Internet-Draft SUIT Trust Domains March 2023
Moran & Takayama Expires 14 September 2023 [Page]
Workgroup:
SUIT
Internet-Draft:
draft-ietf-suit-trust-domains-02
Published:
Intended Status:
Standards Track
Expires:
Authors:
B. Moran
Arm Limited
K. Takayama
SECOM CO., LTD.

SUIT Manifest Extensions for Multiple Trust Domains

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.

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Table of Contents

1. Introduction

Devices that go beyond single-signer update require more complex rules for deploying software updates. For example, devices may require:

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:

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:

One additional assumption is added to the Invocation Procedure:

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).

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 |
                                     | ))                    |
                                     +-----------------------+

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:

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:

  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.

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.

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.

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.

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.

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.

Table 1
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 Dependency exec(current[common]); exec(current[current-segment])
Dependency Integrity verify(current, current.params[image-digest])
Is Dependency assert(current exists in dependencies)
Unlink unlink(current)

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.

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
  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.

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.

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:

The following commands are placed into the dependency resolution sequence:

Then, the validate sequence contains the following operations:

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:

The following operations are placed into the dependency resolution block:

Then, the validate block contains the following operations:

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:

Another example is to fetch and validate all Component Images. The image fetch sequence contains the following commands:

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:

9. IANA Considerations

IANA is requested to allocate the following numbers in the listed registries:

9.1. SUIT Command Sequences

Table 2
Label Name Reference
1 Delegation Section 5
15 Dependency Resolution Section 6.5
24 Uninstall Section 7

9.2. SUIT Commands

Table 3
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

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, , <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, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986]
Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <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, , <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, , <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, , <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, , <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, , <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, , <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, , <https://datatracker.ietf.org/doc/html/draft-ietf-suit-firmware-encryption-11>.
[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, , <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, , <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)

$$SUIT_Common-extensions //= (
        suit-dependencies => SUIT_Dependencies
)
SUIT_Dependencies = {
    + uint => SUIT_Dependency_Metadata
}
SUIT_Dependency_Metadata = {
    ? suit-dependency-prefix => SUIT_Component_Identifier
    * $$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
Ken Takayama
SECOM CO., LTD.