Unidirectional Key Distribution Across Time and Space with Applications to RFID Security

We explore the problem of secret-key distribution in unidirectional channels, those in which a sender transmits information blindly to a receiver. We consider two approaches: (1) Key sharing across space, i.e., across simultaneously emitted values that may follow different data paths and (2) Key sharing across time, i.e., in temporally staggered emissions. Our constructions are of general interest, treating, for instance, the basic problem of constructing highly compact secret shares. Our main motivating problem, however, is that of practical key management in RFID (Radio-Frequency IDentification) systems. We describe the application of our techniques to RFID-enabled supply chains and a prototype privacy-enhancing system.