'Return server and client certificate keys'

def load_certs(self, secret_keys_dir):

    server_secret_file = os.path.join(secret_keys_dir, 'server.key_secret')
    client_secret_file = os.path.join(secret_keys_dir, 'client.key_secret')
    (server_public, server_secret) = zmq.auth.load_certificate(server_secret_file)
    (client_public, client_secret) = zmq.auth.load_certificate(client_secret_file)
    return (server_public, server_secret, client_public, client_secret)
