Path: cactus.org!milano!cs.utexas.edu!wupost!micro-heart-of-gold.mit.edu!uw- + beaver!ubc-cs!unixg.ubc.ca!unruh From: email@example.com (William Unruh [Unruh]) Newsgroups: sci.crypt,comp.compression Subject: Re: Source for _real_ random numbers Message-ID:
Date: 18 Mar 92 00:30:50 GMT References: <1992Mar16.firstname.lastname@example.org> <92Mar16.131831edt.203@neuron. + ai.toronto.edu> <1992Mar17.email@example.com> Sender: firstname.lastname@example.org (Usenet News Maintenance) Distribution: usa Organization: University of British Columbia, Vancouver, B.C., Canada Lines: 18 Xref: cactus.org sci.crypt:5588 comp.compression:2553 Nntp-Posting-Host: physics.ubc.ca email@example.com (John F Carr) writes: >Someone who used to work here used a disk drive to generate random numbers. >He measured the time required to read a disk block and used the variation in >that time (after much preprocessing) as a random number source. A large >part of the variation in disk rotation speed is caused by air turbulence, so >there is some physical as well as observational evidence that these numbers >are random. In fact I think one has to be very careful with using physically generated random numbers. Although the underlying process might well be random, one is introducing all kinds of measuring instruments in between you and the underlying process. Those instruments could well introduce biases and correlations. One approach might be to use the physically generated random numbers as seeds to a deterministic "randomiser" (eg encrypt it with DES say) to get rid of the low order biases or correllations of the physical generator.