In this paper we generalize the structure of the cipher:; Shark, Square. BK
SQ, Crypton and Rijndael. We show that the linear components play an essent
ial role in the effect of the nonlinear S-boxes in providing resistance aga
inst differential and linear cryptanalysis and provide upper bounds for the
probability of differential characteristics and the correlation of linear
approximations for the general structure. We show how good linear component
s can be constructed efficiently from Maximum-Distance Separable codes. The
presented block cipher structure can make optimal use of a wide range of p
rocessor word lengths and its parallelism allows very fast dedicated hardwa
re implementations. Ciphers with variable block length can be constructed b
y varying certain parameters in the presented structure.