# Design Trends and Comparative Analysis of Lightweight Block Ciphers for IoTs
## 4 Related Work
### Generalized Feistel Network (GFN)
practical, its reliance on lightweight structures and compact design may come at the cost of a smaller security margin compared to more robust lightweight ciphers. HDLBC [47] (High Diffusion Lightweight Block Cipher) is a NAND-RX-based LWBC optimized for IoTs devices, offering a strong balance between high diffusion and low area consumption. It adopts a 4-branch generalized Feistel structure (GFS) with only two F-functions (RA1 and RA2), as depicted in Figure 36, built using NAND operations, minimizing hardware footprint while improving diffusion. HDLBC supports 64-bit plaintext and 64-/128-bit keys, running for 25 or 32 rounds, depending on key size. Its hardware implementation is highly efficient, requiring only 1248 GEs on 0.18 \(\upmu\)m CMOS and achieving 256 Kbps throughput at 100 KHz. HDLBC passes stringent avalanche, differential, linear, integral, and zero correlation cryptanalysis tests, showing strong resistance to a wide range of attacks. With its compact design and strong security properties, HDLBC is well-suited for resource-constrained environments such as RFID and IoTs systems. Despite its strengths, HDLBC has a few limitations. Its design focuses heavily on hardware efficiency, which may limit its performance or applicability in software-based or hybrid platforms. While it achieves full diffusion in just 3 rounds, this also means its security margin is relatively tight, with 25 rounds total--leaving less buffer against future cryptanalytic advancements. Additionally, its use of simple NAND-based F-functions, though cost-effective, may offer less flexibility or adaptability compared to more complex non-linear components used in other ciphers. These trade-offs make HDLBC ideal for specific constrained environments but less suitable for broader or evolving cryptographic needs. GFLE [48] is a low energy LWBC designed for IoTs applications, aiming to minimize energy consumption while maintaining high security. Based on a variant of the generalized Feistel structure (GFS) with 4 branches, as confirmed by Figure 37, GFLE incorporates a simplified Lai-Massey structure to enhance diffusion efficiency, achieving full diffusion in just 3 rounds. The cipher uses a low energy, gate-level S-box optimized through a depth-first strategy for improved hardware performance. GFLE consumes only 1596 gate equivalents (GEs) in its ASIC implementation and reduces energy consumption by 61.59% compared to SKINNY, making it highly efficient for resource-constrained devices. It provides strong resistance against cryptographic attacks such as differential, linear, and  
Figure 36: The round function of HDLBC. impossible differential attacks, making it well-suited for environments such as RFID tags and wireless sensor nodes. Despite its low energy consumption and strong cryptographic properties, GFLE's reliance on a smaller number of branches in the GFS structure, while beneficial for energy efficiency, may limit its security under future cryptanalysis techniques. The reduced number of rounds required for full diffusion could potentially expose the cipher to attacks that exploit this faster diffusion process. Additionally, while the cipher's S-box design and permutation layers are optimized for low energy, the complexity of implementing and optimizing these components for specific hardware could be a challenge in more diverse environments. IIoTBC [49] is a 64-bit LWBC with a 128-bit key, built on a flexible generalized Feistel structure that supports 8- or 4-branch modes to match 8- or 16-bit MCUs. It features a lightweight 4 \(\times\) 4 S-box with excellent cryptographic properties (DU = 4, NL = 4, AD = 3) and alternates involutive/non-involutive permutations for rapid diffusion. The cipher achieved strong avalanche performance and was implemented in ASIC using 0.13 \(\upmu\)m tech, with GE \(\sim\)1769 for System A and \(\sim\)2338 for System B. Throughput reached 200 Kbps at 100 MHz, and IIoTBC was practically deployed on a temperature-monitoring platform.