tkbctf4 "Simple Serial Code"

genserial.py

import random
import string
import md5

flag = md5.new()
flag.update("this_is_not_flag!!")
flag_md5 = flag.hexdigest()

print "flag_md5:", flag_md5
flag_md5 = [flag_md5[i:i+4] for i in range(0, len(flag_md5), 4)]

i = 0
res = []
while True:
    serial = ''.join(random.choice(string.ascii_lowercase + \
            string.ascii_uppercase) for _ in range(4))
    m = md5.new()
    m.update(serial)
    md = m.hexdigest()

    if i < len(flag_md5) and md[0:4] == flag_md5[i]:
        res.append(serial)
        i += 1

    if i == len(flag_md5):
        print "found serial: ",''.join(res)
        break