如何在不丢失数据的情况下下载加密的png文件？

Question

我是新来的android。我正在做一个应用程序，它可以将加密的png图像文件下载到sd卡，然后在解密后显示它。但是我注意到，当解密下载的图像时，我得到“javax.crypto.IllegalBlockSizeException: last block incomplete in decryption image decryption”。然后我发现下载的图像大小为0KB（原始 - 150KB）。然后我从浏览器下载了我的加密图像并进行了检查我得到原始图像大小。我确定我的图片下载课程有问题。但我无法弄清楚。请帮帮我。提前致谢。

图片下载的AsyncTask类

public class DownloadImagesTask extends AsyncTask<String, Void, Bitmap> 
{ 
    private String fileName; 

    @Override 
    protected Bitmap doInBackground(String... urls) 
    { 
     //Thread.currentThread().setPriority(Thread.MAX_PRIORITY); 
     return download_Image(urls[0]); 
    } 

    @Override 
    protected void onPostExecute(Bitmap result) 
    { 
     storeImage(result); 

    } 

    private Bitmap download_Image(String url) 
    { 
     Bitmap bm = null; 
     File file = new File(url); 
     fileName = file.getName(); 
     try 
     { 
      URL aURL = new URL(url); 
      URLConnection conn = aURL.openConnection(); 
      conn.connect(); 
      InputStream is = conn.getInputStream(); 
      BufferedInputStream bis = new BufferedInputStream(is); 
      bm = BitmapFactory.decodeStream(bis); 
      bis.close(); 
      is.close(); 
     } 
     catch (OutOfMemoryError e) 
     { 
      Log.e("Hub", "Error getting the image from server : " + e.getMessage().toString()); 
     } 
     catch (IOException e) 
     { 
      Log.e("Hub", "Error getting the image from server : " + e.getMessage().toString()); 
     } 

     return bm; 
    } 

    public void storeImage(Bitmap bm) 
    { 
     BitmapFactory.Options bmOptions; 
     bmOptions = new BitmapFactory.Options(); 
     bmOptions.inSampleSize = 1; 
     String extStorageDirectory = CommonUtils.getDataFromPreferences("metaPath", ""); 

     Log.d("extStorageDirectory", extStorageDirectory); 
     OutputStream outStream = null; 

     File wallpaperDirectory = new File(extStorageDirectory); 
     if (!wallpaperDirectory.exists()) 
     { 
      wallpaperDirectory.mkdirs(); 
     } 
     File outputFile = new File(wallpaperDirectory, fileName); 
     if (!outputFile.exists() || outputFile.length() == 0) 
     { 
      try 
      { 
       outStream = new FileOutputStream(outputFile); 
      } 
      catch (FileNotFoundException e1) 
      { 
       e1.printStackTrace(); 
      } 

      try 
      { 
       bm.compress(Bitmap.CompressFormat.PNG, 100, outStream); 
       outStream.flush(); 
       outStream.close(); 
       Log.d("ScratchActivtiy", "Image Saved"); 

      } 
      catch (FileNotFoundException e) 
      { 
       e.printStackTrace(); 

      } 
      catch (IOException e) 
      { 
       e.printStackTrace(); 
      } 
      catch (Exception e) 
      { 
       e.printStackTrace(); 
      } 
     } 
    } 
} 

（所有图片都是我加密的。而且我主持他们的服务器。有一个在ancryption或解密没有问题。我对它们进行测试，所有工作正常。）

CryptClass

public class CryptClass 
{ 

    public byte[] encrypt(String seed, byte[] cleartext) throws Exception 
    { 

     byte[] rawKey = getRawKey(seed.getBytes()); 
     byte[] result = encrypt(rawKey, cleartext); 
     // return toHex(result); 
     return result; 
    } 

    public byte[] decrypt(String seed, byte[] encrypted) throws Exception 
    { 
     byte[] rawKey = getRawKey(seed.getBytes()); 
     byte[] enc = encrypted; 
     byte[] result = decrypt(rawKey, enc); 

     return result; 
    } 

    //done 
    private byte[] getRawKey(byte[] seed) throws Exception 
    { 
     KeyGenerator kgen = KeyGenerator.getInstance("AES"); 
     SecureRandom sr = SecureRandom.getInstance("SHA1PRNG"); 
     sr.setSeed(seed); 
     kgen.init(128, sr); 
     SecretKey skey = kgen.generateKey(); 
     byte[] raw = skey.getEncoded(); 
     return raw; 
    } 

    private byte[] encrypt(byte[] raw, byte[] clear) throws Exception 
    { 
     SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES"); 
     Cipher cipher = Cipher.getInstance("AES"); 
     cipher.init(Cipher.ENCRYPT_MODE, skeySpec); 
     byte[] encrypted = cipher.doFinal(clear); 
     return encrypted; 
    } 

    private byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception 
    { 
     SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES"); 
     Cipher cipher = Cipher.getInstance("AES"); 
     cipher.init(Cipher.DECRYPT_MODE, skeySpec); 
     byte[] decrypted = cipher.doFinal(encrypted); 
     return decrypted; 
    } 
} 

Answer 1

如果我理解正确你下载图像第一

BufferedInputStream bis = new BufferedInputStream(is); 
bm = BitmapFactory.decodeStream(bis); 

然后将其保存到与PNG压缩文件：

bm.compress(Bitmap.CompressFormat.PNG, 100, outStream); 

，之后做你解密的文件，对不对？

我想你可能想解密字节，然后将它们保存为png，或者甚至在使用decodeStream之前。否则，您将解密解码流和PNG压缩的加密字节。

尝试跳过所有的BitmapFactory的东西，只是保存原来的文件，然后运行你的解密。在您的AsyncTask：

String saveFilePath = <path to the temporary encrypted file>; 

FileOutputStream outputStream = new FileOutputStream(saveFilePath); 
int bytesRead = -1; 
byte[] buffer = new byte[4096]; 
while ((bytesRead = is.read(buffer)) != -1) { 
    outputStream.write(buffer, 0, bytesRead); 
} 

outputStream.close(); 
inputStream.close(); 

然后在保存的文件