C#使用RSA证书文件加密和解密示例

修改MSDN上的示例，使之可以通过RSA证书文件加密和解密，中间遇到一个小问题。

Q:执行ExportParameters()方法时，回报CryptographicException:该项不适于在指定状态下使用(Key not valid for use in specified state)。

A：导入带有私钥的证书时，需要使用"X509KeyStorageFlags"参数标记"私钥可导出"。

X509Certificate2 prvcrt = new X509Certificate2(@"X:\path\to\CA.pfx", "***password***", X509KeyStorageFlags.Exportable);

以下为示例程序：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TeatApp_Crypto
{
    using System;
    using System.Security.Cryptography;
    using System.Security.Cryptography.X509Certificates;
    using System.Text;

    class RSACSPSample
    {

        static void Main()
        {
            try
            {
                //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("Data to Encrypt");
                byte[] encryptedData;
                byte[] decryptedData;

                X509Certificate2 pubcrt = new X509Certificate2(@"X:\path\to\CA.crt");
                RSACryptoServiceProvider pubkey = (RSACryptoServiceProvider)pubcrt.PublicKey.Key;
                X509Certificate2 prvcrt = new X509Certificate2(@"X:\path\to\CA.pfx", "***password***", X509KeyStorageFlags.Exportable);
                RSACryptoServiceProvider prvkey = (RSACryptoServiceProvider)prvcrt.PrivateKey;
                //Create a new instance of RSACryptoServiceProvider to generate
                //public and private key data.
                //using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider())
                //{
                    //Console.WriteLine(RSA.ToXmlString(false));
                    //Pass the data to ENCRYPT, the public key information 
                    //(using RSACryptoServiceProvider.ExportParameters(false),
                    //and a boolean flag specifying no OAEP padding.
                    encryptedData = RSAEncrypt(dataToEncrypt, pubkey.ExportParameters(false), false);
                    Console.WriteLine("Encrypted plaintext: {0}", Convert.ToBase64String(encryptedData));

                    //Pass the data to DECRYPT, the private key information 
                    //(using RSACryptoServiceProvider.ExportParameters(true),
                    //and a boolean flag specifying no OAEP padding.
                    decryptedData = RSADecrypt(encryptedData, prvkey.ExportParameters(true), false); 
                    
                    //Display the decrypted plaintext to the console. 
                    Console.WriteLine("Decrypted plaintext: {0}", ByteConverter.GetString(decryptedData));
                //}
                prvkey.Clear();
                pubkey.Clear();
                Console.Read();
            }
            catch (ArgumentNullException)
            {
                //Catch this exception in case the encryption did
                //not succeed.
                Console.WriteLine("Encryption failed.");

            }
        }

        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;
            }

        }
    }
}