Tradeverifyd

United States orie@or13.io

Fraunhofer SIT

Rheinstrasse 75 Darmstadt 64295 Germany henk.birkholz@ietf.contact

Microsoft

UK antdl@microsoft.com

Microsoft

UK fournet@microsoft.com

Security COSE Internet-Draft COSE (CBOR Object Signing and Encryption) Receipts prove properties of a verifiable data structure to a verifier. Verifiable data structures and associated proof types enable security properties, such as minimal disclosure, transparency and non-equivocation. Transparency helps maintain trust over time, and has been applied to certificates, end to end encrypted messaging systems, and supply chain security. This specification enables concise transparency oriented systems, by building on CBOR (Concise Binary Object Representation) and COSE. The extensibility of the approach is demonstrated by providing CBOR encodings for Certificate Transparency v2 (RFC 9162).

Introduction COSE Receipts are signed proofs that include metadata about certain states of a verifiable data structure (VDS) that are true when the COSE Receipt was issued. COSE Receipts can include proofs that a document is in a database (proof of inclusion), that a database is append only (proof of consistency), that a smaller set of statements are contained in a large set of statements (proof of disclosure, a special case of proof of inclusion), or proof that certain data is not yet present in a database (proofs of non inclusion). Different VDS can produce different verifiable data structure proofs (VDP). The combination of representations of various VDS and VDP can significantly increase the burden for implementers and create interoperability challenges for transparency services. This document describes how to convey VDS and associated VDP types in unified COSE envelopes.

Requirements Notation 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.

New COSE Header Parameters This document defines three new COSE header parameters, which are introduced up-front in this Section and elaborated on later in this document.

TBD_0 (requested assignment 394):

A COSE header parameter named receipts with a value type of array where the array contains one or more COSE Receipts as specified in this document.

TBD_1 (requested assignment 395):

A COSE header parameter named vds (Verifiable Data Structure), which conveys the algorithm identifier for a verifiable data structure. Correspondingly, this document introduces a new registry () defining the integers used to identify verifiable data structures.

TBD_2 (requested assignment 396):

A COSE header parameter named vdp (short for "verifiable data structure proofs"), which conveys a map containing verifiable data structure proofs organized by proof type. Correspondingly, this document introduces a new registry () defining the integers used to identify verifiable data structure proof types.

Terminology

CDDL:

Concise Data Definition Language (CDDL) is defined in .

EDN:

CBOR Extended Diagnostic Notation (EDN) is defined in , where it is referred to as "diagnostic notation", and is revised in .

Verifiable Data Structure (VDS):

A data structure which supports one or more Verifiable Data Structure Proof Types. This property describes an algorithm used to maintain a verifiable data structure, for example a binary Merkle tree algorithm.

Verifiable Data Structure Proofs (VDP):

A data structure used to convey proof types for proving different properties, such as authentication, inclusion, consistency, and freshness. Parameters can include multiple proofs of a given type, or multiple types of proof (inclusion and consistency).

Proof Type:

A property that can be obtained by verifying a given proof over one or more entries in a Verifiable Data Structure. For example, a VDS, such as a binary Merkle tree, can support proofs of type "inclusion" where each proof confirms that a given entry is included in a Merkle root.

Proof Value:

An encoding of a Proof Type in CBOR .

Entry:

An entry in a verifiable data structure for which proofs can be derived.

Receipt:

A COSE object, as defined in , containing the header parameters necessary to convey VDP for an associated VDS.

Verifiable Data Structures in CBOR This section describes representations of verifiable data structure proofs in . For example, construction of a Merkle tree leaf, or an inclusion proof from a leaf to a Merkle root, might have several different representations, depending on the verifiable data structure used. Differences in representations are necessary to support efficient verification, unique security or privacy properties, and for compatibility with specific implementations. This document defines two extension points for enabling verifiable data structures with COSE and provides concrete examples for the structures and proofs defined in . The design of these structures is influenced by the conventions established for COSE Keys.

