Patent ID: 7873827

Claim:
A communication system comprising: a communication device configured to be verified and identified by an authentication device with electronically signed public key certificate; a certificate update device comprising: a transmission unit configured to transmit a request for transmitting the public key certificate to the communication device; a receiving unit configured to receive the public key certificate transmitted from the communication device; a controller configured to determine, based on the public key certificate transmitted from the communication device, whether, when identification information of the communication device is to be changed, the public key certificate is revoked after the identification information is changed; and a certificate update unit configured to execute a process to instruct the authentication device to update the public key certificate of the communication device before a public key certificate would be revoked after the identification information is changed; and an information change unit that changes identification information of the communication device, wherein the public key certificate of the communication device contains identification information of the communication device that is holder information, and wherein the certificate update unit is configured to execute the process to instruct the authentication device to update the public key certificate so that the holder information is changed to be new identification information before the information change unit changes the identification information of the communication device to the new identification information.