  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 $50%$.
