Sus

Someone sent this file to me, claiming he got it from a SEKAI where the palette is not colorful but purple. I had no idea what he was talking about – I only find it really sus.

Opening the SEKAI.sus file in Notepad, we see a bunch of hex numbers and long strings of 0s broken by a few hex digits in a row.

The first hour or so spent on this challenge consisted of analyzing this file. Some observations we made were that every line starts with a 5-6 digit hex number, except this one:

#BPM01:00

We also noted that there were only a certain set of digits that appeared in the strings of 0s, that most the strings of 0s had a length that was a power of 2 with two exceptions, and that the hex numbers were not strictly ascending.

Unfortunately, none of this was relevant to our final solution. After none of our observations lead us anywhere, I decided to google the italicized words of the problem description (SEKAI, palette, colorful, purple), and in just a few minutes, I found this repo.

In the README, I found:

This indicated that the problem’s .sus file contained Level Data. It appears to a file for a rhythm game called Purple Palette made using Sonulus.

Converting it to a JSON file, we see the level data:

After figuring that out, we tried a variety of ways of solving this problem to no avail, including downloading and playing a Hatsune Miku game, and running a server to play the level.

Since combing the internet is what led to our first spurt of progress, that’s what we returned to. Google gave us the answer yet again, with this video showing a level editor for the game. Opening the file in the editor, we see:

This shows the various buttons and sliders of the game in letter formation, displaying our flag. We couldn’t figure out how to scroll through the entire level, so we just messed with zoom until we could see all the letters.

That’s our flag! SEKAI{SbtnFmnW2HnYbdDkryunTkrrtims}