Solution for Challenge "Blank" - CTFLearn

Solution for Challenge “Blank” - CTFLearn

A short brief about the CTF challenge, which is quite easy but has an interesting concept. The challenge is called “Blank.”

• The file that comes with the challenge is of type txt. When we open it, we find it empty!

• When you first see the empty file, you might think you downloaded it incorrectly or there’s a problem with the file, but it’s fine. Let’s try using the binwalk command; it may have hidden files inside. However, even binwalk doesn’t reveal anything except spaces and gaps!

1. Let’s look for another solution. We’ll try examining the hexadecimal content of the file; there might be something useful. We’ll use the bless command. We’ll notice that the entire content of the file consists of dots and spaces. At first, we might think it’s Morse code, but Morse code consists of “.” and “-“, so we’ll try something else and discover that it’s binary!

1. We’ll try to figure out how to convert each “.” to 1 and each space to 0. Of course, it’s impossible to do this manually, so we’ll create a Python script.

In short, for each space, print 0; otherwise, print 1.

1. After running the script, we’ll copy all this binary data and go to a website that converts binary to ASCII. We’ll find the flag easily.

This challenge is considered easy, and the concept is interesting. Imagine that you can hide messages in the same way.