code: public static Algorithm RSA512(RSAPublicKey publicKey, RSAPrivateKey privateKey) throws IllegalArgumentException {
          return RSA512(RSAAlgorithm.providerForKeys(publicKey, privateKey));
      }
docs: Creates a new Algorithm instance using SHA512withRSA. Tokens specify this as "RS512".
  
  @param publicKey  the key to use in the verify instance.
  @param privateKey the key to use in the signing instance.
  @return a valid RSA512 Algorithm.
  @throws IllegalArgumentException if both provided Keys are null.