Internet-Draft Cedulon August 2026
Dogru Expires 27 February 2027 [Page]
Workgroup:
Network Working Group
Internet-Draft:
draft-dogru-cedulon-00
Published:
Intended Status:
Informational
Expires:
Author:
E. C. Dogru
VERAX TEKNOLOJI LIMITED SIRKETI

Cedulon: An Audit Layer for Agent-to-Agent Commerce

Abstract

This document defines the Cedulon Protocol, an audit layer for agent-to-agent commerce. Payment rails such as HTTP 402 flows (x402) and mandate protocols (AP2) already move value. They do not, by themselves, produce a fail-closed policy check and a signed spend receipt that a verifier can reconcile against a rail extract. Cedulon specifies a Trade Manifest (signed offer before payment), a Policy Decision Point with default deny, a Spend Receipt (COSE/CWT claim set after a gated payment), epoch checkpoints, and rail-extract reconciliation that proves completeness against an authenticated rail extract. It also defines a Dispute Evidence Bundle (evidence, not an award) and optional SCITT anchoring. Cedulon is not a competitor to x402 or AP2; it sits above them.

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/.

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 February 2027.

1. Introduction

Note to Readers: This document is submitted as Informational. The author's eventual intended track, if the work is taken up, is a Standards Track profile of COSE [RFC9052] and CWT [RFC8392] for agent-spend receipts. This -00 does not claim IETF consensus.

Agents can now pay. Open HTTP 402 protocols attach stablecoin settlement to ordinary requests. Card networks and processors issue agent-scoped tokens. Google's Agent Payments Protocol (AP2) binds user intent to signed mandates.

What is missing is an interoperable audit layer: a machine-checkable answer to "was this spend allowed by policy, against which offer, and what bytes were delivered?" Without that layer, a prompt-injected or looping agent can drain a rail that has already accepted a valid signature. A counterparty can ship the wrong artifact. A transparency log, if used at all, is proprietary.

Cedulon fills that gap. It does not clear funds, hold custody, or operate a payment facilitator. An optional escrow actor is defined only as a third-party role interface (Section 14.1). Implementations of this specification MUST NOT take custody of funds or operate escrow (MUST-T8-custody).

The completeness claim sits in a long bookkeeping line. Single-entry records (clay tablets, journals) listed events in one place and could not check themselves. Double-entry bookkeeping, set out by Pacioli in 1494 [PACIOLI], posts each event to two books so that the books can check each other. Cedulon is a later step: proven completeness, where an external witness (the authenticated rail extract) is machine-checkable against signed spend receipts. Grigg's triple-entry idea (signed receipts as the third entry) is [GRIGG]. Cedulon's addition is the completeness and reconciliation proof plus an open standard profile, not a claim to be first.

Neighbor drafts are complementary, not substitutes. draft-bates-atp [BATES-ATTP] covers tamper-evident causal lineage as a signed DAG. Cedulon is the completeness layer: a spend that never produced a receipt is visible when an authenticated rail extract is reconciled (MUST-T10-1).

2. Terminology

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.

The following terms are used:

Trade Manifest:

A signed statement produced before payment. It binds a description of goods or service, price, currency, acceptance-criteria hash, cancel condition, expiry, and an optional AP2 mandate reference.

Policy Decision Point (PDP):

The function that evaluates a structured spend request against stored policy. The default is deny.

Spend Receipt:

A signed statement produced after a gated payment attempt. It binds payer, payee, amount, currency, policy hash, manifestHash or an explicit noManifest flag, rail payment reference, timestampMs, nonce, prevReceiptHash, and outcome.

Receipt Issuer:

The party that signs Spend Receipts.

Anchor:

An optional SCITT Transparency Service [RFC9943] that registers a signed statement and returns a COSE receipt [RFC9942].

Dispute Evidence Bundle:

A package of the Trade Manifest, the Spend Receipt, and a delivery hash. It is evidence for a later human or legal process. It is not an arbitral award and not an escrow release.

Decision Token:

A portable, single-use PDP allow encoded as COSE_Sign1. The claim set binds requestHash, policyHash, expiryMs, nonce, and singleUseId. See Section 7.

Rail Extract:

An authenticated list of settlement records for one account, one rail, and one time window. See Section 8.

