HCTF2016-雜項簽到

題目下載了一個+_+.pcapng ，用Wireshark打開， Ctrl-F搜索flag 發現python代碼 將Data導出 

#!/usr/bin/env python
# coding:utf-8
__author__ = 'Aklis'

from Crypto import Random
from Crypto.Cipher import AES

import sys
import base64


def decrypt(encrypted, passphrase):
  IV = encrypted[:16]
  aes = AES.new(passphrase, AES.MODE_CBC, IV)
  return aes.decrypt(encrypted[16:])


def encrypt(message, passphrase):
  IV = message[:16]
  length = 16
  count = len(message)
  padding = length - (count % length)
  message = message + '\0' * padding
  aes = AES.new(passphrase, AES.MODE_CBC, IV)
  return aes.encrypt(message)


IV = 'YUFHJKVWEASDGQDH'

message = IV + 'flag is hctf{xxxxxxxxxxxxxxx}'


print len(message)

example = encrypt(message, 'Qq4wdrhhyEWe4qBF')
print example
example = decrypt(example, 'Qq4wdrhhyEWe4qBF') 
print example

是DES加密，知道VI 與 key

在pcap流量包繼續搜索看到了

mbZoEMrhAO0WWeugNjqNw3U6Tt2C+rwpgpbdWRZgfQI3MAh0sZ9qjnziUKkV90XhAOkIs/OXoYVw5uQDjVvgNA=

猜測是直接加密，發現解不開。

測試得出：

用base64解碼，再用該decrypt()解密。

#!/usr/bin/env python
# coding:utf-8
__author__ = 'Aklis'

from Crypto import Random
from Crypto.Cipher import AES

import sys
import base64


def decrypt(encrypted, passphrase):
  IV = encrypted[:16]
  aes = AES.new(passphrase, AES.MODE_CBC, IV)
  return aes.decrypt(encrypted[16:])


def encrypt(message, passphrase):
  IV = message[:16]
  length = 16
  count = len(message)
  padding = length - (count % length)
  message = message + '\0' * padding
  aes = AES.new(passphrase, AES.MODE_CBC, IV)
  return aes.encrypt(message)

# IV = 'YUFHJKVWEASDGQDH'

# message = IV + 'flag is hctf{xxxxxxxxxxxxxxx}'
#
#
# print len(message)

# example = encrypt(message, 'Qq4wdrhhyEWe4qBF')
# print example
a='mbZoEMrhAO0WWeugNjqNw3U6Tt2C+rwpgpbdWRZgfQI3MAh0sZ9qjnziUKkV90XhAOkIs/OXoYVw5uQDjVvgNA=='
b = base64.b64decode(a)

example = decrypt(b, 'Qq4wdrhhyEWe4qBF')
print example