SEED 블록 암호 알고리즘 확산계층에서 낮은 복잡도를 갖는 부채널 분석

Abstract

When the availability of embedded device is considered, combined countermeasure such as first-order masking and hiding countermeasures is quite attractive because the security and efficiency can be provided at the same time. Especially, combined countermeasure can be applied to the confusion and diffusion layers of the first and last rounds in order to provide the efficiency. Also, the middle rounds only employs first-order masking countermeasure or no countermeasure. In this paper, we suggest a novel side channel analysis with low complexity in the output of diffusion layer. In general, the attack target cannot be set to the output of diffusion layer owing to the high complexity. When the diffusion layer of block cipher is composed of AND operations, we show that the attack complexity can be reduced. Here, we consider that the main algorithm is SEED. Then, the attack complexity with 2^32 can be reduced by 2^16 according to the fact that the correlation between the combination of S-box outputs and that of the outputs of diffusion layer. Moreover, compared to the fact that the main target is the output of S-box in general, we demonstrate that the required number of traces can be reduced by 43~98% in terms of simulated traces. Additionally, we show that only 8,000 traces are enough to retrieve the correct key by suggested scheme, although it fails to reveal the correct key when performing the general approach on 100,000 traces in realistic device.