As smart phones with a GPS receiver have been becoming popular recently, many people have realized the issue of protecting their location privacy. Previous research on location privacy mainly focuses on anonymization techniques for removing identifiable information from users' location traces. Although anonymized location data is useful to many applications, such as traffic monitoring, we can provide a new class of location-based services by utilizing path information of mobile users. In this paper, we present a dynamic pseudonym scheme for constructing alternate possible paths of mobile users to protect their location privacy. We introduce a formal definition of location privacy for pseudonym-based location data sets and show an efficient verification algorithm for determining whether each user in a given location data set has sufficient number of possible paths to disguise the user's true movements.
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