Search Results (374)

Quantum cryptography protocols offering unconditional protection open great rout to full information security in quantum era. Yet, implementing these protocols using the existing fiber networks remains challenging due to high signal losses reducing the efficiency of these protocols to zero. The recently proposed quantum-protected control-based key distribution (QCKD) addresses this issue by physically controlling interceptable losses and ensuring that leaked quantum states remain non-orthogonal. Here, we present the first in-field development and demonstration of the QCKD over an urban fiber link characterized by substantial losses. Using information-theoretic considerations, we configure the system ensuring security and investigate the interplay between line losses and secret key rates. As an example, we present calculation for the communication distance 4 km, QCKD rate 490 bits per second, and find that the corresponding system’s total loss is about 1.628 decibels. Our results, backed by the statistical analysis of the secret key, confirm QCKD’s robustness under real-world conditions, and establish it as a practical solution for quantum-safe communications over existing fiber infrastructures. Full article

Quantum key distribution (QKD), a key application of quantum information technology and “one-time pad” (OTP) encryption, enables secure key exchange with information-theoretic security, meaning its security is grounded in the laws of physics rather than computational assumptions. However, in QKD networks, achieving long-distance communication often requires trusted relays to mitigate channel losses. This reliance introduces significant challenges, including vulnerabilities to compromised relays and the high costs of infrastructure, which hinder widespread deployment. To address these limitations, we propose a zero-trust spatiotemporal diversification framework for multipath–multi-key distribution. The proposed approach enhances the security of end-to-end key distribution by dynamically shuffling key exchange routes, enabling secure multipath key distribution. Furthermore, it incorporates a dynamic adaptive path recovery mechanism that leverages a recursive penalty model to identify and exclude suspicious or compromised relay nodes. To validate this framework, we conducted extensive simulations and compared its performance against established multipath QKD methods. The results demonstrate that the proposed approach achieves a 97.22% lower attack success rate with 20% attacker pervasiveness and a 91.42% reduction in the attack success rate for single key transmission. The total security percentage improves by 35% under 20% attacker pervasiveness, and security enhancement reaches 79.6% when increasing QKD pairs. Additionally, the proposed scheme exhibits an 86.04% improvement in defense against interception and nearly doubles the key distribution success rate compared to traditional methods. The results demonstrate that the proposed approach significantly improves both security robustness and efficiency, underscoring its potential to advance the practical deployment of QKD networks. Full article

With the increasing complexity of cyber threats and the emergence of quantum computing, enhancing secure communication is essential. This study explores an effective hybrid quantum key distribution (QKD) protocol that integrates photonic and atomic systems to leverage their respective strengths. The concept of symmetry plays a crucial role in this context, as it underpins the principles of entanglement and the balance between key generation and error correction. The photonic system is used for the initial key generation, while the atomic system facilitates entanglement swapping, error correction, and privacy amplification. The comprehensive theoretical framework encompasses key components, detailed security proofs, performance metrics, and an analysis of system vulnerabilities, illustrating the resilience of the hybrid protocol against potential threats. Extensive experimental studies demonstrate that the hybrid QKD protocol seamlessly integrates photonic and atomic systems, enabling secure key distribution with minimal errors and loss rates over long distances. This combination of the two systems reveals exceptional resilience against eavesdropping, significantly improving both security and robustness compared with traditional QKD protocols. Consequently, this makes it a compelling solution for secure communication in the increasingly digital world. Full article

We present a framework to optimize the voltage range of electro-optic polarization controllers (EPC) in polarization-based quantum key distribution (QKD) subsystems. In this study, we consider an EPC capable of modifying both the phase difference between its fast and slow axes and the orientation of the fast axis. This capability allows it to transform any input state of polarization (SOP) into any desired output SOP on the Poincaré sphere using a single wave-plate. When multiple wave-plates are available, properly distributing the required polarization modulation across them effectively reduces the electronic demands, lowers the implementation costs, and enhances the polarization modulation speeds. This optimization is achieved through the application of multi-objective optimization (MOO) and wave-plate splitting techniques. Within a simulation model, using the calibration parameters from a commercially available six-wave-plate EPC, we determined the optimized voltage ranges required to achieve the six, four, and three SOPs typically used in polarization-based QKD protocols. Two voltage reference points are considered in our study: bias voltage points, which result in zero birefringence, and zero voltage points. For optimization procedures centered around the bias voltage points, we observe a significant reduction in the voltage range, from $\pm 37$ V, for a single wave-plate, to approximately $\pm 6$ V, for six wave-plates. Furthermore, using wave-plate splitting techniques, we conclude that only two independent wave-plates (four variables) need to be considered in our model to achieve optimized results, which contributes to the efficient design of polarization-based QKD subsystems by minimizing voltage transitions while ensuring precise SOP control, ultimately enabling cost-effective and high-speed polarization modulation. Full article

