public void Menu()
        {
            bool done = false;

            while (!done)
            {
                Console.WriteLine("1. Create Keys");
                Console.WriteLine("2. Encrpyt");
                Console.WriteLine("3. Decrypt");
                Console.WriteLine("4. Exit");
                Console.Write("Selection: ");

                try
                {
                    int response = Convert.ToInt32(Console.ReadLine());

                    switch (response)
                    {
                    case 1:
                        sdes.CreateKeys();
                        break;

                    case 2:
                        sdes.DES(true);
                        break;

                    case 3:
                        sdes.DES(false);
                        break;

                    case 4:
                        done = true;
                        break;

                    default:
                        Console.WriteLine("Please input a value from 1-4.");
                        break;
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine("Enter an integer value from 1-4.");
                }
            }
        }