Hello, CTF
运行一下,请输入序列
查看一下,无壳,32bit
用32位ida打开,找到main函数,F5查看伪代码
int __cdecl main(int argc, const char **argv, const char **envp)
{
signed int v3; // ebx
char v4; // al
int result; // eax
int v6; // [esp+0h] [ebp-70h]
int v7; // [esp+0h] [ebp-70h]
char v8; // [esp+12h] [ebp-5Eh]
char v9[20]; // [esp+14h] [ebp-5Ch]
char v10; // [esp+28h] [ebp-48h]
__int16 v11; // [esp+48h] [ebp-28h]
char v12; // [esp+4Ah] [ebp-26h]
char v13; // [esp+4Ch] [ebp-24h]
strcpy(&v13, "437261636b4d654a757374466f7246756e");
while ( 1 )
{
memset(&v10, 0, 0x20u);
v11 = 0;
v12 = 0;
sub_40134B(aPleaseInputYou, v6);
scanf(aS, v9);
if ( strlen(v9) > 0x11 )
break;
v3 = 0;
do
{
v4 = v9[v3];
if ( !v4 )
break;
sprintf(&v8, asc_408044, v4);
strcat(&v10, &v8);
++v3;
}
while ( v3 < 17 );
if ( !strcmp(&v10, &v13) )
sub_40134B(aSuccess, v7);
else
sub_40134B(aWrong, v7);
}
sub_40134B(aWrong, v7);
result = stru_408090._cnt-- - 1;
if ( stru_408090._cnt < 0 )
return _filbuf(&stru_408090);
++stru_408090._ptr;
return result;
}
发现输入字符串大于17,程序结束0x11 = 17
小于17,则v10与v13比较,相同则输出:aSuccess
而v13一定大于17 ,v13=437261636b4d654a757374466f7246756e
进制转换,发现每位都在1-9 a-f之内,猜测为16位,转换如图
而题目描述为菜鸡发现Flag似乎并不一定是明文比较的
{CrackMeJustForFun}
直接提交,正确