# Multi-Line Prefetch Covert Channel with Huge Pages
## 5 Results
### Throughput and Accuracy
A performance comparison of high-capacity encodings: We further explored the trade-off between accuracy and throughput when transmitting messages of different lengths and cache line counts. The experiments in this section were conducted in the 2 MB huge page read-only setting. Table 3 compares two schemes: (1) transmitting 10-bit messages using 1024 cache lines in a single iteration and (2) transmitting 9-bit messages twice using 512 cache lines each time. The 10-bit scheme demonstrates a higher overall accuracy due to a lower bit error rate, while the 9+9-bit scheme provides a higher raw throughput but at the cost of an increased error probability, resulting in a reduced chance of correctly decoding all bits. These results indicate that if robustness and successful full-message decoding are the priorities, the 10-bit scheme with more cache lines is preferable. However, when  
Figure 2: Bucket Size vs. Accuracy for 2 MB Huge Page, Read-only Setting. maximizing the bandwidth is critical and some errors are acceptable (or can be corrected), the 9+9-bit scheme may be beneficial. To provide a more holistic evaluation of each encoding strategy, we introduce a composite metric that combines both the throughput and decoding accuracy to compute the effective bandwidth in KB/s. This metric estimates the number of correct bits transmitted per second, capturing the real-world utility of the covert channel under noisy conditions. For each scheme, we compute  
* Effective Bits/Round = Bits per iteration \(\times\) Accuracy
* Effective Bandwidth (KB/s) = Raw Bandwidth \(\times\) Accuracy  
10-bit scheme:  
\[\text{Effective Bits}/\text{Round}=10\times 0.6431=6.43\text{ bits}\] \[\text{Effective Bandwidth}=2654\times 0.6431\approx 1707\text{ KB/s}\]  
9+9-bit scheme:  
\[\text{Effective Bits}/\text{Round}=9\times 0.582=5.24\text{ bits (per iteration)}\] \[\text{Effective Bandwidth}=4687\times 0.582\approx 2727\text{ KB/s}\]  
This reveals that while the 9+9-bit scheme achieves a higher raw throughput, its effective bandwidth (factoring in accuracy) also remains superior to that in the 10-bit scheme. However, the 10-bit scheme retains an advantage in scenarios requiring reliable single-round decoding (e.g., short-lived channels with no retransmission). The choice ultimately depends on whether the application prioritizes raw speed or guaranteed correctness. The adoption of huge pages further enhanced the throughput and stability. Huge pages reduce TLB misses and maintain consistent memory access timing, benefiting both accuracy and stealth. Moreover, using varied numbers of cache line accesses per iteration increases the unpredictability of the access patterns, improving the stealth against side-channel detection mechanisms. Unlike traditional binary encoding, our method minimizes observable LLC misses and system-level anomalies, making it more resilient against detection through performance monitoring tools. Overall, the multi-line encoding approach not only provides a higher throughput and accuracy but also expands the covert channel's capacity for efficient, robust, and stealthy data exfiltration.