This is a writeup for the challenge Phasestream 2, part of the Hack the box's Cyberapocalypse CTF 2021, category Crypto.
Prompt
The aliens have learned of a new concept called "security by obscurity". Fortunately for us they think it is a great idea and not a description of a common mistake. We've intercepted some alien comms and think they are XORing flags with a single-byte key and hiding the result inside 9999 lines of random data, Can you find the flag?