[C++知识库]20211026gfsj_re_reverseme120

32位下由C++编译的EXE文件，无壳。

int __cdecl main(int argc, const char **argv, const char **envp)
{
  unsigned int v3; // edx
  unsigned int v4; // ecx
  __m128i v5; // xmm1
  unsigned int v6; // esi
  const __m128i *v7; // eax
  __m128i v8; // xmm0
  int v9; // eax
  char v11; // [esp+0h] [ebp-CCh]
  char v12; // [esp+1h] [ebp-CBh]
  char v13; // [esp+64h] [ebp-68h]
  char v14; // [esp+65h] [ebp-67h]
  unsigned int v15; // [esp+C8h] [ebp-4h]

  printf("please input your flah:");
  v11 = 0;
  memset(&v12, 0, 0x63u);
  scanf("%s", &v11);
  v13 = 0;
  memset(&v14, 0, 0x63u);
  sub_401000(&v15, &v13, (unsigned __int8 *)&v11, strlen(&v11));
  v3 = v15;				//v3=32
  v4 = 0;
  if ( v15 )
  {
    if ( v15 >= 0x10 )
    {
      v5 = _mm_load_si128((const __m128i *)&xmmword_414F20);
      v6 = v15 - (v15 & 0xF);
      v7 = (const __m128i *)&v13;
      do
      {
        v8 = _mm_loadu_si128(v7);
        v4 += 16;
        ++v7;
        _mm_storeu_si128((__m128i *)&v7[-1], _mm_xor_si128(v8, v5));
      }
      while ( v4 < v6 );
    }
    for ( ; v4 < v3; ++v4 )
      *(&v13 + v4) ^= 0x25u;//v4<32，v13[i]=v13[i]^0x25
  }
  v9 = strcmp(&v13, "you_know_how_to_remove_junk_code");//strlen(v13)=32
  if ( v9 )
    v9 = -(v9 < 0) | 1;
  if ( v9 )
    printf("wrong\n");
  else
    printf("correct\n");
  system("pause");
  return 0;
}

signed int __usercall sub_401000@<eax>(unsigned int *a1@<edx>, _BYTE *a2@<ecx>, unsigned __int8 *a3, unsigned int a4)
{//a2=0,a3=输入的字符串,a4=字符串长度
  int v4; // ebx
  unsigned int v5; // eax
  int v6; // ecx
  unsigned __int8 *v7; // edi
  int v8; // edx
  bool v9; // zf
  unsigned __int8 v10; // cl
  char v11; // cl
  _BYTE *v12; // esi
  unsigned int v13; // ecx
  int v14; // ebx
  unsigned __int8 v15; // cl
  char v16; // dl
  _BYTE *v18; // [esp+Ch] [ebp-Ch]
  unsigned int *v19; // [esp+10h] [ebp-8h]
  int v20; // [esp+14h] [ebp-4h]
  unsigned int v21; // [esp+14h] [ebp-4h]
  int i; // [esp+24h] [ebp+Ch]

  v4 = 0;
  v18 = a2;
  v5 = 0;
  v6 = 0;
  v19 = a1;
  v20 = 0;
  if ( !a4 )//长度
    return 0;
  v7 = a3;//输入的字符串
  do
  {
    v8 = 0;
    v9 = v5 == a4;
    if ( v5 < a4 )
    {
      do
      {
        if ( a3[v5] != 32 )//a3[i]不是空格就退出循环
          break;
        ++v5;
        ++v8;//v8算字符串中有多少个空格
      }
      while ( v5 < a4 );
      v9 = v5 == a4;
    }
    if ( v9 )
      break;
    if ( a4 - v5 >= 2 && a3[v5] == 13 && a3[v5 + 1] == 10 || (v10 = a3[v5], v10 == 10) )
    {
      v6 = v20;
    }
    else
    {
      if ( v8 )
        return -44;
      if ( v10 == 61 && (unsigned int)++v4 > 2 )
        return -44;
      if ( v10 > 0x7Fu )
        return -44;
      v11 = byte_414E40[v10];
      if ( v11 == 127 || (unsigned __int8)v11 < 0x40u && v4 )
        return -44;
      v6 = v20++ + 1;
    }
    ++v5;
  }
  while ( v5 < a4 );
  if ( !v6 )
    return 0;
  v12 = v18;
  v13 = ((unsigned int)(6 * v6 + 7) >> 3) - v4;
  if ( v18 && *v19 >= v13 )
  {
    v21 = 3;
    v14 = 0;
    for ( i = 0; v5; --v5 )
    {
      v15 = *v7;
      if ( *v7 != 13 && v15 != 10 && v15 != 32 )
      {
        v16 = byte_414E40[v15];
        v21 -= v16 == 64;
        v14 = v16 & 0x3F | (v14 << 6);
        if ( ++i == 4 )
        {
          i = 0;
          if ( v21 )
            *v12++ = BYTE2(v14);
          if ( v21 > 1 )
            *v12++ = BYTE1(v14);
          if ( v21 > 2 )
            *v12++ = v14;
        }
      }
      ++v7;
    }
    *v19 = v12 - v18;
    return 0;
  }
  *v19 = v13;
  return -42;
}

看不懂啊…看wp说sub_401000()是base64解密算法。也就是说这个程序是将字符串拿去base64解密后再与0x25异或。

char n[33]="you_know_how_to_remove_junk_code";
int flag[33];
int i;
for(i=0; i<32; i++)
{
    flag[i] = n[i] ^ 0x25;
    printf("%c",(char)flag[i]);
}
//\JPzNKJRzMJRzQJzW@HJS@zOPKNzFJA@

拿去base64加密得

XEpQek5LSlJ6TUpSelFKeldASEpTQHpPUEtOekZKQUA=