3. Architecture

Cedulon has three control-plane objects and one optional log:

  Principal --policy--> PDP --allow/deny--> x402/AP2 rail
                              |
                              v
                      Receipt Issuer --> Spend Receipt
                              |
                              v
                      Anchor / SCITT (optional)

The payer agent never talks to the rail except through an adapter that calls the PDP first (MUST-T5-1).

3.1. Policy Decision Point

The PDP evaluates structured fields only (MUST-T1-1): amount, currency, payee, tool identifier, nonce, optional manifest hash, and evaluation time. It applies limit, velocity, and scope checks (MUST-T2-1, MUST-T2-2). If the PDP is unreachable, uninitialized, or throws, the result is deny (MUST-T2-3). Denied attempts do not increment success counters (MUST-T2-4).

An allow produces a Decision Token whose requestHash covers six fields: amount, currency, payee, tool, nonce, and manifestHash (MUST-T3-4, MUST-T6-1). The token is a COSE_Sign1 object (MUST-T6-4), is single-use (MUST-T6-2), and MAY be carried to the adapter that performs settlement.

3.2. Receipt Issuer

After the adapter attempts settlement (success or a recorded deny that still needs an audit trail for an allowed-then-aborted path), the Receipt Issuer signs a Spend Receipt over a canonical encoding (MUST-T4-1). Verifiers reject bad signatures and byte mismatch (MUST-T4-2).

3.3. Anchor / SCITT

Parties MAY register the signed receipt (or a privacy-preserving hash encoding) as a SCITT Signed Statement [RFC9943] and attach the COSE receipt (MAY-T4-6). This document does not operate a Transparency Service.

4. Trade Manifest

A Trade Manifest is the commerce analogue of a promise: it is issued before value moves. It is conceptually symmetric to a later Spend Receipt (promise then proof), and it MAY carry an AP2 mandate hash so that user intent and the Cedulon offer stay linked (SHOULD-T8-5).

A Trade Manifest MUST bind all of the following (MUST-T8-1):

  • goods or service description

  • price (integer minor units, encoded as a decimal string matching 0|[1-9][0-9]*)

  • currency (ISO 4217 alphabetic or a documented token identifier)

  • acceptance-criteria hash (SHA-256 [RFC6234] of the exact delivery bytes or of a declared schema instance)

  • cancel condition (opaque string agreed by the parties)

  • expiry (POSIX milliseconds, expiresAtMs)

It MAY include ap2MandateHash. The corresponding CBOR label is always present; a missing mandate is encoded as CBOR null.

The manifest is COSE_Sign1 [RFC9052] over a deterministic CBOR claim map (Section 6). manifestHash is the SHA-256 of the signed COSE bytes (MUST-T8-7). A spend bound to a manifest MUST be denied if the requested amount or currency differs from the manifest (MUST-T8-2) or if the manifest is expired (MUST-T3-3).

A spend that is not bound to a verified manifest MUST be marked noManifest on the receipt and MUST still pass limit, velocity, and scope checks (MUST-T1-2). An implementation MAY refuse all noManifest spend (MAY-T1-4).

5. Spend Receipt

The Spend Receipt claim set is carried in COSE_Sign1 [RFC9052] wrapping a CWT-compatible map [RFC8392]. New receipts MUST use the COSE profile (Section 6).

Claims (MUST-T4-3, MUST-T4-4, MUST-T4-7):

Table 1
Claim Description
payer Payer agent identifier
payee Payee identifier
amount Minor units as a decimal string 0|[1-9][0-9]*
currency Currency identifier
policyHash SHA-256 of the canonical policy document (lowercase hex)
manifestHash SHA-256 of the signed manifest COSE bytes, or null when noManifest is true
noManifest Boolean; MUST be true if and only if manifestHash is null
x402PaymentRef Rail payment reference, or null
timestampMs POSIX milliseconds
nonce Unique spend nonce; at least 128 bits of randomness; unique in the issuer scope
prevReceiptHash Previous receipt hash, or null for the first receipt (SHOULD-T4-5)
outcome settled or aborted

A receipt with outcome = settled MUST have a non-null x402PaymentRef (MUST-T4-7). An aborted receipt MUST NOT be added into checkpoint totals.

All twelve labels in Section 6.1 are always present. An empty optional value is encoded as CBOR null, never by omitting the label.

receiptHash is the SHA-256 of the receipt's signed COSE bytes, encoded as lowercase hex.

