Efficient designated server identity-based encryption with conjunctive keyword search

Abstract

Public key encryption with keyword search is a useful primitive that provides searchable ciphertexts for some predefined keywords. It allows a user to send a trapdoor to a storage server, which enables the latter to locate all encrypted data containing the keyword(s) encoded in the trapdoor. To remove the requirement of a secure channel between the server and the receiver in identity-based encryption with keyword search, Wu et al. proposed a designated server identity-based encryption scheme with keyword search. However, our cryptanalysis indicates that Wu et al.’s scheme fails in achieving the ciphertext indistinguishability. To overcome the security weakness in the scheme and offer the multiple-keyword search function, we put forward a designated server identity-based encryption scheme with conjunctive keyword search. In the random oracle model, we formally prove that the proposed scheme satisfies the ciphertext indistinguishability, the trapdoor indistinguishability and the off-line keyword-guessing attack security. Comparison analysis shows that it is efficient and practical.