def generate_private_key(key_type):
    """
    Generate a random private key using sensible parameters.

    :param str key_type: The type of key to generate. One of: ``rsa``.
    """
    if key_type == u'rsa':
        return rsa.generate_private_key(
            public_exponent=65537, key_size=2048, backend=default_backend())
    raise ValueError(key_type)