# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Feistel Network (FN)
It is not fully optimized for 64-bit processors, impacting performance on some hardware. It consumes more CPU cycles than some lightweight ciphers and requires further cryptanalysis testing for advanced attack resistance. Its complex implementation with multiple S-boxes and shuffle layers makes deployment challenging. Additionally, real-world performance in IoTs environments needs further evaluation. The LCA [35] (Lightweight Cryptographic Algorithm) is designed to meet the security needs of IoTs and wireless sensor networks with highly constrained resources. It utilizes a Feistel structure, which enables efficient encryption and decryption processes with a 64-bit block size and 256-bit key. LCA incorporates a compact 4-bit S-box with high non-linearity to ensure confusion and a mix of operations such as XOR, addition, and subtraction to ensure diffusion, as depicted in Figure 27. The algorithm is optimized for both software and hardware implementations, ensuring energy efficiency and fast execution. LCA provides strong resistance to cryptanalytic attacks such as linear and differential attacks, making it suitable for applications in environments where power and computational resources are limited. The design principles of simplicity and low resource usage ensure that it can be deployed effectively in various IoTs applications. The LCA algorithm has limited cryptanalysis testing, making its resistance to advanced attacks uncertain. Its dual-key structure (256-bit) adds complexity in key management. While the bit-slice implementation improves efficiency, it may not be optimized for all hardware. The multiple algebraic operations per round increase computational overhead, and its scalability for ultra-low-power devices is limited compared to simpler ciphers. Figure 26: The FlexAEAD encryption diagram. The paper proposes a modification to the SIMECK 32/64 [36] block cipher's round function to enhance its security and performance, specifically targeting improvements in the avalanche effect and runtime efficiency. The original round function on the identified area A was modified as represented in Figure 28 area B by adjusting circular shift constants and altering the shift direction, achieving a significant increase in the avalanche effect (up to 54.67% on average) compared to the original 48.33%. Additionally, the modified algorithm showed improved runtime performance, reducing execution time from 2.44 ms to 1.39 ms. The study also tested the randomness of the modified SIMECK, showing a slightly lower \(p\)-value (0.46931) compared to the original (0.51512), indicating that the modification somewhat affects the algorithm's randomness. Overall, the study concludes that the modified SIMECK 32/64 is more secure and performs better than the original, making it a promising candidate for use in IoTs applications, where both security and efficiency are critical. The improved SIMECK algorithm has increased computational complexity and reduced randomness, which may impact security. While it improves the avalanche effect (54.67%), it comes at the cost of slower processing time. Its resistance to cryptanalytic  
Figure 28: Modification of SIMECK round function. Figure 27: Overall scheme for LCA encryption. attacks remains unverified, and the key schedule may inherit security weaknesses from SPECK. Further evaluation is needed to confirm its overall security. TED [37] is a LWBC specifically designed for IoTs devices, focusing on security and energy efficiency. The cipher employs a Feistel structure and operates with a 64-bit plaintext block and a 128-bit key across 26 rounds. TED integrates a 4 \(\times\) 4 bit S-box, modular addition, and bit permutation to enhance security while minimizing memory usage and energy consumption, as demonstrated by Figure 22:0 It is optimized to resist side-channel attacks (SCAs) through a bit-slice implementation of the S-box, preventing cache-timing attacks.