Yifan Dong
College of Computer Science and Artificial Intelligence, Fudan University, Shanghai, China

YoungBeom Kim
Kookmin University, Seoul, Republic of Korea; Queen’s University Belfast, Northern Ireland, United Kingdom

Jieyu Zheng
College of Computer Science and Artificial Intelligence, Fudan University, Shanghai, China

Zhichuang Liang
College of Computer Science and Artificial Intelligence, Fudan University, Shanghai, China

Boyue Fang
College of Computer Science and Artificial Intelligence, Fudan University, Shanghai, China

Seog Chung Seo
Kookmin University, Seoul, Republic of Korea; Queen’s University Belfast, Northern Ireland, United Kingdom

Maire O’Neill
Queen’s University Belfast, Northern Ireland, United Kingdom

Yunlei Zhao
College of Computer Science and Artificial Intelligence, Fudan University, Shanghai, China

Keywords: Post-quantum cryptography, Lightweight cryptography, 8-bit AVR, Modular multiplication, Lightweight protocol

Abstract

Most PQC schemes remain too resource-intensive for ultra-constrained 8-bit AVR wireless sensor nodes. In this work, we present a comprehensive approach to practical lightweight PQC for such devices, covering scheme design, implementation optimization, and protocol integration. Our contributions are threefold: (i) We propose CTRU-Light, a lattice-based KEM specifically tailored for IoT sensor nodes. It combines small moduli, low-degree polynomials, and NTT-friendly arithmetic for high efficiency, with ASCON used for lightweight symmetric operations. (ii) We explore NTT-friendly moduli for the first time to accelerate modular multiplication on 8-bit AVR platforms and design optimized variants of Montgomery and Barrett multiplication. We show that K-RED2X multiplication exhibits approximate equivalence to Montgomery multiplication under small NTT-friendly moduli. We apply these optimizations to the latest implementations of Kyber (ASIACCS 2025) and Saber (CHES 2025), achieving significant improvements in both speed and code size. Furthermore, we present a highly optimized AVR assembly implementation of CTRU-Light that delivers high efficiency and low stack usage. (iii) We design a Hybrid KEM–MQTT protocol that integrates classical ECDH with post-quantum KEMs. We present the first implementation of this protocol and provide a detailed empirical analysis of its performance. Experiments show that CTRU-Light is the only scheme capable of supporting both pure PQ and hybrid KEM–MQTT on 8-bit WSNs, achieving lower handshake latency than Kyber-512 and LightSaber.