Quantum Cryptographic Protocols Research Articles

Finite‐Size Analysis of Thermal States Quantum Cryptography with the Optimal Noise

AbstractA modified thermal states quantum cryptography is proposed by adding the noise at Bob's side and the impact of finite‐size effects focused on by performing the channel estimation. An optimal noise which can maximize the key rate is demonstrated to exist and, by using numeric simulations, is shown to vary with the transmission distance. Adding the optimal noise can enhance the effectiveness of the thermal states quantum cryptography protocol under noisy and lossy channel in terms of secret key rate, the maximum transmission distance and the tolerable channel noise. Although finite‐size effects deteriorate the performance of thermal quantum cryptography, this approach can compensate the impact of this degradation, and even make the performance of the modified protocol in the finite‐size regime better than that of the original protocol in the ideal asymptotic regime.

Quantum cryptographic resource distillation and entanglement

We look into multipartite quantum states on which quantum cryptographic protocols including quantum key distribution and quantum secret sharing can be perfectly performed, and define the quantum cryptographic resource distillable rate as the asymptotic rate at which such multipartite state can be distilled from a given multipartite state. Investigating several relations between entanglement and the rate, we show that there exists a multipartite bound entangled state whose quantum cryptographic resource distillable rate is strictly positive, that is, there exists a multipartite entangled state which is not distillable, but can be useful for quantum cryptography such as quantum key distribution and quantum secret sharing.

Optimal strategy to certify quantum nonlocality

Certification of quantum nonlocality plays a central role in practical applications like device-independent quantum cryptography and random number generation protocols. These applications entail the challenging problem of certifying quantum nonlocality, something that is hard to achieve when the target quantum state is only weakly entangled, or when the source of errors is high, e.g. when photons propagate through the atmosphere or a long optical fiber. Here we introduce a technique to find a Bell inequality with the largest possible gap between the quantum prediction and the classical local hidden variable limit for a given set of measurement frequencies. Our method represents an efficient strategy to certify quantum nonlocal correlations from experimental data without requiring extra measurements, in the sense that there is no Bell inequality with a larger gap than the one provided. Furthermore, we also reduce the photodetector efficiency required to close the detection loophole. We illustrate our technique by improving the detection of quantum nonlocality from experimental data obtained with weakly entangled photons.

Vulnerabilities of quantum cryptography on geometrically uniform coherent states

It is shown that the quantum cryptography protocol on geometrically uniform coherent states, which uses the restriction for unambiguous discrimination of a set of symmetric coherent states and allows resisting an unambiguous state discrimination attack (USD attack), is not secure to a number of other attacks. The key length formula from the work of ] and the key generation rate for a number of constructive attacks of the eavesdropper are compared and it is shown that the key generation rate in this work is significantly overestimated. This leads to the fact that the distributed key is not secret.

Entropy analysis of the discrete-time quantum walk under bit-flip noise channel

We study the behavior of tunable one-dimensional discrete-time quantum walk (DTQW) in the presence of decoherence modeled by the flip-bit noise channel. By varying the noise intensity, we obtain a wide range of probability distributions of noisy walks, which can be loosely characterized as pure quantum walk, quantum-like walk, semi-classical like walk, and classical-like walk. We show the maximum Shannon entropy of the walk is not obtained under maximum decoherence, but instead at a lower degree of decoherence. This result may be useful for the implementation of quantum error correction, quantum cryptography, and quantum communication protocol, where one might expect the qubit internal state to be flipped due to noise.

Enhanced BB84 quantum cryptography protocol for secure communication in wireless body sensor networks for medical applications.

