]> Arm

paul.howard@arm.com

Linaro

Thomas.Fossati@linaro.org

Fraunhofer SIT

henk.birkholz@ietf.contact

Fujitsu

Shefali.Kamal@fujitsu.com

AMD

gmandyam@amd.com

Alibaba Cloud

xynnn@linux.alibaba.com

Security Remote ATtestation ProcedureS RATS attestation endorsement reference value In the Remote Attestation Procedures (RATS) architecture, Verifiers require Endorsements and Reference Values to assess the trustworthiness of Attesters. This document specifies the Concise Selector for Endorsements and Reference Values (CoSERV), a structured query/result format designed to facilitate the discovery and retrieval of these artifacts from various providers. CoSERV defines a query language and corresponding result structure using CDDL, which can be serialized in CBOR format, enabling efficient interoperability across diverse systems. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Remote ATtestation ProcedureS Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction Remote Attestation Procedures (RATS) enable Relying Parties to evaluate the trustworthiness of remote Attesters by appraising Evidence. This appraisal necessitates access to Endorsements and Reference Values, which are often distributed across multiple providers, including hardware manufacturers, firmware developers, and software vendors. The lack of standardized methods for querying and retrieving these artifacts poses challenges in achieving seamless interoperability. The Concise Selector for Endorsements and Reference Values (CoSERV) addresses this challenge by defining a query language and a corresponding result structure for the transaction of artifacts between a provider and a consumer. The query language format provides Verifiers with a standard way to specify the environment characteristics of Attesters, such that the relevant artifacts can be obtained from Endorsers and Reference Value Providers. In turn, the result format allows those Endorsers and Reference Value Providers to package the artifacts within a standard structure. This facilitates the efficient discovery and retrieval of relevant Endorsements and Reference Values from providers, maximising the re-use of common software tools and libraries within the transactions. The CoSERV query language is intended to form the input data type for tools and services that provide access to Endorsements and Reference Values. The CoSERV result set is intended to form the corresponding output data type from those tools and services. Both the query language and the result set are designed for extensibility. This addresses the need for a common baseline format to optimise for interoperability and software reuse, while maintaining the flexibility demanded by a dynamic and diverse ecosystem. The environment characteristics of Endorsements and Reference Values are derived from the equivalent concepts in CoRIM . CoSERV therefore borrows heavily from CoRIM, and shares some data types for its fields. And, like CoRIM, the CoSERV schema is defined using CDDL . A CoSERV query can be serialized in CBOR format. In addition to the CBOR-based data formats for CoSERV queries and responses, this specification also defines API bindings and behaviours for the exchange of CoSERV queries and responses. This is to facilitate standard interactions between CoSERV producers and consumers. Standard API endpoints and behaviours will encourage the growth of interoperable software tools and modules, not only for parsing and emitting CoSERV-compliant data, but also for implementing the clients and services that need to exchange such data when acting in the capacity of the relevant RATS roles. This will be of greater benefit to the software ecosystem than the CoSERV data format alone. See for the API binding specifications.

Terminology and Requirements Language 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. This document uses terms and concepts defined by the RATS architecture. For a complete glossary, see . This document uses terms and concepts defined by the CoRIM specification. For a complete glossary, see . This document uses the terms "actual state" and "reference state" as defined in . The terminology from CBOR , CDDL and COSE applies; in particular, CBOR diagnostic notation is defined in and . Terms and concepts are always referenced as proper nouns, i.e., with Capital Letters.

Aggregation and Trust Models The roles of Endorser or Reference Value Provider might sometimes be fulfilled by aggregators, which collect from multiple supply chain sources, or even from other aggregators, in order to project a holistic view of the endorsed system. The notion of such an aggregator is not explicit in the RATS architecture. In practice, however, supply chains are complex and multi-layered. Supply chain sources can include silicon manufacturers, device manufacturers, firmware houses, system integrators, service providers and more. In practical terms, an Attester is likely to be a complex entity, formed of components from across such supply chains. Evidence would be likewise structured, with contributions from different segments of the Attester's overall anatomy. A Verifier for such Evidence may find it convenient to contact an aggregator as a single source of truth for Endorsements and Reference Values. An aggregator would have intelligence about the Attester's complete anatomy and supply chain. It would have the ability to contact all contributing supply chain actors for their individual Endorsements and Reference Values, before collecting them into a cohesive set, and delivering them to the Verifier as a single, ergonomic package. In pure RATS terms, an aggregator is still an Endorser or a Reference Value Provider - or, more likely, both. It is not a distinct role, and so there is no distinctly-modeled conveyance between an aggregator and a Verifier. However, when consuming from an aggregator, the Verifier may need visibility of the aggregation process, possibly to the extent of needing to audit the results by inspecting the individual inputs that came from the original supply chain actors. CoSERV addresses this need, catering equally for both aggregating and non-aggregating supply chain sources. To support deployments with aggregators, CoSERV allows for flexible trust models as follows.

• Shallow Trust: in this model, the consumer trusts the aggregator, solely and completely, to provide authentic descriptions of the endorsed system. The consumer does not need to audit the results of the aggregation process.
• Deep Trust: in this model, the consumer has a trust relationship with the aggregator, but does not deem this to be sufficient. The consumer can still use the collected results from the aggregation process, where it is convenient to do so, but also needs to audit those results.

Any given CoSERV transaction can operate according to either model. The consumer decides which model to use when it forms a query. The CoSERV result payload can convey both the aggregated result and the audit trail as needed. The payload size may be smaller when the shallow model is used, but the choice between the two models is a question for implementations and deployments. Although CoSERV is designed to support aggregation, it is not a requirement. When aggregation is not used, CoSERV still fulfills the need for a standard conveyance mechanism between Verifiers and Endorsers or Reference Value Providers.

CoSERV Information Model

Overview CoSERV is designed to facilitate query-response transactions between a producer and a consumer. In the RATS model, the producer is either an Endorser or a Reference Value Provider, and the consumer is a Verifier. CoSERV defines a single top-level data type that can be used for both queries and result sets. Queries are authored by the consumer (Verifier), while result sets are authored by the producer (Endorser or Reference Value Provider) in response to the query. A CoSERV data object always contains a query. When CoSERV is used to express a result set, the query is retained alongside the result set that was yielded by that query. This allows consumers to verify a match between the query that was sent to the producer, and the query that was subsequently returned with the result set. Such verification is useful because it mitigates security threats arising from any untrusted infrastructure or intermediaries that might reside between the producer and the consumer. An example of this is caching in HTTP and CoAP . It might be expensive to compute the result set for a query, which would make caching desirable. However, if caching is managed by an untrusted intermediary, then there is a risk that such an untrusted intermediary might return incorrect results, either accidentally or maliciously. Pairing the original query with each result set provides an end-to-end contract between the consumer and producer, mitigating such risks. The transactional pattern between the producer and the consumer would be that the consumer begins the transaction by authoring a query and sending it to the producer as a CoSERV object. The producer receives the query, computes results, and returns a new CoSERV object formed from the results along with the original query. Notionally, the producer is "adding" the results to the query before sending it back to the consumer.

Artifacts Artifacts are what the consumer (Verifier) needs in order to verify and appraise Evidence from the Attester, and therefore they form the bulk of the response payload in a CoSERV transaction. The common CoSERV query language recognises three artifact types. These correspond to the three categories of endorsement artifact that can be identified natively in the RATS architecture:

• Trust Anchor: A trust anchor is as defined in . An example of a trust anchor would be the public part of the asymmetric signing key that is used by the Attester to sign Evidence, such that the Verifier can verify the cryptographic signature.
• Endorsed Value: An endorsed value is as defined in . This represents a characteristic of the Attester that is not directly presented in the Evidence, such as certification data related to a hardware or firmware module.
• Reference Value: A reference value is as defined in . A reference value specifies an individual aspect of the Attester's desired state. Reference values are sometimes informally called "golden values". An example of a reference value would be the expected hash or checksum of a binary firmware or software image running in the Attester's environment. Evidence from the Attester would then include claims about the Attester's actual state, which the Verifier can then compare with the reference values at Evidence appraisal time.

