# Design of a Lightweight Cryptographic Scheme for Resource-Constrained Internet of Things Devices
## 3 Block Cipher SLA
### Permutation Layer
\begin{table}
\begin{tabular}{c c} \hline \hline
**Rounds** & **Min. No. of Active S-Boxes** \\ \hline First & 1 \\ Second & 3 \\ Third & 9 \\ Fourth & 18 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Differential Characteristics for the SLA scheme. \begin{table}
\begin{tabular}{c c} \hline \hline
**Rounds** & **Input to S-Box** & **Output of S-Box** \\ \hline First & 0000 0000 0008 0000 & 0000 0000 0003 0000 \\ Second & 0000 000 5000 5000 & 0000 0000 0000 0000 000 \\ Third & 0360 0060 0300 0360 & 04b0 000 0400 04b0 \\ Fourth & 2024 2004 0040 204c & 5051 5001 0010 5012 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Linear Characteristics for the SLA scheme. The SLA scheme is designed in such a way that it provides optimum performance. The performance of SLA and relevant LWC algorithms in software on AMD Ryzen 45500U processor are shown in Table 10. Interestingly, the execution times of SLA are small, typically less than 0.000659451 s for all of them, which would fit quite well in current IoT devices. They also require little power to process. SIMON and CLEFIA have the highest execution times of 0.02201274 s and 0.022619188 s, respectively. SLA has the highest throughput of 97,050.44167 kilobytes per second. This performance can further be improved by using faster processors in IoTs. In the autocorrelation coefficients, the absolute indicator for Sbox_Nibble is 8, and for the sum - of - squares indicator is 640. These results show that Sbox_Nibble obtains a reasonably acceptable diffusion since its absolute indicator is closer to the lower bound and is 0 compared to the upper bound, where 16 is. Similarly, the sum - of - squares indicator has theoretical bounds of 256 and 4096, and is extremely close to the 256 lower bound. When the cryptographic functions attain lower bound for both indicators, the ideal diffusion will be attained. The nibble S-box is represented using the algebraic normal form (ANF): \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{6}{c}{**Performance on AMD Ryzen 45500U Processor**} \\ \hline
**Structure** & **LWC Algorithm** & **Block Size** & **Key Size** & **Execution Time** & **Block Size** & **Key Size** \\ \hline \multirow{4}{*}{SP network} & SLA & 64 & 80 & 0.000659451 & 97050.44167 & 1631127 \\  & PRESENT & 64 & 80 & 0.015804805 & 4049.401468 & 238283 \\  & LED & 64 & 64 & 0.020789735 & 3078.442315 & 11398908 \\  & KLEIN & 64 & 64 & 0.021051668 & 3040.139201 & 689344 \\  & AES & 128 & 128 & 0.016058415 & 3985.44933 & 727652 \\ \hline \multirow{4}{*}{Feistel network} & DES & 64 & 56 & 0.015747033 & 4064.257677 & 37362051 \\  & TWINE & 64 & 80 & 0.02186244 & 2927.395138 & 2118524 \\ \cline{1-1}  & SPECK & 48 & 96 & 0.021938369 & 2917.2634 & 228783 \\ \cline{1-1}  & SIMON & 48 & 96 & 0.02201274 & 2907.407207 & 247285 \\ \cline{1-1}  & CLEFIA & 128 & 128 & 0.022619188 & 2829.456145 & 1074972 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: The Performance of SLA and Relevant LWC Algorithms in Software. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Plaintext** & **Key** & **Ciphertext** & **No. of Bits Altered** & **Rate** \\ \hline \multirow{4}{*}{0000 0000 0000 00000} & 00000 0000 & 0010 0000 0000 0000 & 0020313a0\%157 ee & 34 & 53\% \\ \cline{1-1} \cline{2-5}  & 0000 0000 0000 0000 & 0000 010 & bcc58124f3b581 de & 34 & 53\% \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The Effect of the Avalanche on SLA-80. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Plaintext** & **Key** & **Ciphertext** & **No. of Bits Altered** & **Rate** \\ \hline \multirow{4}{*}{0000 0000 00000 00000} & 00000 0000 & 858f96a55 cc4f107 & & \\  & 0000 0000 0000 0000 & 00000 & 48987e3 bd2 bc193b & 34 & 53\% \\ \cline{1-1} \cline{2-5}  & 0000 0000 0000 0000 & 0000 000 & 007818f94a2e296 & 39 & 60\% \\ \hline \hline \end{tabular}
\end{table} 
Table 9: The Effect of the Avalanche on SLA-128. \[