# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Addition-Rotation-XOR (Arx)
A limitation of DABC is its reliance on the ARX-based structure, which, although efficient, may still be vulnerable to certain advanced cryptanalytic techniques such as differential and linear attacks, despite its improved diffusion and dynamic components. While the dynamic permutation layer enhances the cipher's security by introducing greater uncertainty, it also adds complexity to its analysis. Furthermore, the cipher's performance in resource-constrained environments could be impacted as the number of rounds increases or when adapting it to higher security requirements, potentially leading to greater hardware resource consumption. SAECHAM [56] is a variant of the ARX-based block cipher CHAM64, designed to improve both encryption speed and security. By altering the order of operations and adjusting the rotation amounts in CHAM64, SAECHAM reduces the number of operations, resulting in faster encryption on platforms such as AVR, MSP430, ARM Cortex-M3, and  
Figure 40: The operation process of the round function in DABC. Figure 39: The step structure of LiARX. Cortex-M4. The cipher supports a 64-bit block size and a 128-bit key, with 88 rounds of encryption. SAECHAM outperforms CHAM64 in speed, demonstrating up to 14.7% faster performance on MSP430 and up to 33.2% faster on ARM Cortex-M4. Additionally, it shows improved resistance to both differential and linear cryptanalysis. The cipher is particularly suited for resource-constrained environments such as IoTs devices while maintaining strong security. A limitation of SAECHAM is its reliance on the ARX structure, which, while efficient, may still be vulnerable to certain cryptanalysis techniques, particularly as cipher complexity increases. The reduction in operations achieved by adjusting rotation amounts, although improving speed, might result in potential trade-offs in security under advanced attacks. While SAECHAM improves CHAM64's performance and security, the design may still face challenges when scaled to larger block sizes, such as in CHAM128/*, where finding the optimal differential or linear trail remains an open problem. SAND-2 [57] is an optimized version of the ARX-based LWBCSAND, designed to address performance issues such as slow diffusion and ineffective rounds in certain conditions. The improvements include replacing AND operations with NAND operations and introducing dynamic round functions. The cipher also benefits from linear permutations P1 and P2 in the round functions, as shown in Figure 41, enhancing the diffusion rate. As a result, SAND-2 achieves full diffusion in just 4 rounds, significantly faster than SAND, which requires 11 rounds. The new architecture also improves throughput by 10% and requires fewer hardware resources, making it well-suited for resource-constrained environments such as IoTs devices. Security analysis confirms that SAND-2 resists differential attacks more effectively, achieving higher security than its predecessor. While SAND-2 improves upon SAND in terms of performance and security, its reliance on dynamic round function calls and the introduction of additional permutations can make the cipher more complex to analyze and implement, potentially increasing the overhead in specific applications. Furthermore, despite improvements in diffusion, SAND-2 may still face challenges under certain cryptographic attacks, especially as it is optimized for hardware efficiency. The increased complexity in the round functions, although enhancing security, could also pose implementation difficulties for low resource environments when compared to simpler cipher designs. Figure 41: The modified round function in SAND-2.