When artifacts are produced by an aggregator (see ), the following additional classifications apply:

• Collected Artifacts: these refer to artifacts that were derived by the aggregator by collecting and presenting data from original supply chain sources, or from other aggregators. Collected artifacts form a single holistic package, and provide the most ergonomic consumption experience for the Verifier.
• Source Arfifacts: these refer to artifacts that were obtained directly from the original supply chain sources, and used as inputs into the aggregation process, allowing the aggregator to derive the collected artifacts.

In the shallow trust model of aggregation, only the collected artifacts are used by the consumer. In the deep trust model, both the collected artifacts and the source artifacts are used. The source artifacts allow the consumer to audit the collected artifacts and operate the trust-but-verify principle.

Environments The environment defines the scope (or scopes) in which the endorsement artifacts are applicable. Given that the consumer of these artifacts is likely to be a Verifier in the RATS model, the typical interpretation of the environment would be that of an Attester that either has produced evidence, or is expected to produce evidence, that the Verifier needs to appraise. The Verifier consequently needs to query the Endorser or Reference Value Provider for artifacts that are applicable in that environment. There are three mutually-exclusive methods for defining the environment within a CoSERV query. Exactly one of these three methods MUST be used for the query to be valid. All three methods correspond to environments that are also defined within CoRIM .

• Class: A class is an environment that is expected to be common to a group of similarly-constructed Attesters, who might therefore share the same set of endorsed characteristics. An example of this might be a fleet of computing devices of the same model and manufacturer.
• Instance: An instance is an environment that is unique to an individual and identifiable Attester, such as a single computing device or component.
• Group: A group is a collection of common Attester instances that are collected together based on some defined semantics. For example, Attesters may be put into groups for the purpose of anonymity.

Stateful Environments In addition to specifying the Attester environment by class, instance, or group, it is sometimes necessary to constrain the target environment further by specifying aspects of its state. This is because the applicability of Endorsements and Reference Values might vary, depending on these stateful properties. Consider, for example, an Attester instance who signs Evidence using a derived attestation key, where the derivation algorithm is dependent on one or more aspects of the Attester's current state, such as the version number of an upgradable firmware component. This example Attester would, at different points in its lifecycle, sign Evidence with different attestation keys, since the keys would change upon any firmware update. To provide the correct public key to use as the trust anchor for verification, the Endorser would need to know the configured state of the Attester at the time the Evidence was produced. Specifying such an Attester solely by its instance identifier is therefore insufficient for the Endorser to supply the correct artifact. The environment specification would need to include these critical stateful aspects as well. In CoRIM , stateful environments are modeled as an environment identifier plus a collection of measurements, and CoSERV takes the same approach. Therefore, any environment selector in a CoSERV query can optionally be enhanced with a collection of one or more measurements, which specify aspects of the target environment state that might materially impact the selection of artifacts.

Queries The purpose of a query is to allow the consumer (Verifier) to specify the artifacts that it needs. The information that is conveyed in a CoSERV query includes the following:

• A specification of the required artifact type: Reference Value, Endorsed Value or Trust Anchor. See for definitions of artifact types. A single CoSERV query can only specify a single artifact type.
• A specification of the Attester's environment. Environments can be selected according to Attester instance, group or class. Additional properties of the environment state can be specified by adding one or more measurements to the selector. See for full definitions. To facilitate efficient transactions, a single query can specify either multiple instances, multiple groups or multiple classes. However, it is not possible to mix instance-based selectors, group-based selectors and class-based selectors in a single query.
• A timestamp, denoting the time at which the CoSERV query was sent.
• A switch to select the desired supply chain depth. A CoSERV query can request collected artifacts, source artifacts, or both. This switch is especially relevant when the CoSERV query is fulfilled by an aggregator. The collected artifacts are intended for convenient consumption (according to the shallow trust model), while the source artifacts are principally useful for auditing (according to the deep trust model). It is possible for a query to select for source artifacts only, without the collected artifacts. This might happen when the consumer needs to inspect or audit artifacts from across the deep supply chain, while not requiring the convenience of the aggregated view. It could also happen when the consumer is acting as an intermediate broker, gathering artifacts for delivery to another aggregator. See for details on aggregation, auditing and trust models.

Result Sets The result set contains the artifacts that the producer collected in response to the query. The top-level structure of the result set consists of the following three items:

• A collection of one or more result entries. This will be a collection of either reference values, endorsed values or trust anchors. See for definitions of artifact types. In the future, it may be possible to support additional artifact types via an extension mechanism. Artifact types are never mixed in any single CoSERV result set. The artifacts in the result collection therefore MUST match the single artifact type specified in the original CoSERV query.
• A timestamp indicating the expiry time of the entire result set. Consumers MUST NOT consider any part of the result set to be valid after this expiry time.
• A collection of the original source materials from which the producer derived the correct artifacts to include in the result set. These source materials are optional, and their intended purpose is auditing. They are included only when requested by the original CoSERV query. Source materials would typically be requested in cases where the consumer is not willing to place sole trust in the producer, and therefore needs an audit trail to enable additional verifications.

Each individual result entry combines a CoMID triple with an authority delegation chain. CoMID triples are exactly as defined in . Each CoMID triple will demonstrate the association between an environment matching that of the CoSERV query, and a single artifact such as a reference value, trust anchor or endorsed value. The authority delegation chain is composed of one or more authority delegates. Each authority delegate is represented by a public key or key identifier, which the consumer can check against its own set of trusted authorities. The authority delegation chain serves to establish the provenance of the result entry, and enables the Verifier to evaluate the trustworthiness of the associated artifact. The purpose of the authority delegation chain is to allow CoSERV responses to support decentralized trust models, where Verifiers may apply their own policy to determine which authorities are acceptable for different classes of artifact. Because each result entry combines a CoMID triple with an authority delegation chain, the entries are consequently known as quadruples (or "quads" for short).

CoSERV Data Model This section specifies the CBOR data model for CoSERV queries and result sets. CDDL is used to express rules and constraints of the data model for CBOR. These rules must be strictly followed when creating or validating CoSERV data objects. The top-level CoSERV data structure is given by the following CDDL: profile &(query: 1) => query ? &(results: 2) => results } profile = comid.oid-type / ~uri ]]>

Common Data Types CoSERV inherits the following types from the CoRIM data model class-map, $class-id-type-choice, $instance-id-type-choice and $group-id-type-choice. The collated CDDL is in .

Profile In common with EAT and CoRIM, CoSERV supports the notion of profiles. As with EAT and CoRIM, profiles are a way to extend or specialize the structure of a generic CoSERV query in order to cater for a specific use case or environment. In a CoSERV query, the profile can be identified by either a Uniform Resource Identifier (URI) or an Object Identifier (OID). This convention is identical to how EAT profiles are identified using the eat_profile claim as described in .

Query Structure The CoSERV query language enables Verifiers to specify the desired characteristics of Endorsements and Reference Values based on the environment in which they are applicable. The top-level structure of a CoSERV query is given by the following CDDL: artifact-type &(environment-selector: 1) => environment-selector-map &(timestamp: 2) => tdate ; RFC3339 date &(result-type: 3) => result-type } artifact-type = &(endorsed-values: 0) / &(trust-anchors: 1) / &(reference-values: 2) result-type = &(collected-artifacts: 0) / &(source-artifacts: 1) / &(both: 2) ]]> The meanings of these fields are detailed in the following subsections.

Artifact Type The artifact-type field is the foremost discriminator of the query. It is a top-level category selector. Its three permissible values are trust-anchors (codepoint 1), endorsed-values (codepoint 0) and reference-values (codepoint 2). See for full definitions of artifact types. It is expected that implementations might choose to store these different categories of artifacts in different top-level stores or database tables. Where this is the case, the artifact-type field serves to narrow the query down to the correct store or table. Even where this is not the case, the discriminator is useful as a filter for the consumer, resulting in an efficiency gain by avoiding the transfer of unwanted data items.

