Abstract: SIMON and SPECK family ciphers have attracted the attention of cryptographers all over the world since proposed by NSA in June, 2013. At CHES 2015, Simeck, a new block cipher inspired from both SIMON and SPECK is proposed, which is more compact and efficient. However, the security evaluation on Simeck against zero correlation linear cryptanalysis seems missing from the specification. The main focus of this paper is to fill this gap and evaluate the security level on Simeck against zero correlation linear cryptanalysis. According to our study, 11/13/15 rounds zero correlation linear distinguishers on Simeck32/48/64 are proposed respectively, then zero correlation linear cryptanalysis on 20/24/27 rounds Simeck32/48/64 are firstly proposed. As far as we know, for Simeck32, our result is the best result to date.

Abstract. The Simeck family of lightweight block ciphers was proposed in CHES 2015 which combines the good design components from NSA designed ciphers SIMON and SPECK. Dynamic key-guessing techniques were proposed by Wang et al. to greatly reduce the key space guessed in differential cryptanalysis and work well on SIMON. In this paper, we implement the dynamic key-guessing techniques in a program to automatically give out the data in dynamic key-guessing procedure and thus simplify the security evaluation of SIMON and Simeck like block ciphers regarding differential attacks. We use the differentials from Kölbl et al.’s work and also a differential with lower Hamming weight we find using Mixed Integer Linear Programming method to attack Simeck and improve the previously best results on all versions of Simeck by 2 rounds.