Research On Location Privacy Protection Scheme Based On User Collaboration

As an important type of service in positioning technology,location-based service became one of the most important parts of the current mobile application along with the prosperity of the smart phone.In order to get the service,the user has to send the query to the LBS server with the current location and obtain the returned result.But this service also reflects the dual character.Although this service may bring convenience for the user,it may bring potential threat to the privacy of the user.Aiming at coping with this problem,a large number of privacy protection algorithms had been proposed with trusted central server currently.However,as the central server may become the focus of attack or turned into the service bottleneck of server performance,which makes these algorithms be doubted since proposed.Thus,algorithms which are based on the collaboration of adjacent users are proposed and adopted by the user.However,as the diversity of used patterns and environment is complex,using simple utilization of collaborative users is insufficient,and this mode is also confronted with the challenge of some unsolved problems.For example,firstly,in the snapshot query,the collaborative users must share the same maximum anonymity degree of current anonymous group,and no one can lower the degree to obtain a higher service quality.Secondly,in the continuous query,the adversary can utilize the difference of collaborative users,and then identify the special user from the anonymous group.Furthermore,the existing algorithms usually assume the collaborative user has the same direction and velocity,but it is unpractical in the real world.Thirdly,in the environment of the road network,the privacy preserving algorithm based on collaborative users which used in Euclidean space may be failure,as the serious restriction in road network.At last,the semi-collaborative user may filch the privacy of the user in the process of generating anonymous group.In order to cope with above problems,and with the help of the national natural science foundation of China(61472097)as well as the Doctoral Program of Higher Education Research Fund(20132304110017),this dissertation has carried out several research works and the main contents and contributions are summarized as follows.(1)Collaborative users used in privacy preserving of snapshot query.In order to cope with the problem of all users must share the maximum anonymity degree in the same anonymous group,so this dissertation proposes a query information blocks random exchanging scheme which based on the capability of short range communication of the collaborative user.In this scheme,the user can divide the query into several blocks with the anonymity degree and exchange them with the adjacent collaborative users in a random number,and then the collaborative user can also exchange with others,which makes the user can establish an anonymous group in multihop communication range.At the same time,with the character of that each query can establish its own anonymous group,this algorithm can also achieve the objective of personal anonymity.(2)Collaborative users used in privacy preserving of continuous query.In order to cope with the problem of the adversary utilizes the difference of collaborative users to identify the special user as well as to cope with the problem of strong assumption about the collaborative users,so this dissertation proposes a scheme with query block exchanging and results caching to provide query service in continuous query.This scheme is based on the capability of short range communication and the cache of the collaborative user.In this scheme,the query blocks exchanging strategy is used,and with the help of caches of collaborative users,the user can obtain the query result from the collaborative user when passing by in the continuous query.Thus,in this procedure,information interaction between the user and the LBS server will be decreased,and then reduce the probability of privacy leakage.(3)Collaborative users used in the road network.In order to cope with the problem of privacy preserving algorithms used in Euclidean space failure in road network,and also cope with the problem of serious restriction in road network to find enough collaborative users to establish the anonymous group.This dissertation proposes a collaborative users scheme with the help of mix-zone,and then based on the attribute profile sharing the scheme can also resist the attack of profile correlation.In this scheme,user can establish the anonymous group with the adjacent collaborative users in the same mix-zone,and share the attribute profile with them to form the query set and the mutual query interval.When the user leaves the mix-zone,each user will show the similar profile with the correlative user,and the adversary cannot correlate any of them with the background knowledge inferred from the sub-trajectory which is not protected.Further,as the user is gathered by the mix-zone,this scheme also solves the problem of the restriction in road network,and finds out enough users to establish the anonymous group.(4)Semi-trusted collaborative users used in privacy preserving.In order to cope with the problem of semi-trusted collaborative users may contain in the anonymous group,and based on the strategy of ciphertext policy attribute based encryption(short for CP-ABE)we propose a collaborative users partial decryption scheme.In this scheme,the user sets the query information in two rounds of encryption,and sends it to the central server,and then the central server broadcasts this information in a widely region to find out enough collaborative users.The collaborative user who receives this information can decide whether to participate in the anonymous group when he has the same attribute profile.Thus,during the whole process,no entity of this architecture can obtain the privacy of the user,no matter the central server or the semi-trusted collaborative user.Furthermore,as all collaborative users will show the same attribute profile,and this scheme can also resist the attack of profile correlation.(5)A correlation probability indistinguishable location privacy protection algorithm.In order to cope with the shortage of k-anonymity in resisting statistical attack especially in resisting differential attack,and based on the conception of generalized difference privacy,this dissertation proposed a probability indistinguishable mechanism called ?-correlation differential privacy.With this mechanism,a user's location shift scheme is proposed to achieve the purpose of correlation probability indistinguishable,and then three randomized algorithms were defined to accomplish indistinguishable and implement the privacy protection.With the help of location shift,the user and correlative users cannot be distinguished in several types of correlation probability,and this scheme can further guarantee that the adversary infers the location privacy of the user with the background knowledge to initialize the statistical attack and differential attack.