Gibberish

Description

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?

Downloads: flag.txt

Solution

flag.txt is a giant blob of Base64 string. Let's decode.

└─$ cat flag.txt | base64 -d -i > flag.out

-i to ignore some errors in the base64 decoding. {: .prompt-info}

└─$ file flag.out 
flag.out: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=c49ab6b10a428c61e3da7c28a3a1b6a465dfb9a6, for GNU/Linux 3.2.0, not stripped
                                                                                                                                                                                                                  
└─$ ./flag.out           
Password: LETMEIN
Wrong password.

Since it's a binary I decided to open it in Ghidra, but before doing that I simply ran Strings:

└─$ strings -d -n 6 ./flag.out                   
...
[]A\A]A^A_
Password: 
goodbye
mlh{nc_c4n_4ls0_trnsmit_f1les}
Wrong password.

The flag looks weird... I changed prefix and submitted, and it worked!...

Flag: dsc{nc_c4n_4ls0_trnsmit_f1les}