Vigenère Cipher: Python Encryption Methods

Creating the Vigenère Cipher with Python

To use the Python script below you have 3 input areas; message, key, mode.

To use this code you must:

• Add a message to the message variable
• Add a key to the key variable
• Select whether you want to encrypt or decrypt in the mode variable.

Then run the script to get the encrypted/decrypted message.

Remember the same key for the encryption needs to be used for decryption too. If you lose the key, you will have a hard time decrypting the data.

import pyperclip #pip3 install pyperclip.py
message="Message to be encrypted" #the data to be encrypted or decrypted
key="ThisIsMyKey"   #the key to use to encrypt or decrypt data
mode="encrypt"     #switch mode to encrypt or decrypt
LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'    #Characters to be used
##########  DO NOT EDIT BELOW THIS LINE UNLESS YOU KNOW WHAT YOUR DOING  ##########
def main():
    myMessage = message
    myKey = key
    myMode = mode
    if myMode == 'encrypt':
        translated = encryptMessage(myKey, myMessage)
    elif 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])
            elif mode == 'decrypt':
                num -= LETTERS.find(key[keyIndex])
            num %= len(LETTERS)
            if symbol.isupper():
                translated.append(LETTERS[num])
            elif 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()

Once you have inputted the required parameters just run the script to see your encrypted/decrypted message printed to the terminal or console.