Ted Smith (at Tuesday, October 22, 2013, 5:15:09 PM):
It actually works; when you view the webcam you can see the little points of light where an alpha particle hits the sensor.
Is it possible to make an entropy source out of something like that? If so, it was a really simple (less than two hours IIRC) build, and it cost about $40.
you can make entropy source out of anything that you can access from your computer. accessing is actually the harder part. you need to find out how to attach. you need to find out what access interface to use, how to be cross platform if you want to, how to test it on different platforms, how to retest if after new releases of said platforms, and so on. you can run into all sort of driver problems. another hard-ish part is to estimate the true entropy content. it might be much smaller than it looks like. understanding the physics of the underlying phenomenon helps. once you have your data stream in memory, you just need to use some whitening. that is the easy part. virtually every cryptographic primitive can be turned into a secure whitener. for example, i have implemented a small toy/tool to generate random data from the noise of the sound card. it is pretty much the same thing, you just replace the line-in with your data source, and the whitening part is done. it is for windows only. check it out here: https://github.com/krisztianpinter/rnd_wavein disclaimer: the old rule "don't roll your own crypto" is still in effect.