Verifiers MUST reject a receipt if the signature fails or if the decoded claim map does not match the presented claims (MUST-T4-2).

5.1. Optional payee countersignature

A payee MAY attach a countersignature over the issuer's signed Spend Receipt (MAY-T8-9). The profile uses a detached COSE_Sign1 [RFC9052] whose payload is a CBOR map with a single private-use label:

Table 2
Label Claim CBOR type
-70401 receiptCose bstr (exact issuer COSE_Sign1 bytes)

The countersignature uses the header profile in Section 6 and content type application/cedulon-countersign+cbor.

This is a second Sign1 object, not RFC 9052 Countersignature0 (unprotected-header label 11). Countersignature0 would write into the issuer object and change receiptHash after issue, breaking the receipt chain. A detached Sign1 keeps the issuer bytes stable, reuses kid and content-type, and is absent by simply omitting the sibling object.

Absence of a countersignature MUST NOT invalidate the issuer receipt (MAY-T8-9). If a countersignature is present, a verifier MUST reject it when the signature fails, when kid or content type does not match the configured payee key, or when label -70401 is not the issuer COSE bytes (MUST-T8-8). A Dispute Evidence Bundle that includes a verified countersignature has stronger evidence that the payee accepted those bytes; the bundle is still not an award (MUST-T8-4).

6. COSE Profile

This profile uses deterministic CBOR [RFC8949] Section 4.2.1 (definite lengths, shortest integer form, map keys sorted in bytewise lexicographic order of their encoded keys). Implementations MUST encode only the types used by Cedulon claim maps: null, bool, unsigned and negative integers, UTF-8 text, byte strings, arrays, and maps (MUST-T4-1).

6.1. Claim labels

Registered CWT claims [RFC8392] are not required in -00. Cedulon uses CWT private-use integer labels less than -65536 so that the profile does not occupy the 100-110 registry range.

Receipt labels (MUST-T4-3, MUST-T4-4, MUST-T4-7):

Table 3
Label Claim CBOR type
-70001 payer tstr
-70002 payee tstr
-70003 amount tstr
-70004 currency tstr
-70005 policyHash tstr (lowercase hex SHA-256)
-70006 manifestHash tstr / null
-70007 noManifest bool
-70008 x402PaymentRef tstr / null
-70009 timestampMs uint
-70010 nonce tstr
-70011 prevReceiptHash tstr / null
-70012 outcome tstr (settled / aborted)

Checkpoint labels (MUST-T11-1):

Table 4
Label Claim CBOR type
-70101 epoch uint
-70102 startMs uint
-70103 endMs uint
-70104 receiptCount uint
-70105 chainHeadHash tstr / null
-70106 totals map tstr -> tstr
-70107 prevCheckpointHash tstr / null

Manifest labels (MUST-T8-1):

Table 5
Label Claim CBOR type
-70201 description tstr
-70202 amount tstr
-70203 currency tstr
-70204 acceptanceCriteriaHash tstr
-70205 cancelCondition tstr
-70206 expiresAtMs uint
-70207 ap2MandateHash tstr / null

Decision Token labels (MUST-T6-4):

Table 6
Label Claim CBOR type
-70301 requestHash tstr
-70302 policyHash tstr (lowercase hex SHA-256)
-70303 expiryMs uint
-70304 nonce tstr
-70305 singleUseId tstr

6.2. COSE_Sign1 headers

The protected header MUST be a deterministic CBOR map containing (MUST-T4-1, MUST-T4-8):

  • 1 (alg) = -19 (Ed25519, [RFC9864]; the generic EdDSA value -8 from [RFC9053] is deprecated for this profile)

  • 3 (content type) = a tstr that distinguishes the payload: application/cedulon-receipt+cbor, application/cedulon-checkpoint+cbor, application/cedulon-manifest+cbor, application/cedulon-decision+cbor, or application/cedulon-countersign+cbor

  • 4 (kid) = bstr, mandatory. The profile computes kid as the first eight bytes of SHA-256 over the issuer's SubjectPublicKeyInfo DER. A verifier MUST obtain the public key from an authenticated channel (preconfigured issuer set, directory, or transparency statement) and MUST reject a message whose kid does not match that key.

The unprotected header MUST be empty. The payload MUST be the CBOR encoding of the claim map. The signature is Ed25519 [RFC8032] over the COSE Sig_structure ["Signature1", protected, h'', payload].

