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draft-ietf-suit-trust-domains.txt
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SUIT B. Moran
Internet-Draft Arm Limited
Intended status: Standards Track K. Takayama
Expires: 7 June 2025 SECOM CO., LTD.
4 December 2024
SUIT Manifest Extensions for Multiple Trust Domains
draft-ietf-suit-trust-domains-09
Abstract
This specification describes extensions to the SUIT Manifest format
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 7 June 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Changes to SUIT Workflow Model . . . . . . . . . . . . . . . 6
4. Changes to Manifest Metadata Structure . . . . . . . . . . . 7
5. Dependencies . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Changes to Required Checks . . . . . . . . . . . . . . 8
5.2. Changes to Manifest Structure . . . . . . . . . . . . . . 9
5.2.1. Manifest Component ID . . . . . . . . . . . . . . . . 10
5.2.2. SUIT_Dependencies Manifest Element . . . . . . . . . 10
5.3. Changes to Abstract Machine Description . . . . . . . . . 11
5.4. Processing Dependencies . . . . . . . . . . . . . . . . . 12
5.4.1. Multiple Manifest Processors . . . . . . . . . . . . 13
5.5. Dependency Resolution . . . . . . . . . . . . . . . . . . 14
5.6. Added and Modified Commands . . . . . . . . . . . . . . . 14
5.6.1. suit-directive-set-parameters . . . . . . . . . . . . 15
5.6.2. suit-directive-process-dependency . . . . . . . . . . 15
5.6.3. suit-condition-is-dependency . . . . . . . . . . . . 16
5.6.4. suit-condition-dependency-integrity . . . . . . . . . 16
5.6.5. suit-directive-unlink . . . . . . . . . . . . . . . . 17
6. Uninstall . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Staging and Installation . . . . . . . . . . . . . . . . . . 18
7.1. suit-candidate-verification . . . . . . . . . . . . . . . 19
8. Creating Manifests . . . . . . . . . . . . . . . . . . . . . 19
8.1. Dependency Template . . . . . . . . . . . . . . . . . . . 19
8.1.1. Integrated Dependencies . . . . . . . . . . . . . . . 20
8.2. Encrypted Manifest Template . . . . . . . . . . . . . . . 20
8.3. Overriding Encryption Info Template . . . . . . . . . . . 21
8.4. Operating on Multiple Components . . . . . . . . . . . . 23
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9.1. SUIT Envelope Elements . . . . . . . . . . . . . . . . . 25
9.2. SUIT Manifest Elements . . . . . . . . . . . . . . . . . 25
9.3. SUIT Common Elements . . . . . . . . . . . . . . . . . . 25
9.4. SUIT Commands . . . . . . . . . . . . . . . . . . . . . . 26
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.1. Normative References . . . . . . . . . . . . . . . . . . 26
11.2. Informative References . . . . . . . . . . . . . . . . . 27
Appendix A. A. Full CDDL . . . . . . . . . . . . . . . . . . . 28
Appendix B. B. Examples . . . . . . . . . . . . . . . . . . . . 29
B.1. Example 0: Process Dependency . . . . . . . . . . . . . . 30
B.2. Example 1: Integrated Dependency . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
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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:
* 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
* installation performed by a different execution mode than payload
fetch
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
Software with separate signing authorities. Dependencies allow
the Software for the primary processor to reference a Manifest
signed by a different authority.
* 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 Software version before releasing it.
The configuration is delivered as a binary in the same way as a
Software Image. The device operator references the Software
Manifest from the Software author in their own Manifest which also
defines the configuration.
* An Author wants to entrust a Distributor to provide devices with
firmware decryption keys, but not permit the Distributor to sign
code. Dependencies allow the Distributor to deliver a device's
decryption information without also granting code signing
authority.
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* A Trusted Application Manager (TAM) wants to distribute
personalisation information to a Trusted Execution Environment in
addition to a Trusted Application (TA), but does not have code
signing authority. Dependencies enable the TAM to construct an
update containing the personalisation information and a dependency
on the TA, but leaves the TA signed by the TA's Author.
By using Dependencies, Components such as Software, configuration,
and other Resource data authenticated by different Trust Anchors can
be delivered to devices.
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
Firmware/Software, configuration, or Resource data such as text or
images.
* 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.
* Envelope: A container with the Manifest, an authentication wrapper
with cryptographic information protecting the Manifest,
authorization information, and severable elements (see Section 5.1
of [I-D.ietf-suit-manifest]).
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* 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 superset of Staging Procedure and Installation
Procedure.
* Staging Procedure: A procedure that fetches dependencies and
images referenced by an Update and stores them to a Staging Area.
* Installation Procedure: A procedure that installs dependencies and
images stored in a Staging Area; copying (and optionally,
transforming them) into an active Image storage location.
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* Invocation Procedure: A Procedure in which a Recipient verifies
Dependencies and Images, loading Images, and invokes one or more
Image.
* Staging Area: A Component or group of Components that are used for
transient storage of Images between fetch and installation.
Images in this area are opaque, except for use by the Installation
Procedure.
* 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.
* 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.
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.
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Steps 3 and 5 are added to the expected installation workflow of a
Recipient:
1. Verify the signature of the Manifest.
2. Verify the applicability of the Manifest.
3. Resolve Dependencies.
4. Fetch Payload(s).
5. Verify Candidate.
6. Install Payload(s).
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 one more elements: Integrated Dependencies. The
Common metadata section in the Manifest also gains a list of
Dependencies.
The new metadata structure is shown below.
