# Quantum-Secure Coherent Optical Networking for Advanced Infrastructures in Industry 4.0
## 6 Optical Network Security Framework
This configuration removes the risks that are usually associated with the use of conventional ZR modules as far as security and network performance are concerned. Integrating optical transceivers with MACsec provides strong encryption and integrity at Layer 2, while also being compliant with post-quantum cryptographic techniques without having an adverse impact on current security protocols. The security architecture can be described as layered and based on several complementary mechanisms. Physical layer operations utilize spectral phase encoding to improve transmission speed through the implementation of specific distortion patterns that need correct phase detection equipment to be restored. During scenario testing [34], it was proven that this method obstructs attackers from intercepting data since standard coherent receivers fail to retrieve concealed spectral patterns. Meanwhile, QKD runs in parallel but remains synchronized with the data channel to refresh encryption keys. From a case-based perspective [32], each subsystem (MHCD, QKD, and MACsec) was scrutinized independently, then integrated to confirm that the layered security measures did not interfere with one another. The framework's quantum security is not derived by large numbers of computational operations but by its architectural design. In contrast to public key systems that hinge on the computational infeasibility of certain number-theoretic problems, the QKD approach ensures that any eavesdropping attempt alters the quantum state, thereby triggering alarms. The consistent detection of tampering validated that an attacker with advanced quantum capabilities would face a \"double burden\": breaking the optical-layer security (MHCD) while simultaneously circumventing QKD's tamper-evident exchanges. By unifying these approaches in a single design, our solution delivers robust cryptographic strength, forward secrecy, and backward compatibility in coherent optical networks operating at 400 Gbps and above. Although QKD theoretically guarantees tamper-evident key exchange, it does not resolve every vulnerability in a complex network. Specifically, QKD only addresses how keys are shared; it does not inherently secure the data plane or the control plane against attacks such as hardware tampering, management plane manipulation, or overhead exploitation. Additionally, practical QKD implementations may face distance and throughput constraints that necessitate fallback to conventional algorithms. Post-quantum cryptographic (PQC) methods, on the other hand, protect data against quantum-enabled adversaries at the encryption layer, regardless of how keys are generated or distributed. Consequently, a robust, layered security model includes both QKD for tamper-evident key distribution and PQC  
Figure 8: QKD-MHCD integrated architecture for coherent optical networks. algorithms for data encryption. This dual approach fortifies the entire system, ensuring that even if one layer is compromised by sophisticated attacks, the other continues to provide protection. Operation success depends heavily on the correct implementation of the classical-quantum interface. The research utilized an iterative refinement cycle [34] to establish that the integration of classical signals alongside quantum channels on a single fiber does not degrade performance effectiveness between them. Lab tests confirmed that swift data encryption functions independently from slower quantum key distribution exchanges when these keys exist on different light frequencies or when time-based multiplexing occurs. The design methodology adopted by this system implements levels of modularity that allow the replacement or upgrade of individual components for future compatibility [13]. Strong security characteristics emerge from the framework when it encounters advanced adversaries. QKD key exchanges become unreliable when man-in-the-middle attacks happen at the control plane, thus triggering immediate warnings, as documented in Section 3.