CBOR Object Signing and Encryption (COSE) Receipts

Internet Engineering Task Force (IETF)                         O. Steele
Request for Comments: 9942                                  Tradeverifyd
Category: Standards Track                                    H. Birkholz
ISSN: 2070-1721                                           Fraunhofer SIT
                                                      A. Delignat-Lavaud
                                                              C. Fournet
                                                               Microsoft
                                                               June 2026


           CBOR Object Signing and Encryption (COSE) Receipts

Abstract

   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
   https://www.rfc-editor.org/info/rfc9942.

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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include 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

   1.  Introduction
     1.1.  Requirements Notation
   2.  New COSE Header Parameters
   3.  Terminology
   4.  VDSs in CBOR
     4.1.  Structures
     4.2.  Proofs
     4.3.  Usage
     4.4.  Profiles
       4.4.1.  Registration Requirements
   5.  RFC9162_SHA256
     5.1.  Verifiable Data Structure
     5.2.  Inclusion Proof
       5.2.1.  Receipt of Inclusion
     5.3.  Consistency Proof
       5.3.1.  Receipt of Consistency
   6.  Privacy Considerations
     6.1.  Log Length
     6.2.  Header Parameters
   7.  Security Considerations
     7.1.  Choice of Signature Algorithms
     7.2.  Validity Period
     7.3.  Status Updates
   8.  IANA Considerations
     8.1.  COSE Header Parameter
     8.2.  VDS Registries
       8.2.1.  Expert Review
       8.2.2.  Templates and Initial Contents
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  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.

1.1.  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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  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 Section 8.2.2.1 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
      Section 8.2.2.2 for a registry defining the integers used to
      identify VDS Proof Types.

3.  Terminology

   The terms "header" and "payload" are defined in [STD96].  The term
   "claim" is defined in [RFC8392].

   Additionally, this document uses the following terminology:

   CDDL:  Concise Data Definition Language (CDDL) is defined in
      [RFC8610].

   EDN:  CBOR Extended Diagnostic Notation (EDN) is defined in
      [RFC8949], where it is referred to as "diagnostic notation", and
      is revised in [CBOR-EDN].

   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 [RFC8949].

   Receipt:  A COSE Single Signer Data Object, as defined in RFC 9052 of
      [STD96], 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).

4.  VDSs in CBOR

   This section describes representations of VDPs in [RFC8949].  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 Section 2.1.3 of [RFC9162] and
   Section 2.1.4 of [RFC9162].  The design of these structures is
   influenced by the conventions established for COSE Keys.

4.1.  Structures

   Similar to COSE Key Types [IANA.cose_header-parameters], different
   VDSs support different algorithms.

   This document establishes a registry of VDS algorithms; see
   Section 8.2.2.1 for details.

4.2.  Proofs

   As is the case for COSE Key Type Parameters
   [IANA.cose_header-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
   Section 8.2.2.2 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.

4.3.  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.

   Figure 1 defines how Receipts are included in a COSE_Sign1 data item:

   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 ]
   ]

           Figure 1: CDDL for a COSE_Sign1 with Attached Receipts

   The following informative EDN is provided:

   / 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'
   ])

         Figure 2: An Example COSE Signature with Multiple Receipts

   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.

4.4.  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
   [RFC9596] and the similar guidance provided in [RFC9597].

4.4.1.  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 Section 5 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 Section 2.1.3 of [RFC9162] and Section 2.1.4 of [RFC9162], both
   "RFC9162_SHA256" and "RFC9162_SHA3_256" require entries in the
   relevant IANA registries.  This document only defines
   "RFC9162_SHA256".

5.  RFC9162_SHA256

   This section defines how the data structure described in Section 2.1
   of [RFC9162] is mapped to the terminology defined in this document,
   using [RFC8949] and [RFC9053].

5.1.  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 Table 2).  See Section 2.1.1 of [RFC9162] for
   a complete description of this VDS.

5.2.  Inclusion Proof

   See Section 2.1.3.1 of [RFC9162] for a complete description of this
   VDS Proof Type.

   The CBOR representation of an inclusion proof for RFC9162_SHA256 is:

   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 ]
   ]

         Figure 3: CBOR-Encoded Inclusion Proof for RFC9162_SHA256

   The term leaf-index is used for alignment with the use established in
   Section 2.1.3.2 of [RFC9162].

   Note that [RFC9162] 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.

