Abstract: An inter-active key-lock system uses an unlock sequence in which messages exchanged between the key and lock include class-codes and unique-codes as parts of such messages. Dynamic indicators or labels are also stored in the lock memory for control purposes. These labels include "authorities" which indicate whether a key is able to make another key for the same lock or able to deactivate keys from use with the lock, and "parents" which indicate which parent key was used to make an additional key. The system enables an individual lock owner to code a key and control coding of additional keys on an exclusive basis, with the feature that there is no master-key and no emergency code available to the manufacturer or usable by any authorized service representative to unlock the lock.