Bad Qubits — Learn Quantum by Doing

Multiple choice

Privacy amplification compresses a partly-compromised shared string into a shorter, near-secret key. Which entropy measure does it use to quantify Eve's knowledge, and why is that measure (rather than Shannon entropy) the correct one?

The conditional min-entropy H_min(X|E) = -log2(p_guess(X|E)), because security needs a worst-case bound on Eve's single best guess, which Shannon (average) entropy can over-estimate
The max-entropy H_max(X|E), because it gives the most optimistic estimate of the extractable key
The von Neumann entropy of the whole universe, because only a global quantity guarantees secrecy
The Shannon entropy H(X|E), because it measures the average uncertainty and is the tightest bound on extractable key length