(self, key)
Performs necessary validation and conversions on the key and returns
        the key value in the proper format for sign() and verify().
Performs necessary validation and conversions on the key and returns
        the key value in the proper format for sign() and verify().
Performs necessary validation and conversions on the key and returns the key value in the proper format for sign () and verify () .
def prepare_key(self, key):
        """
        Performs necessary validation and conversions on the key and returns
        the key value in the proper format for sign() and verify().
        """
        raise NotImplementedError
def prepare_key ( self , key ) : raise NotImplementedError