A method for registering first and second electronic keys (2a, 2b) to a controller (6) of a communication subject (1) through communication with a data center (10) includes acquiring first and second key identification information (KID-1, KID-2) from the first and second electronic keys (2a, 2b) with the controller (6), transmitting communication subject identification information (VID) together with both of the first and second key identification information (KID-1, KID-2) from the controller (6) to the data center (10), acquiring a first encryption key generation code (SC-A1) corresponding to the first electronic key (2a) together with a second encryption key generation code (SC-A2) corresponding to the second electronic key (2b) from the data center (10) with the controller, generating a first key encryption key (K-1) based on the first encryption key generation code (SC-A1) with the controller, generating a second key encryption key (K-2) based on the second encryption key generation code (SC-A2) with the controller, and storing the first and second key encryption keys (K-1, K-2) in the controller (6).