Bacon's Cipher: The Art of Hiding Messages

Bacon’s Cipher (or the Baconian Cipher) is a unique method of message encoding devised by the English philosopher and statesman Francis Bacon in 1605. Unlike typical ciphers that scramble text, Bacon’s Cipher is technically a form of steganography—the art of hiding a message within another message.

If you want to try encrypting or decrypting messages immediately, use our free Online Bacon Cipher Tool.

1. What is Bacon’s Cipher?

At its core, Bacon’s Cipher is a substitution cipher where each letter of the plaintext is replaced by a group of five characters, composed of only two distinct symbols (usually denoted as A and B).

This binary-like structure makes Bacon’s Cipher a forerunner to modern binary computer code.

1.1 Key Characteristics

Feature	Description
Type	Substitution Cipher / Steganography
Symbols	Two distinct symbols (e.g., A and B)
Length	5 ciphertext characters per plaintext letter
Mechanism	Hiding patterns in font, case, or style

2. The Two Versions

There are two common versions of the Baconian alphabet mapping. It is crucial to know which one is being used to decode a message correctly.

2.1 Standard Version (24-Letter)

In Francis Bacon’s time (17th century), the English alphabet treated I and J as the same letter, and U and V as the same letter. Thus, the original cipher uses a 24-letter alphabet.

Plain	Cipher	Plain	Cipher
A	AAAAA	N	ABBAA
B	AAAAB	O	ABBAB
C	AAABA	P	ABBBA
D	AAABB	Q	ABBBB
E	AABAA	R	BAAAA
F	AABAB	S	BAAAB
G	AABBA	T	BAABA
H	AABBB	U/V	BAABB
I/J	ABAAA	W	BABAA
K	ABAAB	X	BABAB
L	ABABA	Y	BABBA
M	ABABB	Z	BABBB

2.2 Distinct Version (26-Letter)

Modern implementations often use a full 26-letter alphabet where every letter has a unique code.

Plain	Cipher	Plain	Cipher
A	AAAAA	N	ABBAA
B	AAAAB	O	ABBAB
C	AAABA	P	ABBBA
D	AAABB	Q	ABBBB
E	AABAA	R	BAAAA
F	AABAB	S	BAAAB
G	AABBA	T	BAABA
H	AABBB	U	BAABB
I	ABAAA	V	BABAA
J	ABAAB	W	BABAB
K	ABABA	X	BABBA
L	ABABB	Y	BABBB
M	ABBAA	Z	BBAAA

Note: Our online tool supports both the Standard (24-letter) and Distinct (26-letter) modes.

3. The Art of Steganography

The true power of Bacon’s Cipher lies in how the As and Bs are represented. They are rarely written as literal “A” and “B”. Instead, they are hidden within a cover text using two different distinct features.

Common ways to represent A and B:

• Typeface: Font 1 = A, Font 2 = B.
• Case: Lowercase = A, Uppercase = B.
• Style: Regular = A, Bold = B.
• Italics: Upright = A, Italic = B.

3.1 An Example

Let’s encrypt the word “GO” using the 26-letter alphabet.

1. Get Codes:

   • G: AABBA
   • O: ABBAB
   • Cipher string: AABBAABBAB

2. Choose Cover Text:

   • “Please help me” (Needs at least 10 letters)

3. Apply Rule:

   • Let’s use Uppercase for B and Lowercase for A.

   • Pattern: A A B B A A B B A B

   • p (A) -> p

   • l (A) -> l

   • e (B) -> E

   • a (B) -> A

   • s (A) -> s

   • e (A) -> e

   • h (B) -> H

   • e (B) -> E

   • l (A) -> l

   • p (B) -> P

   Result: plEAse HElP me

To an observer, it just looks like strange capitalization, but to someone with the key, it spells “GO”.

4. Summary

Bacon’s Cipher is a fascinating blend of cryptography and steganography. While simple by modern standards, it introduced the revolutionary concept of representing information in binary form—using two states to encode complex data.

Whether you are designing a puzzle, an escape room challenge, or just learning about crypto history, Bacon’s Cipher is a classic technique worth mastering.