Information about the package, fwknop, which is shipped with common Linux distributions. The fwknop package is designed for, A Single Packet Authorization (SPA) implementation.
A Single Packet Authorization (SPA) implementation
fwknop implements an authorization scheme known as Single Packet Authorization (SPA) that requires only a single encrypted packet to communicate various pieces of information including desired access through an iptables policy and/or specific commands to execute on the target system. The main application of this program is to protect services such as SSH with an additional layer of security in order to make the exploitation of vulnerabilities (both 0-day and unpatched code) much more difficult. The authorization server passively monitors authorization packets via libpcap and hence there is no "server" to which to connect in the traditional sense. Any service protected by fwknop is inaccessible (by using iptables to intercept packets within the kernel) before authenticating; anyone scanning for the service will not be able to detect that it is even listening. This authorization scheme offers many advantages over port knocking, include being non-replayable, much more data can be communicated, and the scheme cannot be broken by simply connecting to extraneous ports on the server in an effort to break knock sequences. The authorization packets can easily be spoofed as well, and this makes it possible to make it appear as though, say, www.yahoo.com is trying to authenticate to a target system but in reality the actual connection will come from a seemingly unrelated IP. Although the default data collection method is to use libpcap to sniff packets off the wire, fwknop can also read packets out of a file that is written by the iptables ulogd pcap writer or by a separate sniffer process.
Control the fwknop package with the following handy commands outlined below.
yum install fwknop
This command will install fwknop on the server.
yum remove fwknop
This command will un-install fwknop on the server. When you run this command, you will be asked if you are sure that you want to remove fwknop, so you have to manually confirm that you want to do this.
yum -y remove fwknop
This command will un-install fwknop on the server. When you run this command with th e -y flag, you will not be prompted to check that you are sure you want to remove the package - so be sure you absolutely want to remove fwknop when using the -y flag.
yum update fwknop
This command will update fwknop to the latest version. When you run this command, you will be asked if you are sure that you want to remove fwknop, so you have to manually confirm that you want to do this.
yum -y update fwknop
This command will update fwknop to the latest version. When you run this command with the -y flag, you will not be prompted to check that you are sure you want to remove the package - so be sure you absolutely want to remove fwknop when using the -y flag.
yum info fwknop
This command will show you core information about the fwknop package.
yum deplist fwknop
This command will show you the dependencies for fwknop. Thankfully, when using Yum, if dependencies are required, these are also installed at the same time so you don't have to worry too much about that.
yum check-update fwknop
This command will check if there is an update waiting on fwknop. When you run this command this will return nothing if there is nothing to update, or, will return the package name if the package is due to be updated.