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Towards polarisation-encoded quantum key distribution in optical fibre networks
摘要： Quantum key distribution – a process that encodes digital information – often utilises fibre optic technologies for commercial applications. Fibre provides the benefit of a dark channel as well as the convenience of independence of a line-of-sight connection between the sender and receiver. In order to implement quantum key distribution protocols utilising polarisation encoding, the birefringence effects of fibre must be compensated for. Birefringence is caused by manufacturing impurities in the fibre or a change in environmental conditions and results in a rotation of the state of polarisation of light as it is propagated through the fibre. With dynamic environmental conditions, the birefringence effects should be monitored with a test signal at regular time intervals so that the polarisation of each photon can be appropriately compensated to its original state. Orthogonal states are compensated simultaneously, but most protocols, such as BB84 and B92, require non-orthogonal basis sets. Instead of using a compensator for each basis, the presented scheme fixes the polarisation controller onto the plane on the Poincaré that passes through both bases, compensating both non-orthogonal bases simultaneously.
关键词： cryptography,fibre network,QKD,polarisation encoding,single photon
更新于2025-09-23 15:23:52
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Memory-assisted quantum key distribution resilient against multiple-excitation effects
摘要： Memory-assisted measurement-device-independent quantum key distribution (MA-MDI-QKD) has recently been proposed as a technique to improve the rate-versus-distance behavior of QKD systems by using existing, or nearly-achievable, quantum technologies. The promise is that MA-MDI-QKD would require less demanding quantum memories than the ones needed for probabilistic quantum repeaters. Nevertheless, early investigations suggest that, in order to beat the conventional memory-less QKD schemes, the quantum memories used in the MA-MDI-QKD protocols must have high bandwidth-storage products and short interaction times. Among different types of quantum memories, ensemble-based memories offer some of the required specifications, but they typically suffer from multiple excitation effects. To avoid the latter issue, in this paper, we propose two new variants of MA-MDI-QKD both relying on single-photon sources for entangling purposes. One is based on known techniques for entanglement distribution in quantum repeaters. This scheme turns out to offer no advantage even if one uses ideal single-photon sources. By finding the root cause of the problem, we then propose another setup, which can outperform single memory-less setups even if we allow for some imperfections in our single-photon sources. For such a scheme, we compare the key rate for different types of ensemble-based memories and show that certain classes of atomic ensembles can improve the rate-versus-distance behavior.
关键词： quantum cryptography,quantum networks,quantum key distribution (QKD),quantum memory,single-photon source,quantum communications
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Information and Communication Technology Convergence (ICTC) - Jeju (2018.10.17-2018.10.19)] 2018 International Conference on Information and Communication Technology Convergence (ICTC) - Single Trace Side Channel Analysis on Quantum Key Distribution
摘要： The security of current key exchange protocols such as Dif?e–Hellman key exchange is based on the hardness of number theoretic problems. However, these key exchange protocols are threatened by weak random number generators, advances to CPU power, a new attack from the eavesdropper, and the emergence of a quantum computer. Quantum Key Distribution (QKD) addresses these challenges by using quantum properties to exchange a secret key without the risk of being intercepted. Recent developments on the QKD system resulted in a stable key generation with fewer errors so that the QKD system is rapidly becoming a solid commercial proposition. However, although the security of the QKD system is guaranteed by quantum physics, its careless implementation could make the system vulnerable. In this paper, we proposed the ?rst side-channel attack on plug-and-play QKD system. Through a single electromagnetic trace obtained from the phase modulator on Alice’s side, we were able to classify the electromagnetic trace into four classes, which corresponds to the number of bit and basis combination in the BB84 protocol. We concluded that the plug-and-play QKD system is vulnerable to side-channel attack so that the countermeasure must be considered.
关键词： plug-and-play,Single Trace Attack,QKD,side-channel attack,EM analysis
更新于2025-09-23 15:22:29
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[Advances in Intelligent Systems and Computing] Soft Computing for Problem Solving Volume 817 (SocProS 2017, Volume 2) || Design a New Protocol and Compare with BB84 Protocol for Quantum Key Distribution
摘要： Quantum key distribution is the latest advancement in quantum cryptography. There are several QKD protocols like BB84, B92, Ekert91, COW, SARG04, out of which BB84 is the first protocol developed in 1984. In this paper, we are discussing first about the working of BB84 protocol and then proposing a new protocol which is a variation over BB84 protocol, second the design of simulation setup is discussed, and then we compared the performance of BB84 with the proposed protocol and proved it much better in case of capacity and error estimation. Object-oriented approach is used in the simulation designing for new protocol and BB84 protocol.
