applied cryptography - protocols, algorithms, and source code in c

If the system has been running for a while with a

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Unformatted text preview: an endless stream of alternating bits out of the generator. Even if the resonance isn’t this obvious, the resultant bit stream will be far from random. One random-number generator works this way [918]: Our truly random number generator...works by setting an alarm and then incrementing a counter register rapidly in the CPU until an interrupt occurs. The contents of the register are then XORed with the contents of an output buffer byte (truncating the register’s data to 8 bits). After each byte of the output buffer is filled, the buffer is further processed by doing a right, circular shift of each character by 2 bits. This has the effect of moving the most active (and random) least significant bits into the most significant positions. The entire process is then repeated 3 times. Finally each character of the buffer has been touched by the two most random bits of the counter register after interrupts. That is 4n interrupts have occurred where n is the number of desired random bytes. This method is very sensitive to the randomness of system interrupts and the granularity of the clock. The output looked pretty good when tested on real UNIX machines. Measuring Keyboard Latency People’s typing patterns are both random and nonrandom. They are nonrandom enough that they can be used as a means of identification, but they are random enough that they can be used to generate random bits. Measure the time between successive keystrokes, then take the least significant bits of those measurements. These bits are going to be pretty random. This technique may not work on a UNIX terminal, since the keystrokes pass through filters and other mechanisms before they get to your program, but it will work on most personal computers. Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permissio...
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