]> Fraunhofer SIT

henk.birkholz@ietf.contact

Independent

ned.smith.ietf@outlook.com

Linaro

thomas.fossati@linaro.org

University of the Bundeswehr Munich

Werner-Heisenberg-Weg 39 Institute of Distributed Intelligent Systems Neubiberg 85577 Germany Hannes.Tschofenig@gmx.net

SEC rats evidence attestation results endorsements reference values The conceptual messages introduced by the Remote ATtestation procedureS (RATS) architecture (RFC 9334) are protocol-agnostic data units that are conveyed between RATS roles during RATS interactions. 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 RFC 9334 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 Concise Binary Object Representation (CBOR) tag, corresponding JSON Web Token (JWT) and CBOR Web Token (CWT) claims, and an X.509 extension. Together, these mechanisms allow CMWs to be used in CBOR-based protocols, web APIs using JWTs and CWTs, and PKIX artifacts such as X.509 certificates. Additionally, this document defines media types and CoAP Content-Formats that may be used to identify CMWs when transported over protocols such as HTTP, MIME, and CoAP. The goal is to improve the interoperability and flexibility of remote attestation protocols. Introducing a shared message format such as CMW enables consistent support for different attestation message types, enables the evolution of message serialization formats without breaking compatibility, and avoids the need to redefine how messages are handled within each protocol.

Introduction The conceptual messages introduced by the Remote ATtestation procedureS (RATS) architecture are protocol-agnostic data units that are conveyed between RATS roles during RATS interactions. 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 and includes Evidence, Attestation Results, Endorsements, Reference Values, and Appraisal Policies. Each conceptual message can have multiple claim-encoding and serialization formats (). Throughout their lifetime, RATS conceptual messages are typically transported over different protocols. For example:

• In a "background-check" topology (), Evidence (e.g., Entity Attestation Token (EAT) ) first flows from the Attester to the Relying Party (RP); then it flows from the RP to the Verifier and each leg following a separate protocol path. See .

  Conveyance of RATS Conceptual Messages in the 'background-check' Topology |--' RP | '------------' EAT over TLS '------------']]>

• In a "passport" topology (), an attestation result payload (e.g., EAT Attestation Result (EAR) ) is initially sent from the Verifier to the Attester; later, it is sent via a different channel from the Attester to the RP. See .

  Conveyance of RATS Conceptual Messages in the 'passport' Topology | RP | '------------' EAR over TLS '------------']]>

By using the CMW format outlined in this document, protocol designers can avoid the need to update protocol specifications to accommodate different conceptual messages and serialization formats used by various attestation technologies. This approach streamlines the implementation process for developers, enabling easier support for diverse attestation technologies. For instance, an RP application implementer does not need to parse attestation-related messages, such as Evidence from Attesters on Internet of Things (IoT) devices with Trusted Platform Modules (TPMs) or servers using confidential computing hardware like Intel Trust Domain Extensions (TDX). Instead, they can leverage the CMW format, remaining agnostic to the specific attestation technology. A further design goal is extensibility. This means that adding support for new conceptual messages and new attestation technologies should not change the core of the processor; it also means that a CMW stack can be designed to offer a plug-in interface for both encoding and decoding. To achieve this, the format must provide consistent message encapsulation and explicit typing. These features allow the selection of the appropriate message handler based on its type identifier. An opaque message can then be passed between the core and the handler. This document defines two encapsulation formats for RATS conceptual messages that aim to achieve the goals stated above. These encapsulation formats have been specifically designed to possess the following characteristics:

• They are self-describing: they can convey precise typing information without relying on the framing provided by the embedding protocol or the storage system.
• They are based on media types , which allows the cost of their registration to be spread across numerous usage scenarios.

A protocol designer could use these formats, for example, to:

• convey Evidence, Endorsements, and Reference Values in certificates and Certificate Revocation List (CRL) extensions ;
• embed Attestation Results or Evidence as first-class authentication credentials in TLS handshake messages ;
• transport attestation-related payloads in RESTful APIs (where "RESTful" refers to the Representational State Transfer (REST) architecture); or
• serve as stable storage of Attestation Results in the form of file system objects.

