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thermal noise?

thermal noise?

Posted Dec 13, 2007 14:08 UTC (Thu) by nix (subscriber, #2304)
In reply to: thermal noise? by nettings
Parent article: On entropy and randomness

The thermal circuit noise isn't as random as all that: it gets interference from system
circuitry, which is regular as anything.

It could certainly contribute some randomness, I'd think, but nowhere near as much as 48kbits.


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thermal noise?

Posted Dec 13, 2007 14:26 UTC (Thu) by NRArnot (subscriber, #3033) [Link]

48K samples/second, each 16 bits, of which the least significant should be random regardless
of how much patterned noise is being picked up from the system's innards. In practice one
would run some verification tests first. One wouldn't be relying on it being a truly random
bitstream, just on it containing a reasonable amount of entropy.

thermal noise?

Posted Dec 13, 2007 16:49 UTC (Thu) by nix (subscriber, #2304) [Link]

I've tried it; you don't get anywhere near that much entropy. Quite a lot of it is strongly
correlated, at least with cheap sound cards, even at the least significant bits.

I wish this wasn't true, but it is :/ or at least it was in 2003, when I last looked at it (I
still don't have any sound cards newer than that: I'm not made of money and the newer cards
don't offer anything I can use. I don't have enough speakers or a suitably-shaped room for
surround-sound...)

thermal noise?

Posted Dec 14, 2007 6:02 UTC (Fri) by bronson (subscriber, #4806) [Link]

Electrical engineers learn to become deeply fearful of harmonics.  They show up everywhere!
Thanks to this, (the harmonics, not the fear), I think you'll find that /dev/urandom offers far
more random data than anything arriving over cheap hardware.

Well, unless that hardware was explicitly designed to avoid harmonics, like the transistor
noise RNG on some of Via's chips.


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