COSE
Internet Engineering Task Force (IETF) O. Steele
Internet-Draft
Request for Comments: 9942 Tradeverifyd
Intended status:
Category: Standards Track H. Birkholz
Expires: 5 June 2026
ISSN: 2070-1721 Fraunhofer SIT
A. Delignat-Lavaud
C. Fournet
Microsoft
2 December 2025
COSE (CBOR
March 2026
CBOR Object Signing and Encryption) Encryption (COSE) Receipts
draft-ietf-cose-merkle-tree-proofs-18
Abstract
COSE (CBOR
CBOR Object Signing and Encryption) Encryption (COSE) Receipts prove properties
of a verifiable data structure Verifiable Data Structure (VDS) to a verifier. Verifiable data
structures Data
Structures and associated proof types enable security properties,
such as minimal disclosure, transparency transparency, and non-equivocation.
Transparency helps maintain trust over time, time and has been applied to
certificates, end to end end-to-end encrypted messaging systems, and supply
chain security. This specification enables concise transparency transparency-
oriented systems, systems by building on CBOR (Concise Concise Binary Object
Representation) Representation
(CBOR) and COSE. The extensibility of the approach is demonstrated
by providing CBOR encodings for Merkle inclusion and consistency
proofs.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the CBOR Object Signing
and Encryption Working Group mailing list (cose@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/cose/.
Source for this draft and an issue tracker can be found at
https://github.com/cose-wg/draft-ietf-cose-merkle-tree-proofs.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum 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 six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 June 2026.
https://www.rfc-editor.org/info/rfc9942.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3
2. New COSE Header Parameters . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Verifiable Data Structures in CBOR . . . . . . . . . . . . . 5
4.1. Structures . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Proofs . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.4. Profiles . . . . . . . . . . . . . . . . . . . . . . . . 9
4.4.1. Registration Requirements . . . . . . . . . . . . . . 10
5. RFC9162_SHA256 . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Verifiable Data Structure . . . . . . . . . . . . . . . . 10
5.2. Inclusion Proof . . . . . . . . . . . . . . . . . . . . . 10
5.2.1. Receipt of Inclusion . . . . . . . . . . . . . . . . 11
5.3. Consistency Proof . . . . . . . . . . . . . . . . . . . . 13
5.3.1. Receipt of Consistency . . . . . . . . . . . . . . . 13
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 15
6.1. Log Length . . . . . . . . . . . . . . . . . . . . . . . 16
6.2. Header Parameters . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Choice of Signature Algorithms . . . . . . . . . . . . . 16
7.2. Validity Period . . . . . . . . . . . . . . . . . . . . . 16
7.3. Status Updates . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. COSE Header Parameter . . . . . . . . . . . . . . . . . . 17
8.2. Verifiable Data Structure Registries . . . . . . . . . . 18
8.2.1. Expert Review . . . . . . . . . . . . . . . . . . . . 18
8.2.2. COSE Verifiable Data Structure Algorithms . . . . . . 18 Templates and Initial Contents
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1.
9.1. Normative References . . . . . . . . . . . . . . . . . . 20
10.2.
9.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Implementation Status . . . . . . . . . . . . . . . 22
A.1. Transmute Prototype . . . . . . . . . . . . . . . . . . . 22
Acknowledgements
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
COSE Receipts are signed proofs that include metadata about certain
states of a verifiable data structure 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 (proof of non inclusion). non-inclusion). Different
VDS VDSs can
produce different verifiable data Verifiable Data structure proofs Proofs (VDP). The
combination of representations of various VDS 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 COSE
envelopes.
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 up front in this Section section and elaborated on later in this
document.
TBD_0 (requested assignment 394):
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):
395: A COSE header parameter named vds
(Verifiable (for Verifiable Data
Structure), which conveys the algorithm identifier for a verifiable data structure.
Verifiable Data Structure. Correspondingly, this
document introduces see Section 8.2.2.1
for a new registry (Section 8.2.2) defining the integers used to identify verifiable data structures.
TBD_2 (requested assignment 396): Verifiable
Data Structures.
396: A COSE header parameter named vdp
(short for "verifiable data structure proofs"), (for Verifiable Data
Structure Proofs), which conveys a map containing verifiable data structure proofs Verifiable Data
Structure Proofs organized by proof type. Correspondingly, this document introduces see
Section 8.2.2.2 for a new registry
(Table 2) defining the integers used to
identify verifiable data
structure Verifiable Data Structure proof types.
3. 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 [I-D.draft-ietf-cbor-edn-literals]. [CBOR-EDN].
