Research On Location Privacy Preserving Of Mobile User In Location Based Services

With the rapid development of wireless communication technology,as well as the growing popularity of mobile device,Location-Based Service(LBS)has been more and more widely used in people's daily activities over the past few years.Actually,the LBS is the service that integrate a mobile device's lo-cation or position with other information so as to provide added value to a user.Briefly,the LBS is one of the value-added services,which is provided based on the user's location by the service provider.We can conclude from the definition of the LBS that it contains two aspects:1)Deciding the location of a user or a mobile device;2)Providing kinds of services related to the location.Typi-cal examples of the LBS include route search,PoI search,personal location search,and location based social network,etc.Actually,the LBS,which has greatly changed the way people live,covers almost all fields of human dynamic activities.While enjoying the efficiency and convenience brought by the LBS,the leakage of user's personal information has gradually become a serious prob-lem,which has raised huge concern of people.This is because,when a user wants to enjoy the LBS,he has to submit his current location first to the ser-vice provider,who is normally considered untrusted in the LBS system.As a result,the service provider may track the user directly or release his personal information to third parties.Such information,however,is extremely sensitive,and may endanger the user's physical security if they fall in the wrong hands.An increasing number of cases show that when a user uses the LBS,he may be tracked,or even be informed of his home address,lifestyle,health status and other personal sensitive information.In other words,people's privacy and se-curity are threatened.Thus,it is particularly important for a user to protect his privacy when he enjoys LBS.In this thesis,we do research on privacy preserving of a mobile user in LBS,and the main contributions are summarized as follows:1.We propose a Cache-Based Privacy-Preserving(CBPP)solution for users in peer to peer environment.Although many approaches have been pro-posed to preserve user's privacy,most of them just focus on the user' s loca-tion privacy,but do not consider the query privacy.Moreover,many existing approaches rely heavily on a trusted third-party(TTP)server,which may suf-fer from a single point of failure.To solve the problems above,in this thesis we propose a Cache-Based Privacy-Preserving(CBPP)solution for users in LBSs.Different from the previous approaches,our proposed CBPP solution can protect location privacy and query privacy simultaneously,while avoiding the problem of TTP server by having users collaborating with each other in a mobile peer-to-peer(P2P)environment.In the CBPP solution,each user keeps a buffer in his mobile device(e.g.,smartphone)to record service data and acts as a micro TTP server.When a user needs LBSs,he sends a query to his neighbors first to seek for an answer.The user only contacts the service provider when he cannot obtain the required service data from his neighbors.In this way,the user reduces the number of queries sent to the service provider.We argue that the fewer queries are submitted to the service provider,the less the user's privacy is exposed.To users who have to send live queries to the service provider,we employ the 1-diversity,a powerful privacy protection definition that can guar-antee the user's privacy against attackers using background knowledge,to further protect their privacy.Evaluation results show that the proposed CBPP solution can effectively protect users' location and query privacy with a lower communication cost and better quality of service.2.We propose a Voronoi-Based Privacy-Enhanced Nearest Neighbor(VBPENN)query processing solution.Although the mentioned CBPP solu-tion can effectively protect users' privacy,the CBPP solution also has a fatal shortcoming.Actually,in the CBPP solution,users are usually assumed to be trusted and directly share location information with each other.We argue that,however,this assumption is unrealistic since users could not be fully trusted in practice.In order to solve the problem,in this thesis,we propose a Voronoi-Based Privacy-Enhanced Nearest Neighbor(VBPENN)query processing so-lution,which is used against the untrusted neighboring peers in mobile peer-to-peer(P2P)environment.In our VBPENN solution,no trust relationship is assumed among users.The main idea of VBPENN is that a user hides his exact location in the request into a cloaking region(CR),and broadcasts the request to his neighbors to seek for answer.In this way,neighbors just realize that the user is in the CR,but cannot pinpoint his accurate location,which greatly improves the user's location privacy.After receiving the request from the user,neighbors utilize the Voronoi Diagram(VD)to find the corresponding service data based on the query interest,and then send the service data back to the user.The user only contacts the service provider when he cannot obtain the required service data from his neighbors.Security analysis and evaluation results show that not only our proposed solution can effectively protect users'location privacy,but also can provide better quality of service(QoS)for KNN query without losing the accurate location information of the user.3.We propose a trajectory privacy protection solution(DBSR)against the CELL-ID positioning.We can conclude from the definition of LBS that the po-sitioning is the foundation of LBS.A user can submit a query to his neighbors or service provider when he gets his current location.Although two solutions we mentioned above can effectively protect user's location privacy,none of them considers whether a user could disclose his location information in the positioning process.Actually,the widely used smartphone with powerful posi-tioning capability makes it easy for a user to find his precise physical location.However,this may reveal a user's geo-location information,making the real-time tracking of the user possible.For example,on the basis of a sequence of numbers(i.e.,Cell-IDs)received in the Cell-ID positioning,an entity can gain access to a person's movement routes without his consent.We argue that if the trajectory of a person is traced,then all his visits may be exposed.There-fore,trajectory cloaking against the mobile positioning is urgently necessary.In this thesis,we propose a Dummy Base Station Replacement(DBSR)algo-rithm.It mainly uses the idea of dummy trajectory anonymity,and is achieved by replacing the true Cell-ID provided by the network with a fake but nearby Cell-ID.We also implement our DBSR algorithm on an Android-based smart-phone to evaluate its performance.Experimental results show that the DBSR algorithm can efficiently tackle the privacy breach caused by the single base station positioning in cellular network.