A computer readable program comprising instructions which, when the program is executed by a computer, cause the computer to control a registration server connected to a first network, by carrying out the following steps: receiving user identification information from a communication terminal connected to a second network different from the first network for identifying a user; receiving device identification information from the communication terminal the device identification information identifying, on the second network, an information device connected to the second network; transmitting, to a management server connected to the first network, the received user identification information; receiving authentication information from the management server when the management server transmits the authentication information as a response to the transmitted user identification information; generating registration information which has a format in which the authentication information is allowed to be registered in the information device, the registration information including at least the authentication information and the device identification information; transmitting the generated registration information to the communication terminal; wherein the information device receives and stores the authentication information from the communication terminal; then the information device transmits a connection request to the management server, the connection request including the received authentication information and the information device identification information; then the information device receives permission information for performing communication with the management server; wherein the management server transmits the permission information in response to the connection request transmitted by the information device; and the information device stores the received permission information; wherein the management server and the information device perform secure communication on the basis of the generated and received permission information. receiving user identification information from a communication terminal connected to a second network different from the first network for identifying a user; receiving device identification information from the communication terminal the device identification information identifying, on the second network, an information device connected to the second network; transmitting, to a management server connected to the first network, the received user identification information; receiving authentication information from the management server when the management server transmits the authentication information as a response to the transmitted user identification information; generating registration information which has a format in which the authentication information is allowed to be registered in the information device, the registration information including at least the authentication information and the device identification information; transmitting the generated registration information to the communication terminal; wherein the information device receives and stores the authentication information from the communication terminal; then the information device transmits a connection request to the management server, the connection request including the received authentication information and the information device identification information; then the information device receives permission information for performing communication with the management server; wherein the management server transmits the permission information in response to the connection request transmitted by the information device; and the information device stores the received permission information; wherein the management server and the information device perform secure communication on the basis of the generated and received permission information.