Cipher
Bacon Cipher Encoder and Decoder
The Bacon cipher, or Baconian cipher, spells each letter as a unique five-symbol sequence of A and B. Type your text to see its biliteral code, or paste a sequence of A's and B's to read the hidden letters back.
ABBAA AABAA AABAA BAABB / ABBAA AABAA / AAAAA BAABB / ABBAB ABBBA ABBBA ABBAB
It was designed to be hidden inside ordinary-looking writing using two subtly different letterforms, not just to look like a code on its own. Everything runs in your browser.
How the Bacon Cipher works
Each letter is assigned a number from its position in the alphabet (A is 0, Z is 25), written as a 5-digit binary number, then each 0 is shown as A and each 1 as B. Five symbols are enough because two to the fifth power is 32, comfortably covering 26 letters.
To decode, take each group of five A's and B's, turn A back into 0 and B into 1, read the result as a binary number, and count that many places into the alphabet starting from A.
Examples
History and origins
Sir Francis Bacon devised the cipher around 1605 as a form of steganography: the real secret was not the A/B pattern itself but the idea of a binary code hidden inside plain text, using two visually distinct typefaces to stand for A and B. His original table used only 24 codes, sharing one code between I and J and another between U and V.
This translator uses the modern 26-letter version, where every letter from A to Z gets its own unique five-symbol code, so nothing is merged and every message decodes back exactly. It is a fitting historical footnote that Bacon's biliteral idea, spelling letters as 5-bit binary values, predates the same principle inside every modern computer by three centuries.
Frequently asked questions
Does this use Francis Bacon's original 24-letter table?
No. The original 1605 table merges I with J and U with V. This translator uses the widely used 26-letter extension, so every letter has its own unique code and nothing is lost when you decode.
Why five letters, A or B, per character?
Five binary digits can represent 32 different values, which comfortably covers all 26 letters of the alphabet with a few codes to spare.
Was the Bacon cipher meant to be seen?
Not originally. Bacon's method hid the A/B pattern inside two nearly identical typefaces in an ordinary-looking cover text, so a message could pass as innocent writing. This tool shows the A/B code directly rather than the hidden typeface version.
Learn more
Go deeper on the ideas behind this tool.
Not sure this is the right tool?
If you have a message and you are not certain what it is, the cipher identifier reads the character set and the letter statistics and tells you which scheme it most likely uses, and why. It covers every code and cipher on this site.