buuctf 刮開有獎

正常EXE檔案，無殼，直接開啓。
毫無反應，ENTER退出，拖入IDA。
找到主要部分，開始分析程式。

BOOL __stdcall DialogFunc(HWND hDlg, UINT a2, WPARAM a3, LPARAM a4)
{
  const char *v4; // esi
  const char *v5; // edi
  int v7; // [esp+8h] [ebp-20030h]
  int v8; // [esp+Ch] [ebp-2002Ch]
  int v9; // [esp+10h] [ebp-20028h]
  int v10; // [esp+14h] [ebp-20024h]
  int v11; // [esp+18h] [ebp-20020h]
  int v12; // [esp+1Ch] [ebp-2001Ch]
  int v13; // [esp+20h] [ebp-20018h]
  int v14; // [esp+24h] [ebp-20014h]
  int v15; // [esp+28h] [ebp-20010h]
  int v16; // [esp+2Ch] [ebp-2000Ch]
  int v17; // [esp+30h] [ebp-20008h]
  CHAR String; // [esp+34h] [ebp-20004h]
  char v19; // [esp+35h] [ebp-20003h]
  char v20; // [esp+36h] [ebp-20002h]
  char v21; // [esp+37h] [ebp-20001h]
  char v22; // [esp+38h] [ebp-20000h]
  char v23; // [esp+39h] [ebp-1FFFFh]
  char v24; // [esp+3Ah] [ebp-1FFFEh]
  char v25; // [esp+3Bh] [ebp-1FFFDh]
  char v26; // [esp+10034h] [ebp-10004h]
  char v27; // [esp+10035h] [ebp-10003h]
  char v28; // [esp+10036h] [ebp-10002h]

  if ( a2 == 272 )
    return 1;
  if ( a2 != 273 )
    return 0;
  if ( (_WORD)a3 == 1001 )
  {
    memset(&String, 0, 0xFFFFu);
    GetDlgItemTextA(hDlg, 1000, &String, 0xFFFF);
    if ( strlen(&String) == 8 )
    {
      v7 = 90;
      v8 = 74;
      v9 = 83;
      v10 = 69;
      v11 = 67;
      v12 = 97;
      v13 = 78;
      v14 = 72;
      v15 = 51;
      v16 = 110;
      v17 = 103;
      sub_4010F0((int)&v7, 0, 10);
      memset(&v26, 0, 0xFFFFu);
      v26 = v23;
      v28 = v25;
      v27 = v24;
      v4 = (const char *)sub_401000(&v26, strlen(&v26));
      memset(&v26, 0, 0xFFFFu);
      v27 = v21;
      v26 = v20;
      v28 = v22;
      v5 = (const char *)sub_401000(&v26, strlen(&v26));
      if ( String == v7 + 34
        && v19 == v11
        && 4 * v20 - 141 == 3 * v9
        && v21 / 4 == 2 * (v14 / 9)
        && !strcmp(v4, "ak1w")
        && !strcmp(v5, "V1Ax") )
      {
        MessageBoxA(hDlg, "U g3t 1T!", "@_@", 0);
      }
    }
    return 0;
  }
  if ( (_WORD)a3 != 1 && (_WORD)a3 != 2 )
    return 0;
  EndDialog(hDlg, (unsigned __int16)a3);
  return 1;
}

sub_4010F0進行了一個數據的變換，直接嘗試翻譯成C語言執行。

int __cdecl sub_4010F0(int a1, int a2, int a3)
{
  int result; // eax
  int i; // esi
  int v5; // ecx
  int v6; // edx

  result = a3;
  for ( i = a2; i <= a3; a2 = i )
  {
    v5 = 4 * i;
    v6 = *(_DWORD *)(4 * i + a1);
    if ( a2 < result && i < result )
    {
      do
      {
        if ( v6 > *(_DWORD *)(a1 + 4 * result) )
        {
          if ( i >= result )
            break;
          ++i;
          *(_DWORD *)(v5 + a1) = *(_DWORD *)(a1 + 4 * result);
          if ( i >= result )
            break;
          while ( *(_DWORD *)(a1 + 4 * i) <= v6 )
          {
            if ( ++i >= result )
              goto LABEL_13;
          }
          if ( i >= result )
            break;
          v5 = 4 * i;
          *(_DWORD *)(a1 + 4 * result) = *(_DWORD *)(4 * i + a1);
        }
        --result;
      }
      while ( i < result );
    }
LABEL_13:
    *(_DWORD *)(a1 + 4 * result) = v6;
    sub_4010F0(a1, a2, i - 1);
    result = a3;
    ++i;
  }
  return result;
}

翻譯的C語言程式

 #include<stdio.h>
 int sub_40(int a[10],int a2,int a3)
 {
int result; // eax
 int i; // esi
 int v5; // ecx
 int v6; // edx
result = a3;
 for ( i = a2; i <= a3; a2 = i )
 {
   v5 = i;
   v6 = a[i];
   if ( a2 < result && i < result )
   {
     do
     {
       if ( v6 > a[result] )
       {
         if ( i >= result )
           break;
         ++i;
         a[v5] = a[result];
         if ( i >= result )
           break;
         while ( a[i] <= v6 )
         {
           if ( ++i >= result )
             goto LABEL_13;
         }
         if ( i >= result )
           break;
         v5 = i;
        a[result] = a[i];
       }
       --result;
     }
     while ( i < result );
   }
  LABEL_13:
  a[result] = v6;
   sub_40(a, a2, i - 1);
   result = a3;
   ++i;
  	}
 	return result;
 }
 void main()
 {
 	int i;
 	int a[20]={90,74,83,69,67,97,78,72,51,110,103};
 	sub_40(a,0,10);
 	for (i=0;i<=10;i++)
 		printf("%4c",a[i]);
 	printf("\n");
 	for (i=0;i<=10;i++)
 		printf("%4d",a[i]);
 	printf("\n");
 }

執行結果

繼續分析，sub_401000，猜測是一個base64加密過程。
通過base64解密和上面轉換後的數值，得到最後flag中的內容爲"UJWP1jMp"

2020年8月8日23點04分

buuctf 刮開有獎wp

buuctf 刮開有獎