[HWS]animals

前言

本来都打算退役了，看到一个挺有意思的题目，出来写一下wp，(这个题我只能说作者很会玩)

分析

首先IDA打开

熟悉的味道熟悉的花

整整两段，没有办法，挫一个idapython脚本梭一下

start_add = 0x400800
end_add = 0x406e22
for i in range(start_add,end_add):
    if get_wide_dword(i) == 0x08750a74:
        patch_dword(i,0x90909090)
        patch_dword(i+4,0x90909090)
        patch_dword(i+8,0x90909090)
    elif get_wide_dword(i) == 0x13751574:
        patch_dword(i,0x90909090)
        patch_dword(i+4,0x90909090)
        patch_dword(i+8,0x90909090)
        patch_dword(i+12,0x90909090)
        patch_dword(i+16,0x90909090)
        patch_word(i+20,0x9090)
        patch_byte(i+22,0x90)

main函数分析错了，并且下面这一段不能按p声明。
往下翻找发现

这里有一个字节未识别，按C识别一下

识别完了之后一大段地址全部爆红
此时我们回到main函数下面继续按p

可以按p了，但是出main函数仍旧是有问题的，并且我们tab查看一下函数内容

寄存器丢失的同时还非常的乱，所以不能直接p
我们需要修改main函数的起始地点。

这个时候主函数就正常了

void __fastcall main(__int64 a1, char **a2, char **a3)
{
  size_t v3; // rax
  size_t v4; // rax
  size_t v5; // rax
  size_t v6; // rax
  size_t v7; // rax
  size_t v8; // rax
  int v9; // ecx
  int v10; // eax
  unsigned int v11; // eax
  size_t v12; // rax
  const char *v13; // [rsp+1Ch] [rbp-318h]
  const char *v14; // [rsp+6Ch] [rbp-2C8h]
  const char *v15; // [rsp+84h] [rbp-2B0h]
  const char *v16; // [rsp+9Ch] [rbp-298h]
  const char *v17; // [rsp+B4h] [rbp-280h]
  const char *v18; // [rsp+CCh] [rbp-268h]
  char *src; // [rsp+E4h] [rbp-250h]
  int i; // [rsp+148h] [rbp-1ECh]
  char v21[88]; // [rsp+14Ch] [rbp-1E8h] BYREF
  char v22[24]; // [rsp+1A4h] [rbp-190h] BYREF
  int v23; // [rsp+1BCh] [rbp-178h] BYREF
  int v24; // [rsp+1C0h] [rbp-174h]
  char v25[256]; // [rsp+1C4h] [rbp-170h] BYREF
  char *s; // [rsp+2C4h] [rbp-70h] BYREF
  char *v27; // [rsp+2CCh] [rbp-68h]
  char *v28; // [rsp+2D4h] [rbp-60h]
  char *v29; // [rsp+2DCh] [rbp-58h]
  char *v30; // [rsp+2E4h] [rbp-50h]
  char *v31; // [rsp+2ECh] [rbp-48h]
  pthread_t newthread[2]; // [rsp+2F4h] [rbp-40h] BYREF
  int v33; // [rsp+304h] [rbp-30h]
  int v34; // [rsp+308h] [rbp-2Ch]

