Quantum Key Distribution Research Papers (original) (raw)

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- Physics, Photonics, Optical Communication, Quantum Cryptography

Quantum key distribution allows two parties, traditionally known as Alice and Bob, to establish a secure random cryptographic key if, firstly, they have access to a quantum communication channel, and secondly, they can exchange classical public messages which can be monitored but not altered by an eavesdropper, Eve. Quantum key distribution provides perfect security because, unlike its classical counterpart, it relies on the laws of physics rather than on ensuring that successful eavesdropping would require excessive computational effort. However, security proofs of quantum key distribution are not trivial and are usually restricted in their applicability to specific protocols. In contrast, we present a general and conceptually simple proof which can be applied to a number of different protocols. It relies on the fact that a cryptographic procedure called privacy amplification is equally secure when an adversary's memory for data storage is quantum rather than classical [1].

- by Artur Ekert
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- Quantum Physics, Quantum Key Distribution, Data storage, Quantum Communication

In this paper, we describe a new design of laser diode driver system based on MOSFET current mirror and digital signal controller (DSC). The system is designed to emit stream pairs of photons from three semiconductor laser diodes. The DSC is able to switch between the three laser diodes at constant rate. The duty cycle is maintained at 1% in order to reduce its thermal effect and thus prolong the laser diodes' life cycles. The MOSFET current mirror circuits are capable of delivering constant modulation current with peak current up to 58 mA to each laser diode. This laser driver system will allow the generating biphotons automatically with qubit rate around 8-13% for m less than or equal to 1, thus making it practical for sixstates quantum key distribution implementation.

The quantum "mystery which cannot go away" (in Feynman's words) of wave-particle duality is illustrated in a striking way by Wheeler's delayed-choice GedankenExperiment. In this experiment, the configuration of a two-path interferometer is chosen after a single-photon pulse has entered it : either the interferometer is closed (i.e. the two paths are recombined) and the interference is observed, or the interferometer remains open and the path followed by the photon is measured. We report an almost ideal realization of that GedankenExperiment, where the light pulses are true single photons, allowing unambiguous which-way measurements, and the interferometer, which has two spatially separated paths, produces high visibility interference. The choice between measuring either the open or closed configuration is made by a quantum random number generator, and is space-like separated -in the relativistic sense -from the entering of the photon into the interferometer. Measurements in the closed configuration show interference with a visibility of 94%, while measurements in the open configuration allow us to determine the followed path with an error probability lower than 1%.

- by Jean-françois Roch
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- Science, Multidisciplinary, Quantum Key Distribution, Nitrogen

Single-photon detectors based on superconducting nanowires (SSPDs or SNSPDs) have rapidly emerged as a highly promising photon-counting technology for infrared wavelengths. These devices offer high efficiency, low dark counts and excellent timing resolution. In this review, we consider the basic SNSPD operating principle and models of device behaviour. We give an overview of the evolution of SNSPD device design and the improvements in performance which have been achieved. We also evaluate device limitations and noise mechanisms. We survey practical refrigeration technologies and optical coupling schemes for SNSPDs. Finally we summarize promising application areas, ranging from quantum cryptography to remote sensing. Our goal is to capture a detailed snapshot of an emerging superconducting detector technology on the threshold of maturity.

- by David Pappas
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- Engineering, Materials Engineering, Condensed Matter Physics, Remote Sensing

The appealing feature of quantum key distribution (QKD), from a cryptographic viewpoint, is the ability to prove the information-theoretic security (ITS) of the established keys. As a key establishment primitive, QKD however does not provide a standalone security service in its own: the secret keys established by QKD are in general then used by a subsequent cryptographic applications for which the requirements, the context of use and the security properties can vary. It is therefore important, in the perspective of integrating QKD in security infrastructures, to analyze how QKD can be combined with other cryptographic primitives.The purpose of this survey article, which is mostly centered on European research results, is to contribute to such an analysis. We first review and compare the properties of the existing key establishment techniques, QKD being one of them. We then study more specifically two generic scenarios related to the practical use of QKD in cryptographic infrastructures: 1) using QKD as a key renewal technique for a symmetric cipher over a point-to-point link ; 2) using QKD in a network containing many users with the objective of offering any-to-any key establishment service. We discuss the constraints as well as the potential interest of using QKD in these contexts. We finally give an overview of challenges relative to the development of QKD technology that also constitute potential avenues for cryptographic research.

