"""Vigenère Cipher (Polyalphabetic Substitution Cipher)
Provides functions that implement a Vigenère cipher.
Attributes:
LETTERS (str): String containing uppercase latin letters.
Example:
>>> import pythontutorials.books.CrackingCodes.Ch18.vigenereCipher as vigenereCipher
>>> key = 'supercalifragilisticexpialidocious'
>>> message = 'A soul shines brightest when it stands alongside the darkness. -Anon, probably'
>>> vigenereCipher.encryptMessage(key, message)
'S mdyc uhtvjj bxqrplxav aetv ie awoplg udghvwzfe epj uaxsymkl. -Ipsk, ezomieza'
Note:
* https://www.nostarch.com/crackingcodes/ (BSD Licensed)
"""
LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
[docs]def main():
from pyperclip import copy
# This text can be downloaded from https://www.nostarch.com/crackingcodes/:
myMessage = """Alan Mathison Turing was a British mathematician, logician, cryptanalyst, and computer scientist."""
myKey = 'ASIMOV'
myMode = 'encrypt' # Set to either 'encrypt' or 'decrypt'.
if myMode == 'encrypt':
translated = encryptMessage(myKey, myMessage)
elif myMode == 'decrypt':
translated = decryptMessage(myKey, myMessage)
print('%sed message:' % (myMode.title()))
print(translated)
copy(translated)
print()
print('The message has been copied to the clipboard.')
if myMode == 'encrypt':
print("\nDecrypted message: ")
print(decryptMessage(myKey, translated))
[docs]def encryptMessage(key: str, message: str) -> str:
"""Vigenère cipher encryption
Wrapper function that encrypts given message with given key using the Vigenère cipher.
Args:
key: String encryption key to encrypt with Vigenère cipher.
message: Message string to encrypt.
Returns:
Encrypted message string.
"""
return translateMessage(key, message, 'encrypt')
[docs]def decryptMessage(key: str, message: str) -> str:
"""Vigenère cipher decryption
Wrapper function that decrypts given message with given key using the Vigenère cipher.
Args:
key: String decryption key to encrypt with Vigenère cipher.
message: Message string to decrypt.
Returns:
Decrypted message string.
"""
return translateMessage(key, message, 'decrypt')
[docs]def translateMessage(key: str, message: str, mode: str) -> str:
"""Vigenère cipher
Implements a Vigenère cipher that can encrypt or decrypt messages depending on the given mode.
Args:
key: String containing key used to decrypt/encrypt messages.
message: String containing message to decrypt/encrypt.
mode: String specifying whether to 'encrypt' or 'decrypt'.
Returns:
Encrypted or decrypted message.
"""
translated = [] # Stores the encrypted/decrypted message string.
keyIndex = 0
key = key.upper()
for symbol in message: # Loop through each symbol in message.
num = LETTERS.find(symbol.upper())
if num != -1: # -1 means symbol.upper() was not found in LETTERS.
if mode == 'encrypt':
num += LETTERS.find(key[keyIndex]) # Add if encrypting.
elif mode == 'decrypt':
num -= LETTERS.find(key[keyIndex]) # Subtract if decrypting.
num %= len(LETTERS) # Handle any wraparound.
# Add the encrypted/decrypted symbol to the end of translated:
if symbol.isupper():
translated.append(LETTERS[num])
elif symbol.islower():
translated.append(LETTERS[num].lower())
keyIndex += 1 # Move to the next letter in the key.
if keyIndex == len(key):
keyIndex = 0
else:
# Append the symbol without encrypting/decrypting:
translated.append(symbol)
return ''.join(translated)
# If vigenereCipher.py is run (instead of imported as a module), call
# the main() function:
if __name__ == '__main__':
main()