# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Feistel Network (FN)
Moreover, while M-XXTEA performs well in simulations, it lacks hardware implementation analysis, leaving its real-world performance on constrained embedded systems unverified. The algorithm's novel components (such as the improved S-box and key generator) would  
Figure 22:2 Basic flowchart of the improved SM4 encryption algorithm. benefit from further formal cryptanalysis, especially regarding side-channel resistance and algebraic attacks. SCENERY [40] is a 64-bit LWBC designed for both hardware and software efficiency, targeting resource-constrained IoTs environments. It uses a balanced Feistel structure as represented in Figure 32 with 28 rounds and supports an 80-bit key. The round function combines eight 4 \(\times\) 4 S-boxes with a 32 \(\times\) 32 binary matrix, enhancing confusion and diffusion. SCENERY employs bit-slice techniques to improve performance and resist side-channel attacks, and its key schedule integrates non-linear operations and dynamic permutation to strengthen security. It achieves balanced performance across platforms, requiring only 1438 GE in hardware and offering competitive encryption speed on 8-bit and 64-bit processors. While SCENERY offers a strong balance between performance and security, its balanced Feistel structure inherently slows diffusion, requiring more rounds to achieve sufficient confusion compared to SPN-based ciphers. Although the bit-slice and matrix operations improve efficiency, the cipher's reliance on small 4 \(\times\) 4 S-boxes may limit its non-linearity and resistance to emerging cryptanalysis. Additionally, its key schedule--though improved--still allows partial backward derivation, making it less robust than designs with fully non-invertible expansion methods. LiteEncrypt [41] is a 64-bit LWBC with a 128-bit key based on a Feistel structure. It employs circular shifts, XOR, and modular key addition within a 27-round encryption framework. Subkeys are derived using an LFSR-based key schedule, enhancing diffusion across rounds. Evaluated on several IoTs platforms (e.g., Arduino, ESP32), LiteEncrypt  
Figure 22:3 The M-XXTEA block cipher. demonstrates a strong avalanche effect and consistent superiority in execution time and energy efficiency compared to CLEFIA, SIT, PRIDE, and GFRX. LiteEncrypt has not undergone formal cryptanalysis against differential, linear, or algebraic attacks. While its avalanche performance and speed are promising, the lack of GE metrics or side-channel resistance evaluations limits its comparability to standard LWBCs. Additionally, the 27-round structure and reliance on LFSR-based key scheduling need further review for cryptographic strength under active adversarial conditions. RBFK [42] is an LWBC with a modified Feistel structure supporting 64-bit blocks and 128-bit keys. It integrates randomized butterfly mixing, dual S-boxes, and a genetic-inspired G-function to boost diffusion and confusion. Its key schedule and encryption rounds provide high avalanche effect and key sensitivity, validated through statistical and image-based tests on FELICS and AVR, confirming suitability for constrained IoTs platforms. Despite promising results, RBFK lacks formal cryptanalytic bounds (e.g., linear/differential resistance). The PRNG-based key schedule is not fully specified, raising concerns over deterministic entropy. GE is not explicitly reported, but FELICS-based AVR metrics (~1566 bytes of code, ~34B RAM) imply ~2200 GE, aligning it with similar LWBCs in efficiency and area cost. ANU-II [43] is an LWBC designed for resource-constrained IoTs environments, offering improvements over its predecessor, ANU. It uses a 64-bit block size and supports 80- or 128-bit keys, operating in a 25-round balanced Feistel structure with minimal cryptographic components: a single \(4\times 4\) S-box, a few shift operations, and XOR gates. ANU-II eliminates memory-intensive P-layers and employs carefully selected circular shifts to maximize active S-boxes per round, thereby increasing resistance to linear and differential cryptanalysis.