Google Capture The Flag 2018 (Quals) - Reverse - Beginner's Quest - Gatekeeper

参考链接：https://ctftime.org/task/6264

题目

It's a media PC! All fully purchased through the online subscription revolution empire “GimmeDa$”. The PC has a remote control service running that looks like it'll cause all kinds of problems or that was written by someone who watched too many 1990s movies. You download the binary from the vendor and begin reversing it. Nothing is the right way around.

为了方便下载，我把elf文件后缀改成了jpg，下载下来改回去即可。

解题过程

使用strings看下elf文件里都什么字符串，发现有很像flag的东西：

Usage: %s <username> <password>
 ~> Verifying.
0n3_W4rM
 ~> Incorrect username
zLl1ks_d4m_T0g_I
Correct!
Welcome back!
CTF{%s}

zLl1ks_d4m_T0g_I像flag但其实是颠倒过来的，I_g0T_m4d_sk1lLz才是真的flag。另外也可以在strcmps下断点看下比较的字符串是什么。