Internet DRAFT - draft-ietf-suit-trust-domains
draft-ietf-suit-trust-domains
SUIT B. Moran
Internet-Draft Arm Limited
Intended status: Standards Track K. Takayama
Expires: 14 September 2023 SECOM CO., LTD.
13 March 2023
SUIT Manifest Extensions for Multiple Trust Domains
draft-ietf-suit-trust-domains-02
Abstract
This specification describes extensions to the SUIT manifest format
(as defined in [I-D.ietf-suit-manifest]) for use in deployments with
multiple trust domains. A device has more than one trust domain when
it enables delegation of different rights to mutually distrusting
entities for use for different purposes or components in the context
of firmware or software update.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Changes to SUIT Workflow Model . . . . . . . . . . . . . . . 5
4. Changes to Manifest Metadata Structure . . . . . . . . . . . 6
5. Delegation Chains . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Delegation Chains . . . . . . . . . . . . . . . . . . . . 7
6. Dependencies . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Changes to Required Checks . . . . . . . . . . . . . . 8
6.2. Changes to Manifest Structure . . . . . . . . . . . . . . 9
6.2.1. Manifest Component ID . . . . . . . . . . . . . . . . 9
6.2.2. SUIT_Dependencies Manifest Element . . . . . . . . . 9
6.3. Changes to Abstract Machine Description . . . . . . . . . 11
6.4. Processing Dependencies . . . . . . . . . . . . . . . . . 12
6.4.1. Multiple Manifest Processors . . . . . . . . . . . . 12
6.5. Dependency Resolution . . . . . . . . . . . . . . . . . . 14
6.6. Added and Modified Commands . . . . . . . . . . . . . . . 14
6.6.1. suit-directive-set-parameters . . . . . . . . . . . . 14
6.6.2. suit-directive-process-dependency . . . . . . . . . . 15
6.6.3. suit-condition-is-dependency . . . . . . . . . . . . 15
6.6.4. suit-condition-dependency-integrity . . . . . . . . . 15
6.6.5. suit-directive-unlink . . . . . . . . . . . . . . . . 16
7. Uninstall . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8. Creating Manifests . . . . . . . . . . . . . . . . . . . . . 17
8.1. Dependency Template . . . . . . . . . . . . . . . . . . . 17
8.1.1. Composite Manifests . . . . . . . . . . . . . . . . . 18
8.2. Encrypted Manifest Template . . . . . . . . . . . . . . . 18
8.3. Operating on Multiple Components . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9.1. SUIT Command Sequences . . . . . . . . . . . . . . . . . 21
9.2. SUIT Commands . . . . . . . . . . . . . . . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. A. Full CDDL . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
Devices that go beyond single-signer update require more complex
rules for deploying software updates. For example, devices may
require:
* long-term trust anchors with a mechanism to delegate trust to
short term keys.
* software components from multiple software signing authorities.
* a mechanism to remove an unneeded component
* single-object dependencies
* a partly encrypted manifest so that distribution does not reveal
private information
These mechanisms are not part of the core manifest specification, but
they are needed for more advanced use cases, such as the architecture
described in [I-D.ietf-teep-architecture].
This specification extends the SUIT Manifest specification
([I-D.ietf-suit-manifest]).
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Additionally, the following terminology is used throughout this
document:
* SUIT: Software Update for the Internet of Things, also the IETF
working group for this standard.
* Payload: A piece of information to be delivered. Typically
Software for the purposes of SUIT.
* Resource: A piece of information that is used to construct a
payload.
* Manifest: A manifest is a bundle of metadata about one or more
Components for a device, where to find them, and the devices to
which they apply.
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* Envelope: A container with the manifest, an authentication wrapper
with cryptographic information protecting the manifest,
authorization information, and severable elements (see: TBD).
* Update: One or more manifests that describe one or more payloads.
* Update Authority: The owner of a cryptographic key used to sign
updates, trusted by Recipients.
* Recipient: The system that receives and processes a manifest.
* Manifest Processor: A component of the Recipient that consumes
Manifests and executes the commands in the Manifest.
* Component: An updatable logical block of the Firmware, Software,
configuration, or data of the Recipient.
* Component Set: A group of interdependent Components that must be
updated simultaneously.
* Command: A Condition or a Directive.
* Condition: A test for a property of the Recipient or its
Components.
* Directive: An action for the Recipient to perform.
