Multiple CPUs . . . . . . . . . . . 18
7.1. Single CPU SoC . . . . . . 16
5.4. Dual CPU, shared memory . . . . . . . . . . . . . . . 18
7.2. Single CPU with Secure - Normal Mode Partitioning . . 16
5.5. Dual CPU, other bus . . 18
7.3. Dual CPU, shared memory . . . . . . . . . . . . . . . . . 17
6. Manifests 18
7.4. Dual CPU, other bus . . . . . . . . . . . . . . . . . . . 18
8. Bootloader . . . . . . . 17
7. Securing Firmware Updates . . . . . . . . . . . . . . . . . . 19
8.
9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9. 21
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
10.
11. Security Considerations . . . . . . . . . . . . . . . . . . . 25
11.
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
12. 26
13. Informative References . . . . . . . . . . . . . . . . . . . 26 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 28

1. Introduction

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

When developing Internet of Things (IoT) Software Update (IOTSU)', which took place at Trinity College
Dublin, Ireland on the 13th and 14th devices, one of June, 2016 to 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 most
difficult problems to the formation of the IETF Software Updates for
Internet of Things (SUIT) working group.

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

Firmware updates device are not only done to fix bugs, but they can also bugs in software, to 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 process, among other goals, 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, untrusted
unknown source must be are 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
mitigated or at least made more difficult.
prevented. Obtaining the firmware is often one of the first steps
to mount an attack since it gives the adversary valuable insights
into the used software libraries used, libraries, configuration settings and generic functionality. Even
functionality (even though reverse engineering the binary can be a
tedious process modern
reverse engineering frameworks have made this task process).

This version of the document assumes asymmetric cryptography and a
public key infrastructure. Future versions may also describe a lot easier.
symmetric key approach for very constrained devices.

While the standardization work has been informed by and optimized optimised for
firmware update use cases of Class 1 devices (according to the device
class definitions in RFC 7228 [RFC7228]) devices, [RFC7228]), there is nothing in the
architecture that restricts its use to only these constrained IoT
devices. Moreover, this architecture is not limited to managing
firmware Software update and software updates, but can also be applied to managing
the delivery of arbitrary data, such as
configuration information and
keys. 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
for how to obtain those application layer software binaries then
depends heavily on the platform, programming language used and the
sandbox in which the software is executed.

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 keys, can equally be available as well as the
status tracker functionality. Devices also require a mechanism to
discover the status tracker(s) and/or firmware servers, for example
using pre-configured hostnames or [RFC6763] DNS-SD. These building
blocks have been developed managed 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
manifests.

More details about the IETF and other standards organizations but need to be
considered by firmware authors, as well as device and network
operators. Here security goals are some of them, as highlighted during the IOTSU
workshop:

- Installing firmware updates discussed in 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 offering
recovery strategies when a firmware update is unsuccessful.

- Making firmware updates available in 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
device because a firmware update, particularly radio communication
and writing the firmware image to flash, is an energy-intensive
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 Section 5 and how it
integrates with the firmware update mechanism. Subsequently, we
offer a categorization of IoT devices
requirements are described 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. Section 3.

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. We use the term application
firmware image

- 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 to differentiate it from boot a firmware image that
contains the bootloader. An application is present or
whether to obtain and verify a new firmware image, as image. Since the
name indicates, contains
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 the application program often including
all first stage and resides in
ROM whereas the necessary code to run it (such as protocol stacks, second stage may implement more complex
functionality and
embedded operating system).

- Manifest: resides in flash memory so that it can be
updated in the future (in case bugs have been found). The manifest contains meta-data about exact
split of components into the different stages, the number of
firmware
image. The manifest is protected against modification images stored by an IoT device, and
provides information about the author. detailed
functionality varies throughout different implementations. A more
detailed discussion is provided in Section 8.

- 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 interchangeably 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 MCU, an external, updatable radio, or a device
with internal and external flash memory.

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

- 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.

- Software: Similar to firmware, but typically dynamically loaded by
an Operating System. Used interchangeably with firmware in this
document.

- 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].

2.2. Stakeholders

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

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

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

- Network Operator: The network operator manifest. It is responsible for the
operation of a network to which IoT devices connect.

- Trust Provisioning Authority (TPA): The TPA distributes trust
anchors parsing
and authorization policies to devices verifying the received manifest and various
stakeholders. for storing the obtained
firmware image. The TPA may also delegate rights to stakeholders.
Typically, firmware consumer plays the Original Equipment Manufacturer (OEM) or Original
Design Manufacturer (ODM) will act as a TPA, however complex
supply chains may require a different design. In some cases, role of the
TPA may decide to remain
update component on the IoT device typically running in full control over the
application firmware. It interacts with the firmware update
process of their products.

