# Quantum-Secure Coherent Optical Networking for Advanced Infrastructures in Industry 4.0
## 6 Optical Network Security Framework
Side-channel attacks focused on physical implementation such as spectral phase state measurement and alteration become impossible because MHCD executes a near-real time randomization of optical signals. Real network logs combined with lab test data and theoretical analyses from validate the multiple security measures' ability to make unauthorized network access highly difficult to detect [33]. The system reacts to faults or noise by sophisticating its encryption level instead of shutting down service operations. According to the validation approach [40], the encryption safety in the classical data plane remains functional despite QKD channel device errors or signal deterioration, which allows the baseline protection of data confidentiality and data corpus integrity to persist. The quantum layer makes continued efforts to rebuild secure keys, which stops the system from experiencing permanent failures. The risk model [35] recommends that partial operational capability represents an acceptable approach for preventing the full compromise of systems and services. The architects performed an analysis on upcoming quantum computing patterns to make their decisions. Physical-layer encryption together with QKD possesses physical principles that stay valid beyond all levels of computing capabilities. The necessary redesigns required to expand future capabilities such as quantum-safe algorithm updates and metasurface encryptor integration proved minimal. The approach demonstrates through its flexibility that it will endure over time. The framework shows its main advantage through its capability to operate with current network foundations. The architecture enables invisible encryption changes to upper layers through a Layer 2 encryption boundary alignment. Upgrade procedures involving MHCD-compatible optical transceivers along with QKD system integration need significant action, yet they do not necessitate major changes to routing operations or data hardware equipment. Previous research [33] established that incremental deployment is practical since networks can start QKD on particular links before expanding key distribution to all network links. The precise calibration of spectral phase encoding generates minimal overhead and quantum key generation does not disrupt data flow if multiplexing techniques are properly used according to structured cases [32]. The simultaneous operation of key refreshment with traffic ensures continuous encryption as the keys replace themselves. Multiple tests under different traffic loads showed that standard enterprise and carrier networks could smoothly implement the framework through measurement systems that met strict performance criteria [34]. Due to its modular design structure, the architecture demonstrates an easy pathway for potential growth additions. The system architecture accepts new cryptographic methods,advanced DSP components, and MACsec firmware updates by integrating them into its current framework. The framework's extensibility resulted from specific evaluations that involved examining hypothetical replacement mechanisms at the subsystem level (standard MHCD replacement with meta-hologram-based encryption). The study findings confirmed that system synergy would continue to exist because fundamental interface definitions, wavelength assignment, and synchronization schedules maintained their original state. Scalability also formed part of the iterative validations. Distributed key management and synchronized encryption can handle complex topologies that feature multiple nodes or dynamic routing paths. Although more extensive coordination is required, especially if QKD is shared among numerous endpoints, the architecture's underlying modularity supports expansions. Hence, large carriers or multinational enterprises can protect a wide-ranging set of optical links without incurring exponential complexity.