Security flaw of counterfactual quantum cryptography in practical setting

Abstract

Recently, counterfactual quantum cryptography proposed by T. G. Noh [Phys. Rev. Lett. 103, 230501 (2009)] becomes an interesting direction in quantum cryptography, and has been realized by some researchers (such as Y. Liu et al's [Phys. Rev. Lett. 109, 030501 (2012)]). However, we find out that it is insecure in practical high lossy channel setting. We analyze the secret key rates in lossy channel under a polarization-splitting-measurement attack. Analysis indicates that the protocol is insecure when the loss rate of the one-way channel exceeds $50%$.