Cryptanalysis of Zhu et al.'s Identity-Based Encryption With Equality Test Without Random Oracles

Recently, Zhu et al. proposed a new identity-based encryption with equality test (IBEwET) in the standard model (IEEE Access, 2023). According to the authors, it was claimed that their proposed construction achieves the indistinguishability against adaptive identity and adaptive chosen ciphertext attacks (IND-ID-CCA) by adversaries who do not have trapdoors for equality tests and the one-wayness against adaptive identity and adaptive chosen ciphertext attacks (OW-ID-CCA) by adversaries who have trapdoors. In this paper, we propose adaptive chosen ciphertext attacks against Zhu et al.'s construction that break the IND-ID-CCA security and the OW-ID-CCA security. Subsequently, we discuss how to fix their scheme so that it achieves the security requirements, as claimed in the original paper, however we confirm that a simple modification is no longer superior to the currently existing IBEwET schemes over bilinear groups in the standard model, obtained by generic constructions for IBEwET. Furthermore, we point out another issue that some operations in the original encryption algorithm are incompatible.