Only public keys, Sony fixed the 'random number' fail so private keys cannot be calculated like 3.55 and below. Therefore, at the moment, stuff can't be signed to work with 3.56.
True and its also seems Sony have a checklist of things they have signed, so even if they have a signed key Sony can check this against some kinda look up table and if its not one of thiers even if its signed it wont work. Not including the random security server side checks the PS3 now does, that can update at anytime without you knowing.