zkSync Development: Zero-Knowledge Security with Native Account Abstraction

// Sponsor user gas fees via paymaster contract
import { Provider, Wallet, utils } from 'zksync-ethers';
import { ethers } from 'ethers';

const provider = new Provider('https://mainnet.era.zksync.io');
const wallet = new Wallet(PRIVATE_KEY, provider);

// Deploy paymaster that sponsors transactions
const paymasterAddress = '0x...'; // Your deployed paymaster

const sendGaslessTransaction = async (
  userAddress: string,
  contractAddress: string,
  data: string
) => {
  // User doesn't need ETH - paymaster pays gas
  const tx = {
    to: contractAddress,
    data: data,
    from: userAddress,
    // Paymaster parameters - zkSync-specific
    customData: {
      gasPerPubdata: utils.DEFAULT_GAS_PER_PUBDATA_LIMIT,
      paymasterParams: utils.getPaymasterParams(paymasterAddress, {
        type: 'General',
        innerInput: new Uint8Array(), // Paymaster-specific data
      }),
    },
  };

  // Estimate gas including paymaster overhead
  const gasLimit = await provider.estimateGas(tx);
  const gasPrice = await provider.getGasPrice();

  // Send transaction - paymaster sponsors gas cost
  const txResponse = await wallet.sendTransaction({
    ...tx,
    gasLimit,
    gasPrice,
  });

  await txResponse.wait();
  console.log('Transaction sent without user paying gas!');
};

// Paymaster smart contract (simplified)
contract SimplePaymaster is IPaymaster {
    function validateAndPayForPaymasterTransaction(
        bytes32,
        bytes32,
        Transaction calldata _transaction
    ) external payable returns (bytes4 magic, bytes memory context) {
        // Validate transaction (check rate limits, user eligibility)
        require(isEligibleForSponsorship(_transaction.from), "Not eligible");

        // Pay for gas
        uint256 requiredETH = _transaction.gasLimit * _transaction.maxFeePerGas;
        (bool success, ) = payable(BOOTLOADER_ADDRESS).call{value: requiredETH}("");
        require(success, "Failed to pay gas");

        magic = PAYMASTER_VALIDATION_SUCCESS_MAGIC;
    }
}

// User experience: interact with app without ETH
// No "insufficient funds for gas" errors

// Smart contract wallet with social recovery
contract SocialRecoveryWallet is IAccount {
    address public owner;
    mapping(address => bool) public guardians;
    uint256 public guardianCount;
    uint256 public threshold; // # of guardians needed for recovery

    // zkSync AA: validate transaction signature
    function validateTransaction(
        bytes32,
        bytes32 _suggestedSignedHash,
        Transaction calldata _transaction
    ) external payable override returns (bytes4 magic) {
        // Check if signed by owner
        address signer = ECDSA.recover(_suggestedSignedHash, _transaction.signature);

        if (signer == owner) {
            magic = ACCOUNT_VALIDATION_SUCCESS_MAGIC;
        } else {
            magic = bytes4(0); // Invalid signature
        }
    }

    // Social recovery: guardians can change owner if threshold met
    mapping(address => mapping(address => bool)) public recoveryVotes;

    function initiateRecovery(address newOwner) external {
        require(guardians[msg.sender], "Not a guardian");
        recoveryVotes[newOwner][msg.sender] = true;
    }

    function executeRecovery(address newOwner) external {
        uint256 votes = 0;
        // Count guardian votes (simplified)
        // In production: use array of guardians
        require(votes >= threshold, "Insufficient votes");

        owner = newOwner;
        // Clear recovery votes
    }
}

// Frontend: Add guardians (friends/family)
const addGuardian = async (guardianAddress: string) => {
  const tx = await wallet.sendTransaction({
    to: WALLET_ADDRESS,
    data: walletContract.interface.encodeFunctionData('addGuardian', [
      guardianAddress,
    ]),
  });
  await tx.wait();
};

// If user loses private key:
// 1. Guardians vote for new owner (new key)
// 2. Once threshold met, ownership transfers
// 3. User regains access without centralized recovery

// zkSync AA enables this natively - no need for complex proxy patterns