## 6 Experimental Evaluation and Results
### Comparative Analysis of Defense Strategies  
To evaluate the defense capabilities of our proposed privacy-preserving polymorphic heterogeneous security architecture, we conducted a comprehensive comparative analysis against two representative defense strategies: static redundancy and moving target defense. The evaluation focuses on system resilience under false data injection attacks, measuring both operational performance and availability metrics during attack scenarios. The comparative analysis employs three key reliability metrics to quantify defense effectiveness. Mean time to repair (MTTR) represents the average time required for the system to recover from anomalous states and return to the normal operating range of \(\pm\)3% pressure deviation. Mean time between failures (MTBF) reflects the average operational duration within the acceptable pressure range between consecutive system failures. System availability quantifies the overall operational reliability as a percentage. These metrics are calculated using the following formulas:  
\[\text{MTTR} = \frac{\text{Total Repair Time}}{\text{Number of Failures}}, \tag{32}\] \[\text{MTBF} = \frac{\text{Total Normal Time}}{\text{Number of Failures}},\] (33) \[\text{Availability} = \frac{\text{MTBF}}{\text{MTBF + MTTR}}\times 100\%. \tag{34}\]  
Figure 3 presents the pipeline pressure variations under different defense strategies during the simulation period. The static redundancy approach employs three heterogeneous executors with a majority voting mechanism to determine final executor outputs. The moving target defense strategy implements periodic random switching of active executors according to a predetermined schedule. Experimental results demonstrate that static redundancy methods become increasingly vulnerable as attacks persist, with adversaries capable of progressively compromising individual executors until the entire system falls under attacker control. Moving target defense, while continuously switching active executors, still experiences pressure limit violations when compromised executors are in active states, although the switching cycles prevent emergency shutdowns. In contrast, our proposed defense method effectively detects compromised executors outputting erroneous data and triggers executor switching and sanitization mechanisms within system stability constraints. This approach successfully interrupts false data injection attack paths while maintaining system operational integrity. Figure 4 illustrates the executor output comparisons between our proposed method and baseline defense strategies under attack scenarios. The results reveal that moving target defense may still execute incorrect pressure control operations when compromised executors are online. Static redundancy methods, after adversaries successfully compromise two executors, persistently output erroneous pressure control commands due to compromised majority voting. Our proposed method demonstrates superior performance by initiating executor offline and sanitization procedures upon detecting anomalous outputs, while simultaneously bringing backup executors online within system stability constraints. This ensures that attack influences are promptly contained, and system outputs consistently maintain correct pressure control values, as detailed in Figure 5.  
Table 2 presents the availability metrics comparison among the proposed method, static redundancy, and moving target defense under attack scenarios. The quantitative analysis demonstrates that our proposed approach achieves significantly superior system availability preservation. Static redundancy exhibits 2 failures with an MTTR of 44.92 min and MTBF of 75.08 min, resulting in 62.57% availability. Moving target defense shows improved performance with 2 failures, reduced MTTR of 16.17 min, and extended MTBF of 103.83 min, achieving 86.53% availability. Remarkably, our proposed method maintains zero failures throughout the simulation period, resulting in perfect 100% system availability with MTBF of 240.00 min and zero repair time.