KeyGenUtils API

This is the API I've written for generating Keys, nonces and ivs. It will also convert byte arrays to into SecretKeys, KeyPairs, and a couple other classes. 
I think so, yes. "Private unless you have a good reason not to" seems the way to go, especially in an API (you don't want "clever" programmers to abuse you API in a way you didn't envision, that might cause API breakage of undocumented features in the future).