Abstract: Impregnable locking system of the fastening of display-boxes called "blisters", consisting in a box in two articulated halves having on the side opposite their hinge fastening flaps destined to be held one against the other by this system, characterized in that it consists in a clip destined to cover these two flaps, and between which is attached a transversal shaft, a vertical notch made in the flaps allowing this shaft to go through when the clip is put into place, two gears being slid onto this shaft, between the outer side of each flap and the corresponding side of the clip, the means being provided so that these gears are constantly pushed towards each other, and once this clip placed on the flaps, the gears come to rest in the lodgings made in the outer sides of the flaps, therefore immobilizing the clip onto the flaps, external means being provided to push the gears in the opposite direction to take them out of the lodgings to allow the extraction of the clip and to free the flaps of the blister to all