Ez-XOR Writeup - BCACTF 6.0

Crypto/Ez-XOR - Colin

Please be very ORZ and do some XORing.

Initial Thoughts

We are given encoded_flag.txt, which contains the following:

ICEjITYkOREpKyArBisRNyQkHRArODguJxAvJx0RKyUvIx0OIywmch0DNzAjJS0sHQAjMC0sHRcyJTAjJicmPw==

Methodology

This looks like a Base64 string, but when I use CyberChef to translate it, we get the following, which isn’t exactly a flag.

The challenge is literally called Ez-XOR, so I assume it has something to do with XOR. I tried XOR bruteforce and then decoding it with magic, but that wasn’t working.

I then had the idea to decode from base64 first, and then XOR it. By base64 decoding the string, and then XORing it with a key of 42, I found the flag.

Solution

The flag is bcactf{SkibiDiSuff_RizzleRme_Sigma_Land0_Auragon_Baron_Upgraded}. This was definitely an easy crypto challenge, but it was good for a non-crypto main like me.