Multi-user Forward Secure Dynamic Searchable Symmetric Encryption

Searchable Symmetric Encryption (SSE) makes it possible to privacy-preserving search over encrypted data stored on an untrusted server. Dynamic SSE schemes add the ability for the user to support secure update of encrypted data records. However, recent attacks show that update information can be exploited to recover the underlying values of ciphertexts. To improve the security, the notion of forward security is proposed, which aims to thwart those attacks by adding new documents without revealing if they match previous search queries. Unfortunately, existing forward secure SSE schemes are mostly for single-user settings, and cannot be easily extended to multi-user settings. In this paper, we propose a multi-user forward secure dynamic SSE scheme with optimal search complexity. By introducing a semi-trusted proxy server who does not collude with the cloud server, we take a nice method to solve multi-user queries problem in most forward secure SSE schemes. With the help of proxy server who maintains keywords’ state information, our scheme achieves forward security. Our experimental results demonstrate the efficiency of the proposed scheme.