title: Android CryptoObject usage in fingerprint
body: <p>In Android fingerprint sample code <a href="http://developer.android.com/samples/FingerprintDialog/index.html" rel="noreferrer">FingerprintDialog</a>, the method that starts fingerprint hardware <a href="http://developer.android.com/reference/android/hardware/fingerprint/FingerprintManager.html#authenticate(android.hardware.fingerprint.FingerprintManager.CryptoObject,%20android.os.CancellationSignal,%20int,%20android.hardware.fingerprint.FingerprintManager.AuthenticationCallback,%20android.os.Handler)" rel="noreferrer">FingerprintManager#authenticate</a> takes a parameter of <a href="http://developer.android.com/reference/android/hardware/fingerprint/FingerprintManager.CryptoObject.html" rel="noreferrer">FingerprintManager.CryptoObject</a>. According to the documentation, it's the <code>object associated with the call or null if none required</code>. The description is still not clear for me. Would someone explain when I should or should not use crypto Thanks.</p>