Merge pull request #41 from tornadocash/demo

Demo

README.md

@@ -113,3 +113,12 @@ Example:
 
 Special thanks to @barryWhiteHat and @kobigurk for valuable input,
 and to @jbaylina for awesome [Circom](https://github.com/iden3/circom) & [Websnark](https://github.com/iden3/websnark) framework
+
+## Minimal demo example
+1. `npm i`
+1. `ganache-cli -d`
+1. `npm run downloadKeys`
+1. `npm build:contract`
+1. `cp .env.example .env`
+1. `npm run migrate:dev`
+1. `node minimal-demo.js`

minimal-demo.js

@@ -0,0 +1,163 @@
+const fs = require('fs')
+const assert = require('assert')
+const { bigInt } = require('snarkjs')
+const crypto = require('crypto')
+const circomlib = require('circomlib')
+const merkleTree = require('./lib/MerkleTree')
+const Web3 = require('web3')
+const buildGroth16 = require('websnark/src/groth16')
+const websnarkUtils = require('websnark/src/utils')
+const { toWei } = require('web3-utils')
+
+let web3, contract, netId, circuit, proving_key, groth16
+const RPC_URL = 'http://localhost:8545'
+const CONTRACT_ADDRESS = '0x9561C133DD8580860B6b7E504bC5Aa500f0f06a7'
+const MERKLE_TREE_HEIGHT = 20
+const AMOUNT = '0.1'
+const DEPLOYED_BLOCK = 0
+
+/** Generate random number of specified byte length */
+const rbigint = nbytes => bigInt.leBuff2int(crypto.randomBytes(nbytes))
+
+/** Compute pedersen hash */
+const pedersenHash = data => circomlib.babyJub.unpackPoint(circomlib.pedersenHash.hash(data))[0]
+
+/** BigNumber to hex string of specified length */
+const toHex = (number, length = 32) => '0x' + (number instanceof Buffer ? number.toString('hex') : bigInt(number).toString(16)).padStart(length * 2, '0')
+
+/**
+ * Create deposit object from secret and nullifier
+ */
+function createDeposit(nullifier, secret) {
+  let deposit = { nullifier, secret }
+  deposit.preimage = Buffer.concat([deposit.nullifier.leInt2Buff(31), deposit.secret.leInt2Buff(31)])
+  deposit.commitment = pedersenHash(deposit.preimage)
+  deposit.nullifierHash = pedersenHash(deposit.nullifier.leInt2Buff(31))
+  return deposit
+}
+
+/**
+ * Make an ETH deposit
+ */
+async function deposit() {
+  const deposit = createDeposit(rbigint(31), rbigint(31))
+  console.log('Sending deposit transaction...')
+  await contract.methods.deposit(toHex(deposit.commitment)).send({ value: toWei(AMOUNT), from: web3.eth.defaultAccount, gas:2e6 })
+  return `tornado-eth-${AMOUNT}-${netId}-${toHex(deposit.preimage, 62)}`
+}
+
+/**
+ * Do an ETH withdrawal
+ * @param note Note to withdraw
+ * @param recipient Recipient address
+ */
+async function withdraw(note, recipient) {
+  const deposit = parseNote(note)
+  const { proof, args } = await generateSnarkProof(deposit, recipient)
+  console.log('Sending withdrawal transaction...')
+  await contract.methods.withdraw(proof, ...args).send({ from: web3.eth.defaultAccount, gas: 1e6 })
+}
+
+/**
+ * Parses Tornado.cash note
+ * @param noteString the note
+ */
+function parseNote(noteString) {
+  const noteRegex = /tornado-(?<currency>\w+)-(?<amount>[\d.]+)-(?<netId>\d+)-0x(?<note>[0-9a-fA-F]{124})/g
+  const match = noteRegex.exec(noteString)
+
+  // we are ignoring `currency`, `amount`, and `netId` for this minimal example
+  const buf = Buffer.from(match.groups.note, 'hex')
+  const nullifier = bigInt.leBuff2int(buf.slice(0, 31))
