magic - defcon 2017

magic.py

#!/usr/bin/python2
#
# magic - defcon 2017
#
# @_hugsy_
#
# The flag is: a color map of the sun sokemsUbif
#

import os, base64, telnetlib
from  subprocess import *

def crack(f):

    pre = ""
    while True:
        found = False
        for i in range(256):
            c = chr(i)
            p = Popen(["magic_dist/%s" % f,],
                      stdout=PIPE,
                      stdin=PIPE,
                      close_fds=True
            )
            res = p.stdout.read(11)
            p.stdin.write(pre+chr(i) + '\n')
            p.wait()

            if p.returncode == 0:
                return pre+c

            if p.returncode != len(pre)+1:
                pre += c
                found = True
                break
            if p.returncode==0xFA:
                return pre + c

        if not found:
            raise Exception("bye")

    return pre


t = telnetlib.Telnet("cm2k-magic_b46299df0752c152a8e0c5f0a9e5b8f0.quals.shallweplayaga.me", 12001)
t.read_until('send your solution as base64, followed by a newline\n')

while True:
    h = t.read_until('\n').strip()
    print "<<< ", h
    res = crack(h)
    t.write( base64.b64encode(res)  + '\n')
    print ">>> ", res