TOC

第二题 子鼠开天

算法识别

从字符串信息可知,文件用了openssl_0.9.8这个库,导入相应版本的sig文件后可以识别部分代码
openssl_0.9.8.sig
其他没有识别出来的函数可以通过固定参数或者对比openssl源码识别
sub_4019B0 -> sha512 (0xF3BCC908, 0x6A09E667…)
sub_401560 -> md5 (0x67452301, 0xEFCDAB89…)
sub_404FE0 -> AES_set_encrypt_key
sub_4053A0 -> AES_set_decrypt_key
sub_sub_4010F0 -> 最后一个参数为1是是AES加密,为0时是AES解密
sub_401210 -> rsa

加密过程

sn:AES解密 -> RSA加密
name: sha512 -> md5 -> sha512 -> md5
sn加密结果的后16字节与nams计算hash后的16字节相等且sn的前两个字节为0002,第16个字节为0

solve

#coding=utf-8  
import gmpy2  
import hashlib  
from Crypto.Cipher import AES  
import base64  
import math  
from binascii import b2a_hex, a2b_hex  
  
class prpcrypt():  
  def __init__(self):  
      s = "480b62c3acd6c8a36b18d9e906cd90d2"  
      self.key = s.decode('hex')  
      self.mode = AES.MODE_ECB  
  def encrypt(self, text):  
      cryptor = AES.new(self.key, self.mode)  
      length = 16  
      count = len(text)  
      if count % length != 0:  
              add = length - (count % length)  
      else:  
          add = 0  
          text = text + ('\0' * add)  
          self.ciphertext = cryptor.encrypt(text)  
          return b2a_hex(self.ciphertext)  
     
  def decrypt(self, text):  
      cryptor = AES.new(self.key, self.mode)  
      plain_text = cryptor.decrypt(a2b_hex(text))  
      return plain_text.rstrip('\0')  
  
n = 0x69823028577465ab3991df045146f91d556dee8870845d8ee1cd3cf77e4a0c39  
p = 201522792635114097998567775554303915819  
q = 236811285547763449711675622888914229291  
phi = (p - 1) * (q - 1)  
e = 65537  
d = gmpy2.invert(e, phi)  
x = 0x02000000000000000000000000000014af58ad4d76d59d8d2171ffb4ca2231  
msg = hex(pow(x,d,n)).strip('L')[2:]  
pr = prpcrypt()  
c1 = pr.encrypt(msg[:32].decode('hex'))  
c2 = pr.encrypt(msg[32:64].decode('hex'))  
print c1+c2