This work proposes an algorithm and circuits for a cryptographic wake-up receiver (WuRX). Main contributions include 1) an algorithm and its implementation of OTP-based wake-up code generation that enables resynchronization, 2) implementation of a physically unclonable function (PUF) for the WuRX, 3) temperature-compensated ring-oscillator circuit, and 4) transition-based correlator that prevents accumulation of timing error to extend frequency mismatch tolerance up to 58%.