Gatekeeper One - The Ethernaut - Writeup

Sun, 10 May 2026 00:00:00 +0000

Make it past the gatekeeper and register as an entrant to pass this level.

The goal of the challenge is to successfully execute the function enter on this contract:

// 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;
    }
}

We need to pass the three modifiers gateOne, gateTwo and gateThree. Generate a new instance of the challenge:

Msg.sender on manbolq's Blog

Gatekeeper One - The Ethernaut - Writeup