  v34 = 0;
  v33 = a1;
  newthread[1] = (pthread_t)a2;
  sub_405FF0(a1, a2, a3);
  memset(&s, 0, 0x30uLL);
  s = (_BYTE *)("0. cat" + 3);
  v27 = (_BYTE *)("1. dog" + 3);
  v28 = (_BYTE *)("2. fox" + 3);
  v29 = (_BYTE *)("3. panda" + 3);
  v30 = (_BYTE *)("4. dragon" + 3);
  v31 = (_BYTE *)("5. monkey" + 3);
  memset(v25, 0, sizeof(v25));
  v24 = 0;
  while ( v24 < 9 )
  {
    if ( !((dword_6080F4 < 10) ^ (((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0) | (dword_6080F4 < 10
                                                                                                && ((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0)) )
      goto LABEL_26;
    while ( 1 )
    {
      v23 = 0;
      puts("Welcome Animal shop");
      sub_400900();
      printf("Please input my favorite animal: ");
      __isoc99_scanf("%d", &v23);
      if ( (dword_6080F4 < 10 && ((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0) | (dword_6080F4 < 10) ^ (((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0) )
        break;
LABEL_26:
      v23 = 0;
      puts("Welcome Animal shop");
      sub_400900();
      printf("Please input my favorite animal: ");
      __isoc99_scanf("%d", &v23);
    }
    switch ( v23 )
    {
      case 0:
        src = s;
        v3 = strlen(s);
        strncat(v25, src, v3);
        goto LABEL_16;
      case 1:
        v18 = v27;
        v4 = strlen(v27);
        strncat(v25, v18, v4);
        goto LABEL_16;
      case 2:
        v17 = v28;
        v5 = strlen(v28);
        strncat(v25, v17, v5);
        goto LABEL_16;
      case 3:
        v16 = v29;
        v6 = strlen(v29);
        strncat(v25, v16, v6);
        goto LABEL_16;
      case 4:
        v15 = v30;
        v7 = strlen(v30);
        strncat(v25, v15, v7);
        goto LABEL_16;
      case 5:
        if ( (dword_6080F4 < 10 && ((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0) | ((unsigned __int8)~(dword_6080F4 < 10) ^ (unsigned __int8)~(((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0)) & 1 )
          goto LABEL_12;
        do
        {
          v13 = v31;
          v12 = strlen(v31);
          strncat(v25, v13, v12);
LABEL_12:
          v14 = v31;
          v8 = strlen(v31);
          strncat(v25, v14, v8);
          v9 = (((_BYTE)dword_608138 - 44 + 43) * (_BYTE)dword_608138) & 1;
        }
        while ( !((dword_6080F4 < 10) ^ (v9 == 0) | (dword_6080F4 < 10 && v9 == 0)) );
LABEL_16:
        ++v24;
        break;
      default:
        v10 = (((_BYTE)dword_608138 - 14 + 13) * (_BYTE)dword_608138) & 1;
        if ( (dword_6080F4 < 10) ^ (v10 == 0) | (dword_6080F4 < 10 && v10 == 0) )
        {
          puts("Input Err.");
          exit(0);
        }
        puts("Input Err.");
        exit(0);
    }
  }
  pthread_create(newthread, 0LL, start_routine, 0LL);
  pthread_join(newthread[0], 0LL);
  puts("done.");
  sub_4009A0(v21);
  v11 = strlen(v25);
  sub_400B30(v21, v25, v11);
  sub_4059A0(v21, v22);
  for ( i = 0; ; ++i )
  {
    while ( !((dword_6080F4 < 10) ^ (((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0) | (dword_6080F4 < 10 && ((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0)) )
      ;
    if ( i >= 16 )
      break;
    if ( byte_608090[i] != v22[i] )
    {
      puts("Wrong.");
      exit(0);
    }
  }
  if ( !((dword_6080F4 < 10 && ((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0) | (dword_6080F4 < 10) ^ (((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0)) )
LABEL_30:
    puts("Win! , flag is flag{md5(input)}");
  puts("Win! , flag is flag{md5(input)}");
  if ( !((dword_6080F4 < 10) ^ (((((_BYTE)dword_608138 - 1) * (_BYTE)dword_608138) & 1) == 0) | (dword_6080F4 < 10
                                                                                              && ((((_BYTE)dword_608138
                                                                                                  - 1)
                                                                                                 * (_BYTE)dword_608138) & 1) == 0)) )
    goto LABEL_30;
}

大致就是个猜动物游戏，选择的动物序号md5加密就是flag。
可以发现需要选择9次
每次选6个也就是6^9的选择次数，那么我们查看之后发现只有一千多万次，可以直接使用pwntools进行一个爆破来解决问题，但是这里介绍的方法就是直接分析题目

解题

程序有反调试
分析程序之后可以发现程序是将你选择的动物全称进行一个变异的md5加密去比较的

变异md5

看到一个比较处，我们查看比较内容

可以发现是一串md5数字

我们分析函数可以查找到该函数

该函数对变异md5后的值进行了一个处理
然后看到md5函数

发现md5函数的编码表被替换了，1，2交换3，4交换因此我们可以自己实现脚本来进行一个md5爆破了

exp

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <time.h>
#include <windows.h>
#include<stdio.h>
#include <stdio.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <windows.h>
#include <string.h>
#include <stdio.h>
#include <stdbool.h>
#include <windows.h>
#define MD5_H

typedef struct
{
    unsigned int count[2];
    unsigned int state[4];
    unsigned char buffer[64];   
}MD5_CTX;

