Quantum Stream Cipher Research Articles

Tradeoff Between Reach and Security in Nyquist WDM Transmission of PSK Y-00 Quantum Stream Cipher

Tradeoff Between Reach and Security in Nyquist WDM Transmission of PSK Y-00 Quantum Stream Cipher

Survey on quantum noise stream cipher implemented optical communication systems

Abstract This survey presents on the implementations of Quantum Noise Stream Cipher or Quantum Steam Cipher with various modulation formats – like QAM, PSK. FSK, etc., in optical fiber communication systems – along with other pertinent implementation details. Quantum Stream Cipher can be provably secure in information theoretical terms, and it achieves improved security due its inherent (noisy) randomness. This paper presents also a brief review on its claimed improved security, along with the open issues.

Quantum Stream Cipher Based on Holevo-Yuen Theory.

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.

Non-Orthogonality Measure for a Collection of Pure Quantum States.

Modern optical communication technology can realize a large-scale multilevel (or M-ary) optical signal. Investigating the quantum mechanical nature of such a large-scale M-ary optical signal is essential for a unified understanding of quantum information science and optical communication technology. This article focuses on the quantum-mechanical non-orthogonality for a collection of pure quantum states and proposes a non-orthogonality index based on the least squares error criterion in quantum detection theory. First, we define the index for linearly independent signals, and the proposed index is analyzed through numerical simulations. Next, the index is applied to a highly large-scale M-ary phase-shift keying (PSK) coherent state signal. Furthermore, the index is compared with the capacity of the pure state channel with the PSK signal. As a result, it is shown that a highly large-scale M-ary PSK coherent state signal exhibits a quantum nature even when the signal transmission power is very high. Thus, the theoretical characterization of a highly large-scale M-ary coherent state signal based on the proposed index will be the first step toward a better understanding of cutting-edge optical communication technologies such as the quantum stream cipher Y00.

Experimental demonstration of a 4,294,967,296-QAM-based Y-00 quantum stream cipher template carrying 160-Gb/s 16-QAM signals.

We demonstrate a 4,294,967,296-quadrature amplitude modulation (QAM) based Y-00 quantum stream cipher system carrying a 160-Gb/s 16-QAM signal transmitted over 320-km SSMF. The ultra-dense QAM cipher template is realized by an integrated two-segment silicon photonics I/Q modulator.

Quantum Stream Ciphers: Impossibility of Unconditionally Strong Algorithms

Stream ciphers form one of two large classes of ciphers with private keys in classical cryptography. In this paper, we introduce the concept of a quantum stream cipher. Special types of quantum stream ciphers were proposed earlier by numerous researchers. We prove a general result on the nonexistence of an unconditionally strong quantum stream cipher if the length of a message is much longer than the length of a key. We analyze individual and collective attacks against a quantum stream cipher. A relationship between the problem of guessing the key by the opponent and the problem of distinguishing of random quantum states is established.

Theory and performance analyses in quantum stream cipher based on bitwise NOT operation

Because of the realization of physical layer security, the Quantum Stream Cipher (QSC) is getting more and more attention. However, the error rate of each bit of ciphertexts is different from 0.5 for Eve in QSC. This drawback provides Eve with an opportunity to break QSC system possibly through some attacks, such as fast correlation attacks. Thus, to increase the bit error rate of ciphertexts in the higher bit positions to cope with this kind of attacks, this paper proposes a ciphertext mapping method based on Bitwise NOT Operation (BNO). According to parity of bases, BNO-based mapping performs bitwise NOT operation for some bit positions of ciphertext to expand the difference between adjacent bit positions of ciphertexts in QSC. Besides, BNO-based QSC can be directly employed in multi-bit plaintext mapping in QSC for different modulation formats, such as PSK/QSC and QAM/QSC. The security and transmission performance of QSC based on BNO are mainly investigated with different intensity ASE noises and the number of bases in optical back-to-back simulation. The simulation results demonstrate that bit error rate in each bit position of ciphertext is close to 0.5 by BNO method in QSC. Thus, BNO method can expand the impact of noise on the higher bit positions of ciphertext. In addition, BNO method has little influence on transmission performance of receiver in QSC system.

