JUCS - Journal of Universal Computer Science 19(16): 2453-2471, doi: 10.3217/jucs-019-16-2453
Observations of Skipjack-like Structure with SP/SPS Round Function
expand article infoTing Cui, Chenhui Jin, Guoshuang Zhang§
‡ Information Science and Technology Institute, Zhengzhou, China§ Science and Technology on Information Assurance Laboratory, Beijing, China
Open Access
Impossible differential cryptanalysis is an important tool for evaluating the security level of a block cipher, and the key step of this cryptanalysis is to find the longest impossible differential. This paper focuses on retrieving impossible differentials for m-cell Skipjack-like structure with SP/SPS round function (named SkipjackSP and SkipjackSPS resp.). Up to now, known longest impossible differentials in m-cell Skipjack-like structures is m2 rounds. In this paper, we provide some new m2 rounds impossible differentials for these two structures. Further, we prove that if P layer is chosen from binary matrices, we can always retrieve m2 + 1 rounds impossible differentials for these two structures, and m2 + 2 rounds impossible differentials for SkipjackSP. Moreover, if P layer satisfies some satiable conditions, we may further obtain m2 + 2 rounds impossible differential for SkipjackSPS. Our results show that we should choose P layer carefully when employing these two structures.
block cipher, skipjack-like structure, permutation layer, impossible differential