The Lava Lamp Random Number generator (at http://www.lavarnd.org/)
generates true random numbers from the images of a couple of lava
lamps. Of course, as a source of randomness for cryptographic
purposes, it's useless because it's visible to everyone (though I
suppose it might be used for Rabin's beacons).
At ThinkGeek, you can now, for only $6.99, buy yourself a USB-powered
mini lava lamp (see http://www.thinkgeek.com/gadgets/lights/7825/).
"All you need" is some way to watch the thing - perhaps a USB camera -
and some software to extract random bits. (This isn't *really* a lava
lamp - the lamp is filled with a fluid containing many small
reflective plastic chips, lit from below by a small incandescent bulb
which also generates the heat that keeps the fluid circulating. From
any given vantage point, you get flashes as one of the plastic chips
gets into just the right position to give you a reflected view of the
bulb. These should be pretty easy to extract, and should be quite
random. Based on observation, the bit rate won't be very high - a bit
every couple of seconds - though perhaps you can use cameras at a
couple of vantage points. Still, worth it for the bragging rights.)
An alternative, also at ThinkGeek, is a USB-powered Plasma Ball (at http://www.thinkgeek.com/geektoys/science/964e/)
. The arc discharges should be even easier to convert into a
bitstream, though it's probably a more biased source than the lava
lamp, so will need more post-processing.
-- Jerry
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