SUIT Manifest Extensions for Multiple Trust Domains

SUIT Manifest Extensions for Multiple Trust Domains Arm Limited

brendan.moran.ietf@gmail.com

SECOM CO., LTD.

ken.takayama.ietf@gmail.com

Security SUIT Internet-Draft This specification describes extensions to the SUIT Manifest format (as defined in ) 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.

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 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. 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 . This specification extends the SUIT Manifest specification ().

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 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 ). 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. 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 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 , 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.

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 (): 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. Steps 1 and 4 are added to the expected installation workflow of a Recipient: Verify Delegation Chains. Verify the signature of the Manifest. Verify the applicability of the Manifest. Resolve Dependencies. Fetch Payload(s). 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.

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.

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 CBOR Web Token (CWT). 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 Section 5.2 of ). See for more detail.

Delegation Chains The suit-delegation element MAY carry one or more CBOR Web Tokens (CWTs) , with 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 ). 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 intermediary 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.

Dependencies A Dependency is another SUIT_Envelope that describes additional Components. As described in , Dependencies enable several common use cases.

Changes to Required Checks This section augments the definitions in Required Checks (Section 6.2) of . 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 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: The dependent MUST populate all Command sequences for the current Procedure (Update or Invoke). 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: have sufficient permissions imparted by their signatures specify a digest and a Payload for every Component in the Component Set. The single dependent Manifest is sometimes called a Root Manifest.

Changes to Manifest Structure This section augments the Manifest Structure (Section 8.4) in .

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_Component_Identifier) ]]>

SUIT_Dependencies Manifest Element The suit-common section, as described in , 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 ) 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_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 ). 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 .

Changes to Abstract Machine Description This section augments the Abstract Machine Description (Section 6.4) in . 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: 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 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.

Processing Dependencies As described in , 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: Checks whether the map of Dependencies contains an entry for the current Component Index. If not present, it causes an immediate Abort. Checks whether the Dependency has been the target of a Dependency integrity check. If not, it causes an immediate Abort. Loads the specified Component as a Dependency Manifest Envelope. Authenticates the Dependency Manifest. Executes the common-sequence section of the Dependency Manifest. 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 to ensure that the dependent is processing the Dependency correctly.

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 . 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.

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.

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 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)

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 , 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.

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. 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.

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 for more details.

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: Evaluate any Delegation Chains Verify the signature of the Manifest hash Compare the Manifest hash to the provided hash 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.

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 ). suit-directive-unlink is OPTIONAL to implement in Manifest processors, but Manifest processors that support multiple independent Root Manifests MUST support suit-directive-unlink.

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. WARNING: This can cause faults where there are loose Dependencies (e.g., version range matching, see ), 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 . The suit-uninstall Command Sequence is not severable, since it must always be available to enable uninstalling.

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.

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 ) Set Parameters Directive (see ) for digest (see Section 8.4.8.6 of ). Note that the digest MUST match the SUIT_Digest in the Dependency's suit-authentication-block (see Section 8.3 of ). The following Commands are placed into the Dependency resolution sequence: Set Component Index Directive (see Section 8.4.10.1 of ) Set Parameters Directive (see ) for a URI (see Section 8.4.8.10 of ) Fetch Directive (see Section 8.4.10.4 of ) Dependency Integrity Condition (see ) Process Dependency Directive (see ) Then, the validate sequence contains the following operations: Set Component Index Directive (see Section 8.4.10.1 of ) Dependency Integrity Condition (see ) Process Dependency Directive (see ) 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.

Integrated Dependencies 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.

