Yifan Dong, YoungBeom Kim, Jieyu Zheng, Zhichuang Liang, Boyue Fang, Seog Chung Seo, Maire O’Neill, Yunlei Zhao

Lightweight PQ KEM and Hybrid MQTT Protocol for 8-bit AVR Sensor Nodes

Introduction

Lightweight pq kem and hybrid mqtt protocol for 8-bit avr sensor nodes. Secure 8-bit AVR sensor nodes with CTRU-Light, a lightweight post-quantum KEM. Explore optimized PQC schemes and a hybrid MQTT protocol for efficient, next-gen IoT security.

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.

Review

This paper tackles the critical challenge of deploying Post-Quantum Cryptography (PQC) on severely resource-constrained 8-bit AVR wireless sensor nodes, an area where most existing PQC schemes remain impractical. The authors present a comprehensive and highly relevant approach, encompassing the design of a new lightweight PQC Key Encapsulation Mechanism (KEM), significant implementation optimizations, and its integration into a practical IoT protocol. This work is timely and addresses a fundamental security gap at the ultra-constrained edge of the IoT ecosystem, providing a much-needed pathway for quantum-safe communication in environments traditionally considered beyond the reach of PQC. The technical contributions are substantial and multi-faceted. A core innovation is CTRU-Light, a novel lattice-based KEM specifically engineered for IoT sensor nodes, leveraging small moduli, low-degree polynomials, NTT-friendly arithmetic, and ASCON for symmetric operations to achieve high efficiency. Furthermore, the paper introduces pioneering optimization techniques for 8-bit AVR platforms, notably the first exploration of NTT-friendly moduli and the design of optimized Montgomery, Barrett, and K-RED2X multiplication variants. The claim of approximate equivalence between K-RED2X and Montgomery multiplication under specific conditions is particularly interesting. These optimizations are not only applied to CTRU-Light, achieving high efficiency and low stack usage through optimized AVR assembly, but also demonstrate significant improvements for established schemes like Kyber and Saber, indicating broader applicability. The practical impact of this research is particularly compelling, demonstrated by the design and first implementation of a Hybrid KEM–MQTT protocol that integrates classical ECDH with post-quantum KEMs. Empirical analysis reveals that CTRU-Light stands out as the only scheme capable of supporting both pure PQ and hybrid KEM–MQTT on 8-bit WSNs, achieving lower handshake latency than even highly optimized versions of Kyber-512 and LightSaber. This finding is a crucial step towards making quantum-safe communication a reality for these constrained devices. The paper convincingly shows that the proposed solutions are not merely theoretical but practically viable and demonstrably superior in performance for this challenging target platform.

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