- by John Rarity
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- Quantum Physics, Information Theory, Quantum Cryptography, Quantum Key Distribution

- by Alessandro Gaggero and +1
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- Engineering, Materials Engineering, Condensed Matter Physics, Remote Sensing

As quantum computing matures, it's going to bring unimaginable increases in computational power along with the systems we use to protect our data (and our democratic processes) will become even more vulnerable. It is often said that the power of quantum computer comes from the quantum parallelism, which means instead of processing each input one by one, processor process each input parallelly. Quantum mechanics allow us to do an operation on a superposition of all the possible inputs at the same time. The classical computers have enabled amazing things, but there are still some problems we can't easily solve like-í µí¿ í µí±µ (optimization problems where it grows exponentially).For transferring the information the protocols are very essential for security. Example is quantum key distribution, and its protocols are like-BB84,SA RG04,B9 2 etc. Moreover, quantum cryptography has proved its standing against many weaknesses in the classical cryptography. One of these weaknesses is the ability to copy any type of information using a passive attack without an interruption, which is impossible in the quantum system.

- by Ijariit Journal and +1
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- Quantum Cryptography, Quantum Key Distribution

A Quantum Key Distribution (QKD) network is an infrastructure capable of performing long-distance and high-rate secret key agreement with information-theoretic security. In this paper we study security properties of QKD networks based on trusted repeater nodes. Such networks can already be deployed, based on current technology. We present an example of a trusted repeater QKD network, developed within the SECOQC project. The main focus is put on the study of secure key agreement over a trusted repeater QKD network, when some nodes are corrupted. We propose an original method, able to ensure the authenticity and privacy of the generated secret keys.

For a long time, one of my dreams was to describe the nature of uncertainty axiomatically, and it looks like I've finally done it in my co∼eventum mechanics! Now it remains for me to explain to everyone the co∼eventum mechanics in the most approachable way. This is what I'm trying to do in this work. The co∼eventum mechanics is another name for the co∼event theory, i.e., for the theory of experience and chance which I axiomatized in 2016 [1, 2]. In my opinion, this name best reflects the co∼event-based idea of the new dual theory of uncertainty, which combines the probability theory as a theory of chance, with its dual half, the believability theory as a theory of experience. In addition, I like this new name indicates a direct connection between the co∼event theory and quantum mechanics, which is intended for the physical explanation and description of the conict between quantum observers and quantum observations [4]. Since my theory of uncertainty satises the Kolmogorov axioms of probability theory, to explain this co∼eventum mechanics I will use a way analogous to the already tested one, which explains the theory of probability as a theory of chance describing the results of a random experiment. The simplest example of a random experiment in probability theory is the " tossing a coin ". Therefore, I decided to use this the simplest random experiment itself, as well as the two its analogies: the " "flipping a coin " and the " spinning a coin " to explain the co∼eventum mechanics, which describes the results of a combined experienced random experiment. I would like to resort to the usual for the probability theory " coin-based " analogy to explain (and first of all for myself) the logic of the co∼eventum mechanics as a logic of experience and chance. Of course, this analogy one may seem strange if not crazy. But I did not come up with a better way of tying the explanations of the logic of the co∼eventum mechanics to the coin-based explanations that are commonly used in probability theory to explain at least for myself the logic of the chance through a simple visual " coin-based " model that clarifies what occurs as a result of a combined experienced random experiment in which the experience of observer faces the chance of observation. I hope this analogy can be useful not only for me in understanding the co∼eventum mechanics.

- by Ugochukwu Orji and +1
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- Quantum Cryptography, Quantum Computation, Quantum Information Theory, Quantum Key Distribution

The paper aims to examine the mechanisms of quantum cryptography and review the relationship between quantum and classical encryption schemes. A brief introduction of quantum computation is provided, with a simplified explanation of Shor's Algorithm showcasing the potentials of quantum computation. Related literature such as books, journals, proceedings, lecture notes and webpages on quantum cryptography were reviewed and were sourced from prominent databases like IEEE Xplore, ScienceDirect, and JSTOR. This gave a clearer picture on the mechanisms of quantum cryptography and Shor's algorithm. The authors were able to succinctly describe quantum cryptography, show how encryption is achieved by exploiting the properties of quantum particles, and demonstrated with examples the intricacies with Shor's algorithm. It is expected that interested researchers will be more informed on current research in quantum cryptography and influence potential cryptography scholars to explore further the mechanisms of quantum cryptography, quantum computation, and other principles of the quantum theory.

