Symmetric Key Encryption with Conjunctive Field Free Keyword Search Scheme

Searchable symmetric encryption (SSE) enables a sender to outsource the encrypted files to a cloud server, while maintaining the ability to conditionally search over it without knowing the sensitive data contents. Prior work in this area has focused on single keyword search. Conjunctive Keyword Searches (CKS) schemes improve system usability by retrieving the matched files, but in this type of search the receiver has to provide the server with a trapdoor for every individual keyword in the conjunction and rely on an intersection protocol to retrieve the correct set of files, in other words the receiver has to repeatedly perform the search protocol for many times based on the number of keywords in the conjunction. Most of the existing (CKS) schemes use conjunctive keyword searches with fixed position keyword fields, this type of search is not applicable for many real applications, such as the database text and the body of e-mail. In this paper, we propose a new trapdoor-indistinguishable symmetric key encryption with conjunctive keyword search, which does not need to specify the positions of the keywords. Instead of giving the server one trapdoor for each keyword in the conjunction set, the recipient give it a trapdoor for multiple keywords in the conjunction set to search on encrypted files. Furthermore, the search process could not reveal any information about the number of keywords in the query expression. Our proposed scheme is proven secure against chosen-keyword attacks under the Decisional Diffie-Hellman(DDH) assumption in the random oracle model.