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The Review of Laser Engineering

Quantum Stream Cipher by Yuen-2000 Protocol

Osamu Hirota, Tetsuya Shimizu, Masaki Sohma, Kentaro Kato

Published Jan 1, 2008• 1 citation
Publisher

Abstract

Since quantum key distribution protocol was invented in 1984, huge number of papers on quantum cryptography have been published. However, they have so many serious technical problems which should overcome difficulties. On the other hand, it is reasonable to develop a quantum version of the conventional mathematical symmetric key cipher. In 2000, Yuen protocol was invented to realize a quantum version of stream cipher. In this paper, we introduce the principle and recent progress on quantum stream cipher by Yuen 2000 protocol.

DOI
10.2184/lsj.36.428

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Since quantum key distribution protocol was invented in 1984, huge number of papers on quantum cryptography have been published. However, they have so many serious technical problems which should overcome difficulties. On the other hand, it is reasonable to develop a quantum version of the conventional mathematical symmetric key cipher. In 2000, Yuen protocol was invented to realize a quantum version of stream cipher. In this paper, we introduce the principle and recent progress on quantum stream cipher by Yuen 2000 protocol.
So far, quantum key distribution (QKD) has been the main subject in the field of quantum cryptography, but that is not quantum cryptographic communication, it is only the ability to send keys for cryptographic purposes. To complete cryptographic communication, a technique for encrypting data is necessary, and the conventional cryptographic technique of mathematical symmetric key cipher or One Time Pad (OTP) is adopted in the discussion so far. However, OTP is not the ultimate cipher for data encryption, because it does not satisfy security conditions in the modern cryptology. Around 2000, a new quantum stream cipher was proposed as a technique to challenge the possibility of overcoming drawbacks of OTP in practical use. Recently, we have published some review papers on it in Entropy (Open access journal), and others. This paper introduces an overview and a back ground of our paper that is entitled Quantum stream cipher based on Holevo-Yuen theory.
This paper is dedicated to the late Professor H.P. Yuen in commemoration to our 50-year friendship. He invented the concept of quantum stream cipher. It is designed based on a completely different concept from conventional ciphers. The purpose of this cipher is to provide information-theoretic security of long data and secret key with short key length. It is based on hiding the ciphertext of mathematical cipher with quantum noise, achieving unprecedented information-theoretic security in any cipher. The protocol corresponds to randomizing the ciphertext by means of differentiating the receiving performance of Bob with key and Eve without key according to the principle of quantum communication theory. In this paper, we introduce some progress on the specific method to develop from the standard type to generalized quantum stream cipher (Quantum Enigma Cipher). There are two methods for generalization. One is the additional randomization method by the product cipher form and the other is the M-th order extended quantum coding method. Here we discuss the former. The results proved that it has sufficient information-theoretic security against known plaintext attack on key in comparison with quantum data locking. The latter method will be reported in Part II.
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.
In this review paper, we first introduce the basic concept of quantum computer-resistant cryptography, which is the cornerstone of security technology for the network of a new era. Then, we will describe the positioning of mathematical cryptography and quantum cryptography, that are currently being researched and developed. Quantum cryptography includes QKD and quantum stream cipher, but we point out that the latter is expected as the core technology of next-generation communication systems. Various ideas have been proposed for QKD quantum cryptography, but most of them use a single-photon or similar signal. Then, although such technologies are applicable to special situations, these methods still have several difficulties to provide functions that surpass conventional technologies for social systems in the real environment. Thus, the quantum stream cipher has come to be expected as one promising countermeasure, which artificially creates quantum properties using special modulation techniques based on the macroscopic coherent state. In addition, it has the possibility to provide superior security performance than one-time pad cipher. Finally, we introduce detailed research activity aimed at putting the quantum stream cipher into practical use in social network technology.
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.
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> = 1000 ~ 10000. 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). This is a challenge to overcome Shannon limit in the cryptography theory. 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 scheme consisting of intensity modulation/direct detection optical communication.