With the looming threat of quantum computers capable of breaking classical encryption and the uncertainty regarding the security of post-quantum encryption algorithms, some highly sensitive applications aim for the highest level of security in information transfer: unconditional security. In this work we present an architecture and a practical implementation of a user-friendly unconditionally secure file transfer client based on quantum key distribution and one time pad cipher. We test the implementation on the live QKD research infrastructure within POLITEHNICA Bucharest, thus proving the approach is feasible for real information transfer use-cases. Full article

Symmetric private information retrieval (SPIR) protocol is proposed for users to retrieve items from a database holder without revealing the retrieval address, and meanwhile the users cannot learn any additional entries of the database. Quantum key distribution (QKD)-based quantum private queries (QPQs) are the most practical protocols for the SPIR problem. However, most existing protocols assume ideal devices. To overcome this drawback, we propose a device independent QPQ protocol based on QKD with imperfect sources and detectors. By constructing the semi-definite programming optimization problem, we give the CHSH test threshold and prove the correctness of our protocol. We use the shift and permutation post-processing technique to further improve the security. We compare the performance of our protocol with a recent full device-independent QPQ. and discuss their relative advantages. The simulation results show that our protocol improves database security, user privacy and efficiency. The number of final key bits that Alice knows is close to 1, and Bob’s guessing probability is below 0.15 in our protocol. Moreover, the proposed scheme can be used for any entanglement-based QPQ protocol to remove trust on the devices. Full article

Crypto wallets store and protect the private keys needed to sign transactions for crypto currencies; they are secured by multi-factor authentication schemes. However, the loss of a wallet, or a dysfunctional factor of authentication, can be catastrophic, as the keys are then lost as well as the crypto currencies. Such difficult tradeoffs between the protection of the private keys and factors of authentication that are easy to use are also present in public key infrastructures, banking cards, smartphones and smartcards. In this paper, we present protocols based on novel challenge–response pair mechanisms that protect private keys, while using factors of authentication that can be lost or misplaced without negative consequences. Examples of factors that are analyzed include passwords, tokens, wearable devices, biometry, and blockchain-based non-fungible tokens. In normal operations, the terminal device uses all factors of authentication to retrieve an ephemeral key, decrypt the private key, and finally sign a transaction. With our solution, users can download the software stack into multiple terminal devices, turning all of them into backups. We present a zero-knowledge multi-factor authentication scheme allowing the secure recovery of private keys when one of the factors is lost, such as the token. The challenge–response pair mechanisms also enable a novel key pair generation protocol in which private keys can be kept secret by the user, while a Keystore can securely authenticate the user and transmit the public key to a distributed network. The standardized LWE post-quantum cryptographic CRYSTALS Dilithium protocol was selected in the experimental section. Full article

This research introduces a novel physical-layer encryption technique for metropolitan-optimized optical transport networks (M-OTNs) that integrates real-time optical signal time-domain scrambling/descrambling with decoy-state quantum key distribution (DS-QKD). The method processes real-time optical data from the optical service unit (OSU) using a series of tunable Fabry–Perot cavities (FPCs), synchronized and updated with a running key. Experimental validation demonstrates secure communication within the optical network’s physical layer during standard OTU2 data transmission (10.709 Gbps), achieving an online transmission distance exceeding 100 km over typical single-mode fiber with a power loss of approximately 1.77 dB. The results indicate that this integrated approach significantly enhances the security of the optical physical layer in M-OTNs. Full article

This paper introduces two information-theoretically quantum secure direct communication protocols that accomplish information exchange between Alice and Bob in the first case, and among Alice, Bob, and Charlie in the second case. Both protocols use a novel method, different from existing similar protocols, to embed the secret information in the entangled compound system. This new way of encoding the secret information is one of the main novelties of this paper, and a distinguishing feature compared to previous works in this field. A second critical advantage of our method is its scalability and extensibility because it can be seamlessly generalized to a setting involving three, or more, players, as demonstrated by the second protocol. This trait is extremely beneficial in many real-life situations, where many spatially separated players posses only part the secret information that must be transmitted to Alice, so that she may obtain the complete secret. Using the three-player protocol, this task can be achieved in one go, without the need to apply a typical QSDC protocol twice, where Alice first receives Bob’s and then Charlie’s information. The proposed protocol does not require pre-shared keys or quantum signatures, making it less complicated and more straightforward. Finally, in anticipation of the coming era of distributed quantum computing, our protocols offer the important practical advantage of straightforward implementation on contemporary quantum computers, as they only require standard CNOT and Hadamard gates. Full article