5.2.1.  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-map = {
     &(alg: 1) => int
     &(vds: 395) => int
     * cose-label => cose-value
   }

           Figure 4: Protected Header for a Receipt of Inclusion

   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:

   inclusion-proofs = [ + inclusion-proof ]

   verifiable-proofs = {
     &(inclusion-proof: -1) => inclusion-proofs
   }

   unprotected-header-map = {
     &(vdp: 396) => verifiable-proofs
     * cose-label => cose-value
   }

                  Figure 5: A VDP in an Unprotected Header

   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 [RFC9162].

   An EDN example for a Receipt containing an inclusion proof for
   RFC9162_SHA256 with a detached payload (see Section 4.4) is:

   / 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'
   ])

                       Figure 6: Receipt of Inclusion

   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.

5.3.  Consistency Proof

   See Section 2.1.4.1 of [RFC9162] for a complete description of this
   VDS Proof Type.

   The CBOR representation of a consistency proof for RFC9162_SHA256 is:

   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 ]

   ]

        Figure 7: CBOR-Encoded Consistency Proof for RFC9162_SHA256

5.3.1.  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-map = {
     &(alg: 1) => int
     &(vds: 395) => int
     * cose-label => cose-value
   }

          Figure 8: Protected Header for a Receipt of Consistency

   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 [RFC9162].

   An EDN example for a Receipt containing a consistency proof for
   RFC9162_SHA256 with a detached payload (see Section 4.4) is:

   / 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'
   ])

                   Figure 9: Example Consistency Receipt

   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.

6.  Privacy Considerations

6.1.  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.

6.2.  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.

7.  Security Considerations

   See the Security Considerations sections of:

   *  [RFC9162]

   *  [RFC9053]

7.1.  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.

7.2.  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 [RFC8392] for
   one way to accomplish this.  The details of expressing validity
   periods are out of scope for this document.

7.3.  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.

8.  IANA Considerations

8.1.  COSE Header Parameter

   IANA has added the COSE header parameters defined in Section 2, and
   as listed in Table 1, to the "COSE Header Parameters" subregistry
   [IANA.cose_header-parameters] 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 [RFC8126])).  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.

   +==========+=======+=======+============+==============+===========+
   | Name     | Label | Value | Value      | Description  | Reference |
   |          |       | Type  | Registry   |              |           |
   +==========+=======+=======+============+==============+===========+
   | receipts | 394   | array |            | Priority     | RFC 9942, |
   |          |       |       |            | ordered      | Section 2 |
   |          |       |       |            | sequence of  |           |
   |          |       |       |            | CBOR encoded |           |
   |          |       |       |            | Receipts     |           |
   +----------+-------+-------+------------+--------------+-----------+
   | vds      | 395   | int   | COSE       | Algorithm    | RFC 9942, |
   |          |       |       | Verifiable | identifier   | Section 2 |
   |          |       |       | Data       | for          |           |
   |          |       |       | Structure  | Verifiable   |           |
   |          |       |       |            | Data         |           |
   |          |       |       |            | Structures   |           |
   |          |       |       |            | that is used |           |
   |          |       |       |            | to produce   |           |
   |          |       |       |            | Verifiable   |           |
   |          |       |       |            | Data         |           |
   |          |       |       |            | Structure    |           |
   |          |       |       |            | Proofs       |           |
   +----------+-------+-------+------------+--------------+-----------+
   | vdp      | 396   | map   | map key in | Location for | RFC 9942, |
   |          |       |       | COSE       | Verifiable   | Section 2 |
   |          |       |       | Verifiable | Data         |           |
   |          |       |       | Data       | Structure    |           |
   |          |       |       | Structure  | Proofs in    |           |
   |          |       |       | Proofs     | COSE Header  |           |
   |          |       |       |            | Parameters   |           |
   +----------+-------+-------+------------+--------------+-----------+

             Table 1: Newly Registered COSE Header Parameters

8.2.  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 Section 4.6 of
   [RFC8126].

8.2.1.  Expert Review

   Expert reviewers (see [RFC8126]) 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 Section 2 of [RFC7120].

   *  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.

8.2.2.  Templates and Initial Contents

8.2.2.1.  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.

