我正在研究一个Flutter应用程序，它涉及从互联网上获取PDF文件，加密并将其存储在应用程序文件目录中，并检索，解密以在应用程序中显示。我正在使用https://pub.dev/packages/encrypt和Syncfusion pdf viewer来实现此目的。但是在解密和显示文件时，

ArgumentError{Invalid argument (position): Invalid Position:-1}

在SfPdfViewer中运行调试模式。代码为：

`SfPdfViewer.network( 
          widget.file!.link!, 
          key: _pdfViewerKey, 
          onDocumentLoaded: (PdfDocumentLoadedDetails details) async { 
        // final Directory tempPath = await getApplicationDocumentsDirectory(); 
        // _tempFile = await File('${tempPath.path}/${widget.file!.title}.pdf') 
        //     .writeAsBytes( await details.document.save()); 
      }):FutureBuilder<Uint8List>(
        future: getFileBytes(),
        builder:(context,snapshot){
          if(snapshot.hasData)
          {
            logger.i("Snapshot Data is ${snapshot.data}");
            return SfPdfViewer.memory(snapshot.data!,key: _pdfViewerKey, );
          }
          else if(snapshot.hasData)
          {
            snapshot.printError();
            return Text('Error');
          }
          else
          {
            return const Center(child: CircularProgressIndicator());
          }
        }
      )
      );
    
  }
  Future<Uint8List> getFileBytes() async
  {
    return await fileController.getDecryptedFile(name: widget.file!.title!);
    
  }`

下载、加密和解密的方法有：

Future<void> downloadFile({required Files file})async
  {
    
    logger.e("Link of file to be downloaded is ${file.link}");
    Response response=await download(url: file.link!);
      final directory = await getApplicationDocumentsDirectory();
    final filesDirectory = await Directory('${directory.path}/files').create(recursive: true);
    

    String filePath='${filesDirectory.path}/${file.title!}.aes';

   
    logger.i("Length of key is ${key.length}");
    final encryptor=Encrypter(AES(key,padding: null));
    logger.i("Unencrypted bytes: ${response.data}");
    final encryptedBytes = encryptor.encryptBytes(response.data,iv: iv,);
    final decryptedBytes = encryptor.decryptBytes(encryptedBytes,iv: iv,associatedData: encryptedBytes.bytes);
    logger.i("encrypted bytes: ${encryptedBytes}");
    final encryptedFile=File(filePath);
    encryptedFile.writeAsBytesSync(encryptedBytes.bytes);
    changeDownloadStatus(true);
    
    
  }


  Future<dynamic> download({required String url}) async
{
  try{
    String token=url.substring(url.indexOf("token")+7,url.indexOf("_gl"));
    String alt=url.substring( url.indexOf("alt=")+5,url.indexOf("token="));
    String gl=url.substring(url.indexOf("_gl=")+5);
    Map<String,String> query={
      "token":token,
      "alt":alt,
      "_gl":gl
    };
    Response response =await Dio().get(url.substring(0,url.indexOf("?")),options: Options(responseType: ResponseType.bytes,
            followRedirects: false,contentType: "application/pdf"),queryParameters: query);
    logger.i(response.data);

    changeDownloadStatus(true);
    return response;
  }
  on Exception catch(e)
  {
    logger.e(e.toString());
  }
}

Future<Uint8List> getDecryptedFile({required String name}) async
{
     final directory = await getApplicationDocumentsDirectory();
    final filesDirectory = Directory('${directory.path}/files');
    String filePath='${filesDirectory.path}/$name.aes';
    File encryptedfile=File(filePath);
    bool isPresent=await encryptedfile.exists();
    logger.i("File at path $filePath is present $isPresent");
   
    
      Uint8List encryptedBytes=encryptedfile.readAsBytesSync();
      logger.i("encrypted bytes: ${encryptedBytes}");
      
      // Decrypt the file
      
    final encryptor=Encrypter(AES(key,padding: null));
    final decryptedBytes=encryptor.decryptBytes(Encrypted(encryptedBytes),iv: iv,associatedData: encryptedBytes);

    return Uint8List.fromList(decryptedBytes);
    
   
}

Key和Iv的计算公式如下：

final iv=IV.fromLength(16);
    final key=Key.fromSecureRandom(32);

我得到一个列表中的日志与未加密的字节和解密的字节相同的数据。另外，当在decryptor对象中使用默认填充时，我会得到**解密方法中无效或损坏的填充。**问题在哪里？