Double Time-Memory Trade-Off in OSK RFID Protocol

The OSK/AO protocol has already demonstrated how the application of time-memory trade-off (TMTO) increases the efficiency of a hash chain-based RFID protocol. The complexity of this protocol, both in the preparatory phase and in the tag identification, is greatly influenced by chain generation procedure. Since the hash values in chain nodes are generated independently and randomly, the repetition of the same calculations impairs the protocol efficiency. This paper proposes an improved procedure for a faster chain generation by employing a special table with equidistant states from the tag state space. It provides that hash functions calculations for a node start not from the beginning but from a nearest state stored in the table. Consequently, the number of repeated hash calculations is significantly reduced. After the new OSK/TMTO2 protocol is precisely formalized, a complexity analysis is carried out with detailed consideration of two cases (with and without additional memory for the table). A comparison of the proposed protocol with OSK/AO is also conducted. The practical restrictions on configuration of an RFID system with the new protocol are stated as well. Finally, the conducted analysis is illustrated by numerous examples with wide spectrum of relevant parameter values.