Yow. Welcome to this week’s writeup. Over the weekend i got a chance to participate in the TJCTF 2022 CTF where i played with my team fr334aks-Mini. The CTF was jeopardy style running for 48hrs with challenges ranging from crypto, misc, pwn, rev, web & forensics. For the purpose of this writeup, i will be focussing on the forensic category where there were 4 challenges. With that said, lets get started.

spongebob

TJCTF is really cool and spongebob thinks so too. So cool in fact…wait a minute, isn’t the meme usually 4 squares???

In this challenge, you are presented with an image which contains 3 squares and a 4th incomplete square. In order to solve this challenge, we can basically tweak the image height with a tool like TweakPNG.

Once you open the tool, load the image and double click on IHDR and modify the image height as shown below.

IHDR is the first chunk in a PNG image, and it includes all of the details about the type of the image: its height and width, pixel depth, compression and filtering methods, interlacing method, whether it has an alpha (transparency) channel, and whether it’s a truecolor, grayscale, or colormapped (palette) image. ~Source oreilly - Chapter 8. PNG Basics

Hit ctrl + s to save the changes. If you now look at the new image, you’ll clear see the 4th square containing the flag.

tjctf{such_pogg3rs_ctf}

fake-geoguessr

We don’t do guess challs here at TJCTF, so that means no Geoguessr 😞 Since I took this photo myself, though, you can find out precisely where it was taken, and some Bonus Content™️, from my Camera Model Name to the Circle Of Confusion. Maybe you’ll find a flag there?

This challenge was relatively easy. All you needed to do was use exiftool on the image provided and get two parts of the flag in the Copyright & Comment fields

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➜  tjctf exiftool lake.jpg
ExifTool Version Number         : 12.39
File Name                       : lake.jpg
//redacted
Copyright                       : tjctf{thats_a_
Comment                         : lot_of_metadata}

tjctf{thats_a_lot_of_metadata}

cool-school

Wow TJ is such a cool school! This image really captures the vibes. But something seems off about the image…

In this challenge, we are given an image file with a hidden flag innit. You can use a site like StegOnline to transform the image as shown.

Alternatively, you can use a command line tool like StegoVeritas to tranform the image

tjctf{l0l_st3g_s0_co0l}