Wordpress automatic update system is a convenient way to keep your Wordpress site, including various plugins you may have installed, up to date with their latest version. The automatic update system relies on FTP access to the server hosting the Wordpress site.
FTP is a non-secure protocol which means that when you use it, your FTP user name and password are sent as plain text and can be captured by a third party using the same network.
Wordpress update system can overcome this using FTPS, which is basically the same FTP protocol only it uses encryption (SSL) before sending the data through the network, so a third party may see the data but cannot understand it without breaking the encryption first.
But what happens if you don't have FTPS supported in your hosting server and only have SSH access?
Well, Wordpress out of the box does not give you any solution for that problem and you are compelled to use the non-secure FTP protocol to update your Wordpress site and plugins.
Fortunately, like Drupal, Wordpress basic features can be upgraded and extended using plugins (modules in Drupal). One of those plugins is called SSH SFTP Updater Support. SFTP is not the same thing as FTPS. FTPS is FTP over SSL. SFTP is an extension to SSH (Secure Shell) protocol that gives the same features as FTP. FTP and FTPS use port number 21 for communication and SFTP uses port number 22 (like SSH).
Using the SSH SFTP Updater Support plugin is very simple. Just download it and install like any other Wordpress plugin and then enable. No configuration needed other than that. Once it is enabled, click to update your Wordpress and your plugins automatically and you will have the option to use SSH2 and not only FTP or FTPS like before. Type in your SSH user name and password and that's it – you can now update your Wordpress site and plugins over SSH, which some may claim it is more secured that FTPS.
SSH SFTP Updater Support on Wordpress.org