7. Decision Token

A Decision Token is the portable encoding of a PDP allow. It is COSE_Sign1 with the header profile in Section 6 and the labels in Section 6.1. All five labels are always present (MUST-T6-4).

requestHash MUST be the six-field hash defined for the PDP (MUST-T6-1). policyHash MUST be the SHA-256 of the canonical policy document the PDP evaluated. expiryMs is a Unix time in milliseconds after which the token MUST be treated as expired (SHOULD-T6-3). nonce is the request nonce. singleUseId is the identifier consumed on the first settlement attempt (MUST-T6-2).

A party that accepts a Decision Token MUST reject it if the signature fails, if kid does not match a configured PDP key, if the content type is not application/cedulon-decision+cbor, if the decoded claim map does not match the presented claims, or if expiryMs is in the past (MUST-T6-5).

8. Rail Extract Profile

A verifier checks completeness against a rail extract, not against the issuer's own receipts alone (MUST-T10-7).

8.1. Record schema

Each settlement record MUST contain:

Table 7
Field Type
ref tstr (rail payment reference)
amount tstr matching 0|[1-9][0-9]*
currency tstr
timestampMs uint

8.2. Scope

An extract is scoped to one account identifier, one rail identifier, and one half-open time window [windowStartMs, windowEndMs).

8.3. Authentication

The mock rail in the companion implementation signs the extract with Ed25519 over a canonical encoding of the scoped body. A production verifier MUST obtain the extract from the rail or from a signature the rail published (MUST-T10-7).

If the extract is missing a verifiable signature, the verifier MUST emit finding unauthenticated-extract. Completeness findings may still be computed, but the completeness guarantee is conditional on the extract being authentic. See Section 14.

9. Reconciliation and Epoch Checkpoints

Completeness is the property that, given an authenticated rail extract, every settlement in the extract has a matching settled Spend Receipt, every settled receipt has a matching settlement, receipt and checkpoint hash chains verify, and checkpoint totals equal the sum of settled receipts in the checkpoint window. If a spend occurred without a receipt, the missing receipt is itself the evidence (MUST-T10-2).

9.1. Checkpoint claims

An epoch checkpoint MUST be COSE_Sign1-signed with the header profile in Section 6 and MUST bind all of the following (MUST-T11-1):

epoch, startMs, endMs, receiptCount, chainHeadHash, totals, and prevCheckpointHash.

The checkpoint window is half-open [startMs, endMs) (MUST-T11-7). receiptCount MUST equal the number of receipts (settled and aborted) whose timestampMs falls in that window. chainHeadHash MUST equal receiptHash of the last receipt in that window, or null if the window is empty (MUST-T11-2). totals MUST sum only receipts with outcome = settled.

9.2. Genesis and continuity

The first checkpoint in a presented chain is the genesis checkpoint of that chain. Its prevCheckpointHash MUST be null. Epoch numbers MUST be consecutive integers. Adjacent windows MUST satisfy next.startMs = prev.endMs (MUST-T11-8).

A later checkpoint that omits a prefix of earlier epochs (prefix deletion) is detectable only if an external witness (transparency log) has recorded the missing prefix (MUST-T11-9). Without that witness, T11 guarantees about suppression are conditional.

9.3. Verification algorithm

A verifier MUST perform these steps in order (MUST-T10-1, MUST-T11-2):

  1. If the rail extract signature does not verify, emit unauthenticated-extract and treat the guarantee as conditional (MUST-T10-7).

  2. Decode each Spend Receipt COSE_Sign1. Reject if Ed25519 verify fails, if kid does not match the configured issuer key, if the content type is not the receipt type, or if the decoded claim map does not match the presented claims (MUST-T4-2, MUST-T4-8).

  3. Walk receipts in issuer order. The first prevReceiptHash MUST be null. Each later prevReceiptHash MUST equal receiptHash of the previous receipt. A miss is receipt-chain-break.

  4. Index settled receipts and extract records by ref. A ref that appears more than once on either side is duplicate-ref (MUST-T10-6).

  5. For each unique ref, require a one-to-one match on ref AND amount AND currency (MUST-T10-1). Amount or currency mismatch is settlement-mismatch. A settlement with no receipt is settlement-without-receipt (MUST-T10-2). A settled receipt with no extract row is receipt-without-settlement (MUST-T10-3). A settled receipt with a null rail ref is settled-without-ref.

