Content delivery network Cloudflare use a set of lava lamps to generate random numbers upon which to base their network's encryption:
While Cloudflare uses industry-grade random number generators for its servers, it also decided to incorporate the backbone of its encryption into its office design. Inspired by an idea from engineers at Sun Microsystems, who thought that lava lamps could help generate randomness since modeling how fluid moves within the lamps is incredibly difficult, Prince decided to create an entire wall of lava lamps. Cloudflare calls it the "Wall of Entropy."
Basically, their system uses a frequently-updated image of the wall of lava lamps as part of the input side of their random number generator: if you were an adversary attacking such a system, I wonder how much scope there would be to interfere with the lava lamps' power supply so that all the lamps were turned off for a few seconds and the contents of each lamp settled to a steady (and predictable) state in the absence of any power input. Might that allow an attacker who could arrange the timing of such an outage so as to be able to predict the state of the random number being generated?1
Of course, I can think of potential countermeasures. For a start, presumably you'd have to allow a few seconds for all the lamps' contents to settle once you'd cut the power, and the system might be configured to notice if the output of the snapshots remained the same for more than x consecutive milliseconds and ignore the lava lamps until they started to produce different images in succession once again. Also, if the lava lamps are only part of the random number generator process, the system could be set to only use the lava lamps if they're producing different images in consecutive snapshots and otherwise fall back on other, more conventional, sources of randomness. (Or, given that part of the input from the lava lamps reflects the effect of staff walking past them and thus obscuring the view, perhaps if there seems to be a problem with the lava lamps some poor bloody intern automagically gets a notification ordering him / her to go and take a walk past the lava lamps Right Now!) ↩