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[原创] 南冥神功 writeup
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发表于: 2021-5-11 20:03
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先拖到IDA里分析，当看到字符S后边跟了一堆01的时候就猜到是迷宫了，结合main函数里边的逻辑基本就可以判断是走迷宫了。这里我把main函数加了一些注释可以很清晰看出来迷宫的规则，迷宫是一个9*10的二维数组，S(0x53)是起点，0是路，1是墙。走过的路会被置为1，然后再最后程序会判断数组内所有的值，只要所有的值都为1就成功了。代码逻辑如下：
迷宫如下：
根据这个迷宫的行走规则可以规划出如下路线：
最终flag的每一位可以走两步，计算的公式如下所示：
最终写出了如下计算flag的程序：
最终编译运行即可得到flag
int __cdecl main(int argc, const char **argv, const char **envp)
{ char pinput; // al
int index_input; // esi
int index_key; // ecx
int check2; // edx
int v8; // eax
unsigned int pos_x; // ecx
int check1; // eax
signed int v11; // edx
int v12; // eax
char *pmaze; // eax
char (*v14)[10]; // eax
int v15; // edx
char (*v16)[10]; // ecx
int v17; // eax
int v18; // eax
int v19; // eax
int v20; // [esp+1Ch] [ebp-60h]
unsigned int pos_y; // [esp+20h] [ebp-5Ch]
unsigned int v22; // [esp+24h] [ebp-58h]
char pkey; // [esp+2Bh] [ebp-51h]
int keylength; // [esp+2Ch] [ebp-50h]
char input[76]; // [esp+30h] [ebp-4Ch]
sub_40AD70();
sub_4AF840((int)&dword_4B8860, "Input your code: ");
sub_4B0AB0((int)&dword_4B8680, input);
if ( strlen(input) <= 48 )
{
pinput = input[0];
if ( input[0] )
{
index_input = 0;
pos_y = 0;
v22 = 0;
keylength = keylen;
pkey = key[0];
LABEL_4: if ( keylength > 0 )
{
index_key = 0;
if ( pkey == pinput )
{
LABEL_11: check2 = (index_input + index_key / 6) % 6;
v8 = index_key + index_input;
pos_x = v22;
v20 = check2;
check1 = 5 - v8 % 6;
v11 = 0;
while ( 1 )
{
switch ( check1 )
{
case 1: // 向右走
++pos_x;
break;
case 2: // 偶数行向右下走，奇数行向下走
v17 = (pos_y++ & 1) == 0;
pos_x += v17;
break;
case 3: // 奇数行向左下走，偶数行向下走
v12 = (pos_y++ & 1) != 0;
pos_x -= v12;
break;
case 4: // 向左走
--pos_x;
break;
case 5: // 奇数行向左上走，偶数行向上走
v19 = (pos_y-- & 1) != 0;
pos_x -= v19;
break;
default: // 偶数行向右上走，奇数行向上走
v18 = (pos_y-- & 1) == 0;
pos_x += v18;
break;
}
if ( pos_x > 9 )
break;
if ( pos_y > 8 )
break;
pmaze = &maze[pos_y][pos_x];
if ( *pmaze ) // 判断是否撞墙， 0是路，1是墙
break;
*pmaze = 1;
if ( v11 == 1 )
{
++index_input;
v22 = pos_x;
pinput = input[index_input];
if ( pinput )
goto LABEL_4;
goto LABEL_19;
}
v11 = 1;
check1 = v20;
}
}
else
{
while ( keylength != ++index_key )
{
if ( key[index_key] == pinput )
goto LABEL_11;
}
}
}
}
else
{
LABEL_19: // 遍历迷宫数组，判断所有位置的值是否都为1
v14 = maze;
v15 = 0;
do
{
v16 = v14 + 1;
do
{
v15 += *(_BYTE *)v14 < 1u;
v14 = (char (*)[10])((char *)v14 + 1);
}
while ( v16 != v14 );
}
while ( &End != (_UNKNOWN *)v16 );
if ( !v15 )
{
sub_4ABF30(&dword_4B8860, "Good job!", 9);
sub_4AD980(&dword_4B8860);
return 0;
}
}
}
sub_4ABF30(&dword_4B8860, "Try again...", 12);
sub_4AD980(&dword_4B8860);
return 0;
}int __cdecl main(int argc, const char **argv, const char **envp)
{ char pinput; // al
int index_input; // esi
int index_key; // ecx
int check2; // edx
int v8; // eax
unsigned int pos_x; // ecx
int check1; // eax
signed int v11; // edx
int v12; // eax
char *pmaze; // eax
char (*v14)[10]; // eax
int v15; // edx
char (*v16)[10]; // ecx
int v17; // eax
int v18; // eax
int v19; // eax
int v20; // [esp+1Ch] [ebp-60h]
unsigned int pos_y; // [esp+20h] [ebp-5Ch]
unsigned int v22; // [esp+24h] [ebp-58h]
char pkey; // [esp+2Bh] [ebp-51h]
int keylength; // [esp+2Ch] [ebp-50h]
char input[76]; // [esp+30h] [ebp-4Ch]
sub_40AD70();
sub_4AF840((int)&dword_4B8860, "Input your code: ");
sub_4B0AB0((int)&dword_4B8680, input);
if ( strlen(input) <= 48 )
{
pinput = input[0];
if ( input[0] )
{
index_input = 0;
pos_y = 0;
v22 = 0;
keylength = keylen;
pkey = key[0];
LABEL_4: if ( keylength > 0 )
{
index_key = 0;
if ( pkey == pinput )
{
LABEL_11: check2 = (index_input + index_key / 6) % 6;
v8 = index_key + index_input;
pos_x = v22;
v20 = check2;
check1 = 5 - v8 % 6;
v11 = 0;
while ( 1 )
{
switch ( check1 )
{
case 1: // 向右走
++pos_x;
break;
case 2: // 偶数行向右下走，奇数行向下走
v17 = (pos_y++ & 1) == 0;
pos_x += v17;
break;
case 3: // 奇数行向左下走，偶数行向下走
v12 = (pos_y++ & 1) != 0;
pos_x -= v12;
break;
case 4: // 向左走
--pos_x;
break;
case 5: // 奇数行向左上走，偶数行向上走
v19 = (pos_y-- & 1) != 0;
pos_x -= v19;
break;
default: // 偶数行向右上走，奇数行向上走
v18 = (pos_y-- & 1) == 0;
pos_x += v18;
break;
}
if ( pos_x > 9 )
break;
if ( pos_y > 8 )
break;
pmaze = &maze[pos_y][pos_x];
if ( *pmaze ) // 判断是否撞墙， 0是路，1是墙
break;
*pmaze = 1;
if ( v11 == 1 )
{
++index_input;
v22 = pos_x;
pinput = input[index_input];
if ( pinput )
goto LABEL_4;
goto LABEL_19;
}
v11 = 1;
check1 = v20;
}
}
else
{
while ( keylength != ++index_key )
{
if ( key[index_key] == pinput )
goto LABEL_11;
}
}
}
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