- User: The end-user of a device. The user may interact server and
with
devices via web or smart phone apps, as well as through direct
user interfaces.

2.3. Functions the status tracker, if present.

- (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 successfully succesfully perform an update.

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

- Status Tracker: The information flow is from the
client to the server.
3) It can remotely trigger the firmware update process. The
information flow is from the server to the client.

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

We make no assumptions about where trigger
the server-side component is
deployed. update process. The deployment of status trackers is flexible
and they may be found at used as cloud-based servers, on-premise servers, or may be
embedded in edge computing devices. A status tracker server component may device (such as Internet access
gateways or protocol translation gateways), or even be deployed on an IoT device. For example, if in smart
phones and tablets. While the IoT device
contains multiple MCUs, then itself runs the main MCU may act as client-
side of the status tracker it will most likely not run a status
tracker towards the itself unless it acts as a proxy for other MCUs. Such deployment is useful when
updates have to be synchronized across MCUs.

The IoT devices in
a protocol translation or edge computing device node. How much
functionality a status tracker may be operated by any suitable stakeholder;
typically the Author, Device Operator, or Network Operator.

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

- 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 and these two but those
entities are often physically separated on different devices for
scalability reasons.

- Bootloader: A bootloader is a piece of software that is executed
once a microcontroller has been reset. It is Device Operator: The actor responsible for
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. Sending 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 day-to-day
operation of 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 and even
several megabytes large for fleet of 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. devices.

- Network Operator: The actor responsible for the capability to write the received firmware image to persistent
storage (most likely flash memory).

- a manifest parser with code to verify a digital signature or operation of a
message authentication code.

- the ability to unpack,
network to decompress and/or which IoT devices connect.

In addition to decrypt the
received firmware image.

- a status tracker.

The features listed above are most likely offered by code in the
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 entities in the
same context with the application code.

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

As product, may act as a first step TPA and
may decide to remain in full control over the firmware update process, the status tracker
client needs to be made aware of the availability process
of a new firmware
update by the status tracker server. This can be accomplished their products.

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

- "A trust anchor represents an authoritative entity via
polling (client-initiated), push notifications (server-initiated), or
more complex mechanisms (such as a hybrid approach):

- Client-initiated updates take public
key and associated data. The public key is used to verify digital
signatures, and the form of a status tracker client
proactively checking (polling) for updates.

- With Server-initiated updates associated data is used to constrain the server-side component types
of information for which the
status tracker learns about trust anchor is authoritative."

- "A trust anchor store is a new firmware version and determines
which devices qualify for set of one or more trust anchors stored
in a firmware update. Once the relevant
devices device. A device may have been selected, the status tracker informs these
devices 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.

3. Requirements

The firmware update mechanism described in this specification was
designed with the following requirements in mind:

- Agnostic to how firmware consumers obtain those images and
manifests. Server-initiated updates are important because they
allow a quick response time. Note that the client-side status
tracker needs distributed

- Friendly to broadcast delivery

- Use state-of-the-art security mechanisms

- Rollback attacks must be reachable by the server-side component. This
may require devices to keep reachability information on the
server-side up-to-date and state at NATs and stateful packet
filtering firewalls alive. prevented

- Using High reliability

- Operate with a hybrid approach the server-side of the status tracker
pushes notifications of availability small bootloader

- Small Parsers

- Minimal impact on existing firmware formats

- Robust permissions

- Diverse modes of an update operation

- Suitability to the client
side software and requests the firmware consumer personalization data

3.1. Agnostic to pull the manifest and
the firmware image from the how 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 images are still pending an update. distributed

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

In some cases it may be desirable
manifests.

3.2. Friendly to distribute firmware images using
a multicast or broadcast protocol. delivery

This architecture does not make
recommendations for specify any such specific broadcast 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.

+----------+
| |
| 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

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

Integrity protection ensures that no third party can modify the
manifest or
detached. 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. 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 both approaches.

For distribution 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 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 bundle, vulnerability in
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.
A failure to validate any part of an update must not cause a failure
of the device. One way to achieve this functionality is embedded into 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
manifest. update process after power
down.

Note: This is an implementation requirement rather than a useful approach for deployments where devices
are 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 connected manage the firmware update process. This may give the impression
that the bootloader itself is a completely separate component, which
is mainly responsible for selecting a firmware image to boot.

