Again, I keep hoping I'm wrong and that there are other RFID/NFC contact-less asymmetric encryption options out there that I'm unaware of (please tell me!), but after buying some encrypted tags and finding out that they're still vulnerable to some easy attacks I lost short term interest.
(Of course active<->active NFC is still interesting. I invision a future house with a secret NFC panel that does asym auth with my phone to unlock itself with a batman style swing-open door).
I've been watching and tinkering with NFC for sometime. It gets boring quickly because you can't have cheap fobs that are secure yet because there's no way to do assymmetric encryption without an active NFC (with power).
Thus, your "car openers" that use NFC fobs are open to be cloned, and in fact was just recently a source of BMW theft. With the ability to have RNGs and assymmetric encryption, you can have usable, secure fobs.