At 2:17 PM 11/3/95, Tim Philp wrote:
Would not generating random numbers using video sources be suseptable to the same 'external' influences as generating random numbers from radio static? External RF fields could skew the 'randomness' of the data.
Do a thought experiment, if not an actual experiment. Tune your t.v. to an unused channel. Use no antenna, or perhaps just small rabbit ears. Notice the swirl of snow (as in "Snow Crash"). Imagine sampling bits from this snowstorm, perhaps 10 per frame. Apply the usual tricks to remove biases in one direction or another (*) and apply hashes as desired to distill bits of entropy. (* Such as von Neumann's scheme to turn even biased coins into "fair" sources: toss a coin twice and let H T be a 1 and T H be a 0.) To complete the thought experiment: Imagine the difficulty of an attacker being able to module this snowstorm in any predictable way. Imagine the difficulty when the antenna input has been disconnected, or the rabbit ears moved by air currents in the room, or.... "All crypto is economics." The cost of an attack based on modulating this source of randomness would be in the tens of billions of dollars, or more, and likely impossible at any cost at this time. (Depending on the sampling details, the antenna input, etc. I'm not saying a black bag job could not be done to alter the inputs to the t.v., just that external RF manipulation is unlikely in the extreme to be economically feasible.)
As another thought, has anyone done any work on RNGs involving chaotic processes such as fluid dynamics and turbulent flow? I suspect that pressure, or other parameter variences, in turbulent flow could yield good random numbers. As a bonus, these parameters are easily measurable without special, exotic, equipment and should be inexpensive
Ignoring the work allegedly done on "chaotic encryption," the RF method described above essentially is relying on turbulence: the atmospheric variations ("spherics," "whistlers," are some of the buzz words) affect the snowstorm. Also, the rabbit ear antennas move in response to room air currents. Again, all unpredictable. (And as I noted above, sampling strategy is important...) I don't plan to belabor this point. Radioactive decay sources are certainly fine, though not likely to be purchased by most people. (I have nothing against radioactive decay, as some of you may know--it made my career.) --Tim May Views here are not the views of my Internet Service Provider or Government. ---------:---------:---------:---------:---------:---------:---------:---- Timothy C. May | Crypto Anarchy: encryption, digital money, tcmay@got.net 408-728-0152 | anonymous networks, digital pseudonyms, zero Corralitos, CA | knowledge, reputations, information markets, Higher Power: 2^756839 | black markets, collapse of governments. "National borders are just speed bumps on the information superhighway."