This paper presents extensions to the classical pointto-point protocol PPP [RFC1661] and IPSEC [RFC 2401] in order to build networks that can do unconditionally secure message relay. Our work addresses the problem of how to integrate quantum key distribution (QKD) in networks such that little effort needs to be put on protocol engine adaption and network topology design. This article demonstrates how to ensure correct routing and secure authentication between adjacent QKD-capable nodes, in particular, it is demonstrated how a person-in-the-middle attack can be countered using universal hash functions.

In this Book is an overview of Quantum Information Systems is given. Therefore, the postulates of quantum mechanics are given based on one interpretation that is called the Copenhagen interpretation. The main pillars of quantum mechanics are: Superposition, Interference, and Entanglement. Quantum Information Systems comprise three disciplines: Quantum Computation, Quantum Communication, and Quantum Control. Each one of them has a number of topics with some implementations that have reached the commercial level. Quantum Computation has three models: the circuit model that is using different techniques like superconducting elements and special Silicon-based elements. The Adiabatic quantum model has reached the commercial stage through a start-up company using superconducting chips. The categorical quantum model is based on category theory and one of its main applications is the study and verification of network and cryptographic protocols. Quantum communication started with defining the basic unit of information, the qubit. Then the quantum compression theorem was proved. The quantum channel capacity problem was divided into two problems: transmitting classical information over a quantum channel, and transmitting quantum information over a quantum channel. The first problem was partially resolved. However, the second problem is being researched upon. Two applications will be briefly presented: quantum teleportation and superdense coding. Both of them employs quantum entanglement. Quantum Key Distribution (QKD) using cryptographic protocols has received much attention due its importance in network security. A number of protocols have been proposed and some of them have been implemented, and now a number of commercial products have been announced. Also, some experimental networks have been implemented. QKD using space links have been proposed and experimented with. In few years quantum satellites will be launched. Quantum cryptographic protocols are being proposed to protect infrastructure networks like the electric power grid. Also, it is being used as a countermeasure against global spying networks like ECHELON that are detrimental for national economies. The Quantum Internet is also being considered using quantum teleportation together with Cavity Quantum Electrodynamics with some experimental work going on. Quantum Control is essential for both Quantum Computation and Quantum Communication. Intensive research is going on in: State estimation (called Quantum State Tomography), system identification (called Quantum Process Tomography), and Quantum Feedback Control. The basic concepts will be briefly considered in this presentation. University education has witnessed major changes to support the above developments. At the postgraduate level many universities offer many courses related to the above disciplines. Recently, a number of institutions started to offer undergraduate courses and some of them have even started to introduce Quantum Engineering 4 years undergraduate programs. A brief account will be given to such developments.

- by Jesse Mauck
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- Information Systems, Quantum Computing, Information Technology, Information Security

Abstract: This study shows that secret information can be shared or passed from a sender to a receiver even if not encoded in a secret message. In the protocol designed in this study, no parts of the original secret information ever travel via communication channels between the source and the destination, no encoding/decoding key is ever used. The two communicating partners, Alice and Bob, are endowed with coherent qubits that can be read and set and keep their quantum values over time. Additionally, there exists a central authority that is capable of identifying Alice and Bob to share with each half of entangled qubit pairs. The central authority also performs entanglement swapping. Our protocol relies on the assumption that public information can be protected, an assumption present in all cryptographic protocols. Also any classical communication channel need not be authenticated. As each piece of secret information has a distinct public encoding, the protocol is equivalent to a on...

- by Naya Nagy
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- Security, Quantum Cryptography, Quantum Key Distribution

Quantum key distribution algorithms use a quantum communication channel with quantum information and a classical communication channel for binary information. The classical channel, in all algorithms to date, was required to be authenticated. Moreover, Lomonaco 8 claimed that authentication is not possible using only quantum means. This paper reverses this claim. We design an algorithm for quantum key distribution that does authentication by quantum means only. Although a classical channel is still used, there is no need for the channel to beauthenticated. The algorithm relies on two protected public keys to authenticate the communication partner.

