android 下载时加密音频mp3文件，播放时解密

Question

I have an android application which downloads and play mp3 files. But I want to encrypt audio files while downloading and then decrypt to play it. I have already checked everywhere in the internet but did not find any solution. Could anyone please help me how to encrypt audio files while downloading and then decrypt during playing Here is my code to download the files

     private void download() {
    if (Constant.arrayList_play.size() > 0) {

        File root = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/Myapp/cache");
        if (!root.exists()) {
            root.mkdirs();
        }

        File file = new File(root, Constant.arrayList_play.get(viewpager.getCurrentItem()).getMp3Name() + ".mp3");

        if (!file.exists()) {

            String url = Constant.arrayList_play.get(viewpager.getCurrentItem()).getMp3Url();
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
            request.setDescription(getResources().getString(R.string.downloading) + " - " + Constant.arrayList_play.get(viewpager.getCurrentItem()).getMp3Name());
            request.setTitle(Constant.arrayList_play.get(viewpager.getCurrentItem()).getMp3Name());
            request.allowScanningByMediaScanner();
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            request.setDestinationUri(Uri.parse("file://" + Environment.getExternalStorageDirectory().getAbsolutePath() + "/Myapp/cache/" + Constant.arrayList_play.get(viewpager.getCurrentItem()).getMp3Name() + ".mp3"));
            DownloadManager manager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
            manager.enqueue(request);

            new AsyncTask<String, String, String>() {
                @Override
                protected String doInBackground(String... strings) {
                    String json = JsonUtils.getJSONString(Constant.URL_DOWNLOAD_COUNT + Constant.arrayList_play.get(viewpager.getCurrentItem()).getId());
                    Log.e("aaa - ", json);
                    return null;
                }
            }.execute();
            Toast.makeText(MainActivity.this, getResources().getString(R.string.downloading), Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(MainActivity.this, getResources().getString(R.string.already_download), Toast.LENGTH_SHORT).show();
        }
    } else {
        Toast.makeText(MainActivity.this, getResources().getString(R.string.no_song_selected), Toast.LENGTH_SHORT).show();
    }
}

So could you please help me with a code.

Answer 1

I have found a solution to my question and have been using it in my app since many days without any problem so I think it is good to answer my own question also as many users had asked for solution in comments. So just follow the below codes-

  //Downloading and encrypting the audio

  AesCipherDataSink encryptingDataSink = new AesCipherDataSink(
      Util.getUtf8Bytes("4J95qN8RxBP8hTpk"),
      new DataSink() {
       private FileOutputStream fileOutputStream;

       @Override
       public void open(DataSpec dataSpec) throws IOException {
               fileOutputStream = new FileOutputStream(file);
        }

       @Override
       public void write(byte[] buffer, int offset, int length) throws IOException {
          fileOutputStream.write(buffer, offset, length);
        }

       @Override
       public void close() throws IOException {
             fileOutputStream.close();
         }
        });

   // Push the data through the sink, and close everything.
   encryptingDataSink.open(new DataSpec(Uri.fromFile(file)));
   URL downloadURL = new URL(strings[0]);
   HttpURLConnection connection = (HttpURLConnection) downloadURL.openConnection();
   connection.setChunkedStreamingMode(0);
   connection.setDoInput(true);
   connection.connect();
   if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
      return "Server error";
   }

   InputStream inputStream = connection.getInputStream();
   byte[] buffer = new byte[1024];
   int newLength;
   while ((newLength = inputStream.read(buffer)) > 0) {
        encryptingDataSink.write(buffer, 0, newLength);
    }
   encryptingDataSink.close();
   inputStream.close();



   //decrypting and playing the audio
   DataSource.Factory factory =
                new CustomDataSourceFactory(
                        context,
                        new OkHttpDataSourceFactory(new OkHttpClient(), Util.getUserAgent(context,
                              context.getResources().getString(R.string.app_name)))
                );

    MediaSource videoSource =
                new ProgressiveMediaSource.Factory(factory)
                        .createMediaSource(Uri.parse(tempFile.getAbsolutePath()));
    exoPlayer.addMediaSource(videoSource);

    
   //CustomDataSourceFactoryClass

    public class CustomDataSourceFactory implements DataSource.Factory {

      private final Context context;
      private final DataSource.Factory baseDataSourceFactory;


      public CustomDataSourceFactory(Context context, DataSource.Factory baseDataSourceFactory) {
        this.context = context.getApplicationContext();
        this.baseDataSourceFactory = baseDataSourceFactory;
       }

       @Override
        public DataSource createDataSource() {
         return new CryptedDefaultDataSource(context, baseDataSourceFactory.createDataSource());
         }
      }

   //CryptedDafaultDataSource
    public class CryptedDefaultDataSource implements DataSource {

      private final List<TransferListener> transferListeners;
      private final DataSource baseDataSource;
      private @Nullable
      DataSource fileDataSource,aesCipherDataSource,dataSource;
      private Context context;

      CryptedDefaultDataSource(Context context, DataSource baseDataSource) {
         this.context=context;
         this.baseDataSource = Assertions.checkNotNull(baseDataSource);
         transferListeners = new ArrayList<>();
      }

      @Override
      public void addTransferListener(TransferListener transferListener) {
       baseDataSource.addTransferListener(transferListener);
       transferListeners.add(transferListener);
       maybeAddListenerToDataSource(fileDataSource, transferListener);
       maybeAddListenerToDataSource(aesCipherDataSource, transferListener);
      }

     @Override
     public long open(DataSpec dataSpec) throws IOException {
        Assertions.checkState(dataSource == null);
        if (Util.isLocalFileUri(dataSpec.uri)) {
          dataSource = getCryptedDataSource(getFileDataSource());
        } else {
          dataSource = getCryptedDataSource(baseDataSource);
        }
       return dataSource.open(dataSpec);
      }

     @Override
      public int read(byte[] buffer, int offset, int readLength) throws IOException {
         return Assertions.checkNotNull(dataSource).read(buffer, offset, readLength);
       }

      @Nullable
      @Override
       public Uri getUri() {
        return dataSource == null ? null : dataSource.getUri();
      }

      @Override
      public Map<String, List<String>> getResponseHeaders() {
          return dataSource == null
            ? DataSource.super.getResponseHeaders()
            : dataSource.getResponseHeaders();
       }

     @Override
     public void close() throws IOException {
       if (dataSource != null) {
        try {
            dataSource.close();
        } finally {
            dataSource = null;
        }
      }
     }

    private DataSource getFileDataSource() {
      if (fileDataSource == null) {
         fileDataSource = new FileDataSource();
         addListenersToDataSource(fileDataSource);
       }
       return fileDataSource;
     }

    private DataSource getCryptedDataSource(DataSource upstreamDataSource) {
      if (aesCipherDataSource == null) {
        aesCipherDataSource = new AesCipherDataSource("4J95qN8RxBP8hTpk".getBytes(),upstreamDataSource);
        addListenersToDataSource(aesCipherDataSource);
      }
      return aesCipherDataSource;
     }

   private void addListenersToDataSource(DataSource dataSource) {
     for (int i = 0; i < transferListeners.size(); i++) {
        dataSource.addTransferListener(transferListeners.get(i));
     }
   }

     private void maybeAddListenerToDataSource(
        @Nullable DataSource dataSource, TransferListener listener) {
      if (dataSource != null) {
        dataSource.addTransferListener(listener);
      }
     }
   }