  6. Aborted receipts are not matched to extract rows and are not added to totals.

  7. Decode each checkpoint. Reject a failed signature. Require receiptCount, chainHeadHash, and totals to match the receipts in [startMs, endMs) as defined above (MUST-T11-2).

  8. Every chained receipt MUST fall in exactly one checkpoint window. A gap or double count is window-coverage (MUST-T11-7, MUST-T11-8).

  9. Walk checkpoints in epoch order. prevCheckpointHash MUST equal the SHA-256 of the previous checkpoint COSE bytes, or null for genesis (MUST-T11-4).

  10. If two successfully verified checkpoints share an epoch number and have different hashes, emit equivocation (MUST-T11-3).

  11. If any fail-severity finding exists, the audit MUST fail (MUST-T10-4).

9.4. Finding codes

Table 8
Code Severity Meaning
settlement-without-receipt fail Extract row has no matching settled receipt
receipt-without-settlement fail Settled receipt ref is not on the extract
settlement-mismatch fail Same ref, different amount or currency
duplicate-ref fail Ref appears more than once on one side
settled-without-ref fail outcome is settled and x402PaymentRef is null
receipt-chain-break fail Signature or prevReceiptHash failed
checkpoint-total-mismatch fail Totals, count, signature, or checkpoint chain failed
checkpoint-head-mismatch fail chainHeadHash is not the last in-window receipt
equivocation fail Two distinct hashes for one epoch
window-coverage fail Gap, overlap, or non-adjacent / non-consecutive windows
unauthenticated-extract warn Extract has no verifiable signature; guarantee is conditional
countersign-bad fail Present payee countersignature failed verify

Checkpoints SHOULD be registered with a Transparency Service (SHOULD-T11-5). A test deployment MAY use an in-process append-only log as the witness (MAY-T11-6). Cedulon still MUST NOT take custody.

10. Lifecycle

  1. Manifest. Parties sign a Trade Manifest (optional for metered API spend; required for goods with acceptance criteria).

  2. Policy check. The adapter submits a structured request to the PDP. Default is deny. An allow is a Decision Token (MUST-T6-4).

  3. Payment. On allow, the adapter performs the x402 (or other rail) exchange using exactly the decision fields (MUST-T6-1). The Decision Token is consumed (MUST-T6-2). A reused nonce is denied (MUST-T3-1, MUST-T3-2). A tampered or expired token is denied (MUST-T6-5).

  4. Receipt. The Receipt Issuer signs a Spend Receipt. Rail credentials MUST NOT appear in the receipt, logs, or tool results (MUST-T5-2, MUST-T7-1).

  5. Dispute Evidence Bundle. If delivery bytes do not match the acceptance-criteria hash, an implementation MUST be able to emit a bundle of manifest + receipt + delivery hash (MUST-T8-3). The bundle MUST NOT be described as an arbitral award or escrow release (MUST-T8-4).

11. Policy Semantics

Policy is default deny. The engine understands three families of rule:

  • Limit: maximum amount per payment; maximum cumulative amount per window (MUST-T2-2).

  • Velocity: maximum number of allowed payments per window (MUST-T2-1).

  • Scope: optional allow-lists for payee, currency, and tool name.

Fail-closed: missing engine, crash, or exception yields deny (MUST-T2-3). Implementations SHOULD emit stable reason codes (SHOULD-T2-5). Decision tokens SHOULD expire after a short TTL (SHOULD-T6-3).

The agent-facing spend interface MUST invoke the PDP and MUST NOT expose a parallel ungated rail call to the model (MUST-T5-1).

12. SCITT Anchoring

A Receipt Issuer or relying party MAY construct a SCITT Signed Statement whose payload is either the Spend Receipt COSE object or a privacy profile (Section 13) and register it with a Transparency Service [RFC9943]. The service returns a COSE receipt [RFC9942]. Embedding that receipt yields a Transparent Statement. Cedulon does not define a new transparency algorithm.

13. Privacy Considerations

A public transparency encoding MUST support omitting or hashing payer and payee identifiers and MUST support amount redaction or bucket encoding (MUST-T9-1). Implementations MUST NOT write government-ID numbers, payment-instrument PAN, or street address into a public statement (MUST-T9-2). Default public anchors SHOULD publish policyHash, manifestHash, receiptHash, and timestampMs rather than full claims (SHOULD-T9-3). A private auditor MAY receive an unredacted receipt out of band (MAY-T9-4).

