Optimized Power Consumption Model for Multiplication in Galois Field of AES

Side-channel analysis (SCA) is an analysis method to extract secret information using power consumption, electromagnetic waves, sound, etc., which occur when an encryption algorithm operates in a device. In [2], Lee et al. conducted SCA into the 8-bit based AES-128 algorithm operating on the ChipWhisperer-Lite board. As a result, it was found that Correlation Power Analysis (CPA) using only the most significant bit (MSB) of an 8-bit intermediate value is better than CPA using an 8-bit Hamming weight of the value. In this paper, we demonstrate that CPA using only a specific bit has the superior performance because of the modulo operation in Galois field of the 8-bit based AES-128 encryption algorithm. We performed CPA on the xtime operation part. As a result, we show that power consumption related with the MSB occurs while performing the modulo operation in Galois field.