CBOR Object Signing and Encryption (COSE) Receipts Tradeverifyd
United States of America orie@or13.io
Fraunhofer SIT
Rheinstrasse 75 Darmstadt 64295 Germany henk.birkholz@ietf.contact
Microsoft
United Kingdom antdl@microsoft.com
Microsoft
United Kingdom fournet@microsoft.com
SEC cose COSE CBOR Object Signing and Encryption (COSE) Receipts prove properties of a Verifiable Data Structure (VDS) to a verifier. VDSs 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 Concise Binary Object Representation (CBOR) and COSE. The extensibility of the approach is demonstrated by providing CBOR encodings for Merkle inclusion and consistency proofs.
Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .
Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents () in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.
Table of Contents
  • .  Introduction
    • .  Requirements Notation
  • .  New COSE Header Parameters
  • .  Terminology
  • .  VDSs in CBOR
    • .  Structures
    • .  Proofs
    • .  Usage
    • .  Profiles
      • .  Registration Requirements
  • .  RFC9162_SHA256
    • .  Verifiable Data Structure
    • .  Inclusion Proof
      • .  Receipt of Inclusion
    • .  Consistency Proof
      • .  Receipt of Consistency
  • .  Privacy Considerations
    • .  Log Length
    • .  Header Parameters
  • .  Security Considerations
    • .  Choice of Signature Algorithms
    • .  Validity Period
    • .  Status Updates
  • .  IANA Considerations
    • .  COSE Header Parameter
    • .  VDS Registries
      • .  Expert Review
      • .  Templates and Initial Contents
  • .  References
    • .  Normative References
    • .  Informative References
  • Acknowledgements
  • Contributors
  • Authors' Addresses
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 that certain data is not yet present in a database (proof of non-inclusion). Different VDSs can produce different Verifiable Data Structure Proofs (VDPs). The combination of representations of various VDSs 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 Enveloped COSE Structures.
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.
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.
395:
A COSE header parameter named "vds" (for Verifiable Data Structure), which conveys the algorithm identifier for a VDS. Correspondingly, see for a registry defining the integers used to identify VDSs.
396:
A COSE header parameter named "vdp" (for VDPs), which conveys a map containing VDPs organized by Proof Type. Correspondingly, see for a registry defining the integers used to identify VDS Proof Types.
Terminology The terms "header" and "payload" are defined in . The term "claim" is defined in . Additionally, this document uses the following 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 .
Entry:
An entry in a VDS for which proofs can be derived.
Proof Type:
A property that can be obtained by verifying a given proof over one or more entries in a VDS. For example, a VDS, such as a binary Merkle Tree, can support inclusion proofs where each proof confirms that a given entry is included in a Merkle Tree root.
Proof Value:
An encoding of a Proof Type in CBOR .
Receipt:
A COSE Single Signer Data Object, as defined in RFC 9052 of , containing the header parameters necessary to convey one or more VDP for an associated VDS.
Verifiable Data Structure (VDS):
A data structure that supports one or more VDS Proof Types. This property describes an algorithm used to maintain a VDS, for example, a binary Merkle Tree algorithm.
Verifiable Data Structure Proof (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).
VDSs in CBOR This section describes representations of VDPs in . For example, construction of a Merkle Tree leaf or an inclusion proof from a leaf to a Merkle Tree root might have several different representations, depending on the VDS 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 VDSs with COSE and provides concrete examples for the structures and proofs defined in and . The design of these structures is influenced by the conventions established for COSE Keys.
Structures Similar to COSE Key Types , different VDSs support different algorithms. This document establishes a registry of VDS algorithms; see for details.
