SSH Hardening

The Secure Shell (SSH) suite is one of those must-have tools for Linux administrators. It allows you to take care of Linux servers from the comfort of your cubicle, or even from the comfort of your own home. Either way, it’s a lot better than having to don your parka and jump through security hoops to enter a cold server room. The secure in Secure Shell means that everything that you either type or transfer gets encrypted. That eliminates the possibility of someone obtaining sensitive data by plugging a sniffer into your network.

By this stage in your Linux career, you should already know how to use Secure Shell, or SSH, to do remote logins and remote file transfers. What you may not know is that the default configuration of SSH is actually quite insecure. In this chapter, we’ll look at how to harden the default configuration in various ways. We’ll look at how to use encryption algorithms that are stronger than the default, how to set up passwordless...