code: def sign(self, message):
          
          message = _helpers._to_bytes(message, encoding='utf-8')
          return PKCS1_v1_5.new(self._key).sign(SHA256.new(message))
docs: Signs a message.
  
          Args:
              message: string, Message to be signed.
  
          Returns:
              string, The signature of the message for the given key.