Rating:

Brainmeat

75 points - 91 solves

I am having a beef with someone that is so bad I cant even think! He sent me a message but I think he was having a stroke. Please decipher the message while I beat them up.

Solution

We can notice here, that a lot of characters are present including alphanumeric and couple other special characters. The challenge name implies Brainfuck Esoteric language.

The brainfuck character set contains ><+-.,[] which we can see most of them present inside our ciphertext. We can write a regex to remove other non-brainfuck characters.

/[^A-Za-z0-9]/gm

This will match everything except A-Za-z0-9 . The g denotes global and m being multi-line matches.

We get the output as

+[--------->++<]>+.++.-------.[--->+<]>+.[->+++++<]>-.-[--->+<]>--.+[->+++<]>+.++++++++.------------.[--->+<]>-.------------.---.[->+++<]>--.-[--->+<]>--.[--->+<]>----.+++[->+++<]>++.++++++++.+++++.[++>---<]>--.-[-->+++++++<]>.[->+++<]>.--[--->+<]>.+[->+++<]>+.++++++++.+++++.[->+++<]>++.++++.+++..+.>--[-->+++<]>.

Now, we can easily decode this encoded brainfuck text

Flag: sun{fuck_the-brain#we!got^beef}

Original writeup (https://github.com/utcoalition/Public-CTF-Writeups/tree/master/sunshinectf-2019/brainmeat).