The lock originated in the Near East, with the oldest known example discovered in the ruins of Khorsabad's palace near Nineveh known today as Iraq [3]. It is of the type known as a pin tumbler or, because to its widespread use in Egypt, an Egyptian lock, and is possibly 4,000 years old [3]. It is made up of a huge wooden bolt that secures the door and is perforated by a slot with multiple holes in its upper surface (figure 5) [4]. A door assembly has multiple wooden pins that are positioned to drop into these holes and grasp the bolt [3]. The key is a large wooden bar in the style of a toothbrush, but instead of bristles, it contains upright pegs that match the holes and pins [5]. Inserted into the huge keyhole beneath the vertical pins, it is easily lifted, allowing the pins to clear and the bolt with the key to be moved back [5].

Linus Yale made a significant contribution in 1848 when he invented a pin tumbler lock based on an adaption of the ancient Egyptian principle [5]. In the 1860s, his son Linus Yale, Jr. invented the Yale cylinder lock, with its compact, flat key with a serrated edge, which is currently the most well-known lock and key in the world (figure 7) [5]. The serrations lift the pins in the cylinder to the right heights, allowing the cylinder to be turned [5]. The amount of pin height combinations (typically five), along with the warding effect of the crooked key and keyhole, provide an almost infinite number of variations [5].