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Comment by asafira | Hacker News Reader

Why is it just as unpredictable?

There are measurements you can make that could help you predict Johnson noise. For many quantum schemes, it's much tougher.

(Not that it is easy for an attacker to make those measurements in the first place, but it doesn't seem fair to say it is rigorously just as unpredictable)

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Nope. Johnson noise is quantum mechanical (at least in significant part). If you use a good algorithm, you can sample a partial TRNG into an epsilon-perfect TRNG (as close as you'd like). Not to mention all of this is pointless since even if the noise were classical a few applications of strong hash functions (which is the normal procedure -- they're entirely practical) require would require computers using more energy than the entire universe has available you want.

I definitely appreciate now that there are good algorithms to make your random bits more random, and hash functions can help, but regarding calling johnson noise quantum mechanical: can you give one reference of a description of finite-temperature johnson noise in which at least 1 observable necessitates a quantum mechanical treatment? (I don't think it exists, given that it is a thermal phenomenon, but maybe I'm wrong...)

You can characterize the noise using things like temperature and material properties. But you cannot simulate the system, you cannot reproduce it, the noise itself is the result of subatomic particles interacting.

Two resistors made of the exactly same material, the same cristaline structure down to every atom and heated in the same way up from 0K will generate different noise.

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