This document also defines a corresponding CBOR tag, JWT and CWT claims, and an X.509 extension. These allow embedding the wrapped conceptual messages into CBOR-based protocols, web APIs, and PKIX formats and protocols. In addition, media types and CoAP Content-Formats are defined for transporting CMWs in HTTP, MIME, CoAP, and other Internet protocols.

Conventions and Definitions 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. In this document, Concise Data Definition Language (CDDL) (see , , and ) is used to describe the data formats. The reader is assumed to be familiar with the vocabulary and concepts defined in . This document reuses the terms defined in (e.g., "Content-Type").

Conceptual Message Wrappers A RATS CMW has a tree structure. Leaf nodes are of type "Record" () or "Tag" (). Intermediate nodes are of type "Collection" (); they hold together multiple CMW items. The following snippet outlines the productions associated with the top-level types. The complete CDDL can be found in . Sections and describe the transport of CMWs using CBOR, JWTs, and PKIX formats including Certificate Signing Requests (CSRs), X.509 certificates, and CRLs. This document only defines an encapsulation, not a security format. It is the responsibility of the Attester to ensure that the CMW contents have the necessary security protection. Security considerations are discussed in .

Record CMW The format of the Record CMW is shown in . The JSON and CBOR representations are provided separately. Both the json-record and cbor-record have the same fields, except for slight differences in the types discussed below.

CDDL Definition of the Record CMW

Each contains two or three members:

type:

Either a text string representing a Content-Type (e.g., an EAT media type ) or an unsigned integer corresponding to a CoAP Content-Format ID (). The latter is not used in the JSON serialization.

value:

The RATS conceptual message serialized according to the value defined in the type member. When using JSON, the value field MUST be encoded as Base64 using the URL and filename-safe alphabet () without padding. This always applies, even if the conceptual message format is already textual (e.g., a JWT EAT). When using CBOR, the value field MUST be encoded as a CBOR byte string.

ind:

An optional bitmap with a maximum size of 4 bytes that indicates which conceptual message types are carried in the value field. Any combination (i.e., any value between 1 and 2³²-1 inclusive) is allowed. Only 5 bits are registered in this document, so the acceptable values are currently limited to 1 to 31. This is useful only if the type is potentially ambiguous and there is no further context available to the CMW consumer to decide. For example, this might be the case if the base media type is not profiled (e.g., application/eat+cwt), if the value field contains multiple conceptual messages with different types (e.g., both Reference Values and Endorsements within the same application/rim+cose), or if the same profile identifier is shared by different conceptual messages. The value MUST be non-zero. The absence of information about the conceptual message indicator is indicated by omitting the ind field entirely. For further details, see .

Conceptual Message Type The cm-type type is the control type for the ind field. As such, it indicates which bits are allowed to be set in the ind bitmap.

CDDL Definition of the CM Type

The cm-type as defined by this document has five allowed values: Reference Values, Endorsements, Evidence, Attestation Results, and Appraisal Policy, as defined in . Note that an Appraisal Policy may refer to the appraisal of Evidence or Attestation Results, depending on whether the consumer of the conceptual message is a Verifier or an RP. It is recommended that future specifications extending the RATS conceptual messages add new values to the cm-type using the process defined in .

Tag CMW Tag CMWs derive their tag numbers from a corresponding CoAP Content-Format ID using the TN() transform defined in . Such CBOR tag numbers are in the range [1668546817, 1668612095]. The RATS conceptual message is first serialized according to the Content-Format ID and then encoded as a CBOR byte string, to which the TN-derived tag number is prepended. The Tag CMW is defined in using two different macros: one for CBOR-encoded types and the other for all other types. Both macros take the CBOR tag number tn as a parameter. The tag-cm-cbor macro takes the CDDL definition of the associated conceptual message fmt as a second parameter.