14. Security Considerations

This section is authoritative for the protocol requirements in this document. The companion repository file THREAT_MODEL.md is informative and MUST NOT be read as overriding this section.

Prompt injection (T1):

The PDP MUST use structured fields only (MUST-T1-1). Unbound spend MUST be noManifest and still gated (MUST-T1-2). Hosts SHOULD confirm first-use payees (SHOULD-T1-3).

Runaway spend (T2):

Velocity and limits are mandatory (MUST-T2-1, MUST-T2-2). Fail-closed deny on engine fault (MUST-T2-3). Denied attempts MUST NOT count as success (MUST-T2-4).

Replay (T3):

Unique nonce on allow (MUST-T3-1); reuse denied (MUST-T3-2); expired manifest denied (MUST-T3-3); single-use hashed decision (MUST-T3-4). Nonce stores SHOULD persist outside tests (SHOULD-T3-5).

Forgery (T4):

Signed canonical receipts (MUST-T4-1, MUST-T4-2) with the claim set in MUST-T4-3, MUST-T4-4, and MUST-T4-7. Protected-header kid is mandatory (MUST-T4-8). Hash chaining is recommended (SHOULD-T4-5).

Bypass (T5):

Single gated interface (MUST-T5-1). No rail secrets in prompts (MUST-T5-2). Hosts SHOULD isolate the PDP (SHOULD-T5-3).

TOCTOU (T6):

Settlement fields MUST match the six-field decision hash (MUST-T6-1). The allow is a COSE_Sign1 Decision Token (MUST-T6-4) consumed on first use (MUST-T6-2). A failed signature or expired token MUST be rejected (MUST-T6-5).

Key leakage (T7):

Secret key material MUST NOT appear in artifacts (MUST-T7-1). Examples MUST use mock keys (MUST-T7-2). Production SHOULD use an HSM or OS key store (SHOULD-T7-3).

Counterparty (T8):

Manifest bind (MUST-T8-1, MUST-T8-2). Evidence bundle (MUST-T8-3) is not an award (MUST-T8-4). manifestHash is the SHA-256 of the signed COSE bytes (MUST-T8-7). A present payee countersignature MUST verify (MUST-T8-8); absence is allowed (MAY-T8-9).

Privacy (T9):

See Section 13.

Rail bypass completeness (T10):

Verifiers MUST reconcile an authenticated extract to receipts with one-to-one ref+amount+currency matching (MUST-T10-1, MUST-T10-6, MUST-T10-7) and MUST fail the audit when any fail-severity finding exists (MUST-T10-4). See Section 9.

Checkpoint suppression (T11):

Checkpoints MUST be signed and chained (MUST-T11-1, MUST-T11-4). Totals, count, and chainHeadHash MUST match the half-open window (MUST-T11-2, MUST-T11-7). Equivocation MUST be reported (MUST-T11-3). Continuity and prefix-deletion detection that go beyond the presented chain are conditional on an external transparency witness (MUST-T11-9).

Issuer self-attestation:

A Receipt Issuer that also produces the only copy of the extract can omit settlements. Completeness holds only against an extract the verifier obtained from the rail or from a rail signature.

Key rotation and revocation:

kid identifies the verification key. This -00 does not specify a revocation list. Verifiers MUST pin the issuer keys they accept and MUST stop accepting a kid after an authenticated revocation signal.

Timestamp trust:

timestampMs is issuer-asserted. Window assignment uses that field. A lying issuer can slide a receipt between windows. External timestamping or a transparency log is out of scope for -00.

Collusion:

If the rail operator and the issuer collude, they can publish a matching extract and receipt set that hides a real-world settlement. Cedulon does not detect extract-external agreement.

Reversal, refund, and partial settlement:

State machines for reversal, refund, and partial settlement are out of scope for -00 and are expected in -01.

14.1. Optional escrow role

Parties MAY name an escrow actor in a Trade Manifest as a third-party role that holds funds under rules outside this protocol (MAY-T8-6). Implementations of this specification MUST NOT take custody or operate escrow (MUST-T8-custody).

15. IANA Considerations

This document has no IANA actions. Private-use CWT labels below -65536 are used so that a registry assignment is not required for -00.

