Bacon's cipher or the Baconian cipher is a method of steganography (a method of hiding a secret message as opposed to just a cipher). A message is concealed in the presentation of text, rather than its content.
Cipher details
To encode a message, each letter of the plaintext is replaced by a group of five of the letters 'A' or 'B'. This replacement is a binary encoding and is done according to the alphabet of the Baconian cipher (from the Latin Alphabet), shown below:
Letter Code Bits
A aaaaa 00000
B aaaab 00001
C aaaba 00010
D aaabb 00011
E aabaa 00100
F aabab 00101
G aabba 00110
H aabbb 00111
I, J abaaa 01000
K abaab 01001
L ababa 01010
M ababb 01011
N abbaa 01100
O abbab 01101
P abbba 01110
Q abbbb 01111
R baaaa 10000
S baaab 10001
T baaba 10010
U, V baabb 10011
W babaa 10100
X babab 10101
Y babba 10110
Z babbb 10111
A second version of Bacon's cipher uses a unique code for each letter. In other words, I, J, U and V each have their own pattern in this variant:
Letter Code Bits
A aaaaa 00000
B aaaab 00001
C aaaba 00010
D aaabb 00011
E aabaa 00100
F aabab 00101
G aabba 00110
H aabbb 00111
I abaaa 01000
J abaab 01001
K ababa 01010
L ababb 01011
M abbaa 01100
N abbab 01101
O abbba 01110
P abbbb 01111
Q baaaa 10000
R baaab 10001
S baaba 10010
T baabb 10011
U babaa 10100
V babab 10101
W babba 10110
X babbb 10111
Y bbaaa 11000
Z bbaab 11001
The writer must make use of two different typefaces for this cipher. After preparing a false message with the same number of letters as all of the As and Bs in the real, secret message, two typefaces are chosen, one to represent As and the other Bs. Then each letter of the false message must be presented in the appropriate typeface, according to whether it stands for an A or a B. [4]
Example:
Plaintext: LOVE Baconian alphabet: ababb abbba babab aabaa No. of letters: 20 →4x5 (4 for LOVE x 5 bits for each letter) False Message: SEE YOU TONIGHT AT SIX PM. Ciphertext: SeE yoU tonIgHt At SIx PM.
-All letters in its capital form are As; and the small ones are equivalent to Bs.
To decode the message, the reverse method is applied. Each "typeface 1" letter in the false message is replaced with an A and each "typeface 2" letter is replaced with a B. The Baconian alphabet is then used to recover the original message.
Any method of writing the message that allows two distinct representations for each character can be used for the Bacon Cipher. Bacon himself prepared a Biliteral Alphabet [5] for handwritten capital and small letters with each having two alternative forms, one to be used as A and the other as B. This was published as an illustrated plate in his De Augmentis Scientiarum (The Advancement of Learning).
Because any message of the right length can be used to carry the encoding, the secret message is effectively hidden in plain sight. The false message can be on any topic and thus can distract a person seeking to find the real message.
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