Improved quantum attack on several generalized unbalanced Feistel structures

By studying the attack technology based on Simon, Grover and other quantum algorithms for the security of block cipher structure, this paper proposes new quantum attack on 6 generalized unbalanced Feistel structures. We improve the attack results of n-cell structure, New Structure I/III/IV structure and FBC-like structure, and give a quantum attack on Skipjack structure for the first time. Based on Simon algorithm, this paper constructs a n²-round, a 12/12/6-round and a 4-round quantum distinguisher about n-cell structure, New structure I/III/IV and FBC-like structure, improving n²-n-1 rounds, 6 rounds/3 rounds/1 round and 1 round separately, comparing to the previous results. In addition, this paper also constructs a 9-round quantum distinguisher about Skipjack structure. Moreover, this paper proposes a quantum key recovery attack on the above six structures in combination with Grover algorithm, and the time complexities of attacks are analyzed.