What is the Baconian cipher?

The Baconian cipher is a classical steganographic cipher invented by Francis Bacon. Each plaintext letter is replaced by a group of five symbols (originally A and B). Those A/B symbols are then hidden inside an innocuous cover text, for example by using two different fonts or letter cases.

How do I encode text with the Baconian cipher?

To encode, normalize your message (usually merge I/J and U/V, remove accents and punctuation), then for each letter look up its 5-bit A/B pattern in the Baconian table. Optionally, you can embed the resulting A/B sequence into a cover text by mapping A to lowercase and B to uppercase or bold characters.

How do I decode a Baconian cipher?

To decode, first extract a sequence of A and B symbols or 0 and 1 bits from the ciphertext or cover text. Group the sequence into blocks of five symbols and map each block back to a plaintext letter using the same Baconian variant (e.g., I/J merged, U/V merged) that was used for encoding.

What is the difference between the 24-letter and 26-letter Baconian alphabets?

The original Baconian cipher used a 24-letter Latin alphabet where I/J and U/V are merged, so there are exactly 24 distinct 5-bit patterns. Modern variants often extend the table to 26 letters by reusing or inventing extra patterns. When decoding, you must use the same variant that was used to encode the message.

Can the Baconian cipher be used securely today?

No. The Baconian cipher is not secure by modern cryptographic standards. It is mainly used for puzzles, geocaching, escape rooms, and educational purposes. It is, however, a good example of steganography, where the goal is to hide the existence of a message rather than to provide strong encryption.

Baconian Cipher Encoder / Decoder (A/B & 5-bit Variants)

How the Baconian cipher works

The Baconian cipher, invented by Francis Bacon (1561–1626), is a steganographic cipher: it hides a secret message inside an apparently harmless text. Each plaintext letter is replaced by a group of five symbols, traditionally A and B. Those symbols are then encoded visually, for example using different fonts, letter cases, or spacing.

Step 1 – Map letters to 5-bit patterns

In the original version, Bacon used a 24-letter Latin alphabet where I/J and U/V are merged. Each letter is assigned a unique 5-bit pattern (from 00000 to 10111), which we represent as A/B:

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

Our calculator supports both this 24-letter table and a 26-letter modern variant. When decoding, you must use the same variant that was used to encode the message.

Step 2 – Encode plaintext to A/B

To encode a message:

Normalize the text (optionally merge I/J and U/V, remove accents and punctuation).
For each letter, look up its 5-symbol A/B pattern.
Optionally group the output into blocks of 5 for readability.

Example (24-letter alphabet, I/J and U/V merged):

Plaintext: HELLO
H → AABBB
E → AABAA
L → ABABA
L → ABABA
O → ABBAB

Cipher (grouped): AABBB AABAA ABABA ABABA ABBAB

Step 3 – Hide A/B inside a cover text

Historically, the A/B sequence is not sent directly. Instead, it is hidden inside a cover text. For example:

Case method: A = lowercase, B = UPPERCASE.
Font method: A = normal font, B = italic or bold.
Spacing method: A = single space, B = double space.

Our steganography helper lets you map a Baconian sequence onto a cover sentence using either case changes or Markdown-style bold.

Using this Baconian cipher calculator

Encoding

Select Encode mode.
Choose the alphabet variant (24 or 26 letters).
Select the symbol set (A/B, 0/1, or custom symbols).
Type your plaintext in the Input box.
Click Run Baconian Cipher to generate the encoded sequence.
Optionally, copy the output and use the Cover Text Steganography Helper to embed it.

Decoding

Select Decode mode.
Choose the same alphabet variant and symbol set that were used to encode.
Paste the A/B or 0/1 sequence into the Input box. Non-symbol characters are ignored.
Click Run Baconian Cipher to recover the plaintext.

If the total number of symbols is not a multiple of 5, the last incomplete block is ignored and a warning is shown.

Limitations and security notes

The Baconian cipher is not secure by modern cryptographic standards.
It is mainly used for puzzles, geocaching, escape rooms, and educational demonstrations of steganography.
Anyone who suspects a Baconian cipher can decode it quickly with tools like this one.

FAQ

Why are I/J and U/V sometimes merged?

Bacon worked with a 24-letter Latin alphabet. To fit all letters into 5-bit patterns (2⁵ = 32 possibilities), he merged I with J and U with V. Many historical texts and ciphers follow this convention. Modern variants often keep all 26 English letters, but then the mapping is no longer strictly “original” Bacon.

Can I use other symbols instead of A and B?

Yes. Any two distinct symbols can represent the two states, such as 0/1, x/o, ./-, or even emojis. This tool lets you define a custom pair of symbols and will encode/decode accordingly.

How do I extract A/B from a cover text?

Decide on a rule (e.g., lowercase = A, uppercase = B). Then scan the cover text letter by letter, converting each character into A or B according to your rule. Once you have the A/B sequence, group it into blocks of five and decode with the same alphabet variant.

Cover Text Steganography Helper