CSAW CTF 2014 bin300(2) weissman

weissman.py

import os
import time
import struct
from pwn import *

def extract(fname):
    f = open(fname, 'rb')
    head = header(f)
    for i in range(head[2]):
        fhead = file_header(f)
        extracted = file_extract(f, fhead[1])
        open(fhead[3], 'w+').write(extracted)
        print 'extracted %s' % fhead[3]

def header(f):
    magic = f.read(8)
    version = u32(f.read(4))
    num_files = u32(f.read(4))
    return (magic, version, num_files)

def file_header(f):
    magic = f.read(4)
    compressed_size = u32(f.read(4))
    uncompressed_size = u32(f.read(4))
    filename = f.read(32).strip('\0')
    return (magic, compressed_size, uncompressed_size, filename)

def file_extract(f, compressed_size):
    extracted = ''
    c = 0
    counter = 0
    while c < compressed_size:
        chunk = u8(f.read(1))
        c += 1
        if chunk == 0x13:
            buf = f.read(9)
            extracted += buf
            c += 9
            #print '%x chunk[%02x]: %s (%d)' % (counter, chunk, buf, c - 10)
        else:
            buf = u16(f.read(2))
            extracted += '\0' * (chunk / 2)
            c += 2
            #print '%x chunk[%02x]: %s (%d)' % (counter, chunk, hex(buf), c - 3)
        counter += 1
    return extracted



extract('./weissman.csawlz')