A Firmware Update Architecture for Internet of ThingsArm LimitedBrendan.Moran@arm.comArm Limitedhannes.tschofenig@arm.comLinarodavid.brown@linaro.orgConsultantmilosch@meriac.com
Security
SUITInternet-DraftVulnerabilities with Internet of Things (IoT) devices have raised
the need for a solid and secure firmware update mechanism that is
also suitable for constrained devices. Incorporating such update
mechanism to fix vulnerabilities, to update configuration settings
as well as adding new functionality is recommended by security
experts.This document lists requirements and describes an architecture for
a firmware update mechanism suitable for IoT devices. The
architecture is agnostic to the transport of the firmware images
and associated meta-data.When developing Internet of Things (IoT) devices, one of the most difficult problems
to solve is how to update firmware on the device. Once the
device is deployed, firmware updates play a critical part in its
lifetime, particularly when devices have a long lifetime, are
deployed in remote or inaccessible areas where manual
intervention is cost prohibitive or otherwise difficult. Updates
to the firmware of an IoT device are done to fix 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, among other goals, has to ensure thatThe firmware image is authenticated and integrity protected.
Attempts to flash a modified firmware image or an image from
an unknown source are prevented.The firmware image can be confidentiality protected so that
attempts by an adversary to recover the plaintext binary can
be prevented. Obtaining the firmware is often one of
the first steps to mount an attack since it gives the adversary
valuable insights into used software libraries, configuration
settings and generic 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
a symmetric key approach for very constrained devices.While the standardization work has been informed by and optimised for firmware
update use cases of Class 1 (as defined in RFC 7228 ) devices, there is nothing in
the architecture that restricts its use to only these constrained IoT devices.
Software update and delivery of arbitrary data, such as configuration information
and keys, can equally be managed by manifests. The solution therefore applies to
more capable devices, such as network storage devices, set top boxes, and IP-based cameras as well.More details about the security goals are discussed in
and requirements are described in .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 to boot a firmware image
that is present or whether to obtain and verify a new
firmware image. Since 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 the first stage and resides in ROM whereas the second stage
may implement more complex functionality and resides in flash
memory so that it can be updated in the future (in case bugs
have been found). The exact split of components into the
different stages, the number of firmware images stored by an
IoT device, and the detailed functionality varies throughout
different implementations. A more detailed discussion is
provided in .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 with internal and external flash memory.Trusted Execution Environments (TEEs): An execution environment
that runs alongside of, but 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.Trusted applications (TAs): An application component that runs in
a TEE.For more information about TEEs see .The following entities are used:Author: The author is the entity that creates the firmware image.
There may be multiple authors in a system either when a device
consists of multiple micro-controllers or when the the final
firmware image consists of software components from multiple
companies.Firmware Consumer: The firmware consumer is the recipient of the
firmware image and the manifest. It is responsible for parsing
and verifying the received manifest and for storing the obtained
firmware image. The firmware consumer plays the role of the
update component on the IoT device typically running in the
application firmware. It interacts with the firmware server and
with 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 succesfully perform an update. The terms device and
firmware consumer are used interchangably since the firmware
consumer is one software component running on an MCU on the device.Status Tracker: The status tracker offers device management
functionality to retrieve information about the installed firmware
on a device and other device characteristics (including free memory
and hardware components), to obtain the state of the firmware update
cycle the device is currently in, and to trigger the update process.
The deployment of status trackers is flexible and they may be used
as 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. While the IoT device itself
runs the client-side of the status tracker it will most likely not
run a status tracker itself unless it acts as a proxy for other
IoT devices in a protocol translation or edge computing device node.
How much functionality a status tracker includes depends on the selected
configuration of the device management functionality and the communication
environment it is used in. In a generic networking environment the protocol
used between the client and the server-side of the status tracker need to
deal 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 the status 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 but those entities are often
physically separated on different devices for scalability reasons.Device Operator: The actor responsible for the day-to-day operation
of a fleet of IoT devices.Network Operator: The actor responsible for the operation of a
network to which IoT devices connect.In addition to the entities in the list above there is an orthogonal
infrastructure with a Trust Provisioning Authority (TPA) distributing
trust anchors and authorization permissions to various entities in
the system. The TPA may also delegate rights to install, update,
enhance, or delete trust anchors and authorization permissions to
other parties in the system. This infrastructure overlaps the
communication architecture and different deployments may empower
certain entities while other deployments may not. For example,
in some cases, the Original Design Manufacturer (ODM), which is a
company that designs and manufactures a product, may act as a
TPA and may decide to remain in full control over the firmware
update process of their products.The terms ‘trust anchor’ and ‘trust anchor store’ are defined in
:“A trust anchor 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.”“A trust anchor store 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.The firmware update mechanism described in this specification
was designed with the following requirements in mind:Agnostic to how firmware images are distributedFriendly to broadcast deliveryUse state-of-the-art security mechanismsRollback attacks must be preventedHigh reliabilityOperate with a small bootloaderSmall ParsersMinimal impact on existing firmware formatsRobust permissionsDiverse modes of operationSuitability to software and personalization dataFirmware images can be conveyed to devices in a variety of ways,
including USB, UART, WiFi, BLE, low-power WAN technologies, etc.