Verifiable Data Structure (VDS): A data structure which that supports one
or more Verifiable Data Structure Proof Types. This property
describes an algorithm used to maintain a verifiable data
structure, Verifiable Data
Structure, for example 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, 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 [RFC8949].
Entry: An entry in a verifiable data structure Verifiable Data Structure for which proofs can
be derived.
Receipt: A COSE object, as defined in [RFC9052], containing the
header parameters necessary to convey VDP for an associated VDS.
4. Verifiable Data Structures in CBOR
This section describes representations of verifiable data structure
proofs Verifiable Data Structure
Proofs in [RFC8949]. For example, construction of a Merkle tree
leaf, leaf
or an inclusion proof from a leaf to a Merkle root, root might have several
different representations, depending on the verifiable data
structure 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 Verifiable Data Structures
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 (https://www.iana.org/assignments/cose/
cose.xhtml#key-type), [IANA.cose_header-parameters], different verifiable data structures
Verifiable Data Structures support different algorithms.
This document establishes a registry of verifiable data structure
algorithms, Verifiable Data Structure
algorithms; see Section 8.2.2 8.2.2.1 for details.
4.2. Proofs
Similar to COSE Key Type Parameters
(https://www.iana.org/assignments/cose/cose.xhtml#key-type-
parameters), [IANA.cose_header-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) : (395: 1) supports
both (-1) inclusion and (-2) consistency proofs.
This document establishes a registry of verifiable data structure
algorithm proofs, Verifiable Data Structure
Proofs; see Table 2 Section 8.2.2.2 for details.
Proof types are specific to their associated "verifiable data
structure", "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".
"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 (TBD_0
(requested assignment 394)) (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 Verifiable Data Structure and verifiable
data structure proofs Verifiable
Data Structure Proofs match entries present in the registries
established in this specification, including values added in
subsequent registrations.. registrations.
Receipts MUST be tagged as COSE_Sign1.
The following [RFC8610] definition from [RFC8610] is provided:
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 the proof formats shown here are for RFC9162_SHA256.
; Other verifiable data structures Verifiable Data Structures 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 [
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 [
tree_size_1: uint,
tree_size_2: uint,
consistency_path: [ + bstr ]
]
Figure 1: CDDL for a COSE Sign1 with attached receipts 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 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 / <<{
/ kid / 4 : h'abcdef12...34567890',
/ 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'
])
Figure 2: An example Example COSE Signature with multiple receipts Multiple Receipts
The specific structure of COSE Receipts is dependent on the structure
of the COSE_Sign1 payload and the verifiable data structure proofs Verifiable Data Structure Proofs
contained in the COSE_Sign1 unprotected header. The CDDL definition
for verifiable data structure proofs Verifiable Data Structure Proofs is specific to each verifiable
data structure. Verifiable
Data Structure. This document describes proofs for RFC9162_SHA256 in
the following sections.
4.4. Profiles
New verifiable data structures 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, Parameter; see [RFC9596] and the similar guidance
provided in [RFC9597].
4.4.1. Registration Requirements
Each verifiable data structure Verifiable Data Structure specification applying for inclusion
in this registry MUST define how to encode the verifiable data
structure Verifiable Data
Structure 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
Consistency and
Inclusion Proofs defined respectively 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 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
algorithm (see Table 2. 2). See Section 2.1.1 of [RFC9162] (Definition
of the Merkle Tree), for a
complete description of this verifiable
data structure. Verifiable Data Structure.
5.2. Inclusion Proof
See Section 2.1.3.1 of [RFC9162] (Generating an Inclusion Proof), for a complete description of this verifiable data structure proof
Verifiable Data Structure Proof type.
The CBOR representation of an inclusion proof for RFC9162_SHA256 is:
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 ]
]
Figure 3: CBOR Encoded RFC9162 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 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-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: TBD_1 (requested assignment 395)): 395): REQUIRED. Verifiable data structure Data Structure 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 Verifiable Data Structure Proofs in an Unprotected Header
*
vdp (label: TBD_2 (requested assignment 396)): 396): REQUIRED. Verifiable data structure proofs. 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 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'
])
Figure 6: Receipt of Inclusion
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 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 Second, the
verifier checks the signature of the COSE Sign1. If the resulting
signature verifies, can be verified, the Receipt has proved inclusion of the
entry in the verifiable data structure. Verifiable Data Structure. If the resulting signature does not
verify,
cannot be verified, the signature may have been tampered with.
5.3. Consistency Proof
See Section 2.1.4.1 of [RFC9162] (Generating a Consistency Proof), for a complete description of this verifiable data structure proof
Verifiable Data Structure Proof type.