The article proposes a cryptographic system with absolute security features for use in authenticating access to resources in smart grid systems, taking into account prosumer solutions to ensure a high level of security of transactions on the energy market that meet the requirements established in the Directive of the European Parliament of 14 December 2022 no. 2555 NIS2, requiring “dynamic authentication” prior to the release of transaction data for key services, covers energy market operators as a key service and is particularly important for ensuring security. The article presents an innovative cryptographic system that, according to the authors’ knowledge, is the only one in the world that meets the NIS2 requirements in the field of “dynamic authentication” and the Quantum-Resistant requirements intended for distributed systems and smart grids. The proposed solution eliminates vulnerabilities related to digital identity theft and its reuse, i.e., practically eliminates the possibility of impersonation. Full article

Quantum cryptography continues to be an area of significant research and educational interest. Here, a straightforward and reliable approach to both the experimental and theoretical aspects of quantum key distribution is presented, tailored for senior undergraduate students. Focusing on illustrating the essential concepts of the B92 protocol through a combination of optical experiments and custom-developed computational tools, this work offers a thorough exploration of quantum cryptography according to the principles of the B92 protocol. Full article

Ultrafast fiber lasers have shown exceptional performance across various domains, including material processing, medical applications, and optoelectronic communication. The semiconductor saturable absorber mirror (SESAM) is a key enabler of ultrafast laser operation. However, the narrow wavelength range and limited modulation depth of conventional SESAMs pose challenges to further advancing ultrafast fiber laser technology. To address these limitations, we explored the integration of guided mode resonance (GMR) effects to enhance light–matter interaction within the absorption layer. By incorporating subwavelength dielectric film gratings onto the cap layer of SESAMs, we excited GMR and formed a microcavity structure in conjunction with the distributed Bragg mirror (DBR). This design significantly improved the absorption efficiency of InAs quantum dots. The experimental results demonstrate that the modulation depth of the SESAM increased from 6.7% to 17.3%, while the pulse width was reduced by 2.41 times. These improvements facilitated the realization of a high-quality, stable ultrafast fiber laser. This study not only broadens the application potential of ultrafast lasers in diverse fields but also offers a practical pathway for advancing SESAM technology toward industrial-scale deployment. Full article

Classical and quantum fiber-optic communication channels are vulnerable to possible intrusions. Quantum key distribution (QKD) provides a physically fundamental and theoretically secure communication method, but the key rate decays over long distances. Recently proposed by our group, a quantum communication protocol based on the physical estimation of an eavesdropper’s influence shows extreme efficiency even at distances of thousands of kilometers. In this paper, we investigate the physical limits of eavesdropper detection using optical time domain reflectometry (OTDR) and demonstrate the successful detection of a 0.01 dB leakage over a distance of 1009 km. Full article

Ensuring secure data transmission in agrotechnical monitoring systems using unmanned aerial vehicles (UAVs) is critical due to increasing cyber threats, particularly with the advent of quantum computing. This study proposes the integration of Quantum Key Distribution (QKD), based on the BB84 protocol, as a secure key management mechanism to enhance data security in UAV-based geographic information systems (GIS) for monitoring agricultural fields and forest fires. QKD is not an encryption algorithm but a secure key distribution protocol that provides information-theoretic security by leveraging the principles of quantum mechanics. Rather than replacing traditional encryption methods, QKD complements them by ensuring the secure generation and distribution of encryption keys, while AES-128 is employed for efficient data encryption. The QKD framework is optimized for real-time operations through adaptive key generation and energy-efficient hardware, alongside Lempel–Ziv–Welch (LZW) compression to improve the bandwidth efficiency. The simulation results demonstrate that the proposed system achieves secure key generation rates up to 50 Mbps with minimal computational overhead, maintaining reliability even under adverse environmental conditions. This hybrid approach significantly improves data resilience against both quantum and classical cyber-attacks, offering a comprehensive and robust solution for secure agrotechnical data transmission. Full article

Quantum information has emerged as a frontier in scientific research and is transitioning to real-world technologies and applications. In this work, we explore the integration of quantum secure direct communication (QSDC) with time-sensitive networking (TSN) for the first time, proposing a novel framework to address the security and latency challenges of Ethernet-based networks. Because our QSDC-TSN protocol inherits all the advantages from QSDC, it will enhance the security of the classical communications both in the traditional TSN- and QKD-based TSN by the quantum principle and reduce the communication latency by transmitting information directly via quantum channels without using keys. By analyzing the integration of QSDC and TSN in terms of time synchronization, flow control, security mechanisms, and network management, we show how QSDC enhances the real-time performance and security of TSN. These advantages enable our QSDC-TSN to keep the balance between and meet the requirements of both high security and real-time performance in industrial control, in a digital twin of green power and green hydrogen systems in distributed energy networks, etc., showing its potential applications in future quantum-classical-hybrid systems. Full article