University are building the DARPA Quantum Network, the world's first network that delivers endtoend network security via high-speed Quantum Key Distribution, and testing that Network against sophisticated eavesdropping attacks. The first network link has been up and steadily operational in our laboratory since December 2002. It provides a Virtual Private Network between private enclaves, with user traffic protected by a weak-coherent implementation of quantum cryptography. This prototype is suitable for deployment in metro-size areas via standard telecom (dark) fiber. In this paper, we introduce quantum cryptography, discuss its relation to modern secure networks, and describe its unusual physical layer, its specialized quantum cryptographic protocol suite (quite interesting in its own right), and our extensions to IPsec to integrate it with quantum cryptography.

Two photons in a pair generated in the nonlinear optical process of spontaneous parametric down-conversion are, in general, strongly quantum entangled. Accordingly, they contain extremely strong energy, time, polarization and momentum quantum correlations. This entanglement involves more than one quantum variable and has served as a powerful tool in fundamental studies of quantum theory. It is now playing a large role in the development of novel information processing techniques and new optical measurement technologies. Here we review some of these technologies and their origins.

All Classical cryptographic methods used in our life based on mathematical ideas & computational assumption are actually unsafe, so quantum cryptography is proposed nowadays Quantum key distribution (QKD) promises secure key agreement by using quantum mechanical systems. QKD will be an important part of future cryptographic infrastructures. It can provide long-term confidentiality for encrypted information without reliance on computational assumptions. Although QKD still requires authentication to prevent man-in-the-middle attacks. Firstly, In this paper At quantum key distribution protocol process is introduced. Secondly, several improvements to the basic steps of two references are reviewed because of its defects, mainly about identity authentication in order to prevent communication partners' counterfeit, including errors removing, estimating Attacker's information, secrecy enhancement, etc. At last, based upon original improvements reserved selectively, the whole process of quantum key distribution protocol after improvement & then comparison is introduced in detail.

Quantum key distribution ͑QKD͒ is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel. The security of the key can in principle be guaranteed without putting any restriction on an eavesdropper's power. This article provides a concise up-to-date review of QKD, biased toward the practical side. Essential theoretical tools that have been developed to assess the security of the main experimental platforms are presented ͑discrete-variable, continuous-variable, and distributed-phase-reference protocols͒.

- by Momtchil Peev
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- Quantum Information, Quantum Cryptography, Modulation, Modern physics

Quantum Key Distribution (QKD) or quantum cryptography has been developed within the last decade; it is proved that QKD is secure against computer attacks and it is considered as a promising solution towards absolute security within long-term cryptosystems. Currently, research efforts are required to make strongly secure the existing communication protocols; we suggest as an issue to improve their security levels by integrating QKD. In this paper, we explore the possibility of using QKD for local area networks (LAN); we propose thus a scheme for integrating quantum cryptography in the TLS protocol. This will much contribute to enhance the process of authentication and data encryption. We present also an example to illustrate the feasibility of our scheme's implementation.

Quantum key distribution is a technique that permits the secure distribution of a bit string that is used as key in cryptographic protocols. The security is guaranteed by suitable coding of the information in a quantum property and from the fact that a quantum cannot be both split and cloned. In this article, we give details and show the results of an experimental realization of the B92 quantum key distribution protocol in 1550-nm telecom window. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 236–241, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23025

- by Obed Batista
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- Microwave, Quantum Cryptography, Quantum Key Distribution, Optical physics

This paper presents a multi-stage, multi-photon quantum key distribution protocol based on the double-lock
cryptography. It exploits the asymmetry in the detection strategies between the legitimate users and the
eavesdropper. The security analysis of the protocol is presented with coherent states under the interceptresend
attack, the photon number splitting attack, and the man-in-the-middle attack. It is found that the
mean photon number can be much larger 1. This complements the recent interest in multi-photon quantum
communication protocols that require a pre-shared key between the legitimate users.

We demonstrate that secure quantum key distribution systems based on continuous variables implementations can operate beyond the apparent 3 dB loss limit that is implied by the beam splitting attack . The loss limit was established for standard minimum uncertainty states such as coherent states. We show that by an appropriate postselection mechanism we can enter a region where Eve's knowledge on Alice's key falls behind the information shared between Alice and Bob even in the presence of substantial losses.

