International Association
for Cryptologic Research

SIMON is a family of lightweight block ciphers which are designed by the U.S National Security Agency in 2013. In this paper, we improve the previous differential attacks on SIMON family of block ciphers by considering some bit-difference equations. Combining with some new observations on key guess policies of SIMON family, we mount differential attacks on 21-round SIMON32/64, 22-round SIMON$48/72$, 22-round SIMON48/96, 28-round SIMON$64/96$ and SIMON$64/128$ with time complexity about $2^{46}$, $2^{63}$, $2^{71}$, $2^{60}$ and $2^{60}$ encryptions respectively. As far as we know, these results are the best attacks on reduced-round SIMON versions.