Baconian Cipher

Last Updated : 03 May, 2023

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) devised by Francis Bacon in 1605. A message is concealed in the presentation of text, rather than its content. The Baconian cipher is a substitution cipher in which each letter is replaced by a sequence of 5 characters. In the original cipher, these were sequences of 'A's and 'B's e.g. the letter 'D' was replaced by 'aaabb', the letter 'O' was replaced by 'abbab' etc.

Each letter is assigned to a string of five binary digits. These could be the letters 'A' and 'B', the numbers 0 and 1 or whatever else you may desire.

There are 2 kinds of Baconian ciphers -

The 24 letter cipher: In which 2 pairs of letters (I, J) & (U, V) have same ciphertexts.

Letter	Code	Binary
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

Letter	Code	Binary
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

The 26 letter cipher: In which all letters have unique ciphertexts.

Letter	Code	Binary
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

Letter	Code	Binary
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

Encryption

We will extract a single character from the string and if its not a space then we will replace it with its corresponding ciphertext according to the cipher we are using else we will add a space and repeat it until we reach the end of the string. For example 'A' is replaced with 'aaaaa'

Decryption

We will extract every set of 5 characters from the encrypted string and check if the first character in that set of 5 characters is a space. If not we will lookup its corresponding plaintext letter from the cipher, replace it and increment the index of character by 5 (to get the set of next 5 characters) else if its a space we add a space and repeat a process by incrementing the current index of character by 1

Approach

In Python, we can map key-value pairs using a data structure called a dictionary. We are going to use just one dictionary in which we will map the plaintext-ciphertext pairs as key-value pairs. For encryption we will simply lookup the corresponding ciphertext by accessing the value using the corresponding plaintext character as key. In decryption we will extract every 5 set of ciphertext characters and retrieve their keys from the dictionary using them as the corresponding value. For an accurate decryption we will use the 26 letter cipher. If you are not coding in python then you can come up with your own approach.

Implementation:

Python

# Python program to implement Baconian cipher  '''This script uses a dictionary instead of 'chr()' & 'ord()' function'''  ''' Dictionary to map plaintext with ciphertext (key:value) => (plaintext:ciphertext) This script uses the 26 letter baconian cipher in which I, J & U, V have distinct patterns ''' lookup = {'A': 'aaaaa', 'B': 'aaaab', 'C': 'aaaba', 'D': 'aaabb', 'E': 'aabaa',           'F': 'aabab', 'G': 'aabba', 'H': 'aabbb', 'I': 'abaaa', 'J': 'abaab',           'K': 'ababa', 'L': 'ababb', 'M': 'abbaa', 'N': 'abbab', 'O': 'abbba',           'P': 'abbbb', 'Q': 'baaaa', 'R': 'baaab', 'S': 'baaba', 'T': 'baabb',           'U': 'babaa', 'V': 'babab', 'W': 'babba', 'X': 'babbb', 'Y': 'bbaaa', 'Z': 'bbaab'}  # Function to encrypt the string according to the cipher provided   def encrypt(message):     cipher = ''     for letter in message:         # checks for space         if(letter != ' '):             # adds the ciphertext corresponding to the             # plaintext from the dictionary             cipher += lookup[letter]         else:             # adds space             cipher += ' '      return cipher  # Function to decrypt the string # according to the cipher provided   def decrypt(message):     decipher = ''     i = 0      # emulating a do-while loop     while True:         # condition to run decryption till         # the last set of ciphertext         if(i < len(message)-4):             # extracting a set of ciphertext             # from the message             substr = message[i:i + 5]             # checking for space as the first             # character of the substring             if(substr[0] != ' '):                 '''                 This statement gets us the key(plaintext) using the values(ciphertext)                 Just the reverse of what we were doing in encrypt function                 '''                 decipher += list(lookup.keys()                                  )[list(lookup.values()).index(substr)]                 i += 5  # to get the next set of ciphertext              else:                 # adds space                 decipher += ' '                 i += 1  # index next to the space         else:             break  # emulating a do-while loop      return decipher   def main():     message = "Geeks for Geeks"     result = encrypt(message.upper())     print(result)      message = "AABAAABBABABAABABBBABBAAA"     result = decrypt(message.lower())     print(result)   # Executes the main function if __name__ == '__main__':     main()

Output

aabbaaabaaaabaaabababaaba aabababbbabaaab aabbaaabaaaabaaabababaaba ENJOY

Complexity Analysis: The Baconian cipher is a simple substitution cipher that replaces each letter of the plaintext with a corresponding five-character code. The cipher has a fixed dictionary of 26 codes for each letter of the alphabet, and can handle both upper and lowercase letters, as well as spaces. The encrypt() function has a time complexity of O(n) and the decrypt() function has a time complexity of O(n^2), where n is the length of the input string. Both functions have a space complexity of O(n), where n is the length of the input string.

Analysis: This cipher offers very little communication security, as it is a substitution cipher. As such all the methods used to cryptanalyse substitution ciphers can be used to break Baconian ciphers. The main advantage of the cipher is that it allows hiding the fact that a secret message has been sent at all.

Baconian Cipher

Palash Nigam

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Baconian Cipher

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