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 . The following Commands are added to the shared sequence: Set Component Index Directive (see Section 8.4.10.1 of ) Set Parameters Directive (see ) for digest (see Section 8.4.8.6 of ). Note that the digest MUST match the SUIT_Digest in the Dependency's suit-authentication-block (see Section 8.3 of ). The following operations are placed into the Dependency resolution block: Set Component Index Directive (see Section 8.4.10.1 of ) Set Parameters Directive (see ) for URI (see Section 8.4.8.9 of ) Encryption Info (See ) Fetch Directive (see Section 8.4.10.4 of ) Dependency Integrity Condition (see ) Process Dependency Directive (see ) Then, the validate block contains the following operations: Set Component Index Directive (see Section 8.4.10.1 of ) Check Image Match Condition (see Section 8.4.9.2 of ) Process Dependency Directive (see ) A plaintext Manifest and its encrypted Dependency may also form a composite Manifest ().

Overriding Encryption Info Template The goal of overriding the Encryption Info template is to separate the role of generating encrypted Payload and Encryption Info with Key-Encryption Key addressing Section 3 of . As an example, this template describes two manifests: - The dependent Manifest created by the Distribution System contains Encryption Info, allowing the Device to generate the Content-Encryption Key. - The dependency Manifest created by the Author contains Commands to decrypt the encrypted Payload using Encryption Info above and to validate the plaintext Payload with SUIT_Digest. NOTE: This template also requires the extensions defined in . The following operations are placed into the Dependency resolution block of dependent Manifest: Set Component Index Directive (see Section 8.4.10.1 of ) pointing at dependency Manifest Set Parameters Directive (see ) for Image Digest (see Section 8.4.8.6 of ) URI (see Section 8.4.8.9 of ) of dependency Manifest Fetch Directive (see Section 8.4.10.4 of ) Dependency Integrity Condition (see ) The following Commands are placed into the Fetch/Install block of dependent Manifest Set Component Index Directive (see Section 8.4.10.1 of ) pointing at encrypted Payload Set Parameters Directive (see ) for URI (see Section 8.4.8.9 of ) Set Component Index Directive (see Section 8.4.10.1 of ) pointing at dependency Manifest Set Parameters Directive (see ) for Encryption Info (See ) Process Dependency Directive (see ) The following Commands are placed into the same block of dependency Manifest: Set Component Index Directive (see Section 8.4.10.1 of ) pointing at encrypted Payload Fetch Directive (see Section 8.4.10.4 of ) Set Component Index Directive (see Section 8.4.10.1 of ) pointing at to be decrypted Payload Override Parameters Directive (see Section 8.4.10.3 of ) for Source Component (see Section 8.4.8.11 of ) pointing at encrypted Payload Copy Directive (see Section 8.4.10.5 of ) consuming the Encryption Info above The Distribution System can Set the Parameter URI in the Fetch/Install block of dependent Manifest if it wants to overwrite the URI of encrypted Payload. Because the Author and the Distribution System have different roles and MAY be separate entities, it is highly RECOMMENDED to leverage permissions (see Section 9 of ). For example, The Device can protect itself from attacker who breaches the Distribution System by allowing only the Author's Manifest to modify the Component of (to be) decrypted Payload.

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-dependency. 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 ) Set Parameters Directive (see ) for a URI (see Section 8.4.8.9 of ) Set Component Index Directive, with argument "True" (see Section 8.4.10.1 of ) Try Each Directive Sequence 0 Condition Is Dependency Manifest Fetch Dependency Integrity Condition (see ) 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 ) Set Parameters Directive (see ) for a URI (see Section 8.4.8.9 of ) Set Component Index Directive, with argument "True" (see Section 8.4.10.1 of ) Try Each Directive Sequence 0 Condition Is Dependency Manifest Process Dependency Sequence 1 Fetch Condition Image Match 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 ) Set Parameters Directive (see ) for the Source Component (see Section 8.4.8.11 of ) Set Component Index Directive, with argument containing list of destination Component indices (see Section 8.4.10.1 of ) Copy Set Component Index Directive, with argument containing list Dependency Component indices (see Section 8.4.10.1 of ) Process Dependency

IANA Considerations IANA is requested to allocate the following numbers in the listed registries created by draft-ietf-suit-manifest:

SUIT Envelope Elements Label Name Reference 1 Delegation 15 Dependency Resolution

SUIT Manifest Elements Label Name Reference 5 Manifest Component ID 15 Dependency Resolution 24 Uninstall

SUIT Common Elements Label Name Reference 1 Dependencies

SUIT Commands Label Name Reference 7 Dependency Integrity 8 Is Dependency 11 Process Dependency 19 Set Parameters 33 Unlink

Security Considerations This document is about a Manifest format protecting and describing how to retrieve, install, and invoke 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 and in the information model documents.

