Research Of Verifiable Ciphertext Ranked Search Based On Conjunctive Keywords

In recent years,with the continuous development of the cloud computing technology,people no longer worry about the limitation of storage computing resources,but it also leads to the frequent occurrence of data leakage events,which reminds people of the need to protect the privacy of their data information.Therefore,users usually store encrypted data on the cloud server,which makes it difficult to retrieve ciphertext data.Thus,searchable encryption(SE)technology is proposed,which can match the keywords that users want to query in ciphertext state.However,how to make ciphertext search efficient has become a hot research topic.As cloud server is not completely reliable,it may pry the outsourced ciphertext data,and tamper the ciphertext data that stored in the cloud.Therefore,verification of retrieval results is also one of the hot research topics at present.Based on the above background,this paper proposes a verifiable ciphertext retrieval scheme supporting conjunctive keywords ranked search.The main work of this paper is as follows:(1)Aiming at the privacy security and retrieval efficiency of outsourced data,this paper proposes a ciphertext retrieval scheme based on tree structure to build secure index,which adopts B~+tree to build index and supports ranked search of conjunctive keywords.The scheme adopts TF-IDF algorithm and vector space model.To be specific,the TF value and IDF value in TF-IDF algorithm are used to weight documents and query keywords respectively,and the vector space model is used to vectorize the two,and the cosine distance between vectors can represent the relevance.The secure K-nearest Neighbor(KNN)technique is used to encrypt the two vectors so that the inner product between the encrypted vectors can still be used to measure the relevance between keywords and documents.Pruning technology is used to improve the greedy depth-first algorithm,and the safe index is retrieved to obtain the inner product between vectors,namely the correlation score,which is used as the sorting basis and returned to the user k documents that meet the most conditions.The experiment shows that the efficiency of ciphertext retrieval can be improved through this scheme,and it also provide privacy security protection for data.(2)For untrusted cloud servers,which may tamper with stored ciphertext data,this paper proposes a verifiable ciphertext retrieval scheme of conjunctive keyword ranked search,which verifies the integrity of returned query results on the premise of protecting data privacy.The scheme mainly uses Merkle hash tree to block the document and construct MHT tree.The hash value of the root node is the summary of the document,and the summary is signed,and the corresponding information of each document is stored in the leaf node of B~+tree security index,MHT tree is also constructed for security index to obtain summary and signature.In the end,authorized users can use the authentication algorithm to verify whether the cloud server has tampered with the outsourced data,to solve the problem of semi-trusted cloud server.The paper also analyzes the security and performance of scheme,and experiments show that the validation algorithm can verify the effectiveness of the returned results of cloud server.