Basic payment mixing contract

MixingBasic.sol

/**
 * Basic payment mixing contract
 * Do not copy this contract! It's never been tested or audited
 * It also lacks a withdraw function for payers
 */
pragma solidity 0.4.18;

contract MixingBasic {
    address owner;
    uint public amount;
    mapping(address => bool) recipients;
    mapping(address => bool) payers;
    bool withdrawEnabled = false;
    
    modifier onlyOwner() {
        require(owner == msg.sender);
        _;
    }
    
    modifier onlyRecipient() {
        require(recipients[msg.sender]);
        _;
    }
    
    function MixingBasic(uint _amount) public {
        owner = msg.sender;
        amount = _amount;
    }

    function addRecipient(address addr) onlyOwner() public {
        require(!recipients[addr]);
        recipients[addr] = true;
    }
    
    function openWidthdraw() onlyOwner() public {
        require(!withdrawEnabled);
        withdrawEnabled = true;
    }
    
    function sendMoney() payable public {
        require(!payers[msg.sender]);
        require(msg.value == amount);
        payers[msg.sender] = true;
    }
    
    function recipientWithdraw() onlyRecipient() public {
        require(withdrawEnabled);
        recipients[msg.sender] = false;
        msg.sender.transfer(amount);
    }
}