Structures Similar to COSE Key Types, different verifiable data structures support different algorithms. This document establishes a registry of verifiable data structure algorithms, see for details.

Proofs Similar to COSE Key Type Parameters, as EC2 keys (1: 2) keys require and give meaning to specific parameters, such as -1 (crv), -2 (x), -3 (y), -4 (d), RFC9162_SHA256 (TBD_1 (requested assignment 395) : 1) supports both (-1) inclusion and (-2) consistency proofs. This document establishes a registry of verifiable data structure algorithm proofs, see for details. Proof types are specific to their associated "verifiable data structure", for example, different Merkle trees might support different representations of "inclusion proof" or "consistency proof". Implementers should not expect interoperability across "verifiable data structures". Security analysis MUST be conducted prior to migrating to new structures to ensure the new security and privacy assumptions are acceptable for the use case.

Usage This document registers a new COSE Header Parameter receipts (TBD_0 (requested assignment 394)) to enable Receipts to be conveyed in the protected and unprotected headers of COSE Objects. When the receipts header parameter is present, the verifier MUST confirm that the associated verifiable data structure and verifiable data structure proofs match entries present in the registries established in this specification, including values added in subsequent registrations.. Receipts MUST be tagged as COSE_Sign1. The following definition is provided:

CDDL for a COSE Sign1 with attached receipts Receipt = #6.18(COSE_Sign1) cose-value = any Protected_Header = { * cose-label => cose-value } Unprotected_Header = { &(receipts: 394) => [+ bstr .cbor Receipt] * cose-label => cose-value } COSE_Sign1 = [ protected : bstr .cbor Protected_Header, unprotected : Unprotected_Header, payload : bstr / nil, signature : bstr ]

The following informative EDN is provided:

An example COSE Signature with multiple receipts / cose-sign1 / 18([ / protected / <<{ / key / 4 : "vCl7UcS0ZZY99VpRthDc-0iUjLdfLtnmFqLJ2-Tt8N4", / algorithm / 1 : -7, # ES256 }>>, / unprotected / { / receipts / 394 : { <</ cose-sign1 / 18([ / protected / <<{ / key / 4 : "mxA4KiOkQFZ-dkLebSo3mLOEPR7rN8XtxkJe45xuyJk", / algorithm / 1 : -7, # ES256 / vds / 395 : 1, # RFC9162 SHA-256 }>>, / unprotected / { / proofs / 396 : { / inclusion / -1 : [ <<[ / size / 9, / leaf / 8, / inclusion path / h'7558a95f...e02e35d6' ]>> ], }, }, / payload / null, / signature / h'02d227ed...ccd3774f' ])>>, <</ cose-sign1 / 18([ / protected / <<{ / key / 4 : "ajOkeBTJou_wPrlExLMw7L9OTCD5ZIOBYc-O6LESe9c", / algorithm / 1 : -7, # ES256 / vds / 395 : 1, # RFC9162 SHA-256 }>>, / unprotected / { / proofs / 396 : { / inclusion / -1 : [ <<[ / size / 6, / leaf / 5, / inclusion path / h'9352f974...4ffa7ce0', h'54806f32...f007ea06' ]>> ], }, }, / payload / null, / signature / h'36581f38...a5581960' ])>> }, }, / payload / h'0167c57c...deeed6d4', / signature / h'2544f2ed...5840893b' ])

The specific structure of COSE Receipts is dependent on the structure of the COSE_Sign1 payload and the verifiable data structure proofs contained in the COSE_Sign1 unprotected header. The CDDL definition for verifiable data structure proofs is specific to each verifiable data structure. This document describes proofs for RFC9162_SHA256 in the following sections.

Profiles New verifiable data structures can require the definition of a profile. The payload in such definitions SHOULD be detached. Detached payloads force verifiers to recompute the root from the proof and protect against implementation errors where the signature is verified but the payload is incompatible with the proof. Profiles of proof signatures that define additional protected header parameters are encouraged to make their presence mandatory to ensure that claims are processed with their intended semantics. One way to include this information in the COSE structure is use of the typ (type) Header Parameter, see and the similar guidance provided in .

