rtl-entropy, atmospheric radio noise entropy source

keenerd keenerd at gmail.com
Fri Feb 15 13:43:37 UTC 2013

On 2/15/13, Paul Warren <pwarren at pwarren.id.au> wrote:
> I just finished my first go at an entropy gathering tool for rtl-sdr.

Take a look at snd-egd, http://code.google.com/p/snd-egd/ .  It does
something very similar but with the microphone.  It uses the same
bit-wise algo you do, but adapted to work with the higher bits as
well.  (More of a concern for audio with its limited bandwidth.)  The
one step you are missing is the feedback/mixing.  Snd-egd xors fresh
random bytes with the old random bytes sitting in the ring buffer.
This step seems to be pretty important in most systems.  Others go an
extra mile and xor hashed random numbers with the old stream.

> As I mention in the Readme, I plan on doing these tests and eventually
> getting it to the stage where the entropy can be plumbed in to
> /dev/random.

Snd-egd is also a great example of how to do the plumbing.  Also
mentioned in your readme is frequency hopping, though that looks

Best of luck convincing tinfoil hat folk to use an RNG that is
literally controlled by radio waves.  A 50 ohm terminator + shielding
would probably be a good idea, so that you are tapping into the
thermal noise of the ADC and amps.


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