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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Enhancement of quantum noise effect by classical error control codes in the intensity shift keying Y-00 quantum stream cipher

Kentaro Kato

Published Oct 8, 2014• 5 citations
Publisher

Abstract

The notion of the deliberate error randomization (DER) for the Y-00 quantum stream cipher was introduced by Yuen [arXiv:quant-ph/0311061v6], and concrete schemes of DER were proposed by the author for the phase shift keying Y-00 quantum stream cipher (PSK-Y00) [Proc. SPIE 6305, 630508 (2006)]. In this paper, it is shown that one of our DER schemes, which was referred to as Model B in the literature, is applicable to the intensity shift keying Y-00 quantum stream cipher (ISK-Y00) and the brute-force search complexity Q in the case of ISK-Y00 is enhanced by installing DER as well as in the case of PSK-Y00.

DOI
10.1117/12.2060631

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The notion of the deliberate error randomization (DER) for the Y-00 quantum stream cipher was introduced by Yuen [arXiv:quant-ph/0311061v6], and concrete schemes of DER were proposed by the author for the phase shift keying Y-00 quantum stream cipher (PSK-Y00) [Proc. SPIE 6305, 630508 (2006)]. In this paper, it is shown that one of our DER schemes, which was referred to as Model B in the literature, is applicable to the intensity shift keying Y-00 quantum stream cipher (ISK-Y00) and the brute-force search complexity Q in the case of ISK-Y00 is enhanced by installing DER as well as in the case of PSK-Y00.
In a series of articles concerned with quantum stream cipher by Y-00 protocol on this conference, we have claimed that the quantum stream cipher has a pretty good security against several concrete attacks. On the other hand, it has been pointed out that one can improve the security level by using various additional randomization techniques. In this paper, we will show some concrete randomization techniques for quantum stream cipher. First we will sketch the framework of the deliberate signal randomization (DSR) that is realized by randomizing the signals deliberately with true-random numbers or with pseud-random numbers generated by a secret key. Secondly, we will consider about the deliberate error randomization (DER) by using concrete models. It will be shown that these randomization techniques enhance the security level of the quantum stream cipher.
This paper considers two issues on the quantum stream cipher by Yuen-2000 (Y-00) protocol. In the fist part of this paper we investigate the optimal modulation scheme for the basic model of the quantum stream cipher by Y-00 protocol, and in the remaining part we study the deliberate signal randomization. For the problem on the optimal modulation scheme, several modulation schemes are investigated for the cipher text-only attacks and the known plaintext attack under the error probability criterion and the information criterion to find the preferable modulation scheme. As a result, it will be shown that the phase shift keying signal yields the best performance among the modulation schemes investigated in our consideration by numerical simulations. After that, the roperty of the randomization technique called the deliberate signal randomization is considered for the cipher text-only attacks and the known plaintext attack in the information criterion. From this, it will be shown by numerical simulations that the amount of leakage of information from the legitimate user to the eavesdropper is reduced by the deliberate signal randomization. At the last section we will mention about the implementation issues of the deliberate signal randomization, taking account of the numerical results.
A quantum stream cipher by Yuen 2000 protocol (so-called Y00 protocol or $\ensuremath{\alpha}\ensuremath{\eta}$ scheme) consisting of linear feedback shift register of short key is very attractive in implementing secure 40 Gbits/s optical data transmission, which is expected as a next-generation network. However, a basic model of the Y00 protocol with a very short key needs a careful design against fast correlation attacks as pointed out by Donnet et al. This Brief Report clarifies an effectiveness of irregular mapping between running key and physical signals in the driver for selection of MMM-ary basis in the transmitter, and gives a design method. Consequently, quantum stream cipher by the Y00 protocol with our mapping has immunity against the proposed fast correlation attacks on a basic model of the Y00 protocol even if the key is very short.
In this talk, we present a design of keyed randomization, and an experiment for quantum stream cipher by Yuen protocol which can realize a randomized stream cipher with Gbps for long distance. A simple explanation of why Y-00 is more secure than any type of the conventional stream cipher is given, showing Y-00 with keyed randomization, for example, overlapping selection keying:OSK. That is, the noiseless Y-00 with OSK is equivalent of the conventional stream cipher, but the noise is inevitable. So one can easily see that the security is enhanced by the noise. In addition, we give a design for the implementation of the intensity modulation scheme and report the experimental demonstration of 1 Gbps quantum stream cipher with OSK randomization through 20~40 km long transmission line. This may provide a way to go toward the broad market applications which require security, high speed, compact size, maintenance free, and low price.
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.
Various types of randomizations for the quantum stream cipher by Y00 protocol have been developed so far. In particular, it must be noted that the analysis of immunity against correlation attacks with a new type of randomization by Hirota and Kurosawa prompted a new look at the quantum stream cipher by Y00 protocol (Quant. Inform. Process. 6(2) 2007). From the preceding study on the quantum stream cipher, we recognized that the quantum stream cipher by Y00 protocol would be able to be generalized to a new type of physical cipher that has potential to exceed the Shannon limit by installing additional randomization mechanisms, in accordance with the law of quantum mechanics. We call this new type of physical random cipher the quantum enigma cipher. In this article, we introduce the recent developments for the quantum stream cipher by Y00 protocol and future plans toward the quantum enigma cipher.