A novel 6G-oriented secure bidirectional key exchange scheme based on graphene-assisted terahertz physical layer

This paper proposes a graphene-assisted bidirectional key exchange protocol that integrates terahertz (THz) physical-layer modulation with the Diffie–Hellman (DH) cryptographic framework, addressing a critical gap in secure session establishment over open wireless channels. While prior graphene-based antennas, metasurfaces, and sensing platforms have primarily focused on enhancing electromagnetic performance, secure bidirectional key exchange at the physical layer has remained largely unexplored. The proposed architecture employs a dual-layer graphene metasurface operating at 1 THz, where tunable surface conductivity enables binary phase-shift keying (BPSK) modulation for concurrent transmission. Authenticated public parameters, identity bindings, and freshness values are embedded within the THz waveform, and a shared secret is derived through DH computation. Simulation results over an SNR range of 0–30 dB demonstrate reliable demodulation under AWGN, coherent current density distributions across graphene layers, and consistent key agreement between communicating parties. The bit error rate (BER) decreases sharply between 5 and 10 dB, reaches the 10−3 regime at 10 dB, and converges to zero within simulation resolution for SNR values of 15 dB and above, indicating reliable parameter recovery under practical noise conditions. An informal security analysis conducted under the Dolev–Yao adversarial model, together with a comparative assessment of the defined security requirements, indicates that the proposed scheme demonstrates resistance against both passive and active attacks. Furthermore, the comparative evaluation suggests that the proposed framework more comprehensively satisfies the considered security requirements relative to existing schemes. These findings establish the feasibility of graphene-assisted secure key exchange and provide a structured foundation for secure deployment of graphene-enabled terahertz communication systems, particularly within emerging 6G network architectures, as well as in IoT and biomedical applications.