How to tell if a hardware RNG is rigged? On a related note of building my own RNG, as someone suggested to use several commericial solutions how can I check if it is rigged against me? (although I am still strongly biased to a homebrew solution that is designed to be hard to subvert, taking the shortest possible route from a quantum random source to the ADC)
While unfortunately that is not possible deterministically, if you have a small amount of "guaranteed trustworthy" randomness, you can use several untrusted RNGs together to generate an unlimited supply of good randomness (under some weak assumptions of non-signaling between the RNGs). This is called "randomness expansion" and I am not aware of any use in practice yet, unfortunately.

See these papers by Colbeck and Kent and Coudron and Yuen