区块链安全—溢出的BEC漏洞

pragma solidity ^0.4.16;
/** * @title SafeMath * @dev Math operations with safety checks that throw on error */library SafeMath {  function mul(uint256 a, uint256 b) internal constant returns (uint256) {    uint256 c = a * b;    assert(a == 0 || c / a == b);    return c;  }
  function div(uint256 a, uint256 b) internal constant returns (uint256) {    // assert(b > 0); // Solidity automatically throws when dividing by 0    uint256 c = a / b;    // assert(a == b * c + a % b); // There is no case in which this doesn't hold    return c;  }
  function sub(uint256 a, uint256 b) internal constant returns (uint256) {    assert(b <= a);    return a - b;  }
  function add(uint256 a, uint256 b) internal constant returns (uint256) {    uint256 c = a + b;    assert(c >= a);    return c;  }}
/** * @title ERC20Basic * @dev Simpler version of ERC20 interface * @dev see https://github.com/ethereum/EIPs/issues/179 */contract ERC20Basic {  uint256 public totalSupply;  function balanceOf(address who) public constant returns (uint256);  function transfer(address to, uint256 value) public returns (bool);  event Transfer(address indexed from, address indexed to, uint256 value);}
/** * @title Basic token * @dev Basic version of StandardToken, with no allowances. */contract BasicToken is ERC20Basic {  using SafeMath for uint256;
  mapping(address => uint256) balances;
  /**  * @dev transfer token for a specified address  * @param _to The address to transfer to.  * @param _value The amount to be transferred.  */  function transfer(address _to, uint256 _value) public returns (bool) {    require(_to != address(0));    require(_value > 0 && _value <= balances[msg.sender]);
    // SafeMath.sub will throw if there is not enough balance.    balances[msg.sender] = balances[msg.sender].sub(_value);    balances[_to] = balances[_to].add(_value);    Transfer(msg.sender, _to, _value);    return true;  }
  /**  * @dev Gets the balance of the specified address.  * @param _owner The address to query the the balance of.  * @return An uint256 representing the amount owned by the passed address.  */  function balanceOf(address _owner) public constant returns (uint256 balance) {    return balances[_owner];  }}
/** * @title ERC20 interface * @dev see https://github.com/ethereum/EIPs/issues/20 */contract ERC20 is ERC20Basic {  function allowance(address owner, address spender) public constant returns (uint256);  function transferFrom(address from, address to, uint256 value) public returns (bool);  function approve(address spender, uint256 value) public returns (bool);  event Approval(address indexed owner, address indexed spender, uint256 value);}

/** * @title Standard ERC20 token * * @dev Implementation of the basic standard token. * @dev https://github.com/ethereum/EIPs/issues/20 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol */contract StandardToken is ERC20, BasicToken {
  mapping (address => mapping (address => uint256)) internal allowed;

  /**   * @dev Transfer tokens from one address to another   * @param _from address The address which you want to send tokens from   * @param _to address The address which you want to transfer to   * @param _value uint256 the amount of tokens to be transferred   */
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {    require(_to != address(0));    require(_value > 0 && _value <= balances[_from]);    require(_value <= allowed[_from][msg.sender]);
    balances[_from] = balances[_from].sub(_value);    balances[_to] = balances[_to].add(_value);    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);    Transfer(_from, _to, _value);    return true;  }
  /**   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.   *   * Beware that changing an allowance with this method brings the risk that someone may use both the old   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729   * @param _spender The address which will spend the funds.   * @param _value The amount of tokens to be spent.   */  function approve(address _spender, uint256 _value) public returns (bool) {    allowed[msg.sender][_spender] = _value;    Approval(msg.sender, _spender, _value);    return true;  }
  /**   * @dev Function to check the amount of tokens that an owner allowed to a spender.   * @param _owner address The address which owns the funds.   * @param _spender address The address which will spend the funds.   * @return A uint256 specifying the amount of tokens still available for the spender.   */  function allowance(address _owner, address _spender) public constant returns (uint256 remaining) {    return allowed[_owner][_spender];  }}
/** * @title Ownable * @dev The Ownable contract has an owner address, and provides basic authorization control * functions, this simplifies the implementation of "user permissions". */contract Ownable {  address public owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  /**   * @dev The Ownable constructor sets the original `owner` of the contract to the sender   * account.   */  function Ownable() {    owner = msg.sender;  }

  /**   * @dev Throws if called by any account other than the owner.   */  modifier onlyOwner() {    require(msg.sender == owner);    _;  }

  /**   * @dev Allows the current owner to transfer control of the contract to a newOwner.   * @param newOwner The address to transfer ownership to.   */  function transferOwnership(address newOwner) onlyOwner public {    require(newOwner != address(0));    OwnershipTransferred(owner, newOwner);    owner = newOwner;  }
}
/** * @title Pausable * @dev Base contract which allows children to implement an emergency stop mechanism. */contract Pausable is Ownable {  event Pause();  event Unpause();
  bool public paused = false;