Environment Selector The environment selector forms the main body of the query, and its CDDL is given below: [ + stateful-class ] ) stateful-instance = [ instance: comid.$instance-id-type-choice ? measurements: [ + comid.measurement-map ] ] selector //= ( &(instance: 1) => [ + stateful-instance ] ) stateful-group = [ group: comid.$group-id-type-choice ? measurements: [ + comid.measurement-map ] ] selector //= ( &(group: 2) => [ + stateful-group ] ) ]]> Environments can be specified according to instance, group or class. See for details. Although these three environment definitions are mutually-exclusive in a CoSERV query, all three support multiple entries. This is to gain efficiency by allowing the consumer (Verifier) to query for multiple artifacts in a single transaction. For example, where artifacts are being indexed by instance, it would be possible to specify an arbitrary number of instances in a single query, and therefore obtain the artifacts for all of them in a single transaction. Likewise for classes and groups. However, it would not be possible for a single query to specify more than one kind of environment. For example, it would not be possible to query for both class-level and instance-level artifacts in a single CoSERV transaction. All three environment selector types can optionally be enhanced with one or more measurement-map entries, which are used to express aspects of the environment state. See for a description of stateful environments.

Selector Semantics When multiple environment selectors are present in a single query, such as multiple instances or multiple groups, the implementation of the artifact producer MUST consider these to be alternatives, and hence use a logical OR operation when applying the query to its internal data stores. Below is an illustrative example of how a CoSERV query for endorsed values, selecting for multiple Attester instances, might be transformed into a semantically-equivalent SQL database query: The same applies for class-based selectors; however, since class selectors are themselves composed of multiple inner fields, the implementation of the artifact producer MUST use a logical AND operation in consideration of the inner fields for each class. Also, for class-based selectors, any unset fields in the class are assumed to be wildcard (*), and therefore match any value. Below is an illustrative example of how a CoSERV query for reference values, selecting for multiple Attester classes, might be transformed into a semantically-equivalent SQL database query:

Timestamp The timestamp field records the date and time at which the query was made, formatted according to . Implementations SHOULD populate this field with the current date and time when forming a CoSERV query.

Result Type The result-type field selects for either collected-artifacts (codepoint 0), source-artifacts (codepoint 1) or both (codepoint 2). See for definitions of source and collected artifacts.

Result Set Structure The result set structure is given by the following CDDL: tdate ; RFC3339 date ? &(source-artifacts: 11) => [ + cmw.cbor-record ] } result-set //= reference-values result-set //= endorsed-values result-set //= trust-anchors result-set //= $$result-set-extensions refval-quad = { &(authorities: 1) => [ + comid.$crypto-key-type-choice ] &(rv-triple: 2) => comid.reference-triple-record } reference-values = ( &(rvq: 0) => [ * refval-quad ] ) endval-quad = { &(authorities: 1) => [ + comid.$crypto-key-type-choice ] &(ev-triple: 2) => comid.endorsed-triple-record } cond-endval-quad = { &(authorities: 1) => [ + comid.$crypto-key-type-choice ] &(ce-triple: 2) => comid.conditional-endorsement-triple-record } endorsed-values = ( &(evq: 1) => [ * endval-quad ] &(ceq: 2) => [ * cond-endval-quad ] ) ak-quad = { &(authorities: 1) => [ + comid.$crypto-key-type-choice ] &(ak-triple: 2) => comid.attest-key-triple-record } cots-stmt = { &(authorities: 1) => [ + comid.$crypto-key-type-choice ] &(cots: 2) => cots } trust-anchors = ( &(akq: 3) => [ * ak-quad ] &(tas: 4) => [ * cots-stmt ] ) ; ; import CoTS ; cots = "TODO COTS" ]]>

Encoding Requirements Implementations may wish to use serialized CoSERV queries as canonical identifiers for artifact collections. For example, a Reference Value Provider service may wish the cache the results of a CoSERV query to gain efficiency when responding to a future identical query. For these use cases to be effective, it is essential that any given CoSERV query is always serialized to the same fixed sequence of CBOR bytes. Therefore, CoSERV queries MUST always use CBOR deterministic encoding as specified in . Further, CoSERV queries MUST use CBOR definite-length encoding.

Cryptographic Binding Between Query and Result Set CoSERV is designed to ensure that any result set passed from a producer to a consumer is precisely the result set that corresponds to the consumer's original query. This is the reason why the original query is always included along with the result set in the data model. However, this measure is only sufficient in cases where the conveyance protocol guarantees that CoSERV result sets are always transacted over a secure channel without any untrusted intermediaries. Wherever this is not the case, producers MUST create an additional cryptographic binding between the query and the result. This is achieved by transacting the result set within a cryptographic envelope, with a signature added by the producer, which is verified by the consumer. A CoSERV data object can be signed using COSE . A signed-coserv is a COSE_Sign1 with the following layout: The payload MUST be the CBOR-encoded CoSERV. The protected header MUST include the signature algorithm identifier. The protected header MUST include either the content type application/coserv+cbor or the CoAP Content-Format TBD1. Other header parameters MAY be added to the header buckets, for example a kid that identifies the signing key.

Examples

Query Data Examples This section provides some illustrative examples of valid CoSERV query objects. The following example shows a query for Reference Values scoped by a single class. The artifact-type is set to 2 (reference-values), indicating a query for Reference Values. The profile is given the example value of tag:example.com,2025:cc-platform#1.0.0. Finally, the environment-selector uses the key 0 to select for class, and the value contains a single entry with illustrative settings for the identifier, vendor and model. The next example is similar, but adds a second entry to the set of classes in the environment-map, showing how multiple classes can be queried at the same time. The following example shows a query for Reference Values scoped by instance. Again, the artifact-type is set to 2, and profile is given a demonstration value. The environment-selector now uses the key 1 to select for instances, and the value contains two entries with example instance identifiers.

Result Data Examples This section provides some illustrative examples of valid CoSERV queries with their corresponding result sets. In this next example, the query is a reference value query based on class. The top-level structure is a map with three entries: profile (codepoint 0), query (codepoint 1) and results (codepoint 2). The profile and query structures are the same as in the previous examples. The result structure is a map with two entries: expiry (codepoint 10) and rvq (codepoint 0). The rvq (reference value quad) entry comprises the asserting authority and the asserted triples. A single reference-value triple is shown in this example. Its environment-map, as expected, is the same as the environment-map that was supplied in the query. The rest of the structure is the measurement-map as defined in CoRIM . The following example is for a query that requested the results be provided in the "source artifacts" format. This means one or more original signed manifests containing information that satisfies the query criteria. Compared with the previous example, the rvq entry is empty, while the source-artifacts (codepoint 11) contain two CMW records , each of which contains a (made up) manifest with the type "application/vnd.example.refvals".

API Bindings This section sets out the ways in which CoSERV queries and responses can be exchanged between software components and services using APIs. The CoSERV data format itself is agnostic of any particular API model or transport. The API bindings provided here are intended to complement the data format. They will allow implementations to build the complete functionality of a CoSERV producer or consumer, in a way that is well-suited to any transport or interaction model that is needed. It is intended that these API definitions carry minimal additional semantics, since these are largely the preserve of the CoSERV query language itself. The API definitions are merely vehicles for the exchange of CoSERV queries and responses. Their purpose is to facilitate standard interactions that make the most effective use of available transports and protocols. The only API binding that is specified in this document is a request-response protocol that uses HTTP for transport. This is a simple pattern, and likely to be a commonly occurring one for a variety of use cases. Future specifications may define other API bindings. Such future bindings may introduce further HTTP-based protocols. Alternatively, they may define protocols for use with other transports, such as CoAP .