CDDL Definition of the Tag CMW Macros = #6.(bytes .cbor fmt) tag-cm-data = #6.(bytes)]]>

How to Plug in a New Tag CMW To plug a new Tag CMW into the CDDL defined in , the $cbor-tag type socket must be extended with a new instance of the Tag CMW macro (i.e., one of tag-cm-cbor or tag-cm-data). For instance, if a conceptual message of type my-evidence has the TN-derived CBOR tag 1668612069, $cbor-tag would be extended as follows: my-evidence = { &(eat_nonce: 10) => bytes .size (8..64) }]]> Instead, if a (non-CBOR) conceptual message has the TN-derived CBOR tag 1668612070, $cbor-tag would be extended as follows: ]]> The socket is initialized as described in .

Collection CMW Layered Attesters and composite devices (Sections and of ) generate Evidence that consists of multiple parts. For example, in data center servers, it is not uncommon for separate attesting environments (AEs) to serve a subsection of the entire machine. One AE might measure and attest to what was booted on the main CPU, while another AE might measure and attest to what was booted on a SmartNIC plugged into a PCI Express (PCIe) slot, and a third AE might measure and attest to what was booted on the machine's Graphics Processing Unit (GPU). To allow aggregation of multiple, potentially non-homogeneous evidence formats collected from different AEs, this document defines a Collection CMW as a container that holds several CMW items, each with a label that is unique within the scope of the collection. Although originally designed to support layered Attester and composite device use cases, the Collection CMW can be adapted for other scenarios that require the aggregation of RATS conceptual messages. For instance, collections may be used to group Endorsements, Reference Values, Attestation Results, and more. A single Collection CMW can contain a mix of different message types; it can also be used to carry messages related to multiple devices simultaneously. The Collection CMW () is defined as a CBOR map or JSON object containing CMW values. The position of a cmw entry in the cmw-collection is not significant. Labels can be strings (or integers in the CBOR serialization) that serve as a mnemonic for different conceptual messages in the collection.

CDDL Definition of the Collection CMW json-cmw } cbor-collection = { ? "__cmwc_t": ~uri / oid + &(label: (int / text)) => cbor-cmw }]]>

A collection MUST have at least one CMW entry. The "__cmwc_t" key is reserved for associating an optional type with the overall collection and MUST NOT be used for any purpose other than described here. The value of the "__cmwc_t" key is either a Uniform Resource Identifier (URI) or an object identifier (OID). The OID is always absolute and never relative. The URI MUST be in the absolute form (). The "__cmwc_t" key functions similarly to an EAT profile claim (see ) but at a higher level. It can be used to indicate basics like CBOR serialization and CBOR Object Signing and Encryption (COSE) algorithms just as a profile in EAT does. It provides a namespace in which the collection labels are interpreted. At the higher level, it can be used to describe the allowed Collection CMW assembly (this is somewhat parallel to the way EAT profiles indicate which claims are required and/or allowed). For an example of a "__cmwc_t" that is defined for a bundle of endorsements and reference values, see . Since the Collection CMW is recursive (a Collection CMW is itself a CMW), implementations MAY limit the allowed depth of nesting.

Demuxing The split in the JSON/CBOR decoding path is expected to occur via the media type or content format (see Sections and , respectively) or via the container context of the embedded CMW (see Sections and for CWT/JWT and for X.509). The following pseudocode illustrates how a one-byte look-ahead is sufficient to determine how to decode the remaining byte buffer. This code is provided for informational purposes only. It is not expected that implementations will follow this demuxing strategy.

Cryptographic Protection of CMWs This section highlights a number of mechanisms through which protocol designers can add data origin authentication, integrity, and (if used with a challenge-response protocol) anti-replay protection when employing CMWs. These properties must be evaluated carefully in the context of the overall security model of the protocol.

Signing CBOR CMW Using COSE_Sign1 A CBOR CMW can be signed using COSE . A signed-cbor-cmw is a COSE_Sign1 with the following layout: The payload MUST be the CBOR-encoded Tag, Record, or Collection CMW. int ; alg 3 => "application/cmw+cbor" / 273 ; cty * cose.label => cose.values } signed-cbor-cmw-unprotected-hdr = { * cose.label => cose.values } cose.label = int / text cose.values = any]]> The protected header MUST include the signature algorithm identifier. The protected header MUST include either the media type application/cmw+cbor or the CoAP Content-Format 273. Other header parameters MAY be added to the header buckets, for example, a kid that identifies the signing key.

