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arXiv:1110.1818 · International Journal of Quantum Information

SECURITY OF A NEW TWO-WAY CONTINUOUS-VARIABLE QUANTUM KEY DISTRIBUTION PROTOCOL

MAOZHU SUN, XIANG PENG, YUJIE SHEN, HONG GUO

Published Aug 1, 2012• 42 citations
arXivHTMLPDF

Abstract

The original two-way continuous-variable quantum-key-distribution (CV-QKD) protocols [S. Pirandola, S. Mancini, S. Lloyd and S. L. Braunstein, Nat. Phys. 4 (2008) 726] give the security against the collective attack on the condition of the tomography of the quantum channels. We propose a family of new two-way CV-QKD protocols and prove their security against collective entangling cloner attacks without the tomography of the quantum channels. The simulation result indicates that the new protocols maintain the same advantage as the original two-way protocols whose tolerable excess noise surpasses that of the one-way CV-QKD protocol. We also show that all sub-protocols within the family have higher secret key rate and much longer transmission distance than the one-way CV-QKD protocol for the noisy channel.

DOI
10.1142/s0219749912500591

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The original two-way continuous-variable quantum-key-distribution (CV-QKD) protocols [S. Pirandola, S. Mancini, S. Lloyd and S. L. Braunstein, Nat. Phys. 4 (2008) 726] give the security against the collective attack on the condition of the tomography of the quantum channels. We propose a family of new two-way CV-QKD protocols and prove their security against collective entangling cloner attacks without the tomography of the quantum channels. The simulation result indicates that the new protocols maintain the same advantage as the original two-way protocols whose tolerable excess noise surpasses that of the one-way CV-QKD protocol. We also show that all sub-protocols within the family have higher secret key rate and much longer transmission distance than the one-way CV-QKD protocol for the noisy channel.
We propose an improved two-way continuous-variable quantum key distribution (CV QKD) protocol by adding proper random noise on the receiver's homodyne detection, the security of which is analysed against general collective attacks. The simulation result under the collective entangling cloner attack indicates that despite the correlation between two-way channels decreasing the secret key rate relative to the uncorrelated channels slightly, the performance of the two-way protocol is still far beyond that of the one-way protocols. Importantly, the added noise in detection is beneficial for the secret key rate and the tolerable excess noise of this two-way protocol. With the reasonable reconciliation efficiency of 90%, the two-way CV QKD with added noise allows the distribution of secret keys over 60 km fibre distance.
In this paper, using the full security framework for continuous-variable quantum key distribution (CV-QKD), we provide a composable security proof for the CV-QKD system in a realistic implementation.We take into account equipment losses and contributions from various components of excess noise and evaluate performance against collective and coherent attacks assuming trusted hardware noise.The calculation showed that the system remains operable at channel losses up to 10.2 dB in the presence of collective attacks and up to 7.5 dB in the presence of coherent ones.
Secure communication protocols based on quantum physics compel worldwide attention. Continuous-variable quantum key distribution (CV-QKD) uses a cost-effective detection technique instead of dedicated single-photon-counting technology, and can provide high key rates over metropolitan distances. Traditional coherent-state CV-QKD protocols, however, suffer from low tolerance of channel excess noise. The authors succeed in distributing Einstein-Podolsky-Rosen entangled states over a 50-km standard fiber with negligible excess noise, and further demonstrate CV-QKD in a high-noise environment with performance superior to that of the optimized coherent-state protocol.
Continuous-variable quantum key distribution (CV-QKD) enables information-theoretically secure key generation between legitimate parties. To further enhance system performance, an improved two-way CV-QKD protocol has been proposed, which is accessible in practice and exhibits increased robustness against excess noise. However, in practical implementations, device nonidealities inevitably drive the optical field from the single-mode regime into the continuous-mode regime. In this work, we introduce temporal modes to characterize the evolution of optical fields in the improved two-way protocol and establish a security analysis framework for the continuous-mode scenario based on adaptive normalization with calibrated shot-noise unit. In addition, finite-size effects are taken into account in the analysis. Our results demonstrate that the improved two-way protocol retains a performance advantage over one-way counterpart. The analysis provides useful guidance for the practical implementation and performance optimization of improved two-way CV-QKD systems.
This thesis deals with a detailed study of the unconditional security of Continuous-Variable (CV) Quantum Key Distribution (QKD). We consider general communication architectures based on both point-to-point and end-to-end principle. For the first case we develop an extensive analysis of the unconditional security of both one-way and two-way protocol under several eavesdropping conditions. We describe an effective post-processing strategy, to apply to one-way communications, that allows to neutralise general coherent attacks. This result motivates us to formulate the conjecture that the "de Finettization" of the classical data, typically adopted in the asymptotic limit of many signals exchanged in order to reduce the attacks from a general coherent to a collective one, may not be necessary for Gaussian one-way communication. For what it concerns two-way protocols we show that after the reduction of the general attack using the de Finetti symmetrization, two-mode coherent attacks are the optimal eavesdropping. Our cryptanalysis shows that the parties can exploit a strategy, in combination with the results obtained on the security of one-way protocols against two-mode coherent attacks. In fact we prove explicitly that two-way communication with Gaussian continuous variables is immune to general coherent attacks. This is possible exploiting the random opening and closing of the circuit by Alice (ON/OFF switching), in the limit of many uses of the channel. We then conclude that collective attacks represent, strictly, the best strategy available to Eve. We have then studied the general security of one-way protocol considering not just lossy channel, but extending the cryptanalysis to all physically allowed canonical forms attacks. Finally we extended the study of thermal CV-QKD to two-way communication at different frequencies, in the framework of optimal collective attacks. In the last part of this thesis we focused on CV-QKD considering a modern end-to-end configuration. We then extend CV quantum cryptography to a network configuration. We develop a detailed cryptoanalysis of a communication scheme based on an untrusted relay, assisting the parties during the preparation of the secret key. We find the optimal eavesdropping and prove, both theoretically and experimentally, the feasibility of high-rate CV-QKD over metropolitan distances with of-the-shelves devices.
Continuous-variable quantum key distribution (CV-QKD) has emerged as a promising approach for secure quantum communication, offering advantages such as high key generation rates, compatibility with standard telecommunication infrastructure, and potential for integration on photonic chips. This review provides an accessible introduction to the theory of CV-QKD, aimed at researchers entering this rapidly developing field. We focus on fundamental concepts, key protocols, and security analysis essential for understanding CV-QKD systems, with a special emphasis on prepare-and-measure protocols using coherent states under asymptotic security conditions. We explain their equivalence to entanglement-based protocols and detail the security proof framework against collective attacks, encompassing both Gaussian and discrete modulation schemes. We also briefly address more advanced topics, including measurement-device-independent CV-QKD and finite-size security analysis. This work is motivated by Brazil's growing investment in quantum communication technologies. By presenting a clear learning path from basic concepts to advanced topics, this work aims to equip newcomers with the essential tools to engage with current research in CV-QKD, thereby supporting the training of a new generation of researchers in this strategic field.