From 49bdd1bb6f7bcc10cd16da62759c46f1aec5d1f7 Mon Sep 17 00:00:00 2001 From: poma Date: Fri, 28 Feb 2020 13:22:08 +0300 Subject: [PATCH] minimal demo wip --- minimal-demo.js | 162 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 162 insertions(+) create mode 100644 minimal-demo.js diff --git a/minimal-demo.js b/minimal-demo.js new file mode 100644 index 0000000..6c2553a --- /dev/null +++ b/minimal-demo.js @@ -0,0 +1,162 @@ +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 = '0x47CE0C6eD5B0Ce3d3A51fdb1C52DC66a7c3c2936' +const MERKLE_TREE_HEIGHT = 20 +const AMOUNT = '1' +const DEPLOYED_BLOCK = 9117609 + +/** 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-(?\w+)-(?[\d.]+)-(?\d+)-0x(?[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') +} + +main()