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arXiv:quant-ph/0312029

Reply to comment on Y-00 quantum secure communication protocol

Osamu Hirota

Published Dec 3, 2003• 0 citations
arXivHTMLPDF

Abstract

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.

DOI
10.48550/arxiv.quant-ph/0312029

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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 li=ri⊕k~il_i=r_i\oplus \tilde{k}_ili​=ri​⊕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.
What obstructs the realization of useful quantum cryptography is single photon scheme or entanglement which is not applicable to the current infrastructure of optical communication network. We are concerned with the following question: Can we realize the information theoretically secure symmetric key cipher under "the finite secret key" based on quantum-optical communications? A role of quantum information theory is to give an answer for such a question. As an answer for the question a new quantum cryptography was proposed by H. P. Yuen which can realize a secure symmetric key cipher with high speeds(Gbps) and for long distance(1000 Km). Although some researchers claim that Yuen protocol(Y-OO) is equivalent to the classical cryptography they arc all mistaken. Indeed it has no classical analogue and also provides a generalization even in the conventional cryptography. At present it is proved that a basic model of Y-OO has at least the security such as H(X/YE)=H(K/YE)=H(K), H(K/YE,X)~0 under the average photon number per signal light pulse:<n>~10000. Towards our final goal in this paper we clarify a role of classical randomness(secret key) and quantum randomness in Y-OO and give a rigorous quantum mechanical interpretation of the security showing an analysis of quantum collective attack.
We investigate the Yuen 2000 (so-called Y-00)-protocol, which can realize a randomized stream cipher with high bit rate (Gbit/s) for long distances (several hundreds km). The randomized stream cipher with randomization by quantum noise based on the Y-00 protocol is called a quantum stream cipher in this paper, and it may have security against known plaintext attacks which has no analog with any conventional symmetric key ciphers. We present a simple cryptanalysis based on an attacker's heterodyne measurement and a quantum unambiguous measurement to make clear the strength of the Y-00 protocol in real communication. In addition, we give a design for the implementation of an intensity-modulation scheme and report an experimental demonstration of 1Gbit∕s1\phantom{\rule{0.3em}{0ex}}\mathrm{Gbit}∕\mathrm{s}1Gbit∕s quantum stream cipher through a $20\text{\ensuremath{-}}\mathrm{km}$-long transmission line.
Previously the present protocol was referred as Yuen-Kim second version in our papers. In this paper, it is called Yuen protocol (Y-00) and we present an efficient implementation method of physical layer of Y-00 which can support a secure communication and a quantum key distribution (more generally key expansion) by IMDD (intensity modulation/direct detection) or FSK (frequency shift keying) optical fiber communication network. Although the general proof of the security is not yet given, a brief sketch of security analysis is shown, which involve an entanglement attack.
In 2000, an attractive new quantum cryptography was discovered by H.P.Yuen based on quantum communication theory. It is applicable to direct encryption, for example quantum stream cipher based on Yuen protocol(Y-00), with high speeds and for long distance by sophisticated optical devices which can work under the average photon number per signal light pulse:<n>=1000sim10000<n> = 1000 \\sim 10000<n>=1000sim10000. In addition, it may provide information-theoretic security against known/chosen plaintext attack, which has no classical analogue. That is, one can provide secure communication, even the system has H(K)<<H(X)H(K) << H(X)H(K)<<H(X). In this paper, first, we give a brief review on the general logic of Yuen's theory. Then, we show concrete security analysis of quantum stream cipher to quantum individual measurement attacks. Especially by showing the analysis of Lo-Ko known plaintext attack, the feature of Y-00 is clarified. In addition, we give a simple experimental result on the advantage distillation by scheme consisting of intensity modulation/direct detection optical communication.