A Robust Generation Technique of Common Information Based on Characteristic of Multipath Fading Channel by Shaking Handheld Devices

A rapid increase in handheld devices with wireless communication capabilities, such as cellular phones and smart phones, enables data communication in face-toface situations. The easy realization of secure data communication in such situations is necessary for ensuring safe and reliable networking environments as short-range wireless networks become more popular. One approach involving the generation of secret keys in each communication device using variations of the received signal strength indication (RSSI) values has been proposed in literature. However, it has a problem in that there are positions where eavesdroppers are able to obtain RSSI values that are highly correlated with those of legitimate devices. To address this problem, we propose a filtering technique that eliminates eavesdroppable parts from RSSI variations. Additionally, it is important to shake either one or both of two legitimate devices to change the propagation, considering that the elimination exploits the periodicity of the shake. Furthermore, we implemented a prototype system realizing the proposed method and evaluated its effectiveness. The results indicate that the proposed method can increase the robustness of common information, which is generated into the secret key without degrading its generation speed.