Combined Quantum and Post-Quantum Security Performance Under Finite Keys

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.

💡 Research Summary

This paper addresses two critical gaps in existing hybrid quantum‑post‑quantum (QKD‑PQC) security designs: the neglect of finite‑key effects in quantum key distribution and the lack of a unified strategy for side‑channel leakage from both QKD and PQC primitives. Building on the authors’ earlier “Hybrid Obfuscated Quantum System” (HOQS), the work introduces a refined system, HOQS+, that integrates the tightest known finite‑key security analysis for the entanglement‑based BBM92 protocol and redesigns the hybrid encryption (HE) layer for linear scalability.

The finite‑key implementation follows the composable security frameworks of Refs.