puzzleng.py

import zlib
import struct
import sys
import codecs
from PIL import Image

s = open('flag.puzzle','rb').read()
size = 57

def xor(data, byte):
    return bytes([data[i]^byte for i in range(len(data))])

prekey = b'\x65\x30\x56\xc3\x78' + bytes([255,75,191,247,71,55,227,111,83,38,76,37,244])
good = b''

for i in range(len(prekey)):
    good += xor(s[size*i:size*(i+1)],prekey[i])

print(good)

pregood, good = good.split(b'IDAT')
pregood += b'IDAT'
print(good)
dd = ''
for k in range(len(prekey),19):
    print('chunk',k)
    chunk = s[size*k:size*(k+1)]
    maxi = 0
    maxc = 0
    for i in range(256): # vary?
        try:
            d = zlib.decompressobj() 
            g = good + xor(chunk,i)
            #print(g)
            dd = d.decompress(g)
            #print(dd,len(dd))
            if any([dd[j] not in [0,1,2,3,4] for j in range(0,len(dd),115)]):
                continue
            #print([dd[j] for j in range(1,len(dd),115)])
            if (any([dd[j] not in [255] for j in range(1,len(dd),115)])
                or any([dd[j] not in [255] for j in range(114,len(dd),115)])):
                continue
            print(k,i)
            count = dd.count(b'\xff')
            if count > maxc:
                maxi = i
                maxc = count
                print(k,maxi,maxc)
            #good = g
        except zlib.error:
            continue
    if maxc == 0:
        print("fail")
        sys.exit(1)
    good += xor(chunk,maxi)

im = Image.new('1',(912,912))

for i in range(0,len(dd)-115,115):
    for j in range(114):
        for k in range(8):
            im.putpixel((j*8+k,i//115),dd[i+1+j])

im.show()
im.save('good2.png')

'''
good = pregood + g + xor(s[size*19:size*20],0x1b)

# crc fix
crc = struct.pack(">I",zlib.crc32(b'IDAT'+good.split(b'IDAT')[1].split(b'IEND')[0][:-8]))
good = good[:-16]+crc+good[-12:]

# palette fix
good = good.split(b'PLTE')[0] + b'PLTE\x00\x00\x00\xff\xff\xff\xa5\xd9\x9f\xdd' + good.split(b'PLTE')[1][10:]
#print(good)
open('good.png','wb').write(good)
'''