Alright folks, lemme tell you about my weekend project. I decided to tackle Kerberos authentication – yeah, the whole “secret ticket” thing. Sounded like fun, right? (Spoiler: it was… eventually.)
First off, what’s Kerberos? Basically, it’s a way to prove you are who you say you are to a network service without sending your password all over the place. Think of it like a digital hall pass.
I started by spinning up a couple of VMs. One for the Key Distribution Center (KDC) – the Kerberos brain – and another to act as a client. You gotta have a playground, right?
Setting up the KDC
This was… interesting. I installed `krb5-kdc` and `krb5-admin-server`. The config files, `/etc/*` and `/etc/krb5kdc/*`, are where the magic (and potential for head-scratching) happens.
- I edited `/etc/*` to define my realm – think of it as the Kerberos domain. I called mine “*” (original, I know).
- Then, I tweaked `/etc/krb5kdc/*` to point to the KDC’s database.
Next, I needed to create the Kerberos database. This is where the users and services are stored. Used the `kdb5_util create -s` command. The `-s` option creates a stash file for the master key – important! Made sure to set a strong password for the database. Don’t skimp on the password here; it protects everything.
Creating Principals
With the KDC up and running, I added a user principal. Think of a principal like a Kerberos username. I used `*` to connect to the KDC database locally.
Inside `*`, I did:
addprinc user1@*…and set a password for ‘user1’.
I also created a service principal. This is for the service that the client will authenticate to. Let’s say I wanted to secure access to a web server. I’d create a principal like:
addprinc HTTP/*@*Client Configuration
Over on the client VM, I installed `krb5-user`. I copied the `/etc/*` file from the KDC to the client. This tells the client where the KDC is located.
Now, to get a ticket! I used the `kinit` command:
kinit user1@*It prompted me for the password for ‘user1’. If all went well (and after a few typos, it did), I had a Kerberos ticket.
I could then use `klist` to view my cached tickets. This shows you the ticket you have for different services.
Testing Authentication
To actually use the Kerberos ticket, I needed a service that supported Kerberos authentication. I didn’t want to set up a whole web server at this stage, so for testing, I used `kinit` with the `-k` option to request a service ticket for the HTTP service I had created.
The gotchas: Time synchronization is critical. If the client and KDC clocks are too far out of sync, Kerberos will refuse to issue tickets. I wasted a good hour on this. Use NTP!
Also, DNS is important. Make sure the client can resolve the KDC’s hostname.
Finally: It worked! I was able to get a Kerberos ticket, and the service (well, my simulation of a service) accepted it. It felt like cracking a code.
This was just a basic setup, of course. Real-world Kerberos deployments can be far more complex. But understanding the fundamentals is key. It’s all about principals, tickets, and trust. Now I just need to figure out how to integrate this with my actual web applications… next weekend, maybe!
