A Lightweight Hybrid Authentication and Key Agreement Protocol for Decentralized Device-to-Device Communication with Post-Quantum Confidentiality.

Device-to-device (D2D) communication is expected to become a key component of 6G and IoT systems, enabling low-latency and infrastructure-independent connectivity. A major challenge is to establish secure session keys between previously unknown devices without relying on an online trusted third party, while also ensuring resilience against future quantum adversaries. This paper proposes a lightweight hybrid authentication and key agreement protocol for decentralized D2D communication. The approach combines IPFS-assisted distributed key discovery with a two-message protocol that uses post-quantum key encapsulation for long-term confidentiality, while retaining elliptic curve cryptography (ECC) for efficient real-time authentication under classical security assumptions.This design reflects the different temporal security requirements of confidentiality and authentication and provides a practical trade-off between quantum resilience and computational efficiency. The proposed scheme achieves mutual authentication under classical ECC assumptions, secure session key establishment, and resistance against common attacks, while providing post-quantum confidentiality protection against future quantum adversaries and removing the need for an online trusted third party (TTP) during protocol execution. The results demonstrate that the protocol offers a competitive and practical solution for secure decentralized D2D communication in IoT and future 6G environments.