Glad to see you are interested. I'd be more than happy to help answer any questions you may have (you can post them on this mailing list). For getting started, I recommend checking out the docs and issues lists and working on something that sounds interesting: https://github.com/google/keyczar/issues?q=is%3Aopen+is%3Aissue
Improving the documentation and testing in cases where you find it to be insufficient are also welcome changes.
One thing you should note is that this project isn't incredibly active at the moment and efforts towards the project that is supposed to replace keyczar seem to have stalled. https://github.com/google/K2