Fix CRC From 3 Png

My Friend send me some images, but something wrong, plzz help me repair this image, for get this flag *note: bukan file corrupt author salah format flag:( format flag untuk chall ini : hackfest0x05 author: @wisnuazfarm discord: zzzzzzzzzzzzz#9742

Chall file :

chall_size.zip

Get 3 file png corrupted crc :

ls
 qr.png
 qrr.png
 qrrr.png
pngcheck *
zlib warning:  different version (expected 1.2.11, using 1.3.1)

qr.png  CRC error in chunk IHDR (computed 421d2d39, expected b2b7b9bd)
ERROR: qr.png
qrr.png  CRC error in chunk IHDR (computed ec2a9aa0, expected 4f32eac7)
ERROR: qrr.png
qrrr.png  CRC error in chunk IHDR (computed be792774, expected 95b8e875)
ERROR: qrrr.png

Errors were detected in 3 of the 3 files tested.

Get script for brute crc to get correct width and height.

to get crc :
Pasted image 20240229171646.png match the struct with : https://i.stack.imgur.com/hcIIO.png

after we got the crc, we calculate the correct width and height using this script :

from binascii import crc32


# B2 B7 B9 BD crc for qr.png
# 4F 32 EA C7 crc for qrr.png
# 95 B8 E8 75 crc for qrrr.png

crc_checksum = int.from_bytes(b'\x95\xb8\xe8\x75',byteorder='big') 

for h in range(0xffff):
   for w in range(0xffff):
           #IHDR Chunk + (4 Bytes Width) + (4 Bytes Height) + Bit Depth + Col Type + Compression Method + Filter Method + Interlace Method
           #set byte structure bit depth 2byte setelah size
           crc=b"\x49\x48\x44\x52"+w.to_bytes(4,byteorder='big')+h.to_bytes(4,byteorder='big')+b"\x08\x02\x00\x00\x00"
           if crc32(crc) % (1<<32) == crc_checksum:
               print('Image Width: ',end="")
               print(hex(w))
               print('Image Height :',end="")
               print(hex(h))

after we got the correct image width and height, we edit in in bless . example of qr.png :

python3 solver.py
Image Width: 0xc7
Image Height :0x2d

we edit in bless before it was
Pasted image 20240229172005.png

00 00 AA AA 00 00 AA AA

we edit it to

00 00 00 C7 00 00 00 2D

. and then we check pngcheck. and its correct.

( do same for qr, qrr, qrr )

and combine 3 of this images and we get the flag.
Pasted image 20240229171325.png