The overlap between the Internet firmware update process and cannot contact the bootloader
functionality comes in two forms, namely

- First, a dedicated bootloader must verify the firmware server for image it boots as
part of the secure boot process. Doing so requires meta-data to
be stored alongside the firmware download. It is also applicable
when image so that the bootloader can
cryptographically verify the 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
the firmware image during the update happens via process (with the severable
fields stripped off).

- Second, an IoT device needs a recovery strategy in case 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 a second stage bootloader perform the
firmware update process again using firmware updates over serial,
USB sticks or short range
radio technologies (such as even wireless connectivity like a limited version of
Bluetooth Smart).

Alternatively, 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 distributed detached 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 they 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 from their permissions. For example, an
author may not have the authority to install a firmware
image. Using image on a
device in critical infrastructure without the authorization of a
device operator. In this approach, case, the device may be programmed to
reject firmware updates unless they are signed both by 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 presented with able to reach the manifest first
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 then needs 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 obtain one or more the firmware
images consumer,
and it then downloads the image from a firmware server as soon as dictated
possible.

An alternative view to the operating modes is to consider the steps a
device has to go through in the manifest. course of an update:

- Notification

- Pre-authorisation

- Dependency resolution

- Download

- Installation

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.

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/1.1-based HTTP-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 update.
server-initiated.

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, - or tracker to initiate the installation, may trigger the update
automatically, - or may go through a more complex decision making
process to determine the appropriate timing for an update. Sometimes
the final decision may require confirmation of update (such as
delaying the user of update process to a later time when end users are less
impacted by the device
for safety reasons. update process).

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

Each of these steps may require different when a bootloader is not involved. For example, when an
application is updated in permissions.

3.11. Suitability to software and personalization data

The work on a full-featured operating system, standardized manifest format initially focused on the
updater may halt
most constrained IoT devices and restart the application those devices contain code put
together by a single author (although that author may obtain code
from other developers, some of it only in isolation. Devices
must not fail when binary form).

Later it turns out that other use cases may benefit from a disruption occurs during the update process.
For
standardized manifest format also for conveying software and even
personalization data alongside software. Trusted Execution
Environments (TEEs), for example, greatly benefit from a power failure or network disruption during protocol for
managing the update
process must not cause lifecycle of trusted applications (TAs) running inside 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 the device TEE.

To support this wider range of use cases the manifest format should
therefore be extensible to fail. convey other forms of payloads as well.

4. Invoking the Firmware

Section 3 describes Claims

Claims in the steps for getting manifest offer a way to convey instructions to a device
that impact the firmware image and update process. To have any value the
manifest from the author containing those claims must be authenticated and integrity
protected. The credential used must be directly or indirectly
related to the firmware consumer on trust anchor installed at the IoT device.
Once device by the Trust
Provisioning Authority.

The baseline claims for all manifests are described in
[I-D.ietf-suit-information-model]. For example, there are:

- Do not install firmware consumer has retrieved and successfully processed
the manifest and with earlier metadata than the current
metadata.

- Only install firmware image it needs to invoke the new with a matching vendor, model, hardware
revision, software version, etc.

- Only install firmware image. This that is managed in many different ways, depending before its best-before timestamp.

- Only allow a firmware installation if dependencies have been met.

- Choose the mechanism to install the firmware, based on the type of device, but
firmware it typically involves halting the current
version of is.

5. Communication Architecture

Figure 1 shows the firmware, handing control over to a firmware with communication architecture where a
higher privilege/trust level (the firmware verifier) verifying the
new firmware's authenticity & integrity, and then invoking it.

In an execute-in-place microcontroller, this image
is often done created by
rebooting into a bootloader (simultaneously halting the application &
handing over an author, and uploaded to the higher privilege level) then executing a secure
boot process (verifying and invoking firmware server. The
firmware image/manifest is distributed to the new image).

In device either in a rich OS, this may be done by halting one push
or more processes, then
invoking new applications. In some OSs, this implicitly involves the
kernel verifying pull manner using the code signatures firmware consumer residing on the new applications. device.
The invocation device operator keeps track of the process is security sensitive. An attacker will
typically try to retrieve a firmware image from using the device for
reverse engineering or will try to get status
tracker. This allows the firmware verifier device operator to
execute an attacker-modified firmware image. The firmware verifier
will therefore know and control what
devices have to perform received an update and which of them are still pending
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 checks on mechanisms are used to protect the firmware image
before it can be invoked. These security checks by
and the firmware
verifier happen in addition to manifest although Figure 2 does not show the security checks that took place
when manifest itself
since it may be distributed independently.

