Patent ID: 8775796

Claim:
A certificate authenticating method that authenticates a terminal device capable of connecting to a first network by using a communication ID to allow the terminal device to connect a second network different from the first network, the terminal device having a sub ID, wherein ID is an abbreviation of identifier, comprising: (a) a step by the terminal device of transmitting, via the first network, a certificate issue request including at least the communication ID and the sub ID to a certificate issuing device connected to the first network, the communication ID being a global IP address and the sub ID being a private IP address; (b) a step by the certificate issuing device of requesting a communication ID checking device to check whether or not the communication ID of the terminal device included in the certificate issue request is in use when the certificate issue request is received from the terminal device via the first network, requesting a communication ID/sub ID checking device to check whether or not the association between the communication ID and the sub ID is proper, generating a certificate including at least an ID of the certificate issuing device, the communication ID and the sub ID of the terminal device and a validity period if at least the check results from the communication ID checking device and the communication ID/sub ID checking device are OK, and transmitting the certificate to the terminal device; (c) a step by the terminal device of transmitting an authentication request including at least the sub ID for authentication of the certificate to an authentication device on the second network; and (d) a step by the authentication device of carrying out authentication of the certificate in response to the authentication request.