#define F(x,y,z) ((x & y) | (~x & z))
#define G(x,y,z) ((x & z) | (y & ~z))
#define H(x,y,z) (x^y^z)
#define I(x,y,z) (y ^ (x | ~z))
#define ROTATE_LEFT(x,n) ((x << n) | (x >> (32-n)))
#define FF(a,b,c,d,x,s,ac) \
          { \
          a += F(b,c,d) + x + ac; \
          a = ROTATE_LEFT(a,s); \
          a += b; \
          }
#define GG(a,b,c,d,x,s,ac) \
          { \
          a += G(b,c,d) + x + ac; \
          a = ROTATE_LEFT(a,s); \
          a += b; \
          }
#define HH(a,b,c,d,x,s,ac) \
          { \
          a += H(b,c,d) + x + ac; \
          a = ROTATE_LEFT(a,s); \
          a += b; \
          }
#define II(a,b,c,d,x,s,ac) \
          { \
          a += I(b,c,d) + x + ac; \
          a = ROTATE_LEFT(a,s); \
          a += b; \
          }                                            
void MD5Init(MD5_CTX *context);
void MD5Update(MD5_CTX *context,unsigned char *input,unsigned int inputlen);
void MD5Final(MD5_CTX *context,unsigned char digest[16]);
void MD5Transform(unsigned int state[4],unsigned char block[64]);
void MD5Encode(unsigned char *output,unsigned int *input,unsigned int len);
void MD5Decode(unsigned int *output,unsigned char *input,unsigned int len);
using namespace std;
typedef int status;
typedef int selemtype;

unsigned char PADDING[]={0x80,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
                         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
                         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
                         0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};

void MD5Init(MD5_CTX *context)
{
     context->count[0] = 0;
     context->count[1] = 0;
     context->state[0] = 0xEFCDAB89;
     context->state[1] = 0x67452301;
     context->state[2] = 0x10325476;
     context->state[3] = 0x98BADCFE;
}
void MD5Update(MD5_CTX *context,unsigned char *input,unsigned int inputlen)
{
    unsigned int i = 0,index = 0,partlen = 0;
    index = (context->count[0] >> 3) & 0x3F;
    partlen = 64 - index;
    context->count[0] += inputlen << 3;
    if(context->count[0] < (inputlen << 3))
       context->count[1]++;
    context->count[1] += inputlen >> 29;

