Unformatted text preview: atural randomness of the real world. Often this method requires specialized hardware, but you can play tricks with computers. Find an event that happens regularly but randomly: atmospheric noise peaking at a certain threshold, a toddler falling while learning to walk, or some such. Measure the time interval between one event and the next event. Record it. Measure the time interval between the second event and the third event. Record it as well. If the first time interval is greater than the second, output 1 as the bit. If the second time interval is greater than the first, output 0 as the event. Do it again for the next event. Throw a dart at the New York Stock Exchange closing prices in your local newspaper. Compare the closing price of the stock you hit with the closing price of the stock directly above it. If the one you hit is more, output 0; if it less, output 1. Hook a Geiger counter up to your computer, count emissions over a fixed time interval, and keep the least significant bit. Or measure the time between successive ticks. (Since the radioactive source is decaying, the average time between successive ticks is continuously getting longer. You want to choose a source with the half life long enough to make this negligible—like plutonium. Or, if you’re worried about your health, you can apply appropriate statistical corrections.) G. B. Agnew proposed a real random-bit generator, suitable for integration into a VLSI device . It is a metal insulator semiconduction capacitor (MISC). Two of them are placed in close proximity, and the random bit is a function of the difference in charge between the two. Another random-number generator generates a random-bit stream based on the frequency instability in a free-running oscillator . A commercial chip from AT&T generates random numbers from the same phenomenon . M. Gude built a random-number generator that collected random bits from physical phenomena, such as radioactive decay [668,669]. Manfield R...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips