With the advance of location technologies, people can nowdetermine their location in various ways, for instance, with GPS or basedon nearby cellphone towers. These technologies have led to theintroduction of location-based services, which allow people to getinformation relevant to their current location. Location privacy is ofutmost concern for such location-based services, since knowing a person;;slocation can reveal information about her activities or her interests.In this thesis, we first focus on location-based services that need toknow only a person;;s location, but not her identity. We propose a solutionusing location cloaking based on k-anonymity, which requires neither asingle trusted location broker, which is a central server that knowseverybody;;s location, nor trust in all users of the system and thatintegrates nicely with existing infrastructures. We present two suchprotocols. The evaluation of our sample implementation demonstrates thatone of the protocol is sufficiently fast to be practical, but theperformance of the other protocol is not acceptable for its use inpractice.In addition to the distributed k-anonymity protocol we then propose fourprotocols---Louis, Lester, Pierre and Wilfrid--- for a specific, identityrequired, location-based service: the nearby-friend application, whereusers (and their devices) can learn information about their friends;;location if and only if their friends are actually nearby. Our solutionsdo not require any central trusted server or only require a semi-trustedthird party that dose not learn any location information. Moreover, usersof our protocol do not need to be members of the same cellphone provider,as in existing approaches. The evaluation on our implementation shows thatall of the four protocols are efficient.
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