Design of a New Lightweight Hash Function FLUX-128 and Experimental Evaluation of Its Diffusion and Statistical Properties

The rapid growth of the Internet of Things and embedded platforms increases the demand for cryptographic primitives that provide adequate security under strict resource constraints. This paper introduces FLUX-128 (Fast Lightweight Universal miXing), a new lightweight hash function targeting constrained devices. FLUX-128 is built on a modified sponge construction with a 216-bit state, a 72-bit absorption rate, and a 128-bit tag length. Its main design feature is an additional lightweight diffusion function G applied before the core transformation F, improving mixing while keeping the architecture compact. Diffusion was evaluated via the Strict Avalanche Criterion (SAC) on 5000 messages using systematic single-bit input inversions and a corresponding probability matrix of output-bit changes. In addition, the concatenated output bitstream was tested with the NIST Statistical Test Suite, where all reported p-values exceed the 0.01 significance threshold. Overall, the results provide empirical evidence of near-ideal bit mixing and the absence of pronounced statistical defects within the adopted experimental setup. Together with the security objectives defined by the 128-bit output and the 144-bit sponge capacity, these results support FLUX-128 as a promising lightweight hash construction for integrity-oriented applications in resource-constrained IoT environments. The SAC and NIST STS results are considered complementary experimental evidence of the expected cryptographic behavior rather than stand-alone proofs of resistance to all classes of cryptanalytic attacks.