1. Check first 3-4 n value
2. Google it
3. It's perfect numbers ([wiki](https://en.wikipedia.org/wiki/Perfect_number))
4. Find first 14 perfect numbers in the internet ([perfect numbers list](https://web.archive.org/web/20090503154707/http://amicable.homepage.dk/perfect.htm))
5. `plain_text[i] == cipher[i] ^ perfect_number[i]`
solution script: [solution.py](https://github.com/wetox-team/writeup/blob/master/hacktivitycon/perfect_xor/solution.py)
flag is `flag{tHE_br0kEN_Xor}` 