Francis Bacon and the biliteral cipher: two signs for the alphabet

Among the many ideas of Francis Bacon, philosopher, jurist and Lord Chancellor of England, there is one that strikingly anticipates the language of computers. In the De dignitate et augmentis scientiarum, published in 1623, Bacon describes a system in which every letter of the alphabet is represented by a combination of only two signs. He calls it the biliteral cipher, and says he devised it as a young man during a stay in Paris.

The principle of two letters

The system uses two symbols, written a and b, grouped in fives. Since five positions with two possibilities give thirty-two combinations, these are enough to represent all the letters of the Latin alphabet of the time. Thus A becomes aaaaa, B aaaab, C aaaba, and so on. In modern terms it is a five-element binary code, more than two centuries before the telegraph.

Bacon presents the system in a chapter devoted to ciphers, in the sixth book of the treatise, where he also lists the qualities a good cipher should have: to be easy to write and read, hard for outsiders to decipher and, where possible, such as to arouse no suspicion. This last requirement is the key to understanding his invention.

Hiding one text in another

The most ingenious aspect is the way Bacon proposes to conceal these sequences. One does not actually write the letters a and b, but uses two slightly different forms of writing, for example two typefaces. Each letter of any perfectly harmless text is written in form a or form b, and whoever knows the system reads, by grouping the forms in fives, a second hidden message.

It is therefore a form of steganography rather than pure cryptography: the secret message is hidden within a text that may say something entirely different. Bacon was aware of the power of the idea and observed that by this method one can express omnia per omnia, everything by means of everything, provided one has any two differences, such as the sounds of bells, light signals or knocks.

The Shakespeare controversy

In the nineteenth and early twentieth centuries the biliteral cipher became the heart of a literary controversy. Some supporters of the Baconian theory, according to which Bacon was the true author of Shakespeare's works, searched for hidden messages in the early editions of the plays. The American Elizabeth Wells Gallup claimed to have identified in the First Folio of 1623 typographical differences which, read with the biliteral method, revealed Bacon's confessions.

Her research was funded by George Fabyan at the Riverbank Laboratories near Chicago, where the young William and Elizabeth Friedman, future great cryptologists, also worked. It was the Friedmans who, many years later, in their 1957 book The Shakespearean Ciphers Examined, showed that the alleged typographical differences followed no consistent pattern and that the Baconian readings were groundless.

The biliteral cipher thus remains a brilliant idea surrounded by a myth. On the one hand it is one of the earliest examples of a binary representation of the alphabet and an elegant model of concealment; on the other it fuelled one of the longest literary treasure hunts in history, brought to an end by the rigour of those who had learned to read ciphers precisely by following its trail.