Uniform Resource Identifier (URI): Generic Syntax A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] Trust Anchor Management Requirements A trust anchor represents an authoritative entity via a public key and associated data. The public key is used to verify digital signatures, and the associated data is used to constrain the types of information for which the trust anchor is authoritative. A relying party uses trust anchors to determine if a digitally signed object is valid by verifying a digital signature using the trust anchor's public key, and by enforcing the constraints expressed in the associated data for the trust anchor. This document describes some of the problems associated with the lack of a standard trust anchor management mechanism and defines requirements for data formats and push-based protocols designed to address these problems. This document is not an Internet Standards Track specification; it is published for informational purposes. Terminology for Constrained-Node Networks The Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks. CBOR Web Token (CWT) CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR), and CBOR Object Signing and Encryption (COSE) is used for added application-layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/value pair consisting of a claim name and a claim value. CWT is derived from JSON Web Token (JWT) but uses CBOR rather than JSON. Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs) This specification describes how to declare in a CBOR Web Token (CWT) (which is defined by RFC 8392) that the presenter of the CWT possesses a particular proof-of-possession key. Being able to prove possession of a key is also sometimes described as being the holder-of-key. This specification provides equivalent functionality to "Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)" (RFC 7800) but using Concise Binary Object Representation (CBOR) and CWTs rather than JavaScript Object Notation (JSON) and JSON Web Tokens (JWTs). A Firmware Update Architecture for Internet of Things Vulnerabilities in Internet of Things (IoT) devices have raised the need for a reliable and secure firmware update mechanism suitable for devices with resource constraints. Incorporating such an update mechanism is a fundamental requirement for fixing vulnerabilities, but it also enables other important capabilities such as updating configuration settings and adding new functionality. In addition to the definition of terminology and an architecture, this document provides the motivation for the standardization of a manifest format as a transport-agnostic means for describing and protecting firmware updates. A Manifest Information Model for Firmware Updates in Internet of Things (IoT) Devices Vulnerabilities with Internet of Things (IoT) devices have raised the need for a reliable and secure firmware update mechanism that is also suitable for constrained devices. Ensuring that devices function and remain secure over their service lifetime requires such an update mechanism to fix vulnerabilities, update configuration settings, and add new functionality. One component of such a firmware update is a concise and machine-processable metadata document, or manifest, that describes the firmware image(s) and offers appropriate protection. This document describes the information that must be present in the manifest. A Concise Binary Object Representation (CBOR)-based Serialization Format for the Software Updates for Internet of Things (SUIT) Manifest Arm Limited Fraunhofer SIT Inria Nordic Semiconductor This specification describes the format of a manifest. A manifest is a bundle of metadata about code/data obtained by a recipient (chiefly the firmware for an IoT device), where to find the code/data, the devices to which it applies, and cryptographic information protecting the manifest. Software updates and Trusted Invocation both tend to use sequences of common operations, so the manifest encodes those sequences of operations, rather than declaring the metadata. Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Update Management Extensions for Software Updates for Internet of Things (SUIT) Manifests Arm Limited This specification describes extensions to the SUIT manifest format defined in [I-D.ietf-suit-manifest]. These extensions allow an update author, update distributor or device operator to more precisely control the distribution and installation of updates to IoT devices. These extensions also provide a mechanism to inform a management system of Software Identifier and Software Bill Of Materials information about an updated device. Encrypted Payloads in SUIT Manifests Vigil Security, LLC Arm Limited Linaro SECOM CO., LTD. This document specifies techniques for encrypting software, firmware, machine learning models, and personalization data by utilizing the IETF SUIT manifest. Key agreement is provided by ephemeral-static (ES) Diffie-Hellman (DH) and AES Key Wrap (AES-KW). ES-DH uses public key cryptography while AES-KW uses a pre-shared key. Encryption of the plaintext is accomplished with conventional symmetric key cryptography. Trusted Execution Environment Provisioning (TEEP) Architecture Broadcom Arm Limited Microsoft Amazon A Trusted Execution Environment (TEE) is an environment that enforces the following: any code within the environment cannot be tampered with, and any data used by such code cannot be read or tampered with by any code outside the environment. This architecture document discusses the motivation for designing and standardizing a protocol for managing the lifecycle of Trusted Applications running inside such a TEE.

