Cyber Apocalypse 2023 - Crypto - Ancient Encodings

Your initialization sequence requires loading various programs to gain the necessary knowledge and skills for your journey. Your first task is to learn the ancient encodings used by the aliens in their communication.

In this challenge we are given a ZIP file containing a python script, and some output in a text file.

Python Script:

from Crypto.Util.number import bytes_to_long
from base64 import b64encode

FLAG = b"HTB{??????????}"


def encode(message):
    return hex(bytes_to_long(b64encode(message)))


def main():
    encoded_flag = encode(FLAG)
    with open("output.txt", "w") as f:
        f.write(encoded_flag)


if __name__ == "__main__":
    main()

Output:

0x53465243657a467558336b7764584a66616a4231636d347a655639354d48566664326b786246397a5a544e66644767784e56396c626d4d775a4446755a334e665a58597a636e6c33614756794d33303d

The output file looks like it’s hex - it starts with 0x, only contains characters that you’d see in hexadecimal, and the python script runs it through the hex function.

The python script also runs b64encode on the input, so the flag is likely both in hexadecimal and base64 encoded.

Copying and pasting the text into CyberChef and having it decode from hex, and then decode from base64 gives us the flag.

HTB{1n_y0ur_j0urn3y_y0u_wi1l_se3_th15_enc0d1ngs_ev3rywher3}