[thaumaturgy]

I don't think perfect security needs to be the goal here. You just need to have your device automatically protect the data on it when you're separated from it -- whether it's the state in suits, or just random laptop theft in San Francisco.

If you're up against an enemy capable of realizing ahead of time that you've RFID-protected your device, and capable of cloning your RFID tag without your knowledge, then you're probably screwed no matter what you do.