Categorical Compliance Screening Receipt Format for Agentic-Payment Flows
draft-hopley-x402-compliance-receipt-00
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| Author | MR CHRISTOPHER HOPLEY | ||
| Last updated | 2026-05-23 | ||
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draft-hopley-x402-compliance-receipt-00
Independent Submission C. Hopley
Internet-Draft AlgoVoi
Intended status: Informational 26 May 2026
Expires: 27 November 2026
Categorical Compliance Screening Receipt Format for Agentic-Payment
Flows
draft-hopley-x402-compliance-receipt-00
Abstract
This document specifies a categorical compliance screening receipt
format for agentic-payment flows. The format is designed for use by
AI agents and agentic-payment gateways that perform regulatory
screening at admission time and must retain the screening decision
under framework-bound retention obligations.
The receipt format uses a closed enumeration of categorical outcomes
(ALLOW, REFER, DENY) rather than a continuous score or tier
projection. The categorical outcome is load-bearing for downstream
regulatory obligations: in jurisdictions with mandatory disclosure
obligations triggered by specific screening outcomes, a REFER outcome
can carry a mandatory reporting obligation that a DENY does not, and
a score or tier projection collapses this distinction.
Receipts are canonicalised under JSON Canonicalization Scheme with an
in-band canonicalisation rule pin. The pin enables long-term re-
verification from retained bytes alone, without dependence on an out-
of-band rule registry that the operator must continue to publish.
This document is Informational. It documents an admission-time
compliance screening receipt format used in production and proposes
it for wider adoption; it does not create mandatory implementation
obligations on third-party systems.
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 of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 27 November 2026.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Regulatory frameworks (examples) . . . . . . . . . . . . 4
1.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Relationship to IETF work . . . . . . . . . . . . . . . . 5
1.5. Relationship to draft-vauban-x402-stark-receipts . . . . 5
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 5
2.1. Notation . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. Receipt Format Specification . . . . . . . . . . . . . . . . 6
3.1. payer_ref . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. screen_result Closed Enumeration . . . . . . . . . . . . 7
3.3. screen_timestamp_ms . . . . . . . . . . . . . . . . . . . 8
3.4. screen_provider_did . . . . . . . . . . . . . . . . . . . 8
3.5. jurisdiction_flags . . . . . . . . . . . . . . . . . . . 8
3.6. canon_version . . . . . . . . . . . . . . . . . . . . . . 9
4. Canonicalisation . . . . . . . . . . . . . . . . . . . . . . 9
5. Audit Chain Composition . . . . . . . . . . . . . . . . . . . 10
5.1. Chain Row Shape . . . . . . . . . . . . . . . . . . . . . 10
5.2. Linkage Verification . . . . . . . . . . . . . . . . . . 10
5.3. Selective Disclosure . . . . . . . . . . . . . . . . . . 10
5.4. Retention Storage . . . . . . . . . . . . . . . . . . . . 11
6. Long-Term Auditability Properties . . . . . . . . . . . . . . 11
7. Composition with Other x402 Substrate . . . . . . . . . . . . 12
7.1. Composite Trust-Query . . . . . . . . . . . . . . . . . . 12
7.2. privacy_class Field . . . . . . . . . . . . . . . . . . . 12
7.3. Compliance Category . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
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8.1. URN Namespace . . . . . . . . . . . . . . . . . . . . . . 13
8.2. Media Type . . . . . . . . . . . . . . . . . . . . . . . 13
8.3. Receipt Format Identifier . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9.1. Receipt Tampering . . . . . . . . . . . . . . . . . . . . 13
9.2. Chain Truncation and Reordering . . . . . . . . . . . . . 13
9.3. Bundle Forgery . . . . . . . . . . . . . . . . . . . . . 14
9.4. Operator Continuity Loss . . . . . . . . . . . . . . . . 14
9.5. DID Resolution Compromise . . . . . . . . . . . . . . . . 14
9.6. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.7. Choice of Canonicalisation Scheme . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Regulatory frameworks cited as examples . . . . . . 16
Appendix B. Examples (Informative) . . . . . . . . . . . . . . . 17
B.1. ALLOW under UK + EU joint jurisdiction . . . . . . . . . 17
B.2. REFER under UK with mandatory SAR obligation . . . . . . 17
B.3. DENY under sanctions match across UK + EU + US . . . . . 17
Appendix C. Reference Implementations (Informative) . . . . . . 18
Appendix D. Acknowledgments . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
1.1. Motivation
Agentic-payment flows are payment transactions initiated or routed by
autonomous AI agents acting on behalf of a principal (a natural
person or legal entity). Where these payments cross regulated
payment rails, the payment gateway is obligated to perform compliance
screening at admission time: sanctions screening, anti-money-
laundering checks, and jurisdictional eligibility checks against the
payer and the receiving counterparty.
