Design without default constructor

I want to restrict creating object using default constructor. Because I have a desing like below: ``` class Program { static void Main(string[] args) { BaseClass bc = new BaseClass("",""); XmlSerializer xml = new XmlSerializer(typeof(BaseClass)); StreamWriter sw = new StreamWriter(File.Create("c:\\test.txt")); xml.Serialize(sw,bc); sw.Flush(); sw.Close(); } } [Serializable] public class BaseClass { public string UserName, Password; // I don't want to create default constructor because of Authentication public BaseClass(string _UserName, string _Password) { UserName = _UserName; Password = _Password; f_Authenticate(); } private void f_Authenticate() { } } public class DerivedClass:BaseClass { public DerivedClass(string _UserName, string _Password) : base(_UserName, _Password) { } } ``` This is ok. But when I make BaseClass to Serializable it'll generate this error: `Unhandled Exception: System.InvalidOperationException: ConsoleApplication1.BaseC lass cannot be serialized because it does not have a parameterless constructor.` Now my design is collapsing because I need to have `Username`, `Password` parameters but default constructor is ruining my design.... What should I do?