+  const secret = bigInt.leBuff2int(buf.slice(31, 62))
+  return createDeposit(nullifier, secret)
+}
+
+/**
+ * Generate merkle tree for a deposit.
+ * Download deposit events from the contract, reconstructs merkle tree, finds our deposit leaf
+ * in it and generates merkle proof
+ * @param deposit Deposit object
+ */
+async function generateMerkleProof(deposit) {
+  console.log('Getting contract state...')
+  const events = await contract.getPastEvents('Deposit', { fromBlock: DEPLOYED_BLOCK, toBlock: 'latest' })
+  const leaves = events
+    .sort((a, b) => a.returnValues.leafIndex - b.returnValues.leafIndex) // Sort events in chronological order
+    .map(e => e.returnValues.commitment)
+  const tree = new merkleTree(MERKLE_TREE_HEIGHT, leaves)
+
+  // Find current commitment in the tree
+  let depositEvent = events.find(e => e.returnValues.commitment === toHex(deposit.commitment))
+  let leafIndex = depositEvent ? depositEvent.returnValues.leafIndex : -1
+
+  // Validate that our data is correct (optional)
+  const isValidRoot = await contract.methods.isKnownRoot(toHex(await tree.root())).call()
+  const isSpent = await contract.methods.isSpent(toHex(deposit.nullifierHash)).call()
+  assert(isValidRoot === true, 'Merkle tree is corrupted')
+  assert(isSpent === false, 'The note is already spent')
+  assert(leafIndex >= 0, 'The deposit is not found in the tree')
+
+  // Compute merkle proof of our commitment
+  return await tree.path(leafIndex)
+}
+
+/**
+ * Generate SNARK proof for withdrawal
+ * @param deposit Deposit object
+ * @param recipient Funds recipient
+ */
+async function generateSnarkProof(deposit, recipient) {
+  // Compute merkle proof of our commitment
+  const { root, path_elements, path_index } = await generateMerkleProof(deposit)
+
+  // Prepare circuit input
+  const input = {
+    // Public snark inputs
+    root: root,
+    nullifierHash: deposit.nullifierHash,
+    recipient: bigInt(recipient),
+    relayer: 0,
+    fee: 0,
+    refund: 0,
+
+    // Private snark inputs
+    nullifier: deposit.nullifier,
+    secret: deposit.secret,
+    pathElements: path_elements,
+    pathIndices: path_index,
+  }
+
+  console.log('Generating SNARK proof...')
+  const proofData = await websnarkUtils.genWitnessAndProve(groth16, input, circuit, proving_key)
+  const { proof } = websnarkUtils.toSolidityInput(proofData)
+
+  const args = [
+    toHex(input.root),
+    toHex(input.nullifierHash),
+    toHex(input.recipient, 20),
+    toHex(input.relayer, 20),
+    toHex(input.fee),
+    toHex(input.refund)
+  ]
+
+  return { proof, args }
+}
+
+async function main() {
+  web3 = new Web3(new Web3.providers.HttpProvider(RPC_URL, { timeout: 5 * 60 * 1000 }), null, { transactionConfirmationBlocks: 1 })
+  circuit = require('./build/circuits/withdraw.json')
+  proving_key = fs.readFileSync('build/circuits/withdraw_proving_key.bin').buffer
+  groth16 = await buildGroth16()
+  netId = await web3.eth.net.getId()
+  contract = new web3.eth.Contract(require('./build/contracts/ETHTornado.json').abi, CONTRACT_ADDRESS)
+  web3.eth.defaultAccount = (await web3.eth.getAccounts())[0]
+
+  const note = await deposit()
+  console.log('Deposited note:', note)
+  await withdraw(note, web3.eth.defaultAccount)
+  console.log('Done')
+  process.exit()
+}
+
+main()