LIBC: a low-cost lightweight block cipher for IoT application

With the rapid growth of the Internet of Things (IoT), designing lightweight block ciphers has become essential for securing resource-constrained devices. This necessitates a balance among low-cost implementation, diffusion, and security. To address this challenge, we propose a novel lightweight block cipher named LIBC, which has a 64-bit block size supporting 128-bit keys. In the nonlinear layer, we develop a four-round structure to design optimal 4-bit S-boxes, generating 8,832 S-boxes that provide excellent security and compact hardware overhead. To balance diffusion with resource efficiency, we use a 4 x 4 almost MDS matrix and introduce a type of optimal involutive nibble-based permutations based on SAT. This ensures that LIBC achieves full diffusion within the minimal rounds while providing the required security. Combining the above design, LIBC's encryption and decryption circuits become nearly identical, requiring only 24 additional XOR gates for decryption. Experimental results show that LIBC exhibits strong diffusion and avalanche characteristics, providing sufficient security against various known attacks. Regarding hardware performance, the single-round iteration of the internal state in LIBC occupies only 10.05 GE per bit, which is superior compared to the round-based implementations of Midori, PRESENT, RECTANGLE, etc.