Getting a foot in the door

I'm a pretty new programmer-about halfway through Sweigart's new book on Python and Cryptography. My question is, when the hell do I get to DO something? I can go through exercises and analyze how different cipher programs are written, but I'm really yearning to actually create or contribute to something. Any input?

Look, if you don't have PhD don't bother trying to get your foot in the door with cryptography. The most you will ever do is reliably implement a mathematician's algorithm.

Literally any other field is going to be more rewarding. You love mathy stuff? Work on some algorithmic geometry creation. Work on data mining the news. But a home grown cipher is abso-fucking-useless to everyone.