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

Abstract

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 $O\left(1\right)$. 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.