## 4 Experimental Results and Discussion
### Performance Comparison of NTSA with TEA, XTEA and XXTEA  
Table 2 and 3 presents the encryption and decryption times of the various security algorithms for 48-bit key with varying file sizes from 0.37 kilobytes to 26.7 kilobytes. It is evident from Table 2 that the encryption time for text files using the proposed method NTSA was lower than the other existing security algorithms. NTSA achieved an encryption time of 0.041 ms for a 0.37 kB text file which is much lower compared to 0.059 ms obtained by the TEA algorithm. The two other variations of TEA, XTEA and XXTEA had much higher encryption times because of their complexity in design and implementation. It is observed from the results that, even when the text file size increased, NTSA maintained a lower encryption time compared to the other existing security encryption schemes. NTSA achieved a much lower encryption time of 0.857 ms, 1.211 ms and 1.603 ms for text file size  
Figure 6: Structure of NTSA decryption algorithm. 12.2 kB, 16.2 kB, and 26.7 kB, respectively. This asserts the excellent performance of NTSA even with higher text file sizes. From the results presented in Table 3, it is evident that NTSA achieved a lower decryption time for various text file sizes compared to the other three existing security algorithms in IoT networks. NTSA achieved a decryption time of 0.055 ms for a 0.37 kB text file, which is much lower than the decryption time achieved by other algorithms. For higher file sizes of 12.2 kB, 16.2 kB and 26.7 kB, NTSA achieved 0.890 ms, 1.234 ms, and 1.645 ms decryption times, respectively. So even with higher text file sizes, NTSA achieved lower decryption times similar to the results obtained during encryption. Lower encryption and decryption times are a very important parameter determining the efficiency of a security algorithm in an IoT network. With most of the devices having limited computational capabilities, it is very much required to have a security algorithm that can provide maximum security with less complexity and minimum encryption and decryption times. Thus, the results obtained from our experiments with 48-bit key encryption confirms that the proposed method achieves much lower encryption and decryption times compared to the existing security algorithms in IoT networks. This result is achieved, especially due to the simplicity in design of the proposed algorithm, without compromising the strength in security. The improved strength in security of the algorithm was later verified using the avalanche effect parameter. With lower encryption and decryption time, this algorithm would be highly beneficial for the users to transmit text files through the IoT networks more efficiently. Tables 4 and 5 present the comparison of encryption and decryption time of NTSA with TEA, XTEA and XXTEA for a 128-bit key with varying file sizes from 0.37 kilobytes to 26.7 kilobytes. It is interesting to observe from the results presented in Table 4 that with a larger key size, NTSA achieved lower encryption time compared to all the existing security algorithms in IoT networks. The encryption time for a text file of size 0.37 kB with 128-bit key is 0.51 ms for NTSA which was much lower compared \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**FILE SIZE** & \multicolumn{4}{c}{**ENCRYPTION TIME (in milliseconds)**} \\ \hline
**(IN KILO BYTES)** & **TEA** & **XTEA** & **BLOCK TEA (OXTEA)** & **NTSA** \\ \hline
0.37 & 0.059 & 0.174 & 0.083 & 0.041 \\
0.95 & 0.125 & 0.244 & 0.155 & 0.112 \\
1.6 & 0.214 & 0.451 & 0.271 & 0.201 \\
2.6 & 0.351 & 0.683 & 0.429 & 0.289 \\
6.8 & 0.771 & 1.384 & 1.768 & 0.551 \\
8.6 & 0.817 & 2.120 & 1.192 & 0.801 \\
12.2 & 0.916 & 2.306 & 1.379 & 0.857 \\
16.2 & 1.544 & 3.744 & 1.981 & 1.211 \\
26.7 & 1.802 & 4.176 & 2.712 & 1.603 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Encryption time for key size of 48 bits.