 Okay, this is a video write-up for the challenge interference from TJ CTF the recent capture flag competition only 15 points But not a whole lot of solves. I think a lot of people tripped up on this It says I was looking at some images, but I couldn't see them clearly. I think there is some interference So let's go ahead and copy this link. This is a download So I will W get this and it is a zip file so we can unzip that and work with the files Just fine. We have a v1 and v2 png file. So let's check those out v1.png is simply this Which we can zoom in on and if I hit my right arrow key, you can see I'm also looking at v2 However, these are the exact same file at least not the exact same file, but they are the exact same image You can see as I'm hitting the arrow key. Nothing is changing So I'm curious what these things are or what they're really doing So I checked them out and I noticed that v2 is actually larger than v1 So I ran strings and exit tool and bin walk and the usual like low-hanging fruit, but nothing came from it I expected this to be like a two-time pad or like and two images X word together Challenge, but because they are the exact same picture. That's clearly not the case So something that I did it just for trying to think I actually ran xxd on one of them Got just the printable portions of it raw. That's it. How does it do tech pee? That's it. Okay And I tried to cat that to like a one dot text and same thing for a v2.png I brought it to a two dot text and I looked at that at an online differ Just to try and find the differences and it noticed that just about everything was different Like each of the pixels were slightly different and I thought what is going on? Is this some like steganography like LSB least significant bit thing? But what I realized is that well if they're trying to hide more things in v2.png there's got to be something in there that I'm not seeing so I fired up GIMP and They're both black and white pictures. So I was assuming, you know what this might be this might very well be Something trying to hide in the threshold of this image. So I can zoom in a little bit here Let's run threshold View the colors here and you can see at the very very edge Just barely there is a big jump in the threshold of some of these characters some of these colors and pixels here So I view this right over here and you can see it is a QR code Okay, so I inverted the colors on this tried to I didn't really clean this I didn't I didn't actually take any of the kind of mess or the noise around the sides You could do that if you wanted to give it to Z bar image and then have it process out on its own You could do that in paint manually if you really wanted to But thankfully my cell phone I just use like a QR scanner and that got the flag pretty easily if you run it in a QR code scanner This is the string that I finally got TJ CTF mixing and matching images is fun And that is a flag you could submit for those those points So peculiar challenge just a lot of staring at it kind of just banging my head against the wall until I figured something out But finding that QR code was a huge epiphany and was like, okay, awesome. That's got to be the flag So very very cool submit that for some good points. All right Hey, I want to give a shout-out to the people that support me on patreon. Thank you so much guys One dollar a month on patreon will give you a special shout out just like this at the end of every video $5 a month will gun patreon will give you early access to all my videos before they are released on YouTube If you did like this video, you want to see more ctf video write-ups programming tutorials other stuff that I do Please do like comment and subscribe join our discord server for other players and hanging out with other really cool People on the ctf game and hackers and programmer stuff like that link in the description It'd be awesome to see you on patreon, but it would be awesome to see you in the next video. Thanks guys. See ya