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

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 * $$SUIT_Dependency_Extensions } SUIT_Condition //= ( suit-condition-dependency-integrity, SUIT_Rep_Policy) SUIT_Condition //= ( suit-condition-is-dependency, SUIT_Rep_Policy) SUIT_Directive //= ( suit-directive-process-dependency, SUIT_Rep_Policy) SUIT_Directive //= (suit-directive-set-parameters, {+ $$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 ]]>

B. Examples The following examples demonstrate a small subset of the functionalities in this document. The examples are signed using the following ECDSA secp256r1 key:

The corresponding public key can be used to verify these examples:

Each example uses SHA256 as the digest function.

Example 0: Delegation Chain This example uses functionalities: manifest component id delegation chain

>, / unprotected / { }, / payload: / << { / cnf / 8: { / NOTE: public key of delegated authority / / COSE_Key / 1: { / kty / 1: 2 / EC2 /, / crv / -1: 1 / P-256 /, / x / -2: h'0E908AA8F066DB1F084E0C3652C63952 BD99F2A5BDB22F9E01367AAD03ABA68B', / y / -3: h'77DA1BD8AC4F0CB490BA210648BF79AB 164D49AD3551D71D314B2749EE42D29A' } } } >>, / signature: / h'FB2D5ACF66B9C8573CE92E13BFB8D113F798715CC10B5A0010B11925C155E724 5A64E131073B87AC50CAC71650A21315B82D06CA2298CD1A95519AAE4C4B5315' ]) >> ] ] >>, / NOTE: signed by delegated authority / / authentication-wrapper / 2: << [ << [ / digest-algorithm-id: / -16 / SHA256 /, / digest-bytes: / h'6EA128D7BB19B86F77C4227F2A29F22026A41958ACC45CC0A35BA388B13E2F51' ] >>, << / COSE_Sign1_Tagged / 18([ / protected: / << { / algorithm-id / 1: -7 / ES256 / } >>, / unprotected: / {}, / payload: / null, / signature: / h'99F949043701D7BDBA38904A0B49F004DED6B64A4900DECA5C66AE8A9EBA9135 76DEF136B74EA89C14FA64624DBD33B4C0BB41C153CA51548C73FF71A2BAF274' ]) >> ] >>, / manifest / 3: << { / manifest-version / 1: 1, / manifest-sequence-number / 2: 0, / common / 3: << { / components / 2: [ [ '00' ] ] } >>, / manifest-component-id / 5: [ 'dependent.suit' ], / invoke / 9: << [ / directive-override-parameters / 20, { / parameter-invoke-args / 23: 'cat 00' }, / directive-invoke / 23, 15 ] >>, / install / 17: << [ / directive-override-parameters / 20, { / parameter-content / 18: 'hello world' }, / directive-write / 18, 15 ] >> } >> }) ]]> Total size of Envelope with COSE authentication object: 352 Envelope with COSE authentication object:

Example 1: Process Dependency This example uses functionalities: manifest component id dependency resolution process dependency

