Re: /dev/random -- can I enlarge the `randomness stock'?

From: H. Peter Anvin (
Date: Thu May 25 2000 - 19:22:37 EST

Followup to: <>
By author: Igmar Palsenberg <>
In newsgroup:
> > What if you simply tuned a cheap FM receiver to just static and fed
> > that into a soundcard. Then reading from /dev/dsp or something would
> > return pretty good random data, right ?
> Nope... Unless the receiver recieves a resonable amount of random
> interference, the data isn't considered random enough.

Thermal noise is probably your most easily available source of
randomness. The hard part is estimating the amount of entropy
derivable, unfortunately; electrical interference can cause the
entropy to be less than what you would expect. The /dev/random mixing
function takes care of removing the predictable stuff, but you still
need to get a value (conservative is fine) for the amount of entropy
actually available.


<> at work, <> in private!
"Unix gives you enough rope to shoot yourself in the foot."

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