Wireless Hacks

Quick Logins with SSH Client Keys

Using SSH keys instead of password authentication to speed up and automate logins.

When you’re an admin on more than a few machines, being able to navigate quickly to a shell on any given server is critical. Having to type ssh my.server.com (followed by a password) is not only tedious, but it also breaks your concentration. Suddenly having to shift from “where’s the problem?” to “getting there,” and back to “what’s all this, then?” has led more than one admin to premature senility. It promotes the digital equivalent of “why did I come into this room, anyway?” (and the problem is only made worse by /usr/games/fortune!).

At any rate, more effort spent logging into a machine means less effort spent solving problems. Recent versions of SSH offer a secure alternative to endlessly entering a password: public key exchange.

For these examples, I assume that you’re using OpenSSHv3.4p1 or later. To use public keys with an SSH server, you’ll first need to generate a public/private key pair:

 $ ssh-keygen -t rsa

You can also use -t dsa for DSA keys, or -t rsa1 if you’re using Protocol v1. And shame on you if you are using v1! Upgrade to v2 as soon as you can!

After you enter the above command, you should see something like this:

 Generating public/private rsa key pair.
 Enter file in which to save the key (/home/rob/.ssh/id_rsa):

Just press Enter there. It will then ask you for a passphrase; just press Enter twice (but read the Security note below). Here’s what ...