and use different protocols (e.g., CoAP, HTTP). The specified
mechanism needs to be agnostic to the distribution of the
firmware images and manifests.This architecture does not specify any 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.End-to-end security between the author and the device is shown in
.Authentication ensures that the device can cryptographically identify
the author(s) creating firmware images and manifests. Authenticated
identities may be used 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. 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 as hash-based
signatures , 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 }.A device presented with an old, but valid manifest and firmware
must not be tricked into installing such firmware since a
vulnerability in the old firmware image may allow an attacker to
gain control of the device.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
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.Throughout this document we assume that the bootloader itself is
distinct from the role of the firmware consumer and therefore does not
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 firmware update process and the bootloader
functionality comes in two forms, namelyFirst, 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 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 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 or even
wireless connectivity like a limited version of 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.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.The design of the firmware update mechanism must not require
changes to existing firmware formats.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
on a device in critical infrastructure without the authorization
of a device operator. In this 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.There are three broad classifications of update operating modes.Client-initiated UpdateServer-initiated UpdateHybrid UpdateClient-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 the firmware consumer,
and it then downloads the image from a firmware server
as soon as possible.An alternative view to the operating modes is to consider the steps a
device has to go through in the course of an update:NotificationPre-authorisationDependency resolutionDownloadInstallationThe 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-based firmware server is client-initiated. Pushing a manifest
and firmware image to the transfer to the Package resource of the LwM2M
Firmware Update object is server-initiated.If the firmware consumer has downloaded a new firmware image and is ready to
install it, it may need to wait for a trigger from the status 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 (such as delaying the update
process to a later time when end users are less impacted by the
update process).Installation is the act of processing the payload into a format that
the IoT device can recognise and the bootloader is responsible for
then booting from the newly installed firmware image.Each of these steps may require different permissions.The work on a standardized manifest format initially focused on the
most constrained IoT devices and those devices contain code put together
by a single author (although that author may obtain code from other
developers, some of it only in binary form).Later it turns out that other use cases may benefit from a standardized
manifest format also for conveying software and even personalization data
alongside software. Trusted Execution Environments (TEEs), for example,
greatly benefit from a protocol for managing the 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 TEE.To support this wider range of use cases the manifest format should
therefore be extensible to convey other forms of payloads as well.Claims in the manifest offer a way to convey instructions to
a device that impact the firmware update process. To have any
value the manifest containing those claims must be authenticated
and integrity protected. The credential used must be directly
or indirectly related to the trust anchor installed at the device
by the Trust Provisioning Authority.The baseline claims for all manifests are described in .
For example, there are:Do not install firmware with earlier metadata than the current
metadata.Only install firmware with a matching vendor, model, hardware
revision, software version, etc.Only install firmware that is 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 firmware it is. shows the communication architecture where a
firmware image is created by an author, and uploaded to a firmware
server. The firmware image/manifest is distributed to the device
either in a push or pull manner using the firmware consumer residing on
the device. The device operator keeps track of the process using
the status tracker. This allows the device operator to know and
control what devices have received an update and which of them are
still pending an update.End-to-end security mechanisms are used to protect the firmware
image and the manifest although does not show the
manifest itself since it may be distributed independently.Whether the firmware image and the manifest is pushed to the device or
fetched by the device is a deployment specific decision.The following assumptions are made to allow the firmware consumer to verify the
received firmware image and manifest before updating software:To accept an update, a device needs to verify the signature covering
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 the trust anchors to verify those signatures.
Installing trust anchors to devices via the Trust Provisioning Authority
happens in an out-of-band fashion prior to the firmware update process.Not all entities creating and signing manifests have the same
permissions. A device needs to determine whether the requested action
is indeed covered by the permission of the party that signed the manifest.
