Safe Opener

https://play.picoctf.org/practice/challenge/294?page=9

• looking at the java code, i noticed String encodedkey = "cGwzYXMzX2wzdF9tM18xbnQwX3RoM19zYWYz";

• there are also references to [[base64]] in the file, so going to [[CyberChef]], decode the flag