Privacy preserving routing is crucial for some Ad-hoc networks that require stronger privacy protection. A number of schemes have been proposed to protect privacy in Ad-hoc networks. However, little of these schemes offer complete unlinkability or unobservability property since data packets and control packets are still linkable and distinguishable in these schemes. In this book, the author define stronger privacy requirements regarding privacy preserving routing in mobile Ad-hoc networks. Then he propose an unobservable secure routing scheme USOR to offer complete unlinkability and content unobservability for all types of packets. USOR is efficient as it uses a novel combination of group signature and ID based encryption for route discovery. Security analysis demonstrates that USOR can well protect user privacy against both inside and outside attackers.