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

參考連接：https://ctftime.org/task/6264

題目

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.

爲了方便下載，我把elf文件後綴改爲了jpg，下載下來改回去便可。

解題過程

使用strings看下elf文件裏都什麼字符串，發現有很像flag的東西：

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

zLl1ks_d4m_T0g_I像flag但實際上是顛倒過來的，I_g0T_m4d_sk1lLz纔是真的flag。另外也能夠在strcmps下斷點看下比較的字符串是什麼。