Proofs As is the case for COSE Key Type Parameters , EC2 keys (1: 2) require and give meaning to specific parameters, such as -1 (crv), -2 (x), -3 (y), and -4 (d). RFC9162_SHA256 (395: 1) supports both (-1) inclusion and (-2) consistency proofs. This document establishes a registry of VDS 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" (394) to enable Receipts to be conveyed in the protected and unprotected headers of Enveloped COSE Structures. When the "receipts" header parameter is present, the verifier MUST confirm that the associated VDS and VDPs match entries present in the registries established in this specification, including values added in subsequent registrations. Receipts MUST be tagged as COSE_Sign1. defines how Receipts are included in a COSE_Sign1 data item:
CDDL for a COSE_Sign1 with Attached Receipts Signature_With_Receipt = #6.18(COSE_Sign1) cose-label = int / text cose-values = any Protected_Header = { * cose-label => cose-values } Unprotected_Header = { &(receipts: 394) => [+ bstr .cbor Receipt] * cose-label => cose-values } COSE_Sign1 = [ protected : bstr .cbor Protected_Header unprotected : Unprotected_Header payload : bstr / nil signature : bstr ] Receipt = Receipt_For_Inclusion / Receipt_For_Consistency ; Note the proof formats shown here are for RFC9162_SHA256. ; Other VDSs may have different proof formats. Receipt_For_Inclusion = #6.18(Signed_Inclusion_Proof) Signed_Inclusion_Proof = [ protected : bstr .cbor RFC9162_SHA256_Inclusion_Protected_Header, unprotected : RFC9162_SHA256_Inclusion_Unprotected_Header, payload : bstr / nil, signature : bstr ] RFC9162_SHA256_Inclusion_Protected_Header = { &(alg: 1) => int &(vds: 395) => int * cose-label => cose-values } RFC9162_SHA256_Inclusion_Unprotected_Header = { &(vdp: 396) => RFC9162_SHA256_Verifiable_Inclusion_Proofs * cose-label => cose-values } RFC9162_SHA256_Verifiable_Inclusion_Proofs = { &(inclusion-proof: -1) => RFC9162_SHA256_Inclusion_Proofs } RFC9162_SHA256_Inclusion_Proofs = [ + RFC9162_SHA256_Inclusion_Proof ] RFC9162_SHA256_Inclusion_Proof = bstr .cbor RFC9162_SHA256_Inclusion_Proof_Content RFC9162_SHA256_Inclusion_Proof_Content = [ tree_size: uint, leaf_index: uint, inclusion_path:[ + bstr ] ] Receipt_For_Consistency = #6.18(Signed_Consistency_Proof) Signed_Consistency_Proof = [ protected : bstr .cbor RFC9162_SHA256_Consistency_Protected_Header, unprotected : RFC9162_SHA256_Consistency_Unprotected_Header, payload : bstr / nil, ; Newer Merkle Tree root signature : bstr ] RFC9162_SHA256_Consistency_Protected_Header = { &(alg: 1) => int, &(vds: 395) => int, * cose-label => cose-values } RFC9162_SHA256_Consistency_Unprotected_Header = { &(vdp: 396) => RFC9162_SHA256_Verifiable_Consistency_Proofs * cose-label => cose-values } RFC9162_SHA256_Verifiable_Consistency_Proofs = { &(consistency-proof: -2) => RFC9162_SHA256_Consistency_Proofs } RFC9162_SHA256_Consistency_Proofs = [ + RFC9162_SHA256_Consistency_Proof ] RFC9162_SHA256_Consistency_Proof = bstr .cbor RFC9162_SHA256_Consistency_Proof_Content RFC9162_SHA256_Consistency_Proof_Content = [ tree_size_1: uint, tree_size_2: uint, consistency_path: [ + bstr ] ]
The following informative EDN is provided:
An Example COSE Signature with Multiple Receipts / cose-sign1 / 18([ / protected / <<{ / kid / 4 : h'bc297b51...e4edf0de', / algorithm / 1 : -7, # ES256 }>>, / unprotected / { / receipts / 394 : [ <</ cose-sign1 / 18([ / protected / <<{ / kid / 4 : h'abcdef12...34567890', / algorithm / 1 : -7, # ES256 / vds / 395 : 1, # RFC9162_SHA256 }>>, / unprotected / { / proofs / 396 : { / inclusion / -1 : [ <<[ / size / 9, / leaf / 8, / inclusion path / [ h'7558a95f...e02e35d6' ] ]>> ], }, }, / payload / null, / signature / h'02d227ed...ccd3774f' ])>>, <</ cose-sign1 / 18([ / protected / <<{ / kid / 4 : h'abcdef12...34567890', / algorithm / 1 : -7, # ES256 / vds / 395 : 1, # RFC9162_SHA256 }>>, / 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 VDPs contained in the COSE_Sign1 unprotected header. The CDDL definition for VDPs is specific to each VDS. This document describes proofs for RFC9162_SHA256 in the following sections.
