WAI Extension: Transparency Emission

Mirrored from the canonical text at commit 117bad22 (2026-10-01).

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.
• A registration MAY be recorded on the receipt chain as a log-inclusion claim (jwp-receipts §2.4.7): its subject is the registered receipt’s link hash, and its body carries the Transparency Service’s receipt verbatim with the profile it was registered against. Accepting that claim is not verifying the inclusion (§6).
• An origin that publishes a key log (jwp-receipts §7) SHOULD register each revision as it registers group receipts. A fork in the log is then visible to every Relying Party that checks the log, not only to one that happened to hold both branches. The registration witnesses a revision; it does not anchor the origin (§6).

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:

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. jwp-receipts §7 does, for a signer that names its web origin and publishes its keys there. A log entry naming a key the Relying Party cannot confirm under that section is still unconfirmed, and registering a key-log revision witnesses it without anchoring the origin.