    if(inputlen >= partlen)
    {
       memcpy(&context->buffer[index],input,partlen);
       MD5Transform(context->state,context->buffer);
       for(i = partlen;i+64 <= inputlen;i+=64)
           MD5Transform(context->state,&input[i]);
       index = 0;        
    }  
    else
    {
        i = 0;
    }
    memcpy(&context->buffer[index],&input[i],inputlen-i);
}
void MD5Final(MD5_CTX *context,unsigned char digest[16])
{
    unsigned int index = 0,padlen = 0;
    unsigned char bits[8];
    index = (context->count[0] >> 3) & 0x3F;
    padlen = (index < 56)?(56-index):(120-index);
    MD5Encode(bits,context->count,8);
    MD5Update(context,PADDING,padlen);
    MD5Update(context,bits,8);
    MD5Encode(digest,context->state,16);
}
void MD5Encode(unsigned char *output,unsigned int *input,unsigned int len)
{
    unsigned int i = 0,j = 0;
    while(j < len)
    {
         output[j] = input[i] & 0xFF;  
         output[j+1] = (input[i] >> 8) & 0xFF;
         output[j+2] = (input[i] >> 16) & 0xFF;
         output[j+3] = (input[i] >> 24) & 0xFF;
         i++;
         j+=4;
    }
}
void MD5Decode(unsigned int *output,unsigned char *input,unsigned int len)
{
     unsigned int i = 0,j = 0;
     while(j < len)
     {
           output[i] = (input[j]) |
                       (input[j+1] << 8) |
                       (input[j+2] << 16) |
                       (input[j+3] << 24);
           i++;
           j+=4; 
     }
}
void MD5Transform(unsigned int state[4],unsigned char block[64])
{
     unsigned int a = state[0];
     unsigned int b = state[1];
     unsigned int c = state[2];
     unsigned int d = state[3];
     unsigned int x[64];
     MD5Decode(x,block,64);
     FF(a, b, c, d, x[ 0], 7, 0xd76aa478); /* 1 */
 FF(d, a, b, c, x[ 1], 12, 0xe8c7b756); /* 2 */
 FF(c, d, a, b, x[ 2], 17, 0x242070db); /* 3 */
 FF(b, c, d, a, x[ 3], 22, 0xc1bdceee); /* 4 */
 FF(a, b, c, d, x[ 4], 7, 0xf57c0faf); /* 5 */
 FF(d, a, b, c, x[ 5], 12, 0x4787c62a); /* 6 */
 FF(c, d, a, b, x[ 6], 17, 0xa8304613); /* 7 */
 FF(b, c, d, a, x[ 7], 22, 0xfd469501); /* 8 */
 FF(a, b, c, d, x[ 8], 7, 0x698098d8); /* 9 */
 FF(d, a, b, c, x[ 9], 12, 0x8b44f7af); /* 10 */
 FF(c, d, a, b, x[10], 17, 0xffff5bb1); /* 11 */
 FF(b, c, d, a, x[11], 22, 0x895cd7be); /* 12 */
 FF(a, b, c, d, x[12], 7, 0x6b901122); /* 13 */
 FF(d, a, b, c, x[13], 12, 0xfd987193); /* 14 */
 FF(c, d, a, b, x[14], 17, 0xa679438e); /* 15 */
 FF(b, c, d, a, x[15], 22, 0x49b40821); /* 16 */

 /* Round 2 */
 GG(a, b, c, d, x[ 1], 5, 0xf61e2562); /* 17 */
 GG(d, a, b, c, x[ 6], 9, 0xc040b340); /* 18 */
 GG(c, d, a, b, x[11], 14, 0x265e5a51); /* 19 */
 GG(b, c, d, a, x[ 0], 20, 0xe9b6c7aa); /* 20 */
 GG(a, b, c, d, x[ 5], 5, 0xd62f105d); /* 21 */
 GG(d, a, b, c, x[10], 9,  0x2441453); /* 22 */
 GG(c, d, a, b, x[15], 14, 0xd8a1e681); /* 23 */
 GG(b, c, d, a, x[ 4], 20, 0xe7d3fbc8); /* 24 */
 GG(a, b, c, d, x[ 9], 5, 0x21e1cde6); /* 25 */
 GG(d, a, b, c, x[14], 9, 0xc33707d6); /* 26 */
 GG(c, d, a, b, x[ 3], 14, 0xf4d50d87); /* 27 */
 GG(b, c, d, a, x[ 8], 20, 0x455a14ed); /* 28 */
 GG(a, b, c, d, x[13], 5, 0xa9e3e905); /* 29 */
 GG(d, a, b, c, x[ 2], 9, 0xfcefa3f8); /* 30 */
 GG(c, d, a, b, x[ 7], 14, 0x676f02d9); /* 31 */
 GG(b, c, d, a, x[12], 20, 0x8d2a4c8a); /* 32 */

 /* Round 3 */
 HH(a, b, c, d, x[ 5], 4, 0xfffa3942); /* 33 */
 HH(d, a, b, c, x[ 8], 11, 0x8771f681); /* 34 */
 HH(c, d, a, b, x[11], 16, 0x6d9d6122); /* 35 */
 HH(b, c, d, a, x[14], 23, 0xfde5380c); /* 36 */
 HH(a, b, c, d, x[ 1], 4, 0xa4beea44); /* 37 */
 HH(d, a, b, c, x[ 4], 11, 0x4bdecfa9); /* 38 */
 HH(c, d, a, b, x[ 7], 16, 0xf6bb4b60); /* 39 */
 HH(b, c, d, a, x[10], 23, 0xbebfbc70); /* 40 */
 HH(a, b, c, d, x[13], 4, 0x289b7ec6); /* 41 */
 HH(d, a, b, c, x[ 0], 11, 0xeaa127fa); /* 42 */
 HH(c, d, a, b, x[ 3], 16, 0xd4ef3085); /* 43 */
 HH(b, c, d, a, x[ 6], 23,  0x4881d05); /* 44 */
 HH(a, b, c, d, x[ 9], 4, 0xd9d4d039); /* 45 */
 HH(d, a, b, c, x[12], 11, 0xe6db99e5); /* 46 */
 HH(c, d, a, b, x[15], 16, 0x1fa27cf8); /* 47 */
 HH(b, c, d, a, x[ 2], 23, 0xc4ac5665); /* 48 */

