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[原创]KCTF2021 第二题 write up
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发表于: 2021-5-12 01:05 5549
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系统 ： win10 64bit \ Windows xp
程序 ： pzcrackme.exe
要求 ： 求flag
使用工具 ：ida pro \ ollydbg \ 微步云沙箱
这题有不少迷惑人的手段，所以需要尽可能把程序流程分析清楚，ida中main函数如下：
将程序上传到云沙箱里看下，发现有tls_callback存在，可能是有反调试机制；不过先将程序运行起在等候输入的时候od附加就可以正常调试。
程序需要将一个matrix填满：
可以看到使用switch语句选择方向：
手动填写一下：
接下来构造相应的输入了，这里要注意的一个坑点是一个输入控制两次行动而非一次：
做py如下：
int __cdecl main(int argc, const char **argv, const char **envp)
{ char Tmp_ch_in_input; // al
int index_of_str; // esi
int INDEX_01234567; // ecx
int v7; // edx
int sum_index; // eax
unsigned int column; // ecx
int choice; // eax
signed int SIGNAL; // edx
int T2; // eax
char *a_pointer_of_matrix; // eax
char *MATRIX; // eax
int A_VALUE_SHOULD_BE_ZERO; // edx
char *v16; // ecx
int T1; // eax
int T4; // eax
int T3; // eax
int v20; // [esp+1Ch] [ebp-60h]
unsigned int row; // [esp+20h] [ebp-5Ch]
unsigned int v22; // [esp+24h] [ebp-58h]
char _0x30; // [esp+2Bh] [ebp-51h]
int NUM_0x24; // [esp+2Ch] [ebp-50h]
char STR[76]; // [esp+30h] [ebp-4Ch]
sub_40AD70();
sub_4AF840(&dword_4B8860, "Input your code: ");
sub_4B0AB0(&dword_4B8680, STR);
if ( strlen(STR) <= 0x30 ) // len(str) <= 0x30
{
Tmp_ch_in_input = STR[0];
if ( STR[0] ) // str[0] != null
{
index_of_str = 0;
row = 0;
v22 = 0;
NUM_0x24 = dword_4B7020; // 24 00 00 00
_0x30 = a0123456789abcd[0]; // .data:004B7040 30 31 32 33 34 35+a0123456789abcd db '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',0
While_start: if ( NUM_0x24 > 0 )
{
INDEX_01234567 = 0;
if ( _0x30 == Tmp_ch_in_input ) // assert str[0] == 0x30
{
other_start: v7 = (index_of_str + INDEX_01234567 / 6) % 6;
sum_index = INDEX_01234567 + index_of_str;
column = v22;
v20 = v7;
choice = 5 - sum_index % 6; // 5 - (sum_index % 6)
SIGNAL = 0;
while ( 1 )
{
switch ( choice )
{
case 1:
++column; // ++column
break;
case 2:
T1 = (row++ & 1) == 0; // row++
column += T1; // column += (row%2?0:1)
break;
case 3:
T2 = (row++ & 1) != 0; // row++
column -= T2; // column -= (row%2?1:0)
break;
case 4:
--column; // --column
break;
case 5:
T3 = (row-- & 1) != 0; // row--
column -= T3; // column -= (row%2?1:0)
break;
default:
T4 = (row-- & 1) == 0; // row--
column += T4; // column += (row%2?0:1)
break;
}
if ( column > 9 ) // ten columns
break; // try again
if ( row > 8 ) // 9 rows
break; // try again
a_pointer_of_matrix = &matrix[10 * row + column];
if ( *a_pointer_of_matrix )
break; // try again
*a_pointer_of_matrix = 1;
if ( SIGNAL == 1 ) // skip this at frist time
{
++index_of_str;
v22 = column;
Tmp_ch_in_input = STR[index_of_str];
if ( Tmp_ch_in_input )
goto While_start; // back to start
goto check;
}
SIGNAL = 1;
choice = v20;
}
}
else // _0x30 != Tmp_ch_in_input
{
while ( NUM_0x24 != ++INDEX_01234567 )
{
if ( a0123456789abcd[INDEX_01234567] == Tmp_ch_in_input )// .data:004B7040 30 31 32 33 34 35+a0123456789abcd db '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',0
goto other_start;
}
}
}
}
else
{
check: MATRIX = matrix;
A_VALUE_SHOULD_BE_ZERO = 0;
do // check matrix
{
v16 = MATRIX + 10;
do
A_VALUE_SHOULD_BE_ZERO += *MATRIX++ < 1u;// all element in matrix have not to set as zero
while ( v16 != MATRIX );
}
while ( &unk_4B70DA != v16 );
if ( !A_VALUE_SHOULD_BE_ZERO )
{
printf_4ABF30(&dword_4B8860, "Good job!", 9);
afterprintf_4AD980(&dword_4B8860);
return 0;
}
}
}
printf_4ABF30(&dword_4B8860, "Try again...", 12);
afterprintf_4AD980(&dword_4B8860);
return 0;
}int __cdecl main(int argc, const char **argv, const char **envp)
{ char Tmp_ch_in_input; // al
int index_of_str; // esi
int INDEX_01234567; // ecx
int v7; // edx
int sum_index; // eax
unsigned int column; // ecx
int choice; // eax
signed int SIGNAL; // edx
int T2; // eax
char *a_pointer_of_matrix; // eax
char *MATRIX; // eax
int A_VALUE_SHOULD_BE_ZERO; // edx
