XOR key reuse due to badly programmed parallel code.

Full write-up : [https://github.com/rsa-ctf/write-ups/tree/master/2019/confidencectf#crypto---count-me-in](https://github.com/rsa-ctf/write-ups/tree/master/2019/confidencectf#crypto---count-me-in)

Original writeup (https://github.com/rsa-ctf/write-ups/tree/master/2019/confidencectf#crypto---count-me-in).