Waveguide Eavesdropping Threat for Terahertz Wireless Communications

As wireless communications move to higher frequency band for 5G networks and beyond, resiliency against eavesdropping and other security threats is still one of the key system design considerations. Compared to data transmissions by lower frequencies, terahertz links are inherently more robust against eavesdropping attacks due to their propagation characteristics (e.g., high free-space path loss) and aligned link path by high-gain antennas. However, it does not indicate that eavesdropping is always impossible. Line-of-sight terahertz links have proven to be vulnerable to active/passive eavesdroppers by placing scatterers in the path of data transmission, or by collecting side-lobe leakages. Here, we demonstrate a wave-guide-based approach for signal eavesdropping that can be operated much more feasibly with several advantages, such as lower propagation loss and reliable data interception. Our method relies on a 3D printed rectangular dielectric waveguide and can overcome spatial limitations caused by directional modulation or near-field modulation. We demonstrate successful eavesdropping attacks for a 16-QAM data link at rates up to 5 Gb/s. Our work highlights the importance of system designs in resisting waveguide-based eavesdropping strategies and identifies aspects where the physical-layer security technique needs to be strengthened.