Request Response over HTTP This section defines and mandates the API endpoint behaviours for CoSERV request-response transactions over HTTP. Implementations MUST provide all parts of the API as specified in this section. The API is a simple protocol for the execution of CoSERV queries. It takes a single CoSERV query as input, and produces a corresponding single CoSERV result set as the output. It is a RESTful API because the CoSERV query serves as a unique and stable identifier of the target resource, where that resource is the set of artifacts being selected for by the query. The encoding rules for CoSERV are deterministic as set out in . This means that any given CoSERV query will always encode to the same sequence of bytes. The Base64Url encoding () of the byte sequence becomes the rightmost path segment of the URI used to identify the target resource. The HTTP GET verb is then used with this URI to execute the query. Further details are provided in the subsections below. Authentication is out of scope for this document. Implementations MAY authenticate clients, for example for authorization or for preventing denial of service attacks.

Discovery Clients discover CoSERV HTTP API endpoints by means of a well-known URI that is formed using the /.well-known/ path prefix as defined in . This URI supplies a single discovery document that clients can use to locate the URIs of other API endpoints, in addition to finding out other relevant information about the configuration and capabilities of the service. Implementations that provide CoSERV HTTP API endpoints MUST also provide the discovery endpoint at the path /.well-known/coserv-configuration. This endpoint MUST be available via an HTTP GET method with no additional query parameters, and MUST return an HTTP 200 (OK) response code unless prevented by an error condition outside the scope of this specification. The response body can be formatted using either JSON or CBOR, governed by standard HTTP content-type negotiation. The media types defined for this purpose are application/coserv-discovery+json (for JSON-formatted documents) or application/coserv-discovery+cbor (for CBOR-formatted documents). In either case, the endpoint implementation MUST provide a document that conforms to the CDDL schema as follows: version, capabilities-label => [ + capability ], api-endpoints-label => { + tstr => tstr }, result-verification-key-label => eat.JC } version-label = eat.JC<"version", 1> capabilities-label = eat.JC<"capabilities", 2> api-endpoints-label = eat.JC<"api-endpoints", 3> result-verification-key-label = eat.JC<"result-verification-key", 4> version = tstr capability = { media-type-label => cmw.media-type, artifact-support-label => artifact-support } media-type-label = eat.JC<"media-type", 1> artifact-support-label = eat.JC<"artifact-support", 2> non-empty-array = (M) .and ([ + any ]) artifact-support = non-empty-array<[ ? "source", ? "collected" ]> ]]>

Discovery Document Contents This section defines how to populate and interpret the data fields in the discovery document.

Version The version field is denoted by the label "version" in JSON documents and by the codepoint 1 in CBOR documents. It is a Semantic Versioning (semver) string, which denotes the version and patch level of the service that is providing the API endpoints described by the document. The semver string MUST conform to the ABNF defined in . Version numbers and patch levels are otherwise implementation-defined.

Capabilities The capabilities field is denoted by the label "capabilities" in JSON documents and by the codepoint 2 in CBOR documents. This field allows clients to discover the profiled variants of CoSERV for which the service implementation can satisfy queries and provide artifacts. This field is structured as an array, which allows for service implementations that support more than one profile. Each supported profile is indicated according to its parameterized media type, along with the categories of artifact that can be provided for the profile. The artifact categories are source and collected, as described in . Each profile is paired with a non-empty set of artifact categories, allowing the service implementation to indicate whether it supports the retrieval of source artifacts, collected artifacts, or both. This pairing caters for situations where the service implementation might support different combinations of artifact category for different profiles.

API Endpoints The API endpoints field is denoted by the label "api-endpoints" in JSON documents and by the codepoint 3 in CBOR documents. This field allows clients to derive the correct URL for making HTTP API calls. The field is a map whose keys are the symbolic names of the APIs, and whose values are the URL path for the API endpoint. The symbolic name CoSERVRequestResponse is defined for services that offer the transactional API described in . Service implementations that offer this API MUST include a key with this name in the endpoints map field, and the corresponding endpoint URL path MUST end with /{query}. This allows the consumer to form a valid CoSERV query URI using variable expansion as per , replacing the {query} variable with the Base64Url-encoded CoSERV query object. There MUST NOT be any other variables that require substitution.

Result Verification Key The result verification key is denoted by the label "result-verification-key" in JSON documents and by the codepoint 4 in CBOR documents. This field provides one or more public keys that can be used for the cryptographic verification of CoSERV query results that are returned by the service implementation. In JSON-formatted discovery documents, each key is a JSON Web Key (JWK) as defined in . In CBOR-formatted discovery documents, each key is a COSE Key as defined in .

Discovery Document CBOR Encoding When the discovery document is encoded as CBOR, it is exempt from the encoding rules specified in . These encoding rules are designed to ensure that CoSERV queries can be used as canonical and stable identifiers. The discovery document is an independent structure, and not part of the CoSERV data model itself. Therefore, these encoding rules do not apply.

Discovery Document Examples In the following examples, the contents of bodies are informative examples only. Example HTTP request for retrieving the discovery document in JSON format: Corresponding HTTP response: Example HTTP request for retrieving the discovery document in CBOR format: Corresponding HTTP response:

Execute Query This endpoint executes a single CoSERV query and returns a CoSERV result set. The HTTP method is GET. The URL path is formed of the discovered coserv endpoint (as set out in ), where the {query} template variable is substituted with the CoSERV query to be executed, which is represented as a Base64Url encoding of the query's serialized CBOR byte sequence. There are no additional URL query parameters. Clients MUST set the HTTP Accept header to a suitably-profiled application/coserv+cose or application/coserv+cbor media type. Endpoint implementations MUST respond with an HTTP status code and response body according to one of the subheadings below.

Responses

Successful Transaction (200) This response indicates that the CoSERV query was executed successfully. Example HTTP request: Example HTTP response: >, / unprotected / {}, / payload / << { / profile / 0: "tag:example.com,2025:cc-platform#1.0.0", / query / 1: { / artifact-type / 0: 2, / reference-values / / environment-selector / 1: { / class / 0: [ [ { / class-id / 0: 560(h'00112233'), / tagged-bytes / / vendor / 1: "Example Vendor", / model / 2: "Example Model" } ] ] }, / timestamp / 2: 0("2030-12-01T18:30:01Z"), / result-type / 3: 0 / collected-material / }, / results / 2: { / rvq / 0: [ { / authorities / 1: [ 560(h'abcdef') ], / reference-triple / 2: [ / environment-map / { / class / 0: { / class-id / 0: 560(h'00112233'), / vendor / 1: "Example Vendor", / model / 2: "Example Model" } }, [ / measurement-map / { / mval / 1: { / name / 11: "Component A", / digests / 2: [ [ 1, h'aa' ], [ 2, h'bb' ] ] } }, / measurement-map / { / mval / 1: { / name / 11: "Component B", / digests / 2: [ [ 1, h'cc' ], [ 2, h'dd' ] ] } } ] ] } ], / expiry / 10: 0("2030-12-13T18:30:02Z") } } >>, / signature / h'face5190' ]) ]]>

Failure to Validate Query (400) This response indicates that the supplied query is badly formed. Example HTTP request: Example HTTP response:

Failure to Negotiate Profile (406) This response indicates that the client has specified a CoSERV profile that is not understood or serviceable by the receiving endpoint implementation. Example HTTP request: Example HTTP response:

Caching In practical usage, the artifacts transacted via CoSERV queries (such as trust anchors and reference values) may change significantly less often than they are used. For example, a Verifier needs to use the artifacts whenever it needs to verify or appraise Evidence from an Attester. This might be a very frequent operation, for which a low latency is desirable. By contrast, the artifacts themselves would vary only as a consequence of impactful changes to the Attester's desired state or environment. One example of such an impactful change might be the roll-out of a firmware update, which would result in a new reference value for the impacted firmware component(s). Such changes would tend to be relatively infrequent. The caching of CoSERV artifacts is therefore beneficial for overall system performance. CoSERV is designed to facilitate both client-side and server-side caching by use of the standard HTTP caching mechanisms specified in . This includes use of the HTTP Cache-Control header and its associated directives. It also includes the use of entity-tags (ETags). The following features of CoSERV and its HTTP binding are specifically designed to favor caching implementations:

• CoSERV queries form stable URL paths. As specified in , any given CoSERV query will always serialize to the same fixed sequence of bytes. This allows queries to be used as canonical and stable resource identifiers, which in turn allows them to function effectively as cache keys.
• The result set is cryptographically bound to the query. As specified in , the origin server is required to return a signed response that combines the result set with the client's original query, in any deployment where untrusted intermediaries might exist. This means that the client can always verify the integrity of the result on an end-to-end basis, even in the presence of caching infrastructure.
• The use of safe HTTP methods. CoSERV queries are executed as read-only operations using HTTP GET. The execution of a query does not modify any state on the server, which creates more opportunities for the re-use of cached results.

