3 ms·

one of the dangers of the RTL entropy source project is not that it is predictable, but that it can be made to become predictable. By determining the frequency

one of the dangers of the RTL entropy source project is not that it is predictable, but that it can be made to become predictable. By determining the frequency the device is listening on, you could inject a signal over the air that causes the entropy to conform to a known pattern. Even Lavarand users blend their entropy sources. Ive used the RTL as a blended entropy source for my kubernetes pi cluster project, but blended it with signal data from the open source FST-01 from the flying stone project. this in turn gets randomly audited by dieharder. http://webhome.phy.duke.edu/~rgb/General/dieharder.php http://webhome.phy.duke.edu/~rgb/General/dieharder.php My RTL entropy generator changes frequencies every 6 hours to a frequency determined by a script referencing /dev/urandom.

vvanders 9y ago
One solution there is to pick a frequency(cell/military bands) where the FCC really comes down on transmissions that aren't authorized. Or you could randomize it, the RTL has a pretty wide receive range.
- ladberg 9y ago
  It's still always possible to just generate any radio signal close to the SDR at a low enough power that no one else can pick it up. Also, it would require special SDR transmitters, but you could in theory transmit on every frequency that an RTL-SDR could pick up (again, close by at a low power so you don't disturb other stuff).
  - snops 9y ago
    A simple comb generator would fill all the frequencies nicely, and is very cheap compared to an SDR transmitter. I have no idea how useful the comb waveform is to "break" the RNG output though. Here is one for $99, I'm sure you could DIY one for less with reduced output power: https://www.tekbox.net/test-equipment/comb-generators/tbcg1-radiating-comb-generator https://www.tekbox.net/test-equipment/comb-generators/tbcg1-...
amelius 9y ago
From the readme: > If you're serious about the cryptographic security of your entropy source, you should probably short, or put a 75 Ohm load on the antenna port, and put the whole assembly in a shielded box. Then you're getting entropy from the thermal noise of the amplifiers which is much harder to interfere with than atmospheric radio.
- muxator 9y ago
  And thermal noise is - almost by definition - the best source of white noise you can get in this world...

vvanders 9y ago

One solution there is to pick a frequency(cell/military bands) where the FCC really comes down on transmissions that aren't authorized. Or you could randomize it, the RTL has a pretty wide receive range.

ladberg 9y ago
It's still always possible to just generate any radio signal close to the SDR at a low enough power that no one else can pick it up. Also, it would require special SDR transmitters, but you could in theory transmit on every frequency that an RTL-SDR could pick up (again, close by at a low power so you don't disturb other stuff).
- snops 9y ago
  A simple comb generator would fill all the frequencies nicely, and is very cheap compared to an SDR transmitter. I have no idea how useful the comb waveform is to "break" the RNG output though. Here is one for $99, I'm sure you could DIY one for less with reduced output power: https://www.tekbox.net/test-equipment/comb-generators/tbcg1-radiating-comb-generator https://www.tekbox.net/test-equipment/comb-generators/tbcg1-...

amelius 9y ago

From the readme: > If you're serious about the cryptographic security of your entropy source, you should probably short, or put a 75 Ohm load on the antenna port, and put the whole assembly in a shielded box. Then you're getting entropy from the thermal noise of the amplifiers which is much harder to interfere with than atmospheric radio.

muxator 9y ago
And thermal noise is - almost by definition - the best source of white noise you can get in this world...