Ciphertext only attack for one-way function of the MAP using one ciphertext

Abstract

FEAL-N proposed by NTT is an N-round block cipher which is well suited for a fast software execution. We research the method which improves FEAL algorithm against cryptanalysis based on the careful analysis of data randomizer. Since the round function f used as data randomizer has an inverse function f−1, we have already shown that there exists a key-independent relation between plaintext and ciphertext. In this paper, we apply our attack to the ciphertext only attack for one-way function of the MAP using only one ciphertext. Computer implementation of the proposed attack shows that the improvement of the computational complexity to obtain the plaintext is decreased and given by O(232).