Registration Requirements Each verifiable data structure specification applying for inclusion in this registry MUST define how to encode the verifiable data structure identifier and its proof types in CBOR. Each specification MUST define how to produce and consume the supported proof types. See as an example. Where a specification supports a choice of hash algorithm, a separate IANA registration must be made for each supported algorithm. For example, to provide for both SHA256 and SHA3_256 with Certificate Transparency v2 (), both "RFC9162_SHA256" and "RFC9162_SHA3_256" require entries in the relevant IANA registries.

RFC9162_SHA256 This section defines how the data structures described in are mapped to the terminology defined in this document, using and .

Verifiable Data Structure The integer identifier for this Verifiable Data Structure is 1. The string identifier for this Verifiable Data Structure is "RFC9162_SHA256", a Merkle Tree where SHA256 is used as the hash algorithm. See . See , 2.1.1. Definition of the Merkle Tree, for a complete description of this verifiable data structure.

Inclusion Proof See , 2.1.3.1. Generating an Inclusion Proof, for a complete description of this verifiable data structure proof type. The CBOR representation of an inclusion proof for RFC9162_SHA256 is:

CBOR Encoded RFC9162 Inclusion Proof inclusion-proof = bstr .cbor [ ; tree size at current Merkle root tree-size: uint ; index of leaf in tree leaf-index: uint ; path from leaf to current Merkle root inclusion-path: [ + bstr ] ]

The term leaf-index is used for alignment with the use established in . Note that Certificate Transparency v2 () defines inclusion proofs only for leaf nodes, and that:

• If leaf_index is greater than or equal to tree_size, then fail the proof verification.

The identifying index of a leaf node is relative to all nodes in the tree size for which the proof was obtained.

Receipt of Inclusion In a signed inclusion proof, the payload is the Merkle tree root that corresponds to the log at size tree-size. The protected header for an RFC9162_SHA256 inclusion proof signature is:

Protected Header for a Receipt of Inclusion protected-header-map = { &(alg: 1) => int &(vds: 395) => int * cose-label => cose-value }

• alg (label: 1): REQUIRED. Signature algorithm identifier. Value type: int.
• vds (label: TBD_1 (requested assignment 395)): REQUIRED. Verifiable data structure algorithm identifier. Value type: int.

The unprotected header for an RFC9162_SHA256 inclusion proof signature is:

A Verifiable Data Structure Proofs in an Unprotected Header inclusion-proofs = [ + inclusion-proof ] verifiable-proofs = { &(inclusion-proof: -1) => inclusion-proofs } unprotected-header-map = { &(vdp: 396) => verifiable-proofs * cose-label => cose-value }

• vdp (label: TBD_2 (requested assignment 396)): REQUIRED. Verifiable data structure proofs. Value type: Map.
• inclusion-proof (label: -1): REQUIRED. Inclusion proofs. Value type: Array of bstr.

The payload of an RFC9162_SHA256 inclusion proof signature is the Merkle tree hash as defined in . An EDN example for a Receipt containing an inclusion proof for RFC9162_SHA256 with a detached payload (see ) is:

Receipt of Inclusion / cose-sign1 / 18([ / protected / <<{ / algorithm / 1 : -7, # ES256 / vds / 395 : 1, # RFC9162 SHA-256 }>>, / unprotected / { / proofs / 396 : { / inclusion / -1 : [ <<[ / size / 20, / leaf / 17, / inclusion path / h'fc9f050f...221c92cb', h'bd0136ad...6b28cf21', h'd68af9d6...93b1632b' ]>> ], }, }, / payload / null, / signature / h'de24f0cc...9a5ade89' ])

The VDS in the protected header is necessary to understand the inclusion proof structure in the unprotected header. The inclusion proof and signature are verified in order. First the verifier applies the inclusion proof to a possible entry (set member) bytes. If this process fails, the inclusion proof may have been tampered with. If this process succeeds, the result is a Merkle root, which in the attached as the COSE Sign1 payload. Second the verifier checks the signature of the COSE Sign1. If the resulting signature verifies, the Receipt has proved inclusion of the entry in the verifiable data structure. If the resulting signature does not verify, the signature may have been tampered with.