Signing JSON CMW Using JWS A JSON CMW can be signed using JSON Web Signature (JWS) . A signed-json-cmw uses either the Flattened JSON Serialization () or the Compact Serialization (). The payload MUST be the JSON-encoded Record or Collection CMW. text } signed-json-cmw-unprotected-hdr = { * text => text }]]> The protected header MUST include the signature algorithm identifier and the media type application/cmw+json. Other header parameters MAY be added to the header buckets, for example, a kid that identifies the signing key.

Transporting CMW in COSE and JSON Web Tokens To facilitate the embedding of CMWs in CBOR-based protocols and web APIs, this document defines two "cmw" claims for use with JWT and CWT. The definitions for these claims can be found in Sections and , respectively.

Encoding Requirements A Collection CMW carried in a "cmw" JWT claim MUST be a json-collection. A Collection CMW carried in a "cmw" CWT claim MUST be a cbor-collection. A Record CMW carried in a "cmw" JWT claim MUST be a json-record. A Record CMW carried in a "cmw" CWT claim MUST be a cbor-record.

Transporting CMW in PKIX Formats CMW may need to be transported in PKIX formats, such as CSRs or in X.509 certificates and CRLs. The use of CMW in CSRs is documented in , while one of the possible applications in X.509 certificates and CRLs is detailed in Section 6.1 of . This section outlines the CMW extension designed to carry CMW objects. discusses some privacy considerations related to the transport of CMW in X.509 formats. The CMW extension MAY be included in X.509 certificates, CRLs , and CSRs. The CMW extension MUST be identified by the following object identifier: This extension SHOULD NOT be marked critical. In cases where the wrapped conceptual message is essential for granting resource access, and there is a risk that legacy RPs would bypass crucial controls, it is acceptable to mark the extension as critical. The CMW extension has the following syntax: The CMW MUST include the serialized CMW object in either JSON or CBOR format, utilizing the appropriate CHOICE entry. The DER-encoded CMW is the value of the OCTET STRING for the extnValue field of the extension.

ASN.1 Module This section provides an ASN.1 module for the CMW extension, following the conventions established in and .

Compatibility with Trusted Computing Group (TCG) ConceptualMessageWrapper Section 6.1.8 of specifies the ConceptualMessageWrapper (CMW) format and its corresponding object identifier. The CMW format outlined in permits only a subset of the CMW grammar defined in this document. In particular, the collection format cannot be encoded using TCG CMWs.

Examples The (equivalent) examples in Sections , , and assume that the Media-Type-Name application/vnd.example.rats-conceptual-msg has been registered alongside a corresponding CoAP Content-Format ID, 64999 . The CBOR tag 1668612070 is derived applying the TN() transform as described in . All the examples focus on the wrapping aspects. The wrapped messages are not instances of real conceptual messages.

JSON-Encoded Record

CBOR-Encoded Record with the following wire representation: Note that a Media-Type-Name can also be used with the CBOR-encoded Record form, for example, if it is known that the receiver cannot handle CoAP Content-Formats, or (unlike the case in point) if a CoAP Content-Format ID has not been registered.

CBOR-Encoded Tag CMW with the following wire representation:

CBOR-Encoded Record with an Explicit Conceptual Message Indicator This is an example of a signed CoRIM (Concise Reference Integrity Manifest) with an explicit ind value of 0b0000_0011 (3), indicating that the wrapped message contains both Reference Values and Endorsements. with the following wire representation (this example uses line wrapping per ):

CBOR-Encoded Collection The following example is a CBOR-encoded Collection CMW that assembles conceptual messages from three Attesters: Evidence for Attesters A and B and Attestation Results for Attester C. It is given an explicit "__cmwc_t" using the URI form.

JSON-Encoded Collection The following example is a JSON-encoded Collection CMW that assembles Evidence from two Attesters.

