Repeated Differential Properties of the AES-128 and AES-256 Key Schedules

In this paper, we further study the key schedule of the AES algorithm and present some repeated differential properties of the AES-128 and AES-256 key schedules. We define the concept of repeated differential pattern for the AES 128 key schedule, and the notion of double-sized repeated differential pattern for the AES-256 key schedule. We show that if we use the key schedule to expand two 128-bit (or 256-bit) secret keys with the repeated differential pattern (or double-sized repeated differential pattern), the resultant 10 round (or 14-round) subkeys have a large number of bytes in common and the differential pattern has strong repeated features.