在現今的社會中，如行動電話、PDA、平板電腦等等行動裝置(mobile device)通常都搭配了GPS，這使得攜帶這些行動裝置的使用者們可以很方便地使用適地性服務(location-based services)的功能。在使用適地性服務時，使用者發送自己目前所在的位置以詢問POIs。但是，保持位置資訊的私密性是非常重要的。如果一個使用者無論走到哪裡都被持續地監控，他的行蹤可能會很容易地被人掌握。為了避免暴露使用者的行蹤，在適地性服務中位置資訊應該要受到妥善的保護。我們利用遮蔽(cloaking) 的概念來保護使用者的位置資訊，伺服器端接受一個包含了使用者的區域位置，來取代原本使用者的確切位置。但是，傳統的遮蔽系統受到關連式攻擊(correlation attacks)的影響。藉由觀察遮蔽區域(cloaking region)中行動裝置的移動情形，敵人可以過濾出特定的使用者。為了提供更好的位置資訊保護，在這篇論文中，我們介紹了間諜遮蔽系統(spy-based cloaking system)。在我們的方法中，我們使用數個間諜來做為保護真正使用者的掩護。模擬結果顯示，雖然這個方法將造成較大的負擔，但是間諜遮蔽系統能夠提供更加完善的位置資訊隱私保護來抵禦關連式攻擊。Nowadays, mobile devices are commonly embedded with GPS, such as cell phones, PDAs, and Tablet PCs. This allows people carrying in these mobile devices to enjoy the convenience of location-based services. In LBSs, a user commonly sends its own location to query for POIs. However, the privacy of the location information is very important. If a user whereabout is monitored continuously, his/her activities can be easily inferred. To avoid the exposure of the user’s activity, the location information should be protected in location-based services.The concept of cloaking has been introduced to protect the user’s location information. In cloaking system, an area containing the user’s location is sent to the server for query instead of the user’s true location. However, the traditional cloaking systems suffer from correlation attacks. By observing the traffic of the cloaking region, an adversary can eventually identify a particular client. To provide better location privacy protection, in this thesis we introduce the spy-based cloaking system. In our system, a number of spies are used as the disguise to protect the true identity of the client. The simulation results show that, albeit the higher communication overhead, the proposed spy-based cloaking system is able to provide a much stronger location information privacy protection against correlation attacks.
