InCTF 2014 - Forensics 400 - MODIfied

Every time when I see a stego challenge, I am very frustrated at first but in the end I feel like I achieved something. Stegano challenges keep on changing with different type of tricks. This time it's quite a difficult trick but not beyond our imagination. In this challenge they gave an image of Modi.

File name MODIfied.png itself indicating that it's modified. After some careful observations I stumbled upon some pixels in the white border that are modified which are in 1st column of the image.

(255, 255, 255)
(255, 255, 254)
(255, 255, 255)
(255, 255, 254)
(255, 255, 254)
(255, 255, 255)
(255, 255, 254)
(255, 255, 255)

Then I extracted all the pixels in the 1st column of the white border. After observing some of the pixels I found some of the pixels with 254 values at blue layer, but that's different from a white pixel (255, 255, 255). After that I assumed 255 as 0 and 254 as 1, and got a binary string, after converting it into string I got the flag. Here is the python script that will do the job.

from PIL import Image
a=Image.open('MODIfied.png','r')
pix=list(a.getdata())
mo_i=[]
for i in range(0,len(pix)):
	if((i+1)%804==1):
		mo_i.append(pix[i])
bina=""
for j in mo_i:
	if(j[2]==255):
		bina+="0"
	else:
		bina+="1"
flag=""
print "[+] Checking for Flag ..."
print "[+] Found a flag..."
for i in range(0,len(bina),8):
	flag+=chr(int(bina[i:i+8],2))
print flag
print "[+] Oh! Here it is..."

And the Flag is: {m0d1_thE_NeW_Pm}

Team r3b00+ awarded with 400 points

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