The sys admin's daily grind: Single-packet authentication
Key Experience
Conventional, woodpecker-style port knocking is open to sniffing and brute force knocking attacks. Sending an encrypted packet with an access request to the server is safer and more modern. Learn more about Firewall Knock Operator, a.k.a. Fwknop.
Conventional port knocking, which I described last month [1], protects you against attackers who routinely scan whole networks looking for "low-hanging fruit." A cracker who takes more time and logs communications can also identify knocking signals because the sequences will repeat.
In theory, you might consider using lists of one-off knocking signals that become obsolete after use. Unfortunately, this is really complex. Besides, if the administrator is not creative enough, an attacker could just try out popular knocking sequences (port 7000, 8000, 9000, …) to gain access.
Single-Packet Authentication (SPA) is one possible solution. The knocking system sends a single packet containing the encrypted authentication credentials – typically a pass phrase – and the client request to open a specific port. An SPA implementation that works really well is Firewall Knock Operator, or Fwknop [2]. Besides the normal build tools, the installation requires Perl, the libpcap-dev package, and the CPAN Net::Pcap module. After installing all of these resources, installing Fwknop is a breeze thanks to the Perl-based installer.
[...]
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Framework Laptop 13 Pro Competes with the Best
Framework has released what might be considered the MacBook of Linux devices.
-
The Latest CachyOS Features Supercharged Kernel
The latest release of CachyOS brings with it an enhanced version of the latest Linux kernel.
-
Kernel 7.0 Is a Bit More Rusty
Linux kernel 7.0 has been released for general availability, with Rust finally getting its due.
-
France Says "Au Revoir" to Microsoft
In a move that should surprise no one, France announced plans to reduce its reliance on US technology, and Microsoft Windows is the first to get the boot.
-
CIQ Releases Compatibility Catalog for Rocky Linux
The company behind Rocky Linux is making an open catalog available to developers, hobbyists, and other contributors, so they can verify and publish compatibility with the CIQ lineup.
-
KDE Gets Some Resuscitation
KDE is bringing back two themes that vanished a few years ago, putting a bit more air under its wings.
-
Ubuntu 26.04 Beta Arrives with Some Surprises
Ubuntu 26.04 is almost here, but the beta version has been released, and it might surprise some people.
-
Ubuntu MATE Dev Leaving After 12 years
Martin Wimpress, the maintainer of Ubuntu MATE, is now searching for his successor. Are you the next in line?
-
Kali Linux Waxes Nostalgic with BackTrack Mode
For those who've used Kali Linux since its inception, the changes with the new release are sure to put a smile on your face.
-
Gnome 50 Smooths Out NVIDIA GPU Issues
Gamers rejoice, your favorite pastime just got better with Gnome 50 and NVIDIA GPUs.