Identity-Based Encryption with Equality Test and Flexible Time-Based Authorization for Cloud Computing

Identity-based encryption with equality test (IBEET) extends identity-based encryption to support the comparison between messages in two distinct ciphertexts associated with different identities. Nevertheless, nearly all of the previous IBEET schemes have the problem that once the trapdoor is sent to the cloud server, it becomes uncontrollable. Meanwhile, the only existing IBEET scheme coping with this problem, namely IBEET with datestamp-based authorization (IBEET-DBA), suffers from the following flaws. (1) A trapdoor merely expresses a single time interval, which is inexpressive. (2) It is inflexible due to only supporting limited types of authorization. (3) It is merely proven secure in the random oracle model, which has been pointed out that it may lead to security risks in practicality. Considering the aforementioned problems, we propose an IBEET with flexible time-based authorization (IBEET-FTBA) scheme, supporting wildcards and putting no constraint on authorization types. We prove our scheme secure against adaptive chosen-ciphertext attacks in the standard model. Subsequently, we give a detailed theoretical analysis of our IBEET-FTBA construction and the main existing IBEET ones. Furthermore, we implement ours and the IBEET-DBA construction as a benchmark, and conduct numerous experiments. Both results demonstrate that ours has better performance in the scenario of multiple time intervals.