Abstract
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.