Consistency Proof See , 2.1.4.1. Generating a Consistency Proof, for a complete description of this verifiable data structure proof type. The cbor representation of a consistency proof for RFC9162_SHA256 is:

CBOR Encoded RFC9162 Consistency Proof consistency-proof = bstr .cbor [ ; older Merkle root tree size tree-size-1: uint ; newer Merkle root tree size tree-size-2: uint ; path from older Merkle root to newer Merkle root. consistency-path: [ + bstr ] ]

Receipt of Consistency In a signed consistency proof, the newer Merkle tree root (proven to be consistent with an older Merkle tree root) is an attached payload and corresponds to the log at size tree-size-2. The protected header for an RFC9162_SHA256 consistency proof signature is:

Protected Header for a Receipt of Consistency protected-header-map = { &(alg: 1) => int &(vds: 395) => int * cose-label => cose-value }

• alg (label: 1): REQUIRED. Signature algorithm identifier. Value type: int.
• vds (label: TBD_1 (requested assignment 395)): REQUIRED. Verifiable data structure algorithm identifier. Value type: int.

The unprotected header for an RFC9162_SHA256 consistency proof signature is: consistency-proofs = [ + consistency-proof ] verifiable-proofs = { &(consistency-proof: -2) => consistency-proofs } unprotected-header-map = { &(vdp: 396) => verifiable-proofs * cose-label => cose-value }

• vdp (label: TBD_2 (requested assignment 396)): REQUIRED. Verifiable data structure proofs. Value type: Map.
• consistency-proof (label: -2): REQUIRED. Consistency proofs. Value type: Array of bstr.

The payload of an RFC9162_SHA256 consistency proof signature is: The newer Merkle tree hash as defined in . An example EDN for a Receipt containing a consistency proof for RFC9162_SHA256 with a detached payload (see ) is:

Example consistency receipt / cose-sign1 / 18([ / protected / <<{ / algorithm / 1 : -7, # ES256 / vds / 395 : 1, # RFC9162 SHA-256 }>>, / unprotected / { / proofs / 396 : { / consistency / -2 : [ <<[ / old / 20, / new / 104, / consistency path / h'e5b3e764...c4a813bc', h'87e8a084...4f529f69', h'f712f76d...92a0ff36', h'd68af9d6...93b1632b', h'249efab6...b7614ccd', h'85dd6293...38914dc1' ]>> ], }, }, / payload / null, / signature / h'94469f73...52de67a1' ])

The VDS in the protected header is necessary to understand the consistency proof structure in the unprotected header. The signature and consistency proof are verified in order. First the verifier checks the signature on the COSE Sign1. If the verification fails, the consistency proof is not checked. Second the consistency proof is checked by applying a previous inclusion proof, to the consistency proof. If the verification fails, the append only property of the verifiable data structure is not assured. This approach is specific to RFC9162_SHA256, different verifiable data structures may not support consistency proofs. It is recommended that implementations return a single boolean result for Receipt verification operations, to reduce the chance of accepting a valid signature over an invalid consistency proof.

Privacy Considerations The privacy considerations section of and apply to this document.

Log Length Some structures and proofs leak the size of the log at the time of inclusion. In the case that a log only stores certain kinds of information, this can reveal details that could impact reputation. For example, if a transparency log only stored breach notices, a receipt for a breach notice would reveal the number of previous breaches at the time the notice was made transparent.

Header Parameters Additional header parameters can reveal information about the transparency service or its log entries. The receipt producer MUST perform a privacy analysis for all mandatory fields in profiles based on this specification.

