1---2id: H153title: A single-bit message difference reaches full avalanche within a small number of steps4axis: C5kind: sha2566statement: The mean fraction of flipped state bits after s steps reaches 0.49 within s* steps of the compression function7 for a single-bit difference in W_0 (s* to be measured) and the random-oracle control is at 0.5 from step 1.8motivation: Research question C1 (regularities of reduced rounds).9assumptions: 2000 random messages per configuration.10expected_contribution: Diffusion heatmap and s*.11related_work:12- nist2015fips18013- gilbert2003security14possible_counterexamples: Flip ratio plateauing below 0.5 (would indicate a structural weakness).15verification_strategy: experiments/reduced_round_sha256/diffusion.py16computational_budget: minutes17status: running18classification: pending19evidence: []20verdict: pending21---2223# H15 — A single-bit message difference reaches full avalanche within a small number of steps2425The mean fraction of flipped state bits after s steps reaches 0.49 within s* steps of the compression function for a single-bit difference in W_0 (s* to be measured) and the random-oracle control is at 0.5 from step 1.26