Biclique attack of block cipher SKINNY

Abstract

SKINNY is a lightweight tweakable block cipher, which was proposed at CRYPTO 2016. This paper presents an optimized brute force attack on full SKINNY using biclique attack with partial matching and precomputation. The results show that full round SKINNY64/64 is not secure against balanced biclique attack, the data complexity is 248, and the time complexity is 262.92. That is a very tiny advantage against brute force attack. Furthermore, an unbalanced biclique attack is considered, which improves the time complexity to 262.82. Moreover, in order to be immune to biclique attack, the round of SKINNY64/64 needs to be increased by 4 rounds to 36 rounds. Other versions of SKINNY do not have full round biclique attack owing to more encryption rounds.