关键词： BB84 simulation,Quantum cryptography,QKD protocols
更新于2025-09-23 15:21:21
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Sending-or-Not-Sending with Independent Lasers: Secure Twin-Field Quantum Key Distribution over 509??km
摘要： Twin-field (TF) quantum key distribution (QKD) promises high key rates over long distances to beat the rate-distance limit. Here, applying the sending-or-not-sending TF QKD protocol, we experimentally demonstrate a secure key distribution that breaks the absolute key-rate limit of repeaterless QKD over a 509-km-long ultralow loss optical fiber. Two independent lasers are used as sources with remote-frequency-locking technique over the 500-km fiber distance. Practical optical fibers are used as the optical path with appropriate noise filtering; and finite-key effects are considered in the key-rate analysis. The secure key rate obtained at 509 km is more than seven times higher than the relative bound of repeaterless QKD for the same detection loss. The achieved secure key rate is also higher than that of a traditional QKD protocol running with a perfect repeaterless QKD device, even for an infinite number of sent pulses. Our result shows that the protocol and technologies applied in this experiment enable TF QKD to achieve a high secure key rate over a long distribution distance, and is therefore practically useful for field implementation of intercity QKD.
关键词： remote-frequency-locking technique,repeaterless QKD,ultralow loss optical fiber,secure key distribution,Twin-field quantum key distribution
更新于2025-09-23 15:19:57
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Finite-key effects in multipartite quantum key distribution protocols
摘要： We analyze the security of two multipartite quantum key distribution (QKD) protocols, specifically we introduce an N-partite version of the BB84 protocol and we discuss the N-partite six-state protocol proposed by Epping et al (2017 New J. Phys. 19 093012). The security analysis proceeds from the generalization of known results in bipartite QKD to the multipartite scenario, and takes into account finite resources. In this context we derive a computable expression for the achievable key rate of both protocols by employing the best-known strategies: the uncertainty relation and the postselection technique. We compare the performances of the two protocols both for finite resources and infinitely many signals.
关键词： finite resources,conference key agreement,quantum key distribution,uncertainty relation for smooth entropies,finite-key effects,security analysis,multipartite qkd
更新于2025-09-19 17:15:36
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Simulation of a Telecom-Provider Driven Reference QKD-Network
摘要： In the last 15 years different types of QKD-networks have been demonstrated in the field. These show significant advantages compared to QKD-links and utilize i.a. the following functionalities: switching [1]; trusted nodes to increase distances and resiliency by enabling dynamic routing [2]; lab-demos of star-shaped PON-structures to distribute the keys to many users [3] and star-shaped switched networks incorporating entanglement [4]. Only recently the largest QKD-network has been put into operation in China [5]. So far, all these successful technology demonstrators failed, however, to trigger real-world QKD deployment scenarios by telecom operators. The recently launched EU-flagship program facilitates cross-cutting collaborations. Partners of CiViQ (the flagship QKD project) [6] work on QKD technology improvement adapted to novel use-cases. Securing the critical telecom infrastructure will be realized by QKD-links integrated into novel architectures such as SDN (Software-Defined Networks), whereby simulation and usage optimization of QKD-links in typical environments is pursued. For investigating a large-scale deployment we replace the typical unit cell introduced in SECOQC [2] (four nodes and six edges) by a reference network depicted in Fig. 1a (but keep the hop-by-hop key distribution of [2]). It is derived from Deutsche Telekom’s real aggregation network covering an area of about 170km*140km and consisting of 39 nodes and 66 edges. The distances of deployed fibers L are in the range from L=1.3km up to L=75km and the secure key rate is calculated using the formula R=R0*10^(-0,25dB/km*L/10). Specifically, an initial secret key rate at 0km distance of R0=50kbps is used, leading to specific values of R at the end of each edge. For this particular reference network of 39 nodes we compare two different algorithms to distribute most efficiently the 38 minimally required QKD-links. To secure the overall management plane from the central core node (marked as red dot in Fig. 1) to any node these need to share maximal but uniform secure key. The first algorithm MST (Minimum Spanning Tree) connects all the network nodes together with the minimum possible overall fiber length. The second algorithm, SSSPT (Single-Source Shortest Path Tree), based on e.g. Dijkstra’s algorithm selecting the shortest paths from a single source node to all other nodes of the topology, finds the lowest possible number of N-1 edges. For MST and SSSPT the maximal secure key rate to all nodes is 359bps and 259 bps, respectively.
