Design And Implementation Of Multilevel Security Hash Function

With the rapid development and upgrade of the social network and IT,information security has become increasingly significant.Hash function as one of the important function in cryptography is used to verify message integrity,meanwhile adopted by other fields as well,such as,digital signature,digital currency,block chain technology.Therefore,hash function has become a research key-point in the field of information security.The hash function is a one-way function that can convert messages of any length into a fixed-length hash value.Commonly,hash functions used by people include MD,SHA,etc.In the process of development and improvement of these hash functions,in order to meet the growing security requirements,the output length of hash value is also growing.The output length of SHA has developed from 160 bits to 512 bits.However,each hash function can only generate a fixed-length hash value.When users have different security requirements,they can only choose different hash functions,which brings inconvenience to use.To meeting the requirements of various circumstances,this dissertation puts forward Multilevel Security Hash Function(MSHF).First and foremost,this dissertation analyzes and researches the internal structure and security demands of hush functions that are used currently,and proposed complementary requirements for designing hush functions:Under different usage requirements,the same hash function should achieve different security levels.Then design and implement MSHF,and the security degree is divided into four levels from low to high.MSHF can output hash values of four different lengths,which are 64bits,128bits,256bits,512bits.Secondly,the Merkle tree is generated by using MSHF.According to the characteristics and security level of MSHF,the depth of Merkle tree and the path length of SPV verification are reduced by merging adjacent nodes in Merkle tree.Finally,the performance and application of MSHF are experimentally analyzed.This dissertation compares the safety and operating efficiency of MSHF possessing different output lengths with DES-CBC,MD5,SHA-256 and SHA-512,which has the same output length.The experiments of Merkle tree based on MSHF and traditional methods are carried out in three aspects:SPV verification,creation time and the time required to find wrong data.Experimental results show that in terms of safety,the probability of bad spots in MSHF is lower than that in MD5 and SHA-512 in avalanche effect;In terms of performance,MSHF is more efficient than DES-CBC,SHA-256 and SHA-512.The higher the security level of MSHF,the faster the searching efficiency.The application experiment of MSHF shows that the Merkle tree generated based on MSHF has smaller depth and shorter path length for SPV verification;It takes less time to create a Merkle tree based on MSHF than traditional methods,and it takes less time to find the error data.