Enhancing 6G Network Security with Quantum Key Distribution: A Comprehensive Review

With the considerable progress of sixth-generation (6G) networks further on the horizon, security has attracted much attention in the face of increasingly sophisticated threats, especially from quantum computing. Classical cryptographic schemes based on computational hardness are becoming more and more brittle, as they can easily be attacked with a quantum computer. Quantum Key Distribution (QKD) arises as a promising tool for information-theoretic security through quantum mechanics to obtain an unbreakable key by exchanging unknown bit sequences. In this paper, we provide an extensive survey on the integration of QKD both in the envisioned 6G architecture, including current implementations, technical feasibility, and deployment of QKD in fiber-based and wireless scenarios. We compare performance metrics of QKD systems in simulating 6G systems such as secret key rates, quantum bit error rates, and robustness to noise and mobility. We propose and investigate hybrid security schemes to leverage both classical PQC and QKD technologies to build multilayered security shields. We highlight the importance of the Artificial Intelligence (AI) and Machine Learning (ML) in improving QKD systems in terms of smart error correction, dynamic routing, anomaly detection, and adaptive key management, and more. In spite of efforts, the paper points out important research challenges that remain to be addressed in scalability, standardization, cross-operation comparison and demonstration. We finally summarize new directions for quantum-secured networking, offering a future research agenda which combines AI, standardization works and real testbeds to deliver a QKD shift from a lab-scale proof of concept to global-scale 6G network adoption. This review serves as a useful reference for researchers and practitioners as they develop quantum-safe, next-generation communication networks.