## 3 Results and Discussion
### Complexity Level Estimation  
Further, the complexity level of the proposed security algorithm is also evaluated. The LFSR key generation method generates a key of size 196,608. The complexity level of the proposed method is estimated by considering three different scenarios as follows. In Case 1, if the attacker does not know about the LFSR random generation and stored color image, it takes \(2^{196,608}\) attacks to find the random key. In Case 2, if the attacker knows the color image, each pixel in the red, green, and blue planes is represented by eight bits. So, one bit of the key can be selected from one pixel in eight ways. Therefore, the total number of ways in which a key can be selected from one plane (R, G or B) is \(8^{65,536}\). Thus, the total number of ways a key can be selected from the color image is \(3\times(8^{65,536})\). Case 3 defines the scenarios as if the attacker knows the three-bit LFSR (seven sequences) and a color image, it takes seven! ways to determine each sequence. Therefore, it takes seven \(\times\) (seven!) ways to determine the sequence and extract the key. The complexity analysis in all these scenarios shows that the proposed key is robust and hard to predict. This makes the proposed algorithm applicable to the secured vehicle to vehicle communication using the visual MIMO.  
Moreover, the performance of the proposed security algorithm is compared with the existing techniques [32; 33; 34]. All these techniques are applied to a single random image to make uniform test conditions. The performances of these techniques are compared based on their key size, keyspace, and time taken for key generation, which describes their strength as in Table 2. The key size plays a crucial role in cryptographic applications. A key generation algorithm that generates a considerably large key size provides better security. It is observed that the proposed LFSR based key generation technique has a larger key size when compared to the existing technique ([32; 33]). Although the key size in [34] is larger, the strength of the algorithm is moderate indicated by its lower-key generation time when compared to the proposed technique. The key space is used to determine the strength of the generated key over brute force attacks. It is observed from Table 2 that the proposed technique provides a large key size, thus providing a large key space. In addition to that the higher key generation time certifies that the proposed key generation algorithm is strong enough against brute force attacks.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test** & **Probability** & **Proportion** & **Result** \\ \hline Frequency & 0.2133 & 10/10 & Pass \\ Block Frequency & 0.2133 & 10/10 & Pass \\ Cumulative Sums & 0.3504 & 10/10 & Pass \\ Runs & 0.3504 & 10/10 & Pass \\ Longest Run & 0.5341 & 10/10 & Pass \\ Rank & 0.0351 & 10/10 & Pass \\ FFT & 0.2133 & 10/10 & Pass \\ Non-Overlapping Template & 0.9914 & 10/10 & Pass \\ Approximate Entropy & 0.3504 & 10/10 & Pass \\ Serial & 0.9114 & 10/10 & Pass \\ Linear Complexity & 0.1223 & 10/10 & Pass \\ \hline \hline \end{tabular}
\end{table}
Table 1: National institute of standards and technology (NIST) tool validation result.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Algorithm** & **Key Size (bits)** & **Key Space** & **Key Generation Time (s)** \\ \hline LSB Absolute Difference [32] & 94,260 & \(2^{94,260}\) & 0.1494 \\ LSB Histogram [33] & 1776 & \(2^{1776}\) & 0.1521 \\ LSB [34] & 327,680 & \(2^{327,680}\) & 0.2843 \\ LFSR (Proposed) & 196,608 & \(2^{196,608}\) & 0.3068 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparisons of the proposed key generation with the existing algorithm.