16. Implementation Status

RFC 7942 [RFC7942] note: a companion implementation with a runnable verification suite is published at https://github.com/dogrucanemek-alt/cedulon. The code is a profile of this document, not a second specification. This -00 is not an IETF working-group item.

17. Evolution and Future Work (Informative)

This section is a direction, not a commitment. The structures below are reserved in name only. Normative wire formats, tests, and threat-model MUST lines for them belong in later revisions (-01 or -02), written with the same discipline as this -00.

17.1. Re-attestation profile

Algorithms retire. A Spend Receipt or checkpoint signed under Ed25519 today may need a later verifier that no longer accepts -19. A companion seed [REATTEST] sketches re-attestation: register the original COSE bytes as a SCITT Signed Statement and have a current algorithm countersign or receipt them. The principle is that structures outlive ciphers. The first concrete example is the profile's own move from generic EdDSA (-8) to Ed25519 (-19) in [RFC9864].

17.2. Streaming reconciliation

Epoch checkpoints in this document are batch windows. A later revision (-02) may define a continuous, second-scale profile [STREAMING] in which the same completeness relation is evaluated as settlements arrive, without waiting for an epoch close. That work does not change the -00 matching rules.

17.3. Generalization

Payment is the special case that this -00 implements. The same completeness calculus (an authenticated extract of consumed units reconciled to signed receipts) can apply to other consumable resources such as compute, data, or energy. This document does not specify those profiles.

18. Informative Notes on Adjacent Protocols

x402 uses HTTP 402 [RFC9110] to negotiate stablecoin payment. AP2 uses signed mandates as verifiable credentials. Cedulon does not replace either protocol. Profiles built on HTTP Message Signatures [RFC9421] authenticate bots; they are not a spend receipt. draft-bates-atp [BATES-ATTP] is a lineage neighbor. It does not define rail-extract completeness.

draft-vauban-x402-stark-receipts [VAUBAN] specifies complementary x402 receipt-format variants that a Cedulon Spend Receipt MAY carry as a rail proof; it does not define rail-extract completeness. draft-schrock-ep-outcome-binding [SCHROCK] compares authorized action bytes to independently observed effects; it does not define rail-extract completeness. draft-marques-asqav-compliance-receipts [MARQUES] profiles access-control action receipts (the broader Acta family includes [ACTA]); it does not define rail-extract completeness. draft-hopley-x402-compliance-receipt [HOPLEY] records an admission-time compliance decision; it does not define rail-extract completeness.

19. References

19.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC6234]
Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI 10.17487/RFC6234, , <https://www.rfc-editor.org/rfc/rfc6234>.
[RFC8032]
Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital Signature Algorithm (EdDSA)", RFC 8032, DOI 10.17487/RFC8032, , <https://www.rfc-editor.org/rfc/rfc8032>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8392]
Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, , <https://www.rfc-editor.org/rfc/rfc8392>.
[RFC8949]
Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, , <https://www.rfc-editor.org/rfc/rfc8949>.
[RFC9052]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", STD 96, RFC 9052, DOI 10.17487/RFC9052, , <https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9053]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053, , <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9864]
Jones, M.B. and O. Steele, "Fully-Specified Algorithms for JSON Object Signing and Encryption (JOSE) and CBOR Object Signing and Encryption (COSE)", RFC 9864, DOI 10.17487/RFC9864, , <https://www.rfc-editor.org/rfc/rfc9864>.
[RFC9942]
Steele, O., Birkholz, H., Delignat-Lavaud, A., and C. Fournet, "CBOR Object Signing and Encryption (COSE) Receipts", RFC 9942, DOI 10.17487/RFC9942, , <https://www.rfc-editor.org/rfc/rfc9942>.
[RFC9943]
Birkholz, H., Delignat-Lavaud, A., Fournet, C., Deshpande, Y., and S. Lasker, "An Architecture for Trustworthy and Transparent Digital Supply Chains", RFC 9943, DOI 10.17487/RFC9943, , <https://www.rfc-editor.org/rfc/rfc9943>.