- by Gerd Leuchs
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- Information Theory, Quantum Optics, Communication Theory, Quantum Cryptography

We present a fully operable security gateway prototype, integrating quantum key distribution and realised as a system-on-chip. It is implemented on a field-programmable gate array and provides a virtual private network with low latency and gigabit throughput. The seamless hard-and software integration of a quantum key distribution layer enables high keyupdate rates for the encryption modules. Hence, the amount of data encrypted with one session key can be significantly decreased. We realise a highly modular architecture and make extensive use of software/hardware partitioning. This work is the first approach towards application of a new key distribution technology in dedicated security processors. In particular, it elaborates requirements for the integration of quantum key distribution on a chip level. SPDB Key Man. IPsec SADB MAC MAC QKD Keystore WAN Quantum System LAN

- by Momtchil Peev
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- Computer Architecture, FPGA, Cryptography, Quantum Cryptography

It is well known that optical access networks are able to provide high data rates over long distances and to a reasonable number of users. Security and privacy are always a challenge for public accessible network infrastructures. Especially in timedivision multiplexing passive optical networks (TDM-PONs), in which the downstream signal is broadcasted to all users connected via the same wavelength channel in a shared fiber link, privacy can be a critical concern. Although encryption at the application layer can provide a high level of security, this can be achieved only if the encryption key distribution is perfectly save. On the other hand, encryption on the physical layer such as quantum cryptography or, more precisely, quantum key distribution (QKD) is a very promising approach to achieve secure communication. However, there remain several issues that have to be solved before the quantum cryptography reaches the maturity level needed for a cost effective implementation in practical networks.

- by Gerald Franzl
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- Photonics, Quantum Cryptography, Quantum Key Distribution, Data Privacy

Under the sole assumption that Alice and Bob are connected by a classical authentic communication channel, secret communication-and thus also the generation of a secret key-is impossible . This changes dramatically when quantum mechanics comes into the game. Bennett and Brassard [BB84] (see also ) were the first to propose a quantum key distribution (QKD) scheme which uses communication over a (completely insecure) quantum channel (in addition to the classical authentic channel). The scheme is commonly known as the BB84 protocol.

- by Marco Piani and +1
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- Quantum Information, Optical Communication, Information theoretic security, Quantum Information Theory

This letter proposes a novel key distribution protocol with no key exchange in advance, which is secure as the BB84 quantum key distribution protocol. Our protocol utilizes a photon in superposition state for single-bit data transmission instead of a classical electrical/optical signal. The security of this protocol relies on the fact, that the arbitrary quantum state cannot be cloned, known as the no-cloning theorem. This protocol can be implemented with current technologies.

Securing information in communication networks is an important challenge in today's world. Quantum Key Distribution (QKD) can provide unique capabilities towards achieving this security, allowing intrusions to be detected and information leakage avoided. We report here a record high bit rate prototype QKD system providing a total of 878 Gbit of secure key data over a 34 day period corresponding to a sustained key rate of around 300 kbit/s. The system was deployed over a standard 45 km link of an installed metropolitan telecommunication fibre network in central Tokyo. The prototype QKD system is compact, robust and automatically stabilised, enabling key distribution during diverse weather conditions. The security analysis includes an efficient protocol, finite key size effects and decoy states, with a quantified key failure probability of ε = 10 −10 .

We prove unconditional security for a quantum key distribution (QKD) protocol based on distilling pbits (twisted ebits) [1] from an arbitrary untrusted state that is claimed to contain distillable key. Our main result is that we can verify security using only public communication -via parameter estimation of the given untrusted state. The technique applies even to bound entangled states, thus extending QKD to the regime where the available quantum channel has zero quantum capacity. We also show how to convert our purification-based QKD schemes to prepare-measure schemes.

- by Debbie Leung
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- Mathematics, Quantum Computing, Physics, Information Theory

The quantum bit error rate (QBER) is a measure of the performance of a frequency coded quantum key distribution system. We present a detailed analysis of the system, taking into account the statistics of light at different points in the link. We show that the statistics depends on the choice of phase of both the transmitter and receiver. We also evaluate the effects of crosstalk, out of band noise, and dark count of the gated avalanche photodetector on the QBER. Finally we use QBER to evaluate our implementation of the B92 protocol.

