Passive Cryptanalysis of the UnConditionally Secure Authentication Protocol for RFID Systems

Recently, Alomair et al. proposed the first UnConditionally Secure mutual authentication protocol for low-cost RFID systems(UCSRFID). The security of the UCS-RFID relies on five dynamic secret keys which are updated at every protocol run using a fresh random number (nonce) secretly transmitted from a reader to tags. Our results show that, at the highest security level of the protocol (security parameter= 256), inferring a nonce is feasible with the probability of 0.99 by eavesdropping(observing) about 90 runs of the protocol. Finding a nonce enables a passive attacker to recover all five secret keys of the protocol. To do so, we propose a three-phase probabilistic approach in this paper. Our attack recovers the secret keys with a probability that increases by accessing more protocol runs. We also show that tracing a tag using this protocol is also possible even with less runs of the protocol.