On the possibility of modifying the KB-256 algorithm from the searching for impossible differentials view point

The presence of impossible differentials in a block cipher algorithm can lead to efficient methods for recovering the secret key. A large number of impossible differentials have been found for the KB-256 algorithm. This paper considers the modification of the feedback function to reduce the number of iterations to which they can be extended. A general approach to finding differences with probability 1 is proposed. It is shown that changing the number of summable sub-blocks in the feedback function will not reduce the maximum number of iterations to which an infeasible differential can be extended.