Post-quantum cryptography (PQC) and quantum key distribution (QKD) address the quantum threat from opposite directions: PQC replaces vulnerable public-key algorithms with schemes believed to resist quantum cryptanalysis, while QKD derives keys whose secrecy rests on physical assumptions rather than computational ones. Because each approach has a distinct failure mode, a growing body of work combines them so that a session key remains secure if either component holds. We first establish the deployed baseline, hybrid classical-plus-PQC key exchange, against which QKD-augmented designs must be judged. We then propose a taxonomy of hybrid PQC-QKD designs along eight dimensions (integration layer, combiner construction, authentication scope and source, QKD topology, trusted entities, key-delivery interface, classical component, and evidence type), and use it to compare published protocols, including Muckle and its successors, MACsec and TLS integrations, and IKEv2 mechanisms standardised in RFCs 8784, 9370, and 9867. We examine key-combiner constructions in light of the KEM-combiner literature and of NIST, ETSI, and ITU-T guidance, and map the security arguments for hybrid PQC-QKD protocols onto a common grid of security model, assumptions, permitted compromise, established guarantee, and limitations. We synthesise deployment evidence from metropolitan and national QKD networks, distinguishing the few testbeds that have run PQC in the key path from pure-QKD deployments, and summarise the standards and policy landscape, including the positions of national security agencies that recommend against relying on QKD alone. We close with open problems: authentication of the QKD classical channel, shared-infrastructure threat models, device certification versus formal proofs, formal verification of hybrid handshakes, and the lack of peer-reviewed deployment economics.
Post-quantum cryptography (PQC) and quantum key distribution (QKD) address the quantum threat from opposite directions: PQC replaces vulnerable public-key algorithms with schemes believed to resist quantum cryptanalysis, while QKD derives keys whose secrecy rests on physical assumptions rather than computational ones. Because each approach has a distinct failure mode, a growing body of work combines them so that a session key remains secure if either component holds. We first establish the deployed baseline, hybrid classical-plus-PQC key exchange, against which QKD-augmented designs must be judged. We then propose a taxonomy of hybrid PQC-QKD designs along eight dimensions (integration layer, combiner construction, authentication scope and source, QKD topology, trusted entities, key-delivery interface, classical component, and evidence type), and use it to compare published protocols, including Muckle and its successors, MACsec and TLS integrations, and IKEv2 mechanisms standardised in RFCs 8784, 9370, and 9867. We examine key-combiner constructions in light of the KEM-combiner literature and of NIST, ETSI, and ITU-T guidance, and map the security arguments for hybrid PQC-QKD protocols onto a common grid of security model, assumptions, permitted compromise, established guarantee, and limitations. We synthesise deployment evidence from metropolitan and national QKD networks, distinguishing the few testbeds that have run PQC in the key path from pure-QKD deployments, and summarise the standards and policy landscape, including the positions of national security agencies that recommend against relying on QKD alone. We close with open problems: authentication of the QKD classical channel, shared-infrastructure threat models, device certification versus formal proofs, formal verification of hybrid handshakes, and the lack of peer-reviewed deployment economics.
Abstract Quantum computing exploits superposition and entanglement to process information in an exponentially large state space, enabling algorithms such as Shor’s to factor large integers efficiently and thereby undermining RSA and elliptic curve cryptography. Quantum cryptography, here encompassing post quantum cryptographic (PQC) algorithms and quantum key distribution (QKD), is a leading candidate for protecting data against quantum capable adversaries. PQC designs classical schemes conjectured to be secure against both quantum and classical attacks, whereas QKD uses quantum mechanics to detect eavesdropping and establish information theoretically secure keys. Existing literature and limitations. Recent surveys summarise PQC families and the standardisation process led by the U.S. National Institute of Standards and Technology (NIST), and reviews outline QKD protocols and their challenges. However, most prior work either addresses narrow subtopics or does not systematically synthesise empirical evidence across technical and application domains. As a result, there is still limited integrated understanding of key issues, technologies, mathematical foun dations, algorithms, programming tools and real world deployments. Objective and contributions of this review. This study systematically analyses 61 peer reviewed journal articles published within the last five years that focus on quantum cryptography. Using Covidence to manage study identification, selection, quality assessment, data extraction and narrative synthesis, it (a) characterises current issues and challenges; (b) surveys recent technological advancements and implementations; (c) evaluates algorithmic approaches and their effectiveness; (d) examines the underlying mathematical models; (e) maps the programming languages and tools used to implement quantum schemes; and (f) synthesises evidence on practical applications and future research directions. The review integrates findings on PQC and QKD, highlights gaps in the current evidence base, and offers practitioners, scholars and policymakers guidance for developing quantum secure communication systems. Keywords Quantum cryptography, Post quantum cryptography, Quantum key distribution, Systematic literature review, Quantum secure communication
