Why physical random number source can be weak? I see two kinds of problems: it is hard to control it and make it resistant to some unwanted bias, but also deliberate attacks, it has normal distributuon, while we usually want to have uniform distribution (that's why we use randomness extractors o...

I'm looking at scheme on Wikipedia: https://en.wikipedia.org/wiki/Merkle–Damgård_construction And it looks like function f takes two inputs. So do we have to use in this scheme OWF which can take two inputs or maybe we can somehow combine IV with message block, for example by xoring them? Then f ...