Telling Secrets in the Light: An Efficient Key Extraction Mechanism Via Ambient Light

Due to the benefits of small latency, low energy consumption and increased data rate, device-to-device (D2D) communication is recognized as one of the promising techniques in the 5G era. However, the distributed nature of D2D communication makes it non-trivial to generate symmetric keys for the involving parties. Many efforts have been devoted to dynamically generate cryptographic keys for D2D communication in mobile network. However, most of them have limited applicability to practical scenarios due to low key generation efficiency or limited compatibility with commercial mobile devices. In this paper, we design an ambient light based key generation approach, which works on commercial off-the-shelf mobile devices, and achieves high key generation efficiency. We observe that mobile devices (e.g., smartphones, tablets) are often equipped with ambient light sensors and devices sense different light intensities at different angles towards the light source. We conduct a set of measurement study, and the results show that the light sensor data have several nice properties, i.e., space-varying, sensitive to the angle of measuring device, and time varying. These properties demonstrate that the ambient light is a good medium for secret key generation. We implement a prototype on different mobile devices, and conduct extensive experiments to evaluate its performance. The experiment results show that compared with the state-of-the-art key generation methods, our approach has a superior performance in key generation efficiency and robustness.