This paper studies the security of the block cipher ARIA against impossible differential cryptanalysis. We find a new impossible differential property of ARIA, and propose an attack against ARIA-256 reduced to 7 rounds based on this property, while previous attacks can only attack ARIA up to 6 rounds. Our new attack needs 2
chosen plaintexts and 2
7-round encryptions. This is the best result for impossible differential cryptanalysis of ARIA known so far.