function _generate_identifier()
    {
        $identifier = 'SSH-2.0-phpseclib_2.0';

        $ext = array();
        if (function_exists('\\Sodium\\library_version_major')) {
            $ext[] = 'libsodium';
        }

        if (extension_loaded('openssl')) {
            $ext[] = 'openssl';
        } elseif (extension_loaded('mcrypt')) {
            $ext[] = 'mcrypt';
        }

        if (extension_loaded('gmp')) {
            $ext[] = 'gmp';
        } elseif (extension_loaded('bcmath')) {
            $ext[] = 'bcmath';
        }

        if (!empty($ext)) {
            $identifier .= ' (' . implode(', ', $ext) . ')';
        }

        return $identifier;
    }