Mobile Intelligence

19.5 OBFUSCATION TECHNIQUES FOR USER-PRIVACY

To guarantee user location privacy, we introduce three basic obfuscation techniques that modify a user location to reduce the associated relevance (henceforth the accuracy) until a given level.

19.5.1 Obfuscation by Enlarging the Radius

Obfuscating a location measurement area by increasing its radius (see Figure 19.3(a)) is the technique that most solutions exploit, either explicitly or implicitly by scaling a location to a coarser granularity (e.g., from few meters to hundred of meters, from a city block to the whole town, and so on). The obfuscation is a probabilistic effect due to a decrease in the corresponding joint probability density function (joint pdf), which can be expressed as ∀r, r′, r < r′ : f_r(x, y) > f_r′(x, y). The following proposition allows us to calculate the obfuscated area.

Table 19.2 Examples of access control policies for a healthcare scenario

Proposition 19.1. Given a location area of radius r with relevance _Init and an obfuscated area of radius r′ derived by enlarging the original radius, the relevance _Final of the obfuscated area is calculated by reducing _Init of the ratio f_r′(x, y)/f_r(x, y) of corresponding joint ...