Efficient Forward and Backward Private Conjunctive Searchable Encryption With Comprehensive Verification

Dynamic searchable symmetric encryption (DSSE) enables the retrieval and update of massive encrypted data and is thus widely applied in cloud storage. Malicious cloud servers may tamper with outsourced data or return incorrect search results, making verification indispensable. However, current verifiable conjunctive DSSE with forward and backward privacy cannot simultaneously achieve accurate search and empty result verification. Given the above problems, we propose a novel forward and backward private conjunctive DSSE with comprehensive verification called VCFB. VCFB introduces the notion of random blinding factors and secure dynamic cross-tags to achieve accurate conjunctive search with sublinear overhead. We design the search state and construct chain structures to ensure forward security. The new verification algorithm based on bilinear-map dynamic accumulators can guarantee the verifiability of search results even if an empty result is returned. We use a sample check method to verify the new dynamic cross-tags, reducing computation costs. We precisely define the leakage function of VCFB and give detailed security proof, demonstrating that VCFB is forward and backward private under the malicious server model. Experimental results show that VCFB ensures efficient and accurate conjunctive search, outperforming the similar verifiable conjunctive DSSE scheme regarding indexing storage and update performance.