- by Anil Prabhakar
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- Quantum Key Distribution, Bit Error Rate, Optical physics, Photodetector

Number state filtering in coherent states leads to sub-Poissonian photon statistics. These states are more suitable for phase estimation when compared with the coherent states. Nonclassicality of these states is quantified in terms of the negativity of the Wigner function and the entanglement potential. Filtering of the vacuum from a coherent state is almost like the photon-addition. However, filtering makes the state more resilient against dissipation than photon-addition. Vacuum state filtered coherent states perform better than the photon-added coherent states for a two-way quantum key distribution protocol. A scheme to generate these states in multi-photon atom-field interaction is presented.

Quantum cryptography (QC) 1 can provide unconditional secure communication between two authorized parties based on the basic principles of quantum mechanics 2-4. However, imperfect practical conditions limit its transmission distance and communication speed. Here we implemented the differential phase shift 5 (DPS) quantum key distribution (QKD) with up-conversion assisted hybrid photon detector 6 (HPD) and achieved 1.3 M bits per second secure key rate over a 10-km fiber, which is tolerant against the photon number splitting (PNS) attack 7,8 , general collective attacks on individual photons 9 , and any other known sequential unambiguous state discrimination (USD) attacks 10,11. QC over a fiber link is thought to be the first possible practical applications in quantum information research 1. Currently high bit rate QKD has attracted more and more effort 12-19. The main limited ingredient for high speed QKD is the imperfection of single photon sources and single photon detectors (SPD) at telecom-band. Three

- by Yasuhiro Tokura
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- Quantum Cryptography, Quantum Key Distribution, New, Physical sciences

Quantum key distribution (QKD) is a technique of sharing secret cryptographic keys by using fundamental laws of quantum mechanics. Since the pioneering work of Bennett and Brassard in 1984, the BB84 protocol [1], many unique and interesting protocols for quantum key distribution have been proposed. Practical implementation of these protocols require advance electronic hardware with optical equipments, which is both time consuming and costly. However, the behavior of these optical devices can be observed by simulating the complete hardware with all real components. A complete QKD system can be simulated in order to test the validity of a specific QKD protocol. In this paper, we present a mathematical model for simulating a practical QKD system hardware in order to conveniently evaluate a QKD protocol without having a physical hardware. Apart from the state of the art BB84 protocol [1] we focus on a recently proposed KMB09 protocol [5] which could be generalized to higher dimensions of photon states. Jones and Mueller calculus is used to define the optical devices used in the QKD system. Complete mathematical model of the QKD hardware and the final evaluation with KMB09 protocol is presented in this paper.

- by Journal of Computer Science IJCSIS and +1
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- Mathematical Physics, Computer Science, Theoretical Physics, Information Security

This paper has outlined a method (called OBGP) of extending BGP to support lightpath setup and management across an optical network. The development of OBGP has been discussed by reviewing current BGP behavior and design requirements for OBGP. An implementation of OBGP using simulation tools has been presented, along with initial test results, which have shown that a seamless migration from BGP to OBGP is possible.

- by Mark jan Francisco
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- Optical Networks, Quantum Cryptography, Optical Switch, Proceedings

The performance of three types of InGaAs/InP avalanche photodiodes is investigated for photon counting at 1550 nm in the temperature range of thermoelectric cooling. The best one yields a dark count probability of % 2.8\cdot 10^{-5} per gate (2.4 ns) at a detection efficiency of 10% and a temperature of -60C. The afterpulse probability and the timing jitter are also studied. The results obtained are compared with those of other papers and applied to the simulation of a quantum key distribution system. An error rate of 10% would be obtained after 54 kilometers.

- by John Rarity
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- Quantum Physics, Quantum Information, Nanotechnology, Quantum Key Distribution

Classical cryptography algorithms are based on mathematical functions. The robustness of a given cryptosystem is based essentially on the secrecy of its (private) key and the difficulty with which the inverse of its one-way function(s) can be calculated. Unfortunately, there is no mathematical proof that will establish whether it is not possible to find the inverse of a given one-way function. Since few years ago, the progress of quantum physics allowed mastering photons which can be used for informational ends and these technological progresses can also be applied to cryptography (quantum cryptography). Quantum cryptography or Quantum Key Distribution (QKD) is a method for sharing secret keys, whose security can be formally demonstrated. It aims at exploiting the laws of quantum physics in order to carry out a cryptographic task. Its legitimate users can detect eavesdropping, regardless of the technology which the spy may have. In this study, we present quantum cryptosystems as a tool to attain the unconditional security. We also describe the well known protocols used in the field of quantum cryptography.

