Bacon's cipher facts for kids

Image of Bacon's cipher.

Bacon's cipher, also called the Baconian cipher, is a clever way to hide secret messages. It was invented by Francis Bacon in 1605. This cipher is special because it hides a message in the way text looks, not in what the text actually says. Think of it like a secret code hidden in plain sight! It's a type of steganography, which means hiding messages so that only the sender and receiver know they exist. It's also a substitution cipher because it replaces letters with codes, and a concealment cipher because it hides the message within other text.

How Bacon's Cipher Works

To hide a secret message using Bacon's cipher, you first turn each letter of your secret message into a special five-letter code. This code uses only two "letters": 'A' and 'B'. It's like a simple binary code, where 'A' can be thought of as 0 and 'B' as 1.

Here is the main alphabet Bacon used, showing how each letter turns into a code of five 'A's or 'B's:

There is also a second version of Bacon's cipher. In this version, the letters I, J, U, and V each have their own unique code. This makes the cipher slightly different.

Hiding the Message in Text

After you've turned your secret message into a string of 'A's and 'B's, you need a "cover message." This is a normal-looking message that will carry your secret. The cover message must have enough letters to match all the 'A's and 'B's in your secret code.

Next, you choose two different ways to write letters. These are called "typefaces." One typeface will stand for 'A', and the other for 'B'. For example, you could use regular text for 'A' and bold text for 'B'. Or you could use italic text for 'A' and regular text for 'B'.

Then, you write out your cover message. Each letter in the cover message is written in the typeface that matches the 'A' or 'B' in your secret code. For instance, if your secret code starts with 'B', the first letter of your cover message would be in the 'B' typeface. If the next code is 'A', the second letter of your cover message would be in the 'A' typeface, and so on.

Decoding the Message

To read the secret message, you do the opposite. You look at the cover message and replace every letter written in "typeface 1" with an 'A'. You replace every letter written in "typeface 2" with a 'B'.

Once you have a long string of 'A's and 'B's, you group them into sets of five. Then, you use Bacon's alphabet table to turn each five-letter code back into the original secret letter.

The cool thing about Bacon's cipher is that you can use almost any text as your cover message. This makes the secret message very hard to spot because it's hidden right in front of everyone's eyes! The cover message can be about anything, which helps distract anyone trying to find the real secret.

Bacon himself even created a special "Biliteral Alphabet" for handwritten letters. It showed two different ways to write each capital and small letter, one for 'A' and one for 'B'. He published this in his book, De Augmentis Scientiarum.

Baconian Cipher Example

Let's look at an example. Imagine the secret word is 'steganography'. We'll use standard text for 'A' and bold text for 'B'.

Here's a cover message where the secret word is hidden:

To encode a message each letter of the plaintext is replaced by a group of five of the letters 'A' or 'B'.

Now, let's see the pattern of standard and boldface letters. Remember, standard is 'A' and bold is 'B':

ba aabbaa b aaabaaa abba aaaaaa bb aaa bbabaabba ba aaaaaaaa ab b baaab bb babb ab baa abbaabb 'b' bb 'b'.

If we group these into sets of five and decode them using the first Baconian alphabet table (where I/J and U/V share codes):

baaab (S) baaba (T) aabaa (E) aabba (G) aaaaa (A) abbaa (N) abbab (O) aabba (G) baaaa (R) aaaaa (A) abbba (P) aabbb (H) babba (Y)

The last few groups of 'A's and 'B's might not form a real word. This means they are just extra letters from the cover message, not part of the secret message.

Bacon and Shakespeare's Works

Some people who believe Francis Bacon secretly wrote William Shakespeare's plays have claimed he used this cipher to hide messages in the famous First Folio (a collection of Shakespeare's plays). They thought these hidden messages would reveal that Bacon was the real author.

However, expert code-breakers William and Elizebeth Friedman studied these claims very carefully. In their book The Shakespeare Ciphers Examined (1957), they showed that there was no secret cipher from Bacon or anyone else hidden in Shakespeare's works. They found that many different typefaces were used in the First Folio, not just the two needed for Bacon's cipher. Also, printing methods back then made it very hard to accurately hide such a message.

Interestingly, the tombstone of William and Elizebeth Friedman actually included a message hidden in Bacon's cipher! It took many years for someone to discover it.

See also

• Baudot – Another old 5-bit code used for sending messages.
• Null Cipher – A similar type of cipher where the secret message is hidden within a larger, innocent-looking text.