We provide conditions under which the set of Rijndael-like functions considered as permutations of the state space and based on operations of the finite field GF(p k ) (p ≥ 2) is not closed under functional composition. These conditions justify using a sequential multiple encryption to strengthen generalized Rijndael like ciphers. In [39], R. Sparr and R. Wernsdorf provided conditions under which the group generated by the Rijndael-like round functions based on operations of the finite field

more »

... 2 k ) is equal to the alternating group on the state space. In this paper we provide conditions under which the group generated by the Rijndael-like round functions based on operations of the finite field GF(p k ) (p ≥ 2) is equal to the symmetric group or the alternating group on the state space.