【智能合约审计】————3、CarToken

智能合约解析

最新推荐文章于 2022-12-12 16:27:35 发布

原创最新推荐文章于 2022-12-12 16:27:35 发布 · 425 阅读

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智能合约审计实战

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本文深入解析了一个具体的智能合约代码，详细介绍了其如何利用Solidity语言实现ERC20标准，包括安全数学运算、基本转账功能及授权操作。合约还包含了对地址合法性的检查、余额充足性验证等关键安全措施。

合约地址：https://etherscan.io/address/0x37e55693b71668dd53ed1431a5f2375d7e938ef5#code

pragma solidity ^0.4.18;//>=0.4.0合约无fallback在收到eth时会抛出异常并回退
//指定编译器版本符合推荐做法
//使用了SafeMath进行数值运算处理，符合推荐做法
library SafeMath {
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
          return 0;
        }
        uint256 c = a * b;
        assert(c / a == b);
        return c;
    }
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        assert(c >= a);
        return c;
    }
}
contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}
contract BasicToken is ERC20Basic {
  using SafeMath for uint256;       //通过这种方式引用SafeMath更方便
  mapping(address => uint256) balances;
  uint256 totalSupply_;
  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }
  function transfer(address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));   //检查地址是否合法
    require(_value <= balances[msg.sender]);//检查是否有足够的balance用于交易
    balances[msg.sender] = balances[msg.sender].sub(_value);//使用SafeMath进行数值运算，符合推荐做法，
    balances[_to] = balances[_to].add(_value);  //这里采用先减后加,符合推荐做法
    Transfer(msg.sender, _to, _value);
    return true;
  }
  function balanceOf(address _owner) public view returns (uint256 balance) {
    return balances[_owner];
  }
}
contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender) public view 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);
}
contract StandardToken is ERC20, BasicToken {
  mapping (address => mapping (address => uint256)) internal allowed;
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));//地址检查
    require(_value <= balances[_from]);//balance是否足够检查
    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;
  }
  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
  }
  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
  }
  function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }
  function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    uint oldValue = allowed[msg.sender][_spender];
    if (_subtractedValue > oldValue) {
      allowed[msg.sender][_spender] = 0;
    } else {
      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }
}
contract CheckCarToken is StandardToken{
  string public constant token_description = "This is a first decentralized blockchain platform for the market of diagnostics and selection of cars around the world! More info in http://check-car.io";
  string public constant name = "Check Car Token Private";
  string public constant symbol = "CCR-P";
  uint8 public constant decimals = 18;

  function CheckCarToken () public {
      totalSupply_ = 50000000000000000000000000;//可读性差，建议采用科学计数法
      balances[msg.sender] = 50000000000000000000000000;
  }
}