As unequivocal proof of the ease with which you can build a high quality entropy source, here is one we built on Granny’s wooden breadboard:-
It is a Chekhov circuit, which is the simplest possible entropy generating circuit. So simple in fact that we built it on a wooden board (literally a breadboard). And even used real steel nails. The circuit is named after Anton Chekhov, who said “Only entropy comes easy”. Such wisdom! Essentially, it’s a common BZX 27 volt Zener diode plus 680 kΩ current limiting resistor thus:-
The thermo-nuclear shielding (box made of cryptographic plastic) is necessary to protect the Zener from all light as the junction is within a transparent glass encapsulation. Incident light disrupts the electron avalanche effect and reduces the entropy signal. Nominal reverse current = 18uA as the battery is actually ~39V. 36V is only the nominal value of 4 no. 9V batteries. Frankly, the diode current is somewhat higher, probably nearer 30uA as we use a direct x1 BNC cable. The combined 1MΩ scope impedance and limiting resistor parallel out at about 404 kΩ. This resistance acts with the junction capacitance to marginally distort the expected characteristic log normal signal distribution.
It’s a true quantum entropy source for the reasons explained previously in relation to the Avalanche effect within Zener diodes. It really doesn’t have to involve lasers or vacuum point energy to be quantum based. Although stale bread crumbs, semi-dried tomato juice and rotting pieces of salami can have a deleterious effect on circuit impedances and thus entropy rates. Lunches aside, our Chekhov circuit produces a mean unamplified entropy signal of 1.42Vpp under standard sampling.
This is a proof of concept unequivocally demonstrating the ease with which Kolmogorov random entropy can be generated by most hobbyists and amateur cryptographers. A 1.42Vpp signal is readily manipulated by keen individuals, and guaranteed to be caused by the Avalanche effect rather than some unspecified consequence of huge amplifier gain/power supply noise. And readily extracted from. All that’s necessary is a Zener diode, resistor, batteries and a working hammer.
NIST and at least one popular cryptography forum seem to rigorously promote the diametrically opposite view, repeating over and over the futility of DIY constructions. Why? The proof is on the chopping board. Just turn it on…