At 12:29 PM 9/24/95, Ed Carp [khijol SysAdmin] wrote: ....
I learned the hard way - keep the transmitters away from a reverse-biased doide acting as a noise generator. Only until I examined the output did I realize it wasn't random. I fixed it, though, by looking at the output and testing its randomness. .... Very interesting. I wouldn't be too sure that a transmitted signal at a single frequency is the only signal that an opponent could use to bias your random numbers. How do you "test for randomness". I think that signal to noise arguments, phrased in terms of entropy, can protect you against unknown and unwanted signal. (Ironically you want a very low signal to noise ratio!) Perhaps you merely take n/(S/N) bits from the HRNG when you need n bits and run them thru MD5. Here S is the signal strength of the maximum plausible unwanted signal, and N is the noise of the diode.
I encourage both diode theorists and information theorists to quibble with the above formula!