Internet DRAFT - draft-moran-suit-trust-domains
draft-moran-suit-trust-domains
SUIT B. Moran
Internet-Draft Arm Limited
Intended status: Standards Track 26 October 2021
Expires: 29 April 2022
SUIT Manifest Extensions for Multiple Trust Domains
draft-moran-suit-trust-domains-00
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 uses different trust anchors for different purposes or components
in the context of firmware 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 29 April 2022.
Copyright Notice
Copyright (c) 2021 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 Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Changes to SUIT Workflow Model . . . . . . . . . . . . . . . 5
4. Changes to Manifest Metadata Structure . . . . . . . . . . . 5
5. Delegation Chains . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Delegation Chains . . . . . . . . . . . . . . . . . . . . 7
6. Dependencies . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Changes to Required Checks . . . . . . . . . . . . . . 8
6.2. Changes to Abstract Machine Description . . . . . . . . . 9
6.3. Changes to Special Cases of Component Index and Dependency
Index . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.4. Processing Dependencies . . . . . . . . . . . . . . . . . 10
6.4.1. Multiple Manifest Processors . . . . . . . . . . . . 11
6.5. Added and Modified Commands . . . . . . . . . . . . . . . 12
6.5.1. suit-directive-set-component-index . . . . . . . . . 12
6.5.2. suit-directive-set-dependency-index . . . . . . . . . 13
6.5.3. suit-directive-process-dependency . . . . . . . . . . 14
6.5.4. suit-directive-unlink . . . . . . . . . . . . . . . . 14
6.6. SUIT_Dependency Manifest Element . . . . . . . . . . . . 15
7. Creating Manifests . . . . . . . . . . . . . . . . . . . . . 16
7.1. Dependency Template . . . . . . . . . . . . . . . . . . . 16
7.1.1. Composite Manifests . . . . . . . . . . . . . . . . . 16
7.2. Encrypted Manifest Template . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. SUIT Commands . . . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. A. Full CDDL . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
Devices that go beyond single-signer update require more complex
rules for deploying firmware 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 uneeded component
* single-object dependencies
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* a partly encrypted manifest so that distribution does not reveal
private information
These mechanisms are not part of the core manifest specification, but
they are needed for more advanced use cases, such as the architecture
described in [I-D.ietf-teep-architecture].
This specification extends the SUIT Manifest specification
([I-D.ietf-suit-manifest]).
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Additionally, the following terminology is used throughout this
document:
* SUIT: Software Update for the Internet of Things, also the IETF
working group for this standard.
* Payload: A piece of information to be delivered. Typically
Firmware for the purposes of SUIT.
* Resource: A piece of information that is used to construct a
payload.
* Manifest: A manifest is a bundle of metadata about the firmware
for an IoT device, where to find the firmware, and the devices to
which it applies.
* Envelope: A container with the manifest, an authentication wrapper
with cryptographic information protecting the manifest,
authorization information, and severable elements (see: TBD).
* Update: One or more manifests that describe one or more payloads.
* Update Authority: The owner of a cryptographic key used to sign
updates, trusted by Recipients.
* Recipient: The system, typically an IoT device, that receives and
processes a manifest.
* Manifest Processor: A component of the Recipient that consumes
Manifests and executes the commands in the Manifest.
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* 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 [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
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* Abort: An event in which the Manifest Processor immediately halts
execution of the current Procedure. It creates a Record of an
error condition.
3. Changes to SUIT Workflow Model
The use of the features presented for use with multiple trust domains
requires some augmentation of the workflow presented in the SUIT
Manifest specification ([I-D.ietf-suit-manifest]):
One additional assumption is added for the Update Procedure:
* All dependency manifests should be present before any payload is
fetched.
One additional assumption is added to the Invocation Procedure:
* All dependencies must be validated prior to loading.
Two steps are added to the expected installation workflow of a
Recipient:
1. *Verify delegation chains*
2. Verify the signature of the manifest.
3. Verify the applicability of the manifest.
4. *Resolve dependencies.*
5. Fetch payload(s).
6. Install payload(s).
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 accomodate 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.
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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 | <--+ | +------------------------------+
+-------------------------+ |
| Dependencies | +-> +-----------------------+
| 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.
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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:
* An IoT device may contain a processor in its radio in addition to
the primary processor. These two processors may have separate
firmware with separate signing authorities. Dependencies allow
the firmware for the primary processor to reference a manifest
signed by a different authority.
* A network operator may wish to provide local caching of update
payloads. The network operator overrides the URI of payload by
providing a dependent manifest that references the original
manifest, but replaces its URI.
* A device operator provides a device with some additional
configuration. The device operator wants to test their
configuration with each new firmware version before releasing it.
