Cryptanalysis and improvement of several quantum private comparison protocols

Recently, Wuet al(2019Int. J. Theor. Phys.581854) found a serious information leakage problem in Ye and Ji's quantum private comparison protocol (2017Int. J. Theor. Phys.561517), that is, a malicious participant can steal another's secret data without being detected through an active attack means. In this paper, we show that Wuet al's active attack is also effective for several other existing protocols, including the ones proposed by Jiet aland Zhaet al(2016Commun. Theor. Phys.65711; 2018Int. J. Theor. Phys.573874). In addition, we propose what a passive attack means, which is different from Wuet al's active attack in that the malicious participant can easily steal another's secret data only by using his own secret data after finishing the protocol, instead of stealing the data by forging identities when executing the protocol. Furthermore, we find that several other existing quantum private comparison protocols also have such an information leakage problem. In response to the problem, we propose a simple solution, which is more efficient than the ones proposed by Wuet al, because it does not consume additional classical and quantum resources.