* Trusted Invocation: A process by which a system ensures that only
trusted code is executed, for example secure boot or launching a
Trusted Application.
* A/B images: Dividing a Recipient's storage into two or more
bootable images, at different offsets, such that the active image
can write to the inactive image(s).
* Record: The result of a Command and any metadata about it.
* Report: A list of Records.
* Procedure: The process of invoking one or more sequences of
commands.
* Update Procedure: A procedure that updates a Recipient by fetching
dependencies and images, and installing them.
* Invocation Procedure: A procedure in which a Recipient verifies
dependencies and images, loading images, and invokes one or more
image.
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* Software: Instructions and data that allow a Recipient to perform
a useful function.
* Firmware: Software that is typically changed infrequently, stored
in nonvolatile memory, and small enough to apply to [RFC7228]
Class 0-2 devices.
* Image: Information that a Recipient uses to perform its function,
typically Firmware/Software, configuration, or resource data such
as text or images. Also, a Payload, once installed is an Image.
* Slot: One of several possible storage locations for a given
Component, typically used in A/B image systems
* Abort: An event in which the Manifest Processor immediately halts
execution of the current Procedure. It creates a Record of an
error condition.
3. Changes to SUIT Workflow Model
The use of the features presented for use with multiple trust domains
requires some augmentation of the workflow presented in the SUIT
Manifest specification ([I-D.ietf-suit-manifest]):
One additional assumption is added for the Update Procedure:
* All dependency manifests must be present before any payload is
fetched.
One additional assumption is added to the Invocation Procedure:
* All dependencies must be validated prior to loading.
Two steps are added to the expected installation workflow of a
Recipient:
1. *Verify delegation chains*
2. Verify the signature of the manifest.
3. Verify the applicability of the manifest.
4. *Resolve dependencies.*
5. Fetch payload(s).
6. Install payload(s).
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In addition, when multiple manifests are used for an update, each
manifest's steps occur in a lockstep fashion; all manifests have
dependency resolution performed before any manifest performs a
payload fetch, etc.
4. Changes to Manifest Metadata Structure
To accommodate the additional metadata needed to enable these
features, the envelope and manifest have several new elements added.
The Envelope gains two more elements: Delegation chains and
Integrated Dependencies The Common metadata section in the Manifest
also gains a list of dependencies.
The new metadata structure is shown below.
+-------------------------+
| Envelope |
+-------------------------+
| Delegation Chains |
| Authentication Block |
| Manifest --------------> +------------------------------+
| Severable Elements | | Manifest |
| Human-Readable Text | +------------------------------+
| CoSWID | | Structure Version |
| Integrated Dependencies | | Sequence Number |
| Integrated Payloads | | Reference to Full Manifest |
+-------------------------+ +------ Common Structure |
| +---- Command Sequences |
+-------------------------+ | | | Digests of Envelope Elements |
| Common Structure | <--+ | +------------------------------+
+-------------------------+ |
| Dependency Indices | +-> +-----------------------+
| Component IDs | | Command Sequence |
| Common Command Sequence ---------> +-----------------------+
+-------------------------+ | List of ( pairs of ( |
| * command code |
| * argument / |
| reporting policy |
| )) |
+-----------------------+
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5. Delegation Chains
Delegation Chains allow a Recipient to establish a chain of trust
from a Trust Anchor to the signer of a manifest by validating
delegation claims. Each delegation claim is a [RFC8392] CBOR Web
Tokens (CWTs). The first claim in each list is signed by a Trust
Anchor. Each subsequent claim in a list is signed by the public key
claimed in the preceding list element. The last element in each list
claims a public key that can be used to verify a signature in the
Authentication Block (See Sectino 5.2 of [I-D.ietf-suit-manifest]).
See Section 5.1 for more detail.
5.1. Delegation Chains
The suit-delegation element MAY carry one or more CBOR Web Tokens
(CWTs) [RFC8392], with [RFC8747] cnf claims. They can be used to
perform enhanced authorization decisions. The CWTs are arranged into
a list of lists. Each list starts with a CWT authorized by a Trust
Anchor, and finishes with a key used to authenticate the Manifest
(see Section 8.3 of [I-D.ietf-suit-manifest]). This allows an Update
Authority to delegate from a long term Trust Anchor, down through
intermediaries, to a delegate without any out-of-band provisioning of
Trust Anchors or intermediary keys.
