# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Generalized Feistel Network (GFN)
IIoTBC demonstrates strong avalanche, algebraic, and impossible differential resistance but lacks independent third-party cryptanalysis or open-source implementations for broader validation. While the flexible dual-system design improves adaptability, it adds structural complexity. Side-channel protection is considered only in System B via bit-slicing, leaving System A potentially vulnerable. Moreover, the 32-round count, while securing full diffusion, may increase latency and power cost in ultra-constrained nodes. \(\upmu\)2 [50] is a 64-bit LWBC with an 80-bit key, built on a Type-II generalized Feistel structure using a 16-bit ultra-lightweight SPN-based F-function. It applies PRESENT's s-box and a novel permutation layer within the F-function and follows a modified PRESENT-like key schedule. Designed for constrained devices, \(\upmu\)2 achieves high security margins against  
Figure 37: The encryption procedure of GFLE. known attacks, including differential, linear, integral, and algebraic cryptanalysis, while maintaining simplicity and strong pseudorandomness as validated by NIST STS. While \(\upmu\)2 shows strong theoretical resistance, its security relies heavily on design intuition and has yet to undergo extensive third-party cryptanalysis. The performance comparison is limited to software benchmarks on x86 CPUs, with no hardware GE or FPGA synthesis results provided. Further studies are required to confirm \(\upmu\)2's robustness in side-channel scenarios and its efficiency in constrained hardware environments. LPHD [51] is a 64-bit LWBC with a 128-bit key, based on an 8-branch generalized Feistel structure (Type-2 GFS). It integrates a low-power 4-bit S-box, optimized bit permutation, and a two-stage permutation layer (TP) for rapid diffusion. The cipher achieves full diffusion in just 4 rounds and employs a non-linear key schedule that reuses the encryption core, enhancing security while reducing hardware cost. LPHD achieves only 1276 GEs and 1.914 \(\upmu\)W of power consumption on UMC 0.18 \(\upmu\)m, outperforming SKINNY, PRESENT, and BORON in both area and energy efficiency. It has been practically implemented in a smart door lock platform, encrypting identity-recognition data on STM32-based hardware. Although LPHD achieves excellent hardware efficiency and demonstrates strong resistance to differential, linear, and impossible differential attacks, it has not been subjected to third-party or open-source cryptanalysis. Its security relies heavily on internally defined parameters (e.g., chaotic constant generation and round permutation), and while its S-box and F-function are carefully optimized, the lack of independent validation may limit its adoption in high-assurance environments. Furthermore, its resistance to side-channel and fault attacks remains untested, and its practical application is limited to specific platforms. Tweakable TWINE (T-TWINE) [52] is a dedicated tweakable block cipher (TBC) based on the lightweight cipher TWINE, designed to support secure encryption with an additional 64-bit public input called a tweak. Built upon a generalized Feistel structure (GFS), T-TWINE maintains TWINE's original 64-bit block size and key options (80-bit or 128-bit) while introducing a lightweight permutation-based tweak schedule. This tweak mechanism is independent of the key schedule and efficiently reuses TWINE's components, preserving the 36-round structure. Security evaluations show strong resistance to differential, linear, integral, and impossible differential attacks, especially in chosen tweak scenarios. In hardware, the area overhead is minimal, requiring only \(\sim\)2180 gate equivalents (GEs) for T-TWINE-80, compared to \(\sim\)1627 GE for the original TWINE-80. This modest increase makes it one of the most efficient tweakable ciphers built on a GFS framework. While T-TWINE offers solid security and area-efficient tweakable encryption, it comes with certain limitations.