The configuration is delivered as a binary in the same way as a
firmware image. The device operator references the firmware
manifest from the firmware author in their own manifest which also
defines the configuration.
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By using dependencies, components such as software, configuration,
models, and other resoruces 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
componetns), it MAY choose to skip signature verification of
dependencies, since they are referenced 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, a dependency signed
by the same author as the dependent 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.
If the manifest contains more than one component and/or dependency,
each command sequence MUST begin with a Set Component Index or Set
Dependency Index command.
If a dependency is specified, then the manifest processor MUST
perform the following checks:
1. At the beginning of each section in the dependent: all previous
sections of each dependency have been executed.
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 reject the
manifest.
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
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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 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:
* All commands may target dependency manifests as well as
components. To support this behaviour, there is a new command
instroduced: Set Dependency Index. This change works together
with Set Component Index to choose the object on which the
manifest is operating.
* 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.
A new command, Set Dependency Index, is added and the logic of Set
Componment Index is modified as below:
As in [I-D.ietf-suit-manifest], To simplify the logic describing the
command semantics, the object "current" is used. It represents the
component identified by the Component Index or the dependency
identified by the Dependency Index:
current := components\[component-index\]
if component-index is not false
else dependencies\[dependency-index\]
As a result, Set Component Index is described as current :=
components[arg]. The actual operation performed for Set Component
Index is described by the following pseudocode, however, because of
the definition of current (above), these are semantically equivalent.
component-index := arg
dependency-index := false
Similarly, Set Dependency Index is semantically equivalent to current
:= dependencies[arg], but the actual operation performed is:
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dependency-index := arg
component-index := false
Dependencies are identified by digest, but referenced in commands by
Dependency Index, the index into the array of Dependencies.
6.3. Changes to Special Cases of Component Index and Dependency Index
The considerations that apply in Special Cases of Component Index and
Dependency Index (Section 6.5) of [I-D.ietf-suit-manifest] are
augmented to include Dependency Index as well as Component Index.
The target(s) assigned for each command are defined by the following
pseudocode.
if component-index is true:
current-list = components
else if component-index is array:
current-list = [ components[idx] for idx in component-index ]
else if component-index is integer:
current-list = [ components[component-index] ]
else if dependency-index is true:
current-list = dependencies
else if dependency-index is array:
current-list = [ dependencies[idx] for idx in dependency-index ]
else:
current-list = [ dependencies[dependency-index] ]
for current in current-list:
cmd(current)
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 interpreter
loads the dependency identified by the Current Dependency Index. The
interpreter first executes the common-sequence section of the
identified dependency, then it executes the section of the dependency
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 Manifest Processor MUST also support a Dependency Index of True,
which applies to every dependency, as described in Section 6.3
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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 security domains, each domain might
require independent verification of authenticity or security
policies. Security domains might be divided by separation technology
such as Arm TrustZone, Intel SGX, or another TEE technology.
Security 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 security domains (see
[I-D.ietf-teep-architecture]), 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, 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.
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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 security 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. 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 Component Index | current := components[arg] |
+----------------------+---------------------------------+
| Set Dependency Index | current := dependencies[arg] |
+----------------------+---------------------------------+
| Set Parameters | current.params[k] := v if not k |
| | in params for-each k,v in arg |
+----------------------+---------------------------------+
| Process Dependency | exec(current[common]); |
| | exec(current[current-segment]) |
+----------------------+---------------------------------+
| Unlink | unlink(current) |
+----------------------+---------------------------------+
Table 1
6.5.1. suit-directive-set-component-index
Set Component Index defines the component to which successive
directives and conditions will apply. The supplied argument MUST be
one of three types:
1. An unsigned integer (REQUIRED to implement in parser)
2. A boolean (REQUIRED to implement in parser ONLY IF 2 or more
components supported)
3. An array of unsigned integers (REQUIRED to implement in parser
ONLY IF 3 or more components supported)
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If the following commands apply to ONE component, an unsigned integer
index into the component list is used. If the following commands
apply to ALL components, then the boolean value "True" is used
instead of an index. If the following commands apply to more than
one, but not all components, then an array of unsigned integer
indices into the component list is used. See Section 6.3 for more
details.
If the following commands apply to NO components, then the boolean
value "False" is used. When suit-directive-set-dependency-index is
used, suit-directive-set-component-index = False is implied. When
suit-directive-set-component-index is used, suit-directive-set-
dependency-index = False is implied.
If component index is set to True when a command is invoked, then the
command applies to all components, in the order they appear in suit-
common-components. When the Manifest Processor invokes a command
while the component index is set to True, it must execute the command
once for each possible component index, ensuring that the command
receives the parameters corresponding to that component index.
