Improved Impossible Differential Cryptanalysis of ARIA

Impossible differential cryptanalysis is a method recovering secret key by getting rid of the keys that satisfy impossible differential relations. This cryptanalysis has been used to attack AES and many good results were gotten. For the new block cipher ARIA is similar to AES in structure, it is necessary to research its security against impossible differential cryptanalysis. We find a new impossible differential property of the block cipher ARIA, and we propose an attack against ARIA reduced to six rounds based on this property. In our attack, 10 bytes of round keys are needed to be guessed instead of 12 bytes in the previous one, so the time complexity is reduced by 2¹⁶ times. It needs 2120 chosen plaintexts and 2⁹⁶ encryptions in our attack.