Separating hash families with large universe II

Abstract

For fixed integers $t,k\ge 2$, put $N=(t-1)(k-1)+1$. We prove that the maximum universe size of a $t$-perfect hash family of length $N$ over an alphabet of size $q$ satisfies $p_t(N,q)\ge q^{k-o(1)}$. Together with monotonicity in the length, this gives a positive answer to a question of Blackburn, Etzion, Stinson and Zaverucha for every choice of feasible parameters. Our proof combines the Nash–Williams–Tutte theorem, a graph-theoretic elimination argument, and a solution-free-set theorem established in our previous work.