AquaKey: Exploiting the Randomness of the Underwater Visible Light Communication Channel for Key Extraction

Underwater Visible Light Communication (UVLC) is promising due to its relatively strong penetration capability in water and large frequency bandwidth. Visible Light Communication (VLC) is also considered a safer wireless communication paradigm as light signals can be constrained within the area of interest with obstacles such as walls, reducing the chance of potential attack. However, this intuitional security assumption is not true anymore in underwater environment. Recent research shows that the eavesdropping risk of UVLC is more severe than we thought, attributed to the divergence and scattering effects of light beams in water. In this paper, we harness the dynamic nature of underwater environments as a true random resource to extract symmetric keys for UVLC. Specifically, the proposed AquaKey system incorporates instantaneous bidirectional channel probing, computation of relative channel characteristics, and an environment-adaptive quantization algorithm. The above design addresses unique challenges caused by the dynamic underwater environment, including self-interference, high-frequency disturbance, and mismatch, ensuring the practicality and applicability of AquaKey. Additionally, AquaKey has negligible impact on communication and has no effect on the illumination function. Through extensive real-world experiments, we show that AquaKey can achieve reliable key extraction with cheap hardware, generating a 512-bit key in just 0.5-1 seconds.