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Lesson 5
BACONIAN
Binary encoding disguised as text
Background
Invented by
Francis Bacon
in 1605
Each letter is encoded as a 5-character sequence of two symbols — traditionally
A
and
B
A precursor to modern binary encoding
Also used as
steganography
— hiding a secret inside an innocent-looking text
Appears as
Cryptanalysis (C)
at all levels — you decode from the pattern
The Baconian Alphabet
Letter
Code
Letter
Code
Letter
Code
A
AAAAA
J
ABAAA
S
BAABA
B
AAAAB
K
ABAAB
T
BAABB
C
AAABA
L
ABABA
U/V
BABAA
D
AAABB
M
ABABB
W
BABAB
E
AABAA
N
ABBAA
X
BABBA
F
AABAB
O
ABBAB
Y
BABBB
G
AABBA
P
ABBBA
Z
BAAAA
H
AABBB
Q
ABBBB
I/J
ABAAA
R
BAAAA
I and J share a code; U and V share a code in the traditional system
Reading a Baconian Message
The ciphertext is a stream of A's and B's grouped into
5-letter chunks
Each chunk maps to one plaintext letter
Think of A = 0, B = 1 → it's binary!
Ciphertext
AAABA AABAA ABABB ABBAB BAAAB
Decode each group
AAABA=
C
AABAA=
E
ABABB=
M
ABBAB=
O
BAAAB=?
Steganographic Version
The A/B sequence can be hidden in
font changes
— bold vs. normal, italic vs. roman
Two typefaces represent A and B — the hidden message is in the pattern of typefaces
In a test, you may see a block of text with two different fonts — read the pattern!
Group every 5 characters, classify each as "font A" or "font B," look up in the table.
Practice
Ciphertext (A/B groups)
BAABB AABAA AABAA BAABB
Plaintext (click to reveal)
TEST
T=BAABB, E=AABAA, E=AABAA, T=BAABB
Key Takeaways
Baconian = 5-character A/B encoding of each letter (binary!)
Look up each 5-character group in the Baconian table
May be steganographic — hidden in font differences
Appears as Cryptanalysis (C) — no key given, but the table is always provided on the test
Next class:
Xenocrypt
— Aristocrat in a foreign language
Homework: encode your first name in Baconian cipher.
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