HTTP Caching and Result Set Expiry CoSERV's data model includes a mandatory expiration timestamp on every result set. This is an authoritative marker of the point in time at which the entire result set becomes invalid, and the query must be re-executed to obtain fresh results. This timestamp is established by the origin server. In the presence of HTTP caching infrastructure, the origin server MUST NOT set HTTP cache directives (e.g. Cache-Control: max-age, Expires) such that the freshness lifetime of the HTTP response exceeds the result set expiry timestamp contained within the CoSERV result set payload.

Example HTTP Messages with Caching This section illustrates a caching scenario. In this example, the CoSERV HTTP API server endpoint is hosted by an HTTP origin (coserv.example), while a reverse proxy (cache.example) operates a public cache in front of the origin. Client A sends a request using a specific CoSERV query. As the reverse proxy has a "cache miss" for the resource, it forwards the request to the origin. The origin then constructs the response and returns it to the proxy. The response includes cache-control headers that are compatible with the time-to-live associated with the computed result set. For the purposes of this example, the HTTP response max-age has been set to 10 minutes and the s-maxage to 1 hour. This means that the origin allows intermediaries (e.g., its CDN) to cache this resource for longer than the client. The result is different caching behaviours between clients and intermediaries, which reduces the load on the origin by enabling CDNs to cache content for longer, while ensuring that clients receive fresher content. Before forwarding it to the client, the proxy stores the response in its cache using the request URI as the cache key alongside the entry's time-to-live value. | lookup(obB4I3RhZ..) | | +---. | | | | | | |<--' | | | MISS | | | | | | GET ogB4I3RhZ.. | | +--------------------->| | | +---. compute | | | | result | | |<--' set | | 200 OK | (expiry = now + 1h) | | C-C: max-age=600, | | | s-maxage=3600 | | | #6.18([...]) | | |<---------------------+ | | | | | store(K=obB4I3RhZ.., | | +---. V=#6.18([...], | | | | TTL=3600) | | |<--' | | 200 OK | | | C-C: max-age=600, | | | s-maxage=3600 | | | #6.18([...]) | | |<---------------------+ | | | | ]]> At a later point, after 2 minutes, a different client B makes the same request. This time, the request generates a "cache hit" event on the proxy. The response is therefore served from the public cache, bypassing the origin. This reduces the load on the origin, where computing the result set is generally costly, as well as reducing the overall latency of the transaction. Client B operates a local cache, where it stores a copy of the response. | lookup(obB4I3RhZ..) | | +---. | | | | | | |<--' | | | HIT | | 200 OK | | | C-C: max-age=480, | | | s-maxage=3480 | | | Etag: "xyz" | | | #6.18([...]) | | |<---------------------+ | | | | | store(K=obB4I3RhZ.., | | +---. V=#6.18([...], | | | | TTL=480) | | |<--' | | | | | ]]> After 9 more minutes, B is instructed to make the same request again. The request generates a "cache hit" event on the local cache. However, the cached resource is become stale and needs to be revalidated. Therefore, B sends a conditional request to the proxy. The request generates a "cache hit" event on the proxy where the resource is still fresh due to the differential caching behaviour dictated by the original response from the origin. The proxy returns a 304 (Not modified) status code, which instructs the client to reuse its local copy of the response. | | | +---. | | | | | | |<--' | | | HIT | | 304 Not modified | | | C-C: max-age=0, | | | s-maxage=3060 | | |<---------------------+ | | | | ]]>

Implementation Status RFC Editor: please remove this section prior to publication. This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in . The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to , "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".

Veraison Responsible Organisation: Veraison (open source project within the Confidential Computing Consortium). Location: https://github.com/veraison Description: Veraison provides components that can be used to build a Verifier, and also exemplifies adjacent RATS roles such as the Relying Party. There is an active effort to extend Veraison so that it can act in the capacity of an Endorser or Reference Value Provider, showing how CoSERV can be used as a query language for such services. This includes library code to assist with the creation, parsing and manipulation of CoSERV queries. Level of Maturity: This is a proof-of-concept prototype implementation. License: Apache-2.0. Coverage: This implementation covers all aspects of the CoSERV query language. Contact: Thomas Fossati, Thomas.Fossati@linaro.org

Security Considerations The CoSERV data type serves an auxiliary function in the RATS architecture. It does not directly convey Evidence, Endorsements, Reference Values, Policies or Attestation Results. CoSERV exists only to facilitate the interactions between the Verifier and the Endorser or Reference Value Provider roles. Consequently, there are fewer security considerations for CoSERV, particularly when compared with data objects such as EAT or CoRIM. Certain security characteristics are desirable for interactions between the Verifier and the Endorser or Reference Value Provider. However, these characteristics would be the province of the specific implementations of these roles, and of the transport protocols in between them. They would not be the province of the CoSERV data object itself. Examples of such desirable characteristics might be:

• The Endorser or Reference Value Provider is available to the Verifier when needed.
• The Verifier is authorised to query data from the Endorser or Reference Value Provider.
• Queries cannot be intercepted or undetectably modified by an entity that is interposed between the Verifier and the Endorser or Reference Value Provider.

Forming Native Database Queries from CoSERV Implementations should take care when transforming CoSERV queries into native query types that are compatible with their underlying storage technology (such as SQL queries). There is a risk of injection attacks arising from poorly-formed or maliciously-formed CoSERV queries. Implementations must ensure that suitable sanitization procedures are in place when performing such translations.

Privacy Considerations A CoSERV query can potentially contain privacy-sensitive information. Specifically, the environment-selector field of the query may reference identifiable Attester instances in some cases. This concern naturally also extends to the data objects that might be returned to the consumer in response to the query, although the specifications of such data objects are beyond the scope of this document. Implementations should ensure that appropriate attention is paid to this. Suitable mitigations include the following:

• The use of authenticated secure channels between the producers and the consumers of CoSERV queries and returned artifacts.
• Collating Attester instances into anonymity groups, and referencing the groups rather than the individual instances.

IANA Considerations RFC Editor: replace "RFCthis" with the RFC number assigned to this document.

Media Types Registrations IANA is requested to add the following media types to the "Media Types" registry . CoSERV Media Types

Name	Template	Reference
coserv+cbor	application/coserv+cbor	of RFCthis
coserv+cose	application/coserv+cose	of RFCthis
coserv-discovery+cbor	application/coserv-discovery+cbor	of RFCthis
coserv-discovery+json	application/coserv-discovery+json	of RFCthis

application/coserv+cbor

Type name:

application

Subtype name:

coserv+cbor

Required parameters:

n/a

Optional parameters:

"profile" (CoSERV profile in string format. OIDs must use the dotted-decimal notation.)

Encoding considerations:

binary (CBOR)

Security considerations:

of RFCthis

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type:

Verifiers, Endorsers, Reference Value Providers

Fragment identifier considerations:

The syntax and semantics of fragment identifiers are as specified for "application/cbor". (No fragment identification syntax is currently defined for "application/cbor".)