The output of compliance screening is a categorical decision: either
the payment is allowed to proceed, it is allowed but flagged for
enhanced due diligence and a regulatory report, or it is refused.
This document specifies a receipt format for recording that
categorical decision in a manner suitable for retention under
framework-bound retention obligations.
Publication as an Informational RFC provides the compliance receipt
format with a stable, citeable specification that can serve as a
common reference point across implementations. Standardising the
categorical outcome enumeration (ALLOW / REFER / DENY), the
canonicalisation discipline, and the audit-chain shape enables
interoperability between independent agentic-payment gateways
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performing screening under different regulatory frameworks. The
format is intended to document a deployed practice rather than to
establish a new standards-track mandate.
1.2. Regulatory frameworks (examples)
The receipt format is designed to satisfy retention and re-
verifiability obligations imposed by a range of regulatory
frameworks. Specific examples include UK Money Laundering
Regulations 2017 and Proceeds of Crime Act 2002, EU Anti-Money
Laundering Directives 5 and 6, EU Markets in Crypto-Assets Regulation
Article 80, EU Anti-Money Laundering Regulation Article 56, and EU
Digital Operational Resilience Act Article 14. In jurisdictions with
mandatory disclosure obligations triggered by specific screening
outcomes (for example, where a REFER outcome triggers a Suspicious
Activity Report obligation that a DENY does not), the categorical
enumeration preserves the operational distinction that scoring or
tier projection would collapse. These frameworks are cited as
examples of the design space; the receipt format itself is
jurisdiction-neutral.
1.3. Scope
This document is Informational. It documents the compliance receipt
format and proposes it for wider adoption; it does not define a
protocol standard or create mandatory implementation obligations on
third-party systems.
In scope:
* The categorical receipt format (Section 3)
* The canonicalisation rule applicable to the receipt (Section 4)
* Audit-chain composition properties (Section 5)
* Long-term auditability properties (Section 6)
* Composition with other x402 substrate specifications (Section 7)
Out of scope:
* The screening algorithm itself. The specific business logic that
produces ALLOW / REFER / DENY (the sanctions feeds consulted, the
anti-money-laundering rules applied, the jurisdictional risk-
scoring methodology) is implementation-defined per screening
provider.
* The retention storage backend. Object Lock COMPLIANCE retention
on S3-compatible storage is recommended (informative, Section 5.4)
but the specific backend is deployment-defined.
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* Identity proofing. The payer's identity is referenced through a
content-addressed reference (Section 3.1); how the identity is
established and proofed is the subject of separate work.
1.4. Relationship to IETF work
This document does not conflict with any current IETF chartered work.
The x402 payment protocol operates as an application-layer convention
built on HTTP and does not modify or supersede any IETF protocol
specification. The compliance receipt format described here is
specific to admission-time screening in agentic systems and is not
within the scope of any active IETF working group known to the
authors at the time of submission.
