A Lightweight Certificateless Public Encryption With Multi‐Keyword Search in IIoT

In Industrial IoT ecosystems, resource‐constrained devices increasingly rely on searchable encryption (SE) to offload encrypted data to cloud platforms, reducing local computational burdens while preserving data privacy. However, traditional SE technologies struggle to meet the demands of IoT environments featuring large‐scale distributed devices, due to cumbersome certificate management and inherent key escrow weaknesses. While certificateless searchable encryption (CLSE) schemes have been proposed to overcome these challenges, most existing solutions remain prone to security flaws and lack support for multi‐keyword searches. To address these shortcomings, we present a novel lightweight certificateless public key encryption scheme with multi‐keyword search capabilities (CLPSE). Crucially, compared to prior work, our protocol design does not rely on bilinear pairings, but instead employs an elliptic curve algorithm involving only scalar multiplication and addition operations. In addition, to protect the privacy between keywords and ciphertexts, we design a new matrix index structure using the BM25 retrieval algorithm and VFE function. Users can retrieve the corresponding ciphertexts using their trapdoor and threshold, which improves the flexibility of retrieval. Based on this construction, our scheme (CLPSE) is tailored for devices with limited storage and computational capacity. Compared to existing methods, it guarantees the indistinguishability of keyword ciphertexts and trapdoors, while delivering robust protection against both inside and outside keyword guessing attacks (IKGA and OKGA), thereby enhancing keyword security. Experimental results substantiate that our scheme achieves significant improvements in computational and communication efficiency over prior approaches.