Person & email address to contact for further information:

RATS WG mailing list (rats@ietf.org)

Intended usage:

COMMON

Restrictions on usage:

none

Author/Change controller:

IETF

Provisional registration:

no

application/coserv+cose

Type name:

application

Subtype name:

coserv+cose

Required parameters:

n/a (cose-type is explicitly not supported, as it is understood to be "cose-sign1")

Optional parameters:

"profile" CoSERV profile in string format. OIDs must use the dotted-decimal notation. Note that the cose-type parameter is explicitly not supported, as it is understood to be "cose-sign1".

Encoding considerations:

binary

Security considerations:

of RFCthis

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type:

Verifiers, Endorsers, Reference Value Providers

Fragment identifier considerations:

n/a

Person and email address to contact for further information:

RATS WG mailing list (rats@ietf.org)

Intended usage:

COMMON

Restrictions on usage:

none

Author/Change controller:

IETF

Provisional registration?

no

application/coserv-discovery+cbor

Type name:

application

Subtype name:

coserv-discovery+cbor

Required parameters:

n/a

Optional parameters:

n/a

Encoding considerations:

binary (CBOR)

Security considerations:

of RFCthis

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type:

Verifiers, Endorsers, Reference Value Providers

Fragment identifier considerations:

The syntax and semantics of fragment identifiers are as specified for "application/cbor". (No fragment identification syntax is currently defined for "application/cbor".)

Person & email address to contact for further information:

RATS WG mailing list (rats@ietf.org)

Intended usage:

COMMON

Restrictions on usage:

none

Author/Change controller:

IETF

Provisional registration:

no

application/coserv-discovery+json

Type name:

application

Subtype name:

coserv-discovery+json

Required parameters:

n/a

Optional parameters:

n/a

Encoding considerations:

binary (JSON is UTF-8-encoded text)

Security considerations:

of RFCthis

Interoperability considerations:

n/a

Published specification:

RFCthis

Applications that use this media type:

Verifiers, Endorsers, Reference Value Providers

Fragment identifier considerations:

The syntax and semantics of fragment identifiers are as specified for "application/json". (No fragment identification syntax is currently defined for "application/json".)

Person & email address to contact for further information:

RATS WG mailing list (rats@ietf.org)

Intended usage:

COMMON

Restrictions on usage:

none

Author/Change controller:

IETF

Provisional registration:

no

CoAP Content-Formats IANA is requested to register the following Content-Format IDs in the "CoAP Content-Formats" registry, within the "Constrained RESTful Environments (CoRE) Parameters" registry group : New CoAP Content Formats

Content-Type	Content Coding	ID	Reference
application/coserv+cbor	-	TBD1	of RFCthis
application/coserv+cose	-	TBD2	of RFCthis

If possible, TBD1 and TBD2 should be assigned in the 256..9999 range.

Well-Known URI for CoSERV Configuration IANA is requested to register the following in the "Well-Known URIs" registry : URI suffix: coserv-configuration Change controller: IETF Specification document: RFCthis Related information: N/A

References Normative References This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK] A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data structure that represents a cryptographic key. This specification also defines a JWK Set JSON data structure that represents a set of JWKs. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries established by that specification. This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. This memo defines a path prefix for "well-known locations", "/.well-known/", in selected Uniform Resource Identifier (URI) schemes. In doing so, it obsoletes RFC 5785 and updates the URI schemes defined in RFC 7230 to reserve that space. It also updates RFC 7595 to track URI schemes that support well-known URIs in their registry. Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. There is a need to be able to define basic security services for this data format. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to represent cryptographic keys using CBOR. This document, along with RFC 9053, obsoletes RFC 8152. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. In network protocol exchanges, it is often useful for one end of a communication to know whether the other end is in an intended operating state. This document provides an architectural overview of the entities involved that make such tests possible through the process of generating, conveying, and evaluating evidentiary Claims. It provides a model that is neutral toward processor architectures, the content of Claims, and protocols. Fraunhofer SIT Linaro arm Intel Huawei Technologies Remote Attestation Procedures (RATS) enable Relying Parties to assess the trustworthiness of a remote Attester and therefore to decide whether or not to engage in secure interactions with it. Evidence about trustworthiness can be rather complex and it is deemed unrealistic that every Relying Party is capable of the appraisal of Evidence. Therefore that burden is typically offloaded to a Verifier. In order to conduct Evidence appraisal, a Verifier requires not only fresh Evidence from an Attester, but also trusted Endorsements and Reference Values from Endorsers and Reference Value Providers, such as manufacturers, distributors, or device owners. This document specifies the information elements for representing Endorsements and Reference Values in CBOR format. Fraunhofer SIT Independent Linaro University of Applied Sciences Bonn-Rhein-Sieg Google LLC The Conceptual Messages introduced by the RATS Architecture (RFC9334) are protocol-agnostic data units that are conveyed between RATS roles during remote attestation procedures. Conceptual Messages describe the meaning and function of such data units within RATS data flows without specifying a wire format, encoding, transport mechanism, or processing details. The initial set of Conceptual Messages is defined in Section 8 of RFC9334 and includes Evidence, Attestation Results, Endorsements, Reference Values, and Appraisal Policies. This document introduces the Conceptual Message Wrapper (CMW) that provides a common structure to encapsulate these messages. It defines a dedicated CBOR tag, corresponding JSON Web Token (JWT) and CBOR Web Token (CWT) claims, and an X.509 extension. This allows CMWs to be used in CBOR-based protocols, web APIs using JWTs and CWTs, and PKIX artifacts like X.509 certificates. Additionally, the draft defines a media type and a CoAP content format to transport CMWs over protocols like HTTP, MIME, and CoAP. The goal is to improve the interoperability and flexibility of remote attestation protocols. By introducing a shared message format like the CMW, we can consistently support different attestation message types, evolve message serialization formats without breaking compatibility, and avoid having to redefine how messages are handled in each protocol. 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. 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. JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification. A URI Template is a compact sequence of characters for describing a range of Uniform Resource Identifiers through variable expansion. This specification defines the URI Template syntax and the process for expanding a URI Template into a URI reference, along with guidelines for the use of URI Templates on the Internet. [STANDARDS-TRACK] IANA IANA IANA Informative References The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages. This document obsoletes RFC 7234. 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. This document describes a simple process that allows authors of Internet-Drafts to record the status of known implementations by including an Implementation Status section. This will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. This process is not mandatory. Authors of Internet-Drafts are encouraged to consider using the process for their documents, and working groups are invited to think about applying the process to all of their protocol specifications. This document obsoletes RFC 6982, advancing it to a Best Current Practice. The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation. CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. Armidale Consulting Fraunhofer SIT Linaro In the IETF Remote Attestation Procedures (RATS) architecture, a Verifier accepts Evidence and, using Appraisal Policy typically with additional input from Endorsements and Reference Values, generates Attestation Results in formats that are useful for Relying Parties. This document illustrates the purpose and role of Endorsements and discusses some considerations in the choice of message format for Endorsements in the scope of the RATS architecture. This document does not aim to define a conceptual message format for Endorsements and Reference Values. Instead, it extends RFC9334 to provide further details on Reference Values and Endorsements, as these topics were outside the scope of the RATS charter when RFC9334 was developed. Security Theory LLC Mediatek USA Qualcomm Technologies Inc. Red Hound Software, Inc. An Entity Attestation Token (EAT) provides an attested claims set that describes state and characteristics of an entity, a device like a smartphone, IoT device, network equipment or such. This claims set is used by a relying party, server or service to determine the type and degree of trust placed in the entity. An EAT is either a CBOR Web Token (CWT) or JSON Web Token (JWT) with attestation-oriented claims. This document describes the part of the Content Delivery Network Interconnection (CDNI) Control interface that allows a CDN to trigger activity in an interconnected CDN that is configured to deliver content on its behalf. The upstream CDN can use this mechanism to request that the downstream CDN pre-position metadata or content or to request that it invalidate or purge metadata or content. The upstream CDN can monitor the status of activity that it has triggered in the downstream CDN.

