Private Conjunctive Query over Encrypted Data

In this paper, we propose an efficient protocol to process a private conjunctive query over encrypted data in the cloud using the somewhat homomorphic encryption (SwHE) scheme with a batch technique. In 2016, Cheon, Kim, and Kim (CKK) [IEEE Trans. Inf. Forensics Security] showed conjunctive query processing over encrypted data using search-and-compute circuits and an SwHE scheme and mentioned that their scheme should be improved in performance. To improve the performance of processing a private conjunctive query, we also propose a new packing method to support an efficient batch computation for our protocol using a few multiplications. Our implementation shows that our protocol works more than 50 times as fast as the CKK protocol for conjunctive query processing. In addition, the security level of our protocol is better than the security level of the CKK protocol.