Online/offline attribute-based searchable encryption revised: Flexibility, security and efficiency

Attribute-based encryption with keyword search (ABKS) is a versatile public-key encryption system that supports access control and ciphertext retrieval. However, it often involves complex computations for ciphertext generation. To overcome this challenge, researchers have proposed several online/offline ABKS (OOABKS) schemes. These schemes optimize online ciphertext generation by pre-generating intermediate ciphertexts in an offline manner.However, we find some limitations of existing OOABKS schemes: (1) Some schemes lack flexibility because the intermediate ciphertext is embedded with an access structure and therefore it cannot be used to generate a final ciphertext encrypted under another access structure. (2) Other schemes fail to achieve the basic security requirement.In this work, we conduct a comprehensive analysis of existing OOABKS schemes. Next, we propose a revised OOABKS scheme that offers provable security based on the well-known Bethencourt et al.'s attribute -based encryption scheme. Our scheme retains the advantages of online/offline ciphertext generation in previous OOAKBS schemes while addressing their limitations. Experiment results show that our revised scheme achieves comparable efficiency to previous OOABKS schemes without sacrificing flexibility or security.