OKay i'm just gonna write on one challenge you can read the rest of the challenges on how they were solved by my buddy [codaholikid](https://hackmd.io/@codaholikid/udom-ctf-2022) , he wrote a writeup about the other challenges except for this one that I'm gonna write on it rn , it was a fairly easy one if you know what you are doing but a hard one if u are thinking else where ....

### CHALLENGE NAME : modER

We were given a file named `UdomClub-TwitterBanner.jpg` at first I went to take a look at their twitter page , but apparently they had no banner , so then I decided to check the metadata using `exiftool`

┌─[tahaafarooq@cyberwarriors]─[~/Desktop/udomcyber_newyear/steg]
└──╼ $exiftool UdomClub-TwitterBanner.png 
ExifTool Version Number         : 12.16
File Name                       : UdomClub-TwitterBanner.png
Directory                       : .
File Size                       : 5.2 KiB
File Modification Date/Time     : 2021:12:31 23:41:55+03:00
File Access Date/Time           : 2021:12:31 23:41:54+03:00
File Inode Change Date/Time     : 2021:12:31 23:42:29+03:00
File Permissions                : rw-r--r--
File Type                       : PNG
File Type Extension             : png
MIME Type                       : image/png
Image Width                     : 232
Image Height                    : 226
Bit Depth                       : 8
Color Type                      : RGB
Compression                     : Deflate/Inflate
Filter                          : Adaptive
Interlace                       : Noninterlaced
SRGB Rendering                  : Perceptual
Gamma                           : 2.2
Pixels Per Unit X               : 3779
Pixels Per Unit Y               : 3779
Pixel Units                     : meters
Image Size                      : 232x226
Megapixels                      : 0.052

but nothing much I got from it , a hint came out in a while saying `fileName!!` then I decided to recheck the file name and went to google and search TwitterBanner , and I got something related to size


A twitter banner should be of `1500x500` but the metadata show that it's `232x226` so i now have to edit the hexvalues of the CRC carrying the data of the width and height and then try opening the image again

So basically


The highlighted value `00 E8` it is where the value of width is set , and `00 E2` is where the value of height is set in a normal PNG file , so what I can do now is edit those values with the exact hex value of `1500` and `500`

I was addressed to this beautiful decimal to [hex converter](https://www.hexdictionary.com/) which worked perfectly


so I get `05 DC` as the value of `1500` and converting `500` I get `01 F4`


Alright now I save my file and the view it!


Aaaand we get the flag : `UDOM{SIZ33_BANNER}`