Abstract: A security system includes an electronic lock and an electronic key. The electronic key holds identification data that notifies the lock of the key's functional type and the locks that the key is authorized to open. In one embodiment, circuitry in the lock checks whether an inserted key holds an access code that is more recent than a corresponding access code stored in the lock, indicating that the data on the inserted key is more current than the data stored in the lock. The lock is then automatically reprogrammed with the data stored in the inserted key.