/// <summary>
        /// aes-256-cbc 解码
        /// </summary>
        /// <param name="cipherData"></param>
        /// <param name="keyString"></param>
        /// <param name="ivString"></param>
        /// <returns></returns>
        public static string Decrypt(string cipherData, string keyString, string ivString)
        {
            byte[] key = Encoding.UTF8.GetBytes(keyString);
            byte[] iv = Encoding.UTF8.GetBytes(ivString);

            try
            {
                using (var rijndaelManaged =
                       new RijndaelManaged { Key = key, IV = iv, Mode = CipherMode.CBC })
                using (var memoryStream =
                       new MemoryStream(Convert.FromBase64String(cipherData)))
                using (var cryptoStream =
                       new CryptoStream(memoryStream,
                           rijndaelManaged.CreateDecryptor(key, iv),
                           CryptoStreamMode.Read))
                {
                    return new StreamReader(cryptoStream).ReadToEnd();
                }
            }
            catch (CryptographicException e)
            {
                Console.WriteLine("A Cryptographic error occurred: {0}", e.Message);
                return null;
            }
            // You may want to catch more exceptions here...
        }

        /// <summary>
        /// aes-256-cbc 加密
        /// </summary>
        /// <param name="message"></param>
        /// <param name="KeyString"></param>
        /// <param name="IVString"></param>
        /// <returns></returns>
        public static string EncryptString(string message, string KeyString, string IVString)
        {
            byte[] Key = ASCIIEncoding.UTF8.GetBytes(KeyString);
            byte[] IV = ASCIIEncoding.UTF8.GetBytes(IVString);

            string encrypted = null;
            RijndaelManaged rj = new RijndaelManaged();
            rj.Key = Key;
            rj.IV = IV;
            rj.Mode = CipherMode.CBC;

            try
            {
                MemoryStream ms = new MemoryStream();

                using (CryptoStream cs = new CryptoStream(ms, rj.CreateEncryptor(Key, IV), CryptoStreamMode.Write))
                {
                    using (StreamWriter sw = new StreamWriter(cs))
                    {
                        sw.Write(message);
                        sw.Close();
                    }
                    cs.Close();
                }
                byte[] encoded = ms.ToArray();
                encrypted = Convert.ToBase64String(encoded);

                ms.Close();
            }
            catch (CryptographicException e)
            {
                Console.WriteLine("A Cryptographic error occurred: {0}", e.Message);
                return null;
            }
            catch (UnauthorizedAccessException e)
            {
                Console.WriteLine("A file error occurred: {0}", e.Message);
                return null;
            }
            catch (Exception e)
            {
                Console.WriteLine("An error occurred: {0}", e.Message);
            }
            finally
            {
                rj.Clear();
            }
            return encrypted;
        }
        //call
           string reta = DeEncode.EncryptString("中文cnn", "12345678901234561234567890123456", "1234567890123456");
            string retb = DeEncode.Decrypt(reta, "12345678901234561234567890123456", "1234567890123456");