Extending the Switching Mechanism for 256 bit Block Ciphers Designing

One of the most important methods for checking the resistant of a block cipher against linear and differential analysis is counting of minimum active s-boxes. According to this number, proportion of minimum active s-boxes to all used s-boxes can be obtained. In Feistel structure, left and right half XORing cause difference cancelation reducing this proportion. One method for reducing difference cancelation and improving this proportion is presented previously using multiple MDS matrix. However, this method is suitable for design of 128 bit block ciphers and hasn’t good efficiency in 256 bit block ciphers. In this paper, the problem of finding proper multiple diffusion layers for Switching Structure on big dimension and big field is firstly surveyed. Then, a search algorithm is presented, used for making several categories of Recursive Diffusion Layers. In the next section, by using this Recursive Diffusion Layers, a 256 bit block cipher is designed base on Switching Structure. We verify security and efficiency of this scheme is verified and it is concluded that this scheme is resistant to linear and differential attack showing impossible differential attack and also has a good efficiency compare to other 256 bit block cipher algorithm.