How can I guard my AP?: non-intrusive user identification for mobile devices using WiFi signals

With the development and popularization of WiFi, surfing on the Internet with mobile devices has become an indispensable part of people's daily life. However, as an infrastructure, WiFi APs are easily connected by some undesired users nearby. In this paper, we propose NiFi, a non-intrusive WiFi user identification system based on WiFi signals that enables AP to automatically identify legitimate users in indoor environment such as home, office and hotel. The core idea is that legitimate and undesired users may have different physical constraints, e.g., moving area, walking path, etc, leading to different signal sequences. NiFi analyzes and exploits the characteristics of signal sequences generated by mobile devices. NiFi proposes a practical and effective method to extract useful features and measure similarity for signal sequences, while not relying on precise user location information. We implement NiFi on Commercial Off-The-Shelf (COTS) APs, and the implementation does not require any modification to user devices. The experiment results demonstrate that NiFi is able to achieve an average identification accuracy at 90.83% with true positive rate at 98.89%.