Research And Implementation Of Ciphertext Retrieval System

In the secret sectors and sensitive business sectors, to ensure the security of systems and data information, data in the computer application system is stored in the form of ciphertext. However, retrieving information what user need from the ciphertext quickly and accurately is very difficult. Full-text search technology and encryption algorithms have been developed rapidly, and some very good commercial products have been appeared. But how to retrieval these unstructured encrypted data efficiently has become a pressing problem. The emergence of ciphertext retrieval technologies has sloved the problem. Through constructing ciphertext index for encrypted information, it can provide a safe and efficient retrieval method based on the encrypted storage of information resources.Currently, both at home and abroad, the research in the area of the full-text retrieval and encrypted database retrieval tends to mature, whereas the full-text retrieval based on the encryption technology is needed to be further developed. The core problem of ciphertext retrieval is how to build safe and efficient ciphertext index which not only needs to satisfy the the security needs of index, but also to meet the demand of efficient retrieval.With respect to the aforesaid problems, based on the key technology of cipher retrieval and the research of traditional full-text search technology, a security ciphertext index structure is constructed through transforming the structure of traditional inverted index. In the ciphertext index structure, In order to ensure the safety of the index file, the entries are stored in cipher against the attack of semantic analysis. Meanwhile, two-level index structure and the partitioning encryption mechanisms are used to ensure the balance between efficiency and security. In the index file, the position of vocabulary and the frequency information are screened out for resistance of statistic-based attack. Based on the structure of ciphertext index, a ciphertext index mechanism is designed, including construction, maintenance and retrieval of the encryption index. The performance of the ciphertext index mechanism is also analysed. Through studying the encryption mechanism of ciphertext retrieval system, an encryption solution of ciphertext index for ciphertext retrieval system is designed from three aspects of the encryption hierarchy, the encryption granularity and encryption algorithm, and a multi-hierarchic key management strategy is also provided therein.Finally, based on the aforesaid research, a prototype of the ciphertext retrieval system is designed and implemented. The framework of the system, the core processes and the implement of core functional modules are detailed. The system model of the multi-user environment is studied. The security of the cipher index is analyzed. A performance testing is conducted on the encryption full-text index and retrieval based on the prototype of the ciphertext retrieval system, wherein feasibility and the balance between efficiency and security of the system is verified.