1.5. Relationship to draft-vauban-x402-stark-receipts
At the time of writing, draft-vauban-x402-stark-receipts is an
individual Internet-Draft on the IETF datatracker, with stream
unassigned. It covers cryptographic settlement-time payment-
condition proofs using STARK receipts; this document covers
admission-time compliance screening receipts. The two documents were
developed in coordination and are designed to compose, but each is an
independent submission. Both documents pin the same
urn:x402:canonicalisation:jcs-rfc8785-v1 canonicalisation discipline.
The two receipt families compose via a composite trust-query
algorithm specified in the x402 protocol substrate: a downstream
verifier consuming a composite hash sees one emitter row per
provider, where each emitter row references the JCS-canonical bytes
of its underlying receipt.
2. Conventions and Definitions
2.1. 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.
2.2. Definitions
*screening provider*: an entity that performs compliance screening on
an agentic-payment transaction at admission time and emits a
categorical receipt as the screening decision record.
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*payer_ref*: a content-addressed reference to the payer's identity.
Typically of the form "sha256:<lowercase-hex>" where the hash is
taken over the JCS-canonical bytes of an identity object held by the
screening provider. The receipt does not carry cleartext identity
content -- only the content-addressed reference -- so the screening
provider's retention layer is GDPR Article 5(1)(c) minimal by
construction.
*screen_result*: the categorical screening outcome. One of ALLOW,
REFER, or DENY. The closed set is load-bearing (Section 3.2).
*screen_timestamp_ms*: an integer giving the number of milliseconds
since the Unix epoch (1970-01-01T00:00:00Z) at which the screening
decision was recorded. See Section 3.3.
*screen_provider_did*: a Decentralised Identifier (DID) identifying
the screening provider. See Section 3.4.
*jurisdiction_flags*: an ordered list of regulatory jurisdictions
under which the screening was performed. See Section 3.5.
*canon_version*: an in-band string identifying the canonicalisation
rule under which the receipt was canonicalised. See Section 3.6.
*audit chain*: a monotonic hash-linked sequence of receipts retained
by the screening provider; see Section 5.
3. Receipt Format Specification
A compliance screening receipt is a JSON [RFC8259] object containing
exactly the following required fields. Implementations MUST reject
receipts that omit any required field or include fields not listed
below.
{
"payer_ref": "<string>",
"screen_result": "<enum: ALLOW | REFER | DENY>",
"screen_timestamp_ms": <integer>,
"screen_provider_did": "<DID URI>",
"jurisdiction_flags": ["<jurisdiction-code>", ...],
"canon_version": "jcs-rfc8785-v1"
}
The JSON Schema (draft-07) for this format is published at
https://json.schemastore.org/algovoi-compliance-receipt-v1.json
(https://json.schemastore.org/algovoi-compliance-receipt-v1.json).
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3.1. payer_ref
The payer_ref field MUST be a non-empty string identifying the payer
by content-addressed reference. The recommended form is
"sha256:<lowercase-hex>" where the hex is the lowercase hexadecimal
representation of the SHA-256 digest of the JCS-canonical bytes of
the underlying identity object.
The receipt MUST NOT carry cleartext identity content. This ensures
that the screening provider's retention layer is GDPR Article 5(1)(c)
minimal by construction; identity content can be re-presented to the
receipt holder out-of-band when necessary.
3.2. screen_result Closed Enumeration
The screen_result field MUST be exactly one of the following three
string values:
+=======+===================================================+
| Value | Meaning |
+=======+===================================================+
| ALLOW | The transaction is cleared to proceed under the |
| | regulatory gate at the screening provider's |
| | jurisdictions. |
+-------+---------------------------------------------------+
| REFER | The transaction is flagged for enhanced due |
| | diligence. Depending on the screening provider's |
| | jurisdictions (jurisdiction_flags) this MAY |
| | trigger a mandatory Suspicious Activity Report or |
| | equivalent regulatory filing obligation. |
+-------+---------------------------------------------------+
| DENY | The transaction is refused under a sanctions or |
| | anti-money-laundering rule. |
+-------+---------------------------------------------------+
Table 1
The closed three-value enumeration is load-bearing. Under UK
Proceeds of Crime Act 2002 Section 330, a REFER outcome triggers a
mandatory Suspicious Activity Report obligation to the UK National
Crime Agency for institutions in the regulated sector. A DENY
outcome does not trigger the same obligation: it refuses the
transaction but does not by itself require a SAR.
