I keep all the code and notes related to cryptography in this repo. They're classified under
- stanford - Notes for the Coursera course on cryptography.
- matasano - Code for the Matasano crypto challenges.
- aes - Implementation of the Advanced Encryption Standard
If you're interested in crypto, I'd recommend checking the first two out.
The code for the challenges are WIP, I have finished 16 out of 56 problems in total. In case you'd like to learn more about them, here's a good intro.