Write up for InCTF 2014 - Stegnography 400 solved using python

Write up for InCTF 2014 - Stegnography 400 solved using python .py

import os,sys
import Image

modi_bin = Image.open("modi.png").convert('RGB')

bin = ''

R = open('r.txt','w')
G = open('g.txt','w')
B = open('b.txt','w')

# By Analysing the text docs I found blue Plane First column is embedded with data 
flag = ''
flag1 = ''

for h in range(modi_bin.size[1]): # Fetches Height
 count = 0
 binR = ''
 binG = ''
 binB = ''
 
 for w in range(modi_bin.size[0]): # Fetches Width
  count += 1
  binR += str(modi_bin.getpixel((w,h))[0] & 1)
  binG += str(modi_bin.getpixel((w,h))[1] & 1)
  binB += str(modi_bin.getpixel((w,h))[2] & 1)
  if w == 0: # blue plane first bit 
   flag += str(modi_bin.getpixel((w,h))[2] & 1)
  if count == 8:
   R.write(binR)
   G.write(binG)
   B.write(binB)
   binR=' ';binG=' ';binB=' '
   count = 0
 R.write(binR+'\n')
 G.write(binG+'\n')
 B.write(binB+'\n')


print flag

flag_value = [ str(int(i)^1) for i in flag]

flag = ''.join(flag_value)

print ''.join(chr(int(flag[i:i+8], 2)) for i in xrange(0, len(flag), 8))