Research On Key Techniques In Privacy Of Location Based Service For Pervasive Computing

In recent years, with the rapid development of wireless and mobile computing, Ubiquitous/Pervasive computing is the integration of cyberspace and physical space. In pervasive computing, users can obtain digital services non-intrusively anytime and anywhere. This mobile computing environment promotes the birth and development of Location Based Services(LBS).However, LBS not only make the services more convenient but also introduces a new security challenge. Users private information extend to physical information(such as location) from visual information ( such as ID, password etc.) because of the generation of LBSs. The physical characteristics of the extend privacy information makes it more difficult to protect users'privacy. At the same time, due to the unpredictability of the cooperated principals, it is unsuitable to use traditional security mechanisms suited for static network or closed systems to solve problems occur in pervasive computing environment. Therefore privacy problem is the biggest challenge the pervasive computing will meet.This dissertation aims to research the key issue in both theories and applications of the new privacy protection technology according to the weak link of users'privacy in location based services of pervasive computing. The main research contains several kinds of privacy, such as user location privacy, user identity privacy, user query privacy etc. According to the difference of Customization Service and anonymous service, densely environment and sparse environment are considered in the analysis of privacy connotation and protection technology. The major contributions of this dissertation are as below:(1) A Density-Based Spatial Cloaking Algorithm (DBSCA) is presented. The DBSCA subtly transforms the optimal obfuscating region problem into the maximum density region problem by grid processing of pervasive space .In DBSCA, the Optimized Cloaking Region (OCR) is generated with distribution matrix and relative density matrix of neighboring users. User location privacy is protected with cloaking region, meanwhile, the identity privacy is confused with other users in cloaking. (2) According to analysis of anonymity failure of cloaking and decrease of QoS, a privacy enhance technology based on interference information is proposed. The user cloaking in sparse environment has been mixed with a set of dummy user or interference location to minimize the size of each cloaking area and improve QoS. This technology include two algorithms: The first one called dummy user trigger algorithm is able to achieve the balance of users Location privacy and system performance. The second algorithm enhanced the truthfulness of dummy user through dummy user generation algorithm based on period density matrix.(3) A new method of cutting off users trace by mutil-pseudonym transform is described, as well as associated method of space partition using services information. This technology disconnects users'trajectory into several discontinuous segments. User path privacy has been protected by change pseudonyms between different segments. Adopting this method can effectively avoid the failure of pseudonyms bring by usual route prediction attack.(4) A double threshold privacy technology based on user distribution matrix is proposed for protecting user query privacy, include query location privacy and query content privacy. Users cloaking region had been dynamic modification in query lifecycle by user query privacy model and QoS model to balance user privacy and LBS quality. Experimental results validate the efficiency and effective of proposed technique.(5) Combined with the various demand of protecting privacy and randomness of environmental changes, The users privacy needs of multi-perspective was studied in detail and Platform for Privacy Based on Security Middleware(PPBSM) realized on this basis. Through pre-judgment of users'privacy and environment, the reasonable protection technology been automatic chose by PPBSM. User can realize automatic switching of protection methods and privacy policy. These make the APPs developers and users pay more attention to service logic but not switching of protection methods in different privacy domain by shielding of system complexity and system heterogeneity.