Following the wide adoption of mobile phones equipped with global positioning systems (GPS), location-based services (LBS), such as finding the closest pharmacy or the cheapest gas station within a range, have become commonplace. In a nutshell, a typical LBS model consists of users and providers of the service. The former send queries to the latter so as to obtain location-based information. Many mobile apps, such as Foursquare, Yelp, and Air Comments, allow users to share and find information directly related to their current location, and afford great advantages for users. However, they do not come without privacy risks, since the sharing of locations might lead to the disclosure of a user’s habits, social and economic status, health condition, and so on. This book covers those privacy issues and analyzes several location privacy protection techniques.

The book was published as a part of the “Synthesis Lectures on Information Security, Privacy, and Trust” series, which means that it is limited to 100 pages. Thus, given these space limitations, the author has done a remarkable job of being concise, at the expense of putting aside some relevant studies on privacy protection by means of collaborative schemes, amongst others.

The book could be conceptually divided into four topics. The first involves the protection of query privacy, understood as the protection of the user’s location contained in queries submitted to LBS providers. In chapter 2, the author provides an overview of methods to achieve this goal by distorting the location information submitted, while in chapter 3, he focuses on cryptography-based methods. Next, in chapter 4, the author presents a mixture of the two previous approaches, referred to as hybrid methods.

The second topic relates to the private sharing of location data. Chapter 5 is devoted to this completely different topic, and considers how to privately match location-based data amongst untrusted entities such as companies, location-based social networks, and the like. This problem is clearly related to a more general concept known as privacy-preserving data mining, which pursues the same objective, but focuses not only on location-based data but on any kind of data. In this sense, it is interesting to see the particular characteristics of location-based data and how they could be shared privately.

The third topic, covered in chapter 6, refers to the trajectories of LBS users and their protection. The main difference between this topic and the first is that locations are no longer considered individually, but in lists (known as trajectories). Properly protecting the privacy of trajectories is even more difficult and more important, if possible, since the locations contained in each trajectory are highly correlated and might contain much more information than single location points. For example, if we have a list of locations and we distort one of them, the real, original location could be easily inferred from the others that remain untouched. Thus, preserving location privacy in trajectories requires more sophisticated methods that consider the relations amongst all the trajectory points.

The last topic (covered in chapter 7) explores the use of differential privacy for location privacy. This is probably the most innovative chapter in the book, since differential privacy is a hot topic that has recently gained much attention from the privacy research community. Differential privacy is a very interesting research topic, born in the statistical databases research community. Its aim is to increase the accuracy of the statistical records, while at the same time, minimizing the chances of re-identification (that is, privacy invasion). The fact that differential privacy could be used for the preservation of location privacy opens the door to new paths for research, which this chapter points out. Unfortunately, differential privacy is far from a practical solution in most cases, and still remains in the realm of ideas.

All in all, this is an interesting compendium of discussions about location privacy topics that could be seen as a good introduction for graduate students working in the field of location privacy. The space limitations imposed on these lecture notes prevent them from being comprehensive, but the author has done a remarkable job of assembling many relevant articles and important topics in the field. These notes could be a great foundation for a much more comprehensive book on the important topic of location privacy.