# Quantum-Secure Coherent Optical Networking for Advanced Infrastructures in Industry 4.0
## 4 Vulnerability Analysis  
This section presents a detailed examination of vulnerabilities in coherent optical networks, grounded in a layered qualitative research methodology that ensures academic rigor. This study employed an iterative case-based framework [32] to isolate individual subsystems, used methodological triangulation [33] to confirm the presence and severity of potential threats, and aligned these findings with the CIA (confidentiality, integrity, availability) model's [30; 35] systematic vulnerability assessment guidelines. By applying ref. [34]'s iterative validation process, the research team tested each vulnerability under simulated conditions mirroring real-world attack scenarios while accounting for both classical and quantum adversaries [13; 14]. The results reveal that weaknesses often arise at the confluence of hardware design, protocol integration, and signal processing algorithms in 400G ZR+ coherent systems.  
The analysis began by identifying the structural elements of a 400G ZR+ environment, specifically, the interfaces linking router control planes to coherent optical modules. Each interface and subsystem (bridge architecture, management plane protocols, DSP blocks, OTU4 framing, and physical-layer channels) was treated as a distinct case unit [32]. This segmentation facilitated the close scrutiny of vulnerabilities in synchronization, timing control, overhead byte usage, and optical signal manipulation. Triangulating the data from component specifications, documented exploits, and real-time traffic simulations [33] allowed the team to confirm that these vulnerabilities were neither hypothetical nor limited to a single test environment.  
The focus then turned to systematically categorizing identified threats under the CIA (confidentiality, integrity, and availability) model. Confidentiality threats included the unauthorized interception of data streams, while integrity threats ranged from frame manipulation in OTU4 overhead bytes to the malicious reprogramming of DSP parameters. Availability threats spanned timing-based attacks on synchronization buffers, potentially degrading or halting network services. This classification clarified how each vulnerability affected the core security objectives in a coherent optical environment.  
Drawing on systematic risk assessment, this study rated vulnerabilities by their likelihood, technical complexity, and potential damage [35]. In parallel, an iterative validation approach ensured that the identified weaknesses were re-evaluated under multiple simulated threat profiles, including basic script-kiddie exploits, state-sponsored adversaries with quantum decryption capabilities, and insider threats [34]. This repetition refined the accuracy of the impact ratings, revealing which attacks required minimal effort yet posed widespread danger (e.g., overhead byte manipulation) and which demanded advanced tools (e.g., manipulating phase estimation blocks).  
Below is a comprehensive summary of these vulnerabilities in Table 1, which maps architectural domains to potential exploit vectors and the resulting security implications. To enhance transparency, this Table also lists the primary vulnerability category (bridge architecture, DSP, OTU4 framing, management interfaces, or physical layer) and indicates whether post-quantum threats exacerbate each issue.