SCF-PEPCKS: Secure Channel Free Public Key Encryption With Privacy-Conserving Keyword Search

Searchable encryption is a novel cryptographic primitive that enables a data storage server to retrieve the data ciphertexts without the knowledge of either what is searched for or the contents of the searched data ciphertexts. As a useful extension of the public key encryption with keyword search (PEKS) invented by Boneh et al., secure channel free PEKS (SCF-PEKS) eliminates the limitation that the trapdoors of search keywords should be conveyed to the data storage server through secret communication channels. Nevertheless, the current framework of SCF-PEKS is subjected to the security flaw arising from the keyword guessing (KG) attack and thus fails to provide privacy protection for keyword search. In this paper, we put forward an enhanced SCF-PEKS framework called secure channel free public key encryption with privacy-conserving keyword search (SCF-PEPCKS). Our framework effectively remedies the security weakness in the SCF-PEKS framework and offers resistance against the existing known KG attacks. We develop a concrete SCF-PEPCKS scheme without using random oracles. The security proofs demonstrate that it offers the keyword ciphertext/trapdoor privacy against both the malicious data storage server and the outside attacker. The comparisons and the experimental results indicate that the presented SCF-PEPCKS scheme is secure and practicable.