A receipt format that compresses screen_result to a continuous score
or to a coarser tier set (e.g. "high / medium / low") loses this
load-bearing distinction. A long-term auditor (typically operating
at the year-five mark or beyond) reading a retained receipt under
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such a projection cannot determine, from the retained bytes alone,
whether the historical decision triggered a mandatory regulatory
report. This document REQUIRES the closed three-value enumeration
for that reason.
Future extensions to the receipt format MAY add additional fields
alongside the categorical screen_result (e.g. a continuous score for
internal monitoring use), but MUST NOT remove or alter the closed
enumeration on screen_result itself.
3.3. screen_timestamp_ms
The screen_timestamp_ms field MUST be a non-negative integer giving
the number of milliseconds elapsed since 1970-01-01T00:00:00Z (Unix
epoch).
The field MUST NOT be a floating-point number, MUST NOT be a JSON-
formatted string, and MUST NOT be in RFC 3339 ISO-8601 format.
Implementations that receive a non-integer value MUST reject the
receipt at the validation layer before canonicalisation; silent type-
cast from float to integer is forbidden.
The integer-only restriction is required because RFC 8785
canonicalises floating-point numbers and integers differently. A
receipt whose timestamp was emitted as an integer and later re-
canonicalised after a type-cast from float would produce different
canonical bytes and a different content_hash -- which would fail the
long-term auditability property (Section 6).
3.4. screen_provider_did
The screen_provider_did field MUST be a Decentralised Identifier
(DID) URI conforming to the DID syntax: "did:" followed by one or
more alphanumeric characters identifying the DID method, followed by
a method-specific identifier.
Implementations MAY use any DID method, including but not limited to
did:web, did:key, did:ion, did:peer. The did:web method is
RECOMMENDED where the screening provider operates a stable HTTPS-
resolvable endpoint, because did:web allows verifiers to retrieve the
screening provider's public key directly from a well-known URI
without consulting any external registry.
3.5. jurisdiction_flags
The jurisdiction_flags field MUST be a non-empty JSON array of
strings. Each string identifies a regulatory jurisdiction under
which the screening was performed.
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Recommended values follow ISO 3166-1 alpha-2 country codes (e.g.
"UK", "DE", "JP"). Aggregate jurisdiction codes such as "EU" MAY
also be used.
The array element ORDER is SIGNIFICANT and load-bearing. RFC 8785
Section 3.2.3 specifies that JSON array element order is preserved
during canonicalisation. The array ["UK", "EU"] and the array ["EU",
"UK"] therefore canonicalise to different bytes and produce different
content_hash values.
Producer-side ordering MUST match the order in which the regulatory
rules were applied. Verifiers SHOULD validate ordering consistency
across a screening provider's retained chain.
3.6. canon_version
The canon_version field MUST be the string "jcs-rfc8785-v1" for
receipts emitted under the canonicalisation discipline specified by
this version of this document.
Future revisions of the canonicalisation discipline MAY introduce
successor pin values ("jcs-rfc8785-v2", etc.). Implementations re-
canonicalising a retained receipt MUST consult the receipt's
canon_version field and apply the corresponding canonicalisation
rule.
The in-band pin enables long-term re-verification: the rule active at
emission is recorded in the retained bytes themselves and does not
require an out-of-band rule registry that the screening provider must
continue to publish.
4. Canonicalisation
Compliance receipts are canonicalised using JSON Canonicalization
Scheme (JCS) as specified in [RFC8785]. The canonicalisation
discipline applicable to this document is identified by the URN:
urn:x402:canonicalisation:jcs-rfc8785-v1
The discipline imposes the following rules on receipt content:
* RFC 8785 canonical JSON for the receipt object.
