Abstract: An electronic security device has at least one lock and a control center for generating keys to the lock. When a new key is generated, a new (second) combination is generated by applying a predetermined algorithm and randomly generated (first) calculation data to the previous (first) combination. To calculate a next new (third) combination, another randomly generated (second) calculation data is applied to the second combination using the same algorithm. The control center stores, on the key, the third combination, and the second calculation data used to obtain it and the first calculation data used to obtain the second combination. At the lock, the third combination is compared with a stored combination and if there is no match, the lock calculates a possible second combination by applying an algorithm, which is the inverse of the predetermined algorithm, to the stored combination using the second calculation data read from the key.