Differential Cryptanalysis and Cryptographic Randomness Evaluation of a Lightweight Block Cipher IIoTBC

Since traditional cryptographic algorithms often fall short in resource-constrained environments due to their high computational complexity and memory requirements, lightweight cryptography has emerged as a practical alternative. Recent advancements in lightweight block ciphers have led to the proposal of the Industrial Internet of Things Block Cipher (IIoTBC) for applications within the Industrial Internet of Things, where computational resources and energy are constrained. IIoTBC is a 64-bit block cipher algorithm that offers two design alternatives — IIoTBC-A for 8-bit microcontrollers and IIoTBC-B for 16-bit microcontrollers — allowing it to be tailored to different hardware specifications. The designers gave a 13-round impossible differential path of IIoTBC; however, the lower bounds of the number of active S-boxes along with their corresponding probability in differential cryptanalysis were not disclosed, which are critical for evaluating the cipher’s overall resistance to such attacks. This paper presents a Mixed Integer Linear Programming-based differential cryptanalysis of the IIoTBC algorithm, incorporating exact probabilities in addition to the number of minimum active S-boxes. The analysis identifies a differential characteristic with a probability of 2^{-52} over 15-round. To enhance the structural evaluation with the cipher’s cryptographic randomness, the Strict Avalanche Criterion test also complements the analysis. These combined analyses offer valuable insights into the security posture of the cipher and its reliability for practical applications.