Wireless body sensor network (WBSN) is an interdisciplinary field that could permit continuous health monitoring with constant clinical records updates through the Internet. WBAN is a special category of wireless networks. Coronavirus disease 2019 (COVID-19) pandemic creates the situation to monitor the patient remotely following the social distance. WBSN provides the way to effectively monitor the patient remotely with social distance. The data transmitted in WBSN are vulnerable to attacks and this is necessary to take security procedure like cryptographic protocol to protect the user data from attackers. Several physiological sensors are implanted in the human body that will collect various physiological updates to monitor the patient’s healthcare data remotely. The sensed information will be transmitted wirelessly to doctors all over the world. But it has too many security threats like data loss, masquerade attacks, secret key distribution problems, unauthorized access, and data confidentiality loss. When any attackers are attacking the physiological sensor data, there is a possibility of losing the patient’s information. The creation, cancellation, and clinical data adjustment will produce a mass effect on the healthcare monitoring system. Present-day cryptographic calculations are highly resistant to attacks, but the only weak point is the insecure movement of keys. In this paper, we look into critical security threats: secure key distribution. While sharing the secret key between communicating parties in the wireless body sensor networks in the conventional method like via phone or email, the attackers will catch the private key. They can decrypt and modify more sensitive medical data. It can cause a significant effect like death also. So need an effective, secure key distribution scheme for transmission of human body health related data to medical professional through wireless links. Moreover, a new enhanced BB84 Quantum cryptography protocol is proposed in this paper for sharing the secret key among communicating parties in a secure manner using quantum theory. Besides, a bitwise operator is combined with quantum concepts to secure the patient’s sensed information in the wireless environment. Instead of mail and phone via sharing secret key, quantum theory with the bitwise operator is used here. Therefore, it is not possible to hack the secret key of communication. The body sensor’s constrained assets as far as battery life, memory, and computational limit are considered for showing the efficiency of the proposed security framework. Based on experimental results, it is proven that the proposed algorithm EBB84QCP provides high secure key distribution method without direct sharing the secret key and it used the quantum mechanism and bitwise operator for generating and distributing secret key value to communicating parties for sensitive information sharing in the wireless body sensor networks.

Efficient Implementation for PRINCE Algorithm in FPGA Based on the BB84 Protocol

The current study introduces a hardware-implemented PRINCE block cipher within Field Programmable Gate Array (FPGA) determined by the quantum cryptography protocol (BB84). Most security-related software applications of cryptographic algorithms tend to be rather slow and of no efficiency. So as to present a solution to this issue, a new hardware architecture is suggested for speeding up the execution of the PRINCE algorithm and increasing its flexibility, yet with more security. Concurrent computing designs allow an encryption block data of 64 bits during a single clock cycle, resulting in the reduction of hardware area and the production of a higher throughput and relatively lower latency. Higher speed processing and lower power consumption are other features that have been observed. This could be achieved by means of implementing the encrypting, decrypting and quantum key schedule using little hardware sources, followed by the development of a sufficient hardware architecture model for the PRINCE algorithm through very high speed integrated circuit hardware description language (VHDL). The synthetization of this VHDL design is eventually performed in FPGA boards. As for the present study, two FPGA boards have been employed, namely Virtex-4 and Kintex-7. The resulting data indicates the throughput and efficiency values to be (2.029 Gbps) and (1.9 Mbps/slice) for Virtex-4, and (3.931 Gbps) and (7.290 Mbps/slice) for Kintex-7, all respectively.

A quantum leap in security

One-photon and two-photon interferences have recently led researchers to develop new classes of quantum cryptographic protocols.

Fourier’s Quantum Information Processing

We demonstrate that quantum information processing (QIP) completely rests on quantum Fourier transform (QFT), and 190 years after his death, the work of Jean-Baptiste Joseph Fourier is more present than ever in one of the most important pillars of physics: QIP. Specifically, this study shows the impact of QFT on the main tool of quantum communication: entanglement, with a particular emphasis on its spectral nature, whose study is completed when entanglement is used in teleportation, and quantum secret sharing. Finally, a better understanding of the spectral nature of quantum entanglement will lead to better protocols for quantum communications, in general, and quantum cryptography, in particular.

Agile and Versatile Quantum Communication: Signatures and Secrets

Agile cryptography allows for a resource-efficient swap of a cryptographic core in case the security of an underlying classical cryptographic algorithm becomes compromised. Conversely, versatile cryptography allows the user to switch the cryptographic task without requiring any knowledge of its inner workings. In this paper, we suggest how these related principles can be applied to the field of quantum cryptography by explicitly demonstrating two quantum cryptographic protocols, quantum digital signatures (QDS) and quantum secret sharing (QSS), on the same hardware sender and receiver platform. Crucially, the protocols differ only in their classical post-processing. The system is also suitable for quantum key distribution (QKD) and is highly compatible with deployed telecommunication infrastructures, since it uses standard quadrature phase shift keying (QPSK) encoding and heterodyne detection. For the first time, QDS protocols are modified to allow for postselection at the receiver, enhancing protocol performance. The cryptographic primitives QDS and QSS are inherently multipartite and we prove that they are secure not only when a player internal to the task is dishonest, but also when (external) eavesdropping on the quantum channel is allowed. In our first proof-of-principle demonstration of an agile and versatile quantum communication system, the quantum states were distributed at GHz rates. This allows for a one-bit message to be securely signed using our QDS protocols in less than 0.05 ms over a 2 km fiber link and in less than 0.2~s over a 20 km fiber link. To our knowledge, this also marks the first demonstration of a continuous-variable direct QSS protocol.

