2018腾讯游戏安全竞赛题目分析

今年的腾讯游戏安全竞赛就要开始了，但是我对游戏安全这个方向还不太熟悉，因此找了去年的题目来做赛前练习

资格赛题目

标准版

题目一打开长这样：

赛题说明：

1
2

1.username与regcode是一一对应的关系，填入正确的username和regcode点击Go按钮出现注册成功提示。
2.要求根据CrackMe写出对应注册机，注册机能够根据任意合法用户名生成正确的注册码。

可以看出这是一个CrackMe程序，开始分析。

上图为一神器，可直接通过可视化界面获取到MFC组件的响应函数，神器链接。

如果不使用上面的神器的话，此程序是一个MFC程序，获取输入框的方式有两种GetDlgItem和GetWindowText，查看这两个函数的调用，发现在sub_4026F0中有多处对GetDlgItem的调用，因此分析这个函数，IDA对此函数生成的主要伪C代码如下：

void __thiscall sub_4026F0(HWND *this)
{
  ......
      
  v21 = (CWnd *)this;
  v1 = GetDlgItem(this[8], 1000);
  memset(&lParam, 0, 0x400u);
  SendMessageA(v1, 0xDu, 0x400u, (LPARAM)&lParam);
  v2 = GetDlgItem(*((HWND *)v21 + 8), 1001);
  memset(&v23, 0, 0x400u);
  SendMessageA(v2, 0xDu, 0x400u, (LPARAM)&v23);
  v3 = v21;
  v4 = CWnd::GetDlgItem(v21, 1004);
  v20 = SendMessageW(*((HWND *)v4 + 8), 0xF0u, 0, 0) == 1;
  v21 = (CWnd *)&v14;
  v19 = 15;
  v18 = 0;
  LOBYTE(v14) = 0;
  if ( (_BYTE)v23 )
    v5 = strlen((const char *)&v23);
  else
    v5 = 0;
  sub_402A70(&v14, &v23, v5);
  v49 = 0;
  v13 = 15;
  v12 = 0;
  v8 = 0;
  if ( (_BYTE)lParam )
    v6 = strlen((const char *)&lParam);
  else
    v6 = 0;
  sub_402A70(&v8, &lParam, v6);
  v49 = -1;
  if ( (unsigned __int8)sub_405510(*(LPVOID *)&v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20) )
  {
    v24 = 'e\0R';
    v40 = 0;
    v7 = (wchar_t *)&v24;
    v25 = 'i\0g';
    v26 = 't\0s';
    v27 = 'r\0e';
    v28 = (int)&loc_53001D + 3;
    v29 = 'c\0u';
    v30 = 'e\0c';
    v31 = 's\0s';
    v32 = &loc_43002C;
    v33 = 'n\0o';
    v34 = 'r\0g';
    v35 = 't\0a';
    v36 = 'l\0u';
    v37 = 't\0a';
    v38 = 'o\0i';
    v39 = '!\0n';
  }
  else
  {
    *(_DWORD *)v41 = 'e\0R';
    v7 = v41;
    v42 = 'i\0g';
    v43 = 't\0s';
    v44 = 'r\0e';
    v45 = &loc_460020;
    v46 = 'i\0a';
    v47 = 'e\0l';
    v48 = 'd';
  }
  CWnd::SetDlgItemTextW(v3, 1003, v7);
}

可以看出这是程序的主流程。下面就一步一步分析此函数：

void __thiscall sub_4026F0(HWND *this)
{
  ......
      
  v21 = (CWnd *)this;
  UserName_Text_ID = GetDlgItem(this[8], 1000);
  memset(&UserName, 0, 02000u);
  SendMessageA(UserName_Text_ID, '\r', 02000u, (LPARAM)&UserName);// 存储UserName
  RegCode_Text_ID = GetDlgItem(*((HWND *)v21 + 8), 1001);
  memset(&RegCode, 0, 02000u);
  SendMessageA(RegCode_Text_ID, '\r', 02000u, (LPARAM)&RegCode);// 存储RegCode
  v3 = v21;
  User_Choice = CWnd::GetDlgItem(v21, 1004);
  v20 = SendMessageW(*((HWND *)User_Choice + 8), 0xF0u, 0, 0) == 1;// 判断选择的是标准版还是进阶版
  v21 = (CWnd *)&v14;
  v19 = 15;
  v18 = 0;
  LOBYTE(v14) = 0;
  if ( (_BYTE)RegCode )
    v5 = strlen((const char *)&RegCode);        // 判断RegCode长度
  else
    v5 = 0;
  assign_sub_402A70(&v14, &RegCode, v5);        // string assign 
                                                // 将RegCode的值赋给v14
  v49 = 0;
  v13 = 15;
  v12 = 0;
  v8 = 0;
  if ( (_BYTE)UserName )
    v6 = strlen((const char *)&UserName);       // 判断UserName长度
  else
    v6 = 0;
  assign_sub_402A70(&v8, &UserName, v6);        // string assign 
                                                // 将Username的值赋给v8
  v49 = -1;
  if ( sub_405510(*(LPVOID *)&v8, v9, v10, v11, v12, v13, v14, v15, v16, v17, v18, v19, v20) )// 主检验函数
  {
    v24 = 'e\0R';
    v40 = 0;
    v7 = (wchar_t *)&v24;
    v25 = 'i\0g';
    v26 = 't\0s';
    v27 = 'r\0e';
    v28 = (int)&loc_53001D + 3;
    v29 = 'c\0u';
    v30 = 'e\0c';                               // RegisterSuccess,Congratulation!
    v31 = 's\0s';
    v32 = &loc_43002C;
    v33 = 'n\0o';
    v34 = 'r\0g';
    v35 = 't\0a';
    v36 = 'l\0u';
    v37 = 't\0a';
    v38 = 'o\0i';
    v39 = '!\0n';
  }
  else
  {
    *(_DWORD *)v41 = 'e\0R';
    v7 = v41;
    v42 = 'i\0g';
    v43 = 't\0s';
    v44 = 'r\0e';                               // RegisterFailed
    v45 = &loc_460020;
    v46 = 'i\0a';
    v47 = 'e\0l';
    v48 = 'd';
  }
  CWnd::SetDlgItemTextW(v3, 1003, v7);
}