19.2. Informative References

[ACTA]
Farley, T., "Signed Decision Receipts for Machine-to-Machine Access Control", , <https://datatracker.ietf.org/doc/draft-farley-acta-signed-receipts/>.
[BATES-ATTP]
Bates, D., "Agent Transaction Protocol (ATP)", , <https://datatracker.ietf.org/doc/draft-bates-atp/00/>.
[GRIGG]
Grigg, I., "Triple Entry Accounting", , <https://iang.org/papers/triple_entry.html>.
[HOPLEY]
Hopley, C., "Categorical Compliance Screening Receipt Format for Agentic-Payment Flows", , <https://datatracker.ietf.org/doc/draft-hopley-x402-compliance-receipt/>.
[MARQUES]
Gomes Marques, J. A., "Compliance Profile of Signed Action Receipts for AI Agents", , <https://datatracker.ietf.org/doc/draft-marques-asqav-compliance-receipts/>.
[PACIOLI]
Pacioli, L., "Summa de arithmetica, geometria, proportioni et proportionalita", .
[REATTEST]
Dogru, E. C., "Cedulon Re-Attestation: Carrying Spend Evidence Across Algorithm Retirement", , <https://github.com/dogrucanemek-alt/cedulon/blob/master/spec/draft-dogru-cedulon-reattestation-00.md>.
[RFC7942]
Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, , <https://www.rfc-editor.org/rfc/rfc7942>.
[RFC9110]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9421]
Backman, A., Ed., Richer, J., Ed., and M. Sporny, "HTTP Message Signatures", RFC 9421, DOI 10.17487/RFC9421, , <https://www.rfc-editor.org/rfc/rfc9421>.
[SCHROCK]
Schrock, I., "Outcome Binding for Authorized Actions and Independently Observed Effects", , <https://datatracker.ietf.org/doc/draft-schrock-ep-outcome-binding/>.
[STREAMING]
Dogru, E. C., "Cedulon Streaming Reconciliation: Continuous Completeness for Agent Spend", , <https://github.com/dogrucanemek-alt/cedulon/blob/master/spec/draft-dogru-cedulon-streaming-00.md>.
[VAUBAN]
Vauban Research, "x402 STARK Receipt Format Extension", , <https://datatracker.ietf.org/doc/draft-vauban-x402-stark-receipts/>.

Acknowledgments

Field survey notes and the informative threat-model table in the companion repository helped shape the MUST identifiers used here.

Appendix A. Test Vectors

These vectors use RFC 8032 Ed25519 secret scalar #1 (fixture only; never a production key). Hex is lowercase. They MUST match the locked tests in the companion implementation.

Receipt COSE_Sign1:

Claims: payer=payer-1, payee=payee-1, amount=1, currency=USD, policyHash=aa, manifestHash=null, noManifest=true, x402PaymentRef=null, timestampMs=1700000000000, nonce=n100000000000000, prevReceiptHash=null, outcome=aborted.

COSE_Sign1 hex (whitespace ignored; identical to the locked test):

845830a301320378206170706c69636174696f6e2f636564756c6f6e2d
726563656970742b63626f72044806e3fd8fda29bb60a0587cac3a0001
11706770617965722d313a000111716770617965652d313a0001117261
313a00011173635553443a000111746261613a00011175f63a00011176
f53a00011177f63a000111781b0000018bcfe568003a00011179706e31
30303030303030303030303030303a0001117af63a0001117b6761626f
727465645840685c01aa778a850b9d35250406f092b6f5cb03fb359593
0422533e28ac620ad439f5e7bd8ed1fa5ded90d4421a2de34f94d1d78d
38a65812cb5315ee7f1cf403

Manifest COSE_Sign1:

Body: description=fixture-goods, amount=1, currency=USD, acceptanceCriteriaHash=00, cancelCondition=none, expiresAtMs=1700000000000, ap2MandateHash=null.

COSE_Sign1 hex (whitespace ignored; identical to the locked test):

845831a301320378216170706c69636174696f6e2f636564756c6f6e2d
6d616e69666573742b63626f72044806e3fd8fda29bb60a0584aa73a00
0112386d666978747572652d676f6f64733a0001123961313a0001123a
635553443a0001123b6230303a0001123c646e6f6e653a0001123d1b00
00018bcfe568003a0001123ef65840898628b1524a44ca641b5058c7a4
7e71bd4ce1ca0782e03b511c23e0819c3771407d627216d0b104224ee8
2cacffbd21e66fe035ed5ce4ee85b7bcd9c560ad02

Author's Address

Emek Can Dogru
VERAX TEKNOLOJI LIMITED SIRKETI