6.5.2. suit-directive-set-dependency-index
Set Dependency Index defines the manifest to which successive
directives and conditions will apply. The supplied argument MUST be
either a boolean or an unsigned integer index into the dependencies,
or an array of unsigned integer indices into the list of
dependencies. If the following directives apply to ALL dependencies,
then the boolean value "True" is used instead of an index. If the
following directives apply to NO dependencies, then the boolean value
"False" is used. When suit-directive-set-component-index is used,
suit-directive-set-dependency-index = False is implied. When suit-
directive-set-dependency-index is used, suit-directive-set-component-
index = False is implied.
If dependency index is set to True when a command is invoked, then
the command applies to all dependencies, in the order they appear in
suit-common-components. When the Manifest Processor invokes a
command while the dependency index is set to True, the Manifest
Processor MUST execute the command once for each possible dependency
index, ensuring that the command receives the parameters
corresponding to that dependency index. If the dependency index is
set to an array of unsigned integers, then the Manifest Processor
MUST execute the command once for each listed dependency index,
ensuring that the command receives the parameters corresponding to
that dependency index.
See Section 6.3 for more details.
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Typical operations that require suit-directive-set-dependency-index
include setting a source URI or Encryption Information, invoking
"Fetch," or invoking "Process Dependency" for an individual
dependency.
6.5.3. 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 dependency is False, this directive has no effect. If
the current dependency is True, then this directive applies to all
dependencies. If the current section is "common," then the command
sequence MUST be terminated with an error.
When SUIT_Process_Dependency completes, it forwards the last status
code that occurred in the dependency.
6.5.3.1. suit-directive-set-parameters
suit-directive-set-parameters allows the manifest to configure
behavior of future directives by changing parameters that are read by
those directives. When dependencies are used, suit-directive-set-
parameters also allows a manifest to modify the behavior of its
dependencies.
If a parameter is already set, suit-directive-set-parameters will
skip setting the parameter to its argument. This provides the core
of the override mechanism, allowing dependent manifests to change the
behavior of a manifest.
suit-directive-set-parameters does not specify a reporting policy.
6.5.4. suit-directive-unlink
suit-directive-unlink marks the current component as unused in the
current manifest. This can be used to remove temporary storage or
remove components that are no longer needed. Example use cases:
* Temporary storage for encrypted download
* Temporary storage for verifying decompressed file before writing
to flash
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* Removing Trusted Service no longer needed by Trusted Application
Once the current Command Sequence is complete, the manifest
processors checks each marked component to see whether any other
manifests have referenced it. Those marked components with no other
references are deleted. The manifest processor MAY choose to ignore
a Unlink directive depending on device policy.
suit-directive-unlink is OPTIONAL to implement in manifest
processors.
6.6. SUIT_Dependency Manifest Element
SUIT_Dependency specifies a manifest 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.
The suit-dependency-digest specifies the dependency manifest uniquely
by identifying a particular Manifest structure. This is identical to
the digest that would be present as the payload of any suit-
authentication-block in the dependency's Envelope. The digest is
calculated over the Manifest structure instead of the COSE
Sig_structure or Mac_structure. This is necessary 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.
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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.
7. 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.
7.1. Dependency Template
The goal of the Dependency template is to obtain, verify, and process
a dependency manifest as appropriate.
The following commands are placed into the dependency resolution
sequence:
* Set Dependency Index directive (see Section 6.5.2)
* Set Parameters directive (see Section 6.5.3.1) for URI (see
Section 8.4.8.9 of [I-D.ietf-suit-manifest])
* Fetch directive (see Section 8.4.10.4 of [I-D.ietf-suit-manifest])
* Check Image Match condition (see Section 8.4.9.2 of
[I-D.ietf-suit-manifest] of [I-D.ietf-suit-manifest])
* Process Dependency directive (see Section 6.5.3)
Then, the validate sequence contains the following operations:
* Set Dependency Index directive (see Section 6.5.2)
* Check Image Match condition (see Section 8.4.9.2 of
[I-D.ietf-suit-manifest])
* Process Dependency directive (see Section 6.5.3)
NOTE: Any changes made to parameters in a dependency persist in the
dependent.
7.1.1. 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 NOT be a value between 0 and 24 and it MUST
NOT be used by any other envelope element in the dependent manifest.
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The URI for a dependency enclosed in this way MUST be expressed as a
fragment-only reference, as defined in [RFC3986], Section 4.4. The
fragment identifier is the stringified envelope key of the
dependency. For example, an envelope that contains a dependency at
key 42 would use a URI "#42", key -73 would use a URI "#-73".
