# What is meant by domain separation in the context of KDF?

This is a quote from my cryptography notes:

If $$h$$ is a random function oracle of output length $$n$$ then also the two KDF constructions:

$$K(x) = h([0] \| x) \ldots \| h([L] \| x)$$

$$K(x) = h(x \| [0] ) \ldots \| h(x \| [L])$$

yield random function oracles of otput length $$L \cdot n$$.

They call this property domain separation. What does this property mean? Can it be applied to only this setting or is it more general? What about the proof of this quote, is it inmediate?

• Anything missing from the given answer Javier? It seems like a pretty conclusive answer from my viewpoint, but it hasn't been accepted. – Maarten Bodewes Feb 14 at 16:27