[WP8.1开发]RSA 使用BouncyCastle 公钥解密

写应用的时候遇到个服务器返回私钥加密过的数据 ，然后要在客户端用公钥解密的需求 ，一直没找到方法，应用搁置了一个学期，多方搜索，结论就是.net没有实现公钥解密的方法，要自己实现，于是硬着头皮开始看 portable.bouncycastle

关于RSA的原理,这是我从MSDN盗的图，链接在这https://msdn.microsoft.com/zh-cn/library/system.security.cryptography.rsaparameters.aspx

简单说就是

密文 = (明文 ^privateExponent) mod modulus

明文 = (密文 ^publicExponent) mod modulus

公钥中含有两个参数 一个是modulus ，另一个是publicExponent，私钥中有 modulus和privateExponent两个参数(当然私钥中不止这两个参数，但方法里只用到这两个，其他不管)

由于拿到的公钥和私钥都是PEM格式的，所以要先从PEM格式的公钥和私钥中提取这些参数 ，然后进行大数运算就能得出结果

这里要感谢前辈的努力，详细的解析了PEM文件格式

现在假设假设公钥和私钥分别为

 　　　　 const string PUBLICKEY =
         　　　　 @"-----BEGIN PUBLIC KEY-----
                 MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDpsDr+W45aFHIkvotZaGK/THlF
                 FpuZfUtghhWkHAm3H7yvL42J4xHrTr6IeUDCl4eKe6qiIgvYSNoL3u4SERGOeYmV
                 1F+cocu9IMGnNoicbh1zVW6e8/iGT3xaYQizJoVuWA/TC/zdds2ihCJfHDBDsouO
                 CXecPapyWCGQNsH5sQIDAQAB
                 -----END PUBLIC KEY-----";
         const string PRIVATEKEY =
                 @"-----BEGIN RSA PRIVATE KEY-----
                 MIICXQIBAAKBgQDpsDr+W45aFHIkvotZaGK/THlFFpuZfUtghhWkHAm3H7yvL42J
                 4xHrTr6IeUDCl4eKe6qiIgvYSNoL3u4SERGOeYmV1F+cocu9IMGnNoicbh1zVW6e
                 8/iGT3xaYQizJoVuWA/TC/zdds2ihCJfHDBDsouOCXecPapyWCGQNsH5sQIDAQAB
                 AoGBAM/JbFs4y5WbMncrmjpQj+UrOXVOCeLrvrc/4kQ+zgCvTpWywbaGWiuRo+cz
                 cXrVQ6bGGU362e9hr8f4XFViKemDL4SmJbgSDa1K71i+/LnnzF6sjiDBFQ/jA9SK
                 4PYrY7a3IkeBQnJmknanykugyQ1xmCjbuh556fOeRPaHnhx1AkEA/flrxJSy1Z+n
                 Y1RPgDOeDqyG6MhwU1Jl0yJ1sw3Or4qGRXhjTeGsCrKqV0/ajqdkDEM7FNkqnmsB
                 +vPd116J6wJBAOuNY3oOWvy2fQ32mj6XV+S2vcG1osEUaEuWvEgkGqJ9co6100Qp
                 j15036AQEEDqbjdqS0ShfeRSwevTJZIap9MCQCeMGDDjKrnDA5CfB0YiQ4FrchJ7
                 a6o90WdAHW3FP6LsAh59MZFmC6Ea0xWHdLPz8stKCMAlVNKYPRWztZ6ctQMCQQC8
                 iWbeAy+ApvBhhMjg4HJRdpNbwO6MbLEuD3CUrZFEDfTrlU2MeVdv20xC6ZiY3Qtq
                 /4FPZZNGdZcSEuc3km5RAkApGkZmWetNwDJMcUJbSBrQMFfrQObqMPBPe+gEniQq
                 Ttwu1OULHlmUg9eW31wRI2uiXcFCJMHuro6iOQ1VJ4Qs
                 -----END RSA PRIVATE KEY-----";

于是获取公钥参数的方法为

  // 获取modulus和publicExponent
  string publicKey = PUBLICKEY.Replace("-----BEGIN PUBLIC KEY-----", "").Replace("-----END PUBLIC KEY-----", "").Replace("\n", "").Replace("\r", "");
  byte[] btPem = Convert.FromBase64String(publicKey);
  int pemModulus = , pemPublicExponent = ;
  byte[] btPemModulus = new byte[];
  byte[] btPemPublicExponent = new byte[];
  for (int i = ; i < pemModulus; i++)
  {
      btPemModulus[i] = btPem[ + i];
  }
  for (int i = ; i < pemPublicExponent; i++)
  {
      btPemPublicExponent[i] = btPem[ + i];
  }

