Netsecurity wrote: > Back in the late 60's I was playing with audio and a > magazine I subscribed to had a circuit 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.
If one such chip was so non random that the ear could hear the difference from white noise or pink noise, it is most unlikely that six together would be random enough for cryptographic purposes. As has often been stated on this list, the noise source must be understood, so that we have physical theory as to where the noise is coming from, and also tested to make sure it is functioning in accord with theory. No one really understands where zener diode noise is coming from. True entropy in equals true entropy out. You need to be able to determine the true entropy in from physical theory, and be able to test the hardware to check it is working in accordance with theory. To know that a true random number generator is cryptographically secure, you need knowledge of the underlying hardware, knowledge that shows it derives its randomness from the fundamental randomness of the universe, either thermal entropy, (Johnson noise) or quantum indeterminacy (shot noise), knowledge that enables us to determine the good functioning of the underlying noise amplification circuits from the character of the output. A good circuit would simply directly amplify the underlying noise source, so that the entropy of the output would be somewhat less than one entropy bit per signal bit, thus ensuring that any malfunction of the underlying circuit would be obvious, and then pass that output into a hash generator, which emits hash that outputs less bits than the true entropy. Using SRAM as a source of either randomness or unique device ID is fragile. It might well work, but one cannot know with any great confidence that it is going to work. It might work fine for every device for a year, and then next batch arrives, and it completely fails. Worse still, it might work fine on the test batch, and then on the production run fail in ways that are subtle and not immediately obvious. --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
