A pin-tumbler locking mechanism comprising a lock-core with an elongated key slot and a series of bores arranged in a plane of the key slot for a corresponding series of driver pins of various lengths slidably received in the bores. The lock-core is normally supported in lock casing. A corresponding series of spring-supported key pins is seated in a series of bores coaxially with the driver pins so that normally at least some of the key pins are adapted to push respective driver pins to project into the key slot each by a different extent according to the respective lengths thereof; a key comprising alternately teeth and notches so that when inserted into the key slot, the driver pin ends contacting the key pins become flushed with planar surface to allow a sliding movement of the lock-core within the lock casing.