title: what symmetric keys we can use in angular cryptography?
body: <p>I am using ionic to develop my mobile application.
  To achieve encryption, am using angular mdo cryptography.</p>
  
  <p><a href="https://github.com/middleout/angular-cryptography/blob/master/mdo-angular-cryptography.js" rel="nofollow">https://github.com/middleout/angular-cryptography/blob/master/mdo-angular-cryptography.js</a></p>
  
  <p>Application has Remember Me feature where initially I save server token in localStorage and then check the same while launching the app.</p>
  
  <p>Encryption is done to encrypt sensitive details only which are stored in localStorage.
  I am stuck in knowing the key that can be used in the above angular cryptography library.
  I tried device UUID but seems it gets changed while app. upgrade or while ad-hoc testing builds.</p>
  
  <p>Any ideas of what we can use as key so that it remains same irrespective of install or delete or upgrade ?
  Application is targeted for Android,iOS and Windows</p>
  
  <p>Help is appreciated !</p>