According to the advance of the Internet and development of information technologies, people tend toward establishing virtual communities and asserting their opinions. To build virtual community, most important things are how they can make the community and carry their points in a cyberspace. We can consider many approaches to achieve these goals. The most useful approaches are that we can think peer-to-peer (simply P2P) system as a tool for establishing the community on the Internet, and the Internet voting can be regarded as the way to assert their opinions. However, P2P and the Internet voting system are hesitated people about many security problems. Particularly, authentication problems are considered an important issue. Through this thesis, we propose two mechanisms for efficient authentication: adaptive authentication for P2P system and extension of votopia [29] based on adaptive authentication.
The technology of communication among people on the Internet was previously focused on the server-oriented system, but recently changed into a kind of distributed computing, P2P systems which can not only be applied to instant messaging, collaborate computing, etc., but also be considered the foundation for binding people. Like a real face-to-face trust relationship, each peer with complicated trust relationship faced complex security problems. Especially, an authentication problem among peers will be an important issue. Although P2P network must not only provide pseudonymity but also satisfy strong authentication in case that a peer does business transaction with another one, most of current P2P services just adopt a weak authentication method using pseudonym and password. Hence, we propose an Adaptive Authentication Protocol based on Reputation(AAPR) which can satisfy requirements ranging from pseudonymity to strong authentication based on certificate. Also we consider the context-dependent reputation concept and the minimization of certificate issuing cost by...