Security Considerations See the security considerations section of:

Choice of Signature Algorithms A security analysis ought to be performed to ensure that the digital signature algorithm alg has the appropriate strength to secure receipts. It is recommended to select signature algorithms that share cryptographic components with the verifiable data structure used, for example: Both RFC9162_SHA256 and ES256 depend on the sha-256 hash function.

Validity Period In some cases, receipts MAY include strict validity periods, for example, activation not too far in the future, or expiration, not too far in the past. See the iat, nbf, and exp claims in , for one way to accomplish this. The details of expressing validity periods are out of scope for this document.

Status Updates In some cases, receipts should be "revocable" or "suspendible", after being issued, regardless of their validity period. The details of expressing statuses are out of scope for this document.

IANA Considerations

COSE Header Parameter IANA is requested to add the COSE header parameters defined in , as listed in , to the "COSE Header Parameters" registry in the 'Integer values from 256 to 65535' range ('Specification Required' Registration Procedure). The Value Registry for "vds" is the COSE Verifiable Data Structure registry. The map labels in the "vdp" are assigned from the COSE Verifiable Data Structure Proofs registry. Newly registered COSE Header Parameters

Name	Label	Value Type	Value Registry	Description	Reference
receipts	TBD_0 (requested assignment: 394)	array		Priority ordered sequence of CBOR encoded Receipts	RFCthis,
vds	TBD_1 (requested assignment: 395)	int	COSE Verifiable Data Structure	Algorithm identifier for verifiable data structures, used to produce verifiable data structure proofs	RFCthis,
vdp	TBD_2 (requested assignment: 396)	map	map key in COSE Verifiable Data Structure Proofs	Location for verifiable data structure proofs in COSE Header Parameters	RFCthis,

Verifiable Data Structure Registries IANA established the COSE Verifiable Data Structure Algorithms and COSE Verifiable Data Structure Proofs registries under a Specification Required policy as described in .

Expert Review Expert reviewers should take into consideration the following points:

• Experts are advised to assign the next available positive integer for verifiable data structures.
• Point squatting should be discouraged. Reviewers are encouraged to get sufficient information for registration requests to ensure that the usage is not going to duplicate one that is already registered, and that the point is likely to be used in deployments.
• Specifications are required for all point assignments. Early Allocation is permissible, see Section 2 of .
• It is not permissible to assign points in COSE Verifiable Data Structure Algorithms, for which no corresponding COSE Verifiable Data Structure Proofs entry exists, and vice versa.
• The Change Controller for related registrations of structures and proofs should be the same.

COSE Verifiable Data Structure Algorithms Registration Template:

• Name: This is a descriptive name for the verifiable data structure that enables easier reference to the item.
• Value: This is the value used to identify the verifiable data structure.
• Description: This field contains a brief description of the verifiable data structure.
• Reference: This contains a pointer to the public specification for the verifiable data structure.
• Change Controller: For Standards Track RFCs, list the "IETF". For others, give the name of the responsible party. Other details (e.g., postal address, email address, home page URI) may also be included.

Initial contents: COSE Verifiable Data Structure Algorithms

Name	Value	Description	Reference
Reserved	0	Reserved	Reserved
RFC9162_SHA256	1	SHA256 Binary Merkle Tree

Registration Template:

• Verifiable Data Structure: This value used identifies the related verifiable data structure.
• Name: This is a descriptive name for the proof type that enables easier reference to the item.
• Label: This is the value used to identify the verifiable data structure proof type.
• CBOR Type: This contains the CBOR type for the value portion of the label.
• Description: This field contains a brief description of the proof type.
• Reference: This contains a pointer to the public specification for the proof type.
• Change Controller: For Standards Track RFCs, list the "IETF". For others, give the name of the responsible party. Other details (e.g., postal address, email address, home page URI) may also be included.

Initial contents: COSE Verifiable Data Structure Proofs

Verifiable Data Structure	Name	Label	CBOR Type	Description	Reference
1	inclusion proofs	-1	array (of bstr)	Proof of inclusion	RFCthis,
1	consistency proofs	-2	array (of bstr)	Proof of append only property	RFCthis,

Acknowledgements We would like to thank Maik Riechert, Jon Geater, Michael B. Jones, Mike Prorock, Ilari Liusvaara, Amaury Chamayou, for their contributions (some of which substantial) to this draft and to the initial set of implementations.

