Abstract: A key and lock device comprises a key and a stand-alone lock. The key has an electronic circuitry with a first memory and a first contact. The lock has an electronic circuitry with a second memory means, and a second contact means arranged to co-operate with the first contact means. Also, there is a blocking mechanism adapted to block operation of the lock unless an authorised key is inserted in the lock. The memory of the key stores a public identification item of the key identifying a group of keys having identical mechanical codes. In the memory of the lock, there is provided a list of the public and secret identification items of authorised keys and a list of the public identification item of non-authorised keys, A key is authorised if the public and secret identification items are present in the list of authorised keys and the public identification item thereof is absent in the list of non-authorised keys.