Abstract
SKINNY is a new lightweight tweakable block cipher family proposed by Beierle et al. at CRYPTO 2016. SKINNY has 6 main variants where SKINNY-n-t is a block cipher that operates on n-bit blocks using t-bit tweakey (key and tweak) where \(n=64\) or 128 and \(t=n\), 2n, or 3n. In this paper, we present impossible differential attacks against reduced-round versions of all the 6 members of the SKINNY family in the single-tweakey model. More precisely, using an 11-round impossible differential distinguisher, we present impossible differential attacks against 18-round SKINNY-n-n, 20-round SKINNY-n-2n and 22-round SKINNY-n-3n (\(n=64\) or 128). To the best of our knowledge, these are the best attacks against these 6 variants in the single-tweakey model.
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Notes
- 1.
\({TK}_{19}[0,4]=y_{19}[0,4] \oplus z_{19}[0,4]\) means that \({TK}_{19}[0]=y_{19}[0] \oplus z_{19}[0],{TK}_{19}[4]=y_{19}[4] \oplus z_{19}[4]\).
- 2.
Note that instead of having \(TK_{16}[6]\) that lead to the impossible differential distinguisher, we have \(x_{16}[6]\) that result in the same impossible differential distinguisher.
- 3.
Note that \({ETK}_{1}[6]={ETK}_{1}[14]\) and \({ETK}_{1}[1]={ETK}_{1}[5]\).
- 4.
The second term is computed from step 5(a), 5(b) and 6(a).
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Tolba, M., Abdelkhalek, A., Youssef, A.M. (2017). Impossible Differential Cryptanalysis of Reduced-Round SKINNY. In: Joye, M., Nitaj, A. (eds) Progress in Cryptology - AFRICACRYPT 2017. AFRICACRYPT 2017. Lecture Notes in Computer Science(), vol 10239. Springer, Cham. https://doi.org/10.1007/978-3-319-57339-7_7
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