# SIMECK-T: An Ultra-Lightweight Encryption Scheme for Resource-Constrained Devices
## 2 Methodology
### Implementation
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Attack Type** & \begin{tabular}{c} **Most Freq. Output** \\ **Diff. (Hex)** \\ \end{tabular} & **Frequency** & **Percentage** \\ \hline XOR-based & \
\begin{tabular}{c} (79357347, \\ 018D019B) \\ (3257347, \\ 3479019B) \\ (86B57347, \\ CC39019B) \\ (B27D7347, \\ B079019B) \\ (00208007, \\ 4D39019B) \\ \hline \hline \end{tabular} &
\begin{tabular}{c} 1 \\ \(1.0\times 10^{-5}\)\% \\ \(1.0\times 10^{-5}\)\% \\ \(1.0\times 10^{-5}\)\% \\ \(1.0\times 10^{-5}\)\% \\ \(1.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \(2.0\times 10^{-5}\)\% \\ \hline \hline \end{tabular} \\ \hline \end{tabular}
\end{table} 
Table 9: Most frequent output differences for different attacks. #### 4.3.7 Mean Absolute Error

The mean absolute error for our cryptosystem is 85.330. The full-round SIMECK has a mean absolute error of 85.332, and the full-round TEA has a mean absolute error of 85.330. The values are identical/very close to each other. #### 4.3.8 Normalized Absolute Error

The value of the normalized absolute error obtained through our experiments is \(6.692\times 10^{-1}\). The same value is obtained for the full-round SIMECK and full-round TEA. #### 4.3.9 Maximum Difference

Our experiments resulted in a maximum difference value of \(2.55\times 10^{2}\). The value for SIMECK for all round and TEA for all round is the same. #### 4.3.10 Average Difference

Our result for the average difference is \(-7.548\times 10^{-3}\). The full-round SIMECK has an average difference of \(3.169\times 10^{-4}\), and the full-round TEA has an average difference of \(-3.505\times 10^{-3}\). All values are very close to 0. #### 4.3.11 Structural Content

During our experiments, we obtained a value of \(9.9990\times 10^{-1}\). Full round SIMECK has a structural content value of \(9.9999\times 10^{-1}\), while full round TEA has a structural content value of \(9.9995\times 10^{-1}\). #### 4.3.12 Two-Dimensional Correlation Coefficient

Through our experiments, we have obtained a value of \(2.630\times 10^{-5}\). The value for the full-round SIMECK is \(-7.306\times 10^{-6}\) and for full round TEA is \(5.086\times 10^{-6}\). These values are close to 0. #### 4.3.13 Next Pixel Change Rate

We obtained a value of \(9.9609\times 10^{-1}\) for NPCR and \(3.3463\times 10^{-1}\) for UACI. The same value was obtained for the full-round SIMECK and full-round TEA. #### 4.3.14 Correlation Coefficient

The value we obtained through our experiments is \(2.630\times 10^{-5}\). The SIMECK correlation coefficient is \(-7.306\times 10^{-6}\), while the correlation coefficient for full-round TEA is \(5.086\times 10^{-6}\). All values are close to 0. #### 4.3.15 Entropy

Our value is \(7.99999983\) (N = 8). The entropy for full round SIMECK is \(7.99999983\), and for full round TEA, it is \(7.99999981\). All values are very close to the ideal value of 8. ### TETRA Cryptographic Primitives

TETRA ciphers are stream ciphers. Both TETRA TEA2 and TEA3 pass the NIST statistical tests [71] but TEA3 behaves better when using a reduced number of rounds. Since both ciphers are considered unbroken, a reduced-round version of TEA3 has been tested as a candidate for lightweight cryptography. The measurements have been made on an Intel i7 running GNU/Linux using the reverse-engineered source code published by [32]. The results for the reduced-round TETRA TEA3 cipher are shown in Table 10.

The TETRA TEA3 cipher has 80-bit encryption keys and shows promising protection levels when four rounds are used, which makes it a bit slower than the SIMECK-R and SIMECK-T ciphers. The table used for the substitution box must be stored in memory, and has been criticized in [32], and also requires access to memory and storage space.