open-standards/wai/extensions/provenance.md

WAI Extension: Asset Provenance

Status: Draft. Lever 4 — content-addressing + receipts + measured energy for content that cannot be reduced to instructions. WAI does not reconstruct the asset; it carries the opaque bytes and a signed, energy-accounted lineage. Conformance is content-hash-equivalence (recompute, compare) + signature validity. Reference impl: the provenance feature of wai-rs; tooling: wai_prov; live sink: wai.transaction.science/provenance. Keywords MUST, MUST NOT, SHOULD, MAY are RFC 2119/8174.

1. Scope and model

A wai.asset.provenance object is not a content capability — it is a JWP receipt profile about a carried asset, the way jwp-receipts is. The asset itself declares an ordinary capability (wai.image.jpeg, wai.audio.flac, …) and WAI carries it unchanged; the provenance receipt adds three things the carried bytes do not have on their own:

1. Tamper-evidence — the asset is content-addressed (asset_content_hash, BLAKE3 over the complete WAI envelope); a verifier recomputes it and compares.
2. Lineage — an ordered chain of processing steps, each binding its input and output content hashes, signed as one group.
3. Energy accounting — each step carries its measured/declared microjoules; the receipt totals them.

This is the "verifies whatever it carries" half of the thesis, for the content the reconstruct half cannot touch. WAI never decodes the asset — a sink hands the bytes to whatever native element renders that media.

In scope: the step model, the AssetReceipt group, the verification obligations. Out of scope: a transport; a capture device; the asset's own codec (it is opaque here).

2. The step

A ProvStep is one transformation in the asset's lineage:

field	meaning
op	operation, e.g. "origin.synthesize", "encode.jpeg", "derive.thumbnail"
input_hash	content hash of the input (all-zero for an originating step)
output_hash	content hash of the output
work	exact deterministic work (pixels, samples)
joules_micro	measured/carried microjoules; 0 is the unmetered marker, never 0 J (energy-measurement §2)

Step content hash: BLAKE3("wai:prov-step\x01" || op_len | op | input | output | work | joules).

3. The receipt (AssetReceipt)

A JWP group: the asset's content hash is the identity, the per-step hashes are the Merkle leaves (JWP's exact moq-jwp:merkle-{leaf,node} domains), and one Ed25519 signature covers a profile payload carrying the asset hash, the declared media + capability, the Merkle root, the step chain, and the total joules. It chains across edits via parent_receipt_hash, like the worlds / audio / haptic / splat receipts.

4. Conformance

A conforming verifier MUST: (a) recompute the asset's content hash and require it equal the receipt's asset_hash; (b) require the step chain be linked — each step's input_hash equals the previous step's output_hash, and the final output_hash equals asset_hash; (c) recompute the Merkle root from the step hashes; (d) verify the Ed25519 signature as SPEC §7 Signatures requires. A failure at any point is a failure — the asset is reported unverified, never "probably fine".

There is no tolerance parameter: the content hash matches or it does not.

5. Energy is measured, never invented

joules_micro per step is carried from a meter, exactly as the other receipts carry it: wai_prov measures the real CPU energy of each encode (IOReport via macmon, no sudo) and signs the figure. An unmetered step carries the unmetered marker 0, which a reader presents as unmetered and never totals as zero joules. The receipt never derives energy it did not measure.

Each step's figure carries its acquisition class as an optional label (energy-measurement §2.8), because the steps of one lineage can be metered by different parties in different ways. A labelled step binds its class into its leaf hash; a step with no label keeps its legacy leaf and its figure is unlabelled. wai_prov labels each encode it measures OnChipCounter, with its declared uncertainty, and records an encode whose measurement fails the §4 ratio or the power reader's liveness (§3.1) as unmetered, and writes a measurement report for each step it measured (energy-measurement §6). total_joules_micro carries no class of its own, and a total over steps that include an unmetered one covers only the measured steps (Partial).

Appendix

The reconstruct classes prove WAI can ship a world, a sound, a body, a volume as instructions and have every sink rebuild them identically. Provenance proves the complement: for the photograph that is just a photograph, WAI still adds something a bare file cannot — a tamper-evident identity, a signed lineage, and an honest energy ledger — without ever pretending to understand the pixels. Carries whatever it can reconstruct; verifies whatever it carries.