Fictional combination locks

It would perhaps be remiss not to include a few words about a fictional combination lock that has titillated many readers and moviegoers in recent years: the cryptex in Dan Brown’s The da Vinci Code.

Many great minds in history had invented cryptologic solutions to the challenge of data protection: Julius Caesar devised a code-writing scheme called the Caesar Box; Mary, Queen of Scots created a substitution cipher and sent secret communiqués from prison; and the brilliant Arab scientist Abu Yusuf Ismail al-Kindi protected his secrets with an ingeniously conceived partly alphabetic substitution cipher.

Da Vinci, however, eschewed mathematics and cryptology for a mechanical solution. The cryptex. A portable container that could safeguard letters, maps, diagrams, anything at all. Once information was sealed inside the cryptex, only the individual with the proper password could access it.
“We require a password,” Sophie said, pointing out the lettered dials. “A cryptex works much like a bicycle’s combination lock. If you align the dials in the proper position, the lock slides open. This cryptex has five lettered dials. When you rotate them to their proper sequence, the tumblers inside align, and the entire cylinder slides apart.”
“And inside?”
“Once the cylinder slides apart you have access to a hollow central compartment, which can hold a scroll of paper on which is the information you want to keep private.”

Langdon eyed the device again, still looking skeptical. “But why not just pry it apart? Or smash it? The metal looks delicate, and marble is a soft rock.”
Sophie smiled. “Because da Vinci is too smart for that. He designed the cryptex so that if you try to force it open in any way, the information self-destructs. Watch.” Sophie reached into the box and carefully lifted out the cylinder. “Any information to be inserted is first written on a papyrus scroll.”
“Not vellum?”
Sophie shook her head. “Papyrus. I know sheep’s vellum was more durable and more common in those days, but it had to be papyrus. The thinner the better.”
“Before the papyrus was inserted into the cryptex compartment, it was rolled around a delicate glass vial.” She tipped the cryptex and the liquid inside gurgled. “A vial of liquid.”
“Liquid what?”
Sophie smiled. “Vinegar.”
Langdon hesitated a moment and then began nodding. “Brilliant.”

Vinegar and papyrus, Sophie thought. If someone attempted to force open the cryptex, the glass vial would break, and the vinegar would quickly dissolve the papyrus. By the time anyone extracted secret message, it would be a glob of meaningless pulp.

The cryptex, however, is Dan Brown’s own invention.