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. 
Sure, just declare it with package security (i.e. no public/private
modifier). Make sure to name it appropriately then, with appropriate error
message (your current use of "Type" is ambiguous). Otherwise, declare
UnsupportedTypeException as subclass of IllegalArgumentException.