Production Round-Constant Selection for Poseidon-128 over BN254

Poseidon-128 over BN254 has converged on a small number of canonical parameter sets, but the round-constant tables shipped by widely deployed implementations diverge subtly. We document the methodology by which a production parameter set should be selected — the Grain-LFSR procedure of Grassi et al., the security margin, and the alpha-vs-round-count tradeoff for BN254. We trace the divergence…