A pin-tumbler locking mechanism comprising: a lock-core with an elongated key slot and a series of bores (161H-165H) arranged in a plane of the key slot; a corresponding series of driver pins of various lengths slidably received in the bores; a lock-core casing movably supporting the lock-core, the interface between the lock-core and the lock casing defining a planar surface; a first series of spring-supported key pins seated in a series of bores coaxially with the said driver pins so that normally at least some of the key pins extend beyond the planar surface, being in contact and adapted to push the driver pins to project into the key slot each by a different extent according to the respective lengths thereof; a first key comprising alternately teeth and notches (131;132) so that when inserted into the key slot the driver pin ends contacting the key pins become flushed with the planar surface to allow said movement of the lock-core; wherein the locking of the locking mechanism is attained by sliding the lock-core by the key a pre-set distance ("the core locked position") and withdrawing the key from the key slot; and wherein the lock core is of prismatic shape and said movement is a sliding movement characterized by a second key and a second series of key pins (156;157) in line with the said first series, whereby in the said locked position at least some of the said first series of driver pins (164; 165) become aligned with the key pins (156; 157) of the second series whereby the unlocking of the mechanism is attained by inserting the second key with teeth and noches (130;133) into the key slot and pulling the lock-core by the second key away from the core locked position and withdrawing the key from the key slot ("the unlocked core position"). a lock-core with an elongated key slot and a series of bores (161H-165H) arranged in a plane of the key slot; a corresponding series of driver pins of various lengths slidably received in the bores; a lock-core casing movably supporting the lock-core, the interface between the lock-core and the lock casing defining a planar surface; a first series of spring-supported key pins seated in a series of bores coaxially with the said driver pins so that normally at least some of the key pins extend beyond the planar surface, being in contact and adapted to push the driver pins to project into the key slot each by a different extent according to the respective lengths thereof; a first key comprising alternately teeth and notches (131;132) so that when inserted into the key slot the driver pin ends contacting the key pins become flushed with the planar surface to allow said movement of the lock-core; wherein the locking of the locking mechanism is attained by sliding the lock-core by the key a pre-set distance ("the core locked position") and withdrawing the key from the key slot; and wherein the lock core is of prismatic shape and said movement is a sliding movement characterized by a second key and a second series of key pins (156;157) in line with the said first series, whereby in the said locked position at least some of the said first series of driver pins (164; 165) become aligned with the key pins (156; 157) of the second series whereby the unlocking of the mechanism is attained by inserting the second key with teeth and noches (130;133) into the key slot and pulling the lock-core by the second key away from the core locked position and withdrawing the key from the key slot ("the unlocked core position").