Use in JWT The following example shows the use of the "cmw" JWT claim to transport a Collection CMW in a JWT Claims Set :

Collected CDDL This section contains all the CDDL definitions included in this specification. = #6.(bytes .cbor fmt) tag-cm-data = #6.(bytes) json-collection = { ? "__cmwc_t": ~uri / oid + &(label: text) => json-cmw } cbor-collection = { ? "__cmwc_t": ~uri / oid + &(label: (int / text)) => cbor-cmw } media-type = text .abnf ("Content-Type" .cat Content-Type-ABNF) base64url-string = text .regexp "[A-Za-z0-9_-]+" coap-content-format-type = uint .size 2 oid = text .regexp "([0-2])((\\.0)|(\\.[1-9][0-9]*))*" cm-type = &( reference-values: 0 endorsements: 1 evidence: 2 attestation-results: 3 appraisal-policy: 4 ) Content-Type-ABNF = ' Content-Type = Media-Type-Name *( *SP ";" *SP parameter ) parameter = token "=" ( token / quoted-string ) token = 1*tchar tchar = "!" / "#" / "$" / "%" / "&" / "\'" / "*" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA quoted-string = %x22 *( qdtext / quoted-pair ) %x22 qdtext = SP / %x21 / %x23-5B / %x5D-7E quoted-pair = "\\" ( SP / VCHAR ) Media-Type-Name = type-name "/" subtype-name type-name = restricted-name subtype-name = restricted-name restricted-name = restricted-name-first *126restricted-name-chars restricted-name-first = ALPHA / DIGIT restricted-name-chars = ALPHA / DIGIT / "!" / "#" / "$" / "&" / "-" / "^" / "_" restricted-name-chars =/ "." ; Characters before first dot always ; specify a facet name restricted-name-chars =/ "+" ; Characters after last plus always ; specify a structured syntax suffix DIGIT = %x30-39 ; 0 - 9 POS-DIGIT = %x31-39 ; 1 - 9 ALPHA = %x41-5A / %x61-7A ; A - Z / a - z SP = %x20 VCHAR = %x21-7E ; printable ASCII (no SP) ' signed-cbor-cmw = [ protected: bytes .cbor signed-cbor-cmw-protected-hdr unprotected: signed-cbor-cmw-unprotected-hdr payload: bytes .cbor cbor-cmw signature: bytes ] signed-cbor-cmw-protected-hdr = { 1 => int ; alg 3 => "application/cmw+cbor" / 273 ; cty * cose.label => cose.values } signed-cbor-cmw-unprotected-hdr = { * cose.label => cose.values } cose.label = int / text cose.values = any signed-json-cmw = jws-flattened-json / jws-compact jws-flattened-json = { "protected": protected ? "header": unprotected "payload": payload "signature": signature } jws-compact = (((protected .cat ".") .cat payload) .cat ".") .cat signature signed-json-cmw-protected-hdr = { "alg": text "cty": "application/cmw+json" * text => text } signed-json-cmw-unprotected-hdr = { * text => text } protected = text .b64u (text .json signed-json-cmw-protected-hdr) unprotected = text .b64u (text .json signed-json-cmw-unprotected-hdr) payload = text .b64u (text .json json-cmw) signature = text .b64u bytes $cbor-tag /= tag-cm-cbor<1668547091, cbor-collection> $cbor-tag /= tag-cm-cbor<1668547092, signed-cbor-cmw> $cbor-tag /= tag-cm-data<1668547093> ; bytes(cmw+json collection) $cbor-tag /= tag-cm-data<1668547094> ; bytes(cmw+jws)]]>

Privacy Considerations The privacy considerations outlined in are fully applicable. In particular, when a CMW contains Personally Identifiable Information (PII), which is the case for Evidence and sometimes for other conceptual messages as well, care must be taken to prevent unintended recipients from accessing it. Generally, utilizing secure channels between the parties exchanging CMWs can help address or mitigate these concerns. A specific scenario arises when a public key certificate is issued based on Evidence information provided by the certificate requestor to the issuing Certification Authority (CA). For instance, an individual seeking a publicly trusted code signing certificate may be willing to disclose the details of the hardware where their code signing keys are stored (e.g., a Hardware Security Module (HSM) model, patch level, etc.). However, they likely do not want this information to be publicly accessible. Applications that intend to publicly "broadcast" Evidence claims received from a third party via X.509 certificates should define a certification practice statement that clearly specifies the circumstances under which the CA can include such data in the issued certificate. Note that the aforementioned consideration does not apply to cases where X.509 certificates are explicitly designed as a security envelope for Evidence claims, such as in .

