Research On Several New Cryptanalytic Methods Of Symmetric Ciphers

Under the promotion of standardized projects like ECRYPT Stream Cipher Project?eSTREAM?and Competition for Authenticated Encryption:Security,Applicability,and Robustness?CAESAR?,a great number of symmetric ciphers and cipher structure have emerged,such as Mixed Operation based Cipher?MOC?modle,Non-Linear Feedback Shift Register?NLFSR?-based stream cipher,word-based stream cipher ZUC algorithm and authenticated encryption cipher based on stream cipher with the representation MORUS.Deu to the novel structure and high efficiency,these ciphers have drawn much attention of the researchers and their security is also of great concern.In order to analyze the security of new symmetric ciphers better,new cryptanalytic methods have been proposed,such as completeness analysis,dynamic cube attack and conditional differential attack.These new cryptanalytic methods have a sensible effect on cryptanalysis of new symmetric ciphers.Dynamic cube attack broke NLFSR-based stream cipher Grain-128.Conditional differential attack has a good attack effect on NLFSR-based cipher such as Trivium and Grain-like cipher.However,these methods only appeared for a short time and the related research results are not mature.Hence,it is meaningful to make further study,which will enrich the theory and contribute to the design and cryptanalysis of new symmetric ciphers.The new cryptanalytic methods of symmetric ciphers are deeply studied in this thesis.Full diffusion,dynamic cube attack,conditional differential cryptanalysis and multiple differential cryptanalysis are conducted in this thesis.These new cryptanalytic methods are then utilized to analyze the security of mixed operation based ciphers such as SIMON and SPECK as well as authenticated encryption cipher MORUS and representative stream cipher Gran v1 and ZUC algorithm.The innovative achievements are concluded as follows:?1?Research on full diffusion of mixed operation based cipher model and its application·The completeness computation rules of operation XOR,AND,shift and rotation shift,addition model 2ⁿ and subtractive model 2ⁿ are proposed.Based on these rules,a universal algorithm of completeness against mixed operation based cipher model is presented. Using this algorithm,the input information contained in every internal states can be obtain more precisely.Applying this algorithm,the full diffusion characteristics of SIMON and SPECK family are given.·A method of constructing impossible differential distinguishers of mixed operation based ciphers utilizing completeness is proposed.This method can directly give heavy weight impossible differential distinguishers of mixed operation based cipher with high efficiency.Using this method,all currently existing longest impossible differential distinguishers of SIMON family and some new impossible differential distinguishers of SPECK family are found.?2?Research on dynamic cube attack and its application·In order to improve the present dynamic cube attack,an optimized choosing rule of cube subsets is given.This rule improves the distinguishing ability against right keys and wrong keys of cube set.Then,a new secret information recovery method with increased success rate of recovering secret information is presented.Based on the above progress,an improved dynamic cube attack is proposed.The improved dynamic cube attack is applied on round reduced MORUS.The first dynamic cube attack-key recovery attack on reduced MORUS of 5 initiation rounds is given,with the computation complexity of O(2^95.05)and success rate lager than 92%.?3?Research on conditional differential attack of Grain-like stream cipher and its application·A factor-resolve method is proposed,which can help us obtain the precise expressions of internal states in more rounds.Moreover,a method for recovering key expressions in conditional differential attack as well as its complexity-success probability target is presented.Combining appropriate choosing rules of different type conditions,an improved conditional differential attack is suggested.Using this method,the previous conditional differential-distinguishing attack on 106-round Grain v1 is improved to conditional differential-key recovery attack.In addition,the conditional differential-distinguishing attack of 107-round Grain v1 with lower computation complexity and higher success rate is presented.·Based on the meet-in-the-middle method and combined with the improved conditional differential attack,an advanced conditional differential attack on Grain-like stream cipher is presented.With this method,we can attack Grain-like stream cipher of more rounds in the single-key setting with lower computation complexity.Applying this method,the first distinguishing attack as well as key recovery attack is conducted on 114-round Grain v1and 120-round Grain v1,which is the best known conditional differential result in the single-key setting as far as the attack rounds is concerned.?4?Research on multiple differential cryptanalysis of ZUC family and its application·The differential characters of main operation of ZUC algorithm are analyzed.The output difference and its probability of bit-reorganization and bit shift are specifically given.For XOR and addition modulo 2³²,the algorithm of searching for the output difference with probability larger than one-Nth of the max output probability is presented.Based on the characters,the method of multiple differential cryptanalysis on ZUC algorithm is suggested.Using this method,the differential of internal states with more precious probability in theory can be obtained.Applying this method,a new chosen-IV internal state differential of 24-round ZUC-128 is given with higher probability than previous results.Based on this differential,the first chosen-IV distinguishing attack on ZUC-128of 7 rounds is given.Then,two related-key internal state differentials of 27-round ZUC-256 are given in the weak-key setting.Based on this differential,the first related-key distinguishing attack of 10-round ZUC-256 is presented.