With the current development of quantum computing, some existing cryptographic protocols may be broken in the future, such as RSA with Shor's algorithm. To secure the future secret communications, but also the current ones from retrospective decryption, Pre-Shared Keys (PSK) can be used today, and two types of complementary solutions are currently being studied: Post Quantum Cryptography (PQC) and Quantum Key Distribution (QKD). The objective of this paper is to describe the latest, which relies on the laws of quantum physics to secure the sharing of secret keys. Among the current QKD systems, some are already commercially available. Their distance range is limited, generally around 100 km. To overcome this distance limitation, a first solution is currently being deployed in field trials using trusted nodes, forming the so-called Quantum Communication Infrastructure (QCI). The drawback is that users must trust QCI nodes, in which quantum communication are stopped, going back to classical data processing that can be eavesdropped. To overcome this problem, researchers are investigating solutions to build future quantum networks and Quantum Internet (QI), in which the processing in the networks remains quantum, using quantum buffers and entanglement swapping in quantum repeaters to increase the distance range of QKD. We briefly discuss the advantages and disadvantages of QKD versus PQC, with the two actually being complementary.
With the current development of quantum computing, some existing cryptographic protocols may be broken in the future, such as RSA with Shor's algorithm. To secure the future secret communications, but also the current ones from retrospective decryption, Pre-Shared Keys (PSK) can be used today, and two types of complementary solutions are currently being studied: Post Quantum Cryptography (PQC) and Quantum Key Distribution (QKD). The objective of this paper is to describe the latest, which relies on the laws of quantum physics to secure the sharing of secret keys. Among the current QKD systems, some are already commercially available. Their distance range is limited, generally around 100 km. To overcome this distance limitation, a first solution is currently being deployed in field trials using trusted nodes, forming the so-called Quantum Communication Infrastructure (QCI). The drawback is that users must trust QCI nodes, in which quantum communication are stopped, going back to classical data processing that can be eavesdropped. To overcome this problem, researchers are investigating solutions to build future quantum networks and Quantum Internet (QI), in which the processing in the networks remains quantum, using quantum buffers and entanglement swapping in quantum repeaters to increase the distance range of QKD. We briefly discuss the advantages and disadvantages of QKD versus PQC, with the two actually being complementary.
Large quantum computers will be able to break the cryptographic algorithms on which current secure communications rely on. Post-Quantum Cryptography (PQC) and Quantum key distribution (QKD) are two security technologies that show protection capabilities against the latent quantum threat. While PQC relies on different hard mathematical problems to develop a wide variety of cryptographic operations, QKD is based on quantum physics laws to generate and distribute symmetric cryptographic keys through different QKD protocols. These keys can be used by different applications to perform security transformations. QKD still requires authentication to prevent man-in-the-middle attacks. The hybridization of PQC and QKD is an important step for future secure infrastructures, being able to provide long-term security. In this work we propose authenticated QKD approaches that rely on pre-shared keys and hybrid PQC/QKD alternatives and which are able to securely exchange secret QKD keys through authenticated channels. We identify the different configuration alternatives and their parameters, as well as we develop a wide performance evaluation. Results show that pre-shared keys and PQC-based authentication through Dilithium algorithm are the fastest alternatives. Also, we show the potential of the T12 QKD protocol.
Progress in the development of techniques for the construction of multiuser quantum communications networks is reviewed in light of the plans for an EU quantum communications infrastructure (EU QCI). Quantum key distribution networks may be classified as trusted node; quantum repeater-entanglement-swapping based; point-to-multipoint based on passive beam splitters, active optical switchers or WDM; high dimensional-multipartite entanglement and flexible reconfigurable multipartite networks. Both satellite and terrestrial implementations are possible and ore both planned for EU QCI; their relative merits are discussed. Current technology falls short in several respects of what is required to address use cases well. Bit rates as a function of distance are currently limited by the characteristics of available devices and are an order of magnitude or more below the theoretical bounds. Non-ideal device behaviour can open loopholes for side-channel attacks. Limited range constrains network geometry. New techniques are being developed to overcome these problems. The more sophisticated schemes depend on ongoing advances in the generation and distribution of entanglement. Particularly promising are the measurement device independent protocol, which eliminates photon-detector related security weaknesses, and the twin-field protocol, which uses similar techniques to extend range, in principle even beyond previously accepted theoretical bounds. Agreement of keys between more than two users can be accomplished classically after pairwise quantum key exchange but direct quantum multipartite agreement using may offer advantages. The same applies to secret sharing. Practical quantum repeaters, to eliminate the need for trusted nodes, are closer to being realised due to recent progress in optical memories.
