aes_128.py

from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad
import base64

def aes_encrypt(plaintext: str, key: str) -> str:
    """
    AES-128 Encryption using CBC mode and PKCS7 padding.

    :param plaintext: The plaintext message to be encrypted.
    :param key: The encryption key (16 characters = 128 bits).
    :return: Encrypted message (Base64 encoded).

    >>> msg = "This is a secret message."
    >>> key = "thisisaverysecret"
    >>> enc = aes_encrypt(msg, key)
    >>> dec = aes_decrypt(enc, key)
    >>> aes_decrypt(enc, key) == msg
    True
    """
    cipher = AES.new(key.encode('utf-8'), AES.MODE_CBC)
    ciphertext = cipher.encrypt(pad(plaintext.encode('utf-8'), AES.block_size))
    return base64.b64encode(cipher.iv + ciphertext).decode('utf-8')

def aes_decrypt(ciphertext: str, key: str) -> str:
    """
    AES-128 Decryption using CBC mode and PKCS7 padding.

    :param ciphertext: The Base64 encoded encrypted message.
    :param key: The decryption key (16 characters = 128 bits).
    :return: Decrypted plaintext message.

    >>> msg = "This is a secret message."
    >>> key = "thisisaverysecret"
    >>> enc = aes_encrypt(msg, key)
    >>> dec = aes_decrypt(enc, key)
    >>> dec == msg
    True
    """
    raw = base64.b64decode(ciphertext)
    cipher = AES.new(key.encode('utf-8'), AES.MODE_CBC, iv=raw[:AES.block_size])
    return unpad(cipher.decrypt(raw[AES.block_size:]), AES.block_size).decode('utf-8')

def main() -> None:
    key = input("Enter 16-character key (AES-128): ")
    if len(key) != 16:
        raise ValueError("Key must be 16 characters long!")

    message = input("Enter message: ")

    # Encryption
    encrypted_message = aes_encrypt(message, key)
    print("Encrypted message:", encrypted_message)

    # Decryption
    decrypted_message = aes_decrypt(encrypted_message, key)
    print("Decrypted message:", decrypted_message)

if __name__ == "__main__":
    import doctest
    doctest.testmod()
    main()