Smart home devices are vulnerable to passive inference attacks based on network traffic, even in the presence of encryption. In this paper, we present PingPong, a tool that can automatically extract packet-level signatures (i.e., simple sequences of packet lengths and directions) from the network traffic of smart home devices, and use those signatures to detect occurrences of specific device events (e.g., light bulb turning ON/OFF). We evaluated PingPong on popular smart home devices ranging from smart plugs to thermostats and home security systems. We have successfully: (1) extracted packet-level signatures from 18 devices (11 of which are the most popular smart home devices on Amazon) from 15 popular vendors, (2) used those signatures to detect occurrences of specific device events with an average recall of more than 97%, and (3) shown that the signatures are unique among tens of millions of packets of real world network traffic.

PingPong: Packet-Level Signatures for Smart Home Device Events