Server-aided immediate and robust user revocation mechanism for SM9

Abstract

As the only approved Identity-Based Encryption scheme in China that is also standardized by ISO, SM9-IBE has been widely adopted in many real-world applications. However, similar to other IBE standard algorithms, SM9-IBE currently lacks revocation mechanism, which is vital for a real system. Worse still, we find that existing revocable techniques may not be suitable and efficient when applying to SM9-IBE. Given the widespread use of SM9-IBE, an efficient and robust user revocation mechanism becomes an urgent issue.In this work, we propose a dedicated server-aided revocation mechanism, which for the first time achieves the secure, immediate and robust user revocation for SM9-IBE. Provided with a compact system model, the proposed method leverages an existing server to perform all heavy workloads during user revocation, thus leaving no communication and computation costs for the key generation center and users. Moreover, the mechanism supports key-exposure resistance, meaning the user revocation mechanism is robust even if the revocation key leaks. We then formally define and prove the security. At last, we present theoretical comparisons and an implementation in terms of computational latency and throughput. The results indicate the efficiency and practicability of the proposed mechanism.