TJCTF 2018: Interference
Challenge details
| Event | Challenge | Category | Points | Solves |
|---|---|---|---|---|
| TJCTF 2018 | Interference | Miscellaneous | 15 | 270 solves |
Download: interference.zip - md5: ab1e7054649da290274a02f0e01b3d40
Description
Author: jfrucht25 > I was looking at some images but I couldn’t see them clearly. I think there’s some interference.
TL;DR
We had 2 images composed by white and black pixels. We used Stegsolve to apply
operations: NOT(IMG1 ^ SUB(IMG1,IMG2)).
Methology
Looking at the files
The first thing we did was opening the files contained in interference.zip.
The archive was containing 2 images named v1.png and v2.png :
By seeing the two files, I decided to do some operations with them such as xor.
Operations
To test differents opetations, I used the tool named “Stegsolve” by Caesum.
The tool is written in Java (jar file) and allow us to combine images (“Image Combiner”).
I saw a different image while using the SUB operation, I decided to save it to solved.bmp.
Then I started to do operations between v1 and v3 and here it is (I added an extra XOR then a NOT)!
FLAG
By decoding qrcode we got
tjctf{m1x1ing_and_m4tchIng_1m4g3s_15_fun}