Informing the device about the permissions of the different parties
also happens in an out-of-band fashion and is also a duty of the
Trust Provisioning Authority.For confidentiality protection of firmware images the author needs
to be in possession of the certificate/public key or a pre-shared key
of a device. The use of confidentiality protection of firmware images
is deployment specific.There are different types of delivery modes, which are illustrated
based on examples below.There is an option for embedding a 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 firmware server for the firmware
download. It is also applicable when the firmware update happens via a
USB stick or via Bluetooth Smart. shows this
delivery mode graphically. shows an option for remotely updating a device
where the device fetches the firmware image from some file server. The
manifest itself is delivered independently and provides information about
the firmware image(s) to download.This architecture does not mandate a specific delivery mode but a solution
must support both types.In order for a device to apply an update, it has to make several decisions
about the update:Does it trust the author of the update?Has the firmware been corrupted?Does the firmware update apply to this device?Is the update older than the active firmware?When should the device apply the update?How should the device apply the update?What kind of firmware binary is it?Where should the update be obtained?Where should the firmware be stored?The manifest encodes the information that devices need in order to
make these decisions. It is a data structure that contains the
following information:information about the device(s) the firmware image is intended to
be applied to,information about when the firmware update has to be applied,information about when the manifest was created,dependencies on other manifests,pointers to the firmware image and information about the format,information about where to store the firmware image,cryptographic information, such as digital signatures or message
authentication codes (MACs).The manifest information model is described in .Although these documents attempt to define a firmware update
architecture that is applicable to both existing systems, as well
as yet-to-be-conceived systems; it is still helpful to consider
existing architectures.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 the non-relocatable
nature of the code, firmware updates need to be done in place.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.This configuration has two or more CPUs in a single SoC that share
memory (flash and RAM). Generally, they will be a protection mechanism
to prevent one CPU from accessing the 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.This configuration has two or more 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 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.More devices today than ever before are being 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
RS232. Updating a device over the Internet requires the device to fetch
not only the firmware image but also the manifest. Hence, the following
building blocks are necessary for a firmware update solution:the Internet protocol stack for firmware downloads (*),the capability to write the received firmware image to
persistent storage (most likely flash memory) prior to performing
the update,the ability to unpack, decompress or otherwise process the received
firmware image,the features to verify an image and a manifest, including digital
signature verification or checking a message authentication code,a manifest parsing library, andintegration of the device into a device management server to
perform automatic firmware updates and to track their progress.(*) 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 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.All these features are most likely offered by the application, i.e.
firmware consumer, running
on the device (except for basic security algorithms that may run
either on a trusted execution environment or on a separate hardware
security MCU/module) rather than by the bootloader itself.Once manifests have been processed and firmware images successfully
downloaded and verified the device needs to hand control over to the
bootloader. In most cases this requires the MCU to restart. Once the
MCU has initiated a restart, the bootloader takes over control 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 to the image for reverse
engineering and potentially also for modifying the binary. The
bootloader will therefore have to perform security checks on the
firmware image before it can be booted. These security checks by the
bootloader happen in addition to the security checks that happened
when the firmware image and the manifest were downloaded.The manifest may have been stored alongside the firmware image to
allow re-verification of the firmware image during every boot
attempt. Alternatively, secure boot-specific meta-data may have been
created by the application after a successful firmware download
and verification process. Whether to re-use the standardized
manifest format that was used during the initial firmware retrieval
process or whether it is better to use a different format for the
secure boot-specific meta-data depends on the system design. The
manifest format does, however, have the capability to serve also as a
building block for secure boot with its severable elements that allow
shrinking the size of the manifest by stripping elements that are no
longer needed.If the application image contains the firmware consumer
functionality, as described above, then it is necessary that a
working image is left on the device. This allows the bootloader to
roll back to a working firmware image to execute a firmware download
if the bootloader itself does not have enough functionality to
fetch a firmware image plus manifest from a firmware server over the
Internet. A multi-stage bootloader may soften this requirement at
the expense of a more sophisticated boot process.For a bootloader to offer a secure boot mechanism it needs to provide
the following features:ability to access security algorithms, such as SHA-256 to compute
a fingerprint over the firmware image and a digital signature
algorithm.access keying material directly or indirectly to utilize the
digital signature. The device needs to have a trust anchor store.ability to expose boot process-related data to the application
firmware (such as to the device management software). This allows
a device management server to determine whether the firmware
update has been successful and, if not, what errors occurred.to (optionally) offer attestation information (such as
measurements).While the software architecture of the bootloader and its
security mechanisms are implementation-specific, the manifest can
be used to control the firmware download from the Internet in
addition to augmenting secure boot process. These building blocks
are highly relevant for the design of the manifest. 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. The firmware
and manifest are stored on the same firmware server. This
setup does not use a status tracker and the firmware consumer