Collated CoSERV CDDL profile &(query: 1) => query ? &(results: 2) => results } profile = comid.oid-type / ~uri ;# import comid-autogen environment-selector-map = { selector } stateful-class = [ class: comid.class-map ? measurements: [ + comid.measurement-map ] ] selector //= ( &(class: 0) => [ + stateful-class ] ) stateful-instance = [ instance: comid.$instance-id-type-choice ? measurements: [ + comid.measurement-map ] ] selector //= ( &(instance: 1) => [ + stateful-instance ] ) stateful-group = [ group: comid.$group-id-type-choice ? measurements: [ + comid.measurement-map ] ] selector //= ( &(group: 2) => [ + stateful-group ] ) concise-mid-tag = { ? &(language: 0) => text &(tag-identity: 1) => tag-identity-map ? &(entities: 2) => [ + comid-entity-map ] ? &(linked-tags: 3) => [ + linked-tag-map ] &(triples: 4) => triples-map * $$concise-mid-tag-extension } attest-key-triple-record = [ environment: environment-map key-list: [ + $crypto-key-type-choice ] ? conditions: non-empty< { ? &(mkey: 0) => $measured-element-type-choice, ? &(authorized-by: 1) => [ + $crypto-key-type-choice ] }> ] $class-id-type-choice /= tagged-oid-type $class-id-type-choice /= tagged-uuid-type $class-id-type-choice /= tagged-bytes class-map = non-empty<{ ? &(class-id: 0) => $class-id-type-choice ? &(vendor: 1) => tstr ? &(model: 2) => tstr ? &(layer: 3) => uint ? &(index: 4) => uint }> comid-entity-map = entity-map<$comid-role-type-choice, $$comid-entity-map-extension> $comid-role-type-choice /= &(tag-creator: 0) $comid-role-type-choice /= &(creator: 1) $comid-role-type-choice /= &(maintainer: 2) conditional-endorsement-series-triple-record = [ condition: stateful-environment-record series: [ + conditional-series-record ] ] conditional-series-record = [ selection: [ + measurement-map] addition: [ + measurement-map ] ] COSE_KeySet = [ + COSE_Key ] COSE_Key = { 1 => tstr / int ? 2 => bstr ? 3 => tstr / int ? 4 => [+ (tstr / int) ] ? 5 => bstr * cose-label => cose-value } cose-label = int / tstr cose-value = any coswid-triple-record = [ environment-map [ + concise-swid-tag-id ] ] concise-swid-tag-id = text / bstr .size 16 $crypto-key-type-choice /= tagged-pkix-base64-key-type $crypto-key-type-choice /= tagged-pkix-base64-cert-type $crypto-key-type-choice /= tagged-pkix-base64-cert-path-type $crypto-key-type-choice /= tagged-cose-key-type $crypto-key-type-choice /= tagged-thumbprint-type $crypto-key-type-choice /= tagged-cert-thumbprint-type $crypto-key-type-choice /= tagged-cert-path-thumbprint-type $crypto-key-type-choice /= tagged-pkix-asn1der-cert-type $crypto-key-type-choice /= tagged-bytes tagged-pkix-base64-key-type = #6.554(tstr) tagged-pkix-base64-cert-type = #6.555(tstr) tagged-pkix-base64-cert-path-type = #6.556(tstr) tagged-thumbprint-type = #6.557(digest) tagged-cose-key-type = #6.558(COSE_KeySet / COSE_Key) tagged-cert-thumbprint-type = #6.559(digest) tagged-cert-path-thumbprint-type = #6.561(digest) tagged-pkix-asn1der-cert-type = #6.562(bstr) domain-dependency-triple-record = [ $domain-type-choice [ + $domain-type-choice ] ] domain-membership-triple-record = [ $domain-type-choice [ + environment-map ] ] conditional-endorsement-triple-record = [ conditions: [ + stateful-environment-record ] endorsements: [ + endorsed-triple-record ] ] $domain-type-choice /= uint $domain-type-choice /= text $domain-type-choice /= tagged-uuid-type $domain-type-choice /= tagged-oid-type endorsed-triple-record = [ condition: environment-map endorsement: [ + measurement-map ] ] entity-map = { &(entity-name: 0) => $entity-name-type-choice ? &(reg-id: 1) => uri &(role: 2) => [ + role-type-choice ] * extension-socket } $entity-name-type-choice /= text environment-map = non-empty<{ ? &(class: 0) => class-map ? &(instance: 1) => $instance-id-type-choice ? &(group: 2) => $group-id-type-choice }> flags-map = { ? &(is-configured: 0) => bool ? &(is-secure: 1) => bool ? &(is-recovery: 2) => bool ? &(is-debug: 3) => bool ? &(is-replay-protected: 4) => bool ? &(is-integrity-protected: 5) => bool ? &(is-runtime-meas: 6) => bool ? &(is-immutable: 7) => bool ? &(is-tcb: 8) => bool ? &(is-confidentiality-protected: 9) => bool * $$flags-map-extension } $group-id-type-choice /= tagged-uuid-type $group-id-type-choice /= tagged-bytes identity-triple-record = [ environment: environment-map key-list: [ + $crypto-key-type-choice ] ? conditions: non-empty<{ ? &(mkey: 0) => $measured-element-type-choice, ? &(authorized-by: 1) => [ + $crypto-key-type-choice ] }> ] $instance-id-type-choice /= tagged-ueid-type $instance-id-type-choice /= tagged-uuid-type $instance-id-type-choice /= $crypto-key-type-choice $instance-id-type-choice /= tagged-bytes ip-addr-type-choice = ip4-addr-type / ip6-addr-type ip4-addr-type = bytes .size 4 ip6-addr-type = bytes .size 16 raw-int-type-choice = int / tagged-int-range int-range = [min: int / negative-inf, max: int / positive-inf] tagged-int-range = #6.564(int-range) positive-inf = null negative-inf = null linked-tag-map = { &(linked-tag-id: 0) => $tag-id-type-choice &(tag-rel: 1) => $tag-rel-type-choice } mac-addr-type-choice = eui48-addr-type / eui64-addr-type eui48-addr-type = bytes .size 6 eui64-addr-type = bytes .size 8 $measured-element-type-choice /= tagged-oid-type $measured-element-type-choice /= tagged-uuid-type $measured-element-type-choice /= uint $measured-element-type-choice /= tstr measurement-map = { ? &(mkey: 0) => $measured-element-type-choice &(mval: 1) => measurement-values-map ? &(authorized-by: 2) => [ + $crypto-key-type-choice ] } measurement-values-map = non-empty<{ ? &(version: 0) => version-map ? &(svn: 1) => svn-type-choice ? &(digests: 2) => digests-type ? &(flags: 3) => flags-map ? ( &(raw-value: 4) => $raw-value-type-choice, ? &(raw-value-mask: 5) => raw-value-mask-type ) ? &(mac-addr: 6) => mac-addr-type-choice ? &(ip-addr: 7) => ip-addr-type-choice ? &(serial-number: 8) => text ? &(ueid: 9) => ueid-type ? &(uuid: 10) => uuid-type ? &(name: 11) => text ? &(cryptokeys: 13) => [ + $crypto-key-type-choice ] ? &(integrity-registers: 14) => integrity-registers ? &(raw-int: 15) => raw-int-type-choice * $$measurement-values-map-extension }> non-empty = (M) .and ({ + any => any }) oid-type = bytes tagged-oid-type = #6.111(oid-type) $raw-value-type-choice /= tagged-bytes $raw-value-type-choice /= tagged-masked-raw-value raw-value-mask-type = bytes tagged-masked-raw-value = #6.563([ value: bytes mask : bytes ]) reference-triple-record = [ ref-env: environment-map ref-claims: [ + measurement-map ] ] stateful-environment-record = [ environment: environment-map, claims-list: [ + measurement-map ] ] svn-type = uint svn = svn-type min-svn = svn-type tagged-svn = #6.552(svn) tagged-min-svn = #6.553(min-svn) svn-type-choice = svn / tagged-svn / tagged-min-svn $tag-id-type-choice /= tstr $tag-id-type-choice /= uuid-type tag-identity-map = { &(tag-id: 0) => $tag-id-type-choice ? &(tag-version: 1) => tag-version-type } $tag-rel-type-choice /= &(supplements: 0) $tag-rel-type-choice /= &(replaces: 1) tag-version-type = uint .default 0 tagged-bytes = #6.560(bytes) triples-map = non-empty<{ ? &(reference-triples: 0) => [ + reference-triple-record ] ? &(endorsed-triples: 1) => [ + endorsed-triple-record ] ? &(identity-triples: 2) => [ + identity-triple-record ] ? &(attest-key-triples: 3) => [ + attest-key-triple-record ] ? &(dependency-triples: 4) => [ + domain-dependency-triple-record ] ? &(membership-triples: 5) => [ + domain-membership-triple-record ] ? &(coswid-triples: 6) => [ + coswid-triple-record ] ? &(conditional-endorsement-series-triples: 8) => [ + conditional-endorsement-series-triple-record ] ? &(conditional-endorsement-triples: 10) => [ + conditional-endorsement-triple-record ] * $$triples-map-extension }> ueid-type = bytes .size (7..33) tagged-ueid-type = #6.550(ueid-type) uuid-type = bytes .size 16 tagged-uuid-type = #6.37(uuid-type) version-map = { &(version: 0) => text ? &(version-scheme: 1) => $version-scheme } digest = [ alg: (int / text), val: bytes ] digests-type = [ + digest ] integrity-register-id-type-choice = uint / text integrity-registers = { + integrity-register-id-type-choice => digests-type } concise-swid-tag = { tag-id => text / bstr .size 16, tag-version => integer, ? corpus => bool, ? patch => bool, ? supplemental => bool, software-name => text, ? software-version => text, ? version-scheme => $version-scheme, ? media => text, ? software-meta => one-or-more, entity => one-or-more, ? link => one-or-more, ? payload-or-evidence, * $$coswid-extension, global-attributes, } payload-or-evidence //= ( payload => payload-entry ) payload-or-evidence //= ( evidence => evidence-entry ) any-uri = uri label = text / int $version-scheme /= multipartnumeric $version-scheme /= multipartnumeric-suffix $version-scheme /= alphanumeric $version-scheme /= decimal $version-scheme /= semver $version-scheme /= int / text any-attribute = ( label => one-or-more / one-or-more ) one-or-more = T / [ 2* T ] global-attributes = ( ? lang => text, * any-attribute, ) hash-entry = [ hash-alg-id: int, hash-value: bytes, ] entity-entry = { entity-name => text, ? reg-id => any-uri, role => one-or-more<$role>, ? thumbprint => hash-entry, * $$entity-extension, global-attributes, } $role /= tag-creator $role /= software-creator $role /= aggregator $role /= distributor $role /= licensor $role /= maintainer $role /= int / text link-entry = { ? artifact => text, href => any-uri, ? media => text, ? ownership => $ownership, rel => $rel, ? media-type => text, ? use => $use, * $$link-extension, global-attributes, } $ownership /= shared $ownership /= private $ownership /= abandon $ownership /= int / text $rel /= ancestor $rel /= component $rel /= feature $rel /= installationmedia $rel /= packageinstaller $rel /= parent $rel /= patches $rel /= requires $rel /= see-also $rel /= supersedes $rel /= supplemental $rel /= -256..64436 / text $use /= optional $use /= required $use /= recommended $use /= int / text software-meta-entry = { ? activation-status => text, ? channel-type => text, ? colloquial-version => text, ? description => text, ? edition => text, ? entitlement-data-required => bool, ? entitlement-key => text, ? generator => text / bstr .size 16, ? persistent-id => text, ? product => text, ? product-family => text, ? revision => text, ? summary => text, ? unspsc-code => text, ? unspsc-version => text, * $$software-meta-extension, global-attributes, } path-elements-group = ( ? directory => one-or-more, ? file => one-or-more, ) resource-collection = ( path-elements-group, ? process => one-or-more, ? resource => one-or-more, * $$resource-collection-extension, ) file-entry = { filesystem-item, ? size => uint, ? file-version => text, ? hash => hash-entry, * $$file-extension, global-attributes, } directory-entry = { filesystem-item, ? path-elements => { path-elements-group }, * $$directory-extension, global-attributes, } process-entry = { process-name => text, ? pid => integer, * $$process-extension, global-attributes, } resource-entry = { type => text, * $$resource-extension, global-attributes, } filesystem-item = ( ? key => bool, ? location => text, fs-name => text, ? root => text, ) payload-entry = { resource-collection, * $$payload-extension, global-attributes, } evidence-entry = { resource-collection, ? date => integer-time, ? device-id => text, ? location => text, * $$evidence-extension, global-attributes, } integer-time = #6.1(int) tag-id = 0 software-name = 1 entity = 2 evidence = 3 link = 4 software-meta = 5 payload = 6 hash = 7 corpus = 8 patch = 9 media = 10 supplemental = 11 tag-version = 12 software-version = 13 version-scheme = 14 lang = 15 directory = 16 file = 17 process = 18 resource = 19 size = 20 file-version = 21 key = 22 location = 23 fs-name = 24 root = 25 path-elements = 26 process-name = 27 pid = 28 type = 29 entity-name = 31 reg-id = 32 role = 33 thumbprint = 34 date = 35 device-id = 36 artifact = 37 href = 38 ownership = 39 rel = 40 media-type = 41 use = 42 activation-status = 43 channel-type = 44 colloquial-version = 45 description = 46 edition = 47 entitlement-data-required = 48 entitlement-key = 49 generator = 50 persistent-id = 51 product = 52 product-family = 53 revision = 54 summary = 55 unspsc-code = 56 unspsc-version = 57 multipartnumeric = 1 multipartnumeric-suffix = 2 alphanumeric = 3 decimal = 4 semver = 16384 tag-creator=1 software-creator=2 aggregator=3 distributor=4 licensor=5 maintainer=6 abandon=1 private=2 shared=3 ancestor=1 component=2 feature=3 installationmedia=4 packageinstaller=5 parent=6 patches=7 requires=8 see-also=9 supersedes=10 optional=1 required=2 recommended=3 ]]>