Security Considerations The security considerations discussed in concerning the protection of conceptual messages are fully applicable. The following subsections provide further elaboration on these points, particularly in relation to Collection CMWs.

CMW Protection Record, Tag, and Collection CMWs alone do not offer authenticity, integrity protection, or confidentiality. It is the responsibility of the designer for each use case to determine the necessary security properties and implement them accordingly. RATS conceptual messages are typically secured using cryptography. If the messages are already protected, no additional security requirements are imposed by this encapsulation. If an adversary attempts to modify the payload encapsulation, it will result in incorrect processing of the encapsulated message, leading to an error. If the messages are not protected, additional security must be added at a different layer. For example, a cbor-record containing an Unprotected CWT Claims Set (UCCS) can be signed as described in . describes a number of methods that can be used to add cryptographic protection to CMW.

Using Collection CMWs for Evidence of Composite or Layered Devices When a Collection CMW is used to encapsulate Evidence for composite or layered attestation of a single device, all Evidence messages within the CMW MUST be cryptographically bound together to prevent an attacker from replacing Evidence from a compromised device with that from a non-compromised device. If the Collection CMW is not protected from tampering by external security measures (such as object security primitives) or internal mechanisms (such as intra-item binding), an attacker could manipulate the collection's contents to deceive the Verifier into accepting bogus Evidence as genuine. Authenticity and integrity protection is expected to be provided by the underlying attestation technology. For example, key material used to sign/bind an entire Collection CMW should be an attestation key, handled as described in . The binding does not necessarily have to be a signature over the Collection CMW; it might also be achieved through identifiers, linking claims (e.g., nonces) across Collection CMW items, or signing or hashing between the members of the collection. It is the responsibility of the Attester who creates the Collection CMW to ensure that the contents of the collection are integrity protected.

Integrating CMW into Protocols When CMW is integrated into some hosting protocol (for example, attested CSR or attested TLS ), it is up to that hosting protocol to describe how CMW is intended to be used and how it fits into the overall security model. Such an analysis should consider the types of conceptual messages allowed, including the permitted combinations, the protection requirements, the interface with the hosting protocol, and any other security-relevant aspect arising from the interaction between the CMW assembly and the hosting protocol.

IANA Considerations

CWT cmw Claim Registration IANA has added a new cmw claim to the "CBOR Web Token (CWT) Claims" registry as follows:

Claim Name:

cmw

Claim Description:

RATS Conceptual Message Wrapper

JWT Claim Name:

cmw

Claim Key:

299

Claim Value Type:

CBOR map, CBOR array, or CBOR tag

Change Controller:

IETF

Reference:

Sections , , and of RFC 9999

JWT cmw Claim Registration IANA has added a new cmw claim to the "JSON Web Token Claims" registry within the "JSON Web Token (JWT)" registry group as follows:

Claim Name:

cmw

Claim Description:

RATS Conceptual Message Wrapper

Change Controller:

IETF

Reference:

Sections and of RFC 9999

+jws Structured Syntax Suffix IANA has registered the +jws structured syntax suffix in the "Structured Syntax Suffixes" registry in the manner described in , which can be used to indicate that the media type is encoded as JWS .

Registry Entry

Name:

JSON Web Signature (JWS)

+suffix:

+jws

References:

Encoding Considerations:

binary. Values are represented as a JSON Object or as a series of base64url-encoded values, each separated from the next by a single period ('.') character.

Interoperability Considerations:

N/A

Fragment Identifier Considerations:

N/A

Security Considerations:

See

Contact:

RATS WG mailing list (rats@ietf.org) or IETF Security Area (saag@ietf.org)

Author/Change Controller:

Remote ATtestation procedureS (RATS) Working Group. The IETF has change control over this registration.

