For those that want an (additional) source of entropy, the FSF offers[1] a USB HWRNG[2] that uses ADC quantization noise. It seems to be simple and clever enough to get the job done. True to FSF form the source is available if you want to adapt it to your own MCU. The data provided by mine passed all the randomness quality tests I could throw at it.
I don't know if it's still maintained or not, but the developer proposed a public entropy pool[3] which looks interesting. Full disclosure: I haven't looked at it closely enough to understand how the trust model works.
I don't know if it's still maintained or not, but the developer proposed a public entropy pool[3] which looks interesting. Full disclosure: I haven't looked at it closely enough to understand how the trust model works.
[1]: https://shop.fsf.org/storage-devices/neug-usb-true-random-nu... [2]: https://www.gniibe.org/memo/development/gnuk/rng/neug.html [3]: https://www.gniibe.org/memo/development/kun9be4/idea.html