Decoding the Renaissance exhibition material
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.
Sir Francis Walsingham
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.
Ciphers, Codes, & Steganography
Alphabet Substitution Tables
Alphanumeric tables are one of the first great technical inventions in the field of cryptography, and it may not be an accident that they emerged with the advent of movable type. They took advantage of what the printing press did especially well — distributing permutations of individual letters and numbers in a square or rectangular grid — and they made the work of substituting plain-text with cipher-text easier, more accurate, and far more secure.
Best known for the twentieth century typeface that was named a after him, Palatino was a sixteenth century calligrapher with a gift for designing beautiful and legible letters. Among the model alphabets in his 1566 writing manual (seen at the top of the page) was this set of arbitrary symbols for use as ciphers — complete with “nulls," or meaningless figures that could be interspersed with meaningful ones to make decryption more difficult.
Disks and Volvelles
The cipher disk may be the most iconic image in the history of cryptography, placing a simple but powerful system of alphanumeric substitution into the palm of one's hand. In Renaissance books, the cipher disk was attached to the page with string or paper or parchment strips, and the different layers could be rotated independently to create new cipher alphabets. This moveable book technology was known as a volvelle. Friedman's friend, the classicist and cryptanalyst Charles J. Mendelsohn, considered Giambattista della Porta the outstanding cryptographer of the Renaissance. He had a particularly solid grasp of the use of cipher disks, explaining how they can be converted into tables and vice versa. His books featured some of the period's most ornate volvelles, such as the one seen above.
Alongside the development of cryptography (whereby a message is scrambled using transposition or substitution), there was a parallel field called steganography (in which messages are kept intact but hidden within an innocent cover). An example of this can be seen in Johannes Balthasar Friderici's Cryptographia. At first glance, this image simply depicts a building under siege. But there are letters lurking in the window-panes. Variations in their shaded, unshaded, and dotted panels can be matched up with the alphabetical key on the next page, revealing a desperate message "Wir haben kein Pulver mehr"(We have have no more [gun]powder).
William Friedman and his team at Riverbank were always on the lookout for ways to apply Renaissance codes to modern life. In 1920 they published an article for the Florists' Review on the famous trade slogan, "Say It With Flowers," suggesting that carefully designed bouquets could not only express general sentiments (such as love or sympathy) but also carry hidden messages. They provided an example from a seventeenth century German cryptography manual using a floral wreath and alphabetical key.
Music was another signifying system that could be used both to convey and to cover secret messages, with particular notes standing in for the different letters in the alphabet. The systems shown on the right made it possible for musical compositions to speak to people even when they did not contain words. As in other examples, Friedman used the sheet music (arranged for solo mandolin) for Stephen Foster's famous song, "My Old Kentucky Home, Good Night" to show how, using Bacon's biliteral cipher, anything can be made to signify anything. By making notches in the stems of some notes and leaving others whole, he has turned the music into a sequence of a's and b's that read "Enemy advancing right / We march at daybreak."
Popular scientist, Girolamo Cardano, was credited with an invention that is still in use today. In the so-called “Cardan grille,” a sheet with narrow rectangles of varying widths cut out of it is laid over a blank page and the secret message is written in the spaces. The sheet is then removed and the rest of the spaces are filled in with innocent—or even misleading—text. When the recipient lays the same grid over the paper in the same position, the hidden message is revealed. Della Porta’s popular treatise on secret writing includes clear instructions for using a grille—or a membrane, as he describes it—with windows and gaps (fenestras et vacua). To make sure that the recipient knows where to place the overlay, four points should be drawn to mark the edges
The Friedmans' Cryptographic Christmas Card
Undoubtedly the most ingenious of the Friedmans’ annual cryptographic Christmas cards, this telegram came with a special kind of grille. Each 90-degree turn revealed a different hidden message, and the four directions yielded a rhyming quatrain:
“FOR CHRISTMAS GREETINGS IN 28
WE USE A MEANS QUITE UP TO DATE
A CRYPTOTELEPHOTGRAM HERE
BRINGS YOU WORD OF XMAS CHEER.”