Research On Technology Of Ranked Keyword Search Over Encrypted Data In Cloud Storage

With the continuous development of information technology, the application of cloud computing technology becomes more and more mature. As the key part of cloud computing, cloud storage satisfies the people’s basic demand in storage. However, in order to protect people’s data privacy, sensitive cloud data have to be encrypted before outsourced to the cloud server, which makes effective data utilization in cloud storage a very challenging task. Ciphertext retrieval is different from the plaintext retrieval that ciphertext retrieval have to protect data privacy while ensure the efficiency of search. Although traditional searchable encryption techniques allow users to securely search over encrypted data through keywords, for the cloud storage system storing massive data, the work efficiency of traditional searchable encryption techniques remains to be improved. As a result, the keyword search over encrypted cloud data leaves much to be desired.In present thesis, the existing schemes of the secure ranked search over encrypted cloud data are analyzed. The RKSE scheme, based on traditional symmetric searchable scheme, realizes the single keyword ranked search over encrypted data, but is inefficient due to its linear scan. The MRSE scheme, using binary tree as the index structure and introducing the concept of vector query, realizes the multi-keywords ranked search over encrypted data, and this scheme measures the similarity between the multi-keywords and documents by the cosine of the index vector and the query vector. However, the scheme only supplies the query of the union set of multiple keywords, and the modification of index is too complex, and the efficiency is not high by using binary tree as the index structure as well.Based on the research on the advantages and disadvantages of the existing schemes, a cloud storage system that support the keyword ranked search over encrypted data is developed. In the system, a proxy server to the system model which can ensure the data privacy is added for security, and the index structure that binary trees nested in a B+ tree is applied for efficiency. The efficiency of the proposed index structure is verified by the simulation. Based on the index structure, the efficiency of index building, modification and search is improved obviously. Because of the pre-sort for documents by TF × IDF criteria, the keyword ranked search becomes more efficient. The hash value of keyword is used as the keyword trapdoor, which simplifies the calculation of the trapdoor while ensures the cipher text of keyword not easy to be cracked. For the multi-keyword rankedsearch over encrypted data, the scheme proposed in present thesis supports the ranked search of multiple keywords of different logical relations over encrypted data, and the scheme reduces the calculation amount of the sort for the retrieval results to improve the efficiency.