Mastering SSH Techniques For Secure Remote Access With Keys

Welcome back to the Sysadmin's Corner and the continuing saga of secure communications, SSH-style. Logging in to an SSH server is easy enough and provides you with secure communications, while still opening you up to the whole world. You could set . . . Welcome back to the Sysadmin's Corner and the continuing saga of secure communications, SSH-style. Logging in to an SSH server is easy enough and provides you with secure communications, while still opening you up to the whole world. You could set up a firewall that allows in certain IP addresses only to port 22, but that presents another problem. If you are on the road and you need access to your own system, you might be connecting from an untrusted system with a dynamic IP. A nice iptables rule isn't going to help here, unless you've got somebody permanently standing by who can answer your phone call and enter the commands for you--somebody with root access, no less. No matter how you look at it, it can get messy.

Another option is to leave port 22 wide open and set your server to allow only public key authentication. This option requires a little more work than merely running sshd and forgetting about it. But as an added bonus, you can securely log in without a password. Did he just say "without a password"? Yes, he did, and you can do so securely. In fact, public key authentication can be safer than the classic password system because knowing the password isn't enough.

Here's how it works. Using a key generation program, you create a key pair consisting of a public key, which is copied to the server, and a private key, which you keep on your PC and guard with your life. No authentication can take place without both keys.

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