Meton SDK

SDK to build Groth16 proofs for the Meton deposit / withdraw / transfer circuits, plus the curve/commitment/encrypted-note helpers needed to construct inputs and manage wallet state off-chain.

Install

npm install @metoncash/sdk-v1
# peer runtime dep used for proving:
npm install snarkjs

Usage

import { MetonSDK, deriveViewKey, randomScalar } from "meton-cash/sdk-v1";

// Point at a build directory laid out as <dir>/<c>/<c>_js/<c>.wasm + <dir>/<c>/<c>_final.zkey
const sdk = MetonSDK.fromBuildDir("./build");

// …or pass artifacts explicitly (paths or Uint8Array buffers):
// const sdk = new MetonSDK({
//   deposit:  { wasm, zkey },
//   withdraw: { wasm, zkey },
//   transfer: { wasm, zkey },
// });

// DEPOSIT — commit a public amount
const dep = await sdk.deposit({ amount: 1000n, accountId: 7n, seqNo: 1n });
// → { proof, publicSignals, commitment: [x,y], blinding }   (persist `blinding`)

// WITHDRAW — prove balance ≥ amount
const w = await sdk.withdraw({
  amount: 400n, balance: 1000n, oldBlind, accountId: 7n, seqNo: 2n,
});
// → { proof, publicSignals, newCommitment, remainder, newBlind }

// TRANSFER — hidden amount, encrypted to the receiver's VIEWING key
const recv = deriveViewKey(receiverSpendSecret);   // recipient side
const t = await sdk.transfer({
  amount: 300n, senderBalance: 1000n, senderOldBlind,
  receiverViewPk: recv.pkView, accountId: 7n, seqNo: 3n,
});
// → { proof, publicSignals, newSenderCommitment, amountCommitment, note,
//     remainder, senderNewBlind, amountBlind, ephScalar }

proof + publicSignals are the snarkjs Groth16 outputs. Every result also returns the secrets you must persist (blindings, note) to keep your local opening of the commitment spendable.

Receiving / auditing

import { viewNote } from "meton-cash/sdk-v1";

// recipient (or a granted auditor) holding sk_view:
const seen = viewNote(recv.skView, note, amountCommitment[0], amountCommitment[1]);
// → { amount, amountBlind, valid }   (valid: the note opens the on-chain amount_commit)

What's exported

• Prover: MetonSDK (deposit, withdraw, transfer, fromBuildDir).
• Keys / notes: deriveViewKey, derivePub, encryptNote, decryptNote, viewNote.
• Curve / commitments: commit, add, mul, mod, randomScalar, Point, Gx/Gy/Hx/Hy, r, d, L.
• Hash: mimc5perm. Constants: CONSTANTS.

Notes

• Defaults: blinding, newBlind, senderNewBlind, ephScalar default to fresh randomness; amountBlind defaults to oldBlind − newBlind (mod L) (the homomorphic relation the contract checks). The ephemeral scalar must be fresh per transfer — reuse leaks amounts.
• Proving is CPU-heavy (transfer ≈ 30k constraints); run it off the UI thread / in a worker.