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

Figure 2: End-to-End Security.

Whether the firmware image and the manifest were downloaded is pushed to the device
or fetched by the
firmware consumer. device is a deployment specific decision.

The overlap between following assumptions are made to allow the firmware consumer and the firmware verifier
functionality comes in two forms, namely

- A firmware verifier 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 firmware
verifier can cryptographically
verify the received 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 and manifest obtained with the firmware image during the update
process. before updating
software:

- An IoT To accept an update, a device needs a recovery strategy in case to verify the firmware
update / invocation process fails. The recovery strategy signature
covering the manifest. There may
include storing two be one or more application firmware images on the multiple manifests
that need to be validated, potentially signed by different
parties. The device or offering needs to be in possession of the ability trust
anchors to invoke a recovery image verify those signatures. Installing trust anchors to
devices via the Trust Provisioning Authority happens in an out-of-
band fashion prior to
perform the firmware update process again using firmware updates
over serial, USB or even wireless connectivity like Bluetooth
Smart. In process.

- Not all entities creating and signing manifests have the latter case same
permissions. A device needs to determine whether the firmware consumer functionality requested
action is
contained in the recovery image and requires indeed covered by the necessary
functionality for executing permission of the firmware update process, including
manifest parsing.

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

Using also a bootloader as duty of the Trust Provisioning Authority.

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

4.1. The Bootloader

In most cases images the MCU must restart in order to hand over control author needs
to be in possession of the bootloader. Once the MCU has initiated certificate/public key or a restart, the bootloader
determines whether pre-shared
key of a newly available firmware image should be
executed. If the bootloader concludes that the newly available device. The use of confidentiality protection of
firmware image is invalid, a recovery strategy images is necessary. deployment specific.

There are only two approaches for 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 these approaches have implications for the architecture different types of the
update system.

Assuming the first approach, there delivery modes, which are (at least) three firmware
images available illustrated
based on the device:

- First, the bootloader examples below.

There is also firmware. If an option for embedding a bootloader is
updatable then its firmware image into a manifest.
This is treated like any other
application firmware image.

- Second, the firmware image that has a useful approach for deployments where devices are not
connected to be replaced is still
available on the device as Internet and cannot contact a backup in case the freshly downloaded dedicated firmware image does not boot or operate correctly.

- Third, there is
server for the newly downloaded firmware image.

Therefore, download. It is also applicable when the
firmware consumer must know where to store the new
firmware. In some cases, update happens via a USB stick or via Bluetooth Smart.
Figure 3 shows this may be implicit, delivery mode graphically.

Figure 3: Manifest with attached firmware.

Figure 4 shows an option for example replacing remotely updating a device where the
device fetches the least-recently-used firmware image. In other cases, image from some file server. The
manifest itself is delivered independently and provides information
about the storage
location firmware image(s) to download.

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

Figure 4: Independent retrieval of the new firmware image.

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

6. Manifest

In order for example when a device has one or more application firmware images and a recovery
image with limited functionality, sufficient only to perform apply an
update.

Since many low end IoT devices do not use position-independent code,
either the bootloader needs update, it has to copy make several
decisions about the newly downloaded application
firmware image into update:

- Does it trust the location author of the old application update?

- Has the firmware
image and vice versa or multiple versions of been corrupted?

- Does the firmware need update apply to be
prepared for different locations.

In general, it is assumed that this device?

- Is the bootloader itself, or a minimal
part of it, will not be updated since a failed update of older than the
bootloader poses a reliability risk.

For a bootloader to offer a secure boot functionality it needs to
implement active firmware?

- When should the following functionality: device apply the update?

- The bootloader needs to fetch How should the manifest (or manifest-alike
headers) from nonvolatile storage and parse its contents for
subsequent cryptographic verification. device apply the update?

- Cryptographic libraries with hash functions, digital signatures
(for asymmetric crypto), message authentication codes (for
symmetric crypto) need to What kind of firmware binary is it?

- Where should the update be accessible. obtained?

- Where should the firmware be stored?

The device needs to have a trust anchor store to verify manifest encodes the
digital signature. (Alternatively, access information that devices need in order to
make these decisions. It is a key store for use
with data structure that contains the message authentication code.)
following information:

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

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

- information about when the manifest was created,

- dependencies on other manifests,

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

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

- Produce boot measurements cryptographic information, such as part of an attestation solution. See
[I-D.ietf-rats-architecture] for more information. (optional)

- Ability to 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 digital signatures or message
authentication codes (MACs).

