library/Extlib/Utils.php
public function generateSecurityLink($domain, $path, $prefix, $secret)
    {
        $path = trim($path, Url::SEPARATOR);
        $prefix = trim($prefix, Url::SEPARATOR);
        $domain = rtrim($domain, Url::SEPARATOR);

        $hex = sprintf("%08x", time());
        $md5 = md5($secret . $path . $hex);

        return sprintf('%s/%s/%s/%s/%s', $domain, $prefix, $md5, $hex, $path);
    }
public function generateSecurityLink($domain, $path, $prefix, $secret)
    {
        $path = trim($path, Url::SEPARATOR);
        $prefix = trim($prefix, Url::SEPARATOR);
        $domain = rtrim($domain, Url::SEPARATOR);

        $hex = sprintf("%08x", time());
        $md5 = md5($secret . $path . $hex);

        return sprintf('%s/%s/%s/%s/%s', $domain, $prefix, $md5, $hex, $path);
    }
Return security link for mod_secdownload lighttpd.
http://redmine.lighttpd.net/projects/1/wiki/Docs_ModSecDownload

@param string $domain
@param string $path
@param string $prefix
@param string $secret
@return string