code: def do_local_der(self, filename, keytype, keyusage=None, kid=''):
          
          _bkey = import_private_rsa_key_from_file(filename)
  
          if keytype.lower() != 'rsa':
              raise NotImplemented('No support for DER decoding of that key type')
  
          if not keyusage:
              keyusage = ["enc", "sig"]
          else:
              keyusage = harmonize_usage(keyusage)
  
          for use in keyusage:
              _key = RSAKey().load_key(_bkey)
              _key.use = use
              if kid:
                  _key.kid = kid
              self._keys.append(_key)
  
          self.last_updated = time.time()
docs: Load a DER encoded file amd create a key from it.
           
          :param filename: 
          :param keytype: Presently only 'rsa' supported
          :param keyusage: encryption ('enc') or signing ('sig') or both