On Mon, 17 Sep 2007 11:20:32 -0700 Netsecurity <[EMAIL PROTECTED]> wrote:
> Back in the late 60's I was playing with audio and a magazine I > subscribed to had a circut for creating warble tones for standing > wave and room resonance testing. > > The relevance of this is that they were using a "random" noise > generating chip that they acknowledged was not random enough for good > measurements. The fix suggested was to parallel a number, six as I > recall, to improve the randomness by mixing the signals to achieve > better randomness. I don't recall the math but the approach improved > the randomness by more than an order of magnitude. > > I have also seen the same effect on reverse biased zener diodes used > as random noise generators and that seemed - no real hard > measurements that I can recall - to work quite well. Mind you these > were not zeners all fabricated on a single chip, but rather > individuals soldered together so the charateristics of each were more > random because of the semi-randomness of the manufacturing process. > This is an old technique. We could even go back to von Neumann's scheme: look at two successive bits. If they're equal, discard them. Otherwise, map <0,1> to 0 and <1,0> to 1. See the section on "Software whitening" in http://en.wikipedia.org/wiki/Hardware_random_number_generator (which was correct as of when I looked at it, a few minutes before the timestamp on this email; check the Wiki history to be sure....). --Steve Bellovin, http://www.cs.columbia.edu/~smb --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]