Simon

families of lightweight block ciphers: SIMON and SPECK. Currently, lin-ear and differential cryptanalytic results for SIMON are available in the literature but no fault attacks have been reported so far on these two cipher families. In this paper, we show that these families of ciphers are vulnerable to differential fault attacks. Specifically, we demonstrate two fault attacks on SIMON and one fault attack on SPECK. The first attack on SIMON assumes a bit-flip fault model and recovers the n-bit last round key of SIMON using n/2 bit faults. The second attack on SIMON uses a more practical, random byte fault model and requires n/8 faults on average to retrieve the last round key. The attack presented on SPECK also assumes a bit-flip fault model and recovers the n-bit last round key of SPECK using n/3 bit faults on average.