DAYPASS - Digital Battery Passport on Cardano

EU Battery Regulation 2023/1542 Digital Battery Passport with three disclosure tiers, backed by zero-knowledge attestations on Cardano.

EU Battery Regulation 2023/1542 Digital Battery Passport on Cardano: one CIP-25 NFT per passport plus an anchor metadata label carrying the payload hash, a Merkle content root and the public Point-1 fields. Sensitive data stays AES-encrypted off-chain; three disclosure tiers render lawful views of one backend. Field values can be selectively disclosed with Merkle proofs, and threshold statements ("carbon footprint below X") proven in zero knowledge, with the Groth16 verification executed by the Cardano ledger itself. DAYPASS is the transparent-chain twin of NIGHTPASS (Midnight, shielded ZK) and consumes @odatano/core as a CAP plugin.

Disclosure tiers (Annex XIII)

Tier	Audience	Sees
consumer	public, phone scan	Point 1: id, manufacturer, model, category, date, weight, class
recycler	legitimate interest	+ cell chemistry, capacity, recycled-content shares
authority	notified bodies	+ supplier identities, carbon footprint, docs, on-chain lineage

The boundary is enforced in the API layer; the chain carries the EVIDENCE (anchors, pseudonymous grant audit txs), not the access control.

On-chain

• Mint (attest): CIP-25 NFT under a policy bound to the producer key, plus anchor label 1155 with payloadHash, contentRoot, Point-1 cleartext.
• Reattest: metadata tx with the new payload version, chained via prev.
• Grant / revoke: optional pseudonymous audit anchors, grantee is sha256(did), never PII.
• Burn: revocation; the mint/burn history nets to zero supply.

Selective disclosure reveals ONE field value with a Merkle inclusion proof against the anchored content root. Any Cardano API can re-verify it, no trust in DAYPASS needed.

Two metadata labels split display from evidence:

• Label 721 (CIP-25): standard NFT metadata, what wallets and explorers show. Deliberately lean: name ("DPP "), description, model, QR image. No integrity data lives here.
• Label 1155 (DAYPASS anchor): the machine-verifiable part. op (mint, reattest, grant, revoke), passportId + its hash, payloadHash (blake2b of the canonical payload), contentRoot (Merkle root the field disclosures fold to), poseidonRoot (its ZK twin), anchor version and prev tx hash (the re-attest chain), plus the cleartext Point-1 block with all decimals as scaled integers (weightGrams etc.). Grant/revoke anchors carry the pseudonymous grantee and level; predicate anchors add field key, predicate, threshold and result.

The mint tx carries both labels; reattest and audit anchors are plain metadata txs with only the 1155 label.

Example on Preview: mint + anchor tx ae0d4c2d…05af8f carries the CIP-25 passport NFT and the 1155 anchor label (payloadHash, contentRoot, poseidonRoot, Point-1 fields).

Zero-knowledge predicates

Beyond revealing values, DAYPASS proves THRESHOLD statements about hidden fields ("carbon footprint <= 4000 kg CO2e") without disclosing the number:

• every anchor additionally commits a Poseidon Merkle root over the 9 provable fields (poseidonRoot in the 1155 label)
• a prover sidecar (@odatano/dayzero: pure TypeScript, Groth16 over BLS12-381, coset-FFT domain, multi-core MSM) builds the proof; the Plutus V3 verifier is a hand-written Aiken policy shipped with the trust roots in zk/artifacts/
• provePassportPredicate mints a predicate token whose mint redeemer IS the proof: the validator runs the full Groth16 pairing check on-chain and enforces that the token's asset name commits to the public inputs (blake2b-224 over the serialised datum), so the statement is verified by the Cardano ledger itself. Example on Preview: 5a5c0a64…57d52c proves carbonFootprint lessOrEqual threshold against the poseidonRoot anchored by the mint tx linked above
• the PAC export carries these as zkPredicate entries next to the merkle-disclosure entries

Quick start

npm install
cp .env.example .env        # fill in BLOCKFROST_API_KEY (preview); the server
                            # signing key is OPTIONAL, the cockpit signs in a
                            # CIP-30 browser wallet
npm run deploy              # creates db/daypass.db (+ demo partner seeds)
docker compose up -d daypass-prover   # ZK prover sidecar on :8799; with
                            # DAYPASS_ZK_PROVER_URL set (default in
                            # .env.example) anchoring REQUIRES it; unset the
                            # variable to run Track A only, without Docker
npm start                   # http://localhost:4004

• Producer cockpit: /producer/webapp/index.html (login producer/producer)
• Consumer viewer: /passport/webapp/index.html (tiers: recycler/recycler, authority/authority, partners BPNL000000000ACME/recycler etc.)
• QR landing: /p/<passportId>, hash resolver /resolve/<payloadHash>, public verification JSON /verify/<passportId>

Catena-X / Tractus-X

passportAspectJson exports the CX-0143 BatteryPass aspect; passportCredential builds a W3C-VC Predicate Attestation Credential whose merkle-disclosure entries verify PORTABLY against Cardano:

node tractusx/pac/verify-pac.mjs tractusx/samples/battery-pass-pac.json <BLOCKFROST_KEY>

Dependency patches

patches/ (applied via postinstall: patch-package) carries two fixes for bugs we found in the HarmonicLabs stack while landing the ZK track: permuted BLS12-381 builtin flat tags in @harmoniclabs/uplc and a Buffer-mutating parseMask in @harmoniclabs/crypto. Both are reported upstream.

Docs

• docs/architecture.md: how the pieces fit
• docs/producer-walkthrough.md: cockpit tour with screenshots

Credits

The zero-knowledge track runs on @odatano/dayzero (pure-TypeScript Groth16 prover, Poseidon, and the Aiken on-chain verifier). The design of the predicate flow owes to the bloxbean ZK stack (ZeroJ), which powered the first iterations of this track.