I started solving the challenges in Cryptopals (https://cryptopals.com/) the other day to familiarize myself with the basics of cryptography. Think of it as Project Euler but for cryptography. It's super interesting and useful and thought I'd share it here in the community since I imagine a lot of people here are also interested in cryptography.
I still have a long ways to go! You can see some of my solutions here: https://github.com/arriolac/cryptopals