* Object keys are sorted lexicographically by Unicode code-point
order (per RFC 8785 Section 3.2.3).
* Array element order is preserved (per RFC 8785 Section 3.2.3).
* Numeric values are canonicalised per RFC 8785 Section 3.2.2.3.
* The integer-only restriction on screen_timestamp_ms (Section 3.3)
is applied at the validation layer before canonicalisation.
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The discipline applies to:
* The receipt object itself, for computation of the content_hash
(Section 5).
* The bundle of receipts emitted as a selective-disclosure audit
bundle (out of scope for this document; see related work in
Section 5.4).
5. Audit Chain Composition
A screening provider that emits compliance receipts under this format
SHOULD compose those receipts into a monotonic hash-linked audit
chain.
5.1. Chain Row Shape
Each row in the audit chain MUST carry the following three fields in
addition to the receipt itself:
* chain_position: a non-negative integer that increases
monotonically with each new row, starting at zero for the chain
head.
* content_hash: the lowercase hexadecimal SHA-256 hash of the JCS-
canonical bytes of the receipt object.
* prev_hash: the content_hash of the previous chain row, or null for
the chain head (chain_position = 0).
5.2. Linkage Verification
A verifier walking the chain MUST confirm:
* chain_position increases by exactly one between successive rows.
* prev_hash on row N equals content_hash on row (N - 1).
* content_hash on each row recomputes to SHA-
256(JCS(receipt_object)) from the retained bytes.
Any linkage break MUST cause the verifier to reject the chain.
5.3. Selective Disclosure
A screening provider MAY emit a selective-disclosure audit bundle
containing a subset of the retained chain (typically filtered by a
selection_criteria such as tenant_id, payer_ref, screen_result, or a
time range). Such bundles MAY include "bridging_rows" that fill
chain gaps between selected rows so that the verifier can confirm
linkage continuity across the disclosed subset.
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The specific bundle envelope format is out of scope for this
document. A reference implementation of the selective-disclosure
bundle format and the corresponding verifier is published at
https://github.com/chopmob-cloud/algovoi-audit-verifier
(https://github.com/chopmob-cloud/algovoi-audit-verifier) (MIT
licensed).
5.4. Retention Storage
The retention storage backend for the chain is out of scope for this
document. An S3-compatible Object Lock COMPLIANCE retention is
RECOMMENDED where the screening provider is subject to retention
obligations of seven years or more (e.g. UK MLR 2017 Regulation
40(3)).
6. Long-Term Auditability Properties
Regulatory frameworks including the examples listed in Section 1.2
impose retention periods of five years or more, with re-verification
of retained records expected across the full horizon. The properties
in this section are designed to satisfy re-verification from retained
bytes alone across that horizon.
This receipt format is designed to satisfy the following auditability
properties:
1. *Re-verification from retained bytes alone.* A long-term verifier
reading a retained chain can recompute every content_hash from
the row's payload and confirm linkage against prev_hash without
consulting any external service. The in-band canon_version pin
identifies which canonicalisation rule to apply.
2. *Operator-continuity independence.* Verification does NOT require
the screening provider to continue to publish a canonicalisation
rule registry, a sanctions feed snapshot, or any other out-of-
band resource. The receipt is self-contained.
3. *Cross-implementation verifiability.* The JCS RFC 8785
canonicalisation discipline has been byte-for-byte cross-
validated across multiple independent reference implementations
including Python rfc8785, JavaScript canonicalize, Go gowebpki/
jcs, Java cyberphone/json-canonicalization, and Rust serde_jcs.
A verifier built with any of these implementations produces
identical canonical bytes for any compliance receipt under this
format.
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4. *Tamper detection.* Per-row content_hash and chain prev_hash
linkage detect single-row tampering and chain truncation /
reordering respectively.
5. *Regulatory distinction preserved.* The closed enumeration on
screen_result (Section 3.2) preserves the load-bearing
distinction between REFER (mandatory SAR under UK POCA 2002
s.330) and DENY for the full retention period.
