Neighbor: Ad Hoc Pairing of Nearby Wireless Devices by Multiple Antennas

The proliferation of personal wireless devices requires secure connection between them. While it is easy to securely pair electronic devices by wires, it is very challenging to pair them wirelessly when they have no prior association. We propose Good Neighbor, a novel scheme that securely pairs nearby wireless devices by exploiting multiple antennas built in them. Our scheme requires neither shared se-crets nor out-of-band channels (e.g., audio, visual, keyboard, etc.) between the pairing devices. It only requires that the receiver has multiple antennas and that the sender can be placed nearby the receiver. Our scheme is based on the propagation characteristic of the wireless signal that the power of the re-ceived signal is inversely proportional to some exponent of the distance between the sender and receiver. When a nearby sender moves very close to one antenna on the receiver, the receiver can observe a large difference between the signal strength measured on its two antennas, whereas a faraway sender would be unable to induce such a large difference. We validate our scheme through theoretical analysis and ex-perimental measurements. We discuss the factors that may affect our scheme — including antenna gain, received signal strength (RSS) saturation, dynamic rate adaptation, and multipath effects — and how to mitigate them. Finally, we demonstrate the practicality of our scheme by implementing and evaluating a prototype.