Profiles New VDSs 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 VDS specification applying for inclusion in this registry MUST define how to encode the VDS 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 support for SHA256 and SHA3_256 with Merkle inclusion proofs and Merkle consistency proofs defined, respectively, in and , both "RFC9162_SHA256" and "RFC9162_SHA3_256" require entries in the relevant IANA registries. This document only defines "RFC9162_SHA256".
RFC9162_SHA256 This section defines how the data structure described in is mapped to the terminology defined in this document, using and .
Verifiable Data Structure The integer identifier for this VDS is 1. The string identifier for this VDS is "RFC9162_SHA256", a Merkle Tree where SHA256 is used as the hash algorithm (see ). See for a complete description of this VDS.
Inclusion Proof See for a complete description of this VDS Proof Type. The CBOR representation of an inclusion proof for RFC9162_SHA256 is:
CBOR-Encoded Inclusion Proof for RFC9162_SHA256 inclusion-proof-content = [ ; tree size at current Merkle Tree root tree-size: uint ; index of leaf in tree leaf-index: uint ; path from leaf to current Merkle Tree root inclusion-path: [ + bstr ] ]
The term leaf-index is used for alignment with the use established in . Note that 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 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: 395):
REQUIRED. VDS algorithm identifier. Value type: int.
The unprotected header for an RFC9162_SHA256 inclusion proof signature is:
A VDP 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: 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_SHA256 }>>, / 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. Verification of the inclusion proof and signature occurs in two sequential steps:
  1. Inclusion Proof Verification: The verifier applies the inclusion proof to the bytes of a candidate entry. If this fails, the proof is invalid. If it succeeds, the resulting Merkle Tree root becomes the COSE_Sign1 payload.
  2. Signature Verification: The verifier checks the COSE_Sign1 signature. Successful verification confirms the entry's inclusion in the VDS; otherwise, the signature is invalid.
Consistency Proof See for a complete description of this VDS Proof Type. The CBOR representation of a consistency proof for RFC9162_SHA256 is:
CBOR-Encoded Consistency Proof for RFC9162_SHA256 consistency-proof-content = [ ; older Merkle Tree size tree-size-1: uint ; newer Merkle Tree size tree-size-2: uint ; path from older Merkle Tree to newer Merkle Tree 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 a detached 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: 395):
REQUIRED. VDS 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: 396):
REQUIRED. VDPs. 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 EDN example 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_SHA256 }>>, / 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 VDS is not assured. This approach is specific to RFC9162_SHA256; different VDSs 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
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 sections 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 VDS used; for example, both RFC9162_SHA256 and ES256 depend on the SHA256 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 "suspendable" 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 has added the COSE header parameters defined in , and as listed in , to the "COSE Header Parameters" subregistry in the "CBOR Object Signing and Encryption (COSE)" registry group. These COSE header parameters fall in the 'Integer values from 256 to 65535' range (with a Specification Required registration procedure (see )). The Value Registry listed for "vds" is the "COSE Verifiable Data Structure Algorithm" subregistry. The map labels in the "vdp" are assigned from the "COSE Verifiable Data Structure Proofs" subregistry. Newly Registered COSE Header Parameters
Name Label Value Type Value Registry Description Reference
receipts 394 array   Priority ordered sequence of CBOR encoded Receipts RFC 9942,
vds 395 int COSE Verifiable Data Structure Algorithm identifier for Verifiable Data Structures that is used to produce Verifiable Data Structure Proofs RFC 9942,
vdp 396 map map key in COSE Verifiable Data Structure Proofs Location for Verifiable Data Structure Proofs in COSE Header Parameters RFC 9942,
VDS Registries IANA has established the "COSE Verifiable Data Structure Algorithms" and "COSE Verifiable Data Structure Proofs" subregistries under a Specification Required policy as described in .
Expert Review Expert reviewers (see ) should take into consideration the following points:
  • Experts are advised to assign the next available positive integer for VDSs.
  • 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 .
  • It is not permissible to assign points in the "COSE Verifiable Data Structure Algorithms" registry for which no corresponding entry in the "COSE Verifiable Data Structure Proofs" registry exists, and vice versa.
  • The change controller for related registrations of structures and proofs should be the same.
