Decoding the Renaissance exhibition material

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The Origins of Cryptography

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.

Cryptography in Shakespeare's Time

The cryptographic book emerged with—and through—the invention of movable type, but people had been using cryptographic means to secure their communications for centuries before the advent of print. Diplomatic and commercial business throughout the medieval and early modern periods depended heavily on handwritten codes and ciphers. Official correspondence and private documents alike are peppered with mysterious symbols designed to be read only by those who had the key to the system.

Widely known and feared as England's first spymaster, Secretary of State Sir Francis Walsingham used every trick in the book to search out secrets among his enemies while keeping his own communications secure.

In the letter seen here, he communicates Queen Elizabeth's wishes as the King of France was on his deathbed: he advises "great circumspection" in "the matter" and urges those involved to "beware whom they trust." He is careful to put the most sensitive information into cipher.

Sir Francis Bacon

In addition to leaving secret codes in Shakespeare's plays (a theory that has proven unfounded), famous politician Sir Francis Bacon is known for providing the first English summary of the science of ciphers in his famous work Of the Advancement of Learning.

In Of the Advancement of Learning, Bacon describes his own invention — while just a teenager— of the so-called bilateral cipher. The original 1605 edition mentions the episode only in passing; but the extended Latin edition of 1623 and its English version of 1640 explain the system in detail and show how it works in practice.

Bacon’s Biliteral Cipher

In the course of the sixteenth century, cryptographers found ways to reduce the entire alphabet to only a few letters—and the great scientist and statesman Sir Francis Bacon devised a system using just two. In Bacon’s “biliteral” (or two-letter) system, each letter of the English alphabet is represented by a different five-letter combination of A’s and B’s, from AAAAA for A to BABBB for Z.

What made Bacon’s invention so powerful is that these A’s and B’s could be represented by two types of anything—roman and italic type, pluses and minuses, apples and oranges, and so on. Using this system, as Friedman was fond of quoting, “it is possible to signify omnia per omnia (anything by means of anything).”

William Friedman kept copies of the above photo under the glass on his office desk and on the wall of his home study. It served as the graduation photo for his first course in military cryptanalysis, taught to a group of World War I officers sent to Riverbank for training. It remained his most cherished example of how to make anything signify anything using Bacon’s biliteral cipher. In this case, the A-types look at the camera and the B-types look away, using Bacon’s method of encryption to spell out his famous axiom, KNOWLEDGE IS POWER—which Friedman took as his personal motto and had inscribed on his tomb in Arlington National Cemetery.

Watch a video of curator, Dr. Bill Sherman, discussing the "Knowledge is Power" photograph.