7. Composition with Other x402 Substrate
This receipt format composes with other elements of the x402
substrate:
7.1. Composite Trust-Query
Multiple emitters' attestations -- including compliance receipts
under this format, STARK payment-condition receipts under the
companion draft-vauban-x402-stark-receipts work in progress, and
service-reputation receipts from other providers -- compose into a
single canonical composite_hash via the composite trust-query
algorithm specified in the x402 protocol substrate:
composite_hash = SHA-256(JCS([rows sorted by source_id, sig
excluded]))
A downstream verifier consuming a composite_hash sees one emitter row
per provider, each row containing or referencing the JCS-canonical
bytes of the provider's underlying receipt.
7.2. privacy_class Field
A receipt MAY carry an additional privacy_class field declaring the
settlement-plane visibility of the receipt, as proposed in the x402
protocol substrate. The field is not part of the required-fields set
of this document but is interoperable with it.
7.3. Compliance Category
This receipt format is one of the format options under the broader
Compliance category proposed in the x402 protocol substrate, which
provides the extension mechanism by which downstream registries may
surface compliance attestations.
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8. IANA Considerations
The IANA actions described in this document, if any, are subject only
to allocation policies that do not require IETF Review or Standards
Action.
8.1. URN Namespace
This document uses the URN identifier urn:x402:canonicalisation:jcs-
rfc8785-v1 to name the JCS canonicalisation discipline applied to
receipts under this document and companion documents. Formal
registration of this URN namespace under [RFC8141] is undertaken by
the document authors separately from RFC publication, by direct
submission of the registration template; the registration is not
requested as a publication action of this document. The identifier
itself is used verbatim by implementations regardless of registration
outcome.
8.2. Media Type
This document does not request the registration of a new media type.
Receipts under this format use the application/json media type with
the structural constraints specified in Section 3.
8.3. Receipt Format Identifier
The string algovoi-compliance-receipt-v1 is used by the JSON Schema
identifier in Section 3 to name the receipt format. This is an
informal in-document identifier and does not require a new IANA
registry. Implementations adopting variants of this format are
encouraged to use distinct, self-descriptive identifiers of their
own.
9. Security Considerations
9.1. Receipt Tampering
The per-row content_hash provides single-row tamper detection. A
verifier recomputing content_hash from the receipt's JCS-canonical
bytes detects any modification to the receipt content (including
modification to a single field, byte, or whitespace).
9.2. Chain Truncation and Reordering
The prev_hash linkage detects chain truncation, row removal, and
reordering. A verifier walking the chain confirms that prev_hash on
each row equals content_hash on the previous row; any break in the
walk indicates tampering, truncation, or reordering.
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9.3. Bundle Forgery
A screening provider MAY sign a selective-disclosure audit bundle
with an HMAC-SHA256 over the JCS-canonical bytes of the bundle (minus
the signature field). The shared signing key is the proof-of-
emission secret; verifiers possessing the key can confirm that the
bundle was emitted by the holder of the key.
This document does not REQUIRE bundle signing -- the per-row content
hashes and chain linkage already provide tamper detection -- but it
RECOMMENDS bundle signing for selective-disclosure exchanges where
the verifier must distinguish "bundle emitted by the screening
provider" from "bundle reconstructed from elsewhere."
9.4. Operator Continuity Loss
The in-band canon_version pin (Section 3.6) ensures that re-
verification does not require operator continuity. If the screening
provider ceases operations, retained chains remain verifiable: the
rule named by canon_version is publicly documented and stable.
9.5. DID Resolution Compromise
The screen_provider_did is a Decentralised Identifier. Verifiers
SHOULD resolve it through multiple resolvers (where the DID method
supports multi-resolver patterns) and confirm consistency before
accepting public key material for signature verification on
selective-disclosure bundles.
9.6. Privacy
The privacy analysis in this section follows the framework of
[RFC6973]. The payer_ref content-addressed reference and the
selective-disclosure mechanism (Section 5.3) are designed to support
the data-minimisation principle described therein.
