Cryptography in Shakespeare’s Time

The cryptographic book emerged with—and through—the invention of moveable 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. 


Walsingham Letter

Copy of instructions to an ambassador, November 23, 1577. Manuscript, 17th or 18th century.

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 portrait

Frederick Hendrick van Hove. Right honorable Sir Francis Bacon. Engraving, mid to late 17th century.

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. 


page 631 of “The Second booke” of Francis Bacon

Francis Bacon. The tvvoo bookes of Francis Bacon. Of the proficience and aduancement of learning, diuine and humane. London, 1605.

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.


pages 278 and 279 of augmentis scientiarum

Francis Bacon. De dignitate & augmentis scientiarum libros IX. London, 1623.

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).”


Knowledge is Power photograph
William Friedman. "Knowledge is Power," ca. 1918. Courtesy of the George C. Marshall Foundation.

Friedman and the Biliteral Cipher

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.