Nadael Guindy's Cryptographic Gadget Brings Leon Alberti's Cipher Discs to the Arduino UNO
The hottest new thing in 1460's cryptography can now sit on your desk, no brass required.
Maker Nadael Guindy has brought a classic of cryptography up to date — by building an Alberti cipher disc powered by an Arduino UNO board.
"In 1467, the quintessential 'Renaissance Man' Leon Battista Alberti changed the world of secrets forever," Guindy explains by way of background to the project. "Alberti invented what is now considered the world's first polyalphabetic cipher: a mechanical device featuring two concentric disks that allowed for encryption far more sophisticated than the simple substitution ciphers that had come before it. By translating Alberti's physical brass rings into an Arduino-powered digital system, this project explores how a tool designed over half a millennium ago can still be evolved using modern electronics."
A substitution cipher is a way to take a plain-text message and protect it against casual observation: take each letter and swap it for a different letter, or for symbols or numbers. Without knowing which letters have been swapped, it's difficult to read the message — though not impossible, particularly when all letters have been swapped by the same number of places in the alphabet. A polyaphabetic cipher goes a step beyond a simple substitution cypher, with Alberti's brass disc implementation being one of the first recorded.
Guindy's recreation borrows a similar layout to the dual-disc brass of the original, though this is purely an aesthetic affectation: the hard work is carried out in an Arduino UNO, running a digital Alberti cipher and displaying the result on an OLED screen. Two knobs provide a way to control the cipher: a potentiometer for "coarse" base shift selection, and a rotary encoder for picking individual letters.
"To make the encryption incredibly secure, the device doesn't just use one static shift; it uses a non-linear dynamic key," Guindy explains. "This means that for every few letters you type, the 'inner disc' automatically shifts in a complex, constant pattern based on a mathematical formula. Because the key changes as you go, the same letter will be represented by different characters throughout the message, making it nearly impossible for a codebreaker to spot a pattern without knowing the secret starting position!"
The project is documented in full, including wiring diagrams and source code, on Instructables.