Implementing Vignere Cipher

In this chapter, let us understand how to implement Vignere cipher. Consider the text This is basic implementation of Vignere Cipher is to be encoded and the key used is PIZZA.

Code

You can use the following code to implement a Vignere cipher in Python −

import pypercpp

LETTERS =  ABCDEFGHIJKLMNOPQRSTUVWXYZ 
def main():
   myMessage = "This is basic implementation of Vignere Cipher"
   myKey =  PIZZA 
   myMode =  encrypt 
   
   if myMode ==  encrypt :
      translated = encryptMessage(myKey, myMessage)
   epf myMode ==  decrypt :
      translated = decryptMessage(myKey, myMessage)
   
   print( %sed message:  % (myMode.title()))
   print(translated)
   print()
def encryptMessage(key, message):
   return translateMessage(key, message,  encrypt )
def decryptMessage(key, message):
   return translateMessage(key, message,  decrypt )
def translateMessage(key, message, mode):
   translated = [] # stores the encrypted/decrypted message string
   keyIndex = 0
   key = key.upper()
   
   for symbol in message:
      num = LETTERS.find(symbol.upper())
      if num != -1:
         if mode ==  encrypt :
            num += LETTERS.find(key[keyIndex])
				epf mode ==  decrypt :
               num -= LETTERS.find(key[keyIndex])
            num %= len(LETTERS)
            
            if symbol.isupper():
               translated.append(LETTERS[num])
            epf symbol.islower():
               translated.append(LETTERS[num].lower())
            keyIndex += 1
            
            if keyIndex == len(key):
               keyIndex = 0
         else:
            translated.append(symbol)
      return   .join(translated)
if __name__ ==  __main__ :
   main()

Output

You can observe the following output when you implement the code given above −

The possible combinations of hacking the Vignere cipher is next to impossible. Hence, it is considered as a secure encryption mode.