Combined Quantum and Post-Quantum Security Performance Under Finite Keys

TL;DR

This paper enhances hybrid quantum and post-quantum security systems by integrating tight finite-key security and scalable design, ensuring confidentiality even under primitive compromise, with practical implications for real-world networks.

Contribution

It introduces the tightest finite-key security implementation for BBM92 and improves hybrid system design for better scalability and security in practical settings.

Findings

Finite-key security for BBM92 is now tighter than previous implementations.

System processing time scales linearly with instruction size.

Hybrid system maintains confidentiality even if primitives are compromised.

Abstract

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.