NDH 2k10 public wargame, level3

'''*********************************
|  level3 - brute force cracking   |
|               **                 |
|  http://wargame.nuitduhack.com/  |
|  http://www.nuitduhack.com/      |
*********************************'''
#!/usr/bin/python
import os

target = '/home/level3/crackme'
wanted = '2:8vytm&*9|)].l(ol;a'
arg = 'a'*20
solution_string = ''
size = 1024

print "-->Brute force cracking"
for char in range(20): # bf one by one
 for ascii in range(1, 256): # for all but \0 (ascii)
  arg = solution_string + chr(ascii) + 'a'*(19-char)
  # beware of bad char :
  if arg.find("'") == -1:
   # /home/level3/crackme 'all but single quote'
   cmd = "%s '%s'"%(target, arg)
  else:
   # /home/level3/crackme "all but double quote"
   cmd = '%s "%s"'%(target, arg)
  # reading the output
  res = os.popen(cmd).read(size)
  # searching for ciphered
  pos = res.find('Ciphered:')
  # ciphered is 20 bytes length
  ciphered = res[pos+10:pos+30]
  # check current ciphered char matching with wanted
  if ciphered[char] == wanted[char]:
   solution_string = ''.join([solution_string, chr(ascii)])
   break
 print '>%d%%'%(char*5)

# print solution string
print "\nSolution string: %s"%solution_string
# print string as a list to get unprintable ascii
print "Solution ascii: %s"%[solution_string]