Derivation of Target Transfer Function in Simulated IC Switching Current to Design PCB Secure Against Side-Channel Attack

Side-channel attacks (SCAs) recover cryptographic secret-keys by analyzing switching noises from cryptographic ICs. To design printed circuit board (PCB) secure against SCA, several works have studied the simulation methods of switching noises and SCA results. As a metric for the switching noise simulation, we address the transfer function indicating the propagation characteristic of the switching current from the IC to the noise measurement location. Focusing on the correlation power analysis (CPA) in the frequency domain as the SCA method, our approach derives conditional formulas for the switching current and transfer function to keep the lower correlation than the required value, where the correlation coefficient is the attack index of CPA. By substituting the simulated switching currents into the formulas, we identify secure region of transfer function. During the board design, the secure region enables us to detect vulnerable frequency bands of the simulated transfer function. Furthermore, the region provides the target transfer function, thus we can calculate of target attenuation of transfer function at vulnerable bands. Therefore, our approach offers the efficient support to design board wirings and filter constants. In the validation, we applied our approach for the 128 -bit advanced encryption standard (AES) implemented on an FPGA. As the results, the vulnerable bands obtained by the formulas match well with actual CPA results, thus confirming the validity of the proposed method.