function validateOrderHash(
    bytes32 hash,
    address user,
    uint8 v,
    bytes32 r,
    bytes32 s
  )
    private
    constant
    returns (bool)
  {
    return (
      orders[user][hash] ||
      ecrecover(keccak256("\x19Ethereum Signed Message:\n32", hash), v, r, s) == user
    );
  }