CCA2 attack and modification of Huang et al.'s public key encryption with authorized equality test

Abstract

In this article, we identify a flaw in Huang et al.'s public key encryption with authorized equality test (The Computer Journal, 2015). More precisely, we point out that the proof of the indistinguish-ability under adaptive chosen ciphertext attack (IND-CCA2) security for their scheme has a serious flaw. We illustrate this flaw by presenting a polynomial time CCA2 attack on their scheme. We also provide a solution to correct this flaw by modifying their scheme slightly. Our solution is quite efficient because it provides security against CCA2 attack by exploiting only the hash computation of a two times longer input without any increase in the sizes of ciphertexts and warrants.