7.2. 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 operations are placed into the dependency resolution
block:
* Set Dependency Index directive (see Section 6.5.2)
* Set Parameters directive (see Section 6.5.3.1) for
- URI (see Section 8.4.8.9 of [I-D.ietf-suit-manifest])
- Encryption Info (See [I-D.ietf-suit-firmware-encryption])
* Fetch directive (see Section 8.4.10.4 of [I-D.ietf-suit-manifest])
* Check Image Match condition (see Section 8.4.9.2 of
[I-D.ietf-suit-manifest])
* Process Dependency directive (see Section 6.5.3)
Then, the validate block contains the following operations:
* Set Dependency Index directive (see Section 6.5.2)
* Check Image Match condition (see Section 8.4.9.2 of
[I-D.ietf-suit-manifest])
* Process Dependency directive (see Section 6.5.3)
A plaintext manifest and its encrypted dependency may also form a
composite manifest (Section 7.1.1).
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8. IANA Considerations
IANA is requested to allocate the following numbers in the listed
registries:
8.1. SUIT Commands
+=======+============+===================================+=========+
| Label | Name | Reference | |
+=======+============+===================================+=========+
| 13 | Set | Section 6.5.2 | |
| | Dependency | | |
| | Index | | |
+-------+------------+-----------------------------------+---------+
| 18 | Process | suit-directive-process-dependency | Section |
| | Dependency | | 6.5.3 |
+-------+------------+-----------------------------------+---------+
| 19 | Set | Section 6.5.3.1 | |
| | Parameters | | |
+-------+------------+-----------------------------------+---------+
| 33 | Unlink | Section 6.5.4 | |
+-------+------------+-----------------------------------+---------+
Table 2
9. 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 firmware updates to IoT
devices. A detailed security treatment can be found in the
architecture [RFC9019] and in the information model
[I-D.ietf-suit-information-model] documents.
10. References
10.1. Normative References
[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
"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-14, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-suit-manifest-
14.txt>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/info/rfc8747>.
[RFC9019] Moran, B., Tschofenig, H., Brown, D., and M. Meriac, "A
Firmware Update Architecture for Internet of Things",
RFC 9019, DOI 10.17487/RFC9019, April 2021,
<https://www.rfc-editor.org/info/rfc9019>.
10.2. Informative References
[I-D.ietf-suit-firmware-encryption]
Tschofenig, H., Housley, R., and B. Moran, "Firmware
Encryption with SUIT Manifests", Work in Progress,
Internet-Draft, draft-ietf-suit-firmware-encryption-02, 25
October 2021, <https://www.ietf.org/archive/id/draft-ietf-
suit-firmware-encryption-02.txt>.
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[I-D.ietf-suit-information-model]
Moran, B., Tschofenig, H., and H. Birkholz, "A Manifest
Information Model for Firmware Updates in IoT Devices",
Work in Progress, Internet-Draft, draft-ietf-suit-
information-model-13, 8 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-suit-
information-model-13.txt>.
[I-D.ietf-teep-architecture]
Pei, M., Tschofenig, H., Thaler, D., and D. Wheeler,
"Trusted Execution Environment Provisioning (TEEP)
Architecture", Work in Progress, Internet-Draft, draft-
ietf-teep-architecture-15, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-teep-
architecture-15.txt>.
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
SUIT_Delegation = [ + [ + bstr .cbor CWT ] ]
CWT = SUIT_Authentication_Block
$$SUIT_severable-members-extensions //=
(suit-dependency-resolution => bstr .cbor SUIT_Command_Sequence)
SUIT_Integrated_Dependency = (
suit-integrated-dependency-key => bstr .cbor SUIT_Envelope)
suit-integrated-dependency-key = tstr
$$severable-manifest-members-choice-extensions //= (
suit-dependency-resolution => \
bstr .cbor SUIT_Command_Sequence / SUIT_Digest)
$$SUIT_Common-extensions //= (
suit-dependencies => SUIT_Dependencies
)
SUIT_Dependencies = [ + SUIT_Dependency ]
SUIT_Dependency = {
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suit-dependency-digest => SUIT_Digest,
? suit-dependency-prefix => SUIT_Component_Identifier,
* $$SUIT_Dependency-extensions,
}
SUIT_Directive //= (
suit-directive-set-dependency-index, IndexArg)
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-delegation = 1
suit-dependency-resolution = 7
suit-dependencies = 1
suit-dependency-digest = 1
suit-dependency-prefix = 2
suit-directive-set-dependency-index = 13
suit-directive-process-dependency = 18
suit-directive-set-parameters = 19
suit-directive-unlink = 33
Author's Address
Brendan Moran
Arm Limited
Email: Brendan.Moran@arm.com
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