Note For Ethernaut#0 - Hello

Solidity

pragma solidity ^0.4.18;

contract Instance {

  string public password;
  uint8 public infoNum = 42;
  string public theMethodName = 'The method name is method7123949.';
  bool private cleared = false;

  // constructor
  function Instance(string _password) public {
    password = _password;
  }

  function info() public pure returns (string) {
    return 'You will find what you need in info1().';
  }

  function info1() public pure returns (string) {
    return 'Try info2(), but with "hello" as a parameter.';
  }

  function info2(string param) public pure returns (string) {
    if(keccak256(param) == keccak256('hello')) {
      return 'The property infoNum holds the number of the next info method to call.';
    }
    return 'Wrong parameter.';
  }

  function info42() public pure returns (string) {
    return 'theMethodName is the name of the next method.';
  }

  function method7123949() public pure returns (string) {
    return 'If you know the password, submit it to authenticate().';
  }

  function authenticate(string passkey) public {
    if(keccak256(passkey) == keccak256(password)) {
      cleared = true;
    }
  }

  function getCleared() public view returns (bool) {
    return cleared;
  }
}

在判斷參數時用到 keccak256，文件提到 keccak256 是 “tight pakced”，而 “tightly packed” 是指不會對參數進行 padding 處理。

What I learned From It

• 參數會先經過 keccak256 pack
• 取 public 變數與參數方式一樣

tags: ethernaut solidity