how to validate the password

public string GeneratePassword(string userName)
{
    if (string.IsNullOrEmpty(userName))
        return "NAN";

    userName = userName.ToUpper();

    return string.Format("{0}{1}{2}{3}", "8080110001",EncryptedUserName(userName), userName, DateTime.Now);
}

public int EncryptedUserName(string userName)
{
    int partOfSecurity = 0;
    foreach (char c in userName)
    {
        partOfSecurity += (int)c;
    }
    return partOfSecurity;
}
public bool IsAuthenticated(string userName, string passWord)
{
    if (string.IsNullOrEmpty(userName) || passWord.Length <10)
        return false;
     userName = userName.ToUpper();



     return
         (passWord.Substring(0, 10) == "8080110001" && passWord.Replace(EncryptedUserName(userName).ToString(), string.Empty) != passWord && passWord.Replace(userName, string.Empty) != passWord)
         ? true : false;
}