  Attacks based on power analysis have been long existing and studied, with
some recent works focused on data exfiltration from victim systems without
using conventional communications (e.g., WiFi). Nonetheless, prior works
typically rely on intrusive direct power measurement, either by implanting
meters in the power outlet or tapping into the power cable, thus jeopardizing
the stealthiness of attacks. In this paper, we propose NoDE (Noise for Data
Exfiltration), a new system for stealthy data exfiltration from enterprise
desktop computers. Specifically, NoDE achieves data exfiltration over a
building's power network by exploiting high-frequency voltage ripples (i.e.,
switching noises) generated by power factor correction circuits built into
today's computers. Located at a distance and even from a different room, the
receiver can non-intrusively measure the voltage of a power outlet to capture
the high-frequency switching noises for online information decoding without
supervised training/learning. To evaluate NoDE, we run experiments on seven
different computers from top-vendors and using top brand power supply units.
Our results show that for a single transmitter, NoDE achieves a rate of up to
28.48 bits/second with a distance of 90 feet (27.4 meters) without the line of
sight, demonstrating a practically stealthy threat. Based on the orthogonality
of switching noise frequencies of different computers, we also demonstrate
simultaneous data exfiltration from four computers using only one receiver.
Finally, we present a few possible defenses, such as installing noise filters,
and discuss their limitations.
