android - How to download an encrypted png file without loosing data? -

i'm new android. i'm doing application can download encrypted png image file sd card displaying after decryption. notice i'm getting "javax.crypto.illegalblocksizeexception: last block incomplete in decryption image decryption" when decrypting downloaded image. found downloaded image size 0kb (original - 150kb). downloaded encrypted image browser , checked. i'm getting original image size. i'm sure there wrong in image downloading class. cant figure out. please me. in advance.

image downloading asynctask class

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 = conn.getinputstream();             bufferedinputstream bis = new bufferedinputstream(is);             bm = bitmapfactory.decodestream(bis);             bis.close();             is.close();         }         catch (outofmemoryerror e)         {             log.e("hub", "error getting image server : " + e.getmessage().tostring());         }         catch (ioexception e)         {             log.e("hub", "error getting image 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();             }         }     } } 

(all images encrypted me. , hosted them in server. there no issue in ancryption or decryption. tested them. working fine.)

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;     } } 

if understand correctly downloading image first

bufferedinputstream bis = new bufferedinputstream(is); bm = bitmapfactory.decodestream(bis); 

then saving file png compression:

bm.compress(bitmap.compressformat.png, 100, outstream); 

and after doing decryption on file, right?

i think might want decrypt bytes prior saving them png, or maybe prior using decodestream. otherwise decrypting encrypted bytes decode stream , png compression messed with.

try skipping of bitmapfactory stuff , save initial file as-is, , run decryption. in asynctask:

string savefilepath = <path 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(); 

then run decryption stuff on saved file