用IDA64打開,進入到
get_flag
函數
unsigned __int64 get_flag()
{
unsigned int v0; // eax
char v1; // al
signed int i; // [rsp+4h] [rbp-3Ch]
signed int j; // [rsp+8h] [rbp-38h]
__int64 s; // [rsp+10h] [rbp-30h]
char v6; // [rsp+18h] [rbp-28h]
unsigned __int64 v7; // [rsp+38h] [rbp-8h]
v7 = __readfsqword(0x28u);
v0 = time(0LL);
srand(v0);
for ( i = 0; i <= 4; ++i )
{
switch ( rand() % 200 )
{
case 1:
puts("OK, it's flag:");
memset(&s, 0, 0x28uLL);
strcat((char *)&s, f1);
strcat((char *)&s, &f2);
printf("%s", &s);
break;
case 2:
printf("Solar not like you");
break;
case 3:
printf("Solar want a girlfriend");
break;
case 4:
v6 = 0;
s = 0x7F666F6067756369LL;
strcat(&f2, (const char *)&s);
break;
case 5:
for ( j = 0; j <= 7; ++j )
{
if ( j % 2 == 1 )
v1 = *(&f2 + j) - 2;
else
v1 = *(&f2 + j) - 1;
*(&f2 + j) = v1;
}
break;
default:
puts("emmm,you can't find flag 23333");
break;
}
}
return __readfsqword(0x28u) ^ v7;
}
首先這裡用到了随機數,但是想通過随機數來擷取flag有點不現實,或者說是太難了。。。。
v0 = time(0LL);
srand(v0);
for ( i = 0; i <= 4; ++i )
switch ( rand() % 200 )
是以主要的點在case 1 ~ case 5,但是case 2和case 3這兩個是printf的輸出語句,并沒有什麼用。是以可以不考慮。然後再進一步分析可以看出來具體步驟是case 4 —》 case 5 —》 case 1
case 4:
case 4:
v6 = 0; // 這裡的v6可以不考慮
s = 0x7F666F6067756369LL; // 這裡要把16進制轉為字元串,并且是逆序的(之是以是逆序的應該是和stack的存儲結構有關)
strcat(&f2, (const char *)&s); // 把s的值指派給f2(指派前的f2是空字元)
break;
case 5
for ( j = 0; j <= 7; ++j )
{
if ( j % 2 == 1 ) v1 = *(&f2 + j) - 2;
else v1 = *(&f2 + j) - 1;
*(&f2 + j) = v1;
}
break;
如果看不懂上面的代碼,可以把它改成這樣下面的代碼。它們是等價的:
for ( j = 0; j <= 7; ++j )
{
if ( j % 2 == 1 ) v1 = f2[j] - 2;
else v1 = f2[j] - 1;
f2[j] = v1;
}
break;
case 1
puts("OK, it's flag:");
memset(&s, 0, 0x28uLL);
strcat((char *)&s, f1); // 這裡的f1的值為:GXY{do_not_
strcat((char *)&s, &f2); // 連結f1和f2的字元串就是flag(這個f2是我們逆向出來的)
printf("%s", &s);
break;
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIyVGduV2YfNWawNyZuBnL3ETYzMjM4ADN4kTO0IDM5IGZkRTO3gTMlNTMwATYwMzLc52YucWbp5GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.png)
Python3代碼
key1 = "GXY{do_not_"
# 這裡的key2的值為:0x7F666F6067756369,以兩個一組來分割。這是為将16進制轉成對應的字元
key2 = [ 0x7F, 0x66, 0x6F, 0x60, 0x67, 0x75, 0x63, 0x69 ][::-1] # 注意要把這裡的數組反過來
flag = key1
for i in range(0,len(key2)):
x = key2[i]
if i % 2 == 1: x = x - 2
else: x = x - 1
flag = flag + chr(x)
print(flag) # 輸出的值為:GXY{do_not_hate_me},再把前面的GXY改成flag就是我們要的flag了
是以最終的flag為:
flag{do_not_hate_me}