# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Substitution-Permutation Network (SPN)
The RARE algorithm's limitations include high computational complexity due to its outer-inner structure, requiring at least 9 rounds for linear cryptanalysis resistance and 13 rounds for differential attacks. Its encryption and decryption speeds are slower than some existing lightweight ciphers, impacting real-time IoTs applications. The chaotic Ikeda-based key scheduling enhances security but adds implementation complexity. While optimized for image encryption, its efficiency for securing text and binary data in IoTs remains uncertain. The SAT_Jo [13] block cipher is designed for secure data encryption in IoTs environments, particularly for tag-based applications with resource-constrained devices. Built on a substitution-permutation network (SPN) structure, SAT_Jo employs a 64-bit block size and 80-bit key, performing 31 rounds of encryption as illustrated in Figure 6. It features a 4 \(\times\) 4 5-box derived from the Galois Field (GF(2*)), providing non-linear transformations to strengthen security. A permutation layer, characterized by bijective mappings, ensures additional diffusion. The cipher uses a novel key scheduling technique based on Fibonacci sequences and includes a post-whitening step to enhance the final output. SAT_Jo is specifically optimized to balance security and efficiency, offering adequate protection against common cryptographic attacks while maintaining low resource usage, making it ideal for IoTs applications where computational power and memory are limited. The SAT_Jo algorithm has limitations, including high computational overhead due to its 31 encryption rounds, making it resource-intensive. Its energy consumption may be a concern for ultra-low-power IoTs devices, and its memory requirements for the S-Box and key scheduling could challenge constrained systems. While it enhances security with an SPN structure and key whitening, further cryptanalysis is needed to confirm its resistance  
Figure 5: Outer-inner structure of RARE. Figure 6: Methodology of SAT_Jo. to advanced attacks. Additionally, its design is mainly suited for tag-based encryption, limiting its broader applicability in IoTs security. CRAFT [14] is a lightweight, tweakable block cipher designed with a strong focus on providing efficient protection against Differential Fault Analysis (DFA) attacks. It features a 64-bit block size, 128-bit key, and supports a 64-bit tweak for added security. The cipher utilizes involutory building blocks for encryption and decryption, allowing the same structure for both with minimal area overhead. CRAFT's design incorporates a mix of substitution, permutation, and key-dependent tweaks across 31 rounds as presented in Figure 7, with an additional linear round for extra security. The cipher's main strength lies in its efficient fault-detection capabilities, achieved by integrating error detection codes (EDCs) directly into the cipher structure. Security analysis confirms that CRAFT is resistant to various cryptanalytic attacks, including differential and linear cryptanalysis, and achieves robust fault protection with low implementation costs. It outperforms other lightweight ciphers in terms of area efficiency, making it an ideal candidate for use in resource-constrained environments such as IoTs applications. The CRAFT algorithm has limitations, including higher computational complexity and increased hardware overhead due to fault detection mechanisms, making it less efficient for ultra-constrained IoTs devices. It remains vulnerable to certain fault attacks such as Ineffective Fault Attacks (IFAs) and Fault Sensitivity Analysis (FSA), requiring additional countermeasures. Its encryption and decryption speed may be slower than other lightweight ciphers, and its tweakable design adds implementation complexity, making integration into existing systems more challenging. The DoT [15] cipher is a highly efficient, ultra-LWBC designed for resource-constrained environments such as IoTs and WSN. It uses a 64-bit block size and supports both 80-bit and 128-bit keys.