Long before smartphones, information was processed using punched cards. Early machines could be "programmed" by arranging stacks of cards in a particular order, allowing complex calculations and instructions to be carried out mechanically. One of the most famous (and notorious) machines of the twentieth century was Enigma, used by Germany during World War II to encrypt military communications.
Recently, historians uncovered evidence of several experimental Enigma prototypes that predated the machine's final design. While these early versions never entered widespread service, they reveal the inner workings of how information was routed through physical pathways rather than electronic circuits. Inspired by these discoveries, I have recreated one of these prototype concepts here using nothing more than ordinary cards. Follow the chain of instructions exactly, and you will experience a simple card-based encryption machine remarkably similar in spirit to the devices that once protected some of the world's most closely guarded secrets.