OpenAPI Schema The OpenAPI schema for the request/response HTTP API described in is provided below. A CoSERV result set has been successfully computed. content: application/coserv+cose: schema: type: string format: binary description: > A CoSERV result set enveloped in a COSE Sign1 object. '400': description: > The request was malformed; e.g., the query was not valid base64url, or the CoSERV data item could not be successfully parsed. content: application/concise-problem-details+cbor: schema: type: string format: binary description: > A CBOR-encoded problem details data item. '406': description: > The server cannot produce a response matching the list of acceptable values defined in the request's 'Accept' header field. In particular, the client may have specified a CoSERV profile that is not understood or serviceable by the server. content: application/concise-problem-details+cbor: schema: type: string format: binary description: > A CBOR-encoded problem details data item. /.well-known/coserv-configuration: get: summary: Retrieve the CoSERV configuration document. responses: '200': description: > The CoSERV configuration document has been successfully retrieved. content: application/coserv-discovery+json: schema: type: string format: binary description: > A JSON-encoded CoSERV configuration document. application/coserv-discovery+cbor: schema: type: string format: binary description: > A CBOR-encoded CoSERV configuration document. ]]>

Acknowledgments The participants in the "Staircase meeting" at FOSDEM '25: Henk Birkholz and Jag Raman are puppeteering in the shadows.