On Mon, Oct 23, 2006 at 06:49:21PM +0200, Oliver Fromme wrote: > Matthieu Michaud wrote: > > Oliver Fromme wrote: > > > Also take into account that you usually don't read that > > > much data from /dev/random. Quality is much more important > > > than speed. > > > > you are right. do you know an easy way to evaluate this quality ? > > There is no easy way, I'm afraid.
Start reading here: http://www.random.org/essay.html And follow the links. A test of 1 MB random data with "ent" [http://www.fourmilab.ch/random/]: dd if=/dev/random of=rand.dat bs=1k count=1k ./ent rand.dat Entropy = 7.999843 bits per byte. Optimum compression would reduce the size of this 1048576 byte file by 0 percent. Chi square distribution for 1048576 samples is 227.43, and randomly would exceed this value 75.00 percent of the times. Arithmetic mean value of data bytes is 127.6223 (127.5 = random). Monte Carlo value for Pi is 3.133839164 (error 0.25 percent). Serial correlation coefficient is -0.000504 (totally uncorrelated = 0.0). According to the same fourmilab page this is quite decent. There is about 1 bit of entropy in approx. ~6000 bytes! The chi square value is of the same order as one generated by timing radioactive decay events. Roland -- R.F.Smith http://www.xs4all.nl/~rsmith/ [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725)
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