C#/.Net微信ウィジェットencryptedData復号

public string AES_decrypt(string encryptedDataStr, string key, string iv)  
        {  
            RijndaelManaged rijalg = new RijndaelManaged();  
            //-----------------    
            //   cipher    AES-128-CBC    
  
            rijalg.KeySize = 128;  
  
            rijalg.Padding = PaddingMode.PKCS7;  
            rijalg.Mode = CipherMode.CBC;  
  
            rijalg.Key = Convert.FromBase64String(key);  
            rijalg.IV = Convert.FromBase64String(iv);  
  
  
            byte[] encryptedData= Convert.FromBase64String(encryptedDataStr);  
            //      
            ICryptoTransform decryptor = rijalg.CreateDecryptor(rijalg.Key, rijalg.IV);  
  
            string result;  
              
            using (MemoryStream msDecrypt = new MemoryStream(encryptedData))  
            {  
                using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))  
                {  
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))  
                    {  
  
                        result;= srDecrypt.ReadToEnd();  
                    }  
                }  
            }  
  
            return result;  
        }