Research On GFN Structure Block Cipher Analysis Method

The importance of information security is growing in the modern society. Cryptology, as the base and core of information security, has received the widespread attention. As an important branch of cryptography, block cipher is widely used in a variety of security applications and network protocols. Feistel structure is a very important design block cipher structure, and it has become a hotspot of cipher-algorithm's design and analysis. GFN(Generalized Feistel Networks) structure is a variant Feistel structure and there are a variety of algorithms.The common GFN structure algorithms are: SMS4, MARS, CAST-256, Piccolo,CLEFIA etc. In recent years, many researches of the block cipher have been presented including some papers about GFN ciphers. However, most of all researchers are based on one GFN structure cipher or cryptology, thus, it is easy to cause that the understanding and analysis of the algorithm is not comprehensive.In this paper, we use different analysis methods to analysis different GFN structure ciphers,and we get some new researches:1. Piccolo is a new block cipher proposed by SONY Corporation in 2011. Piccolo supporting 80 and 128-bit keys.The designers had provided the results analysis for Piccolo including the related-key impossible differential attacks. They found an 11 and a 17-round impossible differential distinguisher using an 8-bit truncated differential for Piccolo-80 and Piccolo-128 in the related-key setting. But there are no words about the analysis in tail. This paper provides the differentials of Piccolo-80 and Piccolo-128 with the U-method. We give a new impossible-differential cryptanalysis of Piccolo with the UID-method introduced by Y.Luo et al. UID-method is more effective than the U-method introduced by Kim et al.We study the properties of key scheduling in Piccolo-80 and Piccolo-128. Furthermore, by using UID-method, we find 14-round related key impossible differentials for Piccolo-80 with the properties. Our results are better than those the designers tested with U-method.2. The importance of key scheduling for an algorithm is well known. SC2000-256 algorithm has serious security hole in key scheduling. By using the weak key characteristics of SC2000-256, we obtained the inverse matrix of the matrix M by calculation, which is important for searching a new set of weak key. We realized the algorithm of searching collision keys in C program.