Design and cryptanalysis of a new iterative structure

Abstract

This study proposes a new iterative structure called the L-Feistel structure, which shares similar procedures between encryption and decryption and could unify the Feistel structure and the Lai-Massey structure. This paper evaluates the security of the L-Feistel structure from the perspective of provable security and classical analysis, respectively. Firstly, it is proved that the 4-round Key-Alternating L-Feistel cipher with independent round keys and independent round functions is secure against 2^n/2 queries that is, birthday-bound security. Then by presenting the dual structure of the L-Feistel structure with SP-type round functions, it is proven that a differential of the L-Feistel structure is impossible when and only when it is a zero-correlation linear hull of its dual structure. Finally, the paper constructs impossible differentials, zero-correlation linear hulls and integral distinguishers of the L-Feistel structure with SP-type round functions which cover six and seven rounds, respectively, under different conditions.