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+-------------------------+
| Envelope |
+-------------------------+
| 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 |
| )) |
+-----------------------+
5. Dependencies
A Dependency is another SUIT_Envelope that describes additional
Components.
As described in Section 1, Dependencies enable several common use
cases.
5.1. 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
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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 5.2 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:
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 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.
5.2. Changes to Manifest Structure
This section augments the Manifest Structure (Section 8.4) in
[I-D.ietf-suit-manifest].
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5.2.1. 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:
$$SUIT_Manifest_Extensions //=
(suit-manifest-component-id => SUIT_Component_Identifier)
5.2.2. SUIT_Dependencies Manifest Element
The suit-common section, as described in [I-D.ietf-suit-manifest],
Section 8.4.5 is extended with a map of Component indices that
indicate a Dependency Manifest. The keys of the map are the
Component indices and the values of the map are any extra metadata
needed to describe those Dependency Manifests.
Because some operations treat Dependency Manifests differently from
other Components, it is necessary to identify them.
SUIT_Dependencies identifies which Components from suit-components
(see Section 8.4.5 of [I-D.ietf-suit-manifest]) are to be treated as
Dependency Manifest Envelopes. SUIT_Dependencies is a map of
Components, referenced by Component Index. Optionally, a Component
prefix or other metadata may be delivered with the Component index.
The CDDL for suit-dependencies is shown below:
$$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.
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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.
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 5.4.1.
5.3. 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:
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* Five new Commands are introduced:
- Set Parameters
- Process Dependency
- Is Dependency
- Dependency Integrity
- Unlink
* 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 lockstep 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.
* When a Manifest Processor supports multiple independent
Components, they MAY have shared Dependencies.
* When a Manifest Processor supports shared Dependencies, it MUST
support reference counting of those Dependencies.
* When reference counting is used, Components MUST NOT be
overwritten. The Manifest Uninstall section must be called, then
the component MUST be Unlinked.
5.4. Processing Dependencies
As described in Section 5.1, 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.
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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 5.1 to
ensure that the dependent is processing the Dependency correctly.
5.4.1. 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 Trusted Execution Environment (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.
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.
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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.
5.5. Dependency Resolution
The Dependency Resolution Command Sequence is a container for the
Commands needed to acquire and process the Dependencies of the
current Manifest. 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.
5.6. Added and Modified Commands
All Commands are modified in that they can also target Dependencies.
However, Set Component Index has a larger modification.
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+================+====================================+
| 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
5.6.1. suit-directive-set-parameters
Similar 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.
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.
5.6.2. 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 "Payload Fetch,"
this will execute "Common metadata" in the current Dependency, then
"Payload Fetch" in the current Dependency. Once this is complete,
the Command following suit-directive-process-dependency will be
processed.
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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 metadata," then the
Command sequence MUST Abort.
When SUIT_Process_Dependency completes, it forwards the last status
code that occurred in the Dependency.
5.6.3. suit-condition-is-dependency
Check whether 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.
5.6.4. 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. Verify the signature of the Dependency's suit-authentication-
wrapper.
2. Compare the Dependency's suit-authentication-wrapper digest to
the dependent's suit-parameter-image-digest
3. Verify the Dependency Manifest against the Depedency's suit-
authentication-wrapper digest
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.
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5.6.5. suit-directive-unlink
A manifest processor that supports multiple independent root
manifests MUST support suit-directive-unlink. When a Component is no
longer needed, the Manifest processor unlinks the Component to inform
the Manifest processor that it is no longer needed.
If a Manifest is no longer needed, the Manifest Processor unlinks it.
This causes the Manifest Processor to execute the suit-uninstall
section of the unlinked Manifest, after which it decrements the
reference count of the unlinked Manifest. The suit-uninstall section
of a manifest typically contains an unlink of all its dependencies
and components.
All components, including Manifests must be unlinked before deletion
or overwrite. If the reference count of a component is non-zero, any
command that alters that component MUST cause an immediate ABORT.
Affected commands are:
* suit-directive-copy
* suit-directive-fetch
* suit-directive-write
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 an Unlink Directive depending
on device policy.
When the reference counter of a Manifest reaches zero, the suit-
uninstall Command sequence is invoked (see Section 6).
suit-directive-unlink is OPTIONAL to implement in Manifest
processors, but Manifest processors that support multiple independent
Root Manifests MUST support suit-directive-unlink.
6. 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, the suit-uninstall Command Sequence
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 5.6.5.
The suit-uninstall Command Sequence is not severable, since it must
always be available to enable uninstalling.
7. Staging and Installation
In order to coordinate between download and installation in different
trust domains, the Update Procedure defined in
[I-D.ietf-suit-manifest], Section 8.4.6 is divided into two sub-
procedures:
* The Staging Procedure: This procedure is responsible for
dependency resolution and acquiring all payloads required for the
Update to proceed. It is composed of two command sequences
- suit-dependency-resolution
- suit-payload-fetch
* The Installation Procedure: This procedure is responsible for
verifying staged components and installing them. It is composed
of:
- suit-candidate-verification
- suit-install
This extension is backwards compatible when used with a Manifest
Processor that supports the Update Procedure but = does not support
the Staging Procedure and Installation Procedure: the payload-fetch
command sequence already contains suit-condition-image tests for each
payload (see [I-D.ietf-suit-manifest], section 7.3) which means that
images are already validated when suit-install is invoked. This
makes suit-candidate-verification OPTIONAL to implement and OPTIONAL
to parse.