Implementing Lattice-Based PQC on Resource-Constrained Processors: - A Case Study for Kyber/Saber's Polynomial Multiplication on ARM Cortex-M0/M0+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$+$$\end{document}.