Certificateless Broadcast Searchable Encryption with Application to Cloud-Based Health Data Sharing

Cloud data sharing allows a sender to securely share data with a specific group of recipients through a cloud platform. To address privacy concerns, the data that is shared is usually encrypted and stored on the cloud server, which can make future retrieval challenging. To overcome this limitation, searchable broadcast authenticated encryption schemes have been introduced. These schemes enable the sender to authenticate and encrypt data for the intended recipients through the insecure and unreliable cloud platform. Only the user in the recipients set can perform keyword searches and access target data. However, certain existing schemes exhibit vulnerabilities such as keyword guessing attacks (KGA) and trapdoor misuse. Moreover, all of these schemes are based on either the public key certificate system or some identity base system, and these circumstances give rise to specific challenges, namely the complexities of managing certificates and the potential problems associated with key escrow. To tackle these challenges, we introduce a certificateless broadcast searchable encryption scheme that achieves ciphertext indistinguishability, trapdoor indistinguishability, and receiver anonymity. And we also eliminate the need for public certificates. Furthermore, we strengthen the security of our scheme by restricting search operations on the encrypted data to a designated server. We provide an extensive security analysis of our scheme and perform a thorough performance evaluation to showcase the practicality of the proposed scheme.