Peer-to-Peer Instant Messaging System

With the development of the Internet, instant messaging systems grow and develop rapidly in recent years. Traditional instant messaging systems have been implemented using the client/server model of networking. With huge user base, the servers have to do a lot of work to maintain users'information and message exchanging. Such systems can be costly and hard to expand.Peer-to-Peer is a self-organizing, scalable, robust distributed network. Designing an instant messaging system based on p2p technology will overcome the drawback of traditional client/server model.In this paper, a peer-to-peer instant messaging system is proposed and developed. This system uses DHT p2p protocol for node lookup and user finding. Nodes in the system are divided into two types, super node or ordinary node. The nodes with high capacity and availability are made super-nodes and will provide service for ordinary nodes. XMPP is used as the base protocol for interoperability. XMPP is an open XML technology for real-time communication and easy to make an extension.NAT is another common problem for p2p system. The system provides some mechanism to detect the NAT types. A reliable UDP protocol is also implemented for NAT traversal.In order to protect sensitive information, the system uses AES to encrypt messages. RSA is used to negotiate symmetric AES keys. User public keys are certified by the server. From the test result, this system has more scalability than the traditional client/server model. It also can reduce the burden on the server and can easily traverse NAT.