Several years ago, I gave a talk at a local university on biometric authentication--the security applications of fingerprint recognition, iris scanning, and so forth. A faculty member approached me afterward to ask why I was bothering. After all, wouldn't we all be surgically implanted with digital authentication devices in the not-too-distant future? I laughed at the idea of "prosthetic biometrics." Gently, I hope. Today a company called VeriChip conducted an initial public offering. VeriChip sells small, encapsulated microchips (RFID tags) that transmit unique serial numbers over short distances via radio—surgically implantable authentication devices, in fact. Dogs and cats have been regularly implanted with RFID tags for years. That beta test, if you will, has been has largely successful: Many shelters are equipped to scan RFID tags in animals lacking other identification, and many pets and owners owe their happy reunification to the devices...