Can an RFID chip be made uncloneable? No, but one Palo Alto vendor is arguing that it's gotten quite close.
The vendor's position, according to this well-done NetworkWorld story, is to "create multiple PKI-like key pairs based on integrated circuit impurities so that a given chip will always respond to a particular stimulus in a predictable way. And, because it's the impurities in the silicon that cause this effect, it's impossible to create a chip that will respond to a specific stimulus." For one possible future of RFID, it's worth a read.
