# Design of a Lightweight Cryptographic Scheme for Resource-Constrained Internet of Things Devices
## 3 Block Cipher SLA
### Permutation Layer
According to the Walsh Spectrum, this property is evaluated as follows [31]: \[[k_{63}k_{62}k_{61}k_{60}k_{59}]=[k_{63}k_{62}k_{61}k_{60}k_{59}]\bigoplus\ \ RC^{i} \tag{5}\]6 (20)
7. Algebraic immunity. Algebraic immunity of a Boolean function \(\mathbb{F}\in\mathbb{F}_{\text{n}}\) is defined as the least degree of all annihilators of \(\mathbb{f}\) or \(1+\ \mathbb{f}\) is designated by notation \((\mathcal{AI}\left(\mathbb{f}\right))\)[32; 33; 34]. 8. Global avalanche criterion (GAC). The global avalanche criterion is presented through two indicators [35]. First, the absolute indicator, denoted by MAXAC. \[[k_{63}k_{62}k_{61}k_{60}k_{59}]=[k_{63}k_{62}k_{61}k_{60}k_{59}]\bigoplus\ \ RC^{i} \tag{5}\]7 (21) Second, the sum \(-\) of \(-\) squares indicator, denoted by \(\sigma\). \[[k_{63}k_{62}k_{61}k_{60}k_{59}]=[k_{63}k_{62}k_{61}k_{60}k_{59}]\bigoplus\ \ RC^{i} \tag{5}\]8 (22) When cryptographic functions have achieved low values of both indicators, they reach the best diffusion. 9. Propagation criterion. The propagation criterion of vectorial Boolean function \(\mathbb{F}\in\mathcal{F}_{\text{n,m}}\) satisfies the \(\mathcal{PC}(\mathbb{I})\). This property is from the Walsh spectrum in the manner outlined below [36; 37]: \[[k_{63}k_{62}k_{61}k_{60}k_{59}]=[k_{63}k_{62}k_{61}k_{60}k_{59}]\bigoplus\ \ RC^{i} \tag{5}\]9 (23)
10. Linear potential. The linear potential of a vectorial Boolean function \(\mathbb{F}\in\mathcal{F}_{\text{n,m}}\) is a metric of linearity that fulfills \(2^{-\text{n}}\leq\mathcal{LP}\leq 1\)[38]. Therefore, the upper bound is met when \(\mathbb{F}\) is linear or affine, whereas the tight bound holds if and only if \(\mathbb{F}\) exhibits maximal nonlinearity (\(\mathbb{F}\) is bent), and it is defined as \[\text{K}^{i}=k_{63}k_{62}\cdots k_{0} \tag{6}\]0 (24)
11. Differential potential. The differential potential of a vectorial Boolean function \(\mathbb{F}\in\mathcal{F}_{\text{n,m}}\) is a gauge of resistance to differential attack where \(2^{-\text{m}}\leq\mathcal{DP}\leq 1,\ \text{and the lower bound is valid if }\mathbb{F}\) is bent and the upper bound is met when \(\mathbb{F}\) is linear or affine, and it is defined as \[\text{K}^{i}=k_{63}k_{62}\cdots k_{0} \tag{6}\]1 (25)
12. Fixpoints and negated-fixpoints. A vectorial Boolean function \(\mathbb{F}\in\mathcal{F}_{\text{n,m}}\) represents the fixpoints of \(\mathbb{F}\), that is, \(\{\text{x}|\text{F}(\mathfrak{x})=\text{x}\}\) and negated-fixpoints of \(\mathbb{F}\), that is \(\{\text{x}|\text{F}(\mathfrak{x})=\text{x}\}\). ### The Effect of the Avalanche

A cipher with a strong avalanche effect has a better chance of resisting most possible attacks, since even minor input changes have a big impact on the output. In SLA, by changing just one bit in the plaintext/key bits of the input in SLA, the output was observed. It was observed that more than half of the ciphertext bits are impacted by a single bit change in the SLA cipher's key. Tables 8 and 9 show the effect of the avalanche. This is the intended outcome in the design of SLA in this paper [39]. ### Performance Evaluations

Here, we analyzed the performance of SLA further. Based on the AMD Ryzen 45500U processor with 64-bit 4 GHz, Table 10 provides a thorough comparison between SLA and other contenders. ### Results

An analysis of the probabilistic linear relations shows that the nonlinearity property (item \(\mathcal{NL}\) in Table 2) is four, while the highest value for a Sbox_Nibble is six. The linear potential (item \(\mathcal{LP}\) in Table 2) is 0.25 over the best known for a Sbox_Nibble with four input variables, which is 0.0625. The findings demonstrate that a \(4\times 4\) Sbox_Nibble Layer offers good resistance to linear attacks. Investigation and analysis of the probabilistic differential relations of SLA were undertaken to establish its resistance to probabilistic differential attacks. The result shows that the linearity distance Sbox_Nibble (item \(\mathcal{LD}\) in Table 2) is two over a maximal value of four.