以上步骤完成了基本的数据获取、校验操作，其中有一个主要的校验函数sub_405510，下面来重点分析这个函数：

当返回值v13为True时才能注册成功，因此我们需要关注使v13为True的函数。

if ( sub_404F00((int *)&UserName) )
  {
    sub_405040((int)&UserName, &v26, &v27, &v28, (int *)&v29, &v30);
    v31 = '\0';
    v32 = 0;
    LOBYTE(v34) = 2;
    v14 = &a7;
    if ( (unsigned int)a12 >= 0x10 )
      v14 = a7;
    if ( (unsigned __int8)sub_406080(v14, &v31)
      && ((v16 = HIDWORD(v31), v17 = (__m128i *)v31, a13)
       || (v33 = xmmword_5AC470, (unsigned __int8)sub_403010(&v33, v15, v31)))
      && v16 - (_DWORD)v17 == 32
      && v17[1].m128i_i32[2] == '2018'
      && !v17[1].m128i_i32[3] )
    {
      v18 = *v17;
      *((_QWORD *)&v33 + 1) = v17[1].m128i_i64[0];
      v13 = sub_402F20(
              v26,
              v27,
              v28,
              v29,
              v30,
              __PAIR__(_mm_cvtsi128_si32(_mm_srli_si128(v18, 4)), _mm_cvtsi128_si32(v18)),
              __PAIR__(_mm_cvtsi128_si32(_mm_srli_si128(v18, 12)), _mm_cvtsi128_si32(_mm_srli_si128(v18, 8))),
              *((__int64 *)&v33 + 1));
    }
    else
    {
      v13 = 0;
    }
    sub_405740(&v31);
  }
  else
  {
    v13 = 0;
  }

首先我们查看 sub_404F00函数，同样按照逆向思维，寻找使返回值为True的条件。此函数中有如下几个关键片段：

v1 = UserName;
if ( UserName[4] != 39 )                      // 判断UserName的长度是否为39
  return 0;
v3 = UserName[5];
if ( v3 < 020 )
  v23 = UserName;
else
  v23 = (int *)*UserName;
if ( v3 < 020 )
  v4 = UserName;
else
  v4 = (int *)*UserName;                      // String的相关函数，用于决定字符串的存储位置等
v5 = (unsigned int)v4 + 39;
if ( v3 < 0x10 )
  v6 = UserName;
else
  v6 = (int *)*UserName;
v7 = v5 - (_DWORD)v6;
i = 0;
if ( (unsigned int)v6 > v5 )
  v7 = 0;

将UserName中的小写字母转换为大写：

if ( v7 )
  {
    Username_len = v7;
    do
    {
      *((_BYTE *)v23 + i) = toupper(*((char *)v6 + i));// 将小写字母转换为大写字母
      ++i;
    }
    while ( i != Username_len );
    v1 = UserName;
  }

v16 = 0;                                      // v16为一个字符串
  assign_sub_402A70(&v16, &unk_5AC430, '\x01'); // 给v16赋值为'#'
  sub_404D70((int)v24, (int)UserName_Upper, *(LPVOID *)&v16, v17, v18, v19, v20, v21);// 将大写的UserName用#分割，分割后的结果保存在v24中
  v10 = (_DWORD *)v24[0];
  if ( (unsigned int)(v24[1] - v24[0] - 192) >= 24 )
    goto LABEL_30;
  if ( v24[0] != v24[1] )
  {
    while ( 1 )
    {
      v11 = v10[4];
      v12 = 0;
      if ( v11 > 0 )
        break;
LABEL_28:
      v10 += 6;
      if ( v10 == (_DWORD *)v24[1] )            // 字符串验证成功
        goto LABEL_29;
    }
    while ( 1 )
    {
      v13 = v10[5] < 0x10u ? v10 : *v10;
      v14 = *((_BYTE *)v13 + v12);
      if ( (v14 > 57 || v14 < 48) && (unsigned __int8)(v14 - 'A') > 5u )// 要求Username的范围为数字和ABCDEF
        break;
      if ( ++v12 >= v11 )
        goto LABEL_28;
    }
LABEL_30:
    v15 = 0;
    goto LABEL_31;
  }
LABEL_29:
  v15 = 1;
LABEL_31:
  sub_405A00((char **)v24);
  return v15;
}