The Martini Synch: Device Pairing via Joint Quantization

Device pairing is a significant problem for a large class of increasingly popular resource-constrained wireless protocols such as Bluetooth. The objective of pairing is to establish a secure wireless communication channel between two specific devices without a public-key infrastructure, a secure near-field communication channel, or electrical contact. In this paper, we use a surprising user-device interaction as a solution to this problem. By adding a 3-axis accelerometer, a device can sense its motion in local Cartesian space relative to the inertial space. The idea is to have two devices in a fixed, relative position to each other. The joint object is then moved randomly in 3D for several seconds. The unique and difficult to reproduce motion generates approximately the same distinct signal at each accelerometer. The difference between the signals in the two inertially conjoined sensors should be relatively small under normal motion induced manually except for a fixed attitude offset. The objective is to derive a deterministic key at both sides with maximized entropy that will be used as a private key for symmetric encryption. Currently, our prototype produces 9-20 bits of entropy per second of usual manual motion using off-the-shelf components.