New linear approximation of modular addition and improved differential-linear cryptanalysis of SPARX-64/128

Differential-linear cryptanalysis is an efficient cryptanalysis method to attack ARX ciphers, which have been used to present the best attacks on many ARX primitives such as Chaskey and Chacha. In this paper, we present the differential-linear cryptanalysis of another ARX-based block cipher SPARX-64/128. We first construct multiple 6-round differential-linear distinguishers based on the structure of SPARX-64/128, and then extend them into 14-round differential-linear distinguishers by adding a 7-round differential characteristic before and a one-round linear approximation after the distinguishers. Then we introduce a new linear approximation of modular addition, and use it to extend one more round after the 14-round differential-linear distinguishers. With the 15-round differential-linear distinguishers, we present a differential-linear attack on 18-round SPARX-64/128.