International Association
for Cryptologic Research

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 {\\it 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 K\\\"{o}lbl {\\it 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.