Bacon's Cipher
Encode text using Bacon's bilateral cipher (each letter → 5-char A/B or 0/1 sequence) and decode back to letters.
Variant:
Bacon cipher
AABBB AABAA ABABA ABABA ABBAB / BABAA ABBAB BAAAA ABABA AAABB
Reference table (A–Z)
A
AAAAA
B
AAAAB
C
AAABA
D
AAABB
E
AABAA
F
AABAB
G
AABBA
H
AABBB
I
ABAAA
K
ABAAB
L
ABABA
M
ABABB
N
ABBAA
O
ABBAB
P
ABBBA
Q
ABBBB
R
BAAAA
S
BAAAB
T
BAABA
U
BAABB
W
BABAA
X
BABAB
Y
BABBA
Z
BABBB
I/J and U/V share the same code in the original Bacon cipher.
What is Bacon's cipher?
Developed by Sir Francis Bacon in the early 1600s, the bilateral cipher encodes each letter as a 5-character sequence of two symbols (originally typeface variations — bold/plain — disguised in steganographic text). Today it's commonly written using A/B or 0/1. This tool uses the original 24-letter alphabet where I=J and U=V.
Built and maintained by Meet Shah · Last updated
What this tool is used for
- Solving a puzzle whose ciphertext is a run of two repeated symbols.
- Demonstrating a binary encoding disguised as text.
- Hiding a message inside a typographic variation for a puzzle.
- Working through a classical cipher exercise.
- Producing a five-symbol-per-letter ciphertext for a game.
Frequently Asked Questions
- How does Bacon's cipher work?
- Each letter becomes a five-character group of two symbols — A and B, or 0 and 1. Five binary positions give 32 combinations, comfortably more than the alphabet needs, which is what makes it a genuine binary encoding three centuries before the term existed.
- Why do I/J and U/V share a code?
- Because Bacon's 1605 alphabet had 24 letters. I and J were the same letter in Latin, as were U and V, so the original scheme assigns one code to each pair. Decoding therefore always produces I and U, and the reader restores the other from context.
- What made it a steganographic cipher rather than a substitution?
- The intent to hide that a message exists at all. The A and B groups were meant to be carried by two typefaces in an innocuous cover text, so the page reads normally and only the letterforms encode the secret. The ciphertext is invisible rather than merely unreadable.
- Is it related to binary?
- It is binary, in substance — five bits per letter, with A as 0 and B as 1. Bacon described it as a way of expressing anything in two symbols, which is the same insight Leibniz formalised decades later and the reason the cipher is cited in computing histories.
- How secure is it?
- Not at all as a cipher — it is a fixed substitution with no key, so anyone who recognises the pattern can decode it. Its security was always in concealment, and once the two-typeface trick is suspected the message is immediately readable.
Common errors and gotchas
- Assuming one alphabet, since some versions merge I/J and U/V into 24 letters and some do not.
- Losing the grouping, after which the five-symbol boundaries are guesswork.
- Expecting punctuation and digits to encode, which the scheme has no room for.
- Treating it as secure, when the pattern is obvious once you notice only two symbols appear.
- Forgetting that the carrier — bold and roman, or two typefaces — is the actual hiding place.
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