Templates and Initial Contents
COSE Verifiable Data Structure Algorithms Initial Registry Contents
Registration Template:
Name:
This is a descriptive name for the VDS that enables easier reference to the item.
Value:
This is the value used to identify the VDS.
Description:
This field contains a brief description of the VDS.
Reference:
This contains a pointer to the public specification for the VDS.
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.
COSE Verifiable Data Structure Algorithms Initial Registry Contents
Name Value Description Change Controller Reference
Reserved 0 Reserved RFC 9942
RFC9162_SHA256 1 SHA256 Binary Merkle Tree IETF
COSE Verifiable Data Structure Proofs Registry
Registration Template:
Verifiable Data Structure:
This value used identifies the related VDS.
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 VDS 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.
COSE Verifiable Data Structure Proofs Initial Registry Contents
Verifiable Data Structure Name Label CBOR Type Description Change Controller Reference
1 inclusion proofs -1 array (of bstr) Proof of inclusion IETF RFC 9942,
1 consistency proofs -2 array (of bstr) Proof of append-only property IETF RFC 9942,
References Normative References COSE Header Parameters IANA Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures 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. Concise Binary Object Representation (CBOR) 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. CBOR Object Signing and Encryption (COSE): Initial Algorithms 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. Certificate Transparency Version 2.0 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. CBOR Object Signing and Encryption (COSE) "typ" (type) Header Parameter 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. CBOR Web Token (CWT) Claims in COSE Headers 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. CBOR Object Signing and Encryption (COSE): Structures and Process 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. CBOR Object Signing and Encryption (COSE): Countersignatures Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size. CBOR Object Signing and Encryption (COSE) defines a set of security services for CBOR. This document defines a countersignature algorithm along with the needed header parameters and CBOR tags for COSE. This document updates RFC 9052. Informative References Concise Diagnostic Notation (CDN) Universität Bremen TZI This document formalizes and consolidates the definition of the Concise Diagnostic Notation (CDN) of the Concise Binary Object Representation (CBOR), addressing implementer experience. Replacing CDN's previous informal descriptions, it updates RFC 8949, obsoleting its Section 8, and RFC 8610, obsoleting its Appendix G. It also specifies registry-based extension points and uses them to support text representations such as of epoch-based dates/times and of IP addresses and prefixes. // (This cref will be removed by the RFC editor:) -26 is intended to // address the May/June 2026 Working Group Last Call comments on -25 // and the ensuing WG discussions. Specifically, this update: • is // going further with the idea to entirely replace the non- backwards // compatible update considered for the RFC 8610/G.4 concatenation by // two new application extensions (temporarily named b1/t1), and to // add related application-oriented extensions that deprecate the // original streamstring syntax. • includes the float'' application- // extension so that the entire CBOR format can be covered. • now // uses rules closer to those of markdown for handling data // transparency in raw strings, simplifying their implementation. • // adds security considerations. • proactively reserves the // application-extension identifier "pragma" for potential future // standardization. • This update does not address certain comments // that propose some editorial restructuring requiring moving text // around; this is best done in a next revision after the technical // comments are addressed. Work in Progress Early IANA Allocation of Standards Track Code Points 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. Guidelines for Writing an IANA Considerations Section in RFCs 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. CBOR Web Token (CWT) CBOR Web Token (CWT) is a compact means of representing claims to be transferred between two parties. The claims in a CWT are encoded in the Concise Binary Object Representation (CBOR), and CBOR Object Signing and Encryption (COSE) is used for added application-layer security protection. A claim is a piece of information asserted about a subject and is represented as a name/value pair consisting of a claim name and a claim value. CWT is derived from JSON Web Token (JWT) but uses CBOR rather than JSON.
Acknowledgements We would like to thank , , , , , and for their contributions (some of which substantial) to this document and to the initial set of implementations.
Contributors Microsoft
United Kingdom amaury.chamayou@microsoft.com
stevenlasker@hotmail.com
MITRE Corporation
United States of America ramartin@mitre.org
United States of America mwiseman32@acm.org
United States of America roywill@msn.com
Authors' Addresses Tradeverifyd
United States of America orie@or13.io
Fraunhofer SIT
Rheinstrasse 75 Darmstadt 64295 Germany henk.birkholz@ietf.contact
Microsoft
United Kingdom antdl@microsoft.com
Microsoft
United Kingdom fournet@microsoft.com