Paper 2026/248

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

YoungBeom Kim, Kookmin University, Queen's University Belfast

Jieyu Zheng, Fudan University

Zhichuang Liang, Fudan University

Boyue Fang, Fudan University

Seog Chung Seo, Kookmin University, Queen's University Belfast

Maire O'Neill, Queen's University Belfast

Yunlei Zhao, Fudan University

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.

@misc{cryptoeprint:2026/248,
      author = {Yifan Dong and YoungBeom Kim and Jieyu Zheng and Zhichuang Liang and Boyue Fang and Seog Chung Seo and Maire O'Neill and Yunlei Zhao},
      title = {Lightweight {PQ} {KEM} and Hybrid {MQTT} Protocol for 8-bit {AVR} Sensor Nodes},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/248},
      year = {2026},
      doi = {10.46586/tches.v2026.i2.372-408},
      url = {https://eprint.iacr.org/2026/248}
}