Security Analysis Of A Class Of Feistel Cipher

Block Cipher is widely used in data encryption of message communication. It is the fundamental algorithm and theory of cryptography, and also the rationale and component of designing other ciphers. The discussion on security of block cipher mainly contains differential cryptanalysis, linear cryptanalysis and exhaustive attack. As new ciphers appear constantly, the design and analysis on a class of Feistel cipher developes towards diversified directions, to which the analysis of security has great practical significance.The main works of this paper are as follows:Firstly, we summarize the basis theory of block cipher designing and analysis methods we have known, and mainly introduce Feistel structure. Secondly, based on the research and recognition of the preceding knowledge, this paper introduces a new chosen text attack, the impossible differential-linear attack, on iterated cryptosystem. The attack is a general approach, which can be implemented by constructing a distinguisher catenating the impossible differential and the linear approximation together. It can be applied to the Feistel structure effectively. Then, we introduce CLEFIA, a representative cipher of Feistel families, and present a11-round attack on it with differential-linear cryptanalysis. The data complexity is2116.52, and we recover96-bit keys in total. After that, the paper focuses on analyzing CLEFIA-128with impossible differential-linear attack we proposed. The attack is efficient for16-round CLEFIA with whitening keys. At first we construct a13-round impossible differential-linear distinguisher. Based on the distinguisher, we present an effective attack on CLEFIA-128with data complexity of2122.73,recovering96-bit subkeys in total. It is the best result at present. At last, some other results during the research are introduced, including another13-round impossible differential-linear distinguisher, another16-round attack to CLEFIA-128, and two results of15-round attack to CLEFIA-128, and results on key relations. Our attack can also be applied to CLEFIA-192and CLEFIA-256.