Which of the following statements are correct

Device-independent quantum cryptography cannot be achieved via entanglement related statistical measurement correlations testing alone.

The BB84 protocol is the most popular QKD protocol currently in use.

Depolarisation is a phenomenon that occurs in optical fibres and leads to decoherence that can be also interpreted by the QKD system as eavesdropping.

Quantum key distribution achieves unconditional (information-theoretic) security level as long as laws of quantum mechanics are obeyed.