关键词： MST,telecom operators,QKD-networks,SSSPT,SECOQC
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Field Trial of a Finite-Key Quantum Key Distribution System in the Metropolitan Florence Area
摘要： In a society based on the continuous exchange of sensitive data and information, the importance of secure and trustful communications is essential. Quantum key distribution (QKD) makes it possible to share data in an unconditionally secure way exploiting the basic principles of Quantum Mechanics [1]. During the last 30 years, many QKD protocols have been developed and tested, achieving long distance transmission [2] and secret key rates up to hundreds of Mbits per second [3]. However, this technology is still far from a large-scale deployment in existing fiber networks and telecom infrastructures, due to multiple factors: low secret-key rate, limited distance between users, lack of applications, high costs and high requirements in terms of low noise fiber links. In order to reveal practical issues in real-world deployments, quantum field trials have been implemented by exploiting installed fiber links on a metropolitan scale. While many of these experiments were performed on a dark fiber (thus requiring a dedicated link for quantum key transmission only), other field trials explored the coexistence between weak coherent pulses and classical signals propagating through the same fiber [4-7], see Figure 1 a). In this work we report a low-cost field trial demonstration of a complete QKD system working in the C-band telecom wavelength, performed over an installed fiber situated in Florence. A time-bin three-stateprotocol with one-decoy state method is implemented in the experiment [2]. As illustrated in Figure 1 b), theexperimental setup consists of a transmitter (Alice), working at ch 21 of 100GHz DWDM grid, and a receiver(Bob) connected by a metropolitan dark-fiber link in a loop-back configuration. The total distance covered in thefiber link is about 40 km, with an overall transmission loss of 21 dB. Secure key generation of 3.4 kbps (in thefinite key scenario) is achieved, with simultaneous transmission of a classical synchronization signal, at adifferent wavelength (ch 51 of 100GHz DWDM grid with -29 dBm input power), through the same fiber. InFigure 1 c) we report the secret key rate and the bit error rate, measured for several hours to prove the stability ofthe apparatus.
关键词： metropolitan network,QKD,finite-key analysis,Quantum key distribution,field trial
更新于2025-09-16 10:30:52
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[IEEE 2019 21st International Middle East Power Systems Conference (MEPCON) - Cairo, Egypt (2019.12.17-2019.12.19)] 2019 21st International Middle East Power Systems Conference (MEPCON) - Negative-Positive Neutral Point Based Two-Stage Inverter for Photovoltaic Application
摘要： The quantum key distribution protocol uses one degree of freedom of a single quantum system to encode information. If this information has correlations with the system’s other degrees of freedom, or if the measurement efficiencies on the receiver side depend on them, a security loophole called side channel is created. An eavesdropper can exploit it to gain information without disturbing the system, and thus, without revealing the attack. Here, we analyze side channels in a free-space QKD sender and receiver implementation and focus especially on the dependencies and side channels for the spatial degree of freedom.
关键词： Cryptographic protocols,optical transmitters,optical receivers,quantum key distribution (QKD)
更新于2025-09-16 10:30:52
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Laser-seeding Attack in Quantum Key Distribution
摘要： Quantum key distribution (QKD) based on the laws of quantum physics allows the secure distribution of secret keys over an insecure channel. Unfortunately, imperfect implementations of QKD compromise its information-theoretical security. Measurement-device-independent quantum key distribution (MDI QKD) is a promising approach to remove all side channels from the measurement unit, which is regarded as the “Achilles’ heel” of QKD. An essential assumption in MDI QKD is, however, that the sources are trusted. Here we experimentally demonstrate that a practical source based on a semiconductor laser diode is vulnerable to a laser-seeding attack, in which light injected from the communication line into the laser results in an increase of the intensities of the prepared states. The unnoticed increase of intensity may compromise the security of QKD, as we show theoretically for the prepare-and-measure decoy-state BB84 and MDI QKD protocols. Our theoretical security analysis is general and can be applied to any vulnerability that increases the intensity of the emitted pulses. Moreover, a laser-seeding attack might be launched as well against decoy-state-based quantum cryptographic protocols beyond QKD.
关键词： Quantum key distribution,quantum cryptography,MDI QKD,laser-seeding attack,decoy-state BB84
更新于2025-09-12 10:27:22