You're missing the point that setParameter() provides information used
in all future calls to the signature generation, while init() provides
data specifically for a given key stream production. In Signature()
you call .setParameter() to set up the PSS parameters (or use the
defaults). Each subsequent call to initSign or initVerify uses those
PSS parameters. The equivalent part of .init() in KeyDerivation is
actually the calls to .update() in signature as they provide the
specific information for the production of the output key stream. In
fact, setting up an HMAC signature instance and passing it the mixin
data as part of a .update() is a way of producing the key stream round.
So equivalences:
KeyDerivation.getInstance(PRF) == Signature.getInstance(HMAC)
KeyDerivation.setParameters() == Signature.setParameters()
KeyDerivation.init(key, List<Parameters>) == concatenation of the
results of multiple calls (each key stream round based on the needed
output length) to [Signature.initSign(Key) followed by
Signature.update(converttobytearray(List<Parameters>)) followed by
Signature.sign()] to produce the key stream
KeyDerivation.deriveKey() == various calls to key or object factories
with parts of the key stream (signature).
Are you expecting that setParameters is called once per instantiation?
If so, then the parameters that would go into setParameter (an APS I
assume) could just as easily go into the getInstance call. It also
removes the chance that someone would call it twice.
If you're expecting someone to call setParameter more than once, then I
would expect an init must follow. So why not place it in a form of init
that allows you to change that particular set of params? Either way it
seems like we could coalesce this method into one of the calls that
sandwich it in your proposed model.