The payer_ref content-addressed reference does not by itself leak
identity content. A receipt holder presenting the receipt out-of-
band can also present the underlying identity object; the receipt
holder chooses when and to whom to disclose identity. This is the
selective-disclosure pattern that justifies the content-addressed
reference design.
Implementations MUST NOT log cleartext identity content alongside
receipts in the chain. Implementations MUST NOT recover the
underlying identity object from payer_ref alone -- the reference is a
one-way hash.
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9.7. Choice of Canonicalisation Scheme
JCS [RFC8785] is an Independent Submission Informational RFC. It is
cited normatively here because the canon_version mechanism in
Section 3.6 depends on the specific byte-level canonicalisation rules
defined in JCS. JCS was selected over alternatives (such as RFC 8259
with locally specified ordering rules) because it provides a cross-
implementation byte-deterministic canonicalisation discipline that
has been validated across five independent implementations in four
programming languages, making the long-term re-verification property
of Section 6 reproducible by independent verifiers without relying on
AlgoVoi-provided tooling.
10. References
10.1. Normative References
[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>.
[RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
(URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
<https://www.rfc-editor.org/info/rfc8141>.
[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>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8785] Rundgren, A., Jordan, B., and S. Erdtman, "JSON
Canonicalization Scheme (JCS)", RFC 8785,
DOI 10.17487/RFC8785, June 2020,
<https://www.rfc-editor.org/info/rfc8785>.
10.2. Informative References
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
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Appendix A. Regulatory frameworks cited as examples
The regulatory frameworks referred to in Section 1.2 as examples are
accessible at the following official sources. These are cited as
illustrative examples of the framework-bound retention obligations
the receipt format is designed to satisfy; they are not normative
references.
* HM Treasury, "The Money Laundering, Terrorist Financing and
Transfer of Funds (Information on the Payer) Regulations 2017", SI
2017/692, 2017, https://www.legislation.gov.uk/uksi/2017/692/
contents (https://www.legislation.gov.uk/uksi/2017/692/contents).
* UK Parliament, "Proceeds of Crime Act 2002", Chapter 29, 2002,
https://www.legislation.gov.uk/ukpga/2002/29/contents
(https://www.legislation.gov.uk/ukpga/2002/29/contents).
* European Parliament and of the Council, "Directive (EU) 2018/843",
OJ L 156, 19.6.2018, https://eur-lex.europa.eu/eli/dir/2018/843/oj
(https://eur-lex.europa.eu/eli/dir/2018/843/oj).
* European Parliament and of the Council, "Directive (EU)
2018/1673", OJ L 284, 12.11.2018, https://eur-
lex.europa.eu/eli/dir/2018/1673/oj (https://eur-
lex.europa.eu/eli/dir/2018/1673/oj).
* European Parliament and of the Council, "Regulation (EU) 2023/1114
on Markets in Crypto-Assets", OJ L 150, 9.6.2023, Article 80,
https://eur-lex.europa.eu/eli/reg/2023/1114/oj (https://eur-
lex.europa.eu/eli/reg/2023/1114/oj).
* European Parliament and of the Council, "Regulation (EU) 2024/1624
on Anti-Money Laundering", OJ L 2024/1624, 19.6.2024, Article 56,
https://eur-lex.europa.eu/eli/reg/2024/1624/oj (https://eur-
lex.europa.eu/eli/reg/2024/1624/oj).
* European Parliament and of the Council, "Regulation (EU) 2022/2554
on Digital Operational Resilience", OJ L 333, 27.12.2022, Article
14, https://eur-lex.europa.eu/eli/reg/2022/2554/oj (https://eur-
lex.europa.eu/eli/reg/2022/2554/oj).
The companion individual Internet-Draft draft-vauban-x402-stark-
receipts is a work in progress on the IETF datatracker with stream
unassigned at the time of writing. The x402 protocol substrate
referenced throughout this document is maintained in the working
repository x402-foundation/x402 on GitHub; readers seeking current
substrate specification text should consult the project's
specification directory rather than any individual revision of a
working repository pull request.
