Getting Started with Kerberos
So, I finally decided to roll up my sleeves and figure out this Kerberos thing. People talk about it for security, locking things down properly between machines. Sounded like a solid weekend project, you know, get my hands dirty with something practical.
Setting Up the Brains – The KDC
First off, you need a main server, the Key Distribution Center or KDC. I dusted off an old box I wasn’t using much, put a fresh Linux install on it. The easy part was finding and installing the server software. I think the packages were something like krb5-kdc and krb5-admin-server. A quick command and they were on the system. No big deal there.
Fiddling with Config Files
This next part needed more attention. Configuration files. Always fun, right? There’s a main one, . This file basically tells all your computers where the KDC server lives and what your security zone, they call it a ‘realm’, is named. I just picked a simple name for my setup. You gotta make sure this file is right, otherwise nothing talks to each other. There was another config file just for the KDC server itself, . I mostly left the defaults there but double-checked things like file paths. Oh, and I made sure the firewall wasn’t blocking the Kerberos ports. Gotta remember the firewall.
Creating the Secret Stash
With the configs sorted, I needed to actually create the database that holds all the secret keys for users and services. Ran a command, something like kdb5_util create -s. It asks you to create a master password for the database. Wrote that one down and hid it well! Then, I needed a way to manage this thing, so I created an admin account for myself using a tool called . Added my own admin ‘principal’, that’s what they call usernames in Kerberos.
Getting the Clients On Board
Okay, the server’s humming along. Now I needed my other computers, the clients, to actually use it. Went over to another machine. Installed the client software package, probably called krb5-user. The main task here was editing its own file. Had to make sure it pointed to my KDC server and knew the realm name. Pretty much copied the important bits from the server’s config file.
Making Services Use Kerberos
This was the whole point, right? Making services more secure. Let’s say I wanted to secure SSH logins. I had to create a special Kerberos identity, a ‘principal’, just for the SSH service running on a specific client machine. Used the kadmin tool again, connecting to the KDC server this time. Added something like host/*. Then, I had to export the key for this service principal into a special file called a ‘keytab’ on the client machine. The SSH server uses this keytab file to prove its identity. Lastly, I had to tweak the SSH server’s own config file (sshd_config) to tell it “Hey, use Kerberos for authentication”.
Did it Work? Testing Time!
Moment of truth. Jumped onto a client machine. Typed kinit myusername. It prompted me for my Kerberos password (the one I set up earlier). Typed it in… success! It said I got a ‘ticket’. Cool. Typed klist to see the ticket details. Looked good. Then, the real test: I tried to SSH into the other machine, the one I configured the SSH service for. And guess what? It logged me straight in! No password prompt. That’s the Kerberos magic working right there.
Bumps in the Road
It wasn’t all smooth, though. Ran into a few snags. One big one was clock synchronization. Kerberos is super strict about time. If the KDC server and a client machine have clocks that are off by more than a few minutes, it just fails. Drove me nuts for a bit until I figured it out. Ended up setting up NTP (Network Time Protocol) on all the machines to keep their clocks perfectly synced. That fixed it. Also typo’d a path in a config file once and spent way too long tracking that down. Standard stuff when you’re setting things up from scratch.
Wrapping Up
So, after a bit of fiddling and troubleshooting, I got it all working. It definitely took some effort, lots of little steps to follow. But now I have a real Kerberos system handling logins between my machines. Feels pretty good knowing that’s in place. Learned a ton just by doing it myself, which is always the best way.