A Recipient MAY choose to cache intermediaries and/or delegates. If
an Update Distributor knows that a targeted Recipient has cached some
intermediaries or delegates, it MAY choose to strip any cached
intermediaries or delegates from the Delegation Chains in order to
reduce bandwidth and energy.
6. Dependencies
A dependency is another SUIT_Envelope that describes additional
components.
Dependency manifests enable several additional use cases. In
particular, they enable two or more entities who are trusted for
different privileges to coordinate. This can be used in many
scenarios, for example:
* A device may contain a processor in its radio in addition to the
primary processor. These two processors may have separate
firmware with separate signing authorities. Dependencies allow
the firmware for the primary processor to reference a manifest
signed by a different authority.
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* A network operator may wish to provide local caching of update
payloads. The network operator overrides the URI of a payload by
providing a dependent manifest that references the original
manifest, but replaces its URI.
* A device operator provides a device with some additional
configuration. The device operator wants to test their
configuration with each new firmware version before releasing it.
The configuration is delivered as a binary in the same way as a
firmware image. The device operator references the firmware
manifest from the firmware author in their own manifest which also
defines the configuration.
By using dependencies, components such as Software, configuration,
models, and other resources authenticated by different trust anchors
can be delivered to devices.
6.1. Changes to Required Checks
This section augments the definitions in Required Checks
(Section 6.2) of [I-D.ietf-suit-manifest].
More checks are required when handling dependencies. By default, any
signature of a dependency MUST be verified. However, there are some
exceptions to this rule: where a device supports only one level of
access (no ACLs defining which authorities have access to different
components/commands/parameters), it MAY choose to skip signature
verification of dependencies, since they are verified by digest.
Where a device differentiates between trust levels, such as with an
ACL, it MAY choose to defer the verification of signatures of
dependencies until the list of affected components is known so that
it can skip redundant signature verifications. For example, if a
dependent's signer has access rights to all components specified in a
dependency, then that dependency does not require a signature
verification. Similarly, if the signer of the dependent has full
rights to the device, according to the ACL, then no signature
verification is necessary on the dependency.
Components that should be treated as dependency manifests are
identified in the suit-common metadata. See section Section 6.2 for
details.
If the manifest contains more than one component and/or dependency,
each command sequence MUST begin with a Set Component Index command.
If a dependency is specified, then the manifest processor MUST
perform the following checks:
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1. The dependent MUST populate all command sequences for the current
procedure (Update or Invoke).
2. At the end of each section in the dependent: The corresponding
section in each dependency has been executed.
If the interpreter does not support dependencies and a manifest
specifies a dependency, then the interpreter MUST Abort.
If a Recipient supports groups of interdependent components (a
Component Set), then it SHOULD verify that all Components in the
Component Set are specified by one update, that is: a single manifest
and all its dependencies that together:
1. have sufficient permissions imparted by their signatures
2. specify a digest and a payload for every Component in the
Component Set.
The single dependent manifest is sometimes called a Root Manifest.
6.2. Changes to Manifest Structure
This section augments the Manifest Structure (Section 8.4) in
[I-D.ietf-suit-manifest].
6.2.1. Manifest Component ID
In complex systems, it may not always be clear where the root
manifest should be stored; this is particularly complex when a system
has multiple, independent root manifests. The manifest component ID
resolves this contention. The manifest-component-id is intended to
be used by the root manifest. When a dependency manifest also
declares a component ID, the dependency manifest's component ID is
overridden by the component ID declared by the dependent.
The following CDDL describes the manifest component ID:
$$SUIT_Manifest_Extensions //=
(suit-manifest-component-id => SUIT_Component_Identifier)
6.2.2. SUIT_Dependencies Manifest Element
The suit-common section, as described in [I-D.ietf-suit-manifest],
Section 8.4.5 is extended with a map of component indices that
indicate a dependency manifest. The key of the map are the component
indices and the values of the map are any extra metadata needed to
describe those dependency manifests.
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Because some operations treat dependency manifests differently from
other components, it is necessary to identify them.
SUIT_Dependencies identifies which components from suit-components
(See Section 8.4.5 of [I-D.ietf-suit-manifest]) are to be treated as
dependency manifest envelopes. SUIT_Dependencies is a map of
Components, referenced by Component Index. Optionally, a component
prefix or other metadata may be delivered with the component index.
