C#使用RSA證書文件加密和解密

    public class EncrypHelp
    {
        static public byte[] RSAEncrypt(byte[] DataToEncrypt, RSAParameters RSAKeyInfo, bool DoOAEPPadding)
        {
            try
            {
                byte[] encryptedData;
                //Create a new instance of RSACryptoServiceProvider.
                using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider())
                {


                    //Import the RSA Key information. This only needs
                    //toinclude the public key information.
                    RSA.ImportParameters(RSAKeyInfo);


                    //Encrypt the passed byte array and specify OAEP padding.  
                    //OAEP padding is only available on Microsoft Windows XP or
                    //later.  
                    encryptedData = RSA.Encrypt(DataToEncrypt, DoOAEPPadding);
                }
                return encryptedData;
            }
            //Catch and display a CryptographicException  
            //to the console.
            catch (CryptographicException e)
            {
                Console.WriteLine(e.Message);


                return null;
            }


        }


        static public byte[] RSADecrypt(byte[] DataToDecrypt, RSAParameters RSAKeyInfo, bool DoOAEPPadding)
        {
            try
            {
                byte[] decryptedData;
                //Create a new instance of RSACryptoServiceProvider.
                using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider())
                {
                    //Import the RSA Key information. This needs
                    //to include the private key information.
                    RSA.ImportParameters(RSAKeyInfo);


                    //Decrypt the passed byte array and specify OAEP padding.  
                    //OAEP padding is only available on Microsoft Windows XP or
                    //later.  
                    decryptedData = RSA.Decrypt(DataToDecrypt, DoOAEPPadding);
                }
                return decryptedData;
            }
            //Catch and display a CryptographicException  
            //to the console.
            catch (CryptographicException e)
            {
                Console.WriteLine(e.ToString());


                return null;
            }


        }


        public static String Encrypt(String plaintext, X509Certificate2 pubcrt)
        {
            X509Certificate2 _X509Certificate2 = pubcrt;
            using (RSACryptoServiceProvider RSACryptography = _X509Certificate2.PublicKey.Key as RSACryptoServiceProvider)
            {
                Byte[] PlaintextData = Encoding.UTF8.GetBytes(plaintext);
                int MaxBlockSize = RSACryptography.KeySize / 8 - 11;    //加密塊最大長度限制


                if (PlaintextData.Length <= MaxBlockSize)
                    return Convert.ToBase64String(RSACryptography.Encrypt(PlaintextData, false));


                using (MemoryStream PlaiStream = new MemoryStream(PlaintextData))
                using (MemoryStream CrypStream = new MemoryStream())
                {
                    Byte[] Buffer = new Byte[MaxBlockSize];
                    int BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);


                    while (BlockSize > 0)
                    {
                        Byte[] ToEncrypt = new Byte[BlockSize];
                        Array.Copy(Buffer, 0, ToEncrypt, 0, BlockSize);


                        Byte[] Cryptograph = RSACryptography.Encrypt(ToEncrypt, false);
                        CrypStream.Write(Cryptograph, 0, Cryptograph.Length);


                        BlockSize = PlaiStream.Read(Buffer, 0, MaxBlockSize);
                    }


                    return Convert.ToBase64String(CrypStream.ToArray(), Base64FormattingOptions.None);
                }
            }
        }


        public static String Decrypt(String ciphertext, X509Certificate2 prvpfx)
        {
            X509Certificate2 _X509Certificate2 = prvpfx;
            using (RSACryptoServiceProvider RSACryptography = _X509Certificate2.PrivateKey as RSACryptoServiceProvider)
            {
                Byte[] CiphertextData = Convert.FromBase64String(ciphertext);
                int MaxBlockSize = RSACryptography.KeySize / 8;    //解密塊最大長度限制


                if (CiphertextData.Length <= MaxBlockSize)
                    return Encoding.UTF8.GetString(RSACryptography.Decrypt(CiphertextData, false));


                using (MemoryStream CrypStream = new MemoryStream(CiphertextData))
                using (MemoryStream PlaiStream = new MemoryStream())
                {
                    Byte[] Buffer = new Byte[MaxBlockSize];
                    int BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);


                    while (BlockSize > 0)
                    {
                        Byte[] ToDecrypt = new Byte[BlockSize];
                        Array.Copy(Buffer, 0, ToDecrypt, 0, BlockSize);


                        Byte[] Plaintext = RSACryptography.Decrypt(ToDecrypt, false);
                        PlaiStream.Write(Plaintext, 0, Plaintext.Length);


                        BlockSize = CrypStream.Read(Buffer, 0, MaxBlockSize);
                    }


                    return Encoding.UTF8.GetString(PlaiStream.ToArray());
                }
            }
        }


        private static X509Certificate2 RetrieveX509Certificate()
        {
            return null;    //檢索用於 RSA 加密的 X509Certificate2 證書
        }








        //調用方法

        public void doit()
        {

            //Create a UnicodeEncoder to convert between byte array and string.
            UnicodeEncoding ByteConverter = new UnicodeEncoding();

            //Create byte arrays to hold original, encrypted, and decrypted data.
            byte[] dataToEncrypt = ByteConverter.GetBytes("310991");
            byte[] encryptedData;
            byte[] decryptedData;

            X509Certificate2 pubcrt = new X509Certificate2(AppDomain.CurrentDomain.BaseDirectory + "cmb.cer");
            RSACryptoServiceProvider pubkey = (RSACryptoServiceProvider)pubcrt.PublicKey.Key;
            //X509Certificate2 prvcrt = new X509Certificate2(AppDomain.CurrentDomain.BaseDirectory + "bfkey.pfx", "123456789", X509KeyStorageFlags.Exportable);
            //RSACryptoServiceProvider prvkey = (RSACryptoServiceProvider)prvcrt.PrivateKey;

            encryptedData = EncrypHelp.RSAEncrypt(dataToEncrypt, pubkey.ExportParameters(false), false);
            string encryptedDataStr = Convert.ToBase64String(encryptedData);
            Console.WriteLine("Encrypted plaintext: {0}", Convert.ToBase64String(encryptedData));

            //decryptedData = EncrypHelp.RSADecrypt(encryptedData, prvkey.ExportParameters(true), false);
            //Console.WriteLine("Decrypted plaintext: {0}", ByteConverter.GetString(decryptedData));

            //加密長內容
            String data = @"RSA 是常用的非對稱加密算法。最近使用時卻出現了“不正確的長度”的異常，研究發現是由於待加密的數據超長所致。
　　                    .NET Framework 中提供的 RSA 算法規定：
　　                    待加密的字節數不能超過密鑰的長度值除以 8 再減去 11（即：RSACryptoServiceProvider.KeySize / 8 - 11），而加密后得到密文的字節數，正好是密鑰的長度值除以 8（即：RSACryptoServiceProvider.KeySize / 8）。
　　                    所以，如果要加密較長的數據，則可以采用分段加解密的方式，實現方式如下：";
          
            string encrypt = EncrypHelp.Encrypt(data, pubcrt);
            Console.WriteLine("Encrypted plaintext: {0}", encrypt);
            //string decrypt = EncrypHelp.Decrypt(encrypt, prvcrt);
            //Console.WriteLine("Decrypted plaintext: {0}", decrypt);

            //prvkey.Clear();
            pubkey.Clear();
            Console.Read();

        }
    }