OverTheWire.org - Vortex - Level 5 Writeup

Well, this level is pretty easy.
We have the source code and we know we have to guess a password that is long 5 bytes and the alphabet is {a-z,A-Z,0-9}.
Looking at the code we see a memcmp() call that compares the MD5 hash of the input to a fixed value:

 "\x15\x5f\xb9\x5d\x04\x28\x7b\x75\x7c\x99\x6d\x77\xb5\xea\x51\xf7"

So let's strip off the "\x" and we get the MD5 hash of the unknown password we have to guess.

Now we only have to put this hash into a password cracker or an online service that does it for us (like https://crackstation.net/)

We find that the password is rlTf6

Let's use it:

vortex5@vortex:~$ /vortex/vortex5
Password: rlTf6
6:36
You got the right password, congrats!
$ id
uid=5006(vortex6) gid=5005(vortex5) groups=5006(vortex6),5005(vortex5)
$ cat /etc/vortex_pass/vortex6
********2

$