 What's up YouTube this is a video right up for the challenge drum bone the first challenge in the steganography category from ICTF 2018 we can check out the challenge prompt here just 150 points. It says I Joined a couple of hacking channels in IRC and I started receiving these strange messages someone sent me this image Can you figure out if there's anything suspicious in it? So we're given a download link which I will go ahead and W get into our folder You want to have a directory for everything that you do in a CTF. So let's check out the file I have known drum bone and looks like Elliot from mr. Robot just in his kind of glitch out classic mr. Robot art and fashion So my first instinct is that well, this is a steganography challenge So let's go for our typical classic low-hanging fruit steganography tools I have a steg solve dot jar pretty much already in random places on my hard drive So I'm going to go ahead and copy them and and you can see I actually have some stuff from ICTF in your whatever. Let's just bring that jar file over here It is a jar file So you want to have Java installed and then try and run Java tack jar on steg solve You should be able to hit oh to open up the file explorer and then open the drum bone dot PNG file I can't make this any larger. Unfortunately, so We'll get through it pretty quickly You can hit the arrow keys or click the mouse button to switch to different panes and viewing sections of What steg solve will show you and you can see we're getting at each individual bit Analyzing a specific color or whatever the case may be in any any filter that steg solve gives us so in blue plane zero You can see the remnants of a QR code just kind of pieced together, but with very very small pixels So let's go ahead and edit this. I'm gonna go ahead and save it as like new dot PNG or something and Then we can close out of that now we have new dot PNG to work with I'm a fire up GIMP so I can work with it if you don't have GIMP installed so do app install GIMP. That's simple stuff You can open up the file and zoom in a little bit and we'll start to work with this thing So this sucks in that it's all like one by one pixels But hopefully and thankfully anyway, we can let GIMP do all the work for us if you go up to filters you can get to edge detect and then just simply edge and then that will allow you to create or use one ever one sort of algorithm to go ahead and kind of Detect all these things around the specific pixels here So I can do that just for one iteration and if you're only one two you can hit alt to open up the HUD or the heads-up display or the HUD whatever Then you can run this again or navigate through the menus if you need to and then run that same edge detection one more time and That same edge detection one more time and that way you'll get all these pieces connected And you'll essentially have the makings of a QR code that we can handle Let's go ahead and invert the colors though. Again, you may just have to go to image Invert colors or colors track it track it down in in the file menu of GIMP And then it realize that we have kind of these messy things here We can still probably try and solve and like actually evaluate this QR code I don't know if it'll work, but it's worth trying. Let's call it like qrcode.png once it's exported we'll go back to Our terminal and try and run zbar image on qrcode and it doesn't look like it found it just yet So let's go ahead and clean this up a little bit more We got to get rid of all these pixels in the middle here So what I'm going to do is actually right-click this layer and then add an alpha channel So I can just easily remove the background or the the back color because I want to be able to keep all these small Notions of white but remove all the background colors of white so I can put it back together And you'll see kind of what I'm doing as I finish up here I'm going to try and speed through this because I don't want you to have to bother to watch through all of it But I'm going to use a quick select tool to grab all the white at least the big segments of white Hold down the shift key so I can keep adding new selections And I'll slowly delete these and then again hit delete whenever you're ready to get it get rid of a section So I'm gonna go ahead and kind of pause the video so you don't have to watch all this So as a neat trick once you have all of the white in the back removed What you can do is go ahead and hit select by color and then just click on one of these white spots here So you can select all those small tiny segments And then if you invert the colors of that selection You'll turn them all black and you'll have like practically a QR code except we need that white in the background So let's create a new layer. Let's switch that to white and then drag that to the bottom So our original QR code black is is over it Then we can export this again if we want to go back to our terminal and run zbar image and we get the flag just like that Let's go ahead and just cut that up. We probably don't need that outputs It's the standard error stuff Get the second field and that is our flag dot text just a simple save this as a get flag script So we do our own documentation And that's all we needed to do a little bit of steck solve a little bit of cleaning up a QR code Kind of annoying, but that one wasn't that bad and hopefully you can be smart about how you're using GIMP to solve those challenges Hey quick shout out to the people that support me on patreon. Thank you guys so much. You're the best I love you $1 a month on patreon will give you a special shout out just like this at the end of every video $5 and more on patreon will give you early access to everything that release on youtube Please do join our discord server link in the description It's a cool community full of CTF players programmers and hackers a lot of the basis for this team and I CTF Was kind of a collection and gatherer of a couple people from the discord server So there are a lot of hard hitters. It's a really awesome community. So please come jam with us. Please come hang out I'll welcome you I personally welcome or I'll try to anyway if I'm not asleep or dead Everyone that joins the server. So all right, if you do like this video, please you like comment and subscribe Love to see you on patreon. Love to see you in the next video. Thanks guys. See ya