803bf7f021
What WAI lacks is not verifiability. An Ed25519 signature over a group Merkle root is checkable by anyone holding the publisher key, and jwp-receipts §3 says exactly how. Three properties are missing, and none is a signature property: non-equivocation (nothing stops a publisher showing different chains to different parties — both verify), independent timestamping (a receipt says when the publisher says it was made), and detectability of suppression (a receipt never shown leaves no trace of its absence). Those are LOG properties. The family already owns both halves — a transparency log with consistency proofs exists, and JCR-1 is already the canonical receipt envelope across sibling standards. What nothing in the family has is a standardised external encoding an outside auditor's off-the-shelf tooling can verify with no bespoke verifier. So: align onto JCR-1, then emit RFC 9942 (COSE Receipts) and, where the payload rides by hash, RFC 9995 (COSE Hash Envelope) on top. Strictly additive. The JWP chain is unchanged, emissions are additional encodings of the same facts, and where an emission and the chain disagree the chain is authoritative and the emission is in error. CADENCE (§3). SCITT registers per-artifact Signed Statements over an HTTP API; WAI emits per-object receipts at media-group cadence. Forcing them together would put a registration round-trip in the per-object path, so: MUST NOT register per-object receipts individually; SHOULD register the group receipt or periodic checkpoints; and registration MUST NOT be a precondition for validity — an unregistered receipt is unwitnessed, not wrong. Uses "Relying Party" from the SCITT architecture rather than coining another term. THE HASH CONSTRAINT (§4), which is the part that would have been quietly wrong. RFC 9995's `payload_hash_alg` takes an identifier from the COSE Algorithms registry, and BLAKE3 — which jwp-receipts §2.1 uses throughout — does not appear in it. So an implementation MUST NOT emit a hash envelope naming BLAKE3 by an invented identifier; until a registration exists it MUST either omit that form or carry a second digest under a registered algorithm alongside the BLAKE3 commitment; and a dual-hash carry MUST NOT be presented as evidence that BLAKE3 is registered. Registering it is a separate action with its own process and this text does not assume the outcome. STAGE DISCIPLINE (§5). The referenced work is at mixed maturity and the table says so: architecture and COSE Receipts published, hash envelope published, SCRAPI approved and in the RFC Editor queue, and the concrete log profile in Working Group Last Call — which MUST NOT be described as ratified. §6 states what this is not: it does not replace the chain, does not make registration a trust anchor (a Transparency Service witnesses that a receipt existed, not that it is true), and does not solve key discovery — that is jwp-receipts §7, and a log entry naming an unresolvable key is still unresolvable. Ingest queue item 7 (#80 §3.6). Co-Authored-By: Claude Opus 5 <[email protected]>
5.2 KiB
WAI Extension: Transparency Emission
Status: Draft. Adds an external encoding for WAI receipts so a party with no WAI tooling can check them, and a registration profile so a receipt's existence is independently witnessed. Strictly additive: the JWP receipt chain is unchanged, and nothing here replaces it. Keywords MUST, MUST NOT, SHOULD, MAY are RFC 2119/8174.
1. What is actually missing
Not verifiability. An Ed25519 signature over a group Merkle root is checkable by
anyone holding the publisher key, and jwp-receipts §3
specifies exactly how. Three properties are missing, and none of them is a
signature property:
- Non-equivocation. Nothing prevents a publisher showing one receipt chain to one party and a different chain to another. Both verify.
- Independent timestamping. A receipt says when the publisher says it was made.
- Detectability of suppression. A receipt that was never shown to anyone leaves no trace of its absence.
These are log properties, not envelope properties, and they are why this extension exists.
2. The move, and its shape
The family already owns both halves: a transparency log with consistency proofs exists, and JCR-1 (deterministic CBOR + COSE_Sign1, RFC 9052) is already the canonical receipt envelope across sibling standards. What nothing in the family has is a standardised external encoding that an outside auditor's off-the-shelf tooling can verify with no bespoke verifier.
So the sequence is: bring WAI's receipts onto JCR-1 as its siblings already are, then emit in the standardised encodings on top.
- A WAI receipt SHOULD be expressible as a JCR-1 envelope. This is alignment with the family, not a new format.
- An implementation MAY additionally emit an RFC 9942 (COSE Receipts) encoding of a group receipt, and MAY use the RFC 9995 COSE Hash Envelope form where the payload is carried by hash rather than by value.
- These emissions are additional encodings of the same facts. An implementation MUST NOT let the JWP chain and an emitted encoding disagree, and where they do, the JWP chain is authoritative and the emission is in error.
3. What is registered, and what is not
SCITT registers per-artifact Signed Statements over an HTTP API. WAI emits per-object receipts at media-group cadence. These cadences do not match, and forcing them together would put a registration round-trip in the per-object path.
- An implementation MUST NOT register per-object receipts individually.
- An implementation SHOULD register the group receipt, or periodic checkpoints over the receipt chain, leaving the per-object receipt exactly where it is.
- Registration MUST NOT be a precondition for a receipt being valid. An unregistered receipt is a receipt whose existence is unwitnessed, not a receipt that is wrong.
The checking party is the Relying Party in the terminology of the SCITT architecture; this extension uses that term rather than coining another.
4. The hash-algorithm constraint
RFC 9995's payload_hash_alg takes an identifier from the COSE Algorithms
registry. BLAKE3 — which jwp-receipts §2.1 uses throughout — does not appear
in that registry.
This is a real constraint, not a detail to be waved through:
- An implementation MUST NOT emit a COSE Hash Envelope naming BLAKE3 by an unregistered or invented identifier. An identifier a Relying Party cannot resolve defeats the entire purpose of emitting in a standard encoding.
- Until a registration exists, an implementation MUST either omit the hash envelope form, or carry a second digest under a registered algorithm alongside the BLAKE3 commitment, stating plainly that the two cover the same bytes.
- A dual-hash carry MUST NOT be presented as evidence that BLAKE3 is registered.
Registering BLAKE3 in the COSE Algorithms registry is a separate action with its own process, and this extension does not assume its outcome.
5. Stage discipline
The referenced work is at mixed maturity, and an implementation MUST NOT present any of it as more settled than it is:
| document | status |
|---|---|
| SCITT architecture (RFC 9943) | Standards Track, published |
| COSE Receipts (RFC 9942) | Standards Track, published |
| COSE Hash Envelope (RFC 9995) | published |
| SCRAPI (registration/resolution API) | approved, in the RFC Editor queue |
| a concrete log profile | Working Group Last Call — not ratified |
An implementation MUST NOT describe the log profile as ratified, and SHOULD state which profile it registered against, since a Relying Party cannot check a proof without knowing the log's rules.
6. What this does not do
- It does not replace the JWP receipt chain, and it does not move the per-object commitment anywhere.
- It does not make registration a trust anchor. A Transparency Service witnesses that a receipt existed at a time; it does not attest that the receipt is true, and an implementation MUST NOT report registration as verification.
- It does not solve key discovery. That is
jwp-receipts§7, and a log entry naming a key the Relying Party cannot resolve is still unresolvable.