The Research And Implementation Of An Efficient Ciphertext Retrieval Mechanism

With the development of the times and technology, the information isexpanding day after day. Thanks to the development of the full-text retrievaltechnology, we can retrieval and use information more efficiently. But someinformation should be stored in the encrypted format when its content needs to beprotected. When retrieving such encrypted data, the traditional information retrievalmethods are not applicable. The emergence of ciphertext retrieval technologies hasjust solved the problem. The ciphertext retrieval is the combination of the encryptiontechnology and full-text retrieval technology, providing a security and efficientmethod to retrieve information without its content being disclosed.In this thesis, through researching the index technology of the full-text retrievaland the information security technology, the traditional plaintext index is rebuiltextensively. Our approach is based on the detailed analysis of the security flaws ofthe plaintext index. In this thesis, an improved inverted index for ciphertext isproposed. The entries and the pointer pointing to the inverted list in the word list areencrypted to enhance the overall security of the ciphertext retrieval. The inverted listis organized as a list and the documents are stored in the inverted file randomly andseparately. In this way, the inverted list is difficult to be cracked. In order tooptimize the search in word list, an extended hash table which is based on countingBloom filter is used. A multi-index strategy of the improved inverted index forciphertext is also proposed. Finally, the performance of the improved inverted indexfor ciphertext is analyzed from multiple perspectives.In this thesis, the implementation of the access control policy is to build aRole-Based inverted index based on the improved inverted index for cipthertext. TheRole-Based inverted index works together with the improved inverted index forcipthertext and controls the access to the document field. The two indexes areindependent of each other. On the other hand, through studying the encryptionmechanism of ciphertext retrieval system, a multi-hierarchic key managementstrategy is provided. It not only creates a safe environment to generate and use thesecret key, but also enhances the security of the system further. Based on the research above, a prototype ciphertext retrieval system isprototyped and implemented. The framework of the system and the core functionalmodules will be described in detail. Finally, a performance testing is carried out.Based on the collected experimental data, the balance between information securityand retrieval performance is analyzed. The experimental data shows that the methodproposed in this thesis solves the problem of ciphertext retrieval effectively.