In solving a challenge set by GCHQ (the British intelligence organisation responsible for codebreaking) I came across an interesting method of encryption. Rather than immediately launching into a description of the Bacon Cipher I will give you a little historical context:

William Shakespeare is credited with the creation of some of the greatest works of English literature. His legacy lives to the present day, and generations of high school students have studied the writing of the great man.

There is just one problem. Shakespeare may not have written the plays we give him credit for.

In the Collegiate Church of the Holy Trinity in Stratford-upon-Avon, the town where Shakespeare is believed to have lived, there is a bust of the English bard. The inscription below it was unusual because it uses mixed case letters. It was a study of this inscription which led to the discovery of the Bacon Cipher.

The message found was "Francis Bacon wrote Shakespeare's plays."

How it works

Each letter in the alphabet it given a representative number from A = 1 to Z = 26.

The real message is hidden in plain text. For example, capital letters might be included in the message while lower case letters are discarded.

Letters which are part of the encrypted message are collected into groups of five. Each group of five letters represents a five digit binary number. In our example, it might be the case that vowels represent 1s while consonants represent 0s. Five digits are required in order to represent all the numbers between 1 (00001) and 26 (11010).

When each five digit binary number is converted to its decimal equivalent it gives the position of a letter in the alphabet. This is how a message is concealed in plain text using the Bacon Cipher.



Grouping the capitals together in groups of five letters gives us:


If vowels are 1s and consonants are 0s then we get:

01000, 00101, 01100, 01100, 01111

As decimal these numbers are:

8, 5, 12, 12, 15

Substitute these numbers for the appropriate letters in the alphabet and we have our message:


This is the version of the Bacon cipher used by GCHQ in their original challenge. Since the cipher was only discovered after Bacon's death, all details of the cipher are taken from analysis of examples of the cipher. However, ariels has pointed out to me that the binary system was invented much later by Gottfried Liebniz. Mysterious...