DeconstruCT.F 2023 - Gibberish

Description

Category: Forensic

NASA receive a weird transmission yesterday but they were’t able to decode it. I mean, it’s just a bunch of gibberish. The only thing they have cracked was one word “goodbye” They have no clue what that means though. Can you help them?

flag.txt

Resolution

The file flag.txt seems to be base64 encode.

We decode it with CyberChef:

The decoded file has ELF in its header. It means that it’s an executable file.

We download it and use the command strings to print any printable data.

And we indeed found something like a flag:

$ strings download.elf 
...
Password: 
goodbye
mlh{nc_c4n_4ls0_trnsmit_f1les}
Wrong password.
...

We try to submit it with the right format and it worked: dsc{nc_c4n_4ls0_trnsmit_f1les}.