private function _debug($text)
    {
        if ($this->_debug) {
            if (php_sapi_name() === 'cli') {
                foreach (explode(PHP_EOL, $text) as $line) {
                    echo "Crypt_GPG DEBUG: ", $line, PHP_EOL;
                }
            } else if (is_callable($this->_debug)) {
                call_user_func($this->_debug, $text);
            } else {
                // running on a web server, format debug output nicely
                foreach (explode(PHP_EOL, $text) as $line) {
                    echo "Crypt_GPG DEBUG: <strong>", htmlspecialchars($line),
                        '</strong><br />', PHP_EOL;
                }
            }
        }
    }