Dead or Alive?
Author: Razzor
Network: Goerli
Address: 0xd43678eb793a9b8847ee270900b03e61eadec786

Contract Code

pragma solidity ^0.8.0;

  interface Mortal {
  function deadYet() external view returns (bytes32);
  }

  contract undead{
    bytes20 public want;
    bytes20 public mask;
    address public owner;
    uint256 public wordLength;
    mapping (bytes32 => bool) public UnDeAD;
        
    constructor(bytes20 _want, bytes20 _mask, uint256 _wordLength){
        want = _want;
        mask = _mask;
        wordLength = _wordLength;
        owner = msg.sender;
    }
     
    function deadOrAlive(address _addr) external {
    require(!UnDeAD[keccak256(abi.encodePacked(_addr))], "Not Twice");
    uint256 size;
    require(mortality(_addr), "Want Blood");
    assembly {
        size := extcodesize(_addr)
    }
    require(size == 15);
    Mortal mortal = Mortal(_addr);
    bytes32 answerMe = mortal.deadYet();
    string memory identity = bytes32ToString(answerMe <<= (4 * 52));
    require(keccak256(abi.encodePacked(identity)) == keccak256(abi.encodePacked("UnDeAD")), "MORTAL!");
    UnDeAD[keccak256(abi.encodePacked(_addr))] = true;
    }
      
    function mortality(address _addr) internal returns (bool) {
    bytes20 addr = bytes20(_addr);
    for (uint256 i = 0; i <= (40 - wordLength); i++) {
        if (addr & mask == want) {
            return true;
        }
        mask <<= 4;
        want <<= 4;
    }
    return false;
    }
  }
          
        

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