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
Ting Cui‡, Chenhui Jin‡, Guoshuang Zhang§‡ Information Science and Technology Institute, Zhengzhou, China§ Science and Technology on Information Assurance Laboratory, Beijing, China
Corresponding author: Ting Cui ( cuiting_1209@hotmail.com ) © Ting Cui, Chenhui Jin, Guoshuang Zhang. This article is freely available under the J.UCS Open Content License. Citation:
Cui T, Jin C, Zhang G (2013) Observations of Skipjack-like Structure with SP/SPS Round Function. JUCS - Journal of Universal Computer Science 19(16): 2453-2471. https://doi.org/10.3217/jucs-019-16-2453 |  |
Abstract
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.
Keywords
block cipher, skipjack-like structure, permutation layer, impossible differential