# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Substitution-Permutation Network (SPN)
The cipher's hardware implementation is highly efficient, with area costs lower than comparable ciphers such as PRESENT, and its simplified decryption process contributes to resource savings. Loong is suitable for environments where low memory and fast execution are critical, such as in IoTs applications. The Loong algorithm has limitations, including higher computational complexity due to dual SubCells operations per round and significant hardware overhead, with Loong-128 consuming 1766 GE, making it less ideal for ultra-low-power IoTs devices. Its matrix multiplications may introduce latency, and while it claims resistance to attacks, its security against emerging threats remains unverified. Additionally, its software implementation is relatively slower, affecting efficiency in speed-critical applications. ACT [18] is an ultra-LWBC designed for resource-constrained environments such as IoTs applications. It operates on 64-bit data blocks with an 80-bit key and features a substitution-permutation network (SPN) structure. ACT is designed to achieve low area and power consumption, with a gate count of just 1481 GEs and a dynamic power consumption of 30 mW. The cipher, as evidenced by Figure 11, employs a 4-bit substitution box (S-box) that minimizes linear and differential cardinalities, providing strong resistance against cryptanalytic attacks such as differential, linear, and biclique attacks. With only three rounds for complete diffusion, ACT offers excellent security performance while maintaining efficiency. Its resistance to algebraic cryptanalysis is also highlighted, with a manageable number of inequalities for its S-box. ACT's low resource requirements, along with its robust security properties, make it an ideal candidate for lightweight cryptographic applications in IoTs devices. Figure 4:0 The encryption process of Loong. The ACT algorithm has limitations, including high computational complexity due to its 31-round structure, a gate equivalent count of 1481 that may require further optimization for ultra-low-power devices, and the need for additional cryptanalysis to confirm its resistance to emerging attacks. Its key scheduling adds implementation complexity, and its real-world efficiency in IoTs applications remains unverified, requiring further hardware testing. The Improved Lightweight Encryption Algorithm (ILEA) [19] enhances the PRINCE LWBC by adding two Balanced Block Mixing (BBM) layers, one at the input and another at the output, as observed in Figure 4:1 This modification improves the diffusion of data, making the cipher more unpredictable and resistant to cryptanalysis. ILEA operates on a 64-bit block with a 128-bit key and is optimized for low-power, low latency applications, making it ideal for IoTs devices. The algorithm performs efficiently in both Python and C++ implementations, with ILEA in C++ showing a processing time of 1.6 us per round. A comparative study with other lightweight block ciphers demonstrates ILEA's superior performance in terms of encryption and decryption times. Additionally, ILEA offers enhanced security by increasing the effective key length to 256 bits, making it resistant to brute-force attacks. This makes ILEA suitable for environments requiring both speed and robust security in constrained devices. Figure 4:2 Block diagram of ACT. Figure 4:3 Encryption round of ILEA. The ILEA algorithm's limitations include a 25% increase in encryption and decryption time, which may affect real-time performance in resource-constrained devices. Its higher computational cost makes it less suitable for ultra-low-power applications, and integration challenges arise due to the complexity of its BBM layers. Additionally, while it claims strong security, its resistance to advanced cryptanalysis remains unverified. PriPresent [20] is an LWBC designed for IoTs devices, focusing on providing security services such as confidentiality and integrity while ensuring low resource usage. The cipher, as indicated in Figure 13, operates with a 64-bit block size and supports both 80-bit and 128-bit keys.