component is therefore responsible for periodically checking
whether a new firmware image is available for download. 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 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, the device under management is using
firmware version A.B.C. At a later point in time the author uploads
a new firmware along with the manifest to the firmware server and the
status tracker, respectively. While there is no need to store the
manifest and the firmware 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 the device about the newly available
firmware image. In our example, it does so by pushing the manifest
to the firmware 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.This document does not require any actions by IANA.Firmware updates fix security vulnerabilities and are considered to be
an important building block in securing IoT devices. Due to the
importance of 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 of June, 2016 to take a look at
the big picture. A report about this workshop can be found at
. 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 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, namelyinstalling firmware updates in a robust fashion so that the
update does not break the device functionality of the environment
this device operates in.installing firmware updates in a timely fashion considering the
complexity of the decision making process of updating devices,
potential re-certification requirements, and the need for user
consent to install updates.the distribution of the actual firmware update, potentially 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.The discussion list for this document is located at the e-mail
address suit@ietf.org. Information on the group and information on how to
subscribe to the list is at https://www1.ietf.org/mailman/listinfo/suitArchives of the list can be found at:
https://www.ietf.org/mail-archive/web/suit/current/index.htmlWe would like to thank the following persons for their feedback:Geraint LuffAmyas PhillipsDan RosThomas EichingerMichael RichardsonEmmanuel BaccelliNed SmithJim SchaadCarsten BormannCullen JenningsOlaf BergmannSuhas NandakumarPhillip Hallam-BakerMarti BolivarAndrzej PuzdrowskiMarkus GuellerHenk BirkholzJintao ZhuTakeshi TakahashiJacob BeningoKathleen MoriartyWe would also like to thank the WG chairs, Russ Housley, David Waltermire,
Dave Thaler for their support and their reviews.Transport Layer Security (TLS) / Datagram Transport Layer Security (DTLS) Profiles for the Internet of ThingsA common design pattern in Internet of Things (IoT) deployments is the use of a constrained device that collects data via sensors or controls actuators for use in home automation, industrial control systems, smart cities, and other IoT deployments.This document defines a Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) 1.2 profile that offers communications security for this data exchange thereby preventing eavesdropping, tampering, and message forgery. The lack of communication security is a common vulnerability in IoT products that can easily be solved by using these well-researched and widely deployed Internet security protocols.Report from the Internet of Things Software Update (IoTSU) Workshop 2016This document provides a summary of the Internet of Things Software Update (IoTSU) Workshop that took place at Trinity College Dublin, Ireland on the 13th and 14th of June, 2016. The main goal of the workshop was to foster a discussion on requirements, challenges, and solutions for bringing software and firmware updates to IoT devices. This report summarizes the discussions and lists recommendations to the standards community.Note that this document is a report on the proceedings of the workshop. The views and positions documented in this report are those of the workshop participants and do not necessarily reflect IAB views and positions.Trust Anchor Management RequirementsA trust anchor 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. A relying party uses trust anchors to determine if a digitally signed object is valid by verifying a digital signature using the trust anchor's public key, and by enforcing the constraints expressed in the associated data for the trust anchor. This document describes some of the problems associated with the lack of a standard trust anchor management mechanism and defines requirements for data formats and push-based protocols designed to address these problems. This document is not an Internet Standards Track specification; it is published for informational purposes.Advanced Encryption Standard (AES) Key Wrap with Padding AlgorithmThis document specifies a padding convention for use with the AES Key Wrap algorithm specified in RFC 3394. This convention eliminates the requirement that the length of the key to be wrapped be a multiple of 64 bits, allowing a key of any practical length to be wrapped. This memo provides information for the Internet community.Terminology for Constrained-Node NetworksThe Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks.An Information Model for Firmware Updates in IoT DevicesVulnerabilities with Internet of Things (IoT) devices have raised the need for a solid and secure firmware update mechanism that is also suitable for constrained devices. Ensuring that devices function and remain secure over their service life requires such an update mechanism to fix vulnerabilities, to update configuration settings, as well as adding new functionality One component of such a firmware update is a concise and machine- processable meta-data document, or manifest, that describes the firmware image(s) and offers appropriate protection. This document describes the information that must be present in the manifest.Trusted Execution Environment Provisioning (TEEP) ArchitectureA Trusted Execution Environment (TEE) is an environment that enforces that any code within that environment cannot be tampered with, and that any data used by such code cannot be read or tampered with by any code outside that environment. This architecture document motivates the design and standardization of a protocol for managing the lifecycle of trusted applications running inside such a TEE.Use of the HSS/LMS Hash-based Signature Algorithm with CBOR Object Signing and Encryption (COSE)This document specifies the conventions for using the Hierarchical Signature System (HSS) / Leighton-Micali Signature (LMS) hash-based signature algorithm with the CBOR Object Signing and Encryption (COSE) syntax. The HSS/LMS algorithm is one form of hash-based digital signature; it is described in RFC 8554.A Concise Binary Object Representation (CBOR)-based Serialization Format for the Software Updates for Internet of Things (SUIT) ManifestThis specification describes the format of a manifest. A manifest is a bundle of metadata about the firmware for an IoT device, where to find the firmware, the devices to which it applies, and cryptographic information protecting the manifest. Firmware updates and trusted boot both tend to use sequences of common operations, so the manifest encodes those sequences of operations, rather than declaring the metadata.Lightweight Machine to Machine Technical Specification, Version 1.0.2