encryption lasts too long android -

i've encrypted , decrypted 20 mb file following way

public boolean decryptfile() {      long millis=calendar.getinstance().gettimeinmillis();     try{         string path=environment.getexternalstoragedirectory().getabsolutepath();      inputstream fis = new fileinputstream(path+"/download/circus.pbf");     file outfile = new file(path+"/download/circus.zip");     int read = 0;     if (!outfile.exists())         outfile.createnewfile();      fileoutputstream fos = new fileoutputstream(outfile);      ivparameterspec ive = new ivparameterspec(key2.getbytes("utf-8"));      secretkeyspec skeyspec = new secretkeyspec(key1.getbytes("utf-8"),             "aes");     cipher cipher = cipher.getinstance("aes/cbc/pkcs5padding");     cipher.init(cipher.encrypt_mode, skeyspec, ive);     cipherinputstream cis = new cipherinputstream(fis, cipher);     int b;     byte[] d = new byte[8];     while ((b = cis.read(d)) != -1) {         fos.write(d, 0, b);     }     fos.flush();     fos.close();     cis.close();         log.e("decryption:", (calendar.getinstance().gettimeinmillis() - millis) / (1000 + 0.0) + " sec");         return true;  }     catch(ioexception ex){         ex.printstacktrace();     }     catch(invalidalgorithmparameterexception ex){         ex.printstacktrace();     }     catch(nosuchpaddingexception ex){         ex.printstacktrace();     }     catch(invalidkeyexception ex){         ex.printstacktrace();     }     catch(nosuchalgorithmexception ex){         ex.printstacktrace();     }     return false; }   public boolean encryptfile()  {     long millis= calendar.getinstance().gettimeinmillis();      // here read cleartext.     try {          string path=environment.getexternalstoragedirectory().getabsolutepath();         inputstream fis = new fileinputstream(path+"/download/circus.zip");          /*file folder=new file(dir);         folder.mkdir();*/          file outfile = new file(path+"/download/circus.pbf");         int read = 0;         if (!outfile.exists())             outfile.createnewfile();          fileoutputstream encfos = new fileoutputstream(outfile);           ivparameterspec ive = new ivparameterspec(key2.getbytes("utf-8"));          secretkeyspec skeyspec = new secretkeyspec(key1.getbytes("utf-8"),                 "aes");         cipher cipher = cipher.getinstance("aes/cbc/pkcs5padding");         cipher.init(cipher.decrypt_mode, skeyspec, ive);          // wrap output stream         cipheroutputstream cos = new cipheroutputstream(encfos, cipher);         // write bytes         int b;         byte[] d = new byte[8];         while ((b = fis.read(d)) != -1) {             cos.write(d, 0, b);         }          cos.flush();         cos.close();         fis.close();         log.e("encryption:",(calendar.getinstance().gettimeinmillis()-millis)/(1000+0.0)+" sec");         return true;     }     catch(ioexception ex){         ex.printstacktrace();     }     catch(invalidalgorithmparameterexception ex){         ex.printstacktrace();     }     catch(nosuchpaddingexception ex){         ex.printstacktrace();     }     catch(invalidkeyexception ex){         ex.printstacktrace();     }     catch(nosuchalgorithmexception ex){         ex.printstacktrace();     }     return false; } 

and got 325 sec decrypting time. it's long. how can use decrypting not on file partially on selected bytes

e/decryption:﹕ 325.862 sec 

please recommend me other encryption method or partial encryption

is there reason why using such small byte buffer?

byte[] d = new byte[8];

i suggest play around array size, e.g.

byte[] d = new byte[16 * 1024]; 

or

byte[] d = new byte[1024 * 1024]; 

this should enhance performance.