The CDDL for suit-dependencies is shown below:
$$SUIT_Common-extensions //= (
suit-dependencies => SUIT_Dependencies
)
SUIT_Dependencies = {
+ uint => SUIT_Dependency_Metadata
}
SUIT_Dependency_Metadata = {
? suit-dependency-prefix => SUIT_Component_Identifier
$$SUIT_Dependency_Extensions
}
If no extended metadata is needed for an extension,
SUIT_Dependency_Metadata is an empty map (this is the same encoding
size as a null). SUIT_Dependencies MUST be sorted according to CBOR
canonical encoding.
The components specified by SUIT_Dependency will contain a Manifest
Envelope that describes a dependency of the current manifest. The
Manifest is identified, but the Recipient should expect an Envelope
when it acquires the dependency. This is because the Manifest is the
one invariant element of the Envelope, where other elements may
change by countersigning, adding authentication blocks, or severing
elements.
When executing suit-condition-image-match over a component that is
designated in SUIT_Dependency, the digest MUST be computed over just
the bstr-wrapped SUIT_Manifest contained in the Manifest Envelope
designated by the Component Index. This enables a dependency
reference to uniquely identify a particular Manifest structure. This
is identical to the digest that is present as the first element of
the suit-authentication-block in the dependency's Envelope. The
digest is calculated over the Manifest structure to ensure that
removing a signature from a manifest does not break dependencies due
to missing signature elements. This is also necessary to support the
trusted intermediary use case, where an intermediary re-signs the
Manifest, removing the original signature, potentially with a
different algorithm, or trading COSE_Sign for COSE_Mac.
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The suit-dependency-prefix element contains a
SUIT_Component_Identifier (see Section 8.4.5.1 of
[I-D.ietf-suit-manifest]). This specifies the scope at which the
dependency operates. This allows the dependency to be forwarded on
to a component that is capable of parsing its own manifests. It also
allows one manifest to be deployed to multiple dependent Recipients
without those Recipients needing consistent component hierarchy.
This element is OPTIONAL for Recipients to implement.
A dependency prefix can be used with a component identifier. This
allows complex systems to understand where dependencies need to be
applied. The dependency prefix can be used in one of two ways. The
first simply prepends the prefix to all Component Identifiers in the
dependency.
A dependency prefix can also be used to indicate when a dependency
manifest needs to be processed by a secondary manifest processor, as
described in Section 6.4.1.
6.3. Changes to Abstract Machine Description
This section augments the Abstract Machine Description (Section 6.4)
in [I-D.ietf-suit-manifest]. With the addition of dependencies, some
changes are necessary to the abstract machine, outside the typical
scope of added commands. These changes alter the behaviour of an
existing command and way that the parser processes manifests:
* Three new commands are introduced.
- Process dependency
- Is Dependency
- Dependency Integrity
* Dependency manifests are also Components. All commands may target
dependency manifests as well as Components, with one exception:
process dependency. Commands defined outside of this draft and
[I-D.ietf-suit-manifest] MAY have additional restrictions.
* Dependencies are processed in lock-step with the Root Manifest.
This means that every dependency's current command sequence must
be executed before a dependent's later command sequence may be
executed. For example, every dependency's Dependency Resolution
step MUST be executed before any dependent's payload fetch step.
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6.4. Processing Dependencies
As described in Section 6.1, each manifest must invoke each of its
dependencies' sections from the corresponding section of the
dependent. Any changes made to parameters by the dependency persist
in the dependent.
When a Process Dependency command is encountered, the manifest
processor:
1. Checks whether the map of dependencies contains an entry for the
current Component Index. If not present, it causes an immediate
Abort.
2. Checks whether the dependency has been the target of a dependency
integrity check. If not, it causes an immediate Abort.
3. Loads the specified component as a dependency manifest envelope.
4. Authenticates the dependency manifest.
5. Executes the common-sequence section of the dependency manifest.
6. Executes the section of the dependency manifest that corresponds
to the currently executing section of the dependent.
If the specified dependency does not contain the current section,
Process Dependency succeeds immediately.
The interpreter also performs the checks described in Section 6.1 to
ensure that the dependent is processing the dependency correctly.
6.4.1. Multiple Manifest Processors
When a system has multiple trust domains, each domain might require
independent verification of authenticity or security policies. Trust
domains might be divided by separation technology such as Arm
TrustZone, Intel SGX, or another TEE technology. Trust domains might
also be divided into separate processors and memory spaces, with a
communication interface between them.
For example, an application processor may have an attached
communications module that contains a processor. The communications
module might require metadata signed by a specific Trust Authority
for regulatory approval. This may be a different Trust Authority
than the application processor.
