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EPJ Quantum Technology

Enhancing Quantum Key Distribution via McEliece-based hybrid PQC-QKD architecture

Veeresh R. Maned, Satyabrat Rath, Jothi Ramalingam, Lakshmi Kuppusamy

Published Mar 24, 2026• 1 citation
Publisher

Abstract

Abstract Quantum Key Distribution (QKD) offers information-theoretic security; however, its practicality is limited by an inherently low secret key rate. In this work, we propose a cryptographic enhancement of QKD by incorporating post-quantum public key encryption, namely Classic McEliece. We propose a novel hybrid PQC-QKD protocol named BBM that employs QC-LDPC based McEliece cryptosystem to encrypt the basis string in QKD, thereby skipping the sifting step and consequently improving the secret key rate. We only need to assume the short-term security of the McEliece cryptosystem during the protocol run to achieve the everlasting security of the distilled keys. Our analysis demonstrates that this integration not only enhances the achievable secret key rate by $\sim 2\times $ ∼ 2 × in the BB84 protocol but also provides resistance against photon number splitting attack, and inherits a fallback mechanism in its design. This marks a significant improvement in terms of efficiency, security, and reliability over conventional BB84-like QKD protocols.

DOI
10.1140/epjqt/s40507-026-00498-8

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Abstract Quantum Key Distribution (QKD) offers information-theoretic security; however, its practicality is limited by an inherently low secret key rate. In this work, we propose a cryptographic enhancement of QKD by incorporating post-quantum public key encryption, namely Classic McEliece. We propose a novel hybrid PQC-QKD protocol named BBM that employs QC-LDPC based McEliece cryptosystem to encrypt the basis string in QKD, thereby skipping the sifting step and consequently improving the secret key rate. We only need to assume the short-term security of the McEliece cryptosystem during the protocol run to achieve the everlasting security of the distilled keys. Our analysis demonstrates that this integration not only enhances the achievable secret key rate by ∼2×\sim 2\times ∼2× ∼ 2 × in the BB84 protocol but also provides resistance against photon number splitting attack, and inherits a fallback mechanism in its design. This marks a significant improvement in terms of efficiency, security, and reliability over conventional BB84-like QKD protocols.
As quantum computing technology advances, our traditional methods of securing information are becoming vulnerable to new types of attacks. To counter these threats, Quantum Key Distribution (QKD) methods like the BB84 protocol offer a way to create extremely secure keys. However, QKD alone can have practical limitations and might still be exposed to certain types of attacks. On the other hand, Post-Quantum Cryptography (PQC) provides a robust defense against quantum attacks through complex mathematical algorithms. This research aims to combine the best of both worlds: using the BB84 QKD protocol to generate secure keys and then using these keys with PQC algorithms for encrypting information. By integrating QKD for key generation and Lattice based (Kyber) PQC for encryption, we hope to create a cryptographic system that is both incredibly secure and practical for real-world use. This project will involve designing the hybrid system, testing it through simulations, and evaluating its performance and security against traditional methods.
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 to2.7×2.7 \times2.7×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.
Quantum resistance is vital for emerging cryptographic systems as quantum technologies continue to advance towards large-scale, fault-tolerant quantum computers. Resistance may be offered by quantum key distribution (QKD), which provides information-theoretic security using quantum states of photons, but may be limited by transmission loss at long distances. An alternative approach uses classical means and is conjectured to be resistant to quantum attacks, so-called post-quantum cryptography (PQC), but it is yet to be rigorously proven, and its current implementations are computationally expensive. To overcome the security and performance challenges present in each, here we develop hybrid protocols by which QKD and PQC inter-operate within a joint quantum-classical network. In particular, we consider different hybrid designs that may offer enhanced speed and/or security over the individual performance of either approach. Furthermore, we present a method for analyzing the security of hybrid protocols in key distribution networks. Our hybrid approach paves the way for joint quantum-classical communication networks, which leverage the advantages of both QKD and PQC and can be tailored to the requirements of various practical networks.
Quantum key distribution (QKD) is the most extensively researched quantum cryptographic protocol, leveraging quantum phenomena to enable information-theoretically secure key establishment. Conventional QKD systems rely on authenticated classical post-processing channels to prevent impersonation attacks. However, QKD inherently lacks authentication capabilities, necessitating an external authentication mechanism. Furthermore, the classical post-processing steps introduce information leakage, exposing QKD to additional attack strategies and diminishing the final key rate. In this study, we introduce a novel QKD protocol that eliminates the need for separate authentication, prevents information leakage, and significantly improves the achievable key rate. By removing public classical channels entirely, our design attains perfect secrecy with the use of two reusable pre-shared keys.
In this paper, we consider quantum key distribution (QKD) using pulse-position modulation (PPM) and propose the PPM-based BB84 QKD protocol. With the adoption of PPM, the efficiency of utilizing weak laser pulses can be improved and hence the key rate. We first analyse the potential of using PPM from the perspective of raw key rate. We then provide detailed description of the proposed protocol, the encoding rule of which has to be specifically designed in order to be secure. Lastly, we consider the intercept-resend and photon-number splitting attacks and analyse the secret key rate of the proposed QKD protocol. Our analysis shows that in high-loss channel, the proposed PPM-based BB84 protocol can achieve higher secret key rates compared to the conventional BB84 protocol.
Recent advances in quantum-secure communication have highlighted the value of hybrid schemes that combine Quantum Key Distribution (QKD) with Post-Quantum Cryptography (PQC). Yet most existing hybrid designs omit realistic finite-key effects on QKD key rates and do not specify how to maintain security when both QKD and PQC primitives leak information through side-channels. These gaps limit the applicability of hybrid systems in practical, deployed networks. In this work, we advance a recently proposed hybrid QKD-PQC system by integrating tight finite-key security to the QKD primitive and improving the design for better scalability. This hybrid system employs an information-theoretically secure instruction sequence that determines the configurations of different primitives and thus ensures message confidentiality even when both the QKD and the PQC primitives are compromised. The novelty in our work lies in the implementation of the tightest finite-key security to date for the BBM92 protocol and the design improvements in the primitives of the hybrid system that ensure the processing time scales linearly with the size of secret instructions.