Research On Cipher-Text Retrieval Technology With Support Of Result Sorting In Cloud Storage

Cloud storage has become one of the most widely used along with the popularity of mobile internet and the development of cloud computing.More and more organizations and users outsource data to the cloud server for the purpose of reducing hardware investment and maintenance.Users generally encrypt the documents before uploading to protect the data privacy and prevent information leakage.However,the data loses its semantics after encrypting,which brings the problem of data availability.Searching the required documents from the massive cipher-texts turns into a challenge.The data confidentiality and availability have been the key point in the development of cipher-text retrieval technology.How to quickly and efficiently retrieve the required documents has become an urgent problem when faced with the rapid growth of data in the cloud storage.In this thesis,based on the full-text search techniques,the construction of secure index,index retrieval,keyword security trapdoor and the sorting of search results have been studied deeply.The main research contents are as follows:1)On the basis of the plain inverted index,we construct the encrypted inverted index.The keyword frequency,location and other information are removed,which easily reveal documents and leak the data privacy from the inverted index.In this thesis,the relevance score(RSC)is introduced into the reformed index and is encrypted by Paillier encryption algorithm,which can eliminate the statistical law of the RSC and resist the attack against it.2)We propose the secure index SICBF.It is based upon the counting bloom filter(CBF),which is built on the encrypted inverted index.In this thesis,under the premise of privacy preserving,the secure and quick retrieval on the SICBF has been achieved.Moreover,the pruning algorithm of the CBF is designed to reduce redundancy of SICBF and save storage space.And the original element insertion algorithm is also modified in order that the element can be inserted correctly.3)In order to protect the privacy of the query keyword,we design the secure trapdoor algorithm.The secure trapdoor algorithm is based on random keywords.It can ensure the keyword privacy and prevent the attacker from guessing the contents of query keyword and inferring the information of encrypted documents.4)Applying the homomorphic property of Paillier,the cipher-RSC sorting algorithm is designed,which can return the most relevant top-k documents to the authorized user.In this thesis,we put the main computational work of ranking on the cloud server.This approach greatly reduces the amount of computation on the client.And it enables the resource-constrained clients to achieve fast retrieval and give full play to the high-performance features of the cloud computing.Through the study and analysis of SICBF,index search,keyword trapdoor and encryption sorting mechanism,we design the system of the secure ranked keyword search over the encrypted cloud data based on the SICBF.The experiments and security analysis show that,compared with the trapdoor generation in the TRSE scheme,the trapdoor algorithm based on random keywords in this thesis improves the efficiency of it by 86.21%.And compared with the cipher-text retrieval in the MRSE scheme,the secure index SICBF improves the efficiency of index by 79.14%.In short,the proposed SICBF and keyword security trapdoor achieves a good balance between performance and security,and it is suitable for fast and secure retrieval of massive encrypted documents in the cloud storage.