The existence of quantum computing presents an existential threat to the traditional cryptographic algorithms, and there is a need to create communication mechanisms that are fundamentally secure. In this regard, the concept of Quantum Key Distribution (QKD) provides information-theoretic security, which is founded on quantum mechanics. Nevertheless, conventional QKD protocols have serious shortcomings such as lack of distance in communication, vulnerability to side-channel attacks, and inability to support the large-scale heterogeneous network. We suggest that HQNet-QKD a Hybrid Quantum Key Distribution framework can help solve these issues by offering a more secure, scalable and future-proof key exchange framework in hybrid classical-quantum networks. To support multi-layered security, the proposed architecture is a network ensuring the smoothness of decoy-state BB84, Measurement-Device-Independent QKD (MDI-QKD), entanglement/twin-field-based QKD with verifiable Secret Sharing (VSS) and Post-Quantum Cryptography (PQC). It provides a complete methodology such as system architecture, mathematical modeling, and end-to-end key synthesis. When used over a distance of 300 km, simulation and testing have shown that HQNet-QKD can achieve up to2.7×higher secret key rate (SKR) than conventional methods, secret communication at 700 km and resilience to both quantum and classical attacks more than 96%. In addition, the framework guarantees forward secrecy, detector-side immunity, contextbound key derivation, and composability and thus resistant to current and future adversaries. It has a low-computational overhead modular design, making it trivial to deploy in a real world, in applications like quantum-secured 5G backbones, cloud data centers, critical infrastructure, and satellite-based communication systems. The findings make HQNet-QKD a new generation solution to quantum-safe secure communication and the first step towards the implementation of the quantum internet.
Once a cryptographically relevant quantum computer is built, confidential information that is communicated today can be decrypted and exposed. Key exchange methods currently used can then be broken and the key used to protect the data can be recovered. Depending on the duration for which information needs to remain confidential, quantum-safe solutions have to be used now to protect data transmitted today. In this paper, we review recent advances in integrating the combination of two different quantum-safe solutions, Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC), in existing protocols. We also combine classical cryptography, PQC and QKD to securely exchange a key that remains secure even if only one of the three key exchange methods is secure. This is one of the first steps to update existing communication methods such that they remain secure even if only one of PQC, QKD or classical cryptography is secure.
Quantum Key Distribution (QKD) is a mechanism for ensuring secure key exchange based on the fundamental principles of quantum mechanics. It has evolved significantly over the past four decades. QKD networks have evolved from experiments to large-scale deployments, enabling longer transmission distances and enhanced security performance. Existing information security relies on modern cryptographic primitives such as Elliptic Curve Diffie–Hellman (ECDH), RSA, and AES. Although AES-256 is considered quantum-resistant, ECDH and RSA cannot withstand attacks by a specific quantum computer. Specifically, with enough quantum bits, Shor’s and Grover’s algorithms can break RSA and ECDH through rapid integer factorization and quantum search capabilities, respectively. Consequently, QKD offers a promising method towards information-theoretic security, using trusted nodes, optical routers, and future quantum repeaters. However, completely replacing current infrastructure with QKD systems is both costly and impractical. Thus, existing QKD can be integrated into current infrastructure, including dark fiber and satellite systems. Previous surveys have primarily focused on isolated aspects such as fiber-based QKD, free-space QKD, or theoretical Internet architectures. There is a lack of a comprehensive survey that simultaneously presents fundamentals, QKD protocols and security, network implementations, and experimental advances. This makes it difficult for readers to grasp the full scope of the field. This survey focuses on QKD from the ground up, covering the essential foundations of QKD, exploring various QKD protocols, concerning different types of attacks, reviewing real-world QKD network deployments, and highlighting challenges and future directions.
Quantum computing advances pose a serious threat to conventional public-key cryptographic systems such as RSA and elliptic curve cryptography as quantum algorithms may undermine the computational assumptions that guaranty their security. This challenge has driven the development of quantumsafe security approaches among which Quantum Key Distribution (QKD) represents a fundamentally different paradigm based on quantum mechanical principles rather than mathematical complexity. This paper presents a structured review of recent progress in QKD based on a systematic analysis of literature between 2020 and 2025, we examine core protocols including discrete-variable, continuous-variable, measurement-deviceindependent, and twin-field approaches, while also discussing their relationship with post-quantum cryptography as a complementary strategy for future secure communication systems. We provide a unified comparison framework to support practical design and policy decisions by organizing protocols and implementations along deployment dimensions. The study analyze theoretical foundations, implementation technologies across fiber, free-space, satellite, and integrated photonic platforms, and key performance trade-offs involving scalability, security robustness, and deployment feasibility. Findings indicate substantial progress in transitioning QKD from laboratory research toward practical implementations, supported by advances in network architectures, integrated hardware and hybrid cryptographic designs. The comparative analysis will highlight distinct strengths and limitations among protocol families and emphasize the potential of combining QKD with post-quantum cryptographic methods to enhance resilience. Remaining challenges including scalability constraints, implementation-level vulnerabilities, performance limitations over long distances, and integration with existing communication infrastructures are critically discussed. Finally, emerging research directions such as quantum repeaters, hybrid quantum-classical security models, and exploratory directions such as artificial intelligence-assisted optimizations are identified as key factors in enabling the evolution of QKD toward largescale quantum-secure networking.