On the Key Schedule of Mini-AES and S-AES Algorithms

Abstract Mini-AES and S-AES have been proposed in literature to serve as test beds for students and cryptographers. The key schedule generation of both these algorithms can be considered to be based on a non-linear feedback shift register (NFSR). In this paper, we study the key schedule algorithm used in Mini-AES and S-AES regarding two aspects: (a) to know whether any keys of Mini-AES as well as S-AES are weak in the sense that the round keys generated turn out to be same as the actual key (b) to evaluate the period of the sequence generated by the NFSR under various initial conditions. Further, the possibility of deriving the round keys fast as needed in decryption is also explored. Simulation results using C and implementation related evaluation are also presented.