# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Hybrid  
This paper presents a hybrid [58] cryptographic algorithm combining the PRESENT block cipher and Salsa20 stream cipher as represented in Figure 42, enhanced by a chaotic system to generate pseudo-random keys. The algorithm is designed for lightweight applications, particularly in constrained devices such as IoTs, where efficiency and security are critical. The hybrid approach aims to balance the computational speed and security of both cryptographic systems by reducing the number of rounds in the PRESENT cipher while leveraging Salsa20 for fast key stream generation. Additionally, the chaotic system increases the complexity of the generated keys, making them less predictable and enhancing the algorithm's robustness against attacks. The proposed algorithm was evaluated using the NIST statistical test suite, showing a higher degree of randomness compared to the standard PRESENT cipher. The experimental results demonstrate that the hybrid algorithm performs efficiently with reduced execution times, offering a secure solution suitable for resource-limited devices. The Hybrid PRESENT and Salsa20 algorithm has limitations, including a trade-off between security and speed, increased implementation complexity, and potential security weaknesses due to reducing PRESENT rounds from 31 to 20. While the chaotic system enhances key generation, its effectiveness against advanced attacks remains unverified. Additionally, the algorithm's hardware efficiency and power consumption require further evaluation for ultra-low-power IoTs applications. FeW [59] is an LWBC designed for efficient encryption in software-based environments, with a 64-bit block size and 80/128-bit key lengths. It combines a Feistel and generalized Feistel structure, referred to as Feistel-M, to enhance security against cryptanalytic attacks, such as differential, linear, impossible differential, and zero correlation attacks. The cipher operates in 32 rounds and utilizes a round function with two weight functions (WF1 and WF2) to improve the cipher's resistance to cryptanalysis. FeW employs a key schedule similar to the PRESENT cipher, ensuring strong security for both 80-bit and 128-bit keys. Its efficiency is enhanced by the use of a 4x4 S-box and cyclic shifts, with the decryption algorithm using the same round function as encryption but in reverse. Security analysis shows that FeW is resistant to multiple attacks, including differential and linear cryptanalysis, and achieves high resistance with a lower probability of successful attacks as rounds increase. Figure 42: Block diagram of Hybrid PRESENT and Salsa20. FeW has high computational and key schedule complexity, potentially leading to higher energy consumption. While resistant to known attacks, its security against advanced attacks is unverified. Additionally, real-world performance data in constrained environments is limited. ECLBC [60] is an LWBC designed for IoMTs (Internet of Medical Things) applications that prioritizes both security and reliability, addressing the challenges posed by channel interference in resource-constrained environments. The cipher incorporates error detection and correction mechanisms, ensuring the integrity of transmitted ciphertext. ECLBC transitions from a Feistel structure to a substitution-permutation network (SPN) and integrates the AND-rotation-XOR (AND-RX) operation to strengthen security while optimizing resource usage. The cipher supports error detection and correction through linear block codes, ensuring that data corruption due to interference can be identified and corrected. Performance analyses, including ASIC hardware implementation, show that ECLBC provides robust security with a high avalanche effect and resistance to cryptanalytic attacks, including differential, linear, and related-key differential cryptanalysis. Additionally, ECLBC achieves a balanced trade-off between security and resource efficiency, making it an effective solution for IoMT devices that require secure and reliable data transmission.