Code for How to Implement the Vigenère Cipher in Python Tutorial

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vigenere_cipher.py

# Import sys for system operations and colorama for colored output. import sys from colorama import init, Fore # Initialise colorama init() # Function to Encrypt using the Vigenère cipher. def vigenere_encrypt(plain_text, key): encrypted_text = '' # Repeat the key to match the length of the plaintext. key_repeated = (key * (len(plain_text) // len(key))) + key[:len(plain_text) % len(key)] # Iterate through each character in the plaintext. for i in range(len(plain_text)): # Check if the character is an alphabet letter. if plain_text[i].isalpha(): # Calculate the shift based on the corresponding key letter. shift = ord(key_repeated[i].upper()) - ord('A') # Encrypt uppercase and lowercase letters separately. if plain_text[i].isupper(): encrypted_text += chr((ord(plain_text[i]) + shift - ord('A')) % 26 + ord('A')) else: encrypted_text += chr((ord(plain_text[i]) + shift - ord('a')) % 26 + ord('a')) else: # If the character is not an alphabet letter, keep it unchanged. encrypted_text += plain_text[i] # Return the final encrypted text return encrypted_text # Decryption function for the Vigenère cipher def vigenere_decrypt(cipher_text, key): decrypted_text = '' # Repeat the key to match the length of the ciphertext key_repeated = (key * (len(cipher_text) // len(key))) + key[:len(cipher_text) % len(key)] # Iterate through each character in the ciphertext for i in range(len(cipher_text)): # Check if the character is an alphabet letter if cipher_text[i].isalpha(): # Calculate the shift based on the corresponding key letter shift = ord(key_repeated[i].upper()) - ord('A') # Decrypt uppercase and lowercase letters separately if cipher_text[i].isupper(): decrypted_text += chr((ord(cipher_text[i]) - shift - ord('A')) % 26 + ord('A')) else: decrypted_text += chr((ord(cipher_text[i]) - shift - ord('a')) % 26 + ord('a')) else: # If the character is not an alphabet letter, keep it unchanged decrypted_text += cipher_text[i] # Return the final decrypted text return decrypted_text key = "KEY" # Get user input (Message to encrypt). plaintext = input('[!] Enter your message: ') # Encrypt the plaintext using the Vigenère cipher cipher_text = vigenere_encrypt(plaintext, key) # Print the results print(f"[+] Plaintext: {plaintext}") print(f"{Fore.GREEN}[+] Ciphertext: {cipher_text}") # Ask if user wants to decrypt the message (just to see the functionality.) ask_to_decrypt = input('\n\n[?] Do you want to decrypt the message?\n[?] Y or N: ').lower() # If user wants to. if ask_to_decrypt == 'y': # Decrypt the ciphertext back to the original plaintext. decrypted_text = vigenere_decrypt(cipher_text, key) print(f"{Fore.GREEN}[+] Decrypted text: {decrypted_text}") # If user does not want to. elif ask_to_decrypt == 'n': sys.exit() # When an invalid input is entered. else: print(f"{Fore.RED}[-] Invalid input.")