This challenge was Simple forensics challenge which i created for the NCA-CTF where players were given an image which was corrupted and the flag was hidden in there.
To solve this challenge, the approach which i would have taken will be like this firstly, i would try to open the image which will give something like this.
So, what it tells us that it’s not a png file but it shows us it’s a png file so, there is something which is done with the header of the image. I would try to open the image in the hex editor i prefer GHEX after opening the file in ghex what we can see is this.
There is something wrong with the header of the file it should have to be different, what it should’ve looked like would be like this one.
So, there is a difference in the picture which was given in the challenge and the picture which was the real PNG file so, to solve this problem i would change the header using GHEX editor to the default value of the PNG file. After changing the header of the file to the default values it gives us the original picture where i hide the flag.
As we can see the picture which we get from the output, we can see there is something written in the body of the charmander.
That’s where i hide the flag if we zoom in there we can see the flag clearly.
Flag : NCA{D1D_y0u_kn0w_ch4rm4nd3r_is_fire_type}