# Quantum-Secure Coherent Optical Networking for Advanced Infrastructures in Industry 4.0
## 1 Introduction  
Modern communication systems underpinning **Industry 4.0** require high-capacity optical networks spanning local facilities, regional corridors, and transoceanic links. The latest backbone infrastructures, supporting data rates of 400 Gbps and above, rely on coherent technology enhanced by advanced digital signal processing and phase-sensitive detection [1]. Such systems transmit terabits of data per second to serve the diverse, time-sensitive demands in industrial automation, robotics control, global financial transactions, and e-government databases. As reliance on these coherent networks grows, sodoes the urgency of addressing security vulnerabilities, especially in environments where interconnected machinery, sensors, and cloud-based analytics coexist [2]. The evolution of network hardware design is driven by the surging throughput requirements typical of **smart factories** and **robotic assembly lines**. While earlier optical links depended primarily on upper-layer protocols, such as Transport Layer Security or IP security for data protection [3], advanced Industry 4.0 applications increasingly employ Layer 2 solutions like Media Access Control Security (MACsec) to ensure confidentiality, integrity, and authenticity at the Ethernet layer. However, new technical challenges arise in coherent networks. Management interfaces bridging MACsec-enabled routers and optical modules, often using MDIO or I\({}^{2}\)C protocols, lack robust security measures [4]. Similarly, the overhead field-based structure of Optical Transport Unit level 4 framing is susceptible to interception or manipulation [5]. The combined use of multiple protocols with different security assumptions can introduce unforeseen vulnerabilities, hampering the reliability required by fully automated manufacturing processes. Recent research and development in quantum computing enhance security concerns. The distribution of keys for MACsec security uses cryptographic methods, which depend on finite mathematical assumptions. Modern quantum algorithms, notably [PERSON]'s algorithm, threaten the security of classical cryptography once quantum computing matures to a sufficient level [6; 7]. Adversaries can store intercepted ciphertexts now and decrypt them later, making the immediate adoption of quantum-safe measures critical. Modern data security demands the implementation of quantum-safe cryptographic approaches since attacks can happen while data is stored for later decryption. Although quantum key distribution (QKD) offers a theoretically unbreakable means of key exchange [8], its integration with coherent optical networks has faced practical hurdles. Recent progress suggests that these hurdles are more surmountable than previously believed [9]. Motivated by these challenges, the primary purpose of this research is to explore how coherent optical networks can be protected from both classical exploits and future quantum-based attacks, while preserving compatibility with existing networking standards. This work aligns with calls from the recent literature for quantum-safe encryption strategies in optical environments [10; 11; 12]. The presence of management plane vulnerabilities in 400G ZR+ transceiver modules, as well as protocol weaknesses in OTU4 overhead fields, calls for rigorous investigation. The specific gap in the current literature is that many proposed methods treat optical-layer security, MACsec, and quantum cryptography as separate domains. This fragmentation creates a scenario in which bridging them may introduce further security holes or degrade system performance. In this context, \"quantum-resistant protocols\" refer to cryptographic algorithms and key-exchange methods designed to remain secure even against adversaries equipped with large-scale quantum computing capabilities, typically by relying on mathematically hard problems that cannot be efficiently solved by known quantum algorithms.