The cbor representation of a consistency proof for RFC9162_SHA256 is:
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 ]
]
Figure 7: CBOR Encoded RFC9162 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) 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-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: TBD_1 (requested assignment 395)): 395): REQUIRED. Verifiable data structure 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)): 396): REQUIRED. Verifiable data structure proofs. 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 [RFC9162].
An example 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 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'
])
Figure 9: Example consistency receipt 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
First, the verifier checks the signature on the COSE Sign1. If the
verification fails, the consistency proof is not checked. Second Second,
the consistency proof is checked by applying a previous inclusion proof,
proof to the consistency proof. If the verification fails, the
append only property of the verifiable data structure Verifiable Data Structure is not assured.
This approach is specific to RFC9162_SHA256, RFC9162_SHA256; different verifiable data
structures Verifiable
Data Structures may not support consistency proofs. It is
recommended that implementations return a single boolean result for Receipt
verification operations,
Receipt-verification operations to reduce the chance of accepting a
valid signature over an invalid consistency proof.
6. Privacy Considerations
The privacy considerations section of [RFC9162] and [RFC9053] apply
to this document.
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 section 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 verifiable data structure used, Verifiable Data Structure used; for
example: Both
example, both RFC9162_SHA256 and ES256 depend on the sha-256 hash
function.
7.2. Validity Period
In some cases, receipts MAY include strict validity periods, for
example, activation not too far in the future, future or expiration, expiration not too
far in the past. See the iat, nbf, and exp claims in [RFC8392], [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 "suspendible", "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 is requested to add has added the COSE header parameters defined in Section 2, and
as listed in Table 1, to the "COSE Header Parameters"
registry 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 ('Specification Required' Registration
Procedure). (with a Specification
Required registration procedure (see [RFC8126])). The Value Registry
listed for "vds" is the COSE "COSE Verifiable Data Structure registry. Algorithm"
subregistry. The map labels in the "vdp" are assigned from the COSE "COSE
Verifiable Data Structure Proofs registry.
+========+=============+=====+============+=============+=========+
|Name Proofs" subregistry.
+==========+=======+=======+============+==============+===========+
| Name | Label |Value| | Value | Value | Description |Reference| | Reference | |Type
| | | Type | Registry | | |
+========+=============+=====+============+=============+=========+
|receipts| TBD_0 |array|
+==========+=======+=======+============+==============+===========+
| Priority |RFCthis, receipts | 394 | array | (requested | Priority | RFC 9942, | ordered |Section 2|
| | assignment: | | | sequence of ordered | Section 2 |
| | 394) | | | CBOR sequence of | |
| | | | | CBOR encoded | |
| | | | | Receipts | |
+--------+-------------+-----+------------+-------------+---------+
|vds
+----------+-------+-------+------------+--------------+-----------+
| vds | 395 | TBD_1 |int int | COSE | Algorithm |RFCthis, | RFC 9942, |
| | (requested | | Verifiable | identifier |Section 2| | Section 2 |
| | assignment: | | Data | for | |
| | 395) | | Structure | verifiable Verifiable | |
| | | | | data Data | |
| | | | | structures, Structures | |
| | | | | that is used to | |
| | | | | to produce | |
| | | | | verifiable Verifiable | |
| | | | | data Data | |
| | | | | structure Structure | |
| | | | | proofs Proofs | |
+--------+-------------+-----+------------+-------------+---------+
|vdp
+----------+-------+-------+------------+--------------+-----------+
| TBD_2 |map vdp | 396 | map | map key in | Location |RFCthis, |
| | (requested for | RFC 9942, | COSE
| for |Section 2| | | assignment: | COSE | Verifiable | verifiable Section 2 |
| | | 396) | Verifiable | Data | data |
| | | | Data | Structure | structure |
| | | | Structure | Proofs | proofs in | |
| | | | Proofs | COSE Header | |
| | | | | Parameters | |
+--------+-------------+-----+------------+-------------+---------+
+----------+-------+-------+------------+--------------+-----------+
Table 1: Newly registered Registered COSE Header Parameters
8.2. Verifiable Data Structure Registries
IANA established the COSE "COSE Verifiable Data Structure Algorithms Algorithms" and
COSE
"COSE Verifiable Data Structure Proofs registries 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 verifiable data structures. 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,
registered and that the point is likely to be used in deployments.
* Specifications are required for all point assignments. Early
Allocation early
allocation is permissible, see Section 2 of [RFC7120].
