zk402-wasm

WASM bindings for zk402 client-side proof generation. Enables browser and Node.js clients to generate zero-knowledge payment proofs.

Building

# Install wasm-pack if not already installed
cargo install wasm-pack

# Build for web
wasm-pack build --target web

# Build for Node.js
wasm-pack build --target nodejs

# Build for bundlers (webpack, etc.)
wasm-pack build --target bundler

Usage

TypeScript/JavaScript

import init, { build_payload } from './pkg/zk402_wasm';

await init();

const requirements = {
  scheme: "zk-settle",
  network: "eip155:8453",
  amount: "100",
  asset: "0x0000000000000000000000000000000000000001",
  payTo: "0x0000000000000000000000000000000000000002",
  maxTimeoutSeconds: 3600,
  extra: {
    proofSystem: "groth16",
    circuitId: "zk-settle-transfer-v1",
    verifierAddress: "0x0000000000000000000000000000000000000003"
  }
};

const witness = {
  secretKey: "0x" + "00".repeat(32),
  from: "0x0000000000000000000000000000000000000004",
  paymentNonce: "0x" + "05".repeat(32),
  provingKey: "0x...", // Serialized Groth16 proving key
  validAfter: Math.floor(Date.now() / 1000),
  validBefore: Math.floor(Date.now() / 1000) + 3600
};

try {
  const payloadJson = build_payload(
    JSON.stringify(requirements),
    JSON.stringify(witness)
  );

  const payload = JSON.parse(payloadJson);
  console.log("Generated proof:", payload.proof);

  // Send to facilitator
  const response = await fetch('http://localhost:3000/verify', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      requirements,
      payload
    })
  });

  const result = await response.json();
  console.log("Verification result:", result);
} catch (error) {
  console.error("Proof generation failed:", error);
}

API

`build_payload(requirements_json: string, witness_json: string): string`

Generates a zero-knowledge proof and assembles a complete PaymentPayload.

Arguments:

requirements_json: JSON string of PaymentRequirements (camelCase)
witness_json: JSON string containing:
- secretKey: Hex-encoded private key (0x-prefixed)
- from: Payer address (0x-prefixed, 20 bytes)
- paymentNonce: Random nonce (0x-prefixed, 32 bytes)
- provingKey: Hex-encoded Groth16 proving key
- validAfter: Unix timestamp (seconds)
- validBefore: Unix timestamp (seconds)

Returns:

JSON string of PaymentPayload (camelCase), or throws error

Example witness input:

{
  "secretKey": "0xabcd...",
  "from": "0x1234567890123456789012345678901234567890",
  "paymentNonce": "0x0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f20",
  "provingKey": "0x...",
  "validAfter": 1700000000,
  "validBefore": 1700003600
}

Error Handling

The function throws errors in these cases:

Invalid JSON in either input
Invalid hex encoding
Invalid address/nonce length
Proof generation failure

All errors are JavaScript Error objects with descriptive messages.

Security Notes

Never expose secretKey or provingKey in logs or error messages
Generate paymentNonce cryptographically (e.g., crypto.randomBytes(32))
Always verify validAfter and validBefore are reasonable
This module runs client-side - proof generation happens in the browser/Node process

License

MIT OR Apache-2.0

zk402-wasm 0.1.0