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Appendix B. Examples (Informative)
The following example receipts illustrate the format. All three are
syntactically valid under the JSON Schema at
https://json.schemastore.org/algovoi-compliance-receipt-v1.json
(https://json.schemastore.org/algovoi-compliance-receipt-v1.json).
B.1. ALLOW under UK + EU joint jurisdiction
{
"payer_ref": "sha256:0dd5d0b76c9b9281...0f",
"screen_result": "ALLOW",
"screen_timestamp_ms": 1716460800000,
"screen_provider_did": "did:example:screening-provider-1",
"jurisdiction_flags": ["UK", "EU"],
"canon_version": "jcs-rfc8785-v1"
}
B.2. REFER under UK with mandatory SAR obligation
{
"payer_ref": "sha256:4b781b0d3f8a82c5...72",
"screen_result": "REFER",
"screen_timestamp_ms": 1716460800050,
"screen_provider_did": "did:example:screening-provider-1",
"jurisdiction_flags": ["UK"],
"canon_version": "jcs-rfc8785-v1"
}
Per Section 3.2: institutions in the regulated sector emitting a
REFER under a UK jurisdiction MUST file a SAR with the UK National
Crime Agency per UK POCA 2002 Section 330.
B.3. DENY under sanctions match across UK + EU + US
{
"payer_ref": "sha256:10779e0aeb2e1d3a...38",
"screen_result": "DENY",
"screen_timestamp_ms": 1716460800100,
"screen_provider_did": "did:example:screening-provider-1",
"jurisdiction_flags": ["UK", "EU", "US"],
"canon_version": "jcs-rfc8785-v1"
}
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Appendix C. Reference Implementations (Informative)
The following open-source packages implement the format specified in
this document. None of these implementations is privileged; the
format is fully specified by Section 3.
* algovoi-substrate (Python) on PyPI: https://pypi.org/project/
algovoi-substrate/ (https://pypi.org/project/algovoi-substrate/)
Provides build_compliance_receipt(), action_ref(), and the JCS
canonicalisation primitive. Apache 2.0 licensed.
* @algovoi/substrate (TypeScript) on npm:
https://www.npmjs.com/package/@algovoi/substrate
(https://www.npmjs.com/package/@algovoi/substrate) Byte-for-byte
parity with the Python sibling. Apache 2.0 licensed.
* algovoi-audit-verifier (Python) on PyPI: https://pypi.org/project/
algovoi-audit-verifier/ (https://pypi.org/project/algovoi-audit-
verifier/) Implements the audit-chain verification logic
(Section 5.2) including per-row content_hash recomputation and
chain linkage walk. MIT licensed.
* @algovoi/audit-verifier (TypeScript) on npm:
https://www.npmjs.com/package/@algovoi/audit-verifier
(https://www.npmjs.com/package/@algovoi/audit-verifier) Byte-for-
byte parity with the Python verifier. MIT licensed.
Cross-implementation conformance vectors are published at:
https://github.com/chopmob-cloud/algovoi-jcs-conformance-vectors
(https://github.com/chopmob-cloud/algovoi-jcs-conformance-vectors)
The JSON Schema (draft-07) at https://json.schemastore.org/algovoi-
compliance-receipt-v1.json (https://json.schemastore.org/algovoi-
compliance-receipt-v1.json) is mirrored at the same repository.
Appendix D. Acknowledgments
This document builds on a canonicalisation discipline maintained in
the x402 protocol substrate. The framework-bound-retention scoping
clause in that discipline was contributed by FeedOracle. A receipt-
format fixture compatible with this document is maintained within the
x402 protocol substrate by the Vauban Pay team and references the
AlgoVoi production schema as its source.
Author's Address
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Christopher Hopley
AlgoVoi
United Kingdom
Email: chopmob@gmail.com
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