A lightweight hash-based quantum-resistant bidirectional authentication protocol for IoT devices integrating physical...

IoT devices face mounting security threats: tightly bounded computing budgets on one side, the imminent arrival of quantum adversaries on the other. We present a bidirectional authentication protocol that pairs Physical Unclonable Functions with hash-based primitives so that no long-term key ever sits in device-side non-volatile memory. The scheme is best characterised as Grover-tolerant rather than fully post-quantum: hash one-wayness incurs a quadratic-only slowdown under quantum search, and PUF unclonability adds a physical, non-cryptographic uniqueness assumption - we do not claim parity with NIST-standardised lattice or code-based schemes. Mutual authentication is achieved with conditional forward secrecy and weak unlinkability against external eavesdroppers, while delivering 24.3 ms latency, 15.7 mJ per-authentication energy, and a 136-byte exchange on ESP32. ProVerif symbolic verification, complemented by a sketched QROM reduction with explicit PUF-leakage modelling, covers replay, MITM, impersonation, and physical-capture adversaries. Environmental stressing from 0 °C to 70 °C confirms practical reliability. We deliberately omit ephemeral key exchange and anonymous credentials - the price of doing so is the conditional and partial (rather than full) flavours of forward secrecy and anonymity, which we make explicit throughout.