solver for http://bctf.cn/problems/4

passcode_solver.py

#!/usr/bin/env python2
#-*- coding:utf-8 -*-

# This is solver for problem passcode in BCTF2014
# See http://bctf.cn/problems/4
# By Pengyu CHEN (cpy.prefers.you[at]gmail.com)
# COPY LEFT, ALL WRONGS RESERVED.

import base64
import binascii
import zlib
import os
import random
import itertools

try:
    import passcode
except ImportError:
    raise ImportError('"passcode.py" required. Obtain it from http://bctf.cn/problems/4')
 
def get_func_combination():
    from passcode import f as f
    for (f1, f2, f3, f4) in itertools.product(passcode.f, repeat=4):
        try:
            answer_hash = f['fun6'](f['fun2'](f[f1](f[f2](f[f3](f[f4](passcode.answer))))))
            assert(len(answer_hash) != 0)
            print('Possible function combination: %s' %((f1, f2, f3, f4), ))
        except (TypeError, ValueError, zlib.error, AssertionError):
            pass
    return

def get_answers():
    # obtained via invoking get_func_combination()
    (f1,f2,f3,f4) = ('fun3', 'fun5', 'fun1', 'fun4')

    from passcode import f as f
    f_hash = lambda x: f['fun6'](f['fun2'](f[f1](f[f2](f[f3](f[f4](x))))))
    f_hash_stage2 = lambda x: f[f2](f[f3](f[f4](x)))
    frev_hash_stage2 = lambda x: passcode.hex2dec(passcode.reverse(binascii.hexlify(x)))
    frev_hash_stage1 = lambda x, z_level: zlib.compress(x, z_level)
    frev_hash_stage0 = lambda x: base64.b64encode(x.encode('gb2312'))

    answers = []
    answer_hash = f_hash(passcode.answer)
    for z_level in range(10):    # default is 6
        # ya for yet another
        ya_hash = frev_hash_stage2(frev_hash_stage1(frev_hash_stage0(answer_hash), z_level))
        assert(f_hash(ya_hash) == answer_hash)
        answers += [ya_hash]

    return list(set(answers))

if __name__ == '__main__':
    get_func_combination()
    answers = get_answers()
    print('Here comes answers:')
    for answer in answers:
        print(answer)
    pass