* It is not permissible to assign points in COSE Verifiable Data
Structure Algorithms, Algorithms for which no corresponding COSE Verifiable
Data Structure Proofs entry exists, and vice versa.
* The Change Controller 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 Registry
Registration Template:
*
Name:
This is a descriptive name for the verifiable data structure Verifiable Data Structure
that enables easier reference to the item.
*
Value:
This is the value used to identify the verifiable data
structure.
* Verifiable Data
Structure.
Description:
This field contains a brief description of the
verifiable data structure.
* Verifiable Data
Structure.
Reference:
This contains a pointer to the public specification for the verifiable data structure.
*
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:
+================+=======+===========================+==============+
+================+=======+===============+============+===========+
| Name | Value | Description | Change | Reference |
+================+=======+===========================+==============+
| | | | Controller | |
+================+=======+===============+============+===========+
| Reserved | 0 | Reserved | Reserved |
+----------------+-------+---------------------------+--------------+ RFC 9942 |
+----------------+-------+---------------+------------+-----------+
| RFC9162_SHA256 | 1 | SHA256 Binary | IETF | Section 2.1 |
| | | 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
verifiable data structure.
* 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 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:
+============+=============+=====+=======+=============+===========+
| Verifiable | Name |Label| CBOR | Description | Reference |
| Data | | | Type
+==========+===========+=====+=====+===========+==========+=========+
|Verifiable|Name |Label|CBOR |Description|Change |Reference|
|Data | | |Type | |Controller| | Structure
|Structure | | | | | |
+============+=============+=====+=======+=============+===========+ | 1 | inclusion
+==========+===========+=====+=====+===========+==========+=========+
|1 |inclusion |-1 | array | Proof |array|Proof of |IETF |RFC 9942,|
| RFCthis, | |proofs | |(of |inclusion | proofs | | (of | inclusion | Section |
| | | | bstr) | |Section | 5.2
|
+------------+-------------+-----+-------+-------------+-----------+ | 1 | consistency |-2 |bstr)| | array |5.2 | Proof
+----------+-----------+-----+-----+-----------+----------+---------+
|1 |consistency|-2 |array|Proof of |IETF |RFC 9942,|
| RFCthis, |
| | proofs | | (of | append only | Section | |proofs | |(of |append only| |Section |
| | bstr) | property |bstr)|property | 5.3 |5.3 |
+------------+-------------+-----+-------+-------------+-----------+
+----------+-----------+-----+-----+-----------+----------+---------+
Table 3: COSE Verifiable Data Structure Proofs Initial Registry
Contents
9. 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.
10. References
10.1.
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/rfc/rfc2119>.
<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/rfc/rfc8174>. <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/rfc/rfc8610>. <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/rfc/rfc8949>.
<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/rfc/rfc9053>. <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/rfc/rfc9162>. <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/rfc/rfc9596>.
<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/rfc/rfc9597>.
10.2.
<https://www.rfc-editor.org/info/rfc9597>.
9.2. Informative References
[BCP205] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/rfc/rfc7942>.
[I-D.draft-ietf-cbor-edn-literals]
[CBOR-EDN] Bormann, C., "CBOR Extended Diagnostic Notation (EDN)",
Work in Progress, Internet-Draft, draft-ietf-cbor-edn-
literals-19, 16 October 2025,
literals-20, 2 March 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-cbor-
edn-literals-19>.
edn-literals-20>.
[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/rfc/rfc7120>. <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/rfc/rfc8126>.
<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/rfc/rfc8392>. <https://www.rfc-editor.org/info/rfc8392>.
[RFC9052] 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/rfc/rfc9052>.
Appendix A. Implementation Status
Note to RFC Editor: Please remove this section as well as references
to [BCP205] 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 [BCP205].
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
<https://www.rfc-editor.org/info/rfc9052>.
Acknowledgements
We would like to verify the information presented here that was
supplied by IETF contributors. This is not intended as, thank Maik Riechert, Jon Geater, Michael B. Jones,
Mike Prorock, Ilari Liusvaara, and must not
be construed to be, a catalog of available implementations or Amaury Chamayou for their
features. Readers are advised to note that other implementations may
exist.
According to [BCP205], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit
contributions (some 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 substantial) to use this information as
they see fit".
A.1. Transmute Prototype
An open-source implementation was initiated document and is maintained by the
Transmute Industries Inc. - Transmute. An application demonstrating
the concepts is available at COSE SCITT Receipts (https://github.com/
transmute-industries/cose?tab=readme-ov-file#transparent-statement)
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
initial set 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) 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
Cedric Fournet
Microsoft
United Kingdom
Email: fournet@microsoft.com