## Cryptology ePrint Archive: Report 2018/369

Security Analysis and Modification of ID-Based Encryption with Equality Test from ACISP 2017

Hyung Tae Lee and Huaxiong Wang and Kai Zhang

Abstract: At ACISP 2017, Wu et al. presented an identity-based encryption with equality test (IBEET) that considers to prevent insider attacks. To analyze its security, they proposed a new security notion for IBEET, which is slightly weaker than the indistinguishability under adaptive identity and chosen ciphertext attacks (IND-ID-CCA2) for traditional identity-based encryption. Then, they claimed that their proposed scheme achieves this new security notion under the Bilinear Diffie-Hellman (BDH) assumption in the random oracle model.

In this paper, we demonstrate that their scheme does not achieve the claimed security requirement by presenting an attack. Our attack algorithm is very simple: It requires only a pair of message and ciphertext, and takes one exponentiation and two bilinear map evaluations. Subsequently, we present a modification of their IBEET construction and show that it satisfies their security notion under the BDH assumption and the existence of strong pseudorandom permutation and existentially unforgeable message authentication code in the random oracle model. We remark that our modification has better efficiency than the original construction.

Category / Keywords: identity-based encryption with equality test, insider attacks, chosen ciphertext attacks, modification

Original Publication (with major differences): ACISP 2018