RATS Conceptual Message Wrapper (CMW) Indicators Registry IANA has created a new "RATS Conceptual Message Wrapper (CMW) Indicators" registry within the "Remote Attestation Procedures (RATS)" registry group . The registration procedure for the new registry is IETF Review (). The objective is to register CMW Indicator values for all RATS conceptual messages (see ). Indicator values should be added in ascending order, with no gaps between them. Acceptable values correspond to the RATS conceptual messages defined by the RATS architecture and any updates to it.

Structure of Entries Each entry in the "RATS Conceptual Message Wrapper (CMW) Indicators" registry must include the following:

Indicator Value:

A number corresponding to the bit position in the ind bitmap ().

Conceptual Message Name:

A text string describing the RATS conceptual message this indicator corresponds to.

Reference:

A reference to the document that defines the entry.

The initial contents of the registry are shown in . Initial Contents of the RATS CMW Indicators Registry

Indicator Value	Conceptual Message Name	Reference
0	Reference Values	of RFC 9999
1	Endorsements	of RFC 9999
2	Evidence	of RFC 9999
3	Attestation Results	of RFC 9999
4	Appraisal Policy	of RFC 9999
5-31	Unassigned

Media Types IANA has added the following media types to the "Media Types" registry : CMW Media Types

Name	Template	Reference
cmw+cbor	application/cmw+cbor	Sections , , and of RFC 9999
cmw+json	application/cmw+json	Sections and of RFC 9999
cmw+cose	application/cmw+cose	of RFC 9999
cmw+jws	application/cmw+jws	of RFC 9999

application/cmw+cbor

Type name:

application

Subtype name:

cmw+cbor

Required parameters:

N/A

Optional parameters:

cmwc_t (Collection CMW type in string format. OIDs must use the dotted-decimal notation. The parameter value is case-insensitive. It must not be used for CMWs that are not collections.)

Encoding considerations:

binary (CBOR)

Security considerations:

of RFC 9999

Interoperability considerations:

N/A

Published specification:

RFC 9999

Applications that use this media type:

Attesters, Verifiers, Endorsers and Reference-Value providers, and Relying Parties that need to transfer CMW payloads over HTTP(S), CoAP(S), and other transports.

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

application/cmw+json

Type name:

application

Subtype name:

cmw+json

Required parameters:

N/A

Optional parameters:

cmwc_t (Collection CMW type in string format. OIDs must use the dotted-decimal notation. The parameter value is case-insensitive. It must not be used for CMWs that are not collections.)

Encoding considerations:

binary (JSON is UTF-8-encoded text)

Security considerations:

of RFC 9999

Interoperability considerations:

N/A

Published specification:

RFC 9999

Applications that use this media type:

Attesters, Verifiers, Endorsers and Reference-Value providers, and Relying Parties that need to transfer CMW payloads over HTTP(S), CoAP(S), and other transports.

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

application/cmw+cose

Type name:

application

Subtype name:

cmw+cose

Required parameters:

N/A

Optional parameters:

cmwc_t (Collection CMW type in string format. OIDs must use the dotted-decimal notation. The parameter value is case-insensitive. It must not be used for CMWs that are not collections.) Note that the cose-type parameter is explicitly not supported, as it is understood to be "cose-sign1".

Encoding considerations:

binary (CBOR)

Security considerations:

of RFC 9999

Interoperability considerations:

N/A

Published specification:

RFC 9999

Applications that use this media type:

Attesters, Verifiers, Endorsers and Reference-Value providers, and Relying Parties that need to transfer CMW payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

N/A

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

application/cmw+jws

Type name:

application

Subtype name:

cmw+jws

Required parameters:

N/A

Optional parameters:

cmwc_t (Collection CMW type in string format. OIDs must use the dotted-decimal notation. The parameter value is case-insensitive. It must not be used for CMWs that are not collections.)

Encoding considerations:

8bit. Values are represented as a JSON Object or as a series of base64url-encoded values, each separated from the next by a single period ('.') character.

