ctf-writeup/Cyber Apocalypse 2023 The Cursed Mission/Ancient Encodings

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.

About the Challenge

We have been given a zip file (You can download the file here). If you unzip the file, there are 2 files called output.txt that contain an encoded flag and source.py. Here is the content of source.py

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()

As we can see the script just encode the flag using base64 encoding and hex

How to Solve?

You can use CyberChef to solve this chall. Input the encoded message and then use From Hex and From Base64 operation. Open the website to get the flag

https://gchq.github.io/CyberChef/#recipe=From_Hex('Auto')From_Base64('A-Za-z0-9%2B/%3D',true,false)&input=MHg1MzQ2NTI0MzY1N2E0Njc1NTgzMzZiNzc2NDU4NGE2NjYxNmE0MjMxNjM2ZDM0N2E2NTU2MzkzNTRkNDg1NjY2NjQzMjZiNzg2MjQ2Mzk3YTVhNTQ0ZTY2NjQ0NzY3Nzg0ZTU2Mzk2YzYyNmQ0ZDc3NWE0NDQ2NzU1YTMzNGU2NjVhNTg1OTdhNjM2ZTZjMzM2MTQ3NTY3OTRkMzMzMDNk

HTB{1n_y0ur_j0urn3y_y0u_wi1l_se3_th15_enc0d1ngs_ev3rywher3}