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When there are two or more trust domains, a manifest processor might
be required in each. The first manifest processor is the normal
manifest processor as described for the Recipient in Section 6 of
[I-D.ietf-suit-manifest]. The second manifest processor only
executes sections when the first manifest processor requests it. An
API interface is provided from the second manifest processor to the
first. This allows the first manifest processor to request a limited
set of operations from the second. These operations are limited to:
setting parameters, inserting an Envelope, and invoking a Manifest
Command Sequence. The second manifest processor declares a prefix to
the first, which tells the first manifest processor when it should
delegate to the second. These rules are enforced by underlying
separation of privilege infrastructure, such as TEEs, or physical
separation.
When the first manifest processor encounters a dependency prefix,
that informs the first manifest processor that it should provide the
second manifest processor with the corresponding dependency Envelope.
This is done when the dependency is fetched. The second manifest
processor immediately verifies any authentication information in the
dependency Envelope. When a parameter is set for any component that
matches the prefix, this parameter setting is passed to the second
manifest processor via an API. As the first manifest processor works
through the Procedure (set of command sequences) it is executing,
each time it sees a Process Dependency command that is associated
with the prefix declared by the second manifest processor, it uses
the API to ask the second manifest processor to invoke that
dependency section instead.
This mechanism ensures that the two or more manifest processors do
not need to trust each other, except in a very limited case. When
parameter setting across trust domains is used, it must be very
carefully considered. Only parameters that do not have an effect on
security properties should be allowed. The dependency manifest MAY
control which parameters are allowed to be set by using the Override
Parameters directive. The second manifest processor MAY also control
which parameters may be set by the first manifest processor by means
of an ACL that lists the allowed parameters. For example, a URI may
be set by a dependent without a substantial impact on the security
properties of the manifest.
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6.5. Dependency Resolution
The Dependency Resolution Command Sequence is a container for the
commands needed to acquire and process the dependencies of the
current manifest. Ideally, all dependency manifests should be
fetched before any payload is fetched to ensure that all manifests
are available and authenticated before any of the (larger) payloads
are acquired.
6.6. Added and Modified Commands
All commands are modified in that they can also target dependencies.
However, Set Component Index has a larger modification.
+================+====================================+
| Command Name | Semantic of the Operation |
+================+====================================+
| Set Parameters | current.params[k] := v if not k in |
| | current.params for-each k,v in arg |
+----------------+------------------------------------+
| Process | exec(current[common]); |
| Dependency | exec(current[current-segment]) |
+----------------+------------------------------------+
| Dependency | verify(current, |
| Integrity | current.params[image-digest]) |
+----------------+------------------------------------+
| Is Dependency | assert(current exists in |
| | dependencies) |
+----------------+------------------------------------+
| Unlink | unlink(current) |
+----------------+------------------------------------+
Table 1
6.6.1. suit-directive-set-parameters
Similarly to suit-directive-override-parameters, suit-directive-set-
parameters allows the manifest to configure behavior of future
directives by changing parameters that are read by those directives.
Set Parameters is for use when dependencies are used because it
allows a manifest to modify the behavior of its dependencies.
Available parameters are defined in [I-D.ietf-suit-manifest], section
8.4.8.
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If a parameter is already set, suit-directive-set-parameters will
skip setting the parameter to its argument. This allows dependent
manifests to change the behavior of a manifest, a dependency that
wishes to enforce a specific value of a parameter MAY use suit-
directive-override-parameters instead.
suit-directive-set-parameters does not specify a reporting policy.
6.6.2. suit-directive-process-dependency
Execute the commands in the common section of the current dependency,
followed by the commands in the equivalent section of the current
dependency. For example, if the current section is "fetch payload,"
this will execute "common" in the current dependency, then "fetch
payload" in the current dependency. Once this is complete, the
command following suit-directive-process-dependency will be
processed.
If the current component index does not have an entry in the suit-
dependencies map, then this command MUST Abort.
If the current component index has not been the target of a suit-
condition-dependency-integrity, then this command MUST Abort.
If the current component is True, then this directive applies to all
dependencies. If the current section is "common," then the command
sequence MUST Abort.
When SUIT_Process_Dependency completes, it forwards the last status
code that occurred in the dependency.
