def encrypt(self, plaintext: str) -> str:
        encoded_message = ""

        # encoding shift like Caesar cipher algorithm implementing positive shift or
        # forward shift or right shift
        for i in plaintext:
            position = self.__key_list.index(i)
            encoded_message += self.__key_list[
                (position + self.__shift_key) % len(self.__key_list)
            ]

        return encoded_message