如果你遇到 Uint64 還不夠處理的窘境，可以試試看 BigInteger Class，就可以處理超大數值。

官方網站：http://www.codeproject.com/Articles/2728/C-BigInteger-Class

本地下載：BigInteger_src

public static void Main(string[] args)
{
    // private and public key
    BigInteger bi_e = new BigInteger(
        "a932b948feed4fb2b692609bd22164fc9edb" +
        "59fae7880cc1eaff7b3c9626b7e5b241c27a" +
        "974833b2622ebe09beb451917663d4723248" +
        "8f23a117fc97720f1e7", 16);
    BigInteger bi_d = new BigInteger(
        "4adf2f7a89da93248509347d2ae506d683dd" +
        "3a16357e859a980c4f77a4e2f7a01fae289f" +
        "13a851df6e9db5adaa60bfd2b162bbbe31f7" +
        "c8f828261a6839311929d2cef4f864dde65e" +
        "556ce43c89bbbf9f1ac5511315847ce9cc8d" +
        "c92470a747b8792d6a83b0092d2e5ebaf852" +
        "c85cacf34278efa99160f2f8aa7ee7214de07b7", 16);
    BigInteger bi_n = new BigInteger(
        "e8e77781f36a7b3188d711c2190b560f205a" +
        "52391b3479cdb99fa010745cbeba5f2adc08" +
        "e1de6bf38398a0487c4a73610d94ec36f17f" +
        "3f46ad75e17bc1adfec99839589f45f95ccc" +
        "94cb2a5c500b477eb3323d8cfab0c8458c96" +
        "f0147a45d27e45a4d11d54d77684f65d48f1" +
        "5fafcc1ba208e71e921b9bd9017c16a5231af7f", 16);
    Console.WriteLine("e =\n" + bi_e.ToString(10));
    Console.WriteLine("\nd =\n" + bi_d.ToString(10));
    Console.WriteLine("\nn =\n" + bi_n.ToString(10) + "\n");
    // data
    BigInteger bi_data = new BigInteger(
        "12345678901234567890", 10);
    // encrypt and decrypt data
    BigInteger bi_encrypted = bi_data.modPow(bi_e, bi_n);
    BigInteger bi_decrypted = bi_encrypted.modPow(
        bi_d, bi_n);
    Console.WriteLine("bi_data = " + bi_data);
    Console.WriteLine("\nbi_encrypted =\n" + bi_encrypted);
    Console.WriteLine("\nbi_decrypted = " + bi_decrypted);
}