Fully-incremental public key encryption with adjustable timed-release keyword search

Public Key Encryption with Keyword Search (PEKS) is a promising technique that enables secure search over encrypted data. However, recent legislation mandates specific activation times for information, necessitating time-controlled retrieval. This creates a pressing need to integrate timed-release control into PEKS, allowing data uploaders to "send indices to the future", ensuring that secure, searchable indices for specific keywords can only be searched after the designated release-time. Existing approaches or straightforward candidates have several limitations: they either lack cryptographic search control and precise policy enforcement, fail to support flexible and efficient policy adjustment, or exhibit inefficiencies in index/key size and search complexity. In this paper, we formalize a novel variant called Fully-Incremental Public Key Encryption with Timed-Release Keyword Search (Fi-PETRKS), which well captures the functionalities, efficiency, and security requirements. Notably, the processes of functionalities are all incremental, ensuring that the size of token used for each adjustment remains (9(1). We propose a concrete Fi-PETRKS construction which is secure against full keyword guessing attacks. Furthermore, we introduce an enhanced version, Fi-PETRKS+, which offers sub-linear search efficiency. Both theoretical analysis and experimental results demonstrate the practicality of our scheme.