COMMUNICATION SYSTEM, RELIABLE COMMUNICATION MECHANISM, AND COMMUNICATION METHOD USED FOR THEM

摘要

Provided is a communication system which can solve a problem that may occur in a user terminal, a client, or a server and which can prevent an attack from an indefinite partner. A mediation server (1) accepts an attack from outside instead of a server (34) (server A), directly receives a communication destined to a node-representative ID, and performs a first authentication of the communication. If the authentication shows a reliable user terminal or a client (42) (client B), the mediation server (34) provides a mediation server ID for identifying a mediation server (2) to the device. The mediation server (2) performs a second authentication of the user terminal and the client (42) (client B) which have been successfully authenticated by the mediation server (1). If reliability of the user terminal and the client (42) (client B) is confirmed, the mediation server (2) asks the server (34) (server A) about an ID and provides a traceable identifier acquired from the server (34) (server A), to the user terminal and the client (42) (client B).