title: QR code security
body: <p>I have been reading a lot about QR codes and how the code itself can lead to serious security risks. But one thing that I did not come across is the following.</p>
  
  <p>In the following scenario:
  I have a QR code which displays some of my data lets say:
   - Name
   - Address
   - A list of things I'm allowed to do</p>
  
  <p>And I scans my code to see its contents, add some stuf to the list of things that I'm allowed to do and reprint the QR code.
  The next day I come to work scan my code and am allowed to do the extra thing I added to the code.</p>
  
  <p>My question is: how can I stop this scenario from happening.
  Note that it is not possible to check if my data is consistent with DataBase data.</p>
  
  <p>More info:</p>
  
  <p>I'm using phonegap in combination with Sencha Touch 2 to create my QR code reader.<br>
  It is an Android application designed only for Android 4.0 devices.<br>
  The QR codes are provided once a year.<br>
  If someone would scan his QR code of last year it would not work.<br>
  Note that: in theory if he'd change the date on the code that he would be able to get in, this is exactly what I'm trying to block.<br>
  Some employees have access to the application which reads the code.<br>
  The application does not have any way to verify the data on the QR code, so it has to be something using only the data on the QR code.  </p>