Cracker Barrel

Cracker Barrel (50 points at the end)

Question

I found a USB drive under the checkers board at cracker barrel. My friends told me not to plug it in but surely nothing bad is on it?

I found this file, but I can’t seem to unlock it’s secrets. Can you help me out?

Also.. once you think you’ve got it I think you should try to connect to challenges.auctf.com at port 30000 not sure what that means, but it written on the flash drive..

Original Author: nadrojisk

Long Writeup

There’s a section called check, which uses three parts (check_1, check_2, and check_3).

Keep in mind that the CTF uses sym.remove_newline, which basically changes ‘\n’ to ‘\0’. Therefore, if there are two opposing things, just type the first one, and the second one does NOT matter since strcmp only checks till the next ‘\0’.

So, here’s check_1:

check_1

This checks if arg1 is equal to “starwars”, and then exits if it’s true.

Here’s check_2:

check_2

Basically checks if arg1 is equal to the reverse of “si siht egassem terces”, which i “secret message this is”

Here’s check_3:

check_3

This runs two loops:

One, that compares the values of each element of the array arg1 with an array iVar3 with an offset of 22. In the second loop, the checking function gives true when the check is not equal. (The required boolean is false here).

Since the check is only for the length of the input, we can input whatever little input we want to.

So, finding the value of chr(0x7a - 2^0x14), we have lowercase “l”. This is the third input.

And that gives us the flag.

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