  /**   * @dev Modifier to make a function callable only when the contract is not paused.   */  modifier whenNotPaused() {    require(!paused);    _;  }
  /**   * @dev Modifier to make a function callable only when the contract is paused.   */  modifier whenPaused() {    require(paused);    _;  }
  /**   * @dev called by the owner to pause, triggers stopped state   */  function pause() onlyOwner whenNotPaused public {    paused = true;    Pause();  }
  /**   * @dev called by the owner to unpause, returns to normal state   */  function unpause() onlyOwner whenPaused public {    paused = false;    Unpause();  }}
/** * @title Pausable token * * @dev StandardToken modified with pausable transfers. **/
contract PausableToken is StandardToken, Pausable {
  function transfer(address _to, uint256 _value) public whenNotPaused returns (bool) {    return super.transfer(_to, _value);  }
  function transferFrom(address _from, address _to, uint256 _value) public whenNotPaused returns (bool) {    return super.transferFrom(_from, _to, _value);  }
  function approve(address _spender, uint256 _value) public whenNotPaused returns (bool) {    return super.approve(_spender, _value);  }
  function batchTransfer(address[] _receivers, uint256 _value) public whenNotPaused returns (bool) {    uint cnt = _receivers.length;    uint256 amount = uint256(cnt) * _value;    require(cnt > 0 && cnt <= 20);    require(_value > 0 && balances[msg.sender] >= amount);
    balances[msg.sender] = balances[msg.sender].sub(amount);    for (uint i = 0; i < cnt; i++) {        balances[_receivers[i]] = balances[_receivers[i]].add(_value);        Transfer(msg.sender, _receivers[i], _value);    }    return true;  }}
/** * @title Bec Token * * @dev Implementation of Bec Token based on the basic standard token. */contract BecToken is PausableToken {    /**    * Public variables of the token    * The following variables are OPTIONAL vanities. One does not have to include them.    * They allow one to customise the token contract & in no way influences the core functionality.    * Some wallets/interfaces might not even bother to look at this information.    */    string public name = "BeautyChain";    string public symbol = "BEC";    string public version = '1.0.0';    uint8 public decimals = 18;
    /**     * @dev Function to check the amount of tokens that an owner allowed to a spender.     */    function BecToken() {      totalSupply = 7000000000 * (10**(uint256(decimals)));      balances[msg.sender] = totalSupply;    // Give the creator all initial tokens    }
    function () {        //if ether is sent to this address, send it back.        revert();    }}

function transferOwnership(address newOwner) onlyOwner public {    require(newOwner != address(0));    OwnershipTransferred(owner, newOwner);    owner = newOwner;  }

contract Pausable is Ownable {  event Pause();  event Unpause();
  bool public paused = false;

  /**   * @dev Modifier to make a function callable only when the contract is not paused.   */  modifier whenNotPaused() {    require(!paused);    _;  }
  /**   * @dev Modifier to make a function callable only when the contract is paused.   */  modifier whenPaused() {    require(paused);    _;  }
  /**   * @dev called by the owner to pause, triggers stopped state   */  function pause() onlyOwner whenNotPaused public {    paused = true;    Pause();  }
  /**   * @dev called by the owner to unpause, returns to normal state   */  function unpause() onlyOwner whenPaused public {    paused = false;    Unpause();  }}

/** * @title Pausable token * * @dev StandardToken modified with pausable transfers. **/
contract PausableToken is StandardToken, Pausable {
  function transfer(address _to, uint256 _value) public whenNotPaused returns (bool) {    return super.transfer(_to, _value);  }
  function transferFrom(address _from, address _to, uint256 _value) public whenNotPaused returns (bool) {    return super.transferFrom(_from, _to, _value);  }
  function approve(address _spender, uint256 _value) public whenNotPaused returns (bool) {    return super.approve(_spender, _value);  }
  function batchTransfer(address[] _receivers, uint256 _value) public whenNotPaused returns (bool) {    uint cnt = _receivers.length;    uint256 amount = uint256(cnt) * _value;    require(cnt > 0 && cnt <= 20);    require(_value > 0 && balances[msg.sender] >= amount);
    balances[msg.sender] = balances[msg.sender].sub(amount);    for (uint i = 0; i < cnt; i++) {        balances[_receivers[i]] = balances[_receivers[i]].add(_value);        Transfer(msg.sender, _receivers[i], _value);    }    return true;  }

contract BecToken is PausableToken {    /**    * Public variables of the token    * The following variables are OPTIONAL vanities. One does not have to include them.    * They allow one to customise the token contract & in no way influences the core functionality.    * Some wallets/interfaces might not even bother to look at this information.    */    string public name = "BeautyChain";    string public symbol = "BEC";    string public version = '1.0.0';    uint8 public decimals = 18;
    /**     * @dev Function to check the amount of tokens that an owner allowed to a spender.     */    function BecToken() {      totalSupply = 7000000000 * (10**(uint256(decimals)));      balances[msg.sender] = totalSupply;    // Give the creator all initial tokens    }
    function () {        //if ether is sent to this address, send it back.        revert();    }}

string public name = "BeautyChain";    string public symbol = "BEC";    string public version = '1.0.0';    uint8 public decimals = 18;

totalSupply = 7000000000 * (10**(uint256(decimals)));      balances[msg.sender] = totalSupply;    // Give the creator all initial tokens

function () {        //if ether is sent to this address, send it back.        revert();    }

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