6.6.3. suit-condition-is-dependency
Check whether or not the current component index is present in the
dependency list. If the current component is in the dependency list,
suit-condition-is-dependency succeeds. Otherwise, it fails. This
can be used along with component-id = True to act on all dependencies
or on all non-dependency components. See Section 8 for more details.
6.6.4. suit-condition-dependency-integrity
Verify the integrity of a dependency manifest. When a Manifest
Processor executes suit-condition-dependency-integrity, it performs
the following operations:
1. Evaluate any delegation chains
2. Verify the signature of the manifest hash
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3. Compare the manifest hash to the provided hash
4. Verify the manifest against the manifest hash
If any of these steps fails, the Manifest Process MUST immediately
Abort.
The Manifest Processor MAY cache the results of these operations for
later use from the context of the current manifest. The Manifest
Processor MUST NOT use cached results from any other manifest
context. If the Manifest Processor caches the results of these
checks, it MUST eliminate this cache if any Fetch, or Copy operation
targets the Dependency Manifest's component ID.
6.6.5. suit-directive-unlink
suit-directive-unlink applies to manifests. When the components
defined by a manifest are no longer needed, the manifest processor
unlinks the manifest to inform the manifest processor that they are
no longer needed. The unlink command decrements an implementation-
defined reference counter. This reference counter MUST persist
across restarts. The reference counter MUST NOT be decremented by a
given manifest more than once, and the manifest processor must
enforce this. The manifest processor MAY choose to ignore a Unlink
directive depending on device policy.
When the reference counter reaches zero, the suit-uninstall command
sequence is invoked (see Section 7).
suit-directive-unlink is OPTIONAL to implement in manifest
processors.
7. Uninstall
In some systems, particularly with multiple, independent, optional
components, it may be that there is a need to uninstall the
components that have been installed by a manifest. Where this is
expected, the uninstall command sequence can provide the sequence
needed to cleanly remove the components defined by the manifest and
its dependencies. In general, suit uninstall will contain primarily
unlink directives.
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WARNING: This can cause faults where there are loose dependencies
(e.g., version range matching, see
[I-D.ietf-suit-update-management]), since a component can be removed
while it is depended upon by another component. To avoid dependency
faults, a manifest author MAY use explicit dependencies where
possible, or a manifest processor MAY track references to loose
dependencies via reference counting in the same way as explicit
dependencies, as described in Section 6.6.5.
The Uninstall command sequence is not severable, since it must always
be available to enable uninstalling.
8. Creating Manifests
This section details a set of templates for creating manifests.
These templates explain which parameters, commands, and orders of
commands are necessary to achieve a stated goal.
8.1. Dependency Template
The goal of the Dependency template is to obtain, verify, and process
a dependency manifest as appropriate.
The following commands are added to the shared sequence:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Set Parameters directive (see Section 6.6.1) for digest (see
Section 8.4.8.6 of [I-D.ietf-suit-manifest]). Note that the
digest MUST match the SUIT_Digest in the dependency's suit-
authentication-block (See Section 8.3 of
[I-D.ietf-suit-manifest]).
The following commands are placed into the dependency resolution
sequence:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Set Parameters directive (see Section 6.6.1) for URI (see
Section 8.4.8.10 of [I-D.ietf-suit-manifest])
* Fetch directive (see Section 8.4.10.4 of [I-D.ietf-suit-manifest])
* Dependency Integrity condition (see Section 6.6.4)
* Process Dependency directive (see Section 6.6.2)
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Then, the validate sequence contains the following operations:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Dependency Integrity condition (see Section 6.6.4)
* Process Dependency directive (see Section 6.6.2)
If any dependency is declared, the dependent MUST populate all
command sequences for the current procedure (Update or Invoke).
NOTE: Any changes made to parameters in a dependency persist in the
dependent.
8.1.1. Composite Manifests
An implementer MAY choose to place a dependency's envelope in the
envelope of its dependent. The dependent envelope key for the
dependency envelope MUST be a text string. The URI for the
dependency MUST match the text string key of the dependent's envelope
key. It is RECOMMENDED to make the text string key a resolvable URI
so that a dependency manifest that is removed from the envelope can
still be fetched.
8.2. Encrypted Manifest Template
The goal of the Encrypted Manifest template is to fetch and decrypt a
manifest so that it can be used as a dependency. To use an encrypted
manifest, create a plaintext dependent, and add the encrypted
manifest as a dependency. The dependent can include very little
information.
NOTE: This template also requires the extensions defined in
[I-D.ietf-suit-firmware-encryption].
