We focus on this book on the authentication between the nodes and certificate authorities (CAs) distributed over the network. First, we choose the on-demand routing protocol, like Ad Hoc On-Demand Distance Vector (AODV) protocol, to apply the authentication schemes on MANETs. Second, we choose fully distributed certificate authority to construct our approaches on the certificate authority issue. Routing is a very important function in MANETs. It can also be easily misused, leading to several types of attack. Routing protocols in general are prone to attacks from malicious nodes. These protocols are usually not designed with security in mind and often are very vulnerable to node misbehavior. This is particularly true for MANET routing protocols because they are designed for minimizing the level of overhead and for allowing every node to participate in the routing process. Making routing protocols efficient often increases the security risk of the protocol and allows a single node to significantly impact the operation of the protocol because of the lack of protocol redundancy.