Good Neighbor: Secure Pairing of Nearby Wireless Devices by Multiple Antennas

Liang Cai, Kai Zeng, Hao Chen, and Prasant Mohapatra

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
secrets 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 received 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 experimental 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.