Reply to: “Comment on: 'How much security does Y-00 protocol provide us?' ” [Phys. Lett. A 346 (2005) 1]

In a recent paper titled “Comment on: 'How much security does the Y-00 protocol provide us?' ” [H.P. Yuen, P. Kumar, E. Corndorf, Phys. Lett. A 346 (2005) 1-6], the authors critically examine our idea [T. Nishioka, T. Hasegawa, H. Ishizuka, K. Imafuku, H. Imai, Phys. Lett. A 327 (2004) 28-32] that the Y-00 protocol is essentially as secure as classical stream ciphers. We clarify our idea in more detail than our previous paper and show that the Y-00 protocol can be considered as a classical non-random stream cipher, as was claimed in [T. Nishioka, T. Hasegawa, H. Ishizuka, K. Imafuku, H. Imai, Phys. Lett. A 327 (2004) 28-32]. We also provide an analysis on key generation with the improved Y-00 protocol, which is implemented with weak coherent states.