> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Robert Huff > Sent: Monday, September 22, 2008 9:54 PM > To: [EMAIL PROTECTED] > Subject: using /dev/random > > > > What is the canonical way to get data from /dev/random? > Specifically: having opened the file, how do I read the stream? > I'm currently using > > > union { > float f; > char c[4]; > } foo; > > foo.f = 0.0; > > fscanf(rand_fp,"%4c",foo.c); > > > which doesn't seem to produce anywhere near "random bytes" as > promised by the man page. > > > Robert Huff >
The canonical way is to use the functions random(), or srandom() or srandomdev() or arc4random() depending on what you need the random data for. /dev/random is really only useful for seeding these functions (some of them pull data from /dev/random internally) The thrust behind the FreeBSD /dev/random device is that we know that getting lots of real random data from /dev/random is difficult, however getting non-repeating seeds from /dev/random is easy. The device has thus been optimized for seed generation to feed these other functions. If you really want to roll-your-own and not use these functions then you could read blocks from /dev/random and run a Chi-square and Monte Carlo test on each block and discard the ones that don't pass. I've done my experimenting with the ENT program: http://www.fourmilab.ch/random/ ie: dd if=/dev/urandom bs=3000 count=100 of=random-sample ent random-sample Successive runs of that with different data sets and blocksizes clearly illustrates the generator can't pass Chi-square quite a lot of times. Ted _______________________________________________ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
