8.1 Introduction

User Location Information (LI) has the potential to be the basis of many different services, ranging from route planning to user location in emergency situations. Such services are frequently associated with, but are not limited to, mobile devices. Fixed devices, such as desktop PCs, may also be used to receive such services. As these services become widely available, privacy concerns will also become more significant. Of course, user location is not the only personal attribute which may cause privacy concerns. Medical information and personal bank details are amongst the many other types of personal details a user may not wish to publicise.

In previous work ^[1], a trusted party, referred to as a Location Information Preference Authority (LIPA), was introduced to help protect the privacy of LI. Here LI simply means any data that may be used to help determine the current or recent location of a subject. A simple model for LI protection was introduced, where LI was distributed within the scope of an LI token. This LI token has the property that only the LIPA entity is able to view the information held within it. Along with the LI, constraints are also included in the LI token. Constraints are simply statements which limit the use, distribution and storage of LI. This is discussed further in Reference ^[2]. In our simple model, a Location-Based Service (LBS) provider wishing to use LI may only view it by making requests to...