# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Substitution-Permutation Network (SPN)
It is based on a substitution-permutation network (SPN) and utilizes prime number positions for reordering text blocks before applying encryption. PriPresent ensures data integrity by generating signatures using SHA-256, which are then used to authenticate the sender and verify the message's authenticity. The algorithm is resistant to common attacks such as replay, fabrication, and man-in-the-middle attacks. Performance tests demonstrate that PriPresent offers better throughput compared to the PRESENT cipher while maintaining similar encryption and decryption times, making it an efficient solution for secure communication in IoTs networks. The PriPresent algorithm's limitations include high computational complexity due to its 31-round structure and increased encryption and decryption time from prime number-based block ordering. Its use of SHA-256 for authentication adds computational overhead and memory usage, making it less suitable for ultra-low-power IoTs devices. Additionally, its security against emerging cryptographic attacks remains unverified, requiring further analysis. The 3D RECTANGLE [21] cipher is an enhanced version of the RECTANGLE lightweight block cipher, designed to improve security without increasing block or key sizes. By incorporating a 3D bit rotation technique, it strengthens the cipher's confusion and diffusion properties. The encryption process involves 4 operations reflected in Figure 4:4 3D bit rotation, AddRoundKey, SubColumn, and ShiftRow, significantly enhancing the algorithm's resistance to cryptanalysis. Security analyses, including correlation coefficient, bit error, key sensitivity, and randomness tests, show substantial improvements in non-linearity, key sensitivity, and randomness, with the 3D RECTANGLE outperforming the original RECTANGLE cipher. Despite a slight performance trade-off due to the additional 3D bit rotation function, the 3D RECTANGLE maintains competitive encryption speeds and throughput, making it an efficient and secure option for IoTs devices that require lightweight encryption. Figure 4:5 PriPresent cipher text model. The 3D RECTANGLE algorithm's limitations include higher encryption and decryption times due to added 3D bit rotation, slightly lower efficiency compared to the original RECTANGLE, and a trade-off between security and processing overhead. Additionally, further cryptanalysis is needed to confirm its resistance to emerging attacks. The Ultra-Lightweight Method (ULM) [22] is a cryptographic design approach proposed specifically for IoTs environments that require minimal memory usage, high efficiency, and strong security. ULM combines three lightweight cryptographic techniques, as represented in Figure 15--Bitslice, Wide Trail Strategy (WTS), and involutive operations--to create a design framework that optimizes diffusion, confusion, and execution speed. It uses a 64-bit block size, an 80-bit key, and operates over 15 SPN-based rounds, each including subkey mixing, substitution using a 4 \(\times\) 4 S-box, and an involutive bit permutation. This structure enables the implementation of block ciphers with low RAM and ROM consumption, fast processing time, and robust resistance to linear and differential attacks. A reference cryptosystem built using ULM demonstrates superior performance compared to existing lightweight methods, making ULM an effective foundation for secure encryption in constrained IoTs devices. While ULM offers an efficient and compact approach for designing lightweight ciphers, it has some limitations. Its reliance on small 4 \(\times\) 4 S-boxes and simplified logic operations may result in reduced non-linearity and potential vulnerability to advanced or future cryptanalytic methods. The method is primarily evaluated on 8-bit microcontrollers, which may limit its portability and optimization across more diverse or modern hardware architectures.