   +================+=======+===============+============+===========+
   | Name           | Value | Description   | Change     | Reference |
   |                |       |               | Controller |           |
   +================+=======+===============+============+===========+
   | Reserved       | 0     | Reserved      |            | RFC 9942  |
   +----------------+-------+---------------+------------+-----------+
   | RFC9162_SHA256 | 1     | SHA256 Binary | IETF       | Section   |
   |                |       | Merkle Tree   |            | 2.1 of    |
   |                |       |               |            | [RFC9162] |
   +----------------+-------+---------------+------------+-----------+

        Table 2: COSE Verifiable Data Structure Algorithms Initial
                            Registry Contents

8.2.2.2.  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.

   +==========+===========+=====+=====+===========+==========+=========+
   |Verifiable|Name       |Label|CBOR |Description|Change    |Reference|
   |Data      |           |     |Type |           |Controller|         |
   |Structure |           |     |     |           |          |         |
   +==========+===========+=====+=====+===========+==========+=========+
   |1         |inclusion  |-1   |array|Proof of   |IETF      |RFC 9942,|
   |          |proofs     |     |(of  |inclusion  |          |Section  |
   |          |           |     |bstr)|           |          |5.2      |
   +----------+-----------+-----+-----+-----------+----------+---------+
   |1         |consistency|-2   |array|Proof of   |IETF      |RFC 9942,|
   |          |proofs     |     |(of  |append-only|          |Section  |
   |          |           |     |bstr)|property   |          |5.3      |
   +----------+-----------+-----+-----+-----------+----------+---------+

      Table 3: COSE Verifiable Data Structure Proofs Initial Registry
                                  Contents

9.  References

9.1.  Normative References

   [IANA.cose_header-parameters]
              IANA, "COSE Header Parameters",
              <https://www.iana.org/assignments/cose>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/info/rfc8610>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/info/rfc8949>.

   [RFC9053]  Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
              August 2022, <https://www.rfc-editor.org/info/rfc9053>.

   [RFC9162]  Laurie, B., Messeri, E., and R. Stradling, "Certificate
              Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162,
              December 2021, <https://www.rfc-editor.org/info/rfc9162>.

   [RFC9596]  Jones, M.B. and O. Steele, "CBOR Object Signing and
              Encryption (COSE) "typ" (type) Header Parameter",
              RFC 9596, DOI 10.17487/RFC9596, June 2024,
              <https://www.rfc-editor.org/info/rfc9596>.

   [RFC9597]  Looker, T. and M.B. Jones, "CBOR Web Token (CWT) Claims in
              COSE Headers", RFC 9597, DOI 10.17487/RFC9597, June 2024,
              <https://www.rfc-editor.org/info/rfc9597>.

   [STD96]    Internet Standard 96,
              <https://www.rfc-editor.org/info/std96>.
              At the time of writing, this STD comprises the following:

              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Structures and Process", STD 96, RFC 9052,
              DOI 10.17487/RFC9052, August 2022,
              <https://www.rfc-editor.org/info/rfc9052>.

              Schaad, J., "CBOR Object Signing and Encryption (COSE):
              Countersignatures", STD 96, RFC 9338,
              DOI 10.17487/RFC9338, December 2022,
              <https://www.rfc-editor.org/info/rfc9338>.

9.2.  Informative References

   [CBOR-EDN] Bormann, C., "Concise Diagnostic Notation (CDN)", Work in
              Progress, Internet-Draft, draft-ietf-cbor-edn-literals-26,
              15 June 2026, <https://datatracker.ietf.org/doc/html/
              draft-ietf-cbor-edn-literals-26>.

   [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
              Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
              2014, <https://www.rfc-editor.org/info/rfc7120>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8392]  Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
              "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
              May 2018, <https://www.rfc-editor.org/info/rfc8392>.

Acknowledgements

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

Contributors

   Amaury Chamayou
   Microsoft
   United Kingdom
   Email: amaury.chamayou@microsoft.com


   Steve Lasker
   Email: stevenlasker@hotmail.com


   Robert Martin
   MITRE Corporation
   United States of America
   Email: ramartin@mitre.org


   Monty Wiseman
   United States of America
   Email: mwiseman32@acm.org


   Roy Williams
   United States of America
   Email: roywill@msn.com


Authors' Addresses

   Orie Steele
   Tradeverifyd
   United States of America
   Email: orie@or13.io


   Henk Birkholz
   Fraunhofer SIT
   Rheinstrasse 75
   64295 Darmstadt
   Germany
   Email: henk.birkholz@ietf.contact


   Antoine Delignat-Lavaud
   Microsoft
   United Kingdom
   Email: antdl@microsoft.com


   Cédric Fournet
   Microsoft
   United Kingdom
   Email: fournet@microsoft.com