pragma solidity ^0.4.18; import "https://github.com/ethereum/solidity/std/mortal.sol"; /// @title Chequebook for Ethereum micropayments /// @author Daniel A. Nagy contract chequebook is mortal { // Cumulative paid amount in wei to each beneficiary mapping (address => uint256) public sent; /// @notice Overdraft event event Overdraft(address deadbeat); /// @notice Cash cheque /// /// @param beneficiary beneficiary address /// @param amount cumulative amount in wei /// @param sig_v signature parameter v /// @param sig_r signature parameter r /// @param sig_s signature parameter s /// The digital signature is calculated on the concatenated triplet of contract address, beneficiary address and cumulative amount function cash(address beneficiary, uint256 amount, uint8 sig_v, bytes32 sig_r, bytes32 sig_s) { // Check if the cheque is old. // Only cheques that are more recent than the last cashed one are considered. require(amount > sent[beneficiary]); // Check the digital signature of the cheque. bytes32 hash = keccak256(address(this), beneficiary, amount); require(owner == ecrecover(hash, sig_v, sig_r, sig_s)); // Attempt sending the difference between the cumulative amount on the cheque // and the cumulative amount on the last cashed cheque to beneficiary. uint256 diff = amount - sent[beneficiary]; if (diff <= this.balance) { // update the cumulative amount before sending sent[beneficiary] = amount; beneficiary.transfer(diff); } else { // Upon failure, punish owner for writing a bounced cheque. // owner.sendToDebtorsPrison(); Overdraft(owner); // Compensate beneficiary. selfdestruct(beneficiary); } } }