QLW: a lightweight block cipher with high diffusion

Lightweight block ciphers are critical for ensuring secure data transmission in resource-limited Internet of Things (IoT) devices. In designing secure and efficient lightweight block ciphers, balancing diffusion property and resource consumption becomes a key metric. This paper proposes QLW, a highly diffusive lightweight block cipher, designed to meet the growing security needs of resource-constrained devices. QLW employs a combined variant form of generalized Feistel structure (GFS) and Lai–Massey structure as its underlying structure. The QLW round function adopts a GFS, refined into a double half-round structure. The branch XOR and F-function utilize the Lai–Massey structure. Under the combined effect of both, QLW achieves full diffusion with just two rounds. Meanwhile, the QLW cipher uses a standard genetic algorithm (GA) to optimize a 4-bit S-box, ensuring robust security. The final S-box design occupies only 15.01 gate equivalents (GE) and requires eight logic gates, minimizing hardware overhead. Moreover, QLW achieves high diffusion with low-resource consumption using a linear matrix built from bitwise operations and logic gates. Furthermore, the QLW cipher increases the unpredictability of the rotation by incorporating a dynamic round constant T from the key schedule, enhancing resistance to algebraic attacks. Finally, the QLW is subjected to a security evaluation and hardware implementation. The results demonstrate that the hardware implementation of QLW requires only 1655.26 GE of area, consumes 7.37 μ J/bit of energy, and is resistant to known attacks such as differential cryptanalysis, linear cryptanalysis, and integral attack, with good security redundancy.