Just a quick post to share an awesome website I've just found (thanks to our software security teacher tbh) :
There are a lot of different categories (Cryptanalysis, Reverse, Stegano, Web, etc..) and the challenges range from very easy to very hard, so everyone can have fun (plus levels are independant, you don't need to start with easy ones if you feel confident ).
They hint you some documentation about the level and once you've completed it you can check out Solutions submitted by others.
You only need to create an account to save your progress.
Anyway, hf and HNY !
PS : I had no idea what category this belonged in so feel free to move it if there is a more appropriate place.