Continuous Key Refreshment for Hybrid Quantum Cryptography with BB84 and Post Quantum Signatures

The current paper presents a quantum-classical cryptographic protocol, which is a hybrid of the BB84 Quantum Key Distribution (QKD) protocol and a lattice-based post-quantum signature scheme, CRYSTALS-Dilithium. Such a mix is to create a safe channel of communication that is resistant to classical and quantum assaults. The protocol relies on the unconditional security of QKD to exchange keys in a symmetric way and addresses the vulnerability of QKD to man-in-the-middle (MitM) attacks by strong classical authentication provided by PQC signatures. Another important invention of this work is the ever-refreshing of the keys. This is to enable the periodic updating of the session key without necessarily having to undergo the entire re-authentication two-way handshake. This is enhanced to improve forward secrecy and reduce the computational requirements. To demonstrate the viability and security aspects of the protocol, we give a theoretical framework and a simulation of the protocol by IBMs Qiskit. The protocol showed that it was able to generate secure keys successfully which was in line with the theoretical expectations. The embedded CRYSTALS-Dilithium signature provides effective authentication that ensures that the hybrid system is viable and does not cause any performance problem. The simulation results quantitatively validate the protocol's security and performance, demonstrating a QBER of 0.7% under ideal conditions, which is well below the 25% abort threshold. These findings indicate that this mixed solution is an effective solution to secure long-term communications in the quantum age.