Comment on: 'How much security does Y-00 protocol provide us?' [Phys. Lett. A 327 (2004) 28]

It is claimed by T. Nishioka et al. in [T. Nishioka, T. Hasegawa, H. Ishiziuka, K. Imafuku, H. Imai, Phys. Lett. A 327 (2004) 28-32] that the security of Y-00 is equivalent to that of a classical stream cipher. In this Letter it is shown that the claim is false in either the use of Y-00 for direct encryption or key generation, in all the parameter ranges it is supposed to operate including those of the experiments reported thus far. The security of Y-00 type protocols is clarified.