# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Substitution-Permutation Network (SPN)
Furthermore, while ULM shows resilience to linear and differential attacks, it lacks comprehensive evaluation against side-channel or algebraic attacks, which are critical for many IoTs applications. LAO-3D [23], or the 3D light algorithm operation, is a lightweight symmetric block cipher designed to enhance the security and efficiency of mobile encryption applications. It employs a 3D permutation structure, incorporating a 3D bit rotation function to strengthen the cipher's confusion and diffusion properties without increasing block or key sizes, thus maintaining computational efficiency. The cipher operates on a 64-bit block size with a 128-bit key and features 20 rounds, as illustrated in Figure 4:6 The encryption process includes key addition, non-linear S-box substitution, and a double 3D bit rotation for enhanced permutation. Security analysis demonstrates LAO-3D's resistance to differential  
Figure 4:7 The encryption and decryption of 3D RECTANGLE. and linear cryptanalysis, achieving high non-linearity, a 50% bit error rate, and excellent randomness. Performance tests indicate that it has a competitive encryption speed and throughput compared to existing ciphers, making it ideal for mobile and IoTs applications requiring both strong security and efficiency. Additionally, the cipher was successfully implemented in a mobile encryption application, further proving its practical applicability. The LAO-3D algorithm, despite its advantages in mobile encryption, has several limitations. The 3D permutation design adds computational complexity, which may increase encryption and decryption time, affecting real-time performance in resource-constrained environments. Although it achieves strong security, the trade-off between security and efficiency remains a concern, as stronger diffusion mechanisms can lead to processing overhead. Additionally, while LAO-3D resists differential and linear cryptanalysis, further security analysis is required to confirm its resilience against emerg  
Figure 4:8 LAO-3D block cipher process. Figure 4:9 ULM diagram. Finally, its hardware implementation and energy efficiency remain untested, requiring further evaluation for IoTs and ultra-low-power applications. FUTURE [24] is an LWBC tailored for resource-constrained IoTs devices, utilizing a substitution-permutation network (SPN) structure with 32 rounds. It supports a 64-bit block size and offers key lengths of 64, 96, or 128 bits, making it flexible for varying security requirements. Each encryption round of the FUTURE cipher comprises four sequential transformations: SubCells (SCs), MixColumns (MCs), ShiftRows (SRs), and AddRoundKey (ARK) (see illustration in Figure 17), which together enhance diffusion and strengthen resistance against linear and differential attacks. The cipher is designed to achieve low memory usage, energy efficiency, and high execution speed, making it well-suited for embedded systems. Its structure and operations are kept simple to reduce computational complexity and facilitate implementation on low-power hardware, providing an effective balance between performance and basic security. Despite its efficiency, FUTURE has several limitations. It lacks comprehensive cryptanalytic evaluation, such as resistance to differential, linear, or side-channel attacks, which raises concerns about its robustness. The algorithm's focus on lightweight performance may result in a reduced security margin, particularly in scenarios requiring long-term data protection. Additionally, the key scheduling mechanism is not thoroughly analyzed, potentially exposing it to key-related vulnerabilities. IVLBC [25] (Involutive Lightweight Block Cipher) is a compact, energy-efficient block cipher tailored for resource-constrained IoTs devices. It operates on a 64-bit block size with either 64- or 128-bit keys and leverages an involutive design, meaning encryption and decryption use the same structure, reducing hardware complexity.