[HexagonalKitten]

> This seems contradictory.

Because there are two entirely different things - one is producing an unbiased bitstream from a potentially biased one (the topic of the article) and the other is keying an individual encryption.

When you're trying to generate a bitstream and you expect uniformity (ie, a prng) then seeing obvious non-uniformity over time is a sign that it's biased. You need the type of algorithms from the article to unbias it while preserving the actual entropy. This is what a system's designer should be doing to produce useful output from a hwrng in the first place.

But, looking at an individual piece of randomness, a key, you shouldn't be looking for uniformity at all. Here you want all zeros, all 1s, and any mix, to be equally possible.

> Interesting. Why do you hash the ECDH secret then?

Well, EC is a bit magical and I don't know. Wikipedia says that it prevents 'weak bits' from the handshake. That means correlations, but I don't know why this is true. At any rate uniformity here means what you think, that it's not a random bitstream and should not be used as such.