Computing conditional entropies for quantum correlations

The rates of quantum cryptographic protocols are usually expressed in terms of a conditional entropy minimized over a certain set of quantum states. In particular, in the device-independent setting, the minimization is over all the quantum states jointly held by the adversary and the parties that are consistent with the statistics that are seen by the parties. Here, we introduce a method to approximate such entropic quantities. Applied to the setting of device-independent randomness generation and quantum key distribution, we obtain improvements on protocol rates in various settings. In particular, we find new upper bounds on the minimal global detection efficiency required to perform device-independent quantum key distribution without additional preprocessing. Furthermore, we show that our construction can be readily combined with the entropy accumulation theorem in order to establish full finite-key security proofs for these protocols.

Quantum Internet—Applications, Functionalities, Enabling Technologies, Challenges, and Research Directions

The advanced notebooks, mobile phones, and internet applications in today’s world that we use are all entrenched in classical communication bits of zeros and ones. Classical internet has laid its foundation originating from the amalgamation of mathematics and Claude Shannon’s theory of information. However, today’s internet technology is a playground for eavesdroppers. This poses a serious challenge to various applications that rely on classical internet technology, and it has motivated the researchers to switch to new technologies that are fundamentally more secure. By exploring the quantum effects, researchers paved the way into quantum networks that provide security, privacy, and range of capabilities such as quantum computation, communication, and metrology. The realization of Quantum Internet (QI) requires quantum communication between various remote nodes through quantum channels guarded by quantum cryptographic protocols. Such networks rely upon quantum bits (qubits) that can simultaneously take the value of zeros and ones. Due to the extraordinary properties of qubits such as superposition, entanglement, and teleportation, it gives an edge to quantum networks over traditional networks in many ways. At the same time, transmitting qubits over long distances is a formidable task and extensive research is going on satellite-based quantum communication, which will deliver breakthroughs for physically realizing QI in near future. In this paper, QI functionalities, technologies, applications and open challenges have been extensively surveyed to help readers gain a basic understanding of the infrastructure required for the development of the global QI.

Исследования и анализ эффективности волоконно-оптических линий связи с использованием квантовой технологии

The analysis of the performance indicators fiber-optic communication lines (FOCL) using quantum technology based on the architectural concept of NGN (Next Generation Network) and future networks FN (Future Networks) for the construction highly efficient optical telecommunication networks supporting a wide range cryptographic resistance. Threats of unauthorized access, denial of service, loss information, cryptographic methods and algorithms for information protection are considered. Complex criteria of FOCL efficiency using such quantum technologies as network performance using WDM (Wavelength Division Multiplexing) technology, information security characteristics when using quantum cryptography protocols, taking into account resistance to various threats, informative characteristics photon sources are selected. A new approach is proposed for the study and assessment of complex indicators complex optical information protection systems and effective control of a set quantum key distribution systems for fiber-optic communication lines. The functioning of the investigated FOCL using quantum technology based on the principles "Point-to-point" network topology, which allows organizing a quantum information and service channel, is considered. On the basis of the proposed approach, the efficiency quantum key distribution, the capabilities quantum cryptography protocols under the influence of photon number splitting attack (PNS-Photon Number Splitting Attack) and the information entropy of the characteristics of sources of optical photon qubit fluxes are investigated. Analytical expressions are obtained for assessing the complex indicators of the information security system when using quantum key distribution (QKD) for FOCL. On the basis of the new approach, a numerical analysis was carried out and a graphical dependence of the information entropy of the packet on the packet length in qubits was constructed for the given transfer characteristics of the FOCL. It was found that an increase in the limited packet length in bits, which meets the requirements reliability and efficiency of the operation FOCL system, leads to an increase in the value information entropy as a fraction of the packet, at a given bit rate of the network.

Tight security bounds for decoy-state quantum key distribution

The BB84 quantum key distribution (QKD) combined with decoy-state method is currently the most practical protocol, which has been proved secure against general attacks in the finite-key regime. Thereinto, statistical fluctuation analysis methods are very important in dealing with finite-key effects, which directly affect secret key rate, secure transmission distance and most importantly, the security. There are two tasks of statistical fluctuation in decoy-state BB84 QKD. One is the deviation between expected value and observed value for a given expected value or observed value. The other is the deviation between phase error rate of computational basis and bit error rate of dual basis. Here, we provide the rigorous and optimal analytic formula to solve the above tasks, resulting to higher secret key rate and longer secure transmission distance. Our results can be widely applied to deal with statistical fluctuation in quantum cryptography protocols.

