library ECRecovery {

  /**
   * @dev Recover signer address from a message by using their signature
   * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
   * @param sig bytes signature, the signature is generated using web3.eth.sign()
   */
  function recover(bytes32 hash, bytes sig)
    internal
    pure
    returns (address)
  {
    bytes32 r;
    bytes32 s;
    uint8 v;

    // Check the signature length
    if (sig.length != 65) {
      return (address(0));
    }

    // Divide the signature in r, s and v variables
    // ecrecover takes the signature parameters, and the only way to get them
    // currently is to use assembly.
    // solium-disable-next-line security/no-inline-assembly
    assembly {
      r := mload(add(sig, 32))
      s := mload(add(sig, 64))
      v := byte(0, mload(add(sig, 96)))
    }

    // Version of signature should be 27 or 28, but 0 and 1 are also possible versions
    if (v < 27) {
      v += 27;
    }

    // If the version is correct return the signer address
    if (v != 27 && v != 28) {
      return (address(0));
    } else {
      // solium-disable-next-line arg-overflow
      return ecrecover(hash, v, r, s);
    }
  }

  /**
   * toEthSignedMessageHash
   * @dev prefix a bytes32 value with "\x19Ethereum Signed Message:"
   * @dev and hash the result
   */
  function toEthSignedMessageHash(bytes32 hash)
    internal
    pure
    returns (bytes32)
  {
    // 32 is the length in bytes of hash,
    // enforced by the type signature above
    return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
  }
}
/**
 * @title Eliptic curve signature operations
 *
 * @dev Based on https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/contracts/ECRecovery.sol
 *
 * TODO Remove this library once solidity supports passing a signature to ecrecover.
 * See https://github.com/ethereum/solidity/issues/864
 *
 */
function recover(bytes32 hash, bytes sig)
  internal
  pure
  returns (address)
{
  bytes32 r;
  bytes32 s;
  uint8 v;

  // Check the signature length
  if (sig.length != 65) {
    return (address(0));
  }

  // Divide the signature in r, s and v variables
  // ecrecover takes the signature parameters, and the only way to get them
  // currently is to use assembly.
  // solium-disable-next-line security/no-inline-assembly
  assembly {
    r := mload(add(sig, 32))
    s := mload(add(sig, 64))
    v := byte(0, mload(add(sig, 96)))
  }

  // Version of signature should be 27 or 28, but 0 and 1 are also possible versions
  if (v < 27) {
    v += 27;
  }

  // If the version is correct return the signer address
  if (v != 27 && v != 28) {
    return (address(0));
  } else {
    // solium-disable-next-line arg-overflow
    return ecrecover(hash, v, r, s);
  }
}

/**
 * @dev Recover signer address from a message by using their signature
 * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
 * @param sig bytes signature, the signature is generated using web3.eth.sign()
 */