Abstract: A generating section generates a presentation symbol string for receiving a next authentication request to an authenticated ID, a storing section stores a transformation rule and a sending destination of the presentation symbol string to be associated with each ID, a sending section sends “the generated presentation symbol string” to a display terminal, which is “the sending destination of the presentation symbol string stored in the storing section to be associated with the authenticated ID”, an updating section causes the storing section to further store the presentation symbol string sent to be associated with the authenticated ID to perform update, a receiving section receives an authentication request that designates an ID and a transformed symbol string from an access terminal, and an authenticating section causes authentication of the ID to succeed when a condition is satisfied where “the received transformed symbol string matches a transformation result obtained by applying ‘the transformation rule st

Abstract: A communication system preferable to a technique of allowing only an ISP (151) connecting a user terminal to the Internet to manage information about the charging for the service provided to the user by an ASP (132) in the Internet so as to prevent credit card information on the credit card of the user from leaking into the Internet and preferable to dial-up server for providing connection with access limit to a computer communication network such as the Internet to a terminal, a relay device, a service providing device, a relay method, a service providing method, and a program product for realizing them. The feasibility of the relay between a terminal (111) and an ASP (132)I by an ISP (151) is determined on the basis of the relay condition (for example, the condition determined by the IP address and the port number) correlated with the user using the terminal (111). The system inquires of the ISP (151) if the ASP (132) provides a service to the terminal (111).