Tomography of the two qubit density matrix shared by Alice and Bob is an essential ingredient for guaranteeing an acceptable margin of confidentiality during the establishment of a secure fresh key through the Quantum Key Distribution (QKD) scheme. We show how the Singapore protocol for key distribution is optimal from this point of view, due to the fact that it is based on so called SIC POVM qubit tomography which allows the most accurate full tomographic reconstruction of an unknown density matrix on the basis of a restricted set of experimental data. We illustrate with the help of experimental data the deep connections that exist between SIC POVM tomography and discrete Wigner representations. We also emphasise the special role played by Bell states in this approach and propose a new protocol for Quantum Key Distribution during which a third party is able to concede or to deny A POSTERIORI to the authorized users the ability to build a fresh cryptographic key. arXiv:0806.0272v1 [quant-ph]

- by Thomas Durt
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- Quantum Optics, Quantum Cryptography, Quantum Key Distribution, Mathematical Sciences

The combination of physics, mathematics, and computer science in quantum computing has developed from a visionary idea to one of the most fascinating and promising areas of quantum mechanics in the past two decades. Research in the field of quantum cryptography promises extremely fast, robust, and impenetrable electronic and photonic security; almost unbreakable! Moreover, the long standing eavesdropping problem of the "man in the middle" attack may finally be solved once and for all. As computing power increases, and as hackers and attackers become more sophisticated, it is feared that sooner or later, traditional cryptography based on mathematically intractable algorithms may be no match for parallelized quantum based processors. For this reason, quantum cryptography, based on the laws of quantum statistical mechanics provides a welcome solution to this fear. This paper explores the basic tenets of quantum cryptography and how the mathematical principles therein apply to the quantum key distribution problem; a central concern in the implementation of quantum cryptography in distributed networks. The quantum key distribution protocol implemented in BB84 protocol is also described and compared to traditional cryptographic systems. A short overview of recent commercial implementations of quantum cryptography is presented with the encountered successes and limitations discussed. This paper explores the development of quantum networks, from the onset of the development of secure communication based on quantum cryptography and concludes with a brief outline of the key challenges facing quantum cryptography implementation in wireless applications and long haul communications.

- by Robert Steven Owor
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- Quantum Computing, Quantum Physics, Quantum Information, Quantum Mechanics

Modern optical networking techniques have the potential to greatly extend the applicability of quantum communications by moving beyond simple point-to-point optical links, and by leveraging existing fibre infrastructures. We experimentally demonstrate many of the fundamental capabilities that are required. These include optical-layer multiplexing, switching, and routing of quantum signals; quantum key distribution (QKD) in a dynamically reconfigured optical network; and coexistence of quantum signals with strong conventional telecom traffic on the same fibre. We successfully operate QKD at 1310 nm over a fibre shared with four optically amplified data channels near 1550 nm. We identify the dominant impairment as spontaneous anti-Stokes Raman scattering of the strong signals, quantify its impact, and measure and model its propagation through fibre. We describe a quantum networking architecture which can provide the flexibility and scalability likely to be critical for supporting widespread deployment of quantum applications.

- by Linden Mercer
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- Physics, Quantum Key Distribution, New, Physical sciences

We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-μm telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key.

The use of quantum bits (qubits) in cryptography holds the promise of secure cryptographic quantum key distribution schemes. Unfortunately, the implemented schemes are often operated in a regime which excludes unconditional security. We provide a thorough investigation of security issues for practical quantum key distribution, taking into account channel losses, a realistic detection process, and modifications of the "qubits" sent from the sender to the receiver. We first show that even quantum key distribution with perfect qubits might not be achievable over long distances when fixed channel losses and fixed dark count errors are taken into account. Then we show that existing experimental schemes (based on weak pulses) currently do not offer unconditional security for the reported distances and signal strength. Finally we show that parametric downconversion offers enhanced performance compared to its weak coherent pulse counterpart.

