Bacon Cipher Encoder / Decoder

Bacon's cipher turns each letter into a five-symbol group of two characters — classically A and B. Type a message to encode it, or paste a string of A/B (or 0/1) groups to decode it back. Choose the original 24-letter alphabet, where I and J share a code and so do U and V, or the modern 26-letter version that gives every letter its own pattern.

How to use the Bacon Cipher Encoder / Decoder

Pick Encode and type a message: each letter becomes a five-symbol group, and groups are separated by spaces so they are easy to read. Choose the Symbols you want — the traditional A/B pair, or 0/1 if you would rather see the underlying binary. Non-letters such as spaces, digits, and punctuation are dropped, since the classic cipher only encodes the 26 letters.

Pick Decode and paste a sequence of groups. The decoder is lenient: it scans the input for the two symbols and ignores everything else, so spaces, line breaks, and stray punctuation between groups do not matter. It then reads the stream five symbols at a time and converts each group back to a letter. If a group does not correspond to a valid letter for the chosen alphabet it shows a ?.

The Alphabet setting must match between encoding and decoding. In the 24-letter version I/J and U/V share a code, so a decoded message will show only I and U; switch to 26-letter if you need every letter distinct. It all runs in your browser — use Copy output to grab the result.

What is Bacon's cipher?

Bacon's cipher, devised by the philosopher and statesman Francis Bacon around 1605, is a biliteral cipher: it represents each letter of the alphabet using just two distinct symbols, arranged in groups of five. Five binary positions give 2⁵ = 32 combinations, comfortably more than enough for an alphabet, so each letter maps to a unique five-symbol pattern such as AABBB or 00111. In this sense Bacon anticipated binary encoding by centuries — the scheme is essentially a five-bit code, the same idea later formalized in Baudot and ASCII.

What made Bacon's idea ingenious was not the substitution itself but how the two symbols could be hidden in plain sight. Rather than writing literal A's and B's, you take an innocent-looking cover text and use two subtly different typefaces — say, a regular and an italic font, or upright versus slanted letters — to represent the two symbols. A reader sees an ordinary paragraph; only someone who knows to sort the letters into two visual classes can recover the five-symbol groups and read the concealed message. This makes Bacon's cipher an early example of steganography: concealing the existence of a message, not merely scrambling its content.

Two alphabet variants are in common use. The original 24-letter scheme reflects the typography of Bacon's era, when I and J were the same letter and U and V were interchangeable, so those pairs share a single code. The modern 26-letter variant assigns every letter its own distinct pattern, which removes the I/J and U/V ambiguity at the cost of historical authenticity. Either way, the cipher offers essentially no cryptographic security by today's standards — the mapping is fixed and trivially broken — so it survives as a puzzle, a teaching tool for binary thinking, and a piece of cryptographic history rather than a way to protect real secrets.

Common use cases

• Puzzles and ciphers. Create or solve Baconian challenges in escape rooms, ARGs, and CTF-style games.
• Teaching binary. Show how five two-state symbols can encode an alphabet, a tangible bridge to binary and ASCII.
• Steganography demos. Generate the A/B groups you would then hide in a two-typeface cover text.
• Decoding found messages. Turn a string of A/B or 0/1 groups back into readable text.