The next challenge was encoded and we don't know the key. We were able to recover the script used to encode the challenge and a hint binary.
What we know is that it is a Linux binary running on a x64 Ubuntu 18.04. Maybe by looking at the encoding algorithm and the hint binary you can figure out how to decode it?
The flag for this challenge is the ATR[key] where key is the key you found, in hex, and lower case (for example, if the key is 5566778899aabbcc, the flag will be ATR[5566778899aabbcc])
Good luck!
The hint is in the file ".hint"