Cloudflare is one of those Internet companies you use all the time, but don’t usually know it. Big websites you visit use Cloudflare to shore up their defenses against denial of service attacks. The company needed some truly random numbers for its security solutions, so it turned to some groovy old tech: lava lamps. In their office is a wall of 100 lava lamps monitored by cameras. The reaction of the lamps is unpredictable, and this allows them to generate really random numbers. [Joshua], a Cloudflare employee, talks about the technical details of the system in a recent blog post.
You might think this is a new and novel idea, but it turns out the LavaRnd (or maybe it is LavaRand — there’s some dispute if you read the comments below) system has been around for a while. In fact, we covered it way back in 2005. Silicon Graphics patented the system in 1996.
You would think these lava lamps would be locked in a bunker somewhere. It turns out, you can see the wall of lava lamps by just visiting Cloudflare’s offices in San Francisco. People disturbing the images are one of the sources of random unpredictability.
The company doesn’t directly use the random numbers from the lamps. [Joshua] explains how on a reboot, each production machine grabs a chunk of random numbers and uses it to seed its usual random number generators. This leads to an interesting problem of ensuring everyone is who they say they are without relying on the very secure protocols you are trying to spin up with random numbers. You can read the solution to that conundrum in the blog post.
You can see a video of the Cloudflare lava wall by [Tom Scott], below. If you don’t need a random number generator, maybe you could use a spectrum analyzer.
Thanks to [Ptkwilliams] for the tip.