A novel realization of quantum stream cipher with key-modulated local light

Abstract Quantum-noise stream cipher (QSC) is a potentially information-theoretic secure physical-layer encryption method for high-speed and long-distance fiber communications. In this paper, a novel QSC scheme employing Y-00 protocol is proposed and experimentally demonstrated under general commercial components. The structure of our scheme can provide a convenience for general researchers to perform QSC experimental studies. Specifically, at receiver, the local light is modulated by M/2-ary extended secret key, which is introduced as optical threshold signal, and the balanced photodetector is applied as optical comparator to decode the M-ary encrypted signal. As a result, the error-free secure communication is realized at 2.5 Gb/s over 100-km optically amplified links, where the intensity levels of QSC signals are attained to 1024. Meanwhile, in strict theory, the minimum number of masked levels by only quantum noise is calculated to be more than two, which indicates the security of this realization. The system performance is investigated from both experimental and theoretical results. We reveal the new fact that the increasing number of signal levels will degrade the QSC BER performance for intensity modulation, which is different from that for phase modulation.

Digital coherent PSK Y-00 quantum stream cipher with 217 randomized phase levels.

We report a 10-Gbaud fiber-optic cipher transmission system by using a phase-shift keying (PSK) Y-00 quantum stream cipher. The PSK Y-00 cipher is a symmetric-key direct data encryption technique based on extremely high-order random phase modulation using a pre-shared short key. Neighboring signal phases following encryption are masked by quantum (shot) noise, which provides security based on shot noise's inherent effects. To implement such a system, we utilize coarse-to-fine phase modulation with two cascaded phase modulators and digital decryption incorporated into digital signal processing (DSP) for intra-dyne coherent detection. We demonstrate 10-Gbaud PSK Y-00 cipher transmission over a 400-km standard single-mode fiber (SSMF). The coarse-to-fine phase modulation achieves 217 phase levels for signal masking by shot noise. The DSP with decryption realizes detection of the cipher without penalties. Masking 167 signal phase levels by shot noise is achieved at a bit-error ratio defined by a hard-decision forward-error correction threshold (3.8 × 10-3) in the transmissions over the 400-km SSMF.

Guessing probability under unlimited known-plaintext attack on secret keys for Y00 quantum stream cipher by quantum multiple hypotheses testing

Although quantum key distribution is regarded as promising secure communication, security of Y00 protocol proposed by Yuen in 2000 for the affinity to conventional optical communication is not well-understood yet; its security has been evaluated only by the eavesdropper’s error probabilities of detecting individual signals or masking size, the number of hidden signal levels under quantum and classical noise. Our study is the first challenge of evaluating the guessing probabilities on shared secret keys for pseudorandom number generators in a simplified Y00 communication system based on quantum multiple hypotheses testing theory. The result is that even unlimitedly long known-plaintext attack only lets the eavesdropper guess the shared secret keys of limited lengths with a probability strictly <1. This study will give some insights for detailed future works on this quantum communication protocol.

214Intensity-Level 10-Gbaud Y-00 Quantum Stream Cipher Enabled by Coarse-to-Fine Modulation

For secure fiber-optic transmission, we demonstrate a 10-Gbaud Y-00 quantum stream cipher that achieves quantum noise masking using 214 (=16,384) intensity-level modulation. Coarse-to-fine driving of a dual-drive Mach–Zehnder modulator using two synchronized digital-to-analog converters is employed for the modulation. Successful off-line decryption of the cipher is achieved.

Y-00 quantum stream cipher overlay in a coherent 256-Gbit/s polarization multiplexed 16-QAM WDM system

We present the operation of a 1.5-Gb/s real-time Y-00 quantum stream cipher as an overlay in a modern coherent wavelength-division multiplexed (WDM) transmission system. We investigate transmission performance in two different wavelength allocation scenarios. The first scenario places the Y-00 cipher signal in a vacant 50-GHz channel slot between two 50-GHz spaced real-time processed 32-Gbaud PDM-16-QAM (256-Gbit/s) channels. The second scenario puts the Y-00 cipher signal in the small gap between two adjacent 50-GHz spaced WDM channels, hence implementing a secure channel overlay in a fully loaded WDM system. In both scenarios, the Y-00 cipher signal and the 256-Gbit/s signals are transmitted over 320 km.

