I Invented Port Knocking

Let me tell you about something that’s been bothering me for a while.

I invented Port Knocking. No, really. In 2002.

According to portknocking.org, it was invented by Martin Krzywinski in 2003. I’m not here to debate that he didn’t come up with the idea separately, and choose the same names (it’s a pretty good name for the technology). But I do want to make it clear, for the record.

Wait, hold on, what’s Port Knocking?

Oh, got ahead of myself there.

Port Knocking is a security method where you can cloak a network completely (close all ports or put them in stealth mode) and yet still allow access from any computer in the world, by way of a sequence of “knocks” on a predefined list of ports.

The server can specify a list of ports (say, 53, 91, 2005, 2131, 7) and monitor to see if there are attempts to open them. If an outside computer accesses each of these ports in sequence, without hitting any other ports, and within a time period, the server can open a select set of ports (separate from the knock list) to that IP address only.

In my original designs, before opening the ports after a successful knock sequence, an authentication port would be opened at a predefined port, which the client would have to access, exchanging credentials, before the ports would be open.

And why the controversy?

First, some history.

In mid-2002, I was 18 and interested in security, amongst other things. Along with writing code for Pidgin (then Gaim), and a couple other projects, I was fooling around with firewalls and such.

I had this idea one morning while in the shower to add another layer of security. I really wanted to be able to completely close off my network, but still access it when out of town. I can’t tell you how it came into my head. Just a moment of inspiration. I wasn’t even really looking for another project, just brainstorming, but I liked the idea too much. I started writing code and made it work.

It was a while before I discussed it publicly on my old blog on Advogato. There are many posts, but I’ll highlight a couple here, where I introduce what I was working on:

The blog is full of lots of old teenage angst, so ignore most of it, but I spend the next few weeks going over my progress, answering questions from people who are asking for more information, etc. I was very open about it.

At one point a couple months later, I realized this was stupid. I had a good idea. I should patent it. I took it down for a while. This was after I had already put up the sourcecode, though, and many people had it.

Now, in retrospect, I should have made this into a full-on open source project and gained the recognition myself, continued development. But I was too busy with other things and didn’t really want another major product on my hands. I remember at one point I thought, “maybe I can sell this to a security company, or patent it!”

And since then…

One day, I opened a magazine and saw “port knocking” on the cover. My heart skipped a beat. Somebody wrote an article on my port knocking! I opened the magazine and read through it. “Invented by… Michael Krzywinski? What?!” I re-read to make sure. It was all my terminology, my methods. I was floored.

By that point, he made a name for himself as the inventor. And again, I’m not trying to discredit him, because he very well may have come up with the same thing separately. But it stung, because I had a great idea, a year before he wrote a paper on it, and I didn’t promote it the way he did.

Lesson learned

This is one of those life lessons. You always regret what happened, but you use it to make better decisions in the future. These days, I’m happy working on some awesome products. My day job at VMware and my highly successful code review software, Review Board (for which we’ve recently started a company).

Now, if I have a good idea, I make sure it’s heard, and demonstrated, far and wide. Truly great ideas don’t really come that often, so when you have one, make sure you do something with it, or you may end up regretting it for years to come.