Subject: Hardware random number generator Summary: Very high frequency oscillator sampled by a low frequency oscillator From: battle@cs.utk.edu (David Battle @ University of Tennessee CS Department) I had the following idea for a hardware random number generator. It works something like this: +-------------------------------------+ | High frequency oscillator (~ 10 MHz)>------+ +-------------------------------------+ | | +------------------------------------------------+ | | +----------------------------+ +---> DATA Serial in parallel | | out shift register | +---> SHIFT OUTPUTS | | +---------v-v-v-v-v-v-v-v----+ | outputs go to LED bank or | parallel port input | | | low frequency oscillator could be replaced | with output from parallel port for easy | synchronization +------------------------------------------+ | +-----------------------------------+ | |Low frequency oscillator (~ 10 KHz)>--+ +-----------------------------------+ Presumably the randomness comes from slight fluctuations in the frequency of both the high and low frequency oscillators. Obviously the low frequency oscillator must shift 8 times for a whole byte's worth of bits to be generated. I built one of these and although I haven't conducted any statistical tests, the the output bits *seem* random. I used a crystal oscillator for the high frequency oscillator and a 555 timer for the low frequency one. Does anyone have any comments about the usefulness/practicality/reliability of such a random number generator? -David L. Battle battle@cs.utk.edu