The following commands are added to the shared sequence:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Set Parameters directive (see Section 6.6.1) for digest (see
Section 8.4.8.6 of [I-D.ietf-suit-manifest]). Note that the
digest MUST match the SUIT_Digest in the dependency's suit-
authentication-block (See Section 8.3 of
[I-D.ietf-suit-manifest]).
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The following operations are placed into the dependency resolution
block:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Set Parameters directive (see Section 6.6.1) for
- URI (see Section 8.4.8.9 of [I-D.ietf-suit-manifest])
- Encryption Info (See [I-D.ietf-suit-firmware-encryption])
* Fetch directive (see Section 8.4.10.4 of [I-D.ietf-suit-manifest])
* Dependency Integrity condition (see Section 6.6.4)
* Process Dependency directive (see Section 6.6.2)
Then, the validate block contains the following operations:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Check Image Match condition (see Section 8.4.9.2 of
[I-D.ietf-suit-manifest])
* Process Dependency directive (see Section 6.6.2)
A plaintext manifest and its encrypted dependency may also form a
composite manifest (Section 8.1.1).
8.3. Operating on Multiple Components
In order to produce compact encoding, it is efficient to perform
operations on multiple components simultaneously. Because Dependency
Manifests and Component Images are processed at different times,
there is a mechanism to distinguish between these elements: suit-
condition-is-manifest. This can be used with suit-directive-try-each
to perform operations just on Dependency Manifests or just on
Component Images.
For example, to fetch all dependency manifests, the following
commands are added to the dependency resolution block:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Set Parameters directive (see Section 6.6.1) for
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- URI (see Section 8.4.8.9 of [I-D.ietf-suit-manifest])
* Set Component Index directive, with argument "True" (see
Section 8.4.10.1 of [I-D.ietf-suit-manifest])
* Try Each Directive
- Sequence 0
o Condition Is Manifest
o Fetch
o Dependency Integrity condition (see Section 6.6.4)
o Process Dependency
- Sequence 1 (Empty; no commands, succeeds immediately)
Another example is to fetch and validate all Component Images. The
image fetch sequence contains the following commands:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Set Parameters directive (see Section 6.6.1) for
- URI (see Section 8.4.8.9 of [I-D.ietf-suit-manifest])
* Set Component Index directive, with argument "True" (see
Section 8.4.10.1 of [I-D.ietf-suit-manifest])
* Try Each Directive
- Sequence 0
o Condition Is Manifest
o Process Dependency
- Sequence 1
o Fetch
o Condition Image Match
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When some components are "installed" or "loaded" it is more
productive to use lists of component indices rather than Component
Index = True. For example, to install several components, the
following commands should be placed in the image install sequence:
* Set Component Index directive (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Set Parameters directive (see Section 6.6.1) for
- Source Component (see Section 8.4.8.11 of
[I-D.ietf-suit-manifest])
* Set Component Index directive, with argument containing list of
destination component indices (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Copy
* Set Component Index directive, with argument containing list
dependency component indices (see Section 8.4.10.1 of
[I-D.ietf-suit-manifest])
* Process Dependency
9. IANA Considerations
IANA is requested to allocate the following numbers in the listed
registries:
9.1. SUIT Command Sequences
+=======+=======================+=============+
| Label | Name | Reference |
+=======+=======================+=============+
| 1 | Delegation | Section 5 |
+-------+-----------------------+-------------+
| 15 | Dependency Resolution | Section 6.5 |
+-------+-----------------------+-------------+
| 24 | Uninstall | Section 7 |
+-------+-----------------------+-------------+
Table 2
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9.2. SUIT Commands
+=======+======================+===============+
| Label | Name | Reference |
+=======+======================+===============+
| 7 | Dependency Integrity | Section 6.6.4 |
+-------+----------------------+---------------+
| 8 | Is Dependency | Section 6.6.3 |
+-------+----------------------+---------------+
| 11 | Process Dependency | Section 6.6.2 |
+-------+----------------------+---------------+
| 19 | Set Parameters | Section 6.6.1 |
+-------+----------------------+---------------+
| 33 | Unlink | Section 6.6.5 |
+-------+----------------------+---------------+
Table 3
10. Security Considerations
This document is about a manifest format protecting and describing
how to retrieve, install, and invoke firmware images and as such it
is part of a larger solution for delivering software updates to
devices. A detailed security treatment can be found in the
architecture [RFC9019] and in the information model [RFC9124]
documents.
