Non-standard architectures for symmetric cryptographic algorithms.

Several non-standard approaches to the design of block ciphers are studied with respoect to differential and linear cryptanalysis. The new approach of improving the diffusion of unbalanced Feistel networks with contracting functions and incomplete Feistel networks by using maximum distance separable codes is analyzed. As such constructions have smaller diffusion layers, they can turn out more efficient in many settings than the standard block cipher architectures. Moreover, we aim to identify conditions that have to be imposed on the MDS diffusion layers and additionally treat linear codes with suboptimal distances. Another approach to be taken is to co-design nonlinear functions and linear permutations in a way optimizing the overall cryptanalytic properties. For instande, for a fixed permutation layer, one can forbid certain types of linear and differential characteristics by selecting proper S-boxes. The potential of this approach with respect to block ciphers is far from being exhausted and can result in more efficient lightweight block ciphers.

Keywords:Linear codes, Cryptography, Festel networks, S-boxes