Verifiable Multilevel Dynamic Searchable Encryption With Forward and Backward Privacy in Cloud-Assisted IoT

The Internet of Things (IoT) boom has enabled massive data collection in cloud servers. Therefore, access efficiency and data privacy in cloud storage services have become a significant concern. Data and users are hierarchical in IoT applications, which require fine-grained multilevel access control. Additionally, achieving public verification to resist the malicious server and clients is indispensable. Aiming at the challenge above, we propose a new forward private multilevel dynamic searchable symmetric encryption (MLDSSE) scheme called Peony, employing multilevel linked lists and constrained pseudorandom function, which is more efficient and secure. Then, we introduce a cryptographic primitive named multilevel symmetric revocable encryption (MSRE), and we give a general method for constructing a novel forward and Type-II backward-private MLDSSE scheme Peony++ based on MSRE. Further, we design the multilevel digests and utilize the smart contract as a trusted platform to support public verification for Peony++. Theoretical analysis and experimental evaluations show that Peony achieves higher security and reduces search time by an average of 35.81% compared to the state-of-the-art MLDSSE scheme. To the best of our knowledge, Peony++ is the only multilevel searchable encryption currently available that can achieve forward and Type-II backward privacy, all while balancing efficiency and functionality.