The last TechMail is Realize the flexibility of OpenSSH which talks about some of the basics of using OpenSSH, from setting up keys to modifying sshd_config for user/group access controls and different features per group/user. OpenSSH is another of my favourite tools. Of course, there’s also the linsec wiki page Optimizing OpenSSH that goes into a lot more depth about using OpenSSH. It does, however, need to be updated to note the many new features recent OpenSSH versions provide.