>, << / COSE_Sign1_Tagged / 18([ / protected: / << { / algorithm-id / 1: -7 / ES256 / } >>, / unprotected: / {}, / payload: / null, / signature: / h'C257E23A34960BE215BB9B927A5A3CEEDD675DFD81AE6E55A66FDD2209886889 1DF42D71ADB962A64CC008AEF9465DA2153CCF383F00B505F079DB540F64B916' ]) >> ] >>, / manifest / 3: << { / manifest-version / 1: 1, / manifest-sequence-number / 2: 0, / common / 3: << { / dependencies / 1: { / component-index / 1: { / dependency-prefix / 1: [ 'dependent.suit' ] } }, / components / 2: [ [ '10' ] ] } >>, / manifest-component-id / 5: [ 'depending.suit' ], / invoke / 9: << [ / directive-set-component-index / 12, 0, / directive-override-parameters / 20, { / parameter-invoke-args / 23: 'cat 00 10' }, / directive-invoke / 23, 15 ] >>, / dependency-resolution / 15: << [ / directive-set-component-index / 12, 1, / directive-override-parameters / 20, { / parameter-image-digest / 3: << [ / digest-algorithm-id: / -16 / SHA256 /, / digest-bytes: / h'6C86246B90D644F021671F6D42523B2CB5E156F764BE618AA46BFCD0DB23E768' ] >>, / parameter-image-size / 14: 352, / parameter-uri / 21: "http://example.com/dependent.suit" }, / directive-fetch / 21, 2, / condition-image-match / 3, 15 ] >>, / install / 17: << [ / directive-set-component-index / 12, 1, / directive-override-parameters / 20, { / parameter-image-digest / 3: << [ / digest-algorithm-id: / -16 / SHA256 /, / digest-bytes: / h'6EA128D7BB19B86F77C4227F2A29F22026A41958ACC45CC0A35BA388B13E2F51' ] >> }, / condition-dependency-integrity / 7, 15, / directive-process-dependency / 11, 0, / directive-set-component-index / 12, 0, / directive-override-parameters / 20, { / parameter-content / 18: ' in multiple trust domains' }, / directive-write / 18, 15 ] >> } >> }) ]]> Total size of Envelope with COSE authentication object: 374 Envelope with COSE authentication object:

Example 2: Integrated Dependency manifest component id dependency resolution process dependency integrated dependency

>, << / COSE_Sign1_Tagged / 18([ / protected: / << { / algorithm-id / 1: -7 / ES256 / } >>, / unprotected: / {}, / payload: / null, / signature: / h'287D5AAB44D08A34954663942B2732825426893ACD735BF3A79B8B5B38EC3C99 50D917D72D5586867C8FF58CF5827B0C2B94952359C3971DBF202B0774627DC3' ]) >> ] >>, / manifest / 3: << { / manifest-version / 1: 1, / manifest-sequence-number / 2: 0, / common / 3: << { / dependencies / 1: { / component-index / 1: { / dependency-prefix / 1: [ 'dependent.suit' ] } }, / components / 2: [ [ '10' ] ] } >>, / manifest-component-id / 5: [ 'depending.suit' ], / invoke / 9: << [ / directive-set-component-index / 12, 0, / directive-override-parameters / 20, { / parameter-invoke-args / 23: 'cat 00 10' }, / directive-invoke / 23, 15 ] >>, / dependency-resolution / 15: << [ / directive-set-component-index / 12, 1, / directive-override-parameters / 20, { / parameter-image-digest / 3: << [ / digest-algorithm-id: / -16 / SHA256 /, / digest-bytes: / h'6C86246B90D644F021671F6D42523B2CB5E156F764BE618AA46BFCD0DB23E768' ] >>, / parameter-image-size / 14: 352, / parameter-uri / 21: "#dependent.suit" }, / directive-fetch / 21, 2, / condition-image-match / 3, 15 ] >>, / install / 17: << [ / directive-set-component-index / 12, 1, / directive-process-dependency / 11, 0, / directive-set-component-index / 12, 0, / directive-override-parameters / 20, { / parameter-content / 18: ' in multiple trust domains' }, / directive-write / 18, 15 ] >> } >>, / NOTE: Example 0 / "#dependent.suit": h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}) ]]> Total size of Envelope with COSE authentication object: 683 Envelope with COSE authentication object: