Enhancing wireless location privacy using silent period

The advance of ISM-band radio-based tracking systems (for example, wireless LAN-based tracking system) extends the application of location-based services (LBS), but it also threatens to allow the movement of users to be tracked when they are transmitting frames. Several protection methods based on periodic address updates have already been proposed. However, new correlation attacks, which utilize the correlation between the old and new addresses of the same node, can defeat current protection methods. To combat such attacks, we propose the concept of a silent period. A silent period is defined as a transition period between the use of new and old pseudonyms, when a node is not allowed to disclose either the old or the new address. Through analysis, we find that a silent period should contain a constant period and a variable period. The effect of the constant period is to mix the spatial relation between the node's disappearing points and emerging points. The variable period mixes the temporal relation between the node's disappearing times and emerging times. We evaluate the performance of the silent period through simulation. The results show that the silent period proposal significantly reduces the duration of time a node can be tracked continuously. There are still many open research problems before random address can be implemented to protect wireless location privacy, but silent period protocol is the first step to realizing it.