The manifest information model is described in their characteristics, there are a number of similiaries allowing
us
[I-D.ietf-suit-information-model].

7. Device Firmware Update Examples

Although these documents attempt to categorize in groups.

The define a firmware update architecture, and the manifest format in
particular, needs
architecture that is applicable to offer enough flexibility both existing systems, as well as
yet-to-be-conceived systems; it is still helpful to cover these common
deployment cases.

5.1. consider existing
architectures.

7.1. Single MCU CPU SoC

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). Due to Combined with the non-relocatable
nature of the code, the firmware image needs updates need to be placed in a specific location in flash since the code cannot be
executed from an arbitrary location done in flash. Hence, when the
firmware image is updated it is necessary to swap the old and the new
image.

5.2. place.

7.2. 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.

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, 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.

5.4.

7.3. Dual CPU, shared memory

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

5.5.

7.4. 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, a master, 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.

6. Manifests

In order for a firmware consumer to apply an update, it has

8. Bootloader

More devices today than ever before are being connected to make
several decisions using manifest-provided information and data
available on the 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],
Internet, which offers justifications for each element, and drives the manifest, see
[I-D.ietf-suit-manifest], need for details about how this information is
included in the manifest.

Table 1 provides examples of decisions firmware updates to be made.

- the active firmware? | |
| | |
| When should Internet protocol stack for firmware downloads (*),

Table 1: Firmware Update Decisions.

(1): A device presented with features to verify an old, but valid image and a manifest, including digital
signature verification or checking a message authentication code,

- a manifest parsing library, and firmware
must not be tricked

- integration of the device into installing such firmware since a
vulnerability in the old device management server to
perform automatic firmware image may allow an attacker updates and to gain
control of the device.

Keeping the code track their progress.

(*) Because firmware images are often multiple kilobytes, sometimes
exceeding one hundred kilobytes, in size for low end IoT devices and complexity of a manifest parsers small is
important
even several megabytes large for constrained IoT devices. Since devices running full-fledged
operating systems like Linux, the manifest parsing
code may also be used 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 by the bootloader it is part of application, i.e.
firmware consumer, running on the trusted
computing base.

A manifest device (except for basic security
algorithms that may not only be used to protect firmware images but also
configuration data such as network credentials run either on a trusted execution environment or personalization
data related to
on a separate hardware security MCU/module) rather than by the
bootloader itself.

Once manifests have been processed and firmware or software. Personalization data
demonstrates images successfully
downloaded and verified the need for confidentiality device needs to be maintained between
two or more stakeholders that both deliver images hand control over to the same device.

Personalization data is used with Trusted Execution Environments
(TEEs), which benefit from a protocol for managing
bootloader. In most cases this requires the lifecycle of
trusted applications (TAs) running inside MCU to restart. Once
the MCU has initiated a TEE. TEEs may obtain TAs
from different authors restart, the bootloader takes over control
and those TAs may require personalization
data, such as payment information, to be securely conveyed to determines whether the
TEE. newly downloaded firmware image should be
executed.

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

7. Securing Firmware Updates

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

End-to-end security mechanisms are used to protect checks that happened when the firmware image and the manifest.
manifest were downloaded.

The following assumptions are made to allow manifest may have been stored alongside the firmware consumer image to verify
allow re-verification of the received firmware image and manifest
before updating software:

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

- Integrity protection ensures manifest by stripping elements that are no third party can modify longer needed.

If the
manifest or application image contains the firmware image. To accept an update, consumer
functionality, as described above, then it is necessary that a device
needs to verify the signature covering
working image is left on the manifest. There may be
one or multiple manifests that need to be validated, potentially
signed by different parties. The device needs to be in possession
of device. This allows the trust anchors to verify those signatures. Installing trust
anchors bootloader to devices via the Trust Provisioning Authority happens in
an out-of-band fashion prior
roll back to the firmware update process.

- For confidentiality protection of the firmware image, it must be
done in such a way that the intended working firmware 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 image to Content Distribution
Networks, bulk storage, and broadcast protocols. For
confidentiality protection of execute a firmware images download
if the author needs bootloader itself does not have enough functionality to
be in possession of the certificate/public key or fetch
a pre-shared key
of firmware image plus manifest from a device. The use of confidentiality protection of firmware
images is optional. server over the
Internet. A manifest specification must support different cryptographic
algorithms and algorithm extensibility. Moreover, since RSA- and
ECC-based signature schemes multi-stage bootloader may become vulnerable to quantum-
accelerated key extraction in soften this requirement at
the future, unchangeable expense of a more sophisticated boot process.

