title: android : extract and encrypt header part of a file
body: <p>I am trying to do encryption / decryption of files. I could successfully encrypt the files. But when the file size is huge like video files, the algorithm takes very long time. To solve this, i want to encrypt only part of the file so that it cannot be open by any other app .</p>
  
  <p>I am not sure if this is the right way to do it. SO please help me to find answers for :</p>
  
  <p>Is this a feasible solution to encrypt only part of the file or only header ?
  How can i get only header part ?</p>
  
  <p>Is there a better solution for better performance?</p>
  
  <p>Thanks in advance for your time and help</p>