# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Feistel Network (FN)  
GRANULE [30] is an ultra-LWBC based on a Feistel network, designed to offer efficient encryption for embedded systems, particularly for IoTs applications. It supports 64-bit blocks with key sizes of 80 or 128 bits and utilizes 32 rounds to ensure strong security against common cryptanalytic attacks, such as differential, linear, biclique, and key collision attacks. The F function of GRANULE, as shown in Figure 22, incorporates three distinct layers: a permutation layer (PLayer), a substitution layer (SBoxLayer), and a round permutation layer (RPLayer), each contributing to the cipher's diffusion and non-linearity. The cipher's design prioritizes minimal memory usage and low-power consumption, with a small footprint in both hardware and software implementations. Its resistance to attacks is enhanced by a robust S-box and an asymmetric permutation layer, which prevent the clustering of linear and differential trails. The cipher is highly efficient, consuming fewer gate equivalents (GEs) than many other lightweight ciphers, making it suitable for resource-constrained environments. Moreover, it shows excellent performance in terms of execution time and throughput, demonstrating its viability for devices with limited computational resources. Figure 21: INLEC encryption and decryption process. The GRANULE algorithm, while robust against many cryptanalytic attacks and optimized for low-power and minimal gate count, has some limitations. Its resistance to advanced cryptanalysis relies on current methods, leaving potential vulnerability to future techniques as computational power and attack strategies evolve. Additionally, its performance trade-offs, such as higher execution time and lower throughput compared to some lightweight ciphers, may limit its applicability in environments requiring faster processing. Furthermore, its efficiency depends heavily on custom hardware designs, making it less optimal for general-purpose processors or legacy systems. Lastly, the need for 32 rounds with a strong S-box and permutation layers, though necessary for security, can demand more resources than simpler lightweight ciphers, posing challenges in resource-constrained environments. This paper enhances the DLBCL [31] (Differential LWBC Algorithm) by reducing the number of S-boxes from eight to four, as illustrated in Figure 23, effectively lowering the cost factor without significantly compromising the algorithm's security. The optimized cipher, while maintaining 32 rounds of operations similar to the original DLBCL, utilizes fewer S-boxes, which reduces the overall gate equivalents (GEs) needed for its implementation. Security analysis, including differential and boomerang attacks, demonstrates that the proposed algorithm performs similarly to DLBCL in terms of active S-boxes and rounds, with improved cost efficiency. The results show that the new design offers better resistance to the boomerang attack, with a reduced number of rounds for other ciphers such as TWINE, LBlock, and PRESENT. Additionally, the cost comparison reveals that the proposed algorithm is the most cost-efficient among several lightweight block ciphers, making it highly suitable for resource-constrained environments. The improved DLBCL algorithm reduces the number of S-boxes from 8 to 4 to lower implementation costs, achieving the lowest gate equivalent (GE) compared to similar algorithms. However, this reduction impacts security, particularly against differential cryptanalysis, as the number of active S-boxes is lower than the original DLBCL and some other lightweight ciphers. Additionally, it withstands boomerang attacks for only 3 rounds, similar to the original DLBCL, but falls behind algorithms such as TWINE and LBLOCK, which resist up to 11 rounds. This trade-off between cost efficiency and security may limit its suitability for applications requiring higher resilience against cryptanalysis. Figure 22: ‘F’ Function of GRANULE.