References Normative References 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. 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. 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 a set of algorithms that can be used with the CBOR Object Signing and Encryption (COSE) protocol (RFC 9052). This document, along with RFC 9052, obsoletes RFC 8152. This document describes version 2.0 of the Certificate Transparency (CT) protocol for publicly logging the existence of Transport Layer Security (TLS) server certificates as they are issued or observed, in a manner that allows anyone to audit certification authority (CA) activity and notice the issuance of suspect certificates as well as to audit the certificate logs themselves. The intent is that eventually clients would refuse to honor certificates that do not appear in a log, effectively forcing CAs to add all issued certificates to the logs. This document obsoletes RFC 6962. It also specifies a new TLS extension that is used to send various CT log artifacts. Logs are network services that implement the protocol operations for submissions and queries that are defined in this document. This document describes how to include CBOR Web Token (CWT) claims in the header parameters of any CBOR Object Signing and Encryption (COSE) structure. This functionality helps to facilitate applications that wish to make use of CWT claims in encrypted COSE structures and/or COSE structures featuring detached signatures, while having some of those claims be available before decryption and/or without inspecting the detached payload. Another use case is using CWT claims with payloads that are not CWT Claims Sets, including payloads that are not CBOR at all. This specification adds the equivalent of the JSON Object Signing and Encryption (JOSE) "typ" (type) header parameter to CBOR Object Signing and Encryption (COSE). This enables the benefits of explicit typing (as defined in RFC 8725, "JSON Web Token Best Current Practices") to be brought to COSE objects. The syntax of the COSE type header parameter value is the same as the existing COSE content type header parameter. 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. IANA Informative References This memo describes the process for early allocation of code points by IANA from registries for which "Specification Required", "RFC Required", "IETF Review", or "Standards Action" policies apply. This process can be used to alleviate the problem where code point allocation is needed to facilitate desired or required implementation and deployment experience prior to publication of an RFC, which would normally trigger code point allocation. The procedures in this document are intended to apply only to IETF Stream documents. 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. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. 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. CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR), and CBOR Object Signing and Encryption (COSE) is used for added application-layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/value pair consisting of a claim name and a claim value. CWT is derived from JSON Web Token (JWT) but uses CBOR rather than JSON. Universität Bremen TZI This document formalizes and consolidates the definition of the Extended Diagnostic Notation (EDN) of the Concise Binary Object Representation (CBOR), addressing implementer experience. Replacing EDN's previous informal descriptions, it updates RFC 8949, obsoleting its Section 8, and RFC 8610, obsoleting its Appendix G. It also specifies and uses registry-based extension points, using one to support text representations of epoch-based dates/times and of IP addresses and prefixes. // (This cref will be removed by the RFC editor:) The present -18 // corrects a few omissions from -17; it is not intended to make // technical changes from -17. It is intended for use as an input // document for the CBOR WG meeting at IETF 123.

Implementation Status Note to RFC Editor: Please remove this section as well as references to before AUTH48. 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".

Transmute Prototype An open-source implementation was initiated and is maintained by the Transmute Industries Inc. - Transmute. An application demonstrating the concepts is available at COSE SCITT Receipts Implementation URL: https://github.com/transmute-industries/cose Maturity: The code's level of maturity is considered to be "prototype". Coverage and Version Compatibility: The current version ('main') implements the verifiable data structure algorithm, inclusion proof and consistency proof concepts of this draft. License: The project and all corresponding code and data maintained on GitHub are provided under the Apache License, version 2. Contact: Orie Steele (orie@transmute.industries)

Contributors Microsoft

United Kingdom amaury.chamayou@microsoft.com

stevenlasker@hotmail.com

MITRE Corporation

United States ramartin@mitre.org

USA mwiseman32@acm.org

USA roywill@msn.com