Simultaneous Generation of Arbitrary Assembly of Polarization States with Geometrical-Scaling-Induced Phase Modulation

Manipulating the polarization of light on the microscale or nanoscale is essential for integrated photonics and quantum optical devices. Nowadays, the metasurface allows one to build on-chip devices that efficiently manipulate the polarization states. However, it remains challenging to generate different types of polarization states simultaneously, which is required to encode information for quantum computing and quantum cryptography applications. By introducing geometrical-scaling-induced (GSI) phase modulations, we demonstrate that an assembly of circularly polarized (CP) and linearly polarized (LP) states can be simultaneously generated by a single metasurface made of L-shaped resonators with different geometrical features. Upon illumination, each resonator diffracts the CP state with a certain GSI phase. The interaction of these diffractions leads to the desired output beams, where the polarization state and the propagation direction can be accurately tuned by selecting the geometrical shape, size, and spatial sequence of each resonator in the unit cell. As an example of potential applications, we show that an image can be encoded with different polarization profiles at different diffraction orders and decoded with a polarization analyzer. This approach resolves a challenging problem in integrated optics and is inspiring for on-chip quantum information processing.

Experimental Hong-Ou-Mandel interference using two independent heralded single-photon sources.

Hong-Ou-Mandel (HOM) interference is one of the most important experimental phenomena in quantum optics. It has drawn considerable attention with respect to quantum cryptography and quantum communication because of the advent of the measurement device independent (MDI) quantum key distribution (QKD) protocol. Here, we realize HOM interference, having a visibility of approximately 38.1%, using two independent heralded single-photon sources (HSPSs). The HOM interference between two independent HSPSs is a core technology for realizing the long-distance MDI QKD protocol, the quantum coin-tossing protocol, and other quantum cryptography protocols.

Insecurity of Jiang et al.’s quantum cryptography protocol

Recently, Jiang et al. proposed a quantum cryptography protocol [Mod. Phys. Lett. B 32 (2018) 1850125] which can implement the equal exchange of secret information between the two parties with the help of semi-trusted third party. Here, it will be shown that the protocol is insecure and has the drawback of information leakage.

Asymptotic security analysis of teleportation-based quantum cryptography

We prove that the teleportation-based quantum cryptography protocol presented in Gordon and Rigolin (Opt Commun 283:184, 2010), which is built using only orthogonal states encoding the classical bits that are teleported from Alice to Bob, is asymptotically secure against all types of individual and collective attacks. We then investigate modifications to that protocol leading to greater secret-key rates and to security against coherent attacks. In other words, we show an unconditional secure quantum key distribution protocol that does not need non-orthogonal quantum states to encode the bits of the secret key sent from Alice to Bob. We also revisit the security proof of the BB84 protocol by exploring the non-uniqueness of the Schmidt decomposition of its entanglement-based representation. This allows us to arrive at a secure transmission of the key for a slightly greater quantum bit error rate (quantum communication channel’s noise) when compared to its standard security analysis.

Quantum Locality of N Entangled States

The nonlocality research of quantum entanglement plays an important role in the development of quantum mechanics theory and quantum information technology. As multipartite entangled state is a rare quantum resource, its nonlocality research has always been an important subject in the study of quantum theory. In this paper, we focus on N entangled states composed of N copies of an entangled state. First, a new Bell test with respect to N entangled states is presented, and lifting Bell inequalities are applied to certify nonlocality. Second, we obtain the nonlocality certification standard of N entangled states by parity binning lifting Bell inequality. Third, we prove the conjecture that N + 2 entangled states must be local if N entangled states are local certified by parity binning lifting Bell inequality. The research will promote the theoretical research progress of quantum coherence, and provide theoretical basis and technical support for the multipartite entangled states application in quantum cryptographic protocols.

Monogamy relations within quadripartite Einstein-Podolsky-Rosen steering based on cascaded four-wave mixing processes

Multipartite Einstein-Podolsky-Rosen (EPR) steering has been recognized as an essential resource for secure quantum communication tasks composed of several spatially separated parties who cannot be fully trusted. Nevertheless, this resource cannot be distributed arbitrarily over many parties; for instance, two independent players cannot simultaneously steer the third party by two-setting measurements. This feature is referred to as monogamy of steering, which ensures the security of quantum cryptographic protocols and is thus a very desired property to investigate for multipartite steering. Here, we propose symmetric and asymmetric structures of cascaded four-wave mixing of rubidium atoms to generate versatile quadripartite EPR steering and investigate four distinct types of monogamy relations of Gaussian steering. We find that the distribution constraint described by one of the monogamy relations can be lifted only for the quadripartite steering created by the symmetric setup. This result paves the way for a better understanding of the distribution rules of multipartite EPR steering and its potential applications for secure quantum communication.