The Differential Provable Security Analysis of a Kind of Unbalanced Feistel Networks

The differential provable security of a kind of unbalanced Feistel networks is investigated deeply. The structure of the differential correspondence between round functions whose differential probability is nonzero is given. A distribution of m sequential differential correspondences is given. If pmalt is the maximum of the probability of round function f(x), the upperbounds of the differential probability over at least 2m rounds is proven to be two times of the square of pmax and is proven to be the square of pmax when f(k, xm) is bijective. In conclusion, the unbalanced Feistel networks is discussed.