The Renaissance was the first great age of mass communication, but it was also the period when the art of secret writing came into its own. The new science of codes and ciphers produced some of the period’s most brilliant inventions, most beautiful books, and most enduring legacies.
One of the oldest cryptographic books was written by the quintessential Renaissance Man, Leon Battista Alberti. His short text on ciphers, Opuscoli morali, first published in this 1568 collection, was written a century earlier, making it Europe’s oldest extant treatise on ciphers and earning Alberti the title of Father of Western Cryptology.
However, the first printed cryptographic book was Trithemius’ posthumous work on polygraphic (or multiple writing) systems, Polygraphiae libri sex. The title -page, which can be seen below, depicts Trithemius presenting the book to its dedicatee, Emperor Maximilian I. The monk behind him provides the keys to the locked book, whose secrets are central to the exercise of power in church and state.
Not all secret communication depends on codes and ciphers, and one of the oldest tricks in the book was to make the message itself invisible. Using nothing more than materials found in the average kitchen, such as lemon juice and a candle, it is possible to make written letters disappear and reappear at will. Other methods of creating invisible ink can be found in John Wilkins’ book, Mercury; or the secret and swift messenger. Some of his suggestions include: Sal ammoniac dissolved in water, which will reappear when heated; the “juice of glow-worms,” which is visible only in the dark, and a “glutinous moisture” such as milk or fat that will become legible when sprinkled with dust.