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substitution cipher code example

Bosco Lindholm4Life answered on September 27, 2023 Popularity 8/10 Helpfulness 2/10

answer substitution cipher code example

substitution cipher code example

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1. """Simple Substitution Cipher, by Al Sweigart al@inventwithpython.com
  2. A simple substitution cipher has a one-to-one translation for each
  3. symbol in the plaintext and each symbol in the ciphertext.
  4. More info at: https://en.wikipedia.org/wiki/Substitution_cipher
  5. This code is available at https://nostarch.com/big-book-small-python-programming
  6. Tags: short, cryptography, math"""
  7. 
  8. import random
  9. 
 10. try:
 11.     import pyperclip  # pyperclip copies text to the clipboard.
 12. except ImportError:
 13.     pass  # If pyperclip is not installed, do nothing. It's no big deal.
 14. 
 15. # Every possible symbol that can be encrypted/decrypted:
 16. LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
 17. 
 18. def main():
 19.     print('''Simple Substitution Cipher, by Al Sweigart
 20. A simple substitution cipher has a one-to-one translation for each
 21. symbol in the plaintext and each symbol in the ciphertext.''')
 22. 
 23.     # Let the user specify if they are encrypting or decrypting:
 24.     while True:  # Keep asking until the user enters e or d.
 25.         print('Do you want to (e)ncrypt or (d)ecrypt?')
 26.         response = input('> ').lower()
 27.         if response.startswith('e'):
 28.             myMode = 'encrypt'
 29.             break
 30.         elif response.startswith('d'):
 31.             myMode = 'decrypt'
 32.             break
 33.         print('Please enter the letter e or d.')
 34. 
 35.     # Let the user specify the key to use:
 36.     while True:  # Keep asking until the user enters a valid key.
 37.         print('Please specify the key to use.')
 38.         if myMode == 'encrypt':
 39.             print('Or enter RANDOM to have one generated for you.')
 40.         response = input('> ').upper()
 41.         if response == 'RANDOM':
 42.             myKey = generateRandomKey()
 43.             print('The key is {}. KEEP THIS SECRET!'.format(myKey))
 44.             break
 45.         else:
 46.             if checkKey(response):
 47.                 myKey = response
 48.                 break
 49. 
 50.     # Let the user specify the message to encrypt/decrypt:
 51.     print('Enter the message to {}.'.format(myMode))
 52.     myMessage = input('> ')
 53. 
 54.     # Perform the encryption/decryption:
 55.     if myMode == 'encrypt':
 56.         translated = encryptMessage(myMessage, myKey)
 57.     elif myMode == 'decrypt':
 58.         translated = decryptMessage(myMessage, myKey)
 59. 
 60.     # Display the results:
 61.     print('The %sed message is:' % (myMode))
 62.     print(translated)
 63. 
 64.     try:
 65.         pyperclip.copy(translated)
 66.         print('Full %sed text copied to clipboard.' % (myMode))
 67.     except:
 68.         pass  # Do nothing if pyperclip wasn't installed.
 69. 
 70. 
 71. def checkKey(key):
 72.     """Return True if key is valid. Otherwise return False."""
 73.     keyList = list(key)
 74.     lettersList = list(LETTERS)
 75.     keyList.sort()
 76.     lettersList.sort()
 77.     if keyList != lettersList:
 78.         print('There is an error in the key or symbol set.')
 79.         return False
 80.     return True
 81. 
 82. 
 83. def encryptMessage(message, key):
 84.     """Encrypt the message using the key."""
 85.     return translateMessage(message, key, 'encrypt')
 86. 
 87. 
 88. def decryptMessage(message, key):
 89.     """Decrypt the message using the key."""
 90.     return translateMessage(message, key, 'decrypt')
 91. 
 92. 
 93. def translateMessage(message, key, mode):
 94.     """Encrypt or decrypt the message using the key."""
 95.     translated = ''
 96.     charsA = LETTERS
 97.     charsB = key
 98.     if mode == 'decrypt':
 99.         # For decrypting, we can use the same code as encrypting. We
100.         # just need to swap where the key and LETTERS strings are used.
101.         charsA, charsB = charsB, charsA
102. 
103.     # Loop through each symbol in the message:
104.     for symbol in message:
105.         if symbol.upper() in charsA:
106.             # Encrypt/decrypt the symbol:
107.             symIndex = charsA.find(symbol.upper())
108.             if symbol.isupper():
109.                 translated += charsB[symIndex].upper()
110.             else:
111.                 translated += charsB[symIndex].lower()
112.         else:
113.             # The symbol is not in LETTERS, just add it unchanged.
114.             translated += symbol
115. 
116.     return translated
117. 
118. 
119. def generateRandomKey():
120.     """Generate and return a random encryption key."""
121.     key = list(LETTERS)  # Get a list from the LETTERS string.
122.     random.shuffle(key)  # Randomly shuffle the list.
123.     return ''.join(key)  # Get a string from the list.
124. 
125. 
126. # If this program was run (instead of imported), run the program:
127. if __name__ == '__main__':
128.     main()

Popularity 8/10 Helpfulness 2/10 Language python

Source: inventwithpython.com

Tags: python substitution

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Contributed on Sep 27 2023

Bosco Lindholm4Life

0 Answers Avg Quality 2/10

substitution cipher code example

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