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

- ability to access security algorithms, such as 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 SHA-256 to key extraction
with quantum acceleration is approximately 2030, based on current
research [quantum-factorization].

When a device obtains compute
a monolithic fingerprint over the firmware image from and a single
author without any additional approval steps then digital signature
algorithm.

- access keying material directly or indirectly to utilize the authorization
flow is relatively simple. There are, however, other cases where
more complex policy decisions need
digital signature. The device needs to be made before updating have a
device.

In this architecture trust anchor store.

- ability to expose boot process-related data to the authorization policy is separated from application
firmware (such as to the
underlying communication architecture. device management software). This is accomplished by
separating the entities from their permissions. For example, an
author may not have the authority to install a firmware image on allows
a device in critical infrastructure without management server to determine whether the authorization firmware
update has been successful and, if not, what errors occurred.

- to (optionally) offer attestation information (such as
measurements).

While the software architecture of a
device operator. In this case, the device may bootloader and its security
mechanisms are implementation-specific, the manifest can be programmed used to
reject firmware updates unless they are signed both by
control 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 download from the
device Internet in addition to offload complex permissions calculations
augmenting secure boot process. These building blocks are highly
relevant for the device.

8. design of the manifest.

9. Example

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

+--------+ +-----------------+ +-----------------------------+
| | | Firmware Server | | IoT Device |
| Author | | Status Tracker | | +------------+ +----------+
|
+--------+ | Server | | | Firmware | |Bootloader| |
| +-----------------+ | | Consumer |
| Author | | Firmware Server | | Consumer | |Bootloader|
+--------+ +-----------------+ +------------+ +----------+
| | | | | | |
| | | +-----------------------+ | +
| 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 2: 5: First Example Flow for a Firmware Update. Upate.

Figure 3 6 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
querying
tracker; the details of such exchange will vary with the different
device for its current firmware version. Later, a new management systems being used. In any case, the status
tracker learns about the firmware version becomes available and since this of the devices it manages.
In our example, the device under management is running
an older using firmware version
A.B.C. At a later point in time the status tracker server interacts author uploads a new firmware
along with the device manifest to initiate an update.

The the firmware server and the status
tracker, respectively. While there is no need to store the manifest
and the firmware are stored on different servers in this
example. When 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 the device processes about the manifest newly available firmware
image. In our example, it learns where does so by pushing the manifest to
download the new
firmware version. consumer. 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 | | Status Tracker Firmware Server | | | 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 3: 6: Second Example Flow for a Firmware Update.

9. Upate.

10. IANA Considerations

This document does not require any actions by IANA.

10.

11. Security Considerations

This document describes terminology, requirements

Firmware updates fix security vulnerabilities and are considered to
be an architecture
for firmware updates of important building block in securing IoT devices. The content Due to the
importance of firmware updates for IoT devices the document is
thereby focused Internet
Architecture Board (IAB) organized a 'Workshop on Internet of Things
(IoT) Software Update (IOTSU)', which took place at Trinity College
Dublin, Ireland on improving the 13th and 14th 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 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 IoT devices via 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 firmware updates in a robust fashion so that the update mechanisms and informs
does not break the standardization device functionality of the environment this
device operates in.

- installing firmware updates in a manifest
format.

An in-depth examination timely fashion considering the
complexity of the security considerations decision making process of updating devices,
potential re-certification requirements, and the
architecture is presented need for user
consent to install updates.

- the distribution of the actual firmware update, potentially in [I-D.ietf-suit-information-model].

11. 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. 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

- Mohit Sethi

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

12.

13. 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
draft-ietf-suit-information-model-08 (work in progress),
June
October 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 draft-ietf-suit-manifest-11
(work in progress), July December 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 draft-ietf-teep-architecture-13 (work in
progress), July November 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]
Jiang, S., Britt, K., McCaskey, A., Humble, T., and S.
Kais, "Quantum Annealing for Prime Factorization",
December 2018,
<https://www.nature.com/articles/s41598-018-36058-z>.
V1_0_2-20180209-A/
OMA-TS-LightweightM2M-V1_0_2-20180209-A.pdf>.

[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>.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.

[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>.

[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>.

[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