QAM quantum stream cipher using digital coherent optical transmission

A Quantum Stream Cipher (QSC) using Quadrature Amplitude Modulation (QAM) is presented to greatly increase the secure degree compared with ASK or PSK/QSC. We propose encoding multi-bit data in one symbol with a multi-bit basis state, resulting in QAM/QSC, which employs amplitude and phase encryption of the light beam simultaneously. A 16 QAM/QSC experiment at 10 Gbit/s was successfully carried out over 160 km using a digital coherent optical transmission technique, where 16 QAM data were encrypted in a constellation with 32 × 32~4096 × 4096 symbols. We show experimentally that the Number of Masked Signals (NMS) in the quantum noise Γ(QAM) for QAM/QSC becomes a square multiple larger than Γ(ASK) for ASK/QSC. Γ(QAM) exceeds 10,000. This result indicates that the QSC technique is more robust against eavesdroppers than ASK or PSK/QSC.

Running key mapping in a quantum stream cipher by the Yuen 2000 protocol

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 $M$-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.

Quantum Stream Cipher by Yuen-2000 Protocol

Quantum Stream Cipher by Yuen-2000 Protocol

Practical security analysis of a quantum stream cipher by the Yuen 2000 protocol

There exists a great gap between one-time pad with perfect secrecy and conventional mathematical encryption. The Yuen 2000 (Y00) protocol or $\ensuremath{\alpha}\ensuremath{\eta}$ scheme may provide a protocol which covers from the conventional security to the ultimate one, depending on implementations. This paper presents the complexity-theoretic security analysis on some models of the Y00 protocol with nonlinear pseudo-random-number-generator and quantum noise diffusion mapping (QDM). Algebraic attacks and fast correlation attacks are applied with a model of the Y00 protocol with nonlinear filtering like the Toyocrypt stream cipher as the running key generator, and it is shown that these attacks in principle do not work on such models even when the mapping between running key and quantum state signal is fixed. In addition, a security property of the Y00 protocol with QDM is clarified. Consequently, we show that the Y00 protocol has a potential which cannot be realized by conventional cryptography and that it goes beyond mathematical encryption with physical encryption.

Immunity against Correlation Attack on Quantum Stream Cipher by Yuen 2000 Protocol

This paper presents the security analysis on the quantum stream cipher so called Yuen-2000 protocol (or ?? scheme) against the fast correlation attack, the typical attack on stream ciphers. Although the security of a very simple experimental model of the quantum stream cipher without a randomization may be reduced to a complexity based security against the correlation attacks under a large number of known plaintexts, it is not a basic feature of Yuen 2000 protocol. In fact, we clarify that there exists a randomization scheme which attains the perfect correlation immunity against such attacks under an approximation. And in this scheme, the running key correlation from the second randomization that determines the mapping patterns is broken off also by quantum noise. In such a case, any fast correlation attack does not work on the quantum stream cipher.

Quantum stream cipher by the Yuen 2000 protocol: Design and experiment by an intensity-modulation scheme

This paper shall investigate Yuen protocol, so called Y-00, which can realize a randomized stream cipher with high bit rate(Gbps) for long distance(several hundreds km). The randomized stream cipher with randomization by quantum noise based on Y-00 is called 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 the quantum unambiguous measurement to make clear the strength of Y-00 in real communication. In addition, we give a design for the implementation of an intensity modulation scheme and report the experimental demonstration of 1 Gbps quantum stream cipher through 20 km long transmission line.

Quantum quadrature amplitude modulation system and its applicability to coherent-state quantum cryptography

The quadrature amplitude modulation (QAM) signal of coherent state of light is applied to the quantum stream cipher by Y-00 protocol. We first discuss on the performance of the square-root measurement (SRM) for the QAM signals in comparison with the optimum receiver. It is shown that the quantum stream cipher with the QAM signals is designed by using the SRM, taking account of the ciphertext-only attack and the known/chosen plain attack. Furthermore, the modification of the quantum stream cipher with the QAM signals is considered.