The Research Of Iterative Structure And Compression Function Of Hash Function

Hash function plays an important role in the field of cryptography security and the application of network,and it has been applied to many fields,such as digital signature,password reserve and so on.As the effective collision of MD5,SHA1 and SHA256 has been found in a short time,it suggests that traditional hash functions have suffered serious security threat.Therefore,different hash design schemes have been proposed from two aspects for the safety problems and efficiency,one is the improvement of iterative structure,the other is the design of compression function.The improvement of iterative structure can improve the efficiency and the design of compression function mainly enhances the security of function.The design of parallel structure has attracted the attention of more and more researchers for its high efficiency while the chaotic map has been a unique research approach of hash function for the high sensitivity of the parameters of systems.In order to deal with the poor efficiency and the problem of the collision resistance of the function that can't be proved,we introduced the parallel structure,chaotic maps,the translation based on lattice for the improvement of compression function and iterative structure in this paper.Our main work is arranged as follows in this paper:1)We introduced parallel structure for the low efficiency of SHA256 algorithm.As the classic hash function run in a sequential mode,which means that the processing of message block can't start until the previous one has been processed.In this case,if the length of message is long enough,the efficiency is inevitably low greatly.In order to improve the efficiency,a kind of parallel structure is proposed.First,the values of each message block are calculated after message grouping;next,the values of every two blocks are processed together for several rounds.When the number of message blocks is odd in each round,we add a block which is the same as the last one,so the number of message blocks can reduce nearly half after calculating for one round.The same calculation is performed until only one value is remained,then the value is used as the final hash value.If the index of round is odd,the different methods are applied from the even one when the two adjacent blocks are combined.In the end,the theoretical analysis and experiment simulation are performed.Then the proposed scheme is proved to be feasible and advanced.2)The efficiency of SHA1 algorithm is superior to SHA256 algorithm,but it faces with the serious security problems,the collision of SHA1 has been found at present.In order to solve this problem,the compression function of SHA1 is improved.Chaotic map is introduced in the process of designing compression function.As the chaotic map can be applied to compression function for its transformation of multi-chaotic map,so the intermediate chaining variables can be controlled for the use of multiple iterations,and the avalanche effects can be enhanced.When processing the last message block,we introduced lattice,a function which is proved can resist collision that based on lattice is designed.The value which is processed through the lattice is regarded as the final hash value.In the security certification,the collision resistance of hash function can specification to the difficulties of lattice and prove the difficulty of the problem at the same time.Finally,the theory analysis and experiment simulation are carried.