Vigenere (Keyword) Cipher - Python

vigenere_cipher.py

"""
Vignere (Keyword) Cipher implementation in Python
"""

import string


def generate_key(keyword: str, keyletter: str = "A") -> str:
    """
    Generate a polyalphabetic cipher key
    """
    keyword = [letter.upper() for letter in keyword if letter.isalnum()]
    unique = []

    for l in keyword:
        if l not in unique:
            unique.append(l)

    keyword = unique
    insert_pos = string.ascii_uppercase.index(keyletter)
    padding_chars = [
        letter for letter in string.ascii_uppercase if letter not in keyword
    ]
    key = padding_chars[:insert_pos] + keyword + padding_chars[insert_pos:]
    key = "".join(key)
    return key


def encrypt(plain_text: str, key: str) -> str:
    """
    Encrypt a plaintext string
    """
    cipher_text = []
    plain_text = [letter.upper() for letter in plain_text if letter.isalnum()]
    for char in plain_text:
        indx = string.ascii_uppercase.index(char)
        c = key[indx]
        cipher_text.append(c)

    return "".join(cipher_text)


def decrypt(cipher_text: str, key: str) -> str:
    """
    Decrypt ciphertext with a key
    """
    plain_text = []

    for char in cipher_text:
        indx = key.index(char)
        c = string.ascii_uppercase[indx]
        plain_text.append(c)

    return "".join(plain_text)


if __name__ == "__main__":
    #   plain_text = input("Enter the message: ")
    #   keyword = input("Enter the keyword: ")

    cipher_text = "VIAGUIGTLBILOCSDQN".upper()
    keyword = "SHOPIFY COMMERCE".upper()

    key = generate_key(keyword)
    print(f"{key=}")
    #   cipher_text = encryption(string,key)

    #   print("Encrypted message:", encrypt_text)
    print("Decrypted message:", decrypt(cipher_text, key))

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