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.
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.
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.
With the rapid advancement of quantum computing, existing cryptographic schemes in 4G LTE and 5G networks confront serious security threats. Traditional reliance on protocols like IPsec and Transport Layer Security leaves infrastructure vulnerable to future quantum attacks, particularly “Harvest Now, Decrypt Later” attacks, where adversaries store current encrypted traffic for future decryption. To counter these threats, Post-Quantum Cryptography (PQC) and Quantum Key Distribution (QKD) have become potential solutions. As future 6G networks aim to realize ultra-reliable and ubiquitous secure connectivity, it is essential to incorporate both PQC and QKD solutions to ensure long-term robustness. Therefore, the synergy of these security solutions and 5G draws the attention of researchers and practitioners worldwide. This study systematically reviews the literature in this specific field. We analyzed evidence from reviewed literature to address three research questions, resulting in a novel taxonomy to categorize publications in this area and a vision for a quantum-safe 6G network. Moreover, we discussed several open challenges in 5G, PQC, and QKD, along with future work.
Quantum computing poses a significant threat to classical asymmetric cryptography, which is essential for ensuring confidentiality, authentication, and key exchange in contemporary digital infrastructures. Although post-quantum cryptography (PQC) provides mechanisms that resist quantum attacks, its implementation in Internet of Things (IoT) systems is challenged by constrained resources, including limitations in computation, memory, energy, latency, and bandwidth, and the heterogeneity of devices. This paper offers a comprehensive narrative review of PQC approaches applicable to IoT, systematically organizing 30 peer-reviewed studies published between 2022 and 2026 across four layers: device, communication, distributed trust, and application. Additionally, the review examines two cross-cutting dimensions, privacy and side-channel resistance. The analysis indicates a significant prevalence of lattice-based schemes, hybrid strategies, and integrations with blockchain technology, zero-knowledge proofs, federated learning, homomorphic encryption, AI, and Zero Trust architectures. Notably, key gaps remain in side-channel evaluation, migration pathways, deployment costs, and real-world validation—issues that are particularly critical given the long lifecycles of IoT devices and the ongoing threat of “harvest now, decrypt later” attacks.
The future security of digital communications will increasingly rely on the integration of Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC), indicating a necessary convergence rather than a competitive relationship between these two technologies. Following the publication of NIST FIPS 203, 204 and 205, the industry now possesses standardised algorithmic tools for migrating away from RSA and elliptic-curve cryptography (ECC). At the same time, for critical infrastructure facing “harvest-now, decrypt-later” adversaries, purely software-based measures provide only computational, not information-theoretic, security. We argue that the optimal solution is a hybrid architecture, in which PQC provides authentication and cryptographic agility across heterogeneous endpoints, while QKD supplies an additional physical-layer shield for high-value links. The central engineering challenge is brownfield coexistence: deploying QKD over existing lit telecom fibers that carry high-power classical traffic. We review three spectral coexistence strategies to mitigate Spontaneous Raman Scattering (SpRS) – O-band separation, dense C-band DWDM integration with guard bands, and an “inverted” spectrum approach where data uses the O-band and QKD uses the C-band – and we discuss emerging physical media such as hollow-core and multi-core fibers. At the protocol layer, we discuss hybrid key encapsulation and the role of crypto-agile gateways in combining keys from classical, PQC and QKD sources [1]. Finally, we survey industrial pilots (e.g., SK Telecom, EuroQCI / OPENQKD) and outline open challenges in cost, standardisation and operations. The goal is to provide practitioners with a realistic, engineering-oriented overview of how PQC and QKD can be combined in brownfield optical networks.
Abstract The prospect of cryptanalytically relevant quantum computers (CRQCs) motivates a transition from classical cryptography to post-quantum cryptography (PQC). Shor’s algorithm threatens widely deployed public-key schemes used for key establishment and digital signatures, while Grover’s algorithm reduces effective security margins for symmetric-key and hash-based primitives. The harvest-now, decrypt-later (HNDL) threat further increases urgency because adversaries can store encrypted data today for future decryption, placing long-lived confidentiality requirements and trust infrastructure at risk. This survey frames PQC adoption as a standards-to-deployment program. We review the PQC design space and summarize deployment-critical constraints, including handshake and certificate size growth, latency under network loss, computational cost, memory and storage requirements, implementation complexity, and side-channel robustness. We then present an iterative migration pipeline covering cryptographic inventory, risk-based prioritization using data sensitivity and cryptoperiod, algorithm and parameter profile selection, hybrid classical and PQC constructions for backward compatibility, pilot validation with measurable go/no-go criteria, and long-term operations with crypto-agility. Finally, we connect standardization outputs to concrete integration surfaces and illustrate the workflow across transport layer security (TLS) and the web public key infrastructure (Web PKI), virtual private networks (VPNs) and internet protocol security (IPsec), and constrained Internet of things (IoT) deployments, and we summarize open challenges in interoperability, public key infrastructure (PKI) transition mechanics, implementation maturity and operational governance.
The telecommunications industry faces a dual transformation: the architectural shift toward Open Radio Access Networks (O-RAN) and the emerging threat from quantum computing. O-RAN disaggregated, multi-vendor architecture creates a larger attack surface vulnerable to crypt-analytically relevant quantum computers(CRQCs) that will break current public key cryptography. The Harvest Now, Decrypt Later (HNDL) attack strategy makes this threat immediate, as adversaries can intercept encrypted data today for future decryption. This paper presents Q-RAN, a comprehensive quantum-resistant security framework for O-RAN networks using NIST-standardized Post-Quantum Cryptography (PQC). We detail the implementation of ML-KEM (FIPS 203) and ML-DSA (FIPS 204), integrated with Quantum Random Number Generators (QRNG) for cryptographic entropy. The solution deploys PQ-IPsec, PQ-DTLS, and PQ-mTLS protocols across all O-RAN interfaces, anchored by a centralized Post-Quantum Certificate Authority (PQ-CA) within the SMO framework. This work provides a complete roadmap for securing disaggregated O-RAN ecosystems against quantum adversaries.