title: ios8 TouchID detection if fingerprint was added
body: <p>Im digging into Apple's Touch ID, more precisely the Local Authenticator.
  The documentation as of now is pretty sparse.
  Its mainly just this:</p>
  
  <pre><code>LAContext *myContext = [[LAContext alloc] init];
  NSError *authError = nil;
  NSString *myLocalizedReasonString = &lt;#String explaining why app needs authentication#&gt;;
  
  if ([myContext canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics    error:&amp;authError]) {
  [myContext evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics
                localizedReason:myLocalizedReasonString
                          reply:^(BOOL success, NSError *error) {
          if (success) {
              // User authenticated successfully, take appropriate action
          } else {
              // User did not authenticate successfully, look at error and take appropriate action
          }
      }];
  } else {
  // Could not evaluate policy; look at authError and present an appropriate message to user
  }
  </code></pre>
  
  <p>as taken from <a href="https://developer.apple.com/documentation/localauthentication" rel="nofollow noreferrer">https://developer.apple.com/documentation/localauthentication</a></p>
  
  <p>The idea of using your fingerprint for authentication is nice. But I can add fingerprints in the device if I know the passcode. And its very easy to get the passcode, like you sit in the train next to ur victim and watch him/her enter the passcode. </p>
  
  <p>I want to use the fingerprint as a way of secure authentication but want to be able to detect if new fingerprints were added since the last time I requested the fingerprint.</p>
  
  <p>Apple is doing this for the AppStore. If you want to authenticate a transaction in the AppStore and have added a new Fingerprint since your last transaction, the AppStore requests your AppleId-Password. This is sane behaviour, because the phone might have been taken by someone else who knows the passcode and added his own fingerprint to buy something expensive.</p>
  
  <p>My Question: Can I detect if a new fingerprint was added since the last time that I used Local Authenticator?</p>