公钥解密的方法为

 BigInteger biModulus = new BigInteger(, btPemModulus);
 BigInteger biExponent = new BigInteger(, btPemPublicExponent);
 RsaKeyParameters publicParameters = new RsaKeyParameters(false, biModulus, biExponent);
 IAsymmetricBlockCipher eng = new Pkcs1Encoding(new RsaEngine());
 eng.Init(false, publicParameters);
 // 解密已加密的数据
 byte[] encryptedData = Convert.FromBase64String(rawData);
 encryptedData = eng.ProcessBlock(encryptedData, , encryptedData.Length);
 string result = Encoding.UTF8.GetString(encryptedData, , encryptedData.Length);

公钥加密的方法为

 BigInteger biModulus = new BigInteger(, btPemModulus);
 BigInteger biExponent = new BigInteger(, btPemPublicExponent);
 RsaKeyParameters publicParameters = new RsaKeyParameters(false, biModulus, biExponent);
 IAsymmetricBlockCipher eng = new Pkcs1Encoding(new RsaEngine());
 eng.Init(true, publicParameters);
 // 加密数据
 byte[] encryptData = Encoding.UTF8.GetBytes(rawData);
 encryptData = eng.ProcessBlock(encryptData, , encryptData.Length);
 string result = Convert.ToBase64String(encryptData);

私钥的通过PEM文件格式详细解析里的图也可以方便的写出来，mark下以后写……(￣o￣) . z Z

顺便贴上WP 8.1里自带的RSA公钥加密 私钥解密

 　　　　 /// <summary>
         /// WPRT的RSA公钥加密
         /// </summary>
         /// <param name="rawData">源数据</param>
         /// <returns>加密后的数据</returns>
         public static string PublicEncrypt(string rawData)
         {
             try
             {
                 /*将文本转换成IBuffer*/
                 IBuffer bufferRawData = CryptographicBuffer.ConvertStringToBinary(rawData, BinaryStringEncoding.Utf8);
 
                 /*加密算法提供程序*/
                 AsymmetricKeyAlgorithmProvider provider = AsymmetricKeyAlgorithmProvider.OpenAlgorithm
                     (AsymmetricAlgorithmNames.RsaPkcs1);
 
                 /*导入公钥*/
                 string PUBLIC_KEY = PUBLICKEY.Replace("-----BEGIN PUBLIC KEY-----", "").Replace("-----END PUBLIC KEY-----", "");
                 CryptographicKey publicKey = provider.ImportPublicKey(CryptographicBuffer.DecodeFromBase64String(PUBLIC_KEY));
 
                 //加密
                 IBuffer result = CryptographicEngine.Encrypt(publicKey, bufferRawData, null);
                 byte[] res;
                 CryptographicBuffer.CopyToByteArray(result, out res);
                 Debug.WriteLine("WinRT公钥加密后：" + Convert.ToBase64String(res));
                 return Convert.ToBase64String(res);
             }
             catch (Exception e)
             {
                 Debug.WriteLine("Encrypt Exception：" + e.StackTrace);
                 return rawData;
             }
         }
 
         /// <summary>
         /// WPRT的RSA私钥解密
         /// </summary>
         /// <param name="rawData"></param>
         /// <returns></returns>
         public static string PrivateDecrypt(string rawData)
         {
             try
             {
                 /*将文本转换成IBuffer*/
                 IBuffer bufferRawData = CryptographicBuffer.ConvertStringToBinary(rawData, BinaryStringEncoding.Utf8);
 
                 /*加密算法提供程序*/
                 AsymmetricKeyAlgorithmProvider provider = AsymmetricKeyAlgorithmProvider.OpenAlgorithm
                     (AsymmetricAlgorithmNames.RsaPkcs1);
 
                 /*导入私钥*/
                 string PRIVATE_KEY = PRIVATEKEY.Replace("-----BEGIN RSA PRIVATE KEY-----", "").Replace("-----END RSA PRIVATE KEY-----", "");
                 CryptographicKey privateKey = provider.ImportKeyPair(CryptographicBuffer.DecodeFromBase64String(PRIVATE_KEY));
 
                 //解密
                 IBuffer result = CryptographicEngine.Decrypt(privateKey, bufferRawData, null);
                 byte[] res;
                 CryptographicBuffer.CopyToByteArray(result, out res);
                 Debug.WriteLine("WinRT私钥解密后：" + Encoding.UTF8.GetString(res,,res.Length));
                 return Encoding.UTF8.GetString(res,,res.Length);
             }
             catch (Exception e)
             {
                 Debug.WriteLine("Decrypt Exception：" + e.StackTrace);
                 return rawData;
             }
         }

参考链接

PEM文件格式详细解析

BouncyCastle