The cryptex (keystone) was designed by Leonardo da Vinci

The cryptex is a portable, mechanical vault invented by Leonardo da Vinci to safeguard secret information. Jacques Saunière, a master craftsman and the Grand Master of the Priory of Sion, built this particular cryptex as a hobby, following blueprints from Da Vinci's secret diaries. The device is a marble cylinder composed of six doughnut-shaped disks stacked within a brass framework, each disk carved with the full alphabet. When the five lettered dials are rotated to the correct sequence, internal tumblers align, allowing the cylinder to slide apart and reveal a hollow compartment. Inside that compartment, a papyrus scroll is wrapped around a delicate glass vial filled with vinegar. Any attempt to force the cryptex open will shatter the vial, and the vinegar will dissolve the papyrus, destroying the information forever. This self-destruction mechanism ensures that only the person who knows the proper five-letter password can access the secret within. The cryptex thus embodies Da Vinci's genius for combining cryptology with mechanical engineering, offering a solution to the age-old problem of secure message transmission over long distances. Saunière's cryptex, larger and more ornate than any he had made before, is housed in a rosewood box inlaid with a five-petal rose—the Priory's symbol for the Holy Grail. The box itself contains a hidden engraving beneath the rose inlay, a poem that provides the clues for finding the password. The cryptex is not merely a container; it is the Priory's keystone, the encoded map that, once unlocked, reveals the hiding place of the Holy Grail. Saunière, facing death, transferred this keystone to Sophie, commanding her to find Robert Langdon, the Harvard symbologist who could help her decipher its secrets. The cryptex's design, with its reliance on a password and its built-in defense against tampering, makes it a perfect test of worthiness: only the clever and persistent can unlock it and claim the knowledge it guards.