11. References
11.1. Normative References
[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., Zandberg, K., and
O. Rønningstad, "A Concise Binary Object Representation
(CBOR)-based Serialization Format for the Software Updates
for Internet of Things (SUIT) Manifest", Work in Progress,
Internet-Draft, draft-ietf-suit-manifest-22, 27 February
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
suit-manifest-22>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/info/rfc8747>.
[RFC9019] Moran, B., Tschofenig, H., Brown, D., and M. Meriac, "A
Firmware Update Architecture for Internet of Things",
RFC 9019, DOI 10.17487/RFC9019, April 2021,
<https://www.rfc-editor.org/info/rfc9019>.
[RFC9124] Moran, B., Tschofenig, H., and H. Birkholz, "A Manifest
Information Model for Firmware Updates in Internet of
Things (IoT) Devices", RFC 9124, DOI 10.17487/RFC9124,
January 2022, <https://www.rfc-editor.org/info/rfc9124>.
11.2. Informative References
[I-D.ietf-suit-firmware-encryption]
Tschofenig, H., Housley, R., Moran, B., Brown, D., and K.
Takayama, "Encrypted Payloads in SUIT Manifests", Work in
Progress, Internet-Draft, draft-ietf-suit-firmware-
encryption-11, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-suit-
firmware-encryption-11>.
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[I-D.ietf-suit-update-management]
Moran, B., "Update Management Extensions for Software
Updates for Internet of Things (SUIT) Manifests", Work in
Progress, Internet-Draft, draft-ietf-suit-update-
management-01, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-suit-
update-management-01>.
[I-D.ietf-teep-architecture]
Pei, M., Tschofenig, H., Thaler, D., and D. M. Wheeler,
"Trusted Execution Environment Provisioning (TEEP)
Architecture", Work in Progress, Internet-Draft, draft-
ietf-teep-architecture-19, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-teep-
architecture-19>.
Appendix A. A. Full CDDL
To be valid, the following CDDL MUST be appended to the SUIT Manifest
CDDL. The SUIT CDDL is defined in Appendix A of
[I-D.ietf-suit-manifest]
$$SUIT_Envelope_Extensions //=
(suit-delegation => bstr .cbor SUIT_Delegation)
$$SUIT_Envelope_Extensions //= (
suit-integrated-dependency-key => bstr .cbor SUIT_Envelope)
SUIT_Delegation = [ + [ + bstr .cbor CWT ] ]
CWT = SUIT_Authentication_Block
$$SUIT_Manifest_Extensions //=
(suit-manifest-component-id => SUIT_Component_Identifier)
$$SUIT_severable-members-extensions //=
(suit-dependency-resolution => bstr .cbor SUIT_Command_Sequence)
$$unseverable-manifest-member-extensions //=
(suit-uninstall => bstr .cbor SUIT_Command_Sequence)
suit-integrated-dependency-key = tstr
$$severable-manifest-members-choice-extensions //= (
suit-dependency-resolution =>
bstr .cbor SUIT_Command_Sequence / SUIT_Digest)
$$SUIT_Common-extensions //= (
suit-dependencies => SUIT_Dependencies
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)
SUIT_Dependencies = {
+ uint => SUIT_Dependency_Metadata
}
SUIT_Dependency_Metadata = {
? suit-dependency-prefix => SUIT_Component_Identifier
* $$SUIT_Dependency_Extensions
}
SUIT_Condition //= (
suit-condition-is-dependency, SUIT_Rep_Policy)
SUIT_Directive //= (
suit-directive-process-dependency, SUIT_Rep_Policy)
SUIT_Directive //= (suit-directive-set-parameters,
{+ $$SUIT_Parameters})
SUIT_Directive //= (
suit-directive-unlink, SUIT_Rep_Policy)
suit-manifest-component-id = 5
suit-delegation = 1
suit-dependency-resolution = 15
suit-uninstall = 24
suit-dependencies = 1
suit-dependency-prefix = 1
suit-condition-dependency-integrity = 7
suit-condition-is-dependency = 8
suit-directive-process-dependency = 11
suit-directive-set-parameters = 19
suit-directive-unlink = 33
Authors' Addresses
Brendan Moran
Arm Limited
Email: brendan.moran.ietf@gmail.com
Ken Takayama
SECOM CO., LTD.
Email: ken.takayama.ietf@gmail.com
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