Generate a new private RSA key.  This factory function can be used to
        generate a new host key or authentication key.

        :param int bits: number of bits the generated key should be.
        :param progress_func: Unused
        :return: new `.RSAKey` private key

def generate(bits, progress_func=None):
        """
        Generate a new private RSA key.  This factory function can be used to
        generate a new host key or authentication key.

        :param int bits: number of bits the generated key should be.
        :param progress_func: Unused
        :return: new `.RSAKey` private key
        """
        key = rsa.generate_private_key(
            public_exponent=65537, key_size=bits, backend=default_backend()
        )
        return RSAKey(key=key)