Abstract: This study advances a unifying systems perspective on quantum-safe network security by synthesizing recent progress in quantum cryptography with practical integration patterns across carrier-grade infrastructures. Concept analysis distinguishes the roles of quantum key distribution (QKD), device-independent variants, quantum authentication, and post-quantum cryptography (PQC) within zero-trust architectures. Building on this, a layered framework—spanning physical/entanglement resources, key management, crypto-agility, control plane orchestration, and policy/compliance—is articulated to support end-to-end, composable guarantees. The problem addressed is the realization of verifiable, quantum-resilient security under operational constraints involving latency, key-rate variability, and heterogeneous trust assumptions. Methodology combines a structured literature synthesis with formal composability mapping to universal composability principles, adversarial threat modeling for quantum-enabled attackers, and testbed/simulation evaluation of hybrid QKD–PQC pipelines across L2–L3 segments and 5G/6G backhaul scenarios. Key results indicate that (i) selective QKD deployment on high-value links coupled with PQC at endpoints enhances resilience while preserving crypto-agility; (ii) automated key-lifecycle orchestration reduces exposure windows; and (iii) device-independent assurances strengthen guarantees where trust relaxation is necessary. The impact is a deployment-ready reference architecture, measurable integration metrics, and guidance aligned with emerging standards for critical infrastructure and national networks. The implications extend to procurement, compliance, and roadmap planning for quantum-era network security. Keywords: quantum-safe cryptography, quantum key distribution (QKD), post-quantum cryptography (PQC), hybrid QKD–PQC, composable security, device-independent QKD, zero-trust networks, key management and orchestration, 5G/6G backhaul, network security architecture, standards and interoperability
Post-quantum cryptography (PQC) is moving from evaluation to deployment as NIST finalizes standards for ML-KEM, ML-DSA, and SLH-DSA. This survey maps the space from foundations to practice. We first develop a taxonomy across lattice-, code-, hash-, multivariate-, isogeny-, and MPC-in-the-Head families, summarizing security assumptions, cryptanalysis, and standardization status. We then compare performance and communication costs using representative, implementation-grounded measurements, and review hardware acceleration (AVX2, FPGA/ASIC) and implementation security with a focus on side-channel resistance. Building upward, we examine protocol integration (TLS, DNSSEC), PKI and certificate hygiene, and deployment in constrained and high-assurance environments (IoT, cloud, finance, blockchain). We also discuss complementarity with quantum technologies (QKD, QRNGs) and the limits of near-term quantum computing. Throughout, we emphasize crypto-agility, hybrid migration, and evidence-based guidance for operators. We conclude with open problems spanning parameter agility, leakage-resilient implementations, and domain-specific rollout playbooks. This survey aims to be a practical reference for researchers and practitioners planning quantum-safe systems, bridging standards, engineering, and operations.
Cryptographically relevant quantum computers do not yet exist, but the transition away from classical public-key cryptography is already underway: adversaries can record encrypted traffic today and decrypt it once a sufficiently capable quantum computer becomes available, a threat known as harvest-now, decrypt-later. This paper examines the engineering case for combining post-quantum cryptography (PQC) with quantum key distribution (QKD) as a strategy for securing next-generation communication infrastructure, focusing on 6G core and radio-access networks, Open RAN (O-RAN), and constrained Internet of Things (IoT) deployments. Rather than treating the two mechanisms as symmetric, interchangeable layers, the paper examines what each one actually guarantees, surveys the empirical evidence available for deployment cost, and describes where national security authorities and standards bodies disagree on the value of QKD. The architecture is grounded in the finalized National Institute of Standards and Technology (NIST) PQC standards and its 2025 hybrid key-establishment guidance, drawing on empirical Open RAN latency and energy measurements published during 2025 and 2026, embedded-hardware benchmarks for constrained devices, and the small number of quantum key distribution deployments operating at metropolitan or national backbone scale today. The paper is explicit about which figures are measured results and which remain illustrative proposals, and it closes by naming the specific standardization and field-trial gaps that separate current practice from the architecture it describes. The purpose of the work is to give network architects and policymakers a single, evidence-graded reference for deciding where each mechanism belongs in a real deployment, rather than treating post-quantum and quantum-distributed keying as equivalent options.
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.
The advancement of quantum computing poses a direct threat to classical cryptographic systems, necessitating the adoption of quantum-resistant encryption techniques to maintain data integrity, confidentiality, and trust in digital communications. This study presents a comprehensive evaluation of Quantum Key Distribution (QKD) protocols - specifically BB84, E91, and B92 - alongside post-quantum cryptographic algorithms, including lattice-based, hash-based, and multivariate-quadratic systems. These techniques represent two complementary approaches: QKD leverages quantum mechanical principles for secure key exchange, while PQC reinforces classical cryptography against quantum threats using novel mathematical constructs. A comparative analysis is conducted focusing on security robustness, computational efficiency, and deployment scalability. Real-world constraints such as infrastructure limitations, key management complexity, and algorithmic overhead are also critically examined. The paper also investigates the standardization efforts led by NIST, ISO, and ETSI, highlighting current challenges to global adoption, including the lack of interoperability frameworks and varying readiness levels across industries. The findings underscore the need for hybrid cryptographic models that integrate classical and quantum-resistant mechanisms, offering a pragmatic path forward as quantum capabilities mature. Future directions include integrating quantum cryptography with cloud security, advancing homomorphic encryption, and developing quantum-safe blockchain technologies. These innovations are crucial for building resilient cybersecurity infrastructures capable of supporting next-generation applications such as secure edge computing, confidential AI model sharing, and tamper-proof digital ledgers. This research provides timely insights into the evolving cryptographic landscape and emphasizes the urgency of preparing for the quantum future through interdisciplinary collaboration and proactive technological adaptation.