I’ve been playing with various ciphers and encryption schemes, and needed a true random number generator to ensure secrecy. A Pseudo Random Number Generator uses a algorithm to produce a pseudo random number. If the algorithm can be determined, so can the outcome. A Hardware Random Number Generator uses a external event (sound, light, atmospheric noise, etc.) to seed the random number generator. For a neat project, and more info, see
http://robseward.com/misc/RNG2/
http://en.wikipedia.org/wiki/Hardware_random_number_generator