Related-Key Boomerang Attack on Block Cipher SQUARE

13 years 6 months ago

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Square is 8-round SPN structure block cipher and its round function and key schedule have been slightly modiﬁed to design building blocks of Rijndael. Key schedule of Square is simple and eﬃcient but fully aﬃne, so we apply a related-key attack on it. We ﬁnd a 3-round related-key diﬀerential trail with probability 2−28 , which have zero diﬀerences both on its input and output states, and this trail is called the local collision in [5]. By extending of this related-key diﬀerential, we construct a 7-round related-key boomerang distinguisher and successful attack on full round Square. The best attack on Square have ever been known is the square attack on 6-round reduced variant of Square. In this paper, we present a key recovery attack on the full round of Square using a related-key boomerang distinguisher. We construct a 7-round related-key boomerang distinguisher with probability 2−119 by ﬁnding local collision, and calculate its probability using ladder switch and l...

Bonwook Koo, Yongjin Yeom, Jung Hwan Song

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