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?

OP here: The career doesn't necessarily have to be consisting of cryptography, I just thought that it was slightly relevant as being the book I'm currently using to learn. At what point do i go "Oh I am now ready to go on Github and contribute to shit?"