Using the smoothness of p-1 for computing roots modulo p

Abstract

We prove, without recourse to the Extended Riemann Hypothesis, that the projection modulo $p$ of any prefixed polynomial with integer coefficients can be completely factored in deterministic polynomial time if $p-1$ has a $(\ln p)^{O(1)}$-smooth divisor exceeding $(p-1)^{{1/2}+\delta}$ for some arbitrary small $\delta$. We also address the issue of computing roots modulo $p$ in deterministic time.