 /* Round 4 */
 II(a, b, c, d, x[ 0], 6, 0xf4292244); /* 49 */
 II(d, a, b, c, x[ 7], 10, 0x432aff97); /* 50 */
 II(c, d, a, b, x[14], 15, 0xab9423a7); /* 51 */
 II(b, c, d, a, x[ 5], 21, 0xfc93a039); /* 52 */
 II(a, b, c, d, x[12], 6, 0x655b59c3); /* 53 */
 II(d, a, b, c, x[ 3], 10, 0x8f0ccc92); /* 54 */
 II(c, d, a, b, x[10], 15, 0xffeff47d); /* 55 */
 II(b, c, d, a, x[ 1], 21, 0x85845dd1); /* 56 */
 II(a, b, c, d, x[ 8], 6, 0x6fa87e4f); /* 57 */
 II(d, a, b, c, x[15], 10, 0xfe2ce6e0); /* 58 */
 II(c, d, a, b, x[ 6], 15, 0xa3014314); /* 59 */
 II(b, c, d, a, x[13], 21, 0x4e0811a1); /* 60 */
 II(a, b, c, d, x[ 4], 6, 0xf7537e82); /* 61 */
 II(d, a, b, c, x[11], 10, 0xbd3af235); /* 62 */
 II(c, d, a, b, x[ 2], 15, 0x2ad7d2bb); /* 63 */
 II(b, c, d, a, x[ 9], 21, 0xeb86d391); /* 64 */
     state[0] += a;
     state[1] += b;
     state[2] += c;
     state[3] += d;
}
char choices[][10] = {
    "cat",
    "dog",
    "fox",
    "panda",
    "dragon",
    "monkey"
};
unsigned char answer[] = {
    0xCB, 0xA4, 0x7B, 0xE5, 0xF0, 0x1C, 0xD1, 0x95, 0x5C, 0x85,
    0x46, 0xA2, 0xB2, 0x4F, 0xBD, 0x18
};
int main () {
    //051410233
    MD5_CTX md5;
    unsigned char md5_str[32]={0};
    int length = 9;  // 总共选择的次数

    int choice[length];  // 用于保存每个选择的索引

    // 初始化选择索引
    for (int i = 0; i < length; i++) {
        choice[i] = 0;
    }

    while (1) {
        // 拼接动物名称
        char animalName[length * 10 + 1];  // 假设每个动物名称不超过10个字符
        int index = 0;
        for (int i = 0; i < length; i++) {
            int choiceIndex = choice[i];
            char *animal = choices[choiceIndex];
            while (*animal != '\0') {
                animalName[index] = *animal;
                animal++;
                index++;
            }
        }
        animalName[index] = '\0';
        for(int i = 0 ; i < 16 ; i ++ )
        {
            md5_str[i]=0;
        }
        MD5Init(&md5);
        MD5Update(&md5, (unsigned char *)animalName, strlen((char *)animalName));
        MD5Final(&md5, (unsigned char *)md5_str);
        for (int i = 0 ; i < 16 ; i ++ ) {
            md5_str[i] = (md5_str[i] & 0xE9 | ~md5_str[i] & 0x16);
        }
        for(int i = 0 ; i < 16 ; i ++ )
        {
            if(md5_str[i]!=answer[i])
            {
                break;
            }
            if(i>5)
            {
                printf("%s",animalName);
                return 0;
            }
        }

        // 更新选择索引
        int i = length - 1;
        while (i >= 0 && choice[i] == 5) {
            choice[i] = 0;
            i--;
        }
        if (i < 0) {
            break;
        }
        choice[i]++;
    }

    return 0;
}

得到选择的动物，然后找到他们的编码为051410233
md5加密后即为flag