Rooted!
root@obscure:~# id
uid=0(root) gid=0(root) groups=0(root)
Thanks to EvilT0r13 for nudges.
Few Hints for those who are stuck… Feel free to mark spoiler if it is!
Foothold : You know the file, but don’t know the parent dir… FUZZ accordingly.
User : No need of any custom scripts. Use common sense with encryption<->key<->decryption. You have everything you need.
Root: There are 2 ways to get root. Understand the script. Look what it does and where it does and how can you catch it! Once you catch it, you know what to do with it.
Nice box, but totally CTF like. Thanks to clubby789.
Feel free to PM if need assistance.