Validity of Differential Characteristics of ARX Block Ciphers

In this paper, we examine the validity of the differential characteristics of ARX-based block ciphers. Recently, Peyrin et al. showed that some of the differential characteristics of block ciphers, SKINNY and GIFT, in the literature are not valid. However, their work is limited to SPN-based block ciphers. We find out that some of the differential characteristics of block ciphers, SIMON, SPECK, and CHAM, that appeared in the literature are not valid. Our work indicates that not only the differential characteristics of SPN-based block ciphers, but also the differential characteristics of ARX-based block ciphers may be invalid.