Security considerations:

of RFC 9999

Interoperability considerations:

N/A

Published specification:

RFC 9999

Applications that use this media type:

Attesters, Verifiers, Endorsers and Reference-Value providers, and Relying Parties that need to transfer CMW payloads over HTTP(S), CoAP(S), and other transports.

Fragment identifier considerations:

N/A

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

CoAP Content-Formats IANA has registered the following Content-Format IDs in the "CoAP Content-Formats" registry within the "Constrained RESTful Environments (CoRE) Parameters" registry group : CoAP Content-Formats

Content-Type	Content Coding	ID	Reference
application/cmw+cbor	-	273	Sections , , and of RFC 9999
application/cmw+json	-	274	Sections and of RFC 9999
application/cmw+cose	-	275	of RFC 9999
application/cmw+jws	-	276	of RFC 9999

Registering New CoAP Content-Formats for Parameterized CMW Media Types New CoAP Content-Formats can be created based on parameterized instances of the application/cmw+json, application/cmw+cbor, application/cmw+cose, and application/cmw+jws media types. When assigning a new CoAP Content-Format ID for a CMW media type that utilizes the cmwc_t parameter, the registrar must check (directly or through the designated expert) the following:

• The corresponding CMW is a collection ().
• The cmwc_t value is either an (non-relative) OID or an absolute URI.

CBOR Tags per RFC 9277 Registering the CoAP Content-Formats listed in automatically allocates CBOR tags in the range [1668546817, 1668612095] using the TN() transform defined in . The allocated CBOR tag numbers and the corresponding data items are shown in . Note that CMWs in Tag and Record form are excluded. This is because they can already be represented as a CMW, so the extra wrapping would be redundant. TN-Derived CBOR Tags

Tag Number	Tag Content
1668547091	bytes .cbor cbor-collection
1668547092	bytes .cbor signed-cbor-cmw
1668547093	bytes-wrapped json-collection
1668547094	bytes-wrapped signed-json-cmw

extends the $cbor-tag socket defined in to add the definitions of the associated Tag CMWs.

Tag CMW Definitions $cbor-tag /= tag-cm-cbor<1668547092, signed-cbor-cmw> $cbor-tag /= tag-cm-data<1668547093> ; bytes(cmw+json collection) $cbor-tag /= tag-cm-data<1668547094> ; bytes(cmw+jws)]]>

SMI Number Registration IANA has assigned an OID for the CMW extension defined in in the "SMI Security for PKIX Certificate Extension" registry within the "Structure of Management Information (SMI) Numbers (MIB Module Registrations)" registry group as follows: CMW Extension OID

Decimal	Description	Reference
35	id-pe-cmw	of RFC 9999

IANA has assigned an OID for the ASN.1 module defined in in the "SMI Security for PKIX Module Identifier" registry within the "Structure of Management Information (SMI) Numbers (MIB Module Registrations)" registry group : ASN.1 Module OID

Decimal	Description	Reference
123	id-mod-cmw-extn	of RFC 9999

References Normative References IANA IANA ITU-T ITU-T IANA IANA IANA IANA IANA Informative References Linaro Cisco Arm Limited Fraunhofer SIT Intuit Arm Limited Arm Limited Linaro Nokia TU Dresden Linaro Nokia Intuit University of Applied Sciences Bonn-Rhein-Sieg Arm Limited Cryptic Forest Software Siemens Fraunhofer SIT Fraunhofer SIT Linaro arm Independent Huawei Technologies Trusted Computing Group Version 1.1, Revision 0.18

Registering and Using CMWs describes the registration preconditions for using CMWs in either Record CMW or Tag CMW forms. When using a Collection CMW, the preconditions apply for each entry in the collection.

How to Create a CMW

Acknowledgments The authors would like to thank , , , , , , , , , , , , , , , , , , , , , , , , , , and for their reviews and suggestions. The definition of a Collection CMW has been modeled on a proposal originally made by for an EAT-based Evidence collection type. The Collection CMW aims at superseding it by generalizing the allowed Evidence formats.

Contributors Security Theory LLC

lgl@securitytheory.com

Laurence made significant contributions to enhancing the security requirements and considerations for Collection CMWs.