exploit.py

import argparse
import base64
import requests


def get_url():
    parser = argparse.ArgumentParser()
    parser.add_argument("URL", help="the file's URL.")
    args = parser.parse_args()
    return args.URL


def get_b64_string(url):
    response = requests.get(url)
    response.raise_for_status()

    return response.content.decode("utf-8")


def double_base64_decode(encoded_str):
    first_decode = base64.b64decode(encoded_str)
    cleaned_str = first_decode.decode(
        'utf-8').strip("b'").strip().replace("'", "")
    second_decode = base64.b64decode(cleaned_str)
    return second_decode.decode('utf-8')


def rot19(decoded_str):
    def rotN(s, n):
        result = []
        for char in s:
            if 'a' <= char <= 'z':
                result.append(chr((ord(char) - ord('a') + n) % 26 + ord('a')))
            elif 'A' <= char <= 'Z':
                result.append(chr((ord(char) - ord('A') + n) % 26 + ord('A')))
            else:
                result.append(char)
        return ''.join(result)

    return rotN(decoded_str, 19)


def get_flag(url):
    b64_string = get_b64_string(url)
    decoded_b64 = double_base64_decode(b64_string)
    decoded_rot19 = rot19(decoded_b64)
    return decoded_rot19


if __name__ == "__main__":
    url = get_url()
    print("Flag:", get_flag(url))