RSA Keys -> Numbers Interface

Replaces #1038.

This attempts to address naming while not handling the larger interface question. I'd like to land this to unblock while we continue to discuss the other options. It should be easy to convert if we choose to change this and we can consider it a 0.5 blocker. (a working sub-interfaces example: https://gist.github.com/reaperhulk/1f90d2d03ac9372c30c6).
Is this a Key? Not obvious from the name.