Power analysis attack of QCA circuits: A case study of the Serpent cipher

Quantum-dot cellular automata (QCA) technology is an attractive alternative to CMOS for future digital designs. A powerful attack based on power analysis has become a significant threat to the security of CMOS cryptographic circuits. As there is no current flow in QCA, the power consumption of a QCA circuit is extremely low compared to its CMOS counterpart. Therefore, in this paper an investigation is carried out to ascertain if QCA circuits could be immune to power analysis attacks based on a case study of the Serpent cipher. In comparison to a previous design, the proposed QCA implementation of a sub-module of the Serpent cipher is more efficient in terms of complexity, area and latency. By using an upper bound power model, the first power analysis attack of a QCA cryptographic circuit is presented. Simulation results show that even though the power consumption is low, it can still be correlated with the correct key guess, and all possible subkeys applied to the Serpent sub-module can be revealed in a best case scenario for attackers. The security of practical QCA devices is also discussed and could be greatly improved by applying a smoother clock.