char *v16; // ecx
int T1; // eax
int T4; // eax
int T3; // eax
int v20; // [esp+1Ch] [ebp-60h]
unsigned int row; // [esp+20h] [ebp-5Ch]
unsigned int v22; // [esp+24h] [ebp-58h]
char _0x30; // [esp+2Bh] [ebp-51h]
int NUM_0x24; // [esp+2Ch] [ebp-50h]
char STR[76]; // [esp+30h] [ebp-4Ch]
sub_40AD70();
sub_4AF840(&dword_4B8860, "Input your code: ");
sub_4B0AB0(&dword_4B8680, STR);
if ( strlen(STR) <= 0x30 ) // len(str) <= 0x30
{
Tmp_ch_in_input = STR[0];
if ( STR[0] ) // str[0] != null
{
index_of_str = 0;
row = 0;
v22 = 0;
NUM_0x24 = dword_4B7020; // 24 00 00 00
_0x30 = a0123456789abcd[0]; // .data:004B7040 30 31 32 33 34 35+a0123456789abcd db '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',0
While_start: if ( NUM_0x24 > 0 )
{
INDEX_01234567 = 0;
if ( _0x30 == Tmp_ch_in_input ) // assert str[0] == 0x30
{
other_start: v7 = (index_of_str + INDEX_01234567 / 6) % 6;
sum_index = INDEX_01234567 + index_of_str;
column = v22;
v20 = v7;
choice = 5 - sum_index % 6; // 5 - (sum_index % 6)
SIGNAL = 0;
while ( 1 )
{
switch ( choice )
{
case 1:
++column; // ++column
break;
case 2:
T1 = (row++ & 1) == 0; // row++
column += T1; // column += (row%2?0:1)
break;
case 3:
T2 = (row++ & 1) != 0; // row++
column -= T2; // column -= (row%2?1:0)
break;
case 4:
--column; // --column
break;
case 5:
T3 = (row-- & 1) != 0; // row--
column -= T3; // column -= (row%2?1:0)
break;
default:
T4 = (row-- & 1) == 0; // row--
column += T4; // column += (row%2?0:1)
break;
}
if ( column > 9 ) // ten columns
break; // try again
if ( row > 8 ) // 9 rows
break; // try again
a_pointer_of_matrix = &matrix[10 * row + column];
if ( *a_pointer_of_matrix )
break; // try again
*a_pointer_of_matrix = 1;
if ( SIGNAL == 1 ) // skip this at frist time
{
++index_of_str;
v22 = column;
Tmp_ch_in_input = STR[index_of_str];
if ( Tmp_ch_in_input )
goto While_start; // back to start
goto check;
}
SIGNAL = 1;
choice = v20;
}
}
else // _0x30 != Tmp_ch_in_input
{
while ( NUM_0x24 != ++INDEX_01234567 )
{
if ( a0123456789abcd[INDEX_01234567] == Tmp_ch_in_input )// .data:004B7040 30 31 32 33 34 35+a0123456789abcd db '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',0
goto other_start;
}
}
}
}
else
{
check: MATRIX = matrix;
A_VALUE_SHOULD_BE_ZERO = 0;
do // check matrix
{
v16 = MATRIX + 10;
do
A_VALUE_SHOULD_BE_ZERO += *MATRIX++ < 1u;// all element in matrix have not to set as zero
while ( v16 != MATRIX );
}
while ( &unk_4B70DA != v16 );
if ( !A_VALUE_SHOULD_BE_ZERO )
{
printf_4ABF30(&dword_4B8860, "Good job!", 9);
afterprintf_4AD980(&dword_4B8860);
return 0;
}
}
}
printf_4ABF30(&dword_4B8860, "Try again...", 12);
afterprintf_4AD980(&dword_4B8860);
return 0;
}53 01 01 00 00 01 00 00 01 01
01 01 01 00 01 00 00 01 00 00
01 01 01 00 01 01 01 01 01 00
00 01 01 00 01 00 00 01 00 00
00 00 01 00 00 01 00 00 01 01
01 01 00 01 01 01 00 01 00 01
00 00 01 01 01 01 00 01 00 01
00 01 01 00 00 01 00 01 00 01
00 00 00 01 00 00 01 01 00 00
53 01 01 00 00 01 00 00 01 01
01 01 01 00 01 00 00 01 00 00
01 01 01 00 01 01 01 01 01 00
00 01 01 00 01 00 00 01 00 00
00 00 01 00 00 01 00 00 01 01
01 01 00 01 01 01 00 01 00 01
00 00 01 01 01 01 00 01 00 01
00 01 01 00 00 01 00 01 00 01
00 00 00 01 00 00 01 01 00 00
while ( 1 )
{ switch ( choice )
{
case 1:
++column; // ++column
break;
case 2:
T1 = (row++ & 1) == 0; // row++
column += T1; // column += (row%2?0:1)
break;
case 3:
T2 = (row++ & 1) != 0; // row++
column -= T2; // column -= (row%2?1:0)
break;
case 4:
--column; // --column
break;
case 5:
T3 = (row-- & 1) != 0; // row--
column -= T3; // column -= (row%2?1:0)
break;
default:
T4 = (row-- & 1) == 0; // row--
column += T4; // column += (row%2?0:1)
break;
}
while ( 1 )
{ switch ( choice )
{
case 1:
++column; // ++column
break;
case 2:
T1 = (row++ & 1) == 0; // row++
column += T1; // column += (row%2?0:1)
break;
case 3:
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