Reply to comment on Y-00 quantum secure communication protocol

In 2000, an attractive new quantum cryptography was discovered by H.P.Yuen, which can realize secure communication with high speeds and at long distance by conventional optical devices. Recently, a criticism of the Yuen protocol, so called Y-00, was made by Nishioka, and Imai group(Mitsubishi and University of Tokyo), and they claimed Y-00 is essentially a classical stream cipher. This paper shows that the claim is incorrect. In particular, it is shown that the relation $l_i=r_i\oplus \tilde{k}_i$, which is their basis for attack, has no essential role for any security analysis. In addition, we give a brief introduction of the general logic for the security of Y-00 as direct encryption and also for key generation. Several industries have started to make a test-bed of Y-00 for digital optical fiber highway, following Kumar's leading work. We hope that this discussion encourages experimental works which realize a secure communication against quantum computer and quantum attacks based on physical principle.