We propose a quantum key distribution protocol using Greenberger Horne Zeilinger tripartite coherent states. The sender and the receiver share a similar key by exchanging the correlation coherent states, without basis reconciliation. This allows the protocol to have a transmission efficiency of 100% in a perfect quantum channel. The security of the protocol is ensured by tripartite coherent states correlation and homodyne detection, which allows to detect any eavesdropping easily.

- by Mjid labo
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- Physics, Quantum Key Distribution, Entanglement, Coherent States

The current standard to exchange a secret key for ensuring secure data transmission within the SSL/TLS protocol is based on Public-Key encryption. This method is only secure as long as the computation power of a potential attacker is limited. So far, the only way to make an unconditional secure key exchange, is to use quantum key distribution (QKD). With the latest figures of sifting key rates provided by NIST, we show which authentic theoretical final key rates are possible. Furthermore we present a modified SSL/TLS protocol, which uses quantum key distribution, in different encryption variants.

We show that non-maximally entangled states can be used to build a quantum key distribution (QKD) scheme where the key is probabilistically teleported from Alice to Bob. This probabilistic aspect of the protocol ensures the security of the key without the need of non-orthogonal states to encode it, in contrast to other QKD schemes. Also, the security and key transmission rate of the present protocol is nearly equivalent to those of standard QKD schemes and these aspects can be controlled by properly harnessing the new free parameter in the present proposal, namely, the degree of partial entanglement. Furthermore, we discuss how to build a controlled QKD scheme, also based on partially entangled states, where a third party can decide whether or not Alice and Bob are allowed to share a key.

- by Goren Gordon
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- Quantum Physics, Quantum Cryptography, Quantum Key Distribution, Optical physics

In the next years the data transmission connections will constitute one of the principal tools of communication among cities, enterprises and public administration. With their enhanced connectivity, the systems and nets of information are now exposed to an increased vulnerability and new safety problems are emerging. Insofar Quantum Key Distribution (QKD) has matured to real world applications and can enhance the safety of the communication nets. In this paper we present the QKD network designed and implemented by Selex-SI and we give an overview of the obtained results.

Free-space quantum key distribution links in an urban environment have demanding operating needs such as functioning in daylight and under atmospheric turbulence, which can dramatically impact their performance. Both effects are usually mitigated with a careful design of the field of view of the receiver. However, a trade-off is often required, since a narrow field of view improves background noise rejection but is linked to an increase in turbulence-related losses. We present a high-speed automatic tracking system to overcome these limitations. Both a reduction in the field of view to decrease the background noise and a mitigation of the losses caused by atmospheric turbulence are addressed. Two different designs are presented and discussed, along with technical considerations for the experimental implementation. Finally, preliminary experimental results of beam wander correction are used to estimate the potential improvement of both the quantum bit error rate and secret key rate of a free-space quantum key distribution system.

- by Veronica Fernandez
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- Optical Engineering, Turbulence, Quantum Key Distribution, Optical physics

A significant limitation of practical quantum key distribution (QKD) setups is currently their limited operational range. It has recently been emphasized [1] that entanglement-based QKD systems can tolerate higher channel losses than systems based on weak coherent laser pulses (WCP), in particular when the source is located symmetrically between the two communicating parties, Alice and Bob. In the work presented here, we experimentally study this important advantage by implementing different entanglement-based QKD setups on a 144 km free-space link between the two Canary Islands of La Palma and Tenerife. We established three different configurations where the entangled photon source was placed at Alice's location, asymmetrically between Alice and Bob and symmetrically in the middle between Alice and Bob, respectively. The resulting quantum channel attenuations of 35 dB, 58 dB and 71 dB, respectively, significantly exceed the limit for WCP systems . This confirms that QKD over distances of 300 km and even more is feasible with entangled state sources placed in the middle between Alice and Bob. arXiv:1007.4645v1 [quant-ph]

- by S. Ramelow
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- Quantum Key Distribution, Canary Islands, New, Physical sciences

A wireless sensor network consist distributed sensors which are used to monitor physical or environmental conditions like temperature, sound, pressure and so on. Wireless sensor network are used in future in many applications like military, investigation teams, researches and so on. Security is the main issue in wireless sensor network. Sensor network arrange several types of data packets, packets of routing protocols and packets of key management protocols. Key management is the most effective method for providing better security against several types of attacks. This paper discusses the various key pre-distribution approaches along with their advantages and disadvantages.