Multi-user searchable encryption with a designated server

Abstract

Multi-user searchable encryption (MSE) enables authorized users to search over encrypted documents in the cloud. Generally, security problems in existing MSE schemes are solved as follows: (1) transmitting authority values and search tokens through secure channels to resist keyword guessing attack; (2) involving a trusted third party (TTP) to manage users and (3) relying on online users to distribute the decryption keys. However, these methods result in extra overhead and heavily restrict the scalability of the systems. In this paper, we propose a secure channel-free and TTP-free MSE scheme. It is secure against keyword guessing attack by introducing a designated server. And it achieves fine-grained access control to grant and revoke the privileges of users without TTP. More specifically, each document is encrypted with a unique and independent key, where the key distribution is integrated with user authorization and search procedures. We provide a concrete construction of the scheme and give formal proofs of its security in the random oracle model.