Nah, lava lamps are one of the classics. Other classics are like very fine outside thermometers or noise-collecting radio antennas.
The real creative stuff are e.g. hamster cages or deallocated ram cells.
Really all of these things are fine. Once you have one solution, throw a PRF on it and you're good. No need to overthink it for more solutions
Have you tried those?
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wdym tried? Yes I probably have used keys which included randomness from lava lamps. You probably have too.
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I have just learned about this concept so I surely haven't used it before
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You probably have without knowing when visiting a website with https:// server side keygen :)
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