import zlib
import sys
import binascii
import struct
import os
img = sys.argv[1]


with open(img, 'rb') as fi, open(img+'.sign', 'wb') as fo:
    data = fi.read(4)
    check = 0
    while data:
        check ^= struct.unpack('<I', data)[0]
        data = fi.read(4)

    ln = struct.pack('<I', os.path.getsize(img))
    ck = struct.pack('<I', check)

    fo.write(ln)
    fo.write(ck)
    fo.write('\x00' * 2040)
    fi.seek(0) 
    fo.write(fi.read())
    print 'len', ln.encode('hex'), os.path.getsize(img)
    print 'chk', ck.encode('hex')